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Sample records for 94ag isomeric states

  1. Isomeric states in 253No

    NASA Astrophysics Data System (ADS)

    Lopez-Martens, A.; Hauschild, K.; Yeremin, A. V.; Dorvaux, O.; Belozerov, A. V.; Briançon, Ch.; Chelnokov, M. L.; Chepigin, V. I.; Curien, D.; Désesquelles, P.; Gall, B.; Gorshkov, V. A.; Guttormsen, M.; Hanappe, F.; Kabachenko, A. P.; Khalfallah, F.; Korichi, A.; Larsen, A. C.; Malyshev, O. N.; Minkova, A.; Oganessian, Yu. Ts.; Popeko, A. G.; Rousseau, M.; Rowley, N.; Sagaidak, R. N.; Sharo, S.; Shutov, A. V.; Siem, S.; Stuttgé, L.; Svirikhin, A. I.; Syed, N. U. H.; Theisen, Ch.

    2007-06-01

    Isomeric states in 253No have been investigated by conversion electron and γ -ray spectroscopy with the GABRIELA detection system. The 31μs isomer reported more than 30 years ago is found to decay to the ground state of 253No by the emission of a 167keV M2 transition. The spin and parity of this low-lying isomeric state are established to be 5/2+ . The presence of another longer-lived isomeric state is also discussed.

  2. Spectroscopic characterization of isomerization transition states

    NASA Astrophysics Data System (ADS)

    Baraban, Joshua H.; Changala, P. Bryan; Mellau, Georg Ch.; Stanton, John F.; Merer, Anthony J.; Field, Robert W.

    2015-12-01

    Transition state theory is central to our understanding of chemical reaction dynamics. We demonstrate a method for extracting transition state energies and properties from a characteristic pattern found in frequency-domain spectra of isomerizing systems. This pattern—a dip in the spacings of certain barrier-proximal vibrational levels—can be understood using the concept of effective frequency, ωeff. The method is applied to the cis-trans conformational change in the S1 state of C2H2 and the bond-breaking HCN-HNC isomerization. In both cases, the barrier heights derived from spectroscopic data agree extremely well with previous ab initio calculations. We also show that it is possible to distinguish between vibrational modes that are actively involved in the isomerization process and those that are passive bystanders.

  3. Nearly degenerate isomeric states of 75Cu

    NASA Astrophysics Data System (ADS)

    Petrone, C.; Daugas, J. M.; Simpson, G. S.; Stanoiu, M.; Plaisir, C.; Faul, T.; Borcea, C.; Borcea, R.; Cáceres, L.; Calinescu, S.; Chevrier, R.; Gaudefroy, L.; Georgiev, G.; Gey, G.; Kamalou, O.; Negoita, F.; Rotaru, F.; Sorlin, O.; Thomas, J. C.

    2016-08-01

    The decays of two isomeric states in the neutron-rich nucleus 75Cu have been studied via delayed γ -ray spectroscopy. These states were populated by the fragmentation of a 60.4 A MeV 86Kr primary beam, which impinged on a Be target at the LISE2k spectrometer of GANIL. Isomeric half-lives and branching ratios were measured, and a γ -γ coincidence analysis performed. These have allowed a revised level scheme of 75Cu to be proposed. A comparison with large-scale shell-model calculations using different effective interactions and valence spaces shows the importance of proton excitations across the Z =28 shell gap for reproducing the energy spacing between the isomeric states. The coexisting collective and single-particle properties of the (1 /2-) and (3 /2-) states, respectively, are similar to those of the same states in the neighboring 69,71,73Cu. The small energy spacings between the (1 /2-) , (3 /2-) , and 5 /2- states are responsible for the isomerism.

  4. Spectroscopic Characterization of Isomerization Transition States

    NASA Astrophysics Data System (ADS)

    Baraban, Joshua H.; Changala, Bryan; Mellau, Georg Ch.; Stanton, John F.; Merer, Anthony; Field, Robert W.

    2016-06-01

    Transition state theory is central to our understanding of chemical reaction dynamics. We demonstrate here a method for extracting transition state energies and properties from a characteristic pattern found in frequency domain spectra of isomerizing systems. This pattern, a dip in the spacings of certain barrier-proximal vibrational levels, can be understood using the concept of effective frequency, ωeff. The method is applied to the cis-trans conformational change in the S_1 state of C2H2 and the bond-breaking HCN-HNC isomerization. In both cases, the barrier heights derived from spectroscopic data agree extremely well with previous ab initio calculations. We also show that it is possible to distinguish between vibrational modes that are actively involved in the isomerization process and those that are passive bystanders. (This work has been published in J. H. Baraban, P. B. Changala, G. Ch. Mellau, J. F. Stanton, A. J. Merer, and R. W. Field. Spectroscopic characterization of isomerization transition states. Science, 350(6266):1338--1342, 2015.)

  5. Further results in the search for the direct two-proton decay of ^94Ag^m (J^π= 21^+, 6.7 MeV)

    NASA Astrophysics Data System (ADS)

    Cerny, J.; Lee, D. W.; Perajarvi, K.; Moltz, D. M.; Barquest, B. R.; Grossman, L. E.; Jeong, W.; Jewett, C. C.

    2008-10-01

    Both direct one-proton decay and direct two-proton decay of ^94Ag^m from this 0.4 s isomeric state have been reported in experiments utilizing the GSI on-line mass separator [1]. In the latter decay, coincident events between silicon E detectors with a threshold energy of 0.4 MeV and a summed decay energy of 1.9±0.1 MeV were observed with a yield of 350±210 pb in coincidence with γ-decays in the ^92Rh daughter. We utilized our helium-jet system at the LBNL 88-inch cyclotron to repeat this experiment, again employing the ^58Ni(^40Ca,p3n) reaction at 197 MeV. Reaction products were transported via a capillary to a detection area and collected on a slowly rotating wheel in front of an assembly of 24 δEgas-δEgas-ESi detector telescopes with a threshold of 0.4 MeV for identifying protons. Five of these telescopes observe the 0.79 MeV single proton decay from ^94Ag^m at the reported yield of 1.3 nb. In the 240/276 identified proton detector combinations with low background, no proton-proton coincidences have been observed. Data from the remaining 36 detector combinations require a separate analysis, which is in progress. Monte Carlo analyses of our anticipated proton-proton coincidences for both sets of detector combinations will be presented. ^ 1Mukha et al., Nature 439, 298 (2006).

  6. Isomerism of low-lying states in 86Y

    NASA Astrophysics Data System (ADS)

    Rusu, C.; Bucurescu, D.; Mărginean, N.; Ionescu-Bujor, M.; Iordăchescu, A.; Căta-Danil, G.; Căta-Danil, I.; Deleanu, D.; Filipescu, D.; Ghiţa, D.; Glodariu, T.; Ivaşcu, M.; Mihai, C.; Mărginean, R.; Pascu, S.; Sava, T.; Stroe, L.; Suliman, G.; Zamfir, N. V.

    2010-04-01

    Low-energy isomeric states of 86Y were populated in the reaction 73Ge + 16O at 57MeV and were investigated by means of delayed n γ and γ γ coincidences. A half-life of 70(7)ns was measured for the 5- state at 208keV, yielding an exceptionally small B( M1) value of 2.0(7)×10-5 W.u. and a B( E2) value of 0.34(+24 -13) W.u. For the other three known isomeric states at 218, 243, and 302keV, the half-lives extracted from the present experimental data are in very good agreement with previous measurements. Given the newly observed isomeric character of the 5- 208keV state, the re-analysis of earlier experimental data on the 302keV isomer led to a new spin-parity assignment, 6+, for this state. In addition, this re-evaluation provided two g -factors, -0.083(3) and +0.63(2) , for the 208 and 302keV states, respectively. The results are discussed in terms of spherical-shell model calculations performed with a truncated space of configurations built on the f 5/2 , p 3/2 , p 1/2 , and g 9/2 valence orbitals. Effective spin, orbital, and “tensor” g -factors were determined empirically for protons and neutrons in the considered configuration space.

  7. Proton-proton correlations observed in two-proton radioactivity of 94Ag.

    PubMed

    Mukha, Ivan; Roeckl, Ernst; Batist, Leonid; Blazhev, Andrey; Döring, Joachim; Grawe, Hubert; Grigorenko, Leonid; Huyse, Mark; Janas, Zenon; Kirchner, Reinhard; La Commara, Marco; Mazzocchi, Chiara; Tabor, Sam L; Van Duppen, Piet

    2006-01-19

    The stability and spontaneous decay of naturally occurring atomic nuclei have been much studied ever since Becquerel discovered natural radioactivity in 1896. In 1960, proton-rich nuclei with an odd or an even atomic number Z were predicted to decay through one- and two-proton radioactivity, respectively. The experimental observation of one-proton radioactivity was first reported in 1982, and two-proton radioactivity has now also been detected by experimentally studying the decay properties of 45Fe (refs 3, 4) and 54Zn (ref. 5). Here we report proton-proton correlations observed during the radioactive decay of a spinning long-lived state of the lightest known isotope of silver, 94Ag, which is known to undergo one-proton decay. We infer from these correlations that the long-lived state must also decay through simultaneous two-proton emission, making 94Ag the first nucleus to exhibit one- as well as two-proton radioactivity. We attribute the two-proton emission behaviour and the unexpectedly large probability for this decay mechanism to a very large deformation of the parent nucleus into a prolate (cigar-like) shape, which facilitates emission of protons either from the same or from opposite ends of the 'cigar'.

  8. Isomeric state in {sup 53}Co: A mean field analysis

    SciTech Connect

    Patra, S. K.; Bhat, F. H.; Panda, R. N.; Arumugam, P.; Gupta, Raj K.

    2009-04-15

    We study the ground and the first excited intrinsic states of {sup 53}Co and its mirror nucleus {sup 53}Fe, within the frameworks of the relativistic and nonrelativistic mean field formalisms. The analysis of the single-particle energy spectra of these nuclei show a competition of spins 1/2{sup -} and 3/2{sup -} in a low-lying excited state, which agrees well with the recent experimental observation [D. Rudolph et al., Eur. Phys. J. A 36, 131 (2008)] of spin and parity J{sup {pi}}=3/2{sup -} for the isomeric configuration in {sup 53}Co.

  9. Confirmation of the isomeric state in 26P

    NASA Astrophysics Data System (ADS)

    Pérez-Loureiro, D.; Wrede, C.; Bennett, M. B.; Liddick, S. N.; Bowe, A.; Brown, B. A.; Chen, A. A.; Chipps, K. A.; Cooper, N.; McNeice, E.; Naqvi, F.; Ortez, R.; Pain, S. D.; Pereira, J.; Prokop, C.; Quinn, S. J.; Sakstrup, J.; Santia, M.; Schwartz, S. B.; Shanab, S.; Simon, A.; Spyrou, A.; Thiagalingam, E.

    2017-07-01

    We report the independent experimental confirmation of an isomeric state in the proton drip-line nucleus 26P. The γ -ray energy and half-life determined are 164.4 ±0.3 (sys)±0.2 (stat) keV and 104 ±14 ns, respectively, which are in agreement with the previously reported values. These values are used to set a semiempirical limit on the proton separation energy of 26P, with the conclusion that it can be bound or unbound.

  10. g factors of coexisting isomeric states in {sup 188}Pb

    SciTech Connect

    Ionescu-Bujor, M.; Iordachescu, A.; Marginean, N.; Suliman, G.; Bucurescu, D.; Marginean, R.; Ur, C. A.; Brandolini, F.; Lenzi, S. M.; Pavan, P.; Vedova, F. Della; Napoli, D. R.; Chmel, S.; Medina, N. H.; Ribas, R. V.

    2010-02-15

    The g factors of the 12{sup +}, 11{sup -}, and 8{sup -} isomeric states in {sup 188}Pb were measured using the time-differential perturbed angular distribution method as g(12{sup +})=-0.179(6), g(11{sup -})=+1.03(3), and g(8{sup -})=-0.037(7). The g factor of the 12{sup +} state follows the observed slight down-sloping evolution of the g factors of the i{sub 13/2}{sup 2} neutron spherical states with decreasing N. The g factors of the 11{sup -} and 8{sup -} isomers proposed as oblate and prolate deformed states, respectively, were interpreted within the rotational model, using calculated and empirical g factor values for the involved single-particle orbitals.

  11. High-spin states and a new band based on the isomeric state in 152Nd

    NASA Astrophysics Data System (ADS)

    Yeoh, E. Y.; Zhu, S. J.; Hamilton, J. H.; Ramayya, A. V.; Yang, Y. C.; Sun, Y.; Hwang, J. K.; Liu, S. H.; Wang, J. G.; Luo, Y. X.; Rasmussen, J. O.; Lee, I. Y.; Ding, H. B.; Li, K.; Gu, L.; Xu, Q.; Xiao, Z. G.; Ma, W. C.

    2010-08-01

    High-spin states of the neutron-rich 152Nd nucleus have been reinvestigated by measuring the prompt γ -rays in the spontaneous fission of 252Cf . The ground-state band and a side negative-parity band have been updated. A new band based on the 2243.7keV isomeric state has been identified. The half-life for the isomeric state has been measured to be 63(7)ns. The projected shell model is employed to study the band structure of this nucleus. The results show that the calculated levels of the bands are in good agreement with the experimental ones, and the isomeric state and the negative-parity band are based on the proton π5/2-[532] ⊗ π9/2+[404] and neutron ν3/2-[521] ⊗ ν5/2+[642] two-quasiparticles configurations, respectively.

  12. Cross Section of Isomeric States Produced in Photo-Neutron Reactions

    NASA Astrophysics Data System (ADS)

    Oprea, C.; Oprea, A.; Mihul, A.

    In this work the cross sections of the isomeric states production in (γ,n) reactions and the corresponding isomeric ratios for some isotopes of Cd, Sn, Mo, Sm in the great dipole resonance region with Talys codes using a standard input including Hauser-Feshbach model were evaluated. For the isomeric ratio calculation two methods were proposed, by using the description of incident gamma flux and experimental isomeric ratio. The obtained results are compared with experimental data from nuclear reactions induced by photons obtained by bremsstrahlung.

  13. Single-particle isomeric states in 121Pd and 117Ru

    NASA Astrophysics Data System (ADS)

    Lalkovski, S.; Bruce, A. M.; Bacelar, A. M. Denis; Górska, M.; Pietri, S.; Podolyák, Zs; Bednarczyk, P.; Caceres, L.; Casarejos, E.; Cullen, I. J.; Doornenbal, P.; Farrelly, G. F.; Garnsworthy, A. B.; Geissel, H.; Gelletly, W.; Gerl, J.; Grȩbosz, J.; Hinke, C.; Ilie, G.; Jaworski, G.; Kisyov, S.; Kojouharov, I.; Kurz, N.; Myalski, S.; Palacz, M.; Prokopowicz, W.; Regan, P. H.; Schaffner, H.; Steer, S.; Tashenov, S.; Walker, P. M.; Wollersheim, H. J.; Zhekova, M.

    2012-05-01

    Neutron-rich nuclei were populated in a relativistic fission of 238U. Gamma-rays with energies of 135 keV and 184 keV were associated with two isomeric states in 121Pd and 117Ru. Half-lives of 0.63(5) μs and 2.0(3) μs were deduced and the isomeric states were interpreted in terms of prolate deformed single-particle states.

  14. Unusual Anharmonicities in Isomerizing Systems: the S1 State of C2H2

    NASA Astrophysics Data System (ADS)

    Baraban, J. H.; Field, R. W.; Stanton, J. F.; Merer, A. J.

    2012-06-01

    Low-barrier {cis}-{trans} isomerization profoundly affects the tilde{A}-tilde{X} spectrum of acetylene. We present extensions of the usual effective Hamiltonian model that capture these effects, and thereby enable fits of the complete tilde{A} {}1Au state J=K=0 level structure up to 4300 cm-1 above the {trans} zero point level. The relationship between these new additions to the model and spectroscopic indicators of the transition state energy will also be discussed. One dimensional models will be used to illustrate both the effects of the isomerization dynamics on the spectrum and how they can be exploited to reveal the isomerization barrier height.

  15. Shape coexistence and isomeric states in neutron-rich Tc112 and Tc113

    NASA Astrophysics Data System (ADS)

    Bruce, A. M.; Lalkovski, S.; Denis Bacelar, A. M.; Górska, M.; Pietri, S.; Podolyák, Zs.; Shi, Y.; Walker, P. M.; Xu, F. R.; Bednarczyk, P.; Cáceres, L.; Casarejos, E.; Cullen, I. J.; Doornenbal, P.; Farrelly, G. F.; Garnsworthy, A. B.; Geissel, H.; Gelletly, W.; Gerl, J.; Grębosz, J.; Hinke, C.; Ilie, G.; Jaworski, G.; Kojouharov, I.; Kurz, N.; Myalski, S.; Palacz, M.; Prokopowicz, W.; Regan, P. H.; Schaffner, H.; Steer, S.; Tashenov, S.; Wollersheim, H. J.

    2010-10-01

    Isomeric states in Tc112 and Tc113, with half-lives of 150(17) ns and 500(100) ns, respectively, have been observed following the relativistic fission of U238. The fission fragments have been separated in a fragment separator and identified by means of energy-loss and time-of-flight techniques. In both nuclei, the ground-state configuration is calculated to have an oblate shape and the isomerism is proposed to arise due to transitions from a triaxial excited state to a low-lying oblate state.

  16. Half-life measurements of isomeric states populated in projectile fragmentation

    SciTech Connect

    Bowry, M.; Podolay, Zs.

    2012-10-20

    The half-lives of excited isomeric states observed in {sup 195}Au, {sup 201}Tl and {sup 215}Rn are reported for the first time. Delayed {gamma}-rays were correlated with nuclei produced in the projectile fragmentation of relativistic {sup 238}U ions, unambiguously identified in terms of their atomic number (Z) and mass-to-charge ratio (A/Q) after traversing an in-flight separator. The observation of a long-lived isomeric state in {sup 195}Au with t{sub 1/2} = 16{sub -4}{sup +8}{mu}s is presented. Two shorter-lived isomeric states were detected in {sup 201}Tl and {sup 215}Rn with t{sub 1/2} = 95{sub -21}{sup +39} and 57{sub -12}{sup +21} ns respectively. In total 24 isomeric states were identified in different nuclei from Pt to Rn (A {approx} 200) during the current study, the majority of which were previously reported. The wealth of spectroscopic data provides the opportunity to determine the isomeric ratios over a wide range of Z, A and angular momentum (I h) of the reaction products. In particular, high-spin states with I Greater-Than-Or-Equivalent-To 18 h provide a robust test of theoretical models of fragmentation.

  17. Half-life measurements of isomeric states populated in projectile fragmentation

    NASA Astrophysics Data System (ADS)

    Bowry, M.; Podolyák, Zs.; Kurcewicz, J.; Pietri, S.; Bunce, M.; Regan, P. H.; Farinon, F.; Geissel, H.; Nociforo, C.; Prochazka, A.; Weick, H.; Allegro, P.; Benlliure, J.; Benzoni, G.; Boutachkov, P.; Gerl, J.; Gorska, M.; Gottardo, A.; Gregor, N.; Janik, R.; Knöbel, R.; Kojouharov, I.; Kubo, T.; Litvinov, Y. A.; Merchan, E.; Mukha, I.; Naqvi, F.; Pfeiffer, B.; Pfützner, M.; Plaß, W.; Pomorski, M.; Riese, B.; Ricciardi, M. V.; Schmidt, K.-H.; Schaffner, H.; Kurz, N.; Denis Bacelar, A. M.; Bruce, A. M.; Farrelly, G. F.; Alkhomashi, N.; Al-Dahan, N.; Scheidenberger, C.; Sitar, B.; Spiller, P.; Stadlmann, J.; Strmen, P.; Sun, B.; Takeda, H.; Tanihata, I.; Terashima, S.; Valiente Dobon, J. J.; Winfield, J. S.; Wollersheim, H.-J.; Woods, P. J.

    2012-10-01

    The half-lives of excited isomeric states observed in 195Au, 201Tl and 215Rn are reported for the first time. Delayed γ-rays were correlated with nuclei produced in the projectile fragmentation of relativistic 238U ions, unambiguously identified in terms of their atomic number (Z) and mass-to-charge ratio (A/Q) after traversing an in-flight separator. The observation of a long-lived isomeric state in 195Au with t1/2 = 16-4+8 μs is presented. Two shorter-lived isomeric states were detected in 201Tl and 215Rn with t1/2 = 95-21+39 and 57-12+21 ns respectively. In total 24 isomeric states were identified in different nuclei from Pt to Rn (A ˜ 200) during the current study, the majority of which were previously reported. The wealth of spectroscopic data provides the opportunity to determine the isomeric ratios over a wide range of Z, A and angular momentum (I ħ) of the reaction products. In particular, high-spin states with I ≳ 18 ħ provide a robust test of theoretical models of fragmentation.

  18. High spin states and isomeric decays in doubly-odd 208Fr

    NASA Astrophysics Data System (ADS)

    Kanjilal, D.; Bhattacharya, S.; Goswami, A.; Kshetri, R.; Raut, R.; Saha, S.; Bhowmik, R. K.; Gehlot, J.; Muralithar, S.; Singh, R. P.; Jnaneswari, G.; Mukherjee, G.; Mukherjee, B.

    2010-10-01

    Neutron deficient isotopes of francium ( Z=87, N˜121-123) as excited nuclei were produced in the fusion-evaporation reaction: 197Au( 16O, xn) 213 - xFr at 100 MeV. The γ rays from the residues were observed through the high sensitivity Germanium Clover detector array INGA. The decay of the high spin states and the isomeric states of the doubly-odd 208Fr nuclei, identified from the known sequence of ground state transitions, were observed. The half-lives of the E=194(2) keV isomeric transition, known from earlier observations, was measured to be T=233(18) ns. A second isomeric transition at E=383(2) keV and T=33(7) ns was also found. The measured half-lives were compared with the corresponding single particle estimates, based on the level scheme obtained from the experiment.

  19. No Evidence of Isomerism for the First Excited State of {sup 93}Rb

    SciTech Connect

    Miernik, K.; Gross, C.J.; Grzywacz, R.; Madurga, M.; Mendez, A.J.; Rykaczewski, K.P.; Stracener, D.W.; Zganjar, E.F.

    2014-06-15

    The 253.3–keV excited state located in {sup 93}Rb was studied at the Holifield Radioactive Ion Beam Facility in Oak Ridge. This state, described as isomeric in databases, was populated in the decay of {sup 93}Kr produced by proton–induced fission of {sup 238}U and isolated using the isotope separation on–line technique. We report that the 253.3–keV level does not reveal isomerism and the upper limit of the half-life from our measurement is 4 ns. Our findings are supported by previously reported results that were not taken into account in the latest nuclear databases.

  20. Existence of long-lived isomeric states in naturally-occurring neutron-deficient Th isotopes

    SciTech Connect

    Marinov, A.; Kashiv, Y.; Rodushkin, I.; Halicz, L.; Segal, I.; Pape, A.; Miller, H. W.; Kolb, D.; Brandt, R.

    2007-08-15

    Four long-lived neutron-deficient Th isotopes with atomic mass numbers 211 to 218 and abundances of (1-10)x10{sup -11} relative to {sup 232}Th have been found in a study of naturally-occurring Th using inductively coupled plasma-sector field mass spectrometry. It is deduced that long-lived isomeric states exist in these isotopes. The hypothesis that they might belong to a new class of long-lived high spin super- and hyperdeformed isomeric states is discussed.

  1. First observation of an isomeric state in proton drip-line nucleus 26P

    NASA Astrophysics Data System (ADS)

    Nishimura, D.; Fukuda, M.; Sakai, T.; Tanaka, M.; Abe, K.; Chiba, J.; Fukuda, S.; Furuki, H.; Homma, A.; Hotaka, H.; Ichihashi, N.; Inaba, N.; Iwamoto, K.; Izumikawa, T.; Kamisho, Y.; Kanbe, K.; Kikukawa, N.; Kitagawa, A.; Kouno, J.; Nagashima, M.; Nakamura, Y.; Nishizuka, I.; Matsuta, K.; Mihara, M.; Miyazawa, S.; Morita, Y.; Ono, J.; Ohtsubo, T.; Sato, K.; Sato, S.; Sera, D.; Suzuki, S.; Suzuki, S.; Suzuki, T.; Takechi, M.; Tashiro, K.; Wakabayashi, M.; Watanabe, D.; Yaguchi, M.; Yamaguchi, T.; Yamaki, S.; Yasumoto, S.; Yoshinaga, K.; Zhu, Y.

    2014-03-01

    An isomeric state in the proton drip-line nucleus 26P has been observed by the γ-ray spectroscopy. The γ-ray energy and the half-life are 164.4 ± 0.1 keV and 120 ± 9 ns, respectively. For the isomeric transition of the mirror nucleus 26Na, the γ-ray energy of 82.40 ± 0.04 keV and the half-life of 4.35 ± 0.16 μs are also revised. Comparing the experimental reduced transition probabilities of 26Na and 26P with theoretical ones calculated by the shell model with the USDA interaction, the spin-parity (Jπ) of the isomeric state in 26P is most likely to be 1+.

  2. Level density parameters from excitation cross sections of isomeric states

    NASA Astrophysics Data System (ADS)

    Skakun, E. A.; Batij, V. G.

    1992-03-01

    Cross section ratios were measured for the production of the isomeric pairs99m,gRh,101m,gRh,102m,gRh,104m,gRh and108m,gIn in the (p,n)-reaction,107m,gIn and109m,gIn in the ( p, γ)-reaction over the energy range up to 9 MeV, and116m,gSb and118m,gSb in the (α, n)-reaction up to 24 MeV. The experimental results for these nuclei as well as for other isometric pairs excited in the ( p, n)-reaction were analysed in the frame of the statistical model for extracting the level density parameter values in the vicinity of closed nucleon shells. The level density parameter behaviour is discussed in the range of nuclear mass numbers under study.

  3. Spontaneous fission half-lives of heavy nuclei in ground state and in isomeric state

    NASA Astrophysics Data System (ADS)

    Ren, Zhongzhou; Xu, Chang

    2005-09-01

    We generalize the formulas of spontaneous fission half-lives of even-even nuclei in their ground state to both the case of odd nuclei and the case of fission isomers [Phys. Rev. C 71 (2005) 014309]. The spontaneous fission half-lives of odd- A nuclei and of odd-odd nuclei in the ground state are calculated by Swiatecki's formula, by its generalized form, and by a new formula where the blocking effect of unpaired nucleon on the half-lives has been taken into account with different mechanisms. By introducing a blocking factor or a generalized seniority in the formulas of the half-lives of even-even nuclei, we can reasonably reproduce the experimental fission half-lives of odd- A nuclei and of odd-odd nuclei with the same parameters used in ground state of even-even nuclei. For spontaneous fission of the isomers in transuranium nuclei the new formula can be simplified into a three-parameter formula and the isomeric half-lives can be well reproduced by the formula. The new formula of the isomeric half-lives is as good as Metag's formula of fission isomers. The half-lives of isomers from these formulas are very accurate and therefore these formulas can give reliable predictions for half-lives of new isomers of neighboring nuclei.

  4. Calculations of the production cross sections of high-spin isomeric states in hafnium

    SciTech Connect

    Chadwick, M.B. ); Young, P.G. )

    1991-06-01

    This paper reports on the {sup 178}Hf(16{sup +}) isometric state that has a 31-yr half-life and could pose serious radioactive activation problems in nuclear fusion reactors if its production in 14-MeV neutron induced reactions is significant. The relatively high excitation energy (2.447 MeV) of this state causes it to lie in the continuum region. If rotational band members above this state were populated in a reaction, they would gamma cascade into it. While the existence of such levels can be justified theoretically, they have not been experimentally resolved; therefore, it is necessary to reconstruct the rotational levels built on the isomeric state. Using preequilibrium and compound nucleus theories, the cross sections for this and other hafnium isomeric states are calculated and compared with experimental measurements where available.

  5. Systematic study of α preformation probability of nuclear isomeric and ground states

    NASA Astrophysics Data System (ADS)

    Sun, Xiao-Dong; Wu, Xi-Jun; Zheng, Bo; Xiang, Dong; Guo, Ping; Li, Xiao-Hua

    2017-01-01

    In this paper, based on the two-potential approach combining with the isospin dependent nuclear potential, we systematically compare the α preformation probabilities of odd-A nuclei between nuclear isomeric states and ground states. The results indicate that during the process of α particle preforming, the low lying nuclear isomeric states are similar to ground states. Meanwhile, in the framework of single nucleon energy level structure, we find that for nuclei with nucleon number below the magic numbers, the α preformation probabilities of high-spin states seem to be larger than low ones. For nuclei with nucleon number above the magic numbers, the α preformation probabilities of isomeric states are larger than those of ground states. Supported by National Natural Science Foundation of China (11205083), Construct Program of Key Discipline in Hunan Province, Research Foundation of Education Bureau of Hunan Province, China (15A159), Natural Science Foundation of Hunan Province, China (2015JJ3103, 2015JJ2123), Innovation Group of Nuclear and Particle Physics in USC, Hunan Provincial Innovation Foundation for Postgraduate (CX2015B398)

  6. High-K,t1/2=1.4(1) ms, isomeric state in Lr255

    NASA Astrophysics Data System (ADS)

    Hauschild, K.; Lopez-Martens, A.; Yeremin, A. V.; Dorvaux, O.; Antalic, S.; Belozerov, A. V.; Briançon, Ch.; Chelnokov, M. L.; Chepigin, V. I.; Curien, D.; Gall, B.; Görgen, A.; Gorshkov, V. A.; Guttormsen, M.; Hanappe, F.; Kabachenko, A. P.; Khalfallah, F.; Larsen, A. C.; Malyshev, O. N.; Minkova, A.; Popeko, A. G.; Rousseau, M.; Rowley, N.; Saro, S.; Shutov, A. V.; Siem, S.; Stuttgè, L.; Svirikhin, A. I.; Syed, N. U. H.; Theisen, Ch.; Venhart, M.

    2008-08-01

    An isomeric state in Lr255 with a half-life of t1/2=1.4(1) ms and Ex>720-keV has been observed for the first time using the GABRIELA setup at the focal plane of the VASSILISSA separator. Based on its K-forbiddeness, the configuration of the state is most probably formed by coupling the valence proton to a two quasiparticle neutron excitation. Possible three quasiparticle configurations are discussed.

  7. Discovery of a 10 {mu}s isomeric state in {sub 63}{sup 139}Eu

    SciTech Connect

    Cullen, D. M.; Mason, P. J. R; Kishada, A. M.; Procter, M. G.; Rigby, S. V.; Varley, B. J.; Scholey, C.; Eeckhaudt, S.; Grahn, T.; Greenlees, P. T.; Jakobsson, U.; Jones, P. M.; Julin, R.; Juutinen, S.; Ketelhut, S.; Leino, M.; Leppaenen, A.-P.; Maentyniemi, K.; Nieminen, P.; Nyman, M.

    2011-01-15

    Recoil-isomer tagging with the {sup 54}Fe+{sup 92}Mo reaction was used to establish a 10(2)-{mu}s isomeric state in {sup 139}Eu. Prompt versus delayed {gamma}-ray coincidence data have revealed the presence of a prompt rotational band built upon the isomer. The alignment properties of the states in this band show that the isomer is based upon a proton g{sub 7/2} configuration. The decay of the isomer takes place through a single 26-keV E1 transition. The {gamma}-ray transition strength for this decay is consistent with those established in the neighboring isomeric gamma-soft nuclei. In these nuclei, isomers are expected to form as a consequence of differences in nuclear shapes or configurations, and the natural hindrance associated with configuration-changing E1 transitions. The isomeric nature of the state in {sup 139}Eu is reasoned to be because of difference in shape of the proton g{sub 7/2} state and the proton h{sub 11/2} ground state to which it decays.

  8. Population of isomeric states in fusion and transfer reactions in beams of loosely bound nuclei near the Coulomb barrier

    NASA Astrophysics Data System (ADS)

    Skobelev, N. K.

    2015-07-01

    The influence of the mechanisms of nuclear reactions on the population of 195 m Hg and 197 m Hg(7/2-), 198 m Tl and 196 m Tl(7+), and 196 m Au and 198 m Au(12-) isomeric nuclear states obtained in reactions induced by beams of 3He, 6Li, and 6He weakly bound nuclei is studied. The behavior of excitation functions and high values of isomeric ratios ( δ m/ δ g) for products of nuclear reactions proceeding through a compound nucleus and involving neutron evaporation are explained within statistical models. Reactions in which the emission of charged particles occurs have various isomeric ratios depending on the reaction type. The isomeric ratio is lower in direct transfer reactions involving charged-particle emission than in reactions where the evaporation of charged particles occurs. Reactions accompanied by neutron transfer usually have a lower isomeric ratio, which behaves differently for different direct-reaction types (stripping versus pickup reactions).

  9. Spherical proton-neutron structure of isomeric states in {sup 128}Cd

    SciTech Connect

    Caceres, L.; Gorska, M.; Grawe, H.; Sieja, K.; Geissel, H.; Gerl, J.; Kojouharov, I.; Kurz, N.; Montes, F.; Martinez-Pinedo, G.; Prokopowicz, W.; Schaffner, H.; Tashenov, S.; Wollersheim, H. J.; Jungclaus, A.; Pfuetzner, M.; Werner-Malento, E.; Nowacki, F.

    2009-01-15

    The {gamma}-ray decay of isomeric states in the even-even nucleus {sup 128}Cd has been observed. The nucleus of interest was produced both by the fragmentation of {sup 136}Xe and the fission of {sup 238}U primary beams. The level scheme was unambiguously constructed based on {gamma}{gamma} coincidence relations in conjunction with detailed lifetime analysis employed for the first time on this nucleus. Large-scale shell-model calculations, without consideration of excitations across the N=82 shell closure, were performed and provide a consistent description of the experimental level scheme. The structure of the isomeric states and their decays exhibit coexistence of proton, neutron, and strongly mixed configurations due to {pi}{nu} interaction in overlapping orbitals for both proton and neutron holes.

  10. Spherical proton-neutron structure of isomeric states in Cd128

    NASA Astrophysics Data System (ADS)

    Cáceres, L.; Górska, M.; Jungclaus, A.; Pfützner, M.; Grawe, H.; Nowacki, F.; Sieja, K.; Pietri, S.; Rudolph, D.; Podolyák, Zs.; Regan, P. H.; Werner-Malento, E.; Detistov, P.; Lalkovski, S.; Modamio, V.; Walker, J.; Andgren, K.; Bednarczyk, P.; Benlliure, J.; Benzoni, G.; Bruce, A. M.; Casarejos, E.; Cederwall, B.; Crespi, F. C. L.; Doornenbal, P.; Geissel, H.; Gerl, J.; Grebosz, J.; Hadinia, B.; Hellström, M.; Hoischen, R.; Ilie, G.; Khaplanov, A.; Kmiecik, M.; Kojouharov, I.; Kumar, R.; Kurz, N.; Maj, A.; Mandal, S.; Montes, F.; Martínez-Pinedo, G.; Myalski, S.; Prokopowicz, W.; Schaffner, H.; Simpson, G. S.; Steer, S. J.; Tashenov, S.; Wieland, O.; Wollersheim, H. J.

    2009-01-01

    The γ-ray decay of isomeric states in the even-even nucleus Cd128 has been observed. The nucleus of interest was produced both by the fragmentation of Xe136 and the fission of U238 primary beams. The level scheme was unambiguously constructed based on γγ coincidence relations in conjunction with detailed lifetime analysis employed for the first time on this nucleus. Large-scale shell-model calculations, without consideration of excitations across the N=82 shell closure, were performed and provide a consistent description of the experimental level scheme. The structure of the isomeric states and their decays exhibit coexistence of proton, neutron, and strongly mixed configurations due to πν interaction in overlapping orbitals for both proton and neutron holes.

  11. Resolution of nuclear ground and isomeric states by a Penning trap mass spectrometer

    SciTech Connect

    Bollen, G.; Kluge, H.; Koenig, M.; Otto, T.; Savard, G.; Stolzenberg, H. ); Moore, R.B.; Rouleau, G. ); Audi, G. )

    1992-12-01

    Ground and isomeric states of a nucleus have been resolved for the first time by mass spectrometry. Measurements on [sup 78]Rb[sup [ital m],][ital g] and [sup 84]Rb[sup [ital m],][ital g] were performed using a tandem Penning trap mass spectrometer on-line with the isotope separator ISOLDE/CERN. The effects of ion-ion interaction were investigated for two ion species differing in mass and stored simultaneously in the trap.

  12. Delayed autoionization of recoil ions by the decay of high-spin isomeric states

    NASA Astrophysics Data System (ADS)

    Maidikov, V. Z.

    1985-12-01

    The time dependence of the ionization for isotopically different heavy ion fusion recoil ions has been observed. Delayed nuclear-induced autoionization of recoil ions caused by the decay of high-spin nuclear isomeric states by internal conversion was established. Internal conversion in isolated recoil atoms results in a drastic rearrangement in the atomic cloud with a loss of a great number of orbital electrons. Possibilities for the use of the observed phenomena in atomic and nuclear physics are discussed.

  13. Isomerization, Perturbations, Calculations and the S_{1} State of C_{2}H_{2}

    NASA Astrophysics Data System (ADS)

    Baraban, J. H.; Changala, P. B.; Berk, J. R. P.; Field, R. W.; Stanton, J. F.; Merer, A. J.

    2013-06-01

    Preliminary analysis of the energy region of the cis-trans isomerization transition state on the S_{1} surface of C_{2}H_{2} has revealed novel patterns and surprising perturbations, including unusually large (and high-order) anharmonicities, as well as K-staggerings of several vibrational levels. These effects complicate the analysis considerably, and require new models and calculations to account for and predict features of the observed spectra. The ˜{A}-˜{X} spectrum of acetylene has been studied both experimentally and theoretically for almost a century, and this cycle of unexpected phenomena eliciting innovative responses is found throughout its history. Especially in the last ten years, progress in understanding the S_{1} state rovibrational level structure and cis-trans isomerization has been accelerated by combining the information available from both ab initio computation and spectroscopic observations. The resulting dialogue has then frequently suggested fruitful avenues for further experiments and calculations. Current challenges and recent results in understanding the cis-trans isomerization transition state region will be discussed in this context.

  14. Nanostructure formation by self-assembled monolayers: influence of the isomerization state of azobenzene ligands on monolayer formation

    NASA Astrophysics Data System (ADS)

    Vogel, Florian; Bretthauer, Frauke; Siemeling, Ulrich; Träger, Frank

    2011-03-01

    The monolayer formation of photoswitchable self-assembled monolayers of azobenzene-functionalized molecules was studied in situ and in real time by optical second-harmonic generation. Especially the influence of the isomerization state during the adsorption process was measured in our experiments. As will be shown, the isomerization state has a significant influence on the adsorption process of the investigated molecules. Based on the results of the second-harmonic generation experiments the kinetics of the adsorption process was determined.

  15. Thermal isomerization of azobenzenes: on the performance of Eyring transition state theory

    NASA Astrophysics Data System (ADS)

    Rietze, Clemens; Titov, Evgenii; Lindner, Steven; Saalfrank, Peter

    2017-08-01

    The thermal Z\\to E (back-)isomerization of azobenzenes is a prototypical reaction occurring in molecular switches. It has been studied for decades, yet its kinetics is not fully understood. In this paper, quantum chemical calculations are performed to model the kinetics of an experimental benchmark system, where a modified azobenzene (AzoBiPyB) is embedded in a metal-organic framework (MOF). The molecule can be switched thermally from cis to trans, under solvent-free conditions. We critically test the validity of Eyring transition state theory for this reaction. As previously found for other azobenzenes (albeit in solution), good agreement between theory and experiment emerges for activation energies and activation free energies, already at a comparatively simple level of theory, B3LYP/6-31G* including dispersion corrections. However, theoretical Arrhenius prefactors and activation entropies are in qualitiative disagreement with experiment. Several factors are discussed that may have an influence on activation entropies, among them dynamical and geometric constraints (imposed by the MOF). For a simpler model—Z\\to E isomerization in azobenzene—a systematic test of quantum chemical methods from both density functional theory and wavefunction theory is carried out in the context of Eyring theory. Also, the effect of anharmonicities on activation entropies is discussed for this model system. Our work highlights capabilities and shortcomings of Eyring transition state theory and quantum chemical methods, when applied for the Z\\to E (back-)isomerization of azobenzenes under solvent-free conditions.

  16. Thermal isomerization of azobenzenes: on the performance of Eyring transition state theory.

    PubMed

    Rietze, Clemens; Titov, Evgenii; Lindner, Steven; Saalfrank, Peter

    2017-08-09

    The thermal [Formula: see text] (back-)isomerization of azobenzenes is a prototypical reaction occurring in molecular switches. It has been studied for decades, yet its kinetics is not fully understood. In this paper, quantum chemical calculations are performed to model the kinetics of an experimental benchmark system, where a modified azobenzene (AzoBiPyB) is embedded in a metal-organic framework (MOF). The molecule can be switched thermally from cis to trans, under solvent-free conditions. We critically test the validity of Eyring transition state theory for this reaction. As previously found for other azobenzenes (albeit in solution), good agreement between theory and experiment emerges for activation energies and activation free energies, already at a comparatively simple level of theory, B3LYP/6-31G(*) including dispersion corrections. However, theoretical Arrhenius prefactors and activation entropies are in qualitiative disagreement with experiment. Several factors are discussed that may have an influence on activation entropies, among them dynamical and geometric constraints (imposed by the MOF). For a simpler model-[Formula: see text] isomerization in azobenzene-a systematic test of quantum chemical methods from both density functional theory and wavefunction theory is carried out in the context of Eyring theory. Also, the effect of anharmonicities on activation entropies is discussed for this model system. Our work highlights capabilities and shortcomings of Eyring transition state theory and quantum chemical methods, when applied for the [Formula: see text] (back-)isomerization of azobenzenes under solvent-free conditions.

  17. Insights into excited-state and isomerization dynamics of bacteriorhodopsin from ultrafast transient UV absorption

    PubMed Central

    Schenkl, S.; van Mourik, F.; Friedman, N.; Sheves, M.; Schlesinger, R.; Haacke, S.; Chergui, M.

    2006-01-01

    A visible-pump/UV-probe transient absorption is used to characterize the ultrafast dynamics of bacteriorhodopsin with 80-fs time resolution. We identify three spectral components in the 265- to 310-nm region, related to the all-trans retinal, tryptophan (Trp)-86 and the isomerized photoproduct, allowing us to map the dynamics from reactants to products, along with the response of Trp amino acids. The signal of the photoproduct appears with a time delay of ≈250 fs and is characterized by a steep rise (≈150 fs), followed by additional rise and decay components, with time scales characteristic of the J intermediate. The delayed onset and the steep rise point to an impulsive formation of a transition state on the way to isomerization. We argue that this impulsive formation results from a splitting of a wave packet of torsional modes on the potential surface at the branching between the all-trans and the cis forms. Parallel to these dynamics, the signal caused by Trp response rises in ≈200 fs, because of the translocation of charge along the conjugate chain, and possible mechanisms are presented, which trigger isomerization. PMID:16537491

  18. Watching ultrafast barrierless excited-state isomerization of pseudocyanine in real time.

    PubMed

    Dietzek, Benjamin; Yartsev, Arkady; Tarnovsky, Alexander N

    2007-05-03

    The photoinduced excited-state processes in 1,1'-diethyl-2,2'-cyanine iodine are investigated using femtosecond time-resolved pump-probe spectroscopy. Using a broad range of probe wavelengths, the relaxation of the initially prepared excited-state wavepacket can be followed down to the sink region. The data directly visualize the directed downhill motion along the torsional reaction coordinate and suggest a barrierless excited-state isomerization in the short chain cyanine dye. Additionally, ultrafast ground-state hole and excited-state hole replica broadening is observed. While the narrow excited-state wavepacket broadens during pump-probe overlap, the ground-state hole burning dynamics takes place on a significantly longer time-scale. The experiment reported can be considered as a direct monitoring of the shape and the position of the photoprepared wavepacket on the excited-state potential energy surface.

  19. A system to measure isomeric state half-lives in the 10 ns to 10 μs range

    SciTech Connect

    Toufen, D. L.; Allegro, P. R. P.; Medina, N. H.; Oliveira, J. R. B.; Cybulska, E. W.; Seale, W. A.; Ribas, R. V.; Linares, R.; Silveira, M. A. G.

    2014-07-15

    The Isomeric State Measurement System (SISMEI) was developed to search for isomeric nuclear states produced by fusion-evaporation reactions. The SISMEI consists of 10 plastic phoswich telescopes, two lead shields, one NaI(Tl) scintillation detector, two Compton suppressed HPGe γ-ray detectors, and a cone with a recoil product catcher. The new system was tested at the 8 UD Pelletron tandem accelerator of the University of São Paulo with the measurement of two known isomeric states: {sup 54}Fe, 10{sup +} state (E = 6527.1 (11) keV, T{sub 1/2} = 364(7) ns) and the 5/2{sup +} state of {sup 19}F (E = 197.143 (4) keV, T{sub 1/2} = 89.3 (10) ns). The results indicate that the system is capable of identifying delayed transitions, of measuring isomeric state lifetimes, and of identifying the feeding transitions of the isomeric state through the delayed γ-γ coincidence method. The measured half-life for the 10{sup +} state was T{sub 1/2} = 365(14) ns and for the 5/2{sup +} state, 100(36) ns.

  20. Experimental study of isomeric intruder 12+ states in At197,203

    DOE PAGES

    Auranen, K.; Uusitalo, J.; Juutinen, S.; ...

    2017-04-10

    A newly observed isomeric intruder ½+ state [T½=3.5(6)ms] is identified in 203At using a gas-filled recoil separator and fusion-evaporation reactions. The isomer is depopulated through a cascade of E3 and mixed M1/E2 transitions to the 9/2– ground state, and it is suggested to originate from the π(s½)–1 configuration. In addition, the structures above the ½+ state in 203At and 197At are studied using in-beam γ-ray spectroscopy, recoil-decay tagging, and recoil-isomer decay tagging methods. As a result, the ½+ state is fed from 3/2+ and 5/2+ states, and the origin of these states are discussed.

  1. Photodisintegration of 181Ta leading to the isomeric state 180mTa

    NASA Astrophysics Data System (ADS)

    Goko, S.; Utsunomiya, H.; Makinaga, A.; Kaihori, T.; Akimune, H.; Yamagata, T.; Hohara, S.; Goriely, S.; Koning, A. J.; Hilaire, S.; Toyokawa, H.; Lui, Y.-W.

    Partial photoneutron cross sections for 181 Ta(γ, n)180 Tam (9- ) were measured with laser Compton scattering γ rays. The partial cross section, which reflects selective γ transitions in 180 Ta leading to the isomeric state, cast new light into the spin- and parity-dependent nuclear level density of 180 Ta. Essentially the same selective γ transition is expected in neutron capture on 179 Ta leading to 180 Tam (9- ). The weak s-process branching to the only naturally occurring isomer 180 Tam is discussed.

  2. Search for long-lived isomeric states in neutron-deficient thorium isotopes

    SciTech Connect

    Lachner, J.; Dillmann, I.; Faestermann, T.; Korschinek, G.; Poutivtsev, M.; Rugel, G.

    2008-12-15

    The discovery of naturally occurring long-lived isomeric states (t{sub 1/2}>10{sup 8} yr) in the neutron-deficient isotopes {sup 211,213,217,218}Th[A. Marinov et al., Phys. Rev. C 76, 021303(R) (2007)] was reexamined using accelerator mass spectrometry (AMS). Because AMS does not suffer from molecular isobaric background in the detection system, it is an extremely sensitive technique. Despite our up to two orders of magnitude higher sensitivity we cannot confirm the discoveries of neutron-deficient thorium isotopes and provide upper limits for their abundances.

  3. 20 {mu}s isomeric state in doubly odd {sub 61}{sup 134}Pm

    SciTech Connect

    Cullen, D. M.; Mason, P. J. R; Rigby, S. V.; Kishada, A. M.; Varley, B. J.; Scholey, C.; Eeckhaudt, S.; Grahn, T.; Greenlees, P. T.; Jakobsson, U.; Jones, P. M.; Julin, R.; Juutinen, S.; Ketelhut, S.; Leino, M.; Leppaenen, A.-P.; Maentyniemi, K.; Nieminen, P.; Nyman, M.; Pakarinen, J.

    2009-08-15

    Recoil-isomer tagging at the Accelerator Laboratory of the University of Jyvaeskylae has been used to establish the isomeric nature of a known (7{sup -}) excited state in the doubly odd nucleus {sup 134}Pm. The isomeric state was determined to have a half-life of 20(1) {mu}s and was populated from the decay of a {pi}h{sub 11/2} x {nu}h{sub 11/2} band using the {sup 92}Mo({sup 54}Fe,2{alpha}3pn) reaction at 305 and 315 MeV. The isomer decays by a 71-keV transition that provides an intermediate step in linking the established {sup 134}Pm high-spin level scheme to the lower-spin states observed from the {beta} decay of {sup 134}Sm. Electron-conversion analysis for the 71-keV {gamma}-ray transition reveals that it is of E1 character and its small reduced-transition probability suggests that {sup 134}Pm may have a nuclear shape more rigid than that of the neighboring nuclei.

  4. Microwave assisted synthesis and solid-state characterization of lithocholyl amides of isomeric aminopyridines.

    PubMed

    Ahonen, Kari V; Lahtinen, Manu K; Valkonen, Arto M; Dracínský, Martin; Kolehmainen, Erkki T

    2011-02-01

    Microwave (MW) assisted synthesis and solid state structural characterizations of novel lithocholyl amides of 2-, 3-, and 4-aminopyridine are reported. It is shown that the MW technique is a proper method in the preparation of N-lithocholyl amides of isomeric aminopyridines. It offers many advantages compared to conventional heating. The molecular and crystal structures as well as the polymorphic and hydrated forms of prepared conjugates with their thermodynamic stabilities have been characterized by means of high resolution liquid- and solid-state NMR spectroscopy, single crystal and powder X-ray diffraction, and thermogravimetric analysis. Owing to the many biological functions of bile acids and amino substituted nitrogen heterocycles, knowledge of the crystal packing of these novel conjugates may have relevance for potential pharmaceutical applications. Copyright © 2010 Elsevier Inc. All rights reserved.

  5. Theoretical studies of 2-quinolinol: Geometries, vibrational frequencies, isomerization, tautomerism, and excited states

    NASA Astrophysics Data System (ADS)

    Pan, Yi; Lau, Kai-Chung; Al-Mogren, Muneerah Mogren; Mahjoub, Ahmed; Hochlaf, Majdi

    2014-10-01

    We treat theoretically 2-quinolinol(lactam), an analog of carbostyril and DNA bases. We characterized the ground state structure of 2-quinolinol and its isomer(lactim) using density functional theory(DFT). The reaction profile and energetics for lactam-lactim tautomerization and cis-lactim to trans-lactim isomerization predicted with explicitly correlated methods. We explored the pattern of the lowest singlet and triplet manifolds of states and electronic S1 ← S0 transitions using multiconfigurational methodologies. The theoretical results are compared with available experimental data and used to interpret the on-going photoelectron study of 2-quinolinol. Our analysis should help to understand the effect of tautomerism and aromaticity on the DNA bases.

  6. Partial Photoneutron Cross Sections for the Isomeric State {sup 180}Ta{sup m}

    SciTech Connect

    Goko, S.; Utsunomiya, H.; Makinaga, A.; Kaihori, T.; Hohara, S.; Akimune, H.; Yamagata, T.; Goriely, S.; Lui, Y.-W.; Toyokawa, H.; Koning, A.J.; Hilaire, S.

    2006-05-19

    Photoneutron cross sections for {sup 181}Ta({gamma},n){sup 180}Ta{sup m} were determined from simultaneous measurements of total cross sections ({sigma}{sup tot}) and ground-state cross sections ({sigma}{sup gs}) for {sup 180}Ta in photodisintegration of {sup 181}Ta with laser Compton-backscattered {gamma} rays. Techniques of direct neutron counting and photoactivation were used for the measurement of {sigma}{sup tot} and {sigma}{sup gs}, respectively. The partial cross sections for the isomeric state serves as a novel probe of the nuclear level density of {sup 180}Ta. Implications for the p- and s-process nucleosynthesis of {sup 180}Ta{sup m} are given.

  7. Population of isomeric states in fusion and transfer reactions in beams of loosely bound nuclei near the Coulomb barrier

    SciTech Connect

    Skobelev, N. K.

    2015-07-15

    The influence of the mechanisms of nuclear reactions on the population of {sup 195m}Hg and {sup 197m}Hg(7/2{sup −}), {sup 198m}Tl and {sup 196m}Tl(7{sup +}), and {sup 196m}Au and {sub 198m}Au(12{sup −}) isomeric nuclear states obtained in reactions induced by beams of {sup 3}He, {sup 6}Li, and {sup 6}He weakly bound nuclei is studied. The behavior of excitation functions and high values of isomeric ratios (δ{sub m}/δ{sub g}) for products of nuclear reactions proceeding through a compound nucleus and involving neutron evaporation are explained within statistical models. Reactions in which the emission of charged particles occurs have various isomeric ratios depending on the reaction type. The isomeric ratio is lower in direct transfer reactions involving charged-particle emission than in reactions where the evaporation of charged particles occurs. Reactions accompanied by neutron transfer usually have a lower isomeric ratio, which behaves differently for different direct-reaction types (stripping versus pickup reactions)

  8. A dipole band above the Iπ= 31/2- isomeric state in 189Pb

    NASA Astrophysics Data System (ADS)

    Cullen, D. M.

    2016-09-01

    This contribution focuses on the new observation of a dipole band built upon an Iπ=31/2- isomeric state in 189Pb, identified using recoil-isomer tagging at the University of Jyväskylä, Finland. This is the lightest odd-mass Pb isotope in which a dipole band is known. By comparison with the heavier-mass dipole bands, the dipole band in 189Pb was deduced to be based upon a π {≤ft( {s1/2 - 2{h9/2}{i13/2}} right){{11^ - }}} otimes v{≤ft( {i13/2 - 1} right)13/{2^ + }} configuration. However, in the 189Pb dipole band, the initial aligned angular momentum was larger than that exhibited by the dipole bands in the heavier-mass isotopes. This may be evidence for a reduced repulsive proton/neutron-hole interaction in 189Pb.

  9. Isomeric mirror states as probes for effective charges in the lower pf shell

    NASA Astrophysics Data System (ADS)

    Hoischen, R.; Rudolph, D.; Ma, H. L.; Montuenga, P.; Hellström, M.; Pietri, S.; Podolyák, Zs; Regan, P. H.; Garnsworthy, A. B.; Steer, S. J.; Becker, F.; Bednarczyk, P.; Cáceres, L.; Doornenbal, P.; Gerl, J.; Górska, M.; Grębosz, J.; Kojouharov, I.; Kurz, N.; Prokopowicz, W.; Schaffner, H.; Wollersheim, H. J.; Andersson, L.-L.; Atanasova, L.; Balabanski, D. L.; Bentley, M. A.; Blazhev, A.; Brandau, C.; Brown, J. R.; Fahlander, C.; Johansson, E. K.; Jungclaus, A.

    2011-03-01

    Following the fragmentation of a 550 MeV u-1primary beam of 58Ni, time- and energy-correlated γ decays from isomeric states in neutron-deficient nuclei in the 1f7/2 shell have been identified using the GSI fragment separator in combination with the RISING Ge-detector array. The results on isomers in the mirror pairs 4322Ti21-4321Sc22 (Iπ = 3/2+ and 19/2-), 4524Cr21-4521Sc24 (Iπ = 3/2+) and 4523V22-4522Ti23 (Iπ = 3/2-) are discussed in the framework of large scale pf and sdpf shell-model calculations, the former in conjunction with isospin symmetry breaking effects with emphasis on effective charges.

  10. Femtosecond study on the isomerization dynamics of NK88. II. Excited-state dynamics

    NASA Astrophysics Data System (ADS)

    Vogt, Gerhard; Nuernberger, Patrick; Gerber, Gustav; Improta, Roberto; Santoro, Fabrizio

    2006-07-01

    The molecule 3,3'-diethyl-2,2'-thiacyanine isomerizes after irradiation with light of the proper wavelength. After excitation, it undergoes a transition, in which one or more conical intersections are involved, back to the ground state to form different product photoisomers. The dynamics before and directly after the transition back to the ground state is investigated by transient absorption spectroscopy in a wavelength region of 360-950nm, as well as by fluorescence upconversion. It is shown that the excited-state dynamics are governed by two time scales: a short one with a decay time of less than 2ps and a long one with about 9ps. A thorough comparison of the experimental results with those of configuration interaction singles and time-dependent density functional theory calculations suggests that these dynamics are related to two competing pathways differing in the molecular twisting on the excited surface after photoexcitation. From the experimental point of view this picture arises taking into account the time scales for ground-state bleach, excited-state absorption, stimulated emission, fluorescence, and assumed hot ground-state absorption both in the solvent methanol and ethylene glycol.

  11. Isospin Symmetry at High Spin Studied via Nucleon Knockout from Isomeric States.

    PubMed

    Milne, S A; Bentley, M A; Simpson, E C; Baugher, T; Bazin, D; Berryman, J S; Bruce, A M; Davies, P J; Diget, C Aa; Gade, A; Henry, T W; Iwasaki, H; Lemasson, A; Lenzi, S M; McDaniel, S; Napoli, D R; Nichols, A J; Ratkiewicz, A; Scruton, L; Stroberg, S R; Tostevin, J A; Weisshaar, D; Wimmer, K; Winkler, R

    2016-08-19

    One-neutron knockout reactions have been performed on a beam of radioactive ^{53}Co in a high-spin isomeric state. The analysis is shown to yield a highly selective population of high-spin states in an exotic nucleus with a significant cross section, and hence represents a technique that is applicable to the planned new generation of fragmentation-based radioactive beam facilities. Additionally, the relative cross sections among the excited states can be predicted to a high level of accuracy when reliable shell-model input is available. The work has resulted in a new level scheme, up to the 11^{+} band-termination state, of the proton-rich nucleus ^{52}Co (Z=27, N=25). This has in turn enabled a study of mirror energy differences in the A=52 odd-odd mirror nuclei, interpreted in terms of isospin-nonconserving (INC) forces in nuclei. The analysis demonstrates the importance of using a full set of J-dependent INC terms to explain the experimental observations.

  12. Isospin Symmetry at High Spin Studied via Nucleon Knockout from Isomeric States

    NASA Astrophysics Data System (ADS)

    Milne, S. A.; Bentley, M. A.; Simpson, E. C.; Baugher, T.; Bazin, D.; Berryman, J. S.; Bruce, A. M.; Davies, P. J.; Diget, C. Aa.; Gade, A.; Henry, T. W.; Iwasaki, H.; Lemasson, A.; Lenzi, S. M.; McDaniel, S.; Napoli, D. R.; Nichols, A. J.; Ratkiewicz, A.; Scruton, L.; Stroberg, S. R.; Tostevin, J. A.; Weisshaar, D.; Wimmer, K.; Winkler, R.

    2016-08-01

    One-neutron knockout reactions have been performed on a beam of radioactive 53Co in a high-spin isomeric state. The analysis is shown to yield a highly selective population of high-spin states in an exotic nucleus with a significant cross section, and hence represents a technique that is applicable to the planned new generation of fragmentation-based radioactive beam facilities. Additionally, the relative cross sections among the excited states can be predicted to a high level of accuracy when reliable shell-model input is available. The work has resulted in a new level scheme, up to the 1 1+ band-termination state, of the proton-rich nucleus 52Co (Z =27 , N =25 ). This has in turn enabled a study of mirror energy differences in the A =52 odd-odd mirror nuclei, interpreted in terms of isospin-nonconserving (INC) forces in nuclei. The analysis demonstrates the importance of using a full set of J -dependent INC terms to explain the experimental observations.

  13. Identification of a millisecond isomeric state in 129Cd81via the detection of internal conversion and Compton electrons

    SciTech Connect

    Taprogge, J.; Jungclaus, A.; Grawe, H.; Nishimura, S.; Xu, Z. Y.; Doornenbal, P.; Lorusso, G.; Nacher, E.; Simpson, G. S.; Soderstrom, P. A.; Sumikama, T.; Kondev, F. G.

    2014-11-10

    The decay of an isomeric state in the neutron-rich nucleus 129Cd has been observed via the detection of internal conversion and Compton electrons providing first experimental information on excited states in this nucleus. The isomer was populated in the projectile fission of a 238U beam at the Radioactive Isotope Beam Factory at RIKEN. From the measured yields of γ-rays and internal conversion electrons, a multipolarity of E 3 was tentatively assigned to the isomeric transition. A half-life of T1/2=3.6(2) msT1/2=3.6(2) ms was determined for the new state which was assigned a spin of (21/2+)(21/2+), based on a comparison to shell model calculations performed using state-of-the-art realistic effective interactions.

  14. Identification of a millisecond isomeric state in Cd12981 via the detection of internal conversion and Compton electrons

    NASA Astrophysics Data System (ADS)

    Taprogge, J.; Jungclaus, A.; Grawe, H.; Nishimura, S.; Xu, Z. Y.; Doornenbal, P.; Lorusso, G.; Nácher, E.; Simpson, G. S.; Söderström, P.-A.; Sumikama, T.; Baba, H.; Browne, F.; Fukuda, N.; Gernhäuser, R.; Gey, G.; Inabe, N.; Isobe, T.; Jung, H. S.; Kameda, D.; Kim, G. D.; Kim, Y.-K.; Kojouharov, I.; Kubo, T.; Kurz, N.; Kwon, Y. K.; Li, Z.; Sakurai, H.; Schaffner, H.; Steiger, K.; Suzuki, H.; Takeda, H.; Vajta, Zs.; Watanabe, H.; Wu, J.; Yagi, A.; Yoshinaga, K.; Benzoni, G.; Bönig, S.; Chae, K. Y.; Coraggio, L.; Covello, A.; Daugas, J.-M.; Drouet, F.; Gadea, A.; Gargano, A.; Ilieva, S.; Kondev, F. G.; Kröll, T.; Lane, G. J.; Montaner-Pizá, A.; Moschner, K.; Mücher, D.; Naqvi, F.; Niikura, M.; Nishibata, H.; Odahara, A.; Orlandi, R.; Patel, Z.; Podolyák, Zs.; Wendt, A.

    2014-11-01

    The decay of an isomeric state in the neutron-rich nucleus 129Cd has been observed via the detection of internal conversion and Compton electrons providing first experimental information on excited states in this nucleus. The isomer was populated in the projectile fission of a 238U beam at the Radioactive Isotope Beam Factory at RIKEN. From the measured yields of γ-rays and internal conversion electrons, a multipolarity of E3 was tentatively assigned to the isomeric transition. A half-life of T1/2 = 3.6 (2) ms was determined for the new state which was assigned a spin of (21 /2+), based on a comparison to shell model calculations performed using state-of-the-art realistic effective interactions.

  15. Identification of a millisecond isomeric state in 129Cd81 via the detection of internal conversion and Compton electrons

    DOE PAGES

    Taprogge, J.; Jungclaus, A.; Grawe, H.; ...

    2014-09-26

    The decay of an isomeric state in the neutron-rich nucleus 129Cd has been observed via the detection of internal conversion and Compton electrons providing first experimental information on excited states in this nucleus. The isomer was populated in the projectile fission of a 238U beam at the Radioactive Isotope Beam Factory at RIKEN. From the measured yields of γ-rays and internal conversion electrons, a multipolarity of E3 was tentatively assigned to the isomeric transition. A half-life of T1/2=3.6(2) ms was determined for the new state which was assigned a spin of (21/2+), based on a comparison to shell model calculationsmore » performed using state-of-the-art realistic effective interactions.« less

  16. Effect of nuclear-reaction mechanisms on the population of excited nuclear states and isomeric ratios

    SciTech Connect

    Skobelev, N. K.

    2016-07-15

    Experimental data on the cross sections for channels of fusion and transfer reactions induced by beams of radioactive halo nuclei and clustered and stable loosely bound nuclei were analyzed, and the results of this analysis were summarized. The interplay of the excitation of single-particle states in reaction-product nuclei and direct reaction channels was established for transfer reactions. Respective experiments were performed in stable ({sup 6}Li) and radioactive ({sup 6}He) beams of the DRIBs accelerator complex at the Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, and in deuteron and {sup 3}He beams of the U-120M cyclotron at the Nuclear Physics Institute, Academy Sciences of Czech Republic (Řež and Prague, Czech Republic). Data on subbarrier and near-barrier fusion reactions involving clustered and loosely bound light nuclei ({sup 6}Li and {sup 3}He) can be described quite reliably within simple evaporation models with allowance for different reaction Q-values and couple channels. In reactions involving halo nuclei, their structure manifests itself most strongly in the region of energies below the Coulomb barrier. Neutron transfer occurs with a high probability in the interactions of all loosely bound nuclei with light and heavy stable nuclei at positive Q-values. The cross sections for such reactions and the respective isomeric ratios differ drastically for nucleon stripping and nucleon pickup mechanisms. This is due to the difference in the population probabilities for excited single-particle states.

  17. Effect of nuclear-reaction mechanisms on the population of excited nuclear states and isomeric ratios

    NASA Astrophysics Data System (ADS)

    Skobelev, N. K.

    2016-07-01

    Experimental data on the cross sections for channels of fusion and transfer reactions induced by beams of radioactive halo nuclei and clustered and stable loosely bound nuclei were analyzed, and the results of this analysis were summarized. The interplay of the excitation of single-particle states in reaction-product nuclei and direct reaction channels was established for transfer reactions. Respective experiments were performed in stable (6Li) and radioactive (6He) beams of the DRIBs accelerator complex at the Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, and in deuteron and 3He beams of the U-120M cyclotron at the Nuclear Physics Institute, Academy Sciences of Czech Republic (Řež and Prague, Czech Republic). Data on subbarrier and near-barrier fusion reactions involving clustered and loosely bound light nuclei (6Li and 3He) can be described quite reliably within simple evaporation models with allowance for different reaction Q-values and couple channels. In reactions involving halo nuclei, their structure manifests itself most strongly in the region of energies below the Coulomb barrier. Neutron transfer occurs with a high probability in the interactions of all loosely bound nuclei with light and heavy stable nuclei at positive Q-values. The cross sections for such reactions and the respective isomeric ratios differ drastically for nucleon stripping and nucleon pickup mechanisms. This is due to the difference in the population probabilities for excited single-particle states.

  18. Isomeric states in neutron-deficient A~80-90 nuclei populated in the fragmentation of Ag107

    NASA Astrophysics Data System (ADS)

    Garnsworthy, A. B.; Regan, P. H.; Pietri, S.; Sun, Y.; Xu, F. R.; Rudolph, D.; Górska, M.; Cáceres, L.; Podolyák, Zs.; Steer, S. J.; Hoischen, R.; Heinz, A.; Becker, F.; Bednarczyk, P.; Doornenbal, P.; Geissel, H.; Gerl, J.; Grawe, H.; Grebosz, J.; Kelic, A.; Kojouharov, I.; Kurz, N.; Montes, F.; Prokopwicz, W.; Saito, T.; Schaffner, H.; Tachenov, S.; Werner-Malento, E.; Wollersheim, H. J.; Benzoni, G.; Blank, B.; Brandau, C.; Bruce, A. M.; Camera, F.; Catford, W. N.; Cullen, I. J.; Dombrádi, Zs.; Estevez, E.; Gelletly, W.; Ilie, G.; Jolie, J.; Jones, G. A.; Jungclaus, A.; Kmiecik, M.; Kondev, F. G.; Kurtukian-Nieto, T.; Lalkovski, S.; Liu, Z.; Maj, A.; Myalski, S.; Pfützner, M.; Schwertel, S.; Shizuma, T.; Simons, A. J.; Walker, P. M.; Wieland, O.

    2009-12-01

    The relativistic projectile fragmentation of a 750 MeV per nucleon beam of Ag107 was used to populate isomeric states in neutron-deficient nuclei around A=80-90. Reaction products were separated and unambiguously identified using the GSI FRagment Separator (FRS) and its ancillary detectors. At the final focal plane, the fragments were slowed from relativistic energies by means of an aluminium degrader and implanted in a passive stopper in the center of the high-efficiency, high-granularity Stopped Rare Isotope Spectroscopic INvestigation at GSI (RISING) germanium array. This allowed the identification of excited states in the N=Z nuclei 4386Tc and, for the first time, 4182Nb. Isomeric states have also been identified for the first time in Tc87,88, and a previously unreported isomer was observed in Nb84. Experimental results are presented along with a discussion on the structure of these nuclei based on interpretations provided by several theoretical models.

  19. Femtosecond study on the isomerization dynamics of NK88. I. Ground-state dynamics after photoexcitation

    NASA Astrophysics Data System (ADS)

    Nuernberger, Patrick; Vogt, Gerhard; Gerber, Gustav; Improta, Roberto; Santoro, Fabrizio

    2006-07-01

    Recently, optimal control of a photoisomerization reaction in the liquid phase was demonstrated for the first time on the system 3,3'-diethyl-2,2'-thiacyanine (NK88). Additionally, the class of cyanines to which the molecule NK88 belongs draws a lot of attention in different recent theoretical publications. Therefore, a better understanding of the molecular dynamics of this molecular system is of special interest. Experiments using the femtosecond pump-supercontinuum probe technique with an excitation wavelength of 400nm and a spectral range from 370to620nm for the probe beam have been performed. In order to analyze the dynamics properly the time window has been chosen to comprise the characteristic times of the contributing processes, additionally we have employed two solvents, methanol and ethylene glycol, and have conducted anisotropy measurements. The spectroscopic data have been assigned to different molecular states with the help of density functional theory and second-order Möller-Plesset perturbation theory calculations. The analysis of the data has revealed in the most likely model that three different isomers exist with different lifetimes. On the basis of experimental and theoretical data, a conclusive scheme of the isomerization reaction is presented.

  20. Covalent isomeric state in {sup 12}Be induced by two-neutron transfers

    SciTech Connect

    Ito, M.; Itagaki, N.

    2008-07-15

    The {alpha}+{sup 8}He low-energy reactions and the exotic structures of {sup 12}Be are studied using the generalized two-center cluster ({alpha}+{alpha}+4N) model. In the two-neutron transfer reactions, {alpha}+{sup 8}He{sub g.s.}{yields}{sup 6}He{sub g.s.}+{sup 6}He{sub g.s.}, a resonant peak with J{sup {pi}}=0{sup +} appears around E {approx} 1.3 MeV above the {sup 6}He{sub g.s.}+{sup 6}He{sub g.s.} threshold as the result of the formation of the covalent superdeformation, which has a hybrid structure of covalent and ionic configurations for the valence neutrons. The covalent superdeformation gives rise to an isomeric state with a sharp width of {gamma}{approx}400 keV, which is smaller by about one order of magnitude than the typical width observed in molecular resonances above the Coulomb barrier. The energy-spin systematics for the two-neutron transfer reactions is investigated, and our calculation predicts a sequence of resonant structures in the range of 3-14 MeV in the center-of-mass energy with spins 0({Dirac_h}/2{pi})-8({Dirac_h}/2{pi})

  1. Production and decay properties of the 1.9-s isomeric state in {sup 261}Rf

    SciTech Connect

    Haba, H.; Kaji, D.; Kikunaga, H.; Kudou, Y.; Morimoto, K.; Morita, K.; Ozeki, K.; Sumita, T.; Yoneda, A.; Kasamatsu, Y.; Komori, Y.; Ooe, K.; Shinohara, A.

    2011-03-15

    The 1.9-s isomeric state ({sup 261}Rf{sup b}) in {sup 261}Rf was directly populated in the {sup 248}Cm({sup 18}O,5n){sup 261}Rf{sup b} reaction. Alpha and spontaneous fission (SF) decays of {sup 261}Rf{sup b}, as well as the 68-s state {sup 261}Rf{sup a}, was investigated with a rotating wheel apparatus under low background conditions attained by a gas-jet transport system coupled to the RIKEN gas-filled recoil ion separator. An identification of {sup 261}Rf{sup b} was based on {alpha}-{alpha} correlations linking {alpha} decays of {sup 261}Rf{sup b} and its daughter {sup 257}No. The {alpha}-particle energy of {sup 261}Rf{sup b} was measured to be 8.52 {+-} 0.05 MeV. The half-life was determined to be 1.9 {+-} 0.4 s based on both 8.52-MeV {alpha} and SF decays. The {alpha} and SF branches are 0.27 {+-} 0.06 and 0.73 {+-} 0.06, respectively. The cross section for the {sup 248}Cm({sup 18}O,5n){sup 261}Rf{sup b} reaction is {sigma}({sup 261}Rf{sup b}) = 11 {+-} 2 nb at 95.1 MeV, which gives a cross-section ratio of {sigma}({sup 261}Rf{sup a})/{sigma}({sup 261}Rf{sup b}) = 1.1 {+-} 0.2.

  2. High-spin μs isomeric states in 96Ag

    NASA Astrophysics Data System (ADS)

    Becerril, A. D.; Lorusso, G.; Amthor, A. M.; Baumann, T.; Bazin, D.; Berryman, J. S.; Brown, B. A.; Crawford, H. L.; Estrade, A.; Gade, A.; Ginter, T.; Guess, C. J.; Hausmann, M.; Hitt, G. W.; Mantica, P. F.; Matos, M.; Meharchand, R.; Minamisono, K.; Montes, F.; Perdikakis, G.; Pereira, J.; Portillo, M.; Schatz, H.; Smith, K.; Stoker, J.; Stolz, A.; Zegers, R. G. T.

    2011-10-01

    The isomeric and β decays of the N=Z+2 nucleus 96Ag were investigated at the National Superconducting Cyclotron Laboratory. A cascade of γ-ray transitions originating from the deexcitation of a microsecond isomer was observed for the first time and was found in coincidence with two previously known transitions with energies of 470 and 667 keV. The isomeric half-life was determined as 1.45(7) μs, more precise than previously reported. The existence of a second, longer-lived microsecond isomer, associated with a 743-keV γ transition, is also proposed here. Shell model results within the (p3/2p1/2f5/2g9/2) model space, using the jj44b interaction, reproduced level energies and isomeric decay half-lives reasonably well.

  3. Nitrogen-15 NMR studies of tetrazole complexes of pentamminecobalt(III). Implications concerning the transition state for linkage isomerization

    SciTech Connect

    Hubinger, S.; Hall, J.H.; Purcell, W.L. Los Alamos National Lab., NM )

    1993-05-26

    Synthesis of the N1-bonded (5-methyltetrazolato)pentaamminecobalt(III) complex utilizing sodium azide enriched in [sup 1]N at the terminal nitrogen has produced a complex enriched specifically at the N2 and N4 ring positions. This has permitted the assignment of all four nitrogen signals in the natural-abundance NMR spectrum for a novel chelated amidine complex which is also N1 bonded is reported along with its synthesis and purification. Following the [sup 15]N NMR of the linkage isomerization of the enriched complex in solution to the N2-bonded form has also permitted an [eta][sup 5] and certain [eta][sup 3] transition-state structures to be eliminated from consideration for the isomerization process. The data suggest an [eta][sup 2] transition state is utilized. A subsequent N2-to-N3 isomerization of the N2-bonded complex has also been discovered from the [sup 15]N NMR study. The enrichment study also indicates that previous assignments of ring nitrogen signals N1 and N4 is similar N2-bonded tetrazolato complexes of cobalt(III) may be in error.

  4. Thorium silicate compound as a solid-state target for production of isomeric thorium-229 nuclei by electron beam irradiation

    NASA Astrophysics Data System (ADS)

    Borisyuk, P. V.; Vasilyev, O. S.; Lebedinskii, Y. Y.; Krasavin, A. V.; Tkalya, E. V.; Troyan, V. I.; Habibulina, R. F.; Chubunova, E. V.; Yakovlev, V. P.

    2016-09-01

    In this paper, we discuss an idea of the experiment for excitation of the isomeric transition in thorium-229 nuclei by irradiating with electron beam targets with necessary physical characteristics. The chemical composition and bandgap of ThSi10O22 were determined by X-ray photoelectron spectroscopy and reflection electron energy loss spectroscopy. It was found that the energy gap is equal to 7.7 eV and does not change when the target is exposed to a medium energy electron beam for a long time. This indicates that the compound possesses high electron-beam resistance. A quantitative estimation of the output function of isomeric thorium-229 nuclei generated by interaction of nuclei with the secondary electron flow formed by irradiating the solid-state ThSi10O22-based target is given. The estimation shows that ThSi10O22 is a promising thorium-containing target for investigating excitation of the nuclear low-lying isomeric transition in the thorium-229 isotope using medium-energy electrons.

  5. High-K, t{sub 1/2} = 1.4(1) ms, isomeric state in {sup 255}Lr

    SciTech Connect

    Hauschild, K.; Lopez-Martens, A.; Briancon, Ch.; Yeremin, A. V.; Belozerov, A. V.; Chelnokov, M. L.; Chepigin, V. I.; Gorshkov, V. A.; Kabachenko, A. P.; Malyshev, O. N.; Popeko, A. G.; Shutov, A. V.; Svirikhin, A. I.; Dorvaux, O.; Curien, D.; Gall, B.; Khalfallah, F.; Rousseau, M.; Rowley, N.; Stuttge, L.

    2008-08-15

    An isomeric state in {sup 255}Lr with a half-life of t{sub 1/2} = 1.4(1) ms and E{sub x}>720-keV has been observed for the first time using the GABRIELA setup at the focal plane of the VASSILISSA separator. Based on its K-forbiddeness, the configuration of the state is most probably formed by coupling the valence proton to a two quasiparticle neutron excitation. Possible three quasiparticle configurations are discussed.

  6. The role of dissociation channels of excited electronic states in quantum optimal control of ozone isomerization: A three-state dynamical model

    NASA Astrophysics Data System (ADS)

    Kurosaki, Yuzuru; Ho, Tak-San; Rabitz, Herschel

    2016-05-01

    The prospect of performing the open → cyclic ozone isomerization has attracted much research attention. Here we explore this consideration theoretically by performing quantum optimal control calculations to demonstrate the important role that excited-state dissociation channels could play in the isomerization transformation. In the calculations we use a three-state, one-dimensional dynamical model constructed from the lowest five 1A‧ potential energy curves obtained with high-level ab initio calculations. Besides the laser field-dipole couplings between all three states, this model also includes the diabatic coupling between the two excited states at an avoided crossing leading to competing dissociation channels that can further hinder the isomerization process. The present three-state optimal control simulations examine two possible control pathways previously considered in a two-state model, and reveal that only one of the pathways is viable, achieving a robust ∼95% yield to the cyclic target in the three-state model. This work represents a step towards an ultimate model for the open → cyclic ozone transformation capable of giving adequate guidance about the necessary experimental control field resources as well as an estimate of the ro-vibronic spectral character of cyclic ozone as a basis for an appropriate probe of its formation.

  7. Decay of the Iπ=8- isomeric state in 134Nd and 184Pt studied by electron and γ spectroscopy

    NASA Astrophysics Data System (ADS)

    Perkowski, J.; Andrzejewski, J.; Droste, Ch.; Janiak, Ł.; Grodner, E.; Rohoziński, S. G.; Próchniak, L.; Srebrny, J.; Samorajczyk-Pyśk, J.; Abraham, T.; Hadyńska-KlÈ©k, K.; Kisieliński, M.; Komorowska, M.; Kowalczyk, M.; Kownacki, J.; Marchlewski, T.; Mierzejewski, J.; Napiorkowski, P.; Stolarz, A.; Korman, A.; Zielińska, M.

    2017-01-01

    The properties of the K -isomer decays in the 134Nd and 184Pt nuclei have been investigated. Measurements were carried out in e -γ and γ -γ coincidence modes using electron spectrometers coupled to the central European Array for Gamma Levels Evaluations at the Heavy Ion Laboratory of the University of Warsaw. Internal conversion coefficients were obtained for transitions relevant to the decay of the isomeric states, allowing the determination of multipolarities and mixing ratios as well as hindrance factors. Two possible causes of the weakening of the K forbiddenness, namely rotational K mixing (Coriolis interaction) and triaxiality, are briefly discussed using schematic theoretical models.

  8. A VUV detection system for the direct photonic identification of the first excited isomeric state of 229Th

    NASA Astrophysics Data System (ADS)

    Seiferle, Benedict; von der Wense, Lars; Laatiaoui, Mustapha; Thirolf, Peter G.

    2016-03-01

    With an expected energy of 7.6(5) eV, 229Th possesses the lowest excited nuclear state in the landscape of all presently known nuclei. The energy corresponds to a wavelength of about 160 nm and would conceptually allow for an optical laser excitation of a nuclear transition. We report on a VUV optical detection system that was designed for the direct detection of the isomeric ground-state transition of 229Th. 229(m)Th ions originating from a 233U α-recoil source are collected on a micro electrode that is placed in the focus of an annular parabolic mirror. The latter is used to parallelize the UV fluorescence that may emerge from the isomeric ground-state transition of 229Th. The parallelized light is then focused by a second annular parabolic mirror onto a CsI-coated position-sensitive MCP detector behind the mirror exit. To achieve a high signal-to-background ratio, a small spot size on the MCP detector needs to be achieved. Besides extensive ray-tracing simulations of the optical setup, we present a procedure for its alignment, as well as test measurements using a D2 lamp, where a focal-spot size of ≈100 μm has been achieved. Assuming a purely photonic decay, a signal-to-background ratio of ≈7000:1 could be achieved.

  9. Quantum optimal control pathways of ozone isomerization dynamics subject to competing dissociation: A two-state one-dimensional model

    SciTech Connect

    Kurosaki, Yuzuru; Ho, Tak-San Rabitz, Herschel

    2014-02-28

    We construct a two-state one-dimensional reaction-path model for ozone open → cyclic isomerization dynamics. The model is based on the intrinsic reaction coordinate connecting the cyclic and open isomers with the O{sub 2} + O asymptote on the ground-state {sup 1}A{sup ′} potential energy surface obtained with the high-level ab initio method. Using this two-state model time-dependent wave packet optimal control simulations are carried out. Two possible pathways are identified along with their respective band-limited optimal control fields; for pathway 1 the wave packet initially associated with the open isomer is first pumped into a shallow well on the excited electronic state potential curve and then driven back to the ground electronic state to form the cyclic isomer, whereas for pathway 2 the corresponding wave packet is excited directly to the primary well of the excited state potential curve. The simulations reveal that the optimal field for pathway 1 produces a final yield of nearly 100% with substantially smaller intensity than that obtained in a previous study [Y. Kurosaki, M. Artamonov, T.-S. Ho, and H. Rabitz, J. Chem. Phys. 131, 044306 (2009)] using a single-state one-dimensional model. Pathway 2, due to its strong coupling to the dissociation channel, is less effective than pathway 1. The simulations also show that nonlinear field effects due to molecular polarizability and hyperpolarizability are small for pathway 1 but could become significant for pathway 2 because much higher field intensity is involved in the latter. The results suggest that a practical control may be feasible with the aid of a few lowly excited electronic states for ozone isomerization.

  10. Quantum optimal control pathways of ozone isomerization dynamics subject to competing dissociation: a two-state one-dimensional model.

    PubMed

    Kurosaki, Yuzuru; Ho, Tak-San; Rabitz, Herschel

    2014-02-28

    We construct a two-state one-dimensional reaction-path model for ozone open → cyclic isomerization dynamics. The model is based on the intrinsic reaction coordinate connecting the cyclic and open isomers with the O2 + O asymptote on the ground-state (1)A(') potential energy surface obtained with the high-level ab initio method. Using this two-state model time-dependent wave packet optimal control simulations are carried out. Two possible pathways are identified along with their respective band-limited optimal control fields; for pathway 1 the wave packet initially associated with the open isomer is first pumped into a shallow well on the excited electronic state potential curve and then driven back to the ground electronic state to form the cyclic isomer, whereas for pathway 2 the corresponding wave packet is excited directly to the primary well of the excited state potential curve. The simulations reveal that the optimal field for pathway 1 produces a final yield of nearly 100% with substantially smaller intensity than that obtained in a previous study [Y. Kurosaki, M. Artamonov, T.-S. Ho, and H. Rabitz, J. Chem. Phys. 131, 044306 (2009)] using a single-state one-dimensional model. Pathway 2, due to its strong coupling to the dissociation channel, is less effective than pathway 1. The simulations also show that nonlinear field effects due to molecular polarizability and hyperpolarizability are small for pathway 1 but could become significant for pathway 2 because much higher field intensity is involved in the latter. The results suggest that a practical control may be feasible with the aid of a few lowly excited electronic states for ozone isomerization.

  11. Half-lives of ground and isomeric states in 97Cd and the astrophysical origin of 96Ru

    NASA Astrophysics Data System (ADS)

    Lorusso, G.; Becerril, A.; Amthor, A.; Baumann, T.; Bazin, D.; Berryman, J. S.; Brown, B. A.; Cyburt, R. H.; Crawford, H. L.; Estrade, A.; Gade, A.; Ginter, T.; Guess, C. J.; Hausmann, M.; Hitt, G. W.; Mantica, P. F.; Matos, M.; Meharchand, R.; Minamisono, K.; Montes, F.; Perdikakis, G.; Pereira, J.; Portillo, M.; Schatz, H.; Smith, K.; Stoker, J.; Stolz, A.; Zegers, R. G. T.

    2011-05-01

    First experimental evidence for a high-spin isomer (25/2+) in 97Cd, a waiting point in the astrophysical rapid proton capture process, is presented. The data were obtained in β-decay studies at NSCL using the new RF Fragment Separator system and detecting β-delayed protons and β-delayed γ rays. Decays from ground and isomeric states were disentangled, and proton emission branches were determined for the first time. We find half-lives of 1.10(8) s and 3.8(2) s, and β-delayed proton emission branches of 12(2)% and 25(4)% were deduced for the ground and isomeric states, respectively. With these results, the nuclear data needed to determine an rp-process contribution to the unknown origin of solar 96Ru are in place. When the new data are included in astrophysical rp-process calculations, one finds that an rp-process origin of 96Ru is unlikely.

  12. Isomeric character of the 41+ state in 44S: Mechanisms of breaking of the N = 28 shell

    NASA Astrophysics Data System (ADS)

    Parker, J., IV; Wiedenhover, I.; Baker, J.; Cottle, P.; McPherson, D.; Riley, M.; Santiago-Gonzalez, D.; Volya, A.; Bader, V.; Baugher, T.; Bazin, D.; Gade, A.; Ginter, T.; Iwasaki, H.; Loelius, C.; Morse, C.; Recchia, F.; Smalley, D.; Stroberg, R.; Weisshaar, D.; Whitmore, K.; Lemasson, A.; Crawford, H.; Macchiavelli, A.; Wimmer, K.

    2015-10-01

    The N = 28 nucleus 44S exhibits a rich structure of excitations which illustrates different mechanisms of breaking the N = 28 shell. A Coulomb excitation measurement and an implantation-decay experiment established the coexistence of 2p2h-deformed and 0p0h-spherical configurations. A two-proton knockout reaction indicated a 4+ state which shell model calculations suggest is likely isomeric, prolate-deformed and formed from a 1p1h configuration. A recent two-proton knockout experiment measured the lifetime of this 4+ state using the recoil distance method and the GRETINA array. Results for the lifetime of the 4+ state will be presented and its implication for the mechanisms of breaking the N = 28 shell will be discussed. Supported by the National Science Foundation.

  13. Isomerization of HNO to HON in the singlet state assisted by amino acid residues and/or water molecules

    NASA Astrophysics Data System (ADS)

    Shi, Junyou; Li, Ping; Bu, Yuxiang; Wang, Weihua; Mou, Zhaoxia; Song, Rui

    The effects of amino acid residues in the presence or absence of water molecules on the isomerization of the singlet state of HNO/HON have been systematically investigated at the B3LYP/6-311++G** level of theory. The structural characteristics, proton transfer (PT) mechanisms, and the corresponding thermodynamic and kinetic parameters, have been discussed, respectively. All the optimized complexes have been characterized by the ring structures through the intermolecular H-bonds. The origin of the increase in N bond H stretching frequency (blue shifts) occurring in the reactants has also been investigated using the natural bonding orbital (NBO) analyses, which is mainly attributed to the decrease of the electron densities in the antibonding orbital of the N bond H bonds as well as the increase of the polarization of the N bond H bond. All the PTs proceed with the concerted mechanisms since no ionic intermediates have been located during PT processes. At the same time, the cooperative effects of amino acid residues and water molecules on the selected PT processes have been observed, where the PTs assisted solely by the selected residues cannot occur without the participation of the water molecule. Overall, the introductions of one or two water molecules are more favorable for the isomerization of HNO assisted by the amino acid residues.

  14. Effects of roaming trajectories on the transition state theory rates of a reduced-dimensional model of ketene isomerization.

    PubMed

    Ulusoy, Inga S; Stanton, John F; Hernandez, Rigoberto

    2013-08-15

    The rates of chemical reactions (or any activated process) are by definition determined by the flux of reactants (or initial states) that end up as products (or final states). The forward flux through any surface that divides reactants from products is a constant as long as only those trajectories that were reactants in the infinite past and products in the infinite future are included in the flux once and only once. Transition state theory (TST) ignores this last clause, thereby overestimating the rate if any of the trajectories recross the dividing surface. However, its advantage is that it replaces a dynamical calculation with a statistical integral over the TST geometry. The recent identification of roaming trajectories-those that persist for a long time as neither reactant nor product without ever visiting near the col on the energy landscape-apparently challenges the dogma that TST's only error lies in the omission of recrossing trajectories. This question is investigated using the isomerization reaction of ketene in which the experimental values are verified to be in reasonable agreement with both the exact and TST values. We have found two trajectories for the ketene isomerization that carry the signature of roaming, but their effect on the calculation of the reaction rate constant using classical transition state theory is small. Indeed, the existence of roaming trajectories is seen to impose a limitation on which dividing surfaces are appropriate for the calculation of either exact or approximate TST rates, but in this case, they do not unseat the existence of dividing surfaces that can be used safely to calculate TST rates.

  15. Tuning excited state isomerization dynamics through ground state structural changes in analogous ruthenium and osmium sulfoxide complexes.

    PubMed

    Garg, Komal; Engle, James T; Ziegler, Christopher J; Rack, Jeffrey J

    2013-08-26

    The complexes [Ru(bpy)2(pyESO)](PF6)2 and [Os(bpy)2(pyESO)](PF6)2, in which bpy is 2,2'-bipyridine and pyESO is 2-((isopropylsulfinyl)ethyl)pyridine, were prepared and studied by (1)H NMR, UV-visible and ultrafast transient absorption spectroscopy, as well as by electrochemical methods. Crystals suitable for X-ray structural analysis were grown for [Ru(bpy)2(pyESO)](PF6)2. Cyclic voltammograms of both complexes provide evidence for S→O and O→S isomerization as these voltammograms are described by an ECEC (electrochemical-chemical electrochemical-chemical) mechanism in which isomerization follows Ru(2+) oxidation and Ru(3+) reduction. The S- and O-bonded Ru(3+/2+) couples appear at 1.30 and 0.76 V versus Ag/AgCl in propylene carbonate. For [Os(bpy)2(pyESO)](PF6)2, these couples appear at 0.97 and 0.32 V versus Ag/AgCl in acetonitrile, respectively. Charge-transfer excitation of [Ru(bpy)2(pyESO)](PF6)2 results in a significant change in the absorption spectrum. The S-bonded isomer of [Ru(bpy)2(pyESO)](2+) features a lowest energy absorption maximum at 390 nm and the O-bonded isomer absorbs at 480 nm. The quantum yield of isomerization in [Ru(bpy)2(pyESO)](2+) was found to be 0.58 in propylene carbonate and 0.86 in dichloroethane solution. Femtosecond transient absorption spectroscopic measurements were collected for both complexes, revealing time constants of isomerizations of 81 ps (propylene carbonate) and 47 ps (dichloroethane) in [Ru(bpy)2(pyESO)](2+). These data and a model for the isomerizing complex are presented. A striking conclusion from this analysis is that expansion of the chelate ring by a single methylene leads to an increase in the isomerization time constant by nearly two orders of magnitude.

  16. Multifaceted Quadruplet of Low-Lying Spin-Zero States in 66Ni: Emergence of Shape Isomerism in Light Nuclei

    NASA Astrophysics Data System (ADS)

    Leoni, S.; Fornal, B.; Mǎrginean, N.; Sferrazza, M.; Tsunoda, Y.; Otsuka, T.; Bocchi, G.; Crespi, F. C. L.; Bracco, A.; Aydin, S.; Boromiza, M.; Bucurescu, D.; Cieplicka-Oryǹczak, N.; Costache, C.; Cǎlinescu, S.; Florea, N.; GhiÅ£ǎ, D. G.; Glodariu, T.; Ionescu, A.; Iskra, Ł. W.; Krzysiek, M.; Mǎrginean, R.; Mihai, C.; Mihai, R. E.; Mitu, A.; NegreÅ£, A.; NiÅ£ǎ, C. R.; Olǎcel, A.; Oprea, A.; Pascu, S.; Petkov, P.; Petrone, C.; Porzio, G.; Şerban, A.; Sotty, C.; Stan, L.; Ştiru, I.; Stroe, L.; Şuvǎilǎ, R.; Toma, S.; Turturicǎ, A.; Ujeniuc, S.; Ur, C. A.

    2017-04-01

    A search for shape isomers in the 66Ni nucleus was performed, following old suggestions of various mean-field models and recent ones, based on state-of-the-art Monte Carlo shell model (MCSM), all considering 66Ni as the lightest nuclear system with shape isomerism. By employing the two-neutron transfer reaction induced by an 18O beam on a 64Ni target, at the sub-Coulomb barrier energy of 39 MeV, all three lowest-excited 0+ states in 66Ni were populated and their γ decay was observed by γ -coincidence technique. The 0+ states lifetimes were assessed with the plunger method, yielding for the 02+, 03+, and 04+ decay to the 21+ state the B (E 2 ) values of 4.3, 0.1, and 0.2 Weisskopf units (W.u.), respectively. MCSM calculations correctly predict the existence of all three excited 0+ states, pointing to the oblate, spherical, and prolate nature of the consecutive excitations. In addition, they account for the hindrance of the E 2 decay from the prolate 04+ to the spherical 21+ state, although overestimating its value. This result makes 66Ni a unique nuclear system, apart from U,238236 , in which a retarded γ transition from a 0+ deformed state to a spherical configuration is observed, resembling a shape-isomerlike behavior.

  17. Multifaceted Quadruplet of Low-Lying Spin-Zero States in ^{66}Ni: Emergence of Shape Isomerism in Light Nuclei.

    PubMed

    Leoni, S; Fornal, B; Mărginean, N; Sferrazza, M; Tsunoda, Y; Otsuka, T; Bocchi, G; Crespi, F C L; Bracco, A; Aydin, S; Boromiza, M; Bucurescu, D; Cieplicka-Oryǹczak, N; Costache, C; Călinescu, S; Florea, N; Ghiţă, D G; Glodariu, T; Ionescu, A; Iskra, Ł W; Krzysiek, M; Mărginean, R; Mihai, C; Mihai, R E; Mitu, A; Negreţ, A; Niţă, C R; Olăcel, A; Oprea, A; Pascu, S; Petkov, P; Petrone, C; Porzio, G; Şerban, A; Sotty, C; Stan, L; Ştiru, I; Stroe, L; Şuvăilă, R; Toma, S; Turturică, A; Ujeniuc, S; Ur, C A

    2017-04-21

    A search for shape isomers in the ^{66}Ni nucleus was performed, following old suggestions of various mean-field models and recent ones, based on state-of-the-art Monte Carlo shell model (MCSM), all considering ^{66}Ni as the lightest nuclear system with shape isomerism. By employing the two-neutron transfer reaction induced by an ^{18}O beam on a ^{64}Ni target, at the sub-Coulomb barrier energy of 39 MeV, all three lowest-excited 0^{+} states in ^{66}Ni were populated and their γ decay was observed by γ-coincidence technique. The 0^{+} states lifetimes were assessed with the plunger method, yielding for the 0_{2}^{+}, 0_{3}^{+}, and 0_{4}^{+} decay to the 2_{1}^{+} state the B(E2) values of 4.3, 0.1, and 0.2 Weisskopf units (W.u.), respectively. MCSM calculations correctly predict the existence of all three excited 0^{+} states, pointing to the oblate, spherical, and prolate nature of the consecutive excitations. In addition, they account for the hindrance of the E2 decay from the prolate 0_{4}^{+} to the spherical 2_{1}^{+} state, although overestimating its value. This result makes ^{66}Ni a unique nuclear system, apart from ^{236,238}U, in which a retarded γ transition from a 0^{+} deformed state to a spherical configuration is observed, resembling a shape-isomerlike behavior.

  18. Photon induced isomerization in the first excited state of the 7-azaindole-(H2O)3 cluster.

    PubMed

    Pino, Gustavo A; Alata, Ivan; Dedonder, Claude; Jouvet, Christophe; Sakota, Kenji; Sekiya, Hiroshi

    2011-04-07

    A picosecond pump and probe experiment has been applied to study the excited state dynamics of 7-azaindole-water 1 ∶ 2 and 1 ∶ 3 clusters [7AI(H(2)O)(2,3)] in the gas phase. The vibrational-mode selective Excited-State-Triple-Proton Transfer (ESTPT) in 7AI(H(2)O)(2) proposed from the frequency-resolved study has been confirmed by picosecond decays. The decay times for the vibronic states involving the ESTPT promoting mode σ(1) (850-1000 ps) are much shorter than those for the other vibronic states (2100-4600 ps). In the (1 + 1) REMPI spectrum of 7AI(H(2)O)(3) measured by nanosecond laser pulses, the vibronic bands with an energy higher than 200 cm(-1) above the origin of the S(1) state become very weak. In contrast, the vibronic bands in the same region emerge in the (1 + 1') REMPI spectrum of 7AI(H(2)O)(3) with picosecond pulses. The decay times drastically decrease when increasing the vibrational energy above 200 cm(-1). Ab initio calculations show that a second stable "cyclic-nonplanar isomer" exists in addition to a "bridged-planar isomer", and that an isomerization from a bridged-planar isomer to a cyclic-nonplanar isomer is most probably responsible for the short lifetimes of the vibronic states of 7AI(H(2)O)(3).

  19. Monopole effects, isomeric states, and cross-shell excitations in the A =129 hole nuclei near 132Sn

    NASA Astrophysics Data System (ADS)

    Wang, Han-Kui; Kaneko, Kazunari; Sun, Yang; He, Yi-Qi; Li, Shao-Feng; Li, Jian

    2017-01-01

    We present results of large-scale shell-model calculations for the A =129 hole nuclei below 132Sn. We discuss structures of 129Sn, 129In, and 129Cd with emphasis on the monopole effects and excitations across the neutron N =82 shell gap, and further predict low-lying levels for the more exotic 129Ag. It is demonstrated that the monopole corrections in the Hamiltonian, which dynamically affect occupations of relevant orbits, can lead to interesting consequences for the shell evolution. It is found especially that the monopole terms, previously introduced to reproduce the cross-shell excitations of the 17 /2+ and 21 /2+ states in 131In, shows more pronounced effects on the A =129 nuclei. In 129In, the cross-shell excitations of 17 /2+ and 21 /2+ are pushed down significantly by the monopole terms, and in 129Cd, the same monopole terms reverse the order of the single-hole states of ν d3 /2 and ν h11 /2 , causing 11/2 - as the ground state for this nucleus. The structure of isomeric states in the A =129 nuclei is also discussed.

  20. Is it possible to induce a fast de-excitation of the 16/sup +/ isomeric state in /sup 178/Hf

    SciTech Connect

    Hsu, H.H.; Doolen, G.D.; Talbert, W.L.; Mack, J.M.

    1985-01-01

    The 16/sup +/ level of /sup 178/Hf at 2.446 MeV is interpreted as a four-quasi-particel state with K = 16. It decays mainly to a 13/sup -/ level at 2.433 MeV, a member of rotational band built on a two-quasi-particle 8/sup -/ state (K = 8) at 1.1474 MeV. The 13-keV transition is > 99% E3 character and occurs predominantly through internal conversion. The five-times K-forbidden E3 transition has a large hindrance factor; the half-life of the 16/sup +/ state is known to be 31 years. If this isomeric nucleus can be induced to release its energy quickly, the resulting energy release would be 6 orders of magnitude more energetic per reaction than that for existing high explosives. The following mechanisms to enhance de-excitation of this isomer are presented for discussion: (1) inelastic scattering of high-energy neutrons; (2) inelastic scattering of a high-energy, high-intensity electron beam; and (3) interaction with intense photon fields (rf, laser, x ray, ..gamma.. ray). Experiments to explore such de-excitation mechanisms are discussed. 12 refs., 4 figs., 1 tab.

  1. Cis-trans isomerization in the S1 state of acetylene: identification of cis-well vibrational levels.

    PubMed

    Merer, Anthony J; Steeves, Adam H; Baraban, Joshua H; Bechtel, Hans A; Field, Robert W

    2011-06-28

    A systematic analysis of the S(1)-trans (Ã(1)A(u)) state of acetylene, using IR-UV double resonance along with one-photon fluorescence excitation spectra, has allowed assignment of at least part of every single vibrational state or polyad up to a vibrational energy of 4200 cm(-1). Four observed vibrational levels remain unassigned, for which no place can be found in the level structure of the trans-well. The most prominent of these lies at 46 175 cm(-1). Its (13)C isotope shift, exceptionally long radiative lifetime, unexpected rotational selection rules, and lack of significant Zeeman effect, combined with the fact that no other singlet electronic states are expected at this energy, indicate that it is a vibrational level of the S(1)-cis isomer (Ã(1)A(2)). Guided by ab initio calculations [J. H. Baraban, A. R. Beck, A. H. Steeves, J. F. Stanton, and R. W. Field, J. Chem. Phys. 134, 244311 (2011)] of the cis-well vibrational frequencies, the vibrational assignments of these four levels can be established from their vibrational symmetries together with the (13)C isotope shift of the 46 175 cm(-1) level (assigned here as cis-3(1)6(1)). The S(1)-cis zero-point level is deduced to lie near 44 900 cm(-1), and the ν(6) vibrational frequency of the S(1)-cis well is found to be roughly 565 cm(-1); these values are in remarkably good agreement with the results of recent ab initio calculations. The 46 175 cm(-1) vibrational level is found to have a 3.9 cm(-1) staggering of its K-rotational structure as a result of quantum mechanical tunneling through the isomerization barrier. Such tunneling does not give rise to ammonia-type inversion doubling, because the cis and trans isomers are not equivalent; instead the odd-K rotational levels of a given vibrational level are systematically shifted relative to the even-K rotational levels, leading to a staggering of the K-structure. These various observations represent the first definite assignment of an isomer of

  2. Strongly Enhanced Low Energy α-Particle Decay in Heavy Actinide Nuclei and Long-Lived Superdeformed and Hyperdeformed Isomeric States

    NASA Astrophysics Data System (ADS)

    Marinov, A.; Gelberg, S.; Kolb, D.; Weil, J. L.

    Unidentified low energy and very enhanced α-particle groups have been observed in various actinide fractions produced via secondary reactions in a CERN W target which had been irradiated with 24-GeV protons. In particular, 5.14, 5.27 and 5.53 MeV α-particle groups with corresponding half-lives of 3.8+/-1.0 y, 625+/-84 d and 26+/-7d, have been seen in Bk, Es and Lr-No sources, respectively. The measured energies are a few MeV lower than the known ground state to ground state α-decays in the corresponding neutron-deficient actinide nuclei. The half-lives are 104 to 107 shorter than expected from energy versus lifetime relationship for such low-energy α-particles in this region of nuclei. The deduced evaporation residue cross sections are in the mb region, about 104 times higher than expected. Not only is it impossible to identify these α-decays with any known activity in the whole nuclear chart, but they also could not be due to hypothetically unknown isomeric states in various conceivable neutron deficient nuclei, nor due to unknown isomeric states in the rare-earth region. Based on the fact that in other experiments we have found isomeric states in the second and third minima of the potential for other heavy ion reaction products, one can now understand in a quantitative way, both the unusual low energies, the unusual enhanced lifetimes and the unusual large production cross sections, in terms of production of similar isomeric states in appropriate actinide isotopes. Some consequences regarding the production of the long-lived superheavy elements are also discussed.

  3. Systematic study of unfavored α -decay half-lives of closed-shell nuclei related to ground and isomeric states

    NASA Astrophysics Data System (ADS)

    Deng, Jun-Gang; Zhao, Jie-Cheng; Xiang, Dong; Li, Xiao-Hua

    2017-08-01

    In the present work, the unfavored α -decay half-lives and α preformation probabilities of closed-shell nuclei related to ground and isomeric states around Z =82 , N =82 and 126 shell closures are investigated by adopting the two-potential approach from the perspective of valence nucleon (hole) and isospin asymmetry of the parent nucleus. The results indicate that α preformation probability has linear dependence on NpNn or NpNnI , the same as the case of favored α decay in our previous work [X.-D. Sun et al., Phys. Rev. C 94, 024338 (2016), 10.1103/PhysRevC.94.024338]. Np, Nn, and I represent the number of valence protons (holes), the number of valence neutrons (holes), and the isospin of the parent nucleus, respectively. Fitting the α preformation probability data extracted from the differences between experimental data and calculated half-lives without a shell correction, we give two linear formulas of the α preformation probabilities and the values of corresponding parameters. Based on the formulas and corresponding parameters, we calculate the α -decay half-lives for those nuclei. The calculated results can well reproduce the experimental data.

  4. Isomeric Character of the Lowest Observed 4+ State in 44S

    NASA Astrophysics Data System (ADS)

    Parker, J. J.; Wiedenhöver, I.; Cottle, P. D.; Baker, J.; McPherson, D.; Riley, M. A.; Santiago-Gonzalez, D.; Volya, A.; Bader, V. M.; Baugher, T.; Bazin, D.; Gade, A.; Ginter, T.; Iwasaki, H.; Loelius, C.; Morse, C.; Recchia, F.; Smalley, D.; Stroberg, S. R.; Whitmore, K.; Weisshaar, D.; Lemasson, A.; Crawford, H. L.; Macchiavelli, A. O.; Wimmer, K.

    2017-02-01

    Previous experiments observed a 4+ state in the N =28 nucleus 44S and suggested that this state may exhibit a hindered E 2 -decay rate, inconsistent with being a member of the collective ground state band. We populate this state via two-proton knockout from a beam of exotic 46Ar projectiles and measure its lifetime using the recoil distance method with the GRETINA γ -ray spectrometer. The result, 76 (14 )stat(20 )syst ps , implies a hindered transition of B (E 2 ;4+→21+)=0.61 (19 ) single-particle or Weisskopf units strength and supports the interpretation of the 4+ state as a K =4 isomer, the first example of a high-K isomer in a nucleus of such low mass.

  5. Isomeric Character of the Lowest Observed 4^{+} State in ^{44}S.

    PubMed

    Parker, J J; Wiedenhöver, I; Cottle, P D; Baker, J; McPherson, D; Riley, M A; Santiago-Gonzalez, D; Volya, A; Bader, V M; Baugher, T; Bazin, D; Gade, A; Ginter, T; Iwasaki, H; Loelius, C; Morse, C; Recchia, F; Smalley, D; Stroberg, S R; Whitmore, K; Weisshaar, D; Lemasson, A; Crawford, H L; Macchiavelli, A O; Wimmer, K

    2017-02-03

    Previous experiments observed a 4^{+} state in the N=28 nucleus ^{44}S and suggested that this state may exhibit a hindered E2-decay rate, inconsistent with being a member of the collective ground state band. We populate this state via two-proton knockout from a beam of exotic ^{46}Ar projectiles and measure its lifetime using the recoil distance method with the GRETINA γ-ray spectrometer. The result, 76(14)_{stat}(20)_{syst}  ps, implies a hindered transition of B(E2;4^{+}→2_{1}^{+})=0.61(19) single-particle or Weisskopf units strength and supports the interpretation of the 4^{+} state as a K=4 isomer, the first example of a high-K isomer in a nucleus of such low mass.

  6. Observation of a γ-decaying millisecond isomeric state in 128Cd80

    NASA Astrophysics Data System (ADS)

    Jungclaus, A.; Grawe, H.; Nishimura, S.; Doornenbal, P.; Lorusso, G.; Simpson, G. S.; Söderström, P.-A.; Sumikama, T.; Taprogge, J.; Xu, Z. Y.; Baba, H.; Browne, F.; Fukuda, N.; Gernhäuser, R.; Gey, G.; Inabe, N.; Isobe, T.; Jung, H. S.; Kameda, D.; Kim, G. D.; Kim, Y.-K.; Kojouharov, I.; Kubo, T.; Kurz, N.; Kwon, Y. K.; Li, Z.; Sakurai, H.; Schaffner, H.; Shimizu, Y.; Steiger, K.; Suzuki, H.; Takeda, H.; Vajta, Zs.; Watanabe, H.; Wu, J.; Yagi, A.; Yoshinaga, K.; Benzoni, G.; Bönig, S.; Chae, K. Y.; Coraggio, L.; Daugas, J.-M.; Drouet, F.; Gadea, A.; Gargano, A.; Ilieva, S.; Itaco, N.; Kondev, F. G.; Kröll, T.; Lane, G. J.; Montaner-Pizá, A.; Moschner, K.; Mücher, D.; Naqvi, F.; Niikura, M.; Nishibata, H.; Odahara, A.; Orlandi, R.; Patel, Z.; Podolyák, Zs.; Wendt, A.

    2017-09-01

    A new high-spin isomer in the neutron-rich nucleus 128Cd was populated in the projectile fission of a 238U beam at the Radioactive Isotope Beam Factory at RIKEN. A half-life of T1/2 = 6.3 (8) ms was measured for the new state which was tentatively assigned a spin/parity of (15-). The experimental results are compared to shell model calculations performed using state-of-the-art realistic effective interactions and to the neighbouring nucleus 129Cd. In the present experiment no evidence was found for the decay of a 18+E6 spin-trap isomer, based on the complete alignment of the two-neutron and two-proton holes in the 0h11/2 and the 0g9/2 orbit, respectively, which is predicted to exist by the shell model.

  7. Experiments with neutron-rich isomeric beams

    SciTech Connect

    Rykaczewski, K. |; Grzywacz, R. |; Lewitowicz, M.; Pfuetzner, M.; Grawe, H.

    1998-01-01

    A review of experimental results obtained on microsecond-isomeric states in neutron-rich nuclei produced in fragmentation reactions and studied with SISSI-Alpha-LISE3 spectrometer system at GANIL Caen is given. The perspectives of experiments based on secondary reactions with isomeric beams are presented.

  8. g-Factors of Isomeric States in the Neutron-Rich Nuclei

    SciTech Connect

    Georgiev, G.; Neyens, G.; Hass, M.; Balabanski, Dimiter Loukanov; Bingham, Carrol R; Borcea, C.; Coulier, N.; Coussenment, R.; Daugas, J. M.; De France, Gilles M; Gorska, M.; Grawe, Hubert H; Grzywacz, Robert Kazimierz; Lewitowicz, Marek; Mach, Henryk A; Matea, I.; de Oliveira Santos, F.; Page, R. D.; Pfutzner, Marek; Penionzhkevich, Yu. E.; Podolyak, Zsolt F; Regan, Patrick H; Rykaczewski, Krzysztof Piotr; Sawicka, M.; Smirnova, N. A.; Sobolev, Yu.; Stanoiu, M.; Teughels, S.; Vyvey, K.

    2004-02-01

    We report the results from the first experiment to measure gyromagnetic factors of {micro}s isomers in neutron-rich nuclei produced by intermediate-energy projectile-fragmentation reactions. The Time Dependent Perturbed Angular Distribution (TDPAD) method was applied in combination with the heavy-ion-gamma correlation technique. The nuclides in the vicinity of {sup 68}Ni were produced and spin-oriented following the fragmentation of a {sup 76}Ge, 61.4 MeV/ u beam at GANIL. The results obtained, |g|({sup 69 m}Cu) = 0.225(25) and |g|({sup 67 m}Ni) = 0.125(6) provide another indication of the importance of proton excitation across the Z = 28 shell gap for the description of these states.

  9. On the spectroscopic constants, first electronic state, vibrational frequencies, and isomerization of hydroxymethylene (HCOH+)

    NASA Astrophysics Data System (ADS)

    Theis, Riley A.; Fortenberry, Ryan C.

    2017-09-01

    The hydroxymethylene cation (HCOH+) is believed to be chemically independent of the more stable formaldehyde cation isomer in interstellar chemistry and may likely be a precursor to methanol in chemical reaction networks. Previous work is corroborated here showing that the trans conformer of HCOH+ is 3.48 kcal/mol lower than the cis on the potential energy surface. The small energy difference between the conformers and the much larger dipole moment of cis-HCOH+ (2.73 D) make this conformer more likely to be observed than trans-HCOH+ via telescopic rotational spectroscopy. A strong adiabatic shift is also predicted in the first electronic excitation into the 1 2A‧‧/2 2A state out of either conformer into a C1 structure reducing the excitation wavelength from the near-ultraviolet all the way into the near-infrared. The full set of fundamental vibrational frequencies are also computed here at high-level. The 3306.0 cm-1 and 3225.3 cm-1 hydroxide stretches, respective of bare trans- and cis-HCOH+ , are in agreement with previous theory but are significantly higher than the frequencies determined from previous experiment utilizing argon tagging techniques. This shift is likely because the proton-bound complex created with the argon tag reduces the experimental frequencies. Lower-level computations including the argon tag bring the hydroxide stretches much closer to the experimental frequencies indicating that the predicted frequencies for bare HCOH+ are likely well-described.

  10. Magnetic moments of the isomeric states of /sup 141/Pr and /sup 143/Pm and the paramagnetism of promethium and praseodymium

    SciTech Connect

    Gorbachev, B.I.; Levon, A.I.; Nemets, O.F.; Fedotkin, S.N.; Stepanenko, V.A.

    1984-07-01

    The g-factors of the 11/2/sup -/ and 15/2/sup +/ isomeric states of the /sup 141/Pr and /sup 143/Pm nuclei (Tables I and II) have been measured by the method of differential and integrated perturbed angular distribution. The parametric corrections were determined for /sup 143/Pm from the measured temperature dependence g..beta..(T). The relaxation times have been measured for nuclear states aligned in beam reactions, metal targets, and targets made of La and Pr oxides. The results are analyzed in terms of the quasiparticle-phonon model with allowance for the spin-multipole interaction.

  11. K selection in the decay of the (ν 5/2 [532 ] ⊗3/2 [411 ] ) 4- isomeric state in 102Zr

    NASA Astrophysics Data System (ADS)

    Browne, F.; Bruce, A. M.; Sumikama, T.; Nishizuka, I.; Nishimura, S.; Doornenbal, P.; Lorusso, G.; Söderström, P.-A.; Watanabe, H.; Daido, R.; Patel, Z.; Rice, S.; Sinclair, L.; Wu, J.; Xu, Z. Y.; Yagi, A.; Baba, H.; Chiga, N.; Carroll, R.; Didierjean, F.; Fang, Y.; Fukuda, N.; Gey, G.; Ideguchi, E.; Inabe, N.; Isobe, T.; Kameda, D.; Kojouharov, I.; Kurz, N.; Kubo, T.; Lalkovski, S.; Li, Z.; Lozeva, R.; Nishibata, N.; Odahara, A.; Podolyák, Zs.; Regan, P. H.; Roberts, O. J.; Sakurai, H.; Schaffner, H.; Simpson, G. S.; Suzuki, H.; Takeda, H.; Tanaka, M.; Taprogge, J.; Werner, V.; Wieland, O.

    2017-08-01

    The (ν 5/2 [532 ] ⊗3/2 [411 ] ) 4- state in 102Zr, populated in the β decay of 102Y, has been measured to be isomeric with a mean lifetime of 9.5(7) ns. It decays via four transitions, two of which are Δ K =2 (to the 3+ and 4+ members of the 2γ+ band) and one is Δ K =4 (to the 4+ member of the ground state 0+ band). The fourth (low-energy) transition is inferred to decay to an as-yet unassigned state. Hindrances of 106 were derived for the Δ K =2 transitions compared to Weisskopf estimates and the Δ K =4 transition hindered by a factor of 109. These values are consistent with the decay pattern of the analogous isomeric state in the neighboring N =62 nucleus 100Sr and with the broader systematics of such transitions. A comparison of the hindrances for the Δ K =4 transitions suggests that 102Zr is hardened against the γ degree of freedom compared to 100Sr.

  12. Photoreactivity of a Push-Pull Merocyanine in Static Electric Fields: A Three-State Model of Isomerization Reactions Involving Conical Intersections

    NASA Astrophysics Data System (ADS)

    Xu, X. F.; Kahan, A.; Zilberg, S.; Haas, Y.

    2009-08-01

    The photochemistry of a prototype push-pull merocyanine is discussed using a simple three-state model. As a derivative of butadiene, the model focuses on two isomerization reactions around the two double bonds of the butadiene backbone. As a molecule substituted by an electron donor and electron acceptor at opposite ends, its structure as well as its photochemistry are expected to be strongly affected by the environment. In polar solvents, a zwitterion transition state for each of the isomerization reactions is stabilized, and its energy is on the same order as that of the biradical one; this leads to the symmetry allowed crossing (S0/S1 conical intersection). It is shown that applying an external electric field or varying the solvent polarity changes the relative energies of the different transition states as well as that of the conical intersection, and thus different photochemical products can be obtained. In particular, the very existence of conical intersections is found to depend on these external parameters. This work provides a theoretical foundation for ideas expressed by Squillacote et al. (J. Am. Chem. Soc. 2004, 126, 1940) concerning the electrostatic control of photochemical reactions.

  13. Isomerization of sugars

    SciTech Connect

    Moliner-Marin, Manuel; Roman-Leshkov, Yuriy; Davis, Mark E; Nikolla, Eranda

    2014-05-20

    Disclosed are processes for isomerizing saccharides. Also disclosed are processes for converting saccharides to furan derivatives. Also disclosed are processes for converting starch to furan derivatives.

  14. Transition of rhodopsin into the active metarhodopsin II state opens a new light-induced pathway linked to Schiff base isomerization.

    PubMed

    Ritter, Eglof; Zimmermann, Kerstin; Heck, Martin; Hofmann, Klaus Peter; Bartl, Franz J

    2004-11-12

    Rhodopsin bears 11-cis-retinal covalently bound by a protonated Schiff base linkage. 11-cis/all-trans isomerization, induced by absorption of green light, leads to active metarhodopsin II, in which the Schiff base is intact but deprotonated. The subsequent metabolic retinoid cycle starts with Schiff base hydrolysis and release of photolyzed all-trans-retinal from the active site and ends with the uptake of fresh 11-cis-retinal. To probe chromophore-protein interaction in the active state, we have studied the effects of blue light absorption on metarhodopsin II using infrared and time-resolved UV-visible spectroscopy. A light-induced shortcut of the retinoid cycle, as it occurs in other retinal proteins, is not observed. The predominantly formed illumination product contains all-trans-retinal, although the spectra reflect Schiff base reprotonation and protein deactivation. By its kinetics of formation and decay, its low temperature photointermediates, and its interaction with transducin, this illumination product is identified as metarhodopsin III. This species is known to bind all-trans-retinal via a reprotonated Schiff base and forms normally in parallel to retinal release. We find that its generation by light absorption is only achieved when starting from active metarhodopsin II and is not found with any of its precursors, including metarhodopsin I. Based on the finding of others that metarhodopsin III binds retinal in all-trans-C(15)-syn configuration, we can now conclude that light-induced formation of metarhodopsin III operates by Schiff base isomerization ("second switch"). Our reaction model assumes steric hindrance of the retinal polyene chain in the active conformation, thus preventing central double bond isomerization.

  15. Conceptual Difficulties with Isomerism.

    ERIC Educational Resources Information Center

    Schmidt, Hans-Jurgen

    1992-01-01

    Reports descriptive study concerning student understanding of isomers. Sample of 7,441 senior high school students completed tests which contained 12 questions on isomerism. Results indicate students are inclined to restrict their concept of isomerism to compounds belonging to the same class. There was no evidence students expected molecular…

  16. Conceptual Difficulties with Isomerism.

    ERIC Educational Resources Information Center

    Schmidt, Hans-Jurgen

    1992-01-01

    Reports descriptive study concerning student understanding of isomers. Sample of 7,441 senior high school students completed tests which contained 12 questions on isomerism. Results indicate students are inclined to restrict their concept of isomerism to compounds belonging to the same class. There was no evidence students expected molecular…

  17. Variations of structures and solid-state conductivity of isomeric silver(I) coordination polymers having linear and V-shaped thiophene-centered ditriazole ligands

    SciTech Connect

    Hu, Bin; Geng, Jiao; Zhang, Lie; Huang, Wei

    2014-07-01

    A pair of new linear and V-shaped acceptor–donor–acceptor (A−D−A) thiophene-centered ditriazole structural isomers, i.e., 2,5-di(1H-1,2,4-triazol-1-yl)thiophene (L{sup 1}) and 3,4-di(1H-1,2,4-triazol-1-yl)thiophene (L{sup 2}), has been synthesized and characterized. They are used as μ{sub 2}-bridging ligands to prepare a pair of silver(I) coordination polymers formulated as [Ag(L{sup 1})(NO{sub 3})]{sub n} (1) and [Ag(L{sup 2})(NO{sub 3})]{sub n} (2), which are also structural isomers at the supramolecular level. X-ray single-crystal diffraction analyses for 1 and 2 reveal that they exhibit the same one-dimensional (1D) coordination polymers but different structural architectures because of the distinguishable shape and configuration of isomeric ligands (L{sup 1} and L{sup 2}) and the alterations of the coordination numbers. More interestingly, compared with the free ligands, 1D silver(I) polymeric isomers 1 and 2 show significant enhancement of solid-state conductivity to different extents (1.42×10{sup 4} and 2.17×10{sup 3} times), where 6.96 times' enhancement of solid-state conductivity from 1 to 2 has been observed. The formation of Ag–N coordinative bonds and the configurational discrepancy of L{sup 1} and L{sup 2} are believed to play important roles in facilitating the electron transport between molecules, which can also be supported by Density Function Theory calculations of their band gaps. - Graphical abstract: A pair of linear and V-shaped isomeric thiophene-centered ditriazole ligands (L{sup 1}) and L{sup 2} are used to prepare a pair of silver(I) polymeric isomers (1 and 2), where significant enhancement of solid-state conductivity to different extents are observed originating from the distinguishable shape and configuration of isomeric ligands. - Highlights: • A pair of linear and V-shaped thiophene-centered ditriazole structural isomers is prepared. • They are used as µ{sub 2}-bridging ligands to prepare a pair of silver

  18. Magnetic dipole moments near 132Sn: Measurement on isomeric {11}/{2 -} states in odd- A131Te and 133Te by NMR/ON

    NASA Astrophysics Data System (ADS)

    White, G.; Rikovska, J.; Stone, N. J.; Copnell, J.; Towner, I. S.; Oros, A. M.; Heyde, K.; Fogelberg, B.; Jacobsson, L.; Gustavsson, F.

    1998-09-01

    On-line low temperature nuclear orientation (OLNO) experiments have been performed on the odd- A Te isotopes 131Te and 133Te using the technique of nuclear magnetic resonance on oriented nuclei (NMR/ON). The magnetic moments of the isomeric {11}/{2 -} states have been measured extending the known data on these states in the Te isotopes up to the neutron shell closure at N = 82. The contribution to the {11}/{2 -} magnetic moment in 133Te due to core polarisation is calculated using an RPA shell model as well as corrections to the magnetic dipole operator caused by mesonic exchange currents. The neutron number dependence of the magnetic moments of the {11}/{2 -} isomers in heavy Te isotopes is discussed in terms of particle-core coupling model (PCM) calculations.

  19. Isomeric states observed in heavy neutron-rich nuclei populated in the fragmentation of a 208Pb beam

    NASA Astrophysics Data System (ADS)

    Steer, S. J.; Podolyák, Zs.; Pietri, S.; Górska, M.; Grawe, H.; Maier, K. H.; Regan, P. H.; Rudolph, D.; Garnsworthy, A. B.; Hoischen, R.; Gerl, J.; Wollersheim, H. J.; Becker, F.; Bednarczyk, P.; Cáceres, L.; Doornenbal, P.; Geissel, H.; Grębosz, J.; Kelic, A.; Kojouharov, I.; Kurz, N.; Montes, F.; Prokopwicz, W.; Saito, T.; Schaffner, H.; Tashenov, S.; Heinz, A.; Pfützner, M.; Kurtukian-Nieto, T.; Benzoni, G.; Jungclaus, A.; Balabanski, D. L.; Bowry, M.; Brandau, C.; Brown, A.; Bruce, A. M.; Catford, W. N.; Cullen, I. J.; Dombrádi, Zs.; Estevez, M. E.; Gelletly, W.; Ilie, G.; Jolie, J.; Jones, G. A.; Kmiecik, M.; Kondev, F. G.; Krücken, R.; Lalkovski, S.; Liu, Z.; Maj, A.; Myalski, S.; Schwertel, S.; Shizuma, T.; Walker, P. M.; Werner-Malento, E.; Wieland, O.

    2011-10-01

    Heavy neutron-rich nuclei were populated via the fragmentation of a E/A=1 GeV 20882Pb beam. Secondary fragments were separated and identified and subsequently implanted in a passive stopper. By the detection of delayed γ rays, isomeric decays associated with these nuclei have been identified. A total of 49 isomers were detected, with the majority of them observed for the first time. The newly discovered isomers are in 204,20580Hg, 201,202,204,20579Au, 197,203,20478Pt, 195,199-20377Ir, 193,197-19976Os, 19675Re, 190,19174W, and 18973Ta. Possible level schemes are constructed and the structure of the nuclei discussed. To aid the interpretation, shell-model as well as BCS calculations were performed.

  20. Analysis of isomeric ratios for medium-mass nuclei

    NASA Astrophysics Data System (ADS)

    Danagulyan, A. S.; Hovhannisyan, G. H.; Bakhshiyan, T. M.; Kerobyan, I. A.

    2016-09-01

    Values of the isomeric ratios for product nuclei originating from simple charge-exchange reactions were analyzed. The cross sections for the formation of product nuclei in ground and isomeric states were calculated with the aid of the TALYS 1.4 and EMPIRE 3.2 codes. The calculated values of the isomeric ratios were compared with their experimental counterparts taken from the EXFOR database. For the 86,87Y, 94,95,96,99Tc, and 44Sc nuclei, the experimental values of the isomeric ratios exceed the respective calculated values. The nuclei in question feature weak deformations and have high-spin yrast lines and rotational bands. The possible reason behind the discrepancy between theoretical and experimental isomeric ratios is that the decay of yrast states leads with a high probability to the formation of isomeric states of detected product nuclei.

  1. Analysis of isomeric ratios for medium-mass nuclei

    SciTech Connect

    Danagulyan, A. S.; Hovhannisyan, G. H. Bakhshiyan, T. M.; Kerobyan, I. A.

    2016-09-15

    Values of the isomeric ratios for product nuclei originating from simple charge-exchange reactions were analyzed. The cross sections for the formation of product nuclei in ground and isomeric states were calculated with the aid of the TALYS 1.4 and EMPIRE 3.2 codes. The calculated values of the isomeric ratios were compared with their experimental counterparts taken from the EXFOR database. For the {sup 86,87}Y, {sup 94,95,96,99}Tc, and {sup 44}Sc nuclei, the experimental values of the isomeric ratios exceed the respective calculated values. The nuclei in question feature weak deformations and have high-spin yrast lines and rotational bands. The possible reason behind the discrepancy between theoretical and experimental isomeric ratios is that the decay of yrast states leads with a high probability to the formation of isomeric states of detected product nuclei.

  2. Photo-Reactivity of a Push-Pull Merocyanine in a Static Electric Fields: a Three State Model of Isomerization Reactions Involving Conical Intersections

    NASA Astrophysics Data System (ADS)

    Zilberg, S.; Xu, X. F.; Kahan, A.; Haas, Y.

    2009-06-01

    The photochemistry of a prototype push-pull merocyanine is discussed using a simple three state model. As a derivative of butadiene, two isomerization reactions may take place, around the two double bonds of the butadiene backbone. As a molecule substituted by an electron donor and electron acceptor at opposite ends, its structure as well as its photochemistry are expected to be strongly affected by the environment. It is shown that varying the solvent polarity or the electric field, can lead to different photochemical products. In particular, the existence of conical intersections is found to depend on these external parameters. This work provides a theoretical foundation for ideas expressed by Squillacote et al.* concerning the electrostatic control of photochemical reactions. *Squillacote, M.; Wang, J.; Chen, J. J. Am. Chem. Soc. 2004, 126, 1940.

  3. Structural dynamics of nitrosylruthenium isomeric complexes studied with steady-state and transient pump-probe infrared spectroscopies

    NASA Astrophysics Data System (ADS)

    Zhao, Yan; Yang, Fan; Wang, Jianru; Yu, Pengyun; Pan, Huifen; Wang, Hongfei; Wang, Jianping

    2016-09-01

    The characteristic nitrosyl stretching (NO) in the region of 1800-1900 cm- 1 was used to study the geometric and ligand effect on two nitrosylruthenium complexes, namely [Ru(OAc)(2QN)2NO] (QN = 2-chloro-8-quinolinol (H2cqn) or QN = 2-methyl-8-quinolinol (H2mqn)). The NO stretching frequency (νNO) was found in the following order: νcis-1 (2cqn) > νcis-2 (2cqn) > νcis-1 (2mqn) > νtrans (2mqn). The results exhibited a spectral sensitivity of the NO mode to both charge distribution and ligand arrangement, which was supported by ab initio computations and natural bond orbital (NBO) analyses. Further, the vibrational population of the vibrationally excited NO stretching mode was found to relax on the order of 7-10 ps, showing less than 30% variation from one isomer to another, which were explained on the basis of NO local structures and solute-solvent interactions in these isomeric nitrosylruthenium complexes.

  4. Reduced dimension rovibrational variational calculations of the S{sub 1} state of C{sub 2}H{sub 2}. II. The S{sub 1} rovibrational manifold and the effects of isomerization

    SciTech Connect

    Changala, P. Bryan Baraban, Joshua H.; Field, Robert W.; Stanton, John F.; Merer, Anthony J.

    2014-01-14

    Reduced dimension variational calculations have been performed for the rovibrational level structure of the S{sub 1} state of acetylene. The state exhibits an unusually complicated level structure, for various reasons. First, the potential energy surface has two accessible conformers, trans and cis. The cis conformer lies about 2700 cm{sup −1} above the trans, and the barrier to cis-trans isomerization lies about 5000 cm{sup −1} above the trans minimum. The trans vibrations ν{sub 4} (torsion) and ν{sub 6} (asym. bend) interact very strongly by Darling-Dennison and Coriolis resonances, such that their combination levels and overtones form polyads with unexpected structures. Both conformers exhibit very large x{sub 36} cross-anharmonicity since the pathway to isomerization is a combination of ν{sub 6} and ν{sub 3} (sym. bend). Near the isomerization barrier, the vibrational levels show an even-odd K-staggering of their rotational levels as a result of quantum mechanical tunneling through the barrier. The present calculations address all of these complications, and reproduce the observed K-structures of the bending and C–C stretching levels with good qualitative accuracy. It is expected that they will assist with the assignment of the irregular patterns near the isomerization barrier.

  5. Site-specific electronic couplings in dyads with MLCT excited states. Intramolecular energy transfer in isomeric Ru(II)-Ru(II) cyclometalated complexes.

    PubMed

    Polson, Matthew; Chiorboli, Claudio; Fracasso, Sandro; Scandola, Franco

    2007-04-01

    The rod-like binuclear complexes [(ttpy)Ru(tpy-ph(2)-phbpy)Ru(ttpy)](4+) and [(ttpy)Ru(tpy-ph(2)-tpy)Ru(phtbpy)](4+) (for abbreviations, see text) have been synthesized and characterized. In both complexes, the polypyridine Ru(II) centers have (N--N--N)Ru(N--N--N) and (N--N--N)Ru(C--N--N) coordination environment. The two isomeric species differ in whether the cyclometalating carbon resides on the bridging or on the terminal ligand. The two complexes have virtually identical energy levels, but MLCT excited states of different (bridging or terminal) ligand localization. They are thus ideally suited to investigate possible effects of excited-state localization on intramolecular energy transfer kinetics. In fact, ultrafast spectroscopic measurements yield different energy transfer time constants for the two isomers, with the bridge-cyclometalated complex (2.7 ps) being faster than the terminal-cyclometalated one (8.0 ps). This difference can be explained in terms of different electronic factors for Dexter energy transfer. The study highlights the peculiar intricacies of intramolecular energy transfer in inorganic dyads involving MLCT excited states.

  6. Experiments with isomeric beams

    NASA Astrophysics Data System (ADS)

    Pfützner, M.; Grzywacz, R.; Lewitowicz, M.; Rykaczewski, K.

    1997-02-01

    The results of the search for μs-isomers performed with 112Sn and 86Kr beams at 60 MeV/nucleon with the LISE3 spectrometer at GANIL are summarized. Planned extension of these studies to high energy fragmentation reactions with the FRS separator at GSI is described. Some perspectives for experiments with isomeric beams at GSI are mentioned.

  7. Low-lying isomeric state in {sup 80}Ga from the {beta}{sup -} decay of {sup 80}Zn

    SciTech Connect

    LicA, R.; Marginean, N.; Ghita, D.G.; and others

    2012-10-20

    A new level scheme was constructed for {sup 80}Ga which is significantly different from the one previously reported. The excitation energy of a new low-lying state recently reported in [2] was identified at 22.4 keV. Properties of the level scheme suggest that the ground state has spin J = 6 and the first excited state has spin J = 3. The spin assignments are in agreement with laser spectroscopy values previously measured. Our work provides the first evidence for the J = 6 being the ground state.

  8. Thermal Neutron Capture and Thermal Neutron Burn-up of K isomeric state of 177mLu: a way to the Neutron Super-Elastic Scattering cross section

    SciTech Connect

    Roig, O.; Belier, G.; Meot, V.; Daugas, J.-M.; Romain, P.

    2006-03-13

    Thermal neutron radiative capture and burn-up measurements of the K isomeric state in 177Lu form part of an original method to indirectly obtain the neutron super-elastic scattering cross section at thermal energy. Neutron super-elastic scattering, also called neutron inelastic acceleration, occurs during the neutron collisions with an excited nuclear level. In this reaction, the nucleus could partly transfer its excitation energy to the scattered neutron.

  9. Decay of 185Tl, 185m+gHg, 189m+gPb and energy location of the 13/2+ isomeric states in 185Hg, 189Pb, 193Po and 197Rn

    NASA Astrophysics Data System (ADS)

    Sauvage, J.; Roussière, B.; Genevey, J.; Franchoo, S.; Andreyev, A. N.; Barré, N.; Ben Braham, A.; Bourgeois, C.; Clavelin, J.-F.; De Witte, H.; Fedorov, D. V.; Fedoseyev, V. N.; Fraile, L. M.; Grave, X.; Huber, G.; Huyse, M.; Kilcher, P.; Köster, U.; Kunz, P.; Lesher, S. R.; Marsh, B. A.; Mukha, I.; Oms, J.; Porquet, M. G.; Seliverstov, M.; Stefanescu, I.; Van de Vel, K.; Van Duppen, P.; Volkov, YU. M.; Wojtasiewicz, A.

    2013-09-01

    The /EC decay of 185Tl was studied at the ISOLDE facility, the -rays belonging to 185Hg have been identified and a partial low-spin level scheme of 185Hg has been built. The decay of 185m+gHg was studied at the ISOCELE facility. Conversion electron lines of very low-energy transitions were observed for the first time. Electron data have been obtained for four transitions in 185Au and two transitions in 185Hg . From the analysis performed using an internal energy calibration procedure the energy location of the 185mHg has been determined to be keV. This value is consistent with that determined independently, keV, using 185m+gHg -decay data from literature. New particles emitted from 189m+gPb have been detected and their origins determined by in-source laser spectroscopy at the ISOLDE facility. - coincidence results have served to locate the isomeric state of 189Pb at keV. This latter value added to -decay data from literature have allowed the energy location of the isomeric states of 193Po and 197Rn at 95(7)keV and 194(12)keV, respectively. The nuclear structure of the isomeric and ground states in the nuclei of the three -emitter chains starting with 195m+g, 197m+g, 199m+gRn are discussed.

  10. Symmetry control of radiative decay in linear polyenes: low barriers for isomerization in the S1 state of hexadecaheptaene.

    PubMed

    Christensen, Ronald L; Galinato, Mary Grace I; Chu, Emily F; Fujii, Ritsuko; Hashimoto, Hideki; Frank, Harry A

    2007-02-14

    The room temperature absorption and emission spectra of the 4-cis and all-trans isomers of 2,4,6,8,10,12,14-hexadecaheptaene are almost identical, exhibiting the characteristic dual emissions S1-->S0 (21Ag- --> 11Ag-) and S2-->S0 (11Bu+ --> 11Ag-) noted in previous studies of intermediate length polyenes and carotenoids. The ratio of the S1-->S0 and S2-->S0 emission yields for the cis isomer increases by a factor of approximately 15 upon cooling to 77 K in n-pentadecane. In contrast, for the trans isomer this ratio shows a 2-fold decrease with decreasing temperature. These results suggest a low barrier for conversion between the 4-cis and all-trans isomers in the S1 state. At 77 K, the cis isomer cannot convert to the more stable all-trans isomer in the 21Ag- state, resulting in the striking increase in its S1-->S0 fluorescence. These experiments imply that the S1 states of longer polyenes have local energy minima, corresponding to a range of conformations and isomers, separated by relatively low (2-4 kcal) barriers. Steady state and time-resolved optical measurements on the S1 states in solution thus may sample a distribution of conformers and geometric isomers, even for samples represented by a single, dominant ground state structure. Complex S1 potential energy surfaces may help explain the complicated S2-->S1 relaxation kinetics of many carotenoids. The finding that fluorescence from linear polyenes is so strongly dependent on molecular symmetry requires a reevaluation of the literature on the radiative properties of all-trans polyenes and carotenoids.

  11. Neutron single-particle strengths at N=40 , 42: Neutron knockout from Ni68,70 ground and isomeric states

    DOE PAGES

    Recchia, F.; Weisshaar, D.; Gade, A.; ...

    2016-11-28

    The distribution of single-particle strength in 67,69Ni was characterized with one-neutron knockout reactions from intermediate-energy 68,70Ni secondary beams, selectively populating neutron-hole configurations at N = 39 and 41, respectively. The spectroscopic strengths deduced from the measured partial cross sections to the individual final states, as tagged by their γ-ray decays, is used to identify and quantify neutron configurations in the wave functions. While 69Ni compares well to shell-model predictions, the results for 67Ni challenge the validity of current effective shell-model Hamiltonians by revealing discrepancies that cannot be explained so far. Furthermore, these results suggest that our understanding of the low-lyingmore » states in the neutron-rich, semi-magic Ni isotopes may be incomplete and requires further investigation on both the experimental and theoretical sides.« less

  12. Neutron single-particle strengths at N =40 , 42: Neutron knockout from Ni,7068 ground and isomeric states

    NASA Astrophysics Data System (ADS)

    Recchia, F.; Weisshaar, D.; Gade, A.; Tostevin, J. A.; Janssens, R. V. F.; Albers, M.; Bader, V. M.; Baugher, T.; Bazin, D.; Berryman, J. S.; Brown, B. A.; Campbell, C. M.; Carpenter, M. P.; Chen, J.; Chiara, C. J.; Crawford, H. L.; Hoffman, C. R.; Kondev, F. G.; Korichi, A.; Langer, C.; Lauritsen, T.; Liddick, S. N.; Lunderberg, E.; Noji, S.; Prokop, C.; Stroberg, S. R.; Suchyta, S.; Wimmer, K.; Zhu, S.

    2016-11-01

    The distribution of single-particle strength in Ni,6967 was characterized with one-neutron knockout reactions from intermediate-energy Ni,7068 secondary beams, selectively populating neutron-hole configurations at N =39 and 41, respectively. The spectroscopic strengths deduced from the measured partial cross sections to the individual final states, as tagged by their γ -ray decays, are used to identify and quantify neutron configurations in the wave functions. While 69Ni compares well with shell-model predictions, the results for 67Ni challenge the validity of current effective shell-model Hamiltonians by revealing discrepancies that cannot be explained so far. These results suggest that our understanding of the low-lying states in the neutron-rich, semimagic Ni isotopes may be incomplete and requires further investigation on both the experimental and theoretical sides.

  13. Conformational isomerism in the solid-state structures of tetracaine and tamoxifen with para-sulphonato-calix[4]arene

    NASA Astrophysics Data System (ADS)

    Danylyuk, Oksana; Monachino, Melany; Lazar, Adina N.; Suwinska, Kinga; Coleman, Anthony W.

    2010-02-01

    The solid-state complexes between para-sulphonato-calix[4]arene and the drugs tamoxifen and tetracaine show an unusual 4:1 guest-host stoichiometry with formation of hydrophobic layer of drug molecules held between bilayers of para-sulphonato-calix[4]arene. In both structures each of the four independent drug molecules adopts different conformation due to the different mode of interaction with the anionic host, the neighbouring drug cations and water molecules.

  14. Nuclear structure ''southeast'' of {sup 208}Pb: Isomeric states in {sup 208}Hg and {sup 209}Tl

    SciTech Connect

    Al-Dahan, N.; Podolyak, Zs.; Regan, P. H.; Alkhomashi, N.; Deo, A. Y.; Farrelly, G.; Steer, S. J.; Cullen, I. J.; Gelletly, W.; Swan, T.; Thomas, J. S.; Walker, P. M.; Gorska, M.; Grawe, H.; Gerl, J.; Pietri, S. B.; Wollersheim, H. J.; Boutachkov, P.; Domingo-Pardo, C.; Farinon, F.

    2009-12-15

    The nuclear structure of neutron-rich N>126 nuclei has been investigated following their production via relativistic projectile fragmentation of a E/A=1 GeV {sup 238}U beam. Metastable states in the N=128 isotones {sup 208}Hg and {sup 209}Tl have been identified. Delayed {gamma}-ray transitions are interpreted as arising from the decay of I{sup {pi}}=(8{sup +}) and (17/2{sup +}) isomers, respectively. The data allow for the so far most comprehensive verification of the shell-model approach in the region determined by magic numbers Z<82 and N>126.

  15. Prospects for isomeric energy release

    NASA Astrophysics Data System (ADS)

    Karamian, S. A.

    2008-07-01

    The state of experimental studies and promising proposals for the application of nuclear isomers presented as controlled energy or γ-ray sources are reviewed. The properties of isomeric states, methods of their production, and approaches to their efficient stimulation using various types of radiation are analyzed. The long-lived isomers, which can be accumulated in reactor irradiations or in other nuclear interactions with abundant yield, are listed. The isomers are estimated according to their specific energy accumulated per nucleus and the level of the cross section for their formation in reactions with neutrons. The nuclei are classified as promising either for obtaining controlled γ-ray pulses, for the enhanced release of the radioactive decay energy, or for experimental studies on detecting forbidden electromagnetic transitions from the ground to isomeric state. In all cases, the possibility of external-stimulus action on nuclear transitions has key significance, which should become the subject of investigations. The results of successful observation of stimulation of isomers are described at excitation energy E* > 1 MeV in the reactions with bremsstrahlung photons and Coulomb excitation in the ion beam. The essential increase in the K-hindered transitions with increasing energy and also the K-mixing at high rotational frequency for high-spin levels are discussed. The attention is focused on attempts to detect the triggering induced by the radiation in the x-ray range, in particular, that of the 178 m2Hf isomer with the help of x-ray sources and the synchrotron radiation. Proposals for experiments with other isomers are considered. The possibility of affecting the nuclear states by means of ionization of electron shells of a corresponding atom is discussed as promising, and various schemes of similar experiments are proposed. The atomic cross sections are eight orders of magnitude higher than the nuclear ones; therefore, the stimulation of an isomer can

  16. Molecular Switch for Sub-Diffraction Laser Lithography by Photoenol Intermediate-State Cis-Trans Isomerization.

    PubMed

    Mueller, Patrick; Zieger, Markus M; Richter, Benjamin; Quick, Alexander S; Fischer, Joachim; Mueller, Jonathan B; Zhou, Lu; Nienhaus, Gerd Ulrich; Bastmeyer, Martin; Barner-Kowollik, Christopher; Wegener, Martin

    2017-06-27

    Recent developments in stimulated-emission depletion (STED) microscopy have led to a step change in the achievable resolution and allowed breaking the diffraction limit by large factors. The core principle is based on a reversible molecular switch, allowing for light-triggered activation and deactivation in combination with a laser focus that incorporates a point or line of zero intensity. In the past years, the concept has been transferred from microscopy to maskless laser lithography, namely direct laser writing (DLW), in order to overcome the diffraction limit for optical lithography. Herein, we propose and experimentally introduce a system that realizes such a molecular switch for lithography. Specifically, the population of intermediate-state photoenol isomers of α-methyl benzaldehydes generated by two-photon absorption at 700 nm fundamental wavelength can be reversibly depleted by simultaneous irradiation at 440 nm, suppressing the subsequent Diels-Alder cycloaddition reaction which constitutes the chemical core of the writing process. We demonstrate the potential of the proposed mechanism for STED-inspired DLW by covalently functionalizing the surface of glass substrates via the photoenol-driven STED-inspired process exploiting reversible photoenol activation with a polymerization initiator. Subsequently, macromolecules are grown from the functionalized areas and the spatially coded glass slides are characterized by atomic-force microscopy. Our approach allows lines with a full-width-at-half-maximum of down to 60 nm and line gratings with a lateral resolution of 100 nm to be written, both surpassing the diffraction limit.

  17. Vibrational relaxation and isomerization kinetics of alcohols

    NASA Astrophysics Data System (ADS)

    Self-Medlin, Yehudi

    The vibrational dynamics of the O-H stretch was investigated for a series of alcohols in room temperature gas-phase and dilute solution. A set of alcohols with one stable conformer was measured to determine the intramolecular vibrational energy redistribution (IVR) timescales of basic alcohols for comparison of the isolated to solvated molecule dynamics. It was determined from these experiments the IVR rate of the O-H stretch is unaffected by the presence of solvent. Next, population transfer rates were measured from the initially excited O-H stretch through the molecule to the v = 1 acetylenic C-H bending mode of a series of alkynols. It was found that the IVR and population transfer rates were almost independent of molecule size, distance between the O-H and acetylene moiety, or branching size. However, the excited O-H stretch exhibits very little transfer to the C-H stretch or C-H bend overtone, indicating a mode-specific redistribution pathway. The data, as well as ab initio calculations, suggest non-statistical relaxation of the O-H stretch excited state population through a subset of C-H bending states. Determining the timescales of intramolecular relaxation and population transfer establishes a foundation for developing methods to enhance chemical reactions with lasers. A preliminary step towards this goal is the study of conformational isomerization. The IVR lifetime is the rate limiting step in vibrationally-induced isomerization kinetics. The conformational isomerization takes places so rapidly after IVR completion that it could not be detected with the available time resolution. However, excited state absorption signal was used as a molecular probe to measure the thermal isomerization created by collisions with solvent. The kinetic rate constants of the thermal isomerization were determined from the transient absorption spectra in combination with fixed time frequency scans of the entire absorption and bleach region. The experimentally determined values

  18. Effect of Isomeric Structures of Branched Cyclic Hydrocarbons on Densities and Equation of State Predictions at Elevated Temperatures and Pressures

    SciTech Connect

    Wu, Yue; Bamgbade, Babatunde A; Burgess, Ward A; Tapriyal, Deepak; Baled, Hseen O; Enick, Robert M; McHugh, Mark

    2013-07-25

    The cis and trans conformation of a branched cyclic hydrocarbon affects the packing and, hence, the density, exhibited by that compound. Reported here are density data for branched cyclohexane (C6) compounds including methylcyclohexane, ethylcyclohexane (ethylcC6), cis-1,2-dimethylcyclohexane (cis-1,2), cis-1,4-dimethylcyclohexane (cis-1,4), and trans-1,4-dimethylcyclohexane (trans-1,4) determined at temperatures up to 525 K and pressures up to 275 MPa. Of the four branched C6 isomers, cis-1,2 exhibits the largest densities and the smallest densities are exhibited by trans-1,4. The densities are modeled with the Peng–Robinson (PR) equation of state (EoS), the high-temperature, high-pressure, volume-translated (HTHP VT) PREoS, and the perturbed chain, statistical associating fluid theory (PC-SAFT) EoS. Model calculations highlight the capability of these equations to account for the different densities observed for the four isomers investigated in this study. The HTHP VT-PREoS provides modest improvements over the PREoS, but neither cubic EoS is capable of accounting for the effect of isomer structural differences on the observed densities. The PC-SAFT EoS, with pure component parameters from the literature or from a group contribution method, provides improved density predictions relative to those obtained with the PREoS or HTHP VT-PREoS. However, the PC-SAFT EoS, with either set of parameters, also cannot fully account for the effect of the C6 isomer structure on the resultant density.

  19. Effect of isomeric structures of branched cyclic hydrocarbons on densities and equation of state predictions at elevated temperatures and pressures.

    PubMed

    Wu, Yue; Bamgbade, Babatunde A; Burgess, Ward A; Tapriyal, Deepak; Baled, Hseen O; Enick, Robert M; McHugh, Mark A

    2013-07-25

    The cis and trans conformation of a branched cyclic hydrocarbon affects the packing and, hence, the density, exhibited by that compound. Reported here are density data for branched cyclohexane (C6) compounds including methylcyclohexane, ethylcyclohexane (ethylcC6), cis-1,2-dimethylcyclohexane (cis-1,2), cis-1,4-dimethylcyclohexane (cis-1,4), and trans-1,4-dimethylcyclohexane (trans-1,4) determined at temperatures up to 525 K and pressures up to 275 MPa. Of the four branched C6 isomers, cis-1,2 exhibits the largest densities and the smallest densities are exhibited by trans-1,4. The densities are modeled with the Peng-Robinson (PR) equation of state (EoS), the high-temperature, high-pressure, volume-translated (HTHP VT) PREoS, and the perturbed chain, statistical associating fluid theory (PC-SAFT) EoS. Model calculations highlight the capability of these equations to account for the different densities observed for the four isomers investigated in this study. The HTHP VT-PREoS provides modest improvements over the PREoS, but neither cubic EoS is capable of accounting for the effect of isomer structural differences on the observed densities. The PC-SAFT EoS, with pure component parameters from the literature or from a group contribution method, provides improved density predictions relative to those obtained with the PREoS or HTHP VT-PREoS. However, the PC-SAFT EoS, with either set of parameters, also cannot fully account for the effect of the C6 isomer structure on the resultant density.

  20. Rotational isomerism of vinylmethyltelluride

    SciTech Connect

    Keiko, V.V.; Sinegovskaya, L.M.; Gusarova, N.K.; Tatarinova, A.A.; Kalinina, N.A.; Trofimov, B.A.

    1987-08-10

    In the IR spectrum of solutions of vinylmethyltelluride in n-heptane the doublet form of the valence oscillation band of the double bond is due to rotational isomerism. By analyzing the temperature dependence of the doublet shape, the low-frequency component of the doublet was identified as the s-cis-rotamer. The differences in the enthalpies (4.6 +/- 0.2 kJ/mole) and entropies (-11.1 +/- 0.3 e.u.) of the vinylmethyltelluride rotamers have been calculated and it has been shown that the p,..pi..-conjugation in its molecule is weaker by a factor of 2 than in vinylmethylsulfide.

  1. a Reevaluation of Distortional Isomerism

    NASA Astrophysics Data System (ADS)

    Desrochers, Patrick John

    The blue and green forms of MoOCl_2 (PMe_2Ph)_3 and (LWOCl_2) PF _6 (L = 1,4,7-trimethyltriazacyclononane) are not examples of distortional isomerism. For both systems, the blue form is pure and the green form is a mixture of the blue complex and other components. Characterizations of the green material of each indicates that green "MoOCl _2(PMe_2Ph) _3" is a mixture of MoOCl _2(PMe_2Ph) _3 and MoCl_3(PMe _2Ph)_3 and that green "(LWOCl_2) PF _6" is a mixture of (LWOCl_2 ) PF_6 and two other species; one is a W(IV) and the other a W(VI) compound. Both solid state (XPS, Raman, infrared, powder X-ray diffraction) and solution phase (^1H NMR, UV -visible, EPR, cyclic voltammetry) measurements were applied to the respective green materials, presenting a consistent description of their composite nature. A single crystal X-ray structure determination of a crystal of green "MoOCl _2(PMe_2Ph) _3" allowed the compositional disorder to be partially resolved in this case, due to the high composition of MoOCl_3(PMe _2Ph)_3 in the sample (ca. 0.30 mole percent by XPS and visible spectroscopies). The single crystal X-ray diffraction data from the original single crystal study of green "(LWOCl_2 ) PF_6" were reinvestigated to ascertain whether compositional disorder could also be implicated in this system. Several composite models were applied to these data, resulting in improved fits to the observed data. This indicated that the original data collected for the crystal of green "(LWOCl _2) PF_6" could not support distortional isomerism in green "(LWOCl _2) PF_6". X-ray structure calculations on models of the compositional disorder in both systems illustrated the pronounced effect of disordering chlorine electron density on the derived metal-oxo bond lengths. A calibration curve of Mo-Cl bond length versus composition calculated from these models resulted in a favorable comparison of this present theoretical work with other experimental X-ray studies of the MoOCl_2 (PMe_2Ph)_3

  2. Isomeric oxydiphthalic anhydride polyimides

    NASA Technical Reports Server (NTRS)

    Gerber, Margaret K.; Pratt, J. Richard; Stclair, Terry L.

    1988-01-01

    Much of the polyimide research at Langley Research Center has focused on isomeric modification of the diamine component; polyimides having considerably improved processability and adhesion have resulted. The present structure-property study was designed to investigate how isomeric attachment of the three oxydiphthalic anhydride (ODPA) polyimides affects their properties. Each dianhydride, 3,4,3',4'-oxydiphthalic anhydride (4,4'-OPDA,I), 2,3,2',3'-oxydiphthalic anhydride (3,3'-ODPA,II), and 2,3,3',4'-oxydiphthalic anhydride (3,4'-OPDA,III), was reacted with p-phenylenediamine, 4,4'-oxydianiline, 3,3'-diaminodiphenylsulfone, 3,3'-diaminobenzophenone, and 4,4'-bis(3-aminophenoxy)benzophenone in DMAc. The inherent viscosities of the resulting poly(amic acids) were determined. Thermally imidized films were studied for their creasability and solubility, as well as by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and wide angle X-ray scattering (WAXS). A comparison of these properties will be made.

  3. Low-lying electronic states of FeNC and FeCN: A theoretical journey into isomerization and quartet/sextet competition

    NASA Astrophysics Data System (ADS)

    DeYonker, Nathan J.; Yamaguchi, Yukio; Allen, Wesley D.; Pak, Chaeho; Schaefer, Henry F.; Peterson, Kirk A.

    2004-03-01

    With several levels of multireference and restricted open-shell single-reference electronic structure theory, optimum structures, relative energetics, and spectroscopic properties of the low-lying 6Δ, 6Π, 4Δ, 4Π, and 4Σ- states of linear FeNC and FeCN have been investigated using five contracted Gaussian basis sets ranging from Fe[10s8p3d], C/N[4s2p1d] to Fe[6s8p6d3f2g1h], C/N[6s5p4d3f2g]. Based on multireference configuration interaction (MRCISD+Q) results with a correlation-consistent polarized valence quadruple-zeta (cc-pVQZ) basis set, appended with core correlation and relativistic corrections, we propose the relative energies: Te(FeNC), 6Δ(0)<6Π (2300 cm-1)<4Δ (2700 cm-1)<4Π (4200 cm-1)<4Σ-; and Te(FeCN), 6Δ(0)<6Π (1800 cm-1)<4Δ (2500 cm-1)<4Π (2900 cm-1)<4Σ-. The 4Δ and 4Π states have massive multireference character, arising mostly from 11σ→12σ promotions, whereas the sextet states are dominated by single electronic configurations. The single-reference CCSDT-3 (coupled cluster singles and doubles with iterative partial triples) method appears to significantly overshoot the stabilization of the quartet states provided by both static and dynamical correlation. The 4,6Δ and 4,6Π states of both isomers are rather ionic, and all have dipole moments near 5 D. On the ground 6Δ surface, FeNC is predicted to lie 0.6 kcal mol-1 below FeCN, and the classical barrier for isocyanide/cyanide isomerization is about 6.5 kcal mol-1. Our data support the recent spectroscopic characterization by Lei and Dagdigian [J. Chem. Phys. 114, 2137 (2000)] of linear 6Δ FeNC as the first experimentally observed transition-metal monoisocyanide. Their assignments for the ground term symbol, isotopomeric rotational constants, and the Fe-N ω3 stretching frequency are confirmed; however, we find rather different structural parameters for 6Δ FeNC:re(Fe-N)=1.940 Å and r(N-C)=1.182 Å at the cc-pVQZ MRCISD+Q level. Our results also reveal that the observed band of Fe

  4. Probing cis-trans isomerization in the S{sub 1} state of C{sub 2}H{sub 2} via H-atom action and hot band-pumped IR-UV double resonance spectroscopies

    SciTech Connect

    Changala, P. Bryan; Baraban, Joshua H.; Field, Robert W.; Merer, Anthony J.

    2015-08-28

    We report novel experimental strategies that should prove instrumental in extending the vibrational and rotational assignments of the S{sub 1} state of acetylene, C{sub 2}H{sub 2}, in the region of the cis-trans isomerization barrier. At present, the assignments are essentially complete up to ∼500 cm{sup −1} below the barrier. Two difficulties arise when the assignments are continued to higher energies. One is that predissociation into C{sub 2}H + H sets in roughly 1100 cm{sup −1} below the barrier; the resulting quenching of laser-induced fluorescence (LIF) reduces its value for recording spectra in this region. The other difficulty is that tunneling through the barrier causes a staggering in the K-rotational structure of isomerizing vibrational levels. The assignment of these levels requires data for K values up to at least 3. Given the rotational selection rule K′ − ℓ{sup ′′} = ± 1, such data must be obtained via excited vibrational levels of the ground state with ℓ{sup ′′} > 0. In this paper, high resolution H-atom resonance-enhanced multiphoton ionization spectra are demonstrated to contain predissociated bands which are almost invisible in LIF spectra, while preliminary data using a hyperthermal pulsed nozzle show that ℓ{sup ′′} = 2 states can be selectively populated in a jet, giving access to K′ = 3 states in IR-UV double resonance.

  5. Exercises in anatomy: cardiac isomerism.

    PubMed

    Anderson, Robert H; Sarwark, Anne E; Spicer, Diane E; Backer, Carl L

    2014-01-01

    It is well recognized that the patients with the most complex cardiac malformations are those with so-called visceral heterotaxy. At present, it remains a fact that most investigators segregate these patients on the basis of their splenic anatomy, describing syndromes of so-called asplenia and polysplenia. It has also been known for quite some time, nonetheless, that the morphology of the tracheobronchial tree is usually isomeric in the setting of heterotaxy. And it has been shown that the isomerism found in terms of bronchial arrangement correlates in a better fashion with the cardiac anatomy than does the presence of multiple spleens, or the absence of any splenic tissue. In this exercise in anatomy, we use hearts from the Idriss archive of Lurie Children's Hospital in Chicago to demonstrate the isomeric features found in the hearts obtained from patients known to have had heterotaxy. We first demonstrate the normal arrangements, showing how it is the extent of the pectinate muscles in the atrial appendages relative to the atrioventricular junctions that distinguishes between morphologically right and left atrial chambers. We also show the asymmetry of the normal bronchial tree, and the relationships of the first bronchial branches to the pulmonary arteries supplying the lower lobes of the lungs. We then demonstrate that diagnosis of multiple spleens requires the finding of splenic tissue on either side of the dorsal mesogastrium. Turning to hearts obtained from patients with heterotaxy, we illustrate isomeric right and left atrial appendages. We emphasize that it is only the appendages that are universally isomeric, but point out that other features support the notion of cardiac isomerism. We then show that description also requires a full account of veno-atrial connections, since these can seemingly be mirror-imaged when the arrangement within the heart is one of isomerism of the atrial appendages. We show how failure to recognize the presence of such isomeric

  6. Conformational isomerism in solid state of AMG 853--structure studies using solid-state nuclear magnetic resonance and X-ray diffraction.

    PubMed

    Kiang, Y-H; Nagapudi, Karthik; Wu, Tian; Peterson, Matthew L; Jona, Janan; Staples, Richard J; Stephens, Peter W

    2015-07-01

    Investigation of an additional resonance peak in the (19) F solid-state nuclear magnetic resonance (NMR) spectrum of AMG 853, a dual antagonist of DP and CRTH2 previously in clinical development for asthma, has led to the identification of two conformational isomers coexisting in the crystal lattice in a continuous composition range between 89.7%:10.3% and 96.5%:3.5%. These two isomers differ in the chloro-flurorophenyl moiety orientation-the aromatic ring is flipped by 180° in these two isomers. The level of the minor isomer is directly measured through integration of the two peaks in the (19) F solid-state NMR spectrum. The values obtained from the NMR data are in excellent agreement with the degree of disorder of the fluorine atom in the crystal structure, refined using both single-crystal and high-resolution powder X-ray diffraction data.

  7. A Comparative Account of the Kinetics of Light-Induced E-Z Isomerization of an Anthracene-Based Organogelator in Sol, Gel, Xerogel, and Powder States: Fiber to Crystal Transformation.

    PubMed

    Mondal, Sanjoy; Chakraborty, Priyadarshi; Das, Sujoy; Bairi, Partha; Nandi, Arun K

    2016-05-31

    The organogel of (E)-N'-(anthracene-10-ylmethylene)-3,4,5-tris(dodecyloxy)benzohydrazide (I) in methyl cyclohexane having a fibrillar network structure exhibits excellent fluorescence, which decreases sharply with time upon photoirradiation at λ = 365 nm. It has been attributed to the transformation of the E isomer of I to the Z isomer, and the kinetics of E-Z isomerization are compared for the sol, gel, xerogel, and powder states. The rate constants at different temperatures are measured from Avrami plots and its increase with an increase in temperature, indicating temperature acts as a promoter for photoirradiated E-Z isomeization along the imine (C═N) bond. In the powder form, the rate constant values are the lowest compared to those of other states for all temperatures and the xerogels exhibit the highest rate of E-Z isomerization. The rate constants of sol and gel states mostly lie between the two. The wide-angle X-ray scattering pattern changes after ultraviolet (UV) irradiation with the generation of new sharp peaks whose intensities increase with an increase in irradiation time. A polarized optical microscopic study indicates formation of small crystalline dots on the fibers in the gels, dendritic morphology on the xerogel fibers, and large needlelike morphology at the surface boundary of the solid. The dried I gel exhibits a melting peak at 96.7 °C, but upon irradiation, two peaks are observed at 98.5 and 152.7 °C; the latter has been attributed to the melting of crystals of Z isomers. Similar higher melting peaks are observed both for the xerogel and for powders after UV irradiation; the powders exhibit the highest meting peak at 159.4 °C. Possible reasons for the variation of rate constant values in the four different states and the difference in morphology and melting points of crystals of Z isomers of I are discussed.

  8. Isomeric Ratios for Nuclei with Z=62-67 and A=142-152 Produced in the Relativistic Fragmentation of 208Pb

    NASA Astrophysics Data System (ADS)

    Myalski, S.; Maj, A.; Podolyák, Zs.; Becker, F.; Bednarczyk, P.; Benzoni, G.; Blank, B.; Brandau, C.; Bruce, A. M.; Cáceres, L.; Camera, F.; Catford, W. N.; Cullen, I. J.; Dombradi, Zs.; Doornenbal, P.; Estevez, E.; Garnsworthy, A. B.; Geissel, H.; Gelletly, W.; Gerl, J.; Górska, M.; Grawe, H.; Grębosz, J.; Heinz, A.; Hoischen, R.; Ilie, G.; Jones, G. A.; Jungclaus, A.; Kelic, A.; Kmiecik, M.; Kojouharov, I.; Kondev, F. G.; Kurtukian-Nieto, T.; Kurz, N.; Lalkovski, S.; Liu, Z.; Montes, F.; Pfützner, M.; Pietri, S.; Prokopowicz, W.; Regan, P. H.; Rudolph, D.; Saito, T.; Schaffner, H.; Schwertel, S.; Shizuma, T.; Simons, A. J.; Steer, S. J.; Tashenov, S.; Walker, P. M.; Werner-Malento, E.; Wieland, O.; Wollersheim, H. J.

    2009-03-01

    Isomeric states in nuclei with Z=62-67 and A=142-152 produced in the fragmentation of the relativistic (1 GeV/nucleon) 208Pb beam were investigated. Isomeric ratios were determined for 10 isomeric states. Significant differences between theoretical and experimental values were observed.

  9. Reinvestigation of the direct two-proton decay of the long-lived isomer 94Ag(m) [0.4 s, 6.7 MeV, (21+)].

    PubMed

    Cerny, J; Moltz, D M; Lee, D W; Peräjärvi, K; Barquest, B R; Grossman, L E; Jeong, W; Jewett, C C

    2009-10-09

    An attempt to confirm the reported direct one-proton and two-proton decays of the (21+) isomer at 6.7(5) MeV in 94Ag has been made. The 0.39(4) s half-life of the isomer permitted use of a helium-jet system to transport reaction products from the 40Ca + (nat)Ni reaction at 197 MeV to a low-background area; 24 gas DeltaE-(Si)E detector telescopes were used to identify emitted protons down to 0.4 MeV. No evidence was obtained for two-proton radioactivity with a summed energy of 1.9(1) MeV and a branching ratio of 0.5(3)%. Two groups of one-proton radioactivity from this isomer had also been reported; our data confirm the lower energy group at 0.79(3) MeV with its branching ratio of 1.9(5)%.

  10. Syntheses, structures, and magnetic properties of three one-dimensional end-to-end azide/cyanate-bridged copper(II) compounds exhibiting ferromagnetic interaction: new type of solid state isomerism.

    PubMed

    Sasmal, Sujit; Sarkar, Sohini; Aliaga-Alcalde, Núria; Mohanta, Sasankasekhar

    2011-06-20

    The work in this paper presents the syntheses, structures, and magnetic properties of three end-to-end (EE) azide/cyanate-bridged copper(II) compounds [Cu(II)L(1)(μ(1,3)-NCO)](n)·2nH(2)O (1), [Cu(II)L(1)(μ(1,3)-N(3))](n)·2nH(2)O (2), and [Cu(II)L(2)(μ(1,3)-N(3))](n) (3), where the ligands used to achieve these species, HL(1) and HL(2), are the tridentate Schiff base ligands obtained from [1 + 1] condensations of salicylaldehyde with 4-(2-aminoethyl)-morpholine and 3-methoxy salicylaldehyde with 1-(2-aminoethyl)-piperidine, respectively. Compounds 1 and 2 crystallize in the monoclinic P2(1)/c space group, while compound 3 crystallizes in the orthorhombic Pbca space group. The metal center in 1-3 is in all cases pentacoordinated. Three coordination positions of the metal center in 1, 2, or 3 are satisfied by the phenoxo oxygen atom, imine nitrogen atom, and morpholine (for 1 and 2) or piperidine (for 3) nitrogen atom of one deprotonated ligand, [L(1)](-) or [L(2)](-). The remaining two coordination positions are satisfied by two nitrogen atoms of two end-to-end bridging azide ligands for 2 and 3 and one nitrogen atom and one oxygen atom of two end-to-end bridging cyanate ligands for 1. The coordination geometry of the metal ion is distorted square pyramidal in which one EE azide/cyanate occupies the apical position. Variable-temperature (2-300 K) magnetic susceptibilities of 1-3 have been measured under magnetic fields of 0.05 (from 2 to 30 K) and 1.0 T (from 30 to 300 K). The simulation reveals a ferromagnetic interaction in all three compounds with J values of +0.19 ± 0.01, +0.79 ± 0.01, and +1.25 ± 0.007 cm(-1) for 1, 2, and 3, respectively. Compound 1 is the sole example of a ferromagnetically coupled EE cyanate-bridged 1-D copper(II) system. In addition, a rare example of supramolecular isomerism and a nice example of magnetic isomerism have been observed and most interestingly a new type of solid state isomerism has emerged as a result of the comparison

  11. Homodimerization of the G Protein Srbeta in the Nucleotide-Free State Involves Proline cis/trans Isomerication in the Switch II Region

    SciTech Connect

    Schwartz,T.; Schmidt, D.; Brohawn, S.; Blobel, G.

    2006-01-01

    Protein translocation across and insertion into membranes is essential to all life forms. Signal peptide-bearing nascent polypeptide chains emerging from the ribosome are first sampled by the signal-recognition particle (SRP), then targeted to the membrane via the SRP receptor (SR), and, finally, transferred to the protein-conducting channel. In eukaryotes, this process is tightly controlled by the concerted action of three G proteins, the 54-kD subunit of SRP and the {alpha}- and {beta}-subunits of SR. We have determined the 2.2-Angstroms crystal structure of the nucleotide-free SR{beta} domain. Unexpectedly, the structure is a homodimer with a highly intertwined interface made up of residues from the switch regions of the G domain. The remodeling of the switch regions does not resemble any of the known G protein switch mechanisms. Biochemical analysis confirms homodimerization in vitro, which is incompatible with SR{alpha} binding. The switch mechanism involves cis/trans isomerization of a strictly conserved proline, potentially implying a new layer of regulation of cotranslational transport.

  12. Homodimerization of the G protein SRβ in the nucleotide-free state involves proline cis/trans isomerization in the switch II region

    PubMed Central

    Schwartz, Thomas U.; Schmidt, Daniel; Brohawn, Stephen G.; Blobel, Günter

    2006-01-01

    Protein translocation across and insertion into membranes is essential to all life forms. Signal peptide-bearing nascent polypeptide chains emerging from the ribosome are first sampled by the signal-recognition particle (SRP), then targeted to the membrane via the SRP receptor (SR), and, finally, transferred to the protein-conducting channel. In eukaryotes, this process is tightly controlled by the concerted action of three G proteins, the 54-kD subunit of SRP and the α- and β-subunits of SR. We have determined the 2.2-Å crystal structure of the nucleotide-free SRβ domain. Unexpectedly, the structure is a homodimer with a highly intertwined interface made up of residues from the switch regions of the G domain. The remodeling of the switch regions does not resemble any of the known G protein switch mechanisms. Biochemical analysis confirms homodimerization in vitro, which is incompatible with SRα binding. The switch mechanism involves cis/trans isomerization of a strictly conserved proline, potentially implying a new layer of regulation of cotranslational transport. PMID:16627619

  13. Isomerization of C60 fullerenes

    NASA Astrophysics Data System (ADS)

    Yi, Jae-Yel; Bernholc, J.

    1992-06-01

    Car-Parrinello calculations show that the transformation between C60 isomers involves barriers in excess of 5 eV, although the energetic difference between the buckyball and the next lowest isomer is only 1.6 eV. C60 isomerization thus requires high temperatures and long annealing times.

  14. Simple, Chemoselective, Catalytic Olefin Isomerization

    PubMed Central

    2015-01-01

    Catalytic amounts of Co(SaltBu,tBu)Cl and organosilane irreversibly isomerize terminal alkenes by one position. The same catalysts effect cycloisomerization of dienes and retrocycloisomerization of strained rings. Strong Lewis bases like amines and imidazoles, and labile functionalities like epoxides, are tolerated. PMID:25398144

  15. Synthesis of Positional Isomeric Phenylphenalenones.

    PubMed

    Ospina, Felipe; Ramirez, Adrian; Cano, Marisol; Hidalgo, William; Schneider, Bernd; Otálvaro, Felipe

    2017-03-27

    A series of isomeric phenylphenalenones in which the phenyl ring is located at all possible peripheral positions of the phenalenone nuclei was synthesized. The structural characteristics of the series, in which topological variation is permitted with minimal electronic disturbance, could, in principle, allow for easy pharmacophore recognition when the compounds are aligned in steroidomimetic conformations.

  16. The experimental isomeric cross-section ratio in the nuclear activation technique

    NASA Astrophysics Data System (ADS)

    Vänskä, R.; Rieppo, R.

    1981-02-01

    First, the experimental isomeric cross-section ratio is discussed considering a single metastable state induced. The experimental ratio is given in a straightforward and exact formula, which is generally applicable to any incident particle activation and to any isomeric pair of an exclusive, fractional or non-existing isomeric transition decay. Second, the derived experimental isomeric yield ration is adapted for the present work where neutron induced reactions are considered and gamma-ray spectrometry is utilized in the determination of the 14-15 MeV neutron activation cross-sections and isomeric cross-section ratios for the germanium reactions, 74Ge(n, α) 71m,gZn and 76Ge(n, 2n) 75m,gGe, leading to single metastable and ground states in the product.

  17. The isomeric structure of 132Pr

    NASA Astrophysics Data System (ADS)

    Alharshan, G. A.; Cullen, D. M.; Taylor, M. J.; Procter, M. G.; Lumley, N. M.; Grahn, T.; Greenless, P. T.; Hauschild, K.; Herzon, A.; Jakobsson, U.; Jones, P. M.; Julin, R.; Juutinen, S.; Ketelhut, S.; Leino, M.; Lopez-Martens, A.; Nieminen, P.; Pantanen, J.; Peura, P.; Rahkila, P.; Rinta-Antilla, S.; Ruatsalainen, P.; Sandzelius, H. M.; Saren, J.; Scholey, C.; Sorri, J.; Stolze, S.; Uusitalo, J.

    2012-09-01

    The isomeric structure of the neutron deficient nucleus 132Pr, located in the rare-earth region of the nuclear chart, has been studied with the 98Mo(40Ar,5pn)132Pr reaction at beam energies of 150, 158 and 165 MeV. The experiment was performed at the University of Jyväskylä, Finland where the 40Ar beam was accelerated onto the target by the K130 cyclotron. The JUROGAM II HPGe detector array was employed in conjunction with the RITU gas-filled recoil separator. The focal-plane chamber housed a multi wire proportional counter and a position-sensitive silicon strip detector used for the implantation and identification of recoiling nuclei. The recoil-isomer tagging technique was used to correlate the delayed decays, measured in the Planar and Clover detectors of the GREAT spectrometer, with the known prompt transitions in 132Pr. Two new delayed transitions have been observed at energies of 102 and 118 keV. The corresponding X ray peaks are consistent with Pr Kα and Kβ X rays with energies of 35.63 and 40.91 keV, respectively. The half-life of the newly established isomeric state, from which the 102 and 118-keV transitions proceed, has been measured to be 2.5(3) μs.

  18. Trans-cis isomerization of lipophilic dyes probing membrane microviscosity in biological membranes and in live cells.

    PubMed

    Chmyrov, Volodymyr; Spielmann, Thiemo; Hevekerl, Heike; Widengren, Jerker

    2015-06-02

    Membrane environment and fluidity can modulate the dynamics and interactions of membrane proteins and can thereby strongly influence the function of cells and organisms in general. In this work, we demonstrate that trans-cis isomerization of lipophilic dyes is a useful parameter to monitor packaging and fluidity of biomembranes. Fluorescence fluctuations, generated by trans-cis isomerization of the thiocarbocyanine dye Merocyanine 540 (MC540), were first analyzed by fluorescence correlation spectroscopy (FCS) in different alcohol solutions. Similar isomerization kinetics of MC540 in lipid vesicles could then also be monitored, and the influence of lipid polarity, membrane curvature, and cholesterol content was investigated. While no influence of membrane curvature and lipid polarity could be observed, a clear decrease in the isomerization rates could be observed with increasing cholesterol contents in the vesicle membranes. Finally, procedures to spatially map photoinduced and thermal isomerization rates on live cells by transient state (TRAST) imaging were established. On the basis of these procedures, MC540 isomerization was studied on live MCF7 cells, and TRAST images of the cells at different temperatures were found to reliably detect differences in the isomerization parameters. Our studies indicate that trans-cis isomerization is a useful parameter for probing membrane dynamics and that the TRAST imaging technique can provide spatial maps of photoinduced isomerization as well as both photoinduced and thermal back-isomerization, resolving differences in local membrane microviscosity in live cells.

  19. A case study of proline isomerization in cell signaling.

    PubMed

    Min, Lie; Fulton, D Bruce; Andreotti, Amy H

    2005-01-01

    Protein-mediated interactions and enzymatic function provide the foundation upon which cellular signaling cascades control all of the activities of a cell. Post-translational modifications such as phosphorylation or ubiquitiation are well known means for modulating protein activity within the cell. These chemical modifications create new recognition motifs on proteins or shift conformational preferences such that protein catalytic and binding functions are altered in response to external stimuli. Moreover, detection of such modifications is often straightforward by conventional biochemical methods leading investigators toward mechanistic models of cell signaling involving post-translational modifications such as phosphorylation/dephosphorylation. While there is little doubt that such modifications play a significant role in transmission of information throughout the cell, there are certainly other mechanisms at work that are not as well understood at this time. Of particular interest in the context of this review is the intrinsic conformational switch afforded to a polypeptide by peptidyl prolyl cis/trans isomerization. Proline isomerization is emerging as a critical component of certain cell signaling cascades. In addition to serving as a conformational switch that enables a protein to adopt functionally distinct states, proline isomerization may serve as a recognition element for the ubiquitous peptidyl prolyl isomerases. This overview takes a close look at one particular signaling protein, the T cell specific tyrosine kinase Itk, and examines the role of proline isomerization and the peptidyl prolyl isomerase cyclophilin A in mediating Itk function following T cell receptor engagement.

  20. Catalysis of Protein Disulfide Bond Isomerization in a Homogeneous Substrate†

    PubMed Central

    Kersteen, Elizabeth A.; Barrows, Seth R.; Raines, Ronald T.

    2008-01-01

    Protein disulfide isomerase (PDI) catalyzes the rearrangement of nonnative disulfide bonds in the endoplasmic reticulum of eukaryotic cells, a process that often limits the rate at which polypeptide chains fold into a native protein conformation. The mechanism of the reaction catalyzed by PDI is unclear. In assays involving protein substrates, the reaction appears to involve the complete reduction of some or all of its nonnative disulfide bonds followed by oxidation of the resulting dithiols. The substrates in these assays are, however, heterogeneous, which complicates mechanistic analyses. Here, we report the first analysis of disulfide bond isomerization in a homogeneous substrate. Our substrate is based on tachyplesin I, a 17-mer peptide that folds into a _-hairpin stabilized by two disulfide bonds. We describe the chemical synthesis of a variant of tachyplesin I in which its two disulfide bonds are in a nonnative state and side chains near its N-and C-terminus contain a fluorescence donor (tryptophan) and acceptor (N_-dansyllysine). Fluorescence resonance energy transfer from 280 to 465 nm increases by 28-fold upon isomerization of the disulfide bonds into their native state (which has a lower E°_ = -0.313 V than does PDI). We use this continuous assay to analyze catalysis by wild-type human PDI and a variant in which the C-terminal cysteine residue within each Cys—Gly—His—Cys active site is replaced with alanine. We find that wild-type PDI catalyzes the isomerization of the substrate with kcat/KM = 1.7 _ 105 M–1M s–1, which is the largest value yet reported for catalysis of disulfide bond isomerization. The variant, which is a poor catalyst of disulfide bond reduction and dithiol oxidation, retains virtually all of the activity of wild-type PDI in catalysis of disulfide bond isomerization. Thus, the C-terminal cysteine residues play an insignificant role in the isomerization of the disulfide bonds in nonnative tachyplesin I. We conclude that

  1. Reaction coordinates of biomolecular isomerization

    PubMed Central

    Bolhuis, Peter G.; Dellago, Christoph; Chandler, David

    2000-01-01

    Transition path sampling has been applied to the molecular dynamics of the alanine dipeptide in vacuum and in aqueous solution. The analysis shows that more degrees of freedom than the traditional dihedral angles, φ and ψ, are necessary to describe the reaction coordinates for isomerization of this molecule. In vacuum, an additional dihedral angle is identified as significant. In solution, solvent variables are shown to play a significant role, and this role appears to be more specific than can be captured by friction models. Implications for larger molecules are discussed. PMID:10801977

  2. Reaction coordinates of biomolecular isomerization

    NASA Astrophysics Data System (ADS)

    Bolhuis, Peter G.; Dellago, Christoph; Chandler, David

    2000-05-01

    Transition path sampling has been applied to the molecular dynamics of the alanine dipeptide in vacuum and in aqueous solution. The analysis shows that more degrees of freedom than the traditional dihedral angles, and , are necessary to describe the reaction coordinates for isomerization of this molecule. In vacuum, an additional dihedral angle is identified as significant. In solution, solvent variables are shown to play a significant role, and this role appears to be more specific than can be captured by friction models. Implications for larger molecules are discussed.

  3. Study of ground and excited state decays in N ≈ Z Ag nuclei

    NASA Astrophysics Data System (ADS)

    Moschner, K.; Blazhev, A.; Warr, N.; Boutachkov, P.; Davies, P.; Wadsworth, R.; Ameil, F.; Baba, H.; Bäck, T.; Dewald, M.; Doornenbal, P.; Faestermann, T.; Gengelbach, A.; Gerl, J.; Gernhäuser, R.; Go, S.; Górska, M.; Grawe, H.; Gregor, E.; Hotaka, H.; Isobe, T.; Jenkins, D. G.; Jolie, J.; Jung, H. S.; Kojouharov, I.; Kurz, N.; Lewitowicz, M.; Lorusso, G.; Merchan, E.; Naqvi, F.; Nishibata, H.; Nishimura, D.; Nishimura, S.; Pietralla, N.; Schaffner, H.; Söderström, P.-A.; Steiger, K.; Sumikama, T.; Taprogge, J.; Thöle, P.; Watanabe, H.; Werner, V.; Xu, Z. Y.; Yagi, A.; Yoshinaga, K.; Zhu, Y.

    2015-05-01

    A decay spectroscopy experiment was performed within the EURICA campaign at RIKEN in 2012. It aimed at the isomer and particle spectroscopy of excited states and ground states in the mass region below the doubly magic 100Sn. The N = Z nuclei 98In, 96Cd and 94Ag were of particular interest for the present study. Preliminary results on the neutron deficient nuclei 93Ag and 94Ag are presented. In 94Ag a more precise value for the half-life of the ground state's superallowed Fermi transition was deduced. In addition the energy spectra of the mentioned decay could be reproduced through precise Geant4 simulations of the used active stopper SIMBA. This will enable us to extract Qβ values from the measured data. The decay of 93Ag is discussed based on the observed implantation-decay correlation events.

  4. Imaging the Predicted Isomerism of Oligo(aniline)s: A Scanning Tunneling Microscopy Study.

    PubMed

    Thomas, James O; Andrade, Hugo D; Mills, Benjamin M; Fox, Neil A; Hoerber, Heinrich J K; Faul, Charl F J

    2015-07-01

    The self-assembly of two emeraldine base tetra(aniline) derivatives is investigated using scanning tunneling microscopy. A combination of the scanning tunneling microscopy data and calculations reveals the presence of predicted cis/trans isomerism in this oxidation state. This isomerism is shown to hinder self-assembly into ordered structures, and provides indications as to why the properties of these materials, and their parent polymer, polyaniline, remain unfulfilled.

  5. g-factor and quadrupole moment of the 21/2- isomeric state in 131La: Signature for a weakly-deformed magnetic rotational band head

    NASA Astrophysics Data System (ADS)

    Kaur, Jasmeet; Bansal, Neeraj; Bhati, A. K.; Kumar, R.; Sharma, Vijay R.; Kapoor, K.; Kumar, V.; Kaur, Navneet

    2017-02-01

    The g-factor and the static quadrupole moment of a magnetic rotational band head 21/2- at 2121 keV in 131La have been determined by means of the time-differential perturbed angular distribution technique. The measured value of the g-factor, + 1.060 (4), is in agreement with the theoretical value for a three quasi-proton, π3 {11/2- [ 505 ] ⊗5/2+ [ 422 ] ⊗5/2+ [ 413 ] } Nilsson configuration assignment. The observed spectroscopic quadrupole moment ratio, Qs (21/2- ,131 La)/Qs (19/2- ,137 La) = 0.457 (4), supports the collective oblate shape (γ ∼ - 60 °) with quadrupole deformation β2 < 0.07. The half-life of the 21/2- state, 37.2(1) ns, is re-measured with better accuracy.

  6. Ultrafast Extreme Ultraviolet Induced Isomerization of Acetylene Cations

    SciTech Connect

    Jiang, Y.; Rudenko, Artem; Herrwerth, O.; Foucar, L.; Kurka, M.; Kuhnel, K.; Lezius, M.; Kling, Matthias; van Tilborg, Jeroen; Belkacem, Ali; Ueda, K.; Dusterer, S.; Treusch, R.; Schroter, Claus-Dieter; Moshammer, Robbert; Ullrich, Joachim

    2011-06-17

    Ultrafast isomerization of acetylene cations ([HC = CH]{sup +}) in the low-lying excited A{sup 2}{Sigma}{sub g}{sup +} state, populated by the absorption of extreme ultraviolet (XUV) photons (38 eV), has been observed at the Free Electron Laser in Hamburg, (FLASH). Recording coincident fragments C{sup +} + CH{sub 2}{sup +} as a function of time between XUV-pump and -probe pulses, generated by a split-mirror device, we find an isomerization time of 52 {+-} 15 fs in a kinetic energy release (KER) window of 5.8 < KER < 8 eV, providing clear evidence for the existence of a fast, nonradiative decay channel.

  7. Ultrafast Extreme Ultraviolet Induced Isomerization of Acetylene Cations

    SciTech Connect

    Jiang, Y. H.; Kurka, M.; Kuehnel, K. U.; Schroeter, C. D.; Moshammer, R.; Rudenko, A.; Foucar, L.; Herrwerth, O.; Lezius, M.; Kling, M. F.; Tilborg, J. van; Belkacem, A.; Ueda, K.; Duesterer, S.; Treusch, R.; Ullrich, J.

    2010-12-31

    Ultrafast isomerization of acetylene cations ([HC=CH]{sup +}) in the low-lying excited A{sup 2}{Sigma}{sub g}{sup +} state, populated by the absorption of extreme ultraviolet (XUV) photons (38 eV), has been observed at the Free Electron Laser in Hamburg, (FLASH). Recording coincident fragments C{sup +}+CH{sub 2}{sup +} as a function of time between XUV-pump and -probe pulses, generated by a split-mirror device, we find an isomerization time of 52{+-}15 fs in a kinetic energy release (KER) window of 5.8

  8. Prolyl isomerization as a molecular timer in phage infection.

    PubMed

    Eckert, Barbara; Martin, Andreas; Balbach, Jochen; Schmid, Franz X

    2005-07-01

    Prolyl cis-trans isomerizations are intrinsically slow reactions and known to be rate-limiting in many protein folding reactions. Here we report that a proline is used as a molecular timer in the infection of Escherichia coli cells by the filamentous phage fd. The phage is activated for infection by the disassembly of the two N-terminal domains, N1 and N2, of its gene-3-protein, which is located at the phage tip. Pro213, in the hinge between N1 and N2, sets a timer for the infective state. The timer is switched on by cis-to-trans and switched off by the unusually slow trans-to-cis isomerization of the Gln212-Pro213 peptide bond. The switching rate and thus the infectivity of the phage are determined by the local sequence around Pro213, and can be tuned by mutagenesis.

  9. Favored configurations for four-quasiparticle K isomerism in the heaviest nuclei

    NASA Astrophysics Data System (ADS)

    Liu, H. L.; Walker, P. M.; Xu, F. R.

    2014-04-01

    Configuration-constrained potential-energy-surface calculations are performed including β6 deformation to investigate high-K isomeric states in nuclei around 254No and 270Ds, the heaviest nuclei where there have been some observations of two-quasiparticle isomers, while data for four-quasiparticle isomers are scarce. We predict the prevalent occurrence of four-quasiparticle isomeric states in these nuclei, together with their favored configurations. The most notable examples, among others, are Kπ=20+ states in 266,268Ds and 268,270Cn having very high K value, relatively low excitation energy, and well-deformed axially symmetric shape. The predicted isomeric states, with hindered spontaneous fission and α decay, could play a significant role in the future study of superheavy nuclei.

  10. New candidates for high spin isomeric targets

    NASA Astrophysics Data System (ADS)

    Tonchev, A. P.; Gangrsky, Yu. P.; Belov, A. G.

    1999-02-01

    Experimental results of the accumulation and study of reaction mechanism of the de-excitation of high spin isomeric targets 108mAg ( Jπ=6 +), 166mHo ( Jπ=7 -) and 180mTa ( Jπ=9 -) are discussed. Together with other isomers, such as 178m2Hf ( Jπ=16 +), 186mRe ( Jπ=8 +), 242m Am ( Jπ=5 -), which can be produced by neutron-capture reactions or in reactions involving heavy ions, they can possibly be used for new experiments in nuclear physics. The large integral cross section for neutron capture (usually some barns) and enough cooling time allows the ground state of these isomers to completely decay due to their short half-life. The large integral de-excitation cross section (more 10 mb MeV) in inelastic γ-quanta scattering allows for a successful measurement on a small number of atoms (<10 15) and makes them candidates for γ-laser on the nuclear levels.

  11. Rotational isomerism of molecules in condensed phases

    NASA Astrophysics Data System (ADS)

    Sakka, Tetsuo; Iwasaki, Matae; Ogata, Yukio

    1991-08-01

    A statistical mechanical model is developed for the description of the conformational distribution of organic molecules in the liquid and solid phases. In the model, they are assumed to have one internal freedom of rotation. The molecules are fixed to lattice sites and have two types of ordering, conformational and distributional. The latter is supposed to represent an ordering typical of solid state. The model is compared with the experimental results of the rotational-isomeric ratio of 1,2-dichloro-1,1-difluoroethane, in the temperature range from 77 to 300 K. It explains successfully the experimental results, especially the behavior near the melting point. From the point of view of melting, the present model is an extension of the Lennard-Jones and Devonshire model, because, when the distinctions between the two conformers are neglected, the parameter representing the distributional ordering of the molecules results in the same equation as that derived from the Lennard-Jones and Devonshire model.

  12. HCP CPH ISOMERIZATION: Caught in the Act

    NASA Astrophysics Data System (ADS)

    Ishikawa, H.; Field, R. W.; Farantos, S. C.; Joyeux, M.; Koput, J.; Beck, C.; Schinke, R.

    1999-10-01

    In this overview we discuss the vibrational spectrum of phosphaethyne, HCP, in its electronic ground state, as revealed by complementary experimental and theoretical examinations. The main focus is the evolution of specific spectral patterns from the bottom of the potential well up to excitation energies of approximately 25,000 cm-1, where large-amplitude, isomerization-type motion from H-CP to CP-H is prominent. Distinct structural and dynamical changes, caused by an abrupt transformation from essentially HC bonding to mainly PH bonding, set in around 13,000 cm-1. They reflect saddle-node bifurcations in the classical phase space-a phenomenon well known in the nonlinear dynamics literature-and result in characteristic patterns in the spectrum and the quantum-number dependence of the vibrational fine-structure constants. Two polar opposites are employed to elucidate the spectral patterns: the exact solution of the Schrodinger equation, using an accurate potential energy surface and an effective or resonance Hamiltonian (expressed in a harmonic oscillator basis set and block diagonalized into polyads), which is defined by parameters adjusted to fit either the measured or the calculated vibrational energies. The combination of both approaches-together with classical mechanics and semiclassical analyses-provides a detailed spectroscopic picture of the breaking of one bond and the formation of a new one.

  13. Communication: An accurate calculation of the S1 C2H2 cis-trans isomerization barrier height.

    PubMed

    Baraban, Joshua H; Matthews, Devin A; Stanton, John F

    2016-03-21

    A high level ab initio calculation of the cis-trans isomerization barrier height in the first excited singlet electronic state of acetylene is found to agree very well with a recent experimental determination.

  14. Isomeric island in the vicinity of 66Fe

    SciTech Connect

    Daugas, J. M.; Belier, G.; Girod, M.; Goutte, H.; Meot, V.; Perru, O.; Roig, O.; Sauvestre, J. E.; Matea, I.; Giovinazzo, J.; Grawe, H.; Becker, F.; Mayet, P.; Grzywacz, R.; Achouri, N. L.; Angelique, J. C.; Baiborodin, D.

    2006-04-26

    An island of isomers have recently been observed on both sides of the N=40 shell below the Ni isotopes. Isomeric states in the 65Fe and 67Fe allow the knowledge of the single particle structure around the {nu}g9/2 shell. Moreover, the excitation energy of the first 2+ and 4+ states in the 68Fe have been established by {beta}-{gamma} correlation. The evolution of the structure of the Fe isotopes going far away from the valley of stability is, for the first time, given for N>40.

  15. Special features of isomeric ratios in nuclear reactions induced by various projectile particles

    SciTech Connect

    Danagulyan, A. S.; Hovhannisyan, G. H. Bakhshiyan, T. M.; Martirosyan, G. V.

    2016-05-15

    Calculations for (p, n) and (α, p3n) reactions were performed with the aid of the TALYS-1.4 code. Reactions in which the mass numbers of target and product nuclei were identical were examined in the range of A = 44–124. Excitation functions were obtained for product nuclei in ground and isomeric states, and isomeric ratios were calculated. The calculated data reflect well the dependence of the isomeric ratios on the projectile type. A comparison of the calculated and experimental data reveals, that, for some nuclei in a high-spin state, the calculated data fall greatly short of their experimental counterparts. These discrepancies may be due to the presence of high-spin yrast states and rotational bands in these nuclei. Calculations involving various level-density models included in the TALYS-1.4 code with allowance for the enhancement of collective effects do not remove the discrepancies in the majority of cases.

  16. Special features of isomeric ratios in nuclear reactions induced by various projectile particles

    NASA Astrophysics Data System (ADS)

    Danagulyan, A. S.; Hovhannisyan, G. H.; Bakhshiyan, T. M.; Martirosyan, G. V.

    2016-05-01

    Calculations for ( p, n) and (α, p3 n) reactions were performed with the aid of the TALYS-1.4 code. Reactions in which the mass numbers of target and product nuclei were identical were examined in the range of A = 44-124. Excitation functions were obtained for product nuclei in ground and isomeric states, and isomeric ratios were calculated. The calculated data reflect well the dependence of the isomeric ratios on the projectile type. A comparison of the calculated and experimental data reveals, that, for some nuclei in a high-spin state, the calculated data fall greatly short of their experimental counterparts. These discrepancies may be due to the presence of high-spin yrast states and rotational bands in these nuclei. Calculations involving various level-density models included in the TALYS-1.4 code with allowance for the enhancement of collective effects do not remove the discrepancies in the majority of cases.

  17. Direct dynamics study of hydrogen-transfer isomerization of 1-pentyl and 1-hexyl radicals.

    PubMed

    Zheng, Jingjing; Truhlar, Donald G

    2009-10-29

    The rate constants of three intramolecular hydrogen-transfer isomerization reactions, namely, 1-4 isomerization of the 1-pentyl radical and 1-4 and 1-5 isomerizations of the 1-hexyl radical, are calculated using variational transition state theory with multidimensional tunneling, in particular by using canonical variational theory (CVT, which is the version of variational transition state theory in which the transition state dividing surface is optimized for a canonical ensemble) with small-curvature tunneling (SCT) for the transmission coefficient. The required potential energy surfaces were obtained implicitly by direct dynamics employing interpolated variational transition state theory with mapping (IVTST-M) and variational transition state theory with interpolated single-point energies (VTST-ISPE). Single-level direct dynamics calculations were performed for all of the reactions by IVTST-M using M06-2X/MG3S or M08-HX/cc-pVTZ+ potential energy surfaces or both. The stationary points of 1-4 isomerization of 1-pentyl and the stationary points for the forward reactions of 1-4 and 1-5 isomerizations of 1-hexyl were also optimized by BMC-CCSD, and for all three reactions we also performed dual-level direct dynamics calculations using VTST-ISPE in which MCG3-MPW single-point energies served as the higher level. The calculated MCG3-MPW//M06-2X/MG3S rate constants agree well with experimental values for 1-4 isomerization of the 1-pentyl radical at high temperature, and this validates the accuracy of this theoretical method for 1-4 isomerization. The MCG3-MPW//M06-2X/MG3S method was therefore used to make a reliable prediction for the rata constants of 1-4 isomerization of the 1-hexyl radical for which a direct experimental measurement is not available. The calculated CVT/SCT/M08-HX/cc-pVTZ+ rate constants agree well with experimental values for 1-5 isomerization of the 1-hexyl radical, and they show that the tunneling effect for these reactions was underestimated in

  18. Direct Dynamics Study of Hydrogen-Transfer Isomerization of 1-Pentyl and 1-Hexyl Radicals

    NASA Astrophysics Data System (ADS)

    Zheng, Jingjing; Truhlar, Donald G.

    2009-07-01

    The rate constants of three intramolecular hydrogen-transfer isomerization reactions, namely, 1-4 isomerization of the 1-pentyl radical and 1-4 and 1-5 isomerizations of the 1-hexyl radical, are calculated using variational transition state theory with multidimensional tunneling, in particular by using canonical variational theory (CVT, which is the version of variational transition state theory in which the transition state dividing surface is optimized for a canonical ensemble) with small-curvature tunneling (SCT) for the transmission coefficient. The required potential energy surfaces were obtained implicitly by direct dynamics employing interpolated variational transition state theory with mapping (IVTST-M) and variational transition state theory with interpolated single-point energies (VTST-ISPE). Single-level direct dynamics calculations were performed for all of the reactions by IVTST-M using M06-2X/MG3S or M08-HX/cc-pVTZ+ potential energy surfaces or both. The stationary points of 1-4 isomerization of 1-pentyl and the stationary points for the forward reactions of 1-4 and 1-5 isomerizations of 1-hexyl were also optimized by BMC-CCSD, and for all three reactions we also performed dual-level direct dynamics calculations using VTST-ISPE in which MCG3-MPW single-point energies served as the higher level. The calculated MCG3-MPW//M06-2X/MG3S rate constants agree well with experimental values for 1-4 isomerization of the 1-pentyl radical at high temperature, and this validates the accuracy of this theoretical method for 1-4 isomerization. The MCG3-MPW//M06-2X/MG3S method was therefore used to make a reliable prediction for the rata constants of 1-4 isomerization of the 1-hexyl radical for which a direct experimental measurement is not available. The calculated CVT/SCT/M08-HX/cc-pVTZ+ rate constants agree well with experimental values for 1-5 isomerization of the 1-hexyl radical, and they show that the tunneling effect for these reactions was underestimated in

  19. Global reaction route mapping of isomerization pathways of exotic C{sub 6}H molecular species

    SciTech Connect

    Vikas, E-mail: qlabspu@yahoo.com; Kaur, Gurpreet

    2013-12-14

    C{sub 6}H radical is known to exist in the astrophysical environment in linear form; however, it may originate from nonlinear isomeric forms. Potential energy surface of C{sub 6}H is explored to search isomers of C{sub 6}H and transition states connecting them. This work reports first-ever identification of reaction pathways for isomerization of C{sub 6}H. The reaction route search is performed through global reaction route mapping method, which utilizes an uphill walking technique based on an anharmonic downward distortion following approach to search intermediates and transition states. The computations performed at the CASSCF/aug-cc-pVTZ, CCSD(T)/6-311++G(d,p)//DFT/B3LYP/6-311++G(d,p), and DFT/B3LYP/aug-cc-pVTZ levels of the theory identified 14 isomers (including 8 new isomeric forms of C{sub 6}H) and 28 transition states. Most of the identified isomers are found to have significant multireference character. The kinetic stability and natural bond orbital analysis of the identified isomers is also investigated. The isomeric forms are further characterized using spectral analysis involving rotational constants, vibrational frequencies, and Raman scattering activities as well as analyzing the effect of isotopic substitution of hydrogen on the spectral features. This study proposes that the linear-C{sub 6}H can readily isomerize to a six-member ring isomer.

  20. Global reaction route mapping of isomerization pathways of exotic C6H molecular species

    NASA Astrophysics Data System (ADS)

    Vikas, Kaur, Gurpreet

    2013-12-01

    C6H radical is known to exist in the astrophysical environment in linear form; however, it may originate from nonlinear isomeric forms. Potential energy surface of C6H is explored to search isomers of C6H and transition states connecting them. This work reports first-ever identification of reaction pathways for isomerization of C6H. The reaction route search is performed through global reaction route mapping method, which utilizes an uphill walking technique based on an anharmonic downward distortion following approach to search intermediates and transition states. The computations performed at the CASSCF/aug-cc-pVTZ, CCSD(T)/6-311++G(d,p)//DFT/B3LYP/6-311++G(d,p), and DFT/B3LYP/aug-cc-pVTZ levels of the theory identified 14 isomers (including 8 new isomeric forms of C6H) and 28 transition states. Most of the identified isomers are found to have significant multireference character. The kinetic stability and natural bond orbital analysis of the identified isomers is also investigated. The isomeric forms are further characterized using spectral analysis involving rotational constants, vibrational frequencies, and Raman scattering activities as well as analyzing the effect of isotopic substitution of hydrogen on the spectral features. This study proposes that the linear-C6H can readily isomerize to a six-member ring isomer.

  1. Isomerization of Asp residues plays an important role in αA-crystallin dissociation.

    PubMed

    Takata, Takumi; Fujii, Noriko

    2016-03-01

    Aged cataract formation is caused by the accumulative precipitation of lens proteins incorporating diverse post-translational modifications. α-Crystallin, a major structural and functional lens protein, consists of a large polymeric structure that is dissociated and insolubilized with accumulative post-translational modifications. One such modification, isomerization of Asp, was recently identified in αB-crystallin monomers derived from aged lens. However, the distributions of Asp isomers in each lens fraction remain unknown. Here, α-crystallin fractions from aged lens were separated into heteropolymeric and monomeric forms to determine the Asp isomerization ratios in each fraction. Lens of four different ages were homogenized and centrifuged, and the soluble fraction was applied to size-exclusion chromatography. The heteropolymeric α-crystallin and monomeric crystallin fractions were obtained and concentrated. After trypsin digestion, each fraction was independently applied to liquid chromatography equipped with mass spectrometry to extract α-crystallin-derived peptides containing Asp isomers. The results showed that Asp58, Asp84 and Asp151 of αA-crystallin were highly isomerized in the monomeric fraction, but not isomerized to the same level in the heteropolymeric fraction. Each type of Asp isomerization increased in an age-dependent manner, was site-specific and was similar to previous results from lens water-insoluble fractions. These results imply that isomerization of Asp residues leads to dissociation of αA-crystallin from the heteropolymeric state and induces insolubilization in aged lens. Taken together, our findings suggest that isomerization of Asp might disrupt the higher order polymeric state of α-crystallin, resulting in decreased solubility and function, ultimately contributing to lens protein impairment and cataract formation with aging.

  2. Low-lying isomeric levels in 75Cu

    SciTech Connect

    Daugas, J. M.; Faul, T.; Grawe, H.; Pfutzner, M.; Grzywacz, R.; Lewitowicz, M.; Achouri, N. L.; Bentida, R.; Beraud, R.; Borcea, C.; Bingham, C. R.; Catford, W.; Emsallem, A.; De France, G.; Grzywacz, K. L.; Lemmon, R.; Lopez Jimenez, M. J.; de Oliveira Santos, F.; Regan, P. H.; Rykaczewski, Krzysztof Piotr; Sauvestre, J. E.; Sawicka, M.; Stanoiu, M.; Sieja, K.; Nowacki, F.

    2010-01-01

    Isomeric low-lying states were identified and investigated in the 75Cu nucleus. Two states at 61.8(5)- and 128.3(7)-keV excitation energies with half-lives of 370(40)- and 170(15)-ns were assigned as 75m1Cu and 75m2Cu, respectively. The measured half-lives combined with the recent spin assignment of the ground state allow one to deduce tentatively spin and parity of the two isomers and the dominant multipolarities of the isomeric transitions with respect to the systematics of the Cu isotopes. Shell-model calculations using an up-to-date effective interaction reproduce the evolution of the 1/2 , 3/2 , and 5/2 states for the neutron-rich odd-mass Cu isotopes when filling the g9/2. The results indicate a significant change in the nuclear structure in this region, where a single-particle 5/2 state coexists with more and more collective 3/2 and 1/2 levels at low excitation energies.

  3. Low-lying isomeric levels in {sup 75}Cu

    SciTech Connect

    Daugas, J. M.; Faul, T.; Sauvestre, J. E.; Grawe, H.; Pfuetzner, M.; Sawicka, M.; Grzywacz, R.; Lewitowicz, M.; France, G. de; Lopez Jimenez, M. J.; Oliveira Santos, F. de; Baiborodin, D.; Bentida, R.; Beraud, R.; Emsallem, A.; Bingham, C. R.; Grzywacz, K. L.

    2010-03-15

    Isomeric low-lying states were identified and investigated in the {sup 75}Cu nucleus. Two states at 61.8(5)- and 128.3(7)-keV excitation energies with half-lives of 370(40)- and 170(15)-ns were assigned as {sup 75m1}Cu and {sup 75m2}Cu, respectively. The measured half-lives combined with the recent spin assignment of the ground state allow one to deduce tentatively spin and parity of the two isomers and the dominant multipolarities of the isomeric transitions with respect to the systematics of the Cu isotopes. Shell-model calculations using an up-to-date effective interaction reproduce the evolution of the 1/2{sup -}, 3/2{sup -}, and 5/2{sup -} states for the neutron-rich odd-mass Cu isotopes when filling the nug{sub 9/2}. The results indicate a significant change in the nuclear structure in this region, where a single-particle 5/2{sup -} state coexists with more and more collective 3/2{sup -} and 1/2{sup -} levels at low excitation energies.

  4. Study on mechanism of isomerization between ammonium thiocyanate and thiourea

    NASA Astrophysics Data System (ADS)

    Zhang, Chao-Zhi; Niu, Meng-Xiao

    2016-12-01

    Application of ammonium thiocyanate that can be separated from wastewater in coking plant is limited. It may isomerize to thiourea which has widely applied in industry. However, the isomerization yield is low. Moreover, the isomerization temperature is more than 145 °C. In this paper, the isomerization was investigated. The mechanism of the isomerization was supposed based on quantum chemistry calculations. Ammonia was employed as a catalyst to lower isomerization temperature and improved the yield of thiourea in the isomerization reaction. Results of quantum chemical calculation and experiments support the supposed mechanism. The mechanism can be applied in production of thiourea from isomerization of ammonium thiocyanate. The paper suggests a useful way of resourcizing ammonium thiocyanate in wastewater.

  5. Isomeric Yields Ratios in 120Te(γ,n)119m,gTe Reaction in the E1-GIANT Resonance Region

    NASA Astrophysics Data System (ADS)

    Mazur, V. M.; Symochko, D. M.; Bigan, Z. M.; Poltorzhytska, T. V.

    Isomeric state excitation in the 120Te(γ,n)119m,gTe reaction within the 10-20 MeV energy range has been studied with bremsstrahlung beams. Energy dependences of experimental isomeric yields ratios and reaction cross-sections have been obtained. Experimental results are compared with TALYS-1.2 calculations.

  6. Consequences of acid strength for isomerization and elimination catalysis on solid acids.

    PubMed

    Macht, Josef; Carr, Robert T; Iglesia, Enrique

    2009-05-13

    We address here the manner in which acid catalysis senses the strength of solid acids. Acid strengths for Keggin polyoxometalate (POM) clusters and zeolites, chosen because of their accurately known structures, are described rigorously by their deprotonation energies (DPE). Mechanistic interpretations of the measured dynamics of alkane isomerization and alkanol dehydration are used to obtain rate and equilibrium constants and energies for intermediates and transition states and to relate them to acid strength. n-Hexane isomerization rates were limited by isomerization of alkoxide intermediates on bifunctional metal-acid mixtures designed to maintain alkane-alkene equilibrium. Isomerization rate constants were normalized by the number of accessible protons, measured by titration with 2,6-di-tert-butylpyridine during catalysis. Equilibrium constants for alkoxides formed by protonation of n-hexene increased slightly with deprotonation energies (DPE), while isomerization rate constants decreased and activation barriers increased with increasing DPE, as also shown for alkanol dehydration reactions. These trends are consistent with thermochemical analyses of the transition states involved in isomerization and elimination steps. For all reactions, barriers increased by less than the concomitant increase in DPE upon changes in composition, because electrostatic stabilization of ion-pairs at the relevant transition states becomes more effective for weaker acids, as a result of their higher charge density at the anionic conjugate base. Alkoxide isomerization barriers were more sensitive to DPE than for elimination from H-bonded alkanols, the step that limits 2-butanol and 1-butanol dehydration rates; the latter two reactions showed similar DPE sensitivities, despite significant differences in their rates and activation barriers, indicating that slower reactions are not necessarily more sensitive to acid strength, but instead reflect the involvement of more unstable organic

  7. Ordering of azobenzenes by two-photon isomerization

    SciTech Connect

    Ishitobi, Hidekazu; Sekkat, Zouheir; Kawata, Satoshi

    2006-10-28

    We report on light induced orientation by two-photon isomerization of azobenzenes in films of polymer. The dynamics of isomerization and orientation by one-photon absorption and two-photon absorption (TPA) are similar, and TPA creates a degree of molecular orientation which is comparable to that achieved by single-photon isomerization, in agreement with the theoretical predictions of two-photon isomeric orientation.

  8. Internal electron conversion of the isomeric {sup 57}Fe nucleus state with an energy of 14.4 keV excited by the radiation of the plasma of a high-power femtosecond laser pulse

    SciTech Connect

    Golovin, G V; Savel'ev-Trofimov, Andrei B; Uryupina, D S; Volkov, Roman V

    2011-03-31

    We recorded the spectrum of delayed secondary electrons ejected from the target, which was coated with a layer of iron enriched with the {sup 57}Fe isotope to 98%, under its irradiation by fluxes of broadband X-ray radiation and fast electrons from the plasma produced by a femtosecond laser pulse at an intensity of 10{sup 17} W cm{sup -2}. Maxima were identified at energies of 5.6, 7.2, and 13.6 keV in the spectrum obtained for a delay of 90 - 120 ns. The two last-listed maxima owe their origin to the internal electron conversion of the isomeric level with an energy of 14.4 keV and a lifetime of 98 ns to the K and L shells of atomic iron, respectively; the first-named level arises from a cascade K - L{sub 2}L{sub 3} Auger process. Photoexcitaion by the X-ray plasma radiation is shown to be the principal channel of the isomeric level excitation. (interaction of laser radiation with matter)

  9. Formation, isomerization, and derivatization of keggin tungstoaluminates.

    Treesearch

    Jennifer J. Cowan; Alan J. Bailey; Robert A. Heintz; Bao T. Do; Kenneth I. Hardcastle; Craig L. Hill; Ira A. Weinstock

    2001-01-01

    Trends in the stability of ¥á and ©¬-Keggin heteropolytungstates of the second-row main-group heteroatoms Al(III), Si(IV), and P(V) are elaborated by data that establish the roles of kinetic and thermodynamic control in the formation and isomerization of Keggin tungstoaluminates. Slow, room-temperature co-...

  10. Cryo-EM Structure of Isomeric Molluscan Hemocyanin Triggered by Viral Infection

    PubMed Central

    Feng, Hongli; Liang, Rongfeng; Wang, Jiangyong; Xie, Lianhui; Zhu, Ping

    2014-01-01

    Hemocyanins (Hcs) of arthropods and mollusks function not only as oxygen transporters, but also as phenoloxidases (POs). In invertebrates, PO is an important component in the innate immune cascade, where it functions as the initiator of melanin synthesis, a pigment involved in encapsulating and killing of pathogenic microbes. Although structures of Hc from several species of invertebrates have been reported, the structural basis for how PO activity is triggered by structural changes of Hc in vivo remains poorly understood. Here, we report a 6.8 Å cryo-electron microscopy (cryo-EM) structure of the isomeric form of hemocyanin, which was isolated from Abalone Shriveling syndrome-associated Virus (AbSV) infected abalone (Halitotis diversicolor), and build a pseudoatomic model of isomeric H. diversicolor hemocyanin 1 (HdH1). Our results show that, compared with native form of HdH1, the architecture of isomeric HdH1 turns into a more relaxed form. The interactions between certain functional units (FUs) present in the native form of Hc either decreased or were totally abolished in the isomeric form of Hc. As a result of that, native state Hc switches to its isomeric form, enabling it to play its role in innate immune responses against invading pathogens. PMID:24887432

  11. Coherence-enhanced optical determination of the 229Th isomeric transition.

    PubMed

    Liao, Wen-Te; Das, Sumanta; Keitel, Christoph H; Pálffy, Adriana

    2012-12-28

    The impact of coherent light propagation on the excitation and fluorescence of thorium nuclei in a crystal lattice environment is investigated theoretically. We find that in the forward direction, the fluorescence signal exhibits characteristic intensity modulations dominated by a sped-up initial decay signal that is orders of magnitude faster. This feature can be exploited for the optical determination of the isomeric transition energy. In order to obtain a unmistakable signature of the isomeric nuclear fluorescence, we put forward a novel scheme for the direct measurement of the transition energy via electromagnetically modified nuclear forward scattering involving two fields that couple to three nuclear states.

  12. A theoretical examination of the isomerization of BrONO 2 to BrOONO

    NASA Astrophysics Data System (ADS)

    Kovačič, S.; Lesar, A.; Hodošček, M.; Koller, J.

    2006-04-01

    The structural properties of the BrONO2 ↔ BrOONO isomerization transition states are examined using density functional calculations in conjunction with different basis sets. The energy barriers for the isomerization pathways at the CBS-QB3 level of theory are large enough, from 34.2 up to 32.5 kcal mol -1, to prevent the isomerization of BrONO 2 to either cis-perp or trans-perp BrOONO. But, the energy barriers of only 8.3 and 4.7 kcal mol -1 make feasible an interconversion process of cis-perp BrOONO and trans-perp BrOONO, respectively, to BrONO 2.

  13. Theoretical exploration of the potential energy surface of the HOI → HIO isomerization reaction

    NASA Astrophysics Data System (ADS)

    Sun, Q.; Mackie, J. C.; Dlugogorski, B. Z.; Kennedy, E. M.

    2007-02-01

    The isomerization reaction HOI → HIO has been investigated using quantum mechanical techniques. The activation energy of the reaction at the CCSD(T) level of theory is 77.0 kcal/mol. Molecular parameters and relative energies of HOI, HIO, five HOI-H 2O complexes, three HIO-H 2O complexes and four transition states have been calculated by the B3LYP method. For isomerization assisted by a single water molecule, the activation energy whereby the water molecule directly facilitates proton transfer during isomerization, reduces to 48.4 kcal/mol. Where the water molecule interacts with the HOI/HIO system by forming hydrogen-bond and/or van der Waals complexes, the activation energy is not significantly reduced.

  14. CRIS: A new method in isomeric beam production

    NASA Astrophysics Data System (ADS)

    Lynch, K. M.; Billowes, J.; Bissell, M. L.; Budincevic, I.; Cocolios, T. E.; De Groote, R. P.; De Schepper, S.; Fedosseev, V. N.; Flanagan, K. T.; Franchoo, S.; Garcia Ruiz, R. F.; Heylen, H.; Marsh, B. A.; Mason, P. J. R.; Neyens, G.; Procter, T. J.; Rossel, R. E.; Rothe, S.; Simpson, G. S.; Smith, A. J.; Strashnov, I.; Stroke, H. H.; Walker, P. M.; Wendt, K. D. A.; Wood, R. T.

    2013-12-01

    The Collinear Resonance Ionization Spectroscopy (CRIS) experiment at ISOLDE, CERN, uses laser radiation to stepwise excite and ionize an atomic beam for the purpose of ultra-sensitive detection of rare isotopes, and hyperfine-structure measurements. The technique also offers the ability to purify an ion beam that is heavily contaminated with radioactive isobars, including the ground state of an isotope from its isomer, allowing decay spectroscopy on nuclear isomeric states to be performed. The isomeric ion beam is selected by resonantly exciting one of its hyperfine structure levels, and subsequently ionizing it. This selectively ionized beam is deflected to a decay spectroscopy station (DSS). This consists of a rotating wheel implantation system for alpha- and beta-decay spectroscopy, and up to three germanium detectors around the implantation site for gamma-ray detection. Resonance ionization spectroscopy and the new technique of laser assisted nuclear decay spectroscopy have recently been performed at the CRIS beam line on the neutron-deficient francium isotopes. Here an overview of the two techniques will be presented, alongside a description of the CRIS beam line and DSS.

  15. Regio- and stereoselective isomerization of hexabromocyclododecanes (HBCDs): kinetics and mechanism of gamma- to alpha-HBCD isomerization.

    PubMed

    Heeb, Norbert V; Schweizer, W Bernd; Mattrel, Peter; Haag, Regula; Gerecke, Andreas C; Schmid, Peter; Zennegg, Markus; Vonmont, Heinz

    2008-11-01

    Hexabromocyclododecanes (HBCDs) are high production volume chemicals (>20000 ty(-1)) used as flame retardants for plastics and textiles. Lately, we reported on the stereoselective isomerization of beta-HBCDs. Herein we present insights into the mechanism and kinetics of (+)gamma- to (+)alpha- and of (-)gamma- to (-)alpha-HBCD isomerization. Only two of the six bromine atoms migrated, indicating that rearrangements of gamma- to alpha-HBCDs are regio- and stereoselective as well. The apparent first-order isomerization rate constants increased from 0.0013 to 0.0031 to 0.0070 min(-1) at 120, 130, and 140 degrees C, respectively, corresponding to half-lives of 540, 230, and 99 min. Thus, a thermal treatment of materials containing gamma-HBCDs at temperatures >100 degrees C may induce the formation of alpha-HBCDs and, hence, may alter the diastereomeric ratio of a HBCD mixture. The inversion of vicinal dibromides in like-configurations (RR/SS) prevailed, whereas unlike-configurations (RS/SR) were not affected. An intramolecular, stereoselective migration of neighboring bromine atoms via a four-center transition state would explain the observed stereoisomer pattern and first-order kinetics. Despite the fact that vicinal dibromides in HBCDs prefer synclinal (gauche) conformations, antiperiplanar (staggered) conformations are assumed to facilitate concerted 1.2-shifts of both bromine atoms. A conformation analysis revealed that under kinetic control, only those bromine atoms in the more flexible part of the molecules are migrating, whereas those in the conserved triple-turn motive were not affected. Thus, this structural motive, common to all alpha-, beta-, and gamma-HBCDs, is more rigid and less reactive than the flexible part, containing the reacting dibromides in like-configurations.

  16. Chemical Tools To Decipher Regulation of Phosphatases by Proline Isomerization on Eukaryotic RNA Polymerase II.

    PubMed

    Mayfield, Joshua E; Fan, Shuang; Wei, Shuo; Zhang, Mengmeng; Li, Bing; Ellington, Andrew D; Etzkorn, Felicia A; Zhang, Yan Jessie

    2015-10-16

    Proline isomerization greatly impacts biological signaling but is subtle and difficult to detect in proteins. We characterize this poorly understood regulatory mechanism for RNA polymerase II carboxyl terminal domain (CTD) phosphorylation state using novel, direct, and quantitative chemical tools. We determine the proline isomeric preference of three CTD phosphatases: Ssu72 as cis-proline specific, Scp1 and Fcp1 as strongly trans-preferred. Due to this inherent characteristic, these phosphatases respond differently to enzymes that catalyze the isomerization of proline, like Ess1/Pin1. We demonstrate that this selective regulation of RNA polymerase II phosphorylation state exists within human cells, consistent with in vitro assays. These results support a model in which, instead of a global enhancement of downstream enzymatic activities, proline isomerases selectively boost the activity of a subset of CTD regulatory factors specific for cis-proline. This leads to diversified phosphorylation states of CTD in vitro and in cells. We provide the chemical tools to investigate proline isomerization and its ability to selectively enhance signaling in transcription and other biological contexts.

  17. E/Z Isomers and Isomerization

    NASA Astrophysics Data System (ADS)

    Liaaen-Jensen, Synnøve; Lutnœes, Bjart Frode

    The natural occurrence of several carotenoid cis isomers and their biological significance were not anticipated in 1962, when the classical monograph on cis-trans isomeric carotenoids [1] was published. More recent research has demonstrated that various cis isomers occur naturally in bacteria plants, algae and invertebrate animals, and are present in human blood and tissues. The participation of cis isomers in the biosynthethic route to coloured carotenoids is well established (Volume 3, Chapter 2). Important biological functions of (15Z)-carotenoids in photosynthesis have been revealed [2]. In relation to health aspects of carotenoids, the bioavailability of cis isomers may be higher than that of the all-trans isomer [3], and accumulated evidence suggests that cis/trans isomerization may occur in biological tissues, particularly of lycopene (31) in human serum [4] (Volume 5, Chapter 7).

  18. Isomerization of one molecule observed through tip enhanced Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Zhang, Yanxing; Lee, Joonhee; Apkarian, Vartkess A.; Wu, Ruqian; Ruqian Wu, Yanxing Zhang Team; Joonhee Lee, Vartkess A. Apkarian Team

    While exploring photoisomerization of azobenzyl thiols (ABT) adsorbed on Au(111), through joint scanning tunneling microscopy (STM) and tip-enhanced Raman scattering (TERS) studies, the reversible photoisomerization of one molecule is captured in TERS trajectories. The apparently heterogeneously photo-catalyzed reaction is assigned to cis-trans isomerization of an outlier, which is chemisorbed on the silver tip of the STM. In order to clarify the role of the silver tip of the STM, we perform systematic density functional theory (DFT) calculations. The results show that compared with the case on the flat Ag(111) surface, the energy difference between trans and cis states of ABT decrease as we add one silver atom or a tetrahedron silver cluster on Ag(111) surface which mimic the geometry of a silver tip. In particular, the trans stretches away from the surface on the tetrahedral silver cluster, and the energy difference between trans and cis decreases to 0.27 eV, from ~1 eV for ABT on the flat Ag(111) surface. This significantly increases the possibility of cis-trans isomerization, as observed in our experiments. Work was supported by the National Science Foundation Center for Chemical Innovation on Chemistry at the Space-Time Limit (CaSTL) under Grant No. CHE-1414466.

  19. Confirmed Assignments of Isomeric Dimethylbenzyl Radicals Generated by Corona Discharge

    NASA Astrophysics Data System (ADS)

    Yoon, Young Wook; Lee, Sang Kuk

    2012-06-01

    Polymethylbenzyl radicals, multi-methyl-substituted benzyl radicals, have been believed to be an ideal model for understanding the torsional effect of methyl group and substitution effect on electronic transition. These radicals are mainly generated from polymethylbenzenes by electric discharge for spectroscopic observation. However, the existence of several methyl groups on the benzene ring may produce several isomeric polymethylbenzyl radicals by removing one of the C-H bonds of each methyl group at different substitution position, which makes the assignment of spectrum ambiguous. In this work, the controversial vibronic assignments of isomeric dimethylbenzyl radicals were clearly resolved by using different precursors. By using corresponding dimethylbenzyl chlorides as precursors, we identified the origins of the vibronic bands of the dimethylbenzyl radicals generated by corona discharge of precursors 1,2,3- and 1,2,4-trimethylbenzenes. From the analysis of the spectra observed from the dimethylbenzyl chlorides in a corona excited supersonic expansion using a pinhole-type glass nozzle, we revised previous assignments of the 2,6- and 2,3-dimethylbenzyl radicals as well as the 3,4-, 2,4-, and 2,5-dimethylbenzyl radicals. In addition, spectroscopic data of electronic transition and vibrational mode frequencies in the ground electronic state of each isomer were accurately determined by comparing them with those obtained by an ab initio calculation and with the known vibrational data of precursors.

  20. Skeletal isomerization of n-butenes

    SciTech Connect

    Guisnet, M.; Andy, P.; Gnep, N.S.

    1996-02-01

    The transformation of n-butenes and of isobutene was carried out at 350{degrees}C on a fresh H-FER zeolite (Si/Al = 13.8) with various contact times so as to obtain a large range of conversion (from 5 to 65%). With both reactants the skeletal isomerization was accompanied by the formation of various products. The skeletal isomer, propene, pentenes, octenes (traces), and n-butane (from n-butenes) or isobutane (traces from isobutene) appeared as primary products. The simultaneous formation of the skeletal isomer and of propene and pentenes proved the presence of a dimerization-cracking process. Moreover, the low amount of octenes in the products showed that dimerization was the limiting step of the process. The dimerization step involved two secondary carbenium ions, which explained its slow rate. The dimer was rapidly isomerized through Type A (alkyl shift) or Type B (via protonated cyclopropanes) isomerization into the other octenes. Lastly octenes with a trimethylpentane or a dimethylhexane skeleton were rapidly cracked into isobutene, propene, and pentenes through Type A (involving two tertiary and one secondary carbenium ions) mechanisms. The transformation of n-pentenes and of n-octenes confirmed the high rate of the Type A and B isomerization and cracking steps. The slow rate of octene formation from butenes was also due to an inhibition of the diffusion of branched octenes in the narrow pores of H-FER. The shape selectivity of H-FER was also responsible for the very slow formation of isobutane by hydrogen transfer from coke precursors to isobutene and for the unexpected slow formation of propene and of pentenes from isobutene. 43 refs., 5 figs., 2 tabs.

  1. Isomerization of C.sub.4 alkenes

    DOEpatents

    Smith, Jr., Lawrence A.

    1984-01-01

    A method for isomerizing isobutene or n-butene to produce a mixture of isobutene and normal butene, and polymerizing at least a portion thereof to produce isobutene/n-butene codimer, which comprieses feeding at least 80 weight % of either the isobutene or n-butene to a catalytic distillation reactor containing a fixed bed acidic cation exchange resin catalyst packing which provides both the catalyst sites and distillation sites for the reaction products, isomerizing a portion of the isobutene or n-butene to produce a mixture of isobutene and n-butene and reacting at least a portion of the isobutene and n-butene to form codimer of isobutene and n-butene, whereby an overhead fraction containing any unreacted isobutene and n-butene and a bottoms fraction containing codimer is produced. The result of the reaction is substantially the same regardless whether the feed is isobutene or n-butene. Other aspects of the invention, include combinations of procedures to produce high purity isobutene and n-butene. Either isobutene or n-butene product (depending on the desired product) can be recycled as feed, thus substantially carrying out the isomerization to extinction and total conversion to the desired product.

  2. Isomerization of C[sub 4] alkenes

    DOEpatents

    Smith, L.A. Jr.

    1984-11-13

    A method is described for isomerizing isobutene or n-butene to produce a mixture of isobutene and normal butene, and polymerizing at least a portion thereof to produce isobutene/n-butene co-dimer, which comprises feeding at least 80 weight % of either the isobutene or n-butene to a catalytic distillation reactor containing a fixed bed acidic cation exchange resin catalyst packing which provides both the catalyst sites and distillation sites for the reaction products, isomerizing a portion of the isobutene or n-butene to produce a mixture of isobutene and n-butene and reacting at least a portion of the isobutene and n-butene to form co-dimer of isobutene and n-butene, whereby an overhead fraction containing any unreacted isobutene and n-butene and a bottoms fraction containing co-dimer is produced. The result of the reaction is substantially the same regardless whether the feed is isobutene or n-butene. Other aspects of the invention, include combinations of procedures to produce high purity isobutene and n-butene. Either isobutene or n-butene product (depending on the desired product) can be recycled as feed, thus substantially carrying out the isomerization to extinction and total conversion to the desired product. 1 fig.

  3. Dynamics of radiation induced isomerization for HCN-CNH

    SciTech Connect

    Na, Kyungsun; Jung, Christof; Reichl, L. E.

    2006-07-21

    We have analyzed the dynamics underlying the use of sequential radiation pulses to control the isomerization between the HCN and the CNH molecules. The appearance of avoided crossings among Floquet eigenphases as the molecule interacts with the radiation pulses is the key to understanding the isomerization dynamics, both in the adiabatic and nonadiabatic regimes. We find that small detunings of the incident pulses can have a significant effect on the outcome of the isomerization process for the model we consider.

  4. Methods for suppressing isomerization of olefin metathesis products

    DOEpatents

    Firth, Bruce E.; Kirk, Sharon E.; Gavaskar, Vasudeo S.

    2015-09-22

    A method for suppressing isomerization of an olefin metathesis product produced in a metathesis reaction includes adding an isomerization suppression agent to a mixture that includes the olefin metathesis product and residual metathesis catalyst from the metathesis reaction under conditions that are sufficient to passivate at least a portion of the residual metathesis catalyst. The isomerization suppression agent is phosphorous acid, a phosphorous acid ester, phosphinic acid, a phosphinic acid ester or combinations thereof. Methods of refining natural oils are described.

  5. Amine-Catalyzed Isomerization of Diethylmaleate to Diethylfumarate.

    ERIC Educational Resources Information Center

    Glover, Irving T.; And Others

    1978-01-01

    This reaction is used in an introductory organic chemistry course to illustrate principles of gas-liquid chromatography, geometrical isomerism, homogeneous catalysis, and activation energy determinations. (BB)

  6. Amine-Catalyzed Isomerization of Diethylmaleate to Diethylfumarate.

    ERIC Educational Resources Information Center

    Glover, Irving T.; And Others

    1978-01-01

    This reaction is used in an introductory organic chemistry course to illustrate principles of gas-liquid chromatography, geometrical isomerism, homogeneous catalysis, and activation energy determinations. (BB)

  7. Lycopene degradation and isomerization kinetics during thermal processing of an olive oil/tomato emulsion.

    PubMed

    Colle, Ines J P; Lemmens, Lien; Tolesa, Getachew N; Van Buggenhout, Sandy; De Vleeschouwer, Kristel; Van Loey, Ann M; Hendrickx, Marc E

    2010-12-22

    The stability of lycopene in an olive oil/tomato emulsion during thermal processing (80-140 °C) was studied. Initially, the degradation of total lycopene (all-E plus Z-forms) occurred quickly at temperatures above 100 °C. However, a nonzero plateau value, depending on the processing temperature, was attained after longer treatment times. Besides degradation, the isomerization of total-Z-lycopene as well as the individual isomerization of all-E-, 5-Z-, 9-Z-, and 13-Z-lycopene was studied in detail. After prolonged heating, the isomer conversion reached a temperature-dependent equilibrium state. The degradation of total lycopene and the isomerization could be described by a fractional conversion model. The temperature dependency of the corresponding reaction rate constants was quantified by the Arrhenius equation. The activation energy of degradation was estimated to be 28 kJ/mol, and the activation energy of overall (all-E and total-Z) isomerization was estimated to be 52 kJ/mol.

  8. Free-energy profile along an isomerization pathway: Conformational isomerization in alanine dipeptide

    NASA Astrophysics Data System (ADS)

    Lee, In-Ho

    2013-02-01

    The free-energy profile for the conformational isomerization process in alanine dipeptide is presented in atomistic detail by using an action-derived molecular dynamics (ADMD) method and replica-exchange molecular dynamics (REMD) method. First, by employing ADMD, a dynamic isomerization pathway model of the alanine dipeptide with two available low-energy conformations, C7 ax and C7 eq , is determined. The pathway model is chosen to be the reaction coordinate, so the isomerization process is characterized by the ADMD step index, which is not an a-priori reaction coordinate as found in conventional studies of molecular conformational changes. Second, by employing the REMD method, the free-energy profile is calculated as a function of temperature. This couple of procedures is a quite natural protocol for conformational isomerization process simulations, irrespective of the arbitrary selection of the reaction coordinate. The alliance between the two simulation methods, ADMD and REMD, is demonstrated to have a great synergy effect on understanding the conformational changes in molecules.

  9. TD-DFT calculations of the potential energy curves for the trans-cis photo-isomerization of protonated Schiff base of retinal.

    PubMed

    Tachikawa, Hiroto; Iyama, Tetsuji

    2004-10-25

    One-dimensional potential energy curves for the isomerization of protonated Schiff base of retinal (PSBR) in bacteriorhodopsin (bR), i.e., isomerization from all-trans- to 13-cis-forms, have been calculated by means of time-dependent density functional theory (TD-DFT) calculations, in order to elucidate the mechanism of initial step in photo-absorption. The transition state of the isomerization in the first excited state is located at theta(13-14)=58 degrees , where theta(13-14) means twist angle around the C(13)=C(14) double bond of PSBR The potential barrier is formed by the avoided crossing between S(1) (B(u)-like) and S(2) (A(g)-like) states. The mechanism of the isomerization was discussed on the basis of theoretical results.

  10. A convenient method for experimental determination of yields and isomeric ratios in photonuclear reactions measured by the activation technique

    NASA Astrophysics Data System (ADS)

    Kolev, D.; Dobreva, E.; Nenov, N.; Todorov, V.

    1995-02-01

    A generalized exact formula is derived for a determination of the experimental isomeric ratio in any incident particle activation. For the particular case, when the activity of the ground state results from the simultaneous decay of both states and can be conveniently measured, the appropriate modification of this formula is evaluated and applied to six photonuclear reactions induced by 43 MeV bremsstrahlung. The experimental isomeric yield ratios of (γ, 3n) 110m,gIn; (γ, p) (γ, pn), (γ, 2n2p) 117m,gIn; (γ, n) 164m,gHo and (γ, 3n) 162m,gHo are deduced.

  11. Proton NMR characterization of isomeric sulfmyoglobins: preparation, interconversion, reactivity patterns, and structural features

    SciTech Connect

    Chatfield, M.J.; La Mar, G.N.; Kauten, R.J.

    1987-11-03

    The preparations of sulfmyoglobin (sulf-Mb) by standard procedures have been found heterogeneous by /sup 1/H NMR spectroscopy. Presented here are the results of a comprehensive study of the factors that influence the selection among the three dominant isomeric forms of sperm whale sulf-Mb and their resulting detailed optical and /sup 1/H NMR properties as related to their detectability and structural properties of the heme pocket. A single isomer is formed initially in the deoxy state; further treatment in any desired oxidation/ligation state can yield two other major isomers. Acid catalysis and chromatography facilitate formation of a second isomer, particularly in the high-spin state. At neutral pH, a third isomer is formed by a first-order process. The processes that alter oxidation/ligation state are found to be reversible and are judged to affect only the metal center, but the three isomeric sulf-Mbs are found to exhibit significantly different ligand affinity and chemical stability. The present results allow, for the first time, a rational approach for preparing a given isomeric sulf-Mb in an optimally pure state for subsequent characterization by other techniques. While optical spectroscopy can distinguish the alkaline forms, only /sup 1/H NMR clearly distinguishes all three ferric isomers. The hyperfine shift patterns in the various oxidation/spin states of sulf-Mbs indicate relatively small structural alteration, and the proximal and distal sides of the heme suggest that peripheral electronic effects are responsible for the differentially reduced ligand affinities for the three isomeric sulf-Mbs. The first /sup 1/H NMR spectra of sulfhemoglobins are presented, which indicate a structure similar to that of the initially formed sulf-Mb isomer but also suggest the presence of a similar molecular heterogeneity as found for sulf-Mb, albiet to a smaller extent.

  12. Acid-Catalyzed Isomerization of Carvone to Carvacrol

    ERIC Educational Resources Information Center

    Kjonaas, Richard A.; Mattingly, Shawn P.

    2005-01-01

    The acid-catalyzed isomerization of carvone to carvacrol, first reported by Ritter and Ginsburg, is especially well suited with a permanent-magnet FT instrument. The acid-catalyzed isomerization of carvone to carvacrol produced a 61% yield after a three hour reflux with 30% aqueous sulfuric acid.

  13. Acid-Catalyzed Isomerization of Carvone to Carvacrol

    ERIC Educational Resources Information Center

    Kjonaas, Richard A.; Mattingly, Shawn P.

    2005-01-01

    The acid-catalyzed isomerization of carvone to carvacrol, first reported by Ritter and Ginsburg, is especially well suited with a permanent-magnet FT instrument. The acid-catalyzed isomerization of carvone to carvacrol produced a 61% yield after a three hour reflux with 30% aqueous sulfuric acid.

  14. Infrared-induced conformational isomerization and vibrational relaxation dynamics in melatonin and 5-methoxy-N-acetyl tryptophan methyl amide

    NASA Astrophysics Data System (ADS)

    Dian, Brian C.; Florio, Gina M.; Clarkson, Jasper R.; Longarte, Asier; Zwier, Timothy S.

    2004-05-01

    The conformational isomerization dynamics of melatonin and 5-methoxy N-acetyltryptophan methyl amide (5-methoxy NATMA) have been studied using the methods of IR-UV hole-filling spectroscopy and IR-induced population transfer spectroscopy. Using these techniques, single conformers of melatonin were excited via a well-defined NH stretch fundamental with an IR pump laser. This excess energy was used to drive conformational isomerization. By carrying out the infrared excitation early in a supersonic expansion, the excited molecules were re-cooled into their zero-point levels, partially re-filling the hole created in the ground state population of the excited conformer, and creating gains in population of the other conformers. These changes in population were detected using laser-induced fluorescence downstream in the expansion via an UV probe laser. The isomerization quantum yields for melatonin show some conformation specificity but no hint of vibrational mode specificity. In 5-methoxy NATMA, no isomerization was observed out of the single conformational well populated in the expansion in the absence of the infrared excitation. In order to study the dependence of the isomerization on the cooling rate, the experimental arrangement was modified so that faster cooling conditions could be studied. In this arrangement, the pump and probe lasers were overlapped in space in the high density region of the expansion, and the time dependence of the zero-point level populations of the conformers was probed following selective excitation of a single conformation. The analysis needed to extract isomerization quantum yields from the timing scans was developed and applied to the melatonin timing scans. Comparison between the frequency and time domain isomerization quantum yields under identical experimental conditions produced similar results. Under fast cooling conditions, the product quantum yields were shifted from their values under standard conditions. The results for melatonin

  15. Ultrafast isomerization in a difluoroboryl-coordinated molecular switch

    NASA Astrophysics Data System (ADS)

    Consani, Cristina; Berberich, Martin; Würthner, Frank; Brixner, Tobias

    2017-09-01

    Molecular switches based on light-induced isomerization cycles are promising materials for sensors and biomedical applications. Understanding the details of the isomerization photocycle and identifying the nuclear coordinates involved in the photoreaction are relevant topics. Here we characterize the cis → trans and trans → cis isomerization of a new type of BF2-coordinated azo-dye molecular switch by pump-probe spectroscopy. While cis → trans isomerization is ultrafast and proceeds via a conical intersection, the trans → cis photocycle is more complex and involves at least three reaction channels. Finally, we employ the vibrational wavepackets accompanying isomerization to infer information on the nuclear degrees of freedom involved in the photoreaction.

  16. The mechanism for iron-catalyzed alkene isomerization in solution

    SciTech Connect

    Sawyer, Karma R.; Glascoe, Elizabeth A.; Cahoon, James F.; Schlegel, Jacob P.; Harris, Charles B.

    2008-05-27

    Here we report nano- through microsecond time-resolved IR experiments of iron-catalyzed alkene isomerization in room-temperature solution. We have monitored the photochemistry of a model system, Fe(CO){sub 4}({eta}{sup 2}-1-hexene), in neat 1-hexene solution. UV-photolysis of the starting material leads to the dissociation of a single CO to form Fe(CO){sub 3}({eta}{sup 2}-1-hexene), in a singlet spin state. This CO loss complex shows a dramatic selectivity to form an allyl hydride, HFe(CO){sub 3}({eta}{sup 3}-C{sub 6}H{sub 11}), via an internal C-H bond-cleavage reaction in 5-25 ns. We find no evidence for the coordination of an alkene molecule from the bath to the CO loss complex, but do observe coordination to the allyl hydride, indicating that it is the key intermediate in the isomerization mechanism. Coordination of the alkene ligand to the allyl hydride leads to the formation of the bis-alkene isomers, Fe(CO){sub 3}({eta}{sup 2}-1-hexene)({eta}{sup 2}-2-hexene) and Fe(CO){sub 3}({eta}{sup 2}-1-hexene){sub 2}. Because of the thermodynamic stability of Fe(CO){sub 3}({eta}{sup 2}-1-hexene)({eta}{sup 2}-2-hexene) over Fe(CO){sub 3}({eta}{sup 2}-1-hexene){sub 2} (ca. 12 kcal/mol), nearly 100% of the alkene population will be 2-alkene. The results presented herein provide the first direct evidence for this mechanism in solution and suggest modifications to the currently accepted mechanism.

  17. Coherent ultrafast torsional motion and isomerization of a biomimetic dipolar photoswitch.

    PubMed

    Briand, Julien; Bräm, Olivier; Réhault, Julien; Léonard, Jérémie; Cannizzo, Andrea; Chergui, Majed; Zanirato, Vinizio; Olivucci, Massimo; Helbing, Jan; Haacke, Stefan

    2010-04-07

    Femtosecond fluorescence up-conversion, UV-Vis and IR transient absorption spectroscopy are used to study the photo-isomerization dynamics of a new type of zwitterionic photoswitch based on a N-alkylated indanylidene pyrroline Schiff base framework (ZW-NAIP). The system is biomimetic, as it mimics the photophysics of retinal, in coupling excited state charge translocation and isomerization. While the fluorescence lifetime is 140 fs, excited state absorption persists over 230 fs in the form of a vibrational wavepacket according to twisting of the isomerizing double bond. After a short "dark" time window in the UV-visible spectra, which we associate with the passage through a conical intersection (CI), the wavepacket appears on the ground state potential energy surface, as evidenced by the transient mid-IR data. This allows for a precise timing of the photoreaction all the way from the initial Franck-Condon region, through the CI and into both ground state isomers, until incoherent vibrational relaxation dominates the dynamics. The photo-reaction dynamics remarkably follow those observed for retinal in rhodopsin, with the additional benefit that in ZW-NAIP the conformational change reverses the zwitterion dipole moment direction. Last, the pronounced low-frequency coherences make these molecules ideal systems for investigating wavepacket dynamics in the vicinity of a CI and for coherent control experiments.

  18. Ab initio kinetics for isomerization reaction of normal-chain hexadiene isomers

    NASA Astrophysics Data System (ADS)

    Yang, Feiyu; Deng, Fuquan; Pan, Youshun; Tian, Zemin; Zhang, Yingjia; Huang, Zuohua

    2016-10-01

    The ground-state potential energy surface (PES) of isomerization philosophy of ten normal-chain hexadiene isomers is computed by density functional methods using the geometries optimized at B3LYP/6-311++G (d, p) level of theory. These detailed reaction pathways are used to calculate the rate constants for the unimolecular isomerization reactions by transition state theory (TST) in the temperature range of 500-2500 K. Difference of rate constant between each hexadiene isomer is interpreted through the PES and Ḣ atom transfer, and only 2,4-hexadiene readily fulfills cis-cis to trans-trans conformation conversion. All the conversions are kinetically interpreted from the PES and ST geometry.

  19. Ultrafast deactivation of bilirubin: dark intermediates and two-photon isomerization.

    PubMed

    Carreira-Blanco, Carlos; Singer, Patrick; Diller, Rolf; Luis Pérez Lustres, J

    2016-03-14

    Bilirubin is a neurotoxic product responsible for neonatal jaundice, which is generally treated by phototherapy. The photoreaction involves ultrafast internal conversion via an elusive intermediate and Z-E isomerization with minor yield (less than 3% in solution). The structure of the intermediate remains unclear. Here, the combination of UV-vis and mid-IR ultrafast transient absorption spectroscopy reports a comprehensive picture of the mechanism and provides essential structural information about the intermediate species. Thus, spectral dynamics during the earliest ps unveils a wavepacket travelling from the Franck-Condon region to the crossing point with a dark state. The latter shows a tighter molecular skeleton than the ground state and decays with 15 ps time constant. Remarkably, the relative contribution of a non-decaying component increases linearly with pump energy, suggesting that Z-E isomerization could also be triggered by two-photon excitation. Implications for the photochemistry of protein-bound open tetrapyrroles are discussed.

  20. Thermal Isomerization in Cs_4Cl_3^- Clusters: A Theoretical Study

    NASA Astrophysics Data System (ADS)

    Ashman, Chris; Khanna, S. N.; Pederson, Mark R.; Porezag, Dirk

    1998-03-01

    Theoretical electronic structure studies have been carried out to show that the recently observed thermal isomerization in Cs_4Cl_3^- clusters(D.J. Fatemi, F. K. Fatemi and L. A. Bloomfield, Phys. Rev. A54), 3674 (1996) is due to three energetically close structures with a cuboid, a ladder and an octagonal ring arrangement. We perform all-electron density-functional calculations to determine the equilibrium geometries and cohesive energies of these structures and identify the cuboid as the most stable structure. To verify that these three low-energy structures correspond to the experimental observation we compare the joint density of states and electron affinities to the experimentally determined temperature-dependent photoelectron spectrum of the anions. We present vibrational densities of states and infrared and Raman spectra. An analysis of the low energy vibrational spectra aids in determining the transition pathways between the isomers. Estimates of isomerization barriers will be presented.

  1. Hoono Isomerization to HONO_2 Involving Conical Intersections

    NASA Astrophysics Data System (ADS)

    Kumar, T. J. Dhilip; Stanton, John F.; Barker, John R.

    2009-06-01

    The important atmospheric reactions HO_2 + NO and OH + NO_2 lead to formation and dissociation of the cis- and trans- isomers of the HOONO complex. In the present work, the global HNO_3 potential energy surface (PES) is being studied by using high-level ab initio electronic structure methods. This PES and others in the same class have been studied previously by others. In the F + NO_2 reaction system, UCCSD(T) calculations showed that FONO isomerizes to FNO_2 through a tight transition state involving a two-state avoided curve crossing. A similar mechanism has been invoked for HOONO, which is isoelectronic with FONO. CASSCF multi-configurational calculations on the CH_3O + NO_2 reaction located a conical intersection near where single-configurational DFT methods predict an intrinsic energy barrier; the barrier was suggested to be an artifact. In present work, the global HNO_3 PES is being investigated by both the UCCSD(T) and CASSCF methods in order to study the influence of low-lying excited electronic states on the ground state PES and reaction dynamics. L. P. Olsen, M. D. Bartberger and K. N. Houk, J. Am. Chem. Soc., 125, 3999 (2003) G. B. Ellison, J. M. Herbert, A. B. McCoy, J. F. Stanton and P. G. Szalay, J. Phys. Chem. A 108, 7639 (2004). J. F. Arenas, F. J. Avila, J. C. Otero, D. Peláez and J. Soto, J. Phys. Chem. A 112, 249 (2008).

  2. Two-Photon-Induced Isomerization of Spiropyran/Merocyanine at the Air/Water Interface Probed by Second Harmonic Generation.

    PubMed

    Lin, Lu; Zhang, Zhen; Lu, Zhou; Guo, Yuan; Liu, Minghua

    2016-10-13

    Photochromic molecules often exhibit switchable hyperpolarizabilities upon photoisomerization between two molecular states and can be widely applied in nonlinear optical materials. Photoisomerization can occur through either one-photon or two-photon processes. Two-photon-induced isomerization has several advantages over one-photon process but has not been fully explored. In the present study, we have used second harmonic generation to investigate the two-photon-induced isomerization between spiropyran and merocyanine at the air/water interface. We show that spiropyran and merocyanine can be converted into each other reversibly with 780-nm laser-beam irradiation through two-photon processes. We also investigated the isomerization rates under various incident laser powers. Quantitative analysis revealed that the isomerization rates of spiropyran and merocyanine depend differently on the laser power. We attribute the difference to the distinct molecular structures of spiropyran and merocyanine. At the interface, nonplanar spiropyran molecules exist mainly as monomers, whereas planar merocyanine molecules form aggregates. Upon aggregation, steric hindrance effects and excitonic coupling efficiently arrest the photoisomerization of merocyanine. This work provides an in-depth understanding of two-photon-induced isomerization at the interface, which is beneficial for designing and controlling optical thin-film materials.

  3. Photoactivation of the photoactive yellow protein: why photon absorption triggers a trans-to-cis Isomerization of the chromophore in the protein.

    PubMed

    Groenhof, Gerrit; Bouxin-Cademartory, Mathieu; Hess, Berk; De Visser, Sam P; Berendsen, Herman J C; Olivucci, Massimo; Mark, Alan E; Robb, Michael A

    2004-04-07

    Atomistic QM/MM simulations have been carried out on the complete photocycle of Photoactive Yellow Protein, a bacterial photoreceptor, in which blue light triggers isomerization of a covalently bound chromophore. The "chemical role" of the protein cavity in the control of the photoisomerization step has been elucidated. Isomerization is facilitated due to preferential electrostatic stabilization of the chromophore's excited state by the guanidium group of Arg52, located just above the negatively charged chromophore ring. In vacuo isomerization does not occur. Isomerization of the double bond is enhanced relative to isomerization of a single bond due to the steric interactions between the phenyl ring of the chromophore and the side chains of Arg52 and Phe62. In the isomerized configuration (ground-state cis), a proton transfer from Glu46 to the chromophore is far more probable than in the initial configuration (ground-state trans). It is this proton transfer that initiates the conformational changes within the protein, which are believed to lead to signaling.

  4. Conformational isomerism and the diversity of antibodies.

    PubMed Central

    Foote, J; Milstein, C

    1994-01-01

    The fact that one cell encodes a single antibody sequence does not necessarily mean that the resulting antibody folds into a single structure, although this is a common assumption. Here we challenge this view and suggest that many antibodies do not have a single conformation at the combining site. The basis for this proposal comes from the kinetic analysis of a set of murine hybridomas derived from defined stages of the immune response to 2-phenyl-5-oxazolone (Ox). Among them we have identified three antibodies that exhibit complex hapten-binding kinetics. We observed biphasic or triphasic reactions in stopped-flow fluorescence experiments, indicating that ligand binding involved isomerization, as well as associative steps. The existence of an equilibrium between at least two antibody conformations, with ligands binding preferentially to one form, was deduced from the variation with hapten concentration of the apparent rate of each phase. PMID:7937957

  5. Isomeric amphetamines--a problem for urinalysis?

    PubMed

    Smith, F P; Kidwell, D A

    1991-09-01

    Alkyl amphetamine isomers (amphetamine, 1-phenyl-2-butylamine (PBA), methamphetamine, N-methyl-PBA, N,N-dimethylamphetamine, N-ethylamphetamine, N-ethyl-PBA and N,N-diethylamphetamine) were purchased or synthesized and tested by immunoassay and GC/MS for their detectability in urine. Some cross reactivity was observed with PBA, N-methyl-PBA N-ethylamphetamine, and N-ethyl-PBA when analyzed using a series of commercial amphetamine and methamphetamine immunoassays. Chromatographic co-elution problems were observed for the underivatized isomeric group N,N-dimethylamphetamine, N-ethylamphetamine, and N-methyl-PBA under GC/MS conditions used; and their GC/MS spectra were quite similar. Of the potential derivatives, pentafluoropropionyl (PFP) anhydride and heptafluorobutyryl (HFB) anhydride provided adequate separation and easily distinguishable spectra using the electron-impact GC/MS conditions specified.

  6. Proline isomerization in the C-terminal region of HSP27.

    PubMed

    Alderson, T Reid; Benesch, Justin L P; Baldwin, Andrew J

    2017-07-01

    In mammals, small heat-shock proteins (sHSPs) typically assemble into interconverting, polydisperse oligomers. The dynamic exchange of sHSP oligomers is regulated, at least in part, by molecular interactions between the α-crystallin domain and the C-terminal region (CTR). Here we report solution-state nuclear magnetic resonance (NMR) spectroscopy investigations of the conformation and dynamics of the disordered and flexible CTR of human HSP27, a systemically expressed sHSP. We observed multiple NMR signals for residues in the vicinity of proline 194, and we determined that, while all observed forms are highly disordered, the extra resonances arise from cis-trans peptidyl-prolyl isomerization about the G193-P194 peptide bond. The cis-P194 state is populated to near 15% at physiological temperatures, and, although both cis- and trans-P194 forms of the CTR are flexible and dynamic, both states show a residual but differing tendency to adopt β-strand conformations. In NMR spectra of an isolated CTR peptide, we observed similar evidence for isomerization involving proline 182, found within the IPI/V motif. Collectively, these data indicate a potential role for cis-trans proline isomerization in regulating the oligomerization of sHSPs.

  7. Identification of Sequence Similarities among Isomerization Hotspots in Crystallin Proteins

    PubMed Central

    2017-01-01

    The eye lens crystallins represent an ideal target for studying the effects of aging on protein structure. Herein we examine separately the water-soluble (WS) and water-insoluble (WI) crystallin fractions and identify sites of isomerization and epimerization. Both collision-induced dissociation and radical-directed dissociation are needed for detection of these non-mass-shifting post-translational modifications. Isomerization levels differ significantly between the WS and the WI fractions from sheep, pig, and cow eye lenses. Residues that are most susceptible to isomerization are identified site-specifically and are found to reside in structurally disordered regions. However, isomerization in structured domains, although less common, often yields more dramatic effects on solubility. Numerous isomerization hotspots were also identified and occur in regions with aspartic acid and serine repeats. For example, 128KMEIVDDDVPSLW140 in βB3 crystallin contains three sequential aspartic acid residues and is isomerized heavily in the WI fractions, while it is not modified at all in the WS fractions. Potential causes for enhanced isomerization at sites with acidic residue repeats are presented. The importance of acidic residue repeats extends beyond the lens, as they are found in many other long-lived proteins associated with disease. PMID:28234481

  8. Modulating the physical and electronical properties over positional isomerism: the Dispirofluorene-Dihydroindacenodithiophene (DSF-IDT) family.

    PubMed

    Rault-Berthelot, Joëlle; Peltier, Jean-David; Poriel, Cyril; Heinrich, Benoît; Donnio, Bertrand; Jeannin, Olivier

    2017-09-12

    We report the first studies on the intrinsic properties of a meta-substituted dihydroindacenodithienyl fragment and more generally the strong impact of positional isomerism on dihydroindacenodithiophene derivatives. The influence of the para and meta linkages has notably been highlighted not only on the electronic properties in solution (electrochemical properties, anodic polymerization, HOMO/LUMO energy levels, optical transitions, fluorescence spectra…) but also on the physical properties in the solid state (molecular organization, crystallinity and phase transitions). The positional isomerism hence appears as a very efficient tool to drastically tune the properties of dihydroindacenodithiophene derivatives. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  9. Results of a direct search for the thorium-229 nuclear isomeric transition

    NASA Astrophysics Data System (ADS)

    Schneider, Christian; Jeet, Justin; Sullivan, Scott T.; Rellergert, Wade G.; Mirzadeh, Saed; Cassanho, A.; Jenssen, H. P.; Tkalya, Eugene V.; Hudson, Eric R.

    2015-05-01

    The nucleus of thorium-229 has an exceptionally low-energy isomeric transition in the vacuum-ultraviolet spectrum around 7 . 8 +/- 0 . 5 eV. The prospects of a laser-accessible nuclear transition are manifold but require spectroscopically resolving the transition. Our approach is a direct search using thorium-doped crystals as samples and exciting the isomeric state with vacuum-ultraviolet synchrotron radiation. In a recent experiment, we were able to search for the transition at the Advanced Light Source synchrotron, LBNL, between 7 . 3 eV and 8 . 8 eV. We found no evidence for the transition within a lifetime range of 1-2s to 2000-5600s. This result excludes large parts of the theoretically expected region. We conclude reporting on our efforts of a search using laser-generated vacuum-ultraviolet light.

  10. Femtosecond dynamics of fundamental reaction processes in liquids: Proton transfer, geminate recombination, isomerization and vibrational relaxation

    SciTech Connect

    Schwartz, Benjamin Joel

    1992-11-01

    The fast excited state intramolecular proton transfer of 3-hydroxyflavone is measured and effects of external hydrogen-bonding interactions on the proton transfer are studied. The proton transfer takes place in ~240 fsec in nonpolar environments, but becomes faster than instrumental resolution of 110 fsec in methanol solution. The dynamics following photodissociation of CH2I2 and other small molecules provide the first direct observations of geminate recombination. The recombination of many different photodissociating species occurs on a ~350 fsec time scale. Results show that recombination yields but not rates depend on the solvent environment and suggest that recombination kinetics are dominated by a single collision with surrounding solvent cage. Studies of sterically locked phenyl-substituted butadienes offer new insights into the electronic structure and isomerization behavior of conjugated polyenes. Data show no simple correlation between hinderance of specific large amplitude motions and signatures of isomerizative behavior such as viscosity dependent excited state lifetimes, implying that the isomerization does not provide a suitable for simple condensed phase reaction rate theories. The spectral dynamics of a photochromic spiropyran indicate that recombination, isomerization and vibrational relaxation all play important roles in photoreactivity of complex molecules. The interplay of these microscopic phenomena and their effect on macroscopic properties such as photochromism are discussed. All the results indicate that the initial steps of the photochromic reaction process occur extremely rapidly. Laser system and computer codes for data analysis are discussed.

  11. Spectroscopic Identification of Isomeric Trimethylbenzyl Radicals Generated in Corona Discharge of Tetramethylbenzene

    NASA Astrophysics Data System (ADS)

    Yoon, Young Wook; Lee, Sang Kuk; Lee, Gi Woo

    2011-06-01

    The visible vibronic emission spectra were recorded from the corona discharge of precursor tetramethylbenzene with a large amount of inert carrier gas helium using a pinhole-type glass nozzle coupled with corona excited supersonic expansion (CESE) well developed in this laboratory. The spectra showed a series of vibronic bands in the D_1 → D_0 electronic transition of jet-cooled benzyl-type radicals formed from the precursor in a corona excitation. The analysis confirmed that two isomeric radicals, 2,3,4- and 2,3,6-trimethylbenzyl radicals and three isomeric radicals, 3,4,5-, 2,3,5- and 2,4,6-trimethylbenzyl radicals were produced, respectively, from 1,2,3,4- and 1,2,3,5-tetramethylbenzenes as a result of removal of a hydrogen atom from the methyl group at different substitution position. For each isomeric trimethylbenzyl radical generated in the corona discharge of precursor, the electronic transition and a few vibrational mode frequencies were determined in the ground electronic state by comparing with those from both ab initio calculations and the known vibrational data of the precursor. The substitution effect that states the shift of electronic transition depends on the nature, the number, and the position of substituents on the ring has been qualitatively proved for the case of benzyl-type radicals.

  12. Influence of the octupole mode on nuclear high-K isomeric properties

    NASA Astrophysics Data System (ADS)

    Minkov, Nikolay; Walker, Phil

    2014-05-01

    The influence of quadrupole-octupole deformations on the energy and magnetic properties of high-K isomeric states in even-even actinide (U, Pu, Cm, Fm, No), rare-earth (Nd, Sm and Gd), and superheavy (^{270}\\text{Ds}) nuclei is examined within a deformed shell model with pairing interaction. The neutron two-quasiparticle (2qp) isomeric energies and magnetic dipole moments are calculated over a wide range in the plane of quadrupole and octupole deformations. In most cases the magnetic moments exhibit a pronounced sensitivity to the octupole deformation. At the same time, the calculations outline three different groups of nuclei: with pronounced, shallow, and missing minima in the 2qp energy surfaces with respect to the octupole deformation. The result indicates regions of nuclei with octupole softness as well as with possible octupole deformation in the high-K isomeric states. These findings show the need for further theoretical analysis as well as of detailed experimental measurements of magnetic moments in heavy deformed nuclei.

  13. The photoinduced E → Z isomerization of bisazobenzenes: a surface hopping molecular dynamics study.

    PubMed

    Floss, Gereon; Saalfrank, Peter

    2015-05-21

    The photoinduced E → Z isomerization of azobenzene is a prototypical example of molecular switching. On the way toward rigid molecular rods such as those for opto-mechanical applications, multiazobenzene structures have been suggested in which several switching units are linked together within the same molecule (Bléger et al., J. Phys. Chem. B 2011, 115, 9930-9940). Large differences in the switching efficiency of multiazobenzenes have been observed, depending on whether the switching units are electronically decoupled or not. In this paper we study, on a time-resolved molecular level, the E→ Z isomerization of the simplest multiazobenzene, bisazobenzene (BAB). Two isomers (ortho- and para-BAB), differing only in the connectivity of two azo groups on a shared phenyl ring will be considered.To do so, nonadiabatic semiclassical dynamics after photoexcitation of the isomers are studied by employing an "on-the-fly", fewest switches surface hopping approach. States and couplings are calculated by Configuration Interaction (CI) based on a semiempirical (AM1) Hamiltonian (Persico and co-workers, Chem. Eur. J. 2004, 10, 2327-2341). In the case of para-BAB, computed quantum yields for photoswitching are drastically reduced compared to pristine azobenzene, due to electronic coupling of both switching units. A reason for this (apart from altered absorption spectra and reduced photochromicity) is the drastically reduced lifetimes of electronically excited states which are transiently populated. In contrast for meta-connected species, electronic subsystems are largely decoupled, and computed quantum yields are slightly higher than that for pristine azobenzene because of new isomerization channels. In this case we can also distinguish between single- and double-switch events and we find a cooperative effect: The isomerization of a single azo group is facilitated if the other azo group is already in the Z-configuration.

  14. IsoTex: Texaco`s olefin skeletal isomerization process

    SciTech Connect

    Sawicki, R.A.; Pellet, R.J.; Kuhlmann, E.J.; Huang, H.M.; O`Young, C.L.; Kessler, R.V.; Casey, D.G.

    1995-09-01

    Texaco has developed a new process (IsoTex) for the skeletal isomerization of n-olefins. The IsoTex process can convert normal butenes to isobutylene or normal pentenes to isoamylenes. The resulting product stream is an excellent feed for MTBE, ETBE or TAME units. The process has isomerized an untreated refinery C4 raffinate stream from an MTBE plant. A kinetic model was developed for the butene system. This model accurately predicted IsoTex performance in a one barrel per day skid unit at a Gulf Coast chemical plant. Process economics have been calculated for a once through 54,000 BPD C{sub 4} isomerization plant as well as a 10,000 BPD plant for recycle to an existing MTBE reactor. Economics have also been completed for a 6,800 BPD pentene once through isomerization unit.

  15. Isomerization dynamics and thermodynamics of ionic argon clusters

    NASA Astrophysics Data System (ADS)

    Calvo, F.; Gadéa, F. X.; Lombardi, A.; Aquilanti, V.

    2006-09-01

    The dynamics and thermodynamics of small Arn+ clusters, n =3, 6, and 9, are investigated using molecular dynamics (MD) and exchange Monte Carlo (MC) simulations. A diatomic-in-molecule Hamiltonian provides an accurate model for the electronic ground state potential energy surface. The microcanonical caloric curves calculated from MD and MC methods are shown to agree with each other, provided that the rigorous conservation of angular momentum is accounted for in the phase space density of the MC simulations. The previously proposed projective partition of the kinetic energy is used to assist MD simulations in interpreting the cluster dynamics in terms of inertial, internal, and external modes. The thermal behavior is correlated with the nature of the charged core in the cluster by computing a dedicated charge localization order parameter. We also perform systematic quenches to establish a connection with the various isomers. We find that the Ar3+ cluster is very stable in its linear ground state geometry up to about 300K, and then isomerizes to a T-shaped isomer in which a quasineutral atom lies around a charged dimer. In Ar6+ and Ar9+, the covalent trimer core is solvated by neutral atoms, and the weakly bound solvent shell melts at much lower energies, occasionally leading to a tetramer or pentamer core with weakly charged extremities. At high energies the core itself becomes metastable and the cluster transforms into Ar2+ solvated by a fluid of neutral argon atoms.

  16. Methods for suppressing isomerization of olefin metathesis products

    DOEpatents

    Firth, Bruce E.; Kirk, Sharon E.

    2015-10-27

    A method for suppressing isomerization of an olefin metathesis product produced in a metathesis reaction includes adding an isomerization suppression agent that includes nitric acid to a mixture that includes the olefin metathesis product and residual metathesis catalyst from the metathesis reaction under conditions that are sufficient to passivate at least a portion of the residual metathesis catalyst. Methods of refining a natural oil are described.

  17. Acute Myocardial Infarction in Adult Congenital Patients with Bodily Isomerism.

    PubMed

    Loomba, Rohit S; Aggarwal, Saurabh; Buelow, Matthew; Nijhawan, Karan; Gupta, Navdeep; Alla, Venkata; Arora, Rohit R

    2016-12-01

    Children born with congenital malformations of the heart are increasingly surviving into adulthood. This population of patients possesses lesion-specific complication risks while still being at risk for common illnesses. Bodily isomerism or heterotaxy, is a unique clinical entity associated with congenital malformations of the heart which further increases the risk for future cardiovascular complications. We aimed to investigate the frequency of myocardial infarction in adults with bodily isomerism. We utilized the 2012 iteration of the Nationwide Inpatient Sample to identify adult inpatient admissions associated with acute myocardial infarction in patients with isomerism. Data regarding demographics, comorbidities and various procedures were collected and compared between those with and without isomerism. A total of 6,907,109 admissions were analyzed with a total of 172,394 admissions being associated with an initial encounter for acute myocardial infarction. The frequency of myocardial infarction did not differ between those with and without isomerism and was roughly 2% in both groups. Similarly, the number of procedures and in-hospital mortality did not differ between the two groups. The frequency and short-term prognosis of acute myocardial infarction is similar in patients with and without isomerism. © 2016 Wiley Periodicals, Inc.

  18. Solvent isotope effects on retinal cis-trans isomerization in the dark adaptation of bacteriorhodopsin

    SciTech Connect

    Seltzer, S.

    1992-04-22

    The solvent isotope effect on the first-order rate constant for dark adaptation of bacteriorhodopsin, near neutral pH (pD), is inverse; k{sub D}/k{sub H} = 1.24. The fit of the variation of isotope effect with the atom fraction of deuterium in the solvent to the Gross-Butler equation leads to the conclusion that the proton(s) in motion is (are) less tightly bound in the reactant than in a reactive intermediate, formed prior to the rate-controlling step of cis-trans isomerization. The near-unity isotope effect on the equilibrium between the bound 13-cis- and all-trans-retinals in the dark-adapted state mixture indicates that the isotope effects on the forward and reverse rate constants for isomerization are approximately equal to each other and equal to the isotope effect on the observed rate constant for dark adaptation. The results support a previously proposed mechanism of rate-controlling Asp-212 nucleophilic catalysis of retinal cis-trans isomerication in the dark adaptation process. 27 refs., 2 figs., 1 tab.

  19. Discussion of isomeric ratios in (p, n) and (d, 2n) reaction

    SciTech Connect

    Bakhshiyan, T. M.

    2016-01-15

    Isomeric ratios (IR) in the (p, n) and (d, 2n) reactions are considered. The dependence of IR values on the projectile type and energy, the target- and product-nucleus spin, the spin difference between the isomeric and ground states of products, and the product mass number is discussed. The isomeric ratios for 46 product nuclei (from {sup 44m,g}Sc to {sup 127m,g}Xe) obtained in reactions where target and product nuclei have identical mass numbers were calculated at energies from the reaction threshold to 50 MeV (with a step of ΔE = 1 MeV). The calculations in question were performed with the aid of the TALYS 1.4 code package. The calculated IR values were compared with their experimental counterparts available from the literature (EXFOR database). In the majority of cases, the calculated IR values agree well with the experimental data in question. It is noteworthy that the IR values obtained in (d, 2n) reactions are substantially greater than those in (p, n) reactions.

  20. Sequential picosecond isomerizations in a photochromic ruthenium sulfoxide complex triggered by pump-repump-probe spectroscopy.

    PubMed

    King, Albert W; Jin, Yuhuan; Engle, James T; Ziegler, Christopher J; Rack, Jeffrey J

    2013-02-18

    The complex [Ru(bpy)(2)(bpSO)](PF(6))(2), where bpy is 2,2'-bipydine and bpSO is 1,2-bis(phenylsulfinyl)ethane, exhibits three distinct isomers which are accessible upon metal-to-ligand charge-transfer (MLCT) irradiation. This complex and its parent, [Ru(bpy)(2)(bpte)](PF(6))(2), where bpte is 1,2-bis(phenylthio)ethane, have been synthesized and characterized by UV-visible spectroscopy, NMR, X-ray crystallography, and femtosecond transient absorption spectroscopy. A novel method of 2-color Pump-Repump-Probe spectroscopy has been employed to investigate all three isomers of the bis-sulfoxide complex. This method allows for observation of the isomerization dynamics of sequential isomerizations of each sulfoxide from MLCT irradiation of the S,S-bonded complex to ultimately form the O,O-bonded metastable complex. One-dimensional (1-D) and two-dimensional (2-D) (COSY, NOESY, and TOCSY) (1)H NMR data show the thioether and ground state S,S-bonded sulfoxide complexes to be rigorously C(2) symmetric and are consistent with the crystal structures. Transient absorption spectroscopy reveals that the S,S to S,O isomerization occurs with an observed time constant of 56.8 (±7.4) ps. The S,O to O,O isomerization time constant was found to be 59 (±4) ps by pump-repump-probe spectroscopy. The composite S,S- to O,O-isomer quantum yield is 0.42.

  1. HCP<=>CPH isomerization: caught in the act.

    PubMed

    Ishikawa, H; Field, R W; Farantos, S C; Joyeux, M; Koput, J; Beck, C; Schinke, R

    1999-01-01

    In this overview we discuss the vibrational spectrum of phosphaethyne, HCP, in its electronic ground state, as revealed by complementary experimental and theoretical examinations. The main focus is the evolution of specific spectral patterns from the bottom of the potential well up to excitation energies of approximately 25,000 cm(-1), where large-amplitude, isomerization-type motion from H-CP to CP-H is prominent. Distinct structural and dynamical changes, caused by an abrupt transformation from essentially HC bonding to mainly PH bonding, set in around 13,000 cm(-1). They reflect saddle-node bifurcations in the classical phase space--a phenomenon well known in the nonlinear dynamics literature--and result in characteristic patterns in the spectrum and the quantum-number dependence of the vibrational fine-structure constants. Two polar opposites are employed to elucidate the spectral patterns: the exact solution of the Schrödinger equation, using an accurate potential energy surface and an effective or resonance Hamiltonian (expressed in a harmonic oscillator basis set and block diagonalized into polyads), which is defined by parameters adjusted to fit either the measured or the calculated vibrational energies. The combination of both approaches--together with classical mechanics and semiclassical analyses--provides a detailed spectroscopic picture of the breaking of one bond and the formation of a new one.

  2. Iridium-Catalyzed Selective Isomerization of Primary Allylic Alcohols.

    PubMed

    Li, Houhua; Mazet, Clément

    2016-06-21

    This Account presents the development of the iridium-catalyzed isomerization of primary allylic alcohols in our laboratory over the past 8 years. Our initial interest was driven by the long-standing challenge associated with the development of a general catalyst even for the nonasymmetric version of this seemingly simple chemical transformation. The added value of the aldehyde products and the possibility to rapidly generate molecular complexity from readily accessible allylic alcohols upon a redox-economical isomerization reaction were additional sources of motivation. Certainly influenced by the success story of the related isomerization of allylic amines, most catalysts developed for the selective isomerization of allylic alcohols were focused on rhodium as a transition metal of choice. Our approach has been based on the commonly accepted precept that hydrogenation and isomerization are often competing processes, with the latter being usually suppressed in favor of the former. The cationic iridium complexes [(Cy3P)(pyridine)Ir(cod)]X developed by Crabtree (X = PF6) and Pfaltz (X = BArF) are usually considered as the most versatile catalysts for the hydrogenation of allylic alcohols. Using molecular hydrogen to generate controlled amounts of the active form of these complexes but performing the reaction in the absence of molecular hydrogen enabled deviation from the typical hydrogenation manifold and favored exclusively the isomerization of allylic alcohols into aldehydes. Isotopic labeling and crossover experiments revealed the intermolecular nature of the process. Systematic variation of the ligand on the iridium center allowed us to identify the structural features beneficial for catalytic activity. Subsequently, three generations of chiral catalysts have been investigated and enabled us to reach excellent levels of enantioselectivity for a wide range of 3,3-disubstituted aryl/alkyl and alkyl/alkyl primary allylic alcohols leading to β-chiral aldehydes. The

  3. Phototriggered sulfoxide isomerization in [Ru(pic)2(dmso)2].

    PubMed

    Rachford, Aaron A; Petersen, Jeffrey L; Rack, Jeffrey J

    2007-08-14

    We report the characterization and photochemistry of a simple ruthenium coordination complex containing only picolinate (pic) and dmso, which exhibits a large isomerization quantum yield (Phi(SS-->OO) = 0.50) in various solvents. The picolinate ligands of [Ru(pic)(2)(dmso)(2)] are in a cis arrangement so that the carboxylate oxygen of one pic ligand (O1) is trans to the pyridine of the second picolinate (N2). One dmso ligand (S1) is trans to a pyridine nitrogen (N1), while the second dmso (S2) is trans to a carboxylate oxygen (O3). The cyclic voltammetry, (1)H NMR, IR, and UV-vis spectroscopy data suggest that while both dmso ligands isomerize photochemically, only one dmso ligand isomerizes electrochemically. Isomerization quantum yields for each dmso ligand differ by an order of magnitude (Phi(SS-->SO) = 0.46 and Phi(SO-->OO) = 0.036). In agreement with previous results, the isomerization quantum yield for each dmso is dependent on the ligand that is trans to the dmso.

  4. Prolyl cis-trans isomerization as a molecular timer.

    PubMed

    Lu, Kun Ping; Finn, Greg; Lee, Tae Ho; Nicholson, Linda K

    2007-10-01

    Proline is unique in the realm of amino acids in its ability to adopt completely distinct cis and trans conformations, which allows it to act as a backbone switch that is controlled by prolyl cis-trans isomerization. This intrinsically slow interconversion can be catalyzed by the evolutionarily conserved group of peptidyl prolyl cis-trans isomerase enzymes. These enzymes include cyclophilins and FK506-binding proteins, which are well known for their isomerization-independent role as cellular targets for immunosuppressive drugs. The significance of enzyme-catalyzed prolyl cis-trans isomerization as an important regulatory mechanism in human physiology and pathology was not recognized until the discovery of the phosphorylation-specific prolyl isomerase Pin1. Recent studies indicate that both phosphorylation-dependent and phosphorylation-independent prolyl cis-trans isomerization can act as a novel molecular timer to help control the amplitude and duration of a cellular process, and prolyl cis-trans isomerization might be a new target for therapeutic interventions.

  5. Prenatal diagnosis of atrial isomerism in the Korean population

    PubMed Central

    Lee, Mi-Young; Shim, Jae-Yoon; Lee, Pil-Ryang; Lee, Byong Sop; Kim, Ellen Ai-Rhan; Kim, Young-Hwue; Park, Jeong-Jun; Yun, Tae-Jin; Kim, Ahm

    2014-01-01

    Objective To report our experiences in the prenatal diagnosis of atrial isomerism and postnatal outcomes. Methods A total of 80 fetuses prenatally diagnosed with atrial isomerism were retrospectively analyzed between 1999 and 2011 at a single institution. Results Of 43 fetuses with prenatally diagnosed right atrial isomerism (RAI), 40 cases were analyzed. The diagnostic accuracy was 93%. The main intracardiac anomalies in RAI were atrioventricular septal defect (AVSD), abnormal pulmonary venous connection, bilateral superior vena cava (BSVC), and pulmonary atresia. Among 28 live births, three infants were lost to follow up, and the overall survival rate was 60%. Of 37 fetuses with prenatally diagnosed left atrial isomerism (LAI), 35 were evaluated. The diagnostic accuracy was 97%. The main intracardiac anomalies in LAI were ventricular septal defect, BSVC, AVSD, double outlet right ventricle, and bradyarrhythmia. Among seven patients with bradyarrhythmia, only one showed a complete atrioventricular block. All fetuses had an interrupted inferior vena cava with azygous continuation. The overall survival rate was 90%. Conclusion Our study confirms the previous findings of fetal atrial isomerism. We also demonstrates a much lower prevalence of AVSD and complete heart block in LAI and a better survival rate in RAI. Although the postnatal outcomes for RAI were worse than those for LAI, successful postnatal surgery with active management improved the survival rate. PMID:24883290

  6. Simulation of Photo-isomerization of Functionalized Azobenzene Derivatives

    NASA Astrophysics Data System (ADS)

    Tavazohi, Pedram; Herberger, Zachary; Lewis, James

    Photo-isomerization is the process of changing the isomer (cis , trans) of a molecule using light. In azobenzene this process can be utilized in a Metal Organic Framework (MOF) for adsorption of CO2. MOFs are created by two major components, metal ions, and organic molecules which are called linkers. The metal ions and linkers can be coordinated in a way that they form a porous material. In the cis isomer of azobenzene, the MOF's pore is available to be filled by CO2, but in the trans isomer the pore is filled with a benzene ring. The change from cis to trans will evacuate the pore if CO2 is present. The important considerations in using azobenzene photo-isomerization as a photo-switch in MOFs are, the quantum yield of the process, and the wavelength of the light which triggers photo-isomerization. By substitution of the functional groups of azobenzene and using the fewest switches surface-hopping algorithm in FIREBALL to simulate the photo-isomerization process we can tune the properties of the molecule as we desire and predict the best substitution sites for azobenzene functional groups. We studied the effects of functionalizing the molecule with OH, CH3, NH2, NO2 and COOH on isomerization quantum yield.

  7. A review of drug isomerism and its significance

    PubMed Central

    Chhabra, Naveen; Aseri, Madan L; Padmanabhan, Deepak

    2013-01-01

    Isomerism finds its importance in the field of clinical pharmacology and pharmacotherapeutics, as isomers differ in their pharmacokinetic and pharmacodyanmic properties. Drug isomerism has opened a new era of drug development. Currently, knowledge of isomerism has helped us in introducing safer and more effective drug alternatives of the newer as well as existing drugs. Many existing drugs have gone chiral switch i.e., switching from racemic mixture to one of its isomers. Cetrizine to levocetrizine is one of such examples, where effective and safer drug has been made available. In this article, we have attempted to review the basic concepts of stereochemistry and chirality and their significance in pharmacotherapeutics. Various pharmacological aspects such as pharmacokinetic and pharmacodynamic variations resulting out of chirality has been discussed in detail in this article. PMID:23776834

  8. Cost effective isomerization options for tomorrow's light gasoline processing requirements

    SciTech Connect

    Sager, T.C.; Haizmann, R.J.; Johnson, B.H. )

    1989-01-01

    Light naphtha isomerization has become extremely important in recent years in helping refiners meet their gasoline pool octane demands this is especially true for the modern UOP* Penex* and TIP* technologies because of their octane production efficiency, relatively low capital cost and overall flexibility. Today there are almost 800,000 BPSD of licensed isomerization capacity worldwide; an increase of nearly 550,000 BPSD since 1982. This surge in demand has been the result of lead phase down programs, increased sales of premium gasoline and, in some areas, proposed legislation limiting benzene content of gasoline. The addition of a light naptha isomerization unit can result in a 1.0 to 3.0 octane improvement in the total gasoline pool, depending on feedstock and process configuration. The advantages include reducing reformer severity, increasing the percentage of gasoline sold as premium, or simply meeting the requirements of unleaded gasoline. These advantages are discussed in detail by the authors.

  9. Is the photoinduced isomerization in retinal protonated Schiff bases a single- or double-torsional process?

    PubMed

    Szymczak, Jaroslaw J; Barbatti, Mario; Lischka, Hans

    2009-10-29

    Nonadiabatic photodynamical simulations are presented for the all-trans and 5-cis isomers of the hepta-3,5,7-trieniminium cation (PSB4) with the goal of characterizing the types of torsional modes occurring in the cis-trans isomerization processes in retinal protonated Schiff base (RPSB), the rhodopsin and bacteriorhodopsin chropomhore. Steric hindrance of these processes due to environmental effects have been modeled by imposing different sets of mechanical restrictions on PSB4 and studying its response in the photodynamics. Both the mechanism toward the conical intersection and the initial phase of the hot ground state dynamics has been studied in detail. A total of 600 trajectories have been computed using a complete active space self-consistent field wave function. Careful comparison with higher level methods has been made in order to verify the accuracy of the results. The most important mechanism driving restricted PSB4 isomerization in the excited state is characterized by two concerted twist motions (bipedal and closely related to it nonrigid bipedal) from which only one torsion tends to be continued during the relaxation into the ground state. The one-bond-flip is found to be important for the trans isomer as well. The main isomerization trend is a torsion around C(5)C(6) (equivalent to C(11)C(12) in RPSB) in the case of the cis isomer and around C(3)C(4) (C(13)C(14) in RPSB) in the case of the trans isomer. The simulations show an initial 70 fs relaxation into twisted regions and give an average internal conversion time of 130-140 fs, timings that are fully compatible with the general picture described by femtosecond transient absorption spectroscopic studies.

  10. Benzil-tethered precipitons for controlling solubility: a round-trip energy-transfer mechanism in the isomerization of extended stilbene analogues.

    PubMed

    Ams, Mark R; Wilcox, Craig S

    2007-04-04

    We are investigating photoresponsive molecules called "precipitons" that undergo a solubility change co-incident with isomerization. Isomerization can be induced by light or by catalytic reagents. Previous work demonstrated that covalent attachment of a metal complex, Ru(II)(bpy)3, greatly accelerates photoisomerization and influences the photostationary state. In this paper, we describe precipitons (1,2-biphenylethenes; analogous to stilbenes) that are activated by a covalently attached organic sensitizer (benzil). We find that isomerization of these stilbene analogues is little effected by the presence of benzil in solution but that the intramolecular benzil effect is to increase the rate of isomerization and to significantly change the photostationary state. What is most interesting about these observations is that the precipiton is the primary chromophore in this bichromophoric system (precipiton absorbance is many times greater than benzil absorbance in the 300-400 nm range), yet the neighboring benzil has a significant effect on the rate and the photostationary state. The effect of unattached benzil on the rate was small, about a 24% increase in rate as compared with 4-6-fold changes for an attached benzil. We speculate that the isomerization process occurs by a "round-trip" energy-transfer mechanism. Initial excitation of the precipiton chromophore initiates a sequence that includes (1) formation of the precipiton singlet state, (2) singlet excitation transfer from the precipiton unit to the benzil, (3) benzil-centered intersystem crossing to the localized benzil triplet state, (4) triplet energy transfer from the benzil moiety back to the precipiton, and (5) isomerization.

  11. Catalytic Isomerization of Biomass‐Derived Aldoses: A Review

    PubMed Central

    Delidovich, Irina

    2016-01-01

    Abstract Selected aldohexoses (d‐glucose, d‐mannose, and d‐galactose) and aldopentoses (d‐xylose, l‐arabinose, and d‐ribose) are readily available components of biopolymers. Isomerization reactions of these substances are very attractive as carbon‐efficient processes to broaden the portfolio of abundant monosaccharides. This review focuses on the chemocatalytic isomerization of aldoses into the corresponding ketoses as well as epimerization of aldoses at C2. Recent advances in the fields of catalysis by bases and Lewis acids are considered. The emphasis is laid on newly uncovered catalytic systems and mechanisms of carbohydrate transformations. PMID:26948404

  12. Biventricular repair of right atrial isomerism with complex congenital anomalies.

    PubMed

    Kirali, Kaan; Sasmazel, Ahmet; Mataraci, Ilker; Erdem, Hasan; Guzelmeric, Fusun

    2010-01-01

    Biventricular repair is usually difficult to achieve in patients who have right atrial isomerism, which is typically associated with other complex cardiac anomalies. The procedure can be used in patients who have balanced ventricular structures. Herein, we report a successful surgical reconstruction, including biventricular repair, in a 4-year-old boy. The child's right atrial isomerism was associated with double-outlet right ventricle, a large atrial septal defect, a subaortic ventricular septal defect, valvular and infundibular pulmonary stenosis, left persistent superior vena cava, and hemiazygos continuation of an interrupted inferior vena cava. Balanced ventricles enabled biventricular repair, which we consider to be preferable to the Fontan procedure in such circumstances.

  13. Ethanol production from xylose by enzymic isomerization and yeast fermentation

    SciTech Connect

    Chiang, L.C.; Hsiao, H.Y.; Ueng, P.P.; Chen, L.F.; Tsao, G.T.

    1981-01-01

    Repetitive enzymic isomerization of xylose followed by yeast fermentation of xylulose, and simultaneous enzymic isomerization and yeast fermentation were proven to be methods capable of converting xylose to ethanol. The fermentation product, ethanol, xylitol, or glycerol, has little inhibitory or deactivation effect on the activity of isomerase. In a comparison of the ability of yeasts to ferment xylulose to ethanol, Schizosaccharomyces pombe was found to be superior to industrial bakers' yeast. Under optimal conditions (pH 6, temperature 30/sup 0/C), a final ethanol concentration of 6.3 wt.% was obtained from simulated hemicellulose hydrolysate using a simultaneous fermentation process. The ethanol yield was over 80% of the theoretical value.

  14. Toward spectroscopically accurate global ab initio potential energy surface for the acetylene-vinylidene isomerization

    SciTech Connect

    Han, Huixian; Li, Anyang; Guo, Hua

    2014-12-28

    A new full-dimensional global potential energy surface (PES) for the acetylene-vinylidene isomerization on the ground (S{sub 0}) electronic state has been constructed by fitting ∼37 000 high-level ab initio points using the permutation invariant polynomial-neural network method with a root mean square error of 9.54 cm{sup −1}. The geometries and harmonic vibrational frequencies of acetylene, vinylidene, and all other stationary points (two distinct transition states and one secondary minimum in between) have been determined on this PES. Furthermore, acetylene vibrational energy levels have been calculated using the Lanczos algorithm with an exact (J = 0) Hamiltonian. The vibrational energies up to 12 700 cm{sup −1} above the zero-point energy are in excellent agreement with the experimentally derived effective Hamiltonians, suggesting that the PES is approaching spectroscopic accuracy. In addition, analyses of the wavefunctions confirm the experimentally observed emergence of the local bending and counter-rotational modes in the highly excited bending vibrational states. The reproduction of the experimentally derived effective Hamiltonians for highly excited bending states signals the coming of age for the ab initio based PES, which can now be trusted for studying the isomerization reaction.

  15. Theoretical study of the isomerization mechanism of azobenzene and disubstituted azobenzene derivatives.

    PubMed

    Crecca, Christina R; Roitberg, Adrian E

    2006-07-06

    A series of azobenzenes was studied using ab initio methods to determine the substituent effects on the isomerization pathways. Energy barriers were determined from three-dimensional potential energy surfaces of the ground and electronically excited states. In the ground state (S(0)), the inversion pathway was found to be preferred. Our results show that electron donating substituents increase the isomerization barrier along the inversion pathway, whereas electron withdrawing substituents decrease it. The inversion pathway of the first excited state (S(1)) showed trans --> cis barriers with no curve crossing between S(0) and S(1). In contrast, a conical intersection was found between the ground and first excited states along the rotation pathway for each of the azobenzenes studied. No barriers were found in this pathway, and we therefore postulate that after n --> pi (S(1) <-- S(0)) excitation, the rotation mechanism dominates. Upon pi --> pi (S(2) <-- S(0)) excitation, there may be sufficient energy to open an additional pathway (concerted-inversion) as proposed by Diau. Our potential energy surface explains the experimentally observed difference in trans-to-cis quantum yields between S(1) and S(2) excitations. The concerted inversion channel is not available to the remaining azobenzenes, and so they must employ the rotation pathway for both n --> pi and pi --> pi excitations.

  16. Excitation Localization/Delocalization Isomerism in a Strongly Coupled Covalent Dimer of 1,3-Diphenylisobenzofuran

    SciTech Connect

    Schrauben, Joel N.; Akdag, Akin; Wen, Jin; Havlas, Zdenek; Ryerson, Joseph L.; Smith, Millie B.; Michl, Josef; Johnson, Justin C.

    2016-05-26

    Two isomers of both the lowest excited singlet (S1) and triplet (T1) states of the directly para, para'-connected covalent dimer of the singlet-fission chromophore 1,3-diphenylisobenzofuran have been observed. In one isomer, excitation is delocalized over both halves of the dimer, and in the other, it is localized on one or the other half. For a covalent dimer in solution, such 'excitation isomerism' is extremely rare. The vibrationally relaxed isomers do not interconvert, and their photophysical properties, including singlet fission, differ significantly.

  17. Interfering resonance as an underlying mechanism in the adaptive feedback control of radiationless transitions: Retinal isomerization.

    PubMed

    Lavigne, Cyrille; Brumer, Paul

    2017-09-21

    Control of molecular processes via adaptive feedback often yields highly structured laser pulses that have eluded physical explanation. By contrast, coherent control approaches propose physically transparent mechanisms but are not readily visible in experimental results. Here, an analysis of a condensed phase adaptive feedback control experiment on retinal isomerization shows that it manifests a quantum interference based coherent control mechanism: control via interfering resonances. The result promises deep insight into the physical basis for the adaptive feedback control of a broad class of bound state processes.

  18. Interfering resonance as an underlying mechanism in the adaptive feedback control of radiationless transitions: Retinal isomerization

    NASA Astrophysics Data System (ADS)

    Lavigne, Cyrille; Brumer, Paul

    2017-09-01

    Control of molecular processes via adaptive feedback often yields highly structured laser pulses that have eluded physical explanation. By contrast, coherent control approaches propose physically transparent mechanisms but are not readily visible in experimental results. Here, an analysis of a condensed phase adaptive feedback control experiment on retinal isomerization shows that it manifests a quantum interference based coherent control mechanism: control via interfering resonances. The result promises deep insight into the physical basis for the adaptive feedback control of a broad class of bound state processes.

  19. Comparison of the isomerization mechanisms of human melanopsin and invertebrate and vertebrate rhodopsins.

    PubMed

    Rinaldi, Silvia; Melaccio, Federico; Gozem, Samer; Fanelli, Francesca; Olivucci, Massimo

    2014-02-04

    Comparative modeling and ab initio multiconfigurational quantum chemistry are combined to investigate the reactivity of the human nonvisual photoreceptor melanopsin. It is found that both the thermal and photochemical isomerization of the melanopsin 11-cis retinal chromophore occur via a space-saving mechanism involving the unidirectional, counterclockwise twisting of the =C11H-C12H= moiety with respect to its Lys340-linked frame as proposed by Warshel for visual pigments [Warshel A (1976) Nature 260(5553):679-683]. A comparison with the mechanisms documented for vertebrate (bovine) and invertebrate (squid) visual photoreceptors shows that such a mechanism is not affected by the diversity of the three chromophore cavities. Despite such invariance, trajectory computations indicate that although all receptors display less than 100 fs excited state dynamics, human melanopsin decays from the excited state ∼40 fs earlier than bovine rhodopsin. Some diversity is also found in the energy barriers controlling thermal isomerization. Human melanopsin features the highest computed barrier which appears to be ∼2.5 kcal mol(-1) higher than that of bovine rhodopsin. When assuming the validity of both the reaction speed/quantum yield correlation discussed by Warshel, Mathies and coworkers [Weiss RM, Warshel A (1979) J Am Chem Soc 101:6131-6133; Schoenlein RW, Peteanu LA, Mathies RA, Shank CV (1991) Science 254(5030):412-415] and of a relationship between thermal isomerization rate and thermal activation of the photocycle, melanopsin turns out to be a highly sensitive pigment consistent with the low number of melanopsin-containing cells found in the retina and with the extraretina location of melanopsin in nonmammalian vertebrates.

  20. Comparison of the isomerization mechanisms of human melanopsin and invertebrate and vertebrate rhodopsins

    PubMed Central

    Rinaldi, Silvia; Melaccio, Federico; Gozem, Samer; Fanelli, Francesca; Olivucci, Massimo

    2014-01-01

    Comparative modeling and ab initio multiconfigurational quantum chemistry are combined to investigate the reactivity of the human nonvisual photoreceptor melanopsin. It is found that both the thermal and photochemical isomerization of the melanopsin 11-cis retinal chromophore occur via a space-saving mechanism involving the unidirectional, counterclockwise twisting of the =C11H-C12H= moiety with respect to its Lys340-linked frame as proposed by Warshel for visual pigments [Warshel A (1976) Nature 260(5553):679–683]. A comparison with the mechanisms documented for vertebrate (bovine) and invertebrate (squid) visual photoreceptors shows that such a mechanism is not affected by the diversity of the three chromophore cavities. Despite such invariance, trajectory computations indicate that although all receptors display less than 100 fs excited state dynamics, human melanopsin decays from the excited state ∼40 fs earlier than bovine rhodopsin. Some diversity is also found in the energy barriers controlling thermal isomerization. Human melanopsin features the highest computed barrier which appears to be ∼2.5 kcal mol−1 higher than that of bovine rhodopsin. When assuming the validity of both the reaction speed/quantum yield correlation discussed by Warshel, Mathies and coworkers [Weiss RM, Warshel A (1979) J Am Chem Soc 101:6131–6133; Schoenlein RW, Peteanu LA, Mathies RA, Shank CV (1991) Science 254(5030):412–415] and of a relationship between thermal isomerization rate and thermal activation of the photocycle, melanopsin turns out to be a highly sensitive pigment consistent with the low number of melanopsin-containing cells found in the retina and with the extraretina location of melanopsin in nonmammalian vertebrates. PMID:24449866

  1. Segregating bodily isomerism or heterotaxy: potential echocardiographic correlations of morphological findings.

    PubMed

    Tremblay, Cornelia; Loomba, Rohit S; Frommelt, Peter C; Perrin, Donald; Spicer, Diane E; Backer, Carl; Anderson, Robert H

    2017-10-01

    Bodily isomerism, also referred to as heterotaxy, involves predominantly the thoracic organs, although other organs are usually abnormally positioned. Previously assessed on the basis of splenic anatomy, it is now understood that isomerism is better segregated on the basis of atrial appendage morphology. This allows for anticipation of associated findings. We aimed to assess the accuracy of segregation based on the morphology of the atrial appendages and other structures more easily identified by echocardiography. We reviewed postmortem specimens of hearts from the archives at four institutions categorised as obtained from patients with "heterotaxy". The cardiac structures were analysed using sequential segmental analysis. Non-cardiac structures were also examined if available. Statistical analyses were performed to compare differences in the settings of right as opposed to left isomerism. Specimens were available from 188 patients. Of these, 57 had left isomerism, and 131 had right isomerism. Atrial appendages were isomeric in all patients. A coronary sinus was found only in left isomerism, whereas a terminal crest, or a Eustachian valve, was found only in right isomerism. Interruption of the inferior caval vein was associated with left isomerism, whereas totally anomalous pulmonary venous connection was associated with right isomerism. Isomerism is uniformly segregated on the basis of the morphology of the atrial appendages, itself defined by the extent of the pectinate muscles. Other features such as the presence of a coronary sinus and systemic venous return can further help with such segregation of isomerism.

  2. Rotational bands and isomeric states in 175Lu

    SciTech Connect

    Garrett, P E; Archer, D E; Becker, J A; Bernstein, L A; Hauschild, K; Henry, E A; McNabb, D P; Stoyer, M A; Younes, W; Johns, G D; Nelson, R O; Wilburn, W S

    2003-10-15

    Rotational bands in {sup 175}Lu have been extended through investigation with the (n,n{prime}{gamma}) reaction. Spallation neutrons bombarded Lu samples, and the resulting {gamma} rays were detected in a large-scale Compton-suppressed Ge detector array. Prompt- and delayed-{gamma}{gamma} coincidences have been used to extend most of the existing known bands, and to tentatively assign a new band, based on the 7/2{sup -}[523] configuration, from its band head to spin 13/2. The 3-quasiparticle K{sup {pi}} = 19/2{sup +} isomer is confirmed and its half life determined to be 984 {+-} 13(stat.) {+-} 30(sys.) {micro}s, in agreement with previous results.

  3. Isomerization and decomposition of a Criegee intermediate in the ozonolysis of alkenes: dynamics using a multireference potential.

    PubMed

    Kalinowski, Jaroslaw; Räsänen, Markku; Heinonen, Petri; Kilpeläinen, Ilkka; Gerber, R Benny

    2014-01-03

    The isomerization and decomposition dynamics of the simplest Criegee intermediate CH2 OO have been studied by classical trajectory simulations using the multireference ab initio MR-PT2 potential on the fly. A new, accelerated algorithm for dynamics with MR-PT2 was used. For an initial temperature of 300 K, starting from the transition state from CH2 OO→CH2 O2  , the system reaches the dioxirane structure in around 50 fs, then isomerizes to formic acid (in ca. 2800 fs), and decomposes into CO+H2 O at around 2900 fs. The contributions of different configurations to the multiconfigurational total electronic wave function vary dramatically along the trajectory, with diradical contributions being important for transition states corresponding to H-atom transfers, while being only moderately significant for CH2 OO. The implications for reactions of Criegee intermediates are discussed.

  4. Well-defined transition metal hydrides in catalytic isomerizations.

    PubMed

    Larionov, Evgeny; Li, Houhua; Mazet, Clément

    2014-09-07

    This Feature Article intends to provide an overview of a variety of catalytic isomerization reactions that have been performed using well-defined transition metal hydride precatalysts. A particular emphasis is placed on the underlying mechanistic features of the transformations discussed. These have been categorized depending upon the nature of the substrate and in most cases discussed following a chronological order.

  5. cis- and trans-Stilbenes: Chromatographic Separation and Photochemical Isomerization.

    ERIC Educational Resources Information Center

    Levine, Samuel G.; And Others

    1988-01-01

    Describes an experiment that is to be performed midway in the first semester of an undergraduate organic chemistry laboratory coinciding with the students' introduction to cis-trans isomerism in the study of alkenes. Discusses the apparatus, materials, experimental procedure, historical significance, and results. (CW)

  6. cis- and trans-Stilbenes: Chromatographic Separation and Photochemical Isomerization.

    ERIC Educational Resources Information Center

    Levine, Samuel G.; And Others

    1988-01-01

    Describes an experiment that is to be performed midway in the first semester of an undergraduate organic chemistry laboratory coinciding with the students' introduction to cis-trans isomerism in the study of alkenes. Discusses the apparatus, materials, experimental procedure, historical significance, and results. (CW)

  7. Femtosecond Dynamics of Fundamental Reaction Processes in Liquids: Proton Transfer, Geminate Recombination, Isomerization and Vibrational Relaxation.

    NASA Astrophysics Data System (ADS)

    Schwartz, Benjamin Joel

    Femtosecond and picosecond transient absorption spectroscopy are used to probe several fundamental aspects of chemical reactivity in the condensed phase including proton transfer, germinate recombination, isomerization and vibrational relaxation. The fast excited state intramolecular proton transfer of 3-hydroxyflavone is measured for the first time, and the effects of external hydrogen-bonding interactions on the proton transfer are studied in detail. The proton transfer takes place in ~240 fsec in non-polar environments, but becomes faster than the instrumental resolution of 110 fsec in methanol solutions. A simple model is proposed to explain these results. The dynamics following photodissociation of CH _2I_2 and other small molecules provide the first direct observations of germinate recombination. The recombination of many different photodissociating species occurs on a ~350 fsec time scale. Results also show that recombination yields but not rates depend on the molecular details of the solvent environment and suggest that recombination kinetics are dominated by a single collision with the surrounding solvent cage. Studies of sterically locked phenyl-substituted butadienes offer new insights into the electronic structure and isomerization behavior of conjugated polyenes. The data show no simple correlation between the hinderance of specific large amplitude motions and signatures of isomerizative behavior such as viscosity dependent excited state lifetimes. This strongly implies that the isomerization of these systems does not provide a suitable testing ground for simple condensed phase reaction rate theories. The spectral dynamics of a photochromic spiropyran indicate that recombination, isomerization and vibrational relaxation all play important roles in the photoreactivity of complex molecules. The interplay of these microscopic phenomena and their effect on macroscopic properties such as photochromism are discussed. All the results indicate that the initial

  8. Conformational isomerization and collisional cooling dynamics of bis(2-hydroxyphenyl)methane.

    PubMed

    Pillsbury, Nathan R; Müller, Christian W; Zwier, Timothy S

    2009-04-30

    Stimulated emission pumping-population transfer spectroscopy (SEP-PTS) has been used to directly measure the energy threshold to isomerization between the two conformational isomers of bis(2-hydroxyphenyl)methane. These conformers have been shown in the preceding paper (DOI 10.1021/jp8098686) to be an OH...O H-bonded structure (conformer A) and a doubly OH() ...pi H-bonded conformer (conformer B). Lower and upper bounds on the energy threshold for A-->B isomerization are at 1344 and 1399 cm(-1), respectively, while the corresponding bounds on the B-->A isomerization are 1413 and 1467 cm(-1). The difference between these thresholds provides a measure of the relative energies of the two minima, with DeltaE(AB) = E(A) - E(B) = 14-123 cm(-1). The transition-state structure responsible for this energy threshold has been identified using DFT B3LYP, DFT M05-2X, and MP2 calculations, all with a 6-31+G* basis set. Only the DFT M05-2X calculations correctly reproduce both the energy ordering of the two minima and the magnitude of the barrier separating them. Below the energy threshold to isomerization, we have used the extensive Franck-Condon progressions present in the SEP spectrum of conformer A to undertake an SEP-PT study of its vibrational relaxation rate, as a function of internal energy over the 0-1200 cm(-1) region. The position of SEP excitation in the expansion was systematically varied in order to change the rate and number of cooling collisions that occur between SEP excitation and probe steps and the initial temperature at which SEP occurs. From this data set, three energy regimes were identified, each with a unique value of the average energy lost per collision with helium (region 1: 13 cm(-1)/collision for E = 300-1200 cm(-1), region 2: 0.6 cm(-1)/collision for E = 200-300 cm(-1), and region 3: 7 cm(-1)/collision for E < 200 cm(-1)). In region 1, the vibrational density of states is sufficient to support efficient loss of energy via Deltav = -1 collisions

  9. First spatial separation of a heavy ion isomeric beam with a multiple-reflection time-of-flight mass spectrometer

    NASA Astrophysics Data System (ADS)

    Dickel, T.; Plaß, W. R.; Ayet San Andres, S.; Ebert, J.; Geissel, H.; Haettner, E.; Hornung, C.; Miskun, I.; Pietri, S.; Purushothaman, S.; Reiter, M. P.; Rink, A.-K.; Scheidenberger, C.; Weick, H.; Dendooven, P.; Diwisch, M.; Greiner, F.; Heiße, F.; Knöbel, R.; Lippert, W.; Moore, I. D.; Pohjalainen, I.; Prochazka, A.; Ranjan, M.; Takechi, M.; Winfield, J. S.; Xu, X.

    2015-05-01

    211Po ions in the ground and isomeric states were produced via 238U projectile fragmentation at 1000 MeV/u. The 211Po ions were spatially separated in flight from the primary beam and other reaction products by the fragment separator FRS. The ions were energy-bunched, slowed-down and thermalized in a gas-filled cryogenic stopping cell (CSC). They were then extracted from the CSC and injected into a high-resolution multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS). The excitation energy of the isomer and, for the first time, the isomeric-to-ground state ratio were determined from the measured mass spectrum. In the subsequent experimental step, the isomers were spatially separated from the ions in the ground state by an ion deflector and finally collected with a silicon detector for decay spectroscopy. This pioneering experimental result opens up unique perspectives for isomer-resolved studies. With this versatile experimental method new isomers with half-lives longer than a few milliseconds can be discovered and their decay properties can be measured with highest sensitivity and selectivity. These experiments can be extended to studies with isomeric beams in nuclear reactions.

  10. Unveiling the mechanism of photoinduced isomerization of the photoactive yellow protein (PYP) chromophore

    SciTech Connect

    Gromov, Evgeniy V.

    2014-12-14

    A detailed theoretical analysis, based on extensive ab initio second-order approximate coupled cluster calculations, has been performed for the S{sub 1} potential energy surface (PES) of four photoactive yellow protein (PYP) chromophore derivatives that are hydrogen bonded with two water molecules and differ merely in the carbonyl substituent. The main focus is put on contrasting the isomerization properties of these four species in the S{sub 1} excited state, related to torsion around the chromophore's single and double carbon-carbon bonds. The analysis provides evidence of the different isomerization behavior of these four chromophore complexes, which relates to the difference in their carbonyl substituents. While a stable double-bond torsion pathway exists on the S{sub 1} PES of the chromophores bearing the –O–CH{sub 3} and –NH{sub 2} substituents, this is not the case for the –S–CH{sub 3} and –CH{sub 3} substituted species. The presence of the –S–CH{sub 3} group leads to a strong instability of the chromophore with respect to the single-bond twist, whereas in the case of the –CH{sub 3} substituent a crossing of the S{sub 1} and S{sub 2} PESs occurs, which perturbs the pathway. Based on this analysis, the key factors that support the double-bond torsion have been identified. These are (i) the hydrogen bonds at the phenolic oxygen of the chromophore, (ii) the weak electron-acceptor character of the carbonyl group, and (iii) the ethylene-like pattern of the torsion in the beginning of the process. Our results suggest that the interplay between these factors determines the chromophore's isomerization in the solvent environment and in the native PYP environment.

  11. Coherent control of the isomerization of retinal in bacteriorhodopsin in the high intensity regime

    SciTech Connect

    Prokhorenko, Valentyn I.; Halpin, Alexei; Johnson, Philip J. M.; Miller, R. J. Dwayne; Brown, Leonid S.

    2011-02-28

    Coherent control protocols provide a direct experimental determination of the relative importance of quantum interference or phase relationships of coupled states along a selected pathway. These effects are most readily observed in the high intensity regime where the field amplitude is sufficient to overcome decoherence effects. The coherent response of retinal photoisomerization in bacteriorhodopsin to the phase of the photoexcitation pulses was examined at fluences of 10{sup 15}- 2.5 x 10{sup 16} photons per square centimeter, comparable to or higher than the saturation excitation level of the S{sub 0}-S{sub 1} retinal electronic transition. At moderate excitation levels of {approx}6 x 10{sup 15} photons/cm{sup 2} (<100 GW/cm{sup 2}), chirping the excitation pulses increases the all-trans to 13-cis isomerization yield by up to 16% relative to transform limited pulses. The reported results extend previous weak-field studies [Prokhorenko et al., Science 313, 1257 (2006)] and further illustrate that quantum coherence effects persist along the reaction coordinate in strong fields even for systems as complex as biological molecules. However, for higher excitation levels of {approx}200 GW/cm{sup 2}, there is a dramatic change in photophysics that leads to multiphoton generated photoproducts unrelated to the target isomerization reaction channel and drastically changes the observed isomerization kinetics that appears, in particular, as a red shift of the transient spectra. These results explain the apparent contradictions of the work by Florean et al.[Proc. Natl. Acad. Sci. U.S.A. 106, 10896 (2009)] in the high intensity regime. We are able to show that the difference in observations and interpretation is due to artifacts associated with additional multiphoton-induced photoproducts. At the proper monitoring wavelengths, coherent control in the high intensity regime is clearly observable. The present work highlights the importance of conducting coherent control

  12. Coherent control of the isomerization of retinal in bacteriorhodopsin in the high intensity regime.

    PubMed

    Prokhorenko, Valentyn I; Halpin, Alexei; Johnson, Philip J M; Miller, R J Dwayne; Brown, Leonid S

    2011-02-28

    Coherent control protocols provide a direct experimental determination of the relative importance of quantum interference or phase relationships of coupled states along a selected pathway. These effects are most readily observed in the high intensity regime where the field amplitude is sufficient to overcome decoherence effects. The coherent response of retinal photoisomerization in bacteriorhodopsin to the phase of the photoexcitation pulses was examined at fluences of 10(15) - 2.5 × 10(16) photons per square centimeter, comparable to or higher than the saturation excitation level of the S(0) - S(1) retinal electronic transition. At moderate excitation levels of ∼6 × 10(15) photons/cm(2) (<100 GW/cm(2)), chirping the excitation pulses increases the all-trans to 13-cis isomerization yield by up to 16% relative to transform limited pulses. The reported results extend previous weak-field studies [Prokhorenko et al., Science 313, 1257 (2006)] and further illustrate that quantum coherence effects persist along the reaction coordinate in strong fields even for systems as complex as biological molecules. However, for higher excitation levels of ∼200 GW/cm(2), there is a dramatic change in photophysics that leads to multiphoton generated photoproducts unrelated to the target isomerization reaction channel and drastically changes the observed isomerization kinetics that appears, in particular, as a red shift of the transient spectra. These results explain the apparent contradictions of the work by Florean et al. [Proc. Natl. Acad. Sci. U.S.A. 106, 10896 (2009)] in the high intensity regime. We are able to show that the difference in observations and interpretation is due to artifacts associated with additional multiphoton-induced photoproducts. At the proper monitoring wavelengths, coherent control in the high intensity regime is clearly observable. The present work highlights the importance of conducting coherent control experiments in the low intensity regime

  13. Taple-top imaging of the non-adiabatically driven isomerization in the acetylene cation

    NASA Astrophysics Data System (ADS)

    Beaulieu, Samuel; Ibrahim, Heide; Wales, Benji; Schmidt, Bruno E.; Thiré, Nicolas; Bisson, Éric; Hebeisen, Christoph T.; Wanie, Vincent; Giguere, Mathieu; Kieffer, Jean-Claude; Sanderson, Joe; Schuurman, Michael S.; Légaré, François

    2014-05-01

    One of the primary goals of modern ultrafast science is to follow nuclear and electronic evolution of molecules as they undergo a photo-chemical reaction. Most of the interesting dynamics phenomena in molecules occur when an electronically excited state is populated. When the energy difference between electronic ground and excited states is large, Free Electron Laser (FEL) and HHG-based VUV sources were, up to date, the only light sources able to efficiently initiate those non-adiabatic dynamics. We have developed a simple table-top approach to initiate those rich dynamics via multiphoton absorption. As a proof of principle, we studied the ultrafast isomerization of the acetylene cation. We have chosen this model system for isomerization since the internal conversion mechanism which leads to proton migration is still under debate since decades. Using 266 nm multiphoton absorption as a pump and 800 nm induced Coulomb Explosion as a probe, we have shoot the first high-resolution molecular movie of the non-adiabatically driven proton migration in the acetylene cation. The experimental results are in excellent agreement with high level ab initio trajectory simulations.

  14. DFT study on the isomerization and tautomerism in vitamins B3 (niacin), B5 (pantothenic acid) and B7 (biotin)

    NASA Astrophysics Data System (ADS)

    Valadbeigi, Younes; Farrokhpour, Hossein; Tabrizchi, Mahmoud

    2014-05-01

    Isomerization and tautomerism of the three water soluble vitamins including B3, B5 and B7 were studied applying density functional theory using B3LYP method in gas and aqueous phases. Activation energies (Ea), Gibbs free energies of activation (ΔG#), and imaginary frequencies of the transition state structures were calculated for all the isomerization and tautomerism reactions. Activation energies of the neutral → zwitterion (amine-enamine) tautomerism in vitamin B3 were 310-360 kJ/mol where these values for the keto-enol tautomerism were 100-130 kJ/mol. It was found that water molecule catalyzes the tautomerism and decreases the activation energies about 90-160 kJ/mol.

  15. Isomerization reaction dynamics and equilibrium at the liquid-vapor interface of water. A molecular-dynamics study

    NASA Technical Reports Server (NTRS)

    Benjamin, Ilan; Pohorille, Andrew

    1993-01-01

    The gauche-trans isomerization reaction of 1,2-dichloroethane at the liquid-vapor interface of water is studied using molecular-dynamics computer simulations. The solvent bulk and surface effects on the torsional potential of mean force and on barrier recrossing dynamics are computed. The isomerization reaction involves a large change in the electric dipole moment, and as a result the trans/gauche ratio is considerably affected by the transition from the bulk solvent to the surface. Reactive flux correlation function calculations of the reaction rate reveal that deviation from the transition-state theory due to barrier recrossing is greater at the surface than in the bulk water. This suggests that the system exhibits non-Rice-Ramsperger-Kassel-Marcus behavior due to the weak solvent-solute coupling at the water liquid-vapor interface.

  16. Isomerization reaction dynamics and equilibrium at the liquid-vapor interface of water. A molecular-dynamics study

    NASA Technical Reports Server (NTRS)

    Benjamin, Ilan; Pohorille, Andrew

    1993-01-01

    The gauche-trans isomerization reaction of 1,2-dichloroethane at the liquid-vapor interface of water is studied using molecular-dynamics computer simulations. The solvent bulk and surface effects on the torsional potential of mean force and on barrier recrossing dynamics are computed. The isomerization reaction involves a large change in the electric dipole moment, and as a result the trans/gauche ratio is considerably affected by the transition from the bulk solvent to the surface. Reactive flux correlation function calculations of the reaction rate reveal that deviation from the transition-state theory due to barrier recrossing is greater at the surface than in the bulk water. This suggests that the system exhibits non-Rice-Ramsperger-Kassel-Marcus behavior due to the weak solvent-solute coupling at the water liquid-vapor interface.

  17. Femtosecond isomerization dynamics in the ethylene cation measured in an EUV-pump NIR-probe configuration

    SciTech Connect

    van Tilborg, Jeroen; Allison, Tom; Wright, Travis; Hertlein, Marc; Falcone, Roger; Liu, Yanwei; Merdji, Hamed; Belkacem, Ali

    2009-03-17

    Dynamics in the excited ethylene cation C{sub 2}H{sub 4}{sup +} lead to isomerization to the ethylidene configuration (HC-CH{sub 3}){sup +}, which is predicted to be a transient configuration for electronic relaxation. With an intense femtosecond EUV (extreme ultraviolet) pump pulse to populate the excited state, and an NIR (near infrared) probe pulse to produce the fragments CH{sup +} and CH{sub 3}{sup +} (which provides a direct signature of ethylidene), we measure optimum fragment yields at a probe delay of 80 fs. Also, an H{sub 2}-stretch transient configuration, yielding H{sub 2}{sup +} upon probing, is found to succeed the ethylidene configuration. We find that a simple single- or double-decay model does not match the data, and we present a modified model (introduction of an isomerization delay of 50 {+-} 25 fs) that does provide agreement.

  18. FAST TRACK COMMUNICATION: Femtosecond isomerization dynamics in the ethylene cation measured in an EUV-pump NIR-probe configuration

    NASA Astrophysics Data System (ADS)

    Tilborg, J. van; Allison, T. K.; Wright, T. W.; Hertlein, M. P.; Falcone, R. W.; Liu, Y.; Merdji, H.; Belkacem, A.

    2009-04-01

    Dynamics in the excited ethylene cation C2H+4 lead to isomerization to the ethylidene configuration (HC-CH3)+, which is predicted to be a transient configuration for electronic relaxation. With an intense femtosecond extreme ultraviolet pump pulse to populate the excited state, and a near infrared probe pulse to produce the fragments CH+ and CH+3 (which provides a direct signature of ethylidene), we measure optimum fragment yields at a probe delay of 80 fs. Also, an H2-stretch transient configuration, yielding H+2 upon probing, is found to succeed the ethylidene configuration. We find that a simple single- or double-decay model does not match the data, and we present a modified model (introduction of an isomerization delay of 50 ± 25 fs) that does provide agreement.

  19. Tryptophan-47 rotational isomerization in variant-3 scorpion neurotoxin. A combination thermodynamic perturbation and umbrella sampling study.

    PubMed Central

    Haydock, C; Sharp, J C; Prendergast, F G

    1990-01-01

    A combination thermodynamic perturbation and umbrella sampling study predicts two free energy wells for the rotational isomerization of the variant-3 scorpion neurotoxin tryptophan-47 indole side chain. One well has the indole side chain in the crystallographic orientation; the other has the indole rotated approximately 220 degrees to form a new conformation with a relative free energy of 3 +/- 2 kcal/mol. The activation barrier is 8.5 kcal/mol from the crystallographic well, from which transition state theory predicts a rate of escape of 2 x 10(5) s-1. Correlations in the displacements of side chains neighboring tryptophan-47 and the isomerization reaction coordinate last up to 20 ps. Favorable conditions of experimental verification are discussed. PMID:2393708

  20. New photo-isomerization path of indocyanine green in condensed phase investigated by two-pump excitation

    NASA Astrophysics Data System (ADS)

    Fuyuki, Masanori; Furuta, Koichi; Wada, Akihide

    2010-10-01

    In cyanine dye, a photo-isomerization path involving a multiphoton process was found in addition to a conventional reaction path with a one-photon process by two-pulse correlation of transient absorption and bleaching. That photo-isomerization was completed within 3 ns and its efficiency was dependent on the interval time between two pump pulses indicate that the new path involves a multiphoton process: S0 → S n → S m, where S n is ˜3.1 eV and S m is ˜4.7 eV higher than S0 and the lifetime of intermediate state in S n is approximately 0.2 ps. Changing the pump power controlled the branching ratio between the two paths.

  1. Thermally and vibrationally induced conformational isomerizations, infrared spectra, and photochemistry of gallic acid in low-temperature matrices

    NASA Astrophysics Data System (ADS)

    Justino, Licínia L. G.; Reva, Igor; Fausto, Rui

    2016-07-01

    Near-infrared (near-IR) narrowband selective vibrational excitation and annealing of gallic acid (3,4,5-trihydroxybenzoic acid) isolated in cryogenic matrices were used to induce interconversions between its most stable conformers. The isomerizations were probed by infrared spectroscopy. An extensive set of quantum chemical calculations, carried out at the DFT(B3LYP)/6-311++G(d,p) level of approximation, was used to undertake a detailed analysis of the ground state potential energy surface of the molecule. This investigation of the molecule conformational space allowed extracting mechanistic insights into the observed annealing- or near-IR-induced isomerization processes. The infrared spectra of the two most stable conformers of gallic acid in N2, Xe, and Ar matrices were fully assigned. Finally, the UV-induced photochemistry of the matrix isolated compound was investigated.

  2. Femtosecond dynamics of fundamental reaction processes in liquids: Proton transfer, geminate recombination, isomerization and vibrational relaxation. [Spiropyrans

    SciTech Connect

    Schwartz, B.J.

    1992-11-01

    The fast excited state intramolecular proton transfer of 3-hydroxyflavone is measured and effects of external hydrogen-bonding interactions on the proton transfer are studied. The proton transfer takes place in [approximately]240 fsec in nonpolar environments, but becomes faster than instrumental resolution of 110 fsec in methanol solution. The dynamics following photodissociation of CH[sub 2]I[sub 2] and other small molecules provide the first direct observations of geminate recombination. The recombination of many different photodissociating species occurs on a [approximately]350 fsec time scale. Results show that recombination yields but not rates depend on the solvent environment and suggest that recombination kinetics are dominated by a single collision with surrounding solvent cage. Studies of sterically locked phenyl-substituted butadienes offer new insights into the electronic structure and isomerization behavior of conjugated polyenes. Data show no simple correlation between hinderance of specific large amplitude motions and signatures of isomerizative behavior such as viscosity dependent excited state lifetimes, implying that the isomerization does not provide a suitable for simple condensed phase reaction rate theories. The spectral dynamics of a photochromic spiropyran indicate that recombination, isomerization and vibrational relaxation all play important roles in photoreactivity of complex molecules. The interplay of these microscopic phenomena and their effect on macroscopic properties such as photochromism are discussed. All the results indicate that the initial steps of the photochromic reaction process occur extremely rapidly. Laser system and computer codes for data analysis are discussed.

  3. The thermal Z-isomerization-induced change in solubility and physical properties of (all-E)-lycopene.

    PubMed

    Murakami, Kazuya; Honda, Masaki; Takemura, Ryota; Fukaya, Tetsuya; Kubota, Mitsuhiro; Wahyudiono; Kanda, Hideki; Goto, Motonobu

    2017-09-16

    The effect of Z-isomerization of (all-E)-lycopene on its solubility in organic solvents and physical properties was investigated. Lycopene samples containing different Z-isomer contents (23.8%, 46.9%, and 75.6% of total lycopene) were prepared from high-purity (all-E)-lycopene by thermal Z-isomerization in dichloromethane (CH2Cl2). As the Z-isomer content increased, the relative solubility of lycopene significantly improved. Although (all-E)-lycopene barely dissolved in ethanol (0.6 mg/L), the solubilities of lycopene containing 23.8%, 46.9%, and 75.6% Z-isomers were 484.5, 914.7, and 2401.7 mg/L, respectively. Furthermore, differential scanning calorimetry (DSC), powder X-ray diffraction (XRD), and scanning electron microscopy (SEM) analyses clearly indicated that (all-E)-lycopene was present in the crystal state, while Z-isomers of lycopene were present in amorphous states. A number of studies have suggested that Z-isomers of lycopene are better absorbed in the human body than the all-E-isomer. This may be due to the change in solubility and physical properties of lycopene by the Z-isomerization. Copyright © 2017 Elsevier Inc. All rights reserved.

  4. Identification of Tandem Mass Spectra of Mixtures of Isomeric Peptides

    PubMed Central

    Chen, Xi; Drogaris, Paul; Bern, Marshall

    2010-01-01

    Shotgun proteomics separates peptides by chromatography and precursor mass over charge, yet in almost any large data set of a complex sample there will be some tandem mass spectra containing more than one peptide. These mixture spectra contain two co-eluting peptides with close precursor mass over charge, and sometimes contain exact isomers, often the same peptide with the same modification in two different positions. Isomers present a problem when the position of the modification is of special interest, as in histone modification studies or “oxidative footprinting” studies of protein structure. Here we give algorithms for identifying isomeric mixtures, and present results on two different histones and four oxidative footprinting targets. Five of the six targets contain at least one peptide that appears in isomeric mixtures, but in none of the cases are mixtures so prevalent that they greatly impact the overall identification rate. PMID:20329787

  5. Catalytic Isomerization of Biomass-Derived Aldoses: A Review.

    PubMed

    Delidovich, Irina; Palkovits, Regina

    2016-03-21

    Selected aldohexoses (D-glucose, D-mannose, and D-galactose) and aldopentoses (D-xylose, L-arabinose, and D-ribose) are readily available components of biopolymers. Isomerization reactions of these substances are very attractive as carbon-efficient processes to broaden the portfolio of abundant monosaccharides. This review focuses on the chemocatalytic isomerization of aldoses into the corresponding ketoses as well as epimerization of aldoses at C2. Recent advances in the fields of catalysis by bases and Lewis acids are considered. The emphasis is laid on newly uncovered catalytic systems and mechanisms of carbohydrate transformations. © 2016 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

  6. Geometrical isomerization of fatty acids with sulfur as a catalyst

    SciTech Connect

    Grompone, M.A.; Tancredi, N.A. )

    1991-08-01

    This paper reports on the kinetics of the geometrical isomerization of oleic and palmitoleic acids, both contained in U.S.P. oleic acid that were studied. Sulfur powder was used as a catalyst. The methyl esters of fatty acids were analyzed by GLC with 15% OV-275 columns. The sulfur-catalyzed isomerization at 180 and 225{degrees} C proceeds via two consecutive mechanisms. The position of equilibrium is reached by the second mechanism. For this, at any particular initial concentration of sulfur, the pseudo- first-order rate dependence on substrate for a reversible reaction holds. The full rate has been shown to be proportional to the initial sulfur concentration taken to the 1.2 power. The rate constants at both temperatures and the activation energies were calculated.

  7. Complementing ultrafast shape recognition with an optical isomerism descriptor.

    PubMed

    Zhou, Ting; Lafleur, Karine; Caflisch, Amedeo

    2010-11-01

    We introduce the mixed product of three vectors spanning four molecular locations as a descriptor of optical isomerism. This descriptor is very efficient as it does not require molecular superposition, and is very robust in discriminating between a given isomer and its mirror image. In particular, conformational isomers that are mirror images of each other, as well as optical isomers have opposite sign of the descriptor value. For efficient database searches, the optical isomerism descriptor can be used to complement an available ultrafast shape recognition (USR) method based solely on distances, which is not able to distinguish enantiomers. By an extensive comparison of the USR-based similarity score with an approach based on Gaussian molecular volume overlap, the accuracy and completeness of the former are discussed.

  8. Isomerization of meta-xylene over offretite catalysts

    SciTech Connect

    Sastre, E.; Corma, A.; Perez-Pariente, J. ); Fajula, F.; Figueras, F. )

    1990-12-01

    The conversion of meta-xylene has been investigated over offretites with different levels of ion exchange. The ratio isomerization/disproportionation increases with the degree of exchange, most probably due to an increased accessibility of the reactant to the internal surface and to a higher number and strength of acid sites. The addition of a hydrogenation function, in H{sub 2} atmosphere, slightly increases the activity and decreases the deactivation as a function of time. The conversion of 1-3-dimethylcyclohexene-1 yields experimental evidence that a bifunctional path exists for the reaction in these conditions. The supposed intermediate olefin isomerizes and disproportionates faster than meta-xylene, but the ortho/para selectivity remains unchanged.

  9. Ultrafast spectroscopy and structural characterization of a photochromic isomerizing ruthenium bis-sulfoxide complex.

    PubMed

    King, Albert W; Malizia, Jason P; Engle, James T; Ziegler, Christopher J; Rack, Jeffrey J

    2014-12-21

    Irradiation of [Ru(bpy)2(bpSOp)](PF6)2 (where bpy is 2,2'-bipyridine and bpSOp is 1,3-bis(phenylsulfinyl)propane) results in the formation of two new isomers, namely the S,O- and O,O-bonded species. The crystal structure of the bis-thioether and bis-sulfoxide complexes are reported. NMR spectroscopy of the bis-thioether complex in solution is consistent with the molecular structure determined by diffraction methods. Further, NMR spectroscopy of the bis-sulfoxide complex reveals two conformers in solution, one that is consistent with the solid state structure and a second conformer showing distortion in the aliphatic portion of the chelate ring. Time-resolved visible absorption spectroscopy reveals isomerization time constants of 91 ps in dichloroethane (DCE) and 229 ps in propylene carbonate (PC). Aggregate isomerization quantum yields of 0.57 and 0.42 have been determined in DCE and in PC, respectively. The kinetics of the thermal reversion from the O,O- to S,O-bonded isomer are strongly solvent dependent, occurring with rates of 2.41 × 10(-3) and 4.39 × 10(-5) s(-1) in DCE, and 4.68 × 10(-4) and 9.79 × 10(-6) s(-1) in PC. The two kinetic components are assigned to the two isomers identified in solution.

  10. Schiff Base Switch II Precedes the Retinal Thermal Isomerization in the Photocycle of Bacteriorhodopsin

    PubMed Central

    Wang, Ting; Facciotti, Marc T.; Duan, Yong

    2013-01-01

    In bacteriorhodopsin, the order of molecular events that control the cytoplasmic or extracellular accessibility of the Schiff bases (SB) are not well understood. We use molecular dynamics simulations to study a process involved in the second accessibility switch of SB that occurs after its reprotonation in the N intermediate of the photocycle. We find that once protonated, the SB C15 = NZ bond switches from a cytoplasmic facing (13-cis, 15-anti) configuration to an extracellular facing (13-cis, 15-syn) configuration on the pico to nanosecond timescale. Significantly, rotation about the retinal’s C13 = C14 double bond is not observed. The dynamics of the isomeric state transitions of the protonated SB are strongly influenced by the surrounding charges and dielectric effects of other buried ions, particularly D96 and D212. Our simulations indicate that the thermal isomerization of retinal from 13-cis back to all-trans likely occurs independently from and after the SB C15 = NZ rotation in the N-to-O transition. PMID:23922839

  11. Schiff base switch II precedes the retinal thermal isomerization in the photocycle of bacteriorhodopsin.

    PubMed

    Wang, Ting; Facciotti, Marc T; Duan, Yong

    2013-01-01

    In bacteriorhodopsin, the order of molecular events that control the cytoplasmic or extracellular accessibility of the Schiff bases (SB) are not well understood. We use molecular dynamics simulations to study a process involved in the second accessibility switch of SB that occurs after its reprotonation in the N intermediate of the photocycle. We find that once protonated, the SB C15 = NZ bond switches from a cytoplasmic facing (13-cis, 15-anti) configuration to an extracellular facing (13-cis, 15-syn) configuration on the pico to nanosecond timescale. Significantly, rotation about the retinal's C13 = C14 double bond is not observed. The dynamics of the isomeric state transitions of the protonated SB are strongly influenced by the surrounding charges and dielectric effects of other buried ions, particularly D96 and D212. Our simulations indicate that the thermal isomerization of retinal from 13-cis back to all-trans likely occurs independently from and after the SB C15 = NZ rotation in the N-to-O transition.

  12. The isomerization barrier in cyanocyclobutadienes: an ab initio multireference average quadratic coupled cluster study.

    PubMed

    Eckert-Maksić, Mirjana; Lischka, Hans; Maksić, Zvonimir B; Vazdar, Mario

    2009-07-23

    The energy profiles of the isomerization of mono, di-, and tetracyano-substituted cyclobutadienes (CBDs) are computed at the multireference average quadratic coupled cluster/complete active space self-consistent field level of theory. It was found that the energy barrier heights for the automerization reaction are 2.6 (tetracyano-CBD), 5.1 (1,3-dicyano-CBD), and 6.4 (cyano-CBD) kcal mol(-1), implying that they are lowered relative to that in the parent CBD (6.4 kcal mol(-1)), the monosubstituted derivative being an exception. Since the free CBD shuttles between two equivalent structures even at low temperature of 10 K, it follows that bond-stretch isomerism does not take place in cyanocyclobutadienes. Instead, these compounds exhibit rapid fluxional interconversion at room temperature between two bond-stretch isomers by the double bond flipping mechanism. The reason behind the decrease in the barrier heights is identified as a slightly enhanced resonance effect at the saddle points separating two (equivalent) bond-stretch isomers, compared to that in the equilibrium structures, predominantly due to the diradical character of the former. It is also shown that the energy gap between the singlet ground state saddle point structure and the first triplet equilibrium geometry decreases upon multiple substitution by the cyano groups. The splitting of the S and T energy is small being within the range of 6.5-8.2 kcal mol(-1).

  13. Coupling between the retinal thermal isomerization and the Glu194 residue of bacteriorhodopsin.

    PubMed

    Lazarova, Tzvetana; Querol, Enric; Padrós, Esteve

    2009-01-01

    Glu194 is a residue located at the end of F helix on the extracellular side of the light-induced proton pump bacteriorhodopsin (BR). Currently, it is well recognized that Glu194 and Glu204 residues, along with water clusters, constitute the proton release group of BR. Here we report that the replacement of Glu194 for Gln affects not only the photocycle of the protein but also has tremendous effect on the all-trans to 13-cis thermal isomerization. We studied the pH dependence of the dark adaptation of the E194Q mutant and performed HPLC analysis of the isomer compositions of the light- and partially dark-adapted states of the mutant at several pH values. Our data confirmed that E194Q exhibits extremely slow dark adaptation over a wide range of pH. HPLC data showed that a significantly larger concentration of all-trans isomer was present in the samples of the E194Q mutant even after prolonged dark adaptation. After 14 days in the dark the 13-cis to all-trans ratio was 1:3 in the mutant, compared to 2:1 in the wild type. These data clearly indicate the involvement of Glu194 in control of the rate of all-trans to 13-cis thermal isomerization.

  14. A nuclear magnetic resonance study of three isomeric dinaphthothiophenes

    NASA Astrophysics Data System (ADS)

    Katritzky, Alan R.; Perumal, Subbu; Savage, G. Paul

    The 1H and 13C NMR spectra of three isomeric dinaphthothiophenes are recorded. Chemical shift assignments were made on the basis of substituent chemical shift (SCS) effect arguments, coupling considerations, proton—proton auto-correlated homonulcear (COSY) two-dimensional spectroscopy, and proton—carbon heteronuclear correlation (HETCOR) two-dimensional spectroscopy. Some previously published 1H chemical shifts and coupling constants are compared with our data and some divergences are noted.

  15. Photoinduced isomerization of lycopene and application to tomato cultivation.

    PubMed

    Heymann, Thomas; Raeke, Julia; Glomb, Marcus A

    2013-11-20

    The present study aimed to investigate if growth conditions have an impact on the isomeric composition of lycopene in tomatoes. First a model system for photoinduced isomerization was established. Tomato extracts were irradiated with a halogen lamp, whose wavelength spectrum is close to the spectrum of daylight and thus mimics field-grown cultivation. Different optical filters were interposed between lamp and samples to simulate greenhouse conditions. 5-cis-Lycopene was formed preferentially while the concentration of 7-cis-lycopene decreased in field-grown model systems. The change of isomerization in greenhouse model systems led to a significantly different ratio. Consequently 5-cis- and 7-cis-lycopene were identified as potent markers for the differentiation of various lighting conditions during cultivation. This result was verified in biological samples. Authentic field-grown tomatoes (var. Lycopersicon esculentum Mill. var. commune L. H. Bailey "Harzfeuer") showed a significantly higher content of 5-cis-lycopene 5.90 ± 0.45% compared to tomatoes of the same variety grown under electric lighting 4.11 ± 0.10%. Additionally, the ratio of 7-cis-lycopene was significantly lower under field-grown conditions.

  16. Industrial application of catalytic systems for n-heptane isomerization.

    PubMed

    Alemán-Vázquez, Laura Olivia; Cano-Domínguez, José Luis; Torres-García, Enelio; Villagómez-Ibarra, José Roberto

    2011-07-14

    The ideal gasoline must have a high pump octane number, in the 86 to 94 range, and a low environmental impact. Alkanes, as a family, have much lower photochemical reactivities than aromatics or olefins, but only the highly branched alkanes have adequate octane numbers. The purpose of this work is to examine the possibilities of extending the technological alternative of paraffin isomerization to heavier feedstocks (i.e., n-heptane) using non-conventional catalytic systems which have been previously proposed in the literature: a Pt/sulfated zirconia catalyst and a molybdenum sub-oxide catalyst. Under the experimental conditions at which these catalysts have been evaluated, the molybdenum sub-oxide catalyst maintains a good activity and selectivity to isomerization after 24 h, while the Pt/sulfated zirconia catalyst shows a higher dimethylpentanes/methylhexanes ratio, probably due to a lower operating temperature, but also a high formation of cracking products, and presents signs of deactivation after 8 h. Though much remains to be done, the performance of these catalysts indicates that there are good perspectives for their industrial application in the isomerization of n-heptane and heavier alkanes.

  17. Photochemical isomerization in solution. Photophysics of diphenyl butadiene

    NASA Astrophysics Data System (ADS)

    Velsko, Stephan P.; Fleming, Graham R.

    1982-04-01

    We have examined the radiative and nonradiative decay rates of diphenyl butadiene in hydrocarbon and polar solvents as a function of temperature and pressure. We demonstrate that the radiative rate constant has a small dependence on solvent polarizability, in contrast to what is observed for diphenylhexatriene. We make an explicit separation of the internal molecular barrier to isomerization and the barrier due to frictional forces in the solvent. The energy of the internal barrier to isomerization is less than the activation energy observed in solution, and depends on the polarizability and polarity of the solvent. In contrast to diphenylhexatriene, it decreases, in more polar solvents. We compare the viscosity dependence of the barrier crossing process with Kramers' theory, the recent kinetic theory result of Skinner and Wolynes [J. Chem. Phys. 69, 2143 (1978)], and the free volume theory of Gegiou, Muzkat, and Fischer, [J. Amer. Chem. Soc. 90, 12 (1968)]. Our data clearly show that the isomerization process is in the intermediate friction limit and we obtain experimental values for the parameters of the three theories. Over the viscosity region studied, Kramers' and Skinner and Wolynes' equations coincide exactly and do not reproduce the functional dependence of the radiationless rate pre-exponential factor as well as the free volume theory. We speculate that it may be necessary to consider the frequency dependence of medium viscosity.

  18. Interstellar isomeric species: Energy, stability and abundance relationship

    NASA Astrophysics Data System (ADS)

    Etim, Emmanuel E.; Arunan, Elangannan

    2016-12-01

    Accurate enthalpies of formation are reported for known and potential interstellar isomeric species using high-level ab initio quantum-chemical calculations. A total of 130 molecules comprising of 31 isomeric groups and 24 cyanide/isocyanide pairs with molecules ranging from 3 to 12 atoms have been considered. The results show an interesting relationship between energy, stability and abundance (ESA) existing among these molecules. Among the isomeric species, isomers with lower enthalpies of formation are more easily observed in the interstellar medium compared to their counterparts with higher enthalpies of formation. Available data in the literature confirm the high abundance of the most stable isomer over other isomers in the different groups considered. Potential for interstellar hydrogen bonding accounts for the few exceptions observed. Thus, in general, it suffices to say that the interstellar abundances of related species could be linked to their stabilities if other factors do not dominate. The immediate consequences of this relationship in addressing some of the whys and wherefores among interstellar molecules and in predicting some possible candidates for future astronomical observations are discussed.

  19. Resolving Isomeric Glycopeptide Glycoforms with Hydrophilic Interaction Chromatography (HILIC).

    PubMed

    Huang, Yining; Nie, Yongxin; Boyes, Barry; Orlando, Ron

    2016-09-01

    The ability to resolve glycans while attached to tryptic peptides would greatly facilitate glycoproteomics, as this would enable site-specific glycan characterization. Peptide/glycopeptide separations are typically performed using reversed-phase liquid chromatography (RPLC), where retention is driven by hydrophobic interaction. As the hydrophilic glycans do not interact significantly with the RPLC stationary phase, it is difficult to resolve glycopeptides that differ only in their glycan structure, even when these differences are large. Alternatively, glycans interact extensively with the stationary phases used in hydrophilic interaction chromatography (HILIC), and consequently, differences in glycan structure have profound chromatographic shifts in this chromatographic mode. Here, we evaluate HILIC for the separation of isomeric glycopeptide mixtures that have the same peptide backbone but isomeric glycans. Hydrophilic functional groups on both the peptide and the glycan interact with the HILIC stationary phase, and thus, changes to either of these moieties can alter the chromatographic behavior of a glycopeptide. The interactive processes permit glycopeptides to be resolved from each other based on differences in their amino acid sequences and/or their attached glycans. The separations of glycans in HILIC are sufficient to permit resolution of isomeric N-glycan structures, such as sialylated N-glycan isomers differing in α2-3 and α2-6 linkages, while these glycans remain attached to peptides.

  20. Resolving Isomeric Glycopeptide Glycoforms with Hydrophilic Interaction Chromatography (HILIC)

    PubMed Central

    Huang, Yining; Nie, Yongxin; Boyes, Barry

    2016-01-01

    The ability to resolve glycans while attached to tryptic peptides would greatly facilitate glycoproteomics, as this would enable site-specific glycan characterization. Peptide/glycopeptide separations are typically performed using reversed-phase liquid chromatography (RPLC), where retention is driven by hydrophobic interaction. As the hydrophilic glycans do not interact significantly with the RPLC stationary phase, it is difficult to resolve glycopeptides that differ only in their glycan structure, even when these differences are large. Alternatively, glycans interact extensively with the stationary phases used in hydrophilic interaction chromatography (HILIC), and consequently, differences in glycan structure have profound chromatographic shifts in this chromatographic mode. Here, we evaluate HILIC for the separation of isomeric glycopeptide mixtures that have the same peptide backbone but isomeric glycans. Hydrophilic functional groups on both the peptide and the glycan interact with the HILIC stationary phase, and thus, changes to either of these moieties can alter the chromatographic behavior of a glycopeptide. The interactive processes permit glycopeptides to be resolved from each other based on differences in their amino acid sequences and/or their attached glycans. The separations of glycans in HILIC are sufficient to permit resolution of isomeric N-glycan structures, such as sialylated N-glycan isomers differing in α2-3 and α2-6 linkages, while these glycans remain attached to peptides. PMID:27582638

  1. Volume-conserving trans-cis isomerization pathways in photoactive yellow protein visualized by picosecond X-ray crystallography

    SciTech Connect

    Jung, Yang Ouk; Lee, Jae Hyuk; Kim, Joonghan; Schmidt, Marius; Moffat, Keith; Šrajer, Vukica; Ihee, Hyotcherl

    2013-02-03

    Trans-to-cis isomerization, the key reaction in photoactive proteins, usually cannot occur through the standard one-bond-flip mechanism. Owing to spatial constraints imposed by a protein environment, isomerization probably proceeds through a volume-conserving mechanism in which highly choreographed atomic motions are expected, the details of which have not yet been observed directly. Here we employ time-resolved X-ray crystallography to visualize structurally the isomerization of the p-coumaric acid chromophore in photoactive yellow protein with a time resolution of 100 ps and a spatial resolution of 1.6 Å. The structure of the earliest intermediate (IT) resembles a highly strained transition state in which the torsion angle is located halfway between the trans- and cis-isomers. The reaction trajectory of IT bifurcates into two structurally distinct cis intermediates via hula-twist and bicycle-pedal pathways. The bifurcating reaction pathways can be controlled by weakening the hydrogen bond between the chromophore and an adjacent residue through E46Q mutation, which switches off the bicycle-pedal pathway.

  2. Light-induced geometric isomerization of 1,2-diphenylcyclopropanes included within Y zeolites: role of cation-guest binding.

    PubMed

    Kaanumalle, Lakshmi S; Sivaguru, J; Sunoj, R B; Lakshminarasimhan, P H; Chandrasekhar, J; Ramamurthy, V

    2002-12-13

    Through a systematic study of several diphenylcyclopropane derivatives, we have inferred that the cations present within a zeolite control the excited-state chemistry of these systems. In the parent 1,2-diphenylcylopropane, the cation binds to the two phenyl rings in a sandwich-type arrangement, and such a mode of binding prevents cis-to-trans isomerization. Once an ester or amide group is introduced into the system (derivatives of 2beta,3beta-diphenylcyclopropane-1alpha-carboxylic acid), the cation binds to the carbonyl group present in these chromophores and such a binding has no influence on the cis-trans isomerization process. Cation-reactant structures computed at density functional theory level have been very valuable in rationalizing the observed photochemical behavior of diphenylcyclopropane derivatives included in zeolites. While the parent system, 1,2-diphenylcylopropane, has been extensively investigated in the context of chiral induction in solution, owing to its failure to isomerize from cis to trans, the same could not be investigated in zeolites. However, esters of 2beta,3beta-diphenylcyclopropane-1alpha-carboxylic acid could be studied within zeolites in the context of chiral induction. Chiral induction as high 20% ee and 55% de has been obtained with selected systems. These numbers, although low, are much higher than what has been obtained in solution with the same system or with the parent system by other investigators (maximum approximately 10% ee).

  3. Volume-conserving trans-cis isomerization pathways in photoactive yellow protein visualized by picosecond X-ray crystallography

    PubMed Central

    Jung, Yang Ouk; Lee, Jae Hyuk; Kim, Joonghan; Schmidt, Marius; Moffat, Keith; Šrajer, Vukica; Ihee, Hyotcherl

    2013-01-01

    Trans-to-cis isomerization, the key reaction in photoactive proteins, cannot usually occur through the standard one-bond-flip mechanism. Due to spatial constraints imposed by a protein environment, isomerization is likely to proceed via a “volume-conserving” mechanism in which highly-choreographed atomic motions are expected, the details of which have not yet been directly observed. Here we employ time-resolved X-ray crystallography to structurally visualize isomerization of the p-coumaric acid chromophore in photoactive yellow protein with 100 picosecond time resolution and 1.6 Å spatial resolution. The structure of the earliest intermediate (IT) resembles a highly-strained transition state in which the torsion angle is located halfway between the trans and cis isomers. The reaction trajectory of IT bifurcates into two structurally distinct cis intermediates via hula-twist and bicycle-pedal pathways. The bifurcating reaction pathways can be controlled by weakening the hydrogen bond between the chromophore and an adjacent residue via E46Q mutation, which switches off the bicycle-pedal pathway. PMID:23422563

  4. Elevation of the Energy Threshold for Isomerization of 5-Hydroxyindole-(tert-butyl alcohol)1 Cluster Cations.

    PubMed

    Ikeda, Takamasa; Sakota, Kenji; Sekiya, Hiroshi

    2017-08-10

    Isomerization between two hydrogen-bonded (H-bonded) isomers of 5-hydroxyindole-(tert-butyl alcohol)1 cluster cations ([5HI-(t-BuOH)1](+)) was investigated in the gas phase. In the S0 state, jet-cooled 5HI-(t-BuOH)1 has two structural isomers, 5HI(OH)-(t-BuOH)1 and 5HI(NH)-(t-BuOH)1, in which the t-BuOH molecule is bound to the OH or the NH group of 5HI. The IR photodissociation spectrum of [5HI-(t-BuOH)1](+) generated by two-color resonant two-photon ionization (2C-R2PI) via the S1-S0 origin of 5HI(NH)-(t-BuOH)1 provided evidence of both [5HI(OH)-(t-BuOH)1](+) and [5HI(NH)-(t-BuOH)1](+) coexisting in the D0 state, indicating that [5HI(NH)-(t-BuOH)1](+) isomerizes to [5HI(OH)-(t-BuOH)1](+) after 2C-R2PI of 5HI(NH)-(t-BuOH)1. The lower limit of the energy threshold for the isomerization of [5HI(NH)-(t-BuOH)1](+) to [5HI(OH)-(t-BuOH)1](+) was experimentally determined to be 3362 ± 30 cm(-1), and the corresponding energy threshold for the isomerization of [5HI(NH)-(H2O)1](+) to [5HI(OH)-(H2O)1](+) has been reported to be 2127 ± 30 cm(-1). Thus, the energy threshold for the isomerization is elevated by at least 1200 cm(-1) when the solvent molecule changes from H2O to t-BuOH. The elevation of the energy threshold is explained by the difference in the stabilization energies of [5HI-(t-BuOH)1](+) and [5HI-(H2O)1](+) in the initial and transition states owing to the larger proton affinity of t-BuOH than H2O.

  5. Using torsional forces to explain the gradient temperature Raman spectra of endosulfan isomers and its irreversible isomerization

    NASA Astrophysics Data System (ADS)

    Schmidt, Walter F.; Hapeman, Cathleen J.; McConnell, Laura L.; Rice, Clifford P.; Broadhurst, C. Leigh; Nguyen, Julie K.; Qin, Jianwei; Chao, Kuanglin; Kim, Moon S.; Shelton, Daniel R.

    2017-07-01

    Since the 1950's, the broad-spectrum, organochlorine insecticide endosulfan (6,7,8, 9,10,10-hexachloro-1,5,5a,6,9,9a-hexahydro-6,9-methano-2,4,3-benzodioxathiepine-3-oxide) has been used on numerous crops. Due to its persistence, bioaccumulation, long-range transport, and adverse effects to human health and ecosystems, it was officially identified as a persistent organic pollutant (POP) in 2011. The last uses in the United States were phased out in 2016. Endosulfan consists of two diastereomers, α-endosulfan and β-endosulfan, and while the α-isomer exists as two asymmetrical, twist-chair enantiomers which interchange, the β-isomer is a symmetrical-chair conformation. In addition, the β-isomer was found to isomerize to the α-isomer. Gradient Temperature Raman Spectroscopy (GTRS) enables identification the molecular sites at which bending vibrational modes becomes twisting or wagging vibrational modes. Previous studies using GTRS and chemical calculations afforded evidence for specific bond movements and the irreversibility of the isomerization mechanism. However, not all of the vibrational modes observed in the spectra could be explained. Thus, new analyses of the GTRS data were conducted to examine the effects of torsional forces on the bond movement, which allowed for the identification of all the peaks. These newly-identified torsional forces provide further confirmation of the isomerization mechanism and its irreversibility. Finally, this isomerization explains why β-endosulfan is rarely detected in the atmosphere.

  6. Systematics of isomeric configurations in N=77 odd-Z isotones near the proton drip line

    NASA Astrophysics Data System (ADS)

    Tantawy, M. N.; Bingham, C. R.; Rykaczewski, K. P.; Batchelder, J. C.; Królas, W.; Danchev, M.; Fong, D.; Ginter, T. N.; Gross, C. J.; Grzywacz, R.; Hagino, K.; Hamilton, J. H.; Hartley, D. J.; Karny, M.; Li, K.; Mazzocchi, C.; Piechaczek, A.; Ramayya, A. V.; Rykaczewski, K.; Shapira, D.; Stolz, A.; Winger, J. A.; Yu, C.-H.; Zganjar, E. F.

    2006-02-01

    The systematics of the πh11/2⊗νh11/2 and πh11/2⊗νs1/2 isomeric configurations was studied for the odd-Z N=77 isotones near the proton drip line. The isomeric decays in 140Eu, 142Tb, 144Ho, and 146Tm were measured by means of x-ray, γ-ray, and charged particle spectroscopy at the Recoil Mass Spectrometer at the Holifield Radioactive Ion Beam Facility (ORNL). The spin and parity of Iπ=8+ and 5- were deduced for the isomers in 140Eu and 142Tb. New decay schemes were established, and the half-lives of the 8+ isomers were measured to be 302(4) ns for 140m2Eu and 25(1) μs for 142m2Tb. No evidence for the expected 1+ ground-state was found in the 144Ho decay data. The proton-emission from 146Tm was restudied. Five proton transitions were assigned to two proton-emitting states. The half-lives of 198(3) ms and 68(3) ms and the spin and parity values of Iπ=10+ and 5- were established for 146mTm and 146gsTm, respectively. For the first time for an odd-odd nucleus, the interpretation of the observed decay properties and structure of the proton-emitting states was made by accounting for deformation and proton and neutron coupling to the core excitations. A complex wave-function structure was obtained, with dominating components of πh11/2⊗νh11/2 for the 10+ isomer and πh11/2⊗νs1/2 for the 5- ground state.

  7. Shape-Asymmetry Supramolecular Isomerism in Asymmetrical Ligand PCPs and the Expression Method of Three-Level Isomerism.

    PubMed

    Gao, Xiaonan; Fu, Ai-Yun; Wang, Yao-Yu

    2016-05-02

    We show here the supramolecular isomerism, with respect to shape-asymmetry of ligand and the new hierarchical classification for supramolecular isomerism, the three-level isomerism, which was advanced based on a thorough investigation for the four new Ni/dpt24 polymorphs [Hdpt24 = 3-(2-pyridyl)-5-(4-pyridyl)-1,2,4-triazole)]. Compounds 1, 2, and 3 are three-dimensional twofold interpenetrated porous coordination polymers with NbO topology, while 4 with two-dimensional grid structure is termed as the primary isomer of 1/2/3 due to the difference of dimensionality. Complex 3 possessing different shape-asymmetry of single networks from 1 and 2, is called as the secondary isomer of 1 and 2. Complexes 1 and 2 possess the same topology, single shape-asymmetry networks, but different interpenetration-orientation and interpenetration-asymmetry, and are defined as the tertiary isomers. Distinct differences in H2 and CO2 adsorption capacity were observed among each level of isomers. In addition, the hierarchical classification's relationship with characteristic classifications has been discussed.

  8. Refolding additive, dimethylbenzylammonium propane sulfonate (NDSB- 256), accelerates gly-pro cis-trans isomerization.

    PubMed

    Wang, Haimei; Hosoda, Kazuo; Terawaki, Shin-Ichi; Wakamatsu, Kaori

    2014-01-01

    Proline cis-trans isomerization plays a key role in the rate-determining steps of protein folding, and many different peptide-proline cis-trans isomerases (PPIases) catalyze this reaction. The acceleration of isomerization would be beneficial for in vitro refolding of protein preparations for industrial and research purposes. So we analyzed whether low-molecular-weight compounds that have been reported to enhance protein refolding have the activity to accelerate the isomerization. To evaluate the effects of chemicals on the isomerization rate, we set up a new NMR (EXSY) method that is invulnerable to their inhibitory activity, if any, and to their large NMR signals. With this method, we found that dimethylbenzylammonium propane sulfonate (NDSB-256) increase the isomerization rate in a concentration-dependent manner for the first time. Acceleration by imidazole (suggested but not experimentally confirmed) was also demonstrated. Arginine, a most popular refolding additive, did not show any significant effects on the isomerization reaction as expected.

  9. Direct measurement of the isomerization barrier of the isolated retinal chromophore.

    PubMed

    Dilger, Jonathan; Musbat, Lihi; Sheves, Mordechai; Bochenkova, Anastasia V; Clemmer, David E; Toker, Yoni

    2015-04-13

    Isomerizations of the retinal chromophore were investigated using the IMS-IMS technique. Four different structural features of the chromophore were observed, isolated, excited collisionally, and the resulting isomer and fragment distributions were measured. By establishing the threshold activation voltages for isomerization for each of the reaction pathways, and by measuring the threshold activation voltage for fragmentation, the relative energies of the isomers as well as the energy barriers for isomerization were determined. The energy barrier for a single cis-trans isomerization is (0.64±0.05) eV, which is significantly lower than that observed for the reaction within opsin proteins.

  10. Characteristics of Hospitalizations for the Glenn Procedure in Those With Isomerism Compared to Those Without.

    PubMed

    Loomba, Rohit S; Kouretas, Peter C; Anderson, Robert H

    2016-12-01

    Isomerism, also known as heterotaxy, is a unique clinical entity in which there are mirror imaged findings in the thoracic. In the abdomen, the arrangement of organs can be random. The anatomic findings also have functional consequences. Isomerism has been known to increase morbidity and mortality in those with functionally univentricular hearts. The aim of this study was to determine the impact of isomerism on the Glenn hospitalization. Data from the 1997 to 2012 Kids' Inpatient Database were utilized for this cross-sectional study. Admissions during which a Glenn procedure was done were identified. Next, these admissions were separated into those with and without isomerism. Admission characteristics were then compared in a univariate fashion as well as by regression analysis. Length of hospitalization, cost of hospitalization, extracorporeal membrane oxygenation, and inpatient mortality were the outcomes of interest. A total of 4959 admissions with a Glenn procedure were identified. Of these, 450 were associated with isomerism. The median age at which the Glenn procedure was done was 10 and 13 months in those without and with isomerism, respectively. Neither univariate nor regression analysis demonstrated any significant difference in length of hospitalization, cost of hospitalization, need for extracorporeal membrane oxygenation, and inpatient mortality between those with and without isomerism. Isomerism does not impact the characteristics of the Glenn hospitalization. Those with isomerism did tend to be older when they underwent the Glenn procedure.

  11. Total Isomerization Process - A flexible alternative for meeting the lead phase-down

    SciTech Connect

    Holcombe, T.C.; Mackler, S.E.; Sager, T.C.

    1985-01-01

    The EPA has recently decided to reduce the maximum lead in gasoline to 0.1 gram per gallon by January 1, 1986. One of the most economical means of adding back the lost octane is to isomerize light straight run naphtha (LSR). Union Carbide Corporation's Total Isomerization Process (TIP) offers a quick, low-cost highly flexible approach to isomerization. During the past 15 years, refiners around the world have discovered numerous ways to adapt the rugged, halide-free TIP technologies to their particular needs. These many applications have permitted refining companies to install isomerization both quickly and inexpensively.

  12. Substituent effect in the photochromism of two isomeric asymmetric diarylethenes having pyrrole and thiophene units

    NASA Astrophysics Data System (ADS)

    Wang, Renjie; Zhang, Xiaoxia; Pu, Shouzhi; Liu, Gang; Dai, Yanfeng

    2017-02-01

    Two new asymmetric isomeric diarylethenes having pyrrole and thiophene units have been synthesized by one-pot reaction and characterized by single crystal X-ray diffraction analysis. The two prepared diarylethenes had disparate crystal structures, and they exhibited distinctly different photochromic behavior, both in solution and in the solid state. Their photochromism, fatigue resistance, and fluorescence were investigated systematically. The methyl group at the reactive carbon atom could significantly enhance the quantum yield of cyclization step and decrease the quantum yield of cycloreversion step, whereas a cyano group at the same position could notably suppress the photocyclization reaction and promote the photocycloreversion reaction. The results indicated that the substituent at the reactive carbon atom could readily modulate the optoelectronic and physical properties for these diarylethenes.

  13. Kinetic barriers in the isomerization of substituted ureas: implications for computer-aided drug design

    NASA Astrophysics Data System (ADS)

    Loeffler, Johannes R.; Ehmki, Emanuel S. R.; Fuchs, Julian E.; Liedl, Klaus R.

    2016-05-01

    Urea derivatives are ubiquitously found in many chemical disciplines. N, N'-substituted ureas may show different conformational preferences depending on their substitution pattern. The high energetic barrier for isomerization of the cis and trans state poses additional challenges on computational simulation techniques aiming at a reproduction of the biological properties of urea derivatives. Herein, we investigate energetics of urea conformations and their interconversion using a broad spectrum of methodologies ranging from data mining, via quantum chemistry to molecular dynamics simulation and free energy calculations. We find that the inversion of urea conformations is inherently slow and beyond the time scale of typical simulation protocols. Therefore, extra care needs to be taken by computational chemists to work with appropriate model systems. We find that both knowledge-driven approaches as well as physics-based methods may guide molecular modelers towards accurate starting structures for expensive calculations to ensure that conformations of urea derivatives are modeled as adequately as possible.

  14. Carotene Degradation and Isomerization during Thermal Processing: A Review on the Kinetic Aspects.

    PubMed

    Colle, Ines J P; Lemmens, Lien; Knockaert, Griet; Van Loey, Ann; Hendrickx, Marc

    2016-08-17

    Kinetic models are important tools for process design and optimization to balance desired and undesired reactions taking place in complex food systems during food processing and preservation. This review covers the state of the art on kinetic models available to describe heat-induced conversion of carotenoids, in particular lycopene and β-carotene. First, relevant properties of these carotenoids are discussed. Second, some general aspects of kinetic modeling are introduced, including both empirical single-response modeling and mechanism-based multi-response modeling. The merits of multi-response modeling to simultaneously describe carotene degradation and isomerization are demonstrated. The future challenge in this research field lies in the extension of the current multi-response models to better approach the real reaction pathway and in the integration of kinetic models with mass transfer models in case of reaction in multi-phase food systems.

  15. Effects of PAH isomerizations on mutagenicity of combustion products

    SciTech Connect

    Howard, J.B.; Longwell, J.P.; Marr, J.A.; Pope, C.J.; Busby, W.F. Jr.; Lafleur, A.L.; Taghizadeh, K.

    1995-05-01

    Most of the mutagenicity of mixtures of polycyclic aromatic hydrocarbons (PAH) mixtures found in combustion exhaust gases is contributed by a relatively small number of the many PAH present. Since PAB mutagenicity is structure and hence isomer sensitive. changes in the distribution of isomers can change the mutagenicity of the mixture. Whether isomerization reactions in combustion play a significant role in determining the distributions of PAH isomers and the mutagenicity of product mixtures is assessed here for the following pairs of isomers: (1) fluoranthene-pyrene; (2) fluoranthene-acephenanthrylene; (3) cyclopental[cd]pyrene-benzol[ghi]fluoranthene; and (4) benzol[k]fluoranthene-benzo[a]pyrene. Concentration ratios of the isomer pairs were measured in ethylene combustion with naphthalene injection using a plug flow reactor at equivalence ratios of 1.2 and 2.2 and temperatures of 1520, 1620, and 1705 K, and compared with equilibrium ratios based on proper-ties computed from molecular mechanics and semiempirical quantum mechanical programs. Bacterial mutagenicity was measured by a forward mutation assay using Salmonella in the presence of rat liver supernatant, and found to vary significantly among the above compounds. The measured concentration ratios for isomer pairs (2) and (3) are near the equilibrium values and becoming more so as temperature increases, but the measured ratios for isomer pairs (1) and (4) are far from the equilibrium values at all the temperatures. From kinetics estimations, the characteristic isomerization time for isomer pairs (2) and (3) at 1705 K and perhaps at 1620 K is less than the experimental residence times, while the only isomerization mechanisms envisioned for isomer pairs (1) and (4) would not be kinetically viable at these temperatures.

  16. Competing intermolecular interactions in some 'bridge-flipped' isomeric phenylhydrazones.

    PubMed

    Ojala, William H; Arola, Trina M; Brigino, Ann M; Leavell, Jeremy D; Ojala, Charles R

    2012-07-01

    To examine the roles of competing intermolecular interactions in differentiating the molecular packing arrangements of some isomeric phenylhydrazones from each other, the crystal structures of five nitrile-halogen substituted phenylhydrazones and two nitro-halogen substituted phenylhydrazones have been determined and are described here: (E)-4-cyanobenzaldehyde 4-chlorophenylhydrazone, C(14)H(10)ClN(3), (Ia); (E)-4-cyanobenzaldehyde 4-bromophenylhydrazone, C(14)H(10)BrN(3), (Ib); (E)-4-cyanobenzaldehyde 4-iodophenylhydrazone, C(14)H(10)IN(3), (Ic); (E)-4-bromobenzaldehyde 4-cyanophenylhydrazone, C(14)H(10)BrN(3), (IIb); (E)-4-iodobenzaldehyde 4-cyanophenylhydrazone, C(14)H(10)IN(3), (IIc); (E)-4-chlorobenzaldehyde 4-nitrophenylhydrazone, C(13)H(10)ClN(3)O(2), (III); and (E)-4-nitrobenzaldehyde 4-chlorophenylhydrazone, C(13)H(10)ClN(3)O(2), (IV). Both (Ia) and (Ib) are disordered (less than 7% of the molecules have the minor orientation in each structure). Pairs (Ia)/(Ib) and (IIb)/(IIc), related by a halogen exchange, are isomorphous, but none of the 'bridge-flipped' isomeric pairs, viz. (Ib)/(IIb), (Ic)/(IIc) or (III)/(IV), is isomorphous. In the nitrile-halogen structures (Ia)-(Ic) and (IIb)-(IIc), only the bridge N-H group and not the bridge C-H group acts as a hydrogen-bond donor to the nitrile group, but in the nitro-halogen structures (III) (with Z' = 2) and (IV), both the bridge N-H group and the bridge C-H group interact with the nitro group as hydrogen-bond donors, albeit via different motifs. The occurrence here of the bridge C-H contact with a hydrogen-bond acceptor suggests the possibility that other pairs of `bridge-flipped' isomeric phenylhydrazones may prove to be isomorphous, regardless of the change from isomer to isomer in the position of the N-H group within the bridge.

  17. How is the anionic tetrahedral intermediate involved in the isomerization of aspartyl peptides to iso-aspartyl ones? A DFT study on the tetra-peptide.

    PubMed

    Yamabe, Shinichi; Guan, Wei; Sakaki, Shigeyoshi

    2012-10-21

    An isomerization reaction of a tetra-peptide, Ac-Gly-Asp-Gly-Gly-NHMe → Ac-Gly-isoAsp-Gly-Gly-NHMe, was investigated by DFT calculations. Thirteen water molecules were added to the peptide for simulating proton transfers during the isomerization. As a starting analysis, the number (m) of water molecules participating in ready proton transfers was examined by the use of a small model system, H(3)C-NH-C(=O)-CH(2)-CH(2)-COOH and (H(2)O)(m). The m = 2 stepwise path was found to be of the smallest activation free energy. On the basis of this result, the first isomerization path of the tetra-peptide was obtained with four elementary processes. The m = 2 proton-transfer pattern is involved in them. A different proton transfer gives the second isomerization path with six elementary processes. The second path (with ionization) is more likely than the first one (without ionization). Formation of the five membered rings of the aminosuccinimidyl-residue and anionic tetrahedral intermediates enhances the encapsulation of H(3)O(+) through the wound tetra-peptide ring. The role of the hydrogen bonds on the encapsulation was discussed in terms of the optimized geometries of proton-transfer transition states and intermediates.

  18. Activation cross sections and isomeric ratios in reactions induced by 14.5 MeV neutrons on152Sm,154Sm and178Hf

    NASA Astrophysics Data System (ADS)

    Kirov, A.; Nenoff, N.; Georgieva, E.; Necheva, C.; Ephtimov, I.

    1993-09-01

    Cross sections for the reactions152Sm( n, p)152 g,m1, m2 Pm,154Sm( n, p)154 g,m Pm,178Hf( n, p)178 m,g Lu,154Sm( n, d)153Pm and152Sm( n, α)149Nd were measured at 14.5 MeV neutron energy by the activation method. On the basis of these cross sections, the associated isomeric ratios in154Pm,152Pm,178Lu and the comparison with the predictions of different compound and precompound models, conclusions are drawn about the role of the preequilibrium processes in 14.5 MeV neutron induced reactions. Calculations for equal angular momentum removal by equilibrium and preequilibrium emitted particles better reproduced the experimental isomeric ratios, than for higher angular momentum removal in the preequilibrium phase. The isomeric ratios may be used as a source of additional information about the spin of the isomeric states in152Pm and154Pm for which the spectroscopic information is uncertain.

  19. The trans-cis and the azide-tetrazole ring-chain isomerization of 2-azido-1,3-azoles: Quantum chemical study

    NASA Astrophysics Data System (ADS)

    Karakus, Nihat; Demirel, Merdan

    2015-08-01

    Quantum chemical calculations using Density Functional Theory (DFT) at the B3LYP/6-31++G(d,p) basis set level were performed to investigate the azide group rotation from the trans to the cis isomer and the azido-tetrazole ring-chain isomerism equilibrium of 2-azido-1,3-azoles in the gas phase, carbon tetrachloride (CCl4), acetonitrile (CH3CN) and water (H2O). The solvent effect on the relative stabilities of each species was analyzed within the self-consistent field theory using the Polarized Continuum Model (PCM). The transition states (TSs) of each step was identified and confirmed. The azido-tetrazole ring-chain isomerism equilibrium was investigated in detail. In addition, the electronic characteristics of each species were analyzed by means of Molecular Electrostatic Potential (MEP) and Natural Bond Orbital (NBO) analyses. The relative energies were increased with the increasing electronegativity of X atom in the 1,3-azole ring. The study confirmed that the relative stability of the tetrazole isomers could be maximized to a great extent by increasing the polarity of solvent, and vice versa for the azido isomers. The low rotational barrier of the azido group in the trans ⇋ cis isomerization and the significant increase of the dipole moment of the tetrazole isomers were determined factors in ring-chain isomerization. The results obtained in advance for 2-azido-1,3-thiazoles were found to be consistent with the experimental and theoretically data reported.

  20. Isomerization and increase in the antioxidant properties of lycopene from Momordica cochinchinensis (gac) by moderate heat treatment with UV-Vis spectra as a marker.

    PubMed

    Phan-Thi, Hanh; Waché, Yves

    2014-08-01

    Momordica cochinchinensis (gac) is a plant rich in lycopene. This pigment tends to solubilize in oil and get damaged during extraction. The impact of heating on cis-isomerization of oil-free lycopene in hexane was studied at 50 and 80°C during 240min with UV-Vis spectrometry, DAD-HPLC and TEAC test. The initial all-trans-form isomerized to the 13-cis isomer more rapidly at 80°C. After this treatment, 16% of the lycopene compounds were in the 9-cis-form. This isomer triggered an increase in the antioxidant properties which was detectable from concentrations above 9% and resulted in a change from 2.4 to 3.7μmol Trolox equivalent. It is thus possible to increase the bioactivity of lycopene samples by controlling heating. The evolution of ratios calculated from the global UV-Vis spectrum was representative of cis-isomerization and spectrometry can thus be a simple way to evaluate the state of isomerization of lycopene solutions. Copyright © 2014 Elsevier Ltd. All rights reserved.

  1. Isomerization of Internal Alkynes to Iridium(III) Allene Complexes via C-H Bond Activation: Expanded Substrate Scope, and Progress towards a Catalytic Methodology.

    PubMed

    Phadke, Neha; Findlater, Michael

    2015-11-10

    The synthesis of a series of allene complexes (POCOP)Ir(η²-RC=(.)=CR') 1b-4b (POCOP = 2,6-bis(di-tert-butylphosphonito)benzene) via isomerization of internal alkynes is reported. We have demonstrated that the application of this methodology is viable for the isomerization of a wide variety of alkyne substrates. Deuterium labeling experiments support our proposed mechanism. The structures of the allene complexes 1b-4b were determined using spectroscopic data analysis. Additionally, the solid-state molecular structure of complex 2b was determined using single crystal X-ray diffraction studies and it confirmed the assignment of an iridium-bound allene isomerization product. The rates of isomerization were measured using NMR techniques over a range of temperatures to allow determination of thermodynamic parameters. Finally, we report a preliminary step towards developing a catalytic methodology; the allene may be liberated from the metal center by exposure of the complex to an atmosphere of carbon monoxide.

  2. Asymmetric synthesis and cytotoxic activity of isomeric phytosphingosine derivatives.

    PubMed

    Rives, Arnaud; Baudoin-Dehoux, Cécile; Saffon, Nathalie; Andrieu-Abadie, Nathalie; Génisson, Yves

    2011-12-07

    New phytosphingosine analogues have been conceived, synthesised and their cytotoxicity in B16 murine melanoma cells tested. These compounds embed an isomeric substitution pattern resulting from a formal permutation of the C-2 and C-4 substituents along the aliphatic skeleton of the original sphingoid base. Five different stereoisomers have been accessed through regio- and stereocontrolled opening of the oxirane of long chain epoxyamine precursors. The corresponding N-hexyl and N-octanoyl derivatives have also been prepared. In cell viability experiments all the primary amines were found to be more active than the natural phytosphingosine with IC(50) in the low μM range for the most potent compounds.

  3. Regio- and conformational isomerization critical to design of efficient thermally-activated delayed fluorescence emitters

    NASA Astrophysics Data System (ADS)

    Etherington, Marc K.; Franchello, Flavio; Gibson, Jamie; Northey, Thomas; Santos, Jose; Ward, Jonathan S.; Higginbotham, Heather F.; Data, Przemyslaw; Kurowska, Aleksandra; Dos Santos, Paloma Lays; Graves, David R.; Batsanov, Andrei S.; Dias, Fernando B.; Bryce, Martin R.; Penfold, Thomas J.; Monkman, Andrew P.

    2017-04-01

    Regio- and conformational isomerization are fundamental in chemistry, with profound effects upon physical properties, however their role in excited state properties is less developed. Here two regioisomers of bis(10H-phenothiazin-10-yl)dibenzo[b,d]thiophene-S,S-dioxide, a donor-acceptor-donor (D-A-D) thermally-activated delayed fluorescence (TADF) emitter, are studied. 2,8-bis(10H-phenothiazin-10-yl)dibenzo[b,d]thiophene-S,S-dioxide exhibits only one quasi-equatorial conformer on both donor sites, with charge-transfer (CT) emission close to the local triplet state leading to efficient TADF via spin-vibronic coupling. However, 3,7-bis(10H-phenothiazin-10-yl)dibenzo[b,d]thiophene-S,S-dioxide displays both a quasi-equatorial CT state and a higher-energy quasi-axial CT state. No TADF is observed in the quasi-axial CT emission. These two CT states link directly to the two folded conformers of phenothiazine. The presence of the low-lying local triplet state of the axial conformer also means that this quasi-axial CT is an effective loss pathway both photophysically and in devices. Importantly, donors or acceptors with more than one conformer have negative repercussions for TADF in organic light-emitting diodes.

  4. Regio- and conformational isomerization critical to design of efficient thermally-activated delayed fluorescence emitters

    PubMed Central

    Etherington, Marc K.; Franchello, Flavio; Gibson, Jamie; Northey, Thomas; Santos, Jose; Ward, Jonathan S.; Higginbotham, Heather F.; Data, Przemyslaw; Kurowska, Aleksandra; Dos Santos, Paloma Lays; Graves, David R.; Batsanov, Andrei S.; Dias, Fernando B.; Bryce, Martin R.; Penfold, Thomas J.; Monkman, Andrew P.

    2017-01-01

    Regio- and conformational isomerization are fundamental in chemistry, with profound effects upon physical properties, however their role in excited state properties is less developed. Here two regioisomers of bis(10H-phenothiazin-10-yl)dibenzo[b,d]thiophene-S,S-dioxide, a donor–acceptor–donor (D–A–D) thermally-activated delayed fluorescence (TADF) emitter, are studied. 2,8-bis(10H-phenothiazin-10-yl)dibenzo[b,d]thiophene-S,S-dioxide exhibits only one quasi-equatorial conformer on both donor sites, with charge-transfer (CT) emission close to the local triplet state leading to efficient TADF via spin-vibronic coupling. However, 3,7-bis(10H-phenothiazin-10-yl)dibenzo[b,d]thiophene-S,S-dioxide displays both a quasi-equatorial CT state and a higher-energy quasi-axial CT state. No TADF is observed in the quasi-axial CT emission. These two CT states link directly to the two folded conformers of phenothiazine. The presence of the low-lying local triplet state of the axial conformer also means that this quasi-axial CT is an effective loss pathway both photophysically and in devices. Importantly, donors or acceptors with more than one conformer have negative repercussions for TADF in organic light-emitting diodes. PMID:28406153

  5. Comparison of the interaction between lactoferrin and isomeric drugs.

    PubMed

    Guo, Ming; Lu, Xiaowang; Wang, Yan; Brodelius, Peter E

    2017-02-15

    The binding properties of pentacyclic triterpenoid isomeric drugs, i.e. ursolic acid (UA) and oleanolic acid (OA), to bovine lactoferrin (BLF) have been studied by molecule modeling, fluorescence spectroscopy, UV-visible absorbance spectroscopy and infrared spectroscopy (IR). Molecular docking, performed to reveal the possible binding mode or mechanism, suggested that hydrophobic interaction and hydrogen bonding play important roles to stabilize the complex. The results of spectroscopic measurements showed that the two isomeric drugs both strongly quenched the intrinsic fluorescence of BLF through a static quenching procedure although some differences between UA and OA binding strength and non-radiation energy transfer occurred within the molecules. The number of binding sites was 3.44 and 3.10 for UA and OA, respectively, and the efficiency of Förster energy transfer provided a distance of 0.77 and 1.21nm for UA and OA, respectively. The conformation transformation of BLF affected by the drugs conformed to the "all-or-none" pattern. In addition, the changes of the ratios of α-helices, β-sheets and β-turns of BLF during the process of the interaction were obtained. The results of the experiments in combination with the calculations showed that there are two modes of pentacyclic triterpenoid binding to BLF instead of one binding mode only governed by the principle of the lowest bonding energy.

  6. mer and fac isomerism in tris chelate diimine metal complexes.

    PubMed

    Dabb, Serin L; Fletcher, Nicholas C

    2015-03-14

    In this perspective, we highlight the issue of meridional (mer) and facial (fac) orientation of asymmetrical diimines in tris-chelate transition metal complexes. Diimine ligands have long been the workhorse of coordination chemistry, and whilst there are now good strategies to isolate materials where the inherent metal centered chirality is under almost complete control, and systematic methodologies to isolate heteroleptic complexes, the conceptually simple geometrical isomerism has not been widely investigated. In systems where the two donor atoms are significantly different in terms of the σ-donor and π-accepting ability, the fac isomer is likely to be the thermodynamic product. For the diimine complexes with two trigonal planar nitrogen atoms there is much more subtlety to the system, and external factors such as the solvent, lattice packing and the various steric considerations play a delicate role in determining the observed and isolable product. In this article we discuss the possibilities to control the isomeric ratio in labile systems, consider the opportunities to separate inert complexes and discuss the observed differences in their spectroscopic properties. Finally we report on the ligand orientation in supramolecular systems where facial coordination leads to simple regular structures such as helicates and tetrahedra, but the ability of the ligand system to adopt a mer orientation enables self-assembled structures of considerable beauty and complexity.

  7. Comparison of the interaction between lactoferrin and isomeric drugs

    NASA Astrophysics Data System (ADS)

    Guo, Ming; Lu, Xiaowang; Wang, Yan; Brodelius, Peter E.

    2017-02-01

    The binding properties of pentacyclic triterpenoid isomeric drugs, i.e. ursolic acid (UA) and oleanolic acid (OA), to bovine lactoferrin (BLF) have been studied by molecule modeling, fluorescence spectroscopy, UV-visible absorbance spectroscopy and infrared spectroscopy (IR). Molecular docking, performed to reveal the possible binding mode or mechanism, suggested that hydrophobic interaction and hydrogen bonding play important roles to stabilize the complex. The results of spectroscopic measurements showed that the two isomeric drugs both strongly quenched the intrinsic fluorescence of BLF through a static quenching procedure although some differences between UA and OA binding strength and non-radiation energy transfer occurred within the molecules. The number of binding sites was 3.44 and 3.10 for UA and OA, respectively, and the efficiency of Förster energy transfer provided a distance of 0.77 and 1.21 nm for UA and OA, respectively. The conformation transformation of BLF affected by the drugs conformed to the "all-or-none" pattern. In addition, the changes of the ratios of α-helices, β-sheets and β-turns of BLF during the process of the interaction were obtained. The results of the experiments in combination with the calculations showed that there are two modes of pentacyclic triterpenoid binding to BLF instead of one binding mode only governed by the principle of the lowest bonding energy.

  8. Isocyanurates with planar chirality: design, optical resolution, and isomerization.

    PubMed

    Goto, Hidetoshi; Sudoh, Masanao; Kawamoto, Keiko; Sugimoto, Hiroshi; Inoue, Shohei

    2012-10-01

    Designs and syntheses of isocyanurates (1-3) are described on the basis of a novel concept that two enantiotopic faces of C(s) -symmetric, prochiral planar molecules are differentiated with a location of groups at the top or bottom of the planar skeleton using a rigid linker. Such isocyanurates are atropisomeric. The planar-chiral structures of 1 and 2(anti) (anti-conformer of 2) were confirmed by single-crystal X-ray analyses, and the space groups were P1 (for 1) and P2(1)/c (for 2(anti)), resulting that the crystals were racemates. Optical resolutions of 1-3 were successfully accomplished by using chiral high-performance liquid chromatography technique in combination with circular dichroism, absorption, and nuclear magnetic resonance spectroscopies and mass spectrometry. Furthermore, the rotational barriers (ΔG(‡)s) related to isomerizations of 1-3 were estimated to be 27.2 (for 1 at 50 °C), 27.6 (for 2(anti) at 50 °C), and 40.6 (for 3(syn) at 150 °C) kcal/mol. The ΔG(‡)s of 2 and 3 were higher than that of 1 and, in particular, that of 3 was highest among them. This result indicates that an introduction of bulky substituents and an intramolecular bridging are effective for inhibitions of the isomerizations.

  9. Stereochemistry in self-assembled encapsulation complexes: Constellational isomerism

    PubMed Central

    Yamanaka, Masamichi; Shivanyuk, Alexander; Rebek, Julius

    2004-01-01

    A previously uncharacterized form of stereochemistry, constellational isomerism, is described. The isomerism arises from different arrangements of small-molecule guests in the space of a self-assembled, cylindrical host. The cylindrical host detains three molecules each of CHCl3, 1,2-dichloroethane, or isopropyl chloride. The exchange of guests in and out of the host is slow on the NMR time scale. The dimensions of the capsular host and the sizes of the guests hinder the mobility of molecules inside, and separate NMR signals are seen for guests at the ends of the capsule and those near its center. When two different guests are encapsulated, the spectra show up to four additional species: two sets of constellational isomers. In every pairwise combination of the three guests, all isomers could be identified. The equilibrium distributions of isomers depended on the concentrations of the guests in the bulk solution. The relative stability of the constellational isomers was a function of the polarity of the guest molecule and its ability to interact with the components of the capsule. The different arrangements represent information, and some possibilities for their use in data storage are proposed. PMID:14981269

  10. Iridium-Catalyzed Dynamic Kinetic Isomerization: Expedient Synthesis of Carbohydrates from Achmatowicz Rearrangement Products.

    PubMed

    Wang, Hao-Yuan; Yang, Ka; Bennett, Scott R; Guo, Sheng-rong; Tang, Weiping

    2015-07-20

    A highly stereoselective dynamic kinetic isomerization of Achmatowicz rearrangement products was discovered. This new internal redox isomerization provided ready access to key intermediates for the enantio- and diastereoselective synthesis of a series of naturally occurring sugars. The nature of the de novo synthesis also enables the preparation of both enantiomers.

  11. Using ruthenium-based isomerization to improve properties of bio-based materials

    USDA-ARS?s Scientific Manuscript database

    A new method that combines isomerization with other reactions has been shown to produce a family of isomeric materials. The chemistry involves the addition of a phosphorous-containing group to produce dibutyl-phosphono-octadecanoates. A low level of [Ru(CO)2(EtCO2)]n is first used for the isomerizat...

  12. NMR and GC Analyses of 3-Carene Isomerization Products over Activated Glauconite

    NASA Astrophysics Data System (ADS)

    Utenkova, D. B.; Skakovskii, E. D.; Senkov, G. M.; Agabekov, V. E.; Baranovskii, A. V.; Bogushevich, S. E.; Sidorenko, A. Yu.

    2017-01-01

    The qualitative and quantitative compositions of isomerization products of 3-carene over acid-treated glauconite were established using NMR and GC methods. Chemical shifts of 1H and 13C nuclei of identified compounds were assigned. A possible mechanism of the isomerization transformations was proposed.

  13. Isomerization of Secondary Phosphirane into Terminal Phosphinidene Complexes: An Analogy between Monovalent Phosphorus and Transition Metals.

    PubMed

    Wong, Jonathan; Li, Yongxin; Hao, Yanwei; Tian, Rongqiang; Mathey, François

    2015-10-26

    Secondary phosphirane complexes isomerize above 100 °C to give the corresponding terminal phosphinidene complexes, which can be trapped by alkenes and alkynes. This reaction is a rare instance of the isomerization of a P(III) derivative into a P(I) derivative. It appears to mimic the reductive elimination of alkanes from transition-alkylmetal hydrides.

  14. Communication: One-photon phase control of cis-trans isomerization in retinal

    SciTech Connect

    Arango, Carlos A.; Brumer, Paul

    2013-02-21

    We computationally demonstrate the one-photon phase control of retinal isomerization under conditions of low laser intensity. The calculations, utilizing the multiconfigurational time dependent Hartree method, include coupling between the two modes that are active in isomerization and the background molecular vibrational environment. Noting previously unsuccessful computations highlights the significance of this result.

  15. Isomerism in the setting of the so-called "heterotaxy": The usefulness of computed tomographic analysis.

    PubMed

    Mori, Shumpei; Anderson, Robert H; Nishii, Tatsuya; Matsumoto, Kensuke; Loomba, Rohit S

    2017-01-01

    The most complex combinations of congenital cardiac malformations are found in the setting of bodily isomerism. The question remains, however, as to whether evidence of cardiac isomerism is always to be found in the setting of bodily isomerism, also known as "heterotaxy." We have previously shown that, when assessed on the basis of the extent of the pectinate muscles relative to the atrioventricular junctions, there is always isomerism of the atrial appendages in this setting. Doubt has been remained, however, as to whether these cardiac features can accurately be recognized during life. We have now encountered two patients showing features of the left and right bodily isomerism. Examinations of these patients made using computed tomography show that all features of isomerism, no matter how complex, can now be visualized during life. The images currently presented show, furthermore, that the features of the so-called "heterotaxy" can be seen during life, not only within the heart but also in all the thoracic and abdominal organs, albeit that the isomeric features are confined to the thoracic organs. Based on the images presented, we argue that if each system of organs is analyzed and described in independent fashion; then it is possible for clinicians to exclude any suggestion of ambiguity and to provide accurate descriptions of the overall arrangement. We further discuss the appropriate terminology to describe the entity we prefer to call isomerism, along with the indications and usefulness of computed tomography in revealing the anatomic features of the congenitally malformed heart.

  16. Communication: One-photon phase control of cis-trans isomerization in retinal

    NASA Astrophysics Data System (ADS)

    Arango, Carlos A.; Brumer, Paul

    2013-02-01

    We computationally demonstrate the one-photon phase control of retinal isomerization under conditions of low laser intensity. The calculations, utilizing the multiconfigurational time dependent Hartree method, include coupling between the two modes that are active in isomerization and the background molecular vibrational environment. Noting previously unsuccessful computations highlights the significance of this result.

  17. Automated exploration of isomerization and dissociation pathways of ethylene sulfide cation by the global reaction route mapping method

    NASA Astrophysics Data System (ADS)

    Tokiwa, Takaki; Kishimoto, Naoki; Ohno, Koichi

    2015-11-01

    Isomerization and dissociation reaction pathways of C2H4S+ associated with photoionization of c-C2H4S have been explored on the potential energy surfaces by the global reaction route mapping (GRRM) method. Reaction channels yielding C2H3S+, HCS+, H2S+, C2H3+, and C2H2S+ were disclosed. Calculated values of energy barriers to transition states and direct dissociation energies gave theoretical supports to recent synchrotron radiation experiments generating HCS+ and C2H3S+.

  18. Methods of refining and producing isomerized fatty acid esters and fatty acids from natural oil feedstocks

    DOEpatents

    Snead, Thomas E.; Cohen, Steven A.; Gildon, Demond L.; Beltran, Leslie V.; Kunz, Linda A.; Pals, Tessa M.; Quinn, Jordan R; Behrends, Jr., Raymond T.; Bernhardt, Randal J.

    2016-07-05

    Methods are provided for refining natural oil feedstocks and producing isomerized esters and acids. The methods comprise providing a C4-C18 unsaturated fatty ester or acid, and isomerizing the fatty acid ester or acid in the presence of heat or an isomerization catalyst to form an isomerized fatty ester or acid. In some embodiments, the methods comprise forming a dibasic ester or dibasic acid prior to the isomerizing step. In certain embodiments, the methods further comprise hydrolyzing the dibasic ester to form a dibasic acid. In certain embodiments, the olefin is formed by reacting the feedstock in the presence of a metathesis catalyst under conditions sufficient to form a metathesized product comprising olefins and esters, separating the olefins from the esters in the metathesized product, and transesterifying the esters in the presence of an alcohol to form a transesterified product having unsaturated esters.

  19. Identification of Asp isomerization in proteins by ¹⁸O labeling and tandem mass spectrometry.

    PubMed

    Zhang, Jennifer; Katta, Viswanatham

    2012-01-01

    Isomerization of aspartic acid (Asp) to isoaspartic acid (isoAsp) via succinimide intermediate is a common route of degradation for proteins that can affect their structural integrity. As Asp/isoAsp is isobaric in mass, it is difficult to identify the site of modification by LC-MS/MS peptide mapping. Here, we describe an approach to label the Asp residue involved in isomerization at the protein level by hydrolyzing the succinimide intermediate in H₂¹⁸O. Tryptic digestion of this labeled protein will result in peptides containing the site of isomerization being 2 Da heavier than the ¹⁶O-containing counterparts, due to ¹⁸O incorporation during the hydrolysis process. Comparison of tandem mass spectra of isomerized peptides with and without ¹⁸O incorporation allows easy identification of the Asp residue involved. This method proved to be especially useful in identifying the sites when isomerization occurs in Asp-Asp motifs.

  20. Regio- and stereoselective isomerization of hexabromocyclododecanes (HBCDs): kinetics and mechanism of beta-HBCD racemization.

    PubMed

    Heeb, Norbert V; Schweizer, W Bernd; Mattrel, Peter; Haag, Regula; Kohler, Martin; Schmid, Peter; Zennegg, Markus; Wolfensberger, Max

    2008-04-01

    Hexabromocyclododecanes (HBCDs) are high production volume chemicals currently produced in quantities exceeding 20000ty(-1). They are used as flame retardants for plastics and textiles. HBCDs are thermally labile compounds, rapidly decomposing at temperatures above 250 degrees C to form bromine radicals, which scavenge other radicals formed during pyrolysis. But certain HBCD stereoisomers must reach the environment without decomposition, because their levels in soils, sediments, and biota are increasing worldwide. The fate of individual HBCD stereoisomers during production, product use, disposal, and transformation in the environment remains unclear. Herein we report on the thermally induced, highly selective isomerization of (+) and (-)beta-HBCD. Regio- and stereoselective migration of only two of the six bromine atoms resulted in the racemization of both beta-HBCDs. First order rate constants (k(rac)) increased from 0.005, 0.011, 0.021, to 0.055min(-1) at 130, 140, 150, and 160 degrees C, corresponding to half life times tau(1/2) of 143, 63, 29, and 14min, respectively. From the deduced kinetic model, we conclude that any thermal treatment of enantiomerically enriched beta-HBCDs in the range of 100-160 degrees C will result in a loss of most optical activity within few hours. The simultaneous inversion of two asymmetric centers occurred with perfect stereocontrol. Selectively, vicinal dibromides with the RR- and the SS-configurations migrated at these temperatures. An intramolecular reaction mechanism with a four-center transition state is postulated, based on the obtained stereoisomer pattern and the observed reaction kinetics. Crystal structure analysis revealed that all vicinal dibromides in beta-HBCDs prefer synclinal (gauche) conformations. However, an antiperiplanar (staggered) conformation is assumed to facilitate the concerted 1.2-shifts of both bromine atoms, resulting in an inversion of both neighboring carbon atoms. First experiments with other HBCD

  1. Aborted double bicycle-pedal isomerization with hydrogen bond breaking is the primary event of bacteriorhodopsin proton pumping

    PubMed Central

    Altoè, Piero; Cembran, Alessandro; Olivucci, Massimo; Garavelli, Marco

    2010-01-01

    Quantum mechanics/molecular mechanics calculations based on ab initio multiconfigurational second order perturbation theory are employed to construct a computer model of Bacteriorhodopsin that reproduces the observed static and transient electronic spectra, the dipole moment changes, and the energy stored in the photocycle intermediate K. The computed reaction coordinate indicates that the isomerization of the retinal chromophore occurs via a complex motion accounting for three distinct regimes: (i) production of the excited state intermediate I, (ii) evolution of I toward a conical intersection between the excited state and the ground state, and (iii) formation of K. We show that, during stage ii, a space-saving mechanism dominated by an asynchronous double bicycle-pedal deformation of the C10═C11─C12═C13─C14═N moiety of the chromophore dominates the isomerization. On this same stage a N─H/water hydrogen bond is weakened and initiates a breaking process that is completed during stage iii. PMID:21048087

  2. Aborted double bicycle-pedal isomerization with hydrogen bond breaking is the primary event of bacteriorhodopsin proton pumping.

    PubMed

    Altoè, Piero; Cembran, Alessandro; Olivucci, Massimo; Garavelli, Marco

    2010-11-23

    Quantum mechanics/molecular mechanics calculations based on ab initio multiconfigurational second order perturbation theory are employed to construct a computer model of Bacteriorhodopsin that reproduces the observed static and transient electronic spectra, the dipole moment changes, and the energy stored in the photocycle intermediate K. The computed reaction coordinate indicates that the isomerization of the retinal chromophore occurs via a complex motion accounting for three distinct regimes: (i) production of the excited state intermediate I, (ii) evolution of I toward a conical intersection between the excited state and the ground state, and (iii) formation of K. We show that, during stage ii, a space-saving mechanism dominated by an asynchronous double bicycle-pedal deformation of the C10═C11─C12═C13─C14═N moiety of the chromophore dominates the isomerization. On this same stage a N─H/water hydrogen bond is weakened and initiates a breaking process that is completed during stage iii.

  3. Insights into the isomerization of photochromic oxazines from the excitation dynamics of BODIPY-oxazine dyads.

    PubMed

    Deniz, Erhan; Battal, Mutlu; Cusido, Janet; Sortino, Salvatore; Raymo, Françisco M

    2012-08-07

    We synthesized five BODIPY-oxazine dyads in one to four synthetic steps from known precursors. They differ in the nature of the unsaturated spacer linking the oxazine photochrome to either the conjugated framework or the boron center of the BODIPY fluorophore. Despite the π-character of the linkers, the two functional components are electronically isolated in the ground state and the BODIPY fluorophore maintains its absorption and, with one exception, emission properties unaltered. Instead, the photochemical response of the photochromic component is completely suppressed within all dyads. Rather than the expected opening of the oxazine ring, the laser excitation of these molecular assemblies results in the effective population of the BODIPY triplet in four of the five dyads. Control experiments with appropriate model compounds indicate that the local excitation of the oxazine component results first in intersystem crossing and then energy transfer to the BODIPY component. In fact, the transfer of energy from the triplet state of the former to the triplet state of the latter competes successfully with the opening of the oxazine ring and prevents the isomerization of the photochromic component. These observations demonstrate, for the very first time, that the photoinduced opening of these photochromic oxazines occurs along the potential energy surface of their triplet state. Such valuable mechanistic insights into their excitation dynamics can guide the design of novel members of this family of photochromic compounds with improved photochemical properties.

  4. Optical Pumping and Laser Induced Nuclear Orientation of a Microsecond Isomeric Level in BARIUM-134

    NASA Astrophysics Data System (ADS)

    Bell, Curtis John

    Using optical pumping techniques, on and off-line experiments were performed on a microsecond nuclear isomer (('134m)Ba 10('+) ). Shifts in atomic resonances detected by changes in the angular distribution of characteristic nuclear radiations (expressed as changes in shape and size) yield information on changes in nuclear structure. The 10('+) isomeric state was produced using a 49 MeV pulsed beam of ('13)C on an isotopically enriched ('124)Sn target. The reaction products recoil out of the target and are slowed to thermal velocities in 10 torr of xenon in a region illuminated with circularly polarized light (553.5 nm) from a Coherent 699-21 dye laser. Nuclear parameters measured were the lifetime (3.8(2)(mu)s) and g-factor (g = -.20(1)) of the 10('+) state. Atomic parameters measured for barium were the depolarization cross sections of the ('1)P(,1) atomic level (6.0(6) nm('2)) in xenon, the quenching cross section for hydrogen (0.042(4) nm('2)), and the branching ratio of the metastable (('1,3)D(,1,2,3)) atomic states (0.011(1)). A possible anisotropy signal and the cumulative results (no measurable anisotropy) are presented. Difficulties encountered were insufficient neutralization, and unexpectedly large spatial distribution, and 'trapping' in metastable atomic states.

  5. Initial denaturing conditions influence the slow folding phase of acylphosphatase associated with proline isomerization.

    PubMed Central

    Pertinhez, T. A.; Hamada, D.; Smith, L. J.; Chiti, F.; Taddei, N.; Stefani, M.; Dobson, C. M.

    2000-01-01

    The folding kinetics of human common-type acylphosphatase (cAcP) from its urea- and TFE-denatured states have been determined by stopped-flow fluorescence techniques. The refolding reaction from the highly unfolded state formed in urea is characterized by double exponential behavior that includes a slow phase associated with isomerism of the Gly53-Pro54 peptide bond. However, this slow phase is absent when refolding is initiated by dilution of the highly a-helical denatured state formed in the presence of 40% trifluoroethanol (TFE). NMR studies of a peptide fragment corresponding to residues Gly53-Gly69 of cAcP indicate that only the native-like trans isomer of the Gly-Pro peptide bond is significantly populated in the presence of TFE, whereas both the cis and trans isomers are found in an approximately 1:9 ratio for the peptide bond in aqueous solution. Molecular modeling studies in conjunction with NMR experiments suggest that the trans isomer of the Gly53-Pro54 peptide bond is stabilized in TFE by the formation of a nonnative-like hydrogen bond between the CO group of Gly53 and the NH group of Lys57. These results therefore reveal that a specific nonnative interaction in the denatured state can increase significantly the overall efficiency of refolding. PMID:10975568

  6. Isomeric separation of methamphetamine by HPLC chiral column.

    PubMed

    Lekskulchai, V

    2001-11-01

    Methamphetamine and its active metabolite, amphetamine, are optically active compounds which, based upon synthetic routes, can be found in two forms; pure d-form and racemic mixture. Analysis of their isomers can help to identify which precursor is currently spreading widely in a given region. Since there are many drugs that can be metabolized to amphetamine/methamphetamine, isomeric separation can be a useful tool for evaluation of these drugs, as well. Indirect method by using N-trifluoroacetyl-1-prolyl chloride (1-TPC) was found to have limited accuracy due to the contribution effect. In this presentation a direct method using HPLC Chirex chiral column 3022 was studied. Although the method gave no base-line separation of two different isomer peaks, it gave good sensitivity, reliability, and linearity. No contribution effect was found in the method presented. It also gave excellent correlation with the 1-TPC method.

  7. Ultrafast isomerization initiated by X-ray core ionization

    NASA Astrophysics Data System (ADS)

    Liekhus-Schmaltz, Chelsea E.; Tenney, Ian; Osipov, Timur; Sanchez-Gonzalez, Alvaro; Berrah, Nora; Boll, Rebecca; Bomme, Cedric; Bostedt, Christoph; Bozek, John D.; Carron, Sebastian; Coffee, Ryan; Devin, Julien; Erk, Benjamin; Ferguson, Ken R.; Field, Robert W.; Foucar, Lutz; Frasinski, Leszek J.; Glownia, James M.; Gühr, Markus; Kamalov, Andrei; Krzywinski, Jacek; Li, Heng; Marangos, Jonathan P.; Martinez, Todd J.; McFarland, Brian K.; Miyabe, Shungo; Murphy, Brendan; Natan, Adi; Rolles, Daniel; Rudenko, Artem; Siano, Marco; Simpson, Emma R.; Spector, Limor; Swiggers, Michele; Walke, Daniel; Wang, Song; Weber, Thorsten; Bucksbaum, Philip H.; Petrovic, Vladimir S.

    2015-09-01

    Rapid proton migration is a key process in hydrocarbon photochemistry. Charge migration and subsequent proton motion can mitigate radiation damage when heavier atoms absorb X-rays. If rapid enough, this can improve the fidelity of diffract-before-destroy measurements of biomolecular structure at X-ray-free electron lasers. Here we study X-ray-initiated isomerization of acetylene, a model for proton dynamics in hydrocarbons. Our time-resolved measurements capture the transient motion of protons following X-ray ionization of carbon K-shell electrons. We Coulomb-explode the molecule with a second precisely delayed X-ray pulse and then record all the fragment momenta. These snapshots at different delays are combined into a `molecular movie' of the evolving molecule, which shows substantial proton redistribution within the first 12 fs. We conclude that significant proton motion occurs on a timescale comparable to the Auger relaxation that refills the K-shell vacancy.

  8. The zeolite mediated isomerization of allyl phenyl ether

    NASA Astrophysics Data System (ADS)

    Pebriana, R.; Mujahidin, D.; Syah, Y. M.

    2017-04-01

    Allyl phenyl ether is an important starting material in organic synthesis that has several applications in agrochemical industry. The green transformation of allyl phenyl ether assisted by heterogeneous catalyst is an attractive topic for an industrial process. In this report, we investigated the isomerization of allyl phenyl ether by heating it in zeolite H-ZSM-5 and Na-ZSM-5. The conversion of allyl phenyl ether (neat) in H-ZSM-5 was 67% which produced 40% of 2-allylphenol, 17% of 2-methyldihydrobenzofuran, and other product (4:1.7:1), while in Na-ZSM-5 produced exclusively 2-allylphenol with 52% conversion. These results showed that zeolite properties can be tuned to give a selective transformation by substitution of metal ion into the zeolite interior.

  9. Epoxidation of propylene dimers and isomerization of mixtures obtained

    SciTech Connect

    Dobrev, D.M.; Kurtev, K.S.

    1988-05-10

    Mixtures of hexenes are obtained in the dimerization of propylene on a Ziegler catalyst. By the epoxidation of this mixture by organic peroxides, followed by isomerization of the oxides, C/sub 6/ ketones, which are used as solvents, can be obtained. The hexenes were obtained by dimerization of propylene in the presence of a Ni(C/sub 5/H/sub 7/O/sub 2/)/sub 2/-P(C/sub 6/H/sub 5/)/sub 3/-(C/sub 3/H/sub 5/)/sub 2/AlCl catalytic system. The epoxidation was carried with technical grade isopropylbenzyl hydroperoxide (IPBHP). MoO/sub 2/(C/sub 5/H/sub 7/O/sub 2/)/sub 2/ was used as the catalyst. The relative rates of epoxidation of different isomers contained in the dimeric fraction, with respect to 2-methyl-1-pentene, was determined by means of competing reactions.

  10. Direct observation of disulfide isomerization in a single protein

    NASA Astrophysics Data System (ADS)

    Alegre-Cebollada, Jorge; Kosuri, Pallav; Rivas-Pardo, Jaime Andrés; Fernández, Julio M.

    2011-11-01

    Photochemical uncaging techniques use light to release active molecules from otherwise inert compounds. Here we expand this class of techniques by demonstrating the mechanical uncaging of a reactive species within a single protein. We proved this novel technique by capturing the regiospecific reaction between a thiol and a vicinal disulfide bond. We designed a protein that includes a caged cysteine and a buried disulfide. The mechanical unfolding of this protein in the presence of an external nucleophile frees the single reactive cysteine residue, which now can cleave the target disulfide via a nucleophilic attack on either one of its two sulfur atoms. This produces two different and competing reaction pathways. We used single-molecule force spectroscopy to monitor the cleavage of the disulfides, which extends the polypeptide by a magnitude unambiguously associated with each reaction pathway. This allowed us to measure, for the first time, the kinetics of disulfide-bond isomerization in a protein.

  11. Ultrafast isomerization initiated by X-ray core ionization.

    PubMed

    Liekhus-Schmaltz, Chelsea E; Tenney, Ian; Osipov, Timur; Sanchez-Gonzalez, Alvaro; Berrah, Nora; Boll, Rebecca; Bomme, Cedric; Bostedt, Christoph; Bozek, John D; Carron, Sebastian; Coffee, Ryan; Devin, Julien; Erk, Benjamin; Ferguson, Ken R; Field, Robert W; Foucar, Lutz; Frasinski, Leszek J; Glownia, James M; Gühr, Markus; Kamalov, Andrei; Krzywinski, Jacek; Li, Heng; Marangos, Jonathan P; Martinez, Todd J; McFarland, Brian K; Miyabe, Shungo; Murphy, Brendan; Natan, Adi; Rolles, Daniel; Rudenko, Artem; Siano, Marco; Simpson, Emma R; Spector, Limor; Swiggers, Michele; Walke, Daniel; Wang, Song; Weber, Thorsten; Bucksbaum, Philip H; Petrovic, Vladimir S

    2015-09-10

    Rapid proton migration is a key process in hydrocarbon photochemistry. Charge migration and subsequent proton motion can mitigate radiation damage when heavier atoms absorb X-rays. If rapid enough, this can improve the fidelity of diffract-before-destroy measurements of biomolecular structure at X-ray-free electron lasers. Here we study X-ray-initiated isomerization of acetylene, a model for proton dynamics in hydrocarbons. Our time-resolved measurements capture the transient motion of protons following X-ray ionization of carbon K-shell electrons. We Coulomb-explode the molecule with a second precisely delayed X-ray pulse and then record all the fragment momenta. These snapshots at different delays are combined into a 'molecular movie' of the evolving molecule, which shows substantial proton redistribution within the first 12 fs. We conclude that significant proton motion occurs on a timescale comparable to the Auger relaxation that refills the K-shell vacancy.

  12. Molecular Choreography of Isomerization and Electron Transfer Using One and Two Dimensional Femtosecond Stimulated Raman Spectroscopy

    NASA Astrophysics Data System (ADS)

    Hoffman, David Paul

    Chemical reactions are defined by the change in the relative positions and bonding of nuclei in molecules. I have used femtosecond stimulated Raman spectroscopy (FSRS) to probe these transformations with structural specificity and high time precision revealing the mechanisms of two important classes of reactions; isomerization about an N=N bond and interfacial/intermolecular electron transfer. Isomerization about a double bond is one of the simplest, yet most important, photochemical reactions. In contrast to carbon double bonds, nitrogen double bonds can react via two possible mechanisms; rotation or inversion. To determine which pathway is predominant, I studied an azobenzene derivative using both FSRS and impulsive stimulated Raman spectroscopy (ISRS). The FSRS experiments demonstrated that the photochemical reaction occurs concomitantly with the 700 fs non-radiative decay of the excited state; because no major change in N=N stretching frequency was measured, I surmised that the reaction proceeds through an inversion pathway. My subsequent ISRS experiments confirmed this hypothesis; I observed a highly displaced, low frequency, inversion-like mode, indicating that initial movement out of the Franck-Condon region proceeds along an inversion coordinate. To probe which nuclear motions facilitate electron transfer and charge recombination, I used FSRS and the newly developed 2D-FSRS techniques to study two model systems, triphenylamine dyes bound to TiO2 nanoparticles and a molecular charge transfer (CT) dimer. In the dye-nanoparticle system I discovered that charge separation persists much longer (> 100 ps) than previously thought by using the juxtaposition of the FSRS and transient absorption data to separate the dynamics of the dye from that of the injected electron. Additionally, I discovered that dye constructs with an added vinyl group were susceptible to quenching via isomerization. The CT dimer offered an opportunity to study a system in which charge

  13. Isomerization of the protonated acetone dimer in the gas phase.

    PubMed

    Norrman, K; Sølling, T I; McMahon, T B

    2005-08-01

    Mass spectrometry-based methods have been employed in order to study the reactions of non- (h(6)/h(6)), half (d(6)/h(6)), and fully (d(6)/d(6)) deuterium labeled protonated dimers of acetone in the gas phase. Neither kinetic nor thermodynamic isotope effects were found. From MIKES experiments (both spontaneous and collision-induced dissociations), it was found that the relative ion yield (m/z 65 vs m/z 59) from the dissociation reaction of half deuterium labeled (d(6)/h(6)) protonated dimer of acetone is dependent on the internal energy. A relative ion yield (m/z 65 vs m/z 59) close to unity is observed for cold, nonactivated, metastable ions, whereas the ion yield is observed to increase (favoring m/z 65) when the pressure of the collision gas is increased. This is in striking contrast to what would be expected if a kinetic isotope effect were present. A combined study of the kinetics and the thermodynamics of the association reaction between acetone and protonated acetone implicates the presence of at least two isomeric adducts. We have employed G3(MP2) theory to map the potential energy surface leading from the reactants, acetone and protonated acetone, to the various isomeric adducts. The proton-bound dimer of acetone was found to be the lowest-energy isomer, and protonated diacetone alcohol the next lowest-energy isomer. Protonated diacetone alcohol, even though it is an isomer hidden behind many barriers, can possibly account for the observed relative ion yield and its dependence on the mode of activation.

  14. Mass spectrometric profiling of flavonoid glycoconjugates possessing isomeric aglycones.

    PubMed

    Abrankó, László; Szilvássy, Blanka

    2015-01-01

    In fields such as food and nutrition science or plant physiology, interest in untargeted profiling of flavonoids continues to expand. The group of flavonoids encompasses several thousands of chemically distinguishable compounds, among which are a number of isobaric compounds with the same elemental composition. Thus, the mass spectrometric identification of these compounds is challenging, especially when reference standards are not available to support their identification. Many different types of isomers of flavonoid glycoconjugates are known, i.e. compounds that differ in their glycosylation position, glycan sequence or type of interglycosidic linkage. This work focuses on the mass spectrometric identification of flavonoid glycoconjugate isomers possessing the same glycan mass and differing only in their aglycone core. A non-targeted HPLC-ESI-MS/MS profiling method using a triple quadrupole MS is presented herein, which utilizes in-source fragmentation and a pseudo-MS(3) approach for the selective analysis of flavonoid glycoconjugates with isomeric/isobaric aglycones. A selective MRM-based identification of the in-source formed isobaric aglycone fragments was established. Additionally, utilizing the precursor scanning capability of the employed triple quadrupole instrument, the developed method enabled the determination of the molecular weight of the studied intact flavonoid glycoconjugate. The versatility of the method was proven with various types of flavonoid aglycones, i.e. anthocyanins, flavonols, flavones, flavanones and isoflavones, along with their representative glycoconjugates. The developed method was also successfully applied to a commercially available sour cherry sample, in which 16 different glycoconjugates of pelargonidin, genistein, cyanidin, kaempferol and quercetin could be tentatively identified, including a number of compounds containing isomeric/isobaric aglycones.

  15. Systematics of isomeric configurations in N=77 odd-Z isotones near the proton drip line

    SciTech Connect

    Tantawy, M.N.; Danchev, M.; Hartley, D.J.; Mazzocchi, C.; Bingham, C.R.; Grzywacz, R.; Rykaczewski, K.P.; Gross, C.J.; Shapira, D.; Yu, C.-H.; Batchelder, J.C.; Krolas, W.; Fong, D.; Hamilton, J. H.; Li, K.; Ramayya, A. V.; Ginter, T.N.; Stolz, A.; Hagino, K.; Karny, M.

    2006-02-15

    The systematics of the {pi}h{sub 11/2}x{nu}h{sub 11/2} and {pi}h{sub 11/2}x{nu}s{sub 1/2} isomeric configurations was studied for the odd-Z N=77 isotones near the proton drip line. The isomeric decays in {sup 140}Eu, {sup 142}Tb, {sup 144}Ho, and {sup 146}Tm were measured by means of x-ray, {gamma}-ray, and charged particle spectroscopy at the Recoil Mass Spectrometer at the Holifield Radioactive Ion Beam Facility (ORNL). The spin and parity of I{sup {pi}}=8{sup +} and 5{sup -} were deduced for the isomers in {sup 140}Eu and {sup 142}Tb. New decay schemes were established, and the half-lives of the 8{sup +} isomers were measured to be 302(4) ns for {sup 140m2}Eu and 25(1) {mu}s for {sup 142m2}Tb. No evidence for the expected 1{sup +} ground-state was found in the {sup 144}Ho decay data. The proton-emission from {sup 146}Tm was restudied. Five proton transitions were assigned to two proton-emitting states. The half-lives of 198(3) ms and 68(3) ms and the spin and parity values of I{sup {pi}}=10{sup +} and 5{sup -} were established for {sup 146m}Tm and {sup 146gs}Tm, respectively. For the first time for an odd-odd nucleus, the interpretation of the observed decay properties and structure of the proton-emitting states was made by accounting for deformation and proton and neutron coupling to the core excitations. A complex wave-function structure was obtained, with dominating components of {pi}h{sub 11/2}x{nu}h{sub 11/2} for the 10{sup +} isomer and {pi}h{sub 11/2}x{nu}s{sub 1/2} for the 5{sup -} ground state.

  16. Cis-trans isomerizations of beta-carotene and lycopene: a theoretical study.

    PubMed

    Guo, Wen-Hsin; Tu, Cheng-Yi; Hu, Ching-Han

    2008-09-25

    The all-trans to mono-cis isomerizations of polyenes and two C40H56 carotenes, beta-carotene and lycopene, at the ground singlet (S0) and triplet (T1) states are studied by means of quantum chemistry computations. At the S0 state of polyenes containing n acetylene units (Pn), we find that the energy barrier of the central C=C rotation decreases with n. In contrast, however, at the T 1 state, the rotational barrier increases with n. For the C40H56 carotenes, the rotational barriers of lycopene are lower than those of their beta-carotene counterparts. This difference renders the rotational rates of lycopene to be 1-2 orders of magnitude higher than those of beta-carotene at room temperature. For both these carotenes, the barrier is lowest for the rotation toward the 13-cis isomer. The relative abundances are in the following order: all-trans > 9-cis > 13-cis > 15-cis. Although the 5-cis isomer of lycopene has the lowest energy among the cis isomers, its formation from the all-trans form is restricted, owing to a very large rotational barrier. The possible physiological implications of this study are discussed.

  17. Surface electronic structure and isomerization reactions of alkanes on some transition metal oxides

    NASA Astrophysics Data System (ADS)

    Katrib, A.; Logie, V.; Saurel, N.; Wehrer, P.; Hilaire, L.; Maire, G.

    1997-04-01

    XP spectra of some reduced transition metal oxides are presented. Different number of free nd,( n + 1)s valence electrons in each case could be observed by the presence of a certain density of states (DOS) at the Fermi-level in the valence band (VB) energy region of the XP spectrum. Catalytic isomerization reactions of 2-methylpentane yielding 3-methylpentane and n-hexane at 350°C have been observed on these reduced valence surface states. The bifunctionel mechanism in terms of metallic and acidic sites required for such reactions is proposed by considering the metallic properties of the rutile deformed structure through the C-axis in the case of MoO 2 and WO 2, while the oxygen atom(s) in the lattice structure exhibit Brönsted acidic properties. On the other hand, highly reduced or clean surfaces of these transition metals yield hydrogenolysis catalytic reactions for the same reactant with methane as the major product. In all cases, the exposure of the lower valence oxidation states of bulk transition metal oxides to air results in the surface partial oxidation to the stable oxides such as MoO 3, WO 3, V 2O 5 and Nb 2O 5.

  18. cis-trans-Isomerization of unsaturated fatty acids during /γ-irradiation of barley grains

    NASA Astrophysics Data System (ADS)

    Geißler, Christian; Brede, Ortwin; Reinhardt, Jürgen

    2003-06-01

    Gamma-irradiating barley grains with doses of 10-100 kGy, a dose dependent isomerization of the naturally occurring cis-unsaturated fatty acids such as oleic, cis-vaccenic, linoleic and also of linolenic acid was found. Whereas the effect was negligible up to 10 kGy, at 50 kGy the trans-fatty acid level became comparable to that of other natural products like butter fat which means that there is no essential nutrition danger. The cis-trans-isomerization found in barley grains is explained mainly by a thiyl radical driven process rather than direct isomerization.

  19. Conversion of biomass to ethanol: Isomerization of xylose over HY zeolite

    SciTech Connect

    Lee, C.Y.; Wen, J.; Thomas, S.

    1995-12-31

    Xylose, a pentose indigestible to most yeasts, was converted to ethanol by a two-step isomerization and fermentation. HY zeolite was used to catalyze the isomerization of xylose, and the xylulose produced was directly used as the carbon source in ethanol fermentation. Zeolite catalysts offer pH compatibility with yeast fermentation and the ability to carry out isomerization at higher temperature where equilibrium xylulose concentration is higher. Initial rate studies indicate that xylose consumption follows pseudo-first-order kinetics, with a specific rate constant of 6.2 x 10{sup -4} L/solution/g zeolite/h.

  20. Structure and isomerization of O, O-phenylene penta-coordinated phosphoryl serine

    NASA Astrophysics Data System (ADS)

    Lu, Kui; Tu, Guang-Zhong; Guo, Xiang-Feng; Sun, Xiao-Bin; Liu, Yan; Feng, Yu-Ping; Zhao, Yu-Fen

    2002-06-01

    A stable penta-coordinated serine-carboxylic-phosphoric anhydride may be synthesized at temperatures below -18 °C. Above that temperature, the product was shown to isomerize to another penta-coordinated phosphorus compound, which was proven by the change in the magnitude of observed P-C coupling constants. The mechanism for the anhydride to ester isomerization might provide a clue to the proposal of high-energy supply for biochemistry. Organic bases were shown to exert little influence on the rate of isomerization.

  1. A study of Pd/SO4/ZrO2/Al2O3 catalysts in n-hexane isomerization

    NASA Astrophysics Data System (ADS)

    Dzhikiya, O. V.; Smolikov, M. D.; Kazantsev, K. V.; Yablokova, S. S.; Kireeva, T. V.; Paukshtis, E. A.; Gulyaeva, T. I.; Belyi, A. S.

    2017-08-01

    The effect of palladium concentration in a range from 0.02 to 1.6 wt.% on characteristics of n-hexane isomerization was studied. The (O2-Hchem) titration and O2 chemisorption study revealed that palladium in Pd/SO4/ZrO2/Al2O3 systems adsorbs hydrogen in a ratio H/Pds = 1.13-1.65 at./at. Investigation of the charge state of the metal by IR spectroscopy of adsorbed CO showed the presence of both the metallic (Pd0) and charged palladium species. Pd/SO4/ZrO2/Al2O3 catalysts with charged palladium atoms exhibit high activity and selectivity in n-hexane isomerization.

  2. Isomeric ratios for ^{196,198}Tl and ^{196,198}Au from fusion and transfer in the interaction of 6He with 197Au

    NASA Astrophysics Data System (ADS)

    Kulko, A. A.; Demekhina, N. A.; Kalpakchieva, R.; Kolesnikov, N. N.; Lukashik, V. G.; Penionzhkevich, Yu E.; Rassadov, D. N.; Skobelev, N. K.

    2007-11-01

    Excitation functions and isomeric cross-section ratios have been measured for the isomeric pairs 198m,gTl, 196m,gTl, 198m,gAu and 196m,gAu, formed in fusion-evaporation and transfer processes in reactions of 6He with 197Au in the energy range 7-60 MeV. The population probability of high- and low-spin states in the fusion reaction with the formation of 198Tl and 196Tl (Jπm = 7+, Jπg = 2-), as well as of the transfer products 198Au and 196Au (Jπm = 12-, Jπg = 2-) is compared with calculations within the statistical model and with similar results, obtained in reactions induced by other nuclei.

  3. Observation of Isomeric Decays in the r-Process Waiting-Point Nucleus {sup 130}Cd{sub 82}

    SciTech Connect

    Jungclaus, A.; Poves, A.; Modamio, V.; Walker, J.; Caceres, L.; Gorska, M.; Grawe, H.; Langanke, K.; Martinez-Pinedo, G.; Cuenca-Garcia, J. J.; Doornenbal, P.; Geissel, H.; Gerl, J.; Kojouharov, I.; Kurz, N.; Prokopowicz, W.; Schaffner, H.; Wollersheim, H. J.; Montes, F.; Tashenov, S.

    2007-09-28

    The {gamma} decay of excited states in the waiting-point nucleus {sup 130}Cd{sub 82} has been observed for the first time. An 8{sup +} two-quasiparticle isomer has been populated both in the fragmentation of a {sup 136}Xe beam as well as in projectile fission of {sup 238}U, making {sup 130}Cd the most neutron-rich N=82 isotone for which information about excited states is available. The results, interpreted using state-of-the-art nuclear shell-model calculations, show no evidence of an N=82 shell quenching at Z=48. They allow us to follow nuclear isomerism throughout a full major neutron shell from {sup 98}Cd{sub 50} to {sup 130}Cd{sub 82} and reveal, in comparison with {sup 76}Ni{sub 48} one major proton shell below, an apparently abnormal scaling of nuclear two-body interactions.

  4. Fuel properties of heptadecene isomers prepared via tandem isomerization-decarboxylation of oleic acid

    USDA-ARS?s Scientific Manuscript database

    Heptadecene isomers were prepared via tandem isomerization-decarboxylation of oleic acid using catalytic triruthenium dodecacarbonyl [Ru3(CO)12]. Chromatographic and spectroscopic characterization of the isolated heptadecene mixture indicated that it consisted of 96% internal isomers and 4% aromatic...

  5. Communication: Effective spectroscopic Hamiltonian for multiple minima with above barrier motion: Isomerization in HO(2).

    PubMed

    Barnes, George L; Kellman, Michael E

    2010-09-14

    We present a two-dimensional potential surface for the isomerization in the hydroperoxyl radical HO(2) and calculate the vibrational spectrum. We then show that a simple effective spectroscopic fitting Hamiltonian is capable of reproducing large scale vibrational spectral structure above the isomerization barrier. Polyad breaking with multiple resonances is necessary to adequately describe the spectral features of the system. Insight into the dynamical nature of isomerization related to the effective Hamiltonian is gained through classical trajectories on the model potential. Contrary to physical intuition, the bend mode is not a "reaction mode," but rather isomerization requires excitation in both stretch and bend. The dynamics reveals a Farey tree formed from the 2:1 and 3:1 resonances, corresponding to the resonance coupling terms in the effective Hamiltonian, with the prominent 5:2 (2:1+3:1) feature dividing the tree into parts that we call the 3:1 and 2:1 portions.

  6. An ab initio analysis of charge redistribution upon isomerization of retinal in rhodopsin and bacteriorhodopsin

    NASA Astrophysics Data System (ADS)

    Corn, Brittany; Malinovskaya, Svetlana A.

    In the framework of quantum-chemical methods (RHF, MP2, and DFT), we study the reaction of photoinduced isomerization of biological molecules-retinal in rhodopsin (Rh) and bacteriorhodopsin (BRh)-the key intermediates in the vision process. The charge redistribution in the retinal chromophore of these biological molecules as the mechanism of the photoinduced isomerization is investigated. The results of the Mulliken, Löwdin, Natural Bond, and ESP population analyses are compared and validated. We demonstrate that the isomerization reaction is accompanied by the substantial charge relocation within the isomerization region with the electron localization on C11 for the retinal in Rh and C14 for the retinal in BRh. Content:text/plain; charset="UTF-8"

  7. Radiative lifetime and energy of the low-energy isomeric level in 229Th

    NASA Astrophysics Data System (ADS)

    Tkalya, E. V.; Schneider, Christian; Jeet, Justin; Hudson, Eric R.

    2015-11-01

    We estimate the range of the radiative lifetime and energy of the anomalous, low-energy 3 /2+(7.8 ±0.5 eV) state in the 229Th nucleus. Our phenomenological calculations are based on the available experimental data for the intensities of M 1 and E 2 transitions between excited levels of the 229Th nucleus in the Kπ[N nZΛ ] =5 /2+[633 ] and 3 /2+[631 ] rotational bands. We also discuss the influence of certain branching coefficients, which affect the currently accepted measured energy of the isomeric state. From this work, we establish a favored region, 0.66 ×106seV3/ω3≤τ ≤2.2 ×106seV3/ω3 , where the transition lifetime τ as a function of transition energy ω should lie at roughly the 95% confidence level. Together with the result of Beck et al. [LLNL-PROC-415170 (2009)], we establish a favored area where transition lifetime and energy should lie at roughly the 90% confidence level. We also suggest new nuclear physics measurements, which would significantly reduce the ambiguity in the present data.

  8. Vibrational predissociation and vibrationally induced isomerization of 3-aminophenol-ammonia

    SciTech Connect

    Heid, Cornelia G.; Merrill, Wyatt G.; Case, Amanda S. Crim, F. Fleming

    2015-01-07

    We investigate the vibrational predissociation dynamics of the hydrogen-bonded 3-aminophenol-ammonia cluster (3-AP-NH{sub 3}) in the OH and NH stretching regions. Vibrational excitation provides enough energy to dissociate the cluster into its constituent 3-AP and NH{sub 3} monomers, and we detect the 3-AP fragments via (1 + 1) resonance-enhanced multiphoton ionization (REMPI). The distribution of vibrational states of the 3-AP fragment suggests the presence of two distinct dissociation pathways. The first dissociation channel produces a broad, unstructured feature in the REMPI-action spectrum after excitation of any of the OH or NH stretching vibrations, pointing to a nearly statistical dissociation pathway with extensive coupling among the vibrations in the cluster during the vibrational predissociation. The second dissociation channel produces distinct, resolved features on top of the broad feature but only following excitation of the OH or symmetric NH{sub 3} stretch in the cluster. This striking mode-specificity is consistent with strong coupling of these two modes to the dissociation coordinate (the O–H⋯N bond). The presence of clearly resolved transitions to the electronic origin and to the 10a{sup 2} + 10b{sup 2} state of the cis-3-AP isomer shows that vibrational excitation is driving the isomerization of the trans-3-AP-NH{sub 3} isomer to the cis-3-AP-NH{sub 3} isomer in the course of the dissociation.

  9. "W-X-M" transformations in isomerization of B39- borospherenes

    NASA Astrophysics Data System (ADS)

    Gao, Ting-Ting; Chen, Qiang; Mu, Yue-Wen; Lu, Haigang; Li, Si-Dian

    2016-06-01

    The Stone-Wales transformation plays an important role in the isomerization of fullerenes and graphenic systems. The continuous conversions between neighboring six- and seven-membered rings in the borospherene (all-boron fullerene) B40 had been discovered (Martínez-Guajardo et al. Sci. Rep. 5, 11287 (2015)). In the first axially chiral borospherenes C3 B39- and C2 B39-, we identify three active boron atoms which are located at the center of three alternative sites involving five boron atoms denoted as "W", "X", and "M", respectively. The concerted movements of these active boron atoms and their close neighbors between neighboring six- and seven-membered rings define the "W-X-M" transformation of borospherenes. Extensive first-principles molecular dynamics simulations and quadratic synchronous transit transition-state searches indicate that, via three transition states (TS1, TS2, and TS3) and two intermediate species (M1 and M2), the three-step "W-X-M" transformations convert the C3 B39- global minimum into its C2 isomer at room temperature (300 K) and vice versa. The maximum barriers are only 3.89 kcal/mol from C3 to C2 B39- and 2.1 kcal/mol from C2 to C3 B39-, rendering dynamic fluxionalities to these borospherenes. Therefore, the "W-X-M" transformation plays an important role in the borospherenes and borospherene-based nanostructures.

  10. β and Isomeric Decay of Nuclei in the 100Sn Region

    NASA Astrophysics Data System (ADS)

    Becerril, A. D.; Amthor, A. M.; Baumann, T.; Bazin, D.; Berryman, J. S.; Crawford, H.; Estrade, A.; Gade, A.; Ginter, T.; Guess, C. J.; Hausmann, M.; Hitt, G. W.; Lorusso, G.; Mantica, P. F.; Matos, M.; Meharchand, R.; Minamisono, K.; Montes, F.; Pereira, J.; Perdikakis, G.; Portillo, M.; Schatz, H.; Smith, K.; Stoker, J.; Zegers, R. T. G.

    2010-08-01

    The decay properties of rp-process nuclei in the vicinity of 100Sn have been studied at the National Superconducting Cyclotron Laboratory (NSCL). The measured β-decay half-life for 100Sn is 0.55-0.31+0.70 s, in agreement with a previous measurement. In 98In, the β-decay of the ground state plus that of a long lived isomer were observed with half-lives of 47(13) ms and 0.66(40) s respectively. The half-life of 96Cd, measured for the first time, is 1.03-0.21+0.24 s; however, the existence of a predicted isomeric state in this nucleus could not be confirmed. Additionally, a gamma cascade de-exciting a μ-isomer in the odd-odd nucleus 96Ag was observed. The implications of the measured half-life of 96Cd on the calculated rp-process final abundances are discussed.

  11. Molecular driving forces for Z/E isomerization mediated by heteroatoms: the example hemithioindigo.

    PubMed

    Nenov, Artur; Cordes, Thorben; Herzog, Teja T; Zinth, Wolfgang; de Vivie-Riedle, Regina

    2010-12-23

    A combined experimental and theoretical investigation of photoinduced Z/E isomerizations is presented. Unsubstituted Hemithioindigo is selected as a representative minimal model to unravel the reaction mechanism in the presence of heteroatoms on an atomic level. Time-resolved spectroscopy reveals multiexponential reaction dynamics on the few picoseconds time scale, which are interpreted by quantum chemical calculations at the CASSCF/CASPT2 level of theory. Detailed insight into the processes governing the ultrafast decay from the first excited state, mediated by a number of conical intersections, is provided. Charge separation and charge balance recovery on the reaction pathway play the leading role and are controlled by the electron-donating or -withdrawing character of the heteroatoms. The electronic and geometric structures of the individual minimum energy conical intersections governing the reaction are rationalized, and an extended energetically low lying conical intersection seam is extracted. Comparison to the experimental results permits linking the observed time constants to molecular intermediates and pathways. An explanation is provided for the pronounced differences of Z → E and the E → Z photoreactions upon excitation to the first excited singlet state.

  12. Spectrophotometric studies on alkaline isomerization of spinach ferredoxin.

    PubMed

    Hasumi, H; Nagata, E; Nakamura, S

    1985-10-01

    The gross protein structure, the microenvironment of the iron-sulfur cluster, and the effect of neutral salts on the molecular structure of spinach ferredoxin were studied by CD and absorption spectroscopy in the alkaline pH range. In the pH range of 7-11, the existence of reversible isomerization which consisted of at least two proton dissociation processes was indicated by the statical CD and absorption spectra. The CD changes in the visible and far-UV regions were dramatic upon elevation of the pH from neutral to alkaline, indicating a significant alteration of the microenvironment of the cluster and a decrease in the ordered secondary structures. The absorption change in the visible region due to pH elevation was small but clearly observed with a high signal-to-noise ratio. The numbers of protons involved in the respective processes and the apparent pK values obtained from the pH-dependence of the CD changes were in good agreement with those obtained from the pH-dependence of the absorption changes in the visible region. In addition, the rate constants obtained from the time courses of the CD and absorption changes agreed with one another. By the addition of 1 M NaCl, the CD and absorption spectra at alkaline pH were reversed almost to those at neutral pH without significant pH change. On the other hand, above pH 11, ferredoxin was found to be irreversibly denatured. Based on analyses of the statical CD and absorption spectra and of the time courses of the CD changes, the probable mechanism of the isomerization was considered to be as follows: (Formula: see text) where H stands for a proton, N-form for native ferredoxin at neutral pH, N*-form for alkaline ferredoxin below pH 11 which still has the iron-sulfur cluster but with disordered secondary structures of the polypeptide chain, and D-form for completely denatured ferredoxin above pH 11. These results lead to the conclusions that (1) the interaction between the protein moiety and the iron-sulfur cluster is

  13. Effects of alkali or acid treatment on the isomerization of amino acids.

    PubMed

    Ohmori, Taketo; Mutaguchi, Yuta; Doi, Katsumi; Ohshima, Toshihisa

    2012-10-01

    The effect of alkali treatment on the isomerization of amino acids was investigated. The 100×D/(D+L) values of amino acids from peptide increased with increase in the number of constituent amino acid residues. Furthermore, the N-terminal amino acid of a dipeptide was isomerized to a greater extent than the C-terminal residue. Copyright © 2012. Published by Elsevier B.V.

  14. Metal-centred azaphosphatriptycene gear with a photo- and thermally driven mechanical switching function based on coordination isomerism.

    PubMed

    Ube, Hitoshi; Yasuda, Yoshihiro; Sato, Hiroyasu; Shionoya, Mitsuhiko

    2017-02-08

    Metal ions can serve as a centre of molecular motions due to their coordination geometry, reversible bonding nature and external stimuli responsiveness. Such essential features of metal ions have been utilized for metal-mediated molecular machines with the ability to motion switch via metallation/demetallation or coordination number variation at the metal centre; however, motion switching based on the change in coordination geometry remain largely unexplored. Herein, we report a Pt(II)-centred molecular gear that demonstrates control of rotor engagement and disengagement based on photo- and thermally driven cis-trans isomerization at the Pt(II) centre. This molecular rotary motion transmitter has been constructed from two coordinating azaphosphatriptycene rotators and one Pt(II) ion as a stator. Isomerization between an engaged cis-form and a disengaged trans-form is reversibly driven by ultraviolet irradiation and heating. Such a photo- and thermally triggered motional interconversion between engaged/disengaged states on a metal ion would provide a selector switch for more complex interlocking systems.

  15. Metal-centred azaphosphatriptycene gear with a photo- and thermally driven mechanical switching function based on coordination isomerism

    NASA Astrophysics Data System (ADS)

    Ube, Hitoshi; Yasuda, Yoshihiro; Sato, Hiroyasu; Shionoya, Mitsuhiko

    2017-02-01

    Metal ions can serve as a centre of molecular motions due to their coordination geometry, reversible bonding nature and external stimuli responsiveness. Such essential features of metal ions have been utilized for metal-mediated molecular machines with the ability to motion switch via metallation/demetallation or coordination number variation at the metal centre; however, motion switching based on the change in coordination geometry remain largely unexplored. Herein, we report a PtII-centred molecular gear that demonstrates control of rotor engagement and disengagement based on photo- and thermally driven cis-trans isomerization at the PtII centre. This molecular rotary motion transmitter has been constructed from two coordinating azaphosphatriptycene rotators and one PtII ion as a stator. Isomerization between an engaged cis-form and a disengaged trans-form is reversibly driven by ultraviolet irradiation and heating. Such a photo- and thermally triggered motional interconversion between engaged/disengaged states on a metal ion would provide a selector switch for more complex interlocking systems.

  16. Metal-centred azaphosphatriptycene gear with a photo- and thermally driven mechanical switching function based on coordination isomerism

    PubMed Central

    Ube, Hitoshi; Yasuda, Yoshihiro; Sato, Hiroyasu; Shionoya, Mitsuhiko

    2017-01-01

    Metal ions can serve as a centre of molecular motions due to their coordination geometry, reversible bonding nature and external stimuli responsiveness. Such essential features of metal ions have been utilized for metal-mediated molecular machines with the ability to motion switch via metallation/demetallation or coordination number variation at the metal centre; however, motion switching based on the change in coordination geometry remain largely unexplored. Herein, we report a PtII-centred molecular gear that demonstrates control of rotor engagement and disengagement based on photo- and thermally driven cis–trans isomerization at the PtII centre. This molecular rotary motion transmitter has been constructed from two coordinating azaphosphatriptycene rotators and one PtII ion as a stator. Isomerization between an engaged cis-form and a disengaged trans-form is reversibly driven by ultraviolet irradiation and heating. Such a photo- and thermally triggered motional interconversion between engaged/disengaged states on a metal ion would provide a selector switch for more complex interlocking systems. PMID:28176770

  17. Unexpectedly fast cis/trans isomerization of Xaa-Pro peptide bonds in disulfide-constrained cyclic peptides.

    PubMed

    Shi, Tiesheng; Spain, Stephen M; Rabenstein, Dallas L

    2004-01-28

    Acyclic dithiol and cyclic disulfide forms of the peptides Ac-Cys-Pro-Xaa-Cys-NH2 (Xaa = Phe, His, Tyr, Gly, and Thr) and Ac-Cys-Gly-Pro-Cys-NH2 and the peptide Ac-Ala-Gly-Pro-Ala-NH2 were synthesized and characterized by mass spectrometry and NMR spectroscopy. Rate constants kct and ktc for cis-to-trans and trans-to-cis isomerization, respectively, across the Cys-Pro or Gly-Pro peptide bonds were determined by magnetization transfer NMR techniques over a range of temperatures, and activation parameters were derived from the temperature dependence of the rate constants. It was found that constraints imposed by the disulfide bond confer an unexpected rate enhancement for cis/trans isomerization, ranging from a factor of 2 to 13. It is proposed that the rate enhancements are a result of an intramolecular catalysis mechanism in which the NH proton of the Pro-Xaa peptide bond hydrogen bonds to the proline nitrogen in the transition state. The peptides Ac-Cys-Pro-Xaa-Cys-NH2 and Ac-Cys-Gly-Pro-Cys-NH2 are model compounds for proline-containing active sites of the thioredoxin superfamily of oxidoreductase enzymes; the results suggest that the backbones of the active sites of the oxidized form of these enzymes may have unusual conformational flexibility.

  18. Intramolecular charge transfer and trans-cis isomerization of the DCM styrene dye in polar solvents. A CS INDO MRCI study

    NASA Astrophysics Data System (ADS)

    Marguet, S.; Mialocq, J. C.; Millie, P.; Berthier, G.; Momicchioli, F.

    1992-03-01

    The solvent-induced changes of trans-cis isomerization efficiency and electronic structure of the excited state of the DCM dye have been considered by means of CS INDO MRCI calculations. The potential energy curves, dipole moments and atomic charge densities as a function of two internal coordinates, namely the rotation angle about the central "double" bond and the twisting of the dimethylamino group, have been obtained for the ground state and the lowest excited states. The structural requirements for the existence of ICT (intramolecular charge transfer) excited states have been investigated by considering internal rotations about three single bonds. The reliability of the potential surfaces and of the solvation models has been discussed with reference to test-calculations on the DMABN molecule. In the first excited singlet state of DCM, the low-energy barrier for the trans-cis isomerization has been found unaffected by the solvent polarity. The only singlet excited state presenting a large ICT character has been found to be the S 2 state for a perpendicularly twisted conformation of the dimethylamino group (TICT state). The assumption of a deactivation of the trans-isomer in the locally excited state through the TICT funnel has been largely discussed with reference to the simplifications of the present theoretical approach.

  19. Influence of the steric effect of flexible isomeric phenylenediacetic acids on the resultant lead(II) coordination polymers

    SciTech Connect

    Wu, Yunlong; Zhao, Yanqing; Yang, Guo-Ping Guo, Yanjun; Wang, Yao-Yu Shi, Qi-Zhen

    2015-03-15

    To study the steric effect of the flexible dicarboxylate ligands on the resultant formations of coordination polymers (CPs), four new Pb{sup II} CPs [Pb(1,2-pda)(H{sub 2}O)]{sub n} (1), [Pb(1,3-pda)]{sub n}·nH{sub 2}O (2), [Pb{sub 2}(1,4-pda){sub 2}(H{sub 2}O)]{sub n}·2nH{sub 2}O (3a and 3b) have been produced by the isomeric phenylenediacetic acids (H{sub 2}pda). The X-ray crystallography study reveals that CP 1 is a two-dimensional (2D) 4-connected sql (4{sup 4}.6{sup 2}) network via the weak Pb···O interactions built on 1D chain-like structure. CP 2 crystallizes in orthorhombic system with chiral space group P2{sub 1}2{sub 1}2{sub 1}, showing a 4-connected sra (4{sup 2}.6{sup 3}.8) framework where a left-handed helical motif is formed by Pb{sup II} ions and trans-1,3-pda ligands. More interestingly, CPs 3a and 3b are two true 3D polymorphs and have the different morphology. Topologically, the framework of 3a exhibits a 4-connected lon 6{sup 6} motif, while that of 3b is a (4,6)-connected fsh (4{sup 3}.6{sup 3}){sub 2}(4{sup 6}.6{sup 6}.8{sup 3}) net. It is found that the three isomeric pda anions display the various coordination fashions in four CPs. The different structural arrangements show that the steric effect of the isomeric H{sub 2}pda tectons has a positive role in directing the final products of Pb{sup II} CPs. Also, the fluorescent properties of the CPs were studied in the solid state at room temperature. - Graphical abstract: Four new Pb{sup II}-based CPs have been produced by the isomeric phenylenediacetic acids (H{sub 2}pda). The different structural arrangements show that the steric effect of the isomeric H{sub 2}pda tectons has a positive role in directing the final products of Pb{sup II} CPs. Also, the fluorescent properties of the CPs were studied in the solid state at room temperature. - Highlights: • Four Pb{sup II}-based coordination polymers were produced by phenylenediacetic acids. • The crystal and topological structures of the

  20. Cross sections for the formation of 69Znm,g and 71Znm,g in neutron induced reactions near their thresholds: Effect of reaction channel on the isomeric cross-section ratio

    NASA Astrophysics Data System (ADS)

    Nesaraja, C. D.; Sudár, S.; Qaim, S. M.

    2003-08-01

    Excitation functions were measured for the reactions 72Ge(n,α)69Znm,g, 69Ga(n,p)69Znm,g, 70Zn(n,2n)69Znm,g, 74Ge(n,α)71Znm,g, and 71Ga(n,p)71Znm,g over the neutron energy range of 6.3 12.4 MeV. Quasimonoenergetic neutrons in this energy range were produced via the 2H(d,n)3He reaction using a deuterium gas target at the Jülich variable energy compact cyclotron. Use was made of the activation technique in combination with high-resolution HPGe-detector γ-ray spectroscopy. In a few cases low-level β-counting was also applied. In order to decrease the interfering activities in those cases, either radiochemical separations were performed or isotopically enriched targets were used. For most of the reactions, the present measurements provide the first consistent sets of data near their thresholds. From the available experimental data, isomeric cross-section ratios were determined for the isomeric pair 69Znm,g in (n,α), (n,p), and (n,2n) reactions, and for the pair 71Znm,g in (n,α) and (n,p) reactions. Nuclear model calculations using the code STAPRE, which employs the Hauser-Feshbach (statistical model) and exciton model (precompound effects) formalisms, were undertaken to describe the formation of both isomeric and ground states of the products. The calculational results on the total (n,α), (n,p), and (n,2n) cross sections agree fairly well with the experimental data. The experimental isomeric cross-section ratios, however, are reproduced only approximately by the calculation. For both the isomeric pairs investigated, the isomeric cross-section ratio in the (n,p) reaction is higher than in other reactions.

  1. Ion Mobility Mass Spectrometry Analysis of Isomeric Disaccharide Precursor, Product and Cluster Ions

    PubMed Central

    Li, Hongli; Bendiak, Brad; Siems, William F.; Gang, David R.; Hill, Herbert H.

    2015-01-01

    RATIONALE Carbohydrates are highly variable in structure owing to differences in their anomeric configurations, monomer stereochemistry, inter-residue linkage positions and general branching features. The separation of carbohydrate isomers poses a great challenge for current analytical techniques. METHODS The isomeric heterogeneity of disaccharide ions and monosaccharideglycolaldehyde product ions evaluated using electrospray traveling wave ion mobility mass spectrometry (Synapt G2 high definition mass spectrometer) in both positive and negative ion modes investigation. RESULTS The separation of isomeric disaccharide ions was observed but not fully achieved based on their mobility profiles. The mobilities of isomeric product ions, the monosaccharide-glycolaldehydes, derived from different disaccharide isomers were measured. Multiple mobility peaks were observed for both monosaccharide-glycolaldehyde cations and anions, indicating that there was more than one structural configuration in the gas phase as verified by NMR in solution. More importantly, the mobility patterns for isomeric monosaccharide-glycolaldehyde product ions were different, which enabled partial characterization of their respective disaccharide ions. Abundant disaccharide cluster ions were also observed. The Results showed that a majority of isomeric cluster ions had different drift times and, moreover, more than one mobility peak was detected for a number of specific cluster ions. CONCLUSIONS It is demonstrated that ion mobility mass spectrometry is an advantageous method to assess the isomeric heterogeneity of carbohydrate compounds. It is capable of differentiating different types of carbohydrate ions having identical m/z values as well as multiple structural configurations of single compounds. PMID:24591031

  2. Carrot β-carotene degradation and isomerization kinetics during thermal processing in the presence of oil.

    PubMed

    Knockaert, Griet; Pulissery, Sudheer K; Lemmens, Lien; Van Buggenhout, Sandy; Hendrickx, Marc; Van Loey, Ann

    2012-10-17

    The effect of thermal processing (85-130 °C) on the stability and isomerization of β-carotene in both an olive oil/carrot emulsion and an olive oil phase enriched with carrot β-carotene was studied. During processing, degradation of total β-carotene took place. Initially, total β-carotene concentration decreased quickly, after which a plateau value was reached, which was dependent on the applied temperature. In the oil/carrot emulsion, the total β-carotene concentration could be modeled by a fractional conversion model. The temperature dependence of the degradation rate constants was described by the activation energy and was estimated to be 45.0 kJ/mol. In the enriched oil phase, less degradation took place and the results could not be modeled. Besides degradation, β-carotene isomerization was studied. In both matrices, a fractional conversion model could be used to model total isomerization and formation of 13-Z- and 15-Z-β-carotene. β-Carotene isomerization was similar in both the oil/carrot emulsion and enriched oil phase as the simultaneously estimated kinetic parameters (isomerization reaction rate constant and activation energy) of both matrices did not differ significantly. The activation energies of isomerization were estimated to be 70.5 and 75.0 kJ/mol in the oil/carrot emulsion and enriched oil phase, respectively.

  3. Photochemical Isomerization and Topochemical Polymerization of the Programmed Asymmetric Amphiphiles

    NASA Astrophysics Data System (ADS)

    Kim, Dae-Yoon; Lee, Sang-A.; Jung, Daseal; Jeong, Kwang-Un

    2016-06-01

    For the advancement in multi-stimuli responsive optical devices, we report the elaborate molecular engineering of the dual photo-functionalized amphiphile (abbreviated as AZ1DA) containing both a photo-isomerizable azobenzene and a photo-polymerizable diacetylene. To achieve the efficient photochemical reactions in thin solid films, the self-assembly of AZ1DA molecules into the ordered phases should be precisely controlled and efficiently utilized. First, the remote-controllable light shutter is successfully demonstrated based on the reversible trans-cis photo-isomerization of azobenzene group in the smectic A mesophase. Second, the self-organized monoclinic crystal phase allows us to validate the photo-polymerization of diacetylene moiety for the photo-patterned thin films and the thermo-responsible color switches. From the demonstrations of optically tunable thin films, it is realized that the construction of strong relationships between chemical structures, molecular packing structures and physical properties of the programmed molecules is the core research for the development of smart and multifunctional soft materials.

  4. Roots of Acetate-Vanadium Linkage Isomerism: A QTAIM Study.

    PubMed

    Teixeira, Filipe; Mosquera, Ricardo; Melo, André; Freire, Cristina; Cordeiro, M Natália D S

    2016-04-04

    The possibility of linkage isomerism in a number of vanadium(IV) and vanadium(V) complexes with acetate was surveyed using Density Functional Theory (DFT) and Bader's Quantum Theory of Atoms in Molecules (QTAIM). The results show that vanadium-acetate linkages may be classified as bidentate symmetrical, bidentate asymmetrical, or monodentate, the latter being observed in about 40% of the cases. These latter ones correspond to situations where the two oxygen atoms of the acetate moiety are not equivalent. They are associated with an energy penalty of about 263 kJ·mol(-1), as determined by the distribution of the scaled kinetic energy of the atomic basins forming the acetate ligand. In the presence of bidentate symmetrical vanadium-acetate linkages, the inner valence-shell charge concentrations on the vanadium atom deviate from the traditional VSEPR-derived arrangement, with an energy penalty of about 780 kJ·mol(-1). A compromise situation is partially accomplished in the case of bidentate asymmetrical linkages, which allow a Gillespiean-like arrangement of the inner valence-shell charge concentrations. In this case, one of these local charge concentrations lies close to a V-OAcO bond, which slightly disrupts the equivalence between the two oxygen atoms in the acetate ligand.

  5. Photochemical Isomerization and Topochemical Polymerization of the Programmed Asymmetric Amphiphiles

    PubMed Central

    Kim, Dae-Yoon; Lee, Sang-A; Jung, Daseal; Jeong, Kwang-Un

    2016-01-01

    For the advancement in multi-stimuli responsive optical devices, we report the elaborate molecular engineering of the dual photo-functionalized amphiphile (abbreviated as AZ1DA) containing both a photo-isomerizable azobenzene and a photo-polymerizable diacetylene. To achieve the efficient photochemical reactions in thin solid films, the self-assembly of AZ1DA molecules into the ordered phases should be precisely controlled and efficiently utilized. First, the remote-controllable light shutter is successfully demonstrated based on the reversible trans-cis photo-isomerization of azobenzene group in the smectic A mesophase. Second, the self-organized monoclinic crystal phase allows us to validate the photo-polymerization of diacetylene moiety for the photo-patterned thin films and the thermo-responsible color switches. From the demonstrations of optically tunable thin films, it is realized that the construction of strong relationships between chemical structures, molecular packing structures and physical properties of the programmed molecules is the core research for the development of smart and multifunctional soft materials. PMID:27339163

  6. Randomized Subspace Learning for Proline Cis-Trans Isomerization Prediction.

    PubMed

    Al-Jarrah, Omar Y; Yoo, Paul D; Taha, Kamal; Muhaidat, Sami; Shami, Abdallah; Zaki, Nazar

    2015-01-01

    Proline residues are common source of kinetic complications during folding. The X-Pro peptide bond is the only peptide bond for which the stability of the cis and trans conformations is comparable. The cis-trans isomerization (CTI) of X-Pro peptide bonds is a widely recognized rate-limiting factor, which can not only induces additional slow phases in protein folding but also modifies the millisecond and sub-millisecond dynamics of the protein. An accurate computational prediction of proline CTI is of great importance for the understanding of protein folding, splicing, cell signaling, and transmembrane active transport in both the human body and animals. In our earlier work, we successfully developed a biophysically motivated proline CTI predictor utilizing a novel tree-based consensus model with a powerful metalearning technique and achieved 86.58 percent Q2 accuracy and 0.74 Mcc, which is a better result than the results (70-73 percent Q2 accuracies) reported in the literature on the well-referenced benchmark dataset. In this paper, we describe experiments with novel randomized subspace learning and bootstrap seeding techniques as an extension to our earlier work, the consensus models as well as entropy-based learning methods, to obtain better accuracy through a precise and robust learning scheme for proline CTI prediction.

  7. Isomerization and fragmentation pathways of 1,2-azaborine.

    PubMed

    Edel, Klara; Fink, Reinhold F; Bettinger, Holger F

    2016-01-05

    The generation of 1,2-azaborine (4), the BN-analogue of ortho-benzyne, was recently achieved by elimination of tert-butyldimethylchlorosilane under the conditions of flash vacuum pyrolysis. The present investigation identifies by computational means pathways for the thermal isomerization and fragmentation of 1,2-azaborine. The computations were performed using single reference (hybrid/density functional, second order Møller-Plesset perturbation, and coupled cluster theories) as well as multiconfiguration methods (complete active space SCF based second order perturbation theory, multireference configuration interaction, and multiconfiguration coupled electron pair approximation) with basis sets up to polarized triple-ζ quality. The 1,2-azaborine is, despite the distortion of its molecular structure, the most stable C4H4BN isomer investigated. The formation of BN-endiyne isomers is highly unfavorable as the identified pathways involve barriers close to 80 kcal mol(-1). The concerted fragmentation to ethyne and 2-aza-3-bora-butadiyne even has a barrier close to 120 kcal mol(-1). The fragmentation of BN-enediynes has energetic requirements similar to enediynes. © 2015 Wiley Periodicals, Inc.

  8. Cyclophilin A catalyzes proline isomerization by an electrostatic handle mechanism

    SciTech Connect

    Camilloni, Carlo; Sahakyan, Aleksander B.; Holliday, Michael; Isern, Nancy G.; Zhang, Fengli; Eisenmesser, Elan Z.; Vendruscolo, Michele

    2014-07-15

    Proline isomerization is a ubiquitous process that plays a key role in the folding of proteins and in the regulation of their functions1-3. Different families of enzymes, known as peptidyl-prolyl isomerases (PPIases), catalyse this reaction, which involves the interconversion between the cis and trans isomers of the Nterminal amide bond of the amino acid proline2,3. A complete description of the mechanisms by which these enzymes function, however, has remained elusive. Here, we show that cyclophilin A, one of the most common PPIases4, provides a catalytic environment that acts on the substrate through an electrostatic lever mechanism. In this mechanism, the electrostatic field in the catalytic site turns the electric dipole associated with the carboxylic group of the amino acid preceding the proline in the substrate, thus causing the rotation of the peptide bond between the two residues. This mechanism resulted from the analysis of an ensemble of conformations populated by cyclophilin A during the enzymatic reaction using a combination of NMR measurements, molecular dynamics simulations and density functional theory calculations. We anticipate that this approach will be helpful in elucidating whether the electrostatic lever mechanism that we describe is common to other PPIases, and more generally to characterise other enzymatic processes.

  9. An automated exploration of the isomerization and dissociation pathways of (E)-1,2-dichloroethene cations and anions

    NASA Astrophysics Data System (ADS)

    Kishimoto, Naoki; Nishi, Yuito

    2017-04-01

    Isomerization and dissociation pathways after the photoionization or electron attachment of (E)-1,2-dichloroethene were calculated with an automated exploration method utilizing a scaled hypersphere search of the anharmonic downward distortion following algorithm at the UB3LYP/6-311G(2d,d,p) level of theory. The potential energies of transition states and dissociation channels were calculated by a composite method ((RO)CBS-QB3) and compared with the breakdown diagrams and electron attachment spectra observed in previous spectroscopic studies. The results of single point calculations with several DFT and post-SCF methods are compared using the root mean square deviations from the (RO)CBS-QB3 energies for six states of anionic dichloroethene.

  10. A bacterial tyrosine aminomutase proceeds through retention or inversion of stereochemistry to catalyze its isomerization reaction.

    PubMed

    Wanninayake, Udayanga; Walker, Kevin D

    2013-07-31

    β-Amino acids are biologically active compounds of interest in medicinal chemistry. A class I lyase-like family of aminomutases isomerizes (S)-α-arylalanines to the corresponding β-amino acids by exchange of the NH2/H pair. This family uses a 3,5-dihydro-5-methylidene-4H-imidazol-4-one (MIO) group within the active site to initiate the reaction. The absolute stereochemistry of the product is known for an MIO-dependent tyrosine aminomutase from Chondromyces crocatus (CcTAM) that isomerizes (S)-α-tyrosine to (R)-β-tyrosine. To evaluate the cryptic stereochemistry of the CcTAM mechanism, (2S,3S)-[2,3-(2)H2]- and (2S,3R)-[3-(2)H]-α-tyrosine were stereoselectively synthesized from unlabeled (or [(2)H]-labeled) (4'-hydroxyphenyl)acrylic acids by reduction with D2 (or H2) gas and a chiral Rh-Prophos catalyst. GC/EIMS analysis of the [(2)H]-β-tyrosine biosynthesized by CcTAM revealed that the α-amino group was transferred to Cβ of the phenylpropanoid skeleton with retention of configuration. These labeled substrates also showed that the pro-(3S) proton exchanges with protons from the bulk media during its migration to Cα during catalysis. (1)H- and (2)H NMR analyses of the [(2)H]-β-tyrosine derived from (2S)-[3,3-(2)H2]-α-tyrosine by CcTAM catalysis showed that the migratory proton attached to Cα of the product also with retention of configuration. CcTAM is stereoselective for (R)-β-tyrosine (85%) yet also forms the (S)-β-tyrosine enantiomer (15%) through inversion of configuration at both migration termini, as described herein. The proportion of the (S)-β-isomer made by CcTAM during steady state interestingly increased with solvent pH, and this effect on the proposed reaction mechanism is also discussed.

  11. Computational studies of the isomerization and hydration reactions of acetaldehyde oxide and methyl vinyl carbonyl oxide.

    PubMed

    Kuwata, Keith T; Hermes, Matthew R; Carlson, Matthew J; Zogg, Cheryl K

    2010-09-02

    Alkene ozonolysis is a major source of hydroxyl radical (*OH), the most important oxidant in the troposphere. Previous experimental and computational work suggests that for many alkenes the measured *OH yields should be attributed to the combined impact of both chemically activated and thermalized syn-alkyl Criegee intermediates (CIs), even though the thermalized CI should be susceptible to trapping by molecules such as water. We have used RRKM/master equation and variational transition state theory calculations to quantify the competition between unimolecular isomerization and bimolecular hydration reactions for the syn and anti acetaldehyde oxide formed in trans-2-butene ozonolysis and for the CIs formed in isoprene ozonolysis possessing syn-methyl groups. Statistical rate theory calculations were based on quantum chemical data provided by the B3LYP, QCISD, and multicoefficient G3 methods, and thermal rate constants were corrected for tunneling effects using the Eckart method. At tropospheric temperatures and pressures, all thermalized CIs with syn-methyl groups are predicted to undergo 1,4-hydrogen shifts from 2 to 8 orders of magnitude faster than they react with water monomer at its saturation number density. For thermalized anti acetaldehyde oxide, the rates of dioxirane formation and hydration should be comparable.

  12. Resolution of isomeric new designer stimulants using gas chromatography - Vacuum ultraviolet spectroscopy and theoretical computations.

    PubMed

    Skultety, Ludovit; Frycak, Petr; Qiu, Changling; Smuts, Jonathan; Shear-Laude, Lindsey; Lemr, Karel; Mao, James X; Kroll, Peter; Schug, Kevin A; Szewczak, Angelica; Vaught, Cory; Lurie, Ira; Havlicek, Vladimir

    2017-06-08

    Distinguishing isomeric representatives of "bath salts", "plant food", "spice", or "legal high" remains a challenge for analytical chemistry. In this work, we used vacuum ultraviolet spectroscopy combined with gas chromatography to address this issue on a set of forty-three designer drugs. All compounds, including many isomers, returned differentiable vacuum ultraviolet/ultraviolet spectra. The pair of 3- and 4-fluoromethcathinones (m/z 181.0903), as well as the methoxetamine/meperidine/ethylphenidate (m/z 247.1572) triad, provided very distinctive vacuum ultraviolet spectral features. On the contrary, spectra of 4-methylethcathinone, 4-ethylmethcathinone, 3,4-dimethylmethcathinone triad (m/z 191.1310) displayed much higher similarities. Their resolution was possible only if pure standards were probed. A similar situation occurred with the ethylone and butylone pair (m/z 221.1052). On the other hand, majority of forty-three drugs was successfully separated by gas chromatography. The detection limits for all the drug standards were in the 2-4 ng range (on-column amount), which is sufficient for determinations of seized drugs during forensics analysis. Further, state-of-the-art time-dependent density functional theory was evaluated for computation of theoretical absorption spectra in the 125-240 nm range as a complementary tool. Copyright © 2017 Elsevier B.V. All rights reserved.

  13. Extrapolating potential energy surfaces by scaling electron correlation: Isomerization of bicyclobutane to butadiene

    NASA Astrophysics Data System (ADS)

    Lutz, Jesse J.; Piecuch, Piotr

    2008-04-01

    The recently proposed potential energy surface (PES) extrapolation scheme, which predicts smooth molecular PESs corresponding to larger basis sets from the relatively inexpensive calculations using smaller basis sets by scaling electron correlation energies [A. J. C. Varandas and P. Piecuch, Chem. Phys. Lett. 430, 448 (2006)], is applied to the PESs associated with the conrotatory and disrotatory isomerization pathways of bicyclo[1.1.0]butane to buta-1,3-diene. The relevant electronic structure calculations are performed using the completely renormalized coupled-cluster method with singly and doubly excited clusters and a noniterative treatment of connected triply excited clusters, termed CR-CC(2,3), which is known to provide a highly accurate description of chemical reaction profiles involving biradical transition states and intermediates. A comparison with the explicit CR-CC(2,3) calculations using the large correlation-consistent basis set of the cc-pVQZ quality shows that the cc-pVQZ PESs obtained by the extrapolation from the smaller basis set calculations employing the cc-pVDZ and cc-pVTZ basis sets are practically identical, to within fractions of a millihartree, to the true cc-pVQZ PESs. It is also demonstrated that one can use a similar extrapolation procedure to accurately predict the complete basis set (CBS) limits of the calculated PESs from the results of smaller basis set calculations at a fraction of the effort required by the conventional pointwise CBS extrapolations.

  14. Highly selective Lewis acid sites in desilicated MFI zeolites for dihydroxyacetone isomerization to lactic acid.

    PubMed

    Dapsens, Pierre Y; Mondelli, Cecilia; Pérez-Ramírez, Javier

    2013-05-01

    Desilication of commercial MFI-type (ZSM-5) zeolites in solutions of alkali metal hydroxides is demonstrated to generate highly selective heterogeneous catalysts for the aqueous-phase isomerization of biobased dihydroxyacetone (DHA) to lactic acid (LA). The best hierarchical ZSM-5 sample attains a LA selectivity exceeding 90 %, which is comparable to that of the state-of-the-art catalyst (i.e., the Sn-beta zeolite); this optimized hierarchical catalyst is recyclable over three runs. The Lewis acid sites, which are created through desilication along with the introduction of mesoporosity, are shown to play a crucial role in the formation of the desired product; these cannot be achieved by using other post-synthetic methods, such as steaming or impregnation of aluminum species. Desilication of other metallosilicates, such as Ga-MFI, also leads to high LA selectivity. In the presence of a soluble aluminum source, such as aluminum nitrate, alkaline-assisted alumination can introduce these unique Lewis acid centers in all-silica MFI zeolites. These findings highlight the potential of zeolites in the field of biomass-to-chemical conversion, and expand the applicability of desilication for the generation of selective catalytic centers.

  15. Modeling trans-cis chromophore isomerization for the asFP595 kindling protein

    NASA Astrophysics Data System (ADS)

    Grigorenko, Bella L.; Nemukhin, Alexander V.

    2007-02-01

    We present the results of modeling properties of the chromophore, 2-acetyl-4-(p-hydroxybenzylidene)-1-methyl-5- imidazolone (AHBMI), from the newly discovered fluorescent protein asFP595 inside the protein environment by using the combined quantum mechanical - molecular mechanical (QM/MM) method. In this approach, the chromophore unit and the side chains of the nearest amino acid residues are assigned to the quantum subsystem. The starting coordinates of heavy atoms were taken from the relevant crystal structures of the protein. Hydrogen atoms were added manually, and the structure of the model protein system was optimized by using QM/MM energy minimization for the trans-form of the chromophore. The Hartree-Fock/6-31G quantum chemical approximation and the AMBER force field parameters were employed in geometry optimization. The points on potential energy surfaces of the ground and first and second excited electronic states were computed with the complete active space self-consistent field approximation in the quantum subsystem under different choices of the QM/MM partitioning. Possible pathways for the trans-cis photo isomerization presumably responsible for the kindling properties of asFP595 as well as other mechanisms of photo excitation are discussed.

  16. Photofragmentation of I2-ṡArn clusters: Observation of metastable isomeric ionic fragments

    NASA Astrophysics Data System (ADS)

    Vorsa, Vasil; Campagnola, Paul J.; Nandi, Sreela; Larsson, Mats; Lineberger, W. C.

    1996-08-01

    We report the 790 nm photofragmentation of mass-selected I-2ṡArn clusters, n=1 to 27. We determine the I-+I caging efficiency as a function of the number of solvent Ar atoms and compare these results with I-2 in CO2 clusters. Caging is much less effective with Ar. In addition to ``normal'' caged photoproducts (I-2ṡArm, where mstate or as a solvent-separated pair at an internuclear separation of ˜5.5 Å. The photofragmentation data also exhibit the existence of two distinct isomeric forms of the precursor I-2ṡArn, for n≤14. These forms are evaporatively distinct in that one isomer displays highly nonstatistical fragmentation, probably arising from a cluster in which the I-2 resides on the surface, rather than in the interior. The photofragmentation distribution of the other form exhibits statistical behavior, consistent with the evaporation of an I-2 solvated inside the cluster.

  17. Intramolecular interactions, isomerization and vibrational frequencies of two paracetamol analogues: A spectroscopic and a computational approach

    NASA Astrophysics Data System (ADS)

    Viana, Rommel B.; Ribeiro, Gabriela L. O.; Santos, Sinara F. F.; Quintero, David E.; Viana, Anderson B.; da Silva, Albérico B. F.; Moreno-Fuquen, Rodolfo

    2016-06-01

    The aim of this investigation was to determine the molecular properties and provide an interpretation of the vibrational mode couplings of these two paracetamol analogues: 2-bromo-2-methyl-N-(4-nitrophenyl)-propanamide and 2-bromo-2-methyl-N-p-tolyl-propanamide. E/Z isomers, keto/enol unimolecular rearrangement and prediction of the transition state structures in each mechanism were also assessed using the Density Functional Theory (DFT). The DFT estimates a high energy gap between E and Z isomers (9-11 kcal·mol- 1), with barrier heights ranging from 16 to 19 kcal·mol- 1. In contrast, the barrier energies on the keto/enol isomerization are almost 10 kcal·mol- 1 higher than those estimated for the E/Z rearrangement. The kinetic rate constant was also determined for each reaction mechanism. Natural bond orbital analysis and the quantum theory of atoms in molecules were used to interpret the intramolecular hydrogen bonds and to understand the most important interactions that govern the stabilization of each isomer. Furthermore, an analysis of the atomic charge distribution using different population methodologies was also performed.

  18. Tin-containing zeolites are highly active catalysts for the isomerization of glucose in water

    PubMed Central

    Moliner, Manuel; Román-Leshkov, Yuriy; Davis, Mark E.

    2010-01-01

    The isomerization of glucose into fructose is a large-scale reaction for the production of high-fructose corn syrup (HFCS; reaction performed by enzyme catalysts) and recently is being considered as an intermediate step in the possible route of biomass to fuels and chemicals. Here, it is shown that a large-pore zeolite that contains tin (Sn-Beta) is able to isomerize glucose to fructose in aqueous media with high activity and selectivity. Specifically, a 10% (wt/wt) glucose solution containing a catalytic amount of Sn-Beta (1∶50 Sn:glucose molar ratio) gives product yields of approximately 46% (wt/wt) glucose, 31% (wt/wt) fructose, and 9% (wt/wt) mannose after 30  min and 12 min of reaction at 383 K and 413 K, respectively. This reactivity is achieved also when a 45 wt% glucose solution is used. The properties of the large-pore zeolite greatly influence the reaction behavior because the reaction does not proceed with a medium-pore zeolite, and the isomerization activity is considerably lower when the metal centers are incorporated in ordered mesoporous silica (MCM-41). The Sn-Beta catalyst can be used for multiple cycles, and the reaction stops when the solid is removed, clearly indicating that the catalysis is occurring heterogeneously. Most importantly, the Sn-Beta catalyst is able to perform the isomerization reaction in highly acidic, aqueous environments with equivalent activity and product distribution as in media without added acid. This enables Sn-Beta to couple isomerizations with other acid-catalyzed reactions, including hydrolysis/isomerization or isomerization/dehydration reaction sequences [starch to fructose and glucose to 5-hydroxymethylfurfural (HMF) demonstrated here]. PMID:20308577

  19. Tin-containing zeolites are highly active catalysts for the isomerization of glucose in water

    SciTech Connect

    Moliner, Manuel; Roman-Leshkov, Yuriy; Davis, Mark E.

    2010-04-06

    The isomerization of glucose into fructose is a large-scale reaction for the production of high-fructose corn syrup (HFCS; reaction performed by enzyme catalysts) and recently is being considered as an intermediate step in the possible route of biomass to fuels and chemicals. Here, it is shown that a large-pore zeolite that contains tin (Sn-Beta) is able to isomerize glucose to fructose in aqueous media with high activity and selectivity. Specifically, a 10% (wt/wt) glucose solution containing a catalytic amount of Sn-Beta (1:50 Sn:glucose molar ratio) gives product yields of approximately 46% (wt/wt) glucose, 31% (wt/wt) fructose, and 9% (wt/wt) mannose after 30 min and 12 min of reaction at 383 K and 413 K, respectively. This reactivity is achieved also when a 45 wt% glucose solution is used. The properties of the large-pore zeolite greatly influence the reaction behavior because the reaction does not proceed with a medium-pore zeolite, and the isomerization activity is considerably lower when the metal centers are incorporated in ordered mesoporous silica (MCM-41). The Sn-Beta catalyst can be used for multiple cycles, and the reaction stops when the solid is removed, clearly indicating that the catalysis is occurring heterogeneously. Most importantly, the Sn-Beta catalyst is able to perform the isomerization reaction in highly acidic, aqueous environments with equivalent activity and product distribution as in media without added acid. This enables Sn-Beta to couple isomerizations with other acid-catalyzed reactions, including hydrolysis/isomerization or isomerization/dehydration reaction sequences [starch to fructose and glucose to 5-hydroxymethylfurfural (HMF) demonstrated here].

  20. A Novel Technique that Enables Efficient Conduct of Simultaneous Isomerization and Fermentation (SIF) of Xylose

    NASA Astrophysics Data System (ADS)

    Rao, Kripa; Chelikani, Silpa; Relue, Patricia; Varanasi, Sasidhar

    Of the sugars recovered from lignocellulose, D-glucose can be readily converted into ethanol by baker's or brewer's yeast (Saccharomyces cerevisiae). However, xylose that is obtained by the hydrolysis of the hemicellulosic portion is not fermentable by the same species of yeasts. Xylose fermentation by native yeasts can be achieved via isomerization of xylose to its ketose isomer, xylulose. Isomerization with exogenous xylose isomerase (XI) occurs optimally at a pH of 7-8, whereas subsequent fermentation of xylulose to ethanol occurs at a pH of 4-5. We present a novel scheme for efficient isomerization of xylose to xylulose at conditions suitable for the fermentation by using an immobilized enzyme system capable of sustaining two different pH microenvironments in a single vessel. The proof-of-concept of the two-enzyme pellet is presented, showing conversion of xylose to xylulose even when the immobilized enzyme pellets are suspended in a bulk solution whose pH is sub-optimal for XI activity. The co-immobilized enzyme pellets may prove extremely valuable in effectively conducting "simultaneous isomerization and fermentation" (SIF) of xylose. To help further shift the equilibrium in favor of xylulose formation, sodium tetraborate (borax) was added to the isomerization solution. Binding of tetrahydroxyborate ions to xylulose effectively reduces the concentration of xylulose and leads to increased xylose isomerization. The formation of tetrahydroxyborate ions and the enhancement in xylulose production resulting from the complexation was studied at two different bulk pH values. The addition of 0.05 M borax to the isomerization solution containing our co-immobilized enzyme pellets resulted in xylose to xylulose conversion as high as 86% under pH conditions that are suboptimal for XI activity. These initial findings, which can be optimized for industrial conditions, have significant potential for increasing the yield of ethanol from xylose in an SIF approach.

  1. Thermal Dissociation and Roaming Isomerization of Nitromethane: Experiment and Theory.

    PubMed

    Annesley, Christopher J; Randazzo, John B; Klippenstein, Stephen J; Harding, Lawrence B; Jasper, Ahren W; Georgievskii, Yuri; Ruscic, Branko; Tranter, Robert S

    2015-07-16

    The thermal decomposition of nitromethane provides a classic example of the competition between roaming mediated isomerization and simple bond fission. A recent theoretical analysis suggests that as the pressure is increased from 2 to 200 Torr the product distribution undergoes a sharp transition from roaming dominated to bond-fission dominated. Laser schlieren densitometry is used to explore the variation in the effect of roaming on the density gradients for CH3NO2 decomposition in a shock tube for pressures of 30, 60, and 120 Torr at temperatures ranging from 1200 to 1860 K. A complementary theoretical analysis provides a novel exploration of the effects of roaming on the thermal decomposition kinetics. The analysis focuses on the roaming dynamics in a reduced dimensional space consisting of the rigid-body motions of the CH3 and NO2 radicals. A high-level reduced-dimensionality potential energy surface is developed from fits to large-scale multireference ab initio calculations. Rigid body trajectory simulations coupled with master equation kinetics calculations provide high-level a priori predictions for the thermal branching between roaming and dissociation. A statistical model provides a qualitative/semiquantitative interpretation of the results. Modeling efforts explore the relation between the predicted roaming branching and the observed gradients. Overall, the experiments are found to be fairly consistent with the theoretically proposed branching ratio, but they are also consistent with a no-roaming scenario and the underlying reasons are discussed. The theoretical predictions are also compared with prior theoretical predictions, with a related statistical model, and with the extant experimental data for the decomposition of CH3NO2, and for the reaction of CH3 with NO2.

  2. Quantum chemical and master equation simulations of the oxidation and isomerization of vinoxy radicals.

    PubMed

    Kuwata, Keith T; Hasson, Alam S; Dickinson, Ray V; Petersen, Erin B; Valin, Lukas C

    2005-03-24

    The vinoxy radical, a common intermediate in gas-phase alkene ozonolysis, reacts with O2 to form a chemically activated alpha-oxoperoxy species. We report CBS-QB3 energetics for O2 addition to the parent (*CH2CHO, 1a), 1-methylvinoxy (*CH2COCH3, 1b), and 2-methylvinoxy (CH3*CHCHO, 1c) radicals. CBS-QB3 predictions for peroxy radical formation agree with experimental data, while the G2 method systematically overestimates peroxy radical stability. RRKM/master equation simulations based on CBS-QB3 data are used to estimate the competition between prompt isomerization and thermalization for the peroxy radicals derived from 1a, 1b, and 1c. The lowest energy isomerization pathway for radicals 4a and 4c (derived from 1a and 1c, respectively) is a 1,4-shift of the acyl hydrogen requiring 19-20 kcal/mol. The resulting hydroperoxyacyl radical decomposes quantitatively to form *OH. The lowest energy isomerization pathway for radical 4b (derived from 1b) is a 1,5-shift of a methyl hydrogen requiring 26 kcal/mol. About 25% of 4a, but only approximately 5% of 4c, isomerizes promptly at 1 atm pressure. Isomerization of 4b is negligible at all pressures studied.

  3. Kinetics of the thermal decomposition and isomerization of pyrazine (1,4 diazine)

    SciTech Connect

    Doughty, A.; Mackie, J.C.; Palmer, J.M.

    1994-12-31

    The isomerization and decomposition of pyrazine have been studied over the temperature range 1,200--1,480 K. The major products of decomposition were found to be acetylene and HCN, with cyanoacetylene and acrylonitrile also being significant products, although lower yields of these products were observed. The decomposition has been successfully modeled using a free radical mechanisms, with the major chain carriers being CN radicals and H atoms. The initiation reaction was found to be C{single_bond}H bond fission, to yield H atoms and pyrazyl radicals. Kinetic modeling allowed the rate of initiation to be determined, yielding a first-order rate constant given by the expression k = 10{sup 15.7} exp({minus}96.5 kcal/mol/RT) s{sup {minus}1}. The importance of CN radicals as chain carriers appears to be a significant difference in the decomposition of the dizziness compared with pyridine or 2-picoline. Accompanying the decomposition of pyrazine was the isomerization of pyrazine to pyrimidine. By kinetic modeling, the isomerization of pyrazine to pyrimidine was found to occur via a fulvenelike intermediate. The rate and mechanism of the isomerization are analogous to the isomerization of fulvene to benzene described by Melius and Miller. The thermal reactions of these species are being studied because of their relevance to the mechanism of formation of NO{sub x} through the oxidation of fuel-bound nitrogen (FBN) in coal during the combustion of coal and heavy fuels.

  4. Isomeric yield ratios and excitation functions in α-induced reactions on 107,109Ag

    NASA Astrophysics Data System (ADS)

    Guin, R.; Saha, S. K.; Prakash, Satya; Uhl, M.

    1992-07-01

    Isomeric yield ratios for the reactions 107Ag(α,3n)108In, 107Ag(α,α3n)104Ag, 109Ag(α,2n)111In, and 109Ag(α,3n)110In are determined in the energy range of 20-63 MeV α particles. Excitation functions for the above reactions as well as for the 107Ag(α,2n)109In, 107Ag(α,α2n)105Ag, 109Ag(α,4n)109In, 109Ag(α,5n)108In, and 109Ag(α,α4n)105Ag reactions are also presented. Experimental excitation functions are compared with statistical model calculations taking into account precompound particle emission. Isomeric yield ratios are found to depend strongly on the root mean square orbital angular momentum in the entrance channel. A semiempirical method for the prediction of isomeric yield ratios failed to reproduce experimental data even for compoundlike reactions. Isomeric yield ratios were also calculated in the frame of a statistical model under consideration of angular momentum effects in the preequilibrium and the equilibrium stage. Overall agreement between the theory and the experiment for isomeric yield ratios was found to be satisfactory especially at low bombarding energy when compound nucleus reaction channel is dominant. The discrepancy observed at higher bombarding energies needs to be theoretically investigated in greater detail.

  5. Stability and isomerization of complexes formed by metal ions and cytosine isomers in aqueous phase.

    PubMed

    Ai, Hongqi; Liu, Jingjing; Chan, Kwaichow

    2013-08-01

    We present a systematic study of the stability of the formation of complexes produced by four metal ions (M(+/2+)) and 14 cytosine isomers (Cn). This work predicts theoretically that predominant product complexes are associated with higher-energy C4M(+/2+) and C5M(+/2+) rather than the most stable C1M(+/2+). The prediction resolves successfully several experimental facts puzzling two research groups. Meanwhile, in-depth studies further reveal that direct isomerization of C1↔C4 is almost impossible, and also that the isomerization induced by either metalation or hydration, or by a combination of the two unfavorable. It is the single water molecule locating between the H1(-N1) and O2 of the cytosine that plays the dual roles of being a bridge and an activator that consequently improves the isomerization greatly. Moreover, the cooperation of divalent metal ion and such a monohydration actually leads to an energy-free C1←C4 isomerization in the gas phase. Henceforth, we are able to propose schemes inhibiting the free C1←C4 isomerization, based purely on extended hydration at the divalent metal ion.

  6. Formation, isomerization, and dissociation of alpha-carbon-centered and pi-centered glycylglycyltryptophan radical cations

    SciTech Connect

    Ng, Dominic C.; Song, Tao; Siu, Shiu On; Siu, Chi-Kit; Laskin, Julia; Chu, Ivan K.

    2010-02-11

    Gas phase fragmentations of two isomeric radical cationic tripeptides of glycylglycyltryptophan-G•GW+ and [GGW]•+—with well-defined initial radical sites at the α-carbon atom and the 3-methylindole ring, respectively, have been studied using collision-induced dissociation (CID), density functional theory (DFT), and Rice-Ramsperger-Kassel-Marcus (RRKM) theory. Substantially different low-energy CID spectra were obtained for these two isomeric GGW structures, suggesting that they did not interconvert on the time scale of these experiments. DFT and RRKM calculations were used to investigate the influence of the kinetics, stabilities, and locations of the radicals on the competition between the isomerization and dissociation channels. The calculated isomerization barrier between the GGW radical cations (>35.4 kcal/mol) was slightly higher than the barrier for competitive dissociation of these species (<30.5 kcal/mol); the corresponding microcanonical rate constants for isomerization obtained from RRKM calculations were all considerably lower than the dissociation rates at all internal energies. Thus, interconversion between the GGW isomers examined in this study cannot compete with their fragmentations.

  7. Effect of positional isomerism and vanadium substitution on (51)V magic angle spinning NMR Spectra Of Wells-Dawson polyoxotungstates.

    PubMed

    Gupta, Rupal; Huang, Wenlin; Francesconi, Lynn C; Polenova, Tatyana

    We examined the positional isomerism and vanadium substitution on the (51)V magic angle spinning NMR spectra of potassium salts of vanadium-substituted polyoxotungstates of the Wells-Dawson series. NMR parameters of this class of catalytically active polyoxotungstates effect of are reported. Multiple species, indicative of differences in the local environment at the substitution sites, are observed in solid-state NMR spectra of the di- and tri- substituted complexes in contrast to solution NMR spectra, where single average chemical shift was observed. The quadrupolar and chemical shift anisotropy parameters depend strongly on the position and the degree of the vanadium substitution into the oxoanion core establishing (51)V SATRAS NMR spectroscopy as a sensitive probe of the local electronic environment in these catalytically active solids. Copyright © 2016 Elsevier Inc. All rights reserved.

  8. ETS-NOCV Decomposition of the Reaction Force: The HCN/CNH Isomerization Reaction Assisted by Water.

    PubMed

    Díaz, Silvia; Brela, Mateusz Z; Gutiérrez-Oliva, Soledad; Toro-Labbé, Alejandro; Michalak, Artur

    2017-09-15

    The partitioning of the reaction force based on the extended-transition-state natural orbital for chemical valence (ETS-NOCV) scheme has been proposed. This approach, together with the analysis of reaction electronic flux (REF), has been applied in a description of the changes in the electronic structure along the IRC pathway for the HCN/CNH isomerization reaction assisted by water. Two complementary ways of partitioning the system into molecular fragments have been considered ("reactant perspective" and "product perspective"). The results show that the ETS-NOCV picture is fully consistent with REF and bond-order changes. In addition, proposed ETS-NOCV decomposition of the reaction force allows for the quantitative assessment of the influence of the observed bond-breaking and bond-formation processes, providing detailed information about the reaction-driving and reaction-retarding force components within the assumed partitioning scheme. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

  9. Interplay between metal binding and cis/trans isomerization in legume lectins: structural and thermodynamic study of P. angolensis lectin.

    PubMed

    Garcia-Pino, Abel; Buts, Lieven; Wyns, Lode; Loris, Remy

    2006-08-04

    The interplay between metal binding, carbohydrate binding activity, stability and structure of the lectin from Pterocarpus angolensis was investigated. Removal of the metals leads to a more flexible form of the protein with significantly less conformational stability. Crystal structures of this metal-free form show significant structural rearrangements, although some structural features that allow the binding of sugars are retained. We propose that substitution of an asparagine residue at the start of the C-terminal beta-strand of the legume lectin monomer hinders the trans-isomerization of the cis-peptide bond upon demetallization and constitutes an intramolecular switch governing the isomer state of the non-proline bond and ultimately the lectin phenotype.

  10. Formation and decay of fluorobenzene radical anions affected by their isomeric structures and the number of fluorine atoms.

    PubMed

    Higashino, Saki; Saeki, Akinori; Okamoto, Kazumasa; Tagawa, Seiichi; Kozawa, Takahiro

    2010-08-12

    Aryl fluoride has attracted much attention as a resist component for extreme ultraviolet (EUV) lithography, because of the high absorption cross section of fluorine for EUV photons; however, less is known about electron attachment to fluorobenzene (FBz) and the stability of the reduced state. Picosecond and nanosecond pulse radiolysis of tetrahydrofuran solutions of FBz from mono-, di-, tri-, tetra-, penta-, and hexafluorobenzene was performed, and the effects of isomeric structure and number of fluorine atoms were examined. Scavenging of solvated electrons was found to correlate with the electron affinity obtained by density functional theory in the gas phase, whereas the decay of FBz radical anions was dominated by the activation energy of fluorine anion dissociation calculated using a polarized continuum model (PCM). A sharp contrast in the lifetimes of ortho-, meta-, and para-position difluorobenzene was observed, which could provide information on the molecular design of functional materials.

  11. Ab initio studies of isomerization and dissociation reactions of peroxyacetyl nitrate (PAN)

    NASA Astrophysics Data System (ADS)

    Wei, Wen-Mei; Tan, Wei; Zheng, Ren-Hui; He, Tian-Jing; Chen, Dong-Ming; Liu, Fan-Chen

    2005-06-01

    The complex potential energy surface for the unimolecular isomerization and decomposition of peroxyacetyl nitrate (PAN, CH3C(O)OONO2), including 11 isomers, 45 interconversion transition states and 18 major dissociation products, is probed theoretically at the G2MP2//B3LYP/6-311G(2d,2p) level of theory. The geometries and relative energies for various stationary points are determined. Based on the calculated G2MP2 potential energy surface, the possible unimolecular decomposition mechanism of PAN is proposed. It is shown that the most feasible decomposition channels of PAN are those leading to 2CH3C(O)OO + NO2, 2CH3C(O)O + 2NO3, and 2CH3 + CO2 + 2NO3, respectively. Among them, the formations of the products of the first two channels are produced by the homolytic O-N and O-O bond ruptures of PAN with the bond dissociation energies of 32.3 and 33.9 kcal/mol, respectively, while the last one is initiated by the concerted C-C and O-O bond fissions via a barrier of 36.5 kcal/mol. Our results suggest that besides the first two decomposition pathways which have been reported by the literature, the last concerted bond fission dissociation channel via a well-defined transition state is also feasible, which has been confirmed by using CBS-Q and CBS-QB3 methods. Therefore, PAN dissociation occurs mainly via the homolytic O-N or O-O bond ruptures or via the concerted C-C and O-O bond fissions while the first channel is more favorable than the last two channels.

  12. Molecular polymorphism: microwave spectra, equilibrium structures, and an astronomical investigation of the HNCS isomeric family.

    PubMed

    McGuire, Brett A; Martin-Drumel, Marie-Aline; Thorwirth, Sven; Brünken, Sandra; Lattanzi, Valerio; Neill, Justin L; Spezzano, Silvia; Yu, Zhenhong; Zaleski, Daniel P; Remijan, Anthony J; Pate, Brooks H; McCarthy, Michael C

    2016-08-10

    The rotational spectra of thioisocyanic acid (HNCS), and its three energetic isomers (HSCN, HCNS, and HSNC) have been observed at high spectral resolution by a combination of chirped-pulse and Fabry-Pérot Fourier-transform microwave spectroscopy between 6 and 40 GHz in a pulsed-jet discharge expansion. Two isomers, thiofulminic acid (HCNS) and isothiofulminic acid (HSNC), calculated here to be 35-37 kcal mol(-1) less stable than the ground state isomer HNCS, have been detected for the first time. Precise rotational, centrifugal distortion, and nitrogen hyperfine coupling constants have been determined for the normal and rare isotopic species of both molecules; all are in good agreement with theoretical predictions obtained at the coupled cluster level of theory. On the basis of isotopic spectroscopy, precise molecular structures have been derived for all four isomers by correcting experimental rotational constants for the effects of rotation-vibration interaction calculated theoretically. Formation and isomerization pathways have also been investigated; the high abundance of HSCN relative to ground state HNCS, and the detection of strong lines of SH using CH3CN and H2S, suggest that HSCN is preferentially produced by the radical-radical reaction HS + CN. A radio astronomical search for HSCN and its isomers has been undertaken toward the high-mass star-forming region Sgr B2(N) in the Galactic Center with the 100 m Green Bank Telescope. While we find clear evidence for HSCN, only a tentative detection of HNCS is proposed, and there is no indication of HCNS or HSNC at the same rms noise level. HSCN, and tentatively HNCS, displays clear deviations from a single-excitation temperature model, suggesting weak masing may be occurring in some transitions in this source.

  13. “W-X-M” transformations in isomerization of B{sub 39}{sup −} borospherenes

    SciTech Connect

    Gao, Ting-Ting; Chen, Qiang; Mu, Yue-Wen; Lu, Haigang E-mail: lisidian@sxu.edu.cn; Li, Si-Dian E-mail: lisidian@sxu.edu.cn

    2016-06-15

    The Stone-Wales transformation plays an important role in the isomerization of fullerenes and graphenic systems. The continuous conversions between neighboring six- and seven-membered rings in the borospherene (all-boron fullerene) B{sub 40} had been discovered (Martínez-Guajardo et al. Sci. Rep. 5, 11287 (2015)). In the first axially chiral borospherenes C{sub 3} B{sub 39}{sup −} and C{sub 2} B{sub 39}{sup −}, we identify three active boron atoms which are located at the center of three alternative sites involving five boron atoms denoted as “W”, “X”, and “M”, respectively. The concerted movements of these active boron atoms and their close neighbors between neighboring six- and seven-membered rings define the “W-X-M” transformation of borospherenes. Extensive first-principles molecular dynamics simulations and quadratic synchronous transit transition-state searches indicate that, via three transition states (TS1, TS2, and TS3) and two intermediate species (M1 and M2), the three-step “W-X-M” transformations convert the C{sub 3} B{sub 39}{sup −} global minimum into its C{sub 2} isomer at room temperature (300 K) and vice versa. The maximum barriers are only 3.89 kcal/mol from C{sub 3} to C{sub 2} B{sub 39}{sup −} and 2.1 kcal/mol from C{sub 2} to C{sub 3} B{sub 39}{sup −}, rendering dynamic fluxionalities to these borospherenes. Therefore, the “W-X-M” transformation plays an important role in the borospherenes and borospherene-based nanostructures.

  14. Structural and spectral comparisons between isomeric benzisothiazole and benzothiazole based aromatic heterocyclic dyes

    NASA Astrophysics Data System (ADS)

    Wang, Yin-Ge; Wang, Yue-Hua; Tao, Tao; Qian, Hui-Fen; Huang, Wei

    2015-09-01

    A pair of isomeric heterocyclic compounds, namely 3-amino-5-nitro-[2,1]-benzisothiazole and 2-amino-6-nitrobenzothiazole, are used as the diazonium components to couple with two N-substituted 4-aminobenzene derivatives. As a result, two pairs of isomeric aromatic heterocyclic azo dyes have been produced and they are structurally and spectrally characterized and compared including single-crystal structures, electronic spectra, solvatochromism and reversible acid-base discoloration, thermal stability and theoretically calculations. It is concluded that both benzisothiazole and benzothiazole based dyes show planar molecular structures and offset π-π stacking interactions, solvatochromism and reversible acid-base discoloration. Furthermore, benzisothiazole based aromatic heterocyclic dyes exhibit higher thermal stability, larger solvatochromic effects and maximum absorption wavelengths than corresponding benzothiazole based ones, which can be explained successfully by the differences of their calculated isomerization energy, dipole moment and molecular band gaps.

  15. Efficient isomerization of glucose to fructose over zeolites in consecutive reactions in alcohol and aqueous media.

    PubMed

    Saravanamurugan, Shunmugavel; Paniagua, Marta; Melero, Juan A; Riisager, Anders

    2013-04-10

    Isomerization reactions of glucose were catalyzed by different types of commercial zeolites in methanol and water in two reaction steps. The most active catalyst was zeolite Y, which was found to be more active than the zeolites beta, ZSM-5, and mordenite. The novel reaction pathway involves glucose isomerization to fructose and subsequent reaction with methanol to form methyl fructoside (step 1), followed by hydrolysis to re-form fructose after water addition (step 2). NMR analysis with (13)C-labeled sugars confirmed this reaction pathway. Conversion of glucose for 1 h at 120 °C with H-USY (Si/Al = 6) gave a remarkable 55% yield of fructose after the second reaction step. A main advantage of applying alcohol media and a catalyst that combines Brønsted and Lewis acid sites is that glucose is isomerized to fructose at low temperatures, while direct conversion to industrially important chemicals like alkyl levulinates is viable at higher temperatures.

  16. Femtosecond Structural Dynamics Drives the Trans/Cis Isomerization in Photoactive Yellow Protein

    PubMed Central

    Pande, Kanupriya; Hutchison, Christopher D. M.; Groenhof, Gerrit; Aquila, Andy; Robinson, Josef S.; Tenboer, Jason; Basu, Shibom; Boutet, Sébastien; DePonte, Daniel P.; Liang, Mengning; White, Thomas A.; Zatsepin, Nadia A.; Yefanov, Oleksandr; Morozov, Dmitry; Oberthuer, Dominik; Gati, Cornelius; Subramanian, Ganesh; James, Daniel; Zhao, Yun; Koralek, Jake; Brayshaw, Jennifer; Kupitz, Christopher; Conrad, Chelsie; Roy-Chowdhury, Shatabdi; Coe, Jesse D.; Metz, Markus; Xavier, Paulraj Lourdu; Grant, Thomas D.; Koglin, Jason E.; Ketawala, Gihan; Fromme, Raimund; Šrajer, Vukica; Henning, Robert; Spence, John C. H.; Ourmazd, Abbas; Schwander, Peter; Weierstall, Uwe; Frank, Matthias; Fromme, Petra; Barty, Anton; Chapman, Henry N.; Moffat, Keith; van Thor, Jasper J.; Schmidt, Marius

    2017-01-01

    A variety of organisms have evolved mechanisms to detect and respond to light, in which the response is mediated by protein structural changes following photon absorption. The initial step is often the photo-isomerization of a conjugated chromophore. Isomerization occurs on ultrafast timescales, and is substantially influenced by the chromophore environment. Here we identify structural changes associated with the earliest steps in the trans to cis isomerization of the chromophore in photoactive yellow protein. Femtosecond, hard X-ray pulses emitted by the Linac Coherent Light Source were used to conduct time-resolved serial femtosecond crystallography on PYP microcrystals over the time range from 100 femtoseconds to 3 picoseconds to determine the structural dynamics of the photoisomerization reaction. PMID:27151871

  17. Isomerization and optical bistability of DR1 doped organic-inorganic sol-gel thin film

    NASA Astrophysics Data System (ADS)

    Gao, Tianxi; Que, Wenxiu; Shao, Jinyou

    2015-10-01

    To investigate the isomerization process of the disperse red 1 (DR1) doped TiO2/ormosil thin film, both the photo-isomerization and the thermal isomerization of the thin films were observed as a change of the absorption spectrum. Under a real-time heat treatment, the change of the linear refractive index shows a thermal stable working temperature range below Tg. The optical bistability (OB) effect of the DR1 doped thin films based on different matrices was studied and measured at a wavelength of 532 nm. Results indicate that the TiO2/ormosils based thin film presents a better OB-gain than that of the poly (methyl methacrylate) (PMMA) based thin film due to its more rigid network structure. Moreover, it is also noted that higher titanium content is helpful for enhancing the OB-gain of the as-prepared hybrid thin films.

  18. Experimental and DFT studies of initiation processes for butane isomerization over sulfated-zirconia catalysts

    SciTech Connect

    Hong, Z.; Watwe, R.M.; Natal-Santiago, M.A.; Hill, J.M.; Dumesic, J.A.; Fogash, K.B.; Kim, B.; Masqueda-Jimenez, B.I.

    1998-09-10

    Reaction kinetics studies were conducted of isobutane and n-butane isomerization at 423 K over sulfated-zirconia, with the butane feeds purified of olefins. Dihydrogen evolution was observed during butane isomerization over fresh catalysts, as well as over catalysts selectively poisoned by preadsorbed ammonia. Butane isomerization over sulfated-zirconia can be viewed as a surface chain reaction comprised of initiation, propagation, and termination steps. The primary initiation step in the absence of feed olefins is considered to be the dehydrogenation of butane over sulfated-zirconia, generating butenes which adsorb onto acid sites to form protonated olefinic species associated with the conjugate base form of the acid sites. Quantum-chemical calculations, employing density-functional theory, suggest that the dissociative adsorption of dihydrogen, isobutylene hydrogenation, and dissociative adsorption of isobutane are feasible over the sulfated-zirconia cluster, and these reactions take place over Zr-O sites.

  19. Evidence from Chlamydomonas on the photoactivation of rhodopsins without isomerization of their chromophore

    PubMed Central

    Foster, Kenneth W.; Saranak, Jureepan; Krane, Sonja; Johnson, Randy L.; Nakanishi, Koji

    2011-01-01

    SUMMARY Attachment of retinal to opsin forms the chromophore N-retinylidene which isomerizes during photoactivation of rhodopsins. To test whether isomerization is crucial, custom-tailored chromophores lacking the β-ionone ring and any isomerizable bonds were incorporated in vivo into the opsin of a blind mutant of the eukaryote Chlamydomonas reinhardtii. The analogues restored phototaxis with the anticipated action spectra, ruling out the need for isomerization in photoactivation. To further elucidate photoactivation, responses to chromophores formed from naphthalene aldehydes were studied. The resulting action spectral shifts suggest that charge separation within the excited chromophore leads to electric field induced polarization of nearby amino-acid residues and altered hydrogen bonding. This redistribution of charge faciliates the reported multiple bond rotations and protein rearrangements of rhodopsin activation. These results provide new insight into the activation of rhodopsins and related GPCRs. PMID:21700209

  20. Lycopene inhibits the isomerization of β-carotene during quenching of singlet oxygen and free radicals.

    PubMed

    Heymann, Thomas; Heinz, Philipp; Glomb, Marcus A

    2015-04-01

    The present study aimed to investigate the influence of singlet oxygen and radical species on the isomerization of carotenoids. On the one hand, lycopene and β-carotene standards were incubated with 1,4-dimethylnaphthalene-1,4-endoperoxide that produced singlet oxygen in situ. (13Z)- and (15Z)-β-carotene were preferentially generated at low concentrations of singlet oxygen, while high concentrations resulted in formation of (9Z)-β-carotene. The addition of different concentrations of lycopene led to the same isomerization progress of β-carotene, but resulted in a decreased formation of (9Z)-β-carotene and retarded degradation of (all-E)-β-carotene. On the other hand, isomerization of β-carotene and lycopene was induced by ABTS-radicals, too. As expected from the literature, chemical quenching was observed especially for lycopene, while physical quenching was preferred for β-carotene. Mixtures of β-carotene and lycopene resulted in a different isomerization progress compared to the separate β-carotene model. As long as lycopene was present, almost no isomerization of β-carotene was triggered; after that, strong formation of (13Z)-, (9Z)-, and (15Z)-β-carotene was initiated. In summary, lycopene protected β-carotene against isomerization during reactions with singlet oxygen and radicals. These findings can explain the pattern of carotenoid isomers analyzed in fruits and vegetables, where lycopene containing samples showed higher (all-E)/(9Z)-β-carotene ratios, and also in in vivo samples such as human blood plasma.

  1. Mechanism of isomerization of 11-cis-retinal in lipid dispersions by aromatic amines

    SciTech Connect

    Fulton, B.S.; Rando, R.R.

    1987-01-13

    It has previously been shown that retinotoxic, primary aromatic amines catalyze the isomerization of 11-cis-retinal to its all-trans congener after Schiff base formation. This process led to the short-circuiting of the visual cycle and the observed retinotoxicity when it occurred in vivo. The catalysis was also observed to occur in vitro in phosphatidylcholine-based vesicles but not in hydrocarbon solutions. The rate of isomerization of an aromatic amine Schiff base of 11-cis-retinal in the phospholipid vesicles was typically 10/sup 3/-fold more rapid than in hydrocarbon solutions. In this article, the mechanistic basis of this apparently membrane-specific catalysis is described. It was found that the rate enhancement effect observed was independent of the lipid used. Moreover, a bilayer structure was not important because rate enhancements were also observed in micelles. The rapid isomerization rates observed in lipid dispersions appear not be free radical initiated because free radical quenching agents, such as ..cap alpha..-tocopherol and BETA-carotene, had little effect on the isomerization rates. It was further found that aliphatic amines, such as n-dodecylamine, could be substituted for the aromatic amines in phospholipid. Finally, and most importantly, it was found that the isomerization of the aromatic amine retinal Schiff bases in phospholipid vesicles was acid-catalyzed. It is concluded that the rate enhancements observed for the isomerization of 11-cis-retinal aromatic amine Schiff bases in lipid dispersions over that in hydrocarbon solvents are due to the occurrence of acid-base catalysis in the former.

  2. Isomerization of Cyclooctadiene to Cyclooctyne with a Zinc/Zirconium Heterobimetallic Complex

    PubMed Central

    Butler, Michael J.; White, Andrew J. P.

    2016-01-01

    Abstract Reaction of a zinc/zirconium heterobimetallic complex with 1,5‐cyclooctadiene (1,5‐COD) results in slow isomerization to 1,3‐cyclooctadiene (1,3‐COD), along with the formation of a new complex that includes a cyclooctyne ligand bridging two metal centers. While analogous magnesium/zirconium and aluminum/zirconium heterobimetallic complexes are competent for the catalytic isomerization of 1,5‐COD to 1,3‐COD, only in the case of the zinc species is the cyclooctyne adduct observed. PMID:27071992

  3. Identification of a new isomer from a reversible isomerization of ceftriaxone in aqueous solution.

    PubMed

    Tian, Ye; Lu, Li; Chang, Yan; Zhang, Dou-sheng; Li, Jin; Feng, Yan-Chun; Hu, Chang-Qin

    2015-01-01

    A reversible isomerization of ceftriaxone in aqueous solution was observed, and the structure of the isomer was determined by mass spectrometry and various 1D and 2D NMR techniques. The mechanism of isomerization was also discussed. Finally, molecular docking simulations were performed and the antimicrobial activities of the isomers were measured. This showed that the biological activity of ceftriaxone was stronger than that of its isomer. The results reported in this article may be important to quality control requirements and to the stability of ceftriaxone products.

  4. Strategies for expanding structural diversity available from olefin isomerization-claisen rearrangement reactions.

    PubMed

    Stevens, Benjamin D; Bungard, Christopher J; Nelson, Scott G

    2006-08-18

    Boron-substituted di(allyl) ethers provide an efficient conduit for expanding the structural diversity available from olefin isomerization-Claisen rearrangement (ICR) reactions. Easily prepared allyl propargyl ethers undergo chemoselective Zr(IV)-catalyzed hydroboration to afford the boron-substituted ICR substrates. The boron-substituted allyl residue undergoes chemoselective Ir(I)-catalyzed olefin isomerization and in situ Claisen rearrangement to afford stereodefined beta-boryl aldehyde products. Functionalization of the C-B linkage by oxidation or Suzuki cross-coupling provides a route to Claisen adducts previously inaccessible from the ICR methodology.

  5. Right isomerism with complex cardiac anomalies presenting with dysphagia - A case report

    PubMed Central

    Agarwal, Himanshu; Mittal, Shireesh Kumar; Kulkarni, Chaitanya D; Verma, Ashok Kumar; Srivastava, Saurabh Kumar

    2011-01-01

    Isomerism or Heterotaxy syndromes are rare multifaceted congenital anomalies with multi-system involvement. Grouped under the broad category of Situs Ambiguous defects, these often pose diagnostic difficulties due to their varied and confusing anatomy. Since patients rarely survive into adulthood due to cardiovascular complications, the etiology and natural history of such conditions are not fully understood. Imaging provides the most accurate non invasive method for diagnosis and thereby, prognosis in such cases. We present a case of right sided Isomerism with complex cardiac anomalies in a 17 year old adolescent, who presented with dysphagia as one of the main complaints. Multi modality imaging demonstrated the intricate abnormalities in vital systems. PMID:22470785

  6. Isomeric ratio measurements for the radiative neutron capture 176Lu(n,γ) at DANCE

    NASA Astrophysics Data System (ADS)

    Denis-Petit, D.; Roig, O.; Méot, V.; Morillon, B.; Romain, P.; Jandel, M.; Kawano, T.; Vieira, D. J.; Bond, E. M.; Bredeweg, T. A.; Couture, A. J.; Haight, R. C.; Keksis, A. L.; Rundberg, R. S.; Ullmann, J. L.

    2017-09-01

    The isomeric ratios for the neutron capture reaction 176Lu(n,γ) to the Jπ = 5/2-, 761.7 keV, T1/2 = 32.8 ns and the Jπ = 15/2+, 1356.9 keV, T1/2 = 11.1 ns levels of 177Lu, have been measured for the first time with the Detector for Advanced Neutron Capture Experiments (DANCE) at the Los Alamos National Laboratory. These measured isomeric ratios are compared with TALYS calculations.

  7. A search for thermal isomerization of olefins to carbenes: Thermal generations of the silicon-nitrogen double bond

    SciTech Connect

    Zhang, Xianping.

    1990-09-21

    The first part of this thesis will search for the thermal isomerization of olefins to carbenes which is predicted to be a high energy process by calculations and has only been observed in a few strained olefins. The possibility of thermal isomerization of simple olefins to carbenes will be explored. Substitution of a silyl group on the double bond of an olefin allows a potential intermediate which has a {beta}-radical to the silyl group during the cis-trans isomerization. The effects of a trimethylsilyl group on this isomerization are the subject of this study. The second part of this thesis will include the generation and chemistry of intermediates containing a silicon-nitrogen double bond. The isomerization of parent silanimine to the aminosilylene was calculated to be a high energy process. New approaches to the silicon-nitrogen double bond will also be presented. 92 refs., 12 figs., 11 tabs.

  8. Pump-Probe Spectroscopy of Thermal Cis-Trans Isomerization Process of Methyl Red in 1-Octanol

    NASA Astrophysics Data System (ADS)

    Joukai, Tatsuya; Kita, Kenji; Yano, Ryuzi

    Thermal cis-trans isomerization process of Methyl Red in 1-Octanol at room temperature was studied by pump-probe spectroscopy. The isomerization rate increased as the dye concentration was increased. However, at concentrations above ~ 3 × 10-5 mol/L, the isomerization rate became almost constant regardless of the dye concentration. We interpreted that the concentration dependence of the thermal isomerization rate was caused by the creation of hydrogen-bonded dimer molecules. When a dimer is formed, one of the dye molecules which form the dimer easily changes its form from the cis isomer to the trans isomer. As the dye concentration is increased, the ratio of dyes which form dimer molecules will increase. When the dye concentration is high enough, most dye molecules form dimer molecules. Thus the isomerization rate averaged over the dye molecules is constant.

  9. Linkage Isomerization in Heme–NOx Compounds: Understanding NO, Nitrite, and Hyponitrite Interactions with Iron Porphyrins

    PubMed Central

    Xu, Nan; Yi, Jun

    2011-01-01

    Nitric oxide (NO) and its derivatives such as nitrite and hyponitrite are biologically important species of relevance to human health. Much of their physiological relevance stems from their interactions with the iron centers in heme proteins. The chemical reactivities displayed by the heme-NOx species (NOx = NO, nitrite, hyponitrite) are a function of the binding modes of the NOx ligands. Hence, an understanding of the types of binding modes extant in heme-NOx compounds is important if we are to unravel the inherent chemical properties of these NOx metabolites. In this Forum article, the experimentally characterized linkage isomers of heme-NOx models and proteins are presented and reviewed. Nitrosyl linkage isomers of synthetic Fe and Ru porphyrins have been generated by photolysis at low temperatures and characterized by spectroscopy and DFT calculations. Nitrite linkage isomers in synthetic metalloporphyrin derivatives have been generated from photolysis experiments and in low-temperature matrices. In the case of nitrite adducts of heme proteins, both N-binding and O-binding have been determined crystallographically, and the role of the distal Hbonding residue in myoglobin in directing the O-binding mode of nitrite has been explored using mutagenesis. To date, only one synthetic metalloporphyrin complex containing a hyponitrite ligand (displaying an O-binding mode) has been characterized by crystallography. This is contrasted with other hyponitrite binding modes experimentally determined for coordination compounds and computationally for NO reductase enzymes. Although linkage isomerism in heme-NOx derivatives is still in its infancy, opportunities now exist for a detailed exploration of the existence and stabilities of the metastable states in both heme models and heme proteins. PMID:20666385

  10. Proline cis-trans isomerization in staphylococcal nuclease: multi-substrate free energy perturbation calculations.

    PubMed Central

    Hodel, A.; Rice, L. M.; Simonson, T.; Fox, R. O.; Brünger, A. T.

    1995-01-01

    Staphylococcal nuclease A exists in two folded forms that differ in the isomerization state of the Lys 116-Pro 117 peptide bond. The dominant form (90% occupancy) adopts a cis peptide bond, which is observed in the crystal structure. NMR studies show that the relatively small difference in free energy between the cis and trans forms (delta Gcis-->trans approximately 1.2 kcal/mol) results from large and nearly compensating differences in enthalpy and entropy (delta Hcis-->trans approximately delta TScis-->trans approximately 10 kcal/mol). There is evidence from X-ray crystal structures that the structural differences between the cis and the trans forms of nuclease are confined to the conformation of residues 112-117, a solvated protein loop. Here, we obtain a thermodynamic and structural description of the conformational equilibrium of this protein loop through an exhaustive conformational search that identified several substates followed by free energy simulations between the substrates. By partitioning the search into conformational substates, we overcame the multiple minima problem in this particular case and obtained precise and reproducible free energy values. The protein and water environment was implicitly modeled by appropriately chosen nonbonded terms between the explicitly treated loop and the rest of the protein. These simulations correctly predicted a small free energy difference between the cis and trans forms composed of larger, compensating differences in enthalpy and entropy. The structural predictions of these simulations were qualitatively consistent with known X-ray structures of nuclease variants and yield a model of the unknown minor trans conformation. PMID:7613463

  11. Photophysical studies of the trans to cis isomerization of the push-pull molecule: 1-(pyridin-4-yl)-2-(N-methylpyrrol-2-yl)ethene (mepepy).

    PubMed

    Mokdad, Audrey; Belof, Jonathan L; Yi, Sung Wook; Shuler, Stephen E; McLaughlin, Mark L; Space, Brian; Larsen, Randy W

    2008-09-11

    Organic molecules possessing intramolecular charge-transfer properties (D-pi-A type molecules) are of key interest particularly in the development of new optoelectronic materials as well as photoinduced magnetism. One such class of D-pi-A molecules that is of particular interest contains photoswitchable intramolecular charge-transfer states via a photoisomerizable pi-system linking the donor and acceptor groups. Here we report the photophysical and electronic properties of the trans to cis isomerization of 1-(pyridin-4-yl)-2-(N-methylpyrrol-2-yl)ethene ligand (mepepy) in aqueous solution using photoacoustic calorimetry (PAC) and theoretical methods. Density functional theory (DFT) calculations demonstrate a global energy difference between cis and trans isomers of mepepy to be 8 kcal mol(-1), while a slightly lower energy is observed between the local minima for the trans and cis isomers (7 kcal mol(-1)). Interestingly, the trans isomer appears to exhibit two ground-state minima separated by an energy barrier of approximately 9 kcal mol(-1). Results from the PAC studies indicate that the trans to cis isomerization results in a negligible volume change (0.9 +/- 0.4 mL mol(-1)) and an enthalpy change of 18 +/- 3 kcal mol(-1). The fact that the acoustic waves associated with the trans to cis transition of mepepy overlap in frequency with those of a calorimetric reference implies that the conformational transition occurs faster than the approximately 50 ns response time of the acoustic detector. Comparison of the experimental results with theoretical studies provide evidence for a mechanism in which the trans to cis isomerization of mepepy results in the loss of a hydrogen bond between a water molecule and the pyridine ring of mepepy.

  12. How Accurate Are the Minnesota Density Functionals for Noncovalent Interactions, Isomerization Energies, Thermochemistry, and Barrier Heights Involving Molecules Composed of Main-Group Elements?

    SciTech Connect

    Mardirossian, Narbe; Head-Gordon, Martin

    2016-08-18

    The 14 Minnesota density functionals published between the years 2005 and early 2016 are benchmarked on a comprehensive database of 4986 data points (84 data sets) involving molecules composed of main-group elements. The database includes noncovalent interactions, isomerization energies, thermochemistry, and barrier heights, as well as equilibrium bond lengths and equilibrium binding energies of noncovalent dimers. Additionally, the sensitivity of the Minnesota density functionals to the choice of basis set and integration grid is explored for both noncovalent interactions and thermochemistry. By and large, the main strength of the hybrid Minnesota density functionals is that the best ones provide very good performance for thermochemistry (e.g., M06-2X), barrier heights (e.g., M08-HX, M08-SO, MN15), and systems heavily characterized by self-interaction error (e.g., M06-2X, M08-HX, M08-SO, MN15), while the main weakness is that none of them are state-of-the-art for the full spectrum of noncovalent interactions and isomerization energies (although M06-2X is recommended from the 10 hybrid Minnesota functionals). Similarly, the main strength of the local Minnesota density functionals is that the best ones provide very good performance for thermochemistry (e.g., MN15-L), barrier heights (e.g., MN12-L), and systems heavily characterized by self-interaction error (e.g., MN12-L and MN15-L), while the main weakness is that none of them are state-of-the-art for the full spectrum of noncovalent interactions and isomerization energies (although M06-L is clearly the best from the four local Minnesota functionals). Finally, as an overall guide, M06-2X and MN15 are perhaps the most broadly useful hybrid Minnesota functionals, while M06-L and MN15-L are perhaps the most broadly useful local Minnesota functionals, although each has different strengths and weaknesses.

  13. How Accurate Are the Minnesota Density Functionals for Noncovalent Interactions, Isomerization Energies, Thermochemistry, and Barrier Heights Involving Molecules Composed of Main-Group Elements?

    PubMed

    Mardirossian, Narbe; Head-Gordon, Martin

    2016-09-13

    The 14 Minnesota density functionals published between the years 2005 and early 2016 are benchmarked on a comprehensive database of 4986 data points (84 data sets) involving molecules composed of main-group elements. The database includes noncovalent interactions, isomerization energies, thermochemistry, and barrier heights, as well as equilibrium bond lengths and equilibrium binding energies of noncovalent dimers. Additionally, the sensitivity of the Minnesota density functionals to the choice of basis set and integration grid is explored for both noncovalent interactions and thermochemistry. Overall, the main strength of the hybrid Minnesota density functionals is that the best ones provide very good performance for thermochemistry (e.g., M06-2X), barrier heights (e.g., M08-HX, M08-SO, MN15), and systems heavily characterized by self-interaction error (e.g., M06-2X, M08-HX, M08-SO, MN15), while the main weakness is that none of them are state-of-the-art for the full spectrum of noncovalent interactions and isomerization energies (although M06-2X is recommended from the 10 hybrid Minnesota functionals). Similarly, the main strength of the local Minnesota density functionals is that the best ones provide very good performance for thermochemistry (e.g., MN15-L), barrier heights (e.g., MN12-L), and systems heavily characterized by self-interaction error (e.g., MN12-L and MN15-L), while the main weakness is that none of them are state-of-the-art for the full spectrum of noncovalent interactions and isomerization energies (although M06-L is clearly the best from the four local Minnesota functionals). As an overall guide, M06-2X and MN15 are perhaps the most broadly useful hybrid Minnesota functionals, while M06-L and MN15-L are perhaps the most broadly useful local Minnesota functionals, although each has different strengths and weaknesses.

  14. Spectroscopic and structural studies of quinoline derivatives—II. Forrier transform i.r. spectroscopy. 1. Rotational isomerism in 3-ethoxycarbonyl-4(1H)-quinolone and some of its substituted derivatives,

    NASA Astrophysics Data System (ADS)

    Mirek, Julian; Urbanek, Zbigniew H.

    Rotational isomerism associated with internal rotation about the ring carbon(3)-ester carbonyl carbon single bond in a series of 3-ethoxycarbonyl-4(1H)-quinolones have been investigated spectroscopically in the solid state using Fourier transform i.r. and laser Raman spectroscopy. Particular attention is given to the 1700, 1300 and 1100 cm -1 spectral regions related primarily to the vibrations of the CO 2C 2H 5 group. Within these regions rotational isomerism appeared in the compounds examined. The conformational changes are discussed and evidence is reported for occurrence of the unsubstituted compound 1 itself in the solid state at ambient temperature as an equilibrium mixture of both the s-trans ( 1a) and s-cis ( 1b) rotamers (this is in contrast to previous findings), and of its Bz-substituted derivatives.

  15. CBS-QB3 calculation of quantum chemical molecular descriptors of isomeric thiadiazoles.

    PubMed

    Glossman-Mitnik, Daniel

    2006-12-01

    The results of the calculation of several molecular descriptors of isomeric thiadiazoles through the CBS-QB3 model chemistry are presented in this work. The results could be useful in quantitative structure-activity relationship (QSAR) or quantitative structure-property relationship (QSPR) studies of derivatives of the nitrogen-containing analogs of thiophene.

  16. Antenatal diagnosis of left atrial isomerism and heterotaxy syndrome in fetus with Meckel-Gruber syndrome.

    PubMed

    Kurtulmuş, Seçil; Demirpençe, Savaş; Can Öztekin, Deniz; Koç, Altuğ; Tavlı, Vedide

    2014-03-01

    We aimed to present a fetus with Meckel-Gruber syndrome (MKS) who had left atrial isomerism, heterotaxy syndrome and complete heart block. A 26-year-old healthy female was referred to our clinic in the 23rd week of her pregnancy. The fetus had multiple systemic anomalies including fetal heart. Fetal echocardiography revealed a horizontal liver, left-sided stomach and vena cava interruption with azygos continuation. There was also an apical trabecular ventricular septal defect, aorta and pulmonary artery arising from the left ventricle, pulmonary artery hypoplasia, pulmonary valve stenosis and left atrial isomerism. The heart rate was 46/min, consistent with third-degree atrioventricular block. Multiple anomalies including occipital encephalocele, bilateral polycystic kidneys, cleft lip, cleft palate, and polydactyly were also detected in the obstetric ultrasonography. The pregnancy was terminated in the 23rd gestational week based on the consensus of perinatology council. The autopsy examination confirmed the diagnosis of MKS, left atrial isomerism and heterotaxy syndrome. Although some cardiac defects have been reported previously in MKS fetuses, here we expand the cardiac spectrum of anomalies associated with MKS to include left atrial isomerism and heterotaxy syndrome.

  17. Model mechanisms for the thermal cis—trans isomerization of cyanines

    NASA Astrophysics Data System (ADS)

    Schöffel, Klaus; Dietz, Fritz; Krossner, Thomas

    1990-08-01

    Quantum-chemical calculations have been performed for rotations around the different CC bonds of streptocyanine cations and of various ion pairs of TMC + and PMC + with Cl - as the gegenion (counterion) in order to explain the experimentally well known temperature dependence of the activation energy for the thermal isomerization.

  18. The Isomerization of (-)-Menthone to (+)-Isomenthone Catalyzed by an Ion-Exchange Resin

    ERIC Educational Resources Information Center

    Ginzburg, Aurora L.; Baca, Nicholas A.; Hampton, Philip D.

    2014-01-01

    A traditional organic chemistry laboratory experiment involves the acid-catalyzed isomerization of (-)-menthone to (+)-isomenthone. This experiment generates large quantities of organic and aqueous waste, and only allows the final ratio of isomers to be determined. A "green" modification has been developed that replaces the mineral acid…

  19. Surprising photochemical and thermal isomerizations of a cyclic 1,2,3-butatriene

    SciTech Connect

    Chen, Yiyuan; Ma, Zhongxin; Ijadi-Maghsoodi, Sina; Barton, T.J. |

    1997-12-31

    Photolysis of cyclic 1,2,3-butatriene 1 exclusively affords cyclopropane 2 for which an unprecedented initial isomerization to a methylenecyclopropanylidene is proposed. Thermolysis of 1 produces butadiene 3 in 83% yield. Formation of 3 is an apparent disallowed S, A [2+2] cycloaddition but we will argue that it is actually an allowed [4+2] cycloaddition.

  20. Bio-olefins via tandem isomerization-decarboxylation catalysis upon fatty acids

    USDA-ARS?s Scientific Manuscript database

    A facile Ru-catalyzed route to bio-alkenes from alkenoic fatty acids will be discussed. A readily accessible pre-catalyst [Ru(CO)2RCO2]n. apparently functions in a tandem mode by dynamically isomerizing the positions of double bonds in an aliphatic chain and, subsequently, decarboxylating specific i...

  1. Tandem isomerization-decarboxylation for converting alkenoic fatty acids into alkenes

    USDA-ARS?s Scientific Manuscript database

    We report a facile Ru-catalyzed route to alkenes from alkenoic fatty acids via a readily accessible pre-catalyst [Ru(CO)2RCO2]n. The catalyst apparently functions in a tandem mode by dynamically isomerizing the positions of double bonds in an aliphatic chain and, subsequently, decarboxylating specif...

  2. Fuel properties of heptadecene isomers prepared via tandem isomerization-decarboxylation of oleic acid

    USDA-ARS?s Scientific Manuscript database

    Heptadecene isomers were prepared via tandem isomerization-decarboxylation of oleic acid using catalytic triruthenium dodecacarbonyl [Ru3(CO)12]. Chromatographic and spectroscopic characterization of the isolated heptadecene mixture indicated that it consisted of 96% internal trans isomers and 4% ar...

  3. Xylose isomerization with zeolites in a two-step alcohol-water process.

    PubMed

    Paniagua, Marta; Saravanamurugan, Shunmugavel; Melian-Rodriguez, Mayra; Melero, Juan A; Riisager, Anders

    2015-03-01

    Isomerization of xylose to xylulose was efficiently catalyzed by large-pore zeolites in a two-step methanol-water process that enhanced the product yield significantly. The reaction pathway involves xylose isomerization to xylulose, which, in part, subsequently reacts with methanol to form methyl xyluloside (step 1) followed by hydrolysis after water addition to form additional xylulose (step 2). NMR spectroscopy studies performed with (13) C-labeled xylose confirmed the proposed reaction pathway. The most active catalyst examined was zeolite Y, which proved more active than zeolite beta, ZSM-5, and mordenite. The yield of xylulose obtained over H-USY (Si/Al=6) after 1 h of reaction at 100 °C was 39%. After water hydrolysis in the second reaction step, the yield increased to 47%. Results obtained from pyridine adsorption studies confirm that H-USY (6) is a catalyst that combines Brønsted and Lewis acid sites, and isomerizes xylose in alcohol media to form xylulose at low temperature. The applied zeolites are commercially available; do not contain any auxiliary tetravalent metals, for example, tin, titanium, or zirconium; isomerize xylose efficiently; are easy to regenerate; and are prone to recycling. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. Synthesis and thermocatalytic isomerization of 1,2,3-triphenyl-3-(diacylmethyl)cyclopropenes

    SciTech Connect

    Plotkin, V.N.; Domnin, I.N.; Dmitrieva, E.F.; Komendantov, M.I.

    1987-10-20

    The authors investigate the thermocatalytic isomerization of the title compounds to the corresponding substituted cyclopentadienes with high yields under the action of an organic copper carbonyl catalyst. Kinetics are established for reaction pathways and times. Infrared spectra, determined in potassium bromide and carbon tetrachloride, and NMR spectra, determined in deuterated chloroform and carbon tetrachloride, are analyzed.

  5. Ligand induced structural isomerism in phosphine coordinated gold clusters revealed by ion mobility mass spectrometry

    SciTech Connect

    Ligare, Marshall R.; Baker, Erin S.; Laskin, Julia; Johnson, Grant E.

    2017-01-01

    Structural isomerism in ligated gold clusters is revealed using electrospray ionization ion mobility spectrometry mass spectrometry. Phosphine ligated Au8 clusters are shown to adopt more “extended” type structures with increasing exchange of methyldiphenylphosphine (MePPh2) for triphenylphosphine (PPh3). These ligand-dependant structure-property relationships are critical to applications of clusters in catalysis.

  6. Competitive Adsorption of Substrate and Solvent in Sn‐Beta Zeolite During Sugar Isomerization

    PubMed Central

    van der Graaff, William N. P.; Tempelman, Christiaan H. L.; Li, Guanna; Mezari, Brahim; Kosinov, Nikolay

    2016-01-01

    Abstract The isomerization of 1,3‐dihydroxyactone and d‐glucose over Sn‐Beta zeolite was investigated by in situ 13C NMR spectroscopy. The conversion rate at room temperature is higher when the zeolite is dehydrated before exposure to the aqueous sugar solution. Mass transfer limitations in the zeolite micropores were excluded by comparing Sn‐Beta samples with different crystal sizes. Periodic density functional theory (DFT) calculations show that sugar and water molecules compete for adsorption on the active framework Sn centers. Careful solvent selection may thus increase the rate of sugar isomerization. Consistent with this prediction, batch catalytic experiments show that the use of a co‐solvent, such as tetrahydrofuran, that strongly interacts with the Sn centers suppresses glucose isomerization. On the other hand, the use of ethanol as cosolvent results in significantly higher isomerization activity in comparison with pure water because of decreased competition with glucose adsorption on zeolitic Sn sites. PMID:27791334

  7. Roaming Isomerization of Photoexcited Halogenated Alkanes in the Gas and Liquid Phases

    NASA Astrophysics Data System (ADS)

    Borin, Veniamin A.; Matveev, Sergey M.; Budkina, Darya S.; Hicks, Christopher M.; Mereshchenko, Andrey S.; Butaeva, Evgeniia V.; Vorobyev, Vasily V.; Tarnovsky, Alexander N.

    2017-06-01

    Recent experimental and computational gas-phase studies have brought to light a new type of unimolecular decomposition called a "roaming mechanism. It has only been observed in the gas phase, and whether it also occurs in solution is an intriguing question. Using ultrafast transient absorption spectroscopy, we report direct isomerization of CHBr_{3}, BBr_{3}, and PBr_{3} geminal tribromides in solution within the first 100 fs after S_{1}-excitation. The gas-phase conditions do not affect the earliest course of similar isomerization of CHBr_{3}. High-level ab initio simulations on XBr_{3} (X = B, P, and CH) suggest that isomerization is governed by an energetically and dynamically accessible S_{1}/S_{0} conical intersection and can be best described as a roaming-mediated pathway. Following the initial relaxation from the Franck-Condon point, "wandering" of the central atoms and migration of Br atom starts on a planar region of the S_{1} surface, and in the vicinity of the conical intersection ( 40 fs) the XBr_{2} and Br fragments become separated to ≥ 3 Å. After passage through the conical intersection, the partially dissociated bromine atom slips off the XBr_{2} bisector plane, and forms the Br-Br bond of the BrXBr-Br isomer ( 60 fs). We give examples of similar roaming isomerization in several other di- and polyhalogenated alkanes. The authors gratefully acknowledges grants from the National Science Foundation (CHE-0847707, 0923360, and 1626420) which supported this work.

  8. Photoisomerization and thermal isomerization of shuttlecock- and bowl-equipped (phenylazo)pyridines.

    PubMed

    Suwa, Kazuya; Otsuki, Joe; Goto, Kei

    2010-01-21

    The photoisomerization and thermal isomerization of sterically hindered (phenylazo)pyridine derivatives with a shuttlecock-shaped (TbetNNPy) or a bowl-shaped framework (BmtNNPy as well as the azoxy counterpart, BmtNN(O)Py) have been investigated. The crystal structures of these compounds revealed a planar conformation of the (phenylazo)pyridine moiety for TbetNNPy and severely distorted conformations for BmtNNPy and BmtNN(O)Py. The quantum yields of the trans-to-cis photoisomerization of TbetNNPy and BmtNNPy is lower than those of unsubstituted (phenylazo)pyridines. The low quantum yields may, to a large part, be attributed to electronic factors rather than steric factors. While the shuttlecock framework in TbetNNPy does not affect the thermal cis-to-trans isomerization, as the activation parameters for TbetNNPy are quite similar to those of azobenzene and azopyridine derivatives, the bowl framework in BmtNNPy renders the thermal isomerization process slower by lowering the frequency factor to an extent that more than compensates for the lowered activation energy. The process is characterized with a large negative activation entropy and a small activation enthalpy, implying that the isomerization proceeds through a limited range of intermediates stabilized by the presence of the bowl framework.

  9. Isomerization of cis-1,2-dimethylcyclohexane in single-pulse shock tube experiments.

    PubMed

    Rosado-Reyes, Claudette M; Tsang, Wing

    2014-09-11

    Cyclic hydrocarbons are major constituents of jet fuels and reference compounds in jet fuel surrogates. The kinetic and thermal stability and reaction mechanisms of fuel molecules are essential input parameters in the models and simulations used in the design of novel fuels, renewable energy technologies, and devices. A detailed study and analysis of the pyrolytic chemistry of cis-1,2-dimethylcyclohexane has been performed in single-pulse shock tube experiments. The investigations are carried out over the temperature range of 1100 to 1200 K at about 2.5 atm pressure. The isomeric products are trans-1,2-dimethylcyclohexane, 1-octene, and (cis + trans)-2-octene. The three octene isomers can be attributed to internal disproportionation processes. Assuming a diradical mechanism and that cis-1,2-dimethylcyclohexane is formed in equal amount with respect to its trans isomer, the total rate expression for isomerization is kC-C = 10(15.5±0.8) exp(-38,644 ± 2061 K/T) s(-1). The rate constants are over an order of magnitude smaller than the equivalent noncyclic hydrocarbon system. The presence of the isomeric octenes suggests that internal disproportionation is an important component of the isomerization process.

  10. Linkage isomerism in trimeric and polymeric 2,3-cis-procyanindins

    Treesearch

    Richard W. Hemingway; Lai Yeap Foo; Lawrence J. Porter

    1982-01-01

    Procyanindins polymers consist of chains of 5,7,3',4'-tetrahydroxyflavan-3-ol units linked by C(4)-C(6) or C(4)-C(8) bonds.1 Whereas the procyanidin-B group of dimers are known to exist as pairs of isomers with common flavan-3-ol units, but different interflavanoid linkages,2,3 the extent of such isomerism in...

  11. Voltammetry of two single-stranded isomeric end-labeled -SH deoxyoligonucleotides on mercury electrodes.

    PubMed

    Kizek, R; Havran, L; Kubicárová, T; Yosypchuk, B; Heyrovský, M

    2002-04-01

    Voltammetry of isomeric end-labeled -SH deoxyoligonucleotides on a hanging mercury drop electrode depends on the dislocation of the electroactive components along the strand as well as on their adsorptivity with respect to adsorptivity of the other parts of the molecule.

  12. The phytohormone precursor OPDA is isomerized in the insect gut by a single, specific glutathione transferase

    PubMed Central

    Dąbrowska, Paulina; Freitak, Dalial; Vogel, Heiko; Heckel, David G.; Boland, Wilhelm

    2009-01-01

    Oxylipins play important roles in stress signaling in plants. The compound 12-oxophytodienoic acid (cis-OPDA) is an early biosynthetic precursor of jasmonic acid (JA), the key phytohormone orchestrating the plant anti-herbivore defense. When consumed by feeding Lepidopteran larvae, plant-derived cis-OPDA suffers rapid isomerization to iso-OPDA in the midgut and is excreted in the frass. Unlike OPDA epimerization (yielding trans-OPDA), the formation of iso-OPDA is enzyme-dependent, and is catalyzed by an inducible glutathione transferase (GSTs) from the larval gut. Purified GST fractions from the gut of Egyptian cotton leafworm (Spodoptera littoralis) and cotton bollworm (Helicoverpa armigera) both exhibited strong OPDA isomerization activity, most likely via transient formation of a glutathione-OPDA conjugate. Out of 16 cytosolic GST proteins cloned from the gut of cotton bollworm larvae and expressed in E. coli, only one catalyzed the OPDA isomerization. The biological function of the double bond shift might be seen in an inactivation of cis-OPDA, similar to the inactivation of prostaglandin A1 to prostaglandin B1 in mammalian tissue. The enzymatic isomerization is particularly widespread among generalist herbivores that have to cope with various amounts of cis-OPDA in their spectrum of host plants. PMID:19805297

  13. Retardation of the orientation relaxation of azo-dye doped amorphous polymers upon photoinduced isomerization

    NASA Astrophysics Data System (ADS)

    Chan, S. W.; Quatela, A.; Casalboni, M.; Nunzi, J.-M.

    2006-08-01

    The orientation relaxation upon photo-induced isomerization of azo-dyes was studied. All-optical poling (AOP) and photo-induced birefringence, which are based on the mechanism of angular selective photo-isomerization, were employed to manipulate the angular distribution of azo-dyes (Disperse-red 1) doped in three different amorphous polymers: (poly(methyl methacrylate) PMMA, poly(carbonate) PC and poly(sulfone) PSU), with different glass transition temperature (T g). In the case of AOP, quasi-permanent macroscopic second-order nonlinear optical susceptibility χ (2) was inscribed in the dye-doped centro-symmetric polymer systems, while in the case of photo-induced birefringence, quasi-permanent birefringence Δn was inscribed in the dye-doped isotropic polymer systems. Relaxation of χ (2) and Δn were monitored upon different duration of AOP and photo-induced birefringence preparation. Experimental results show that azo-dye orientation relaxation follows the duration of the photo-nduced isomerization process: the longer the photo-induced isomerization process, the slower the relaxation of the inscribed χ (2) and Δn. In addition, retardation of the orientation relaxation does not follow a simple relation with hardness (T g) of the polymer host. Causes of the orientation relaxation retardation are discussed.

  14. The Isomerization of (-)-Menthone to (+)-Isomenthone Catalyzed by an Ion-Exchange Resin

    ERIC Educational Resources Information Center

    Ginzburg, Aurora L.; Baca, Nicholas A.; Hampton, Philip D.

    2014-01-01

    A traditional organic chemistry laboratory experiment involves the acid-catalyzed isomerization of (-)-menthone to (+)-isomenthone. This experiment generates large quantities of organic and aqueous waste, and only allows the final ratio of isomers to be determined. A "green" modification has been developed that replaces the mineral acid…

  15. Isomerization of 4-vinylcyclohexene radical cation. A tandem mass spectrometry study

    SciTech Connect

    Vollmer, D.; Rempel, D.L.; Gross, M. L. ); Williams, F. )

    1995-02-08

    Investigation by matrix-isolation ESR has shown that 4-vinylcyclohexene, 1, surprisingly undergoes isomerization to the bicyclo[3.2.1]oct-2-ene ion, 3. Here we demonstrate the occurrence of this isomerization in the gas phase by use of tandem (MS/MS) sector and Fourier transform (FT) mass spectrometries. The radical cations of 4-vinylcyclohexene (IE = 8.93 eV) or bicyclo[3.2.1]oct-2-ene (approximately 14 kcal/mol more stable than that of 4-vinylcyclohexene) were formed, in separate trials, in a chemical ionization (CI) source by electron ionization (EI). The radical cations were then studied by obtaining their collisionally activated decomposition (CAD) spectra. The CAD spectra are similar, indicating that the isomerization has occurred. Both the sector and the FT mass spectrometer results reflect those obtained in the matrix-isolation ESR investigation. That is isomerizes to 3 at high internal energy, but is stable at low internal energy. Two mechanisms explain this rearrangement. The second mechanism is questionable because the most stable olefin radical cation formed from 5 is that of bicyclo[2.2.2]-2-octene, which gives different ESR and CAD spectra than those of 1 or 3. The CAD spectrum of bicyclo[2.2.2]-2-octene radical cation indicates that the retro-Diels-Alder loss of ethylene is more facile than that from 1 or 3. 18 refs., 3 figs.

  16. Polymeric proanthocyanidins: Interflavanoid linkage isomerism in (epicatechin-4)-(epicatechin-4)-catechin procyanidins

    Treesearch

    Richard W. Hemingway; L. Yeap Foo; L. J. Porter

    1981-01-01

    Procyanidin trimers have been isolated from a variety of plants,1-3 but their structures remain unresolved. We have now isolated three configurational isomers of (epicatechin-4)-(epicatechin-4)-catechin from Pinus taeda L. (loblolly pine) phloem which exhibit isomerism of the interflavanoid linkages.

  17. A novel base-induced isomerization gives access to unprecedented (E)-exo-glycals.

    PubMed

    Eppe, Guillaume; Dumitrescu, Lidia; Pierrot, Olivier; Li, Tianlei; Pan, Weidong; Vincent, Stéphane P

    2013-08-26

    Bump the base: This study reports the discovery of the base-induced Z-to-E isomerization of exo-glycals bearing an electron-withdrawing group (EWG). The scope of this novel transformation regarding the carbohydrate unit is also discussed. After elucidating the mechanism, preparation of novel (E)-exo- glycals was performed (TBS = tert-butyldimethylsilyl).

  18. Kinetic studies of lycopene isomerization in a tributyrin model system at gastric pH.

    PubMed

    Moraru, Catalin; Lee, Tung-Ching

    2005-11-16

    A semi-preparative HPLC method was developed in order to isolate and purify the 13-cis-lycopene isomer in tomato-based materials. The result was compared with the naturally predominant all-trans-lycopene isomer, in terms of stability to gastric pH at physiological temperature in a tributyrin model system. Kinetic experiments confirmed that lycopene isomerization is a reversible reaction, and under these conditions the all-trans isomer is more stable than the 13-cis isomer. In addition, it was found that at gastric pH 13-cis-lycopene would predominantly isomerize to the all-trans form rather than undergo oxidation/breakdown. A simulation based on the rate constants calculated in the kinetic study indicated that at gastric pH the lycopene isomeric distribution aimed toward an equilibrium characterized by approx 16% 13-cis-, 16% 9-cis-, and 68% all-trans-lycopene. This study suggests that pH-driven isomerization in the stomach is at least partially responsible for the relatively high cis-lycopene proportion found in vivo.

  19. Ab initio reaction pathways for photodissociation and isomerization of nitromethane on four singlet potential energy surfaces with three roaming paths

    SciTech Connect

    Isegawa, Miho; Liu, Fengyi; Morokuma, Keiji; Maeda, Satoshi

    2014-06-28

    Photodissociation pathways of nitromethane following π → π{sup *} electronic excitation are reported. The potential energy surfaces for four lowest singlet states are explored, and structures of many intermediates, dissociation limits, transition states, and minimum energy conical intersections were determined using the automated searching algorism called the global reaction route mapping strategy. Geometries are finally optimized at CASSCF(14e,11o) level and energies are computed at CAS(14o,11e)PT2 level. The calculated preferable pathways and important products qualitatively explain experimental observations. The major photodissociation product CH{sub 3} and NO{sub 2} ({sup 2}B{sub 2}) is formed by direct dissociation from the S{sub 1} state. Important pathways involving S{sub 1} and S{sub 0} states for production of various dissociation products CH{sub 3}NO + O ({sup 1}D), CH{sub 3}O(X{sup 2}E) + NO (X{sup 2}Π), CH{sub 2}NO + OH, and CH{sub 2}O + HNO, as well as various isomerization pathways have been identified. Three roaming processes also have been identified: the O atom roaming in O dissociation from CH{sub 3}NO{sub 2}, the OH radical roaming in OH dissociation from CH{sub 2}N(O)(OH), and the NO roaming in NO dissociation from CH{sub 3}ONO.

  20. A classical trajectory study of the intramolecular dynamics, isomerization, and unimolecular dissociation of HO2

    NASA Astrophysics Data System (ADS)

    Perry, Jamin W.; Dawes, Richard; Wagner, Albert F.; Thompson, Donald L.

    2013-08-01

    The classical dynamics and rates of isomerization and dissociation of HO2 have been studied using two potential energy surfaces (PESs) based on interpolative fittings of ab initio data: An interpolative moving least-squares (IMLS) surface [A. Li, D. Xie, R. Dawes, A. W. Jasper, J. Ma, and H. Guo, J. Chem. Phys. 133, 144306 (2010)] and the cubic-spline-fitted PES reported by Xu, Xie, Zhang, Lin, and Guo (XXZLG) [J. Chem. Phys. 127, 024304 (2007)]. Both PESs are based on similar, though not identical, internally contracted multi-reference configuration interaction with Davidson correction (icMRCI+Q) electronic structure calculations; the IMLS PES includes complete basis set (CBS) extrapolation. The coordinate range of the IMLS PES is limited to non-reactive processes. Surfaces-of-section show similar generally regular phase space structures for the IMLS and XXZLG PESs with increasing energy. The intramolecular vibrational energy redistribution (IVR) at energies above and below the threshold of isomerization is slow, especially for O-O stretch excitations, consistent with the regularity in the surfaces-of-section. The slow IVR rates lead to mode-specific effects that are prominent for isomerization (on both the IMLS and XXZLG) and modest for unimolecular dissociation to H + O2 (accessible only on the XXZLG PES). Even with statistical distributions of initial energy, slow IVR rates result in double exponential decay for isomerization, with the slower rate correlated with slow IVR rates for O-O vibrational excitation. The IVR and isomerization rates computed for the IMLS and XXZLG PESs are quantitatively, but not qualitatively, different from one another with the largest differences ascribed to the ˜2 kcal/mol difference in the isomerization barrier heights. The IMLS and XXZLG results are compared with those obtained using the global, semi-empirical double-many-body expansion DMBE-IV PES [M. R. Pastrana, L. A. M. Quintales, J. Brandão, and A. J. C. Varandas, J. Chem

  1. A classical trajectory study of the intramolecular dynamics, isomerization, and unimolecular dissociation of HO2.

    PubMed

    Perry, Jamin W; Dawes, Richard; Wagner, Albert F; Thompson, Donald L

    2013-08-28

    The classical dynamics and rates of isomerization and dissociation of HO2 have been studied using two potential energy surfaces (PESs) based on interpolative fittings of ab initio data: An interpolative moving least-squares (IMLS) surface [A. Li, D. Xie, R. Dawes, A. W. Jasper, J. Ma, and H. Guo, J. Chem. Phys. 133, 144306 (2010)] and the cubic-spline-fitted PES reported by Xu, Xie, Zhang, Lin, and Guo (XXZLG) [J. Chem. Phys. 127, 024304 (2007)]. Both PESs are based on similar, though not identical, internally contracted multi-reference configuration interaction with Davidson correction (icMRCI+Q) electronic structure calculations; the IMLS PES includes complete basis set (CBS) extrapolation. The coordinate range of the IMLS PES is limited to non-reactive processes. Surfaces-of-section show similar generally regular phase space structures for the IMLS and XXZLG PESs with increasing energy. The intramolecular vibrational energy redistribution (IVR) at energies above and below the threshold of isomerization is slow, especially for O-O stretch excitations, consistent with the regularity in the surfaces-of-section. The slow IVR rates lead to mode-specific effects that are prominent for isomerization (on both the IMLS and XXZLG) and modest for unimolecular dissociation to H + O2 (accessible only on the XXZLG PES). Even with statistical distributions of initial energy, slow IVR rates result in double exponential decay for isomerization, with the slower rate correlated with slow IVR rates for O-O vibrational excitation. The IVR and isomerization rates computed for the IMLS and XXZLG PESs are quantitatively, but not qualitatively, different from one another with the largest differences ascribed to the ~2 kcal/mol difference in the isomerization barrier heights. The IMLS and XXZLG results are compared with those obtained using the global, semi-empirical double-many-body expansion DMBE-IV PES [M. R. Pastrana, L. A. M. Quintales, J. Brandão, and A. J. C. Varandas, J. Chem

  2. Ibuprofen Impairs Allosterically Peroxynitrite Isomerization by Ferric Human Serum Heme-Albumin*

    PubMed Central

    Ascenzi, Paolo; di Masi, Alessandra; Coletta, Massimo; Ciaccio, Chiara; Fanali, Gabriella; Nicoletti, Francesco P.; Smulevich, Giulietta; Fasano, Mauro

    2009-01-01

    Human serum albumin (HSA) participates in heme scavenging; in turn, heme endows HSA with myoglobin-like reactivity and spectroscopic properties. Here, the allosteric effect of ibuprofen on peroxynitrite isomerization to NO3− catalyzed by ferric human serum heme-albumin (HSA-heme-Fe(III)) is reported. Data were obtained at 22.0 °C. HSA-heme-Fe(III) catalyzes peroxynitrite isomerization in the absence and presence of CO2; the values of the second order catalytic rate constant (kon) are 4.1 × 105 and 4.5 × 105 m−1 s−1, respectively. Moreover, HSA-heme-Fe(III) prevents peroxynitrite-mediated nitration of free added l-tyrosine. The pH dependence of kon (pKa = 6.9) suggests that peroxynitrous acid reacts preferentially with the heme-Fe(III) atom, in the absence and presence of CO2. The HSA-heme-Fe(III)-catalyzed isomerization of peroxynitrite has been ascribed to the reactive pentacoordinated heme-Fe(III) atom. In the absence and presence of CO2, ibuprofen impairs dose-dependently peroxynitrite isomerization by HSA-heme-Fe(III) and facilitates the nitration of free added l-tyrosine; the value of the dissociation equilibrium constant for ibuprofen binding to HSA-heme-Fe(III) (L) ranges between 7.7 × 10−4 and 9.7 × 10−4 m. Under conditions where [ibuprofen] is ≫L, the kinetics of HSA-heme-Fe(III)-catalyzed isomerization of peroxynitrite is superimposable to that obtained in the absence of HSA-heme-Fe(III) or in the presence of non-catalytic HSA-heme-Fe(III)-cyanide complex and HSA. Ibuprofen binding impairs allosterically peroxynitrite isomerization by HSA-heme-Fe(III), inducing the hexacoordination of the heme-Fe(III) atom. These results represent the first evidence for peroxynitrite isomerization by HSA-heme-Fe(III), highlighting the allosteric modulation of HSA-heme-Fe(III) reactivity by heterotropic interaction(s), and outlining the role of drugs in modulating HSA functions. The present results could be relevant for the drug-dependent protective role

  3. Computer Molecular Dynamics Simulation Study of Isomerization and Melting of Small Alkali-Halide Clusters.

    NASA Astrophysics Data System (ADS)

    Luo, Jia

    1987-09-01

    In this study we have systematically investigated, using Molecular Dynamics simulations, the energetics, structure and dynamics of alkali-halide clusters of variable sizes ((NaCl)_{n}, for n = 4, 16 and 108) over a wide temperature range. Our simulations show that the very nature of the phase transformation and the underlying physical processes involved, depend on the size of the system. We conclude that at the lower end of the size spectrum, the phase space of the system is characterized by a small number of stable configuration (solid isomers) between which the system transforms in a diffusionless manner, with temperature dependent rates and branching ratios. As the system size is increased the number of accessible conformers increases leading to a hierarchical kinetics of isomerization events which exhibits itself as a broadening of the transition region. For these small clusters coexistence is between solid isomers rather than inter-phase (solid-liquid) coexistence. The latter develops for clusters of sufficient size, characterized by a dense spectrum of accessible states, separated by thermally surmountable barriers. Under these circumstances conventional melting is observed as a sharp transition, the separation of time-scales for inter-well and intra -well dynamics ceases, and true solid-liquid coexistence is found. In the Methods section of the text, we describe the potential model, the computer program algorithm, the molecular dynamics running initial conditions, and the method of temperature control. In the Results section, we discuss and demonstrate the structures of alkali-halide clusters as a function of temperature and the curves of the caloric equation of state; the time evolution of the kinetic energy and the distribution of short time average of the kinetic energy; the coordination number function and the function n(r), which is related to the pair correlation function, as a function of temperature and size; the mean square displacement, the

  4. Impact of Amino Acids on the Isomerization of the Aluminum Tridecamer Al13.

    PubMed

    Deschaume, Olivier; Breynaert, Eric; Radhakrishnan, Sambhu; Kerkhofs, Stef; Haouas, Mohamed; Adam de Beaumais, Ségolène; Manzin, Valeria; Galey, Jean-Baptiste; Ramos-Stanbury, Laure; Taulelle, Francis; Martens, Johan A; Bartic, Carmen

    2017-09-26

    The stability of the Keggin polycation ε-Al13 is monitored by (27)Al NMR and ferron colorimetric assay upon heating aluminum aqueous solutions containing different amino acids with overall positive, negative, or no charge at pH 4.2. A focus on the effect of the amino acids on the isomerization process from ε- to δ-Al13 is made, compared and discussed as a function of the type of organic additive. Amino acids such as glycine and β-alanine, with only one functional group interacting relatively strongly with aluminum polycations, accelerate isomerization in a concentration-dependent manner. The effect of this class of amino acids is also found increasing with the pKa of their carboxylic acid moiety, from a low impact from proline up to more than a 15-fold increased rate from the stronger binders such as glycine or β-alanine. Amino acids with relatively low C-terminal pKa, but bearing additional potential binding moieties such as free alcohol (hydroxyl group) moiety of serine or the amide of glutamine, speed the isomerization comparatively and even more than glycine or β-alanine, glutamine leading to the fastest rates observed so far. With aspartic and glutamic acids, changes in aluminum speciation are faster and significant even at room temperature but rather related to the reorganization toward slow reacting complexed oligomers than to the Al13 isomerization process. The linear relation between the apparent rate constant of isomerization and the additive concentration points to a first-order process with respect to the additives. Most likely, the dominant process is an accelerated ε-Al13 dissociation, increasing the probability of δ isomer formation.

  5. Thrombocytosis in the Setting of Isomerism and a Functionally Univentricular Heart

    PubMed Central

    2015-01-01

    Introduction Bodily isomerism, also known as heterotaxy, is a unique entity in which there is mirror imagery in various organ systems. Those with isomerism will often have congenital malformations of the heart requiring functionally univentricular palliation. Anecdotally, thrombocytosis has been noted with higher frequency in patients with isomerism. This study aimed to determine the prevalence of thrombocytosis at different stages and identify independent predictors of thrombocytosis. Methods We identified patients with isomerism and a functionally univentricular heart who received care at our institution between January 1998 and January 2014. Clinical data regarding these patients was collected via chart review. Platelet counts were collected before initial surgical palliation, the day prior to second surgical palliation, and the day prior to the third surgical palliation. Platelet counts from the first postoperative day following all three surgical palliations was also collected. Mean platelet counts were compared between consecutive stages as well as to the initial platelet count. The frequency of thrombocytosis was also calculated at each point with a binomial logistic regression conducted to determine independent risk factors of thrombocytosis at each time point. Results A total of 57 patients were included in the analysis. The mean platelet count before initial surgical palliation was 349.21 x 109/L and decreased with age. Thrombocytosis was noted in 15.8% prior to initial surgical palliation and 23.6% prior to second surgical palliation. Thrombocytosis was no longer noted after second surgical palliation. No independent risk factors for thrombocytosis were identified. Conclusion Thrombocytosis is not infrequent during the first year of life in those with isomerism. It is important to be vigilant of platelet counts in this population as thrombocytosis may lead to increased thromboembolic events, particularly in the setting of a Blalock-Taussig shunt

  6. Bronchial isomerism in a Kabuki syndrome patient with a novel mutation in MLL2 gene

    PubMed Central

    2014-01-01

    Background Kabuki syndrome (KS) is a rare, multiple congenital anomalies/intellectual disability syndrome caused by mutations of MLL2 gene, which codifies for a histone methyltrasferase that regulates the embryogenesis and the tissue development. Left-bronchial isomerism is a rare congenital abnormality that can be defined as the absence of the normal lateralizing features which distinguish right and left-sides in the lungs. To date, this is the first report of left-bronchial isomerism in association with KS. Case presentation A one-month-old Caucasian male patient underwent our attention for microcephaly, dysmorphic features (long palpebral fissures, eyebrows with sparse lateral third, everted lower eyelids, blue sclerae, large dysplastic ears, lower lip pits), persistent fetal fingertip pads, short stature, heart defects (interventricular defect and aortic coarctation), unilateral cryptorchidism, hypotonia and delay in gross motor skills. These features suggested a diagnosis of KS and a molecular analysis confirmed a novel frame-shift mutation in the exon 11 of MLL2 gene. Subsequently, given recurrent respiratory infections with a normal immunological status, he underwent a chest CT scan that showed a left bronchial isomerism. Conclusion We report a patient affected by KS, with a novel MLL2 mutation and an atypical phenotype characterized by left-side bronchial isomerism. Interestingly, genes involved in the heterotaxia/isomerism such as ROCK2 and SHROOM3 are known to interact with MLL2 gene. In order to achieve a correct diagnosis and an appropriate therapy, the presence of pulmonary anatomical variations should be investigated in KS patients with respiratory signs not associated to immunological deficiency. Finally, our findings support the hypothesis that the mutations leading to a complete loss of function of MLL2 gene is often associated with complex visceral malformations. PMID:24472332

  7. Neutron single-particle strengths at N=40 , 42: Neutron knockout from Ni68,70 ground and isomeric states

    SciTech Connect

    Recchia, F.; Weisshaar, D.; Gade, A.; Tostevin, J. A.; Janssens, R. V. F.; Albers, M.; Bader, V. M.; Baugher, T.; Bazin, D.; Berryman, J. S.; Brown, B. A.; Campbell, C. M.; Carpenter, M. P.; Chen, J.; Chiara, C. J.; Crawford, H. L.; Hoffman, C. R.; Kondev, F. G.; Korichi, A.; Lauritsen, T.; Liddick, S. N.; Lunderberg, E.; Noji, S.; Prokop, C.; Stroberg, S. R.; Suchyta, S.; Wimmer, K.; Zhu, S.

    2016-11-28

    The distribution of single-particle strength in 67,69Ni was characterized with one-neutron knockout reactions from intermediate-energy 68,70Ni secondary beams, selectively populating neutron-hole configurations at N = 39 and 41, respectively. The spectroscopic strengths deduced from the measured partial cross sections to the individual final states, as tagged by their γ-ray decays, is used to identify and quantify neutron configurations in the wave functions. While 69Ni compares well to shell-model predictions, the results for 67Ni challenge the validity of current effective shell-model Hamiltonians by revealing discrepancies that cannot be explained so far. Furthermore, these results suggest that our understanding of the low-lying states in the neutron-rich, semi-magic Ni isotopes may be incomplete and requires further investigation on both the experimental and theoretical sides.

  8. Identification of isomerization and racemization of aspartate in the Asp-Asp motifs of a therapeutic protein.

    PubMed

    Zhang, Jennifer; Yip, Holly; Katta, Viswanatham

    2011-03-15

    A thermally stressed Fab molecule showed a significant increase of basic variants in imaged capillary isoelectric focusing (iCIEF) analysis. Mass analyses of the reduced protein found an increase in -18Da species from both light chain and heavy chain. A tryptic peptide map identified two isoAsp-containing peptides, both containing Asp-Asp motifs and located in complementarity-determining regions (CDRs) of light chains and heavy chains, respectively. The approaches of hydrolyzing succinimide in H(2)(18)O followed by tryptic digestion were used to label and identify the sites of isomerization. This method enabled identification of the isomerization site by comparing the MS/MS spectra of isomerized peptides with and without (18)O incorporation. The light chain peptide L2 VTITCITSTDID(12)DDMNWYQQKPGK underwent simultaneous isomerization and recemization at residue Asp-12 after thermal stress as evidenced by the coinjection of synthetic peptide L2 with l-Asp-12, l-isoAsp-12, d-Asp-12, and d-isoAsp-12, respectively. A thermal stress study of the synthetic peptide (l-)L2 showed that the isomerization and racemization did not occur, indicating that the Asp degradation in this Asp-Asp motif is more related to the protein conformation than the primary sequence. Another isomerization site was identified as Asp-24 in the heavy chain peptide H5 QAPGQGLEWMGWINTYTGETTYAD(24)DFK. No other isomerizations were detected in CDR peptides containing either Asp-Ser or Asp-Thr motifs.

  9. Impact of Era, Type of Isomerism, and Ventricular Morphology on Survival in Heterotaxy: Implications for Therapeutic Management.

    PubMed

    Loomba, Rohit S; Nijhawan, Karan; Anderson, Robert

    2016-01-01

    Heterotaxy has been demonstrated to reduce survival. There are several different subgroups of patients, however, and no single study has had a large number of patients and analyzed survival across the different subgroups such as patients born in different eras, patients with right and left isomerism, and patients with biventricular or functionally univentricular hearts. This study pools previously reported data from Kaplan-Meier curves and performs such subgroup analysis. A systematic review of the literature was performed to identify studies reporting survival of patients with the so-called "heterotaxy" by means of Kaplan-Meier survival curves. Data were extracted from these survival curves and then pooled together. A polynomial regression was then used to generate a pooled survival curve. This was done for all patients, those born in a more recent era, those with right and left isomerism, and those with biventricular or functionally univentricular hearts. Those born in the more recent era (after 2000) had increased survival compared to the overall cohort. Those with left isomerism tended to have a survival benefit compared to those with right isomerism until about 16 years of age, beyond which those with right isomerism developed a survival benefit. Those with biventricular hearts had a survival benefit compared to those with left isomerism. Survival in the so-called heterotaxy syndrome is based on several factors, which include era of birth, sidedness of isomerism, and whether the heart is biventricular or functionally univentricular. © The Author(s) 2015.

  10. Cis-trans isomerization of the (5-nitro-2-furyl)acrylamide, AF-2, initiated by ascorbate, glutathione, Fe(II) and OH-.

    PubMed

    Clarke, E D; Wardman, P; Wilson, I

    1984-01-01

    The cis-trans isomerization of the (5-nitro-2-furyl)acrylamide, AF-2, has been investigated using some important biological reducing agents to initiate reaction. Physiological concentrations of L-ascorbic acid, glutathione and iron(II) all accomplish isomerization in a catalytic manner over a period of minutes. Base-catalysed isomerization has also been observed. In all cases, the presence of oxygen severely inhibits isomerization. It is proposed that the mechanism involves a free-radical chain process; AF-2 or analogues are thus extremely sensitive probes for the generation of nitro radicals in biochemical reducing systems because of the high efficiency of isomerization.

  11. DFT studies on catalytic properties of isolated and carbon nanotube supported Pd9 cluster. Part II. Hydro-isomerization of butene isomers.

    PubMed

    D'Anna, Vincenza; Duca, Dario; Ferrante, Francesco; La Manna, Gianfranco

    2010-02-14

    The processes involved in the butene hydro-isomerization, occurring on a small palladium cluster in the presence of dissociated hydrogen, have been investigated by means of DFT and DFT/MM approaches. This study has been performed both on an isolated (unsupported) Pd(9) cluster and on the same cluster when it is supported on a portion of a single-walled armchair(6,6) carbon nanotube. The study follows another investigation which has already been published concerning the adsorption, fragmentation and diffusion of hydrogen on the same metal cluster. The main aspects involved in the parallel reaction steps of the whole hydro-isomerization mechanisms are not strongly affected by the presence of the support, which does, however, modify the energetics involved, likely due to the presence of strong metal surface interaction (SMSI) effects. Noticeably, a common step corresponding to the diffusion of one hydrogen atom is present. This diffusion step creates a characteristic semihydrogenated surface species along the occurrence of all the reaction pathways. Hence, the semihydrogenated species is a kind of molecular node able to connect the transformation pathways of the different surface species involved in the hydro-isomerization processes. Considering the energetics involved in the processes of both supported and unsupported systems and being aware of the simplification introduced in studying the same systems, it is still possible (i) to emphasize the basis importance of taking account of the support in modeling catalytic properties and (ii) to state that the models proposed here are able to capture the main characteristics of the title reaction.

  12. Overtone-induced dissociation and isomerization dynamics of the hydroxymethyl radical (CH2OH and CD2OH). I. A theoretical study

    NASA Astrophysics Data System (ADS)

    Kamarchik, E.; Rodrigo, C.; Bowman, J. M.; Reisler, H.; Krylov, A. I.

    2012-02-01

    The dissociation of the hydroxymethyl radical, CH2OH, and its isotopolog, CD2OH, following the excitation of high OH stretch overtones is studied by quasi-classical molecular dynamics calculations using a global potential energy surface (PES) fitted to ab initio calculations. The PES includes CH2OH and CH3O minima, dissociation products, and all relevant barriers. Its analysis shows that the transition states for OH bond fission and isomerization are both very close in energy to the excited vibrational levels reached in recent experiments and involve significant geometry changes relative to the CH2OH equilibrium structure. The energies of key stationary points are refined using high-level electronic structure calculations. Vibrational energies and wavefunctions are computed by coupled anharmonic vibrational calculations. They show that high OH-stretch overtones are mixed with other modes. Consequently, trajectory calculations carried out at energies about ˜3000 cm-1 above the barriers reveal that despite initial excitation of the OH stretch, the direct OH bond fission is relatively slow (10 ps) and a considerable fraction of the radicals undergoes isomerization to the methoxy radical. The computed dissociation energies are: D0(CH2OH → CH2O + H) = 10 188 cm-1, D0(CD2OH → CD2O + H) = 10 167 cm-1, D0(CD2OH → CHDO + D) = 10 787 cm-1. All are in excellent agreement with the experimental results. For CH2OH, the barriers for the direct OH bond fission and isomerization are: 14 205 and 13 839 cm-1, respectively.

  13. The dynamics of conformational isomerization in flexible biomolecules. I. Hole-filling spectroscopy of N-acetyl tryptophan methyl amide and N-acetyl tryptophan amide.

    PubMed

    Dian, Brian C; Longarte, Asier; Winter, Paul R; Zwier, Timothy S

    2004-01-01

    The conformational isomerization dynamics of N-acetyl tryptophan methyl amide (NATMA) and N-acetyl tryptophan amide (NATA) have been studied using the methods of IR-UV hole-filling spectroscopy (HFS) and IR-induced population transfer spectroscopy (IR-PTS), which were developed for this purpose. Single conformations of these molecules were selectively excited in well-defined NH stretch fundamentals. This excess energy was used to drive conformational isomerization. By carrying out the infrared excitation early in a supersonic expansion, the excited molecules were recooled into their zero-point levels, partially refilling the hole created in the ground state population of one of the conformers, and creating gains in population in other conformers. These changes in population were detected using laser-induced fluorescence downstream in the expansion. In HFS, the IR wavelength is fixed and the UV laser tuned in order to determine where the population went following selective infrared excitation. In IR-PTS, the UV is fixed to monitor the population of a given conformation, and the IR is tuned to record the IR-induced changes in the population of the monitored conformer. Besides demonstrating the capability of the experiment to change the downstream conformational population distribution, the IR-PTS scans were used to extract two quantitative results: (i) The fractional populations of the conformers in the absence of the infrared, and (ii) the isomerization quantum yields for each of the six unique amide NH stretch fundamentals (three conformers each with two amide groups). The method for obtaining quantum yields is described in detail. In both NATMA and NATA, the quantum yields show modest conformational specificity, but only a hint of vibrational mode specificity. The prospects for the hole-filling technique for providing insight into energy flow in large molecules are discussed, leaving a more detailed theoretical modeling to the adjoining paper [Evans et al. J. Chem

  14. Proline isomerism leads to multiple folded conformations of calbindin D9k: direct evidence from two-dimensional 1H NMR spectroscopy.

    PubMed Central

    Chazin, W J; Kördel, J; Drakenberg, T; Thulin, E; Brodin, P; Grundström, T; Forsén, S

    1989-01-01

    A complete analysis of calbindin D9k by two-dimensional 1H nuclear magnetic resonance spectroscopy has established the existence of two conformations for the folded protein in solution. Well-resolved major and minor resonances in a ratio of 3:1 are observed throughout the 1H NMR spectrum. Two-dimensional exchange experiments show that the major and minor species are related by an equilibrium process. Analysis of short proton-proton distances along the peptide backbone, identified by two-dimensional nuclear Overhauser effect spectroscopy, provides unambiguous evidence that the two forms of the folded protein differ only in the isomerization state of the peptide bond between Gly-42 and Pro-43. Cis-trans isomerism of Pro-43 is thereby directly identified as the cause of multiple conformations for the folded protein in solution. In addition, when Pro-43 is mutated to a glycine residue there is no indication of multiple conformations. These results provide evidence for the possibility of conformational heterogeneity in the native state of globular proteins. PMID:2928325

  15. Excitation functions and isomeric cross section ratios of the 63Cu(n,α)60Com,g, 65Cu(n,α)62Com,g, and 60Ni(n,p)60Com,g processes from 6 to 15 MeV

    NASA Astrophysics Data System (ADS)

    Cserpák, F.; Sudár, S.; Csikai, J.; Qaim, S. M.

    1994-03-01

    Excitation functions were measured for the 63Cu(n,α)60Com, 65Cu(n,α)62Com, and 65Cu(n,α)62Cog reactions over the neutron energy range of 6.3 to 14.8 MeV. Use was made of the activation technique in combination with high resolution γ-ray spectroscopy. The nuetrons were produced via the 2H(d,n)3He reaction using a deuterium gas target at a variable energy compact cyclotron (En=6.3-11.9 MeV) and via the 3H(d,n)4He reaction using a solid Ti-T target at a neutron generator (En=13.7-14.8 MeV). From the available experimental data isomeric cross section ratios were determined for the isomeric pair 60Com,g in 63Cu(n,α) and 60Ni(n,p) reactions, and for the pair 62Com,g in the 65Cu(n,α) reaction. Statistical model calculations taking into account precompound effects were performed for the formation of both the isomeric and ground states of the products. The calculational results on the total (n,p) and (n,α) cross sections agree well with the experimental data; in the case of isomeric states, however, some deviations occur. The experimental isomeric cross section ratios are reproduced only approximately by the calculation; at 15 MeV the spin distribution of the level density has a significant effect on the calculation. For low-lying levels the isomeric cross section ratio depends strongly on the spins of the levels involved and not on their excitation energies. At a given neutron energy the population of the higher spin isomer appears to be higher in the (n,α) process than in the (n,p) reaction.

  16. Energetics of the all-trans{yields}13-cis isomerization of the retinal chromophore of bacteriorhodopsin: Electronic structure calculations for a simple model system

    SciTech Connect

    Woywod, Clemens; Vallet, Valerie; Li, Jingrui; Goerling, Andreas

    2008-12-08

    Understanding the molecular mechanism for the photoinduced transmembrane proton pump in the bacteriorhodopsin system is of fundamental importance. This study attempts to investigate the energetics of the initial step of the proton transport cycle, the photoisomerization of the retinal chromophore. The exact reaction pathway and the question of how many excited electronic states are involved in the internal conversion process are still unresolved. The problem is approached by constructing a reaction coordinate suggested by crystallographic studies for a simplified chromophore model system. The CASSCF and CASPT2 electronic structure methods are employed to calculate the energies of the four lowest lying singlet states as a function of the reaction coordinate. The effect of negatively charged protein residues on the reaction is simulated by inclusion of a negative point charge in the model. The results indicate that trans{yields}cis isomerization around the C{sub {beta}} = C{sub {gamma}} bond may be accompanied by twisting around the C{sub {alpha}}-C{sub {beta}} bond in order to drive the proton pump. The presence of a counterion does not seem to reduce the barrier for isomerization or the S{sub 0}-S{sub 1} energy difference but clearly stabilizes the cis--product. At first sight the results appear to support the idea of a participation of no other electronic states beyond S{sub 0} and first singly {pi}{pi}* excited state in the photoreaction. However, the relevance of this prediction is rather limited because of the small size of the model system. Other states of retinal, corresponding in particular to the partly doubly {pi}{pi}* excited S{sub 2} state of the model, are likely to have a vertical excitation energy similar to the first singly {pi}{pi}* excited state or even below.

  17. Isomeric ruthenium terpyridine complexes [Ru(trpy)(L)Cl]n+ containing the unsymmetrically bidentate acceptor L=3-amino-6-(3,5-dimethylpyrazol-1-yl)-1,2,4,5-tetrazine. Synthesis, structures, electrochemistry, spectroscopy and DFT calculations.

    PubMed

    Patra, Srikanta; Sarkar, Biprajit; Ghumaan, Sandeep; Patil, Mahendra P; Mobin, Shaikh M; Sunoj, Raghavan B; Kaim, Wolfgang; Lahiri, Goutam Kumar

    2005-04-07

    The isomeric title complexes were obtained in almost equimolar ratio from the reaction of Ru(trpy)Cl3 and L. Crystal structure analyses of the perchlorate hemihydrates, electrochemical and spectroscopic (NMR, UV/VIS, EPR) studies, supported by DFT calculations, reveal distinct differences between the isomeric redox series [1]n+(tetrazine-Nt trans to Cl) and [2]n+(pyrazolyl-Np trans to Cl; n= 0, 1, 2). The latter system with the pi acceptors trpy and tetrazine in the equatorial plane and the pyrazolyl and chloride donors in the axial positions exhibits facilitated oxidation, lower energy MLCT transitions, more balanced chelate coordination, and a higher g anisotropy in the oxidised (RuIII) state. According to partially resolved EPR spectra of one-electron reduced neutral compounds and they have the unpaired electron predominantly in the tetrazine ring of L.

  18. Core-coupled states and split proton-neutron quasiparticle multiplets in 122-126Ag

    NASA Astrophysics Data System (ADS)

    Lalkovski, S.; Bruce, A. M.; Jungclaus, A.; Górska, M.; Pfützner, M.; Cáceres, L.; Naqvi, F.; Pietri, S.; Podolyák, Zs.; Simpson, G. S.; Andgren, K.; Bednarczyk, P.; Beck, T.; Benlliure, J.; Benzoni, G.; Casarejos, E.; Cederwall, B.; Crespi, F. C. L.; Cuenca-García, J. J.; Cullen, I. J.; Denis Bacelar, A. M.; Detistov, P.; Doornenbal, P.; Farrelly, G. F.; Garnsworthy, A. B.; Geissel, H.; Gelletly, W.; Gerl, J.; Grebosz, J.; Hadinia, B.; Hellström, M.; Hinke, C.; Hoischen, R.; Ilie, G.; Jaworski, G.; Jolie, J.; Khaplanov, A.; Kisyov, S.; Kmiecik, M.; Kojouharov, I.; Kumar, R.; Kurz, N.; Maj, A.; Mandal, S.; Modamio, V.; Montes, F.; Myalski, S.; Palacz, M.; Prokopowicz, W.; Reiter, P.; Regan, P. H.; Rudolph, D.; Schaffner, H.; Sohler, D.; Steer, S. J.; Tashenov, S.; Walker, J.; Walker, P. M.; Weick, H.; Werner-Malento, E.; Wieland, O.; Wollersheim, H. J.; Zhekova, M.

    2013-03-01

    Neutron-rich silver isotopes were populated in the fragmentation of a 136Xe beam and the relativistic fission of 238U. The fragments were mass analyzed with the GSI Fragment Separator and subsequently implanted into a passive stopper. Isomeric transitions were detected by 105 high-purity germanium detectors. Eight isomeric states were observed in 122-126Ag nuclei. The level schemes of 122,123,125Ag were revised and extended with isomeric transitions being observed for the first time. The excited states in the odd-mass silver isotopes are interpreted as core-coupled states. The isomeric states in the even-mass silver isotopes are discussed in the framework of the proton-neutron split multiplets. The results of shell-model calculations, performed for the most neutron-rich silver nuclei are compared to the experimental data.

  19. Coulomb excitation of a Am242 isomeric target: E2 and E3 strengths, rotational alignment, and collective enhancement

    NASA Astrophysics Data System (ADS)

    Hayes, A. B.; Cline, D.; Moody, K. J.; Ragnarsson, I.; Wu, C. Y.; Becker, J. A.; Carpenter, M. P.; Carroll, J. J.; Gohlke, D.; Greene, J. P.; Hecht, A. A.; Janssens, R. V. F.; Karamian, S. A.; Lauritsen, T.; Lister, C. J.; Macri, R. A.; Propri, R.; Seweryniak, D.; Wang, X.; Wheeler, R.; Zhu, S.

    2010-10-01

    A 98% pure 242mAm (K=5-, t1/2=141 years) isomeric target was Coulomb excited with a 170.5-MeV Ar40 beam. The selectivity of Coulomb excitation, coupled with the sensitivity of Gammasphere plus CHICO, was sufficient to identify 46 new states up to spin 18ℏ in at least four rotational bands; 11 of these new states lie in the isomer band, 13 in a previously unknown yrast Kπ=6- rotational band, and 13 in a band tentatively identified as the predicted yrast Kπ=5+ band. The rotational bands based on the Kπ=5- isomer and the 6- bandhead were populated by Coulomb excitation with unexpectedly equal cross sections. The γ-ray yields are reproduced by Coulomb excitation calculations using a two-particle plus rotor model (PRM), implying nearly complete ΔK=1 mixing of the two almost-degenerate rotational bands, but recovering the Alaga rule for the unperturbed states. The degeneracy of the 5- and 6- bands allows for precise determination of the mixing interaction strength V, which approaches the strong-mixing limit; this agrees with the 50% attenuation of the Coriolis matrix element assumed in the model calculations. The fractional admixture of the IKπ=66- state in the nominal 65- isomer band state is measured within the PRM as 45.6-1.1+0.3%. The E2 and M1 strengths coupling the 5- and 6- bands are enhanced significantly by the mixing, while E1 and E2 couplings to other low-K bands are not measurably enhanced. The yields of the 5+ band are reproduced by an E3 strength of ≈15 W.u., competitive with the interband E2 strength. Alignments of the identified two-particle Nilsson states in Am242 are compared with the single-particle alignments in Am241.

  20. Structural and dynamic implications of an effector-induced backbone amide cis-trans isomerization in cytochrome P450cam

    PubMed Central

    Asciutto, Eliana K.; Madura, Jeffry D.; Pochapsky, Susan Sondej; OuYang, Bo; Pochapsky, Thomas C.

    2009-01-01

    Experimental evidence has been provided for a functionally relevant cis-trans isomerization of the Ile 88-Pro 89 peptide bond in cytochrome P450cam (CYP101). The isomerization is proposed to be a key element of the structural reorganization leading to the catalytically competent form of CYP101 upon binding of the effector protein putidaredoxin (Pdx). A detailed comparison of the results of molecular dynamics simulations on the cis and trans conformations of substrate- and carbonmonoxy-bound ferrous CYP101 with sequence-specific Pdx-induced structural perturbations identified by nuclear magnetic resonance is presented, providing insight into the structural and dynamic consequences of the isomerization. The mechanical coupling between the Pdx binding site on the proximal face of CYP101 and the site of isomerization is described. PMID:19327368

  1. Hydroboration/amination of N-trimethylsilyl protected olefinic amines and diolefins: Synthesis of isomerically pure diamines

    SciTech Connect

    Kabalka, G.W.; Zhe Wang )

    1990-01-01

    N-Trimethylsilyl protected olefinic amines and terminal diolefins were hydroborated with dimethylborane and the resulting organoboranes were treated with in situ generated chloramine or chloralkylamines to produce isomerically pure diamines or N-substituted diamines in good yields.

  2. Distinguishing PCB Isomeric Congeners with their Gas Chromatographic and Mass Spectrometric Ortho Effect using Comprehensive Gas Chromatography

    EPA Science Inventory

    The 209 polychlorinated biphenyl (PCB) congeners and associated nine isomeric groups (nine groups of PCBs with the same degree of chlorination) have been long recorded as high endocrine disrupting chemicals in the environment. Difficult analytical problems exist, in those frequen...

  3. Distinguishing PCB Isomeric Congeners with their Gas Chromatographic and Mass Spectrometric Ortho Effect using Comprehensive Gas Chromatography

    EPA Science Inventory

    The 209 polychlorinated biphenyl (PCB) congeners and associated nine isomeric groups (nine groups of PCBs with the same degree of chlorination) have been long recorded as high endocrine disrupting chemicals in the environment. Difficult analytical problems exist, in those frequen...

  4. Green-lighting green fluorescent protein: Faster and more efficient folding by eliminating a cis–trans peptide isomerization event

    PubMed Central

    Rosenman, David J; Huang, Yao-ming; Xia, Ke; Fraser, Keith; Jones, Victoria E; Lamberson, Colleen M; Van Roey, Patrick; Colón, Wilfredo; Bystroff, Christopher

    2014-01-01

    Wild-type green fluorescent protein (GFP) folds on a time scale of minutes. The slow step in folding is a cis–trans peptide bond isomerization. The only conserved cis-peptide bond in the native GFP structure, at P89, was remodeled by the insertion of two residues, followed by iterative energy minimization and side chain design. The engineered GFP was synthesized and found to fold faster and more efficiently than its template protein, recovering 50% more of its fluorescence upon refolding. The slow phase of folding is faster and smaller in amplitude, and hysteresis in refolding has been eliminated. The elimination of a previously reported kinetically trapped state in refolding suggests that X-P89 is trans in the trapped state. A 2.55 Å resolution crystal structure revealed that the new variant contains only trans-peptide bonds, as designed. This is the first instance of a computationally remodeled fluorescent protein that folds faster and more efficiently than wild type. PMID:24408076

  5. Trans/13-cis isomerization is essential for both the photocycle and proton pumping of bacteriorhodopsin

    SciTech Connect

    Chang, C.H.; Govindjee, R.; Ebrey, T.; Bagley, K.A.; Dollinger, G.; Eisenstein, L.; Marque, J.; Roder, H.; Vittitow, J.; Fang, J.M.

    1985-04-01

    An analogue of bacteriorhodopsin whose chromophore is based on all-trans retinal was studied. A five-membered ring was built around the 13-14 double bond so as to prohibit trans to 13-cis isomerization. No light-induced photochemical changes were seen, other than those due to a small amount (approximately 5%) of unbleached bacteriorhodopsin remaining in the apomembrane used for regeneration. The techniques used included flash photolysis at room and liquid nitrogen temperatures and Fourier-transform infrared difference spectroscopy. When the trans-fixed pigment was incorporated into phospholipid vesicles, no evidence of light-initiated proton pumping could be found. The results indicate that trans to 13-cis isomerization is essential for the photochemical transformation and function of bacteriorhodopsin.

  6. Tuning the Effects of Bacterial Membrane Permeability through Photo-Isomerization of Antimicrobial Cationic Amphiphiles.

    PubMed

    Salta, Joana; Benhamou, Raphael I; Herzog, Ido M; Fridman, Micha

    2017-09-18

    Several important antimicrobial drugs act by permeabilizing cell membranes. In this study, we showed that the intensity of membrane permeability caused by antimicrobial cationic amphiphiles can be modified not only by their concentration but also through light-induced isomerization of their lipid segment. Two types of photo-isomerizable cationic amphiphiles were developed and the effects of photo-isomerization on bacterial growth and membrane permeability were evaluated. One photo-isomer inhibited cell growth and division, whereas the other photo-isomer led to a rapid and lethal bacterial membrane-disrupting effect. The switch from "on" to "off" can be obtained by either the cis- or trans-isomer depending on the bacterial strain and the type of cationic amphiphile. These cationic amphiphiles offer a novel tool for research and industrial applications that require light-controlled bacterial membrane permeabilization. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. Ultrashort IR Laser Pulse Isomerization Of All-Trans Retinal To 11 CIS Retinal

    NASA Astrophysics Data System (ADS)

    Taboada, J.; Liegner, J.; Tsin, A. T.

    1987-01-01

    The mammalian ocular system possesses a significant IR transmission window between the longest visually detectable light wavelength at 700 nm and the cut off water absorption band at 1400 nm. This near IR optical band may provide a channel for controlling vision processes. Of particular interest is the regeneration process which involves the re -Wmerization of all-trans retinal to 11-cis retinal and the molecular recoupling of retinal with opsin.". This re-isomerization, moving against potential energy gradient, is the rate limiting step is assumed to involve either a vitamin A intermediate or a directly applied enzyme, "isomerase"). The concept investigated in this study concerns the possibility of directly influencing the isomerization process by ultrashort IR laser pulses.

  8. Synthesis and optical properties of isomeric branched pi-conjugated systems.

    PubMed

    Nierengarten, Jean-François; Zhang, Sheng; Gégout, Aline; Urbani, Maxence; Armaroli, Nicola; Marconi, Giancarlo; Rio, Yannick

    2005-09-16

    [structure: see text] Branched conjugated systems with a terminal alkyne function have been prepared starting from 4-(triisopropylsilylethynyl) phenylacetylene by applying the following iterative reaction sequence: (i) metal-catalyzed cross-coupling reaction of the terminal alkyne with 3,4-dibromobenzaldehyde or 2,5- dibromobenzaldehyde; (ii) Corey-Fuchs dibromoolefination and treatment with an excess of LDA. The building blocks thus prepared have been subjected to a Pd-catalyzed cross-coupling reaction with 1,4-diiodobenzene to yield isomeric branched pi-conjugated systems containing 7 (first generation) or 15 (second generation) phenyl units connected by ethynyl spacers. The different pi-conjugation patterns in those isomeric derivatives have a dramatic effect on their electronic properties, as attested by the differences observed in their absorption and emission spectra. Finally, theoretical calculations have been performed to rationalize the optical properties of these compounds.

  9. Isomerization of methyl linoleate on ruthenium(III) alkoxide complex; Mathematical modeling

    SciTech Connect

    Mukesh, D.; Narasimhan, C.S.; Ramnarayan, K.; Deshpande, V.M

    1989-08-01

    The isomerization of methyl linoleate using ruthenium alkoxide complexes is described. With alcohols, such as isopropyl alcohol (IPA), 1-butanol, 1-hexanol, and 1-octanol, isomerization of double bonds to produce a conjugated system is the main reaction, with hydrogenation being the side reaction. The latter is formed via the conjugated product. Based on kinetic and infrared spectroscopic data, it is concluded that the active catalytic species is a ruthenium hydride complex formed by the decomposition of the unstable alkoxide. The reaction is mathematically modeled, and the rate parameters are obtained by fitting the simulation to experimental data. These values are compared with data obtained from reactions carried out with supported ruthenium-nickel heterogeneous catalyst.

  10. Application of Δ- and Λ-Isomerism of Octahedral Metal Complexes for Inducing Chiral Nematic Phases

    PubMed Central

    Sato, Hisako; Yamagishi, Akihiko

    2009-01-01

    The Δ- and Λ-isomerism of octahedral metal complexes is employed as a source of chirality for inducing chiral nematic phases. By applying a wide range of chiral metal complexes as a dopant, it has been found that tris(β-diketonato)metal(III) complexes exhibit an extremely high value of helical twisting power. The mechanism of induction of the chiral nematic phase is postulated on the basis of a surface chirality model. The strategy for designing an efficient dopant is described, together with the results using a number of examples of Co(III), Cr(III) and Ru(III) complexes with C2 symmetry. The development of photo-responsive dopants to achieve the photo-induced structural change of liquid crystal by use of photo-isomerization of chiral metal complexes is also described. PMID:20057959

  11. A kinetic study on the isomerization of hop alpha-acids.

    PubMed

    Jaskula, Barbara; Kafarski, Pawel; Aerts, Guido; De Cooman, Luc

    2008-08-13

    In this article, a detailed study on hop alpha-acid isomerization kinetics is presented. Because of the complex wort matrix and interfering interactions occurring during real wort boiling (i.e., trub formation and alpha-acids/iso-alpha-acids complexation), this investigation on alpha-acid isomerization kinetics was performed in aqueous buffer solution as a function of time (0-90 min) and heating temperature (80-100 degrees C). Rate constants and activation energies for the formation of individual iso-alpha-acids were determined. It was found that iso-alpha-acid formation follows first-order kinetics and Arrhenius behavior. Differences in activation energies for the formation of trans- and cis-isomers were noticed, the activation energy for the formation of trans-iso-alpha-acids being approximately 9 kJmol (-1) lower.

  12. Quantum mechanical calculation of resonance tunneling in acetylene isomerization via the vinylidene intermediate

    SciTech Connect

    Germann, T.C.; Miller, W.H. |

    1998-07-01

    Microcanonical rate constants for the acetylene isomerization reaction have been computed using the direct cumulative reaction probability methodology of Seideman and Miller [J. Chem. Phys. {bold 96}, 4412 (1992); {bold 97}, 2499 (1992)] and Manthe and Miller [J. Chem. Phys. {bold 99}, 3411 (1993)]. Two- and three-degree-of-freedom calculations are reported using a normal mode Hamiltonian based on the geometry of the vinylidene intermediate. Due to the vinylidene well, numerous resonances are found in the isomerization rate. Little coupling is found between the CH{sub 2} rock reaction coordinate and the other normal modes, so that the resonances are readily assignable as normal mode progressions. Qualitatively similar results are obtained using two different potential energy surfaces, or different reduced dimensionality sets of coordinates. {copyright} {ital 1998 American Institute of Physics.} thinsp

  13. Effect of Isomeric Structures on Photovoltaic Performance of D-A Copolymers.

    PubMed

    Xie, Fangyuan; He, Dan; Pan, Han; Jiang, Jiaxing; Ding, Liming

    2017-06-01

    Two donor-acceptor copolymers based on isomeric acceptor units, [7,7'-bithieno[2',3':4,5]thieno[2,3-d]thieno[3,2-b]pyridine]-5,5'(4H,4'H)-dione (BTTP) and [2,2'-bithieno[2',3':4,5]thieno[2,3-d]thieno[3,2-b]pyridine]-5,5'(4H,4'H)-dione (iBTTP), are developed to study the effect of isomeric structures on photovoltaic performance. Compared with PBDTBTTP, PBDTiBTTP possesses a smaller bandgap for good light harvesting and a better π-π stacking for higher hole mobility. PBDTiBTTP solar cells present balanced mobilities and good nanoscale phase separation, giving a power conversion efficiency (PCE) of 6.51%, with higher short-circuit current (Jsc ) and fill factor (FF). © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. Pin1-Induced Proline Isomerization in Cytosolic p53 Mediates BAX Activation and Apoptosis.

    PubMed

    Follis, Ariele Viacava; Llambi, Fabien; Merritt, Parker; Chipuk, Jerry E; Green, Douglas R; Kriwacki, Richard W

    2015-08-20

    The cytosolic fraction of the tumor suppressor p53 activates the apoptotic effector protein BAX to trigger apoptosis. Here we report that p53 activates BAX through a mechanism different from that associated with activation by BH3 only proteins (BIM and BID). We observed that cis-trans isomerization of proline 47 (Pro47) within p53, an inherently rare molecular event, was required for BAX activation. The prolyl isomerase Pin1 enhanced p53-dependent BAX activation by catalyzing cis-trans interconversion of p53 Pro47. Our results reveal a signaling mechanism whereby proline cis-trans isomerization in one protein triggers conformational and functional changes in a downstream signaling partner. Activation of BAX through the concerted action of cytosolic p53 and Pin1 may integrate cell stress signals to induce a direct apoptotic response. Copyright © 2015 Elsevier Inc. All rights reserved.

  15. Ethanol production from xylose by enzymic isomerization and yeast fermentation. [Schizosaccharomyces pombe

    SciTech Connect

    Chiang, L.C.; Hsiao, H.Y.; Ueng, P.P.; Chen, L.F.; Tsao, G.T.

    1981-01-01

    Repetitive enzymic isomerization of xylose followed by yeast fermentation of xylulose, and simultaneous enzymic isomerization and yeast fermentation, were proven to be methods capable of converting xylose to EtOH. The fermentation product (EtOH, xylitol, or glycerol) has little inhibitory or deactivation effect on the activity of isomerase. In a comparison of the ability of yeasts to ferment xylulose to EtOH, Schizosaccharomyces pombe was found to be superior to industrial bakers' yeast. Under optimal conditions (pH 6, temperature 30 degrees), a final EtOH concentration of 6.3% was obtained from simulated hemicellulose hydrolyzate using a simultaneous fermentation process. The EtOH yield was more than 80% of theoretical.

  16. Reversible Z-E isomerism and pharmaceutical implications for SU5416.

    PubMed

    Sistla, Anand; Shenoy, Narmada

    2005-12-01

    SU5416 (Z-isomer), the first in its class of angiogenesis inhibitors, in solution converts to the E-isomer following light exposure and reverts to the Z-isomer in the dark. Kinetics of this Z-E isomerism in pharmaceutical media is reported. Analytical solutions need light protection at 5 degrees C to maintain integrity. While E-isomer in light-exposed product increased to 0.9% in 24 hours, light-protected product showed no change (25 degrees C, 18 months). Infusate studies indicated that < 1.9% E-isomer will be dosed to patients and would likely convert to the Z-isomer, following administration. This report implies Z-E isomerism in SU5416 is controllable with no limitations towards ensuring pharmaceutical product quality.

  17. Mechanistic interpretation of selective catalytic hydrogenation and isomerization of alkenes and dienes by ligand deactivated Pd nanoparticles.

    PubMed

    Zhu, Jie S; Shon, Young-Seok

    2015-11-14

    Unsupported thiolate-capped palladium nanoparticle catalysts are found to be highly substrate-selective for alkene hydrogenation and isomerization. Steric and poisoning effects from thiolate ligands on the nanoparticle surface control reactivity and selectivity by influencing alkene adsorption and directing either di-σ or mono-σ bond formation. The presence of overlapping p orbitals and α protons in alkenes greatly influences the catalytic properties of deactivated palladium nanoparticles leading to easily predictable hydrogenation or isomerization products.

  18. Experimental study of water-ice catalyzed thermal isomerization of cyanamide into carbodiimide: implication for prebiotic chemistry.

    PubMed

    Duvernay, Fabrice; Chiavassa, Thierry; Borget, Fabien; Aycard, Jean-Pierre

    2004-06-30

    Cyanamide (NH2CN) is a molecule of interstellar interest which can be implied in prebiotic chemistry. We showed, by FTIR spectroscopy, that cyanamide can be isomerized in carbodiimide (HNCNH), another interstellar relevant molecule, by a reaction involving the amorphous water-ice surface as catalyst. This isomerization occurs at low temperature (T < 100 K) which agrees quite well with that expected in the interstellar clouds composed of dust grains in which water is the most predominant constituent.

  19. Isomerism in the setting of the so-called “heterotaxy”: The usefulness of computed tomographic analysis

    PubMed Central

    Mori, Shumpei; Anderson, Robert H; Nishii, Tatsuya; Matsumoto, Kensuke; Loomba, Rohit S

    2017-01-01

    The most complex combinations of congenital cardiac malformations are found in the setting of bodily isomerism. The question remains, however, as to whether evidence of cardiac isomerism is always to be found in the setting of bodily isomerism, also known as “heterotaxy.” We have previously shown that, when assessed on the basis of the extent of the pectinate muscles relative to the atrioventricular junctions, there is always isomerism of the atrial appendages in this setting. Doubt has been remained, however, as to whether these cardiac features can accurately be recognized during life. We have now encountered two patients showing features of the left and right bodily isomerism. Examinations of these patients made using computed tomography show that all features of isomerism, no matter how complex, can now be visualized during life. The images currently presented show, furthermore, that the features of the so-called “heterotaxy” can be seen during life, not only within the heart but also in all the thoracic and abdominal organs, albeit that the isomeric features are confined to the thoracic organs. Based on the images presented, we argue that if each system of organs is analyzed and described in independent fashion; then it is possible for clinicians to exclude any suggestion of ambiguity and to provide accurate descriptions of the overall arrangement. We further discuss the appropriate terminology to describe the entity we prefer to call isomerism, along with the indications and usefulness of computed tomography in revealing the anatomic features of the congenitally malformed heart. PMID:28566826

  20. Reactions of platinum(IV)-bound nitriles with isomeric nitroanilines: addition vs. substitution.

    PubMed

    Chernyshev, Alexander N; Bokach, Nadezhda A; Gushchin, Pavel V; Haukka, Matti; Kukushkin, Vadim Yu

    2012-11-07

    The platinum(IV) complex trans-[PtCl(4)(EtCN)(2)] reacts smoothly and under mild conditions with isomeric o-, m- and p-nitroanilines (NAs) yielding two different types of products depending on the NA isomer, viz. the nitroaniline complexes cis/trans-[PtCl(4)(NA)(2)] (cis/trans-1-3) and the amidine species trans-[PtCl(4){NH=C(Et)NHC(6)H(4)NO(2)-m}(EtCN)] (4), trans-[PtCl(4){NH=C(Et)NHC(6)H(4)NO(2)-m}(2)] (5) and trans-[PtCl(4){NH=C(Et)NHC(6)H(4)NO(2)-p}(EtCN)] (6). Complexes 4 and 5 undergo cyclometalation, furnishing mer-[PtCl(3){NH=C(Et)NHC(6)H(3)NO(2)-m}(EtCN)] (7) and mer-[PtCl(3){NH=C(Et)NHC(6)H(4)NO(2)-m}{NH=C(Et)NHC(6)H(3)NO(2)-m}] (8), respectively. Moreover, 8 both in the solid state and in solution undergoes the second step of the cyclometalation, generating [PtCl(2){NH=C(Et)NHC(6)H(3)NO(2)-m}(2)] (9). In 4, the nitrile ligand is highly reactive toward nucleophilic addition and it undergoes facile hydration accompanied by the elimination of the nitrile, thus producing cis-[PtCl(4)(NH(2)C(6)H(4)NO(2)-m){NH=C(OH)Et}] (10), or methanol addition providing trans-[PtCl(4){NH=C(Et)NHC(6)H(4)NO(2)-m}{NH=C(Et)OMe}] (11). All compounds, besides 9, were characterized by C, H, and N elemental analyses, high-resolution ESI-MS, IR, (1)H and (13)C{(1)H} NMR spectroscopic techniques. Complex 9, which was not isolated as a pure compound, was identified in the reaction mixture by ESI-MS and (1)H and (13)C{(1)H} NMR spectroscopies. Complexes trans-1, trans-2, 4, 5, 6, 8, 10, and 11 were additionally studied by X-ray diffraction.

  1. Large-amplitude dynamics in vinyl radical: the role of quantum tunneling as an isomerization mechanism.

    PubMed

    Sharma, Amit R; Bowman, Joel M; Nesbitt, David J

    2012-01-21

    We report tunneling splittings associated with the large amplitude 1,2 H-atom migration to the global minima in the vinyl radical. These are obtained using a recent full-dimensional ab initio potential energy surface (PES) [A. R. Sharma, B. J. Braams, S. Carter, B. C. Shepler, and J. M. Bowman, J. Chem. Phys. 130(17), 174301 (2009)] and independently, directly calculated "reaction paths." The PES is a multidimensional fit to coupled cluster single and double and perturbative treatment of triple excitations coupled-cluster single double triple (CCSD(T)) with the augmented correlation consistent triple zeta basis set (aug-cc-pVTZ). The reaction path potentials are obtained from a series of CCSD(T)/aug-cc-pVnTZ calculations extrapolated to the complete basis set limit. Approximate 1D calculations of the tunneling splitting for these 1,2-H atom migrations are obtained using each of these potentials as well as quite different 1D Hamiltonians. The splittings are calculated over a large energy ranges, with results from the two sets of calculations in excellent agreement. Though negligibly slow (>1 s) for the vibrational ground state, this work predicts tunneling-promoted 1,2 hydride shift dynamics in vinyl to exhibit exponential growth with internal vibrational excitation, specifically achieving rates on the sub-μs time scale at energies above E ≈ 7500 cm(-1). Most importantly, these results begin to elucidate the possible role of quantum isomerization through barriers without dissociation, in competition with the more conventional picture of classical roaming permitted over a much narrower window of energies immediately below the bond dissociation limit. Furthermore, when integrated over a Boltzmann distribution of thermal energies, these microcanonical tunneling rates are consistent with sub-μs time scales for 1,2 hydride shift dynamics at T > 1400 K. These results have potential relevance for combustion modeling of low-pressure flames, as well as recent

  2. Proline Isomerization of the Immune Receptor-Interacting Protein RIN4 by a Cyclophilin Inhibits Effector-Triggered Immunity in Arabidopsis

    PubMed Central

    Li, Meng; Ma, Xiqing; Chiang, Yi-Hsuan; Yadeta, Koste A.; Ding, Pengfei; Dong, Liansai; Zhao, Yan; Li, Xiuming; Yu, Yufei; Zhang, Ling; Shen, Qian-Hua; Xia, Bin; Coaker, Gitta; Liu, Dong; Zhou, Jian-Min

    2016-01-01

    SUMMARY In the absence of pathogen infection, plant effector-triggered immune (ETI) receptors are maintained in a preactivation state by intermolecular interactions with other host proteins. Pathogen effector-induced alterations activate the receptor. In Arabidopsis, the ETI receptor RPM1 is activated via bacterial effector AvrB-induced phosphorylation of the RPM1-interacting protein RIN4 at Threonine 166. We find that RIN4 also interacts with the prolyl-peptidyl isomerase (PPIase) ROC1, which is reduced upon RIN4 Thr166 phosphorylation. ROC1 suppresses RPM1 immunity in a PPIase-dependent manner. Consistent with this, RIN4 Pro149 undergoes cis/trans isomerization in the presence of ROC1. While the RIN4P149V mutation abolishes RPM1 resistance, the deletion of Pro149 leads to RPM1 activation in the absence of RIN4 phosphorylation. These results support a model in which RPM1 directly senses conformational changes in RIN4 surrounding Pro149 that is controlled by ROC1. RIN4 Thr166 phosphorylation indirectly regulates RPM1 resistance by modulating the ROC1-mediated RIN4 isomerization. PMID:25299333

  3. Temperature-dependent Raman spectroscopic evidence of and molecular mechanism for irreversible isomerization of β-endosulfan to α-endosulfan.

    PubMed

    Schmidt, Walter F; Hapeman, Cathleen J; McConnell, Laura L; Mookherji, Swati; Rice, Clifford P; Nguyen, Julie K; Qin, Jianwei; Lee, Hoyoung; Chao, Kuanglin; Kim, Moon S

    2014-03-05

    Endosulfan (6,7,8, 9,10,10-hexachloro-1,5,5a,6,9,9a-hexahydro-6,9-methano-2,4,3-benzodioxathiepine-3-oxide) is a broad-spectrum, organochlorine insecticide used on numerous crops since the 1950s. It is has been identified as a persistent organic pollutant (POP) due to its persistence, bioaccumulation, long-range transport, and adverse effects to human health and aquatic ecosystems; it will be phased out in the United States in 2016. Endosulfan consists of two diastereomers, α and β; α-endosulfan exists as two asymmetrical, twist-chair enantiomers which interchange, while β-endosulfan has a symmetrical-chair conformation. β-Endosulfan has been shown to isomerize to α-endosulfan. Here we document the previously proposed isomerization mechanism using temperature-dependent Raman (TDR) spectroscopy. The bending frequencies in the fingerprint region were assigned to specific bonds. Changes in the signal intensity as a function of temperature were used to identify detailed ring movements and thus conversion of β to α. These movements cannot occur simultaneously nor symmetrically, precluding conversion of α-endosulfan to β-endosulfan.

  4. Ligand noninnocence of thiolate/disulfide in dinuclear copper complexes: solvent-dependent redox isomerization and proton-coupled electron transfer.

    PubMed

    Thomas, Andrew M; Lin, Bo-Lin; Wasinger, Erik C; Stack, T Daniel P

    2013-12-18

    Copper thiolate/disulfide interconversions are related to the functions of several important proteins such as human Sco1, Cu-Zn superoxide dismutase (SOD1), and mammalian zinc-bonded metallothionein. The synthesis and characterization of well-defined synthetic analogues for such interconversions are challenging yet provide important insights into the mechanisms of such redox processes. Solvent-dependent redox isomerization and proton-coupled electron transfer mimicking these interconversions are observed in two structurally related dimeric μ,η(2):η(2)-thiolato Cu(II)Cu(II) complexes by various methods, including X-ray diffraction, XAS, NMR, and UV-vis. Spectroscopic evidence shows that a solvent-dependent equilibrium exists between the dimeric μ-thiolato Cu(II)Cu(II) state and its redox isomeric μ-disulfido Cu(I)Cu(I) form. Complete formation of μ-disulfido Cu(I)Cu(I) complexes, however, only occurs after the addition of 2 equiv of protons, which promote electron transfer from thiolate to Cu(II) and formation of disulfide and Cu(I) via protonation of the coordinating ligand. Proton removal reverses this reaction. The reported unusual reductive protonation/oxidative deprotonation of the metal centers may serve as a new chemical precedent for how related proteins manage Cu ions in living organisms.

  5. Theoretical study on the isomeric structures and the stability of silylenoid (Tsi)Cl2SiLi (Tsi = C(SiMe3)3).

    PubMed

    Xie, Ju; Feng, Dacheng; Feng, Shengyu

    2006-06-01

    The structures and isomerization of silylenoid (Tsi)Cl(2)SiLi (Tsi = C(SiMe(3))(3)) were studied by density functional theory (DFT) at the B3LYP/6-31G(d) level. Four equilibrium structures and three isomeric transition states were located. The three-membered ring and p-complex structures, 1 and 2, are the two most stable forms. Two other local minima, the sigma-complex 3 and tetrahedron structure 4, should rearrange to 1 with very low barriers, and then to the most stable isomer 2. To exploit further the stability of silylenoid (Tsi)Cl(2)SiLi, the insertion reactions of 2 and silylene (Tsi)ClSi into the HF molecule have been investigated at the B3LYP/6-31G(d) level, respectively. The results show that the insertion of 2 into HF is very similar to that of (Tsi)ClSi into HF, but the latter is more favorable. To probe the influence of the substituent Tsi on the stability of silylenoid (Tsi)Cl(2)SiLi, the isomers and insertion reaction of silylenoid CH(3)Cl(2)SiLi were investigated in a similar way of those with (Tsi)Cl(2)SiLi. The results indicate that silylenoid containing very bulky group Tsi exhibits unusual stability because of the severe steric hindrance produced by Tsi at the center to which it is attached.

  6. Isomeric ratio measurements for the radiative neutron capture 176Lu(n,γ) at DANCE

    NASA Astrophysics Data System (ADS)

    Denis-Petit, D.; Roig, O.; Méot, V.; Jandel, M.; Vieira, D. J.; Bond, E. M.; Bredeweg, T. A.; Couture, A. J.; Haight, R. C.; Keksis, A. L.; Rundberg, R. S.; Ullmann, J. L.

    2016-03-01

    The isomeric ratio for the neutron capture reaction 176Lu(n,γ) on the Jπ= 5/2-, 761.7 keV, T1/2=32.8 ns level of 177mLu, has been determined in the neutron energy range 8.5 eV-100 keV for the first time using the DANCE array at the Los Alamos National Laboratory.

  7. Aspartate-bond isomerization affects the major conformations of synthetic peptides.

    PubMed

    Szendrei, G I; Fabian, H; Mantsch, H H; Lovas, S; Nyéki, O; Schön, I; Otvos, L

    1994-12-15

    The aspartic acid bond changes to an beta-aspartate bond frequently as a side-reaction during peptide synthesis and often as a post-translational modification of proteins. The formation of beta-asparate bonds is reported to play a major role not only in protein metabolism, activation and deactivation, but also in pathological processes such as deposition of the neuritic plaques of Alzheimer's disease. Recently, we reported how conformational changes following the aspartic-acid-bond isomerization may help the selective aggregation and retention of the amyloid beta peptide in affected brains (Fabian et al., 1994). In the current study we used circular dichroism, Fourier-transform infrared spectroscopy, and molecular modeling to characterize the general effect of the beta-aspartate-bond formation on the conformation of five sets of synthetic model peptides. Each of the non-modified, parent peptides has one of the major secondary structures as the dominant spectroscopically determined conformation: a type I beta turn, a type II beta turn, short segments of alpha or 3(10) helices, or extended beta strands. We found that both types of turn structures are stabilized by the aspartic acid-bond isomerization. The isomerization at a terminal position did not affect the helix propensity, but placing it in mid-chain broke both the helix and the beta-pleated sheet with the formation of reverse turns. The alteration of the geometry of the lowest energy reverse turn was also supported by molecular dynamics calculations. The tendency of the aspartic acid-bond isomerization to stabilize turns is very similar to the effect of incorporating sugars into synthetic peptides and suggests a common feature of these post-translational modifications in defining the secondary structure of protein fragments.

  8. Isomeric yield ratios of 87m,gY from different nuclear reactions

    NASA Astrophysics Data System (ADS)

    Naik, H.; Kim, G. N.; Kim, K.; Zaman, M.; Sahid, M.; Yang, S.-C.; Lee, M. W.; Kang, Y. R.; Shin, S. G.; Cho, M.-H.; Goswami, A.; Song, T. Y.

    2014-07-01

    The independent isomeric yield ratios of 87m,gY produced from the 93Nb( γ, α2n) and natZr( γ, p xn) reactions with the end-point bremsstrahlung energy of 45-70 MeV have been determined by an off-line γ-ray spectrometric technique using 100 MeV electron linac at the Pohang accelerator laboratory, Korea. The isomeric yield ratios of 87m,gY were also determined from the natZr(p, αxn) and the 89Y(p,p2n) reactions with E P = 15-45 MeV as well as those from the 89Y( α, α2n) reaction with E α = 32-43 MeV using the MC-50 cyclotron at the Korea Institute of Radiological and Medical Science, Korea. The isomeric yield ratios of 87m,gY from the present work in the 93Nb( γ, α2n), natZr( γ, p xn), natZr(p, αxn), 89Y(p,p2n), and 89Y( α, α2n) reactions were compared with those of the literature data in the 85Rb( α, 2n), the 86,87,88Sr(d, xn), 89Y(n,3n), and the 89Y( γ, 2n) reactions to examine the role of target, projectiles, and ejectiles through compound nucleus excitation energy and input angular momentum. The isomeric yield ratios of 87m,gY in the above eleven reactions were also calculated using the computer code TALYS 1.4 and compared with the experimental data. The different behaviors between photon- and neutron-induced reactions and charged-particle-induced reactions are discussed from the viewpoint of compound and non-compound (pre-equilibrium) process.

  9. Mechanism of Glucose Isomerization Using a Solid Lewis Acid Catalyst in Water

    SciTech Connect

    Roman-Leshkov, Yuriy; Moliner, Manuel; Labinger, J. A.; Davis, Mark E.

    2010-10-20

    1H and 13C NMR spectroscopy on isotopically labeled glucose reveals that in the presence of tin-containing zeolite Sn-Beta, the isomerization reaction of glucose in water proceeds by way of an intramolecular hydride shift rather than proton transfer. This is the first mechanistic demonstration of Sn-Beta acting as a Lewis acid in a purely aqueous environment.

  10. A classical trajectory study of the dissociation and isomerization of C2H5.

    PubMed

    Wagner, Albert F; Rivera-Rivera, Luis A; Bachellerie, Damien; Perry, Jamin W; Thompson, Donald L

    2013-11-21

    Motivated by photodissociation experiments in which non-RRKM nanosecond lifetimes of the ethyl radical were reported, we have performed a classical trajectory study of the dissociation and isomerization of C2H5 over the energy range 100-150 kcal/mol. We used a customized version of the AIREBO semiempirical potential (Stuart, S. J.; et al. J. Chem. Phys. 2000, 112, 6472-6486) to more accurately describe the gas-phase decomposition of C2H5. This study constitutes one of the first gas-phase applications of this potential form. At each energy, 10,000 trajectories were run and all underwent dissociation in less than 100 ps. The calculated dissociation rate constants are consistent with RRKM models; no evidence was found for nanosecond lifetimes. An analytic kinetics model of isomerization/dissociation competition was developed that incorporated incomplete mode mixing through a postulated divided phase space. The fits of the model to the trajectory data are good and represent the trajectory results in detail through repeated isomerizations at all energies. The model correctly displays single exponential decay at lower energies, but at higher energies, multiexponential decay due to incomplete mode mixing becomes more apparent. At both ends of the energy range, we carried out similar trajectory studies on CD2CH3 to examine isotopic scrambling. The results largely support the assumption that a H or a D atom is equally likely to dissociate from the mixed-isotope methyl end of the molecule. The calculated fraction of products that have the D atom dissociation is ∼20%, twice the experimental value available at one energy within our range. The calculated degree of isotopic scrambling is non-monotonic with respect to energy due to a non-monotonic ratio of the isomerization to dissociation rate constants.

  11. Simulation of chemical isomerization reaction dynamics on a NMR quantum simulator.

    PubMed

    Lu, Dawei; Xu, Nanyang; Xu, Ruixue; Chen, Hongwei; Gong, Jiangbin; Peng, Xinhua; Du, Jiangfeng

    2011-07-08

    Quantum simulation can beat current classical computers with minimally a few tens of qubits. Here we report an experimental demonstration that a small nuclear-magnetic-resonance quantum simulator is already able to simulate the dynamics of a prototype laser-driven isomerization reaction using engineered quantum control pulses. The experimental results agree well with classical simulations. We conclude that the quantum simulation of chemical reaction dynamics not computable on current classical computers is feasible in the near future.

  12. Direct Measurement of the Isomerization Barrier of the Isolated Retinal Chromophore

    DTIC Science & Technology

    2015-11-03

    cis-trans isomerization is 0.64 ± 0.05 eV, which is significantly lower than that observed for the reaction within opsin proteins. Thus the protein...is 0.64±0.05 eV, which is significantly lower than that observed for the reaction within opsin proteins. Thus the protein has a signifi- cant role in

  13. A Cascade Isomerization/Prins Strategy through Iridium(III)/Brønsted Acid Cooperative Catalysis**

    PubMed Central

    Lombardo, Vince M.; Thomas, Christopher D.; Scheidt, Karl A.

    2014-01-01

    A mild and efficient isomerization/protonation sequence involving an appropriately functionalized indole precursor to generate a wide variety of pyran-fused indoles utilizing cooperative catalysis between cationic iridium (III) and bismuth triflate has been developed. Three distinct cyclization manifolds lead to bioactive scaffolds that can be obtained in good yields. In addition, N-substituted indoles can be synthesized enantioselectively via an oxocarbenium• chiral phosphate counterion strategy. PMID:24218144

  14. An unexpected isomerization of 1,3-benzothiazine and isoquinoline-condensed β-lactams

    NASA Astrophysics Data System (ADS)

    Fodor, Lajos; Csomós, Péter; Fülöp, Ferenc; Csámpai, Antal; Sohár, Pál

    2010-11-01

    A series of novel aryl-substituted β-lactams condensed with 1,3-benzothiazines, isoquinolines or 1,4-benzothiazepine were obtained by means of the Staudinger reaction and isomerized in the presence of sodium methoxide to the thermodynamically more stable form. The structures of the new molecules were determined by NMR spectroscopy. Theoretical calculations corroborate the experimentally observed structure-reactivity relationships.

  15. Viscosities of Binary Mixtures Containing Isomeric Chlorobutanes and Diisopropylether: Experimental and Predicted Values

    NASA Astrophysics Data System (ADS)

    Montaño, D.; Guerrero, H.; Bandrés, I.; López, M. C.; Lafuente, Carlos

    2010-03-01

    In this work, viscosities of binary mixtures of isomeric chlorobutanes with diisopropylether have been determined as a function of composition under atmospheric pressure and in the temperature range from 283.15 K to 313.15 K with steps of 5 K. Kinematics viscosities were measured using an Ubbelohde viscosimeter; absolute viscosities were obtained from kinematic viscosities and densities. Finally, we have used the Asfour method for predicting the dependence of viscosity with composition and comparing it with our experimental data.

  16. Catalytic cascade hydroalkoxylation/isomerization/ [4 + 2] cycloaddition using enyne alcohols as latent dienes or dienophiles.

    PubMed

    Guo, Rui; Li, Kang-Nan; Gong, Liu-Zhu

    2013-10-21

    Enyne alcohols can react as precursors of either dienes or dienophiles with different substrates after hydroxylation and isomerization by gold catalysis. As such, oxa-bridged tricyclo[5.2.2.02,6]-undec-8-ene-3,5-dione derivatives have been obtained by the Diels–Alder reaction and tetrahydro-1H-furo[3,4-c]pyran derivatives could be accessed by the hetero-Diels–Alder cycloaddition.

  17. Solution phase isomerization of vibrationally excited singlet nitrenes to vibrationally excited 1,2-didehydroazepine.

    PubMed

    Burdzinski, Gotard T; Middleton, Chris T; Gustafson, Terry L; Platz, Matthew S

    2006-11-22

    Photolysis of phenyl and o-biphenylyl azide (at 270 nm) releases vibrationally excited singlet nitrene which isomerizes to the corresponding hot 1,2-didehydroazepine at a rate competitive with thermal relaxation. Using ultrafast vibrational spectroscopy we observe the formation of vibrationally excited 1,2-4,6-azacycloheptatetraene (1,2-didehydroazepine) in picoseconds following photolysis of phenyl azide in chloroform and o-biphenylyl azide in acetonitrile at ambient temperature.

  18. Novel domino procedures for the synthesis of chromene derivatives and their isomerization.

    PubMed

    Zonouzi, Afsaneh; Izakian, Zakieh; Ng, Seik Weng

    2016-08-01

    Novel tricyclic keto diesters have been synthesized by a one-pot three-component procedure via DABCO-catalyzed domino Knoevenagel-Michael addition reactions. Also, an efficient four-component reaction for the synthesis of another new group of tricyclic keto diesters has been developed via domino Knoevenagel-intramolecular oxo-Diels-Alder reactions. A selective thermal isomerization of the synthesized chromenes to fumarates is also described. X-ray analyses confirm unambiguously the structures of the products.

  19. Qualification of a Quantitative Method for Monitoring Aspartate Isomerization of a Monoclonal Antibody by Focused Peptide Mapping.

    PubMed

    Cao, Mingyan; Mo, Wenjun David; Shannon, Anthony; Wei, Ziping; Washabaugh, Michael; Cash, Patricia

    Aspartate (Asp) isomerization is a common post-translational modification of recombinant therapeutic proteins that can occur during manufacturing, storage, or administration. Asp isomerization in the complementarity-determining regions of a monoclonal antibody may affect the target binding and thus a sufficiently robust quality control method for routine monitoring is desirable. In this work, we utilized a liquid chromatography-mass spectrometry (LC/MS)-based approach to identify the Asp isomerization in the complementarity-determining regions of a therapeutic monoclonal antibody. To quantitate the site-specific Asp isomerization of the monoclonal antibody, a UV detection-based quantitation assay utilizing the same LC platform was developed. The assay was qualified and implemented for routine monitoring of this product-specific modification. Compared with existing methods, this analytical paradigm is applicable to identify Asp isomerization (or other modifications) and subsequently develop a rapid, sufficiently robust quality control method for routine site-specific monitoring and quantitation to ensure product quality. This approach first identifies and locates a product-related impurity (a critical quality attribute) caused by isomerization, deamidation, oxidation, or other post-translational modifications, and then utilizes synthetic peptides and MS to assist the development of a LC-UV-based chromatographic method that separates and quantifies the product-related impurities by UV peaks. The established LC-UV method has acceptable peak specificity, precision, linearity, and accuracy; it can be validated and used in a good manufacturing practice environment for lot release and stability testing.

  20. New insights on molybdenum suboxide: nature of carbons in isomerization reactions.

    PubMed

    Torres-García, Enelio; Rodríguez-Gattorno, Geonel; Ascencio, Jorge A; Aleman-Vazquez, Laura O; Cano-Domínguez, José L; Martínez-Hernandez, Angel; Santiago-Jacinto, Patricia

    2005-09-22

    MoO3 transformations under isomerization process conditions were studied. The products obtained after different times under stream (H2/n-heptane mixture, 18.5 bar, at 370 degrees C) were characterized by X-ray diffraction, Raman spectroscopy, thermal analysis, and high-resolution transmission electron microscopy (HRTEM). Theoretical quantum calculations were carried out with the aim of understanding the paradox of the real active phase in isomerization reactions. Theoretical calculations predict the existence of a metallic-like MoO phase with a structure that matches the X-ray diffraction experimental results. From experimental and simulated HRTEM images it was possible to identify the presence of small MoO cubic crystallites inside MoOx matrix phases. These results also support the previously proposed idea that isomerization reactions take place as a result of the existence of a bifunctional catalyst. The Raman and thermo-programmed oxidation (TPO) analyses show the existence of at least two types of carbonaceous deposits which tend to increase its ordering with the increase of time under stream. The carbon K edge in electron energy loss spectroscopy (EELS) of a sample after 24 h under stream shows that these carbonaceous deposits consist of a mixture of sp2- and sp3-hybridized carbons.