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Sample records for 94ag isomeric states

  1. Spectroscopic characterization of isomerization transition states.

    PubMed

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

    2015-12-11

    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, ω(eff). 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. PMID:26659051

  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. Isomeric States and Collective Excitations of Heaviest Nuclei

    NASA Astrophysics Data System (ADS)

    Adamian, G. G.; Antonenko, N. V.; Jolos, R. V.; Kuzmina, A. N.; Malov, L. A.; Shirikova, N. Yu.; Sushkov, A. V.

    2013-03-01

    The isotopic dependence of two-quasiparticle isomeric states in Fm and No is treated. An α-decay chain through the isomeric states of super-heavy nuclei is demonstrated. The excitation energies and the structure of the low lying states with Kπ = 0‒ 1‒ 2‒ are calculated with the quasiparticle phonon model.

  5. Solid State Photochemical Isomerization: A Convenient Laboratory Experiment.

    ERIC Educational Resources Information Center

    Burton, W. B.

    1979-01-01

    Describes the use of benzophenone in the role of a solid state sensitizer in a photochemical isomerization and as an indicator in preparative layer chromatography for purification of the isomeride. (Author/SA)

  6. Excited state dynamics and isomerization in ruthenium sulfoxide complexes.

    PubMed

    King, Albert W; Wang, Lei; Rack, Jeffrey J

    2015-04-21

    Molecular photochromic compounds are those that interconvert between two isomeric forms with light. The two isomeric forms display distinct electronic and molecular structures and must not be in equilibrium with one another. These light-activated molecular switch compounds have found wide application in areas of study ranging from chemical biology to materials science, where conversion from one isomeric form to another by light prompts a response in the environment (e.g., protein or polymeric material). Certain ruthenium and osmium polypyridine sulfoxide complexes are photochromic. The mode of action is a phototriggered isomerization of the sulfoxide from S- to O-bonded. The change in ligation drastically alters both the spectroscopic and electrochemical properties of the metal complex. Our laboratory has pioneered the preparation and study of these complexes. In particular, we have applied femtosecond pump-probe spectroscopy to reveal excited state details of the isomerization mechanism. The data from numerous complexes allowed us to predict that the isomerization was nonadiabatic in nature, defined as occurring from a S-bonded triplet excited state (primarily metal-to-ligand charge transfer in character) to an O-bonded singlet ground state potential energy surface. This prediction was corroborated by high-level density functional theory calculations. An intriguing aspect of this reactivity is the coupling of nuclear motion to the electronic wave function and how this coupling affects motions productive for isomerization. In an effort to learn more about this coupling, we designed a project to examine phototriggered isomerization in bis-sulfoxide complexes. The goal of these studies was to determine whether certain complexes could be designed in which a single photon excitation event would prompt two sulfoxide isomerizations. We employed chelating sulfoxides in this study and found that both the nature of the chelate ring and the R group on the sulfoxide affect

  7. Excited State Isomerization of a Stilbene Analog: E / Z Phenylvinylacetylene

    NASA Astrophysics Data System (ADS)

    Newby, Josh J.; Müller, Christian W.; Liu, Ching-Ping; Lee, Hsiupu D.; Zwier, Timothy S.

    2009-06-01

    The excited state isomerization of the E and Z forms of phenylvinylacetylene (PVA, 1-phenyl-1-buten-3-yne) has been studied using ultraviolet population transfer spectroscopy (UVPT). UVPT is a pump-probe experiment, where single isomers are selectively excited and after a wait time, the induced change in population of reactant and product isomers is probed. In these experiments, after initial cooling, an isomer of PVA is selectively excited to vibrational levels in the S_{1} electronic state. If the energy supplied by the excitation is above the barrier to isomerization population can be transferred into a product well. Excited molecules are collisionally cooled via supersonic expansion and a new population distribution can be detected downstream via R2PI spectroscopy. From these experiments, product isomerization quantum yields have been determined for both E to Z and Z to E excited state pathways as a function of excess energy above the S_{1} origin.

  8. 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).

  9. g-factor measurements of isomeric states in 174W

    NASA Astrophysics Data System (ADS)

    Rocchini, M.; Nannini, A.; Benzoni, G.; Melon, B.; John, P. R.; Ur, C. A.; Avigo, R.; Bazzacco, D.; Blasi, N.; Bocchi, G.; Bottoni, S.; Bracco, A.; Camera, F.; Ceruti, S.; Crespi, F. C. L.; Georgiev, G.; Giaz, A.; Gottardo, A.; Leoni, S.; Menegazzo, R.; Mengoni, D.; Michelagnoli, C.; Million, B.; Modamio, V.; Morales, A. I.; Napoli, D. R.; Ottanelli, M.; Pellegri, L.; Perego, A.; Valiente-Dobon, J. J.; Wieland, O.

    2016-05-01

    The experimental setup GAMIPE used for gyro magnetic factor measurements at Laboratori Nazionali di Legnaro and a recent experimental work regarding K-isomers in 174W are described. Aim of the experiment is to study the detailed structure of the isomeric states wave functions, by the measurement of the magnetic dipole moments. This piece of information can provide interesting hints for theoretical models. Preliminary results concerning the population of the isomers of interest and half-lives are presented.

  10. Conversion coefficients of the isomeric state in {sup 72}Br

    SciTech Connect

    Briz, J. A.; Borge, M. J. G.; Maira, A.; Perea, A.; Tengblad, O.; Agramunt, J.; Algora, A.; Estevez, E.; Nacher, E.; Rubio, B.; Fraile, L. M.; Deo, A.; Farrelly, G.; Gelletly, W.; Podolyak, Z.

    2010-04-26

    In order to determine the Gamow-Teller strength distribution for the N Z nucleus {sup 72}Kr an experiment was performed with a Total Absorption Gamma Spectrometer. To fully accomplish this task it is crucial to determine the multipolarity of the low energy transitions as the spin-parity of the daughter ground state has been debated. This is done by experimental determination of the conversion coefficients. Preliminary results for the multipolarity and conversion coefficients of the transition connecting the isomeric state at 101 keV with the {sup 72}Br ground state are presented.

  11. 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.

  12. 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.

  13. Method for detecting the isomeric state I =(3/2 ) + in 229Th with laser-induced fluorescence

    NASA Astrophysics Data System (ADS)

    Dembczyński, J.; Elantkowska, M.; Ruczkowski, J.

    2015-07-01

    There are different predictions regarding the position of the isomeric state of Thm229. There is some question as to whether it even exists. We propose simple experiments to provide the evidence of the existence of this isomeric state. If the metastable isomeric state exists, we should be able to observe the effects of mixing of the nuclear wave functions of the ground state I =5 /2 and the isomeric I =3 /2 state via electronic shells. It will be shown as the differences between the hyperfine A and B constants, which will be measured by means of the laser-induced fluorescence methods and those predicted by semiempirical calculations. The wave function for the atomic state |conf . S L J I F > contains contributions from both nuclear states I =5 /2 and 3 /2 , thus its effects on the hyperfine-structure patterns of spectral lines should be observed, confirming the existence of this isomeric state.

  14. 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.

  15. 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.

  16. Mass Measurements and Implications for the Energy of the High-Spin Isomer in {sup 94}Ag

    SciTech Connect

    Kankainen, A.; Elomaa, V.-V.; Eronen, T.; Hager, U.; Hakala, J.; Jokinen, A.; Moore, I. D.; Penttilae, H.; Rahaman, S.; Rinta-Antila, S.; Rissanen, J.; Saastamoinen, A.; Sonoda, T.; Weber, C.; Aeystoe, J.; Batist, L.; Popov, A.; Seliverstov, D. M.; Eliseev, S.; Novikov, Yu. N.

    2008-10-03

    Nuclides in the vicinity of {sup 94}Ag have been studied with the Penning trap mass spectrometer JYFLTRAP at the Ion-Guide Isotope Separator On-Line. The masses of the two-proton-decay daughter {sup 92}Rh and the beta-decay daughter {sup 94}Pd of the high-spin isomer in {sup 94}Ag have been measured, and the masses of {sup 93}Pd and {sup 94}Ag have been deduced. When combined with the data from the one-proton- or two-proton-decay experiments, the results lead to contradictory mass excess values for the high-spin isomer in {sup 94}Ag, -46 370(170) or -44 970(100) keV, corresponding to excitation energies of 6960(400) or 8360(370) keV, respectively.

  17. Photo-Induced Population of the h11/2 Isomeric States in ({gamma}, n) Reactions

    SciTech Connect

    Angell, C. T.; Karwowski, H. J.; Kelley, J. H.; Tonchev, A. P.; Tornow, W.

    2006-03-13

    The mechanism of excitation of isomeric h11/2 states in nuclei around the closed shell at N=82 have been studied at the High-Intensity Gamma Source (HI{gamma}S). We have taken advantage of the monoenergetic ({delta}E/E=1.5%) and pulsed {gamma}-ray-beam from HI{gamma}S to perform in-beam spectroscopy measurements with an improved level of precision and sensitivity. The giant dipole resonances at 15 MeV in the N=82 target isotones 138Ba, 140Ce, and 142Nd have been excited, and following neutron emission the {gamma}-ray cascades leading to the isomeric h11/2 state and the ground state were observed in the N=81 isotones. For all three nuclei a very similar de-excitation scheme was found. The only level observed from which the isomeric state was populated was found to be J{pi} = 7/2-. The ground state is principally populated from the states with spin and parities J{pi} = 1/2+, 5/2+, and 7/2+. The structure of the N=81 isotones and the role of the gateway states in isomer population will be discussed. The results of the measurements will be compared with statistical model calculations.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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

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

    PubMed

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

    2007-05-01

    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. PMID:17417893

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

    NASA Astrophysics Data System (ADS)

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

    2014-07-01

    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: 54Fe, 10+ state (E = 6527.1 (11) keV, T1/2 = 364(7) ns) and the 5/2+ state of 19F (E = 197.143 (4) keV, T1/2 = 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+ state was T1/2 = 365(14) ns and for the 5/2+ state, 100(36) ns.

  5. 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.

  6. Magnetic moment of the 13 /2 + isomeric state in 69Cu: Spin alignment in the one-nucleon removal reaction

    NASA Astrophysics Data System (ADS)

    Kusoglu, A.; Georgiev, G.; Sotty, C.; Balabanski, D. L.; Goasduff, A.; Ishii, Y.; Abe, Y.; Asahi, K.; Bostan, M.; Chevrier, R.; Chikamori, M.; Daugas, J. M.; Furukawa, T.; Nishibata, H.; Ichikawa, Y.; Ishibashi, Y.; Lozeva, R.; Miyatake, H.; Nagae, D.; Nanao, T.; Niikura, M.; Niwa, T.; Okada, S.; Ozawa, A.; Saito, Y.; Shirai, H.; Ueno, H.; Yordanov, D. T.; Yoshida, N.

    2016-05-01

    We report on a new measurement of the g factor of the (13 /2 + ) isomeric state in the neutron-rich nucleus 69Cu. This study demonstrates the possibility of obtaining considerable nuclear spin alignment for multi-quasiparticle states in single-nucleon removal reactions. The time-dependent perturbed angular distribution (TDPAD) method was used to extract the gyromagnetic factor of the (13 /2+ ) [T1 /2=351 (14 ) ns] isomeric state of 69Cu. Its g factor was obtained as g (13 /2+) =0.248 (9 ) . The experimentally observed spin alignment for the state of interest was deduced as A =-3.3 (9 )% .

  7. 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.

  8. Shape isomerism at N=40: Discovery of a proton intruder state in {sup 67}Co

    SciTech Connect

    Pauwels, D.; Ivanov, O.; Bree, N.; Buescher, J.; Cocolios, T. E.; Gentens, J.; Huyse, M.; Kudryavtsev, Yu.; Raabe, R.; Sawicka, M.; Walle, J. van de; Bergh, P. van den; Duppen, P. van; Korgul, A.; Stefanescu, I.; Walters, W. B.

    2008-10-15

    The nuclear structure of {sup 67}Co has been investigated through {sup 67}Fe {beta} decay. The {sup 67}Fe isotopes were produced at the LISOL facility in proton-induced fission of {sup 238}U and selected using resonant laser ionization combined with mass separation. The application of a new correlation technique unambiguously revealed a 496(33) ms isomeric state in {sup 67}Co at an unexpected low energy of 492 keV. A {sup 67}Co level scheme was deduced. Proposed spin and parities suggest a spherical (7/2{sup -}) {sup 67}Co ground state and a deformed first excited (1/2{sup -}) state at 492 keV, interpreted as a proton 1p-2h prolate intruder state.

  9. Rotational isomerism and physical properties of long-chain molecules in solid states

    NASA Astrophysics Data System (ADS)

    Kobayashi, M.

    1985-01-01

    Rotational isomerism occurring in solid state of organic long-chain compounds, including synthetic linear polymers, have been concerned in connection with the macroscopic physical properties of bulk materials. The conformational order in the non-crystalline part of polyethylene has been investigated by Raman spectra, and related to the elastic behaviors of bulk samples. In the solid-state phase transition induced by mechanical forces of poly(butylene terephthalate) the macroscopic strain has been related directly to the conformational conversion of the molecules. Concerning the piezoelectric and pyroelectric activities of poly(vinylidene fluoride), polymorphism, phase transition, and structural change on the poling process have been investigated. A ferroelectric-paraelectric phase transition has been found for a series of copolymers of vinylidene fluoride and trifluoroethylene. On the phase transition a great change in molecular conformation is accompanied with the scrambling of the dipolar orientation. This is the characteristic of polymer ferroelectrics in which the dipolar units are linked with each other by covalent bonds in a molecular chain. Spectroscopic evidences are presented indicating that the thermodynamic stability of polymorphs of n-fatty acids is closely related to the rotational isomerism occurring in the carboxyl groups.

  10. 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.

  11. 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)

  12. Experimental confirmation of ground state isotopic isomerization from OC⋯HI to OC⋯ID

    NASA Astrophysics Data System (ADS)

    Scott, Kevin W.; McElmurry, Blake A.; Leonov, Igor I.; Lucchese, Robert R.; Bevan, John W.

    2015-01-01

    The ν1 spectra of 16O12C-DI and 16O12C-ID, as well as ν2 of 16O12C-DI, 16O12C-ID have been recorded using a quantum cascade laser pulsed slit supersonic jet spectrometer. Intensity measurements made simultaneously in the same expansion for transitions in ν216O12C-HI: 16O12C-IH and ν116O12C-DI: 16O12C-ID isomers permit determination of the isomerization for the former pair to be +2.8(1.0) and the latter -6.0(1.0) cm-1. These results confirm prediction of ground state deuterium isotopic isomerization made using a generated morphed potential. Further analyses indicate OC.HI is a prototype for complexities associated with isomerization and isotopic effects in excited stretching vibrations.

  13. 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.

  14. 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. PMID:27588851

  15. 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.

  16. Rotational isomeric state theory applied to the stiffness prediction of an anion polymer electrolyte membrane

    SciTech Connect

    Gao, Fei; Weiland, L.M.; Kitchin, J.R.

    2008-05-01

    While the acidic polymer electrolyte membrane (PEM) Nafion® has garnered considerable attention, the active response of basic PEMs offers another realm of potential applications. For instance, the basic PEM Selemion® is currently being considered in the development of a CO2 separation prototype device to be employed in coal power plant flue gas. The mechanical integrity of this material and subsequent effects in active response in this harsh environment will become important in prototype development. A multiscale modeling approach based on rotational isomeric state theory in combination with a Monte Carlo methodology may be employed to study mechanical integrity. The approach has the potential to be adapted to address property change of any PEM in the presence of foreign species (reinforcing or poisoning), as well as temperature and hydration variations. The conformational characteristics of the Selemion® polymer chain and the cluster morphology in the polymer matrix are considered in the prediction of the stiffness of Selemion® in specific states.

  17. Ensemble of Transition State Structures for the Cis-Trans Isomerization of N-Methylacetamide

    SciTech Connect

    Mantz, Yves A.; Branduardi, Davide; Bussi, Giovanni; Parrinello, Michele

    2009-09-17

    The cis-trans isomerization of N-methylacetamide (NMA), a model peptidic fragment, is studied theoretically in vacuo and in explicit water solvent at 300 K using the metadynamics technique. The computed cis-trans free energy difference is very similar for NMA(g) and NMA(aq), in agreement with experimental measurements of population ratios and theoretical studies at 0 K. By exploiting the flexibility in the definition of a pair of recently introduced collective variables (Branduardi, D.; Gervasio, F. L.; Parrinello, M. J. Chem. Phys. 2007, 126, 054103), an ensemble of transition state structures is generated at finite temperature for both NMA(g) and NMA(aq), as verified by computing committor distribution functions. Ensemble members of NMA(g) are shown to have correlated values of the backbone dihedral angle and a second dihedral angle involving the amide hydrogen atom. The dynamical character of these structures is preserved in the presence of solvent, whose influence on the committor functions can be modeled using effective friction/noise terms.

  18. Comment on ``Existence of long-lived isomeric states in naturally-occurring neutron-deficient Th isotopes''

    NASA Astrophysics Data System (ADS)

    Barber, R. C.; de Laeter, J. R.

    2009-04-01

    In their article “Existence of Long-Lived Isomeric States in Naturally-Occuring Neutron-Deficient Th Isotopes” [Phys. Rev. C 76, 021303 (2007)], Marinov fail to demonstrate that basic mass spectrometric protocols, such as abundance sensitivity, linearity, and freedom from possible interferences, have been met. In particular, the claim that four isomeric states of Th have been discovered, using an inductively coupled plasma-sector field mass spectrometer (ICP-SFMS), with abundances from (1-10)×10-11 relative to Th232, cannot be accepted, given the known abundance sensitivities of other sector field mass spectrometers. Accelerator mass spectrometry is the only mass spectrometric methodology capable of measuring relative abundances of the magnitude claimed by Marinov

  19. Identification of isomeric states in the N=73 neutron-deficient nuclei 132Pr and 130La

    NASA Astrophysics Data System (ADS)

    Taylor, M. J.; Alharshan, G. A.; Cullen, D. M.; Procter, M. G.; Lumley, N. M.; Grahn, T.; Greenlees, P. T.; Hauschild, K.; Herzan, A.; Jakobsson, U.; Jones, P.; Julin, R.; Juutinen, S.; Ketelhut, S.; Leino, M.; Lopez-Martens, A.; Nieminen, P.; Partanen, J.; Peura, P.; Rahkila, P.; Rinta-Antila, S.; Ruotsalainen, P.; Sandzelius, M.; Sarén, J.; Scholey, C.; Sorri, J.; Stolze, S.; Uusitalo, J.; Xu, F. R.; Bai, Z. J.

    2012-10-01

    Decays from isomeric states in the neutron-deficient N=73 nuclei 132Pr and 130La have been observed for the first time. Half-lives of 486(70) ns and 2.46(4) μs were measured for two isomeric states in 132Pr. The decay from the 486 ns (8-) isomer has been interpreted as a hindered E1 transition from the bandhead state of the excited πh11/2⊗νg7/2 configuration. The decay from the 2.5 μs (8+) isomer is consistent with the Weisskopf estimate for a low-energy E2 transition. An analogous 0.74(3) μs decay from an (8+) isomer in the neighboring isotone 130La has also been observed which similarly can be explained if the transition has E2 character. The Weisskopf interpretation for the isomer hindrance is strengthened by the lack of evidence for shape or K isomerism due to the γ-soft shapes predicted by configuration-constrained potential-energy-surface calculations.

  20. 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.

  1. Spectroscopy of 201At including the observation of a shears band and the 29 /2+ isomeric state

    NASA Astrophysics Data System (ADS)

    Auranen, K.; Uusitalo, J.; Juutinen, S.; Jakobsson, U.; Grahn, T.; Greenlees, P. T.; Hauschild, K.; HerzáÅ, A.; Julin, R.; Konki, J.; Leino, M.; Pakarinen, J.; Partanen, J.; Peura, P.; Rahkila, P.; Ruotsalainen, P.; Sandzelius, M.; Sarén, J.; Scholey, C.; Sorri, J.; Stolze, S.

    2015-02-01

    The excited states of 201At were studied and an isomeric 29 /2+ state [T½=3.39 (9 ) μ s ] was identified by using a fusion-evaporation reaction, a gas-filled recoil separator, and recoil gating techniques. The 29 /2+ state is suggested to originate from the π (h9 /2) ⊗| 200Po ;11-> configuration, and it decays through the 269- and 339-keV E 2 - and E 3 -type transitions, respectively. Moreover, a cascade of magnetic dipole transitions that is suggested to originate from a shears band was observed by using recoil-gated γ -γ (-γ ) coincidence techniques.

  2. 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.

  3. Nuclear g-factor measurements of the (9/2){sup -} and (21/2){sup -} isomeric states in {sup 173}Ta

    SciTech Connect

    Thakur, P.; Kumar, V.; Bhati, A. K.; Bedi, S. C.; Singh, R. P.; Bhowmik, R. K.; Stuchbery, A. E.

    2006-09-15

    The nuclear g-factors of the one-quasiparticle isomeric state (9/2){sup -} at 165.8 keV and the three-quasiparticle isomeric state (21/2){sup -} at 1713.2 keV in {sup 173}Ta nuclei have been measured using the time differential perturbed angular distribution technique. The nuclear reaction {sup 165}Ho({sup 12}C, 4n{gamma}){sup 173}Ta was used to populate these isomeric states, and the recoiling {sup 173}Ta nuclei were implanted into a thick tantalum backing in the presence of a 7.04(4) kG external magnetic field. The measured value g((9/2){sup -}) = +0.591(18) shows that the (9/2){sup -} isomeric state is not a pure single-particle state but may have a collective contribution due to the octupole excitation of the core. Based on the measured value g((21/2){sup -}) = + 0.620(15) and multi-quasiparticle calculations, the (21/2){sup -} isomeric state is assigned a mixed configuration: {pi}{sup 3}((9/2){sup -}[514], (7/2){sup +}[404] (5/2){sup +}[402]) (39%) and {pi}{sup 1}((7/2){sup +}[404])(multiply-in-circle sign) {nu}{sup 2}((7/2){sup -}[514], (7/2){sup +}[633]) (61%)

  4. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-02-01

    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 1A' 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.

  6. 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.

  7. 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.

  8. Isomeric states in neutron-rich 129In and the πg-19/2 vh-111/2 multiplet

    NASA Astrophysics Data System (ADS)

    Taprogge, J.; Jungclaus, A.; Simpson, G.

    2014-09-01

    Within the RISING stopped beam campaign the neutron-rich indium isotopes with masses A=125-130 have been studied using the method of isomer spectroscopy. The decays of several isomeric states have been observed and here we compare our results for 129In to previous measurements for this nucleus. The isomeric states were populated in the fragmentation of a 136Xe beam at 750 MeV/u and in the relativistic fission of a 238U beam at 650 MeV/u at the accelerator facility GSI (Darmstadt, Germany).

  9. Reduced dimension rovibrational variational calculations of the S(1) state of C2H2. II. The S(1) rovibrational manifold and the effects of isomerization.

    PubMed

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

    2014-01-14

    Reduced dimension variational calculations have been performed for the rovibrational level structure of the S1 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(-1) above the trans, and the barrier to cis-trans isomerization lies about 5000 cm(-1) above the trans minimum. The trans vibrations ν4 (torsion) and ν6 (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 x36 cross-anharmonicity since the pathway to isomerization is a combination of ν6 and ν3 (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. PMID:24437883

  10. Excited-state structure and isomerization dynamics of the retinal chromophore in rhodopsin from resonance Raman intensities.

    PubMed Central

    Loppnow, G R; Mathies, R A

    1988-01-01

    Resonance Raman excitation profiles have been measured for the bovine visual pigment rhodopsin using excitation wavelengths ranging from 457.9 to 647.1 nm. A complete Franck-Condon analysis of the absorption spectrum and resonance Raman excitation profiles has been performed using an excited-state, time-dependent wavepacket propagation technique. This has enabled us to determine the change in geometry upon electronic excitation of rhodopsin's 11-cis-retinal protonated Schiff base chromophore along 25 normal coordinates. Intense low-frequency Raman lines are observed at 98, 135, 249, 336, and 461 cm-1 whose intensities provide quantitative, mode-specific information about the excited-state torsional deformations that lead to isomerization. The dominant contribution to the width of the absorption band in rhodopsin results from Franck-Condon progressions in the 1,549 cm-1 ethylenic normal mode. The lack of vibronic structure in the absorption spectrum is shown to be caused by extensive progressions in low-frequency torsional modes and a large homogeneous linewidth (170 cm-1 half-width) together with thermal population of low-frequency modes and inhomogeneous site distribution effects. The resonance Raman cross-sections of rhodopsin are unusually weak because the excited-state wavepacket moves rapidly (approximately 35 fs) and permanently away from the Franck-Condon geometry along skeletal stretching and torsional coordinates. PMID:3416032

  11. Crystal Structure of the 11-cis Isomer of Pharaonis Halorhodopsin: Structural Constraints on Interconversions among Different Isomeric States.

    PubMed

    Chan, Siu Kit; Kawaguchi, Haruki; Kubo, Hiroki; Murakami, Midori; Ihara, Kunio; Maki, Kosuke; Kouyama, Tsutomu

    2016-07-26

    Like other microbial rhodopsins, the light driven chloride pump halorhodopsin from Natronomonas pharaonis (pHR) contains a mixture of all-trans/15-anti and 13-cis/15-syn isomers in the dark adapted state. A recent crystallographic study of the reaction states of pHR has shown that reaction states with 13-cis/15-syn retinal occur in the anion pumping cycle that is initiated by excitation of the all-trans isomer. In this study, we investigated interconversions among different isomeric states of pHR in the absence of chloride ions. The illumination of chloride free pHR with red light caused a large blue shift in the absorption maximum of the retinal visible band. During this "red adaptation", the content of the 11-cis isomer increased significantly, while the molar ratio of the 13-cis isomer to the all-trans isomer remained unchanged. The results suggest that the thermally activated interconversion between the 13-cis and the all-trans isomers is very rapid. Diffraction data from red adapted crystals showed that accommodation of the retinal chromophore with the 11-cis/15-syn configuration was achieved without a large change in the retinal binding pocket. The measurement of absorption kinetics under illumination showed that the 11-cis isomer, with a λmax at 565 nm, was generated upon excitation of a red-shifted species (λmax = 625 nm) that was present as a minor component in the dark adapted state. It is possible that this red-shifted species mimics an O-like reaction state with 13-cis/15-syn retinal, which was hypothesized to occur at a late stage of the anion pumping cycle. PMID:27352034

  12. Application of a sealed tube neutron generator to the characterization of very short half-life isomeric states

    NASA Astrophysics Data System (ADS)

    Antonot, B.; Cluzeau, S.; Le Tourneur, P.; Bergamo, F.

    1995-05-01

    A SODERN sealed tube neutron generator producing 14 MeV neutrons has been used for detecting radionuclides with a half-life from about 20 μs to 1 s. An interesting feature of this kind of sealed tube neutron generator is the pulsed operation at adjustable pulse width from 5 μs to 10 ms or more, and at frequencies from continuous mode to 10 kHz. This capability allows the study of very short-lived isotopes down to a few microseconds with the cyclic activation method. A semiconductor γ ray detector Ge(HP) and ORTEC electronics were used for spectrometric measurements. The half-life measurement of short-lived activation products is performed with a fast multiscaler. Seven isomeric states have been successfully studied, characterized and their activation cross sections evaluated by the cyclic activation method: 114In ∗, 181Ta ∗, 181W ∗, 205Pb ∗, 206Pb ∗, 207Pb ∗, and 208Bi ∗.

  13. 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.

  14. Manifestations of bodily isomerism.

    PubMed

    Loomba, Rohit S; Ahmed, Muhammad M; Spicer, Diane E; Backer, Carl L; Anderson, Robert H

    2016-01-01

    We report the findings present in 49 postmortem specimens from patients with so-called heterotaxy, concentrating on those found in the extracardiac systems of organs. Also known as bodily isomerism, we suggest that it is important to segregate the syndromes into their isomeric subtypes to be able to make inferences regarding likely extracardiac and intracardiac findings to allow for proper surveillance. We demonstrate that this is best done on the basis of the atrial appendages, which were isomeric in all the hearts obtained from the specimens available for our inspection. The abdominal organs do not demonstrate isomerism, and they show variable features when compared to the isomeric atrial appendages. PMID:26872066

  15. 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.

  16. 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.

  17. Characterization of the Oxidation State of 229 Th Recoils Implanted in MgF2 for the Search of the Low-lying 229 Th Isomeric State

    NASA Astrophysics Data System (ADS)

    Barker, Beau; Meyer, Edmund; Schacht, Mike; Collins, Lee; Wilkerson, Marianne; Zhao, Xinxin

    2016-05-01

    The low-lying (7.8 eV) isomeric state in 229 Th has the potential to become a nuclear frequency standard. 229 Th recoils from 233 U decays have been collected in MgF2 for use in the direct search of the transition. Of interest is the oxidation state of the implanted 229 Th atoms as this can have an influence on the decay mechanisms and photon emission rate. Too determine the oxidation state of the implanted 229 Th recoils we have employed laser induced florescence (LIF), and plan-wave pseudopotential DFT calculations to search for emission from thorium ions in oxidation states less than + 4. Our search focused on detecting emission from Th3+ ions. The DFT calculations predicted the Th3+ state to be the most likely to be present in the crystal after Th4+. We also calculated the band structure for the Th3+ doped MgF2 crystal. For LIF spectra a number of excitation wavelengths were employed, emission spectra in the visible to near-IR were recorded along with time-resolved emission spectra. We have found no evidence for Th3+ in the MgF2 plates. We also analyzed the detection limit of our apprentice and found that the minimum number of Th3+ atoms that we could detect is quite small compared to the number of implanted 229 Th recoils. The number of implanted 229 Th recoils was derived from a γ-ray spectrum by monitoring emission from the daughters of 228 Th. These were present in the MgF2 plates due to a 232 U impurity, which decays to 228 Th, in the source. LA-UR-16-20442.

  18. Proposal for precision determination of 7.8 eV isomeric state in 229Th at heavy ion storage ring

    NASA Astrophysics Data System (ADS)

    Ma, X.; Wen, W. Q.; Huang, Z. K.; Wang, H. B.; Yuan, Y. J.; Wang, M.; Sun, Z. Y.; Mao, L. J.; Yang, J. C.; Xu, H. S.; Xiao, G. Q.; Zhan, W. L.

    2015-11-01

    The ultraviolet optical transition of the isomeric state in 229Th has attracted much attention recently due to its potential application to building an atomic/nuclear clock with ultra-high precision. However, the lowest nuclear excitation energy and the lifetime of the first excited state of 229Th were not measured directly and precisely until now, and how to precisely determine this isomer state of the 229Th is an urgent requirement. Here an experimental approach of using a technique similar to that of dielectronic recombination to measure the transition energy of the isomer state of 229Th at heavy ion storage rings is described. It is expected that the resonant transition can be found and determined with a precision better than several milli-eV.

  19. Least Squares Fitting of Perturbed Vibrational Polyads Near the Isomerization Barrier in the S_1 State of C_2H_2

    NASA Astrophysics Data System (ADS)

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

    2013-06-01

    The S_1 electronic state of acetylene has recently been shown to have two potential minima, corresponding to cis- and trans-bent structures. The trans-bent isomer is the more stable, with the cis-bent isomer lying about 2670 cm^{-1} higher; the barrier to isomerization lies roughly 5000 cm^{-1} above the trans zero-point level. The ``isomerization coordinate'' (along which the molecule moves to get from the trans minimum to the barrier) is a combination of the ν_3 (trans bending) and ν_6 (cis bending) vibrational normal coordinates, but the spectrum is very confused because the ν_6 vibration interacts strongly with the ν_4 (torsion) vibration through Coriolis and Darling-Dennison resonances. Since the ν_4 and ν_6 fundamental frequencies are almost equal, the bending vibrational structure consists of polyads. At low vibrational energies the polyads where these three vibrations are excited can be fitted by least squares almost to experimental accuracy with a simple model of Coriolis and Darling-Dennison interactions, but at higher energies the huge x_{36} cross-anharmonicity, which is a symptom that the levels are approaching the isomerization barrier, progressively destroys the polyad structure; in addition the levels show an increasing even-odd staggering of their K-rotational structures, as predicted by group theory. It is not possible to fit the levels near the barrier with a simple model, though some success has been achieved with extended models. Progress with the fitting of the polyads near the barrier will be reviewed. A. L. Utz, J. D. Tobiason, E. Carrasquillo M., L. J. Sanders and F. F. Crim, J. Chem. Phys. {98}, 2742, 1993.

  20. 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…

  1. 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

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

    PubMed

    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 1800-1900cm(-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 7-10ps, 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. PMID:27209490

  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. Isomeric ratio measurements with the ILL LOHENGRIN spectrometer

    NASA Astrophysics Data System (ADS)

    Chebboubi, A.; Kessedjian, G.; Litaize, O.; Serot, O.; Faust, H.; Bernard, D.; Blanc, A.; Köster, U.; Méplan, O.; Mutti, P.; Sage, C.

    2016-03-01

    The modelling of γ heating and neutron damage inside a nuclear reactor is essential to design the next generation of nuclear reactors. The determination of the fission fragment momentum is a key element to perform accurate calculations of the γ heating. One way to assess this information is to look at the isomeric ratio of different nuclei. According to the lifetime of the isomeric state, different experimental techniques were developed at the LOHENGRIN spectrometer. A focus on the measurement of isomeric ratios of 136I in neutron induced fission of 241Pu is presented. A discussion with the current assumptions used in the evaluation process for isomeric ratio is also shown.

  5. 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.

  6. Direct observation of an isomeric state in 98Rb and nuclear properties of exotic rubidium isotopes measured by laser spectroscopy

    NASA Astrophysics Data System (ADS)

    Procter, T. J.; Behr, J. A.; Billowes, J.; Buchinger, F.; Cheal, B.; Crawford, J. E.; Dilling, J.; Garnsworthy, A. B.; Leary, A.; Levy, C. D. P.; Mané, E.; Pearson, M. R.; Shelbaya, O.; Stolz, M.; Al Tamimi, W.; Voss, A.

    2015-02-01

    Fast-beam collinear laser spectroscopy experiments on rubidium have been performed at the ISAC radioactive ion beam facility at TRIUMF. Most recently, the neutron-rich 98Rb isotope has been studied for the investigation of shape coexistence. Two long-lived nuclear states in 98Rb have been clearly observed for the first time: a low-spin state, assigned a spin of I = 0, and a high-spin state. The high-spin state is tentatively assigned a spin of I = 3 based on this analysis in combination with gamma decay results. The measured nuclear properties of the two states are presented, alongside unpublished values of the neutron-deficient isotopes investigated previously. The mean-square charge radii of both states in 98Rb are observed to continue along the isodeformation line present after the N = 60 onset of deformation.

  7. Clinical implications of atrial isomerism.

    PubMed Central

    Chiu, I S; How, S W; Wang, J K; Wu, M H; Chu, S H; Lue, H C; Hung, C R

    1988-01-01

    Right atrial isomerism or left atrial isomerism is frequently diagnosed as situs ambiguous without further discrimination of the specific morbid anatomy. Thirty six cases of right atrial isomerism and seven cases of left atrial isomerism were collected from the records and pathological museum at the National Taiwan University Hospital. There was a necropsy report for 18 cases. In all patients one or more of the following conditions was met: (a) isomeric bronchial anatomy, (b) echocardiographic and angiocardiographic evidence of isomerism, and (c) surgical or necropsy evidence of abnormal atrial anatomy. An anomalous pulmonary venous connection was present in 55% of patients with right atrial isomerism; in left atrial isomerism one case (14%) had a partial anomalous pulmonary venous connection. Forty per cent of cases of anomalous pulmonary venous connection with right atrial isomerism had obstruction. Six (86%) of seven cases with left atrial isomerism had an ambiguous biventricular atrioventricular connection. In contrast, univentricular atrioventricular connection (26 of 36, 72%) was significantly more common in right atrial isomerism. A common atrioventricular valve was the most frequent mode of connection in both forms. Two discrete atrioventricular valves were significantly more common in left atrial isomerism. Atrioventricular valve regurgitation was detected in 14 cases. Double outlet right ventricle was the most common type of ventriculoarterial connection. The most commonly cited causes of death after either palliative or definitive operation were undetected anomalous pulmonary venous connection, pulmonary venous stricture, and uncorrected atrioventricular valve or aortic regurgitation complicated by abnormal coagulation. Although the prognosis is poor, successful operation depends on knowledge of the precise anatomical arrangement associated with atrial isomerism. Images Fig 1 Fig 2 Fig 3 PMID:3408620

  8. 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.

  9. 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.

  10. 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. PMID:23815675

  11. 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.

  12. 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.

  13. 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.

  14. Probing cis-trans isomerization in the S1 state of C2H2 via H-atom action and hot band-pumped IR-UV double resonance spectroscopies.

    PubMed

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

    2015-08-28

    We report novel experimental strategies that should prove instrumental in extending the vibrational and rotational assignments of the S1 state of acetylene, C2H2, in the region of the cis-trans isomerization barrier. At present, the assignments are essentially complete up to ∼500 cm(-1) below the barrier. Two difficulties arise when the assignments are continued to higher energies. One is that predissociation into C2H + H sets in roughly 1100 cm(-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('') = ± 1, such data must be obtained via excited vibrational levels of the ground state with ℓ('') > 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('') = 2 states can be selectively populated in a jet, giving access to K' = 3 states in IR-UV double resonance. PMID:26328846

  15. Probing cis-trans isomerization in the S1 state of C2H2 via H-atom action and hot band-pumped IR-UV double resonance spectroscopies

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

    We report novel experimental strategies that should prove instrumental in extending the vibrational and rotational assignments of the S1 state of acetylene, C2H2, in the region of the cis-trans isomerization barrier. At present, the assignments are essentially complete up to ˜500 cm-1 below the barrier. Two difficulties arise when the assignments are continued to higher energies. One is that predissociation into C2H + H sets in roughly 1100 cm-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'' = ± 1, such data must be obtained via excited vibrational levels of the ground state with ℓ'' > 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'' = 2 states can be selectively populated in a jet, giving access to K' = 3 states in IR-UV double resonance.

  16. Evidence of shell effects in the excitation function of 0.136-MeV isomeric state populated in the {sup 93}Nb(n,2n){sup 92}Nb{sup m} reaction

    SciTech Connect

    Gul, K.

    2004-09-01

    Calculation for the excitation function of 0.136-MeV (2{sup +}) isomeric state in {sup 92}Nb has been carried out using Hauser-Feshbach and pre-equilibrium nuclear reaction models in 10-20 MeV energy range. A satisfactory agreement between the calculation and measurements requires the suppression of contribution from the negative-parity doublet consisting of the 0.226-MeV (2{sup -}) and 0.390-MeV (3{sup -}) states in {sup 92}Nb. This can be explained on the basis of highly retarded gamma transitions of higher energy states to the negative-parity doublet on account of its different shell model configuration compared to the shell model configuration of positive-parity states.

  17. Ortho-para nuclear-spin isomerization energies for all bound vibrational states of ditritium (T2) from non-Born-Oppenheimer variational calculations performed with explicitly correlated all-particle Gaussian functions

    NASA Astrophysics Data System (ADS)

    Kirnosov, Nikita; Sharkey, Keeper L.; Adamowicz, Ludwik

    2015-11-01

    Direct variational calculations, where the Born-Oppenheimer (BO) approximation is not assumed, are performed for all 26 bound rovibrational states corresponding to the lowest rotational excitation (i.e. the N = 1 states) of the tritium molecule (T2). The non-BO energies are used to determine the ortho-para isomerization energies. All-particle explicitly correlated Gaussian basis functions are employed in the calculations and over 11 000 Gaussians independently generated for each state are used. The exponential parameters of the Gaussians are optimized with the aid of analytically calculated energy gradient determined with respect to these parameters. The non-BO wave functions are used to calculate expectation values of the inter-particle distances and the triton-triton correlation functions.

  18. Isomerization Intermediates In Solution Phase Photochemistry Of Stilbenes

    NASA Astrophysics Data System (ADS)

    Doany, F. E.; Hochstrasser, R. M.; Greene, B. I.

    1985-04-01

    Picosecond and subpicosecond spectroscopic studies have revealed evidence for an isomerization intermediate between cis and trans in the photoinduced isomerism of both stilbene and biindanyledene ("stiff" stilbene). In stiff stilbene, a transient absorption at 351 nm displays time evolution and viscosity dependence consistent with absorption by a twisted intermediate ("phantom" state) with a lOps lifetime. An analagous bottleneck state with a life-time of 4ps is also consistent with the ground state recovery dynamics of t-stilbene following excitation of c-stilbene when monitored with 0.1ps resolution.

  19. 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. PMID:25912152

  20. 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. PMID:27159227

  1. Isomeric decay spectroscopy of the Bi217 isotope

    NASA Astrophysics Data System (ADS)

    Gottardo, A.; Valiente-Dobón, J. J.; Benzoni, G.; Lunardi, S.; Gadea, A.; Algora, A.; Al-Dahan, N.; de Angelis, G.; Ayyad, Y.; Bazzacco, D.; Benlliure, J.; Boutachkov, P.; Bowry, M.; Bracco, A.; Bruce, A. M.; Bunce, M.; Camera, F.; Casarejos, E.; Cortes, M. L.; Crespi, F. C. L.; Corsi, A.; Denis Bacelar, A. M.; Deo, A. Y.; Domingo-Pardo, C.; Doncel, M.; Engert, T.; Eppinger, K.; Farrelly, G. F.; Farinon, F.; Farnea, E.; Geissel, H.; Gerl, J.; Goel, N.; Górska, M.; Grebosz, J.; Gregor, E.; Habermann, T.; Hoischen, R.; Janik, R.; John, P. R.; Klupp, S.; Kojouharov, I.; Kurz, N.; Lenzi, S. M.; Leoni, S.; Mandal, S.; Menegazzo, R.; Mengoni, D.; Million, B.; Modamio, V.; Morales, A. I.; Napoli, D. R.; Naqvi, F.; Nicolini, R.; Nociforo, C.; Pfützner, M.; Pietri, S.; Podolyák, Zs.; Prochazka, A.; Prokopowicz, W.; Recchia, F.; Regan, P. H.; Reed, M. W.; Rudolph, D.; Sahin, E.; Schaffner, H.; Sharma, A.; Sitar, B.; Siwal, D.; Steiger, K.; Strmen, P.; Swan, T. P. D.; Szarka, I.; Ur, C. A.; Walker, P. M.; Weick, H.; Wieland, O.; Wollersheim, H.-J.

    2014-09-01

    The structure of the neutron-rich bismuth isotope Bi217 has been studied for the first time. The fragmentation of a primary U238 beam at the FRS-RISING setup at GSI was exploited to perform γ-decay spectroscopy, since μs isomeric states were expected in this nucleus. Gamma rays following the decay of a t1/2=3 μs isomer were observed, allowing one to establish the low-lying structure of Bi217. The level energies and the reduced electric quadrupole transition probability B (E2) from the isomeric state are compared to large-scale shell-model calculations.

  2. Retinal isomerization dynamics in dry bacteriorhodopsin films

    NASA Astrophysics Data System (ADS)

    Colonna, Anne; Groma, Géza I.; Vos, Marten H.

    2005-10-01

    The primary photoprocesses in neutral and acid forms of oriented dried bacteriorhodopsin films were investigated by femtosecond absorption spectroscopy. The excitation energy dependence of the signals was used to distinguish photochemistry from processes involving photophysics of photocycle intermediates. Both the kinetics and the quantum yield of all- trans excited state decay by retinal photoisomerization and subsequent J → K transition were found to be very similar as in hydrated environments. Therefore, unlike slower photocycle phases, communication of the retinal with the environment does not play a role in retinal isomerization. Our results are important for understanding recent nonlinear optical applications of such films.

  3. 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.

  4. Ultrafast excited state dynamics controlling photochemical isomerization of N-methyl-4-[trans-2-(4-pyridyl)ethenyl]pyridinium coordinated to a {Re I(CO)3(2,2'-bipyridine)} chromophore.

    PubMed

    Busby, Michael; Hartl, Frantisek; Matousek, Pavel; Towrie, Mike; Vlcek, Antonín

    2008-01-01

    Two multifunctional photoactive complexes [Re(Cl)(CO)(3)(MeDpe(+))(2)](2+) and [Re(MeDpe(+))(CO)(3)(bpy)](2+) (MeDpe(+)=N-methyl-4-[trans-2-(4-pyridyl)ethenyl]pyridinium, bpy=2,2'-bipyridine) were synthesized, characterized, and their redox and photonic properties were investigated by cyclic voltammetry; ultraviolet-visible-infrared (UV/Vis/IR) spectroelectrochemistry, stationary UV/Vis and resonance Raman spectroscopy; photolysis; picosecond time-resolved absorption spectroscopy in the visible and infrared regions; and time-resolved resonance Raman spectroscopy. The first reduction step of either complex occurs at about -1.1 V versus Fc/Fc(+) and is localized at MeDpe(+). Reduction alone does not induce a trans-->cis isomerization of MeDpe(+). [Re(Cl)(CO)(3)(MeDpe(+))(2)](2+) is photostable, while [Re(MeDpe(+))(CO)(3)(bpy)](2+) and free MeDpe(+) isomerize under near-UV irradiation. The lowest excited state of [Re(Cl)(CO)(3)(MeDpe(+))(2)](2+) has been identified as the Re(Cl)(CO)(3)-->MeDpe(+ 3)MLCT (MLCT=metal-to-ligand charge transfer), decaying directly to the ground state with lifetimes of approximately 42 (73 %) and approximately 430 ps (27 %). Optical excitation of [Re(MeDpe(+))(CO)(3)(bpy)](2+) leads to population of Re(CO)(3)-->MeDpe(+) and Re(CO)(3)-->bpy (3)MLCT states, from which a MeDpe(+) localized intraligand (3)pipi* excited state ((3)IL) is populated with lifetimes of approximately 0.6 and approximately 10 ps, respectively. The (3)IL state undergoes a approximately 21 ps internal rotation, which eventually produces the cis isomer on a much longer timescale. The different excited-state behavior of the two complexes and the absence of thermodynamically favorable interligand electron transfer in excited [Re(MeDpe(+))(CO)(3)(bpy)](2+) reflect the fine energetic balance between excited states of different orbital origin, which can be tuned by subtle structural variations. The complex [Re(MeDpe(+))(CO)(3)(bpy)](2+) emerges as a prototypical

  5. Elucidation of Isomerization Pathways of a Single Azobenzene Derivative Using an STM.

    PubMed

    Kazuma, Emiko; Han, Mina; Jung, Jaehoon; Oh, Junepyo; Seki, Takahiro; Kim, Yousoo

    2015-11-01

    The predominant pathway for the isomerization between cis- and trans-azobenzenes-either (i) inversion by the bending of an NNC bond or (ii) rotation by the torsion of two phenyl rings-continues to be a controversial topic. To elucidate each isomerization pathway, a strategically designed and synthesized azobenzene derivative was investigated on a Ag(111) surface. This was achieved by exciting the molecule with tunneling electrons from the tip of a scanning tunneling microscope (STM). Structural analyses of the molecularly resolved STM images reveal that both inversion and rotation pathways are available for isomerization on a metal surface and strongly depend on the initial adsorption structures of the molecule. On the basis of the potential energy diagrams for the isomerization, it is concluded that isomerization pathways on a metal surface are not simply related to the excited states. PMID:26722964

  6. Thermal isomerization of spiropyran to merocyanine in aqueous media and its application to colorimetric temperature indication.

    PubMed

    Shiraishi, Yasuhiro; Itoh, Masataka; Hirai, Takayuki

    2010-11-01

    Thermally-induced isomerization of spiropyran derivatives in aqueous media has been studied. The colorless spirocyclic (SP) forms of spiropyran derivatives are isomerized to colored merocyanine (MC) forms even in dark conditions at elevated temperature. Equilibrium, kinetic, and deuterium experiments reveal that the thermal SP → MC isomerization is due to the stabilization of MC form by a hydrogen bonding interaction with water molecules. This leads to the ground state energy of the MC form decreasing to lower than that of the SP form, resulting in SP → MC isomerization. The thermal isomerization property is applicable to a rough indication of solution temperature. The spiropyran derivatives, when dissolved in aqueous media under irradiation of visible light with an appropriate light intensity, demonstrate an increase in MC absorbance with a rise in temperature. The absorption response occurs reversibly regardless of the heating/cooling sequence. The spiropyran derivatives therefore have a potential for colorimetric temperature indication. PMID:20877830

  7. Subnanosecond isomerization in an osmium-dimethyl sulfoxide complex.

    PubMed

    Mockus, Nicholas V; Petersen, Jeffrey L; Rack, Jeffrey J

    2006-01-01

    We report the structure, spectroscopy, and electrochemistry of cis-[Os(bpy)(2)(DMSO)(2)](OTf)(2), where bpy is 2,2'-bipyridine, DMSO is dimethyl sulfoxide, and OTf is trifluoromethanesulfonate. Electrochemical measurements are consistent with S-to-O isomerization following the oxidation of Os(2+) (1.8 V vs Ag/AgCl). Visible irradiation of the metal-to-ligand charge-transfer transition (355 nm) of [Os(bpy)(2)(DMSO)(2)](2+) in the solid state and solution yields an emissive S-bonded excited state and S-to-O excited-state isomerization on a subnanosecond time scale. These results and a comparison to the nonphotoactive [Os(bpy)(2)Cl(DMSO)](+) are discussed. PMID:16390034

  8. EXPLANATION FOR THE ISOMERIC COMPARTMENTALIZATION OF ENDOSULFAN

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Endosulfan, an insecticide used on vegetables, fruits, cereals and cotton, exists as 7:3 isomeric mixture of alpha and beta when applied. However, this isomeric ratio is not conserved throughout the environmental compartments and the ratio is dependent on the compartment. Studies examining endosulf...

  9. Peptide Bond Isomerization in High-Temperature Simulations.

    PubMed

    Neale, Chris; Pomès, Régis; García, Angel E

    2016-04-12

    Force fields for molecular simulation are generally optimized to model macromolecules such as proteins at ambient temperature and pressure. Nevertheless, elevated temperatures are frequently used to enhance conformational sampling, either during system setup or as a component of an advanced sampling technique such as temperature replica exchange. Because macromolecular force fields are now put upon to simulate temperatures and time scales that greatly exceed their original design specifications, it is appropriate to re-evaluate whether these force fields are up to the task. Here, we quantify the rates of peptide bond isomerization in high-temperature simulations of three octameric peptides and a small fast-folding protein. We show that peptide octamers with and without proline residues undergo cis/trans isomerization every 1-5 ns at 800 K with three classical atomistic force fields (AMBER99SB-ILDN, CHARMM22/CMAP, and OPLS-AA/L). On the low microsecond time scale, these force fields permit isomerization of nonprolyl peptide bonds at temperatures ≥500 K, and the CHARMM22/CMAP force field permits isomerization of prolyl peptide bonds ≥400 K. Moreover, the OPLS-AA/L force field allows chiral inversion about the Cα atom at 800 K. Finally, we show that temperature replica exchange permits cis peptide bonds developed at 540 K to subsequently migrate back to the 300 K ensemble, where cis peptide bonds are present in 2 ± 1% of the population of Trp-cage TC5b, including up to 4% of its folded state. Further work is required to assess the accuracy of cis/trans isomerization in the current generation of protein force fields. PMID:26866899

  10. Deconstructing field-induced ketene isomerization through Lagrangian descriptors.

    PubMed

    Craven, Galen T; Hernandez, Rigoberto

    2016-02-01

    The time-dependent geometrical separatrices governing state transitions in field-induced ketene isomerization are constructed using the method of Lagrangian descriptors. We obtain the stable and unstable manifolds of time-varying transition states as dynamic phase space objects governing configurational changes when the ketene molecule is subjected to an oscillating electric field. The dynamics of the isomerization reaction are modeled through classical trajectory studies on the Gezelter-Miller potential energy surface and an approximate dipole moment model which is coupled to a time-dependent electric field. We obtain a representation of the reaction geometry, over varying field strengths and oscillation frequencies, by partitioning an initial phase space into basins labeled according to which product state is reached at a given time. The borders between these basins are in agreement with those obtained using Lagrangian descriptors, even in regimes exhibiting chaotic dynamics. Major outcomes of this work are: validation and extension of a transition state theory framework built from Lagrangian descriptors, elaboration of the applicability for this theory to periodically- and aperiodically-driven molecular systems, and prediction of regimes in which isomerization of ketene and its derivatives may be controlled using an external field. PMID:26778728

  11. Isomeric and ground-state properties of {sub 78}{sup 171}Pt, {sub 76}{sup 167}Os, and {sub 74}{sup 163}W

    SciTech Connect

    Scholey, C.; Eeckhaudt, S.; Grahn, T.; Greenlees, P. T.; Jones, P.; Julin, R.; Juutinen, S.; Ketelhut, S.; Leino, M.; Leppaenen, A.-P.; Nieminen, P.; Nyman, M.; Pakarinen, J.; Rahkila, P.; Saren, J.; Sorri, J.; Uusitalo, J.; Andgren, K.; Cederwall, B.; Hadinia, B.

    2010-01-15

    Decay paths, half-lives, and excitation energies of the i{sub 13/2} bandheads of the neutron-deficient nuclei {sup 171}Pt, {sup 167}Os, and {sup 163}W have been established for the first time. Gamma-ray transitions, X-rays, and internal conversion electrons have been observed, allowing internal-conversion coefficients to be measured and B(M2) reduced transition probabilities to be extracted. These results elucidate the low-lying single-quasiparticle structures and give the energy level spacings between the nuf{sub 7/2}, nuh{sub 9/2}, and nui{sub 13/2} quasineutron states for all three nuclei. Moreover, ground-state spin assignments have been made for the first time, along with the measurement of the {alpha}-decay branching ratio for {sup 171}Pt. The decay paths of the i{sub 13/2} bandheads were followed by favored {alpha} decays, indicating that all three nuclei have the same I{sup {pi}}=7/2{sup -} ground state.

  12. Incoherent Control of the Retinal Isomerization in Rhodopsin

    NASA Astrophysics Data System (ADS)

    Lucas, Felix; Hornberger, Klaus

    2014-08-01

    We propose to control the retinal photoisomerization yield through the backaction dynamics imparted by a nonselective optical measurement of the molecular electronic state. This incoherent effect is easier to implement than comparable coherent pulse shaping techniques, and is also robust to environmental noise. A numerical simulation of the quantum dynamics shows that the isomerization yield of this important biomolecule can be substantially increased above the natural limit.

  13. Isomerization controlled photopolymerization: effect of dye photophysics on photoinitiation efficiency.

    PubMed

    Ley, C; Ibrahim, A; Allonas, X

    2016-08-01

    The efficiency of free radical polymerization by photoinitiating systems based on two Astrazon orange cyanine dyes was shown to be directly related to the isomerization process of the dye in the excited states. The impact of resin viscosity on photopolymerization reactions was measured and related to the overall radical quantum yields. The quantum yields were calculated according to the photocyclic behaviour of the initiating systems based on the Astrazon orange dyes. These dyes are characterized by a viscosity dependent photophysics, which leads to an isomerization-diffusion-controlled photopolymerization. Besides this demonstration, Astrazon orange dyes appeared to be very good candidates for free radical photopolymerization in the visible, presenting high absorption coefficient, low cost and good sensitivity. PMID:27443964

  14. 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.

  15. 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

  16. Controlled subnanosecond isomerization of HCN to CNH in solution

    SciTech Connect

    Gong Jiangbin; Ma Ao; Rice, Stuart A.

    2005-05-22

    We report a study of control of the HCN{yields}CNH isomerization in a liquid Ar solution. We show, using molecular dynamics simulations, nearly complete conversion from HCN to CNH can be achieved in solution on the subnanosecond time scale without requiring laser pulse shaping or molecular alignment. The mechanism of the isomerization reaction involves multiphoton rovibrational excitation on the ground electronic state potential energy surface coupled with rapid rovibrational relaxation in solution. The results demonstrate the important role of rotation-vibration coupling in multiphoton excitation of small molecules and constitute the first realistic computational demonstration of fast, robust, and high-yield laser field manipulation of solution-phase molecular processes.

  17. Linkage isomerism in coordination polymers.

    PubMed

    Benmansour, Samia; Setifi, Fatima; Triki, Smail; Gómez-García, Carlos J

    2012-02-20

    The use of the recently prepared polynitrile ligand tcnopr3OH(-) ([(NC)(2)CC(OCH(2)CH(2)CH(2)OH)C(CN)(2)](-)) with different salts of Fe(II), Co(II), and Ni(II) has led to a very rare example of linkage isomerism in a coordination chain. These pairs of linkage isomers can be formulated as [M(tcnopr3OH-κN,κO)(2)(H(2)O)(2)]; M = Fe (1), Co (3), and Ni(5) and [M(tcnopr3OH-κN,κN')(2)(H(2)O)(2)]; M = Fe (2), Co (4), and Ni (6). Compounds 1-2, 3-4, and 5-6 are three pairs of linkage isomers since they present the same formula and chain structure and they only differ in the connectivity of the polynitrile ligand bridging the metal ions in the chain: through a N and an O atom (1κN:2κO-isomer) or through two N atoms (1κN:2κN'-isomer). The magnetic properties show, as expected, very similar behaviors for both isomers. PMID:22296602

  18. Isomerically Pure Tetramethylrhodamine Voltage Reporters.

    PubMed

    Deal, Parker E; Kulkarni, Rishikesh U; Al-Abdullatif, Sarah H; Miller, Evan W

    2016-07-27

    We present the design, synthesis, and application of a new family of fluorescent voltage indicators based on isomerically pure tetramethylrhodamines. These new Rhodamine Voltage Reporters, or RhoVRs, use photoinduced electron transfer (PeT) as a trigger for voltage sensing, display excitation and emission profiles in the green to orange region of the visible spectrum, demonstrate high sensitivity to membrane potential changes (up to 47% ΔF/F per 100 mV), and employ a tertiary amide derived from sarcosine, which aids in membrane localization and simultaneously simplifies the synthetic route to the voltage sensors. The most sensitive of the RhoVR dyes, RhoVR 1, features a methoxy-substituted diethylaniline donor and phenylenevinylene molecular wire at the 5'-position of the rhodamine aryl ring, exhibits the highest voltage sensitivity to date for red-shifted PeT-based voltage sensors, and is compatible with simultaneous imaging alongside green fluorescent protein-based indicators. The discoveries that sarcosine-based tertiary amides in the context of molecular-wire voltage indicators prevent dye internalization and 5'-substituted voltage indicators exhibit improved voltage sensitivity should be broadly applicable to other types of PeT-based voltage-sensitive fluorophores. PMID:27428174

  19. Conformational Isomerism Can Limit Antibody Catalysis

    SciTech Connect

    Debler, E.W.; Muller, R.; Hilvert, D.; Wilson, I.A.

    2009-05-14

    Ligand binding to enzymes and antibodies is often accompanied by protein conformational changes. Although such structural adjustments may be conducive to enzyme catalysis, much less is known about their effect on reactions promoted by engineered catalytic antibodies. Crystallographic and pre-steady state kinetic analyses of antibody 34E4, which efficiently promotes the conversion of benzisoxazoles to salicylonitriles, show that the resting catalyst adopts two interconverting active-site conformations, only one of which is competent to bind substrate. In the predominant isomer, the indole side chain of Trp{sup L91} occupies the binding site and blocks ligand access. Slow conformational isomerization of this residue, on the same time scale as catalytic turnover, creates a deep and narrow binding site that can accommodate substrate and promote proton transfer using Glu{sup H50} as a carboxylate base. Although 34E4 is among the best catalysts for the deprotonation of benzisoxazoles, its efficiency appears to be significantly limited by this conformational plasticity of its active site. Future efforts to improve this antibody might profitably focus on stabilizing the active conformation of the catalyst. Analogous strategies may also be relevant to other engineered proteins that are limited by an unfavorable conformational pre-equilibrium.

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

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

    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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. Ordering of azobenzenes by two-photon isomerization.

    PubMed

    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. PMID:17092131

  6. 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.

  7. Double well isomerization rate constants in solution

    NASA Astrophysics Data System (ADS)

    Zawadzki, Anthony G.; Hynes, James T.

    1985-02-01

    The rate constant k for a double well isomerization in solution is calculated over the entire friction range. The importance of frequency-dependent friction for both the vibrational energy transfer (VET) and barrier passage components of k is described. Rapid suppression of the VET transfer component with increasing degrees of freedom is discussed.

  8. Stability and isomerization reactions of phenyl cation C6H5+ isomers

    NASA Astrophysics Data System (ADS)

    Shi, Dandan; Yang, Xue; Zhang, Xiaomei; Shan, Shimin; Xu, Haifeng; Yan, Bing

    2016-03-01

    As a key polyatomic molecular cation that plays a pivotal role in growth of the polycyclic aromatic hydrocarbons, phenyl cation C6H5+ exhibits various isomers and isomerization reactions. Investigation on the structure and stability of the isomers as well as the isomerization is important for better understanding the chemical reactions involving C6H5+ cations. In this work, we have performed a theoretical study on the stability and isomerization reactions of C6H5+ isomers at density functional theory B3LYP/6-311G (d, p) level. We have obtained a total of 60 isomers of C6H5+ cations, most of which are reported for the first time. The geometries, vibrational frequencies, thermodynamic properties and stability of 28 out of 60 isomers have been summarized in detail. Different ring-to-ring and ring-to-chain isomerization pathways, which are connected via 28 transition states, have been investigated using the intrinsic reaction coordinate method. The results show that the isomerization reactions occur via hydrogen migration followed by bond-breaking and reconstruction.

  9. Laser-driven isomerization of HCN → HNC: the importance of rotational excitation.

    PubMed

    Sun, Zhaopeng; Zheng, Yujun

    2015-03-26

    We report a time-dependent quantum wave packet theory, which is employed to interpret the isomerization dynamics of HCN molecules induced by an intense picosecond infrared laser field. Considering the molecular rotational degrees of the freedom, the wave functions are expanded in terms of molecular rotational bases. Our full-dimensional quantum model includes the full Coriolis coupling in the molecular kinetic energy Hamiltonian and dipole approximation in interaction terms. The numerical results show that the field-induced molecule rotational excitation plays an important role in the isomerization dynamical process. Some phenomena appear such as two-step two-photon absorption and highly oscillatory structure in rotational state distributions. The centrifugal sudden (CS) approximation calculation is also carried out and compared in this work; it is shown that the Coriolis couplings may lead to a significant decrease in the isomerization rate but highly enhanced molecular rotational excitation. PMID:25746130

  10. Ground-state and isomeric-state cross sections for 181Ta( n,2n )180Ta between 8 and 15 MeV

    SciTech Connect

    Bhatia, C.; Gooden, M. E.; Tornow, W.; Tonchev, A. P.

    2013-03-21

    Using the activation technique, the cross section for the reaction 181Ta(n,2n)180gTa was measured from 8 to 15 MeV in small energy steps to resolve inconsistencies in the existing database. The 93.4 keV γ ray from the decay of the 180gTa ground state was recorded with a high-purity germanium (HPGe) detector. The monitor reactions 27Al(n,α)24Na and 197Au(n,2n)196Au were used for neutron fluence determination. The ENDF VII.1 and TENDL 2011 evaluations are in considerable disagreement with the present data, which in turn agree very well with the majority of the existing data in the 14 MeV energy region. Furthermore, a detailed analysis using the code TALYS was performed to describe the present data and to predict the (n,2n) cross section to the isomeric state of 180Ta.

  11. Vapor-controlled linkage isomerization of a vapochromic bis(thiocyanato)platinum(II) complex: new external stimuli to control isomerization behavior.

    PubMed

    Kobayashi, Atsushi; Fukuzawa, Yuki; Chang, Ho-Chol; Kato, Masako

    2012-07-16

    We synthesized a novel Pt(II)-diimine complex with a typical ambidentate thiocyanato ligand, [Pt(thiocyanato)(2)(H(2)dcbpy)] (1; H(2)dcbpy =4,4'-dicarboxy-2,2'-bipyridine), and found that the complex 1 exhibits unique linkage isomerizations with drastic color and luminescence changes driven by exposure to volatile organic chemical (VOC) vapors in the solid state. Reaction between [PtCl(2)(H(2)dcbpy)] and KSCN in aqueous solution at 0 °C enabled successful isolation of an isomer with the S-coordinated thiocyanato ligand, [Pt(SCN)(2)(H(2)dcbpy)] (1SS·H(2)O), as a nonluminescent orange solid. Interestingly, 1SS·H(2)O was isomerized completely to one isomer with the N-coordinated isothiocyanato ligand, [Pt(NCS)(2)(H(2)dcbpy)] (1NN·3DMF) by exposure to DMF vapor, and this isomerization was accompanied by significant color and luminescence changes from nonluminescent orange to luminescent red. IR spectroscopy and thermogravimetric analysis revealed that adsorption of the DMF vapor and transformation of the hydrogen-bonded structure both played important roles in this vapor-induced linkage isomerization. Another isomer containing both S- and N-coordinated thiocyanato ligands, [Pt(SCN)(NCS)(H(2)dcbpy)] (1SN), was obtained as a nonluminescent yellow solid simply by exposure of 1SS·H(2)O to acetone vapor at room temperature, and about 80% of 1SS·H(2)O was found to be converted to 1SN. In the solution state, each isomer changed gradually to an isomeric mixture, but pure 1SS was regenerated by UV light irradiation (λ(irr.) = 300 nm) of an MeOH solution of the mixture. In the crystal structure of 1SN, the complex molecules were hydrogen-bonded to each other through the carboxyl groups of the H(2)dcbpy ligand and the N site of the thiocyanato ligand, whereas the 1NN molecules in the 1NN·4DMF crystal were hydrogen-bonded to the solvated DMF molecules. Competition of the hydrogen-bonding ability among the carboxyl groups of the H(2)dcbpy ligand, N and S atoms of the

  12. Tungsta and platinum-tungsta supported on zirconia catalysts for alkane isomerization

    SciTech Connect

    Larsen, G.; Lotero, E.; Parra, R.D.

    1996-12-31

    Tungsta- and platinum-tungsta supported on zirconia catalysts (WZ and PtWZ) were tested for isomerization of n-butane with hydrogen at 573 K. The catalysts reduction kinetics and the chemical state of tungsten were studied by X-ray absorption near-edge spectroscopy (XANES) and conventional temperature-programmed (TPR) techniques. Platinum was found to catalyze the reduction of the support and the tungsta co-catalyst. An effective n-butane isomerization catalyst results from the combination of high-temperature calcination and low-temperature reduction. Pyridine adsorption, as monitored by diffuse reflectance infrared spectroscopy (DRIFTS), indicates that water of reduction generates Bronsted acid sites.

  13. 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.

  14. 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).

  15. Theoretical Study of Isomerization and Decomposition Reactions for Methyl-nitramine

    NASA Astrophysics Data System (ADS)

    Wei, Wen-mei; Zheng, Ren-hui; Tian, Yan; He, Tian-jing; He, Li; Chen, Dong-ming; Liu, Fan-chen

    2007-04-01

    The complex potential energy surface and reaction mechanisms for the unimolecular isomerization and decomposition of methyl-nitramine (CH3NHNO2) were theoretically probed at the QCISD(T)/6-311+Gast//B3LYP/6-311+Gast level of theory. The results demonstrated that there are four low-lying energy channels: (i) the N-N bond fission pathway; (ii) a sequence of isomerization reactions via CH3NN(OH)O; (IS2a); (iii) the HONO elimination pathway; (iv) the isomerization and the dissociation reactions via CH3NHONO (IS3). The rate constants of each initial step (rate-determining step) for these channels were calculated using the canonical transition state theory. The Arrhenius expressions of the channels over the temperature range 298-2000 K are k6(T)=1014.8e-46.0/RT, k7(T)=1013.7e-42.1/RT, k8(T)=1013.6e-51.8/RT and k9(T)=1015.6e-54.3/RT s-1, respectively. The calculated overall rate constants is 6.9×10-4 at 543 K, which is in good agreement with the experimental data. Based on the analysis of the rate constants, the dominant pathway is the isomerization reaction to form CH3NN(OH)O at low temperatures, while the N-N bond fission and the isomerization reaction to produce CH3NHONO are expected to be competitive with the isomerization reaction to form CH3NN(OH)O at high temperatures.

  16. 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.

  17. 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.

  18. Connectivity matters - ultrafast isomerization dynamics of bisazobenzene photoswitches.

    PubMed

    Slavov, Chavdar; Yang, Chong; Schweighauser, Luca; Boumrifak, Chokri; Dreuw, Andreas; Wegner, Hermann A; Wachtveitl, Josef

    2016-06-01

    We have investigated the ultrafast dynamics of o-, m- and p-bisazobenzenes, which represent elementary building blocks for photoswitchable multiazobenzene nanostructures. The connectivity pattern within bisazobenzenes and the ensuing complex interactions between the individual azobenzene units determines the ultrafast dynamics of these compounds and their photochemical properties. While retaining a relatively high E → Z isomerization quantum yield, o-bisazobenzene exhibits a very high thermal relaxation rate (half-life of 1.6 ms). Our theoretical calculations reveal that the geometry allows intramolecular excitonic interaction between the azobenzene units, which is reflected in the femtosecond transient absorption data via the simultaneous bleaching of the two excitonic bands. In contrast, the properties of m-bisazobenzene are very similar to the monomeric azobenzene, with the two units acting nearly independently from each other. The highest degree of π conjugation extending over the two azobenzene units was observed for p-bisazobenzene, which results in strong planarity of the molecule, reduced excited state lifetime and relatively low isomerization quantum yield. Multiphotochromic systems bridge the gap between molecular photoswitches and macroscopic function and thus, understanding the properties of bisazobenzenes opens the way to the design and development of new structures with extensive and versatile applications. PMID:26996604

  19. 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.

  20. 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.

  1. Kinematic effects associated with molecular frames in structural isomerization dynamics of clusters

    NASA Astrophysics Data System (ADS)

    Yanao, Tomohiro; Takatsuka, Kazuo

    2004-05-01

    Kinematic effects associated with movements of molecular frames, which specify instantaneous orientation of molecules, is investigated in structural isomerization dynamics of a triatomic cluster whose total angular momentum is zero. The principal-axis frame is employed to introduce the so-called principal-axis hyperspherical coordinates, with which the mechanism of structural isomerization dynamics of the cluster is systematically analyzed. A force called "democratic centrifugal force" is extracted from the associated kinematics. This force arises from an intrinsic non-Euclidean metric in the internal space and has an effect of distorting the triatomic cluster to a collapsed shape and of trapping the system around collinear transition states. The latter effect is particularly important in that the kinematics effectively makes a basin at the saddle (transition state) on the potential surface. Based on this framework, we study the effect of the gauge field associated with the Eckart frame in internal space, which has not been carefully examined in the conventional reaction rate theories. Numerical comparison between the dynamics with and without the gauge field has revealed that this field has an effect to suppress the rate of isomerization reaction to a considerable amount. Thus a theory neglecting this effect will significantly overestimate the rate of isomerization. We show the physical origin of this suppressing effect.

  2. Photochromic ruthenium sulfoxide complexes: evidence for isomerization through a conical intersection.

    PubMed

    McClure, Beth Anne; Mockus, Nicholas V; Butcher, Dennis P; Lutterman, Daniel A; Turro, Claudia; Petersen, Jeffrey L; Rack, Jeffrey J

    2009-09-01

    The complexes [Ru(bpy)(2)(OS)](PF(6)) and [Ru(bpy)(2)(OSO)](PF(6)), where bpy is 2,2'-bipyridine, OS is 2-methylthiobenzoate, and OSO is 2-methylsulfinylbenzoate, have been studied. The electrochemical and photochemical reactivity of [Ru(bpy)(2)(OSO)](+) is consistent with an isomerization of the bound sulfoxide from S-bonded (S-) to O-bonded (O-) following irradiation or electrochemical oxidation. Charge transfer excitation of [Ru(bpy)(2)(OSO)](+) in MeOH results in the appearance of two new metal-to-ligand charge transfer (MLCT) maxima at 355 and 496 nm, while the peak at 396 nm diminishes in intensity. The isomerization is reversible at room temperature in alcohol or propylene carbonate solution. In the absence of light, solutions of O-[Ru(bpy)(2)(OSO)](+) revert to S-[Ru(bpy)(2)(OSO)](+). Kinetic analysis reveals a biexponential decay with rate constants of 5.66(3) x 10(-4) s(-1) and 3.1(1) x 10(-5) s(-1). Cyclic voltammograms of S-[Ru(bpy)(2)(OSO)](+) are consistent with electron-transfer-triggered isomerization of the sulfoxide. Analysis of these voltammograms reveal E(S)(o)' = 0.86 V and E(O)(o)' = 0.49 V versus Ag/Ag(+) for the S- and O-bonded Ru(3+/2+) couples, respectively, in propylene carbonate. We found k(S-->O) = 0.090(15) s(-1) in propylene carbonate and k(S-->O) = 0.11(3) s(-1) in acetonitrile on Ru(III), which is considerably slower than has been reported for other sulfoxide isomerizations on ruthenium polypyridyl complexes following oxidation. The photoisomerization quantum yield (Phi(S-->O) = 0.45, methanol) is quite large, indicating a rapid excited state isomerization rate constant. The kinetic trace at 500 nm is monoexponential with tau = 150 ps, which is assigned to the excited S-->O isomerization rate. There is no spectroscopic or kinetic evidence for an O-bonded (3)MLCT excited state in the spectral evolution of S-[Ru(bpy)(2)(OSO)](+) to O-[Ru(bpy)(2)(OSO)](+). Thus, isomerization occurs nonadiabatically from an S-bonded (or eta(2

  3. Chemical Kinetic Analysis of Thermal Decay of Rhodopsin Reveals Unusual Energetics of Thermal Isomerization and Hydrolysis of Schiff Base*

    PubMed Central

    Liu, Jian; Liu, Monica Yun; Fu, Li; Zhu, Gefei Alex; Yan, Elsa C. Y.

    2011-01-01

    The thermal properties of rhodopsin, which set the threshold of our vision, have long been investigated, but the chemical kinetics of the thermal decay of rhodopsin has not been revealed in detail. To understand thermal decay quantitatively, we propose a kinetic model consisting of two pathways: 1) thermal isomerization of 11-cis-retinal followed by hydrolysis of Schiff base (SB) and 2) hydrolysis of SB in dark state rhodopsin followed by opsin-catalyzed isomerization of free 11-cis-retinal. We solve the kinetic model mathematically and use it to analyze kinetic data from four experiments that we designed to assay thermal decay, isomerization, hydrolysis of SB using dark state rhodopsin, and hydrolysis of SB using photoactivated rhodopsin. We apply the model to WT rhodopsin and E181Q and S186A mutants at 55 °C, as well as WT rhodopsin in H2O and D2O at 59 °C. The results show that the hydrogen-bonding network strongly restrains thermal isomerization but is less important in opsin and activated rhodopsin. Furthermore, the ability to obtain individual rate constants allows comparison of thermal processes under various conditions. Our kinetic model and experiments reveal two unusual energetic properties: the steep temperature dependence of the rates of thermal isomerization and SB hydrolysis in the dark state and a strong deuterium isotope effect on dark state SB hydrolysis. These findings can be applied to study pathogenic rhodopsin mutants and other visual pigments. PMID:21921035

  4. 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.

  5. Methods for suppressing isomerization of olefin metathesis products

    SciTech Connect

    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.

  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. Confirmed assignments of isomeric dimethylbenzyl radicals generated by corona discharge.

    PubMed

    Yoon, Young Wook; Lee, Sang Kuk

    2011-12-01

    The controversial vibronic assignments of isomeric dimethylbenzyl radicals were clearly resolved by using different precursors. By employing corresponding dimethylbenzyl chlorides as precursors, we identified the origins of the vibronic bands of the dimethylbenzyl radicals generated by corona discharge of 1,2,4-trimethylbenzene. From the analysis of the spectra observed from the dimethylbenzyl chlorides in a corona excited supersonic expansion, we revised previous assignments of the 3,4-, 2,4-, and 2,5-dimethylbenzyl radicals. 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 1,2,4-trimethylbenzene. PMID:22149790

  8. A comparison of tunneling transfer theories for asymmetric isomerization reactions

    NASA Astrophysics Data System (ADS)

    Cribb, Peter H.; Nordholm, Sture; Hush, N. S.

    1982-08-01

    In this paper, we discuss the basis of the transition state/trasmission coefficient theory of tunneling contributions to the rate of isomerization reactions. This theory, which is currently widely used, is found to deviate both quantitatively and qualitatively from an alternative theory, we have developed on the basis of a more rigorous interpretation of the reaction mechanism in accord with the original suggestion of Lindermann. We focus attention on the discrepancies which arise when there is asymmetry between the reactant and product potential wells. Comparative calculations are reported for a model potential advanced on the basis of spectroscopic measurements to represent the level spectrum associated with the ring- puckering motion in azetidine. Large differences are shown to exist between the predictions of the two types of theories.

  9. The gating isomerization of neuromuscular acetylcholine receptors

    PubMed Central

    Auerbach, Anthony

    2010-01-01

    Acetylcholine receptor-channels are allosteric proteins that isomerize (‘gate’) between conformations that have a low vs. high affinity for the transmitter and conductance for ions. In order to comprehend the mechanism by which the affinity and conductance changes are linked it is of value to know the magnitude, timing and distribution of energy flowing through the system. Knowing both the di- and unliganded gating equilibrium constants (E2 and E0) is a foundation for understanding the AChR gating mechanism and for engineering both the ligand and the protein to operate in predictable ways. In adult mouse neuromuscular receptors activated by acetylcholine, E2= 28 and E0≈ 6.5 × 10−7. At each (equivalent) transmitter binding site acetylcholine provides ∼5.2 kcal mol−1 to motivate the isomerization. The partial agonist choline provides ∼3.3 kcal mol−1. The relative time of a residue's gating energy change is revealed by the slope of its rate–equilibrium constant relationship. A map of this parameter suggests that energy propagates as a conformational cascade between the transmitter binding sites and the gate region. Although gating energy changes are widespread throughout the protein, some residues are particularly sensitive to perturbations. Several specific proposals for the structural events that comprise the gating conformational cascade are discussed. PMID:19933754

  10. 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.

  11. Modification of isomerization activity and selectivity over sulfated zirconia catalysts

    SciTech Connect

    Soled, S.L.; Iglesia, E.; Kramer, G.M.; McVicker, G.B.

    1993-12-31

    The family of anion-modified oxide strong solid acid catalysts (oxides of Zr, Ti, Sn, or Fe, modified with sulfate) that have been recently reported in the literature were examined for the isomerization of C{sub 5}-C{sub 8} n-paraffins. Isomerization of C{sub 7+} feeds on conventional solid and liquid acids leads to extensive cracking; in particular, paraffins with seven or more carbon atoms are known to undergo acid cracking to undesirable light gases during isomerization over acid catalysts; thus, commercial isomerization practice is limited to C{sub 4}-C{sub 6} feeds. Cracking occurs because isobutane and propane are excellent leaving groups in carbonium ion rearrangements. Since both isomerization and cracking occur on strong acid sites it has been difficult to control one at the expense of the other. The authors have observed that low levels of that low levels of adamantane, a hydride transfer agent, added to a heptane or octain feed will double the isomerization rate while dramatically limiting cracking reactions. The adamantane enhances the rate determining hydride transfer step and limits the surface residence time of carbocation intermediates. This behavior contrasts with that of aromatic addition where poisoning of strong acid sites inhibits cracking but dramatically decreases the isomerization rate. This paper will suggest a mechanism that involves a nonfunctional acid catalyzed chain mechanism proceeding through intermolecular hydride transfer reactions. Finally we will discuss the remaining issues in obtaining a viable C{sub 7}+ isomerization process.

  12. 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.

  13. 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.

  14. Cavity Ringdown Spectroscopy and Kinetics of Butoxy Isomerization: Detection of the {A}- {XCAVITY Ringdown Spectroscopy and Kinetics of Butoxy Isomerization: Detection of the {A}- {X

    NASA Astrophysics Data System (ADS)

    Sprague, Matthew K.; Okumura, Mitchio; Sander, Stanley P.

    2011-06-01

    Alkoxy radicals are atmospherically important species, playing a direct role in the HO_x and NO_x cycles that affect tropospheric air pollution. Alkoxy radicals that can form a six membered transition state can isomerize into a hydroxyalkyl radical. In the presence of O_2, a rapid association reaction occurs, forming a hydroxyalkylperoxy radical. The n-butoxy radical is the smallest alkoxy to undergo isomerization, forming the γ-hydroxybutylperoxy radical (HOC_4H_8OO). Direct detection of HOC_4H_8OO opens the door to measuring alkoxy reaction kinetics with higher precision than previous end product studies. In this talk, we report the first detection of the tilde{A}-tilde{X} electronic spectrum of the HOC_4H_8OO radical. The spectrum is similar in shape to the tilde{A}-tilde{X} spectrum of n-butyl peroxy: a broad spectroscopic band due to the multiple molecular conformers that are present. We also use the tilde{A}-tilde{X} band to measure the alkoxy isomerization kinetics relative to the alkoxy radical's reaction with O_2, similar to the previous kinetics studies. R. Atkinson, D. L. Baulch, R. A. Cox, J. N. Crowley, R. F. Hampson, R. G. Hynes, M. E. Jenkin, M. J. Rossi, and J. Troe J. Atmos. Chem. and Phys. 2006, 6, 3625. B. G. Glover and T. A. Miller. J. Phys. Chem. A 2005, 109, 11191.

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

    PubMed

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

    2016-03-01

    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. PMID:26887629

  16. A comprehensive study of isomerization and protonation reactions in the photocycle of the photoactive yellow protein.

    PubMed

    Wei, Lili; Wang, Hongjuan; Chen, Xuebo; Fang, Weihai; Wang, Haobin

    2014-12-14

    The light-activated photoactive yellow protein (PYP) chromophore uses a series of reactions to trigger photo-motility and biological responses, and generate a wide range of structural signals. To provide a comprehensive mechanism of the overall process at the atomic level, we apply a CASPT2//CASSCF/AMBER QM/MM protocol to investigate the relaxation pathways for a variety of possible isomerization and proton transfer reactions upon photoexcitation of the wild-type PYP. The nonadiabatic relay through an S1/S0 conical intersection [CI(S1/S0)] is found to play a decisive major role in bifurcating the excited state relaxation into a complete and short photocycle. Two major and one minor deactivation channels were found starting from the CI(S1/S0)-like intermediate IT, producing the cis isomers pR1, ICP, and ICT through "hula twist", "bicycle pedal" and one-bond flip isomerization reactions. The overall photocycle can be achieved by competitive parallel/sequential reactions, in which the ground state recovery is controlled by a series of slow volume-conserving bicycle pedal/hula twist and one-bond flip isomerization reactions, as well as fast protonation-deprotonation processes and the hydrophobic-hydrophilic state transformation. PMID:25195953

  17. Roaming-mediated isomerization in the photodissociation of nitrobenzene

    NASA Astrophysics Data System (ADS)

    Hause, Michael L.; Herath, Nuradhika; Zhu, Rongshun; Lin, M. C.; Suits, Arthur G.

    2011-12-01

    Roaming reactions comprise a new class of reaction in which a molecule undergoes frustrated dissociation to radicals, followed by an intramolecular abstraction reaction. Nitro compounds have long been known to dissociate to give NO as a major product. However, rates based upon isomerization via calculated tight transition states are implausibly slow, so the key dissociation pathway for this important class of molecules remains obscure. Here, we present an imaging study of the photodissociation of nitrobenzene with state-specific detection of the resulting NO products. We observe a bimodal translational energy distribution in which the slow products are formed with low NO rotational excitation, and the fast component is associated with high rotational excitation. High-level ab initio calculations identified a ‘roaming-type’ saddle point on the ground state. Branching ratio calculations then show that thermal dissociation of nitrobenzene is dominated by ‘roaming-mediated isomerization’ to phenyl nitrite, which subsequently decomposes to give C6H5O + NO.

  18. Theoretical study on the mechanism of iron carbonyls mediated isomerization of allylic alcohols to saturated carbonyls.

    PubMed

    Branchadell, Vicenç; Crévisy, Christophe; Grée, René

    2003-05-01

    The conversion of allylic alcohols to enols mediated by Fe(CO)(3) has been studied through density functional theoretical calculations. From the results obtained a complete catalytic cycle has been proposed in which the first intermediate is the [(allyl alcohol)Fe(CO)(3)] complex. This intermediate evolves to the [(enol)Fe(CO)(3)] complex through two consecutive 1,3-hydrogen shifts involving a pi-allyl hydride intermediate. The highest Gibbs energy transition state corresponds to the partial decoordination ot the enol ligand prior to the coordination of a new allyl alcohol molecule that regenerates the first intermediate. Alternative processes for the [(enol)Fe(CO)(3)] complex such as [Fe(CO)(3)]-mediated enol-aldehyde transformation and enol isomerization have also been considered. The results obtained show that the former process is unfavourable, whereas the enol isomerization may compete with the enol decoordination step of the catalytic cycle. PMID:12740854

  19. 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.

  20. Control of retinal isomerization in bacteriorhodopsin in the high-intensity regime

    PubMed Central

    Florean, Andrei C.; Cardoza, David; White, James L.; Lanyi, J. K.; Sension, Roseanne J.; Bucksbaum, Philip H.

    2009-01-01

    A learning algorithm was used to manipulate optical pulse shapes and optimize retinal isomerization in bacteriorhodopsin, for excitation levels up to 1.8 × 1016 photons per square centimeter. Below 1/3 the maximum excitation level, the yield was not sensitive to pulse shape. Above this level the learning algorithm found that a Fourier-transform-limited (TL) pulse maximized the 13-cis population. For this optimal pulse the yield increases linearly with intensity well beyond the saturation of the first excited state. To understand these results we performed systematic searches varying the chirp and energy of the pump pulses while monitoring the isomerization yield. The results are interpreted including the influence of 1-photon and multiphoton transitions. The population dynamics in each intermediate conformation and the final branching ratio between the all-trans and 13-cis isomers are modified by changes in the pulse energy and duration. PMID:19564608

  1. Photo-induced isomerization and chemical reaction dynamics in superfluid helium droplets

    NASA Astrophysics Data System (ADS)

    Merritt, Jeremy; Douberly, Gary; Miller, Roger

    2008-03-01

    Near threshold photo-induced isomerization and photo-induced chemical reactions have long been sough after as sensitive probes of the underlying potential energy surface. One of the most important questions asked is how the initially bright quantum state couples to the reaction coordinate, and thus relates to energy transfer in general. Helium droplets have now allowed us to stabilize entrance channel clusters behind very small reaction barriers such that vibrational excitation may result in reaction. Through two examples, namely the isomerization of the 2 binary complexes of HF-HCN Douberly et al. PCCP 2005, 7,463, and the induced reaction of the gallium-HCN complex Merritt et al. JPCA 2007, DOI:10.1021/jp074981e we will show how the branching ratios for reaction and predissociation can determined and the influence of the superfluid He solvent.

  2. 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.

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

    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.

  4. 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.

  5. Oxidative trans to cis Isomerization of Olefins in Polyketide Biosynthesis.

    PubMed

    Yamamoto, Tsuyoshi; Tsunematsu, Yuta; Hara, Kodai; Suzuki, Tomohiro; Kishimoto, Shinji; Kawagishi, Hirokazu; Noguchi, Hiroshi; Hashimoto, Hiroshi; Tang, Yi; Hotta, Kinya; Watanabe, Kenji

    2016-05-17

    Geometric isomerization can expand the scope of biological activities of natural products. The observed chemical diversity among the pseurotin-type fungal secondary metabolites is in part generated by a trans to cis isomerization of an olefin. In vitro characterizations of pseurotin biosynthetic enzymes revealed that the glutathione S-transferase PsoE requires participation of the bifunctional C-methyltransferase/epoxidase PsoF to complete the trans to cis isomerization of the pathway intermediate presynerazol. The crystal structure of the PsoE/glutathione/presynerazol complex indicated stereospecific glutathione-presynerazol conjugate formation is the principal function of PsoE. Moreover, PsoF was identified to have an additional, unexpected oxidative isomerase activity, thus making it a trifunctional enzyme which is key to the complexity generation in pseurotin biosynthesis. Through the study, we identified a novel mechanism of accomplishing a seemingly simple trans to cis isomerization reaction. PMID:27072782

  6. Photochromism of isomeric diarylethenes with a methylpyridine substituent

    NASA Astrophysics Data System (ADS)

    Sun, Fengxia; Cui, Shiqiang; Liu, Gang; Zheng, Chunhong; Pu, Shouzhi

    2015-04-01

    Two new isomeric photochromic diarylethenes with a methylpyridine unit have been synthesized and their structures have been determined by single-crystal X-ray diffraction analysis. Both diarylethenes exhibited photochromism in both solution and PMMA films. In the single crystalline phase, the two isomeric compounds displayed different photochromism based on their various molecular conformations. In addition, their fluorescent properties are also diverse due to the distinct substitution position of the methyl group on the terminal pyridine.

  7. Methods for suppressing isomerization of olefin metathesis products

    SciTech Connect

    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.

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

    NASA Astrophysics Data System (ADS)

    Bakhshiyan, T. M.

    2016-01-01

    Isomeric ratios (IR) in the (p, n) and (d, 2 n) 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 44m,gSc to 127m,gXe) 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 Δ E = 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, 2 n) reactions are substantially greater than those in (p, n) reactions.

  9. Understanding the isomerization of the HIV-1 dimerization initiation domain by the nucleocapsid protein

    PubMed Central

    Turner, Kevin B.; Hagan, Nathan A.

    2008-01-01

    The specific binding of HIV-1 nucleocapsid (NC) to the hinge region of the kissing-loop (KL) dimer formed by stemloop 1 (SL1) can have significant consequences on its ability to isomerize into the corresponding extended duplex (ED) form. The binding determinants and the effects on the isomerization process were investigated in vitro by a concerted strategy involving ad hoc RNA mutants and electrospray ionization-Fourier transform ion cyclotron resonance (ESI-FTICR) mass spectrometry, which enabled us to characterize the stoichiometry and conformational state of all possible protein-RNA and RNA-RNA assemblies present simultaneously in solution. For the first time, NC-hinge interactions were observed in constructs including at least one unpaired guanine at the 5′-end of the loop-loop duplex, whereas no interactions were detected when the unpaired guanine was placed at its 3′-end. This binding mode is supported by the presence of a grip-like motif described by recent crystal structures, which is formed by the 5′-purines of both hairpins held together by mutual stacking interactions. Using tandem mass spectrometry, hinge interactions were clearly shown to reduce the efficiency of KL/ED isomerization without inducing its complete block. This outcome is consistent with the partial stabilization of the extra-helical grip by the bound protein, which can hamper the purine components from parting ways and initiate the strand exchange process. These findings confirm that the broad binding and chaperone activities of NC induce unique effects that are clearly dependent on the structural context of the cognate nucleic acid substrate. For this reason, the presence of multiple binding sites on the different forms assumed by SL1 can produce seemingly contrasting effects that contribute to a fine modulation of the two-step process of RNA dimerization and isomerization. PMID:17466332

  10. Prolyl Isomerization as a Molecular Memory in the Allosteric Regulation of the Signal Adapter Protein c-CrkII

    PubMed Central

    Schmidpeter, Philipp A. M.; Schmid, Franz X.

    2015-01-01

    c-CrkII is a central signal adapter protein. A domain opening/closing reaction between its N- and C-terminal Src homology 3 domains (SH3N and SH3C, respectively) controls signal propagation from upstream tyrosine kinases to downstream targets. In chicken but not in human c-CrkII, opening/closing is coupled with cis/trans isomerization at Pro-238 in SH3C. Here, we used advanced double-mixing experiments and kinetic simulations to uncover dynamic domain interactions in c-CrkII and to elucidate how they are linked with cis/trans isomerization and how this regulates substrate binding to SH3N. Pro-238 trans → cis isomerization is not a simple on/off switch but converts chicken c-CrkII from a high affinity to a low affinity form. We present a double-box model that describes c-CrkII as an allosteric system consisting of an open, high affinity R state and a closed, low affinity T state. Coupling of the T-R transition with an intrinsically slow prolyl isomerization provides c-CrkII with a kinetic memory and possibly functions as a molecular attenuator during signal transduction. PMID:25488658

  11. Prolyl isomerization as a molecular memory in the allosteric regulation of the signal adapter protein c-CrkII.

    PubMed

    Schmidpeter, Philipp A M; Schmid, Franz X

    2015-01-30

    c-CrkII is a central signal adapter protein. A domain opening/closing reaction between its N- and C-terminal Src homology 3 domains (SH3N and SH3C, respectively) controls signal propagation from upstream tyrosine kinases to downstream targets. In chicken but not in human c-CrkII, opening/closing is coupled with cis/trans isomerization at Pro-238 in SH3C. Here, we used advanced double-mixing experiments and kinetic simulations to uncover dynamic domain interactions in c-CrkII and to elucidate how they are linked with cis/trans isomerization and how this regulates substrate binding to SH3N. Pro-238 trans → cis isomerization is not a simple on/off switch but converts chicken c-CrkII from a high affinity to a low affinity form. We present a double-box model that describes c-CrkII as an allosteric system consisting of an open, high affinity R state and a closed, low affinity T state. Coupling of the T-R transition with an intrinsically slow prolyl isomerization provides c-CrkII with a kinetic memory and possibly functions as a molecular attenuator during signal transduction. PMID:25488658

  12. Isomerism of Cyanomethanimine: Accurate Structural, Energetic, and Spectroscopic Characterization.

    PubMed

    Puzzarini, Cristina

    2015-11-25

    The structures, relative stabilities, and rotational and vibrational parameters of the Z-C-, E-C-, and N-cyanomethanimine isomers have been evaluated using state-of-the-art quantum-chemical approaches. Equilibrium geometries have been calculated by means of a composite scheme based on coupled-cluster calculations that accounts for the extrapolation to the complete basis set limit and core-correlation effects. The latter approach is proved to provide molecular structures with an accuracy of 0.001-0.002 Å and 0.05-0.1° for bond lengths and angles, respectively. Systematically extrapolated ab initio energies, accounting for electron correlation through coupled-cluster theory, including up to single, double, triple, and quadruple excitations, and corrected for core-electron correlation and anharmonic zero-point vibrational energy, have been used to accurately determine relative energies and the Z-E isomerization barrier with an accuracy of about 1 kJ/mol. Vibrational and rotational spectroscopic parameters have been investigated by means of hybrid schemes that allow us to obtain rotational constants accurate to about a few megahertz and vibrational frequencies with a mean absolute error of ∼1%. Where available, for all properties considered, a very good agreement with experimental data has been observed. PMID:26529434

  13. Wavelength Dependent Cis-Trans Isomerization in Vision†

    PubMed Central

    Kim, Judy E.; Tauber, Michael J.; Mathies, Richard A.

    2005-01-01

    The primary event in vision is the light-driven cis-trans isomerization of the 11-cis-retinal chromophore in the G-protein coupled receptor rhodopsin. Early measurements showed that this photoisomerization has a reaction quantum yield Φ of ∼0.67 [Dartnall (1936) Proc. R. Soc. A 156, 158-170; Dartnall (1968) Vision Res. 8, 339-358] and suggested that the quantum yield was wavelength independent [Schneider (1939) Proc. Natl. Acad. Sci. U.S.A. 170, 102-112]. Here we more accurately determine Φ 500) = 0.65 ± 0.01 and reveal that Φ surprisingly depends on the wavelength of the incident light. Although there is no difference in the quantum yield between 450 and 480 nm, the quantum yield falls significantly as the photon energy is reduced below 20 000 cm-1 (500 nm). At the reddest wavelength measured (570 nm), the quantum yield is reduced by 5 ± 1% relative to the 500 nm value. These experiments correct the long-held presumption that the quantum yield in vision is wavelength independent, and support the hypothesis that the 200 fs photoisomerization reaction that initiates vision is dictated by nonstationary excited-state vibrational wave packet dynamics. PMID:11705366

  14. Wavelength dependent cis-trans isomerization in vision.

    PubMed

    Kim, J E; Tauber, M J; Mathies, R A

    2001-11-20

    The primary event in vision is the light-driven cis-trans isomerization of the 11-cis-retinal chromophore in the G-protein coupled receptor rhodopsin. Early measurements showed that this photoisomerization has a reaction quantum yield phi of approximately 0.67 [Dartnall (1936) Proc. R. Soc. A 156, 158-170; Dartnall (1968) Vision Res. 8, 339-358] and suggested that the quantum yield was wavelength independent [Schneider (1939) Proc. Natl. Acad. Sci. U.S.A. 170, 102-112]. Here we more accurately determine phi(500) = 0.65 +/- 0.01 and reveal that phi surprisingly depends on the wavelength of the incident light. Although there is no difference in the quantum yield between 450 and 480 nm, the quantum yield falls significantly as the photon energy is reduced below 20 000 cm(-1) (500 nm). At the reddest wavelength measured (570 nm), the quantum yield is reduced by 5 +/- 1% relative to the 500 nm value. These experiments correct the long-held presumption that the quantum yield in vision is wavelength independent, and support the hypothesis that the 200 fs photoisomerization reaction that initiates vision is dictated by nonstationary excited-state vibrational wave packet dynamics. PMID:11705366

  15. 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

  16. 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.

  17. A review of drug isomerism and its significance.

    PubMed

    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

  18. Nitric Oxide Catalysis of Diazene E/Z Isomerization.

    PubMed

    Bohle, D Scott; Rosadiuk, Kristopher A

    2015-08-01

    Nitric oxide is an efficient catalyst for the cis-trans (E/Z) isomerization of diazenes. We compare the effect of room temperature solutions bearing low concentrations of nitric oxide, nitrogen dioxide, or oxygen on the rate of cis-trans isomerization, CTI, of the alkene bond in stilbene and on the azo double bond in azobenzene, as well as in four azo derivatives as measured by UV-vis spectroscopy. These rate enhancements can be as large as 3 orders of magnitude for azobenzene in solution. A mechanism is proposed where catalysis is promoted by the interaction of the nitric oxide with the diazene nitrogen lone pairs. Density functional theory, B3LYP/6-311++g** suggests that the binding of NO to the diazene should be weak and reversible but that its NO adduct has an E/Z isomerization barrier of 7.5 kcal/mol. PMID:26200101

  19. 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

  20. 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. PMID:26948404

  1. 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.

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

    PubMed

    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. PMID:27158903

  3. 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.

  4. 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

  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. 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

  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. 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.

  9. 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.

  10. Lewis acid catalysis of photochemical reactions. 5. Selective isomerization of conjugated butenoic and dienoic esters

    SciTech Connect

    Lewis, F.D.; Howard, D.K.; Barancyk, S.V.; Oxman, J.D.

    1986-05-28

    The effects of Lewis and Broensted acids upon the photoisomerization reactions of several conjugated butenoic and dienoic esters have been investigated. Lewis acids inhibit the photochemical deconjugation of ..cap alpha..,..beta..- to ..beta..,..gamma..-unsaturated butenoic esters and shift the photoequilibrium between E and Z isomers toward the Z isomer. As such, irradiation of E ..cap alpha..,..beta..-unsaturated esters in the presence of EtAlCl/sub 2/ provides a convenient method for the preparation of the thermodynamically less stable Z isomer. Irradiation of methyl (E,E)-2,4-hexadienoate and methyl (E,E)-5-phenyl-2,4-pentadienoate in the absence of added catalysts results in nonselective E,Z isomerization to give mixtures of all four stereoisomers in roughly comparable yields. In the presence of the Broensted acid trifluoroacetic acid, quantitative conversion of methyl 2,4-hexadienoates to methyl 3,4-hexadienoate is observed. The acid serves as a catalyst for the thermal 1,3-hydrogen shift of an allenic enol ester formed via a photochemical 1,5-hydrogen shift of the conjugated esters. Irradiation of the ground-state complexes of the conjugated esters with the Lewis acids EtAlCl/sub 2/ or BF/sub 3/ results in selective E,Z isomerization about the ..cap alpha..,..beta..-double bond in methyl 2,4-hexadienoate and the ..gamma..,delta-double bond in methyl 5-phenyl-24-pentadienoate. The mechanistic bases for the observed effects of Lewis acids are selective excitation of the more strongly absorbing E complex and more efficient isomerization of the excited E vs. Z complex.

  11. A comprehensive mechanistic picture of the isomerizing alkoxycarbonylation of plant oils.

    PubMed

    Roesle, Philipp; Caporaso, Lucia; Schnitte, Manuel; Goldbach, Verena; Cavallo, Luigi; Mecking, Stefan

    2014-12-01

    Theoretical studies on the overall catalytic cycle of isomerizing alkoxycarbonylation reveal the steric congestion around the diphosphine coordinated Pd-center as decisive for selectivity and productivity. The energy profile of isomerization is flat with diphosphines of variable steric bulk, but the preference for the formation of the linear Pd-alkyl species is more pronounced with sterically demanding diphosphines. CO insertion is feasible and reversible for all Pd-alkyl species studied and only little affected by the diphosphine. The overall rate-limiting step associated with the highest energetic barrier is methanolysis of the Pd-acyl species. Considering methanolysis of the linear Pd-acyl species, whose energetic barrier is lowest within all the Pd-acyl species studied, the barrier is calculated to be lower for more congesting diphosphines. Calculations indicate that energy differences of methanolysis of the linear versus branched Pd-acyls are more pronounced for more bulky diphosphines, due to involvement of different numbers of methanol molecules in the transition state. Experimental studies under pressure reactor conditions showed a faster conversion of shorter chain olefin substrates, but virtually no effect of the double bond position within the substrate. Compared to higher olefins, ethylene carbonylation under identical conditions is much faster, likely due not just to the occurrence of reactive linear acyls exclusively but also to an intrinsically favorable insertion reactivity of the olefin. The alcoholysis reaction is slowed down for higher alcohols, evidenced by pressure reactor and NMR studies. Multiple unsaturated fatty acids were observed to form a terminal Pd-allyl species upon reaction with the catalytically active Pd-hydride species. This process and further carbonylation are slow compared to isomerizing methoxycarbonylation of monounsaturated fatty acids, but selective. PMID:25415929

  12. Isomeric cross section of the {sup 197}Au(n,2n) reaction

    SciTech Connect

    Tsinganis, A.; Diakaki, M.; Kokkoris, M.; Mara, E.; Papadopoulos, C. T.; Vlastou, R.; Lagoyannis, A.

    2011-02-15

    In the present work, the {sup 197}Au(n,2n) reaction cross section is experimentally determined relative to the {sup 27}Al(n,{alpha}){sup 24}Na reaction at incident neutron energies of 9.0-10.5 MeV by means of the activation technique. The quasimonoenergetic fast neutron beam was produced via the {sup 2}H(d,n){sup 3}He reaction at the 5.5-MV Tandem Van de Graaff accelerator at the National Centre of Scientific Research (NCSR) ''Demokritos'' and was studied to determine the contribution of background 'parasitic' neutrons using the multiple foil activation technique and the SULSA unfolding code. The cross sections for the population of the second isomeric state (12{sup -}) of {sup 196}Au and the sum of the ground (2{sup -}) and first isomeric state (5{sup -}) population cross sections were independently determined. Auxiliary Monte Carlo simulations were performed with the MCNP code. Theoretical calculations of the above cross sections in the 8-25 MeV region were carried out with the use of the STAPRE-F, EMPIRE, and TALYS codes, which were also compared in their implementation of the generalized superfluid model. The theoretical results are compared with previous work in the same mass region, and the strong dependence on the level scheme of the nuclei involved was revealed.

  13. Combined CASSCF and MR-CI study on photoinduced dissociation and isomerization of acryloyl chloride.

    PubMed

    Cui, Gang-Long; Li, Qian-Song; Zhang, Feng; Fang, Wei-Hai; Yu, Jian-Guo

    2006-10-26

    The potential energy surfaces of isomerization and dissociation reactions for CH2CHCOCl in the S0, T1, T2, and S1 states have been mapped with DFT, CASSCF, MP2, and MR-CI calculations. Rate constants for adiabatic and nonadiabatic processes have been calculated with the RRKM rate theory, in conjugation with the vibronic interaction method. Mechanistic photochemistry of CH2CHCOCl at 230-310 nm has been characterized through the computed potential energy surfaces and rate constants. Upon photoexcitation of CH2CHCOCl at 310 nm, the S1-->T1 intersystem crossing is the dominant primary process, which is followed by the 1,3-Cl migration along the T1 pathway. Meanwhile, the S1-->S0 internal conversion occurs with considerable probability and the subsequent trans-cis isomerization proceeds in the ground state. The C-Cl bond cleavage is an exclusive primary channel upon photoexcitation of gaseous CH2CHCOCl at 230 nm. The direct C-Cl bond cleavage is partially blocked by effects of the matrix, and the internal conversion from S1 to S0 becomes an important process for the excited molecule to deactivate in the condensed phase. The present calculations not only provide a reasonable explanation of the experimental findings, but also give new insight into the mechanistic photochemistry of CH2CHCOCl. PMID:17048815

  14. 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.

  15. 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.

  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. Performance of the major semiempirical, ab initio, and DFT methods for isomerization enthalpies of linear to branched heptanes.

    PubMed

    Rayne, Sierra; Forest, Kaya

    2016-06-01

    The gas phase standard state (298.15 K, 1 atm) isomerization enthalpy (ΔisomH°(g)) prediction performance of the major semiempirical, ab initio, and density functional levels of theory for environmentally relevant transformations was investigated using the linear to branched heptanes as a representative case study. The M062X density functional, MP2 (and higher) levels of Moller-Plesset perturbation theory, and the CBS and Gaussian-n composite methods are well suited for investigating the thermodynamic properties of environmentally interesting isomerizations, although the M062X functional may not be appropriate for all systems. Where large molecular systems prohibit the use of higher levels of theory, the PM6 and PDDG semiempirical methods may offer an appropriate computational cost-accuracy compromise. PMID:26979512

  18. 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.

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

    PubMed

    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. PMID:27394105

  20. 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

  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. 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.

  4. 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

    2011-01-01

    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. PMID:21760573

  5. 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. PMID:27582638

  6. 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

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

    NASA Astrophysics Data System (ADS)

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

    2013-03-01

    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.

  8. 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.

  9. 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

    2016-05-01

    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. PMID:27058739

  10. The Photochemical Isomerization of Maleic to Fumaric Acid: An Undergraduate Organic Chemistry Experiment.

    ERIC Educational Resources Information Center

    Castro, Albert J.; And Others

    1983-01-01

    Describes an undergraduate organic chemistry experiment on the photochemical isomerization of maleic to fumaric acid. Background information, chemical reactions involved, and experimental procedures are included. (JN)

  11. 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.

  12. 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. PMID:25830560

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

    PubMed

    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. PMID:27272323

  14. Slow and stored light by photo-isomerization induced transparency in dye doped chiral nematics.

    PubMed

    Wei, D; Bortolozzo, U; Huignard, J P; Residori, S

    2013-08-26

    Decelerating and stopping light is fundamental for optical processing, high performance sensor technologies and digital signal treatment, many of these applications relying on the ability of controlling the amplitude and phase of coherent light pulses. In this context, slow-light has been achieved by various methods, as coupling light into resonant media, Brillouin scattering in optical fibers, beam coupling in photorefractive and liquid crystal media or engineered dispersion in photonic crystals. Here, we present a different mechanism for slowing and storing light, which is based on photo-isomerization induced transparency of azo-dye molecules hosted in a chiral liquid crystal structure. Sharp spectral features of the medium absorption/dispersion, and the long population lifetime of the dye metastable state, enable the storage of light pulses with a significant retrieval after times much longer than the medium response time. PMID:24105502

  15. Trivalent nickel. The quinone oximate family: synthesis and redox regulation of isomerism and ligand redistribution

    SciTech Connect

    Ray, D.; Chakravorty, A.

    1988-09-21

    The synthesis of the tris chelates Ni/sup III/(RQ)/sub 3/ by electrooxidation of Ni/sup II/(RQ)/sub 3/- (HRQ = quinone monoximes) is reported. These complexes have afforded a unique opportunity for voltammetric and spectroscopic examination of geometric isomerism and isomer preferences of the two oxidation states of nickel in a N/sub 2/O/sub 3/ environment. A redox-driven ligand redistribution reaction that furnishes Ni(RQ)/sub 3/ following electrooxidation of Ni/sup II/(RQ)/sub 3/(N,N) to Ni/sup III/(RQ)/sub 2/(N,N)/sup +/, where N,N represents amine coordination is reported. The effects of geometric structure, substituents, and ligands on the Ni(III)-Ni(II) reduction potential in Ni(RQ)/sub 3/ and Ni(RQ)/sub 2/(N,N)/sup +/ are noted. 29 references, 5 figures, 4 tables.

  16. 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. PMID:24629938

  17. 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

    2015-01-01

    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. PMID:26569203

  18. 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.

  19. Isostructuralism among bridge-flipped' isomeric benzylideneanilines and phenylhydrazones.

    PubMed

    Ojala, William H; Smieja, Jonathan M; Spude, Jill M; Arola, Trina M; Kuspa, Marika K; Herrera, Nell; Ojala, Charles R

    2007-06-01

    Bridge-flipped' isomers may be defined as pairs of molecules related by a reversal of a bridge of atoms connecting two major parts of the individual molecules. This kind of isomerism is commonly found among benzylideneanilines and phenylhydrazones. Isostructural pairs might be suitable for co-crystallization and are thus useful in the preparation of new solid materials. Although most of the examples of bridge-flipped isomeric benzylideneanilines and phenylhydrazones in the crystallographic literature are not isostructural, a small number of isostructural pairs have been reported by previous workers. This paper describes the molecular and crystal structures of four pairs of bridge-flipped isomers: two isostructural phenylhydrazones, (E)-2-bromobenzaldehyde 4-cyanophenylhydrazone (I) and (E)-4-cyanobenzaldehyde 2-bromophenylhydrazone (II); two pairs of isostructural benzylideneanilines, N-(2-trifluoromethylbenzylidene)-2-methylaniline (III) and N-(2-methylbenzylidene)-2-trifluoromethylaniline (IV), and N-(2-bromobenzylidene)-2-methylaniline (V) and N-(2-methylbenzylidene)-2-bromoaniline (VI); and a pair of benzylideneanilines with closely similar unit-cell dimensions but different packing arrangements, N-(4-methylbenzylidene)-4-cyanoaniline (VII) and N-(4-cyanobenzylidene)-4-methylaniline (VIII). The structure of (V) is disordered. The packing arrangement of (VIII) resembles that of the chloro-/methyl-substituted benzylideneanilines MBZCLA/MBZCLB [N-(4-methylbenzylidene)-4-chloroaniline and N-(4-chlorobenzylidene)-4-methylaniline]. Although intermolecular hydrogen bonding plays a part in the isostructuralism of the two phenylhydrazones, the other examples of isostructuralism occur in the absence of similar, relatively strong intermolecular interactions. PMID:17507762

  20. 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. PMID:25600485

  1. Quantum theory of rotational isomerism and Hill equation

    SciTech Connect

    Ugulava, A.; Toklikishvili, Z.; Chkhaidze, S.; Abramishvili, R.; Chotorlishvili, L.

    2012-06-15

    The process of rotational isomerism of linear triatomic molecules is described by the potential with two different-depth minima and one barrier between them. The corresponding quantum-mechanical equation is represented in the form that is a special case of the Hill equation. It is shown that the Hill-Schroedinger equation has a Klein's quadratic group symmetry which, in its turn, contains three invariant subgroups. The presence of these subgroups makes it possible to create a picture of energy spectrum which depends on a parameter and has many merging and branch points. The parameter-dependent energy spectrum of the Hill-Schroedinger equation, like Mathieu-characteristics, contains branch points from the left and from the right of the demarcation line. However, compared to the Mathieu-characteristics, in the Hill-Schroedinger equation spectrum the 'right' points are moved away even further for some distance that is the bigger, the bigger is the less deep well. The asymptotic wave functions of the Hill-Schroedinger equation for the energy values near the potential minimum contain two isolated sharp peaks indicating a possibility of the presence of two stable isomers. At high energy values near the potential maximum, the height of two peaks decreases, and between them there appear chaotic oscillations. This form of the wave functions corresponds to the process of isomerization.

  2. On the isomerization of ent-kaurenic acid.

    PubMed

    Rojas, Julio; Aparicio, Rosa; Villasmil, Thayded; Peña, Alexis; Usubillaga, Alfredo

    2011-07-01

    Kaurenic acid (1a) is a tetracyclic diterpene that has an exocyclic double bond at delta16. Isokaurenic acid (2a) has an endocyclic delta15double bond. This compound has been isolated from Espeletia tenore (Espeletinae), a resinous plant from the Venezuelan Andes, but its occurrence is rare. In order to obtain a larger amount of 2a, the isomerization of la, which is easily obtained from other Espeletinae, was tried. Kaurenic acid methyl ester (1b) was treated with dil. HCl in CH3Cl/EtOH, after 6 h under reflux a yield of 41.5% isokaurenic acid methyl ester (2b) was obtained but 35.7% 16alpha-ethoxy-kauran-19-oic acid methyl ester (3b) had formed as a byproduct. Treating 1b with CF3COOH in refluxing CH2Cl2 permitted to obtain a yield of 66.6% of 2b in 4 h and only traces of 16alpha-hydroxy-kauran-19-oic acid methyl ester (3a) as a byproduct. Both isomers were separated on a silica gel column impregnated with 20% AgNO3. Treating 2b with KOH in refluxing DMSO yielded pure isokaurenic acid, no back isomerization was observed. PMID:21834227

  3. 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.

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

    Technology Transfer Automated Retrieval System (TEKTRAN)

    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...

  5. 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.

  6. 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

  7. cis-to-trans isomerization of azobenzene investigated by using thin films of metal-organic frameworks.

    PubMed

    Yu, Xiaojuan; Wang, Zhengbang; Buchholz, Maria; Füllgrabe, Nena; Grosjean, Sylvain; Bebensee, Fabian; Bräse, Stefan; Wöll, Christof; Heinke, Lars

    2015-09-21

    The activation barrier for cis-to-trans isomerization is a key parameter for governing the properties of photoswitchable molecules. This quantity can be computed by using theoretical methods, but experimental determination is not straightforward. Photoswitchable molecules typically do not change their conformation in the pure crystalline state. When the molecules are in solution, the switching is affected by the viscosity and polarity of the solvent and when embedded in polymers, the conformational change is affected by the polymer matrix. Here, we describe a novel approach where the photoswitchable group is integrated in a highly crystalline, porous molecular framework. Sufficiently large pore sizes in such metal-organic frameworks, MOFs, allow unhindered switching and the strictly periodic structure of the lattice eliminates virtually all contributions from inhomogeneities. Using IR spectroscopy to probe the conformational state of azobenzene, the energy barrier separating the cis and the trans state could be determined by an Arrhenius analysis of the data accumulated in a temperature regime between 314 K and 385 K. The result, 1.09 ± 0.09 eV, is in very good agreement with the activation energy reported for the thermal cis-to-trans isomerization of free azobenzene as computed by DFT calculations. PMID:26255748

  8. 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.

  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. Influence of isomerization on nonlinear optical properties of molecules.

    PubMed

    Kinnibrugh, T; Bhattacharjee, S; Sullivan, P; Isborn, C; Robinson, B H; Eichinger, B E

    2006-07-13

    The influence of rotational and geometrical isomerism on the nonlinear optical (NLO) properties, specifically the first-order hyperpolarizability beta, of chromophores of current interest has been investigated with density functional theory (DFT). In the first of this two-part study, the rotational isomerism of a linear chromophore was explored. Calculation of the torsion potentials about two of the rotatable and conformation-changing single bonds in a chromophore demonstrated the near equality of the molecular energies at 0 degrees and 180 degrees rotational angles. To explore the consequences of this near conformational energy degeneracy to NLO behavior, the eight low energy rotational isomers of FTC [Robinson, B. H.; et al. Chem. Phys. 1999, 245, 35] were investigated. This study provides the first-reported DFT-based calculation of the statistical mechanical average of beta over the conformational space of a molecule having substantial nonlinear optical behavior. The influence of the solvent reaction field on rotameric populations and on the beta tensor is reported. In the second part, two molecules having two donors and two acceptors bonded respectively in ortho and meta positions on a central benzene ring are shown to have substantially different beta tensors. These two so-called molecular Xs have different highest occupied molecular orbital to lowest unoccupied molecular orbital (HOMO-LUMO) distributions, and consistent with expectations, it is found that the larger beta(zzz) is associated with a large spatial asymmetry between the HOMOs and LUMOs. Large hyperpolarizability correlates with the HOMO concentrated on the donor groups and the LUMO on the acceptor groups. PMID:16821878

  11. 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.

  12. Cross sections and isomeric cross-section ratios in the interactions of fast neutrons with isotopes of mercury

    SciTech Connect

    Al-Abyad, M.; Sudar, S.; Qaim, S. M.; Comsan, M.N.H.

    2006-06-15

    Excitation functions were measured for the reactions {sup 196}Hg(n, 2n){sup 195}Hg{sup m,g},{sup 198}Hg(n, 2n){sup 197}Hg{sup m,g},{sup 204}Hg(n, 2n){sup 203}Hg,{sup 198}Hg(n,p){sup 198}Au{sup g}, and {sup 199}Hg(n,p){sup 199}Au over the neutron energy range of 7.6-12.5 MeV. Quasimonoenergetic neutrons were produced via the {sup 2}H(d,n){sup 3}He reaction using a deuterium gas target at the Juelich variable energy compact cyclotron CV 28. Use was made of the activation technique in combination with high-resolution, high-purity Ge detector {gamma}-ray spectroscopy. All the data were measured for the first time over the investigated energy range. The transition from the present low-energy data to the literature data around 14 MeV is generally good. Nuclear model calculations using the codes STAPRE and EMPIRE-2.19, which employ the statistical and precompound model formalisms, were undertaken to describe the formation of both the isomeric and ground states of the products. The total reaction cross section of a particular channel is reproduced fairly well by the model calculations, with STAPRE giving slightly better results. Regarding the isomeric cross sections, the agreement between the experiment and theory is only in approximate terms. A description of the isomeric cross-section ratio by the model was possible only with a very low value of {eta}, i.e., the {theta}{sub eff}/{theta}{sub rig} ratio.

  13. Photochromism of halorhodopsin. cis/trans isomerization of the retinal around the 13-14 double bond.

    PubMed

    Lanyi, J K

    1986-10-25

    The isomeric composition of retinal in membrane-bound and in purified but detergent-free, dark-adapted halorhodopsin was found to be about 70% 13-cis and 30% all-trans. Any illumination increased the all-trans content relative to the dark-adapted state, but blue illumination shifted the isomeric composition more toward all-trans while red illumination of blue-adapted samples shifted it more toward 13-cis. In the presence of chloride this photoisomerization caused the kind of photochromic behavior reported earlier in Smith, S. O., Marvin, M. J., Bogomolni, R. A., and Mathies, R. A. (1984) J. Biol. Chem. 259, 12326-12329, i.e. blue light caused the absorption maximum to move toward longer wavelengths and red light reversed the shift. Only the all-trans chromophore exhibited the complete photocycle described earlier in detergent-solubilized halorhodopsin, and this was the form that could be associated with light-driven chloride transport activity in cell envelope vesicles. In the absence of chloride the spectroscopic changes caused by illumination were much smaller. Reconstitution of bleached preparations with 13-cis- and all-trans-retinal, in the presence and absence of chloride, confirmed that the difference between the absorption maxima of the two isomeric forms of the chromophore is affected by chloride: 13-cis-halorhodopsin absorbs at about 567-568 nm with and without chloride, and the all-trans pigment absorbs near 568 nm in the absence of chloride, but at 578 nm in its presence. The simplest explanation of this finding is that most of the red-shift which accompanies the 13-cis----all-trans transition originates from electrostatic interaction of the retinal with chloride bound in its vicinity. PMID:3771521

  14. Homogeneous hydrogenation and isomerization of 1-octene catalyzed by nickel(II) complexes with bidentate diarylphosphane ligands.

    PubMed

    Mooibroek, Tiddo J; Wenker, Erica C M; Smit, Wietse; Mutikainen, Ilpo; Lutz, Martin; Bouwman, Elisabeth

    2013-07-15

    A systematic library of 24 nickel(II) complexes with bidentate diphosphane ligands was synthesized, and the solid-state structures of five of them were determined with X-ray crystallography. The compounds C1-C3 are common P2Ni(II)X2-type complexes, while C4 contains a unique [P2Ni(II)(NH3)(OAc)](+) square-planar structure with a P2NO donor set and C5 constitutes a rare [(P2Ni(II))2(μ-OH)2](2+) dinuclear compound. The catalytic activity of all complexes was tested in the hydrogenation and/or isomerization of 1-octene in a CH2Cl2/CH3OH reaction medium. Catalyst precursors bearing ligands with o-alkoxy aryl rings selectively hydrogentate 1-octene to n-octane, while catalytic systems comprising ligands without the o-alkoxy functionality selectively isomerize the substrate to a mixture of internal alkenes, mostly cis- and trans-2-octene. The conversion is enhanced by equipping the ligand aryl rings with electron-donating alkoxy groups, by increasing the steric bulk of the backbone and/or the aryl rings, by employing relatively noncoordinating anions, and by adding a base as the cocatalyst. Using the compound [Ni(L3X)I2] as the catalyst precursor and upon application of standard hydrogenation conditions, full conversion of the substrate was achieved in 1 h to isomerization products only (TON = 1940). When a catalytic amount of the base is added, a similar result is obtained even in the absence of H2. A maximum TON of 4500 in 1 h with 96% selectivity for n-octane was achieved by employing [Ni(oMeO-L3X)(NH3)(OAc)]PF6 as the catalyst precursor. PMID:23822166

  15. Femtosecond spectroscopy of a 13-demethylrhodopsin visual pigment analogue: The role of nonbonded interactions in the isomerization process

    SciTech Connect

    Wang, Q.; Shank, C.V.; Kochendoerfer, G.G.; Mathies, R.A.; Schoenlein, R.W.; Verdegem, P.J.E.; Lugtenburg, J.

    1996-10-24

    The photoisomerization reaction of the visual pigment analogue 11-cis-13-demethylrhodopsin is investigated using femtosecond pump-probe techniques. Following excitation with a 40-fs pump pulse at 500 nm, differential trasnsient absorption spectra are measured from 470 to 560 nm using a 10-fs probe pulse centered at 500 nm and from 560 to 650 nm using a 10-fs probe pulse centered at 620 nm. The persistence of the excited-state absorption, the recovery kinetics of the ground-state bleach, and the formation time of the photoproduct absorption all indicate that this photoisomerization reaction is complete on the 400-fs time scale. Comparison of the reaction dynamics of 11-cis-rhodopsin with 11-cis-13-demethylrhodopsin suggests that the removal of the nonbonded steric intersection between the C{sub 13}-methyl group and the C{sub 10}-hydrogen atom slows down the initial torsional dynamics and that this in turn results in a lower isomerization quantum yield and a slower overall reaction time. Our results support the hypothesis that the quantum yield and the speed of the isomerization reaction are coupled according to a dynamic potential-sulfate crossing mechanism. 27 refs., 5 figs.

  16. 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.

  17. trans- cis Isomerism and acylimine formation in DsRed chromophore models: Intrinsic rotation barriers

    NASA Astrophysics Data System (ADS)

    Olsen, Seth; Smith, Sean C.

    2006-07-01

    The chromophore of the red fluorescent protein DsRed contains an acylimine substituent to a GFP-like chromophore structure. The acylimine is formed from the trans peptide linkage between residues F65 and Q66 in immature DsRed, but has a cis configuration in the mature protein. The relationship between acylimine formation and trans- cis isomerization is unresolved. We have calculated bond rotation profiles for models of mature and immature DsRed chromophores using B3LYP DFT. The isomerization barrier is substantially reduced in acylimine-substituted models, providing prima facie evidence that acylimine formation precedes trans- cis isomerization in DsRed chromophores.

  18. Exploitation of solar energy storage systems. Valence isomerization between norbornadiene and quadricyclane derivatives

    SciTech Connect

    Maruyama, K.; Teraka, K.; Yamamoto, Y.

    1981-01-01

    Use of copper(I)-nitrogen ligand catalysts such as Ph/sub 3/PCuCl.bpy, Ph/sub 3/PCuCl.phen, Ph/sub 3/PCuCl.phtha, and Ph/sub 3/PCuBr.py enables the photochemical isomerization of norbornadiene to quadricyclane to be performed at a longer wavelength than 350 nm, at which CuCl catalyst itself cannot induce such an isomerization. Among the norbornadiene derivatives bearing various chromophores, 3-(phenylcarbamoyl)norbornadiene-2-carboxylic acid undergoes a facile and quantitative isomerization into the corresponding quadricyclane derivative in sunlight. The back-isomerization of quadricyclane to 3-(phenylcarbamoyl)norbornadiene-2-carboxylic acid proceeds quantitatively by use of catalytic amounts of Rh/sub 2/(CO)/sub 4/Cl/sub 2/.

  19. Fuel properties of heptadecene isomers prepared via tandem isomerization-decarboxylation of oleic acid

    Technology Transfer Automated Retrieval System (TEKTRAN)

    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...

  20. 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.

  1. "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.

  2. Vibrational predissociation and vibrationally induced isomerization of 3-aminophenol-ammonia.

    PubMed

    Heid, Cornelia G; Merrill, Wyatt G; Case, Amanda S; Crim, F Fleming

    2015-01-01

    We investigate the vibrational predissociation dynamics of the hydrogen-bonded 3-aminophenol-ammonia cluster (3-AP-NH3) in the OH and NH stretching regions. Vibrational excitation provides enough energy to dissociate the cluster into its constituent 3-AP and NH3 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 NH3 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(2) + 10b(2) state of the cis-3-AP isomer shows that vibrational excitation is driving the isomerization of the trans-3-AP-NH3 isomer to the cis-3-AP-NH3 isomer in the course of the dissociation. PMID:25573564

  3. 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.

  4. Enzyme-like effect of metmyoglobin on the thermal cis-trans isomerization of stilbazolium betaine.

    PubMed

    Pastukhov, A V; Vogel, V R; Kotelnikov, A I

    2000-06-01

    A photochromic compound, stilbazolium betaine M, when associated with metmyoglobin undergoes an accelerated thermal cis-trans isomerization. A study of the pH and ionic strength dependence of the isomerization reaction rate of the photochrome associated with metmyoglobin was performed. A comparative investigation of the reaction carried out in the presence of three proteins, metmyoglobin, apomyoglobin, and human albumin, indicates a specific influence of the heme pocket environment on the reaction. Possible mechanisms of the reaction acceleration are considered. PMID:10907741

  5. Iridium complexes of new NCP pincer ligands: catalytic alkane dehydrogenation and alkene isomerization.

    PubMed

    Jia, Xiangqing; Zhang, Lei; Qin, Chuan; Leng, Xuebing; Huang, Zheng

    2014-09-28

    Iridium complexes of novel NCP pincer ligands containing pyridine and phosphinite arms have been synthesized. One Ir complex shows good catalytic activity for alkane dehydrogenation, and all complexes are highly active for olefin isomerization. A combination of the Ir complex and a (PNN)Fe pincer complex catalyzes the formation of linear alkylboronates selectively from internal olefins via sequential olefin isomerization-hydroboration. PMID:25101950

  6. Isomerization of alkanes on sulfated zirconia: Promotion by Pt and by adamantyl hydride transfer species

    SciTech Connect

    Iglesia, E.; Soled, S.L.; Kramer, G.M. )

    1993-11-01

    The work shows that hydride transfer species, such as adamantane, increase isomerization rates and inhibit C-C scission reactions. n-Heptane isomerization rates show positive hydrogen kinetic orders, suggesting that the reaction proceeds on Pt/ZrO[sub 2]-SO[sub 4] via chain transfer pathways, in which carbenium ions propagate, after a chain initiation step involvings loss of hydrogen from alkanes, by hydride transfer from neutral species to carbonations. These pathways contrast with those involved in the bifunctional (metal-acid) catalytic sequences usually required for alkane isomerization, in which metal sites catalyze alkane dehydrogenation and acid sites catalyze skeletal rearrangements of alkenes. Rate-limiting hydride transfer steps are consistent with the strong influence of molecular hydride transfer agents such as adamantane, which act as co-catalysts and increase isomerization rate and selectivity. The addition of small amounts of adamantane (0.1-0.8 wt%) to n-heptane increases isomerizations rates by a factor of 3 and inhibits undesirable cracking reactions. Adamantane increases hydride transfer and carbenium ion termination rates, thus reducing the surface residence time required for a catalytic turnover. As a result, desorption occurs before secondary cracking of isomerized carbenium ions. Less effective hydride transfer agents (n-alkanes, isoalkanes) also increase n-alkanes isomerization rate and selectivity, but require much higher concentrations than adamantane. Dihydrogen also acts as a hydride source in alkane isomerization catalysis, but it requires the additional presence of metals or reducible oxides, which catalyze H[sub 2] dissociation and the formation of hydridic and protonic forms of hydrogen. 40 refs., 10 figs., 4 tabs.

  7. Role of the protein cavity in phytochrome chromoprotein assembly and double-bond isomerization: a comparison with model compounds.

    PubMed

    Rohmer, Thierry; Lang, Christina; Gärtner, Wolfgang; Hughes, Jon; Matysik, Jörg

    2010-01-01

    Difference patterns of (13)C NMR chemicals shifts for the protonation of a free model compound in organic solution, as reported in the literature (M. Stanek, K. Grubmayr [1998] Chem. Eur. J.4, 1653-1659), were compared with changes in the protonation state occurring during holophytochrome assembly from phycocyanobilin (PCB) and the apoprotein. Both processes induce identical changes in the NMR signals, indicating that the assembly process is linked to protonation of the chromophore, yielding a cationic cofactor in a heterogeneous, quasi-liquid protein environment. The identity of both difference patterns implies that the protonation of a model compound in solution causes a partial stretching of the geometry of the macrocycle as found in the protein. In fact, the similarity of the difference pattern within the bilin family for identical chemical transformations represents a basis for future theoretical analysis. On the other hand, the change of the (13)C NMR chemical shift pattern upon the Pr --> Pfr photoisomerization is very different to that of the free model compound upon ZZZ --> ZZE photoisomerization. Hence, the character of the double-bond isomerization in phytochrome is essentially different from that of a classical photoinduced double-bond isomerization, emphasizing the role of the protein environment in the modulation of this light-induced process. PMID:20492561

  8. 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

  9. Isomerization of 11-cis-retinol to all-trans-retinol in bovine rod outer segments.

    PubMed

    Shimizu, T; Ishiguro, S; Tamai, M

    1998-05-01

    It is known that exogenous 11-cis-retinol inhibits the recovery of photosensitivity of bleached rod outer segments (ROS) and 11-cis-retinol exists in the interphotorecepter matrix. We examined the conversion of 11-cis-retinol with bovine ROS. ROS was incubated with 11-cis-retinol under dim red light. Retinoids were extracted from the reaction mixture with hexane and analyzed by HPLC coupled with a fluorescence spectrophotometer. Isomerization of 11-cis-retinol to all-trans-retinol was observed in the presence of ROS. This isomerization was not suppressed by heat treatment and did not have stereospecificity. In addition, we incubated purified rhodopsin and phospholipids extracted from ROS with 11-cis-retinol. Rhodopsin was found to isomerize 11-cis-retinol to all-trans-retinol as well as ROS, but phospholipids did not. In contrast, the phospholipids inhibited the isomerization of 11-cis-retinol to all-trans-retinol by the purified rhodopsin. Commercially available phospholipids, especially phosphatidylserine, also inhibited the isomerization. Our results suggest that rhodopsin has activity for the isomerization of 11-cis-retinol to all-trans-retinol and may play an important role in the detoxification of 11-cis-retinol in the ROS. PMID:9562631

  10. 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

  11. Photochemical Isomerization and Topochemical Polymerization of the Programmed Asymmetric Amphiphiles.

    PubMed

    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

  12. Photochemical generation, isomerization, and oxygenation of stilbene cation radicals

    SciTech Connect

    Lewis, F.D.; Bedell, A.M.; Dykstra, R.E.; Elbert, J.E. ); Gould, I.R.; Farid, S. )

    1990-10-24

    The cation radicals of cis- and trans-stilbene and several of their ring-substituted derivatives have been generated in solution directly by means of pulsed-laser-induced electron transfer to singlet cyanoanthracenes or indirectly via electron transfer from biphenyl to the singlet cyanoanthracene followed by secondary electron transfer from the stilbenes to the biphenyl cation radical. Transient absorption spectra of the cis- and trans-stilbene cation radicals generated by secondary electron transfer are similar to those previously obtained in 77 K matrices. Quantum yields for radical ion-pair cage escape have been measured for direct electron transfer from the stilbenes to three neutral and one charged singlet acceptor. These values increase as the ion-pair energy increases due to decreased rate constants for radical ion-pair return electron transfer, in accord with the predictions of Marcus theory for highly exergonic electron transfer. Cage-escape efficiencies are larger for trans- vs cis-stilbene cation radicals, possibly due to the greater extent of charge delocalization in the planar trans vs nonpolar cis cation radicals. Cage-escape stilbene cation radicals can initiate a concentration-dependent one way cis- {yields} trans-stilbene isomerization reaction.

  13. Isomerization and fragmentation pathways of 1,2-azaborine.

    PubMed

    Edel, Klara; Fink, Reinhold F; Bettinger, Holger F

    2016-01-01

    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. PMID:26418051

  14. 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.

  15. 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.

  16. 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

  17. Thiocyanate linkage isomerism in a ruthenium polypyridyl complex.

    PubMed

    Brewster, Timothy P; Ding, Wendu; Schley, Nathan D; Hazari, Nilay; Batista, Victor S; Crabtree, Robert H

    2011-12-01

    Ruthenium polypyridyl complexes have seen extensive use in solar energy applications. One of the most efficient dye-sensitized solar cells produced to date employs the dye-sensitizer N719, a ruthenium polypyridyl thiocyanate complex. Thiocyanate complexes are typically present as an inseparable mixture of N-bound and S-bound linkage isomers. Here we report the synthesis of a new complex, [Ru(terpy)(tbbpy)SCN][SbF(6)] (terpy = 2,2';6',2''-terpyridine, tbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine), as a mixture of N-bound and S-bound thiocyanate linkage isomers that can be separated based on their relative solubility in ethanol. Both isomers have been characterized spectroscopically and by X-ray crystallography. At elevated temperatures the isomers equilibrate, the product being significantly enriched in the more thermodynamically stable N-bound form. Density functional theory analysis supports our experimental observation that the N-bound isomer is thermodynamically preferred, and provides insight into the isomerization mechanism. PMID:22066656

  18. Full-dimensional quantum dynamics study of vinylidene-acetylene isomerization: a scheme using the normal mode Hamiltonian.

    PubMed

    Ren, Yinghui; Li, Bin; Bian, Wensheng

    2011-02-14

    Full-dimensional quantum dynamics calculations of vinylidene-acetylene isomerization are performed and the state-specific resonance decay lifetimes of vinylidene(-d(2)) are computed. The theoretical scheme is a combination of several methods: normal coordinates are chosen to describe the nuclear motion of vinylidene, with both the parity and permutation symmetry exploited; phase space optimization in combination with physical considerations is used to generate an efficient discrete variable representation; the reaction coordinate is defined by us according to the three most relevant normal coordinates, along which a kind of optimal complex absorbing potential is imposed; the preconditioned inexact spectral transform method combined with an efficient preconditioner is employed to extract the energies and lifetimes of vinylidene. The overall computation is efficient. The computed energy levels generally agree with experiment well, and several state-specific lifetimes are reported for the first time. PMID:21186383

  19. Overtone-induced dissociation and isomerization dynamics of the hydroxymethyl radical (CH2OH and CD2OH). II. Velocity map imaging studies.

    PubMed

    Ryazanov, M; Rodrigo, C; Reisler, H

    2012-02-28

    The dissociation of the hydroxymethyl radical, CH(2)OH, and its isotopolog, CD(2)OH, following excitation in the 4ν(1) region (OH stretch overtone, near 13,600 cm(-1)) was studied using sliced velocity map imaging. A new vibrational band near 13,660 cm(-1) arising from interaction with the antisymmetric CH stretch was discovered for CH(2)OH. In CD(2)OH dissociation, D atom products (correlated with CHDO) were detected, providing the first experimental evidence of isomerization in the CH(2)OH ↔ CH(3)O (CD(2)OH ↔ CHD(2)O) system. Analysis of the H (D) fragment kinetic energy distributions shows that the rovibrational state distributions in the formaldehyde cofragments are different for the OH bond fission and isomerization pathways. Isomerization is responsible for 10%-30% of dissociation events in all studied cases, and its contribution depends on the excited vibrational level of the radical. Accurate dissociation energies were determined: D(0)(CH(2)OH → CH(2)O + H) = 10,160 ± 70 cm(-1), D(0)(CD(2)OH → CD(2)O + H) = 10,135 ± 70 cm(-1), D(0)(CD(2)OH → CHDO + D) = 10,760 ± 60 cm(-1). PMID:22380040

  20. 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. PMID:23800193

  1. 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. PMID:23554234

  2. The mechanism of sugar phosphate isomerization by glucosamine 6-phosphate synthase.

    PubMed Central

    Teplyakov, A.; Obmolova, G.; Badet-Denisot, M. A.; Badet, B.

    1999-01-01

    Glucosamine 6-phosphate synthase converts fructose-6P into glucosamine-6P or glucose-6P depending on the presence or absence of glutamine. The isomerase activity is associated with a 40-kDa C-terminal domain, which has already been characterized crystallographically. Now the three-dimensional structures of the complexes with the reaction product glucose-6P and with the transition state analog 2-amino-2-deoxyglucitol-6P have been determined. Glucose-6P binds in a cyclic form whereas 2-amino-2-deoxyglucitol-6P is in an extended conformation. The information on ligand-protein interactions observed in the crystal structures together with the isotope exchange and site-directed mutagenesis data allow us to propose a mechanism of the isomerase activity of glucosamine-6P synthase. The sugar phosphate isomerization involves a ring opening step catalyzed by His504 and an enolization step with Glu488 catalyzing the hydrogen transfer from C1 to C2 of the substrate. The enediol intermediate is stabilized by a helix dipole and the epsilon-amino group of Lys603. Lys485 may play a role in deprotonating the hydroxyl O1 of the intermediate. PMID:10091662

  3. Ru-Zn heteropolynuclear complexes containing a dinucleating bridging ligand: synthesis, structure, and isomerism.

    PubMed

    Mognon, Lorenzo; Benet-Buchholz, Jordi; Rahaman, S M Wahidur; Bo, Carles; Llobet, Antoni

    2014-12-01

    Mononuclear complexes in- and out-[Ru(Cl)(trpy)(Hbpp)](+) (in-0, out-0; Hbpp is 2,2'-(1H-pyrazole-3,5-diyl)dipyridine and trpy is 2,2':6',2″-terpyridine) are used as starting materials for preparation of Ru-Zn heterodinuclear out-{[Ru(Cl)(trpy)][ZnCl2](μ-bpp)} (out-2) and heterotrinuclear in,in- and out,out-{[Ru(Cl)(trpy)]2(μ-[Zn(bpp)2])}(2+) (in-3, out-3) constitutional isomers. Further substitution of the Cl ligand from the former complexes leads to Ru-aqua out,out-{[Ru(trpy)(H2O)]2(μ-[Zn(bpp)2])}(4+) (out-4) and the oxo-bridged Ru-O-Ru complex in,in-{[Ru(III)(trpy)]2(μ-[Zn(bpp)2(H2O)]μ-(O)}(4+) (in-5). All complexes are thoroughly characterized by the usual analytical techniques as well as by spectroscopy by means of UV-vis, MS, and when diamagnetic NMR. CV and DPV are used to extract electrochemical information and monocrystal X-ray diffraction to characterize complexes out-2, in-3, out-3, and in-5 in the solid state. Complex out-3 photochemically isomerizes toward in-3, as can be observed by NMR spectroscopy and rationalized by density functional theory based calculations. PMID:25393055

  4. 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.

  5. Intramolecular interactions, isomerization and vibrational frequencies of two paracetamol analogues: A spectroscopic and a computational approach.

    PubMed

    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. PMID:26974474

  6. 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].

  7. 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.

  8. Intersubunit disulfide isomerization controls membrane fusion of human T-cell leukemia virus Env.

    PubMed

    Li, Kejun; Zhang, Shujing; Kronqvist, Malin; Wallin, Michael; Ekström, Maria; Derse, David; Garoff, Henrik

    2008-07-01

    Human T-cell leukemia virus (HTLV-1) Env carries a typical disulfide isomerization motif, C(225)XXC, in the C-terminal domain SU. Here we have tested whether this motif is used for isomerization of the intersubunit disulfide of Env and whether this rearrangement is required for membrane fusion. We introduced the C225A and C228A mutations into Env and found that the former but not the latter mutant matured into covalently linked SU-TM complexes in transfected cells. Next, we constructed a secreted Env ectodomain and showed that it underwent incubation-dependent intersubunit disulfide isomerization on target cells. However, the rearrangement was blocked by the C225A mutation, suggesting that C(225) carried the isomerization-active thiol. Still, it was possible to reduce the intersubunit disulfide of the native C225A ectodomain mutant with dithiothreitol (DTT). The importance of the CXXC-mediated disulfide isomerization for infection was studied using murine leukemia virus vectors pseudotyped with wild-type or C225A HTLV-1 Env. We found that the mutant Env blocked infection, but this could be rescued with DTT. The fusion activity was tested in a fusion-from-within assay using a coculture of rat XC target and transfected BHK-21 effector cells. We found that the mutation blocked polykaryon formation, but this could be reversed with DTT. Similar DTT-reversible inhibition of infection and fusion was observed when a membrane-impermeable alkylator was present during the infection/fusion incubation. We conclude that the fusion activity of HTLV-1 Env is controlled by an SU CXXC-mediated isomerization of the intersubunit disulfide. Thus, this extends the applicability of the isomerization model from gammaretroviruses to deltaretroviruses. PMID:18480461

  9. 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. PMID:25886024

  10. Identification of geometrical isomers and comparison of different isomeric samples of astaxanthin.

    PubMed

    Qiu, Dan; Wu, Yue-Chan; Zhu, Wen-Li; Yin, Hong; Yi, Long-Tao

    2012-09-01

    A high-performance liquid chromatographic (HPLC) analysis system for isomeric astaxanthin was developed. The separation system consisted of a C(30) column and an elution system of methanol/MTBE/water/dichloromethane (77:13:8:2, v/v/v/v). Using the combination of HPLC diode array detector and HPLC atmospheric pressure chemical ionization mass spectrometry, 11 geometrical isomers and 4 epoxides of astaxanthin were successfully identified. Referred to crystal, only isomerization with different degrees was found for solvent dissolving and iodine catalysis, while melting of astaxanthin caused isomerization, slight oxidation, and more noticeable polymerization confirmed by gel permeation chromatography. Chemical changes in isomeric samples all caused a decrease in UV content. The vibrational spectra (infrared and Raman) showed that epoxide was the only new functional group generated for melting. Changes of several key bands and formations of new bands were found in iodine catalysis and melting samples because of isomerization. Practical Application:  Eleven geometrical isomers and 4 epoxides, which were normally generated for solvent dissolving, iodine catalysis, and melting of astaxanthin, have been identified by C(30) -HPLC-MS technology. Furthermore, different samples were measured by gel permeation chromatography, UV, infrared, and Raman, based on the analysis of messages, the effect of each processing was well understood. PMID:22900833