Research and Development Services: Methods Development

DTIC Science & Technology

1982-07-23

At an applied potential of -1.15 volts, the minimum detectable amount was 500 ng, which was not very sensitive. From Hammett linear free energy... Equation 1, the value of N was optimized by using two columns. The other factors which can influence resolution are the capacity factor, k, and the

Linear free-energy relationships and the density functional theory: an analog of the hammett equation.

PubMed

Simón-Manso, Yamil

2005-03-10

Density functional theory has been applied to describe electronic substituent effects, especially in the pursuit of linear relationships similar to those observed from physical organic chemistry experiments. In particular, analogues for the Hammett equation parameters (sigma, rho) have been developed. Theoretical calculations were performed on several series of organic molecules in order to validate our model and for comparison with experimental results. The trends obtained by Hammett-like relations predicted by the model were found to be in qualitative agreement with the experimental data. The results obtained in this study suggest the applicability of similar correlation analysis based on theoretical methodologies that do not make use of empirical fits to experimental data can be useful in the study of substituent effects in organic chemistry.

Munitions Executive Summit 2010 Held in San Diego, California on February 8-10, 2010

DTIC Science & Technology

2010-02-10

INDUSTRIAL CAPABILITIES · Mr. Dick Hammett , President, Winchester Ammunition AMMUNITION ENTERPRISE CROSS SERVICE PANEL PANEL CHAIR: BG Jonathan...complacency 7 Aligning Commercial Industrial Capabilities with Munitions Requirements & Resources Dick Hammett , President, Winchester Ammunition...Immature – Quantum Dot FPAs maturing – Devices have been demonstrated under less than optimal conditions – Measured results equate to less than 0.1

Measurement of a linear free energy relationship one molecule at a time

PubMed Central

Rao, B. V.; Kwon, K.-Y.; Liu, A.; Bartels, L.

2004-01-01

A systematic study of the dehydrogenation of substituted thiophenols by controlled charge injection from the tip of a scanning tunneling microscope (STM) reveals a pronounced dependence of the reaction yield on the position and the chemical nature of the substituent. We evaluate the dehydrogenation rate of para-halo-substituted species within a linear free energy relationship, namely the Hammett equation. The resultant ρ value of 1.4 can faithfully predict the reaction rates of molecules that are meta-halo-substituted or para-methyl-substituted. The positive sign of ρ suggests a negatively charged transition state at the core of the STM-induced process, and the magnitude of the ρ value indicates that the presence of the substrate does not preclude substantial substituent effects. The applicability of the Hammett equation to single-molecule chemistry offers facile prediction of the rate of STM-based single-molecule chemistry in a field, which so far has been addressed by focusing on involved quantum-mechanical modeling of its underlying processes. PMID:15601774

Measurement of a linear free energy relationship one molecule at a time.

PubMed

Rao, B V; Kwon, K-Y; Liu, A; Bartels, L

2004-12-28

A systematic study of the dehydrogenation of substituted thiophenols by controlled charge injection from the tip of a scanning tunneling microscope (STM) reveals a pronounced dependence of the reaction yield on the position and the chemical nature of the substituent. We evaluate the dehydrogenation rate of para-halo-substituted species within a linear free energy relationship, namely the Hammett equation. The resultant rho value of 1.4 can faithfully predict the reaction rates of molecules that are meta-halo-substituted or para-methyl-substituted. The positive sign of rho suggests a negatively charged transition state at the core of the STM-induced process, and the magnitude of the rho value indicates that the presence of the substrate does not preclude substantial substituent effects. The applicability of the Hammett equation to single-molecule chemistry offers facile prediction of the rate of STM-based single-molecule chemistry in a field, which so far has been addressed by focusing on involved quantum-mechanical modeling of its underlying processes.

The Hammett relationship and reactions in the excited electronic state: hemithioindigo Z/E-photoisomerization.

PubMed

Cordes, Thorben; Schadendorf, Torsten; Priewisch, Beate; Rück-Braun, Karola; Zinth, Wolfgang

2008-01-31

The photochemical reaction dynamics of a set of photochromic compounds based on thioindigo and stilbene molecular parts (hemithioindigos, HTI) are presented. Photochemical Z/E isomerization around the central double bond occurs with time constants of 216 ps (Z --> E) and 10 ps (E --> Z) for a 5-methyl-hemithioindigo. Chemical substitution on the stilbene moiety causes unusually strong changes in the reaction rate. Electron-donating substituents in the position para to the central double bond (e.g., para-methoxy) strongly accelerate the reaction, while the reaction is drastically slowed by electron-withdrawing groups in this position (e.g., para-nitrile). We correlate the experimental data of seven HTI-compounds in a quantitative manner using the Hammett equation and present a qualitative explanation for the application of ground-state Hammett constants to describe the photoisomerization reaction.

Competition Experiments as a Means of Evaluating Linear Free Energy Relationships

ERIC Educational Resources Information Center

Mullins, Richard J.; Vedernikov, Andrei; Viswanathan, Rajesh

2004-01-01

The use of competition experiments as a means of evaluating linear free energy relationship in the undergraduate teaching laboratory is reported. The use of competition experiments proved to be a reliable method for the construction of Hammett plots with good correlation providing great flexibility with regard to the compounds and reactions that…

Mass Spectrometry in Organic Synthesis: Claisen-Schmidt Base-Catalyzed Condensation and Hammett Correlation of Substituent Effects

ERIC Educational Resources Information Center

Bain, Ryan M.; Pulliam, Christopher J.; Yan, Xin; Moore, Kassandra F.; Mu¨ller, Thomas; Cooks, R. Graham

2014-01-01

Undergraduate laboratories generally teach an understanding of chemical reactivity using bulk or semimicroscale experiments with product isolation and subsequent chemical and spectroscopic analysis. In this study students were exposed to mass spectrometry as a means of chemical synthesis as well as analysis. The ionization method used, paper…

Background of the Hammett equation as observed for isolated molecules: meta- and para-substituted benzoic acids.

PubMed

Exner, Otto; Böhm, Stanislav

2002-09-06

Fundamental model compounds for the Hammett equation, meta- and para-substituted benzoic acids, were investigated by the density functional theory at the B3LYP/6-311+G(d,p) level. Energies of 25 acids and of their anions were calculated in all possible conformations and from them the energies of the assumed mixture of conformers. Relative acidities correlated with the experimental gas-phase acidities almost within the experimental uncertainty, much more precisely than in the case of previous calculations at lower levels. Dissection of the substituent effects into those operating in the acid molecule and in the anion was carried out by means of isodesmic reactions starting from monosubstituted benzenes. Both effects are cooperating in the resulting effect on the acidity; those in the acid molecule are smaller but not negligible. They are also responsible for some deviations from the Hammett equation (through-resonance of para donor substituents) and for the weaker resonance in the acid molecule in meta derivatives; in the anions the inductive and resonance effects are almost equal. On the other hand, the cooperation of effects in the acid and in the anion makes the relative acidity more sensitive to electron withdrawing and is probably one of the reasons why the Hammett equation is so generally valid.

Amylase and Lipase Detection in Hemorrhaged Animals Treated with HBOC-201

DTIC Science & Technology

2011-01-01

Biopure Corp., Cambridge, MA, and Abbott Laboratories, Chicago, n.., respectively. We are thankful to Yao Yang and Mike Hammett for technical...amylase readings above baseline. Regression Equations : Amyl (%) = 1001J.0899 * HBOC-201 concentration (r = 0.993) for serum; Amyl (%) = 1000·0sss... Hammett , M., Asher, L., Philbin, N., Rice, J., Dong, F., Pearce, B., Flournoy, W., Nicholson, C., McCarron, R., and Freilich, D. (2005). Effects of bovine

Evaluating differences in the active-site electronics of supported Au nanoparticle catalysts using Hammett and DFT studies

NASA Astrophysics Data System (ADS)

Kumar, Gaurav; Tibbitts, Luke; Newell, Jaclyn; Panthi, Basu; Mukhopadhyay, Ahana; Rioux, Robert M.; Pursell, Christopher J.; Janik, Michael; Chandler, Bert D.

2018-03-01

Supported metal catalysts, which are composed of metal nanoparticles dispersed on metal oxides or other high-surface-area materials, are ubiquitous in industrially catalysed reactions. Identifying and characterizing the catalytic active sites on these materials still remains a substantial challenge, even though it is required to guide rational design of practical heterogeneous catalysts. Metal-support interactions have an enormous impact on the chemistry of the catalytic active site and can determine the optimum support for a reaction; however, few direct probes of these interactions are available. Here we show how benzyl alcohol oxidation Hammett studies can be used to characterize differences in the catalytic activity of Au nanoparticles hosted on various metal-oxide supports. We combine reactivity analysis with density functional theory calculations to demonstrate that the slope of experimental Hammett plots is affected by electron donation from the underlying oxide support to the Au particles.

Class Projects in Physical Organic Chemistry: The Hammett Equation

NASA Astrophysics Data System (ADS)

Marrs, Peter S.

2001-04-01

This paper provides a brief introduction to the Hammett equation. A laboratory experiment is described that requires students to determine the pKa of three para-substituted phenols through the use of UV-spectroscopy. A student's individual data are combined with other students' data to provide a class set. The students analyze the class set of data to determine whether sp or sp- is more appropriate for the reaction studied, and they also determine r for the reaction.

Mechanistic Comparison Between Pd-Catalyzed Ligand Directed C-H Chlorination and C-H Acetoxylation

PubMed Central

Stowers, Kara J.; Sanford, Melanie S.

2009-01-01

This communication describes detailed investigations of the mechanism of the Pd-catalyzed C-H chlorination and acetoxylation of 2-ortho-tolylpyridine. Under the conditions examined, both reactions proceed via rate limiting cyclopalladation. However, substrate and catalyst order as well as Hammett data indicate that the intimate mechanism of cyclopalladation differs significantly between PdCl2-catalyzed chlorination and Pd(OAc)2-catalyzed acetoxylation. PMID:19754074

Mechanistic Investigation of Molybdate-Catalysed Transfer Hydrodeoxygenation.

PubMed

Larsen, Daniel B; Petersen, Allan R; Dethlefsen, Johannes R; Teshome, Ayele; Fristrup, Peter

2016-11-07

The molybdate-catalysed transfer hydrodeoxygenation (HDO) of benzyl alcohol to toluene driven by oxidation of the solvent isopropyl alcohol to acetone has been investigated by using a combination of experimental and computational methods. A Hammett study that compared the relative rates for the transfer HDO of five para-substituted benzylic alcohols was carried out. Density-functional theory (DFT) calculations suggest a transition state with significant loss of aromaticity contributes to the lack of linearity observed in the Hammett study. The transfer HDO could also be carried out in neat PhCH 2 OH at 175 °C. Under these conditions, PhCH 2 OH underwent disproportionation to yield benzaldehyde, toluene, and significant amounts of bibenzyl. Isotopic-labelling experiments (using PhCH 2 OD and PhCD 2 OH) showed that incorporation of deuterium into the resultant toluene originated from the α position of benzyl alcohol, which is in line with the mechanism suggested by the DFT study. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Substituent effect on the oxidation of phenols and aromatic amines by horseradish peroxidase compound I.

PubMed

Job, D; Dunford, H B

1976-07-15

A stopped-flow kinetic study shows that the reduction rate of horseradish peroxidase compound I by phenols and aromatic amines is greatly dependent upon the substituent effect on the benzene ring. Morever it has been possible to relate the reduction rate constants of monosubstituted substrates by a linear free-energy relationship (Hammett equation). The correlation of log (rate constants) with sigma values (Hammett equation) and the absence of correlation with sigma+ values (Okamoto-Brown equation) can be explained by a mechanism of aromatic substrate oxidations, in which the substrate gives an electron to the enzyme compound I and simultaneously loses a proton. The analogy which has been made with oxidation potentials of phenols or anilines strengthens the view that the reaction is only dependent on the relative ease of oxidation of the substrate. The rate constant obtained for p-aminophenol indicates that a value of 2.3 X 10(8) M-1 S-1 probably approaches the diffusion-controlled limit for a bimolecular reaction involving compound I and an aromatic substrate.

Comparing the acidities of aqueous, frozen, and freeze-dried phosphate buffers: Is there a "pH memory" effect?

PubMed

Vetráková, Ľubica; Vykoukal, Vít; Heger, Dominik

2017-09-15

The concept of "pH memory" has been established in the literature for the correlation between the pH of a pre-lyophilization solution and the ionization state of freeze-dried powder (lyophile). In this paper, the concept of "pH memory" is explored for the system of an aqueous solution, a frozen solution, and a lyophile. Sodium and potassium phosphate buffers in the pH range of 5-9 were frozen and lyophilized with sulfonephthalein indicators as acidity probes, and their Hammett acidity functions were compared to the initial pH of the aqueous solution. The results show that the acidities of the lyophiles are somewhat changed compared to the initial pHs, but the acidities in the frozen state differ more substantially. The Hammett acidity functions of the frozen buffers were found to be markedly dissimilar from the initial pH, especially in the sodium phosphate frozen at 233K, where an increase in the initial pH led to a decrease in the Hammett acidity function of the frozen state at a certain pH range. The large acidification observed after freezing the sodium phosphate buffer was not detected in the lyophiles after the sample had been dried; the phenomenon is explained considering the formed crystals analyzed by X-ray powder diffraction. The results suggest that monitoring the final acidity of a lyophile is not sufficient to predict all the acidity changes throughout the whole lyophilization process. The importance of well-controlled freezing and lyophilization conditions follows from the results of the research. Copyright © 2017 Elsevier B.V. All rights reserved.

Removal of Noise from a Voice Signal by Synthesis

DTIC Science & Technology

1973-05-01

for 102.4 millisecond windows is about five times as great as the cost of computing for 25.6 millisecond windows. Hammett in his work on an adaptive...spectrum analysis vocoder, has examined the selection of data window widths in detail [18]. The solution Hammett used to optimize the trade off between...result is: n s(t) E Ri(t - i . T) i-1 In this equation n is the number of impulse responses under consideration, s(t) is the resulting synthetic signal

Stereochemical control factors in the Hantzsch thiazole synthesis: a Hammett substitution correlation analysis.

PubMed

Qiao, Q; So, S S; Goodnow, R A

2001-11-15

[reaction--see text] It is possible to correlate the distribution of stereochemical products produced during a Hantzsch thiazole synthesis according to the Hammett free-energy equation. This analysis confirms the presumed control of the rate of epimerization during thiazole formation due to stabilization of a cationic transition state intermediate during dehydration of the thiazoline ring system. In the chemical system under study, the stereochemical outcome of the reaction also appears to occur according to a kinetically controlled protonation of a thiazoline tautomer.

Evaluation of a novel electronic eigenvalue (EEVA) molecular descriptor for QSAR/QSPR studies: validation using a benchmark steroid data set.

PubMed

Tuppurainen, Kari; Viisas, Marja; Laatikainen, Reino; Peräkylä, Mikael

2002-01-01

A novel electronic eigenvalue (EEVA) descriptor of molecular structure for use in the derivation of predictive QSAR/QSPR models is described. Like other spectroscopic QSAR/QSPR descriptors, EEVA is also invariant as to the alignment of the structures concerned. Its performance was tested with respect to the CBG (corticosteroid binding globulin) affinity of 31 benchmark steroids. It appeared that the electronic structure of the steroids, i.e., the "spectra" derived from molecular orbital energies, is directly related to the CBG binding affinities. The predictive ability of EEVA is compared to other QSAR approaches, and its performance is discussed in the context of the Hammett equation. The good performance of EEVA is an indication of the essential quantum mechanical nature of QSAR. The EEVA method is a supplement to conventional 3D QSAR methods, which employ fields or surface properties derived from Coulombic and van der Waals interactions.

Calculation of Hammett Equation parameters for some N,N‧-bis (substituted-phenyl)-1,4-quinonediimines by density functional theory

NASA Astrophysics Data System (ADS)

Sein, Lawrence T.

2011-08-01

Hammett parameters σ' were determined from vertical ionization potentials, vertical electron affinities, adiabatic ionization potentials, adiabatic electron affinities, HOMO, and LUMO energies of a series of N, N' -bis (3',4'-substituted-phenyl)-1,4-quinonediimines computed at the B3LYP/6-311+G(2d,p) level on B3LYP/6-31G ∗ molecular geometries. These parameters were then least squares fit as a function of literature Hammett parameters. For N, N' -bis (4'-substituted-phenyl)-1,4-quinonediimines, the least squares fits demonstrated excellent linearity, with the square of Pearson's correlation coefficient ( r2) greater than 0.98 for all isomers. For N, N' -bis (3'-substituted-3'-aminophenyl)-1,4-quinonediimines, the least squares fits were less nearly linear, with r2 approximately 0.70 for all isomers when derived from calculated vertical ionization potentials, but those from calculated vertical electron affinities usually greater than 0.90.

Bond strengths of toluenes, anilines, and phenols: to hammett or not.

PubMed

Pratt, Derek A; DiLabio, Gino A; Mulder, Peter; Ingold, K U

2004-05-01

The Hammett equation correlates the effects of Y on many different chemical properties of YC(6)H(4)ZX families of compounds. One of the most surprising is that the Z-X bond dissociation enthalpy (BDE), a homolytic property, can be correlated for some 4-YC(6)H(4)ZX families with electrophilic substituent constants, sigma(p)(+)(Y), which were largely derived from the rates of the heterolytic S(N)1 solvolyses of para-substituted cumyl chlorides. Although there is no Hammett correlation of the C-X BDEs in 4-YC(6)H(4)CH(2)X (X = H, halide, OPh) families, there are good correlations of N-X BDEs with sigma(p)(+)(Y) in 4-YC(6)H(4)NHX (X = H, CH(3), OH, F) and excellent correlations of O-X BDEs with sigma(p)(+)(Y) in 4-YC(6)H(4)OX (X = H, CH(3), CH(2)Ph) families. The reasons for this varied behavior are discussed.

Hydroxamic acids as weak base indicators: protonation in strong acid media.

PubMed

García, B; Ibeas, S; Hoyuelos, F J; Leal, J M; Secco, F; Venturini, M

2001-11-30

The protonation equilibria of N-phenylbenzohydroxamic, benzohydroxamic, salicylhydroxamic, and N-p-tolylcinnamohydroxamic acids have been studied at 25 degrees C in concentrated sulfuric, hydrochloric, and perchloric acid media; the UV-vis spectral measurements were analyzed using the Hammett equation and the Bunnett-Olsen and excess acidity methods. The medium effects observed in the UV spectral curves were corrected with the Cox-Yates and vector analysis methods. The H(A) acidity function based on benzamides provided the best results. The range of variation of the solvation coefficient m is similar to that of amides, this indicating similar solvation requirements for amides and hydroxamic acids. For the same substrate, the observed variations of pK(BH)(+) with the mineral acid used was justified by formation of solvent-separated ion pairs; for the same mineral acid, the observed changes in pK(BH)(+) can be explained by the solvation of BH(+). The change of the pK(BH)(+) values was in reasonably good agreement with the sequence of the catalytic efficiency of the mineral acids used, HCl > H(2)SO(4) > HClO(4).

Study of gas-phase O-H bond dissociation enthalpies and ionization potentials of substituted phenols - Applicability of ab initio and DFT/B3LYP methods

NASA Astrophysics Data System (ADS)

Klein, Erik; Lukeš, Vladimír

2006-11-01

In this paper, the study of phenol and 37 compounds representing various ortho-, para-, and meta-substituted phenols is presented. Molecules and their radical structures were studied using ab initio methods with inclusion of correlation energy and DFT in order to calculate the O-H bond dissociation enthalpies (BDEs) and vertical ionization potentials (IPs). Calculated BDEs and IPs were compared with available experimental values to ascertain the suitability of used methods, especially for the description of the substituent induced changes in BDE and IP. MP2, MP3, and MP4 methods do not give reliable results, since they significantly underestimate substituent induced changes in BDE and do not reflect distinct effect of substituents related to para and meta position correctly. DFT/B3LYP method reflects the effect of substituents on BDE satisfactorily, though ΔBDEs are in narrower range than experimental values. BDE of phenol was calculated also using CCSD(T) method in various basis sets. Both, DFT and HF methods describe the effect of substituents on IP identically. However, DFT considerably underestimates individual values. HF method gives IPs in very good agreement with experimental data. Obtained results show that dependences of BDEs and IPs on Hammett constants of the substituents are linear. Linearity of DFT BDE vs. IP dependence is even better than the dependences on Hammett constants and obtained equations allow estimating of O-H BDEs of meta- and para-substituted phenols from calculated IPs.

Estimation of Hammett sigma constants of substituted benzenes through accurate density-functional calculation of core-electron binding energy shifts

NASA Astrophysics Data System (ADS)

Takahata, Yuji; Chong, Delano P.

For substituted benzenes such as (p-F-C6H4-Z), Linderberg et al. 1 demonstrated the validity of an equation similar to: ΔCEBE ≈ κσ, where ΔCEBE is the difference in core-electron binding energies (CEBEs) of the fluorinated carbon in p-F-C6H4-Z and that in FC6H5, the parameter κ is a function of the type of reaction, and σ is the Hammett substituent (σ) constant. In this work, CEBEs of ring carbon atoms for a series of para disubstituted molecules p-F-C6H4-Z were first calculated using Density Functional Theory (DFT) with the scheme ΔEKS (PW86-PW91)/TZP+Crel//HF/6-31G*. An average absolute deviation of 0.13 eV from experiment was obtained for the CEBEs. Then we performed a linear regression analysis in the form of Y = A+B*X for a plot of Hammett σp constants against calculated shifts ΔCEBEs (in eV) for the fluorinated carbon. The results were: A = -0.08 and B = 1.01, with correlation coefficient R = 0.973, standard deviation = 0.12, and P < 0.0001. The intercept A of the fitted line, close to zero, shows that the Hammett σp constant is proportional to the calculated ΔCEBEs. On the other hand, the slope B of the straight line gives an estimate of the parameter κ. Similar statistical correlations were obtained for the carbon atoms ortho and meta to the substituent Z.

Linear free energy study of ring-substituted aniline ozonation for developing treatment of aniline-based pesticide wastes.

PubMed

Pierpoint, A C; Hapeman, C J; Torrents, A

2001-08-01

The relative rate constants for the reaction of ozone were determined for several substituted anilines in aqueous solutions at pH 6.5 and 1.5. At pH 6.5, with the exception of m- and p-nitroaniline, the rate constants obey Hammett's equation: log(k(X)/k(H)) = rho sigma. The departure of m- and p-nitroaniline may be explained by direct conjugation of the reaction center. The commonly used sigma(p)(-) value of 1.27, which extends the range of applicability of the Hammett equation, was insufficient to account for the conjugation effects on ozonation of p-nitroaniline; rho = -1.48 (R = 0.973). Use of amine group atomic charge determinations significantly improved correlations: (k(X)/k(H)) = 48.7 delta - 18.2 (R = 0.996). A linear plot of Hammett constants versus relative rate data at pH 1.5 showed poor correlation: rho = 0.72 (R = 0.572). Poor correlation was similarly observed for amine group atomic charge determinations, suggesting varied reaction mechanisms.

Enantiodivergent Hydroboration Reactions of a Racemic Allenylsilane with Diisopinocampheylborane and Curtin-Hammett Controlled Double Asymmetric Crotylboration Reactions of (S)-E-α-phenyldimethylsilyl(ddiisopinocampheyl)-crotylborane

PubMed Central

Chen, Ming; Roush, William R.

2013-01-01

The enantiodivergent hydroboration reactions of racemic allenylsilane (±)-4 with (dIpc)2BH and subsequent crotylboration of achiral aldehydes with the product crotylborane (S)-E-5 at −78 °C provide (E)-δ-silyl-anti-homoallylic alcohols 6 in 71–89% yield and with 93–96% ee. Intriguingly, mismatched double asymmetric crotylboration reactions of enantioenriched chiral aldehydes 20 with (S)-E-5 proceed under Curtin-Hammett control to give anti-3-hydroxylcrotylsilanes 24 as the only products. PMID:24039304

Enantiodivergent hydroboration reactions of a racemic allenylsilane with diisopinocampheylborane and Curtin–Hammett controlled double asymmetric crotylboration reactions of (S)-E-αphenyldimethylsilyl(ddiisopinocampheyl)-crotylborane

PubMed Central

Chen, Ming; Roush, William R.

2013-01-01

The enantiodivergent hydroboration reactions of racemic allenylsilane (±)-4 with (dIpc)2BH and subsequent crotylboration of achiral aldehydes with the product crotylborane (S)-E-5 at −78 °C provide (E)-δ-silyl-anti-homoallylic alcohols 6 in 71–89% yield and with 93–96% ee. Intriguingly, mismatched double asymmetric crotylboration reactions of enantioenriched chiral aldehydes 20 with (S)-E-5 proceed under Curtin–Hammett control to give anti-β-hydroxylcrotylsilanes 24 as the only products. PMID:24068848

Regioselective Formation of α-Vinylpyrroles from the Ruthenium-Catalyzed Coupling Reaction of Pyrroles and Terminal Alkynes Involving C–H Bond Activation

PubMed Central

Gao, Ruili; Yi, Chae S.

2010-01-01

The cationic ruthenium catalyst, Ru3(CO)12/NH4PF6, was found to be highly effective for the intermolecular coupling reaction of pyrroles and terminal alkynes to give gem-selective α-vinylpyrroles. The carbon isotope effect on the α-pyrrole carbon and the Hammett correlation from a series of para-substituted N-arylpyrroles (ρ = −0.90) indicate a rate-limiting C–C bond formation step of the coupling reaction. PMID:20384382

Positron annihilation studies in solid substituted aromatic compounds

NASA Astrophysics Data System (ADS)

Oliveira, F. C.; Oliveira, A. M.; Donnici, C. L.; Machado, J. C.; Magalhães, W. F.; Windmöller, D.; Fulgêncio, F. H.; Souza, L. R.

2011-04-01

Positronium formation was investigated in benzene and naphthalene compounds with electron donating (sbnd NH2 and sbnd OH) and electron withdrawing (sbnd CN and sbnd NO2) substituents. The results exhibit an increase in the positronium formation yield whenever donating groups are bound to the ring and a decrease with withdrawing groups. These results can be attributed to the π-system electronic density variation in the aromatic ring. The amount of positronium obtained, I3 parameter, has been correlated with the Hammett (σ) and Brown-Okamoto (σp+) constants and adjusted through the modified Hammett equation, which employs the ratio I3/I3ϕ, yielding a satisfactory fit.

Verification of the electron/proton coupled mechanism for phenolic H-atom transfer using a triplet π,π ∗ carbonyl

NASA Astrophysics Data System (ADS)

Yamaji, Minoru; Oshima, Juro; Hidaka, Motohiko

2009-06-01

Evidence for the coupled electron/proton transfer mechanism of the phenolic H-atom transfer between triplet π,π ∗ 3,3'-carbonylbis(7-diethylaminocoumarin) and phenol derivatives is obtained by using laser photolysis techniques. It was confirmed that the quenching rate constants of triplet CBC by phenols having positive Hammett constants do not follow the Rehm-Weller equation for electron transfer while those by phenols with negative Hammett constants do it. From the viewpoint of thermodynamic parameters for electron transfer, the crucial factors for phenolic H-atom transfer to π,π ∗ triplet are discussed.

Semiquantitative FMO Analysis of Substituent Effect on the Reaction of Permanganate Ion with Unsymmetrical Alkenes.

PubMed

Ogino, Toshio; Watanabe, Toru; Matsuura, Masato; Watanabe, Chikara; Ozaki, Hidetoshi

1998-04-17

The substituent effects on the reactions of permanganate ion with unsymmetrical alkenes are analyzed on the assumption of a concerted (3 + 2) cycloaddition model by using an equation obtained by approximation based on the FMO theory in which development and localization of the frontier molecular orbitals at the reaction sites with progress of the reaction are considered. The Hammett plots are successfully reproduced with the newly obtained rate data for the reactions of trans-chalcone and its derivatives and the data for methyl cinnamates, cinnamate ions, and alkyl vinyl ethers taken from the literature using FMO energies and orbital coefficients calculated by the PM3 method. It was indicated that a factor introduced to the basic equation in order to estimate the extent of localization of the molecular orbitals at the transition state is closely related to the position of the transition state along the reaction path.

Toroidal gyro-Landau fluid model turbulence simulations in a nonlinear ballooning mode representation with radial modes

NASA Astrophysics Data System (ADS)

Waltz, R. E.; Kerbel, G. D.; Milovich, J.

1994-07-01

The method of Hammett and Perkins [Phys. Rev. Lett. 64, 3019 (1990)] to model Landau damping has been recently applied to the moments of the gyrokinetic equation with curvature drift by Waltz, Dominguez, and Hammett [Phys. Fluids B 4, 3138 (1992)]. The higher moments are truncated in terms of the lower moments (density, parallel velocity, and parallel and perpendicular pressure) by modeling the deviation from a perturbed Maxwellian to fit the kinetic response function at all values of the kinetic parameters: k∥vth/ω, b=(k⊥ρ)2/2, and ωD/ω. Here the resulting gyro-Landau fluid equations are applied to the simulation of ion temperature gradient (ITG) mode turbulence in toroidal geometry using a novel three-dimensional (3-D) nonlinear ballooning mode representation. The representation is a Fourier transform of a field line following basis (ky',kx',z') with periodicity in toroidal and poloidal angles. Particular emphasis is given to the role of nonlinearly generated n=0 (ky' = 0, kx' ≠ 0) ``radial modes'' in stabilizing the transport from the finite-n ITG ballooning modes. Detailing the parametric dependence of toroidal ITG turbulence is a key result.

Toroidal turbulence simulations with gyro-Landau fluid models in a nonlinear ballooning mode representation

NASA Astrophysics Data System (ADS)

Waltz, R. E.; Kerbel, G. D.

1994-05-01

The method of Hammett and Perkins [Phys. Rev. Lett. 64, 3019 (1990)] to model Landau damping has been recently applied to the moments of the gyro-kinetic equation with curvature drift by Waltz, Dominguez, and Hammett [Phys. Fluids B 4, 3138 (1992)]. The higher moments are truncated in terms of the lower moments (density, parallel velocity, and parallel and perpendicular pressure) by modeling the deviation from a perturbed Maxwellian to fit the kinetic response function at all values of the kinetic parameters: k∥vth/ω, b=(k⊥ρ)2/2, and ωD/ω. Here the resulting gyro-Landau fluid equations are applied to the simulation of ion temperature gradient (ITG) mode turbulence in toroidal geometry using a novel 3D nonlinear ballooning mode representation. The representation is a Fourier transform of the Cowley et al. [Phys. Fluids B 3, 2767 (1991)] field line following twisted eddy basis (kx',ky',z') with periodicity in toroidal and poloidal angles. Particular emphasis is given to the role of nonlinearly generated n=0 (ky'=0, kx'≠0) ``radial modes'' in stabilizing the transport from the finite-n ITG ballooning modes.

Tandem Reduction/Cyclization of O-Nitrophenyl Propargyl Alcohols-A Novel Synthesis of 2- & 2,4-Disubstituted Quinolines and Application to the Synthesis of Streptonigrin

DTIC Science & Technology

2008-01-01

surrogate” acrolein, which was synthesized from vinyl acetate (Scheme 11, upper equation )31. This mild method was an improvement over their previous work...11, lower equation ). Both cyclizations were facile with N,S-acetals bearing strongly activating groups on aniline. The resulting 2-methylthio...kinetic studies of the MS rearrangement.144 Using a combination of Hammett analysis of substituent effects and solvent isotope effects, Edens concluded

Observation of inductive effects that cause a change in the rate-determining step for the conversion of rhenium azides to imido complexes.

PubMed

Travia, Nicholas E; Xu, Zhenggang; Keith, Jason M; Ison, Elon A; Fanwick, Phillip E; Hall, Michael B; Abu-Omar, Mahdi M

2011-10-17

The cationic oxorhenium(V) complex [Re(O)(hoz)(2)(CH(3)CN)][B(C(6)F(5))(4)] [1; Hhoz = 2-(2'-hydroxyphenyl)-2-oxazoline] reacts with aryl azides (N(3)Ar) to give cationic cis-rhenium(VII) oxoimido complexes of the general formula [Re(O)(NAr)(hoz)(2)][B(C(6)F(5))(4)] [2a-2f; Ar = 4-methoxyphenyl, 4-methylphenyl, phenyl, 3-methoxyphenyl, 4-chlorophenyl, and 4-(trifluoromethyl)phenyl]. The kinetics of formation of 2 in CH(3)CN are first-order in both azide (N(3)Ar) and oxorhenium(V) complex 1, with second-order rate constants ranging from 3.5 × 10(-2) to 1.7 × 10(-1) M(-1) s(-1). A strong inductive effect is observed for electron-withdrawing substituents, leading to a negative Hammett reaction constant ρ = -1.3. However, electron-donating substituents on phenyl azide deviate significantly from this trend. Enthalpic barriers (ΔH(‡)) determined by the Eyring-Polanyi equation are in the range 14-19 kcal mol(-1) for all aryl azides studied. However, electron-donating 4-methoxyphenyl azide exhibits a large negative entropy of activation, ΔS(‡) = -21 cal mol(-1) K(-1), which is in sharp contrast to the near zero ΔS(‡) observed for phenyl azide and 4-(trifluoromethyl)phenyl azide. The Hammett linear free-energy relationship and the activation parameters support a change in the mechanism between electron-withdrawing and electron-donating aryl azides. Density functional theory predicts that the aryl azides coordinate via N(α) and extrude N(2) directly. For the electron-withdrawing substituents, N(2) extrusion is rate-determining, while for the electron-donating substituents, the rate-determining step becomes the initial attack of the azide. The barriers for these two steps are inverted in their order with respect to the Hammett σ values; thus, the Hammett plot appears with a break in its slope.

Conformer-specific hydrogen atom tunnelling in trifluoromethylhydroxycarbene

NASA Astrophysics Data System (ADS)

Mardyukov, Artur; Quanz, Henrik; Schreiner, Peter R.

2017-01-01

Conformational control of organic reactions is at the heart of the biomolecular sciences. To achieve a particular reactivity, one of many conformers may be selected, for instance, by a (bio)catalyst, as the geometrically most suited and appropriately reactive species. The equilibration of energetically close-lying conformers is typically assumed to be facile and less energetically taxing than the reaction under consideration itself: this is termed the 'Curtin-Hammett principle'. Here, we show that the trans conformer of trifluoromethylhydroxycarbene preferentially rearranges through a facile quantum-mechanical hydrogen tunnelling pathway, while its cis conformer is entirely unreactive. Hence, this presents the first example of a conformer-specific hydrogen tunnelling reaction. The Curtin-Hammett principle is not applicable, due to the high barrier between the two conformers.

L-proline-based deep eutectic solvents (DESs) for deep catalytic oxidative desulfurization (ODS) of diesel.

PubMed

Hao, Lingwan; Wang, Meiri; Shan, Wenjuan; Deng, Changliang; Ren, Wanzhong; Shi, Zhouzhou; Lü, Hongying

2017-10-05

A series of L-proline-based DESs was prepared through an atom economic reaction between L-proline (L-Pro) and four different kinds of organic acids. The DESs were characterized by Fourier transform infrared spectroscopy (FT-IR), H nuclear magnetic resonance ( 1 HNMR), cyclic voltammogram (CV) and the Hammett method. The synthesized DESs were used for the oxidative desulfurization and the L-Pro/p-toluenesultonic acid (L-Pro/p-TsOH) system shows the highest catalytic activity that the removal of dibenzothiophene (DBT) reached 99% at 60°C in 2h, which may involve the dual activation of the L-Pro/p-TsOH. The acidity of four different L-proline-based DESs was measured and the results show that it could not simply conclude that the correlation between the acidity of DESs and desulfurization capability was positive or negative. The electrochemical measurements evidences and recycling experiment indicate a good stability performance of L-Pro/p-TsOH in desulfurization. This work will provide a novel and potential method for the deep oxidation desulfurization. Copyright © 2017 Elsevier B.V. All rights reserved.

A modification of the Hammett equation for predicting ionisation constants of p-vinyl phenols.

PubMed

Sipilä, Julius; Nurmi, Harri; Kaukonen, Ann Marie; Hirvonen, Jouni; Taskinen, Jyrki; Yli-Kauhaluoma, Jari

2005-01-01

Currently there are several compounds used as drugs or studied as new chemical entities, which have an electron withdrawing group connected to a vinylic double bond in a phenolic or catecholic core structure. These compounds share a common feature--current computational methods utilizing the Hammett type equation for the prediction of ionisation constants fail to give accurate prediction of pK(a)'s for compounds containing the vinylic moiety. The hypothesis was that the effect of electron-withdrawing substituents on the pK(a) of p-vinyl phenols is due to the delocalized electronic structure of these compounds. Thus, this effect should be additive for multiple substituents attached to the vinylic double bond and quantifiable by LFER-based methods. The aim of this study was to produce an improved equation with a reduced tendency to underestimate the effect of the double bond on the ionisation of the phenolic hydroxyl. To this end a set of 19 para-substituted vinyl phenols was used. The ionisation constants were measured potentiometrically, and a training set of 10 compounds was selected to build a regression model (r2 = 0.987 and S.E. = 0.09). The average error with an external test set of six compounds was 0.19 for our model and 1.27 for the ACD-labs 7.0. Thus, we have been able to significantly improve the existing model for prediction of the ionisation constants of substituted p-vinyl phenols.

Linear free energy relationship and deuterium kinetic isotope effect observed on phospho and thiophosphoryl transfer reactions in some organophosphorous compounds

NASA Astrophysics Data System (ADS)

Lumbiny, B. J.; Hui, Z.; Islam, M. A.; Quader, M. A.; Rahman, M.

2014-04-01

Tetracoordinated organophosphorous compounds were synthesized, characterized and nucleophilic substitution reaction were investigated by varying substituents around phosphorous centre or in nucleophile considering its utility in biological and environmental system. The reactivity is expressed in terms of second-order rate constant, k2 and measured conductometrically. Linear Free Energy Relationship (LFER) tools mainly Hammett (ρ), Brönsted (β) LFER coefficients and deuterium kinetic isotope effects (KIEs) being determined for the pyridinolysis of 4 - chlorophenyl 4 - methoxy phenyl chlorophosphate, 1 in acetonitrile at 5.0 °C. The experimental data's were compared with those of structurally similar organophosphorous compounds reported earlier in quest for the mechanistic information. Nice linear correlation being found for Hammett (logk2 vs σx), having negative value of the ρX = -5.85 and Brönsted (logk2 vs pKa(x)) plots having large positive value for βX = 1.18 for 1 can be interpreted as SN2 process with greater extent of bond formation in transition state (TS) of 1. The observed kH/kD values of 1 is 1.00 ± 0.05 and net KIE, 1.32 suggests the primary KIE and indicates frontside nucleophilic attack through the partial deprotonation of pyridine occurs by the hydrogen bonding in the rate-determining step.

Prediction of distribution coefficient from structure. 1. Estimation method.

PubMed

Csizmadia, F; Tsantili-Kakoulidou, A; Panderi, I; Darvas, F

1997-07-01

A method has been developed for the estimation of the distribution coefficient (D), which considers the microspecies of a compound. D is calculated from the microscopic dissociation constants (microconstants), the partition coefficients of the microspecies, and the counterion concentration. A general equation for the calculation of D at a given pH is presented. The microconstants are calculated from the structure using Hammett and Taft equations. The partition coefficients of the ionic microspecies are predicted by empirical equations using the dissociation constants and the partition coefficient of the uncharged species, which are estimated from the structure by a Linear Free Energy Relationship method. The algorithm is implemented in a program module called PrologD.

Emission color tuning in AlQ3 complexes with extended conjugated chromophores.

PubMed

Pohl, Radek; Anzenbacher, Pavel

2003-08-07

[reaction: see text] A new method for the synthesis of 5-arylethynyl-8-hydroxyquinoline ligands using Sonogashira-Hagihara coupling was developed. The electronic nature of arylethynyl substituents affects the emission color and quantum yield of the resulting Al(III) complex. Photophysical properties of the metallocomplexes correspond to the electron-withdrawing/-donating character of the arylethynyl substituents. Optical properties of such Al(III) complexes correlate with the Hammett constant values of the respective substituents. This strategy offers a powerful tool for the preparation of electroluminophores with predictable photophysical properties.

Comparisons of Measurements and Simulations of Turbulence and Transport for DIII-D Discharges with Off-Axis Modulated ECH

NASA Astrophysics Data System (ADS)

Bravenec, R. V.; Ross, D. W.; Austin, M. E.; Gentle, K. W.; Deboo, J. C.; DIII-D Team; McKee, G. R.; Dorland, W.; Rhodes, T. L.; Zeng, L.

2002-11-01

Experiments to elucidate the nature of electron thermal transport have been conducted in DIII-D plasmas using modulated off-axis electron-cyclotron heating (ECH). Density fluctuations were measured using beam-emission spectroscopy, microwave reflectometry, and far-infrared scattering. Simulations of the experiment are performed with the gyrokinetic and gyrofluid flux-tube codes GS2(F. Jenko, W. Dorland, M. Kotschenreuther, and B.N. Rogers, Phys. Plasmas 7), 1904 (2000) and refs. therein. and GRYFFIN,(W. Dorland and G.W. Hammett, Phys. Fluids B 5), 812 (1993); M.A. Beer and G.W. Hammett, Phys. Plasmas 3, 4046 (1996). respectively. Comparisons of experiment and simulation results for the fluctuations and transport fluxes (ion and electron) will be presented for both time-averaged and modulated quantities.

Solvent and structural effects on the spectral shifts of 5-(substituted phenylazo)-3-cyano-6-hydroxy-1-(2-hydroxyethyl)-4-methyl-2-pyridones

NASA Astrophysics Data System (ADS)

Mirković, Jelena M.; Božić, Bojan Đ.; Mutavdžić, Dragosav R.; Ušćumlić, Gordana S.; Mijin, Dušan Ž.

2014-11-01

Spectral properties, solvatochromism and azo-hydrazone tautomerism of ten 5-(substituted phenylazo)-3-cyano-6-hydroxy-1-(2-hydroxyethyl)-4-methyl-2-pyridones in twenty-two solvents are investigated. For quantitative evaluation of the solvent effects on the UV-vis absorption maxima, the principles of the linear solvation energy relationships are used, i.e. models proposed by Kamlet-Taft and Catalán. Linear free energy relationships are applied to the UV-vis absorption spectra and correlation of absorption frequencies with Hammett substituent constants are performed. Furthermore, the influence of the electronic nature of the substituents on 1H and 13C NMR shifts is investigated by simple and extended Hammett equations, as well as by Swain-Lupton equation.

Kinetics and mechanism of degradation of some 2-sulfanilamidopyrimidine derivatives. Part III. The use of Hammett equation for kinetic investigation of 2-sulfanilamidopyrimidine derivatives autoxidation.

PubMed

Zajac, M

1977-01-01

General first-order rate constants for autoxidation of sulfadiazine, sulfamerazine, sulfadimidine, sulfaperine and sulfamethoxydiazine in the air oxygen atmosphere, in solutions of pH 4-7, at 403, 411 and 418 K were determined from the absorbance measurements in 0-1 mole/dm3 HCl at 243 or 333 nm, using the so-called "subtraction technique". The thermodynamic parameters of this reaction were determined (deltaHa, deltaH not equal to, deltaS not equal to, deltaG not equal to and logA). The effect of the substituents in positions 4, 5 and 6 of the pyrimidine ring on the rate of autoxidation was interpreted in terms of the Hammett equation.

Synthesis and electronic factors in thermal cyclodimerization of functionalized aromatic trifluorovinyl ethers.

PubMed

Spraul, Bryan K; Suresh, S; Jin, Jianyong; Smith, Dennis W

2006-05-31

A series of 19 p-substituted aromatic trifluorovinyl ether compounds were prepared from versatile intermediate p-Br-C(6)H(4)-O-CF=CF(2) and underwent thermal radical mediated cyclodimerization to new difunctional compounds containing the 1,2-disubstituted perfluorocyclobutyl (PFCB) linkage. The synthetic scope demonstrates the functional group transformation tolerance of the fluorovinyl ether, and the dimers are useful as monomers for traditional step-growth polymerization methods. (19)F NMR spectra confirmed that p-substitution affects the trifluorovinyl ether group chemical shifts. The first kinetic studies and substituent effects on thermal cyclodimerization were performed, and the results indicated that electron-withdrawing groups slow the rate of cyclodimerization. The data were further analyzed using the Hammett equation, and reaction constants (rho) of -0.46 at 120 degrees C and -0.59 at 130 degrees C were calculated. This study presents the first liner free energy relationship reported for the cyclodimerization of aromatic trifluorovinyl ethers to PFCB compounds.

Mechanisms for the adsorption of substituted nitrobenzenes by smectite clays.

PubMed

Boyd, S A; Sheng, G; Teppen, B J; Johnston, C T

2001-11-01

To more fully understand the potential for transport of nitroaromatic compounds in soils and subsoils,the adsorption of a series of para- and meta-substituted nitrobenzenes (SNBs) by K-smectite clay was measured. Adsorption isotherms were fit to the Freundlich equation, and the resultant Freundlich adsorption coefficients (log(Kf) were positively correlated with the Hammett substituent constant (r2 = 0.80). This relationship and a positive reaction constant (p = 1.15) indicate that the adsorption reaction is favored by electron-withdrawing substituents. These results are consistent with an electron donor (smectite)-acceptor (substituted nitrobenzene) mechanism offered previously. However, quantum calculations did not reveal any systematic relationship between the Hammett constant and the electron density on the aromatic ring, which would explain a donor-acceptor relationship. Rather, electron density donated by a second substituent on nitrobenzene appears to be appropriated by the nitro group leaving ring electron density unchanged. Fourier transform infrared spectroscopy revealed shifts in the -NO2 vibrational modes of 1,3,5-trinitrobenzene (TNB) upon adsorption to K+-smectite that were consistent with the complexation of K+ by -NO2 groups. Such TNB vibrational shifts were not observed for SWy-1 saturated with more strongly hydrated cations (i.e., Na+, Mg2+, Ca2+, and Ba2+). The simultaneous interaction of multiple -NO2 groups with exchangeable K+ was indicated by molecular dynamic simulations. Adsorption of SNBs by smectite clays appears to result from the additive interactions of -NO2 groups and secondary substituents with interlayer K+ ions. Adsorption occurs to a greater or lesser extent depending on the abilities of substituents to complex additional interlayer cations and the water solubilities of SNBs. We conclude that the adsorption trends of SNBs on K-SAz-1 can be explained without recourse to hypothetical electron donor-acceptor complexes.

Continuum limit of electrostatic gyrokinetic absolute equilibrium

NASA Astrophysics Data System (ADS)

Zhu, Jian-Zhou

2012-06-01

Electrostatic gyrokinetic absolute equilibria with continuum velocity field are obtained through the partition function and through the Green function of the functional integral. The new results justify and explain the prescription for quantization/discretization or taking the continuum limit of velocity. The mistakes in the Appendix D of our earlier work [J.-Z. Zhu and G. W. Hammett, Phys. Plasmas 17, 122307 (2010)] are explained and corrected. If the lattice spacing for discretizing velocity is big enough, all the invariants could concentrate at the lowest Fourier modes in a negative-temperature state, which might indicate a possible variation of the dual cascade picture in 2D plasma turbulence.

Determination of thermodynamic affinities of various polar olefins as hydride, hydrogen atom, and electron acceptors in acetonitrile.

PubMed

Cao, Ying; Zhang, Song-Chen; Zhang, Min; Shen, Guang-Bin; Zhu, Xiao-Qing

2013-07-19

A series of 69 polar olefins with various typical structures (X) were synthesized and the thermodynamic affinities (defined in terms of the molar enthalpy changes or the standard redox potentials in this work) of the polar olefins obtaining hydride anions, hydrogen atoms, and electrons, the thermodynamic affinities of the radical anions of the polar olefins (X(•-)) obtaining protons and hydrogen atoms, and the thermodynamic affinities of the hydrogen adducts of the polar olefins (XH(•)) obtaining electrons in acetonitrile were determined using titration calorimetry and electrochemical methods. The pure C═C π-bond heterolytic and homolytic dissociation energies of the polar olefins (X) in acetonitrile and the pure C═C π-bond homolytic dissociation energies of the radical anions of the polar olefins (X(•-)) in acetonitrile were estimated. The remote substituent effects on the six thermodynamic affinities of the polar olefins and their related reaction intermediates were examined using the Hammett linear free-energy relationships; the results show that the Hammett linear free-energy relationships all hold in the six chemical and electrochemical processes. The information disclosed in this work could not only supply a gap of the chemical thermodynamics of olefins as one class of very important organic unsaturated compounds but also strongly promote the fast development of the chemistry and applications of olefins.

Substituent effects on photosensitized splitting of thymine cyclobutane dimer by an attached indole.

PubMed

Tang, Wenjian; Zhou, Hongmei; Wang, Jing; Pan, Chunxiao; Shi, Jingbo; Song, Qinhua

2012-12-21

In chromophore-containing cyclobutane pyrimidine dimer (CPD) model systems, solvent effects on the splitting efficiency may depend on the length of the linker, the molecular conformation, and the oxidation potential of the donor. To further explore the relationship between chromophore structure and splitting efficiency, we prepared a series of substituted indole-T< >T model compounds 2 a-2 g and measured their splitting quantum yields in various solvents. Two reverse solvent effects were observed: an increase in splitting efficiency in solvents of lower polarity for models 2 a-2 d with an electron-donating group (EDG), and vice versa for models 2 e-2 g with an electron-withdrawing group (EWG). According to the Hammett equation, the negative value of the slope of the Hammett plot indicates that the indole moiety during the T< >T-splitting reaction loses negative charge, and the larger negative value implies that the repair reaction is more sensitive to substituent effects in low-polarity solvents. The EDGs of the models 2 a-2 d can delocalize the charge-separated state, and low-polarity solvents make it more stable, which leads to higher splitting efficiency in low-polarity solvents. Conversely, the EWGs of models 2 e-2 g favor destabilization of the charge-separated state, and high-polarity solvents decrease the destabilization and hence lead to more efficient splitting in high-polarity solvents. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Thermal isomerizations of ketenimines to nitriles: evaluations of sigma-Dot (sigma(*)) constants for spin-delocalizations

PubMed

Kim; Zhu; Lee

2000-05-19

Rate constants (k(Y)) of the isomerizations of 11 diphenyl N-(substituted benzyl) ketenimines were measured at 40, 50, 60, and 70 degrees C. Activation parameters DeltaH()(Y) and DeltaS()(Y) were obtained using the Eyring equation. The relative rates (k(Y)/k(H)) were fitted into Hammett single correlations (log k(Y)/k(H) = rhosigma and log k(Y)/k(H) = rho(*)sigma(*)). The single correlations have been compared with Hammett dual correlations (log k(Y)/k(H) = rhosigma + rho(*)sigma(*) ). Separate treatments of para and meta substituents yielded even better correlations. Para substituents control the rates through spin-delocalizations and inductive effects. The former outweighs the latter when the latter exerts a modest but distinct influence on the rates. On the other hand, inductive effects are the "major" or the sole interactions triggered by meta substituents.

Kinetics and mechanism of degradation of some 2-sulfanilamidopyrimidine derivatives. Part VI. The use of Hammett equation for kinetic investigation of 2-sulfanilamidopyrimidine derivatives hydrolysis.

PubMed

Zajac, M

1977-01-01

General, k, and specific, k1 and k2, first-order rate constants for the parallel reaction of hydrolysis catalized by H+ ions were estimated for sulfadiazine (I), sulfamerazine (II), sulfadimidine (III), sulfaperine (IV) and sulfamethoxydiazine (V), hydrolyzed in 1 mole/dm3 HCl at 333, 343, 355 and 363 K. General first-order rate constants for the spontaneous hydrolysis of I--V in borate buffer pH 9.20 at 403, 411 and 418 K were also determined. Thermodynamic parameters of the reaction (delta Ha, deltaH not equal to, deltaS not equal to, deltaG not equal to and log A) were calculated. The effect of substituents in positions 4, 5 and 6 of the pyrimidine ring on the rate of hydrolysis was interpreted in terms of Hammett equation.

Designing multistep transformations using the Hammett equation: imine exchange on a copper(I) template.

PubMed

Schultz, David; Nitschke, Jonathan R

2006-08-02

Herein, we quantify how imine exchange may be used to selectively transform one metallo-organic structure into another. A series of imine exchange reactions were studied, involving a set of 4-substituted anilines, their 2-pyridylimines and 1,10-phenanthrolyl-2,9-diimines, as well as the copper complexes of these imine ligands. Electron-rich anilines were found to displace electron-poor anilines in all cases. Linear free energy relationships (LFERs) were discovered connecting the electron-donating or -withdrawing character of the 4-substituent of an aniline, as measured by the Hammett sigma(para) parameter, to that aniline's ability to compete with unsubstituted aniline to form imines. The quality of these LFERs allowed for quantitative predictions: to obtain the desired degree of selectivity in an imine exchange between anilines A and B, the required sigma(para) differential could be predicted using a variant of the Hammett equation, log(K(AB)) = rho(sigma(A) - sigma(B)). We validated this methodology by designing and executing a three-step transformation of a series of copper(I)-containing structures. Each step proceeded in predictably high yield, as calculated from sigma differentials. At each step in the series of transformations, macrocyclic structures could be created or destroyed through the selection of mono- or di-amines as subcomponents. The same methodology could be used to predict the formation of a diverse dynamic library of helicates from a set of four aniline precursors, as well as the collapse of this library into one helicate upon the addition of a fifth aniline.

NMR investigation of substituent effects on strength the intramolecular hydrogen bonding interaction in X-phenylhydrazones switches: A theoretical study

NASA Astrophysics Data System (ADS)

Gholipour, Alireza; Sadat Neyband, Razeih; Farhadi, Saeed

2017-05-01

We proved by computational NMR data the effect of electron-withdrawing and donating substituents on sbnd H⋯Nsbnd and sbnd H⋯Osbnd intramolecular hydrogen bond of the E and Z isomers in X-phenylhydrazones switches. These interactions were analyzed in detail in terms of the energetic and geometrical parameters properties. In addition, atoms in molecules (AIM) and natural bond orbital (NBO) were also employed to characterize the interactions and to examine the strengthening of the interactions. Computational results indicate an enhanced hydrogen bond for all substituted related to an unsubstituted case. There are good relationships between the NMR, AIM, NBO, energy data and Hammett constants.

One-pot syntheses of blue-luminescent 4-aryl-1H-benzo[f]isoindole-1,3(2H)-diones by T3P® activation of 3-arylpropiolic acids.

PubMed

Denißen, Melanie; Kraus, Alexander; Reiss, Guido J; Müller, Thomas J J

2017-01-01

In situ activation of 3-arylpropiolic acids with T3P ® ( n -propylphosphonic acid anhydride) initiates a domino reaction furnishing 4-arylnaphtho[2,3- c ]furan-1,3-diones in excellent yields. Upon employing these anhydrides as reactive intermediates blue-luminescent 4-aryl-1 H -benzo[ f ]isoindole-1,3(2 H )-diones are formed by consecutive pseudo three-component syntheses in a one-pot fashion. The Stokes shifts correlate excellently with the Hammett-Taft σ R parameter indicating an extended degree of resonance stabilization in the vibrationally relaxed excited singlet state.

Kinetics studies of rapid strain-promoted [3 + 2]-cycloadditions of nitrones with biaryl-aza-cyclooctynone.

PubMed

McKay, Craig S; Chigrinova, Mariya; Blake, Jessie A; Pezacki, John Paul

2012-04-21

Strain-promoted cycloadditions of cyclic nitrones with biaryl-aza-cyclooctynone (BARAC) proceed with rate constants up to 47.3 M(-1) s(-1), this corresponds to a 47-fold rate enhancement relative to reaction of BARAC with benzyl azide and a 14-fold enhancement over previously reported strain promoted alkyne-nitrone cycloadditions (SPANC). Studies of the SPANC reaction using the linear free energy relationship defined by the Hammett equation demonstrated that the cycloaddition reaction has a rho value of 0.25 ± 0.04, indicating that reaction is not sensitive to substituents and thus should have broad applicability. This journal is © The Royal Society of Chemistry 2012

The computational analysis and modelling of substitution effects on hydrolysis of formanilides in acidic aqueous solutions

NASA Astrophysics Data System (ADS)

Lukeš, Vladimír; Škorňa, Peter; Michalík, Martin; Klein, Erik

2017-11-01

Various para, meta and ortho substituted formanilides have been theoretically studied. For trans and cis-isomers of non-substituted formanilide, the calculated B3LYP vibration normal modes were analyzed. Substituent effect on the selected normal modes was described and the comparison with the available experimental data is presented. The calculated B3LYP proton affinities were correlated with Hammett constants, Fujita-Nishioka equation and the rate constants of the hydrolysis in 1 M HCl. Found linear dependences allow predictions of dissociation constants (pKBH+) and hydrolysis rate constants. Obtained results indicate that protonation of amide group may represent the rate determining step of acid catalyzed hydrolysis.

Unusual para-substituent effects on the intramolecular hydrogen-bond in hydrazone-based switches.

PubMed

Su, Xin; Lõkov, Märt; Kütt, Agnes; Leito, Ivo; Aprahamian, Ivan

2012-11-04

A "V"-shaped Hammett plot shows that resonance-assisted hydrogen bonding does not dictate the strength of the intramolecular hydrogen bond in the E isomers of hydrazone-based switches because it involves an aromatic pyridyl ring.

A novel model to predict gas-phase hydroxyl radical oxidation kinetics of polychlorinated compounds.

PubMed

Luo, Shuang; Wei, Zongsu; Spinney, Richard; Yang, Zhihui; Chai, Liyuan; Xiao, Ruiyang

2017-04-01

In this study, a novel model based on aromatic meta-substituent grouping was presented to predict the second-order rate constants (k) for OH oxidation of PCBs in gas-phase. Since the oxidation kinetics are dependent on the chlorination degree and position, we hypothesized that it may be more accurate for k value prediction if we group PCB congeners based on substitution positions (i.e., ortho (o), meta (m), and para (p)). To test this hypothesis, we examined the correlation of polarizability (α), a quantum chemical based descriptor for k values, with an empirical Hammett constant (σ + ) on each substitution position. Our result shows that α is highly linearly correlated to ∑σ o,m,p + based on aromatic meta-substituents leading to the grouping based predictive model. With the new model, the calculated k values exhibited an excellent agreement with experimental measurements, and greater predictive power than the quantum chemical based quantitative structure activity relationship (QSAR) model. Further, the relationship of α and ∑σ o,m,p + for PCDDs congeners, together with highest occupied molecular orbital (HOMO) distribution, were used to validate the aromatic meta-substituent grouping method. This newly developed model features a combination of good predictability of quantum chemical based QSAR model and simplicity of Hammett relationship, showing a great potential for fast and computational tractable prediction of k values for gas-phase OH oxidation of polychlorinated compounds. Copyright © 2017 Elsevier Ltd. All rights reserved.

QSAR modeling of flotation collectors using principal components extracted from topological indices.

PubMed

Natarajan, R; Nirdosh, Inderjit; Basak, Subhash C; Mills, Denise R

2002-01-01

Several topological indices were calculated for substituted-cupferrons that were tested as collectors for the froth flotation of uranium. The principal component analysis (PCA) was used for data reduction. Seven principal components (PC) were found to account for 98.6% of the variance among the computed indices. The principal components thus extracted were used in stepwise regression analyses to construct regression models for the prediction of separation efficiencies (Es) of the collectors. A two-parameter model with a correlation coefficient of 0.889 and a three-parameter model with a correlation coefficient of 0.913 were formed. PCs were found to be better than partition coefficient to form regression equations, and inclusion of an electronic parameter such as Hammett sigma or quantum mechanically derived electronic charges on the chelating atoms did not improve the correlation coefficient significantly. The method was extended to model the separation efficiencies of mercaptobenzothiazoles (MBT) and aminothiophenols (ATP) used in the flotation of lead and zinc ores, respectively. Five principal components were found to explain 99% of the data variability in each series. A three-parameter equation with correlation coefficient of 0.985 and a two-parameter equation with correlation coefficient of 0.926 were obtained for MBT and ATP, respectively. The amenability of separation efficiencies of chelating collectors to QSAR modeling using PCs based on topological indices might lead to the selection of collectors for synthesis and testing from a virtual database.

Oxygen-atom transfer reactivity of axially ligated Mn(V)-oxo complexes: evidence for enhanced electrophilic and nucleophilic pathways.

PubMed

Neu, Heather M; Yang, Tzuhsiung; Baglia, Regina A; Yosca, Timothy H; Green, Michael T; Quesne, Matthew G; de Visser, Sam P; Goldberg, David P

2014-10-01

Addition of anionic donors to the manganese(V)-oxo corrolazine complex Mn(V)(O)(TBP8Cz) has a dramatic influence on oxygen-atom transfer (OAT) reactivity with thioether substrates. The six-coordinate anionic [Mn(V)(O)(TBP8Cz)(X)](-) complexes (X = F(-), N3(-), OCN(-)) exhibit a ∼5 cm(-1) downshift of the Mn-O vibrational mode relative to the parent Mn(V)(O)(TBP8Cz) complex as seen by resonance Raman spectroscopy. Product analysis shows that the oxidation of thioether substrates gives sulfoxide product, consistent with single OAT. A wide range of OAT reactivity is seen for the different axial ligands, with the following trend determined from a comparison of their second-order rate constants for sulfoxidation: five-coordinate ≈ thiocyanate ≈ nitrate < cyanate < azide < fluoride ≪ cyanide. This trend correlates with DFT calculations on the binding of the axial donors to the parent Mn(V)(O)(TBP8Cz) complex. A Hammett study was performed with p-X-C6H4SCH3 derivatives and [Mn(V)(O)(TBP8Cz)(X)](-) (X = CN(-) or F(-)) as the oxidant, and unusual "V-shaped" Hammett plots were obtained. These results are rationalized based upon a change in mechanism that hinges on the ability of the [Mn(V)(O)(TBP8Cz)(X)](-) complexes to function as either an electrophilic or weak nucleophilic oxidant depending upon the nature of the para-X substituents. For comparison, the one-electron-oxidized cationic Mn(V)(O)(TBP8Cz(•+)) complex yielded a linear Hammett relationship for all substrates (ρ = -1.40), consistent with a straightforward electrophilic mechanism. This study provides new, fundamental insights regarding the influence of axial donors on high-valent Mn(V)(O) porphyrinoid complexes.

Hammett equation and generalized Pauling's electronegativity equation.

PubMed

Liu, Lei; Fu, Yao; Liu, Rui; Li, Rui-Qiong; Guo, Qing-Xiang

2004-01-01

Substituent interaction energy (SIE) was defined as the energy change of the isodesmic reaction X-spacer-Y + H-spacer-H --> X-spacer-H + H-spacer-Y. It was found that this SIE followed a simple equation, SIE(X,Y) = -ksigma(X)sigma(Y), where k was a constant dependent on the system and sigma was a certain scale of electronic substituent constant. It was demonstrated that the equation was applicable to disubstituted bicyclo[2.2.2]octanes, benzenes, ethylenes, butadienes, and hexatrienes. It was also demonstrated that Hammett's equation was a derivative form of the above equation. Furthermore, it was found that when spacer = nil the above equation was mathematically the same as Pauling's electronegativity equation. Thus it was shown that Hammett's equation was a derivative form of the generalized Pauling's electronegativity equation and that a generalized Pauling's electronegativity equation could be utilized for diverse X-spacer-Y systems. In addition, the total electronic substituent effects were successfully separated into field/inductive and resonance effects in the equation SIE(X,Y) = -k(1)F(X)F(Y) - k(2)R(X)R(Y) - k(3)(F(X)R(Y) + R(X)F(Y)). The existence of the cross term (i.e., F(X)R(Y) and R(X)F(Y)) suggested that the field/inductive effect was not orthogonal to the resonance effect because the field/inductive effect from one substituent interacted with the resonance effect from the other. Further studies on multi-substituted systems suggested that the electronic substituent effects should be pairwise and additive. Hence, the SIE in a multi-substituted system could be described using the equation SIE(X1, X2, ..., Xn) = Sigma(n-1)(i=1)Sigma(n)(j=i+1)k(ij)sigma(X)isigma(X)j.

Synthesis and Photoluminescent Properties of Arylethynyl substituted 9,10-Anthraquinones

NASA Technical Reports Server (NTRS)

Yang, Jin-Hua; Dass, Amala; Sotiriou-Leventis, Chariklia; Leventis, Nicholas

2003-01-01

A series of arylethynyl substituted anthraquinones were synthesized via Sonogashira coupling reactions of 2,7- dibromo-, 2,6-dibromo- and 2-bromoanthraquinone with para-substituted phenylacetylenes. While the redox properties of those compounds are almost insensitive to substitution, their absorption maxima are linearly related to the Hammett constants for electron donating and electron withdrawing groups separately. All compounds are photoluminescent both in solution (quantum yield of emission approximately 2%) and as solids. X-ray crystallographic characterization of 2,7-bisphenylethynyl anthraquinone indicates a monoclinic p2(l/n) space group and no indication for pi-overlap that would promote self-quenching. The emission maxima are red- shifted by both electron donating and electron withdrawing groups alike. The Stokes shifts of all compounds are significant and are correlated to the electronic properties of the substituents. The reduced forms of these compounds are also photoluminescent and the emission originates from the dihydroanthraquinone core.

Reinterpretation of curved Hammett plots in reaction of nucleophiles with aryl benzoates: change in rate-determining step or mechanism versus ground-state stabilization.

PubMed

Um, Ik-Hwan; Han, Hyun-Joo; Ahn, Jung-Ae; Kang, Swan; Buncel, Erwin

2002-11-29

A kinetic study is reported for the reaction of the anionic nucleophiles OH-, CN-, and N 3 - with aryl benzoates containing substituents on the benzoyl as well as the aryloxy moiety, in 80 mol % H2O - 20 mol % dimethyl sulfoxide at 25.0 degrees C. Hammett log k vs sigma plots for these systems are consistently nonlinear. However, a possible traditional explanation in terms of a mechanism involving a tetrahedral intermediate with curvature resulting from a change in rate-determining step is considered but rejected. The proposed explanation involves ground-state stabilization through resonance interaction between the benzoyl substituent and the electrophilic carbonyl center in the two-stage mechanism. Accordingly, the data are nicely accommodated on the basis of the Yukawa-Tsuno equation, which gives linear plots for all three nuceophiles. Literature reports of the mechanism of acyl transfer processes are reconsidered in this light.

Creative Movement and Physical Development. Books for Professionals.

ERIC Educational Resources Information Center

Hagens, Helen E.

1994-01-01

Reviews three books on creative movement and physical development appropriate for early childhood teachers: (1) "Hello Toes! Movement Games for Children" (A. F. Barlin and N. Kalev); (2) "Movement Activities for Early Childhood" (C. T. Hammett); and (3) "Designing Preschool Movement Programs" (S. W. Sanders). (MDM)

Dissipative closures for statistical moments, fluid moments, and subgrid scales in plasma turbulence

NASA Astrophysics Data System (ADS)

Smith, Stephen Andrew

1997-11-01

Closures are necessary in the study physical systems with large numbers of degrees of freedom when it is only possible to compute a small number of modes. The modes that are to be computed, the resolved modes, are coupled to unresolved modes that must be estimated. This thesis focuses on dissipative closures models for two problems that arises in the study of plasma turbulence: the fluid moment closure problem and the subgrid scale closure problem. The fluid moment closures of Hammett and Perkins (1990) were originally applied to a one-dimensional kinetic equation, the Vlasov equation. These closures are generalized in this thesis and applied to the stochastic oscillator problem, a standard paradigm problem for statistical closures. The linear theory of the Hammett- Perkins closures is shown to converge with increasing numbers of moments. A novel parameterized hyperviscosity is proposed for two- dimensional drift-wave turbulence. The magnitude and exponent of the hyperviscosity are expressed as functions of the large scale advection velocity. Traditionally hyperviscosities are applied to simulations with a fixed exponent that must be arbitrarily chosen. Expressing the exponent as a function of the simulation parameters eliminates this ambiguity. These functions are parameterized by comparing the hyperviscous dissipation to the subgrid dissipation calculated from direct numerical simulations. Tests of the parameterization demonstrate that it performs better than using no additional damping term or than using a standard hyperviscosity. Heuristic arguments are presented to extend this hyperviscosity model to three-dimensional (3D) drift-wave turbulence where eddies are highly elongated along the field line. Preliminary results indicate that this generalized 3D hyperviscosity is capable of reducing the resolution requirements for 3D gyrofluid turbulence simulations.

Cross enyne metathesis of para-substituted styrenes: a kinetic study of enyne metathesis.

PubMed

Giessert, Anthony J; Diver, Steven T

2005-01-20

[Reaction: see text] The intermolecular enyne metathesis between alkynes and styrene derivatives was developed to study electronic effects in enyne metathesis. A Hammett plot for the overall reaction, catalyst initiation and vinyl carbene turnover was determined with the second generation Grubbs ruthenium carbene catalyst.

13-C NMR Spectra of Styrene Derivatives: An Undergraduate Experiment Involving the Application of the Hammett Equation.

ERIC Educational Resources Information Center

Blunt, J. W.; Happer, D. A. R.

1979-01-01

In this experiment, the observation that, for meta- and para-substituted styrene derivatives, the magnitude of the C-13 shielding value for the beta-carbon is linearly related to sigma for the ring substituent is used to determine sigma. (BB)

A Hamiltonian electromagnetic gyrofluid model

NASA Astrophysics Data System (ADS)

Waelbroeck, F. L.; Hazeltine, R. D.; Morrison, P. J.

2009-03-01

An isothermal truncation of the electromagnetic gyrofluid model of Snyder and Hammett [Phys. Plasmas 8, 3199 (2001)] is shown to be Hamiltonian. The corresponding noncanonical Lie-Poisson bracket and its Casimir invariants are presented. The invariants are used to obtain a set of coupled Grad-Shafranov equations describing equilibria and propagating coherent structures.

Neural Correlates of Visual-Spatial Attention in Electrocorticographic Signals in Humans

DTIC Science & Technology

2011-09-23

PEST) procedure (Taylor and Creelman , 1967; Hammett and Snowden, 1995) that was run at the beginning of the session. The PEST procedure selected the...Medical Publishers, Inc. Taylor, M. M., and Creelman , C. D. (1967). PEST: efficient estimates on probabil- ity functions. J. Acoust. Soc. Am. 41

Solvent-free synthesis, spectral correlations and antimicrobial activities of some aryl E 2-propen-1-ones

NASA Astrophysics Data System (ADS)

Sathiyamoorthi, K.; Mala, V.; Sakthinathan, S. P.; Kamalakkannan, D.; Suresh, R.; Vanangamudi, G.; Thirunarayanan, G.

2013-08-01

Totally 38 aryl E 2-propen-1-ones including nine substituted styryl 4-iodophenyl ketones have been synthesised using solvent-free SiO2-H3PO4 catalyzed Aldol condensation between respective methyl ketones and substituted benzaldehydes under microwave irradiation. The yields of the ketones are more than 80%. The synthesised chalcones were characterized by their analytical, physical and spectroscopic data. The spectral frequencies of synthesised substituted styryl 4-iodophenyl ketones have been correlated with Hammett substituent constants, F and R parameters using single and multi-linear regression analysis. The antimicrobial activities of 4-iodophenyl chalcones have been studied using Bauer-Kirby method.

DFT calculation of pKa’s for dimethoxypyrimidinylsalicylic based herbicides

NASA Astrophysics Data System (ADS)

Delgado, Eduardo J.

2009-03-01

Dimethoxypyrimidinylsalicylic derived compounds show potent herbicidal activity as a result of the inhibition of acetohydroxyacid synthase, the first common enzyme in the biosynthetic pathway of the branched-chain aminoacids (valine, leucine and isoleucine) in plants, bacteria and fungi. Despite its practical importance, this family of compounds have been poorly characterized from a physico-chemical point of view. Thus for instance, their pK a's have not been reported earlier neither experimentally nor theoretically. In this study, the acid-dissociation constants of 39 dimethoxypyrimidinylsalicylic derived herbicides are calculated by DFT methods at B3LYP/6-31G(d,p) level of theory. The calculated values are validated by two checking tests based on the Hammett equation.

Computational and spectroscopic data correlation study of N,N'-bisarylmalonamides (Part II).

PubMed

Arsovski, Violeta M; Božić, Bojan Đ; Mirković, Jelena M; Vitnik, Vesna D; Vitnik, Željko J; Petrović, Slobodan D; Ušćumlić, Gordana S; Mijin, Dušan Ž

2015-09-01

To complement a previous UV study, we present a quantitative evaluation of substituent effects on spectroscopic data ((1)H and (13)C NMR chemical shifts as well as FT-IR absorption frequency) applied to N,N'-bisarylmalonamides, using simple and extended Hammett equations as well as the Swain-Lupton equation. Furthermore, the DFT CAM-B3LYP/6-311+G(d,p) method was applied to study the impact of different solvents on the geometry of the molecules and their spectral data. Additionally, experimental data are correlated with theoretical results; excellent linear dependence was obtained. The overall results presented in this paper show that N,N'-bisarylmalonamides are prominent candidates for model molecules.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Powers, Andrew R.; Ghiviriga, Ion; Abboud, Khalil A.

This report outlines the investigation of the iClick mechanism between gold(I)-azides and gold(I)-acetylides to yield digold triazolates. Isolation of digold triazolate complexes offer compelling support for the role of two copper(I) ions in CuAAC. In addition, a kinetic investigation reveals the reaction is first order in both Au(I)-N 3 and Au(I)-C≡C-R equivalent to C-R, thus second order overall. A Hammett plot with a ρ = 1.02(5) signifies electron-withdrawing groups accelerate the cycloaddition by facilitating the coordination of the second gold ion in a π-complex. Rate inhibition by the addition of free triphenylphosphine to the reaction indicates that ligand dissociation ismore » a prerequisite for the reaction. The mechanistic conclusions mirror those proposed for the CuAAC reaction.« less

Theoretical Hammett Plot for the Gas-Phase Ionization of Benzoic Acid versus Phenol: A Computational Chemistry Lab Exercise

ERIC Educational Resources Information Center

Ziegler, Blake E.

2013-01-01

Computational chemistry undergraduate laboratory courses are now part of the chemistry curriculum at many universities. However, there remains a lack of computational chemistry exercises available to instructors. This exercise is presented for students to develop skills using computational chemistry software while supplementing their knowledge of…

Literary Aspects of a Girlie Magazine: The Literary Contributions of Esquire, 1933-43.

ERIC Educational Resources Information Center

Peterson, Thane

From its inauspicious beginnings as a men's store giveaway and a "girlie" magazine in 1933, "Esquire" magazine quickly established a policy of literary excellence. By 1945, the magazine included the works on such major literary figures as Erskine Caldwell, John Dos Passos, Dashiell Hammett, Ernest Hemingway, Ring Lardner, James…

Determination of Hammett Equation Rho Constant for the Hydrolysis of p-Nitrophenyl Benzoate Esters

ERIC Educational Resources Information Center

Keenan, Sheue L.; Peterson, Karl P.; Peterson, Kelly; Jacobson, Kyle

2008-01-01

Seven p-nitrophenyl benzoate esters (p-nitrophenyl benzoate, p-nitrophenyl m-anisate, p-nitrophenyl p-anisate, p-nitrophenyl m-chlorobenzoate, p-nitrophenyl p-chlorobenzoate, p-nitrophenyl m-toluate, p-nitrophenyl p-toluate) were synthesized and characterized by students in a second-semester organic laboratory course. In a subsequent laboratory…

Sulfonamido tripods: tuning redox potentials via ligand modifications

PubMed Central

Lau, Nathanael; Ziller, Joseph W.

2014-01-01

A series of FeII–OH2 complexes were synthesized with ligands based on the tetradentate sulfonamido tripod N,N',N"-[2,2',2"-nitrilotris(ethane-2,1-diyl)]-tris-({R-Ph}-sulfonamido). These complexes differ by the substituent on the aryl rings and were fully characterized, including their molecular structures via X-ray diffraction methods. All the complexes were five-coordinate with trigonal bipyramidal geometry. A linear correlation was observed between the electronic effects of each ligand, given by the Hammett constants of the para-substituents, and the potential of the FeII/FeIII redox couple, which were determined using cyclic voltammetry. It was found that the range of redox potentials for the complexes spanned approximately 160 mV. PMID:25419035

Sulfonamido tripods: tuning redox potentials via ligand modifications.

PubMed

Lau, Nathanael; Ziller, Joseph W; Borovik, A S

2015-01-08

A series of Fe II -OH 2 complexes were synthesized with ligands based on the tetradentate sulfonamido tripod N , N ', N "-[2,2',2"-nitrilotris(ethane-2,1-diyl)]-tris-({R-Ph}-sulfonamido). These complexes differ by the substituent on the aryl rings and were fully characterized, including their molecular structures via X-ray diffraction methods. All the complexes were five-coordinate with trigonal bipyramidal geometry. A linear correlation was observed between the electronic effects of each ligand, given by the Hammett constants of the para -substituents, and the potential of the Fe II /Fe III redox couple, which were determined using cyclic voltammetry. It was found that the range of redox potentials for the complexes spanned approximately 160 mV.

A Hamiltonian electromagnetic gyrofluid model

NASA Astrophysics Data System (ADS)

Waelbroeck, F. L.; Hazeltine, R. D.; Morrison, P. J.

2009-11-01

An isothermal truncation of the electromagnetic gyrofluid model of Snyder and Hammett [Phys. Plasmas 8, 3199 (2001)] is shown to be Hamiltonian. The corresponding noncanonical Lie-Poisson bracket and its Casimir invariants are presented. The model describes the evolution of the density, the electrostatic potential, and the component of the vector potential along a strong background field. This makes it suitable for describing such phenomena as the propagation of kinetic-Alfv'en modons, the nonlinear saturation of drift-tearing modes, and the diamagnetic stabilization of the internal kink. The invariants are used to obtain a set of coupled Grad-Shafranov equations describing equilibria and propagating coherent structures. They also lead to a Lagrangian formulation of the equations of motion that is well suited to solution with the PIC method.

Optimized diazo scaffold for protein esterification.

PubMed

Mix, Kalie A; Raines, Ronald T

2015-05-15

The O-alkylation of carboxylic acids with diazo compounds provides a means to esterify carboxylic acids in aqueous solution. A Hammett analysis of the reactivity of diazo compounds derived from phenylglycinamide revealed that the (p-methylphenyl)glycinamide scaffold has an especially high reaction rate and ester/alcohol product ratio and esterifies protein carboxyl groups more efficiently than any known reagent.

Quantitative structure activity relationship studies of mushroom tyrosinase inhibitors

NASA Astrophysics Data System (ADS)

Xue, Chao-Bin; Luo, Wan-Chun; Ding, Qi; Liu, Shou-Zhu; Gao, Xing-Xiang

2008-05-01

Here, we report our results from quantitative structure-activity relationship studies on tyrosinase inhibitors. Interactions between benzoic acid derivatives and tyrosinase active sites were also studied using a molecular docking method. These studies indicated that one possible mechanism for the interaction between benzoic acid derivatives and the tyrosinase active site is the formation of a hydrogen-bond between the hydroxyl (aOH) and carbonyl oxygen atoms of Tyr98, which stabilized the position of Tyr98 and prevented Tyr98 from participating in the interaction between tyrosinase and ORF378. Tyrosinase, also known as phenoloxidase, is a key enzyme in animals, plants and insects that is responsible for catalyzing the hydroxylation of tyrosine into o-diphenols and the oxidation of o-diphenols into o-quinones. In the present study, the bioactivities of 48 derivatives of benzaldehyde, benzoic acid, and cinnamic acid compounds were used to construct three-dimensional quantitative structure-activity relationship (3D-QSAR) models using comparative molecular field (CoMFA) and comparative molecular similarity indices (CoMSIA) analyses. After superimposition using common substructure-based alignments, robust and predictive 3D-QSAR models were obtained from CoMFA ( q 2 = 0.855, r 2 = 0.978) and CoMSIA ( q 2 = 0.841, r 2 = 0.946), with 6 optimum components. Chemical descriptors, including electronic (Hammett σ), hydrophobic (π), and steric (MR) parameters, hydrogen bond acceptor (H-acc), and indicator variable ( I), were used to construct a 2D-QSAR model. The results of this QSAR indicated that π, MR, and H-acc account for 34.9, 31.6, and 26.7% of the calculated biological variance, respectively. The molecular interactions between ligand and target were studied using a flexible docking method (FlexX). The best scored candidates were docked flexibly, and the interaction between the benzoic acid derivatives and the tyrosinase active site was elucidated in detail. We believe that the QSAR models built here provide important information necessary for the design of novel tyrosinase inhibitors.

Development of a Computer-Assisted Simulation of Tactical Voice Communications. Phase I. Conceptual Design.

DTIC Science & Technology

1983-12-01

the output signal. As the number of coefficients increases (as n is made larger in the above equation ), a larger number of spectral peaks can be...kicij’Q,1. Im .6*.* . . ..f’ Hammett , J.C. (June 1979) Tactical commun ations-a precious resource (Student Essay). Carlisle Barracks, PA: U.S. Army War

Historical Perspective and Contribution of U.S. Researchers Into the Field of Self-Propagating High-Temperature Synthesis (SHS)/Combustion Synthesis (CS): Personal Reflections

DTIC Science & Technology

2008-07-01

Gas - Solid Systems. Chem. Eng. Comm. 1990, 92, 199. 74. Dimitriou, P.; Puszynski, J. A.; Hlavacek, V. On the Dynamic of Equations Describing...Yu, L. H.; Thadani, N. N.; Meyers, M. A.; Graham, R. A.; Hammetter , W. F. Shock-Induced Chemical Synthesis of Intermetallic Compounds. In

Linear solvation energy relationships. Solvent effects on the fluorescence of thiabendazole homologues

NASA Astrophysics Data System (ADS)

Tway, Patricia C.; Cline Love, L. J.

1982-03-01

The solvatochromic equations describing the effects of solvent polarity/polarizability (π*), solvent hydrogen bond donor acidity (α), and solvent hydrogen bond acceptor basicity (β) have been determined for several thiabendazole homologues. The s coefficient was found to be linearly related to the Hammett σ + values, and can be used as a measure of substituent effects on the lumiphor.

Toward New Horizons. Volume 10. Explosives and Terminal Ballistics

DTIC Science & Technology

1946-05-01

DuBridge Dr. W. J. Sweeney Dr. Pol Duwez Dr. H. S. Tsien Dr. G. Gamow Dr. G. E. Valley Dr. I. A. Getting Dr. F. L. Wattendorf Dr. L. P. Hammett Dr. F...can be calculated, if the heat quantities for the explosive are known, and some assumptions are made concerning the equation of the state of the

An Assessment of Wave and Wind Data for Use in Design of Tension Leg Platforms - U.S. Offshore Areas.

DTIC Science & Technology

1984-07-01

level crossing rate equations first developed by Rice are commonly employed, reference 4. If one assumes that the wave height variance spectrum is...wave photo was kindly furnished by Mr. Dillard Hammett of SEDCO, Inc. : "The photo was taken in November, 1982. The location was the Ekofisk Field

Optimized Diazo Scaffold for Protein Esterification

PubMed Central

Mix, Kalie A.

2015-01-01

The O-alkylation of carboxylic acids with diazo compounds provides a means to esterify carboxylic acids in aqueous solution. A Hammett analysis of the reactivity of diazo compounds derived from phenylglycinamide revealed that the p-methylphenylglycinamide scaffold has an especially high reaction rate and ester:alcohol product ratio, and esterifies protein carboxyl groups more efficiently than does any known reagent. PMID:25938936

Infrared and Raman studies of hydrogen bonded complexes involving acetone, acetophenone and benzophenone—I. Thermodynamic constants and frequency shifts of the ν OH and ν CO stretching vibrations

NASA Astrophysics Data System (ADS)

Thijs, R.; Zeegers-Huyskens, Th.

The hydrogen bonded complexes between phenol derivatives and acetone ( I), acetophenone ( II) and benzophenone ( III) have been studied in carbon tetrachloride solution by i.r. spectroscopy. The formation constants, the enthalpies of complex formation, the Δν OH and Δν CO values have been determined. For a given phenol derivative, the thermodynamic constants and Δν OH are ordered according to I > II > III and the influence of a substituent implanted on the phenolic ring can be expressed by the Hammett relationship. The ϱ coefficients of the Hammett equation are related to the complexation enthalpies. The Badger—Bauer relation is valid for the three bases. The comparison with complexes involving other carbonyl bases allows to precise the influence of the substituent implanted on the carbonyl group. The Δν OH values obey the dual substituent parameter equation using σ I and σ +R; the ϱ I/ϱ R ratio is higher than one. The Δν CO values are shown to depend on the complexation enthalpy and on the delocalization effect of the substituents.

Papain hydrolysis of X-phenyl-N-methanesulfonyl glycinates: a quantitative structure-activity relationship and molecular graphics analysis.

PubMed

Carotti, A; Smith, R N; Wong, S; Hansch, C; Blaney, J M; Langridge, R

1984-02-15

The hydrolysis of 32 X-phenyl-N-methanesulfonyl glycinates by papain was investigated. It was found that the variation in the Michaelis constants could be rationalized by the following correlation equation: log 1/Km = 0.61 pi '3 + 0.46 MR4 + 0.55 sigma + 2.00 with a correlation coefficient of 0.945. In this expression, pi '3 is the hydrophobic constant for the more lipophilic of the two possible meta substituents, MR4 is the molar refractivity of 4-substituents, and sigma is the Hammett constant summed for all substituents. Using this equation, we designed, synthesized, and successfully predicted Km for a new congener intended to maximize binding (1/Km). The interactions involved in enzyme-substrate binding, as characterized by the correlation equation, are interpreted using a computer-constructed color three-dimensional-graphics molecular model of the enzyme active site. The nonenzymatic hydrolysis (both acid and basic) of phenyl hippurates yield rate constants which are well correlated by Hammett equations; however, log k for both acid and alkaline hydrolysis are not linearly related to log 1/Km or log kcat/Km.

Carboxylate-assisted C–H activation of phenylpyridines with copper, palladium and ruthenium: a mass spectrometry and DFT study† †Electronic supplementary information (ESI) available: Details on the mass-spectrometry experiments and theoretical calculations, Hammett studies, potential energy surfaces, energies, optimized Gaussian geometries and laser-power dependence during the IRMPD spectra measurements. See DOI: 10.1039/c5sc01729g

PubMed Central

Gray, A.; Tsybizova, A.

2015-01-01

The C–H activation of 2-phenylpyridine, catalyzed by copper(ii), palladium(ii) and ruthenium(ii) carboxylates, was studied in the gas phase. ESI-MS, infrared multiphoton dissociation spectroscopy and quantum chemical calculations were combined to investigate the intermediate species in the reaction. Collision induced dissociation (CID) experiments and DFT calculations allowed estimation of the energy required for this C–H activation step and the subsequent acetic acid loss. Hammett plots constructed from the CID experiments using different copper carboxylates as catalysts revealed that the use of stronger acids accelerates the C–H activation step. The reasoning can be traced from the associated transition structures that suggest a concerted mechanism and the key effect of the carbon–metal bond pre-formation. Carboxylates derived from stronger acids make the metal atom more electrophilic and therefore shift the reaction towards the formation of C–H activated products. PMID:29861892

Geologic and hydrostratigraphic map of the Anhalt, Fischer, and Spring Branch 7.5-minute quadrangles, Blanco, Comal, and Kendall Counties, Texas

USGS Publications Warehouse

Clark, Allan K.; Robert R. Morris,

2015-01-01

The hydrostratigraphic units of the Edwards and Trinity aquifers have been mapped and described herein using a classification system developed by Choquette and Pray (1970), which is based on porosity types being fabric or not-fabric selective. The naming of hydrostratigraphic units is also based on preexisting names and topographic or historical features that occur in outcrop. The only hydrostratigraphic unit of the Edwards aquifer present in the study area is VIII hydrostratigraphic unit. The mapped hydrostratigraphic units of the upper Trinity aquifer are, from top to bottom: the cavernous, Camp Bullis, upper evaporite, fossiliferous, and lower evaporite and they are interval equivalent to the upper member of the Glen Rose Limestone. The middle Trinity aquifer (interval equivalent to the lower member of the Glen Rose Limestone) contains, from top to bottom: the Bulverde, Little Blanco, Twin Sisters, Doeppenschmidt, Rust, and Honey Creek hydrostratigraphic units. The lower part of the middle Trinity aquifer is formed by the Hensell, Cow Creek, and Hammett hydrostratigraphic units which are interval equivalent to the Hensell Sand Member, the Cow Creek Limestone, and the Hammett Shale Member, respectively, of the Pearsall Formation.

Structural model of dioxouranium(VI) with hydrazono ligands.

PubMed

Mubarak, Ahmed T

2005-04-01

Synthesis and characterization of several new coordination compounds of dioxouranium(VI) heterochelates with bidentate hydrazono compounds derived from 1-phenyl-3-methyl-5-pyrazolone are described. The ligands and uranayl complexes have been characterized by various physico-chemical techniques. The bond lengths and the force constant have been calculated from asymmetric stretching frequency of OUO groups. The infrared spectral studies showed a monobasic bidentate behaviour with the oxygen and hydrazo nitrogen donor system. The effect of Hammett's constant on the bond distances and the force constants were also discussed and drawn. Wilson's matrix method, Badger's formula, Jones and El-Sonbati equations were used to determine the stretching and interaction force constant from which the UO bond distances were calculated. The bond distances of these complexes were also investigated.

Structural model of dioxouranium(VI) with hydrazono ligands

NASA Astrophysics Data System (ADS)

Mubarak, Ahmed T.

2005-04-01

Synthesis and characterization of several new coordination compounds of dioxouranium(VI) heterochelates with bidentate hydrazono compounds derived from 1-phenyl-3-methyl-5-pyrazolone are described. The ligands and uranayl complexes have been characterized by various physico-chemical techniques. The bond lengths and the force constant have been calculated from asymmetric stretching frequency of O sbnd U sbnd O groups. The infrared spectral studies showed a monobasic bidentate behaviour with the oxygen and hydrazo nitrogen donor system. The effect of Hammett's constant on the bond distances and the force constants were also discussed and drawn. Wilson's matrix method, Badger's formula, Jones and El-Sonbati equations were used to determine the stretching and interaction force constant from which the U sbnd O bond distances were calculated. The bond distances of these complexes were also investigated.

Generation of highly stable and active strong base sites on organized nano-porous alumina by calcium oxide

NASA Astrophysics Data System (ADS)

Tarlani, Aliakbar; Zarabadi, Mir Pouyan

2013-02-01

In a new approach, strong basic sites has been successfully prepared by loading of calcium nitrate (Ca) on organized nano-porous alumina (ONPA). The prepared CaONPAs were characterized by low-angle X-ray diffraction (XRD), N2 adsorption-desorption isotherms (Brunauer-Emmett-Teller (BET)-Barret-Joyner-Halenda (BJH)), transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). Measuring of the amount of the basic sites and the basicity was carried out by titration method, temperature-programmed desorption (TPD-CO2) and Hammett indicators. Resistance of the basic sites was also tested by washing with water. N2 sorption measurements showed that supporting of the calcium nitrate on ONPA can lead to the bimodal porosity at lower loading. BET surface area of the bare ONPA was 212 m2/g which decreased to 111 m2/g for the 25% of loading of Ca (25CaONPA). The results pointed out that CaONPA samples have basicity between 18.4 < H_ < 22 for 15 and 25% of loadings and well-preserved of the basicity after washing with water especially for 5 and 15% samples. Also no crystalline phase of CaO was observed for 25CaONPA which was calcined at 600 °C.

Manual for Courts-Martial, United States, 1984. Revision.

DTIC Science & Technology

1984-01-01

301(d); 301a(c). See also S. Rep. No. 544. 89th Cong., Ist Sess. 13 (1965) which equates "all out war" to a declared war. The legislative history... Hammett v. Texas, 448 U.S. 725 )1974): Shellmun v. U.S. Lines, Inc.. 528 F. 2d 675 (9th Cir. 1975), cert. denied, 425 U.S. 936 (1976). Subsection (41 is

Au-iClick mirrors the mechanism of copper catalyzed azide–alkyne cycloaddition (CuAAC)

DOE PAGES

Powers, Andrew R.; Ghiviriga, Ion; Abboud, Khalil A.; ...

2015-07-20

This report outlines the investigation of the iClick mechanism between gold(I)-azides and gold(I)-acetylides to yield digold triazolates. Isolation of digold triazolate complexes offer compelling support for the role of two copper(I) ions in CuAAC. In addition, a kinetic investigation reveals the reaction is first order in both Au(I)-N 3 and Au(I)-C≡C-R equivalent to C-R, thus second order overall. A Hammett plot with a ρ = 1.02(5) signifies electron-withdrawing groups accelerate the cycloaddition by facilitating the coordination of the second gold ion in a π-complex. Rate inhibition by the addition of free triphenylphosphine to the reaction indicates that ligand dissociation ismore » a prerequisite for the reaction. The mechanistic conclusions mirror those proposed for the CuAAC reaction.« less

Ultrasonic-assisted production of biodiesel from transesterification of palm oil over ostrich eggshell-derived CaO catalysts.

PubMed

Chen, Guanyi; Shan, Rui; Shi, Jiafu; Yan, Beibei

2014-11-01

In this study, waste ostrich eggshell-derived calcium oxide (denoted as CaO(OE)) particles were synthesized and explored as cost-effective catalysts for the ultrasonic-assisted transesterification of palm oil. The physicochemical properties of the resultant catalysts were characterized by XRD, N2 adsorption, XRF and Hammett indicator, while the catalytic activity was evaluated through transesterification of palm oil with methanol under ultrasonic conditions. More specifically, the CaO(OE) showed comparable catalytic activity to the one derived from commercial calcium carbonate (denoted as CaO(Lab)). Moreover, under ultrasonic conditions, the catalytic activity of CaO(OE) could be enhanced significantly. The maximum yield of fatty acid methyl esters could reach 92.7% under the optimal condition of reaction time of 60 min with ultrasonic power of 60% (120 W), methanol-to-oil ratio of 9:1, and catalyst loading of 8 wt.%. The results indicated that the CaO(OE) catalysts showed good catalytic performance and reusability, and may potentially reduce the cost of biodiesel production. Copyright © 2014 Elsevier Ltd. All rights reserved.

Effect of the chemical modification of a macrocycle and the acidity of a medium on the spectral properties and basicity of tetraphenylporphyrin in HCl- N, N-dimethylformamide system at 298 K

NASA Astrophysics Data System (ADS)

Ivanova, Yu. B.; Razgonyaev, O. V.; Semeikin, A. S.; Mamardashvili, N. Zh.

2016-05-01

Spectrophotometric titration is used to study the basicity of tetraphenylporphine and its derivatives with electron-donor and electron-acceptor substituents in the 4-positions of meso-aryl fragments (5,10,15,20-tetra(4-R-phenyl)porphine, R:-OH,-NH2,-COOH,-Cl) in a system HCl- N, N-dimethylformamide at 298 K. An equation for calculating the dependence of the Hammett constant ( H 0) on the HCl concentration in a HCl- N, N-dimethylformamide system at 298 K is proposed. It is found that protonation of the intracycle nitrogen atoms of tetrapyrrole macrocycles of the indicated compounds occurs in two stages in this system. The corresponding ionization constants and concentration ranges of the existence of mono- and doubly-protonated dication forms of the indicated compounds are determined. It is found that both the introduction of strong substituents into the macrocycle of porphyrin and the properties of the medium facilitate the formation of mono- and doubly-protonated forms of porphyrins in solutions.

Basicity of pyridine and some substituted pyridines in ionic liquids.

PubMed

Angelini, Guido; De Maria, Paolo; Chiappe, Cinzia; Fontana, Antonella; Pierini, Marco; Siani, Gabriella

2010-06-04

The equilibrium constants for ion pair formation of some pyridines have been evaluated by spectrophotometric titration with trifluoroacetic acid in different ionic liquids. The basicity order is the same in ionic liquids and in water. The substituent effect on the equilibrium constant has been discussed in terms of the Hammett equation. Pyridine basicity appears to be less sensitive to the substituent effect in ionic liquids than in water.

Archaeological Investigations at Site 45-DO-326, Chief Joseph Dam Project, Washington.

DTIC Science & Technology

1984-01-01

Neal Crozier, Sarah K. Campbell and Julia E. Hammett wrote Chapter 2. Stephanie Livingston analyzed .- the faunal assemblage and wrote Chapter 4. Dorothy...mathematical equations derived from analysis of cases with known memberships. First, we assembled representative specimens for each -~~ ~ ,%, -. 79 Table 3-25...we used derived equations called discriminant functions to assign specimens In our collection lo the statistically defined projectile point types

Anticancer Agents Based on a New Class of Transition- State Analog Inhibitors for Serine and Cysteine Proteases

DTIC Science & Technology

1999-08-01

electrostatic repulsion between the het- eroatom and the ketone. Swain and Lupton31 have constructed a modified Hammett equation (eq 2) in which they...determined by nonlinear fit to the Michaelis-Menten equation for competitive inhibition using simple weighing. Competitive inhibition was confirmed... equation for competitive inhibition using simple weighing. Competitive inhibition was confirmed by Lineweaver - Burk analysis using simple

Analysis of the Inhibition of Mammalian Carboxylesterases by Novel Fluorobenzoins and Fluorobenzils

PubMed Central

Hicks, Latorya D.; Hyatt, Janice L; Moak, Teri; Edwards, Carol C.; Tsurkan, Lyudmila; Wierdl, Monika; Ferreira, Antonio; Wadkins, Randy M.; Potter, Philip M.

2007-01-01

We have synthesized and assessed the ability of symmetrical fluorobenzoins and fluorobenzils to inhibit mammalian carboxylesterases (CE). The majority of the latter were excellent inhibitors of CEs however unexpectedly, the fluorobenzoins were very good enzyme inhibitors. Positive correlations were seen with the charge on the hydroxyl carbon atom, the carbonyl oxygen, and the Hammett constants for the derived Ki values with the fluorobenzoins. PMID:17399985

Density functional theory study of hydrogen atom abstraction from a series of para-substituted phenols: why is the Hammett σ(p)+ constant able to represent radical reaction rates?

PubMed

Yoshida, Tatsusada; Hirozumi, Koji; Harada, Masataka; Hitaoka, Seiji; Chuman, Hiroshi

2011-06-03

The rate of hydrogen atom abstraction from phenolic compounds by a radical is known to be often linear with the Hammett substitution constant σ(+), defined using the S(N)1 solvolysis rates of substituted cumyl chlorides. Nevertheless, a physicochemical reason for the above "empirical fact" has not been fully revealed. The transition states of complexes between the 2,2-diphenyl-1-picrylhydrazyl radical (dpph·) and a series of para-substituted phenols were determined by DFT (Density Functional Theory) calculations, and then the activation energy as well as the homolytic bond dissociation energy of the O-H bond and charge distribution in the transition state were calculated. The heterolytic bond dissociation energy of the C-Cl bond and charge distribution in the corresponding para-substituted cumyl chlorides were calculated in parallel. Excellent correlations among σ(+), charge distribution, and activation and bond dissociation energies revealed quantitatively that there is a strong similarity between the two reactions, showing that the electron-deficiency of the π-electron system conjugated with a substituent plays a crucial role in determining rates of the two reactions. The results provide a new insight into and physicochemical understanding of σ(+) in the hydrogen abstraction from substituted phenols by a radical.

Estimation of hydrolysis rate constants for carbamates ...

EPA Pesticide Factsheets

Cheminformatics based tools, such as the Chemical Transformation Simulator under development in EPA’s Office of Research and Development, are being increasingly used to evaluate chemicals for their potential to degrade in the environment or be transformed through metabolism. Hydrolysis represents a major environmental degradation pathway; unfortunately, only a small fraction of hydrolysis rates for about 85,000 chemicals on the Toxic Substances Control Act (TSCA) inventory are in public domain, making it critical to develop in silico approaches to estimate hydrolysis rate constants. In this presentation, we compare three complementary approaches to estimate hydrolysis rates for carbamates, an important chemical class widely used in agriculture as pesticides, herbicides and fungicides. Fragment-based Quantitative Structure Activity Relationships (QSARs) using Hammett-Taft sigma constants are widely published and implemented for relatively simple functional groups such as carboxylic acid esters, phthalate esters, and organophosphate esters, and we extend these to carbamates. We also develop a pKa based model and a quantitative structure property relationship (QSPR) model, and evaluate them against measured rate constants using R square and root mean square (RMS) error. Our work shows that for our relatively small sample size of carbamates, a Hammett-Taft based fragment model performs best, followed by a pKa and a QSPR model. This presentation compares three comp

Molecular basis of quantitative structure-properties relationships (QSPR): a quantum similarity approach.

PubMed

Ponec, R; Amat, L; Carbó-Dorca, R

1999-05-01

Since the dawn of quantitative structure-properties relationships (QSPR), empirical parameters related to structural, electronic and hydrophobic molecular properties have been used as molecular descriptors to determine such relationships. Among all these parameters, Hammett sigma constants and the logarithm of the octanol-water partition coefficient, log P, have been massively employed in QSPR studies. In the present paper, a new molecular descriptor, based on quantum similarity measures (QSM), is proposed as a general substitute of these empirical parameters. This work continues previous analyses related to the use of QSM to QSPR, introducing molecular quantum self-similarity measures (MQS-SM) as a single working parameter in some cases. The use of MQS-SM as a molecular descriptor is first confirmed from the correlation with the aforementioned empirical parameters. The Hammett equation has been examined using MQS-SM for a series of substituted carboxylic acids. Then, for a series of aliphatic alcohols and acetic acid esters, log P values have been correlated with the self-similarity measure between density functions in water and octanol of a given molecule. And finally, some examples and applications of MQS-SM to determine QSAR are presented. In all studied cases MQS-SM appeared to be excellent molecular descriptors usable in general QSPR applications of chemical interest.

Molecular basis of quantitative structure-properties relationships (QSPR): A quantum similarity approach

NASA Astrophysics Data System (ADS)

Ponec, Robert; Amat, Lluís; Carbó-dorca, Ramon

1999-05-01

Since the dawn of quantitative structure-properties relationships (QSPR), empirical parameters related to structural, electronic and hydrophobic molecular properties have been used as molecular descriptors to determine such relationships. Among all these parameters, Hammett σ constants and the logarithm of the octanol- water partition coefficient, log P, have been massively employed in QSPR studies. In the present paper, a new molecular descriptor, based on quantum similarity measures (QSM), is proposed as a general substitute of these empirical parameters. This work continues previous analyses related to the use of QSM to QSPR, introducing molecular quantum self-similarity measures (MQS-SM) as a single working parameter in some cases. The use of MQS-SM as a molecular descriptor is first confirmed from the correlation with the aforementioned empirical parameters. The Hammett equation has been examined using MQS-SM for a series of substituted carboxylic acids. Then, for a series of aliphatic alcohols and acetic acid esters, log P values have been correlated with the self-similarity measure between density functions in water and octanol of a given molecule. And finally, some examples and applications of MQS-SM to determine QSAR are presented. In all studied cases MQS-SM appeared to be excellent molecular descriptors usable in general QSPR applications of chemical interest.

Predicting the photoinduced electron transfer thermodynamics in polyfluorinated 1,3,5-triarylpyrazolines based on multiple linear free energy relationships†

PubMed Central

Verma, Manjusha; Chaudhry, Aneese F.; Fahrni, Christoph J.

2010-01-01

The photophysical properties of 1,3,5-triarylpyrazolines are strongly influenced by the nature and position of substituents attached to the aryl-rings, rendering this fluorophore platform well suited for the design of fluorescent probes utilizing a photoinduced electron transfer (PET) switching mechanism. To explore the tunability of two key parameters that govern the PET thermodynamics, the excited state energy ΔE00 and acceptor potential E(A/A−), a library of polyfluoro-substituted 1,3-diaryl-5-phenyl-pyrazolines was synthesized and characterized. The observed trends for the PET parameters were effectively captured through multiple Hammett linear free energy relationships (LFER) using a set of independent substituent constants for each of the two aryl rings. Given the lack of experimental Hammett constants for polyfluoro substituted aromatics, theoretically derived constants based on the electrostatic potential at the nucleus (EPN) of carbon atoms were employed as quantum chemical descriptors. The performance of the LFER was evaluated with a set of compounds that were not included in the training set, yielding a mean unsigned error of 0.05 eV for the prediction of the combined PET parameters. The outlined LFER approach should be well suited to design and optimize the performance of cation-responsive 1,3,5-triarylpyrazolines. PMID:19343239

The Role of the Y-Located TSPY Gene in Prostatic Oncongenesis

DTIC Science & Technology

2006-02-01

Vizantios Y, Freeman R, Sicurella C, Hammett F, Armes J, Venter D. Cyclooxygenase-2, a colorectal cancer nonsteroidal anti - inflammatory drug target, is...antibodies were detected using ap- propriate secondary antibodies (1:4,000 peroxidase conjugated Donkey anti rabbit/Sheep anti mouse [Amersham...known as ( non )dysgerminomas of the ovary and dysgenetic gonad, and ( non )germinomas of the brain. Various risk factors for these types of GCTs have beenary

Geometric Universality in Brain Allosteric Protein Dynamics: Complex Hydrophobic Transformation Predicts Mutual Recognition by Polypeptides and Proteins,

DTIC Science & Technology

1986-10-01

organic acids using the Hammett equation , has been called the hydrophobic effect.’ Water adjusts its geometry to maximize the number of intact hydrogen...understanding both structural stability with respect to the underlying equations (not initial values) and phase transitions in these dynamical hierarchies...for quantitative characterization. Although the complicated behavior is gen- erated by deterministic equations , its description in entropies leads to

A Common Mechanism for Resistance to Oxime Reactivation of Acetylcholinesterase Inhibited by Organophosphorus Compounds

DTIC Science & Technology

2013-01-01

application of the Hammett equation with the constants rph in the chemistry of organophosphorus compounds, Russ. Chem. Rev. 38 (1969) 795–811. [13...of oximes and OP compounds and the ability of oximes to reactivate OP- inhibited AChE. Multiple linear regression equations were analyzed using...phosphonate pairs, 21 oxime/ phosphoramidate pairs and 12 oxime/phosphate pairs. The best linear regression equation resulting from multiple regression anal

Nitrous Acid as an Oxidant in Acidic Media

DTIC Science & Technology

1979-09-25

nitroso oxidations were run in sulfuric acid. The Hammett acidity function is used as the abscissa because it conveniently represents the acidity region...oxidation. 13 Consistent with the general mechanism, equations (1)-(3), and in contrast to nitration, phenol nitrosation displays a primary kinetic...oxidized 1(III) + Alc - 104O + C-O (4) with the only route now removing HNO being NO+ + H - H + + 2N0 (5) Apparently while alcohol remains, equation (5

Substituent Effects on Thermal Decolorization Rates of Bisbenzospiropyrans

PubMed Central

Lu, Nina T.; Nguyen, Vi N.; Kumar, Satish; McCurdy, Alison

2009-01-01

A novel application of photochromic molecules is to mimic physiological oscillatory calcium signals by reversibly binding and releasing calcium ions in response to light. Substituent changes on the largely unexplored photochromic bisbenzospiropyran scaffold led to significant changes in thermal fading rates in several organic solvents. Excellent correlations have been found between fading rates and empirical Hammett constants as well as calculated ground-state energies. These correlations can be used to improve scaffold design. PMID:16238356

Substituent effect study on experimental ¹³C NMR chemical shifts of (3-(substituted phenyl)-cis-4,5-dihydroisoxazole-4,5-diyl)bis(methylene)diacetate derivatives.

PubMed

Kara, Yesim S

2015-12-05

Eleven novel (3-(substituted phenyl)-cis-4,5-dihydroisoxazole-4,5-diyl)bis(methylene) diacetate derivatives were synthesized in the present study. These dihydroisoxazole derivatives were characterized by IR, (1)H NMR, (13)C NMR and elemental analyses. Their (13)C NMR spectra were measured in Deuterochloroform (CDCl3). The correlation analysis for the substituent-induced chemical shift (SCS) with Hammett substituent constant (σ), inductive substituent constant (σI), different of resonance substituent constants (σR, σR(o)) and Swain-Lupton substituent parameters (F, R) were performed using SSP (single substituent parameter), and DSP (dual substituent parameter) methods, as well as single and multiple regression analysis. From the result of regression analysis, the effect of substituent on the (13)C NMR chemical shifts was explained. Copyright © 2015 Elsevier B.V. All rights reserved.

Linearly exact parallel closures for slab geometry

NASA Astrophysics Data System (ADS)

Ji, Jeong-Young; Held, Eric D.; Jhang, Hogun

2013-08-01

Parallel closures are obtained by solving a linearized kinetic equation with a model collision operator using the Fourier transform method. The closures expressed in wave number space are exact for time-dependent linear problems to within the limits of the model collision operator. In the adiabatic, collisionless limit, an inverse Fourier transform is performed to obtain integral (nonlocal) parallel closures in real space; parallel heat flow and viscosity closures for density, temperature, and flow velocity equations replace Braginskii's parallel closure relations, and parallel flow velocity and heat flow closures for density and temperature equations replace Spitzer's parallel transport relations. It is verified that the closures reproduce the exact linear response function of Hammett and Perkins [Phys. Rev. Lett. 64, 3019 (1990)] for Landau damping given a temperature gradient. In contrast to their approximate closures where the vanishing viscosity coefficient numerically gives an exact response, our closures relate the heat flow and nonvanishing viscosity to temperature and flow velocity (gradients).

Functional analogue reaction systems of the DMSO reductase isoenzyme family: probable mechanism of S-oxide reduction in oxo transfer reactions mediated by bis(dithiolene)-tungsten(IV,VI) complexes.

PubMed

Sung, Kie-Moon; Holm, R H

2002-04-24

The recent development of structural and functional analogues of the DMSO reductase family of isoenzymes allows mechanistic examination of the minimal oxygen atom transfer paradigm M(IV) + QO M(VI) O + Q with the biological metals M = Mo and W. Systematic variation of the electronic environment at the WIV center of desoxo bis(dithiolene) complexes is enabled by introduction of para-substituted phenyl groups in the equatorial (eq) dithiolene ligand and the axial (ax) phenolate ligand. The compounds [W(CO)2(S2C2(C6H4-p-X)2)2] (54-60%) have been prepared by ligand transfer from [Ni(S2C2(C6H4-p-X)2)2] to [W(CO)3(MeCN)3]. A series of 25 complexes [W(IV)(OC6H4-p-X')(S2C2(C6H4-p-X)2)2]1- ([X4,X'], X = Br, F, H, Me, OMe; X' = CN, Br, H, Me, NH2; 41-53%) has been obtained by ligand substitution of five dicarbonyl complexes with five phenolate ligands. Linear free energy relationships between E1/2 and Hammett constant p for the electron-transfer series [Ni(S2C2(C6H4-p-X)2)2]0,1-,2- and [W(CO)2(S2C2(C6H4-p-X)2)2]0,1-,2- demonstrate a substituent influence on electron density distribution at the metal center. The reactions [WIV(OC6H4-p-X')(S2C2(C6H4-p-X)2)2]1- + (CH2)4SO [W(VI)O(OC6H4-p-X')(S2C2(C6H4-p-X)2)2]1- + (CH2)4S with constant substrate are second order with large negative activation entropies indicative of an associative transition state. Rate constants at 298 K adhere to the Hammett equations log(k([X4,X']/k[X4,H]) = rho(ax)sigma(p) and log(k[X4,X']/k([H4,X']) = 4rho(eq)sigma(p). Electron-withdrawing groups (EWG) and electron-donating groups (EDG) have opposite effects on the rate such that k(EWG) > k(EDG). The effects of X' on reactivity are found to be approximately 5 times greater than that of X (rho(ax) = 2.1, rho(eq) = 0.44) in the Hammett equation. Using these and other findings, a stepwise oxo transfer reaction pathway is proposed in which an early transition state, of primary W(IV)-O(substrate) bond-making character, is rate-limiting. This is followed by a six-coordinate substrate complex and a second transition state proposed to involve atom and electron transfer leading to the development of the W(VI)=O group. This work is the most detailed mechanistic investigation of oxo transfer mediated by a biological metal.

Development and Resuscitation of a Sedated, Mature Male Miniature Swine Severe Hemorrhage Model

DTIC Science & Technology

2011-07-01

control. Results: Hemorrhage resulted in a characteristic hypotension and metabolic acidosis . Survival time for the control swine was 64 minutes...domestic swine4 and was characteristic of a hemorrhage- induced metabolic acidosis , with a decrease in blood HCO3, and BE and an increase in blood...Hammett M, Asher L, et al. Effects of bovine polymerized hemoglobin on coagulation in controlled hemorrhagic shock in swine. Shock. 2005;24:145–152

Applications of Correlation Techniques for Battlefield Identification I.

DTIC Science & Technology

1984-06-30

Participants: .. Carolynn Black Rick Clough Jeanie Fiskin Fif Ghobadian P- Bob Hammett Mary Hernried Lee Leong . Joe Martinetto. d ,i,=r:,,ti b ,: ., , . Glenn... equations . The Clinic team named the process of finding the coefficients matrix "backsolving" since the algorithm starts with the. desired result (the...independent of one another. The jth component of each vector satisfies the equation x3(t) -P + YO(t) where xj(t) is the value of the ith characteristic at

Quantitative structure-activity relationship analysis of substituted arylazo pyridone dyes in photocatalytic system: Experimental and theoretical study.

PubMed

Dostanić, J; Lončarević, D; Zlatar, M; Vlahović, F; Jovanović, D M

2016-10-05

A series of arylazo pyridone dyes was synthesized by changing the type of the substituent group in the diazo moiety, ranging from strong electron-donating to strong electron-withdrawing groups. The structural and electronic properties of the investigated dyes was calculated at the M062X/6-31+G(d,p) level of theory. The observed good linear correlations between atomic charges and Hammett σp constants provided a basis to discuss the transmission of electronic substituent effects through a dye framework. The reactivity of synthesized dyes was tested through their decolorization efficiency in TiO2 photocatalytic system (Degussa P-25). Quantitative structure-activity relationship analysis revealed a strong correlation between reactivity of investigated dyes and Hammett substituent constants. The reaction was facilitated by electron-withdrawing groups, and retarded by electron-donating ones. Quantum mechanical calculations was used in order to describe the mechanism of the photocatalytic oxidation reactions of investigated dyes and interpret their reactivities within the framework of the Density Functional Theory (DFT). According to DFT based reactivity descriptors, i.e. Fukui functions and local softness, the active site moves from azo nitrogen atom linked to benzene ring to pyridone carbon atom linked to azo bond, going from dyes with electron-donating groups to dyes with electron-withdrawing groups. Copyright © 2016 Elsevier B.V. All rights reserved.

Density Functional Theory and ab Initio Computational Evidence for Nitrosamine Photoperoxides: Hammett Substituent Effects in the Photogeneration of the Nitrooxide Intermediate.

PubMed

Greer, Edyta M; Kwon, Kitae

2018-05-20

Little attention has been focused on diradical and zwitterionic photoperoxides formed from nitrosamine compounds. Here, an attempt is made to probe the electronic character of the nitrooxide intermediate formed in photochemical reactions with triplet oxygen ( 3 O 2 ). Theoretical studies have been conducted to screen para-substituted phenyl nitrosamines. In particular, we find that electron-withdrawing substituents produce low-lying triplet nitrooxide diradicals. A clear electronic dependence in the S 0 - T 1 and S 0 - S 1 energy gaps of nitrooxides was found using Hammett plots. Computed geometries show a twisted diradical triplet nitrooxide moiety, which contrasts to the nearly flat singlet zwitterionic ground-state nitrooxide moiety; analyses of charges (natural bond order), molecular orbitals (HOMO/LUMO), and spin densities enable these assignments. Calculations predict the former triplet species is photogenerated initially from nitrosamine with O 2 . The conversion of the triplet nitrooxide diradical to the singlet ground state is an example where longer-lived zwitterionic nitrooxide structures become possible. The reaction mechanism is consistent with a zwitterionic ground-state nitrooxide playing an important role in the bimolecular oxygen-transfer reaction with phosphine and phosphite trapping agents as has been observed experimentally. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.

Catechol-Cation Synergy in Wet Adhesive Materials

NASA Astrophysics Data System (ADS)

Maier, Gregory Peter

In physiological fluids and seawater, adhesion of synthetic polymers to solid surfaces is impaired by high salt, pH, and hydration. However, mussels have evolved effective strategies for wet adhesion despite these impediments. Inspection of mussel foot proteins (Mfps) provides insights into adhesive adaptations. Catecholic Dopa (3,4-dihydroxyphenylalanine) and lysine residues are present in high mole percent in the interfacial Mfps. The siderophore cyclic trichrysobactin also contains high mole percent of catechol and lysine and serves as a simplified mimic of Mfps. This work is focused on use of Mfp-mimetic siderophores and synthetic siderophore analogs as model systems for dissecting the chemical and physical interactions that enable wet adhesion. Variation in number and identity of functional groups appended to the synthetic siderophore analogs allows identification of the specific contributions of those functional groups to wet adhesion. Both catechol and amine functional groups are critical to strong wet adhesion. The primary amine of lysine and catechol cooperatively displace interfacial hydration and bind to the underlying substrate. Variation in the amine identity as well as the amine to catechol ratio within siderophore analogs also has a significant impact on wet adhesive performance. Catechol undergoes a pH-dependent autoxidation in which higher pH leads to faster oxidation by dioxygen. This oxidation abolishes all adhesion of Mfps to mica by pH 7.5, yet many applications of synthetic wet adhesives require adhesion at physiological or oceanic pH. A better understanding of catechol redox chemistry is critical to the design of wet adhesives. To this end, the pH-dependent autoxidation of catechol and substituted catechols was investigated and results are consistent with a mechanism in which O2 oxidizes both the mono-deprotonated and di-deprotonated catechol. A linear Hammett correlation for the pH-independent second order rate constants for catechol autoxidation indicates that catechols become resistant to autoxidation when functionalized with electron withdrawing groups and more susceptible to autoxidation when functionalized with electron donating groups. Analysis of substituent effects through Hammett correlation allows for selection of functionalized catechols with redox properties ideally suited for a given application.

Equilibrium constants and protonation site for N-methylbenzenesulfonamides

PubMed Central

Rosa da Costa, Ana M; García-Río, Luis; Pessêgo, Márcia

2011-01-01

Summary The protonation equilibria of four substituted N-methylbenzenesulfonamides, X-MBS: X = 4-MeO (3a), 4-Me (3b), 4-Cl (3c) and 4-NO2 (3d), in aqueous sulfuric acid were studied at 25 °C by UV–vis spectroscopy. As expected, the values for the acidity constants are highly dependent on the electron-donor character of the substituent (the pK BH+ values are −3.5 ± 0.2, −4.2 ± 0.2, −5.2 ± 0.3 and −6.0 ± 0.3 for 3a, 3b, 3c and 3d, respectively). The solvation parameter m* is always higher than 0.5 and points to a decrease in the importance of solvation on the cation stabilization as the electron-donor character of the substituent increases. Hammett plots of the equilibrium constants showed a better correlation with the σ+ substituent parameter than with σ, which indicates that the initial protonation site is the oxygen atom of the sulfonyl group. PMID:22238552

Synthesis, Characterization, Tautomeric Structure and Solvatochromic Behavior of Novel 4-(5-Arylazo-2-Hydroxystyryl)-1-Methylpyridinium Iodide as Potential Molecular Photoprobe

PubMed Central

Altalbawy, Farag; Darwish, Elham; Medhat, Mohamed; El-Zaiat, Sayed; Saleh, Hagar

2016-01-01

A novel series of the title compound 4-(5-arylazo-2-hydroxystyryl)-1-methylpyridinium iodide 6 has been synthesized via condensation reactions of the arylazosalicylaldehyde derivatives 4a–i with 1-methyl-picolinium iodide 5. The structures of the new arylazo compounds were characterized by 1H NMR, IR, mass spectroscopy, as well as spectral and elemental analyses. The electronic absorption spectra of arylazomerocyanine compounds 6 were measured in different buffer solutions and solvents. The pK′s and pK*′s in both the ground and excited states, respectively, were determined for the series and their correlations with the Hammett equation were examined. The results indicated that the title arylazomerocyanine dyes 6 exist in the azo form 6A in both ground and excited states. The substituent and solvent effects (solvatochromism) of the title compound arylazomerocyanine dyes were determined using the Kamlet-Taft equation and subsequently discussed. PMID:28774142

Synthesis, Characterization, Tautomeric Structure and Solvatochromic Behavior of Novel 4-(5-Arylazo-2-Hydroxystyryl)-1-Methylpyridinium Iodide as Potential Molecular Photoprobe.

PubMed

Altalbawy, Farag; Darwish, Elham; Medhat, Mohamed; El-Zaiat, Sayed; Saleh, Hagar

2016-12-19

A novel series of the title compound 4-(5-arylazo-2-hydroxystyryl)-1-methylpyridinium iodide 6 has been synthesized via condensation reactions of the arylazosalicylaldehyde derivatives 4a - i with 1-methyl-picolinium iodide 5 . The structures of the new arylazo compounds were characterized by ¹H NMR, IR, mass spectroscopy, as well as spectral and elemental analyses. The electronic absorption spectra of arylazomerocyanine compounds 6 were measured in different buffer solutions and solvents. The pK's and pK*'s in both the ground and excited states, respectively, were determined for the series and their correlations with the Hammett equation were examined. The results indicated that the title arylazomerocyanine dyes 6 exist in the azo form 6A in both ground and excited states. The substituent and solvent effects (solvatochromism) of the title compound arylazomerocyanine dyes were determined using the Kamlet-Taft equation and subsequently discussed.

Highly Cooperative Tetrametallic Ruthenium-μ-Oxo-μ-Hydroxo Catalyst for the Alcohol Oxidation Reaction

PubMed Central

Yi, Chae S.; Zeczycki, Tonya N.; Guzei, Ilia A.

2008-01-01

The tetrametallic ruthenium-oxo-hydroxo-hydride complex {[(PCy3)(CO)RuH]4(μ4-O)(μ3-OH)(μ2-OH)} (1) was synthesized in two steps from the monomeric complex (PCy3)(CO)RuHCl (2). The tetrameric complex 1 was found to be a highly effective catalyst for the transfer dehydrogenation of alcohols. Complex 1 showed a different catalytic activity pattern towards primary and secondary benzyl alcohols, as indicated by the Hammett correlation for the oxidation reaction of p-X-C6H4CH2OH (ρ = −0.45) and p-X-C6H4CH(OH)CH3 (ρ = +0.22) (X = OMe, CH3, H, Cl, CF3). Both a sigmoidal curve from the plot of initial rate vs [PhCH(OH)CH3] (K0.5 = 0.34 M; Hill coefficient, n = 4.2±0.1) and the phosphine inhibition kinetics revealed the highly cooperative nature of the complex for the oxidation of secondary alcohols. PMID:18726005

IR and NMR spectral studies of 4-bromo-1-naphthyl chalcones-assessment of substituent effects

NASA Astrophysics Data System (ADS)

Thirunarayanan, G.; Gopalakrishnan, M.; Vanangamudi, G.

2007-07-01

Infrared νCO (cm -1) of s-cis and s-trans frequencies and nuclear magnetic resonance chemical shifts δ1H (ppm) of H-α and H-β, δ13C (ppm) of C-α and C-β data were assigned from their respective spectra of a series of various substituted styryl 4-bromo-1-naphthyl chalcones. These values are correlated with various Hammett substituent constants. From the results of statistical analysis, the effect of substituents can be explained.

Anilinomethylrhodamines: pH sensitive probes with tunable photophysical properties by substituent effect.

PubMed

Best, Quinn A; Liu, Chuangjun; van Hoveln, Paul D; McCarroll, Matthew E; Scott, Colleen N

2013-10-18

A series of pH dependent rhodamine analogues possessing an anilino-methyl moiety was developed and shown to exhibit a unique photophysical response to pH. These anilinomethylrhodamines (AnMR) maintain a colorless, nonfluorescent spirocyclic structure at high pH. The spirocyclic structures open in mildly acidic conditions and are weakly fluorescent; however, at very low pH, the fluorescence is greatly enhanced. The equilibrium constants of these processes show a linear response to substituent effects, which was demonstrated by the Hammett equation.

Substituent and solvent effects on electronic spectra of some substituted phenoxyacetic acids.

PubMed

Shanthi, M; Kabilan, S

2007-06-01

The effects of substituents and solvents have been studied through the absorption spectra of nearly 19 para- and ortho-substituted phenoxyacetic acids in the range of 200-400 nm. The effects of substituent on the absorption spectra of compounds under present investigation are interpreted by correlation of absorption frequencies with simple and extended Hammett equations. Effect of solvent polarity and hydrogen bonding on the absorption spectra are interpreted by means of Kamlet equation and the results are discussed.

Substituent and solvent effects on electronic spectra of some substituted phenoxyacetic acids

NASA Astrophysics Data System (ADS)

Shanthi, M.; Kabilan, S.

2007-06-01

The effects of substituents and solvents have been studied through the absorption spectra of nearly 19 para- and ortho-substituted phenoxyacetic acids in the range of 200-400 nm. The effects of substituent on the absorption spectra of compounds under present investigation are interpreted by correlation of absorption frequencies with simple and extended Hammett equations. Effect of solvent polarity and hydrogen bonding on the absorption spectra are interpreted by means of Kamlet equation and the results are discussed.

Substituent and solvent effects on electronic absorption spectra of some N-(substitutedphenyl)benzene sulphonamides

NASA Astrophysics Data System (ADS)

Suganya, Krishnasamy; Kabilan, Senthamaraikannan

2004-04-01

The effects of substituents and solvents have been studied through the absorption spectra of nearly 23 ortho- and para-N-(substitutedphenyl)benzene sulphonamides in the range of 200-400 nm. The effects of substituents on the absorption spectra of compounds under present investigation are interpreted by correlation of absorption frequencies with simple and extended Hammett equations. Effect of solvent polarity and hydrogen bonding on the absorption spectra are interpreted by means of Kamlet equation and the results are discussed.

Archaeological Investigations at Sites 45-OK-2 and 45-OK-2A, Chief Joseph Dam Project, Washington.

DTIC Science & Technology

1984-01-01

Under the direction of Karen Whittlesey and Kathy Lewin, Judith Groves, Cindy Amdur, and Julie Hammett did the technological artifact * analysis and...with ash and charcoal was observed which equates to our floor. A hearth was found on the floor near the center .q4 of the depression. Charred timbers...chronologies developed for the Wells Reservoir and Kettle Falls, Zone 4 equates with the ChIliwist and Ksunku phases respectively, although If Zone 4 is

Propargylic activation across a heterobimetallic ir-sn catalyst: nucleophilic substitution and indene formation with propargylic alcohols.

PubMed

Chatterjee, Paresh Nath; Roy, Sujit

2010-07-02

A nucleophilic substitution of propargylic alcohols with carbon (arene, heteroarene, and allyltrimethylsilane), sulfur (thiol), oxygen (alcohol), and nitrogen (sulfonamide) nucleophiles has been demonstrated using a high-valent [Ir(COD)(SnCl(3))Cl(mu-Cl)](2) catalyst in 1,2-dichloroethane to afford the corresponding propargylic products in moderate to excellent yields. Alkyl or aryl substituted tertiary propargylic alcohols produce substituted indenes with bulky arenes via allenylic intermediate. An electrophilic mechanism is proposed from Hammett correlation.

Biodiesel production from non-edible Silybum marianum oil using heterogeneous solid base catalyst under ultrasonication.

PubMed

Takase, Mohammed; Chen, Yao; Liu, Hongyang; Zhao, Ting; Yang, Liuqing; Wu, Xiangyang

2014-09-01

The aim of this study is to investigate modified TiO2 doped with C4H4O6HK as heterogeneous solid base catalyst for transesterification of non-edible, Silybum marianum oil to biodiesel using methanol under ultrasonication. Upon screening the catalytic performance of modified TiO2 doped with different K-compounds, 0.7 C4H4O6HK doped on TiO2 was selected. The preparation of the catalyst was done using incipient wetness impregnation method. Having doped modified TiO2 with C4H4O6HK, followed by impregnation, drying and calcination at 600 °C for 6 h, the catalyst was characterized by XRD, FTIR, SEM, BET, TGA, UV and the Hammett indicators. The yield of the biodiesel was proportional to the catalyst basicity. The catalyst had granular and porous structures with high basicity and superior performance. Combined conditions of 16:1 molar ratio of methanol to oil, 5 wt.% catalyst amount, 60 °C reaction temperature and 30 min reaction time was enough for maximum yield of 90.1%. The catalyst maintained sustained activity after five cycles of use. The oxidative stability which was the main problem of the biodiesel was improved from 2.0 h to 3.2h after 30 days using ascorbic acid as antioxidant. The other properties including the flash point, cetane number and the cold flow ones were however, comparable to international standards. The study indicated that Ti-0.7-600-6 is an efficient, economical and environmentally, friendly catalyst under ultrasonication for producing biodiesel from S. marianum oil with a substantial yield. Copyright © 2014 Elsevier B.V. All rights reserved.

Comparing simulation of plasma turbulence with experiment

NASA Astrophysics Data System (ADS)

Ross, David W.; Bravenec, Ronald V.; Dorland, William; Beer, Michael A.; Hammett, G. W.; McKee, George R.; Fonck, Raymond J.; Murakami, Masanori; Burrell, Keith H.; Jackson, Gary L.; Staebler, Gary M.

2002-01-01

The direct quantitative correspondence between theoretical predictions and the measured plasma fluctuations and transport is tested by performing nonlinear gyro-Landau-fluid simulations with the GRYFFIN (or ITG) code [W. Dorland and G. W. Hammett, Phys. Fluids B 5, 812 (1993); M. A. Beer and G. W. Hammett, Phys. Plasmas 3, 4046 (1996)]. In an L-mode reference discharge in the DIII-D tokamak [J. L. Luxon and L. G. Davis, Fusion Technol. 8, 441 (1985)], which has relatively large fluctuations and transport, the turbulence is dominated by ion temperature gradient (ITG) modes. Trapped electron modes and impurity drift waves also play a role. Density fluctuations are measured by beam emission spectroscopy [R. J. Fonck, P. A. Duperrex, and S. F. Paul, Rev. Sci. Instrum. 61, 3487 (1990)]. Experimental fluxes and corresponding diffusivities are analyzed by the TRANSP code [R. J. Hawryluk, in Physics of Plasmas Close to Thermonuclear Conditions, edited by B. Coppi, G. G. Leotta, D. Pfirsch, R. Pozzoli, and E. Sindoni (Pergamon, Oxford, 1980), Vol. 1, p. 19]. The shape of the simulated wave number spectrum is close to the measured one. The simulated ion thermal transport, corrected for E×B low shear, exceeds the experimental value by a factor of 1.5 to 2.0. The simulation overestimates the density fluctuation level by an even larger factor. On the other hand, the simulation underestimates the electron thermal transport, which may be accounted for by modes that are not accessible to the simulation or to the BES measurement.

Studies on photoinduced H-atom and electron transfer reactions of o-naphthoquinones by laser flash photolysis.

PubMed

Pan, Yang; Fu, Yao; Liu, Shaoxiong; Yu, Haizhu; Gao, Yuhe; Guo, Qingxiang; Yu, Shuqin

2006-06-15

The quenching of the triplets of 1,2-naphthoquinone (NQ) and 1,2-naphthoquinone-4-sulfonic acid sodium salt (NQS) by various electron and H-atom donors was investigated by laser flash photolysis measurement in acetonitrile and benzene. The results showed that the reactivities and configurations of 3NQ* (3NQS*) are governed by solvent polarity. All the quenching rate constants (kq) measured in benzene are larger than those in acetonitrile. The SO3Na substituent at the C-4 position of NQS makes 3NQS* more reactive than 3NQ* in electron/H-atom transfer reactions. Large differences of kq values were discovered in H-atom transfer reactions for alcohols and phenols, which can be explained by different H-abstraction mechanisms. Detection of radical cations of amines/anilines in time-resolved transient absorption spectra confirms an electron transfer mechanism. Triplets are identified as precursors of formed radical anions of NQ and NQS in photoinduced reactions. The dependence of electron transfer rate constants on the free energy changes (DeltaG) was treated by using the Rehm-Weller equation. For the four anilines with different substituents on the para or meta position of amidocyanogen, good correlation between log kq values with Hammett sigma constants testifies the correctness of empirical Hammett equation. Charge density distributions, adiabatic ionization/affinity potentials and redox potentials of NQ (NQS) and some quenchers were studied by quantum chemistry calculation.

Esterification of oil adsorbed on palm decanter cake into methyl ester using sulfonated rice husk ash as heterogeneous acid catalyst

NASA Astrophysics Data System (ADS)

Hindryawati, Noor; Erwin, Maniam, Gaanty Pragas

2017-02-01

Palm Decanter cake (PDC) which is categorized as the waste from palm oil mill has been found to contain residual crude palm oil. The oil adsorbed on the PDC (PDC-oil) can be extracted and potentially used as feedstock for biodiesel production. Feedstock from waste like PDC-oil is burdened with high free fatty acids (FFAs) which make the feedstock difficult to be converted into biodiesel using basic catalyst. Therefore, in this study, a solid acid, RHA-SO3H catalyst was synthesized by sulfonating rice husk ash (RHA) with concentrated sulfuric acid. The RHA-SO3H prepared was characterized with TGA, FTIR, BET, XRD, FE-SEM, and Hammett indicators (methyl red, bromophenol blue, and crystal violet). PDC was found to have about 11.3 wt. % oil recovered after 1 hour extraction using ultrasound method. The presence of sulfonate group was observed in IR spectrum, and the surface area of RHA-SO3H was reduced to 37 m2.g-1 after impregnation of sulfonate group. The RHA-SO3H catalyst showed that it can work for both esterification of free fatty acid which is present in PDC-oil, and transesterification of triglycerides into methyl ester. The results showed highest methyl ester content of 70.2 wt.% at optimal conditions, which was 6 wt.% catalyst amount, methanol to oil molar ratio of 17:1 for 5 hours at 120 °C.

Effect of preparation method and CuO promotion in the conversion of ethanol into 1,3-butadiene over SiO₂-MgO catalysts.

PubMed

Angelici, Carlo; Velthoen, Marjolein E Z; Weckhuysen, Bert M; Bruijnincx, Pieter C A

2014-09-01

Silica-magnesia (Si/Mg=1:1) catalysts were studied in the one-pot conversion of ethanol to butadiene. The catalyst synthesis method was found to greatly influence morphology and performance, with materials prepared through wet-kneading performing best both in terms of ethanol conversion and butadiene yield. Detailed characterization of the catalysts synthesized through co-precipitation or wet-kneading allowed correlation of activity and selectivity with morphology, textural properties, crystallinity, and acidity/basicity. The higher yields achieved with the wet-kneaded catalysts were attributed to a morphology consisting of SiO2 spheres embedded in a thin layer of MgO. The particle size of the SiO2 catalysts also influenced performance, with catalysts with smaller SiO2 spheres showing higher activity. Temperature-programmed desorption (TPD) measurements showed that best butadiene yields were obtained with SiO2-MgO catalysts characterized by an intermediate amount of acidic and basic sites. A Hammett indicator study showed the catalysts' pK(a) value to be inversely correlated with the amount of dehydration by-products formed. Butadiene yields could be further improved by the addition of 1 wt% of CuO as promoter to give butadiene yields and selectivities as high as 40% and 53%, respectively. The copper promoter boosts the production of the acetaldehyde intermediate changing the rate-determining step of the process. TEM-energy-dispersive X-ray (EDX) analyses showed CuO to be present on both the SiO2 and MgO components. UV/Vis spectra of promoted catalysts in turn pointed at the presence of cluster-like CuO species, which are proposed to be responsible for the increased butadiene production. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Tuning of the ionization potential of paddlewheel diruthenium(II, II) complexes with fluorine atoms on the benzoate ligands.

PubMed

Miyasaka, Hitoshi; Motokawa, Natsuko; Atsuumi, Ryo; Kamo, Hiromichi; Asai, Yuichiro; Yamashita, Masahiro

2011-01-21

A series of paddlewheel diruthenium(ii, ii) complexes with various fluorine-substituted benzoate ligands were isolated as THF adducts and structurally characterized: [Ru(2)(F(x)PhCO(2))(4)(THF)(2)] (F(x)PhCO(2)(-) = o-fluorobenzoate, o-F; m-fluorobenzoate, m-F; p-fluorobenzoate, p-F; 2,6-difluorobenzoate, 2,6-F(2); 3,4-difluorobenzoate, 3,4-F(2); 3,5-difluorobenzoate, 3,5-F(2); 2,3,4-trifluorobenzoate, 2,3,4-F(3); 2,3,6-trifluorobenzoate, 2,3,6-F(3); 2,4,5-trifluorobenzoate, 2,4,5-F(3); 2,4,6-trifluorobenzoate, 2,4,6-F(3); 3,4,5-trifluorobenzoate, 3,4,5-F(3); 2,3,4,5-tetrafluorobenzoate, 2,3,4,5-F(4); 2,3,5,6-tetrafluorobenzoate, 2,3,5,6-F(4); pentafluorobenzoate, F(5)). By adding fluorine atoms on the benzoate ligands, it was possible to tune the redox potential (E(1/2)) for [Ru(2)(II,II)]/[Ru(2)(II,III)](+) over a wide range of potentials from -40 mV to 350 mV (vs. Ag/Ag(+) in THF). 2,3,6-F(3), 2,3,4,5-F(4), 2,3,5,6-F(4) and F(5) were relatively air-stable compounds even though they are [Ru(2)(II,II)] species. The redox potential in THF was dependent on an electronic effect rather than on a structural (steric) effect of the o-F atoms, although more than one substituent in the m- and p-positions shifted E(1/2) to higher potentials in relation to the general Hammett equation. A quasi-Hammett parameter for an o-F atom (σ(o)) was estimated to be ∼0.2, and a plot of E(1/2)vs. a sum of Hammett parameters including σ(o) was linear. In addition, the HOMO energy levels, which was calculated based on atomic coordinates of solid-state structures, as well as the redox potential were affected by adding F atoms. Nevertheless, a steric contribution stabilizing their static structures in the solid state was present in addition to the electronic effect. On the basis of the electronic effect, the redox potential of these complexes is correlated to the HOMO energy level, and the electronic effect of F atoms is the main factor controlling the ionization potential of the complexes with ligands free from the rotational constraint, i.e. complexes in solution.

Study of charge transfer complexes of menadione (vitamin K 3) with a series of anilines

NASA Astrophysics Data System (ADS)

Pal, Purnendu; Saha, Avijit; Mukherjee, Asok K.; Mukherjee, Dulal C.

2004-01-01

Menadione (vitamin K 3) has been shown to form charge transfer complexes with N, N-dimethyl aniline, N, N-dimethyl p-toluidine and N, N-dimethyl m-toluidine in CCl 4 medium. The CT transition energies are well correlated with the ionisation potentials of the anilines. The formation constants of the complexes have been determined at a number of temperatures from which the enthalpies and entropies of formation have been obtained. The formation constants exhibit a very good linear free energy relationship (Hammett) at all the temperatures studied.

AnilinoMethylRhodamines: pH Sensitive Probes with Tunable Photophysical Properties by Substituent Effect

PubMed Central

Best, Quinn A.; Liu, Chuangjun; van Hoveln, Paul D.; McCarroll, Matthew E.

2013-01-01

A series of pH dependent rhodamine analogs possessing an anilino-methyl moiety was developed and shown to exhibit a unique photophysical response to pH. These Anilinomethylrhodamines (AnMR) maintain a colorless, non-fluorescent spiro-cyclic structure at high pH. The spiro-cyclic structures open in mildly acidic conditions and are weakly fluorescent; however at very low pH, the fluorescence is greatly enhanced. The equilibrium constants of these processes show a linear response to substituent effects, which was demonstrated by the Hammett equation. PMID:24050117

Substituent and solvent effects on electronic absorption spectra of some N-(substitutedphenyl)benzene sulphonamides.

PubMed

Suganya, Krishnasamy; Kabilan, Senthamaraikannan

2004-04-01

The effects of substituents and solvents have been studied through the absorption spectra of nearly 23 ortho- and para-N-(substitutedphenyl)benzene sulphonamides in the range of 200-400 nm. The effects of substituents on the absorption spectra of compounds under present investigation are interpreted by correlation of absorption frequencies with simple and extended Hammett equations. Effect of solvent polarity and hydrogen bonding on the absorption spectra are interpreted by means of Kamlet equation and the results are discussed. Copyright 2003 Elsevier B.V.

Speciation of Trace Di- and Triorganotins in Water by Ion Exchange HPLC-GFAA.

DTIC Science & Technology

1980-08-05

Equation 2 are available (38,40) in the form, pKa = pKo C0 4 for all of the R groups examined on organotins in this paper. The new Hammett - type QSAR o...specified by Equation 1. barring influences of competing neutral ligands (such an methanol in the solvent). Thus K presumes either an "inert" neutral or an...different anionic groups in order to test the validity of Equation I with the SCX column and its relevance to Scheme 1. Fertinent daia are summarized in

A Comparison of QSAR Based Thermo and Water Solvation Property Prediction Tools and Experimental Data for Selected Traditional Chemical Warfare Agents and Simulants

DTIC Science & Technology

2014-07-01

Labs uses parameterized Hammett -type equations to describe 1500 possible combinations of more than 650 ionizable functional groups. The change in...of the form ⋯ , ⋯ Equation (1) where Ypred is the predicted property, c0 is a constant, c1 to cn are coefficients from the...regression to the training set of measurements, X1 to Xn represent molecular or fragment or field-based descriptors, and the final term in Equation 1

An Analysis of Proposed Alternatives to the Defense Technical Information Center’s Announcement Products and Services

DTIC Science & Technology

1985-10-01

Aberdeen - 22 Jun 84 W. J. Hammett - Center for Naval Analyses - 14 Mar 85 -40- Marilyn Harned - Naval Air Systems Command - 10 Jan 84 Jan... Equations lor Airmail Simulation. ADA119 543 GRASI ARL’AERO-TM-340 Design of a New Contraction. Wide Angle Dif- ’user and Flow Manipulators for...In the Burnthrough Ranga Equation . Al, A119 557 GRA&I Application ol Rapidly Solidilied Alloys. A:in.x;.’’>i’.t Ftd-Opii/6 Application ol the

Nonlinear Gyro-Landau-Fluid Equations

NASA Astrophysics Data System (ADS)

Raskolnikov, I.; Mattor, Nathan; Parker, Scott E.

1996-11-01

We present fluid equations which describe the effects of both linear and nonlinear Landau damping (wave-particle-wave effects). These are derived using a recently developed analytical method similar to renormalization group theory. (Scott E. Parker and Daniele Carati, Phys. Rev. Lett. 75), 441 (1995). In this technique, the phase space structure inherent in Landau damping is treated analytically by building a ``renormalized collisionality'' onto a bare collisionality (which may be taken as vanishingly small). Here we apply this technique to the nonlinear ion gyrokinetic equation in slab geometry, obtaining nonlinear fluid equations for density, parallel momentum and heat. Wave-particle resonances are described by two functions appearing in the heat equation: a renormalized ``collisionality'' and a renormalized nonlinear coupling coeffient. It will be shown that these new equations may correct a deficiency in existing gyrofluid equations, (G. W. Hammett and F. W. Perkins, Phys. Rev. Lett. 64,) 3019 (1990). which can severely underestimate the strength of nonlinear interaction in regimes where linear resonance is strong. (N. Mattor, Phys. Fluids B 4,) 3952 (1992).

Mechanism of the coupling of diazonium to single-walled carbon nanotubes and its consequences.

PubMed

Schmidt, Grégory; Gallon, Salomé; Esnouf, Stéphane; Bourgoin, Jean-Philippe; Chenevier, Pascale

2009-01-01

On the tube: The coupling of diazonium ions onto single-walled carbon nanotubes is shown to proceed through a radical chain reaction by kinetic analysis of the absorption peak drop (see picture). Radical species are also revealed by ESR. Metallic (m) nanotubes play a special catalytic role in the functionalization of semiconducting (sc) nanotubes.Due to its simplicity and versatility, diazonium coupling is the most widely used method for carbon nanotube (CNT) functionalization to increase CNT processability and add new functionalities. Yet, its mechanism is so far mostly unknown. Herein, we use kinetic analysis to shed light on this complex mechanism. A free-radical chain reaction is revealed by absorption spectroscopy and ESR. Metallic CNTs are shown to play an unexpected catalytic role. The step determining the selectivity towards metallic CNTs is identified by a Hammett correlation. A mechanistic model is proposed that predicts reactivity and selectivity as a function of diazonium electrophilicity and metallic-to-semiconducting CNT ratio, thus opening perspectives of controlled high-yield functionalization and purification.

Kinetics and mechanism of vanadium catalysed asymmetric cyanohydrin synthesis in propylene carbonate

PubMed Central

Omedes-Pujol, Marta

2010-01-01

Summary Propylene carbonate can be used as a green solvent for the asymmetric synthesis of cyanohydrin trimethylsilyl ethers from aldehydes and trimethylsilyl cyanide catalysed by VO(salen)NCS, though reactions are slower in this solvent than the corresponding reactions carried out in dichloromethane. A mechanistic study has been undertaken, comparing the catalytic activity of VO(salen)NCS in propylene carbonate and dichloromethane. Reactions in both solvents obey overall second-order kinetics, the rate of reaction being dependent on the concentration of both the aldehyde and trimethylsilyl cyanide. The order with respect to VO(salen)NCS was determined and found to decrease from 1.2 in dichloromethane to 1.0 in propylene carbonate, indicating that in propylene carbonate, VO(salen)NCS is present only as a mononuclear species, whereas in dichloromethane dinuclear species are present which have previously been shown to be responsible for most of the catalytic activity. Evidence from 51V NMR spectroscopy suggested that propylene carbonate coordinates to VO(salen)NCS, blocking the free coordination site, thus inhibiting its Lewis acidity and accounting for the reduction in catalytic activity. This explanation was further supported by a Hammett analysis study, which indicated that Lewis base catalysis made a much greater contribution to the overall catalytic activity of VO(salen)NCS in propylene carbonate than in dichloromethane. PMID:21085513

Spectral and kinetic studies of the oxidation of monosubstituted phenols and anilines by recombinant Synechocystis catalase-peroxidase compound I.

PubMed

Regelsberger, G; Jakopitsch, C; Engleder, M; Rüker, F; Peschek, G A; Obinger, C

1999-08-10

A high-level expression in Escherichia coli of a fully active recombinant form of a catalase-peroxidase (KatG) from the cyanobacterium Synechocystis PCC 6803 is reported. Since both physical and kinetic characterization revealed its identity with the wild-type protein, the large quantities of recombinant KatG allowed the first examination of second-order rate constants for the oxidation of a series of aromatic donor molecules (monosubstituted phenols and anilines) by a bifunctional catalase-peroxidase compound I using the sequential-mixing stopped-flow technique. Because of the overwhelming catalase activity, peroxoacetic acid has been used for compound I formation. A >/=50-fold excess of peroxoacetic acid is required to obtain a spectrum of relatively pure and stable compound I which is characterized by about 40% hypochromicity, a Soret maximum at 406 nm, and isosbestic points between the native enzyme and compound I at 357 and 430 nm. The apparent second-order rate constant for formation of compound I from ferric enzyme and peroxoacetic acid is (8.74 +/- 0.26) x 10(3) M(-)(1) s(-)(1) at pH 7. 0. Reduction of compound I by aromatic donor molecules is dependent upon the substituent effect on the benzene ring. The apparent second-order rate constants varied from (3.6 +/- 0.1) x 10(6) M(-)(1) s(-)(1) for p-hydroxyaniline to (5.0 +/- 0.1) x 10(2) M(-)(1) s(-)(1) for p-hydroxybenzenesulfonic acid. They are shown to correlate with the substituent constants in the Hammett equation, which suggests that in bifunctional catalase-peroxidases the aromatic donor molecule donates an electron to compound I and loses a proton simultaneously. The value of rho, the susceptibility factor in the Hammett equation, is -3.4 +/- 0.4 for the phenols and -5.1 +/- 0.8 for the anilines. The pH dependence of compound I reduction by aniline exhibits a relatively sharp maximum at pH 5. The redox intermediate formed upon reduction of compound I has spectral features which indicate that the single oxidizing equivalent in KatG compound II is contained on an amino acid which is not electronically coupled to the heme.

Quantitative Reactivity Scales for Dynamic Covalent and Systems Chemistry.

PubMed

Zhou, Yuntao; Li, Lijie; Ye, Hebo; Zhang, Ling; You, Lei

2016-01-13

Dynamic covalent chemistry (DCC) has become a powerful tool for the creation of molecular assemblies and complex systems in chemistry and materials science. Herein we developed for the first time quantitative reactivity scales capable of correlation and prediction of the equilibrium of dynamic covalent reactions (DCRs). The reference reactions are based upon universal DCRs between imines, one of the most utilized structural motifs in DCC, and a series of O-, N-, and S- mononucleophiles. Aromatic imines derived from pyridine-2-carboxyaldehyde exhibit capability for controlling the equilibrium through distinct substituent effects. Electron-donating groups (EDGs) stabilize the imine through quinoidal resonance, while electron-withdrawing groups (EWGs) stabilize the adduct by enhancing intramolecular hydrogen bonding, resulting in curvature in Hammett analysis. Notably, unique nonlinearity induced by both EDGs and EWGs emerged in Hammett plot when cyclic secondary amines were used. This is the first time such a behavior is observed in a thermodynamically controlled system, to the best of our knowledge. Unified quantitative reactivity scales were proposed for DCC and defined by the correlation log K = S(N) (R(N) + R(E)). Nucleophilicity parameters (R(N) and S(N)) and electrophilicity parameters (R(E)) were then developed from DCRs discovered. Furthermore, the predictive power of those parameters was verified by successful correlation of other DCRs, validating our reactivity scales as a general and useful tool for the evaluation and modeling of DCRs. The reactivity parameters proposed here should be complementary to well-established kinetics based parameters and find applications in many aspects, such as DCR discovery, bioconjugation, and catalysis.

Exact Dissipative Moment Closures for Simulation of Magnetospheric Plasmas

NASA Astrophysics Data System (ADS)

Newman, D. L.; Sen, N.; Goldman, M. V.

2004-11-01

Dissipative fluid closures produce a kinetic-like plasma response in simulations based on the evolution of moments of the Vlasov equation. Such methods were previously shown to approximate the kinetic susceptibility of a Maxwellian plasma.(G. W. Hammett and F. W. Perkins Phys. Rev. Lett.) 64, 3019 (1990). We show here that dissipative closures can yield the exact linear response for kappa velocity distributions (i.e., f(v)∝(v^2+w^2)^-κ in 1-D, where w∝ v_th), provided κ is an integer and κ+1 moments are retained in the closure. This finding is particularly relevant to the simulation of collisionless space plasmas, which frequently exhibit power-law tails characteristic of kappa distributions. Such dissipative algorithms can be made energy conserving by evolving the thermal parameter w. Dominant nonlinearities (e.g., ponderomotive effects) can also be incorporated into the algorithm. These methods have proven especially valuable in the context of reduced 2-D Vlasov simulations,(N. Sen, et al., Reduced 2-D Vlasov Simulationsldots), this meeting. where they have been used to model perpendicular ion dynamics in the evolution of nonlinear structures (e.g., double layers) in the auroral ionosphere.

Fluid simulation of tokamak ion temperature gradient turbulence with zonal flow closure model

NASA Astrophysics Data System (ADS)

Yamagishi, Osamu; Sugama, Hideo

2016-03-01

Nonlinear fluid simulation of turbulence driven by ion temperature gradient modes in the tokamak fluxtube configuration is performed by combining two different closure models. One model is a gyrofluid model by Beer and Hammett [Phys. Plasmas 3, 4046 (1996)], and the other is a closure model to reproduce the kinetic zonal flow response [Sugama et al., Phys. Plasmas 14, 022502 (2007)]. By including the zonal flow closure, generation of zonal flows, significant reduction in energy transport, reproduction of the gyrokinetic transport level, and nonlinear upshift on the critical value of gradient scale length are observed.

Fluid simulation of tokamak ion temperature gradient turbulence with zonal flow closure model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yamagishi, Osamu, E-mail: yamagisi@nifs.ac.jp; Sugama, Hideo

Nonlinear fluid simulation of turbulence driven by ion temperature gradient modes in the tokamak fluxtube configuration is performed by combining two different closure models. One model is a gyrofluid model by Beer and Hammett [Phys. Plasmas 3, 4046 (1996)], and the other is a closure model to reproduce the kinetic zonal flow response [Sugama et al., Phys. Plasmas 14, 022502 (2007)]. By including the zonal flow closure, generation of zonal flows, significant reduction in energy transport, reproduction of the gyrokinetic transport level, and nonlinear upshift on the critical value of gradient scale length are observed.

Examination of the Mechanism of Rh2(II)-Catalyzed Carbazole Formation Using Intramolecular Competition Experiments

PubMed Central

Stokes, Benjamin J.; Richert, Kathleen J.; Driver, Tom G.

2009-01-01

The use of a rhodium(II) carboxylate catalyst enables the mild and stereoselective formation of carbazoles from biaryl azides. Intramolecular competition experiments of triaryl azides suggested the source of the selectivity. A primary intramolecular kinetic isotope effect was not observed and correlation of the product ratios with Hammett σ+-values produced a plot with two intersecting lines with opposite ρ-values. These data suggest that electronic donation by the biaryl π-system accelerates the formation of rhodium nitrenoid and that C–N bond formation occurs through a 4π-electron-5-atom electrocyclization. PMID:19663433

Quantitative Estimation of the Electronic Effects of Substituents in Five-membered Nitrogen-containing Aromatic Heterocycles

NASA Astrophysics Data System (ADS)

Lopyrev, Valentin A.; Larina, Ludmila I.; Vakul'skaya, Tamara I.

1986-05-01

Data, characterising quantitatively the effect of substituents on the reactivity and physicochemical properties of five-membered nitrogen-containing heterocyclic compounds, which have accumulated in the literature during the last 15 years, are compiled in the review and discussed. The possibility of applying the Hammett and Jaffe equations in the determination of the direction of transmission of the electronic effects of substituents is analysed and the likely usefulness of this approach to the study of electronic influences by taking into account separately the inductive and resonance constants is demonstrated. The bibliography includes 215 references.

Electrochemical and Spectroscopic Studies of 9, 10-Anthraquinone in a Room Temperature Molten Salt.

DTIC Science & Technology

1980-07-01

is uncomplexed in the basic melt, AQ + m A1C14 + 2e : AQ (ALCl3 )m + m C1-, with the corresponding Nernst equation [AQ]_, [A 4- E 0 +RT lnmRT l A~ 4Eo...these values. No attempt was made to include activity coefficients in the equilibrium equations . -24- Since the protonation of AQ has been studied by...numerous authors in connection with the Hammett Pidity scale, it is possible, at least in a qualitative sense, to relate the acidity of the ACl3:BuPyCl

A quantitative quantum chemical model of the Dewar-Knott color rule for cationic diarylmethanes

NASA Astrophysics Data System (ADS)

Olsen, Seth

2012-04-01

We document the quantitative manifestation of the Dewar-Knott color rule in a four-electron, three-orbital state-averaged complete active space self-consistent field (SA-CASSCF) model of a series of bridge-substituted cationic diarylmethanes. We show that the lowest excitation energies calculated using multireference perturbation theory based on the model are linearly correlated with the development of hole density in an orbital localized on the bridge, and the depletion of pair density in the same orbital. We quantitatively express the correlation in the form of a generalized Hammett equation.

Gyro-Landau fluid models for toroidal geometry

NASA Astrophysics Data System (ADS)

Waltz, R. E.; Dominguez, R. R.; Hammett, G. W.

1992-10-01

Gyro-Landau fluid model equations provide first-order time advancement for a limited number of moments of the gyrokinetic equation, while approximately preserving the effects of the gyroradius averaging and Landau damping. This paper extends the work of Hammett and Perkins [Phys. Rev. Lett. 64, 3019 (1990)] for electrostatic motion parallel to the magnetic field and E×B motion to include the gyroaveraging linearly and the curvature drift motion. The equations are tested by comparing the ion-temperature-gradient mode linear growth rates for the model equations with those of the exact gyrokinetic theory over a full range of parameters.

Kinetics of the Reaction Between Alcohols and Isocyanates Catalyzed by Ferric Acetylacetonate

NASA Technical Reports Server (NTRS)

Schieler, Leroy

1961-01-01

The rate and temperature dependence of reaction for the ferric acetylacetonate catalyzed reaction between a-naphthyl, ortho-tolyl, and para-tolyl isocyanates and n-butyl alcohol are investigated. The effect of substituents on the reactivity of isocyanate and hydroxyl group are reported and for substituted isocyanates are correlated by means of the Hammett equation. Several metal chelates were studied and their catalytic activity was compared to that of ferric acetylacetonate. All rate data are interpreted in terms of a mechanism involving simultaneous second-order uncatalyzed and catalyzed reactions between alcohol and isocyanate.

Secondary benzylation with benzyl alcohols catalyzed by a high-valent heterobimetallic Ir-Sn complex.

PubMed

Podder, Susmita; Choudhury, Joyanta; Roy, Sujit

2007-04-13

A highly efficient secondary benzylation procedure has been demonstrated using a high-valent heterobimetallic complex [Ir2(COD)2(SnCl3)2(Cl)2(mu-Cl)2] 1 as the catalyst in 1,2-dichloroethane to afford the corresponding benzylated products in moderate to excellent yields. The reaction was performed not only with carbon nucleophiles (arenes and heteroarenes) but also with oxygen (alcohol), nitrogen (amide and sulfonamide), and sulfur (thiol) nucleophiles. Mechanistic investigation showed the intermediacy of the ether in this reaction. An electrophilic mechanism is proposed from Hammett correlation.

Ionizing power and nucleophilicity in water in oil AOT-based microemulsions.

PubMed

García-Río, Luis; Hervella, Pablo; Leis, José Ramón

2005-08-16

A study was carried out on the solvolysis of substituted phenyl chloroformates in AOT/isooctane/water microemulsions. (AOT is the sodium salt of bis(2-ethyhexyl)sulfosuccinate.) The results obtained have been interpreted by taking into account the distribution of the chloroformates between the continuous medium and the interface of the microemulsions, where the reactions take place. The values obtained for the rate constant in the interface, k(i), decreases as the water content of the microemulsions increases, as a consequence of the decrease in its nucleophilic capacity. This behavior is consistent with a rate-determining step of water addition to the carbonyl group. The values of k(i) allow us to obtain the slopes of the Hammett correlations at the interface of the microemulsions, rho = 2.25, whose values are greater than those obtained in an aqueous medium, rho = 0.82. This increase in the Hammett slope is similar to that observed in ethanol/water mixtures and is a consequence of a variation in the structure of the transition state of the reaction where there is a smaller extension of the expulsion of the leaving group. The values of the rate constants at the interface of the microemulsions have allowed us, by means of the Grunwald-Winstein equation, to obtain the solvent ionizing power and the nucleophilicity of the solvent. The values obtained for Y(Cl) increase together with the water content of the microemulsion, whereas the values of N(T) decrease. These variations are a consequence of the interaction between the AOT headgroups and the interfacial water, where the water molecules act like electronic acceptors. The intensity of this interaction is greater if the system has a small water content, which explains the variation of Y(Cl) and N(T).

Substituent effects and pH profiles for stability constants of arylboronic acid diol esters.

PubMed

Martínez-Aguirre, Mayte A; Villamil-Ramos, Raul; Guerrero-Alvarez, Jorge A; Yatsimirsky, Anatoly K

2013-05-17

Stability constants of boronic acid diol esters in aqueous solution have been determined potentiometrically for a series of meta-, para-substituted phenylboronic acids and diols of variable acidity. The constants β(11-1) for reactions between neutral forms of reactants producing the anionic ester plus proton follow the Hammett equation with ρ depending on pKa of diol and varying from 2.0 for glucose to 1.29 for 4-nitrocatechol. Observed stability constants (K(obs)) measured by UV-vis and fluorometric titrations at variable pH for esters of 4,5-dihydroxy-1,3-benzenedisulfonate (Tiron) generally agree with those expected on the basis of β(11-1) values, but the direct fitting of K(obs) vs pH profiles gives shifted pKa values both for boronic acids and diol as a result of significant interdependence of fitting parameters. The subsituent effects on absorption and fluorescence spectra of Tiron arylboronate esters are characterized. The K(obs) for Tiron determined by (11)B NMR titrations are approximately 1 order of magnitude smaller than those determined by UV-vis titrations under identical conditions. A general equation, which makes possible an estimate of β(11-1) for any pair of boronic acid and diol from their pKa values, is proposed on the basis of established Brönsted-type correlation of Hammett parameters for β(11-1) with acidity of diols. The equation allows one to calculate stability constants expected only on basis of acid-base properties of the components, thus permitting more strict evaluation of contributions of additional factors such as steric or charge effects to the ester stability.

Three-dimensional model of the hydrostratigraphy and structure of the area in and around the U.S. Army-Camp Stanley Storage Activity Area, northern Bexar County, Texas

USGS Publications Warehouse

Pantea, Michael P.; Blome, Charles D.; Clark, Allan K.

2014-01-01

A three-dimensional model of the Camp Stanley Storage Activity area defines and illustrates the surface and subsurface hydrostratigraphic architecture of the military base and adjacent areas to the south and west using EarthVision software. The Camp Stanley model contains 11 hydrostratigraphic units in descending order: 1 model layer representing the Edwards aquifer; 1 model layer representing the upper Trinity aquifer; 6 model layers representing the informal hydrostratigraphic units that make up the upper part of the middle Trinity aquifer; and 3 model layers representing each, the Bexar, Cow Creek, and the top of the Hammett of the lower part of the middle Trinity aquifer. The Camp Stanley three-dimensional model includes 14 fault structures that generally trend northeast/southwest. The top of Hammett hydrostratigraphic unit was used to propagate and validate all fault structures and to confirm most of the drill-hole data. Differences between modeled and previously mapped surface geology reflect interpretation of fault relations at depth, fault relations to hydrostratigraphic contacts, and surface digital elevation model simplification to fit the scale of the model. In addition, changes based on recently obtained drill-hole data and field reconnaissance done during the construction of the model. The three-dimensional modeling process revealed previously undetected horst and graben structures in the northeastern and southern parts of the study area. This is atypical, as most faults in the area are en echelon that step down southeasterly to the Gulf Coast. The graben structures may increase the potential for controlling or altering local groundwater flow.

(13)C NMR substituent-induced chemical shifts in 4-(substituted phenyl)-3-phenyl-1,2,4-oxadiazol-5(4H)-ones (thiones).

PubMed

Kara, Yesim Saniye

2015-01-01

In the present, study mostly novel ten 4-(substituted phenyl)-3-phenyl-1,2,4-oxadiazol-5(4H)-ones and ten 4-(substituted phenyl)-3-phenyl-1,2,4-oxadiazol-5(4H)-thiones were synthesized. These oxadiazole derivatives were characterized by IR, (1)H NMR, (13)C NMR and elemental analyses. Their (13)C NMR spectra were measured in Deuterochloroform (CDCl3). The correlation analysis for the substituent-induced chemical shift (SCS) with Hammett substituent constants (σ), Brown Okamoto substituent constants (σ(+), σ(-)), inductive substituent constants (σI) and different of resonance substituent constants (σR, σR(o)) were performed using SSP (single substituent parameter), DSP (dual substituent parameter) and DSP-NLR (dual substituent parameter-non-linear resonance) methods, as well as single and multiple regression analysis. Negative ρ values were found for all correlations (reverse substituent effect). The results of all statistical analyses, (13)C NMR chemical shift of CN, CO and CS carbon of oxadiazole rings have shown satisfactory correlation. Copyright © 2015 Elsevier B.V. All rights reserved.

Mechanistic Studies of ε-Caprolactone Polymerization by (salen)AlOR Complexes and a Predictive Model for Cyclic Ester Polymerizations

PubMed Central

2016-01-01

Aluminum alkoxide complexes (2) of salen ligands with a three-carbon linker and para substituents having variable electron-withdrawing capabilities (X = NO2, Br, OMe) were prepared, and the kinetics of their ring-opening polymerization (ROP) of ε-caprolactone (CL) were investigated as a function of temperature, with the aim of drawing comparisons to similar systems with two-carbon linkers investigated previously (1). While 1 and 2 exhibit saturation kinetics and similar dependences of their ROP rates on substituents X (invariant Keq, similar Hammett ρ = +1.4(1) and 1.2(1) for k2, respectively), ROP by 2 was significantly faster than for 1. Theoretical calculations confirm that, while the reactant structures differ, the transition state geometries are quite similar, and by analyzing the energetics of the involved distortions accompanying the structural changes, a significant contribution to the basis for the rate differences was identified. Using this knowledge, a simplified computational method for evaluating ligand structural influences on cyclic ester ROP rates is proposed that may have utility for future catalyst design. PMID:26900488

Competition kinetics using the UV/H2O2 process: a structure reactivity correlation for the rate constants of hydroxyl radicals toward nitroaromatic compounds.

PubMed

García Einschlag, Fernando S; Carlos, Luciano; Capparelli, Alberto L

2003-10-01

The rate constants for hydroxyl radical reaction toward a set of nitroaromatic substrates kS, have been measured at 25 degrees C using competition experiments in the UV/H2O2 process. For a given pair of substrates S1 and S2, the relative reactivity beta (defined as kS1/kS2) was calculated from the slope of the corresponding double logarithmic plot, i.e., of ln[S1] vs. ln[S2]. This method is more accurate and remained linear for larger conversions in comparison with the plots of ln[S1] and ln[S2] against time. The rate constants measured ranged from 0.33 to 8.6 x 10(9) M(-1)s(-1). A quantitative structure-reactivity relationship was found using the Hammett equation. Assuming sigma values to be additive, a value of -0.60 was obtained for the reaction constant rho. This value agrees with the high reactivity and the electrophilic nature of HO* radical.

Mechanism of the sulfurisation of phosphines and phosphites using 3-amino-1,2,4-dithiazole-5-thione (xanthane hydride).

PubMed

Hanusek, Jirí; Russell, Mark A; Laws, Andrew P; Jansa, Petr; Atherton, John H; Fettes, Kevin; Page, Michael I

2007-02-07

Contrary to a previous report, the sulfurisation of phosphorus(III) derivatives by 3-amino-1,2,4-dithiazole-5-thione (xanthane hydride) does not yield carbon disulfide and cyanamide as the additional reaction products. The reaction of xanthane hydride with triphenyl phosphine or trimethyl phosphite yields triphenyl phosphine sulfide or trimethyl thiophosphate, respectively, and thiocarbamoyl isothiocyanate which has been trapped with nucleophiles. The reaction pathway involves initial nucleophilic attack of the phosphorus at sulfur next to the thiocarbonyl group of xanthane hydride followed by decomposition of the phosphonium intermediate formed to products. The Hammett rho-values for the sulfurisation of substituted triphenyl phosphines and triphenyl phosphites in acetonitrile are approximately -1.0. The entropies of activation are very negative (-114+/-15 J mol-1 K-1) with little dependence on solvent which is consistent with a bimolecular association step leading to the transition state. The negative values of DeltaS(not equal) and rho values indicate that the rate limiting step of the sulfurisation reaction is formation of the phosphonium ion intermediate which has an early transition state with little covalent bond formation. The site of nucleophilic attack has been also confirmed using computational calculations.

Hydrogen Abstraction from Individual Thiophenol Molecules Adsorbed on Cu(111)

NASA Astrophysics Data System (ADS)

Rao, Bommisetty; Kwon, Ki-Young; Liu, Anwei; Zhang, Jin-Tao; Bartels, Ludwig

2004-03-01

Thiol compounds on metal surfaces have been studied intensively because of their ability to form self-assembled monolayers (SAMs). However, the transition from the thiol to the surface thiolate is difficult to investigate in detail in the solution phase. Here we report on STM measurements that address the adsorption of a variety of substituted thiophenols on Cu(111) at 15K in vacuum. At this temperature, adsorption does not cause immediate scission of the S-H bond. We confirmed this by STM-based vibrational spectroscopy. Consequently, the sulfur atom of the thiol group adsorbs on-top of a substrate atom, which results in a sufficient separation of the aryl group from the substrate to allow its free rotation even at 15K. Asymmetrically substituted thiophenols result in STM images of pronounced helicity, which indicates that the molecules cannot tilt upright to exchange their adsorption side. Attachment of electrons from the tunneling current can cause hydrogen abstraction from the thiophenols, which locks them into the substrate. We investigated the dependence of the yield of the hydrogen abstraction on the thiophenol substituent identity and position. We find pronounced variations which may follow the Hammett Equation known from Standard Organic Chemistry.

Employing NMR Spectroscopy To Evaluate Transmission of Electronic Effects in 4-Substituted Chalcones

NASA Astrophysics Data System (ADS)

Wachter-Jurcsak, Nanette; Zamani, Hossein

1999-05-01

Described is an organic synthesis experiment that demonstrates the electronic transmission by substituents. The effect of substitution at the para-position of the styryl ring of 1,3-diphenyl-2-propenones (chalcones) by typical electron-donating or -accepting groups can be observed by proton and carbon-13 NMR spectroscopy. A linear correlation is observed when the differences in chemical shift measurements for H are plotted against the corresponding Hammett substituent constant values. Good correlation between carbon-13 chemical shifts of the alpha carbon are also observed. The syntheses of the 4-substituted chalcones is presented as well as a brief discussion of the theory.

Discovery of potent, selective, orally active benzoxazepine-based Orexin-2 receptor antagonists.

PubMed

Fujimoto, Tatsuhiko; Kunitomo, Jun; Tomata, Yoshihide; Nishiyama, Keiji; Nakashima, Masato; Hirozane, Mariko; Yoshikubo, Shin-Ichi; Hirai, Keisuke; Marui, Shogo

2011-11-01

During our efforts to identify a series of potent, selective, orally active human Orexin-2 Receptor (OX2R) antagonists, we elucidated structure-activity relationship (SAR) on the 7-position of a benzoxazepine scaffold by utilizing Hammett σ(p) and Hansch-Fujita π value as aromatic substituent constants. The attempts led to the discovery of compound 1m, possessing good in vitro potency with over 100-fold selectivity against OX1R, good metabolic stability in human and rat liver microsome, good oral bioavailability in rats, and in vivo antagonistic activity in rats by oral administration. Copyright © 2011 Elsevier Ltd. All rights reserved.

Substituent and solvent effects on the UV/vis absorption spectra of 5-(3- and 4-substituted arylazo)-4,6-dimethyl-3-cyano-2-pyridones

NASA Astrophysics Data System (ADS)

Mijin, Dušan Ž.; Ušćumlić, Gordana S.; Perišić-Janjić, Nada U.; Valentić, Nataša V.

2006-01-01

Absorption spectra of seventeen 5-(3- and 4-substituted arylazo)-4,6-dimethyl-3-cyano-2-pyridones have been recorded in 12 protic and aprotic solvents in the range 200-600 nm. The effects of substituents on the absorption spectra of these new azo dyes are interpreted by correlation of absorption frequencies with Hammett equation. The solute-solvent interactions were clarified on the basis of linear solvation energy relationships concept proposed by Kamlet and Taft. The 2-pyridone/2-hydroxypiridine tautomeric equilibration is found to depend upon substituents as well as on solvents.

Effects of neutral and anionic substituents on the carbonyl stretching bands of substituted methylbenzoates

NASA Astrophysics Data System (ADS)

Vassileva, P. J.; Binev, I. G.; Juchnovski, I. N.

Effects of neutral and anionic substitutents on frequencies (ν CO) and integrated intensities ( ACO) of the carbonyl stretching bands of substituted methylbenzoates (solvent dimethyl sulphoxide) have been studied in relation to Hammett's equation: satisfactory correlations have been found between ν CO and σ + constants, as well as by using the dual-parameter equations to Yukawa, Tsuno and Taft; ACO have been found to increase in cases of strong electron-releasing substituents. It has been found that constants of anionic substituents, determined on the basis of nitrile i.r. frequencies and intensities, reflect satisfactorily the effects of these substituents on ν CO and ACO of methylbenzoates.

Department of the Air Force Environmental Statement. Construction and Operation of the West Coast OTH-B Radar System, Lake and Klamath Counties, Oregon; Modoc and Sacramento Counties, California; Pierce County, Washington; Elmore County, Idaho

DTIC Science & Technology

1984-02-01

readily available. EXCEPTION: In the past decade, the Glenns Ferry, Hammett , Grandview, Bruneau, and Boise areas being within an hour or less driving...density, the exclusion fence would be located at a distance where the power density would not exceed 0.1 mW/cm2 . Consistent with Equation 19 on the...distances between 250 and 1,500 ft (per Equation 3, p. B-7). These values imply averaging over substantial periods of time, whereas individuals in aircraft

Application of ChemDraw NMR Tool: Correlation of Program-Generated 13C Chemical Shifts and pKa Values of para-Substituted Benzoic Acids

NASA Astrophysics Data System (ADS)

Wang, Hongyi

2005-09-01

An application of ChemDraw NMR Tool was demonstrated by correlation of program-generated 13 C NMR chemical shifts and p K a values of para-substituted benzoic acids. Experimental 13 C NMR chemical shifts were analyzed in the same way for comparison. The project can be used as an assignment at the end of the first-year organic chemistry course to review topics or explore new techniques: Hammett equation, acid base equilibrium theory, electronic nature of functional groups, inductive and resonance effects, structure reactivity relationship, NMR spectroscopy, literature search, database search, and ChemDraw software.

Aromatic hydroxylation by cytochrome P450: model calculations of mechanism and substituent effects.

PubMed

Bathelt, Christine M; Ridder, Lars; Mulholland, Adrian J; Harvey, Jeremy N

2003-12-10

The mechanism and selectivity of aromatic hydroxylation by cytochrome P450 enzymes is explored using new B3LYP density functional theory computations. The calculations, using a realistic porphyrin model system, show that rate-determining addition of compound I to an aromatic carbon atom proceeds via a transition state with partial radical and cationic character. Reactivity is shown to depend strongly on ring substituents, with both electron-withdrawing and -donating groups strongly decreasing the addition barrier in the para position, and it is shown that the calculated barrier heights can be reproduced by a new dual-parameter equation based on radical and cationic Hammett sigma parameters.

A Landau fluid model for dispersive magnetohydrodynamics

NASA Astrophysics Data System (ADS)

Passot, T.; Sulem, P. L.

2004-11-01

A monofluid model with Landau damping is presented for strongly magnetized electron-proton collisionless plasmas whose distribution functions are close to bi-Maxwellians. This description that includes dynamical equations for the gyrotropic components of the pressure and heat flux tensors, extends the Landau-fluid model of Snyder, Hammett, and Dorland [Phys. Plasmas 4, 3974 (1997)] by retaining Hall effect and finite Larmor radius corrections. It accurately reproduces the weakly nonlinear dynamics of dispersive Alfvén waves whose wavelengths are large compared to the ion inertial length, whatever their direction of propagation, and also the rapid Landau dissipation of long magnetosonic waves in a warm plasma.

Rhodium-catalyzed asymmetric aqueous Pauson-Khand-type reaction.

PubMed

Kwong, Fuk Yee; Li, Yue Ming; Lam, Wai Har; Qiu, Liqin; Lee, Hang Wai; Yeung, Chi Hung; Chan, Kin Shing; Chan, Albert S C

2005-06-20

An interesting rhodium-catalyzed asymmetric aqueous Pauson-Khand-type reaction was developed. A chiral atropisomeric dipyridyldiphosphane ligand was found to be highly effective in this system. This operationally simple protocol allows both catalyst and reactants to be handled under air without precautions. Various enynes were transformed to the corresponding bicyclic cyclopentenones in good yield and enantiomeric excess (up to 95 % ee). A study of the electronic effects of the enyne substrates revealed a correlation between the electronic properties of the substrates and the ee value obtained in the product of the Pauson-Khand-type reaction. A linear free-energy relationship was observed from a Hammett study.

Biotransformation of nitroso aromatic compounds and 2-oxo acids to N-hydroxy-N-arylacylamides by thiamine-dependent enzymes in rat liver.

PubMed

Yoshioka, T; Uematsu, T

1998-07-01

The formation of N-hydroxy-N-arylacylamides from nitroso aromatic compounds and 2-oxo acids was investigated using rat liver subcellular fractions. Activities were found in both mitochondria and cytosol, except for activities for phenylpyruvate and glyoxylate; the former did not produce N-hydroxy-N-phenylphenylacetamide and the latter nonenzymatically produced N-hydroxy-N-phenylformamide with nitrosobenzene (NOB). The cytosolic activity of N-hydroxy-N-phenylglycolamide formation was indicated to be due to transketolase, which utilized hydroxypyruvate as a glycolic aldehyde donor to NOB. With mitochondria, 2-oxo acids (including hydroxypyruvate) served as substrates for the biotransformation of NOB to the corresponding N-hydroxy-N-phenylacylamides. The substrate preference was 2-oxobutyrate > pyruvate > 2-oxoisovalerate > 2-oxoisocaproate > 2-oxovalerate > 2-oxo-3-methylvalerate, judging from Vmax/half-saturating concentration for mitochondria values. The half-saturating concentrations for NOB were nearly constant. The mitochondrial activity was due to pyruvate dehydrogenase complex and branched-chain 2-oxo acid dehydrogenase complex (BCDHC). By using partially purified BCDHC, pyruvate and 2-oxobutyrate were found to be common substrates for both of the enzymes, and 2-oxoisovalerate was shown to be the most effective substrate for BCDHC. Analysis by the Taft equation indicated that the polar effects, rather than the steric effects, of the alkyl groups of 2-oxo acids are important for BCDHC-catalyzed formation of N-hydroxy-N-phenylacylamides. A positive Hammett constant obtained for the formation of N-hydroxy-N-arylisobutyramides indicates that an electron-withdrawing substituent makes the nitroso compounds susceptible to BCDHC-catalyzed biotransformation.

Replacing Conventional Carbon Nucleophiles with Electrophiles: Nickel-Catalyzed Reductive Alkylation of Aryl Bromides and Chlorides

PubMed Central

2012-01-01

A general method is presented for the synthesis of alkylated arenes by the chemoselective combination of two electrophilic carbons. Under the optimized conditions, a variety of aryl and vinyl bromides are reductively coupled with alkyl bromides in high yields. Under similar conditions, activated aryl chlorides can also be coupled with bromoalkanes. The protocols are highly functional-group tolerant (−OH, −NHTs, −OAc, −OTs, −OTf, −COMe, −NHBoc, −NHCbz, −CN, −SO2Me), and the reactions are assembled on the benchtop with no special precautions to exclude air or moisture. The reaction displays different chemoselectivity than conventional cross-coupling reactions, such as the Suzuki–Miyaura, Stille, and Hiyama–Denmark reactions. Substrates bearing both an electrophilic and nucleophilic carbon result in selective coupling at the electrophilic carbon (R–X) and no reaction at the nucleophilic carbon (R–[M]) for organoboron (−Bpin), organotin (−SnMe3), and organosilicon (−SiMe2OH) containing organic halides (X–R–[M]). A Hammett study showed a linear correlation of σ and σ(−) parameters with the relative rate of reaction of substituted aryl bromides with bromoalkanes. The small ρ values for these correlations (1.2–1.7) indicate that oxidative addition of the bromoarene is not the turnover-frequency determining step. The rate of reaction has a positive dependence on the concentration of alkyl bromide and catalyst, no dependence upon the amount of zinc (reducing agent), and an inverse dependence upon aryl halide concentration. These results and studies with an organic reductant (TDAE) argue against the intermediacy of organozinc reagents. PMID:22463689

DOE Office of Scientific and Technical Information (OSTI.GOV)

Poutsma, Marvin L.

Recently we presented structure-reactivity correlations for the gas-phase ambient-temperature rate constants for hydrogen abstraction from sp 3-hybridized carbon by chlorine atom and hydroxyl radical (Cl•/HO• + HCR 3 → HCl/HOH + •CR 3); the reaction enthalpy effect was represented by the independent variable Δ rH and the polar effect by the independent variables F and R, the Hammett constants for field/inductive and resonance effects. Both these reactions are predominantly exothermic and have early transition states. Here we present a parallel treatment for Br• whose reaction is significantly endothermic with a correspondingly late transition state. In spite of lower expectations becausemore » the available data base is less extensive and much more scattered and because long temperature extrapolations are often required, the resulting least-squares fit (log k 298,Br = –0.147 Δ rH –4.32 ΣF –4.28 ΣR –12.38 with r 2 = 0.92) was modestly successful and useful for initial predictions. The coefficient of Δ rH was ~4-fold greater, indicative of the change from an early to a late transition state; meanwhile the sizable coefficients of ΣF and ΣR indicate the persistence of the polar effect. Although the mean unsigned deviation of 0.79 log k 298 units is rather large, it must be considered in the context of a total span of over 15 log units in the data set. Lastly, the major outliers are briefly discussed.« less

Extension of Structure-Reactivity Correlations for the Hydrogen Abstraction Reaction by Bromine Atom and Comparison to Chlorine Atom and Hydroxyl Radical.

PubMed

Poutsma, Marvin L

2016-01-21

Recently we presented structure-reactivity correlations for the gas-phase ambient-temperature rate constants for hydrogen abstraction from sp(3)-hybridized carbon by chlorine atom and hydroxyl radical (Cl•/HO• + HCR3 → HCl/HOH + •CR3); the reaction enthalpy effect was represented by the independent variable ΔrH and the "polar effect" by the independent variables F and R, the Hammett constants for field/inductive and resonance effects. Both these reactions are predominantly exothermic and have early transition states. Here, we present a parallel treatment for Br• whose reaction is significantly endothermic with a correspondingly late transition state. Despite lower expectations because the available database is less extensive and much more scattered and because long temperature extrapolations are often required, the resulting least-squares fit (log k298,Br = -0.147 ΔrH - 4.32 ΣF - 4.28 ΣR - 12.38 with r(2) = 0.92) was modestly successful and useful for initial predictions. The coefficient of ΔrH was ∼4-fold greater, indicative of the change from an early to a late transition state; meanwhile the sizable coefficients of ΣF and ΣR indicate the persistence of the "polar effect". Although the mean unsigned deviation of 0.79 log k298 units is rather large, it must be considered in the context of a total span of over 15 log units in the data set. The major outliers are briefly discussed.

Intramolecular cation-π interactions in protonated phenylalanine derivatives.

PubMed

Fu, Weiqiang; Carr, Patrick J J; Lecours, Michael J; Burt, Michael; Marta, Rick A; Steinmetz, Vincent; Fillion, Eric; McMahon, Terrance B; Hopkins, W Scott

2016-12-21

The structures and properties of a series of phenylalanine (Phe) derivatives have been investigated in a joint computational and experimental infrared multiple photon dissociation (IRMPD) study. IRMPD spectra in the 1000-2000 cm -1 region show that protonation is localized on the amine group in all cases. Intramolecular cation-π interactions between the ammonium group and the phenyl ring heavily influence molecular geometries and properties such as gas phase basicity and proton affinity. By varying substituents on the phenyl ring, one can sensitively tune the cation-π interaction and, therefore, the molecular structure and properties. Variations in molecular structures and properties as a function of phenyl ring substitution are shown to correlate with substituent Hammett parameters.

Synthesis, spectral studies, antimicrobial, antioxidant and insect antifeedant activities of some 9 H-fluorene-2-yl keto-oxiranes

NASA Astrophysics Data System (ADS)

Thirunarayanan, G.; Vanangamudi, G.

2011-10-01

Thirteen ee (α S, β R) 9 H-fluorene-2-yl keto-oxiranes (2-(9 H)-fluorene-4-yl[3-(substituted phenyl)oxiran-2-yl]methanones) have been synthesized by phase transfer catalysed epoxidation of 9 H-fluorene-2-yl chalcones. The yields of oxiranes are more than 95%. The synthesized oxiranes have been characterized by IR, 1H, 13C and GC-MS spectral data. The spectral data are correlated with Hammett substituent constants and Swain-Lupton parameters. From the regression analysis, the effect of substituents on the group frequencies has been predicted. The antimicrobial, antioxidant and insect antifeedant activities of all the synthesized oxiranes have been studied.

Laser photolysis studies of the phenolic H-atom transfer mechanism for a triplet π,π ∗ ketone in solution revisited

NASA Astrophysics Data System (ADS)

Yamaji, Minoru; Aoyama, Yutaka; Furukawa, Takashi; Itoh, Takao; Tobita, Seiji

2006-03-01

The mechanism of the H-atom transfer from phenols or thiophenols to triplet π,π ∗ 5,12-naphthacenequinone (5,12-NQ) has been examined by means of laser flash photolysis at 295 K. Based on the Hammett plots and the Rehm-Weller equation for the quenching rate constants, the phenolic H-atom transfer from phenols or thiophenols to triplet π,π ∗ 5,12-NQ is shown to proceed via the electron transfer followed by proton transfer. The previously proposed mechanism for H-atom transfer of π,π ∗ triplets, that proton transfer is followed by electron transfer, was not verified in the present systems.

Post-assembly Modification of Tetrazine-Edged Fe(II)4L6 Tetrahedra.

PubMed

Roberts, Derrick A; Pilgrim, Ben S; Cooper, Jonathan D; Ronson, Tanya K; Zarra, Salvatore; Nitschke, Jonathan R

2015-08-19

Post-assembly modification (PAM) is a powerful tool for the modular functionalization of self-assembled structures. We report a new family of tetrazine-edged Fe(II)4L6 tetrahedral cages, prepared using different aniline subcomponents, which undergo rapid and efficient PAM by inverse electron-demand Diels-Alder (IEDDA) reactions. Remarkably, the electron-donating or -withdrawing ability of the para-substituent on the aniline moiety influences the IEDDA reactivity of the tetrazine ring 11 bonds away. This effect manifests as a linear free energy relationship, quantified using the Hammett equation, between σ(para) and the rate of the IEDDA reaction. The rate of PAM can thus be adjusted by varying the aniline subcomponent.

QSPR/QSAR in N-[(dimethylamine)methyl] benzamides substituents groups influence upon electronic distribution and local anesthetics activity.

PubMed

Tavares, Leoberto Costa; do Amaral, Antonia Tavares

2004-03-15

It was determined, with a systematic mode, the carbonyl group frequency in the region of the infrared of N-[(dimethylamine)methyl] benzamides 4-substituted (set A) and their hydrochlorides (set B), that had its local anesthetical activity evaluated. The application of the Hammett equation considering the values of the absorption frequency of carbonyl group, nu(C=O,) using the electronic constants sigma, sigma(I), sigma(R), I and R leads to meaningful correlation. The nature and the contribution of substituent group electronic effects on the polarity of the carbonyl group was also analyzed. The use of the nu(C=O) as an experimental electronic parameter for QSPR studies was validated.

Enzymatic reduction of acetophenone derivatives with a benzil reductase from Pichia glucozyma (KRED1-Pglu): electronic and steric effects on activity and enantioselectivity.

PubMed

Contente, Martina L; Serra, Immacolata; Palazzolo, Luca; Parravicini, Chiara; Gianazza, Elisabetta; Eberini, Ivano; Pinto, Andrea; Guidi, Benedetta; Molinari, Francesco; Romano, Diego

2016-04-07

A recombinant ketoreductase from Pichia glucozyma (KRED1-Pglu) was used for the enantioselective reduction of various mono-substituted acetophenones. Reaction rates of meta- and para-derivatives were consistent with the electronic effects described by σ-Hammett coefficients; on the other hand, enantioselectivity was determined by an opposite orientation of the substrate in the binding pocket. Reduction of ortho-derivatives occurred only with substrates bearing substituents with low steric impact (i.e., F and CN). Reactivity was controlled by stereoelectronic features (C[double bond, length as m-dash]O length and charge, shape of LUMO frontier molecular orbitals), which can be theoretically calculated.

Structure dependence of the rate coefficients of hydroxyl radical+aromatic molecule reaction

NASA Astrophysics Data System (ADS)

Wojnárovits, László; Takács, Erzsébet

2013-06-01

The rate coefficients of hydroxyl radical addition to the rings of simple aromatic molecules (kOH) were evaluated based on the literature data. By analyzing the methods of kOH determination and the data obtained the most probable values were selected for the kOH's of individual compounds and thereby the most reliable dataset was created for monosubstituted aromatics and p-substituted phenols. For these compounds the rate coefficients fall in a narrow range between 2×109 mol-1 dm3 s-1 and 1×1010 mol-1 dm3 s-1. Although the values show some regular trend with the electron donating/withdrawing nature of the substituent, the log kOH-σp Hammett substituent constant plots do not give straight lines because these high kOH's are controlled by both, the chemical reactivity and the diffusion. However, the logarithms of the rate coefficients of the chemical reactivity controlled reactions (kchem), are calculated by the equation 1/kOH=1/kchem+1/kdiff, and accepting for the diffusion controlled rate coefficient kdiff=1.1×1010 mol-1 dm3 s-1, show good linear correlation with σp.

Natural bond orbital approach to the transmission of substituent effect through the fulvene and benzene ring systems.

PubMed

Oziminski, Wojciech P; Krygowski, Tadeusz M

2011-03-01

Electronic structure of 22 monosubstituted derivatives of benzene and exocyclically substituted fulvene with substituents: B(OH)(2), BH(2), CCH, CF(3), CH(3), CHCH(2), CHO, Cl, CMe(3), CN, COCH(3), CONH(2), COOH, F, NH(2), NMe(2), NO, NO(2), OCH(3), OH, SiH(3), SiMe(3) were studied theoretically by means of Natural Bond Orbital analysis. It is shown, that sum of π-electron population of carbon atoms of the fulvene and benzene rings, pEDA(F) and pEDA(B), respectively correlate well with Hammett substituent constants [Formula in text] and aromaticity index NICS. The substituent effect acting on pi-electron occupation at carbon atoms of the fulvene ring is significantly stronger than in the case of benzene. Electron occupations of ring carbon atoms (except C1) in fulvene plotted against each other give linear regressions with high correlation coefficients. The same is true for ortho- and para-carbon atoms in benzene. Positive slopes of the regressions indicate similar for fulvene and benzene kind of substituent effect - mostly resonance in nature. Only the regressions of occupation at the carbon atom in meta- position of benzene against ortho- and para-positions gives negative slopes and low correlation coefficients.

Efficient n-doping of graphene films by APPE (aminophenyl propargyl ether): a substituent effect.

PubMed

Kim, Youngsoo; Yoo, Je Min; Jeon, Hak Rim; Hong, Byung Hee

2013-11-14

We report the synthesis and applications of APPE (aminophenyl propargyl ether) as a novel n-type dopant for graphene. The characteristics of APPE-doped graphene films were investigated using Raman spectroscopy as well as electron transport measurements. The Raman 2D/G peak ratio decreased by more than 40%, and the minimum conductivity voltage (Dirac voltage) was shifted to -133 V as the pristine graphene was doped with APPE, indicating that the graphene was strongly n-doped. We suppose that the electron donating property of the amine group (-NH2) is the origin of such an intense n-doping effect. In contrast, a similar molecule with an electron withdrawing nitro group (-NO2) (nitrophenyl propargyl ether, NPPE) showed a slight p-doping effect. Thus, we conclude that the doping effect of a molecular framework strongly depends on the functional substituents, which can be represented by the Hammett equation. We also confirmed that the sheet resistance of the APPE doped graphene film was reduced by ∼70%, which is crucial to enhance the electrical conductivity of graphene for various electronic applications. In addition, the acetylene group of APPE appears promising to be utilized in "click chemistry" to further functionalize the π-surface of graphene for sensors and bio applications.

Racemization of (S)-profen thioesters by strong neutral bases in nonpolar organic solvents: implication for ion-pair kinetic basicity.

PubMed

Chen, Chia-Yin; Chang, Yu-Shang; Lin, Shun-An; Wen, Hui-I; Cheng, Yu-Chi; Tsai, Shau-Wei

2002-05-17

The racemization of (S)-profen 2,2,2-trifluoroethyl thioesters in isooctane with trioctylamine as base was carried out, in which the Hammett equation log(k(int)) = 3.584sigma - 3.745 was successfully applied to describe the electron-withdrawing effect of the substituents to the alpha-phenyl moiety of the thioesters. A combination of neutral strong organic bases with different nonpolar solvents was employed to determine the second-order interconversion constants for the racemization of (S)-naproxen 2,2,2-trifluoroethyl thioester, in which solvent hydrophobicity was found to have less effect on the racemization. Implication for ion-pair kinetic basicity scale for the neutral strong bases in isooctane was further discussed.

Effect of substituent groups (R= sbnd CH3, sbnd Br and sbnd CF3) on the structure, stability and redox property of [Cr(R-pic)2(H2O)2]NO3·H2O complexes

NASA Astrophysics Data System (ADS)

Chai, Jie; Liu, Yanfei; Liu, Bin; Yang, Binsheng

2017-12-01

Complexes [Cr(3-CH3-pic)2(H2O)2]NO3·H2O (1), [Cr(5-Br-pic)2(H2O)2]NO3·H2O (2) and [Cr(5-CF3-pic)2(H2O)2]NO3·H2O (3) were synthesized (pic = pyridine-2-carboxylic acid) and characterized by X-ray crystal diffraction. Crystal structure indicates that two bidentate ligands occupy equatorial position and two H2O occupy axial positions in trans-configuration. (i) Decomposition of complexes 1, 2 and 3 in different medium (phosphate buffered saline (PBS), apo-ovotransferrin (apootf) and EDTA) indicates that decomposition rate constants of these complexes follow the sequence of 1 < 2 < 3. (ii) The redox potential of Cr(III)/Cr(II) by cyclic voltammetry follows the sequence of 1 (-1.20 V) > 3 (-1.29 V) > 2 (-1.31 V). (iii) In addition, ·OH-generation of the new synthesized complexes was determined by Fenton-like reaction in comparison with Cr(pic)3, and it may be related to the reduction potential of the complexes. (iv) Moreover, Hammett substituent constants σp (inductive) and σm (resonance) (R = 3-CH3, 5-Br, 5-CF3) were introduced to evaluate the impact of substituent groups on the bond length and decomposition kinetics. The substituent group on the ligand has great effect on the properties of the complexes.

Extension of structure-reactivity correlations for the hydrogen abstraction reaction by bromine atom and comparison to chlorine atom and hydroxyl radical

DOE PAGES

Poutsma, Marvin L.

2015-12-14

Recently we presented structure-reactivity correlations for the gas-phase ambient-temperature rate constants for hydrogen abstraction from sp 3-hybridized carbon by chlorine atom and hydroxyl radical (Cl•/HO• + HCR 3 → HCl/HOH + •CR 3); the reaction enthalpy effect was represented by the independent variable Δ rH and the polar effect by the independent variables F and R, the Hammett constants for field/inductive and resonance effects. Both these reactions are predominantly exothermic and have early transition states. Here we present a parallel treatment for Br• whose reaction is significantly endothermic with a correspondingly late transition state. In spite of lower expectations becausemore » the available data base is less extensive and much more scattered and because long temperature extrapolations are often required, the resulting least-squares fit (log k 298,Br = –0.147 Δ rH –4.32 ΣF –4.28 ΣR –12.38 with r 2 = 0.92) was modestly successful and useful for initial predictions. The coefficient of Δ rH was ~4-fold greater, indicative of the change from an early to a late transition state; meanwhile the sizable coefficients of ΣF and ΣR indicate the persistence of the polar effect. Although the mean unsigned deviation of 0.79 log k 298 units is rather large, it must be considered in the context of a total span of over 15 log units in the data set. Lastly, the major outliers are briefly discussed.« less

C-glycosylation reactions of sulfur-substituted glycosyl donors: evidence against the role of neighboring-group participation.

PubMed

Beaver, Matthew G; Billings, Susan B; Woerpel, K A

2008-02-13

Nucleophilic substitution reactions of C-4 sulfur-substituted tetrahydropyran acetals revealed that neighboring-group participation does not control product formation. Spectroscopic evidence for the formation of an intermediate sulfonium ion is provided, as are data from nucleophilic substitution reactions demonstrating that products are formed from oxocarbenium ion intermediates. The selectivity was not sensitive to solvent or to which Lewis acid was employed. The identity of the heteroatom at the C-4 position also did not significantly impact diastereoselectivity. Consequently, neighboring-group participation was not responsible for the formation of either the major or the minor products. These studies implicate a Curtin-Hammett kinetic scenario in which the formation of a low-energy intermediate does not necessitate its involvement in the product-forming pathway.

Substituent and solvent effects on the UV/Vis absorption spectra of 5-(4-substituted arylazo)-6-hydroxy-4-methyl-3-cyano-2-pyridones

NASA Astrophysics Data System (ADS)

Ušćumlić, Gordana S.; Mijin, Dusanˇ Z. ˇ; Valentić, Nataša V.; Vajs, Vlatka V.; Sušić, Biljana M.

2004-10-01

Absorption spectra of ten 5-(4-substituted arylazo)-6-hydroxy-4-methyl-3-cyano-2-pyridones have been recorded in fifteen solvents in the range 200-600 nm. The substituents at the phenyl nucleus are as follows: OH, OCH 3, CH 3, C 2H 5, H, Cl, Br, I, COOH and NO 2. The effects of substituents on the absorption spectra of investigated compounds are interpreted by correlation of absorption frequencies with simple Hammett equation. The effects of solvent polarity and solvent/solute hydrogen bonding interactions are analyzed by means of linear solvation energy relationships concept proposed by Kamlet and Taft. The azo-hydrazone tuatomeric equilibration is found to depend upon substituents as well as on solvents.

Mechanistic insights into hydroacylation with non-chelating aldehydes†Electronic supplementary information (ESI) available: Materials and methods, reaction procedures, characterization data. CCDC 1012849. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c4sc02026jClick here for additional data file.

PubMed

Murphy, Stephen K; Bruch, Achim; Dong, Vy M

2015-01-01

The combination of a small-bite-angle diphosphine bis(dicyclohexylphosphino)methane (dcpm) and [Rh(cod)OMe] 2 catalyses the hydroacylation of 2-vinylphenols with a wide range of non-chelating aldehydes. Here we present a detailed experimental study that elucidates the factors contributing to the broad aldehyde scope and high reactivity. A variety of catalytically relevant intermediates were isolated and a [Rh(dcpm)(vinylphenolate)] complex was identified as the major catalytically relevant species. A variety of off-cycle intermediates were also identified that can re-enter the catalytic cycle by substrate- or 1,5-cyclooctadiene-mediated pathways. Saturation kinetics with respect to the 2-vinylphenol were observed, and this may contribute to the high selectivity for hydroacylation over aldehyde decarbonylation. A series of deuterium labelling experiments and Hammett studies support the oxidative addition of Rh to the aldehyde C-H bond as an irreversible and turnover-limiting step. The small bite angle of dcpm is crucial for lowering the barrier of this step and providing excellent reactivity with a variety of aldehydes.

Interrogating selectivity in catalysis using molecular vibrations

NASA Astrophysics Data System (ADS)

Milo, Anat; Bess, Elizabeth N.; Sigman, Matthew S.

2014-03-01

The delineation of molecular properties that underlie reactivity and selectivity is at the core of physical organic chemistry, and this knowledge can be used to inform the design of improved synthetic methods or identify new chemical transformations. For this reason, the mathematical representation of properties affecting reactivity and selectivity trends, that is, molecular parameters, is paramount. Correlations produced by equating these molecular parameters with experimental outcomes are often defined as free-energy relationships and can be used to evaluate the origin of selectivity and to generate new, experimentally testable hypotheses. The premise behind successful correlations of this type is that a systematically perturbed molecular property affects a transition-state interaction between the catalyst, substrate and any reaction components involved in the determination of selectivity. Classic physical organic molecular descriptors, such as Hammett, Taft or Charton parameters, seek to independently probe isolated electronic or steric effects. However, these parameters cannot address simultaneous, non-additive variations to more than one molecular property, which limits their utility. Here we report a parameter system based on the vibrational response of a molecule to infrared radiation that can be used to mathematically model and predict selectivity trends for reactions with interlinked steric and electronic effects at positions of interest. The disclosed parameter system is mechanistically derived and should find broad use in the study of chemical and biological systems.

Experimental and theoretical study on the structure-property relationship of novel 1-aryl-3-methylsuccinimides

NASA Astrophysics Data System (ADS)

Banjac, Nebojša R.; Božić, Bojan Đ.; Mirković, Jelena M.; Vitnik, Vesna D.; Vitnik, Željko J.; Valentić, Nataša V.; Ušćumlić, Gordana S.

2017-02-01

A series of ten 1-aryl-3-methylsuccinimides was synthesized and their solvatochromic properties were studied in a set of fifteen binary solvent mixtures. The solute-solvent interactions were analyzed on the basis of the linear solvation energy relationship (LSER) concept proposed by Kamlet and Taft. The electronic effect of the substituents on the UV-Vis absorption and NMR spectra was analyzed using the simple Hammett equation. Moreover, the B3LYP, CAM-B3LYP, and M06-2X functionals using the 6-311G(d,p) basic set have been assessed in light of the position of experimental absorption maxima obtained for these compounds. The integration grid effects have also been evaluated. An interpretation of the substituent-effect transmission through the molecular skeleton and the nature of the HOMO and LUMO orbitals based on quantum-chemical calculations is given. The values of partial atomic charges from the atomic polar tenzors (APT), natural population analysis (NBO), and charges fit to the electrostatic potential using the B3LYP, CAM-B3LYP, and M06-2X methods are produced and correlated with different experimental properties. In order to estimate the chemical activity of the molecule, the molecular electrostatic potential (MEP) surface map is calculated for the optimized geometry of 1-phenyl-3-methylsuccinimide.

Multidimensional kinetic simulations using dissipative closures and other reduced Vlasov methods for differing particle magnetizations

NASA Astrophysics Data System (ADS)

Newman, David L.

2006-10-01

Kinetic plasma simulations in which the phase-space distribution functions are advanced directly via the coupled Vlasov and Poisson (or Maxwell) equations---better known simply as Vlasov simulations---provide a valuable low-noise complement to the more commonly employed Particle-in-Cell (PIC) simulations. However, in more than one spatial dimension Vlasov simulations become numerically demanding due to the high dimensionality of x--v phase-space. Methods that can reduce this computational demand are therefore highly desirable. Several such methods will be presented, which treat the phase-space dynamics along a dominant dimension (e.g., parallel to a beam or current) with the full Vlasov propagator, while employing a reduced description, such as moment equations, for the evolution perpendicular to the dominant dimension. A key difference between the moment-based (and other reduced) methods considered here and standard fluid methods is that the moments are now functions of a phase-space coordinate (e.g. moments of vy in z--vz--y phase space, where z is the dominant dimension), rather than functions of spatial coordinates alone. Of course, moment-based methods require closure. For effectively unmagnetized species, new dissipative closure methods inspired by those of Hammett and Perkins [PRL, 64, 3019 (1990)] have been developed, which exactly reproduce the linear electrostatic response for a broad class of distributions with power-law tails, as are commonly measured in space plasmas. The nonlinear response, which requires more care, will also be discussed. For weakly magnetized species (i.e., φs<φs) an alternative algorithm has been developed in which the distributions are assumed to gyrate about the magnetic field with a fixed nominal perpendicular ``thermal'' velocity, thereby reducing the required phase-space dimension by one. These reduced algorithms have been incorporated into 2-D codes used to study the evolution of nonlinear structures such as double layers and electron holes in Earth's auroral zone.

Is there substituent cross-interaction effect in all the conjugated systems containing Cdbnd N polar bond? The substituent effects on the NMR chemical shifts of 2,5-disubstituted pyrimidines

NASA Astrophysics Data System (ADS)

Yuan, Hua; Zhang, Yan; Chen, Chun-Ni; Li, Meng-Yang

2018-03-01

The substituent cross-interaction effect in the substituted benzylidene anilines (p-Xsbnd C6H4sbnd CHdbnd Nsbnd C6H4sbnd Y-p) has been observed and widely investigated. In order to investigate whether the substituent cross-interaction effect exist in all the conjugated systems containing Cdbnd N polar bond, this paper employed 2-X-5-Y pyrimidines as the model compounds for study. The influences of substituents X and Y on the 1H NMR and 13C NMR chemical shifts of 2, 5-disubsitituted pyrimidines have been systematically investigated. Quantitative structure-chemical shifts relationship models have been built for δ(H4,6), δ(C2), δ(C4,6) and δ(C5) with four to six molecular descriptors. These models were confirmed of good stability and predictive performances by leave-one-out cross validation. This study indicates that the substituent effects of 2,5-disubstituted pyrimidines are much more complex than that of the substituted benzylidene anilines. More structural factors besides of Hammett parameter should be taken into consideration. Different from the substituted benzylidene anilines, the cross-interaction effect (Δσ2) of substituents X and Y has little contribution to δ(H4,6), δ(C2), δ(C5) and δ(C4,6) of 2,5-disubstituted pyrimidines.

Theoretical study of the hydrogen abstraction of substituted phenols by nitrogen dioxide as a source of HONO.

PubMed

Shenghur, Abraham; Weber, Kevin H; Nguyen, Nhan D; Sontising, Watit; Tao, Fu-Ming

2014-11-20

The mild yet promiscuous reactions of nitrogen dioxide (NO2) and phenolic derivatives to produce nitrous acid (HONO) have been explored with density functional theory calculations. The reaction is found to occur via four distinct pathways with both proton coupled electron transfer (PCET) and hydrogen atom transfer (HAT) mechanisms available. While the parent reaction with phenol may not be significant in the gas phase, electron donating groups in the ortho and para positions facilitate the reduction of nitrogen dioxide by electronically stabilizing the product phenoxy radical. Hydrogen bonding groups in the ortho position may additionally stabilize the nascent resonantly stabilized radical product, thus enhancing the reaction. Catechol (ortho-hydroxy phenol) has a predicted overall free energy change ΔG(0) = -0.8 kcal mol(-1) and electronic activation energy Ea = 7.0 kcal mol(-1). Free amines at the ortho and para positions have ΔG(0) = -3.8 and -1.5 kcal mol(-1); Ea = 2.3 and 2.1 kcal mol(-1), respectively. The results indicate that the hydrogen abstraction reactions of these substituted phenols by NO2 are fast and spontaneous. Hammett constants produce a linear correlation with bond dissociation energy (BDE) demonstrating that the BDE is the main parameter controlling the dark abstraction reaction. The implications for atmospheric chemistry and ground-level nitrous acid production are discussed.

Antibody-catalyzed benzoin oxidation as a mechanistic probe for nucleophilic catalysis by an active site lysine.

PubMed

Sklute, Genia; Oizerowich, Rachel; Shulman, Hagit; Keinan, Ehud

2004-05-03

Aldolase antibody 24H6, which was obtained by reactive immunization against a 1,3-diketone hapten, is shown to catalyze additional reactions, including H/D exchange and oxidation reactions. Comparison of the H/D exchange reaction at the alpha-position of a wide range of aldehydes and ketones by 24H6 and by other aldolase antibodies, such as 38C2, pointed at the significantly larger size of the 24H6 active site. This property allowed for the catalysis of the oxidation of substituted benzoins to benzils by potassium ferricyanide. This reaction was used as a mechanistic probe to learn about the initial steps of the 24H6-catalyzed aldol condensation reaction. The Hammett correlation (rho=4.7) of log(k(cat)) versus the substituent constant, sigma, revealed that the reaction involves rapid formation of a Schiff base intermediate from the ketone and an active site lysine residue. The rate-limiting step in this oxidation reaction is the conversion of the Schiff base to an enamine intermediate. In addition, linear correlation (rho=3.13) was found between log(K(M)) and sigma, indicating that electronic rather than steric factors are dominant in the antibody-substrate binding phenomenon and confirming that the reversible formation of a Schiff base intermediate comprises part of the substrate-binding mechanism.

Modeling Biophysical and Biological Properties From the Characteristics of the Molecular Electron Density, Electron Localization and Delocalization Matrices, and the Electrostatic Potential

PubMed Central

Matta*, Chérif F

2014-01-01

The electron density and the electrostatic potential are fundamentally related to the molecular hamiltonian, and hence are the ultimate source of all properties in the ground- and excited-states. The advantages of using molecular descriptors derived from these fundamental scalar fields, both accessible from theory and from experiment, in the formulation of quantitative structure-to-activity and structure-to-property relationships, collectively abbreviated as QSAR, are discussed. A few such descriptors encode for a wide variety of properties including, for example, electronic transition energies, pKa's, rates of ester hydrolysis, NMR chemical shifts, DNA dimers binding energies, π-stacking energies, toxicological indices, cytotoxicities, hepatotoxicities, carcinogenicities, partial molar volumes, partition coefficients (log P), hydrogen bond donor capacities, enzyme–substrate complementarities, bioisosterism, and regularities in the genetic code. Electronic fingerprinting from the topological analysis of the electron density is shown to be comparable and possibly superior to Hammett constants and can be used in conjunction with traditional bulk and liposolubility descriptors to accurately predict biological activities. A new class of descriptors obtained from the quantum theory of atoms in molecules' (QTAIM) localization and delocalization indices and bond properties, cast in matrix format, is shown to quantify transferability and molecular similarity meaningfully. Properties such as “interacting quantum atoms (IQA)” energies which are expressible into an interaction matrix of two body terms (and diagonal one body “self” terms, as IQA energies) can be used in the same manner. The proposed QSAR-type studies based on similarity distances derived from such matrix representatives of molecular structure necessitate extensive investigation before their utility is unequivocally established. © 2014 The Author and the Journal of Computational Chemistry Published by Wiley Periodicals, Inc. PMID:24777743

N-benzoylimido complexes of palladium. Synthesis, structural characterisation and structure-reactivity relationship.

PubMed

Besenyei, Gábor; Párkányi, László; Szalontai, Gábor; Holly, Sándor; Pápai, Imre; Keresztury, Gábor; Nagy, Andrea

2004-07-07

Benzoyl azides, ArC(O)N3, 2, (Ar = phenyl or substituted phenyl), react with [Pd2Cl2(dppm)2], 1, [dppm = bis(diphenylphosphino)methane] with the formation of novel [Pd2Cl2(mu-NC(O)Ar)(dppm)2], 3, benzoylnitrene complexes that were structurally characterised by multinuclear magnetic resonance and IR spectroscopy and, in several instances, by single crystal X-ray diffraction. As shown by crystallographic studies, the C2P4Pd2 rings adopt extended twist-boat conformations with methylene groups bending towards the bridging benzoylimido moieties. X-ray diffraction studies have revealed the chiral nature of the imido complexes, the chiral element being the propeller-like C2P4Pd2 ring. Structural data accumulated on complexes 3 such as short C-N distances (1.32 A), elongated C=O bonds (1.30 A) as well as the outstandingly high barrier to internal rotation around the N-C(O) linkage (88.3 kJ mol(-1)) are in line with extensive ppi-ppi interaction between the bridging nitrogen and the carbonyl carbon atoms. Theoretical calculations indicate an electron shift from the dimer towards the apical nitrogen atom, which, in turn, facilitates the donation of electrons towards the carbonyl moiety. To elucidate the structure-reactivity relationship of benzoyl azides towards 1, crystallographic and solution IR spectroscopic studies were carried out on a series of para-substituted benzoyl azides. The reaction obeys the Hammett equation. The large positive value of the reaction constant indicates that the azides act as electrophiles in the reaction studied. The enhanced reactivity of 2-nitrobenzoyl azide has been attributed to a decreased conjugation of the phenyl and carbonyl moieties in this reagent.

Quantitative structure-activity relationships (QSARs) for the transformation of organic micropollutants during oxidative water treatment.

PubMed

Lee, Yunho; von Gunten, Urs

2012-12-01

Various oxidants such as chlorine, chlorine dioxide, ferrate(VI), ozone, and hydroxyl radicals can be applied for eliminating organic micropollutant by oxidative transformation during water treatment in systems such as drinking water, wastewater, and water reuse. Over the last decades, many second-order rate constants (k) have been determined for the reaction of these oxidants with model compounds and micropollutants. Good correlations (quantitative structure-activity relationships or QSARs) are often found between the k-values for an oxidation reaction of closely related compounds (i.e. having a common organic functional group) and substituent descriptor variables such as Hammett or Taft sigma constants. In this study, we developed QSARs for the oxidation of organic and some inorganic compounds and organic micropollutants transformation during oxidative water treatment. A number of 18 QSARs were developed based on overall 412 k-values for the reaction of chlorine, chlorine dioxide, ferrate, and ozone with organic compounds containing electron-rich moieties such as phenols, anilines, olefins, and amines. On average, 303 out of 412 (74%) k-values were predicted by these QSARs within a factor of 1/3-3 compared to the measured values. For HO(·) reactions, some principles and estimation methods of k-values (e.g. the Group Contribution Method) are discussed. The developed QSARs and the Group Contribution Method could be used to predict the k-values for various emerging organic micropollutants. As a demonstration, 39 out of 45 (87%) predicted k-values were found within a factor 1/3-3 compared to the measured values for the selected emerging micropollutants. Finally, it is discussed how the uncertainty in the predicted k-values using the QSARs affects the accuracy of prediction for micropollutant elimination during oxidative water treatment. Copyright © 2012 Elsevier Ltd. All rights reserved.

Synthesis, spectral studies and antimicrobial activities of some 2-naphthyl pyrazoline derivatives

NASA Astrophysics Data System (ADS)

Sakthinathan, S. P.; Vanangamudi, G.; Thirunarayanan, G.

A series of 2-naphthyl pyrazolines were synthesized by the cyclization of 2-naphthyl chalcones and phenylhydrazine hydrochloride in the presence of sodium acetate. The yields of pyrazoline derivatives are more than 80%. The synthesized pyrazolines were characterized by their physical constants, IR, 1H, 13C and MS spectra. From the IR and NMR spectra the Cdbnd N (cm-1) stretches, the pyrazoline ring proton chemical shifts (ppm) of δ, Hb and Hc and also the carbon chemical shifts (ppm) of δCdbnd N are correlated with Hammett substituent constants, F and R, and Swain-Lupton's parameters using single and multi-regression analyses. From the results of linear regression analysis, the effect of substituents on the group frequencies has been predicted. The antimicrobial activities of all synthesized pyrazolines have been studied.

Substituent effects in double-helical hydrogen-bonded AAA-DDD complexes.

PubMed

Wang, Hong-Bo; Mudraboyina, Bhanu P; Wisner, James A

2012-01-27

Two series of DDD and AAA hydrogen-bond arrays were synthesized that form triply-hydrogen-bonded double-helical complexes when combined in CDCl(3) solution. Derivatization of the DDD arrays with electron-withdrawing groups increases the complex association constants by up to a factor of 30 in those arrays examined. Derivatization of the AAA arrays with electron donating substituents reveals a similar magnitude effect on the complex stabilities. The effect of substitution on both types of arrays are modeled quite satisfactorily (R(2) > 0.96 in all cases) as free energy relationships with respect to the sums of their Hammett substituent constants. In all, the complex stabilities can be manipulated over more than three orders of magnitude (>20 kJ mol(-1)) using this type of modification. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Linear Response Function of Bond-Order

PubMed Central

Suzuki, Nayuta; Mitsuta, Yuki; Okumura, Mitsutaka; Yamanaka, Shusuke

2016-01-01

We present the linear response function of bond-orders (LRF-BO) based on a real space integration scheme for molecular systems. As in the case of the LRF of density, the LRF-BO is defined as the response of the bond order of the molecule for the virtual perturbation. Our calculations show that the LRF-BO enables us not only to detect inductive and resonating effects of conjugating systems, but also to predict pKa values on substitution groups via linear relationships between the Hammett constants and the LRF-BO values for meta- and para-substituted benzoic acids. More importantly, the LRF-BO values for the O-H bonds strongly depend on the sites to which the virtual perturbation is applied, implying that the LRF-BO values include essential information about reaction mechanism of the acid-dissociation of substituted benzoic acids. PMID:27792148

Molecular geometry as a source of chemical information. 5. Substituent effect on proton transfer in para-substituted phenol complexes with fluoride--a B3LYP/6-311+G study.

PubMed

Krygowski, Tadeusz M; Szatyłowicz, Halina; Zachara, Joanna E

2005-01-01

The simplified model system [p-X-PhO...H...F](-), where -X are -NO, -NO(2), -CHO, -H, -CH(3), -OCH(3), and -OH, with various O...F distance was used to simulate the wide range of the H-bond strength. Structural changes due to variation of the substituent as well as the H-bond strength are well monitored by the changes in the aromaticity index HOMA and by two empirical measures of the H-bond strength-the (1)H NMR chemical shift of proton involved and the C-O bond length. Changes in H-bonding strengths and the position of proton transfer while shortening the O...F distance are well described by the Hammett equation.

Towards the comprehensive, rapid, and accurate prediction of the favorable tautomeric states of drug-like molecules in aqueous solution

NASA Astrophysics Data System (ADS)

Greenwood, Jeremy R.; Calkins, David; Sullivan, Arron P.; Shelley, John C.

2010-06-01

Generating the appropriate protonation states of drug-like molecules in solution is important for success in both ligand- and structure-based virtual screening. Screening collections of millions of compounds requires a method for determining tautomers and their energies that is sufficiently rapid, accurate, and comprehensive. To maximise enrichment, the lowest energy tautomers must be determined from heterogeneous input, without over-enumerating unfavourable states. While computationally expensive, the density functional theory (DFT) method M06-2X/aug-cc-pVTZ(-f) [PB-SCRF] provides accurate energies for enumerated model tautomeric systems. The empirical Hammett-Taft methodology can very rapidly extrapolate substituent effects from model systems to drug-like molecules via the relationship between pKT and pKa. Combining the two complementary approaches transforms the tautomer problem from a scientific challenge to one of engineering scale-up, and avoids issues that arise due to the very limited number of measured pKT values, especially for the complicated heterocycles often favoured by medicinal chemists for their novelty and versatility. Several hundreds of pre-calculated tautomer energies and substituent pKa effects are tabulated in databases for use in structural adjustment by the program Epik, which treats tautomers as a subset of the larger problem of the protonation states in aqueous ensembles and their energy penalties. Accuracy and coverage is continually improved and expanded by parameterizing new systems of interest using DFT and experimental data. Recommendations are made for how to best incorporate tautomers in molecular design and virtual screening workflows.

Supramolecular structures for determination and identification of the bond lengths in novel uranyl complexes from their infrared spectra

NASA Astrophysics Data System (ADS)

El-Sonbati, A. Z.; Diab, M. A.; Morgan, Sh. M.; Seyam, H. A.

2018-02-01

Novel dioxouranium (VI) heterochelates with neutral bidentate compounds (Ln) have been synthesized. The ligands and the heterochelates [UO2(Ln)2(O2NO)2] were confirmed and characterized by elemental analysis, 1H NMR, UV.-Vis, IR, mass spectroscopy, X-ray diffraction and thermogravimetric analysis (TGA). IR spectral data suggest that the molecules of the Schiff base are coordinated to the central uranium atom (ON donor). The nitrato groups are coordinated as bidentate ligands. The thermodynamic parameters were calculated using Coats-Redfern and Horowitz-Metzger methods. The ligands (Ln) and their complexes (1-3) showed the υ3 frequency of UO22+ has been shown to be an excellent molecular probe for studying the coordinating power of the ligands. The values of υ3 of the prepared complexes containing UO22+ were successfully used to calculate the force constant, FUO (1n 10-8N/Å) and the bond length RUO (Å) of the Usbnd O bond. A strategy based upon both theoretical and experimental investigations has been adopted. The theoretical aspects are described in terms of the well-known theory of 5d-4f transitions. Wilson's, matrix method, Badger's formula, and Jones and El-Sonbati equations were used to calculate the Usbnd O bond distances from the values of the stretching and interaction force constants. The most probable correlation between Usbnd O force constant to Usbnd O bond distance were satisfactorily discussed in term of Badger's rule and the equations suggested by Jones and El-Sonbati. The effect of Hammett's constant is also discussed.

Development of Selective Colorimetric Probes for Hydrogen Sulfide Based on Nucleophilic Aromatic Substitution

PubMed Central

Montoya, Leticia A.; Pearce, Taylor F.; Hansen, Ryan J.; Zakharov, Lev N.; Pluth, Michael D.

2013-01-01

Hydrogen sulfide is an important biological signalling molecule and an important environmental target for detection. A major challenge in developing H2S detection methods is separating the often similar reactivity of thiols and other nucleophiles from H2S. To address this need, the nucleophilic aromatic substitution (SNAr) reaction of H2S with electron-poor aromatic electrophiles was developed as a strategy to separate H2S and thiol reactivity. Treatment of aqueous solutions of nitrobenzofurazan (7-nitro-1,2,3-benzoxadiazole, NBD) thioethers with H2S resulted in thiol extrusion and formation of nitrobenzofurazan thiol (λmax = 534 nm). This reactivity allows for unwanted thioether products to be converted to the desired nitrobenzofurazan thiol upon reaction with H2S. The scope of the reaction was investigated using a Hammett linear free energy relationship study, and the determined ρ = +0.34 is consistent with the proposed SN2Ar reaction mechanism. The efficacy of the developed probes was demonstrated in buffer and in serum with associated sub-micromolar detection limits as low as 190 nM (buffer) and 380 nM (serum). Furthermore, the sigmoidal response of nitrobenzofurazan electrophiles with H2S can be fit to accurately quantify H2S. The developed detection strategy offers a manifold for H2S detection that we foresee being applied in various future applications. PMID:23735055

Advances in the simulation of toroidal gyro-Landau fluid model turbulence

NASA Astrophysics Data System (ADS)

Waltz, R. E.; Kerbel, G. D.; Milovich, J.; Hammett, G. W.

1995-06-01

The gyro-Landau fluid (GLF) model equations for toroidal geometry [R. E. Waltz, R. R. Dominguez, and G. W. Hammett, Phys. Fluids B 4, 3138 (1992)] have been recently applied to study ion temperature gradient (ITG) mode turbulence using the three-dimensional (3-D) nonlinear ballooning mode representation (BMR) outlined earlier [R. E. Waltz, G. D. Kerbel, and J. Milovich, Phys. Plasmas 1, 2229 (1994)]. The present paper extends this work by treating some unresolved issues concerning ITG turbulence with adiabatic electrons. Although eddies are highly elongated in the radial direction, long time radial correlation lengths are short and comparable to poloidal lengths. Although transport at vanishing shear is not particularly large, transport at reverse global shear, is significantly less. Electrostatic transport at moderate shear is not much affected by inclusion of local shear and average favorable curvature. Transport is suppressed when critical E×B rotational shear is comparable to the maximum linear growth rate with only a weak dependence on magnetic shear. Self-consistent turbulent transport of toroidal momentum can result in a transport bifurcation at sufficiently large r/(Rq). However, the main thrust of the new formulation in the paper deals with advances in the development of finite beta GLF models with trapped electrons and BMR numerical methods for treating the fast parallel field motion of the untrapped electrons.

Development of selective colorimetric probes for hydrogen sulfide based on nucleophilic aromatic substitution.

PubMed

Montoya, Leticia A; Pearce, Taylor F; Hansen, Ryan J; Zakharov, Lev N; Pluth, Michael D

2013-07-05

Hydrogen sulfide is an important biological signaling molecule and an important environmental target for detection. A major challenge in developing H2S detection methods is separating the often similar reactivity of thiols and other nucleophiles from H2S. To address this need, the nucleophilic aromatic substitution (SNAr) reaction of H2S with electron-poor aromatic electrophiles was developed as a strategy to separate H2S and thiol reactivity. Treatment of aqueous solutions of nitrobenzofurazan (7-nitro-1,2,3-benzoxadiazole, NBD) thioethers with H2S resulted in thiol extrusion and formation of nitrobenzofurazan thiol (λmax = 534 nm). This reactivity allows for unwanted thioether products to be converted to the desired nitrobenzofurazan thiol upon reaction with H2S. The scope of the reaction was investigated using a Hammett linear free energy relationship study, and the determined ρ = +0.34 is consistent with the proposed SN2Ar reaction mechanism. The efficacy of the developed probes was demonstrated in buffer and in serum with associated submicromolar detection limits as low as 190 nM (buffer) and 380 nM (serum). Furthermore, the sigmoidal response of nitrobenzofurazan electrophiles with H2S can be fit to accurately quantify H2S. The developed detection strategy offers a manifold for H2S detection that we foresee being applied in various future applications.

Catalytic dehydration of fructose to 5-hydroxymethylfurfural over Nb2O5 catalyst in organic solvent.

PubMed

Wang, Fenfen; Wu, Hai-Zhen; Liu, Chun-Ling; Yang, Rong-Zhen; Dong, Wen-Sheng

2013-03-07

The catalytic dehydration of fructose to 5-hydroxymethylfurfural (HMF) in DMSO was performed over Nb2O5 derived from calcination of niobic acid at various temperatures (300-700 °C). The catalysts were characterized by powder X-ray diffraction, N2 physical adsorption, temperature-programed desorption of NH3, n-butylamine titration using Hammett indicators, infrared spectroscopy of adsorbed pyridine, and X-ray photoelectron spectroscopy. It was found that both catalytic activity and surface acid sites decrease with increasing calcination temperatures. The Nb2O5 derived from calcination of niobic acid at 400 °C reveals the maximum yield of HMF among all the catalysts, although the amount of acid sites on the catalyst is lower than that on the sample calcined at 300 °C. The results suggest that the presence of larger amounts of strong acid sites on the surface of the Nb2O5 calcined at 300 °C may promote side reactions. The Nb2O5 prepared at 400 °C shows 100% fructose conversion with 86.2% HMF yield in DMSO at 120 °C after 2 h. The activity of the catalyst decreases gradually during recycle because of coke deposition; however, it can be fully recovered by calcination at 400 °C for 2 h, suggesting that this catalyst is of significance for practical applications. Copyright © 2012 Elsevier Ltd. All rights reserved.

Substituent Effects In a Series of 1,7-C60(RF)2 Compounds (RF = CF3, C2F5, n-C3F7, i-C3F7, n-C4F9, s-C4F9, n-C8F17): Electron Affinities, Reduction Potentials, and E(LUMO) Values Are Not Always Correlated

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kuvychko, Igor V.; Whitaker, James B.; Larson, Bryon W.

Substituent effects are of paramount importance in virtually all fields of fundamental and applied chemistry. Classical and modern examples can be found in organic chemistry (Hammett parameters and Charton steric parameters), inorganic chemistry (trans effect and trans influence), organometallic chemistry (phosphine cone angles), physical chemistry (linear free energy relationships and DFT), biochemistry (protein tertiary structure), medicinal chemistry (SAR maps and BioMAP analysis), polymer chemistry (nonlinear optical and permeation properties and glass transition temperatures), and materials chemistry (stability and luminescent properties of electroluminescent devices and light-to-power conversion efficiencies of fullerene-derivative-based OPV devices).

Methane negative chemical ionization analysis of 1,3-dihydro-5-phenyl-1,4-benzodiazepin-2-ones.

PubMed Central

Garland, W A; Miwa, B J

1980-01-01

The methane negative chemical ionization (NCI) mass spectra of the medically important 1,3-dihydro-5-phenyl-1,4-benzodiazepin-2-ones generally consisted solely of M- and (M-H)- ions. Attempts to find the location of the H lost in the generation of the (M-H)- ion were unsuccessful, although many possibilities were eliminated. A Hammett correlation analysis of the relative sensitivities of a series of 7-substituted benzodiazepines suggested that the initial ionization takes place at the 4,5-imine bond. For certain benzodiazepines, the (M-H)- ion generated by methane NCI was 20 times more intense than the MH+ ion generated by methane positive chemical ionization (PCI). By using NCI, a sensitive and simple GC-MS assay for nordiazepam was developed that can quantitate this important metabolite of many of the clinically used benzodiazepines in the blood and brain of rats. PMID:6775944

Coumaraz-2-on-4-ylidene: Ambiphilic N-heterocyclic Carbenes with a Fine-Tunable Electronic Structure.

PubMed

Song, Hayoung; Kim, Hyunho; Lee, Eunsung

2018-05-16

Herein, a coumaraz-2-on-4-ylidene (1) as a new example of ambiphilic N-heterocyclic carbenes with fine tunable electronic properties is reported. The N-carbamic and aryl groups on carbene carbon provide exceptionally high electrophilicity and nucleophilicity simultaneously to the carbene center, as evidenced by the 77Se NMR chemical shifts of their selenoketone derivatives and the CO stretching strengths of their rhodium carbonyl complexes. Since the precursors of 1 could be synthesized from various functionalized Schiff bases in a practical and scalable manner, the electronic properties of 1 can be fine-tuned in quantitative and predictable way using the Hammett σ constant of the functional groups on aryl ring. The facile electronic tuning capability of 1 may be further applicable to eliciting novel properties in main-group and transition metal chemistry. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Mechanism of silver-mediated di-tert-butylsilylene transfer from a silacyclopropane to an alkene.

PubMed

Driver, Tom G; Woerpel, K A

2004-08-18

Kinetic studies of the reactions of cyclohexene silacyclopropane 1 and monosubstituted alkenes in the presence of 5 mol % of (Ph3P)2AgOTf suggested a possible mechanism for silver-mediated di-tert-butylsilylene transfer. The kinetic order in cyclohexene silacyclopropane 1 was determined to be one. Inverse kinetic saturation behavior (rate inhibition) was observed in monosubstituted alkene and cyclohexene concentrations. Saturation kinetic behavior in catalyst concentration was observed. A reactive intermediate, a silylsilver complex, was observed using low temperature 29Si NMR spectroscopy. Competition experiments between substituted styrenes and a deficient amount of 1 correlated well with the Hammett equation and provided a rho value of -0.62 +/- 0.02 using sigmap constants. These data support a mechanism involving reversible silver-promoted di-tert-butylsilylene extrusion from 1 followed by irreversible concerted electrophilic attack of the silylsilver intermediate on the alkene.

Ring[bond]chain tautomerism of 2-Aryl-substituted cis- and trans-decahydroquinazolines.

PubMed

Lázár, László; Göblyös, Anikó; Martinek, Tamás A; Fülöp, Ferenc

2002-07-12

In CDCl(3) at 300 K, 2-aryl-substituted cis- and trans-3-isopropyldecahydroquinazolines and trans-3-phenyldecahydroquinazolines proved to be three-component (r(1)[bond]o[bond]r(2)) ring[bond]chain tautomeric mixtures, whereas only ring-closed tautomers could be detected for the 3-methyl-substituted analogues. The proportions of the ring-chain tautomeric forms at equilibrium were strongly influenced by the N-substitutents and the cis-trans ring junction and could be described by the equation log K(X) = rho sigma(+) + log K(X=H). These are the first examples among 2-aryl-1,3-N,N-heterocycles of a three-component ring-chain tautomeric equilibrium characterized by a Hammett-type equation. The stabilities of the ring-closed forms of cis- and trans-2-aryldecahydroquinazolines and the corresponding 3,1-benzoxazines were found to increase in the following sequence of the heteroatom at position 3: NPh < N-i-Pr < O < NMe.

Atropisomerization of di-para-substituted propyl-bridged biphenyl cyclophanes.

PubMed

Rotzler, Jürgen; Gsellinger, Heiko; Bihlmeier, Angela; Gantenbein, Markus; Vonlanthen, David; Häussinger, Daniel; Klopper, Wim; Mayor, Marcel

2013-01-07

The influence of electron donors and electron acceptors of variable strength in the 4 and 4' position of 2 and 2' propyl-bridged axial chiral biphenyl cyclophanes on their atropisomerization process was studied. Estimated free energies ΔG(‡)(T) of the rotation around the central biphenyl bond which were obtained from (1)H-NMR coalescence measurements were correlated to the Hammett parameters σ(p) as a measure for electron donor and acceptor strength. It is demonstrated that the resulting nice linear correlation is mainly based on the influence of the different substituents on the π-system of the biphenyl cyclophanes. By lineshape analysis the rate constants were calculated and by the use of the Eyring equation the enthalpic and entropic contributions were evaluated. Density functional theory calculations show a planar transition state of the isomerization process and the calculated energy barriers based on this reaction mechanism are in good agreement with the experimentally obtained free energies.

Testing an H-mode Pedestal Model Using DIII-D Data

NASA Astrophysics Data System (ADS)

Kritz, A. H.; Onjun, T.; Bateman, G.; Guzdar, P. N.; Mahajan, S. M.; Osborne, T.

2004-11-01

Tests against experimental data are carried out for a model of the pedestal at the edge of H-mode plasmas based on double-Beltrami solutions of the two-fluid Hall-MHD equations for the interaction of the magnetic and velocity fields.(S.M. Mahajan and Z. Yoshida, PRL 81 (1998) 4863, Phys. Plasmas 7 (2000) 635.) The width and height of the pedestal predicted by the model are tested against experimental data from the DIII-D tokamak. The model for the pedestal width, which has a particularly simple form, namely, inversely proportional to the square root of the density, does not appear to capture the parameter dependence of the experimental data. When the model for the pedestal temperature is rescaled to optimize agreement with data, the RMS error is found to be comparable with the RMS error found using other pedestal models.(T. Onjun, G. Bateman, A.H. Kritz, G. Hammett, Phys. Plasmas 9 (2002) 5018.)

Toroidal gyrofluid equations for simulations of tokamak turbulence

NASA Astrophysics Data System (ADS)

Beer, M. A.; Hammett, G. W.

1996-11-01

A set of nonlinear gyrofluid equations for simulations of tokamak turbulence are derived by taking moments of the nonlinear toroidal gyrokinetic equation. The moment hierarchy is closed with approximations that model the kinetic effects of parallel Landau damping, toroidal drift resonances, and finite Larmor radius effects. These equations generalize the work of Dorland and Hammett [Phys. Fluids B 5, 812 (1993)] to toroidal geometry by including essential toroidal effects. The closures for phase mixing from toroidal ∇B and curvature drifts take the basic form presented in Waltz et al. [Phys. Fluids B 4, 3138 (1992)], but here a more rigorous procedure is used, including an extension to higher moments, which provides significantly improved accuracy. In addition, trapped ion effects and collisions are incorporated. This reduced set of nonlinear equations accurately models most of the physics considered important for ion dynamics in core tokamak turbulence, and is simple enough to be used in high resolution direct numerical simulations.

An Iron(II)(1,3-bis(2'-pyridylimino)isoindoline) Complex as a Catalyst for Substrate Oxidation with H2O2. Evidence for a Transient Peroxodiiron(III) Species.

PubMed

Pap, József S; Cranswick, Matthew A; Balogh-Hergovich, E; Baráth, Gábor; Giorgi, Michel; Rohde, Gregory T; Kaizer, József; Speier, Gábor; Que, Lawrence

2013-08-01

The complex [Fe(indH)(solvent) 3 ](ClO 4 ) 2 ( 1 ) has been isolated from the reaction of equimolar amounts of 1,3-bis(2'-pyridylimino)isoindoline (indH) and Fe(ClO 4 ) 2 in acetonitrile and characterized by X-ray crystallography and several spectroscopic techniques. It is a suitable catalyst for the oxidation of thioanisoles and benzyl alcohols with H 2 O 2 as the oxidant. Hammett correlations and kinetic isotope effect experiments support the involvement of an electrophilic metal-based oxidant. A metastable green species ( 2 ) is observed when 1 is reacted with H 2 O 2 at -40 °C, which has been characterized to have a Fe III ( μ -O)( μ -O 2 )Fe III core on the basis of UV-Vis, electron paramagnetic resonance, resonance Raman, and X-ray absorption spectroscopic data.

Synthesis, Properties, and Light-Emitting Electrochemical Cell (LEEC) Device Fabrication of Cationic Ir(III) Complexes Bearing Electron-Withdrawing Groups on the Cyclometallating Ligands

PubMed Central

2016-01-01

The structure–property relationship study of a series of cationic Ir(III) complexes in the form of [Ir(C^N)2(dtBubpy)]PF6 [where dtBubpy = 4,4′-di-tert-butyl-2,2′-bipyridine and C^N = cyclometallating ligand bearing an electron-withdrawing group (EWG) at C4 of the phenyl substituent, i.e., −CF3 (1), −OCF3 (2), −SCF3 (3), −SO2CF3 (4)] has been investigated. The physical and optoelectronic properties of the four complexes were comprehensively characterized, including by X-ray diffraction analysis. All the complexes exhibit quasireversible dtBubpy-based reductions from −1.29 to −1.34 V (vs SCE). The oxidation processes are likewise quasireversible (metal + C^N ligand) and are between 1.54 and 1.72 V (vs SCE). The relative oxidation potentials follow a general trend associated with the Hammett parameter (σ) of the EWGs. Surprisingly, complex 4 bearing the strongest EWG does not adhere to the expected Hammett behavior and was found to exhibit red-shifted absorption and emission maxima. Nevertheless, the concept of introducing EWGs was found to be generally useful in blue-shifting the emission maxima of the complexes (λem = 484–545 nm) compared to that of the prototype complex [Ir(ppy)2(dtBubpy)]PF6 (where ppy = 2-phenylpyridinato) (λem = 591 nm). The complexes were found to be bright emitters in solution at room temperature (ΦPL = 45–66%) with microsecond excited-state lifetimes (τe = 1.14–4.28 μs). The photophysical properties along with density functional theory (DFT) calculations suggest that the emission of these complexes originates from mixed contributions from ligand-centered (LC) transitions and mixed metal-to-ligand and ligand-to-ligand charge transfer (LLCT/MLCT) transitions, depending on the EWG. In complexes 1, 3, and 4 the 3LC character is prominent over the mixed 3CT character, while in complex 2, the mixed 3CT character is much more pronounced, as demonstrated by DFT calculations and the observed positive solvatochromism effect. Due to the quasireversible nature of the oxidation and reduction waves, fabrication of light-emitting electrochemical cells (LEECs) using these complexes as emitters was possible with the LEECs showing moderate efficiencies. PMID:27681985

Dynamics of Turbulence-generated E × B Flows: Simulation and Theory

NASA Astrophysics Data System (ADS)

Hahm, T. S.

1998-11-01

Many magnetic confinement experiments have indicated that E × B shear can suppress turbulence and consequently lead to significant reduction of plasma transport.^1 It has been observed in flux-tube gyrofluid^2,3 and gyrokinetic^4 simulations that small radial scale fluctuating E × B flows driven by turbulence (often called radial modes,^3 or zonal flows) play a dominant role in regulating toroidal ITG (ion temperature gradient) turbulence. Furthermore, the radial modes with similar characteristics and significant impact on transport have been also observed in the recent global gyrokinetic simulations with improved numerical capabilities^5 as well as in edge turbulence simulations with a collisional poloidal flow damping.^6 In this work, we analyze turbulence and flow statistics from gyrofluid and gyrokinetic simulations and compare to various theoretical predictions. The observed radial modes contain significant components with radial scales and frequencies comparable to those of turbulence. While the fast time varying components (including Geodesic Acoustic Modes) contribute the most to the instantaneous E × B shearing rate, they are less influential in suppressing turbulence. The effective E × B shearing rate capturing this important physics is analytically derived and evaluated from the recent nonlinear simulation results. Its magnitude is much smaller than the instantaneous E × B shearing rate, but typically of the order of the decorrelation rate of the ambient turbulence. This is consistent with the reduced, not completely stabilized level of turbulence with broadened kr spectrum observed in simulations. Zonal flows are linearly stable, but can be generated either by incoherent emission of turbulence or by inverse cascade of spectrum yielding negative turbulent viscosity which is related to the Reynolds' stress.^7 Various analytical calculations and proposed mechanisms for zonal flow generation and saturation^7,8 will be tested numerically. Finally, the collisional damping of flows and its effect on transport will be studied via gyrokinetic simulations with momentum and energy conserving Fokker-Planck operator.^5 renewcommandthempfootnotefnsymbolmpfootnote footnotetext[1]This work supported by DOE contract DE-AC02-76-CHO-3073. footnotetext[2]In collaboration with M. A. BEER, Z. LIN, G. W. HAMMETT, W. W. LEE, and W. M. TANG. renewcommandthempfootnotearabicmpfootnote setcountermpfootnote0 footnotetext[1]K. H. Burrell, Phys. Plasmas 4, 1499 (1997); E. J. Synakowski, Plasma Phys. Control. Fusion, 40, 581 (1998). footnotetext[2]M. A. Beer, Ph.D. Thesis, Princeton University, 1995; G. W. Hammett et al., Plasma Phys. Control. Fusion, 35, 973 (1993) footnotetext[3]R. E. Waltz, G. D. Kerbel, and J. Milovich, Phys. Plasmas 1, 2229 (1994). footnotetext[4]A. M. Dimits et al., Phys. Rev. Lett. 77, 71 (1996). footnotetext[5]Z. Lin et al., To be submitted to Phys. Plasmas (1998). footnotetext[6]B. N. Rogers, J. F. Drake, and A. Zeiler, Submitted to Phys. Rev. Lett.(1998). footnotetext[7]P. H. Diamond and Y. B. Kim, Phys. Fluids B 3, 1626 (1991); P. H. Diamond, J. Fleischer, and F. L. Hinton, Presented at Transport Task Force Meeting (1998). footnotetext[8]M. N. Rosenbluth and F.L. Hinton, Phys. Rev. Lett. 80, 724 (1998).

Structure-property relationship of 3-(4-substituted benzyl)-1,3-diazaspiro[4.4]nonane-2,4-diones as new potentional anticonvulsant agents. An experimental and theoretical study

NASA Astrophysics Data System (ADS)

Lazić, Anita M.; Božić, Bojan Đ.; Vitnik, Vesna D.; Vitnik, Željko J.; Rogan, Jelena R.; Radovanović, Lidija D.; Valentić, Nataša V.; Ušćumlić, Gordana S.

2017-01-01

The structure-property relationship of newly synthesized 3-(4-substituted benzyl)-1,3-diazaspiro [4.4]nonane-2,4-diones was studied by experimental and calculated methods. The prepared compounds were characterized by UV-Vis, FT-IR, 1H NMR and 13C NMR spectroscopy and elemental analysis. The crystal structure was elucidated by single-crystal X-ray diffraction. The 3-benzyl-1,3-diazaspiro[4.4]nonane-2,4-dione crystallizes in triclinic P-1 space group, with two crystallographically independent molecules in the asymmetric unit. Cyclopentane ring adopts an envelope conformation. A three-dimensional crystal packing is governed by hydrogen N-H⋯O bonds, numerous C-H⋯O/N and C-H … π interactions between neighboring molecules. Density functional theory (DFT) calculations with B3LYP and M06-2X methods using 6-311++G(d,p) basis set were performed to provide structural and spectroscopic information. Comparisons between experimental and calculated UV-Vis spectral properties suggest that the monomeric form of the investigated spirohydantoins is dominant in all used solvents. The effects of substituents on the absorption spectra of spirohydantoins are interpreted by correlation of absorption frequencies with Hammett equation. The lipophilicities of the investigated molecules were estimated by calculation of their log P values. Some of the spirohydantoins synthesized in this work, exhibit the lipophilicities comparable to the standard medicine anticonvulsant drug Phenytoin. The results obtained in this investigation afford guidelines for the preparation of new derivatives of spirohydantoin as potential anticonvulsant agents and for better understanding the structure-activity relationship.

Negative kinetic temperature effect on the hydride transfer from NADH analogue BNAH to the radical cation of N-benzylphenothiazine in acetonitrile.

PubMed

Zhu, Xiao-Qing; Zhang, Jian-Yu; Cheng, Jin-Pei

2006-09-01

The reaction rates of 1-(p-substituted benzyl)-1,4-dihydronicotinamide (G-BNAH) with N-benzylphenothiazine radical cation (PTZ(*+)) in acetonitrile were determined. The results show that the reaction rates (k(obs)) decreased from 2.80 x 10(7) to 2.16 x 10(7) M(-1) s(-1) for G = H as the reaction temperature increased from 298 to 318 K. The activation enthalpies of the reactions were estimated according to Eyring equation to give negative values (-3.4 to -2.9 kcal/mol). Investigation of the reaction intermediate shows that the charge-transfer complex (CT-complex) between G-BNAH and PTZ(*+) was formed in front of the hydride transfer from G-BNAH to PTZ(*+). The formation enthalpy of the CT-complex was estimated by using the Benesi-Hildebrand equation to give the values from -6.4 to -6.0 kcal/mol when the substituent G in G-BNAH changes from CH(3)O to Br. Detailed thermodynamic analyses on each elementary step in the possible reaction pathways suggest that the hydride transfer from G-BNAH to PTZ(*+) occurs by a concerted hydride transfer via a CT-complex. The effective charge distribution on the pyridine ring in G-BNAH at the various stages-the reactant G-BNAH, the charge-transfer complex, the transition-state, and the product G-BNA(+)-was estimated by using the method of Hammett-type linear free energy analysis, and the results show that the pyridine ring carries relative effective positive charges of 0.35 in the CT-complex and 0.45 in the transition state, respectively, which indicates that the concerted hydride transfer from G-BNAH to PTZ(*+) was practically performed by the initial charge (-0.35) transfer from G-BNAH to PTZ(*+) and then followed by the transfer of hydrogen atom with partial negative charge (-0.65). It is evident that the present work would be helpful in understanding the nature of the negative temperature effect, especially on the reaction of NADH coenzyme with the drug phenothiazine in vivo.

Arylethynyl Substituted 9,lO-Anthraquinones: Tunable Stokes Shifts by Substitution and Solvent Polarity

NASA Technical Reports Server (NTRS)

Yang, Jinhua; Dass, Amala; Rawashdeh, Abdel-Monem M.; Sotiriou-Leventis, Chariklia; Panzner, Matthew J.; Tyson, Daniel S.; Kinder, James D.; Leventis, Nicholas

2004-01-01

2-Arylethynyl- and 2,6- and 2,7-diarylethynyl-substituted 9,lO-anthraquinones were synthesized via Sonogashira coupling reactions of 2-bromo-, 2,6-dibromo-, and 2,7-dibromo-9,10- anthraquinone with para-substituted phenylacetylenes. While the redox properties of those compounds are almost insensitive to substitution, their absorption maxima are linearly related to the Hammett constants with different slopes for electron donors and electron acceptors. ABI compounds are photoluminescent both in solution (quantum yields of emission <= 6 %), and as solids. The emission spectra have the characteristics of charge-transfer bands with large Stokes shifts (100-250 nm). The charge-transfer character of the emitting state is supported by large dipole moment differences between the ground and the excited state as concluded on the basis of molecular modeling and Lippert-Mataga correlations of the Stokes shifts with solvent polarity. Maximum Stokes shifts are attained by both electron-donating and -withdrawing groups. This is explained by a destabilization of the HOMO by electron donors and a stabilization of the LUMO by electron acceptors. X-ray crystallographic analysis of, for example, 2,7-bisphenylethynfl- 9,lO-anthraquinone reveals a monoclinic P21In space group and no indication for pi-overlap that would promote quenching, thus explaining emission from the solid state. Representative reduced forms of the title compounds were isolated as stable acetates of the corresponding dihydrs-9,10- anthraquinones. The emission of these compounds is blue-shifted relative to the parent oxidized forms and is attributed to internal transitions in the dihydro-9,lO-anthraquinone core.

Growth Inhibition and DNA Damage Induced by X-Phenols in Yeast: A Quantitative Structure–Activity Relationship Study

PubMed Central

2017-01-01

Phenolic compounds and their derivatives are ubiquitous constituents of numerous synthetic and natural chemicals that exist in the environment. Their toxicity is mostly attributed to their hydrophobicity and/or the formation of free radicals. In a continuation of the study of phenolic toxicity in a systematic manner, we have examined the biological responses of Saccharomyces cerevisiae to a series of mostly monosubstituted phenols utilizing a quantitative structure–activity relationship (QSAR) approach. The biological end points included a growth assay that determines the levels of growth inhibition induced by the phenols as well as a yeast deletion (DEL) assay that assesses the ability of X-phenols to induce DNA damage or DNA breaks. The QSAR analysis of cell growth patterns determined by IC50 and IC80 values indicates that toxicity is delineated by a hydrophobic, parabolic model. The DEL assay was then utilized to detect genomic deletions in yeast. The increase in the genotoxicity was enhanced by the electrophilicity of the phenolic substituents that were strong electron donors as well as by minimal hydrophobicity. The electrophilicities are represented by Brown’s sigma plus values that are a variant of the Hammett sigma constants. A few mutant strains of genes involved in DNA repair were separately exposed to 2,6-di-tert-butyl-4-methyl-phenol (BHT) and butylated hydroxy anisole (BHA). They were subsequently screened for growth phenotypes. BHA-induced growth defects in most of the DNA repair null mutant strains, whereas BHT was unresponsive. PMID:29302629

Ortho effects in quantitative structure-activity relationships for acetylcholinesterase inhibition by aryl carbamates.

PubMed

Lin, Gialih; Liu, Yu-Chen; Lin, Yan-Fu; Wu, Yon-Gi

2004-10-01

Ortho-substituted phenyl-N-butyl carbamates (1-9) are characterized as "pseudo-pseudo-substrate" inhibitors of acetylcholinesterase. Since the inhibitors protonate at pH 7.0 buffer solution, the virtual inhibition constants (K'is) of the protonated inhibitors are calculated from the equation, - logK'i = - logKi - logKb. The logarithms of the inhibition constant (Ki), the carbamylation constant (k(c)), and the bimolecular inhibition constant (k(i)) for the enzyme inhibitions by carbamates 1-9 are multiply linearly correlated with the Hammett para-substituent constant (sigma(p)), the Taft-Kutter-Hansch ortho steric constant (E(S)), and the Swan-Lupton ortho polar constant (F). Values of rho, delta, and f for the - logKi-, logk(c)-, and logk(i)-correlations are -0.6, -0.16, 0.7; 0.11, 0.03, -0.3; and - 0.5, - 0.12, 0.4, respectively. The Ki step further divides into two steps: 1) the pre-equilibrium protonation of the inhibitors, Kb step and 2) formation of a negatively charged enzyme-inhibitor Michaelis-Menten complex--virtual inhibition, K'i step. The Ki step has little ortho steric enhancement effect; moreover, the k(c)step is insensitive to the ortho steric effect. The f value of 0.7 for the Ki step indicates that ortho electron-withdrawing substituents of the inhibitors accelerate the inhibition reactions from the ortho polar effect; however, the f value of -0.3 for the k(c)step implies that ortho electron-withdrawing substituents of the inhibitors lessen the inhibition reactions from the ortho polar effect.

Reactivity of superoxide radical anion and hydroperoxyl radical with alpha-phenyl-N-tert-butylnitrone (PBN) derivatives.

PubMed

Durand, Grégory; Choteau, Fanny; Pucci, Bernard; Villamena, Frederick A

2008-12-04

Nitrones have exhibited pharmacological activity against radical-mediated pathophysiological conditions and as analytical reagents for the identification of transient radical species by electron paramagnetic resonance (EPR) spectroscopy. In this work, competitive spin trapping, stopped-flow kinetics, and density functional theory (DFT) were employed to assess and predict the reactivity of O(2)(*-) and HO(2)(*) with various para-substituted alpha-phenyl-N-tert-butylnitrone (PBN) spin traps. Rate constants of O(2)(*-) trapping by nitrones were determined using competitive UV-vis stopped-flow method with phenol red (PR) as probe, while HO(2)(*) trapping rate constants were calculated using competition kinetics with 5,5-dimethylpyrroline N-oxide (DMPO) by employing EPR spectroscopy. The effects of the para substitution on the charge density of the nitronyl-carbon and on the free energies of nitrone reactivity with O(2)(*-) and HO(2)(*) were computationally rationalized at the PCM/B3LYP/6-31+G(d,p)//B3LYP/6-31G(d) level of theory. Theoretical and experimental data show that the rate of O(2)(*-) addition to PBN derivatives is not affected by the polar effect of the substituents. However, the reactivity of HO(2)(*) follows the Hammett equation and is increased as the substituent becomes more electron withdrawing. This supports the conclusion that the nature of HO(2)(*) addition to PBN derivatives is electrophilic, while the addition of O(2)(*-) to PBN-type compounds is only weakly electrophilic.

Turbulent Heating and Fluctuation Characteristics in Alfvenic Turbulence

NASA Astrophysics Data System (ADS)

Dorland, William

2005-10-01

Alfve'n waves are ubiquitous in natural and laboratory plasmas. In this talk, the main focus is on astrophysical plasmas that are turbulent, magnetized, hot and diffuse. The dynamically important characteristics of these plasmas are often well- described by magnetohydrodynamics [see e.g., Ref. 1]. However, much of what we actually observe is critically affected by how much of the turbulent energy is absorbed by (highly radiative) electrons [2], the amplitude of density fluctuations [3], and the spectral indices of turbulent, Alfve'nic cascades. These questions each have essentially kinetic aspects. In this talk, we present detailed simulations and analyses of of the cascade of shear Alfve'n waves, to and through scales comparable to the ion Larmor radius in the direction perpendicular to the magnetic field. We demonstrate analytically and numerically that the nonlinear gyrokinetic equations, originally developed for fusion applications, are perfectly suited to these astrophysical problems. We present extensive linear and nonlinear gyrokinetic simulation results from the GS2 code. We demonstrate accurate resolution of the damping of kinetic Alfve'n waves in plasmas with beta small, large and comparable to unity, for a wide range of electron-to-ion temperature ratios, in linear and nonlinear contexts. We have used the GS2 code to calculate the turbulent energy absorption, density fluctuation characteristics, and spectral indices for plasmas with parameters taken from hot accretion flows and from the interstellar plasma. These results will be compared with theoretical predictions [2] and to observations. Co-authors: S. C. Cowley (UCLA), G. W. Hammett (PPPL), E. Quataert and G. Howes (UC-Berkeley), and A. Scheckochihin (Cambridge) 1. S. Balbus and J. Hawley, Rev Mod Phys, Vol. 70, p. 1. 2. E. Quataert and A. Gruzinov, Ap J, Vol. 520, p. 248; E. Quataert, Ap J, Vol. 500, p. 978.3. Y. Lithwick and P. Goldreich, Ap J, Vol. 562, p. 279.4. P. Goldreich and Sridhar, Ap J, Vol. 438, p. 763; P. Goldreich and Sridhar, Ap J, Vol. 485, p. 680.

QSAR by LFER model of cytotoxicity data of anti-HIV 5-phenyl-1-phenylamino-1H-imidazole derivatives using principal component factor analysis and genetic function approximation.

PubMed

Roy, Kunal; Leonard, J Thomas

2005-04-15

Cytotoxicity data of anti-HIV 5-phenyl-1-phenylamino-1H-imidazole derivatives were subjected to quantitative structure-activity relationship (QSAR) study using linear free energy related (LFER) model of Hansch using electronic (Hammett sigma), hydrophobicity (pi) and steric (molar refractivity and STERIMOL L, B1, B2, B3 and B4) parameters of phenyl ring substituents of the compounds, along with appropriate indicator variables. Principal component factor analysis (FA) was used as the data-preprocessing step to identify the important predictor variables contributing to the response variable and to avoid collinearities among them. The generated multiple linear regression (MLR) equations were statistically validated using leave-one-out technique. Genetic function approximation (GFA) was also used on the same data set to develop QSAR equations, which produced the same best equation as obtained with FA-MLR. The final equation is of acceptable statistical quality (explained variance 80.2%) and predictive potential (leave-one-out predicted variance 74%). The analysis explores the structural and physicochemical contributions of the compounds for cytotoxicity. A thiol substituent at 2 position of the imidazole nucleus decreases cytotoxicity when compared to the corresponding unsubstituted congener. Presence of hydrogen bond donor group at meta position of the phenyl ring present at 5 position of the imidazole nucleus also reduces cytotoxicity. Additionally, absence of any substituent at 2 and 3 positions of the phenyl ring of 1-phenylamino fragment reduces the cytotoxicity. The negative coefficient of sigmap indicates that presence of electron-withdrawing substituents at the para position of the phenyl ring of the 1-phenylamino fragment is not favourable for the cytotoxicity. Again, lipophilicity of meta substituents of the 5-phenyl ring increases cytotoxicity. The coefficients of molar refractivity (MRm) and STERIMOL parameters for meta substituents (Lm, B1m and B4m) of the phenyl ring of 1-phenylamino fragment indicate that the length, width and overall size of meta substituents are conducive factors for the cytotoxicity.

Quinone 1 e – and 2 e – /2 H + Reduction Potentials: Identification and Analysis of Deviations from Systematic Scaling Relationships

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huynh, Mioy T.; Anson, Colin W.; Cavell, Andrew C.

Quinones participate in diverse electron transfer and proton-coupled electron transfer processes in chemistry and biology. An experimental study of common quinones reveals a non-linear correlation between the 1 e – and 2 e –/2 H + reduction potentials. This unexpected observation prompted a computational study of 128 different quinones, probing their 1 e – reduction potentials, pKa values, and 2 e –/2 H + reduction potentials. The density functional theory calculations reveal an approximately linear correlation between these three properties and an effective Hammett constant associated with the quinone substituent(s). However, deviations from this linear scaling relationship are evident formore » quinones that feature halogen substituents, charged substituents, intramolecular hydrogen bonding in the hydroquinone, and/or sterically bulky substituents. These results, particularly the different substituent effects on the 1 e – versus 2 e – /2 H + reduction potentials, have important implications for designing quinones with tailored redox properties.« less

Hydroxyapatite catalyzed aldol condensation: Synthesis, spectral linearity, antimicrobial and insect antifeedant activities of some 2,5-dimethyl-3-furyl chalcones

NASA Astrophysics Data System (ADS)

Subramanian, M.; Vanangamudi, G.; Thirunarayanan, G.

2013-06-01

A series of 2,5-dimethyl-3-furyl chalcones [2E-1-(2,5-dimethyl-3-furyl)-3-(substituted phenyl)-2-propen-1-ones] have been synthesized by Hydrotalcite catalyzed aldol condensation between 3-acetyl-2,5-dimethylfuron and substituted benzaldehydes. Yields of chalcones are more than 80%. These chalcones were characterized by their physical constants and spectral data. The group frequencies of infrared ν(cm-1) of CO s-cis and s-trans, CH in-plane and out of plane, CHdbnd CH out of plane, lbond2 Cdbnd Crbond2 out of plane modes, NMR chemical shifts δ(ppm) of Hα, Hβ, CO, Cα and Cβ of these chalcones were correlated with Hammett substituent constants, F and R parameters using single and multi-regression analyses. From the results of statistical analyses, the effects of substituents on the group frequencies are explained. Antibacterial, antifungal and insect antifeedant activities of these chalcones have been studied.

Fine-tuning the nucleophilic reactivities of boron ate complexes derived from aryl and heteroaryl boronic esters.

PubMed

Berionni, Guillaume; Leonov, Artem I; Mayer, Peter; Ofial, Armin R; Mayr, Herbert

2015-02-23

Boron ate complexes derived from thienyl and furyl boronic esters and aryllithium compounds have been isolated and characterized by X-ray crystallography. Products and mechanisms of their reactions with carbenium and iminium ions have been analyzed. Kinetics of these reactions were monitored by UV/Vis spectroscopy, and the influence of the aryl substituents, the diol ligands (pinacol, ethylene glycol, neopentyl glycol, catechol), and the counterions on the nucleophilic reactivity of the boron ate complexes were examined. A Hammett correlation confirmed the polar nature of their reactions with benzhydrylium ions, and the correlation lg k(20 °C)=sN (E+N) was employed to determine the nucleophilicities of the boron ate complexes and to compare them with those of other borates and boronates. The neopentyl and ethylene glycol derivatives were found to be 10(4) times more reactive than the pinacol and catechol derivatives. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Employment of electrodonating capacity as an index of reactive modulation by substituent effects: application for electron-transfer-controlled hydrogen bonding.

PubMed

Martínez-González, Eduardo; Frontana, Carlos

2014-02-07

Evaluation of the substituent effect in reaction series is an issue of interest, as it is fundamental for controlling chemical reactivity in molecules. Within the framework of density functional theory, employment of the chemical potential, μ, and the chemical hardness, η, leads to the calculation of properties of common use, such as the electrodonating (ω(-)) and electroaccepting (ω(+)) powers, in many chemical systems. In order to examine the predictive character of the substituent effect by these indexes, a comparison between these and experimental binding constants (Kb) for binding of a series of radical anions from para- and ortho-substituted nitrobenzenes with 1,3-diethylurea in acetonitrile was performed, and fair correlations were obtained; furthermore, this strategy was suitable for all of the studied compounds, even those for which empirical approximations, such as Hammett's model, are not valid. Visual representations of substituent effects are presented by considering the local electrodonating power ω(-)(r).

Regioselectivity of pyridine deprotonation in the gas phase.

PubMed

Schafman, Bonnie S; Wenthold, Paul G

2007-03-02

The regioselective deprotonation of pyridine in the gas phase has been investigated by using chemical reactivity studies. The mixture of regioisomers, trapped as carboxylates, formed in an equilibrium mixture is determined to result from 70-80% deprotonation in the 4-position, and 20-30% deprotonation at the 3-position. The ion formed by deprotonation in the 2-position is not measurably deprotonated at equilibrium because the ion is destabilized by lone-pair repulsion. From the composition of the mixture, the gas-phase acidities (DeltaH degrees acid) at the 4-, 3-, and 2-positions are determined to be 389.9 +/- 2.0, 391.2-391.5, and >391.5 kcal/mol, respectively. The relative acidities of the 4- and 3-positions are explained by using Hammett-Taft parameters, derived by using the measured gas-phase acidities of pyridine carboxylic acids. The values of sigmaF and sigmaR are -0.18 and 0.74, respectively, showing the infused nitrogen in pyridine to have a strong pi electron-withdrawing effect, but with little sigma-inductive effect.

Extension of Structure-Reactivity Correlations for the Hydrogen Abstraction Reaction to the Methyl Radical and Comparison to the Chlorine Atom, Bromine Atom, and Hydroxyl Radical.

PubMed

Poutsma, Marvin L

2016-07-07

Recently, we presented structure-reactivity correlations for the gas-phase rate constants for hydrogen abstraction from sp(3)-hybridized carbon by three electrophilic radicals (X(•) + HCR3 → XH + (•)CR3; X = Cl(•), HO(•), and Br(•)); the reaction enthalpy effect was represented by the independent variable ΔrH and the "polar effect" by the independent variables F and R, the Hammett-Taft constants for field/inductive and resonance effects. Here we present a parallel treatment for the less electronegative CH3(•). In spite of a limited and scattered database, the resulting least-squares fit [log k437(CH3(•)) = -0.0251(ΔrH) + 0.96(ΣF) - 0.56(ΣR) - 19.15] was modestly successful and useful for initial predictions. As expected, the polar effect appears to be minor and its directionality, i.e., the "philicity" of CH3(•), may depend on the nature of the substituents.

Molecular basis of LFER. Modeling of the electronic substituent effect using fragment quantum self-similarity measures.

PubMed

Gironés, Xavier; Carbó-Dorca, Ramon; Ponec, Robert

2003-01-01

A new approach allowing the theoretical modeling of the electronic substituent effect is proposed. The approach is based on the use of fragment Quantum Self-Similarity Measures (MQS-SM) calculated from domain averaged Fermi Holes as new theoretical descriptors allowing for the replacement of Hammett sigma constants in QSAR models. To demonstrate the applicability of this new approach its formalism was applied to the description of the substituent effect on the dissociation of a broad series of meta and para substituted benzoic acids. The accuracy and the predicting power of this new approach was tested on the comparison with a recent exhaustive study by Sullivan et al. It has been shown that the accuracy and the predicting power of both procedures is comparable, but, in contrast to a five-parameter correlation equation necessary to describe the data in the study, our approach is more simple and, in fact, only a simple one-parameter correlation equation is required.

An Iron(II)(1,3-bis(2′-pyridylimino)isoindoline) Complex as a Catalyst for Substrate Oxidation with H2O2. Evidence for a Transient Peroxodiiron(III) Species

PubMed Central

Pap, József S.; Cranswick, Matthew A.; Balogh-Hergovich, É.; Baráth, Gábor; Giorgi, Michel; Rohde, Gregory T.; Kaizer, József; Speier, Gábor; Que, Lawrence

2014-01-01

The complex [Fe(indH)(solvent)3](ClO4)2 (1) has been isolated from the reaction of equimolar amounts of 1,3-bis(2′-pyridylimino)isoindoline (indH) and Fe(ClO4)2 in acetonitrile and characterized by X-ray crystallography and several spectroscopic techniques. It is a suitable catalyst for the oxidation of thioanisoles and benzyl alcohols with H2O2 as the oxidant. Hammett correlations and kinetic isotope effect experiments support the involvement of an electrophilic metal-based oxidant. A metastable green species (2) is observed when 1 is reacted with H2O2 at −40 °C, which has been characterized to have a FeIII(μ-O)(μ-O2)FeIII core on the basis of UV-Vis, electron paramagnetic resonance, resonance Raman, and X-ray absorption spectroscopic data. PMID:24587695

Formation and characterization of a multicomponent equilibrium system derived from cis- and trans-1-aminomethylcyclohexane-1,2-diol.

PubMed

Hetényi, Anasztázia; Szakonyi, Zsolt; Klika, Karel D; Pihlaja, Kalevi; Fülöp, Ferenc

2003-03-21

Both cis and trans isomers of amino diols 3-6 were prepared stereoselectively. In the reactions between 3-6 and phenyl isothiocyanate, the ring closure proceeded regioselectively and resulted only in spiro derivatives of 2-phenyliminooxazolidines 9, 10, 13, and 14. The reaction of cis- (or trans-)1-aminomethylcyclohexane-1,2-diol 4 (or 6) with 1 equiv of an aromatic aldehyde 15a-g in EtOH at room temperature resulted in a complex, multicomponent equilibrium mixture of 16a-g and 18a-g (or 17a-g and 19a-g), in each case consisting of a five-component, ring-chain tautomeric system 16A-E (or 17A-E), involving the Schiff base, two epimeric spirooxazolidines, two epimeric condensed 1,3-oxazines, and some of the four tricyclic compounds 18A-D (or 19A-D). The five-component, ring-chain equilibria were found to be adequately described by the Hammett-Brown linear free energy equation.

Synthesis, structural elucidation, solvatochromism and spectroscopic properties of some azo dyes derived from 6-chloro-4-hydroxyquinoline-2(1H)-one

NASA Astrophysics Data System (ADS)

Rufchahi, E. O. Moradi; Gilani, A. Ghanadzadeh; Taghvaei, V.; Karimi, R.; Ramezanzade, N.

2016-03-01

Malondianilide (I) derived from p-chloroaniline was cyclized to 6-chloro-4-hydroxyquinoline-2(1H)-one (II) in moderately good yield using polyphosphoric acid as catalyst. This compound was then coupled with some diazotized aromatic amines to give the corresponding azo disperse dyes 1-12. A systematic study of the effect of solvent, acid, base and pH upon the electronic absorption spectra of the dyes 1-12 was carried out. In DMSO, DMF, CH3CN, CHCl3, EtOH and acidic media (CH3COOH, acidified EtOH) these dyes that theoretically may be involved in azo-hydrazone tautomerism have been detected only as hydrazone tautomers T1 and T2. The acidic dissociation constants of the dyes were measured in 80 vol% ethanol-water solution at room temperature and ionic strength of 0.1. The results were correlated by the Hammett-type equation using the substituent constants σx.

Solubility, ionization, and partitioning behavior of unsymmetrical disulfide compounds: alkyl 2-imidazolyl disulfides.

PubMed

Hashash, Ahmad; Kirkpatrick, D Lynn; Lazo, John S; Block, Lawrence H

2002-07-01

Alkyl 2-imidazolyl disulfide compounds are novel antitumor agents, one of which is currently being evaluated in Phase I clinical trials. These molecules contain an unsymmetrical disulfide fragment, the lipophilic and electronic contributions of which are still not defined in the literature. Lipophilicity, ionization, and solubility of a number of alkyl 2-imidazolyl disulfides were studied. Based on the additivity of lipophilicity and ionization properties, the contribution of the unsymmetrical disulfide fragment to lipophilicity and ionization was elucidated. The unsymmetrical disulfide fragment contributed a Rekker's hydrophobic constant of 0.761 to the lipophilicity of these compounds and an approximated Hammett constant (sigma) of 0.30 to their ionization. The applicability of the general solubility equation (GSE) proposed by Jain and Yalkowsky in predicting the aqueous solubility of these analogs was evaluated. The GSE correctly ranked the aqueous solubilities of these compounds and estimated their log molar solubilities with an average absolute error of 0.35. Copyright 2002 Wiley-Liss Inc.

Acid- and base-catalysis in the mononuclear rearrangement of some (Z)-arylhydrazones of 5-amino-3-benzoyl-1,2,4-oxadiazole in toluene: effect of substituents on the course of reaction.

PubMed

D'Anna, Francesca; Frenna, Vincenzo; Ghelfi, Franco; Marullo, Salvatore; Spinelli, Domenico

2011-04-15

The reaction rates for the rearrangement of eleven (Z)-arylhydrazones of 5-amino-3-benzoyl-1,2,4-oxadiazole 3a-k into the relevant (2-aryl-5-phenyl-2H-1,2,3-triazol-4-yl)ureas 4a-k in the presence of trichloroacetic acid or of piperidine have been determined in toluene at 313.1 K. The results have been related to the effect of the aryl substituent by using Hammett and/or Ingold-Yukawa-Tsuno correlations and have been compared with those previously collected in a protic polar solvent (dioxane/water) as well as with those on the analogous rearrangement of the corresponding (Z)-arylhydrazones of 3-benzoyl-5-phenyl-1,2,4-oxadiazole 1a-k in benzene. Some light can thus be shed on the general differences of chemical reactivity between protic polar (or dipolar aprotic) and apolar solvents.

Transesterification of edible, non-edible and used cooking oils for biodiesel production using calcined layered double hydroxides as reusable base catalysts.

PubMed

Sankaranarayanan, Sivashunmugam; Antonyraj, Churchil A; Kannan, S

2012-04-01

Fatty acid methyl esters (FAME) were produced from edible, non-edible and used cooking oils with different fatty acid contents by transesterification with methanol using calcined layered double hydroxides (LDHs) as solid base catalysts. Among the catalysts, calcined CaAl2-LDH (hydrocalumite) showed the highest activity with >90% yield of FAME using low methanol:oil molar ratio (<6:1) at 65 °C in 5 h. The activity of the catalyst was attributed to its high basicity as supported by Hammett studies and CO(2)-TPD measurements. The catalyst was successfully reused in up to four cycles. Some of the properties such as density, viscosity, neutralization number and glycerol content of the obtained biodiesel matched well with the standard DIN values. It is concluded that a scalable heterogeneously catalyzed process for production of biodiesel in high yields from a wide variety of triglyceride oils including used oils is possible using optimized conditions. Copyright © 2012 Elsevier Ltd. All rights reserved.

Oxidations of Organic and Inorganic Substrates by Superoxo-, hydroperoxo-, and oxo-compounds of the transition metals.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vasbinder, Michael John

2006-01-01

Chapters 1 and 2 dealt with the chemistry of superoxo-, hydroperoxo-, and oxo- complexes of chromium, rhodium and cobalt. Chapter 3 dealt with the mechanism of oxygen-atom transfer catalyzed by an oxo-complex of rhenium. In Chapter 1, it was shown that hydroperoxometal complexes of cobalt and rhodium react with superoxochromium and chromyl ions, generating reduced chromium species while oxidizing the hydroperoxometal ions to their corresponding superoxometal ions. It was shown that the chromyl and superoxochromium ions are the more powerful oxidants. Evidence supports hydrogen atom transfer from the hydroperoxometal ion to the oxidizing superoxochromium or chromyl ion as the reactionmore » mechanism. There is a significant H/D kinetic isotope effect. Comparisons to the rate constants of other known hydrogen atom transfer reactions show the expected correlation with bond dissociation energies. In Chapter 2, it was found that the superoxometal complexes Cr{sub aq}OO 2+ and Rh(NH 3) 4(H 2O)OO 2+ oxidize stable nitroxyl radicals of the TEMPO series with rate constants that correlate with the redox potentials of both the oxidant and reductant. These reactions fit the Marcus equation for electron transfer near the theoretical value. Acid catalysis is important to the reaction, especially the thermodynamically limited cases involving Rh(NH 3) 4(H 2O)OO 2+ as the oxidant. The rate constants are notably less than those measured in the reaction between the same nitroxyl radicals and other strong free-radical oxidants, an illustration of the delocalized and stabilized nature of the superoxometal ions. Chapter 3 showed that oxo-rhenium catalysts needed a nucleophile to complete the catalytic oxygen-atom transfer from substituted pyridine-N-oxides to triphenylphosphine. The reaction was studied by introducing various pyridine-derived nucleophiles and monitoring their effect on the rate, then fitting the observed rate constants to the Hammett correlation. It was found that the values of the Hammett reaction constant PN were -1.0(1) for 4-nitro-2-methylpyridine-N-oxide and -2.6(4) for 4-methylpyridine-N-oxide as substrates. The negative value confirms pyridine is acting as a nucleophile. Nucleophiles other than pyridine derivatives were also tested. In the end, it was found that the most effective nucleophiles were the pyridine-N-oxides themselves, meaning that a second equivalent of substrate serves as the most efficient promoter of this oxygen-atom transfer reaction. This relative nucleophilicity of pyridines and pyridine-N-oxides is similar to what is observed in other OAT reactions generating high-valent metal-oxo species.« less

On the interpretation of quantitative structure–function activity relationship data for lactate oxidase

PubMed Central

Yorita, Kazuko; Misaki, Hideo; Palfey, Bruce A.; Massey, Vincent

2000-01-01

The native flavin, FMN, has been removed from the l-lactate oxidase of Aerococcus viridans, and the apoprotein reconstituted with 12 FMN derivatives with various substituents at the flavin 6- and 8-positions. Impressive linear relationships are exhibited between the sum of the Hammett σpara and σortho parameters and the redox potentials of the free flavins, and between the redox potentials of the free and enzyme-bound flavins. Rapid reaction kinetics studies of the reconstituted enzymes with the substrates l-lactate and l-mandelate show an increase in the reduction rate constant with increasing redox potential, except that, with lactate, a limiting rate constant of ≈700 s−1 is obtained with flavins of high potential. Similar breakpoints are found in plots of the rate constants for flavin N5-sulfite adduct formation and for the reaction of the reduced enzymes with molecular oxygen. These results are interpreted in terms of a two-step equilibrium preceding the chemical reaction step, in which the second equilibrium step provides an upper limit to the rate with which the particular substrate or ligand is positioned with the flavin in the correct fashion for the observed chemical reaction to occur. The relationship of rate constants for flavin reduction and N5-sulfite adduct formation with flavin redox potential below the observed breakpoint indicate development of significant negative charge in the transition states of the reactions. In the case of reduction by substrate, the results are consistent either with a hydride transfer mechanism or with the so called “carbanion” mechanism, in which the substrate α-proton is abstracted by an enzyme base protected from exchange with solvent. These conclusions are supported by substrate α-deuterium isotope effects and by solvent viscosity effects on sulfite binding. PMID:10706608

Quantitative structure-activity relationship for the oxidation of aromatic organic contaminants in water by TAML/H2O2.

PubMed

Su, Hanrui; Yu, Chunyang; Zhou, Yongfeng; Gong, Lidong; Li, Qilin; Alvarez, Pedro J J; Long, Mingce

2018-05-02

Tetra-amido macrocyclic ligand (TAML) activator is a functional analog of peroxidase enzymes, which activates hydrogen peroxide (H 2 O 2 ) to form high valence iron-oxo complexes that selectively degrade persistent aromatic organic contaminants (ACs) in water. Here, we develop quantitative structure-activity relationship (QSAR) models based on measured pseudo first-order kinetic rate coefficients (k obs ) of 29 ACs (e.g., phenols and pharmaceuticals) oxidized by TAML/H 2 O 2 at neutral and basic pH values to gain mechanistic insight on the selectivity and pH dependence of TAML/H 2 O 2 systems. These QSAR models infer that electron donating ability (E HOMO ) is the most important AC characteristic for TAML/H 2 O 2 oxidation, pointing to a rate-limiting single-electron transfer (SET) mechanism. Oxidation rates at pH 7 also depend on AC reactive indices such as f min - and qH + , which respectively represent propensity for electrophilic attack and the most positive net atomic charge on hydrogen atoms. At pH 10, TAML/H 2 O 2 is more reactive towards ACs with a lower hydrogen to carbon atoms ratio (#H:C), suggesting the significance of hydrogen atom abstraction. In addition, lnk obs of 14 monosubstituted phenols is negatively correlated with Hammett constants (σ) and exhibits similar sensitivity to substituent effects as horseradish peroxidase. Although accurately predicting degradation rates of specific ACs in complex wastewater matrices could be difficult, these QSAR models are statistically robust and help predict both relative degradability and reaction mechanism for TAML/H 2 O 2 -based treatment processes. Copyright © 2018 Elsevier Ltd. All rights reserved.

Homoleptic nickel(II) complexes of redox-tunable pincer-type ligands.

PubMed

Hewage, Jeewantha S; Wanniarachchi, Sarath; Morin, Tyler J; Liddle, Brendan J; Banaszynski, Megan; Lindeman, Sergey V; Bennett, Brian; Gardinier, James R

2014-10-06

Different synthetic methods have been developed to prepare eight new redox-active pincer-type ligands, H(X,Y), that have pyrazol-1-yl flanking donors attached to an ortho-position of each ring of a diarylamine anchor and that have different groups, X and Y, at the para-aryl positions. Together with four previously known H(X,Y) ligands, a series of 12 Ni(X,Y)2 complexes were prepared in high yields by a simple one-pot reaction. Six of the 12 derivatives were characterized by single-crystal X-ray diffraction, which showed tetragonally distorted hexacoordinate nickel(II) centers. The nickel(II) complexes exhibit two quasi-reversible one-electron oxidation waves in their cyclic voltammograms, with half-wave potentials that varied over a remarkable 700 mV range with the average of the Hammett σ(p) parameters of the para-aryl X, Y groups. The one- and two-electron oxidized derivatives [Ni(Me,Me)2](BF4)n (n = 1, 2) were prepared synthetically, were characterized by X-band EPR, electronic spectroscopy, and single-crystal X-ray diffraction (for n = 2), and were studied computationally by DFT methods. The dioxidized complex, [Ni(Me,Me)2](BF4)2, is an S = 2 species, with nickel(II) bound to two ligand radicals. The mono-oxidized complex [Ni(Me,Me)2](BF4), prepared by comproportionation, is best described as nickel(II) with one ligand centered radical. Neither the mono- nor the dioxidized derivative shows any substantial electronic coupling between the metal and their bound ligand radicals because of the orthogonal nature of their magnetic orbitals. On the other hand, weak electronic communication occurs between ligands in the mono-oxidized complex as evident from the intervalence charge transfer (IVCT) transition found in the near-IR absorption spectrum. Band shape analysis of the IVCT transition allowed comparisons of the strength of the electronic interaction with that in the related, previously known, Robin-Day class II mixed valence complex, [Ga(Me,Me)2](2+).

Potent and selective alpha-ketoheterocycle-based inhibitors of the anandamide and oleamide catabolizing enzyme, fatty acid amide hydrolase.

PubMed

Romero, F Anthony; Du, Wu; Hwang, Inkyu; Rayl, Thomas J; Kimball, F Scott; Leung, Donmienne; Hoover, Heather S; Apodaca, Richard L; Breitenbucher, J Guy; Cravatt, Benjamin F; Boger, Dale L

2007-03-08

A study of the structure-activity relationships (SAR) of 2f (OL-135), a potent inhibitor of fatty acid amide hydrolase (FAAH), is detailed, targeting the 5-position of the oxazole. Examination of a series of substituted benzene derivatives (12-14) revealed that the optimal position for substitution was the meta-position with selected members approaching or exceeding the potency of 2f. Concurrent with these studies, the effect of substitution on the pyridine ring of 2f was also examined. A series of small, nonaromatic C5-substituents was also explored and revealed that the K(i) follows a well-defined correlation with the Hammett sigma(p) constant (rho = 3.01, R2 = 0.91) in which electron-withdrawing substituents enhance potency, leading to inhibitors with K(i)s as low as 400 pM (20n). Proteomic-wide screening of the inhibitors revealed that most are exquisitely selective for FAAH over all other mammalian proteases, reversing the 100-fold preference of 20a (C5 substituent = H) for the enzyme TGH.

Extension of structure-reactivity correlations for the hydrogen abstraction reaction to methyl radical and comparison to chlorine atom, bromine atom, and hydroxyl radical

DOE PAGES

Poutsma, Marvin L.

2016-06-07

In this study, we presented structure-reactivity correlations for the gas-phase rate constants for hydrogen abstraction from sp3-hybridized carbon by three electrophilic radicals (X • + HCR 3 → XH + •CR 3; X = Cl •, HO •, and Br); the reaction enthalpy effect was represented by the independent variable Δ rH and the polar effect by the independent variables F and R, the Hammett-Taft constants for field/inductive and resonance effects. Here we present a parallel treatment for the less electronegative CH 3 •. In spite of a limited and scattered data base, the resulting least-squares fit [log k 437(CHmore » 3 •) = 0.0251(Δ rH) + 0.96(ΣF) 0.56(ΣR) – 19.15] was modestly successful and useful for initial predictions. As expected, the polar effect appears to be minor and its directionality, i.e., the philicity of CH 3, may depend on the nature of the substituents.« less

The Influence of Noise on Turbulent Transport.

NASA Astrophysics Data System (ADS)

Krommes, J. A.

2006-10-01

Recently there have been considerable discussions and contradictory conclusions about the possible influence of numerical noise on measured turbulent fluxes. In the present work, some of the conceptual and analytical foundations of noise-related calculations are reconsidered, and some paradoxes are resolved. An elementary model involving coupled random processes shows that extra noise (e.g., related to numerical sampling errors in δf particle simulations can reduce total transport. (Intuition to the contrary stems from oversimplified models involving independent, additive, and passive advection velocities.) This result is interpreted in terms of the structure of the steady-state spectral balance equation for turbulence in the presence of discreteness-induced noise. The relationship of the Fluctuation-- Dissipation Theorem to general nonequilibrium statistical balances is also discussed. W. M. Nevins, G. W. Hammett, A. M. Dimits, W. Dorland, and D. E. Shumaker, Phys. Plasmas 12, 122305 (2005) W. W. Lee, Bull. Am. Phys. Soc., http://www.aps.org/meet/APR06, abstr.I16.00004 (2006). G. Hu and J. A. Krommes, Phys. Plasmas 1, 863 (1994).) H. A. Rose, J. Stat.Phys.20, 415 (1979).

Extension of structure-reactivity correlations for the hydrogen abstraction reaction to methyl radical and comparison to chlorine atom, bromine atom, and hydroxyl radical

DOE Office of Scientific and Technical Information (OSTI.GOV)

Poutsma, Marvin L.

In this study, we presented structure-reactivity correlations for the gas-phase rate constants for hydrogen abstraction from sp3-hybridized carbon by three electrophilic radicals (X • + HCR 3 → XH + •CR 3; X = Cl •, HO •, and Br); the reaction enthalpy effect was represented by the independent variable Δ rH and the polar effect by the independent variables F and R, the Hammett-Taft constants for field/inductive and resonance effects. Here we present a parallel treatment for the less electronegative CH 3 •. In spite of a limited and scattered data base, the resulting least-squares fit [log k 437(CHmore » 3 •) = 0.0251(Δ rH) + 0.96(ΣF) 0.56(ΣR) – 19.15] was modestly successful and useful for initial predictions. As expected, the polar effect appears to be minor and its directionality, i.e., the philicity of CH 3, may depend on the nature of the substituents.« less

Electronic tuning of the lability of Pt(II) complexes through pi-acceptor effects. Correlations between thermodynamic, kinetic, and theoretical parameters.

PubMed

Hofmann, Andreas; Jaganyi, Deogratius; Munro, Orde Q; Liehr, Günter; van Eldik, Rudi

2003-03-10

pi-Acceptor effects are often used to account for the unusual high lability of [Pt(terpy)L]((2)(-)(n)+) (terpy = 2,2':6',2' '-terpyridine) complexes. To gain further insight into this phenomenon, the pi-acceptor effect was varied systematically by studying the lability of [Pt(diethylenetriamine)OH(2)](2+) (aaa), [Pt(2,6-bis-aminomethylpyridine)OH(2)](2+) (apa), [Pt(N-(pyridyl-2-methyl)-1,2-diamino-ethane)OH(2)](2+) (aap), [Pt(bis(2-pyridylmethyl)amine)OH(2)](2+) (pap), [Pt(2,2'-bipyridine)(NH(3))(OH(2))](2+) (app), and [Pt(terpy)OH(2)](2+) (ppp). The crystal structure of the apa precursor [Pt(2,6-bis-aminomethylpyridine)Cl]Cl.H(2)O was determined. The substitution of water by a series of nucleophiles, viz. thiourea, N,N-dimethylthiourea, N,N,N',N'-tetramethylthiourea, I(-), and SCN(-), was studied under pseudo-first-order conditions as a function of concentration, pH, temperature, and pressure, using stopped-flow techniques. The data enable an overall comparison of the substitution behavior of these complexes, emphasizing the role played by the kinetic cis and trans pi-acceptor effects. The results indicate that the cis pi-acceptor effect is larger than the trans pi-acceptor effect, and that the pi-acceptor effects are multiplicative. DFT calculations at the B3LYP/LACVP level of theory show that, by the addition of pi-acceptor ligands to the metal, the positive charge on the metal center increases, and the energy separation of the frontier molecular orbitals (E(LUMO) - E(HOMO)) of the ground state Pt(II) complexes decreases. The calculations collectively support the experimentally observed additional increase in reactivity when two pi-accepting rings are adjacent to each other (app and ppp), which is ascribed to "electronic communication" between the pyridine rings. The results furthermore indicate that the pK(a) value of the platinum bound water molecule is controlled by the pi-accepting nature of the chelate system and reflects the electron density around the metal center. This in turn controls the rate of the associative substitution reaction and was analyzed using the Hammett equation.

Hydride affinity scale of various substituted arylcarbeniums in acetonitrile.

PubMed

Zhu, Xiao-Qing; Wang, Chun-Hua

2010-12-23

Combined with the integral equation formalism polarized continuum model (IEFPCM), the hydride affinities of 96 various acylcarbenium ions in the gas phase and CH(3)CN were estimated by using the B3LYP/6-31+G(d)//B3LYP/6-31+G(d), B3LYP/6-311++G(2df,2p)//B3LYP/6-31+G(d), and BLYP/6-311++G(2df,2p)//B3LYP/6-31+G(d) methods for the first time. The results show that the combination of the BLYP/6-311++G(2df,2p)//B3LYP/6-31+G(d) method and IEFPCM could successfully predict the hydride affinities of arylcarbeniums in MeCN with a precision of about 3 kcal/mol. On the basis of the calculated results from the BLYP method, it can be found that the hydride affinity scale of the 96 arylcarbeniums in MeCN ranges from -130.76 kcal/mol for NO(2)-PhCH(+)-CN to -63.02 kcal/mol for p-(Me)(2)N-PhCH(+)-N(Me)(2), suggesting most of the arylcarbeniums are good hydride acceptors. Examination of the effect of the number of phenyl rings attached to the carbeniums on the hydride affinities shows that the increase of the hydride affinities takes place linearly with increasing number of benzene rings in the arylcarbeniums. Analyzing the effect of the substituents on the hydride affinities of arylcarbeniums indicates that electron-donating groups decrease the hydride affinities and electron-withdrawing groups show the opposite effect. The hydride affinities of arylcarbeniums are linearly dependent on the sum of the Hammett substituent parameters σ(p)(+). Inspection of the correlation of the solution-phase hydride affinities with gas-phase hydride affinities and aqueous-phase pK(R)(+) values reveals a remarkably good correspondence of ΔG(H(-)A)(R(+)) with both the gas-phase relative hydride affinities only if the α substituents X have no large electron-donating or -withdrawing properties and the pK(R)(+) values even though the media are dramatically different. The solution-phase hydride affinities also have a linear relationship with the electrophilicity parameter E, and this dependence can certainly serve as one of the most effective ways to estimate the new E values from ΔG(H(-)A)(R(+)) or vice versa. Combining the hydride affinities and the reduction potentials of the arylcarbeniums, we obtained the bond homolytic dissociation Gibbs free energy changes of the C-H bonds in the corresponding hydride adducts in acetonitrile, ΔG(HD)(RH), and found that the effects of the substituent on ΔG(HD)(RH) are very small. Simple thermodynamic analytic platforms for the three C-H cleavage modes were constructed. It is evident that the present work would be helpful in understanding the nature of the stabilities of the carbeniums and mechanisms of the hydride transfers between carbeniums and other hydride donors.

Efficient conversion of lignocellulosic biomass to levulinic acid using acidic ionic liquids.

PubMed

Khan, Amir Sada; Man, Zakaria; Bustam, Mohamad Azmi; Nasrullah, Asma; Ullah, Zahoor; Sarwono, Ariyanti; Shah, Faiz Ullah; Muhammad, Nawshad

2018-02-01

In the present research work, dicationic ionic liquids, containing 1,4-bis(3-methylimidazolium-1-yl) butane ([C 4 (Mim) 2 ]) cation with counter anions [(2HSO 4 )(H 2 SO 4 ) 0 ], [(2HSO 4 )(H 2 SO 4 ) 2 ] and [(2HSO 4 )(H 2 SO 4 ) 4 ] were synthesised. ILs structures were confirmed using 1 H NMR spectroscopy. Thermal stability, Hammett acidity, density and viscosity of ILs were determined. Various types of lignocellulosic biomass such as rubber wood, palm oil frond, bamboo and rice husk were converted into levulinic acid (LA). Among the synthesized ionic liquids, [C 4 (Mim) 2 ][(2HSO 4 )(H 2 SO 4 ) 4 ] showed higher % yield of LA up to 47.52 from bamboo biomass at 110°C for 60min, which is the better yield at low temperature and short time compared to previous reports. Surface morphology, surface functional groups and thermal stability of bamboo before and after conversion into LA were studied using SEM, FTIR and TGA analysis, respectively. This one-pot production of LA from agro-waste will open new opportunity for the conversion of sustainable biomass resources into valuable chemicals. Copyright © 2017 Elsevier Ltd. All rights reserved.

Competitive/co-operative interactions in acid base sandwich: role of cation vs. substituents.

PubMed

Kalpana, Ayyavoo; Akilandeswari, Lakshminarayanan

2017-11-15

The cation-π interaction can be envisaged as a lewis acid base interaction, and it is in line with Pearson's acid base concept. The critical examination of interactions between the π-acids (alkali metal cations - Li + , Na + and alkaline earth metal cations Mg 2+ , Ca 2+ ) on one face and tripodal Cr(CO) 3 moiety on the other π face of substituted arenes demonstrates the role of cation and substitutents in manipulating the interactions between them. The interaction of the two π acids on both faces of arene is not expectedly additive, rather it shows either depreciation of interaction energy revealing the competition of acids toward the base or enhancement of interaction energy denoting a cooperative effect. Among the metal cations under study, Mg 2+ shows a cooperative gesture. Although the substituents play a meek role, they unfailingly exert their electronic effects and are amply documented by excellent correlation of various parameters with the Hammett constant σ m . The elusive switching of λ max from the UV to IR region on binding Mg 2+ with substituted arene-Cr(CO) 3 complex is a characteristic clue that TDDFT can help design the ionic sensors for Mg 2+ cations.

Effects of single bond-ion and single bond-diradical form on the stretching vibration of Cdbnd N bridging bond in 4,4‧-disubstituted benzylidene anilines

NASA Astrophysics Data System (ADS)

Cao, Chao-Tun; Bi, Yakun; Cao, Chenzhong

2016-06-01

Fifty-seven samples of model compounds, 4,4‧-disubstituted benzylidene anilines, p-X-ArCH = NAr-p-Y were synthesized. Their infrared absorption spectra were recorded, and the stretching vibration frequencies νCdbnd N of the Cdbnd N bridging bond were determined. New stretching vibration mode was proposed by means of the analysis of the factors affecting νCdbnd N, that is there are mainly three modes in the stretching vibration of Cdbnd N bond: (I) polar double bond form Cdbnd N, (II) single bond-ion form C+-N- and (III) single bond-diradical form Crad -Nrad . The contributions of the forms (I) and (II) to the change of νCdbnd N can be quantified by using Hammett substituent constant (including substituent cross-interaction effects between X and Y groups), whereas the contribution of the form (III) can be quantified by employing the excited-state substituent constant. The most contribution of these three forms is the form (III), the next is the form (II), whose contribution difference was discussed with the viewpoint of energy requirements in vibration with the form (III) and form (II).

Linear free energy relationships of the 1H and 13C NMR chemical shifts of 3-methylene-2-substituted-1,4-pentadienes

NASA Astrophysics Data System (ADS)

Valentić, Nataša V.; Vitnik, Željko; Kozhushkov, Sergei I.; de Meijere, Armin; Ušćumlić, Gordana S.; Juranić, Ivan O.

2005-06-01

Linear free energy relationships (LFER) were applied to the 1H and 13C NMR chemical shifts ( δN, N= 1H and 13C, respectively) in the unsaturated backbone of cross-conjugated trienes 3-methylene-2-substituted-1,4-pentadienes. The NMR data were correlated using five different LFER models, based on the mono, the dual and the triple substituent parameter (MSP, DSP and TSP, respectively) treatment. The simple and extended Hammett equations, and the three postulated unconventional LFER models obtained by adaptation of the later, were used. The geometry data, which are needed in Karplus-type and McConnell-type analysis, were obtained using semi-empirical MNDO-PM3 calculations. In correlating the data the TSP approach was more successful than the MSP and DSP approaches. The fact that the calculated molecular geometries allow accurate prediction of the NMR data confirms the validity of unconventional LFER models used. These results suggest the s- cis conformation of the cross-conjugated triene as the preferred one. Postulated unconventional DSP and TSP equations enable the assessment of electronic substituent effects in the presence of other interfering influences.

A nonlocal fluid closure for antiparallel reconnection

NASA Astrophysics Data System (ADS)

Ng, J.; Hakim, A.; Bhattacharjee, A.

2016-12-01

The integration of kinetic effects in fluid models is an important problem in global simulations of the Earth's magnetosphere and space weather modelling. In particular, it has been shown that ion kinetics play an important role in the dynamics of large reconnecting systems, and that fluid models can account of some of these effects[1,2] . Here we introduce a new fluid model and closure for collisionless magnetic reconnection and more general applications. Taking moments of the kinetic equation, we evolve the full pressure tensor for electrons and ions, which includes the off diagonal terms necessary for reconnection. Kinetic effects are recovered by using a nonlocal heat flux closure, which approximates linear Landau damping in the fluid framework [3]. Using the island coalescence problem as a test, we show how the nonlocal ion closure improves on the typical collisional closures used for ten-moment models and circumvents the need for a colllisional free parameter. Finally, we extend the closure to study guide-field reconnection and discuss the implementation of a twenty-moment model.[1] A. Stanier et al. Phys Rev Lett (2015)[2] J. Ng et al. Phys Plasmas (2015)[3] G. Hammett et al. Phys Rev Lett (1990)

Reactions of the phthalimide N-oxyl radical (PINO) with activated phenols: the contribution of π-stacking interactions to hydrogen atom transfer rates.

PubMed

D'Alfonso, Claudio; Bietti, Massimo; DiLabio, Gino A; Lanzalunga, Osvaldo; Salamone, Michela

2013-02-01

The kinetics of reactions of the phthalimide N-oxyl radical (PINO) with a series of activated phenols (2,2,5,7,8-pentamethylchroman-6-ol (PMC), 2,6-dimethyl- and 2,6-di-tert-butyl-4-substituted phenols) were investigated by laser flash photolysis in CH(3)CN and PhCl in order to establish if the reactions with PINO can provide a useful tool for evaluating the radical scavenging ability of phenolic antioxidants. On the basis of the small values of deuterium kinetic isotope effects, the relatively high and negative ρ values in the Hammett correlations and the results of theoretical calculations, we suggest that these reactions proceed by a hydrogen atom transfer (HAT) mechanism having a significant degree of charge transfer resulting from a π-stacked conformation between PINO and the aromatic ring of the phenols. Kinetic solvent effects were analyzed in detail for the hydrogen transfer from 2,4,6-trimethylphenol to PINO and the data obtained are in accordance with the Snelgrove-Ingold equation for HAT. Experimental rate constants for the reactions of PINO with activated phenols are in accordance with those predicted by applying the Marcus cross relation.

New insights into aldol reactions of methyl isocyanoacetate catalyzed by heterogenized homogeneous catalysts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ye, Rong; Zhao, Jie; Yuan, Bing

The Hayashi–Ito aldol reaction of methyl isocyanoacetate (MI) and benzaldehydes, a classic homogeneous Au(I)-catalyzed reaction, was studied with heterogenized homogeneous catalysts. Among dendrimer encapsulated nanoparticles (NPs) of Au, Pd, Rh, or Pt loaded in mesoporous supports and the homogeneous analogues, the Au NPs led to the highest yield and highest diastereoselectivity of products in toluene at room temperature. The Au catalyst was stable and was recycled for at least six runs without substantial deactivation. Moreover, larger pore sizes of the support and the use of a hydrophobic solvent led to a high selectivity for the trans diastereomer of the product.more » The activation energy is sensitive to neither the size of Au NPs nor the support. A linear Hammett plot was obtained with a positive slope, suggesting an increased electron density on the carbonyl carbon atom in the rate-limiting step. As a result, IR studies revealed a strong interaction between MI and the gold catalyst, supporting the proposed mechanism, in which rate-limiting step involves an electrophilic attack of the aldehyde on the enolate formed from the deprotonated MI.« less

Kinetics of self-decomposition and hydrogen atom transfer reactions of substituted phthalimide N-oxyl radicals in acetic acid.

PubMed

Cai, Yang; Koshino, Nobuyoshi; Saha, Basudeb; Espenson, James H

2005-01-07

Kinetic data have been obtained for three distinct types of reactions of phthalimide N-oxyl radicals (PINO(.)) and N-hydroxyphthalimide (NHPI) derivatives. The first is the self-decomposition of PINO(.) which was found to follow second-order kinetics. In the self-decomposition of 4-methyl-N-hydroxyphthalimide (4-Me-NHPI), H-atom abstraction competes with self-decomposition in the presence of excess 4-Me-NHPI. The second set of reactions studied is hydrogen atom transfer from NHPI to PINO(.), e.g., PINO(.) + 4-Me-NHPI <=> NHPI + 4-Me-PINO(.). The substantial KIE, k(H)/k(D) = 11 for both forward and reverse reactions, supports the assignment of H-atom transfer rather than stepwise electron-proton transfer. These data were correlated with the Marcus cross relation for hydrogen-atom transfer, and good agreement between the experimental and the calculated rate constants was obtained. The third reaction studied is hydrogen abstraction by PINO(.) from p-xylene and toluene. The reaction becomes regularly slower as the ring substituent on PINO(.) is more electron donating. Analysis by the Hammett equation gave rho = 1.1 and 1.8 for the reactions of PINO(.) with p-xylene and toluene, respectively.

Gyrofluid turbulence models with kinetic effects

NASA Astrophysics Data System (ADS)

Dorland, W.; Hammett, G. W.

1993-03-01

Nonlinear gyrofluid equations are derived by taking moments of the nonlinear, electrostatic gyrokinetic equation. The principal model presented includes evolution equations for the guiding center n, u∥, T∥, and T⊥ along with an equation expressing the quasineutrality constraint. Additional evolution equations for higher moments are derived that may be used if greater accuracy is desired. The moment hierarchy is closed with a Landau damping model [G. W. Hammett and F. W. Perkins, Phys. Rev. Lett. 64, 3019 (1990)], which is equivalent to a multipole approximation to the plasma dispersion function, extended to include finite Larmor radius effects (FLR). In particular, new dissipative, nonlinear terms are found that model the perpendicular phase mixing of the distribution function along contours of constant electrostatic potential. These ``FLR phase-mixing'' terms introduce a hyperviscositylike damping ∝k⊥2‖Φkk×k'‖, which should provide a physics-based damping mechanism at high k⊥ρ which is potentially as important as the usual polarization drift nonlinearity. The moments are taken in guiding center space to pick up the correct nonlinear FLR terms and the gyroaveraging of the shear. The equations are solved with a nonlinear, three-dimensional initial value code. Linear results are presented, showing excellent agreement with linear gyrokinetic theory.

Effect of nitro substituent on electrochemical oxidation of phenols at boron-doped diamond anodes.

PubMed

Jiang, Yi; Zhu, Xiuping; Li, Hongna; Ni, Jinren

2010-02-01

In order to investigate nitro-substitutent's effect on degradation of phenols at boron-doped diamond (BDD) anodes, cyclic voltammetries of three nitrophenol isomers: 2-nitrophenol (2NP), 3-nitrophenol (3NP) and 4-nitrophenol (4NP) were studied, and their bulk electrolysis results were compared with phenol's (Ph) under alkaline condition. The voltammetric study showed nitrophenols could be attacked by hydroxyl radicals and nitro-group was released from the aromatic ring. Results of bulk electrolysis showed degradation of all phenols were fit to a pseudo first-order equation and followed in this order: 2NP>4NP>3NP>Ph. Molecular structures, especially carbon atom charge, significantly influenced the electrochemical oxidation of these isomers. Intermediates were analyzed during the electrolysis process, and were mainly catechol, resorcinol, hydroquinone, and carboxylic acids, such as acetic acid and oxalic acid. A simple degradation pathway was proposed. Moreover, a linear increasing relationship between degradation rates and Hammett constants of the studied phenols was observed, which demonstrated that electrochemical oxidation of these phenols was mainly initiated by electrophilic attack of hydroxyl radicals at BDD anodes. Copyright (c) 2009 Elsevier Ltd. All rights reserved.

Nanocrystal sensitized photovoltaics and photodetectors with performance enhanced using ligand engineering

NASA Astrophysics Data System (ADS)

Schut, David M.; Williams, George M., Jr.; Arteaga, Stefan; Allen, Thomas L.; Novet, Thomas

2011-06-01

Nanocrystal quantum dot photovoltaics and photodetectors with performance optimized by engineering the nanocrystals size and the optoelectronic properties of the nanocrystal's chemical coating are reported. Due to the large surface-to-volume ratio inherent to nanocrystals, the surface effects of ligands used to chemically coat and passivate nanocrystals play a significant role in device performance. However, the optoelectronic properties of ligands are difficult to ascertain, as the band structure of the ligand-capped nanoparticle system is complex and difficult to model. Using density-of-states measurements, we demonstrate that modeling of electropositive and electronegative substituents and use of the Hammett equation, are useful tools in optimizing nanocrystal detector performance. A new particle, the Janus-II nanoparticles, developed using 'charge-donating' and 'charge-withdrawing' ligands distributed over opposite surfaces of the nanocrystal, is described. The polarizing ligands of the Janus-II nanoparticle form a degeneracy-splitting dipole, which reduces the overlap integral between excitonic states, and thus reduces the probability of carrier recombination, allowing carrier extraction to take place more efficiently. This is shown to allow increased photodetection efficiencies and to allow the capture of multiple exciton events in working photodetectors.

Electron transfer reaction of oxo(salen)chromium(V) ion with anilines.

PubMed

Premsingh, Sundarsingh; Venkataramanan, Natarajan Sathiyamoorthy; Rajagopal, Seenivasan; Mirza, Shama P; Vairamani, Mariappanadar; Rao, P Sambasiva; Velavan, K

2004-09-06

The kinetics of oxidation of 16 meta-, ortho-, and para-substituted anilines with nine oxo(salen)chromium(V) ions have been studied by spectrophotometric, ESIMS, and EPR techniques. During the course of the reaction, two new peaks with lambda(max) at 470 and 730 nm appear in the absorption spectrum, and these peaks are due to the formation of emeraldine forms of oligomers of aniline supported by the ESIMS peaks with m/z values 274 and 365 (for the trimer and tetramer of aniline). The rate of the reaction is highly sensitive to the change of substituents in the aryl moiety of aniline and in the salen ligand of chromium(V) complexes. Application of the Hammett equation to analyze kinetic data yields a rho value of -3.8 for the substituent variation in aniline and +2.2 for the substituent variation in the salen ligand of the metal complex. On the basis of the spectral, kinetic, and product analysis studies, a mechanism involving an electron transfer from the nitrogen of aniline to the metal complex in the rate controlling step has been proposed. The Marcus equation has been successfully applied to this system, and the calculated values are compliant with the measured values.

Laser flash photolysis and CIDNP studies of steric effects on coupling rate constants of imidazolidine nitroxide with carbon-centered radicals, methyl isobutyrate-2-yl and tert-butyl propionate-2-yl.

PubMed

Zubenko, Dmitry; Tsentalovich, Yuri; Lebedeva, Nataly; Kirilyuk, Igor; Roshchupkina, Galina; Zhurko, Irina; Reznikov, Vladimir; Marque, Sylvain R A; Bagryanskaya, Elena

2006-08-04

Time-resolved chemically induced dynamic nuclear polarization (TR-CIDNP) and laser flash photolysis (LFP) techniques have been used to measure rate constants for coupling between acrylate-type radicals and a series of newly synthesized stable imidazolidine N-oxyl radicals. The carbon-centered radicals under investigation were generated by photolysis of their corresponding ketone precursors RC(O)R (R = C(CH3)2-C(O)OCH3 and CH(CH3)-C(O)-OtBu) in the presence of stable nitroxides. The coupling rate constants kc for modeling studies of nitroxide-mediated polymerization (NMP) experiments were determined, and the influence of steric and electronic factors on kc values was addressed by using a Hammett linear free energy relationship. The systematic changes in kc due to the varied steric (Es,n) and electronic (sigmaL,n) characters of the substituents are well-described by the biparameter equation log(kc/M- 1s(-1)) = 3.52sigmaL,n + 0.47Es,n + 10.62. Hence, kc decreases with the increasing steric demand and increases with the increasing electron-withdrawing character of the substituents on the nitroxide.

New insights into aldol reactions of methyl isocyanoacetate catalyzed by heterogenized homogeneous catalysts

DOE PAGES

Ye, Rong; Zhao, Jie; Yuan, Bing; ...

2016-12-14

The Hayashi–Ito aldol reaction of methyl isocyanoacetate (MI) and benzaldehydes, a classic homogeneous Au(I)-catalyzed reaction, was studied with heterogenized homogeneous catalysts. Among dendrimer encapsulated nanoparticles (NPs) of Au, Pd, Rh, or Pt loaded in mesoporous supports and the homogeneous analogues, the Au NPs led to the highest yield and highest diastereoselectivity of products in toluene at room temperature. The Au catalyst was stable and was recycled for at least six runs without substantial deactivation. Moreover, larger pore sizes of the support and the use of a hydrophobic solvent led to a high selectivity for the trans diastereomer of the product.more » The activation energy is sensitive to neither the size of Au NPs nor the support. A linear Hammett plot was obtained with a positive slope, suggesting an increased electron density on the carbonyl carbon atom in the rate-limiting step. As a result, IR studies revealed a strong interaction between MI and the gold catalyst, supporting the proposed mechanism, in which rate-limiting step involves an electrophilic attack of the aldehyde on the enolate formed from the deprotonated MI.« less

Radical Chemistry and Structural Relationships of PPCP Degradation by UV/Chlorine Treatment in Simulated Drinking Water.

PubMed

Guo, Kaiheng; Wu, Zihao; Shang, Chii; Yao, Bo; Hou, Shaodong; Yang, Xin; Song, Weihua; Fang, Jingyun

2017-09-19

The UV/chlorine process is an emerging advanced oxidation process (AOP) used for the degradation of micropollutants. However, the radical chemistry of this AOP is largely unknown for the degradation of numerous structurally diverse micropollutants in water matrices of varying quality. These issues were addressed by grouping 34 pharmaceuticals and personal care products (PPCPs) according to the radical chemistry of their degradation in the UV/chlorine process at practical PPCP concentrations (1 μg L -1 ) and in different water matrices. The contributions of HO • and reactive chlorine species (RCS), including Cl • , Cl 2 •- , and ClO • , to the degradation of different PPCPs were compound specific. RCS showed considerable reactivity with olefins and benzene derivatives, such as phenols, anilines, and alkyl-/alkoxybenzenes. A good linear relationship was found between the RCS reactivity and negative values of the Hammett ∑σ p + constant for aromatic PPCPs, indicating that electron-donating groups promote the attack of benzene derivatives by RCS. The contribution of HO • , but not necessarily RCS, to PPCP removal decreased with increasing pH. ClO • showed high reactivity with some PPCPs, such as carbamazepine, caffeine, and gemfibrozil, with second-order rate constants of 9.2 × 10 7 , 1.03 × 10 8 , and 4.16 × 10 8 M -1 s -1 , respectively, which contributed to their degradation. Natural organic matter (NOM) induced significant scavenging of ClO • and greatly decreased the degradation of PPCPs that was attributable to ClO • , with a second-order rate constant of 4.5 × 10 4 (mg L -1 ) -1 s -1 . Alkalinity inhibited the degradation of PPCPs that was primarily attacked by HO • and Cl • but had negligible effects on the degradation of PPCPs by ClO • . This is the first study on the reactivity of RCS, particularly ClO • , with structurally diverse PPCPs under simulated drinking water condition.

Kinetic and Mechanistic Examination of Acid–Base Bifunctional Aminosilica Catalysts in Aldol and Nitroaldol Condensations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Collier, Virginia E.; Ellebracht, Nathan C.; Lindy, George I.

The kinetic and mechanistic understanding of cooperatively catalyzed aldol and nitroaldol condensations is probed using a series of mesoporous silicas functionalized with aminosilanes to provide bifunctional acid–base character. Mechanistically, a Hammett analysis is performed to determine the effects of electron-donating and electron-withdrawing groups of para-substituted benzaldehyde derivatives on the catalytic activity of each condensation reaction. This information is also used to discuss the validity of previously proposed catalytic mechanisms and to propose a revised mechanism with plausible reaction intermediates. For both reactions, electron-withdrawing groups increase the observed rates of reaction, though resonance effects play an important, yet subtle, role inmore » the nitroaldol condensation, in which a p-methoxy electron-donating group is also able to stabilize the proposed carbocation intermediate. Additionally, activation energies and pre-exponential factors are calculated via the Arrhenius analysis of two catalysts with similar amine loadings: one catalyst had silanols available for cooperative interactions (acid–base catalysis), while the other was treated with a silanol-capping reagent to prevent such cooperativity (base-only catalysis). The values obtained for activation energies and pre-exponential factors in each reaction are discussed in the context of the proposed mechanisms and the importance of cooperative interactions in each reaction. The catalytic activity decreases for all reactions when the silanols are capped with trimethylsilyl groups, and higher temperatures are required to make accurate rate measurements, emphasizing the vital role the weakly acidic silanols play in the catalytic cycles. The results indicate that loss of acid sites is more detrimental to the catalytic activity of the aldol condensation than the nitroaldol condensation, as evidenced by the significant decrease in the pre-exponential factor for the aldol condensation when silanols are unavailable for cooperative interactions. Cooperative catalysis is evidenced by significant changes in the pre-exponential factor, rather than the activation energy for the aldol condensation.« less

Kinetics of beta-haematin formation from suspensions of haematin in aqueous benzoic acid.

PubMed

Egan, Timothy J; Tshivhase, Mmboneni G

2006-11-14

Kinetics of beta-haematin (synthetic malaria pigment) formation from haematin have been studied in the presence of aqueous benzoic acid and derivatives of benzoic acid. Formation of the beta-haematin product is demonstrated by X-ray diffraction and IR spectroscopy. Reactions were followed by determining the fraction of unreacted haematin at various time points during the process via reaction of extracted aliquots with pyridine. The kinetics can be fitted to the Avrami equation, indicating that the process involves nucleation and growth. Reaction kinetics in stirred benzoic acid are similar to those previously observed in acetic acid, except that benzoic acid is far more active in promoting the reaction than acetic acid. The reaction reaches completion within 2 h in the presence of 0.050 M benzoic acid (pH 4.5, 60 degrees C). This compares with 1 h in the presence of 4.5 M acetic acid and 4 h in the presence of 2 M acetic acid. The reaction rate in benzoic acid is not affected if the stirring rate is decreased to zero, but very vigorous stirring appears to disrupt nucleation. The rate constant for beta-haematin formation in benzoic acid has a linear dependence on benzoic acid concentration and follows Arrhenius behaviour with temperature. There is a bell-shaped dependence on pH. This suggests that the haematin species in which one propionate group is protonated and the other is deprotonated is optimal for beta-haematin formation. When the reaction is conducted in para-substituted benzoic acid derivatives, the log of the rate constant increases linearly with the Hammett constant. These findings suggest that the role of the carboxylic acid may be to disrupt hydrogen bonding and pi-stacking in haematin, facilitating conversion to beta-haematin. The large activation energy for conversion of precipitated haematin to beta-haematin suggests that the reaction in vivo most likely involves direct nucleation from solution and probably does not occur in aqueous medium.

Kinetic and Mechanistic Examination of Acid–Base Bifunctional Aminosilica Catalysts in Aldol and Nitroaldol Condensations

DOE PAGES

Collier, Virginia E.; Ellebracht, Nathan C.; Lindy, George I.; ...

2015-12-09

The kinetic and mechanistic understanding of cooperatively catalyzed aldol and nitroaldol condensations is probed using a series of mesoporous silicas functionalized with aminosilanes to provide bifunctional acid–base character. Mechanistically, a Hammett analysis is performed to determine the effects of electron-donating and electron-withdrawing groups of para-substituted benzaldehyde derivatives on the catalytic activity of each condensation reaction. This information is also used to discuss the validity of previously proposed catalytic mechanisms and to propose a revised mechanism with plausible reaction intermediates. For both reactions, electron-withdrawing groups increase the observed rates of reaction, though resonance effects play an important, yet subtle, role inmore » the nitroaldol condensation, in which a p-methoxy electron-donating group is also able to stabilize the proposed carbocation intermediate. Additionally, activation energies and pre-exponential factors are calculated via the Arrhenius analysis of two catalysts with similar amine loadings: one catalyst had silanols available for cooperative interactions (acid–base catalysis), while the other was treated with a silanol-capping reagent to prevent such cooperativity (base-only catalysis). The values obtained for activation energies and pre-exponential factors in each reaction are discussed in the context of the proposed mechanisms and the importance of cooperative interactions in each reaction. The catalytic activity decreases for all reactions when the silanols are capped with trimethylsilyl groups, and higher temperatures are required to make accurate rate measurements, emphasizing the vital role the weakly acidic silanols play in the catalytic cycles. The results indicate that loss of acid sites is more detrimental to the catalytic activity of the aldol condensation than the nitroaldol condensation, as evidenced by the significant decrease in the pre-exponential factor for the aldol condensation when silanols are unavailable for cooperative interactions. Cooperative catalysis is evidenced by significant changes in the pre-exponential factor, rather than the activation energy for the aldol condensation.« less

Effects of para-substituents of styrene derivatives on their chemical reactivity on platinum nanoparticle surfaces

NASA Astrophysics Data System (ADS)

Hu, Peiguang; Chen, Limei; Deming, Christopher P.; Lu, Jia-En; Bonny, Lewis W.; Chen, Shaowei

2016-06-01

Stable platinum nanoparticles were successfully prepared by the self-assembly of para-substituted styrene derivatives onto the platinum surfaces as a result of platinum-catalyzed dehydrogenation and transformation of the vinyl groups to the acetylene ones, forming platinum-vinylidene/-acetylide interfacial bonds. Transmission electron microscopic measurements showed that the nanoparticles were well dispersed without apparent aggregation, suggesting sufficient protection of the nanoparticles by the organic capping ligands, and the average core diameter was estimated to be 2.0 +/- 0.3 nm, 1.3 +/- 0.2 nm, and 1.1 +/- 0.2 nm for the nanoparticles capped with 4-tert-butylstyrene, 4-methoxystyrene, and 4-(trifluoromethyl)styrene, respectively, as a result of the decreasing rate of dehydrogenation with the increasing Taft (polar) constant of the para-substituents. Importantly, the resulting nanoparticles exhibited unique photoluminescence, where an increase of the Hammett constant of the para-substituents corresponded to a blue-shift of the photoluminescence emission, suggesting an enlargement of the HOMO-LUMO band gap of the nanoparticle-bound acetylene moieties. Furthermore, the resulting nanoparticles exhibited apparent electrocatalytic activity towards oxygen reduction in acidic media, with the best performance among the series of samples observed with the 4-tert-butylstyrene-capped nanoparticles due to an optimal combination of the nanoparticle core size and ligand effects on the bonding interactions between platinum and oxygen species.Stable platinum nanoparticles were successfully prepared by the self-assembly of para-substituted styrene derivatives onto the platinum surfaces as a result of platinum-catalyzed dehydrogenation and transformation of the vinyl groups to the acetylene ones, forming platinum-vinylidene/-acetylide interfacial bonds. Transmission electron microscopic measurements showed that the nanoparticles were well dispersed without apparent aggregation, suggesting sufficient protection of the nanoparticles by the organic capping ligands, and the average core diameter was estimated to be 2.0 +/- 0.3 nm, 1.3 +/- 0.2 nm, and 1.1 +/- 0.2 nm for the nanoparticles capped with 4-tert-butylstyrene, 4-methoxystyrene, and 4-(trifluoromethyl)styrene, respectively, as a result of the decreasing rate of dehydrogenation with the increasing Taft (polar) constant of the para-substituents. Importantly, the resulting nanoparticles exhibited unique photoluminescence, where an increase of the Hammett constant of the para-substituents corresponded to a blue-shift of the photoluminescence emission, suggesting an enlargement of the HOMO-LUMO band gap of the nanoparticle-bound acetylene moieties. Furthermore, the resulting nanoparticles exhibited apparent electrocatalytic activity towards oxygen reduction in acidic media, with the best performance among the series of samples observed with the 4-tert-butylstyrene-capped nanoparticles due to an optimal combination of the nanoparticle core size and ligand effects on the bonding interactions between platinum and oxygen species. Electronic supplementary information (ESI) available: TGA curves and additional voltammograms. See DOI: 10.1039/c6nr02296k

Understanding the interplay of weak forces in [3,3]-sigmatropic rearrangement for stereospecific synthesis of diamines.

PubMed

So, Soon Mog; Mui, Leo; Kim, Hyunwoo; Chin, Jik

2012-08-21

Chiral diamines are important building blocks for constructing stereoselective catalysts, including transition metal based catalysts and organocatalysts that facilitate oxidation, reduction, hydrolysis, and C-C bond forming reactions. These molecules are also critical components in the synthesis of drugs, including antiviral agents such as Tamiflu and Relenza and anticancer agents such as oxaliplatin and nutlin-3. The diaza-Cope rearrangement reaction provides one of the most versatile methods for rapidly generating a wide variety of chiral diamines stereospecifically and under mild conditions. Weak forces such as hydrogen bonding, electronic, steric, oxyanionic, and conjugation effects can drive this equilibrium process to completion. In this Account, we examine the effect of these individual weak forces on the value of the equilibrium constant for the diaza-Cope rearrangement reaction using both computational and experimental methods. The availability of a wide variety of aldehydes and diamines allows for the facile synthesis of the diimines needed to study the weak forces. Furthermore, because the reaction generally takes place cleanly at ambient temperature, we can easily measure equilibrium constants for rearrangement of the diimines. We use the Hammett equation to further examine the electronic and oxyanionic effects. In addition, computations and experiments provide us with new insights into the origin and extent of stereospecificity for this rearrangement reaction. The diaza-Cope rearrangement, with its unusual interplay between weak forces and the equilibrium constant of the reaction, provides a rare opportunity to study the effects of the fundamental weak forces on a chemical reaction. Among these many weak forces that affect the diaza-Cope rearrangement, the anion effect is the strongest (10.9 kcal/mol) followed by the resonance-assisted hydrogen-bond effect (7.1 kcal/mol), the steric effect (5.7 kcal/mol), the conjugation effect (5.5 kcal/mol), and the electronic effect (3.2 kcal/mol). Based on both computation and experimental data, the effects of these weak forces are additive. Understanding the interplay of the weak forces in the [3,3]-sigmatropic reaction is interesting in its own right and also provides valuable insights for the synthesis of chiral diamine based drugs and catalysts in excellent yield and enantiopurity.

ITER Simulations Using the PEDESTAL Module in the PTRANSP Code

NASA Astrophysics Data System (ADS)

Halpern, F. D.; Bateman, G.; Kritz, A. H.; Pankin, A. Y.; Budny, R. V.; Kessel, C.; McCune, D.; Onjun, T.

2006-10-01

PTRANSP simulations with a computed pedestal height are carried out for ITER scenarios including a standard ELMy H-mode (15 MA discharge) and a hybrid scenario (12MA discharge). It has been found that fusion power production predicted in simulations of ITER discharges depends sensitively on the height of the H-mode temperature pedestal [1]. In order to study this effect, the NTCC PEDESTAL module [2] has been implemented in PTRANSP code to provide boundary conditions used for the computation of the projected performance of ITER. The PEDESTAL module computes both the temperature and width of the pedestal at the edge of type I ELMy H-mode discharges once the threshold conditions for the H-mode are satisfied. The anomalous transport in the plasma core is predicted using the GLF23 or MMM95 transport models. To facilitate the steering of lengthy PTRANSP computations, the PTRANSP code has been modified to allow changes in the transport model when simulations are restarted. The PTRANSP simulation results are compared with corresponding results obtained using other integrated modeling codes.[1] G. Bateman, T. Onjun and A.H. Kritz, Plasma Physics and Controlled Fusion, 45, 1939 (2003).[2] T. Onjun, G. Bateman, A.H. Kritz, and G. Hammett, Phys. Plasmas 9, 5018 (2002).

Proton-Coupled Electron Transfer and Substituent Effects in Catechol-Based Deep Eutectic Solvents: Gross and Fine Tuning of Redox Activity.

PubMed

Smith, Parker J; Goeltz, John C

2017-12-07

The 1,2-diol moiety in a variety of substituted catechols allows formation of room temperature ionic melts in a 2:1 ratio with choline chloride or choline dihydrogen citrate. These deep eutectic solvents were 4.3-6.6 M in redox active catechols. Substituents on 3- and 4-substituted catechols shift both E° and pK a such that Hammett parameters predict the observed E p for oxidation in square wave voltammetry. The proton acceptor for the proton-coupled oxidation shifts the observed E p more strongly than the substituents within the substituents and acceptors reported here. The shift is predicted well by the pK a of the conjugate acid of the proton acceptor, i.e., water in aqueous solutions or chloride or dihydrogen citrate in the DESs in this study. Together, the substituent and the proton acceptor allow gross and fine-tuning of the oxidation potential for catechol over 750 mV, the first demonstration of control of the thermodynamics of proton-coupled electron transfer in deep eutectic solvents. Changing the substituents on the HBD affords fine control in tens of millivolts, while changing the base strength of the anion of the organic salt affords gross control across hundreds of millivolts.

Unexpected Hydrolytic Instability of N-Acylated Amino Acid Amides and Peptides

PubMed Central

2015-01-01

Remote amide bonds in simple N-acyl amino acid amide or peptide derivatives 1 can be surprisingly unstable hydrolytically, affording, in solution, variable amounts of 3 under mild acidic conditions, such as trifluoroacetic acid/water mixtures at room temperature. This observation has important implications for the synthesis of this class of compounds, which includes N-terminal-acylated peptides. We describe the factors contributing to this instability and how to predict and control it. The instability is a function of the remote acyl group, R2CO, four bonds away from the site of hydrolysis. Electron-rich acyl R2 groups accelerate this reaction. In the case of acyl groups derived from substituted aromatic carboxylic acids, the acceleration is predictable from the substituent’s Hammett σ value. N-Acyl dipeptides are also hydrolyzed under typical cleavage conditions. This suggests that unwanted peptide truncation may occur during synthesis or prolonged standing in solution when dipeptides or longer peptides are acylated on the N-terminus with electron-rich aromatic groups. When amide hydrolysis is an undesired secondary reaction, as can be the case in the trifluoroacetic acid-catalyzed cleavage of amino acid amide or peptide derivatives 1 from solid-phase resins, conditions are provided to minimize that hydrolysis. PMID:24617596

Colorless to purple-red switching electrochromic anthraquinone imides with broad visible/near-IR absorptions in the radical anion state: simulation-aided molecular design.

PubMed

Chen, Fengkun; Zhang, Jie; Jiang, Hong; Wan, Xinhua

2013-07-01

The large redshift of near-infrared (NIR) absorptions of nitro-substituted anthraquinone imide (Nitro-AQI) radical anions, relative to other AQI derivatives, is rationalized based on quantum chemical calculations. Calculations reveal that the delocalization effects of electronegative substitution in the radical anion states is dramatically enhanced, thus leading to a significant decrease in the HOMO-LUMO band gap in the radical anion states. Based on this understanding, an AQI derivative with an even stronger electron-withdrawing dicyanovinyl (di-CN) substituent was designed and prepared. The resulting molecule, di-CN-AQI, displays no absorption in the Vis/NIR region in the neutral state, but absorbs intensively in the range of λ=700-1000 (λmax ≈860 nm) and λ=1100-1800 nm (λmax ≈1400 nm) upon one-electron reduction; this is accompanied by a transition from a highly transmissive colorless solution to one that is purple-red. The relationship between calculated radical anionic HOMO-LUMO gaps and the electron-withdrawing capacity of the substituents is also determined by employing Hammett parameter, which could serve as a theoretical tool for further molecular design. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Influencing the electronic interaction in diferrocenyl-1-phenyl-1H-pyrroles.

PubMed

Hildebrandt, Alexander; Lang, Heinrich

2011-11-28

Functionalised diferrocenyl-1-phenyl-1H-pyrroles were synthesised using Negishi C,C cross-coupling reactions. The influence of different substituents at the phenyl moiety on the electronic interaction was studied using electrochemistry (cyclic and square-wave voltammetry) and spectro-electrochemistry (in situ UV/Vis-NIR spectroscopy). The ferrocenyl moieties gave rise to two sequential, reversible redox processes in each of the diferrocenyl-1-phenyl-1H-pyrroles. The observed ΔE(1/2) values (ΔE(1/2) = difference between first and second oxidation) range between 420 and 480 mV. A linear relationship between the Hammett constants σ of the substituents and the separation of the redox potentials exists. The NIR measurements confirm electronic communication between the iron centers as intervalence charge transfer (IVCT) absorptions were observed in the corresponding mixed-valent monocationic species. All compounds were classified as class II systems according to Robin and Day (M. B. Robin and P. Day, Adv. Inorg. Chem., 1967, 10, 247-423). The oscillator strength of the charge transfer transition highly depends on the electron donating or electron withdrawing character of the phenyl substituents. This enables direct tuning of the intermetallic communication by simple modification of the molecule's functional group. Hence, this series of molecules may be regarded as model compounds for single molecule transistors.

Substituent effect in spin-crossover behavior of iron(II)-Ar-pybox complexes (Ar-pybox = 4-aryl-2,6-bis(oxazolin-2-yl)pyridine)

NASA Astrophysics Data System (ADS)

Kimura, Akifumi; Ishida, Takayuki

2018-01-01

Spin-crossover (SCO) is a reversible transition between low-spin (LS) and high-spin (HS) states by external stimuli like heat. The SCO behavior of [Fe(Ar-pybox)2](ClO4)2 was investigated, where Ar-pybox stands for 4-aryl-2,6-bis(oxazolin-2-yl)pyridine with Ar = 4-pyridyl (4Py), 3-thienyl (3Th), and phenyl (Ph). They were characterized by means of single-crystal X-ray diffraction study, being consistent with the results of the magnetic measurements. The SCO temperatures (T1/2) in the polycrystalline state were determined to be 360 and 230 K for Ar = 4Py and Ph, respectively. The 3Th derivative possessed a HS state in all the temperature range. The solution susceptometry was also performed to purge intermolecular interaction and rigid crystal lattice effects, affording T1/2 = 310, 240, and 240 K for Ar = 4Py, 3Th, and Ph, respectively, in acetone. The substituent effect analysis using the Hammett substituent constant (σp) clarified that electron-withdrawing groups raise T1/2. A plausible model describing the substituent effect on T1/2 is proposed based on d-π interaction. The present result is regarded as a successful example of crystal field engineering.

The Alkaline Hydrolysis of Sulfonate Esters: Challenges in Interpreting Experimental and Theoretical Data

PubMed Central

2013-01-01

Sulfonate ester hydrolysis has been the subject of recent debate, with experimental evidence interpreted in terms of both stepwise and concerted mechanisms. In particular, a recent study of the alkaline hydrolysis of a series of benzene arylsulfonates (Babtie et al., Org. Biomol. Chem.10, 2012, 8095) presented a nonlinear Brønsted plot, which was explained in terms of a change from a stepwise mechanism involving a pentavalent intermediate for poorer leaving groups to a fully concerted mechanism for good leaving groups and supported by a theoretical study. In the present work, we have performed a detailed computational study of the hydrolysis of these compounds and find no computational evidence for a thermodynamically stable intermediate for any of these compounds. Additionally, we have extended the experimental data to include pyridine-3-yl benzene sulfonate and its N-oxide and N-methylpyridinium derivatives. Inclusion of these compounds converts the Brønsted plot to a moderately scattered but linear correlation and gives a very good Hammett correlation. These data suggest a concerted pathway for this reaction that proceeds via an early transition state with little bond cleavage to the leaving group, highlighting the care that needs to be taken with the interpretation of experimental and especially theoretical data. PMID:24279349

Mechanism of di-tert-butylsilylene transfer from a silacyclopropane to an alkene.

PubMed

Driver, Tom G; Woerpel, K A

2003-09-03

Kinetic and thermodynamic studies of the reactions of cyclohexene silacyclopropane 1 and monosubstituted alkenes suggested a possible mechanism for di-tert-butylsilylene transfer. The kinetic order in cyclohexene silacyclopropane 1 and cyclohexene were determined to be 1 and -1, respectively. Saturation kinetic behavior in monosubstituted alkene concentration was observed. Competition experiments between substituted styrenes and a deficient amount of di-tert-butylsilylene from 1 correlated well with the Hammett equation and provided a rho value of -0.666 +/- 0.008, using sigma(p) constants. These data supported a two-step mechanism involving reversible di-tert-butylsilylene extrusion from 1, followed by irreversible concerted electrophilic attack of the silylene on the monosubstituted alkene. Eyring activation parameters were found to be DeltaH++ = 22.1 +/- 0.9 kcal.mol(-1) and DeltaS++ = -15 +/- 2 eu. Competition experiments between cycloalkenes and allylbenzene determined cycloalkenes to be more efficient silylene traps (k(rel) =1.3, DeltaDeltaG++ = 0.200 kcal.mol(-1)). A summary of the data resulted in a postulated reaction coordinate diagram. The mechanistic studies enabled rational modification of reaction conditions that improved the synthetic utility of silylene transfer. Removal of the volatile cyclohexene from the reaction mixture into an evacuated headspace led to the formation of previously inaccessible cyclohexene-derived silacyclopropanes.

Effects of Functional Groups in Redox-Active Organic Molecules: A High-Throughput Screening Approach

DOE PAGES

Pelzer, Kenley M.; Cheng, Lei; Curtiss, Larry A.

2016-12-08

Nonaqueous redox flow batteries have attracted recent attention with their potential for high electrochemical storage capacity, with organic electrolytes serving as solvents with a wide electrochemical stability window. Organic molecules can also serve as electroactive species, where molecules with low reduction potentials or high oxidation potentials can provide substantial chemical energy. To identify promising electrolytes in a vast chemical space, high-throughput screening (HTS) of candidate molecules plays an important role, where HTS is used to calculate properties of thousands of molecules and identify a few organic molecules worthy of further attention in battery research. Here, in this work, we presentmore » reduction and oxidation potentials obtained from HTS of 4178 molecules. The molecules are composed of base groups of five- or six-membered rings with one or two functional groups attached, with the set of possible functional groups including both electron-withdrawing and electron-donating groups. In addition to observing the trends in potentials that result from differences in organic base groups and functional groups, we analyze the effects of molecular characteristics such as multiple bonds, Hammett parameters, and functional group position. In conclusion, this work provides useful guidance in determining how the identities of the base groups and functional groups are correlated with desirable reduction and oxidation potentials.« less

Biological activity of aldose reductase and lipophilicity of pyrrolyl-acetic acid derivatives

NASA Astrophysics Data System (ADS)

Kumari, A.; Kumari, R.; Kumar, R.; Gupta, M.

2011-12-01

Quantitative Structure-Activity Relationship modeling is a powerful approach for correlating an organic compound to its lipophilicity. In this paper QSAR models are established for estimation of correlation of the lipophilicity of a series of pyrrolyl-acetic acid derivatives, inhibitors of the aldose reductase enzyme, in the n-octanol-water system with biological activity of aldose reductase. Lipophilicity, expressed by the logarithm of n-octnol-water partition coefficient log P and biological activity of aldose reductase inhibitory activity by log it. Result obtained by QSAR modeling of compound series reveal a definite trend in biological activity and a further improvement in quantitative relationships are established if, beside log P, Hammett electronic constant σ and connectivity index chi-3 (3 χ) term included in the regression equation. The tri-parametric model with log P, 3 χ and σ as correlating parameters have been found to be the best which gives a variance of 87% ( R 2 = 0.8743). A compound has been found to be serious outlier and when the same has been excluded the model explains about 94% variance of the data set ( R 2 = 0.9447). The topological index (3 χ) has been found to be a good parameter for modeling the biological activity.

Effects of Functional Groups in Redox-Active Organic Molecules: A High-Throughput Screening Approach

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pelzer, Kenley M.; Cheng, Lei; Curtiss, Larry A.

Nonaqueous redox flow batteries have attracted recent attention with their potential for high electrochemical storage capacity, with organic electrolytes serving as solvents with a wide electrochemical stability window. Organic molecules can also serve as electroactive species, where molecules with low reduction potentials or high oxidation potentials can provide substantial chemical energy. To identify promising electrolytes in a vast chemical space, high-throughput screening (HTS) of candidate molecules plays an important role, where HTS is used to calculate properties of thousands of molecules and identify a few organic molecules worthy of further attention in battery research. Here, in this work, we presentmore » reduction and oxidation potentials obtained from HTS of 4178 molecules. The molecules are composed of base groups of five- or six-membered rings with one or two functional groups attached, with the set of possible functional groups including both electron-withdrawing and electron-donating groups. In addition to observing the trends in potentials that result from differences in organic base groups and functional groups, we analyze the effects of molecular characteristics such as multiple bonds, Hammett parameters, and functional group position. In conclusion, this work provides useful guidance in determining how the identities of the base groups and functional groups are correlated with desirable reduction and oxidation potentials.« less

[Microspeciation of amphoteric molecules of unusual acid-base properties].

PubMed

Kóczián, Kristóf

2007-01-01

The phisico-chemical properties of bio- and drug molecules greatly influence their interactions in the body and strongly effect the mechanism of drug action. Among these properties, macroscopic and site-specific protonation constants are of crucial importance. Latter one is the tool to calculate the relative concentration of the various microspecies in the compartments of the body at different pH values, and also, it is the versatile parameter to improve the pharmacokinetic properties of a new molecule in a particular family of drugs. In the present thesis work, the microspeciation of three molecules of great pharmaceutical importance and unusual acid-base properties, were carried out. The microconstants of tenoxicam, the non-steroidal anti-inflammatory drug, were described, introducing a novel deductive method using Hammett constants. For this purpose, a total of 8 tenoxicam and piroxicam derivatives were synthesised. To the best of our knowledge, the log k(N)O microconstant of tenoxicam obtained thus is the lowest enolate basicity value, which, however, can be well explained by the effects of the intramolecular environment. The developed evaluation procedure is suitable for microconstant determination of compounds in other molecule families. Besides, prodrug-type compounds and analogues similar to the structures of selective COX-2 isoenzyme inhibitors were synthesised. The other two molecules studied, the 6-aminopenicillanic acid and 7-cephalosporanic acid, the core molecules of the two most important beta-lactam antibiotic-types were derivatised and investigated by 1D and 2D NMR techniques. The NMR-pH titration on the parent compounds and their ester derivatives, combined with in situ pH-measurements allowed the microspeciation of these easily decomposing molecules. One of the protonation constant of 7-ACA (log kN(O) = 4.12), to the best of our knowledge, is the least non-aromatic basic amino-site among the natural compounds.

A mechanistic investigation on copolymerization of ethylene with polar monomers using a cyclophane-based Pd(II) alpha-diimine catalyst.

PubMed

Popeney, Chris S; Guan, Zhibin

2009-09-02

A detailed mechanistic investigation of the copolymerization of ethylene and methyl acrylate (MA) by a Pd(II) cyclophane-based alpha-diimine catalyst is reported. Our previous observations of unusually high incorporations of acrylates in copolymerization using this catalyst (J. Am. Chem. Soc. 2007, 129, 10062) prompted us to conduct a full mechanistic study on ethylene/MA copolymerization, which indicates a dramatic departure from normal Curtin-Hammett kinetic behavior as observed in copolymerization using the normal Brookhart type of Pd(II) alpha-diimine catalysts. Further investigation reveals that this contrasting behavior originates from the axial blocking effect of the cyclophane ligand hindering olefin substitution and equilibration. In equilibrium studies of ethylene with nitriles, the cyclophane catalyst was found to more strongly favor the linearly binding nitrile ligands as compared to the standard acyclic Pd(II) alpha-diimine catalysts. Ethylene exchange rates in the complexes [(N--N)PdMe(C(2)H(4))](+) (N--N = diimine) were measured by 2D EXSY NMR spectroscopy and found to be over 100 times slower in the cyclophane case. Measurement of the slow equilibration of ethylene, methyl acrylate, and 4-methoxystyrene in cyclophane-based Pd(II) olefin complexes by (1)H NMR and fitting of the obtained kinetic plots allowed for the estimation of exchange rates and equilibrium constants of the olefins. After extrapolation to typical polymerization temperature, DeltaG(double dagger) = 20.6 and 16.4 kcal/mol for ethylene-methyl acrylate exchange in the forward (ethylene displacement by methyl acrylate) and reverse directions, respectively. These values are of similar magnitude to the previously determined migratory insertion barriers of ethylene (DeltaG(double dagger) = 18.9 kcal/mol) and methyl acrylate (DeltaG(double dagger) = 16.3 kcal/mol) under equivalent conditions, but contrast strongly to the rapid olefin exchange seen in the Brookhart acyclic catalyst. The large barrier to olefin exchange hinders olefin pre-equilibrium, decreasing the cyclophane catalyst's ability to preferentially incorporate one monomer (in this case ethylene) over the other, thus giving rise to high comonomer incorporations.

Substitution Effects and Linear Free Energy Relationships During Reduction of 4- Benzoyl-n-(4-substituted Benzyl)pyridinium Cations

NASA Technical Reports Server (NTRS)

Leventis, Nicholas; Zhang, Guo-Hui; Rawashdeh, Abdel-Monem M.; Sotiriou-Leventis, Chariklia; Gray, Hugh R. (Technical Monitor)

2003-01-01

In analogy to 4-(para-substituted benzoyl)-N-methylpyridinium cations (1-X's), the title species (2-X's, -X = -OCH3, -CH3, -H, -Br, -COCH3, -NO2) undergo two reversible, well-separated (E(sub 1/2) greater than or equal to 650 mV) one-electron reductions. The effect of substitution on the reduction potentials of 2-X's is much weaker than the effect of the same substituents on 1-X's: the Hammett rho-values are 0.80 and 0.93 for the 1st- and 2nd-e reduction of 2-X's vs. 2.3 and 3.3 for the same reductions of 1-X's, respectively. Importantly, the nitro group of 2-NO2 undergoes reduction before the 2nd-e reduction of the 4-benzoylpyridinium system. These results suggest that the redox potentials of the 4-benzoylpyridinium system can be course-tuned via p-benzoyl substitution and fine-tuned via para-benzyl substitution. Introducing the recently derived substituent constant of the -NO2(sup)- group (sigma para-NO2(sup)- = -0.97) yields an excellent correlation for the 3rd-e reduction of 2- NO2 (corresponding to the reduction of the carbonyl group) with the 2nd-e reduction of the other 2-X's, and confirms the electron donating properties of -NO2(sup)-.

α-Keto phenylamides as P1'-extended proteasome inhibitors.

PubMed

Voss, Constantin; Scholz, Christoph; Knorr, Sabine; Beck, Philipp; Stein, Martin L; Zall, Andrea; Kuckelkorn, Ulrike; Kloetzel, Peter-Michael; Groll, Michael; Hamacher, Kay; Schmidt, Boris

2014-11-01

The major challenge for proteasome inhibitor design lies in achieving high selectivity for, and activity against, the target, which requires specific interactions with the active site. Novel ligands aim to overcome off-target-related side effects such as peripheral neuropathy, which is frequently observed in cancer patients treated with the FDA-approved proteasome inhibitors bortezomib (1) or carfilzomib (2). A systematic comparison of electrophilic headgroups recently identified the class of α-keto amides as promising for next generation drug development. On the basis of crystallographic knowledge, we were able to develop a structure-activity relationship (SAR)-based approach for rational ligand design using an electronic parameter (Hammett's σ) and in silico molecular modeling. This resulted in the tripeptidic α-keto phenylamide BSc4999 [(S)-3-(benzyloxycarbonyl-(S)-leucyl-(S)-leucylamino)-5-methyl-2-oxo-N-(2,4-dimethylphenyl)hexanamide, 6 a], a highly potent (IC50 = 38 nM), cell-permeable, and slowly reversible covalent inhibitor which targets both the primed and non-primed sites of the proteasome's substrate binding channel as a special criterion for selectivity. The improved inhibition potency and selectivity of this new α-keto phenylamide makes it a promising candidate for targeting a wider range of tumor subtypes than commercially available proteasome inhibitors and presents a new candidate for future studies. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Oxidation Kinetics of Bromophenols by Nonradical Activation of Peroxydisulfate in the Presence of Carbon Nanotube and Formation of Brominated Polymeric Products.

PubMed

Guan, Chaoting; Jiang, Jin; Pang, Suyan; Luo, Congwei; Ma, Jun; Zhou, Yang; Yang, Yi

2017-09-19

This work demonstrated that bromophenols (BrPs) could be readily oxidized by peroxydisulfate (PDS) activated by a commercial carbon nanotube (CNT), while furfuryl alcohol (a chemical probe for singlet oxygen ( 1 O 2 )) was quite refractory. Results obtained by radical quenching experiments, electron paramagnetic resonance spectroscopy, and Fourier transform infrared spectroscopy further confirmed the involvement of nonradical PDS-CNT complexes rather than 1 O 2 . Bicarbonate and chloride ion exhibited negligible impacts on BrPs degradation by the PDS/CNT system, while a significant inhibitory effect was observed for natural organic matter. The oxidation of BrPs was influenced by solution pH with maximum rates occurring at neutral pH. Linear free energy relationships (LFERs) were established between the observed pseudo-first-order oxidation rates of various substituted phenols and the classical descriptor variables (i.e., Hammett constant σ + , and half-wave oxidation potential E 1/2 ). Products analyses by liquid chromatography tandem mass spectrometry clearly showed the formation of hydroxylated polybrominated diphenyl ethers and hydroxylated polybrominated biphenyls on CNT surface. Their formation pathway possibly involved the generation of bromophenoxyl radicals from BrPs one-electron oxidation and their subsequent coupling reactions. These results suggest that the novel nonradical PDS/CNT oxidation technology is a good alternative for selectively eliminating BrPs with alleviating toxic byproducts in treated water effluent.

Structure-Activity Relationships for Rates of Aromatic Amine Oxidation by Manganese Dioxide.

PubMed

Salter-Blanc, Alexandra J; Bylaska, Eric J; Lyon, Molly A; Ness, Stuart C; Tratnyek, Paul G

2016-05-17

New energetic compounds are designed to minimize their potential environmental impacts, which includes their transformation and the fate and effects of their transformation products. The nitro groups of energetic compounds are readily reduced to amines, and the resulting aromatic amines are subject to oxidation and coupling reactions. Manganese dioxide (MnO2) is a common environmental oxidant and model system for kinetic studies of aromatic amine oxidation. In this study, a training set of new and previously reported kinetic data for the oxidation of model and energetic-derived aromatic amines was assembled and subjected to correlation analysis against descriptor variables that ranged from general purpose [Hammett σ constants (σ(-)), pKas of the amines, and energies of the highest occupied molecular orbital (EHOMO)] to specific for the likely rate-limiting step [one-electron oxidation potentials (Eox)]. The selection of calculated descriptors (pKa, EHOMO, and Eox) was based on validation with experimental data. All of the correlations gave satisfactory quantitative structure-activity relationships (QSARs), but they improved with the specificity of the descriptor. The scope of correlation analysis was extended beyond MnO2 to include literature data on aromatic amine oxidation by other environmentally relevant oxidants (ozone, chlorine dioxide, and phosphate and carbonate radicals) by correlating relative rate constants (normalized to 4-chloroaniline) to EHOMO (calculated with a modest level of theory).

Parabola-like shaped pH-rate profile for phenols oxidation by aqueous permanganate.

PubMed

Du, Juanshan; Sun, Bo; Zhang, Jing; Guan, Xiaohong

2012-08-21

Oxidation of phenols by permanganate in the pH range of 5.0-9.0 generally exhibits a parabola-like shape with the maximum reaction rate obtained at pH close to phenols' pK(a). However, a monotonic increase or decrease is observed if phenols' pK(a) is beyond the pH range of 5.0-9.0. A proton transfer mechanism is proposed in which the undissociated phenol is directly oxidized by permanganate to generate products while a phenolate-permanganate adduct, intermediate, is formed between dissociated phenol and permanganate ion and this is the rate-limiting step for phenolates oxidation by permanganate. The intermediate combines with H(+) and then decomposes to products. Rate equations derived based on the steady-state approximation can well simulate the experimentally derived pH-rate profiles. Linear free energy relationships (LFERs) were established among the parameters obtained from the modeling, Hammett constants, and oxygen natural charges in phenols and phenolates. LFERs reveal that chlorine substituents have opposite influence on the susceptibility of phenols and phenolates to permanganate oxidation and phenolates are not necessarily more easily oxidized than their neutral counterparts. The chlorine substituents regulate the reaction rate of chlorophenolates with permanganate mainly by influencing the natural charges of the oxygen atoms of dissociated phenols while they influence the oxidation of undissociated chlorophenols by permanganate primarily by forming intramolecular hydrogen bonding with the phenolic group.

Evolution of structure-reactivity correlations for the hydrogen abstraction reaction by chlorine atom.

PubMed

Poutsma, Marvin L

2013-01-31

Empirical structure-reactivity correlations are developed for log k(298), the gas-phase rate constants for the reaction (Cl(•) + HCR(3) → ClH + CR(3)(•)). It has long been recognized that correlation with Δ(r)H is weak. The poor performance of the linear Evans-Polanyi formulation is illustrated and was little improved by adding a quadratic term, for example, by making its slope smoothly dependent on Δ(r)H [η ≡ (Δ(r)H - Δ(r)H(min))/(Δ(r)H(max) - Δ(r)H(min))]. The "polar effect" ((δ-)Cl---H---CR(3)(δ+))(++) has also been long discussed, but there is no formalization of this dependence based on widely available independent variable(s). Using the sum of Hammett constants for the R substituents also gave at best modest correlations, either for σ(para) or for its dissection into F (field/inductive) and R (resonance) effects. Much greater success was achieved by combining these approaches with the preferred independent variable set being either [(Δ(r)H)(2), Δ(r)H, ΣF, and ΣR] or [η, Δ(r)H, ΣF, and ΣR]. For 64 rate constants that span 7 orders of magnitude, these correlation formulations give r(2) > 0.87 and a mean unsigned deviation of <0.5 log k units, with even better performance if primary, secondary, and tertiary reaction centers are treated separately.

Perfluoroalkyl phosphonic and phosphinic acids as proton conductors for anhydrous proton-exchange membranes.

PubMed

Herath, Mahesha B; Creager, Stephen E; Kitaygorodskiy, Alex; DesMarteau, Darryl D

2010-09-10

A study of proton-transport rates and mechanisms under anhydrous conditions using a series of acid model compounds, analogous to comb-branch perfluorinated ionomers functionalized with phosphonic, phosphinic, sulfonic, and carboxylic acid protogenic groups, is reported. Model compounds are characterized with respect to proton conductivity, viscosity, proton, and anion (conjugate base) self-diffusion coefficients, and Hammett acidity. The highest conductivities, and also the highest viscosities, are observed for the phosphonic and phosphinic acid model compounds. Arrhenius analysis of conductivity and viscosity for these two acids reveals much lower activation energies for ion transport than for viscous flow. Additionally, the proton self-diffusion coefficients are much higher than the conjugate-base self-diffusion coefficients for these two acids. Taken together, these data suggest that anhydrous proton transport in the phosphonic and phosphinic acid model compounds occurs primarily by a structure-diffusion, hopping-based mechanism rather than a vehicle mechanism. Further analysis of ionic conductivity and ion self-diffusion rates by using the Nernst-Einstein equation reveals that the phosphonic and phosphinic acid model compounds are relatively highly dissociated even under anhydrous conditions. In contrast, sulfonic and carboxylic acid-based systems exhibit relatively low degrees of dissociation under anhydrous conditions. These findings suggest that fluoroalkyl phosphonic and phosphinic acids are good candidates for further development as anhydrous, high-temperature proton conductors.

Kinetic Control in the Cleavage of Unsymmetrical Disilanes.

PubMed

Hevesi, Làszlò; Dehon, Michael; Crutzen, Raphael; Lazarescu-Grigore, Adriana

1997-04-04

A series of 12 phenyl-substituted arylpentamethyldisilanes 1a-l have been synthesized in order to examine the regioselectivity of their nucleophilic Si,Si bond cleavage reactions under Still's conditions (MeLi/HMPA/0 degrees C). It has been found that the sensitivity of these reactions to the electronic effects of the substituents in the phenyl ring could be described by the Hammett-type equation log(k(A)/k(B)) = 0.4334 + 2.421(Sigmasigma); (correlation coefficient R = 0.983). The k(A)/k(B) ratio represents the relative rate of attack at silicon atom A (linked to the aryl ring) or at silicon atom B (away from the aryl ring) of the unsymmetrical disilanes. Thus, the present investigation shows that the earlier belief according to which the nucleophilic cleavage of unsymmetrical disilanes always produces the more stable silyl anionic species (thermodynamic control) should be abandoned, or at least seriously amended: kinetic factors appear to exert a primary influence on the regioselectivity of such reactions. Since the two major kinetic factors (i.e., electrophilic character of and steric hindrance at a given silicon atom) have opposite effects on the orientation of the reaction, it may happen that kinetic and thermodynamic control lead to the same result. For some of the unsymmetrical disilanes studied, the major reaction path was not the Si,Si bond cleavage; instead, Si-aryl bond breaking occurred, producing the corresponding aryl anions.

Electron Transport and Nonlinear Optical Properties of Substituted Aryldimesityl Boranes: A DFT Study

PubMed Central

Pandith, Altaf Hussain; Islam, Nasarul

2014-01-01

A comprehensive theoretical study was carried out on a series of aryldimesityl borane (DMB) derivatives using Density Functional theory. Optimized geometries and electronic parameters like electron affinity, reorganization energy, frontiers molecular contours, polarizability and hyperpolarizability have been calculated by employing B3PW91/6-311++G (d, p) level of theory. Our results show that the Hammett function and geometrical parameters correlates well with the reorganization energies and hyperpolarizability for the series of DMB derivatives studied in this work. The orbital energy study reveals that the electron releasing substituents increase the LUMO energies and electron withdrawing substituents decrease the LUMO energies, reflecting the electron transport character of aryldimesityl borane derivatives. From frontier molecular orbitals diagram it is evident that mesityl rings act as the donor, while the phenylene and Boron atom appear as acceptors in these systems. The calculated hyperpolarizability of secondary amine derivative of DMB is 40 times higher than DMB (1). The electronic excitation contributions to the hyperpolarizability studied by using TDDFT calculation shows that hyperpolarizability correlates well with dipole moment in ground and excited state and excitation energy in terms of the two-level model. Thus the results of these calculations can be helpful in designing the DMB derivatives for efficient electron transport and nonlinear optical material by appropriate substitution with electron releasing or withdrawing substituents on phenyl ring of DMB system. PMID:25479382

Solvolysis of para-substituted cumyl chlorides. Brown and Okamoto's electrophilic substituent constants revisited using continuum solvent models.

PubMed

DiLabio, Gino A; Ingold, K U

2004-03-05

Brown and Okamoto (J. Am. Chem. Soc. 1958, 80, 4979) derived their electrophilic substitutent constants, sigma(p)+, from the relative rates of solvolysis of ring-substituted cumyl chlorides in an acetone/water solvent mixture. Application of the Hammett equation to the rates for the meta-substituted cumyl chlorides, where there could be no resonance interaction with the developing carbocation, gave a slope, rho(+) = -4.54 ( identical with 6.2 kcal/mol free energy). Rates for the para-substituted chlorides were then used to obtain sigma(p)+ values. We have calculated gas-phase C-Cl heterolytic bond dissociation enthalpy differences, Delta BDE(het) (= BDE(het)(4-YC(6)H(4)CMe(2)Cl) - BDE(het)(C(6)H(5)CMe(2)Cl)), for 16 of the 4-Y substituents employed by Brown and Okamoto. The plot of Delta BDE(het) vs sigma(p)+ gave rho(+) (SD) = 16.3 (2.3) kcal/mol, i.e., a rho(+) value roughly 2.5 times greater than experiment. Inclusion of solvation (water) energies, calculated using three continuum solvent models, reduced rho(+) and SD. The computationally least expensive model used, SM5.42R (Li et al. Theor. Chem. Acc. 1999, 103, 9) gave the best agreement with experiment. This model yielded rho(+) (SD) = 7.7 (0.9) kcal/mol, i.e., a rho(+) value that is only 24% larger than experiment.

High Throughput Biodegradation-Screening Test To Prioritize and Evaluate Chemical Biodegradability.

PubMed

Martin, Timothy J; Goodhead, Andrew K; Acharya, Kishor; Head, Ian M; Snape, Jason R; Davenport, Russell J

2017-06-20

Comprehensive assessment of environmental biodegradability of pollutants is limited by the use of low throughput systems. These are epitomized by the Organisation for Economic Cooperation and Development (OECD) Ready Biodegradability Tests (RBTs), where one sample from an environment may be used to assess a chemical's ability to readily biodegrade or persist universally in that environment. This neglects the considerable spatial and temporal microbial variation inherent in any environment. Inaccurate designations of biodegradability or persistence can occur as a result. RBTs are central in assessing the biodegradation fate of chemicals and inferring exposure concentrations in environmental risk assessments. We developed a colorimetric assay for the reliable quantification of suitable aromatic compounds in a high throughput biodegradation screening test (HT-BST). The HT-BST accurately differentiated and prioritized a range of structurally diverse aromatic compounds on the basis of their assigned relative biodegradabilities and quantitative structure-activity relationship (QSAR) model outputs. Approximately 20 000 individual biodegradation tests were performed, returning analogous results to conventional RBTs. The effect of substituent group structure and position on biodegradation potential demonstrated a significant correlation (P < 0.05) with Hammett's constant for substituents on position 3 of the phenol ring. The HT-BST may facilitate the rapid screening of 100 000 chemicals reportedly manufactured in Europe and reduce the need for higher-tier fate and effects tests.

Toward Hypoxia-Selective DNA-Alkylating Agents Built by Grafting Nitrogen Mustards onto the Bioreductively Activated, Hypoxia-Selective DNA-Oxidizing Agent 3-Amino-1,2,4-benzotriazine 1,4-Dioxide (Tirapazamine)

PubMed Central

2015-01-01

Tirapazamine (3-amino-1,2,4-benzotriazine 1,4-dioxide) is a heterocyclic di-N-oxide that undergoes enzymatic deoxygenation selectively in the oxygen-poor (hypoxic) cells found in solid tumors to generate a mono-N-oxide metabolite. This work explored the idea that the electronic changes resulting from the metabolic deoxygenation of tirapazamine analogues might be exploited to activate a DNA-alkylating species selectively in hypoxic tissue. Toward this end, tirapazamine analogues bearing nitrogen mustard units were prepared. In the case of the tirapazamine analogue 18a bearing a nitrogen mustard unit at the 6-position, it was found that removal of the 4-oxide from the parent di-N-oxide to generate the mono-N-oxide analogue 17a did indeed cause a substantial increase in reactivity of the mustard unit, as measured by hydrolysis rates and DNA-alkylation yields. Hammett sigma values were measured to quantitatively assess the magnitude of the electronic changes induced by metabolic deoxygenation of the 3-amino-1,2,4-benzotriazine 1,4-dioxide heterocycle. The results provide evidence that the 1,2,4-benzotiazine 1,4-dioxide unit can serve as an oxygen-sensing prodrug platform for the selective unmasking of bioactive agents in hypoxic cells. PMID:25029663

Toward hypoxia-selective DNA-alkylating agents built by grafting nitrogen mustards onto the bioreductively activated, hypoxia-selective DNA-oxidizing agent 3-amino-1,2,4-benzotriazine 1,4-dioxide (tirapazamine).

PubMed

Johnson, Kevin M; Parsons, Zachary D; Barnes, Charles L; Gates, Kent S

2014-08-15

Tirapazamine (3-amino-1,2,4-benzotriazine 1,4-dioxide) is a heterocyclic di-N-oxide that undergoes enzymatic deoxygenation selectively in the oxygen-poor (hypoxic) cells found in solid tumors to generate a mono-N-oxide metabolite. This work explored the idea that the electronic changes resulting from the metabolic deoxygenation of tirapazamine analogues might be exploited to activate a DNA-alkylating species selectively in hypoxic tissue. Toward this end, tirapazamine analogues bearing nitrogen mustard units were prepared. In the case of the tirapazamine analogue 18a bearing a nitrogen mustard unit at the 6-position, it was found that removal of the 4-oxide from the parent di-N-oxide to generate the mono-N-oxide analogue 17a did indeed cause a substantial increase in reactivity of the mustard unit, as measured by hydrolysis rates and DNA-alkylation yields. Hammett sigma values were measured to quantitatively assess the magnitude of the electronic changes induced by metabolic deoxygenation of the 3-amino-1,2,4-benzotriazine 1,4-dioxide heterocycle. The results provide evidence that the 1,2,4-benzotiazine 1,4-dioxide unit can serve as an oxygen-sensing prodrug platform for the selective unmasking of bioactive agents in hypoxic cells.

Effects of para-substituents of styrene derivatives on their chemical reactivity on platinum nanoparticle surfaces.

PubMed

Hu, Peiguang; Chen, Limei; Deming, Christopher P; Lu, Jia-En; Bonny, Lewis W; Chen, Shaowei

2016-06-09

Stable platinum nanoparticles were successfully prepared by the self-assembly of para-substituted styrene derivatives onto the platinum surfaces as a result of platinum-catalyzed dehydrogenation and transformation of the vinyl groups to the acetylene ones, forming platinum-vinylidene/-acetylide interfacial bonds. Transmission electron microscopic measurements showed that the nanoparticles were well dispersed without apparent aggregation, suggesting sufficient protection of the nanoparticles by the organic capping ligands, and the average core diameter was estimated to be 2.0 ± 0.3 nm, 1.3 ± 0.2 nm, and 1.1 ± 0.2 nm for the nanoparticles capped with 4-tert-butylstyrene, 4-methoxystyrene, and 4-(trifluoromethyl)styrene, respectively, as a result of the decreasing rate of dehydrogenation with the increasing Taft (polar) constant of the para-substituents. Importantly, the resulting nanoparticles exhibited unique photoluminescence, where an increase of the Hammett constant of the para-substituents corresponded to a blue-shift of the photoluminescence emission, suggesting an enlargement of the HOMO-LUMO band gap of the nanoparticle-bound acetylene moieties. Furthermore, the resulting nanoparticles exhibited apparent electrocatalytic activity towards oxygen reduction in acidic media, with the best performance among the series of samples observed with the 4-tert-butylstyrene-capped nanoparticles due to an optimal combination of the nanoparticle core size and ligand effects on the bonding interactions between platinum and oxygen species.

Reactions of Charged Substrates. 5. The Solvolysis and Sodium Azide Substitution Reactions of Benzylpyridinium Ions in Deuterium Oxide.

PubMed

Buckley, Neil; Oppenheimer, Norman J.

1996-10-18

Second-order rate constants and activation values were measured for the reactions with NaN(3) of a series of 4-Y-substituted (Y = MeO, Me, H, Cl, and NO(2)) benzyl 3'-Z-substituted (Z = CN, CONH(2), H, F, Ac) pyridinium chlorides in deuterium oxide. 3'-Cyanopyridine substrates reacted much faster than nicotinamide and pyridine substrates; in the pyridine series the 4-Me, 4-H, and 4-Cl benzyl analogs did not react for up to 6 months at 96()() degrees C in 1.7 M NaN(3). The 3'-cyanopyridine substrates do not exhibit borderline kinetic behavior, but the nicotinamide substrates do. The Hammett plot is flat for the NaN(3) reaction of 3'-cyanopyridine substrates and increasingly V-shaped for the nicotinamide and pyridine substrates. The values of beta(LG) (four-point plot) for the NaN(3) reaction of the 4-MeO benzyl substrates is -1.45, which is usually interpreted as being a very "late" activated complex. Two-point Brønsted "plots" for the other benzyl derivatives and for two N-methylpyridinium ions give values of beta(LG) in the same range. The second-order rate constant and activation values for N-methyl-3'-cyanopyridinium iodide are within the same range as those for the benzyl substrates. For the hydrolysis reaction, the Hammett plot is linear for 3'-cyanopyridine substrates (rho(+) = -1.24) and flat for the nicotinamide substrates. The extent of hydrolysis of 0.005-0.05 M solutions of the 3'-cyanopyridinie substrates depended on the initial concentration of substrate, and hydrolysis was slowed significantly or stopped completely in the presence of exogenous 3-cyanopyridine. These results show that an equilibrium is established among the products for the 4-MeO, 4-Me, 4-H, and 4-Cl substrates; the 4-NO(2) substrate reacted too slowly to discern any difference. Data for the extent of hydrolysis were fitted by an equation derived assuming the equilibrium. Despite this limitation on a classic test of mechanism, the rates and rho values are consistent with direct displacement by solvent and not with a unimolecular process. These results, which are rationalized in terms of the Pross-Shaik model, suggest that there are no ion-dipole complex intermediates in the benzyl series and show that borderline kinetic behavior is a function of leaving group ability and is not necessarily related to a change in mechanism. A computational approach was used to evaluate anomalous beta(LG) values for the hydrolysis and nucleophilic substitution reactions of the methypyridinium ion substrates. It was found that neither the Nu-substrate bond lengths nor the difference in charge matched the beta(LG) values. The value of DeltaDeltaS() of -15 gibbs/mol between (4-methoxybenzyl)-3'-cyanopyridinium chloride and the corresponding dimethylsulfonium chloride in the NaN(3) reaction, which is the result of the solvation of the pyridine at the transition state and the lack of solvation of SMe(2), is used to argue that the source of NAD(+) glycohydrolase "catalysis" of NAD(+) bond cleavage is the result of desolvation of the leaving group upon binding.

Comparison of Spring and Cave Drip Water in Westcave Preserve, Central Texas May Reveal Epikarst CO2 Degassing

NASA Astrophysics Data System (ADS)

Carlson, P.; Banner, J. L.; Casteel, R. C.; Breecker, D.

2013-12-01

The cave at Westcave Preserve, in central Texas, is a unique location to study karst processes due to its low, nearly atmospheric cave-air CO2 levels and seasonally variable temperature. The source of water that drips into the cave, however, has not been constrained, limiting interpretation of climate proxies in the cave. It is possible that a nearby spring and the cave drip-waters share a common source. Alternatively, the drip-waters could represent precipitation that has infiltrated the host rock. These hypotheses should be tested using Sr isotope ratios and/or other tracers. If they do share a common source, analysis of dissolved inorganic carbon (DIC) concentration , δ13CDIC, and cation concentrations of the two waters could provide insight into epikarst processes such as CO2 degassing and prior calcite precipitation (PCP) that are otherwise difficult to constrain. Westcave Preserve includes outcrops of the Hensell Sand, the Cow Creek Limestone, and the Hammett Shale, with a small cave at the contact between the Cow Creek and Hammett formations. The overlying Hensell Sand contains water that emerges at the surface as a spring near the cave. Water also drips directly into the cave, forming speleothems. Previous research has established that although δ18O values of rainfall in the area vary seasonally, between -10.5 and 1.1‰ with a weighted mean of -6.5‰ (VSMOW), the drip-water varies only between -4.7 and -4.3‰ with a weighted mean of -4.5‰ (Feng et al., in review). This suggests a large well-mixed reservoir above the cave. The soils above the cave have high CO2 of up to 17,500 ppmv, but because the cave is shallow with multiple large openings, cave CO2 levels are near-atmospheric (Casteel and Banner, in review). This creates a steep CO2 gradient between the soil and the cave air. The spring water DIC is nearly in carbon-isotope equilibrium with the soil CO2, suggesting that soil respiration, here controlled by C3 plants, is the primary source of CO2 for this reservoir. The drip water δ13CDIC is higher than the spring water (-10.3‰ versus -13.0‰). Although the spring water has higher DIC concentration than the drip water, with mean values of 128 mg/L C versus 113 mg/L C, respectively, preliminary data suggest that for some drips, the drip water DIC concentrations and δ13CDIC may vary with spring DIC values. We propose that if the spring and the drip water prove to be derived from the same source, the differences in DIC and δ13CDIC between spring and drip water are due to epikarst CO2 degassing as the water percolates down the CO2 gradient toward the cave ceiling. If the spring represents the source of the drip water, the calculated δ13 value of degassed CO2 is -33.3‰, assuming no PCP. PCP may occur, leading to a δ13C of degassed CO2 lower than calculated, but would result in a decrease or no change in δ13CDIC and therefore does not explain the observed difference between spring water and drip water.

Mechanistic studies on covalent assemblies of metal-mediated hemi-aminal ethers† †Electronic supplementary information (ESI) available. CCDC 1018457. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c4sc02495h Click here for additional data file. Click here for additional data file. Click here for additional data file.

PubMed Central

Jo, Hyun Hwa; Edupuganti, Ramakrishna; You, Lei; Dalby, Kevin N.

2015-01-01

The use of reversible covalent bonding in a four-component assembly incorporating chiral alcohols was recently reported to give a method for determining the enantiomeric excess of the alcohols via CD spectroscopy. Experiments that probe the mechanism of this assembly, which consists of 2-formylpyridine (2-PA), dipicolylamine (DPA), Zn(ii) and alcohols to yield zinc complexes of tren-like ligands, are presented. The studies focus upon the mechanism of conversion of a hemi-aminal (1) to a hemi-aminal ether (3), thereby incorporating the fourth component. It was found that molecular sieves along with 3 to 4 equivalents of alcohol are required to drive the conversion of 1 to 3. Attempts to isolate an intermediate in this reaction via addition of strong Lewis acids led to the discovery of a five-membered ring pyridinium salt (5), but upon exposure to Zn(ii) and alcohols gave different products to the assembly. This was interpreted to support the intermediacy of an iminium species. Kinetic studies reveal that the conversion of 1 to 3 is zero-order in alcohol in large excesses of alcohol, supporting rate-determining formation of an intermediate prior to reaction with alcohol. Further, the magnitudes of the rate constants for interconversion of 1 and 3 are similar, supporting the notion that there are similar rate-determining steps (rds) for the forward and reverse reactions. Hammett plots show that the rds involves creation of a negative charge (interpreted as the loss of positive charge), supporting the notion that the decomplexation of Zn(ii) from the assemblies to generate apo-forms of 1 and 3 is rate-determining. The individual mechanistic conclusions are combined to create a qualitative reaction coordinate diagram for the interconversion of 1 and 3. PMID:25530834

Thermodynamics of various F420 coenzyme models as sources of electrons, hydride ions, hydrogen atoms and protons in acetonitrile.

PubMed

Xia, Ke; Shen, Guang-Bin; Zhu, Xiao-Qing

2015-06-14

32 F420 coenzyme models with alkylation of the three different N atoms (N1, N3 and N10) in the core structure (XFH(-)) were designed and synthesized and the thermodynamic driving forces (defined in terms of the molar enthalpy changes or the standard redox potentials in this work) of the 32 XFH(-) releasing hydride ions, hydrogen atoms and electrons, the thermodynamic driving forces of the 32 XFH˙ releasing protons and hydrogen atoms and the thermodynamic driving forces of XF(-)˙ releasing electrons in acetonitrile were determined using titration calorimetry and electrochemical methods. The effects of the methyl group at N1, N3 and N10 and a negative charge on N1 and N10 atoms on the six thermodynamic driving forces of the F420 coenzyme models and their related reaction intermediates were examined; the results show that seating arrangements of the methyl group and the negative charge have remarkably different effects on the thermodynamic properties of the F420 coenzyme models and their related reaction intermediates. The effects of the substituents at C7 and C8 on the six thermodynamic driving forces of the F420 coenzyme models and their related reaction intermediates were also examined; the results show that the substituents at C7 and C8 have good Hammett linear free energy relationships with the six thermodynamic parameters. Meanwhile, a reasonable determination of possible reactions between members of the F420 family and NADH family in vivo was given according to a thermodynamic analysis platform constructed using the elementary step thermodynamic parameter of F420 coenzyme model 2FH(-) and NADH model MNAH releasing hydride ions in acetonitrile. The information disclosed in this work can not only fill a gap in the chemical thermodynamics of F420 coenzyme models as a class of very important organic sources of electrons, hydride ions, hydrogen atoms and protons, but also strongly promote the fast development of the chemistry and applications of F420 coenzyme.

Graphite-supported gold nanoparticles as efficient catalyst for aerobic oxidation of benzylic amines to imines and N-substituted 1,2,3,4-tetrahydroisoquinolines to amides: synthetic applications and mechanistic study.

PubMed

So, Man-Ho; Liu, Yungen; Ho, Chi-Ming; Che, Chi-Ming

2009-10-05

Selective oxidation of amines using oxygen as terminal oxidant is an important area in green chemistry. In this work, we describe the use of graphite-supported gold nanoparticles (AuNPs/C) to catalyze aerobic oxidation of cyclic and acyclic benzylic amines to the corresponding imines with moderate-to-excellent substrate conversions (43-100%) and product yields (66-99%) (19 examples). Oxidation of N-substituted 1,2,3,4-tetrahydroisoquinolines in the presence of aqueous NaHCO3 solution gave the corresponding amides in good yields (83-93%) with high selectivity (up to amide/enamide=93:4) (6 examples). The same protocol can be applied to the synthesis of benzimidazoles from the reaction of o-phenylenediamines with benzaldehydes under aerobic conditions (8 examples). By simple centrifugation, AuNPs/C can be recovered and reused for ten consecutive runs for the oxidation of dibenzylamine to N-benzylidene(phenyl)methanamine without significant loss of catalytic activity and selectivity. This protocol "AuNPs/C+O2" can be scaled to the gram scale, and 8.9 g (84 % isolated yield) of 3,4-dihydroisoquinoline can be obtained from the oxidation of 10 g 1,2,3,4-tetrahydroisoquinoline in a one-pot reaction. Based on the results of kinetic studies, radical traps experiment, and Hammett plot, a mechanism involving the hydrogen-transfer reaction from amine to metal and oxidation of M-H is proposed.

Electronically Strongly Coupled Divinylheterocyclic-Bridged Diruthenium Complexes.

PubMed

Pfaff, Ulrike; Hildebrandt, Alexander; Korb, Marcus; Oßwald, Steffen; Linseis, Michael; Schreiter, Katja; Spange, Stefan; Winter, Rainer F; Lang, Heinrich

2016-01-11

Complexes [{Ru(CO)Cl(PiPr3 )2 }2 (μ-2,5-(CH-CH)2 -(c) C4 H2 E] (E=NR; R=C6 H4 -4-NMe2 (10 a), C6 H4 -4-OMe (10 b), C6 H4 -4-Me (10 c), C6 H5 (10 d), C6 H4 -4-CO2 Et (10 e), C6 H4 -4-NO2 (10 f), C6 H3 -3,5-(CF3 )2 (10 g), CH3 (11); E=O (12), S (13)) are discussed. The solid state structures of four alkynes and two complexes are reported. (Spectro)electrochemical studies show a moderate influence of the nature of the heteroatom and the electron-donating or -withdrawing substituents R in 10 a-g on the electrochemical and spectroscopic properties. The CVs display two consecutive one-electron redox events with ΔE°'=350-495 mV. A linear relationship between ΔE°' and the σp Hammett constant for 10 a-f was found. IR, UV/Vis/NIR and EPR studies for 10(+) -13(+) confirm full charge delocalization over the {Ru}CH-CH-heterocycle-CH-CH{Ru} backbone, classifying them as Class III systems according to the Robin and Day classification. DFT-optimized structures of the neutral complexes agree well with the experimental ones and provide insight into the structural consequences of stepwise oxidations. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Differential substrate behaviour of phenol and aniline derivatives during oxidation by horseradish peroxidase: kinetic evidence for a two-step mechanism.

PubMed

Gilabert, María Angeles; Hiner, Alexander N P; García-Ruiz, Pedro Antonio; Tudela, José; García-Molina, Francisco; Acosta, Manuel; García-Cánovas, Francisco; Rodríguez-López, José Neptuno

2004-06-01

The catalytic constant (k(cat)) and the second-order association constant of compound II with reducing substrate (k(5)) of horseradish peroxidase C (HRPC) acting on phenols and anilines have been determined from studies of the steady-state reaction velocities (V(0) vs. [S(0)]). Since k(cat)=k(2)k(6)/k(2)+k(6), and k(2) (the first-order rate constant for heterolytic cleavage of the oxygen-oxygen bond of hydrogen peroxide during compound I formation) is known, it has been possible to calculate the first-order rate constant for the transformation of each phenol or aniline by HRPC compound II (k(6)). The values of k(6) are quantitatively correlated to the sigma values (Hammett equation) and can be rationalized by an aromatic substrate oxidation mechanism in which the substrate donates an electron to the oxyferryl group in HRPC compound II, accompanied by two proton additions to the ferryl oxygen atom, one from the substrate and the other the protein or solvent. k(6) is also quantitatively correlated to the experimentally determined (13)C-NMR chemical shifts (delta(1)) and the calculated ionization potentials, E (HOMO), of the substrates. Similar dependencies were observed for k(cat) and k(5). From the kinetic analysis, the absolute values of the Michaelis constants for hydrogen peroxide and the reducing substrates (K(M)(H(2)O(2)) and K(M)(S)), respectively, were obtained.

Additivity rules using similarity models for chemical reactivity: calculation and interpretation of electrofugality and nucleofugality.

PubMed

Bentley, T William

2006-08-25

A recently proposed, multi-parameter correlation: log k (25 degrees C)=s(f) (Ef + Nf), where Ef is electrofugality and Nf is nucleofugality, for the substituent and solvent effects on the rate constants for solvolyses of benzhydryl and substituted benzhydryl substrates, is re-evaluated. A new formula (Ef=log k (RCl/EtOH/25 degrees C) -1.87), where RCl/EtOH refers to ethanolysis of chlorides, reproduces published values of Ef satisfactorily, avoids multi-parameter optimisations and provides additional values of Ef. From the formula for Ef, it is shown that the term (sfxEf) is compatible with the Hammett-Brown (rho+sigma+) equation for substituent effects. However, the previously published values of N(f) do not accurately account for solvent and leaving group effects (e.g. nucleofuge Cl or X), even for benzhydryl solvolyses; alternatively, if the more exact, two-parameter term, (sfxNf) is used, calculated effects are less accurate. A new formula (Nf=6.14 + log k(BX/any solvent/25 degrees C)), where BX refers to solvolysis of the parent benzhydryl as electrofuge, defines improved Nf values for benzhydryl substrates. The new formulae for Ef and Nf are consistent with an assumption that sf=1.00(,) and so improved correlations for benzhydryl substrates can be obtained from the additive formula: log k(RX/any solvent/25 degrees C)=(Ef + Nf). Possible extensions of this approach are also discussed.

Unusual pi-donating effects of pi-accepting substituents on the stabilities of benzylic cations: a theoretical study.

PubMed

Kim, Chang Kon; Han, In Suk; Ryu, Wang Sun; Lee, Hai Whang; Lee, Bon-Su; Kim, Chan Kyung

2006-02-23

The pi-donating effects of pi-accepting X-substituents in substituted benzylic cations, X-C(6)H(5)-CHR(+) where R = CF(3), H and OCH(3), and X = p-NH(2), p-OCH(3), p-CH(3), H, p-F, p-Cl, p-CHO, m-CN, p-CN, m-NO(2) or p-NO(2), have been studied theoretically by using isodesmic hydride transfer reactions at various levels of theory. It might be difficult to determine the pi-donating effects of pi-acceptors using the simple Hammett-type linear equation, because it is not sensitive enough to include small pi-donating effects. Therefore, this effect was estimated using the NBO deletion energy (DeltaE(D)) of the second-order charge-transfer interaction (DeltaE(ct)) between the pi-orbitals (or lone pair orbitals) of the X-substituent and the pi-orbitals of phenyl ring. The extents of pi-donating effects increased in the order X = p-NO(2) < p-CHO < p-CN < p-Cl for both neutral and cationic species, and these effects were found to be more important for para- than for meta-substituents. Moreover, this could represent a general trend for pi-donation by pi-acceptors. On the other hand, the effects of R-substituents on this pi-donating effect were found to be in the order R = OCH(3) < H congruent with CF(3), as predicted by natural resonance theory (NRT) analyses.

Electronic regioselectivity of diarylalkynes in cobalt-mediated Pauson-Khand reaction: an experimental and computational study with para- and meta-substituted diarylalkynes and norbornene.

PubMed

Fager-Jokela, Erika; Muuronen, Mikko; Patzschke, Michael; Helaja, Juho

2012-10-19

Both steric and electronic factors of substituted alkynes are known to guide α/β-cyclopentenone regioselectivity in the cobalt-mediated Pauson-Khand reaction (PKR). In synthetic applications of the PKR, the steric factors can often override or render possible electronic effects. This study examined alkyne-dependent electronic regioselectivity of cyclopentenone formation in PKR with norbornene and sterically equivalent, but electronically unsymmetrical, meta- and para-substituted diarylethynyls to unveil the role of electronic effects alone. In agreement with the literature reports, EDG para-substituted aryls, to some extent, favored the cyclopentenone α-regioisomer, while the EWG-substituted aryls correspondingly preferred the β-regioisomer. The cooperation of EGW and EDG in diaryl-substituted alkynes did not lead to any increased regioselectivities that could be expected by a "push-pull" effect. Both EWG and EDG meta-substituted aryls preferred the β-regioisomer, which was demonstrated by 3,5-dimethoxy- and 3,5-bis(trifluoromethyl)-1-phenylethynyls that yielded 1/1.6 and 1/2.0 α/β-regioselectivities, respectively. Theoretically, inspection of Hammett values of α-alkyne carbons gave qualitatively satisfactory prediction for para-substituted aryls but correlated only weakly with meta-substituted effects. Computational investigations at the DFT level revealed a correlation between NBO charges and the regioselectivity. Overall, the results suggest that the polarity of an alkyne, also designated by the relative polarization of aryl α-carbons, dictates the regioselectivity in the absence of steric effects.

QSAR analyses of 3-(4-benzylpiperidin-1-yl)-N-phenylpropylamine derivatives as potent CCR5 antagonists.

PubMed

Roy, Kunal; Leonard, J Thomas

2005-01-01

CCR5 receptor binding affinity of a series of 3-(4-benzylpiperidin-1-yl)propylamine congeners was subjected to QSAR study using the linear free energy related (LFER) model of Hansch. Appropriate indicator variables encoding different group contributions and different physicochemical variables such as hydrophobicity (pi), electronic (Hammett sigma), and steric (molar refractivity, STERIMOL values) parameters of phenyl ring substituents of the compounds were used as predictor variables. The Hansch analysis explores the importance of the lipophilicity and electron-donating substituents for the binding affinity. However, this method could not give more insight into the structure-activity relationships because of the diverse molecular features in the data set. 3D-QSAR analyses of the same data set using Molecular Shape Analysis (MSA), Receptor Surface Analysis (RSA), and Molecular Field Analysis (MFA) techniques were also performed. The best model with acceptable statistical quality was derived from the MSA, which showed the importance of the relative negative charge (RNCG): substituents with a high RNCG value have more binding affinity than the unsubstituted piperidine and phenyl (R1 position) congeners. The relative negative charge surface area (RNCS) is detrimental (e.g. R2 = 3,4-Cl2) for the activity. An increase in the length of the molecule in the Z dimension (Lz) is conducive (e.g. R3 = sulfonylmorpholino), while an increase in the area of the molecular shadow in the XZ plane (Sxz) is detrimental (e.g. R1 = N-c-hexylmethyl-5-oxopyrrolidin-3-yl) for the binding affinity. The presence of a chiral center makes the molecule less active (e.g. R1 = N-methyl-5-oxopyrrolidin-3-yl). An increase in the van der Waals area, the molecular volume, and the difference between the volume of the individual molecule and the shape reference compound are conducive (e.g. R3 = (CH3)2NSO2-) for the binding affinity. Substituents with higher JursFPSA_2 values (fractional charged partial surface area) like the N-methylsulfonylpiperidin-4-yl (R1 position) group have better binding affinity than the substituents such as 4-chlorophenylamino (R1 position). Unsubstituted piperidines (R1 position) with less JursFNSA_1 values have lower binding affinity than the 4-chlorophenyl substituted compounds. The MFA derived equation shows interaction energies at different grid points, while the RSA model shows the importance of hydrophobicity and charge at different regions of the molecules. The models were validated through the leave-one-out, leave-15%-out, and leave-25%-out cross-validation techniques. The developed models were also subjected to a randomization test (99% confidence level). Although the MSA derived models had excellent statistical qualities both for the training as well as test sets, RSA and MFA results for the test sets are not comparable statistically with the MSA derived models.

ABTS as an Electron Shuttle to Enhance the Oxidation Kinetics of Substituted Phenols by Aqueous Permanganate.

PubMed

Song, Yang; Jiang, Jin; Ma, Jun; Pang, Su-Yan; Liu, Yong-Ze; Yang, Yi; Luo, Cong-Wei; Zhang, Jian-Qiao; Gu, Jia; Qin, Wen

2015-10-06

In this study, it was, interestingly, found that 2,2'-azino-bis(3-ethylbenzothiazoline)-6-sulfonate (ABTS), a widely used electron shuttle, could greatly accelerate the oxidation of substituted phenols by potassium permanganate (Mn(VII)) in aqueous solutions at pH 5-9. This was attributed to the fact that these substituted phenols could be readily oxidized by the stable radical cation (ABTS(•+)), which was quickly produced from the oxidation of ABTS by Mn(VII). The reaction of Mn(VII) with ABTS exhibited second-order kinetics, with stoichiometries of ∼5:1 at pH 5-6 and ∼3:1 at pH 7-9, and the rate constants varied negligibly from pH 5 to 9 (k = (9.44 ± 0.21) × 10(4) M(-1) s(-1)). Comparatively, the reaction of ABTS(•+) with phenol showed biphasic kinetics. The second-order rate constants for the reactions of ABTS(•+) with substituted phenols obtained in the initial phase were strongly affected by pH, and they were several orders of magnitude higher than those for the reactions of Mn(VII) with substituted phenols at each pH. Good Hammett-type correlations were found for the reactions of ABTS(•+) with undissociated (log(k) = 2.82-4.31σ) and dissociated phenols (log(k) = 7.29-5.90σ). The stoichiometries of (2.2 ± 0.06):1 (ABTS(•+) in excess) and (1.38 ± 0.18):1 (phenol in excess) were achieved in the reaction of ABTS(•+) with phenol, but they exhibited no pH dependency.

Controlling the Conformational Energy of a Phenyl Group by Tuning the Strength of a Nonclassical CH···O Hydrogen Bond: The Case of 5-Phenyl-1,3-dioxane.

PubMed

Bailey, William F; Lambert, Kyle M; Stempel, Zachary D; Wiberg, Kenneth B; Mercado, Brandon Q

2016-12-16

Anancomeric 5-phenyl-1,3-dioxanes provide a unique opportunity to study factors that control conformation. Whereas one might expect an axial phenyl group at C(5) of 1,3-dioxane to adopt a conformation similar to that in axial phenylcyclohexane, a series of studies including X-ray crystallography, NOE measurements, and DFT calculations demonstrate that the phenyl prefers to lie over the dioxane ring in order to position an ortho-hydrogen to participate in a stabilizing, nonclassical CH···O hydrogen bond with a ring oxygen of the dioxane. Acid-catalyzed equilibration of a series of anancomeric 2-tert-butyl-5-aryl-1,3-dioxane isomers demonstrates that remote substituents on the phenyl ring affect the conformational energy of a 5-aryl-1,3-dioxane: electron-withdrawing substituents decrease the conformational energy of the aryl group, while electron-donating substituents increase the conformational energy of the group. This effect is correlated in a very linear way to Hammett substituent parameters. In short, the strength of the CH···O hydrogen bond may be tuned in a predictable way in response to the electron-withdrawing or electron-donating ability of substituents positioned remotely on the aryl ring. This effect may be profound: a 3,5-bis-CF 3 phenyl group at C(5) in 1,3-dioxane displays a pronounced preference for the axial orientation. The results are relevant to broader conformational issues involving heterocyclic systems bearing aryl substituents.

Linear Free Energy Relationships in Dinuclear Compounds. 2. Inductive Redox Tuning via Remote Substituents in Quadruply Bonded Dimolybdenum Compounds.

PubMed

Lin, Chun; Protasiewicz, John D.; Smith, Eugene T.; Ren, Tong

1996-10-23

Syntheses and characterizations are reported for dimolybdenum(II) compounds supported by the diarylformamidinate (ArNC(H)NAr(-)) ligand, where Ar is XC(6)H(4)(-), with X as p-OMe (1), H (2), m-OMe (3), p-Cl (4), m-Cl (5), m-CF(3) (6), p-COMe (7), p-CF(3) (8), or Ar is 3,4-Cl(2)C(6)H(3)(-) (9) or 3,5-Cl(2)C(6)H(3)(-) (10). The (quasi)reversible oxidation potentials measured for the Mo(2)(5+)/Mo(2)(4+) couple were found to correlate with the Hammett constant (sigma(X)) of the aryl substituents according to the following equation: DeltaE(1/2) = E(1/2)(X) - E(1/2)(H) = 87(8sigma(X)) mV. Molecular structure determinations of compounds 1, 2, 5, and 10 revealed an invariant core geometry around the Mo(2) center, with statistically identical Mo-Mo quadruple bond lengths of 2.0964(5), 2.0949[8], 2.0958(6), and 2.0965(5) Å, respectively. Magnetic anisotropies for compounds 1-10 estimated on the basis of (1)H NMR data were similar and unrelated to sigma(X). Similarity in UV-vis spectra was also found within the series, which, in conjunction with the features of both molecular structures and (1)H NMR spectra, was interpreted as the existence of a constant upper valence structure across the series. Results of Fenske-Hall calculations performed for several model compounds paralleled the experimental observations.

Sulphoxidation reaction catalysed by myeloperoxidase from human leucocytes.

PubMed

Capeillère-Blandin, C; Martin, C; Gaggero, N; Pasta, P; Carrea, G; Colonna, S

1998-10-01

The oxidation of alkyl aryl sulphides by myeloperoxidase (MPO) at the expense of hydrogen peroxide was investigated under steady-state conditions. The sulphide concentration effect was studied under saturating H2O2 concentrations at pH 5.0 and 20 degreesC. The kinetic constants, kcat and Km, of the different substrates were determined and the values were in the 1-10 s-1 range and around 43+/-26 microM respectively, whatever the sulphide considered. In the case of p-substituted thioanisoles, the oxidation rate was dependent upon the substituent effect. The correlation of log(kcat) with the substituent constants (sigma+ values) (Hammett equation) could be explained by a reaction mechanism involving the enzyme compound II and a sulphenium radical cation. This conclusion was also supported by spectrophotometric analysis of catalytic intermediates of the enzyme, showing the accumulation of compound II. Moreover, chiral HPLC analyses showed that MPO oxidation of alkyl aryl sulphides produced the corresponding (R)-sulphoxides with a low enantioselectivity (4-8%). Chloride ion effects on the MPO-catalysed oxygenation of sulphides were also studied. Chloride acted as a substrate for MPO and as an activator in MPO-catalysed sulphoxidation. Inhibition occurred at chloride concentrations above 120 mM, whereas below 120 mM, chloride increased the reaction rate when using p-tolyl methyl sulphide as the substrate. In the presence of 100 mM chloride the catalytic efficiency (kcat/Km) of MPO increased 3-4-fold, whatever the sulphide considered, but racemic products were obtained. These data have been interpreted in the light of known structural information on the accessibility of the distal haem cavity.

Reference scales for the characterization of cationic electrophiles and neutral nucleophiles.

PubMed

Mayr, H; Bug, T; Gotta, M F; Hering, N; Irrgang, B; Janker, B; Kempf, B; Loos, R; Ofial, A R; Remennikov, G; Schimmel, H

2001-10-03

Twenty-three diarylcarbenium ions and 38 pi-systems (arenes, alkenes, allyl silanes and stannanes, silyl enol ethers, silyl ketene acetals, and enamines) have been defined as basis sets for establishing general reactivity scales for electrophiles and nucleophiles. The rate constants of 209 combinations of these benzhydrylium ions and pi-nucleophiles, 85 of which are first presented in this article, have been subjected to a correlation analysis to determine the electrophilicity parameters E and the nucleophilicity parameters N and s as defined by the equation log k(20 degrees C) = s(N + E) (Mayr, H.; Patz, M. Angew. Chem., Int. Ed. Engl. 1994, 33, 938-957). Though the reactivity scales thus obtained cover more than 16 orders of magnitude, the individual rate constants are reproduced with a standard deviation of a factor of 1.19 (Table 1). It is shown that the reactivity parameters thus derived from the reactions of diarylcarbenium ions with pi-nucleophiles (Figure 3) are also suitable for characterizing the nucleophilic reactivities of alkynes, metal-pi-complexes, and hydride donors (Table 2) and for characterizing the electrophilic reactivities of heterosubstituted and metal-coordinated carbenium ions (Table 3). The reactivity parameters in Figure 3 are, therefore, recommended for the characterization of any new electrophiles and nucleophiles in the reactivity range covered. The linear correlation between the electrophilicity parameters E of benzhydryl cations and the corresponding substituent constants sigma(+) provides Hammett sigma(+) constants for 10 substituents from -1.19 to -2.11, i.e., in a range with only very few previous entries.

Conversion and origin of normal and abnormal temperature dependences of kinetic isotope effect in hydride transfer reactions.

PubMed

Zhu, Xiao-Qing; Li, Xiu-Tao; Han, Su-Hui; Mei, Lian-Rui

2012-05-18

The effects of substituents on the temperature dependences of kinetic isotope effect (KIE) for the reactions of the hydride transfer from the substituted 5-methyl-6-phenyl-5,6-dihydrophenanthridine (G-PDH) to thioxanthylium (TX(+)) in acetonitrile were examined, and the results show that the temperature dependences of KIE for the hydride transfer reactions can be converted by adjusting the nature of the substituents in the molecule of the hydride donor. In general, electron-withdrawing groups can make the KIE to have normal temperature dependence, but electron-donating groups can make the KIE to have abnormal temperature dependence. Thermodynamic analysis on the possible pathways of the hydride transfer from G-PDH to TX(+) in acetonitrile suggests that the transfers of the hydride anion in the reactions are all carried out by the concerted one-step mechanism whether the substituent is an electron-withdrawing group or an electron-donating group. But the examination of Hammett-type free energy analysis on the hydride transfer reactions supports that the concerted one-step hydride transfer is not due to an elementary chemical reaction. The experimental values of KIE at different temperatures for the hydride transfer reactions were modeled by using a kinetic equation formed according to a multistage mechanism of the hydride transfer including a returnable charge-transfer complex as the reaction intermediate; the real mechanism of the hydride transfer and the root that why the temperature dependences of KIE can be converted as the nature of the substituents are changed were discovered.

Exploring selectivity requirements for COX-2 versus COX-1 binding of 2-(5-phenyl-pyrazol-1-yl)-5-methanesulfonylpyridines using topological and physico-chemical parameters.

PubMed

Chakraborty, Santanu; Sengupta, Chandana; Roy, Kunal

2005-04-01

Considering the current need for development of selective cyclooxygenase-2 (COX-2) inhibitors, an attempt has been made to explore physico-chemical requirements of 2-(5-phenyl-pyrazol-1-yl)-5-methanesulfonylpyridines for binding with COX-1 and COX-2 enzyme subtypes and also to explore the selectivity requirements. In this study, E-states of different common atoms of the molecules (calculated according to Kier & Hall), first order valence connectivity and physicochemical parameters (hydrophobicity pi, Hammett sigma and molar refractivity MR of different ring substituents) were used as independent variables along with suitable dummy parameters in the stepwise regression method. The best equation describing COX-1 binding affinity [n = 25, Q2 = 0.606, R(a)2 = 0.702, R2 = 0.752, R = 0.867, s = 0.447, F = 15.2 (df 4, 20)] suggests that the COX-1 binding affinity increases in the presence of a halogen substituent at R1 position and a p-alkoxy or p-methylthio substituent at R2 position. Furthermore, a difluoromethyl group is preferred over a trifluoromethyl group at R position for the COX-1 binding. The best equation describing COX-2 binding affinity [n = 32, Q2 = 0.622, R(a)2= 0.692, R2 = 0.732, R = 0.856, s = 0.265, F = 18.4 (df 4, 27)] shows that the COX-2 binding affinity increases with the presence of a halogen substituent at R1 position and increase of size of R2 substituents. However, it decreases in case of simultaneous presence of 3-chloro and 4-methoxy groups on the phenyl nucleus and in the presence of highly lipophilic R2 substituents. The best selectivity relation [n = 25, Q2 = 0.455, R(a)2 = 0.605, R2 = 0.670, R = 0.819, s = 0.423, F = 10.2 (df 4, 20)] suggests that the COX-2 selectivity decreases in the presence of p-alkoxy group and electron-withdrawing para substituents at R2 position. Again, a trifluoro group is conductive for the selectivity instead of a difluoromethyl group at R position. Furthermore, branching may also play significant role in determining the selectivity as evidenced from the connectivity parameter.

Chemical stability of amorphous materials: specific and general media effects in the role of water in the degradation of freeze-dried zoniporide.

PubMed

Luthra, Suman A; Shalaev, Evgenyi Y; Medek, Ales; Hong, Jinyang; Pikal, Michael J

2012-09-01

The objective of the present work was to determine whether hydrolysis in a model lyophile was influenced by general media effects with water-changing properties of the medium or via a specific mechanism of water as a reactant. Four formulations of zoniporide and sucrose (1:10) were prepared with variable amounts of sorbitol [0%-25% (w/v) of total solids). These formulations were then equilibrated at 6% and 11% relative humidity using saturated salt solutions. The lyophile cakes were analyzed by differential scanning calorimetery (DSC), (isothermal microcalorimetry (IMC), solid- state nuclear magnetic resonance (ssNMR) spectroscopy, and ultraviolet-visible diffuse reflectance (DFR) spectroscopy. DSC and IMC were used to assess the global molecular mobility. ssNMR relaxation times were measured to access local mobility. The DFR was used to determine the solid-state acidity expressed as the Hammett acidity function. Stability of samples was evaluated at 40°C by monitoring potency and purity by high-performance liquid chromatography (HPLC). Results were interpreted in terms of the various roles of water: media effect, plasticization, polarity, and reactant. The kinetics of hydrolysis was observed to be correlated with either/both specific "chemical" effects, that is, water reactant as well as media effect, specifically global molecular mobility of the matrix. Increase in reaction rate with increase in water content is not linear and is a weaker dependence than in some hydrolytic reactions in organic solvents. A moderate amount of an inert plasticizer, sorbitol, conferred additional stabilization, possibly by restricting the amplitude and frequency of fast motions that are on a small length scale. Copyright © 2012 Wiley Periodicals, Inc.

Hemoglobin binding of aromatic amines: molecular dosimetry and quantitative structure-activity relationships for N-oxidation.

PubMed Central

Sabbioni, G

1993-01-01

Aromatic amines are important intermediates in industrial manufacturing. N-Oxidation to N-hydroxyarylamines is a key step in determining the genotoxic properties of aromatic amines. N-Hydroxyarylamines can form adducts with DNA, with tissue proteins, and with the blood proteins albumin and hemoglobin in a dose-dependent manner. The determination of hemoglobin adducts is a useful tool for biomonitoring exposed populations. We have established the hemoglobin binding index (HBI) [(mmole compound/mole hemoglobin)/(mmole compound/kg body weight)] of several aromatic amines in female Wistar rats. Including the values from other researchers obtained in the same rat strain, the logarithm of hemoglobin binding (logHBI) was plotted against the following parameters: the sum of the Hammett constants(sigma sigma = sigma p + sigma m), pKa, logP (octanol/water), the half-wave oxidation potential (E1/2), and the electronic descriptors of the amines and their corresponding nitrenium ions obtained by semi-empirical calculations (MNDO, AMI, and PM3), such as atomic charge densities, energies of the highest occupied molecular orbit and lowest occupied molecular orbit and their coefficients, the bond order of C-N, the dipole moments, and the reaction enthalpy [MNDOHF, AM1HF or PM3HF = Hf(nitrenium) - Hf(amine)]. The correlation coefficients were determined from the plots of all parameters against log HBI for all amines by means of linear regression analysis. The amines were classified in three groups: group 1, all parasubstituted amines (maximum, n = 9); group 2, all amines with halogens (maximun, n = 11); and group 3, all amines with alkyl groups (maximum, n = 13).(ABSTRACT TRUNCATED AT 250 WORDS) PMID:8319626

Sulphoxidation reaction catalysed by myeloperoxidase from human leucocytes.

PubMed Central

Capeillère-Blandin, C; Martin, C; Gaggero, N; Pasta, P; Carrea, G; Colonna, S

1998-01-01

The oxidation of alkyl aryl sulphides by myeloperoxidase (MPO) at the expense of hydrogen peroxide was investigated under steady-state conditions. The sulphide concentration effect was studied under saturating H2O2 concentrations at pH 5.0 and 20 degreesC. The kinetic constants, kcat and Km, of the different substrates were determined and the values were in the 1-10 s-1 range and around 43+/-26 microM respectively, whatever the sulphide considered. In the case of p-substituted thioanisoles, the oxidation rate was dependent upon the substituent effect. The correlation of log(kcat) with the substituent constants (sigma+ values) (Hammett equation) could be explained by a reaction mechanism involving the enzyme compound II and a sulphenium radical cation. This conclusion was also supported by spectrophotometric analysis of catalytic intermediates of the enzyme, showing the accumulation of compound II. Moreover, chiral HPLC analyses showed that MPO oxidation of alkyl aryl sulphides produced the corresponding (R)-sulphoxides with a low enantioselectivity (4-8%). Chloride ion effects on the MPO-catalysed oxygenation of sulphides were also studied. Chloride acted as a substrate for MPO and as an activator in MPO-catalysed sulphoxidation. Inhibition occurred at chloride concentrations above 120 mM, whereas below 120 mM, chloride increased the reaction rate when using p-tolyl methyl sulphide as the substrate. In the presence of 100 mM chloride the catalytic efficiency (kcat/Km) of MPO increased 3-4-fold, whatever the sulphide considered, but racemic products were obtained. These data have been interpreted in the light of known structural information on the accessibility of the distal haem cavity. PMID:9742209

Mechanistic Studies on the Cis to Trans Epimerization of Trisubstituted-1,2,3,4-Tetrahydro-β-Carbolines

PubMed Central

Van Linn, Michael L.; Cook, James M.

2010-01-01

It is well known that Nb-benzyl tryptophan alkyl esters undergo the Pictet-Spengler reaction with aldehydes to furnish both cis and trans 1,2,3,4-tetrahydro-β-carbolines, with the trans isomer predominating. Epimerization at C-1 took place under acidic conditions to produce, exclusively, the thermodynamically more stable trans diastereomer via internal asymmetric induction. Recent kinetic experiments provided insight into the cis to trans epimerization mechanism involved in the Pictet-Spengler reaction of 1,2,3-trisubsituted tetrahydro-β-carbolines. Since the epimerization reaction had been shown to be sensitive to electronic effects at C-1, the rate data for a series of 1-phenyl-substituted-1,2,3,4-tetrahydro-β-carbolines was investigated via a Hammett study. Analysis of the data supported the presence of a positively charged intermediate with a ρ value of −1.4, although the existence of an iminium ion intermediate or a carbocationic intermediate could not be determined from this data alone. Analysis of the rate of epimerization demonstrated first-order kinetics with respect to TFA following the initial protonation of the substrate. This observation was consistent with the formation of a doubly protonated intermediate as the rate determining step in the carbocation-mediated cis to trans epimerization process. In addition, the observed first-order rate dependence was inconsistent with the retro Pictet-Spengler mechanism since protonation at the indole-2 position was not rate determining as demonstrated by kinetic isotope effects. Based on this kinetic data, the retro Pictet-Spengler pathway was ruled out for the cis to trans epimerization of 1,2,3-trisubstituted-1,2,3,4-tetrahydro-β-carbolines, while the olefinic mechanism had been ruled out by experiments carried out in TFA-d. PMID:20429580

Fluid equations with nonlinear wave-particle resonances^

NASA Astrophysics Data System (ADS)

Mattor, Nathan

1997-11-01

We have derived fluid equations that include linear and nonlinear wave-particle resonance effects. This greatly extends previous ``Landau-fluid'' closures, which include linear Landau damping. (G.W. Hammett and F.W. Perkins, Phys. Rev. Lett. 64,) 3019 (1990).^, (Z. Chang and J. D. Callen, Phys. Fluids B 4,) 1167 (1992). The new fluid equations are derived with no approximation regarding nonlinear kinetic interaction, and so additionally include numerous nonlinear kinetic effects. The derivation starts with the electrostatic drift kinetic equation for simplicity, with a Maxwellian distribution function. Fluid closure is accomplished through a simple integration trick applied to the drift kinetic equation, using the property that the nth moment of Maxwellian distribution is related to the nth derivative. The result is a compact closure term appearing in the highest moment equation, a term which involves a plasma dispersion function of the electrostatic field and its derivatives. The new term reduces to the linear closures in appropriate limits, so both approaches retain linear Landau damping. But the nonlinearly closed equations have additional desirable properties. Unlike linear closures, the nonlinear closure retains the time-reversibility of the original kinetic equation. We have shown directly that the nonlinear closure retains at least two nonlinear resonance effects: wave-particle trapping and Compton scattering. Other nonlinear kinetic effects are currently under investigation. The new equations correct two previous discrepancies between kinetic and Landau-fluid predictions, including a propagator discrepancy (N. Mattor, Phys. Fluids B 4,) 3952 (1992). and a numerical discrepancy for the 3-mode shearless bounded slab ITG problem. (S. E. Parker et al.), Phys. Plasmas 1, 1461 (1994). ^* In collaboration with S. E. Parker, Department of Physics, University of Colorado, Boulder. ^ Work performed at LLNL under DoE contract No. W7405-ENG-48.

Evidence that the mechanism of antibody-catalysed hydrolysis of arylcarbamates can be determined by the structure of the immunogen used to elicit the catalytic antibody.

PubMed

Boucher, Guillaume; Said, Bilal; Ostler, Elizabeth L; Resmini, Marina; Brocklehurst, Keith; Gallacher, Gerard

2007-02-01

A kinetically homogeneous anti-phosphate catalytic antibody preparation was shown to catalyse the hydrolysis of a series of O-aryl N-methyl carbamates containing various substituents in the 4-position of the O-phenyl group. The specific nature of the antibody catalysis was demonstrated by the adherence of these reactions to the Michaelis-Menten equation, the complete inhibition by a hapten analogue, and the failure of the antibody to catalyse the hydrolysis of the 2-nitrophenyl analogue of the 4-nitrophenylcarbamate substrate. Hammett sigma-rho analysis suggests that both the non-catalysed and antibody-catalysed reactions proceed by mechanisms in which development of the aryloxyanion of the leaving group is well advanced in the transition state of the rate-determining step. This is probably the ElcB (elimination-addition) mechanism for the non-catalysed reaction, but for the antibody-catalysed reaction might be either ElcB or B(Ac)2 (addition-elimination), in which the elimination of the aryloxy group from the tetrahedral intermediate has become rate-determining. This result provides evidence of the dominance of recognition of phenolate ion character in the phosphate hapten in the elicitation process, and is discussed in connection with data from the literature that suggest a B(Ac)2 mechanism, with rate-determining formation of the tetrahedral intermediate for the hydrolysis of carbamate substrates catalysed by an antibody elicited by a phosphonamidate hapten in which phenolate anion character is minimized. The present paper contributes to the growing awareness that small differences in the structure of haptens can produce large differences in catalytic characteristics.

Hydrogen-Bonding Catalysis and Inhibition by Simple Solvents in the Stereoselective Kinetic Epoxide-Opening Spirocyclization of Glycal Epoxides to Form Spiroketals

PubMed Central

Wurst, Jacqueline M.; Liu, Guodong; Tan, Derek S.

2011-01-01

Mechanistic investigations of a MeOH-induced kinetic epoxide-opening spirocyclization of glycal epoxides have revealed dramatic, specific roles for simple solvents in hydrogen-bonding catalysis of this reaction to form spiroketal products stereoselectively with inversion of configuration at the anomeric carbon. A series of electronically-tuned C1-aryl glycal epoxides was used to study the mechanism of this reaction based on differential reaction rates and inherent preferences for SN2 versus SN1 reaction manifolds. Hammett analysis of reaction kinetics with these substrates is consistent with an SN2 or SN2-like mechanism (ρ = −1.3 vs. ρ = −5.1 for corresponding SN1 reactions of these substrates). Notably, the spirocyclization reaction is second-order dependent on MeOH and the glycal ring oxygen is required for second-order MeOH catalysis. However, acetone cosolvent is a first-order inhibitor of the reaction. A transition state consistent with the experimental data is proposed in which one equivalent of MeOH activates the epoxide electrophile via a hydrogen bond while a second equivalent of MeOH chelates the sidechain nucleophile and glycal ring oxygen. A paradoxical previous observation that decreased MeOH concentration leads to increased competing intermolecular methyl glycoside formation is resolved by the finding that this side reaction is only first-order dependent on MeOH. This study highlights the unusual abilities of simple solvents to act as hydrogen-bonding catalysts and inhibitors in epoxide-opening reactions, providing both stereoselectivity and discrimination between competing reaction manifolds. This spirocyclization reaction provides efficient, stereocontrolled access to spiroketals that are key structural motifs in natural products. PMID:21539313

Evidence that the mechanism of antibody-catalysed hydrolysis of arylcarbamates can be determined by the structure of the immunogen used to elicit the catalytic antibody

PubMed Central

Boucher, Guillaume; Said, Bilal; Ostler, Elizabeth L.; Resmini, Marina; Brocklehurst, Keith; Gallacher, Gerard

2006-01-01

A kinetically homogeneous anti-phosphate catalytic antibody preparation was shown to catalyse the hydrolysis of a series of O-aryl N-methyl carbamates containing various substituents in the 4-position of the O-phenyl group. The specific nature of the antibody catalysis was demonstrated by the adherence of these reactions to the Michaelis–Menten equation, the complete inhibition by a hapten analogue, and the failure of the antibody to catalyse the hydrolysis of the 2-nitrophenyl analogue of the 4-nitrophenylcarbamate substrate. Hammett σ–ρ analysis suggests that both the non-catalysed and antibody-catalysed reactions proceed by mechanisms in which development of the aryloxyanion of the leaving group is well advanced in the transition state of the rate-determining step. This is probably the ElcB (elimination–addition) mechanism for the non-catalysed reaction, but for the antibody-catalysed reaction might be either ElcB or BAc2 (addition–elimination), in which the elimination of the aryloxy group from the tetrahedral intermediate has become rate-determining. This result provides evidence of the dominance of recognition of phenolate ion character in the phosphate hapten in the elicitation process, and is discussed in connection with data from the literature that suggest a BAc2 mechanism, with rate-determining formation of the tetrahedral intermediate for the hydrolysis of carbamate substrates catalysed by an antibody elicited by a phosphonamidate hapten in which phenolate anion character is minimized. The present paper contributes to the growing awareness that small differences in the structure of haptens can produce large differences in catalytic characteristics. PMID:17020536

Series of structural and functional models for the ES (enzyme-substrate) complex of the Co(II)-containing quercetin 2,3-dioxygenase.

PubMed

Sun, Ying-Ji; Huang, Qian-Qian; Zhang, Jian-Jun

2014-03-17

A series of mononuclear Co(II)-flavonolate complexes [Co(II)L(R)(fla)] (L(R)H = 2-{[bis(pyridin-2-ylmethyl)amino]methyl}-p/m-R-benzoic acid; R = p-OMe (1), p-Me (2), m-Br (4), and m-NO2 (5); fla = flavonolate) were designed and synthesized as structural and functional models for the ES (enzyme-substrate) complexes to mimic the active site of the Co(II)-containing quercetin 2,3-dioxygenase (Co-2,3-QD). The metal center Co(II) ion in each complex shows a similar distorted octahedral geometry. The model complexes display high enzyme-type dioxygenation reactivity (oxidative O-heterocyclic ring opening of the coordinated substrate flavonolate) at low temperature, presumably due to the attached carboxylate group in the ligands. The reactivity exhibits a substituent group dependent order of -OMe (1) > -Me (2) > -H (3)14b > -Br (4) > -NO2 (5), and the Hammett plot is linear (ρ = -0.78). This can be explained as the electronic nature of the substituent group in the ligands may influence the conformation and redox potential of the bound flavonolate and finally bring different reactivity. The structures, properties, and reactivity of the model complexes show some dependence on the substituent group in the supporting model ligands, and there is some relationship among them. This study is the first example of a series of structural and functional ES models of Co-2,3-QD, with focus on the effects of the electronic nature of substituted groups and the carboxylate group of the ligands to the dioxygenation reactivity, that will provide important insights into the structure-property-reactivity relationship and the catalytic role of Co-2,3-QD.

Speciation of Reactive Sulfur Species and their Reactions with Alkylating Agents: Do we have any clue about what is present inside the cell?

PubMed

Bogdándi, Virág; Ida, Tomoaki; Sutton, Thomas R; Bianco, Christopher; Ditrói, Tamás; Koster, Grielof; Henthorn, Hillary A; Minnion, Magda; Toscano, John P; van der Vliet, Albert; Pluth, Michael D; Feelisch, Martin; Fukuto, Jon M; Akaike, Takaaki; Nagy, Péter

2018-06-17

Posttranslational modifications of cysteine (Cys) residues represent a major aspect of redox biology, and their reliable detection is key in providing mechanistic insights. The metastable character of these modifications and cell lysis-induced artifactual oxidation render current state-of-the-art protocols to rely on alkylation-based stabilization of labile Cys derivatives before cell/tissue rupture. An untested assumption in these procedures is that for all Cys derivatives alkylation rates are faster than their dynamic interchange. However, when the interconversion of Cys derivatives is not rate-limiting, then electrophilic labeling is under Curtin-Hammett control and hence the final alkylated mixture may not represent the speciation that prevailed before alkylation. We here present evidence that in the majority of cases, the speciation of alkylated polysulfide/thiol derivatives indeed depends on the experimental conditions. Our results reveal that alkylation perturbs sulfur speciation in both a concentration- and time-dependent manner, and that strong alkylating agents can cleave polysulfur chains. Moreover, we show that labeling of sulfenic acids with dimedone also affects Cys speciation, suggesting that part of the endogenous pool of products previously believed to represent sulfenic acid species may in fact represent polysulfides. These observations were obtained using buffered aqueous solutions of inorganic-, organic-, cysteine-, glutathione- and GAPDH-polysulfide species. Additional experiments in human plasma and serum revealed that monobromobimane can extract sulfide from the endogenous sulfur pool by shifting speciation equilibria, suggesting caution should be exercised when interpreting experimental results using this tool. We highlight methodological caveats potentially arising from these pitfalls and conclude that current derivatization strategies often fail to adequately capture physiologic speciation of sulfur species. This article is protected by copyright. All rights reserved.

Hydroxylation of p-substituted phenols by tyrosinase: Further insight into the mechanism of tyrosinase activity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Munoz-Munoz, Jose Luis; Berna, Jose; Garcia-Molina, Maria del Mar

2012-07-27

Highlights: Black-Right-Pointing-Pointer The action the copper complexes and tyrosinase on phenols is equivalent. Black-Right-Pointing-Pointer Isotope effect showed that nucleophilic attack to copper atom may be the slower step. Black-Right-Pointing-Pointer The value of {rho} (Hammett constant) supports an electrophilic aromatic substitution. Black-Right-Pointing-Pointer Data obtained in steady state pH 7 conditions support the mechanism of Scheme 1SM. -- Abstract: A study of the monophenolase activity of tyrosinase by measuring the steady state rate with a group of p-substituted monophenols provides the following kinetic information: k{sub cat}{sup m} and the Michaelis constant, K{sub M}{sup m}. Analysis of these data taking into account chemicalmore » shifts of the carbon atom supporting the hydroxyl group ({delta}) and {sigma}{sub p}{sup +}, enables a mechanism to be proposed for the transformation of monophenols into o-diphenols, in which the first step is a nucleophilic attack on the copper atom on the form E{sub ox} (attack of the oxygen of the hydroxyl group of C-1 on the copper atom) followed by an electrophilic attack (attack of the hydroperoxide group on the ortho position with respect to the hydroxyl group of the benzene ring, electrophilic aromatic substitution with a reaction constant {rho} of -1.75). These steps show the same dependency on the electronic effect of the substituent groups in C-4. Furthermore, a study of a solvent deuterium isotope effect on the oxidation of monophenols by tyrosinase points to an appreciable isotopic effect. In a proton inventory study with a series of p-substituted phenols, the representation of k{sub cat}{sup f{sub n}}/k{sub cat}{sup f{sub 0}} against n (atom fractions of deuterium), where k{sub cat}{sup f{sub n}} is the catalytic constant for a molar fraction of deuterium (n) and k{sub cat}{sup f{sub 0}} is the corresponding kinetic parameter in a water solution, was linear for all substrates. These results indicate that only one of the proton transfer processes from the hydroxyl groups involved the catalytic cycle is responsible for the isotope effects. We suggest that this step is the proton transfer from the hydroxyl group of C-1 to the peroxide of the oxytyrosinase form (E{sub ox}). After the nucleophilic attack, the incorporation of the oxygen in the benzene ring occurs by means of an electrophilic aromatic substitution mechanism in which there is no isotopic effect.« less

Radical Ions of 3-Styryl-quinoxalin-2-one Derivatives Studied by Pulse Radiolysis in Organic Solvents.

PubMed

Skotnicki, Konrad; De la Fuente, Julio R; Cañete, Álvaro; Berrios, Eduardo; Bobrowski, Krzysztof

2018-04-12

The absorption-spectral and kinetic behaviors of radical ions and neutral hydrogenated radicals of seven 3-styryl-quinoxalin-2(1 H)-one (3-SQ) derivatives, one without substituents in the styryl moiety, four others with electron-donating (R = -CH 3 , -OCH 3 , and -N(CH 3 ) 2 ) or electron-withdrawing (R = -OCF 3 ) substituents in the para position in their benzene ring, and remaining two with double methoxy substituents (-OCH 3 ), however, at different positions (meta/para and ortho/meta) have been studied by UV-vis spectrophotometric pulse radiolysis in neat acetonitrile saturated with argon (Ar) and oxygen (O 2 ) and in 2-propanol saturated with Ar, at room temperature. In acetonitrile solutions, the radical anions (4R-SQ •- ) are characterized by two absorption maxima located at λ max = 470-490 nm and λ max = 510-540 nm, with the respective molar absorption coefficients ε 470-490 = 8500-13 100 M -1 cm -1 and ε 510-540 = 6100-10 300 M -1 cm -1 , depending on the substituent (R). All 4R-SQ •- decay in acetonitrile via first-order kinetics, with the rate constants in the range (1.2-1.5) × 10 6 s -1 . In 2-propanol solutions, they decay predominantly through protonation by the solvent, forming neutral hydrogenated radicals (4R-SQH • ), which are characterized by weak absorption bands with λ max = 480-490 nm. Being oxygen-insensitive, the radical cations (4R-SQ •+ ) are characterized by a strong absorption with λ max = 450-630 nm, depending on the substituent (R). They are formed in a charge-transfer reaction between a radical cation derived from acetonitrile (ACN •+ ) and substituted 3-styryl-quinoxalin-2-one derivatives (4R-SQ) with a pseudo-first-order rate constant k = (2.7-4.7) × 10 5 s -1 measured in solutions containing 0.1 mM 4R-3-SQ. The Hammett equation plot gave a very small negative slope (ρ = -0.08), indicating a very weak influence of the substituents in the benzene ring on the rate of charge-transfer reaction. The decay of 4R-SQ •+ in Ar-saturated acetonitrile solutions occurs with a pseudo-first-order rate constant k = (1.6-6.2) × 10 4 s -1 and, in principle, is not affected by the presence of O 2 , suggesting charge-spin delocalization over the whole 3-SQ molecule. Most of the radiolytically generated transient spectra are reasonably well-reproduced by semiempirical PM3-ZINDO/S (for 4R-SQ •- ) and density functional theory quantum mechanics calculations employing M06-2x hybrid functional together with the def2-TZVP basis set (for 4R-SQ •+ ).

Equilibrium Acidities and Homolytic Bond Dissociation Enthalpies of the Acidic C-H Bonds in P-(Para-substituted benzyl)triphenylphosphonium Cations and Related Cations.

PubMed

Zhang, Xian-Man; Fry, Albert J.; Bordwell, Frederick G.

1996-06-14

Equilibrium acidities (pK(HA)) of six P-(para-substituted benzyl)triphenylphosphonium (p-GC(6)H(4)CH(2)PPh(3)(+)) cations, P-allyltriphenylphosphonium cation, P-cinnamyltriphenylphosphonium cation, and As-(p-cyanobenzyl)triphenylarsonium cation, together with the oxidation potentials [E(ox)(A(-))] of their conjugate anions (ylides) have been measured in dimethyl sulfoxide (DMSO) solution. The acidifying effects of the alpha-triphenylphosphonium groups on the acidic C-H bonds in toluene and propene were found to be ca 25 pK(HA) units (34 kcal/mol). Introduction of an electron-withdrawing group such as 4-NO(2), 4-CN, or 4-Br into the para position of the benzyl ring in p-GC(6)H(4)CH(2)PPh(3)(+) cations resulted in an additional acidity increase, but introduction of the 4-OEt electron-donating group decreases the acidity. The equilibrium acidities of p-GC(6)H(4)CH(2)PPh(3)(+) cations were nicely linearly correlated with the Hammett sigma(-) constants of the substituents (G) with a slope of 4.78 pK(HA) units (R(2) = 0.992) (Figure 1). Reversible oxidation potentials of the P-(para-substituted benzyl)triphenylphosphonium ylides were obtained by fast scan cyclic voltammetry. The homolytic bond dissociation enthalpies (BDEs) of the acidic C-H bonds in these cations, estimated by combining their equilibrium acidities with the oxidation potentials of their corresponding conjugate anions, showed that the alpha-Ph(3)P(+) groups have negligible stabilizing or destabilizing effects on the adjacent radicals. The equilibrium acidity of As-(p-cyanobenzyl)triphenylarsonium cation is 4 pK(HA) units weaker than that of P-(p-cyanobenzyl)triphenylphosphonium cation, but the BDE of the acidic C-H bond in As-(p-cyanobenzyl)triphenylarsonium cation is ca 2 kcal/mol higher than that in P-(p-cyanobenzyl)triphenylphosphonium cation.

Scope and Mechanistic Investigations on the Solvent-Controlled Regio- and Stereoselective Formation of Enol Esters from the Ruthenium-Catalyzed Coupling Reaction of Terminal Alkynes and Carboxylic Acids

PubMed Central

Yi, Chae S.; Gao, Ruili

2009-01-01

The ruthenium-hydride complex (PCy3)2(CO)RuHCl was found to be a highly effective catalyst for the alkyne-to-carboxylic acid coupling reaction to give synthetically useful enol ester products. Strong solvent effect was observed for the ruthenium catalyst in modulating the activity and selectivity; the coupling reaction in CH2Cl2 led to the regioselective formation of gem-enol ester products, while the stereoselective formation of (Z)-enol esters was obtained in THF. The coupling reaction was found to be strongly inhibited by PCy3. The coupling reaction of both PhCO2H/PhC≡CD and PhCO2D/PhC≡CH led to the extensive deuterium incorporation on the vinyl positions of the enol ester products. An opposite Hammett value was observed when the correlation of a series of para-substituted p-X-C6H4CO2H (X = OMe, CH3, H, CF3, CN) with phenylacetylene was examined in CDCl3 (ρ = +0.30) and THF (ρ = −0.68). Catalytically relevant Ru-carboxylate and –vinylidene-carboxylate complexes, (PCy3)2(CO)(Cl)Ru(κ2-O2CC6H4-p-OMe) and (PCy3)2(CO)(Cl)RuC(=CHPh)O2CC6H4-p-OMe, were isolated, and the structure of both complexes was completely established by X-ray crystallography. A detailed mechanism of the coupling reaction involving a rate-limiting C-O bond formation step was proposed on the basis of these kinetic and structural studies. The regioselective formation of the gem-enol ester products in CH2Cl2 was rationalized by a direct migratory insertion of the terminal alkyne via a Ru-carboxylate species, whereas the stereoselective formation of (Z)-enol ester products in THF was explained by invoking a Ru-vinylidene species. PMID:20161379

Voltammetry of 6,6'-dithiodinicotinic acid on a self-assembled phospholipid monolayer prive

NASA Astrophysics Data System (ADS)

Herrero, R.; Vilariño, T.; Barriada, J. L.; Sastre de Vicente, M. E.; López-Fonseca, J. M.; Moncelli, M. R.

1999-04-01

This paper reports a voltammetric study of 6,6'-dithiodinicotinic acid (CPDS) across a biomimetic membrane system consisting of a monolayer of dioleoylphosphatidylcholine, deposited on mercury. Because of the low solubility of this compound and its potential decomposition in alkaline media, estimation of pK values for the carboxyl and amino groups of the pyridine ring of the CPDS entailed using the Hammett equation. UV spectra seem to confirm the presence of the dianionic form of CPDS above pH=3-4. Differential capacity and cyclic voltammetry measurements were made in order to characterize the voltammetric behavior directly on mercury and through a monolayer of dioleoylphosphatidylcholine. Estimation of the CPDS hydrophobicity degree from the partition coefficient in octanol/ water suggests no penetration of the dianion into the monolayer and supports the fact that the named dianion undergoes protonation at the phospholipid/solution interface to give a neutral specie which penetration into the phospholipid region, favored by its higher hydrophobicity, is followed by electrochemical reduction at the mercury surface. Nous avons étudié par voltampérométrie le comportement de l'acide 6,6'-dithiodinicotinique (CPDS) sur l'électrode de mercure couverte par une monocouche de dioleoyl-phosphatidylcholine. La caractérisation électrochimique a été effectuée par des mesures de la capacité différentielle et par voltamétrie cyclique au dessus d'un pH 3-4. Le spectre UV paraît confirmer la présence de la forme dianionique du CPDS. Cependant les données expérimentales associées à une estimation de l'hydrophobicité de la forme dianionique suggèrent que seule la forme neutre du CPDS peut être réduite sur la surface de l'électrode.

A method to assess social sustainability of capture fisheries: An application to a Norwegian trawler

DOE Office of Scientific and Technical Information (OSTI.GOV)

Veldhuizen, L.J.L., E-mail: linda.veldhuizen@wur.nl; Berentsen, P.B.M.; Bokkers, E.A.M.

Social sustainability assessment of capture fisheries is, both in terms of method development and measurement, not well developed. The objective of this study, therefore, was to develop a method consisting of indicators and rubrics (i.e. categories that articulate levels of performance) to assess social sustainability of capture fisheries. This method was applied to a Norwegian trawler that targets cod and haddock in the northeast Atlantic. Based on previous research, 13 social sustainability issues were selected. To measure the state of these issues, 17 process and outcome indicators were determined. To interpret indicator values, rubrics were developed for each indicator, usingmore » standards set by international conventions or data retrieved from national statistics, industry agreements or scientific publications that explore rubric scales. The indicators and rubrics were subsequently used in a social sustainability assessment of a Norwegian trawler. This assessment indicated that overall, social sustainability of this trawler is relatively high, with high rubric scores, for example, for worker safety, provisions aboard for the crew and companies' salary levels. The assessment also indicated that the trawler could improve on healthy working environment, product freshness and fish welfare during capture. This application demonstrated that our method provides insight into social sustainability at the level of the vessel and can be used to identify potential room for improvement. This method is also promising for social sustainability assessment of other capture fisheries. - Highlights: • A method was developed for social sustainability assessment of capture fisheries. • This method entailed determining outcome and process indicators for important issues. • To interpret indicator values, a rubric was developed for each indicator. • Use of this method gives insight into social sustainability and improvement options. • This method is promising for social sustainability assessment of capture fisheries.« less

24 CFR 985.3 - Indicators, HUD verification methods and ratings.

Code of Federal Regulations, 2010 CFR

2010-04-01

... 24 Housing and Urban Development 4 2010-04-01 2010-04-01 false Indicators, HUD verification..., HUD verification methods and ratings. This section states the performance indicators that are used to assess PHA Section 8 management. HUD will use the verification method identified for each indicator in...

Similarity indices based on link weight assignment for link prediction of unweighted complex networks

NASA Astrophysics Data System (ADS)

Liu, Shuxin; Ji, Xinsheng; Liu, Caixia; Bai, Yi

2017-01-01

Many link prediction methods have been proposed for predicting the likelihood that a link exists between two nodes in complex networks. Among these methods, similarity indices are receiving close attention. Most similarity-based methods assume that the contribution of links with different topological structures is the same in the similarity calculations. This paper proposes a local weighted method, which weights the strength of connection between each pair of nodes. Based on the local weighted method, six local weighted similarity indices extended from unweighted similarity indices (including Common Neighbor (CN), Adamic-Adar (AA), Resource Allocation (RA), Salton, Jaccard and Local Path (LP) index) are proposed. Empirical study has shown that the local weighted method can significantly improve the prediction accuracy of these unweighted similarity indices and that in sparse and weakly clustered networks, the indices perform even better.

Method for characterization of the redox condition of cementitious materials

DOEpatents

Almond, Philip M.; Langton, Christine A.; Stefanko, David B.

2015-12-22

Disclosed are methods for determining the redox condition of cementitious materials. The methods are leaching methods that utilize an in situ redox indicator that is present in the cementitious materials as formed. The in situ redox indicator leaches from cementitious material and, when the leaching process is carried out under anaerobic conditions can be utilized to determine the redox condition of the material. The in situ redox indicator can exhibit distinct characteristics in the leachate depending upon the redox condition of the indicator.

Deterministic and fuzzy-based methods to evaluate community resilience

NASA Astrophysics Data System (ADS)

Kammouh, Omar; Noori, Ali Zamani; Taurino, Veronica; Mahin, Stephen A.; Cimellaro, Gian Paolo

2018-04-01

Community resilience is becoming a growing concern for authorities and decision makers. This paper introduces two indicator-based methods to evaluate the resilience of communities based on the PEOPLES framework. PEOPLES is a multi-layered framework that defines community resilience using seven dimensions. Each of the dimensions is described through a set of resilience indicators collected from literature and they are linked to a measure allowing the analytical computation of the indicator's performance. The first method proposed in this paper requires data on previous disasters as an input and returns as output a performance function for each indicator and a performance function for the whole community. The second method exploits a knowledge-based fuzzy modeling for its implementation. This method allows a quantitative evaluation of the PEOPLES indicators using descriptive knowledge rather than deterministic data including the uncertainty involved in the analysis. The output of the fuzzy-based method is a resilience index for each indicator as well as a resilience index for the community. The paper also introduces an open source online tool in which the first method is implemented. A case study illustrating the application of the first method and the usage of the tool is also provided in the paper.

Constrained multiple indicator kriging using sequential quadratic programming

NASA Astrophysics Data System (ADS)

Soltani-Mohammadi, Saeed; Erhan Tercan, A.

2012-11-01

Multiple indicator kriging (MIK) is a nonparametric method used to estimate conditional cumulative distribution functions (CCDF). Indicator estimates produced by MIK may not satisfy the order relations of a valid CCDF which is ordered and bounded between 0 and 1. In this paper a new method has been presented that guarantees the order relations of the cumulative distribution functions estimated by multiple indicator kriging. The method is based on minimizing the sum of kriging variances for each cutoff under unbiasedness and order relations constraints and solving constrained indicator kriging system by sequential quadratic programming. A computer code is written in the Matlab environment to implement the developed algorithm and the method is applied to the thickness data.

Implications of construction method and spatial scale on measures of the built environment.

PubMed

Strominger, Julie; Anthopolos, Rebecca; Miranda, Marie Lynn

2016-04-28

Research surrounding the built environment (BE) and health has resulted in inconsistent findings. Experts have identified the need to examine methodological choices, such as development and testing of BE indices at varying spatial scales. We sought to examine the impact of construction method and spatial scale on seven measures of the BE using data collected at two time points. The Children's Environmental Health Initiative conducted parcel-level assessments of 57 BE variables in Durham, NC (parcel N = 30,319). Based on a priori defined variable groupings, we constructed seven mutually exclusive BE domains (housing damage, property disorder, territoriality, vacancy, public nuisances, crime, and tenancy). Domain-based indices were developed according to four different index construction methods that differentially account for number of parcels and parcel area. Indices were constructed at the census block level and two alternative spatial scales that better depict the larger neighborhood context experienced by local residents: the primary adjacency community and secondary adjacency community. Spearman's rank correlation was used to assess if indices and relationships among indices were preserved across methods. Territoriality, public nuisances, and tenancy were weakly to moderately preserved across methods at the block level while all other indices were well preserved. Except for the relationships between public nuisances and crime or tenancy, and crime and housing damage or territoriality, relationships among indices were poorly preserved across methods. The number of indices affected by construction method increased as spatial scale increased, while the impact of construction method on relationships among indices varied according to spatial scale. We found that the impact of construction method on BE measures was index and spatial scale specific. Operationalizing and developing BE measures using alternative methods at varying spatial scales before connecting to health outcomes allows researchers to better understand how methodological decisions may affect associations between health outcomes and BE measures. To ensure that associations between the BE and health outcomes are not artifacts of methodological decisions, researchers would be well-advised to conduct sensitivity analysis using different construction methods. This approach may lead to more robust results regarding the BE and health outcomes.

Evaluation of three indices for biofilm accumulation on complete dentures.

PubMed

Paranhos, Helena de Freitas Oliveira; Lovato da Silva, Claudia Helena; de Souza, Raphael Freitas; Pontes, Karina Matthes de Freitas

2010-03-01

The objective of this study was to evaluate the accuracy and reproducibility of three complete denture biofilm indices (Prosthesis Hygiene Index; Jeganathan et al. Index; Budtz-Jørgensen Index) by means of a computerised comparison method. Clinical studies into denture hygiene have employed a large number of biofilm indices among their outcome variables. However, the knowledge about the validity of these indices is still scarce. Sixty-two complete denture wearers were selected. The internal surfaces of the upper complete dentures were stained (5% erythrosine) and photographed. The slides were projected on paper, and the biofilm indices were applied over the photos by means of a scoring method. For the computerised method, the areas (total and biofilm-covered) were measured by dedicated software (Image Tool). In addition, to compare the results of the computerised method and Prosthetic Hygiene Index, a new scoring scale (including four and five graded) was introduced. For the Jeganathan et al. and Budtz-Jørgensen indices, the original scales were used. Values for each index were compared with the computerised method by the Friedman test. Their reproducibility was measured by means of weighed kappa. Significance for both tests was set at 0.05. The indices tested provided similar mean measures but they tended to overestimate biofilm coverage when compared with the computerised method (p < 0.001). Agreement between the Prosthesis Hygiene Index and the computerised method was not significant, regardless of the scale used. Jeghanathan et al. Index showed weak agreement, and consistent results were found for Budtz-Jorgensen Index (kappa = 0.19 and 0.39 respectively). Assessment of accuracy for the biofilm indices showed instrument bias that was similar among the tested methods. Weak inter-instrument reproducibility was found for the indices, except for the Budtz-Jørgensen Index. This should be the method of choice for clinical studies when more sophisticated approaches are not possible.

A multiple indicator solution approach to endogeneity in discrete-choice models for environmental valuation.

PubMed

Mariel, Petr; Hoyos, David; Artabe, Alaitz; Guevara, C Angelo

2018-08-15

Endogeneity is an often neglected issue in empirical applications of discrete choice modelling despite its severe consequences in terms of inconsistent parameter estimation and biased welfare measures. This article analyses the performance of the multiple indicator solution method to deal with endogeneity arising from omitted explanatory variables in discrete choice models for environmental valuation. We also propose and illustrate a factor analysis procedure for the selection of the indicators in practice. Additionally, the performance of this method is compared with the recently proposed hybrid choice modelling framework. In an empirical application we find that the multiple indicator solution method and the hybrid model approach provide similar results in terms of welfare estimates, although the multiple indicator solution method is more parsimonious and notably easier to implement. The empirical results open a path to explore the performance of this method when endogeneity is thought to have a different cause or under a different set of indicators. Copyright © 2018 Elsevier B.V. All rights reserved.

A chemical risk ranking and scoring method for the selection of harmful substances to be specially controlled in occupational environments.

PubMed

Shin, Saemi; Moon, Hyung-Il; Lee, Kwon Seob; Hong, Mun Ki; Byeon, Sang-Hoon

2014-11-20

This study aimed to devise a method for prioritizing hazardous chemicals for further regulatory action. To accomplish this objective, we chose appropriate indicators and algorithms. Nine indicators from the Globally Harmonized System of Classification and Labeling of Chemicals were used to identify categories to which the authors assigned numerical scores. Exposure indicators included handling volume, distribution, and exposure level. To test the method devised by this study, sixty-two harmful substances controlled by the Occupational Safety and Health Act in Korea, including acrylamide, acrylonitrile, and styrene were ranked using this proposed method. The correlation coefficients between total score and each indicator ranged from 0.160 to 0.641, and those between total score and hazard indicators ranged from 0.603 to 0.641. The latter were higher than the correlation coefficients between total score and exposure indicators, which ranged from 0.160 to 0.421. Correlations between individual indicators were low (-0.240 to 0.376), except for those between handling volume and distribution (0.613), suggesting that each indicator was not strongly correlated. The low correlations between each indicator mean that the indicators and independent and were well chosen for prioritizing harmful chemicals. This method proposed by this study can improve the cost efficiency of chemical management as utilized in occupational regulatory systems.

Validity of Eye Movement Methods and Indices for Capturing Semantic (Associative) Priming Effects

ERIC Educational Resources Information Center

Odekar, Anshula; Hallowell, Brooke; Kruse, Hans; Moates, Danny; Lee, Chao-Yang

2009-01-01

Purpose: The purpose of this investigation was to evaluate the usefulness of eye movement methods and indices as a tool for studying priming effects by verifying whether eye movement indices capture semantic (associative) priming effects in a visual cross-format (written word to semantically related picture) priming paradigm. Method: In the…

Assessment of composite index methods for agricultural vulnerability to climate change.

PubMed

Wiréhn, Lotten; Danielsson, Åsa; Neset, Tina-Simone S

2015-06-01

A common way of quantifying and communicating climate vulnerability is to calculate composite indices from indicators, visualizing these as maps. Inherent methodological uncertainties in vulnerability assessments, however, require greater attention. This study examines Swedish agricultural vulnerability to climate change, the aim being to review various indicator approaches for assessing agricultural vulnerability to climate change and to evaluate differences in climate vulnerability depending on the weighting and summarizing methods. The reviewed methods are evaluated by being tested at the municipal level. Three weighting and summarizing methods, representative of climate vulnerability indices in general, are analysed. The results indicate that 34 of 36 method combinations differ significantly from each other. We argue that representing agricultural vulnerability in a single composite index might be insufficient to guide climate adaptation. We emphasize the need for further research into how to measure and visualize agricultural vulnerability and into how to communicate uncertainties in both data and methods. Copyright © 2015 Elsevier Ltd. All rights reserved.

The transmission of fluctuation among price indices based on Granger causality network

NASA Astrophysics Data System (ADS)

Sun, Qingru; Gao, Xiangyun; Wen, Shaobo; Chen, Zhihua; Hao, Xiaoqing

2018-09-01

In this paper, we provide a method of statistical physics to analyze the fluctuation of transmission by constructing Granger causality network among price indices (PIGCN) from a systematical perspective, using complex network theory combined with Granger causality method. In economic system, there are numerous price indices, of which the relationships are extreme complicated. Thus, time series data of 6 types of price indices of China, including 113 kinds of sub price indices, are selected as example of empirical study. Through the analysis of the structure of PIGCN, we identify important price indices with high transmission range, high intermediation capacity, high cohesion and the fluctuation transmission path of price indices, respectively. Furthermore, dynamic relationships among price indices are revealed. Based on these results, we provide several policy implications for monitoring the diffusion of risk of price fluctuation. Our method can also be used to study the price indices of other countries, which is generally applicable.

A simplified method of performance indicators development for epidemiological surveillance networks--application to the RESAPATH surveillance network.

PubMed

Sorbe, A; Chazel, M; Gay, E; Haenni, M; Madec, J-Y; Hendrikx, P

2011-06-01

Develop and calculate performance indicators allows to continuously follow the operation of an epidemiological surveillance network. This is an internal evaluation method, implemented by the coordinators in collaboration with all the actors of the network. Its purpose is to detect weak points in order to optimize management. A method for the development of performance indicators of epidemiological surveillance networks was developed in 2004 and was applied to several networks. Its implementation requires a thorough description of the network environment and all its activities to define priority indicators. Since this method is considered to be complex, our objective consisted in developing a simplified approach and applying it to an epidemiological surveillance network. We applied the initial method to a theoretical network model to obtain a list of generic indicators that can be adapted to any surveillance network. We obtained a list of 25 generic performance indicators, intended to be reformulated and described according to the specificities of each network. It was used to develop performance indicators for RESAPATH, an epidemiological surveillance network of antimicrobial resistance in pathogenic bacteria of animal origin in France. This application allowed us to validate the simplified method, its value in terms of practical implementation, and its level of user acceptance. Its ease of use and speed of application compared to the initial method argue in favor of its use on broader scale. Copyright © 2011 Elsevier Masson SAS. All rights reserved.

METHODS, VALUE, LIMITATIONS, AND INDICATIONS OF THE RADIOLOGICAL STUDY OF THE LYMPHATIC SYSTEM BY LYMPHOGRAPHY (in Italian)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rossi, L.

1963-01-01

The methods, limitations, and indications in the radiological study of the lymphatic system are reviewed. The value of the various methods is indicated. The topics discussed are lymphadenographic techniques, radiographic antomy, physiology of the lymphatic system, physiopathology of the lymphatic system, modifications of the lymph system, lymph nodes, and the thoracic duct. 824 references. (J.S.R.)

50 CFR 218.11 - Permissible methods of taking.

Code of Federal Regulations, 2013 CFR

2013-10-01

... 50 Wildlife and Fisheries 10 2013-10-01 2013-10-01 false Permissible methods of taking. 218.11... Range Complex) § 218.11 Permissible methods of taking. (a) Under Letters of Authorization issued... following species, by the indicated method of take and the indicated number of times: (1) Level B Harassment...

Compression embedding

DOEpatents

Sandford, M.T. II; Handel, T.G.; Bradley, J.N.

1998-07-07

A method and apparatus for embedding auxiliary information into the digital representation of host data created by a lossy compression technique and a method and apparatus for constructing auxiliary data from the correspondence between values in a digital key-pair table with integer index values existing in a representation of host data created by a lossy compression technique are disclosed. The methods apply to data compressed with algorithms based on series expansion, quantization to a finite number of symbols, and entropy coding. Lossy compression methods represent the original data as ordered sequences of blocks containing integer indices having redundancy and uncertainty of value by one unit, allowing indices which are adjacent in value to be manipulated to encode auxiliary data. Also included is a method to improve the efficiency of lossy compression algorithms by embedding white noise into the integer indices. Lossy compression methods use loss-less compression to reduce to the final size the intermediate representation as indices. The efficiency of the loss-less compression, known also as entropy coding compression, is increased by manipulating the indices at the intermediate stage. Manipulation of the intermediate representation improves lossy compression performance by 1 to 10%. 21 figs.

Compression embedding

DOEpatents

Sandford, II, Maxwell T.; Handel, Theodore G.; Bradley, Jonathan N.

1998-01-01

A method and apparatus for embedding auxiliary information into the digital representation of host data created by a lossy compression technique and a method and apparatus for constructing auxiliary data from the correspondence between values in a digital key-pair table with integer index values existing in a representation of host data created by a lossy compression technique. The methods apply to data compressed with algorithms based on series expansion, quantization to a finite number of symbols, and entropy coding. Lossy compression methods represent the original data as ordered sequences of blocks containing integer indices having redundancy and uncertainty of value by one unit, allowing indices which are adjacent in value to be manipulated to encode auxiliary data. Also included is a method to improve the efficiency of lossy compression algorithms by embedding white noise into the integer indices. Lossy compression methods use loss-less compression to reduce to the final size the intermediate representation as indices. The efficiency of the loss-less compression, known also as entropy coding compression, is increased by manipulating the indices at the intermediate stage. Manipulation of the intermediate representation improves lossy compression performance by 1 to 10%.

Instrumental Landing Using Audio Indication

NASA Astrophysics Data System (ADS)

Burlak, E. A.; Nabatchikov, A. M.; Korsun, O. N.

2018-02-01

The paper proposes an audio indication method for presenting to a pilot the information regarding the relative positions of an aircraft in the tasks of precision piloting. The implementation of the method is presented, the use of such parameters of audio signal as loudness, frequency and modulation are discussed. To confirm the operability of the audio indication channel the experiments using modern aircraft simulation facility were carried out. The simulated performed the instrument landing using the proposed audio method to indicate the aircraft deviations in relation to the slide path. The results proved compatible with the simulated instrumental landings using the traditional glidescope pointers. It inspires to develop the method in order to solve other precision piloting tasks.

Evaluation of Rock Joint Coefficients

NASA Astrophysics Data System (ADS)

Audy, Ondřej; Ficker, Tomáš

2017-10-01

A computer method for evaluation of rock joint coefficients is described and several applications are presented. The method is based on two absolute numerical indicators that are formed by means of the Fourier replicas of rock joint profiles. The first indicator quantifies the vertical depth of profiles and the second indicator classifies wavy character of profiles. The absolute indicators have replaced the formerly used relative indicators that showed some artificial behavior in some cases. This contribution is focused on practical computations testing the functionality of the newly introduced indicators.

Apparatus and methods for detecting chemical permeation

DOEpatents

Vo-Dinh, Tuan

1994-01-01

Apparatus and methods for detecting the permeation of hazardous or toxic chemicals through protective clothing are disclosed. The hazardous or toxic chemicals of interest do not possess the spectral characteristic of luminescence. The apparatus and methods utilize a spectrochemical modification technique to detect the luminescence quenching of an indicator compound which upon permeation of the chemical through the protective clothing, the indicator is exposed to the chemical, thus indicating chemical permeation.

A novel method of estimation of lipophilicity using distance-based topological indices: dominating role of equalized electronegativity.

PubMed

Agrawal, Vijay K; Gupta, Madhu; Singh, Jyoti; Khadikar, Padmakar V

2005-03-15

Attempt is made to propose yet another method of estimating lipophilicity of a heterogeneous set of 223 compounds. The method is based on the use of equalized electronegativity along with topological indices. It was observed that excellent results are obtained in multiparametric regression upon introduction of indicator parameters. The results are discussed critically on the basis various statistical parameters.

Issues in the construction of wealth indices for the measurement of socio-economic position in low-income countries

PubMed Central

Howe, Laura D; Hargreaves, James R; Huttly, Sharon RA

2008-01-01

Background Epidemiological studies often require measures of socio-economic position (SEP). The application of principal components analysis (PCA) to data on asset-ownership is one popular approach to household SEP measurement. Proponents suggest that the approach provides a rational method for weighting asset data in a single indicator, captures the most important aspect of SEP for health studies, and is based on data that are readily available and/or simple to collect. However, the use of PCA on asset data may not be the best approach to SEP measurement. There remains concern that this approach can obscure the meaning of the final index and is statistically inappropriate for use with discrete data. In addition, the choice of assets to include and the level of agreement between wealth indices and more conventional measures of SEP such as consumption expenditure remain unclear. We discuss these issues, illustrating our examples with data from the Malawi Integrated Household Survey 2004–5. Methods Wealth indices were constructed using the assets on which data are collected within Demographic and Health Surveys. Indices were constructed using five weighting methods: PCA, PCA using dichotomised versions of categorical variables, equal weights, weights equal to the inverse of the proportion of households owning the item, and Multiple Correspondence Analysis. Agreement between indices was assessed. Indices were compared with per capita consumption expenditure, and the difference in agreement assessed when different methods were used to adjust consumption expenditure for household size and composition. Results All indices demonstrated similarly modest agreement with consumption expenditure. The indices constructed using dichotomised data showed strong agreement with each other, as did the indices constructed using categorical data. Agreement was lower between indices using data coded in different ways. The level of agreement between wealth indices and consumption expenditure did not differ when different consumption equivalence scales were applied. Conclusion This study questions the appropriateness of wealth indices as proxies for consumption expenditure. The choice of data included had a greater influence on the wealth index than the method used to weight the data. Despite the limitations of PCA, alternative methods also all had disadvantages. PMID:18234082

50 CFR 216.272 - Permissible methods of taking.

Code of Federal Regulations, 2013 CFR

2013-10-01

... 50 Wildlife and Fisheries 10 2013-10-01 2013-10-01 false Permissible methods of taking. 216.272... (SOCAL Range Complex) § 216.272 Permissible methods of taking. (a) Under Letters of Authorization issued... species, by the indicated method of take and the indicated number of times: (1) Level B Harassment (±10...

50 CFR 218.2 - Permissible methods of taking.

Code of Federal Regulations, 2013 CFR

2013-10-01

... 50 Wildlife and Fisheries 10 2013-10-01 2013-10-01 false Permissible methods of taking. 218.2... (VACAPES Range Complex) § 218.2 Permissible methods of taking. (a) Under Letters of Authorization issued... following species, by the indicated method of take and the indicated number of times: (1) Level B Harassment...

50 CFR 218.21 - Permissible methods of taking.

Code of Federal Regulations, 2013 CFR

2013-10-01

... 50 Wildlife and Fisheries 10 2013-10-01 2013-10-01 false Permissible methods of taking. 218.21... Permissible methods of taking. (a) Under Letters of Authorization issued pursuant to §§ 216.106 of this... species, by the indicated method of take and the indicated number of times: (1) Level B Harassment: (i...

50 CFR 218.112 - Permissible methods of taking.

Code of Federal Regulations, 2013 CFR

2013-10-01

... 50 Wildlife and Fisheries 10 2013-10-01 2013-10-01 false Permissible methods of taking. 218.112....112 Permissible methods of taking. (a) Under Letters of Authorization issued pursuant to §§ 216.106...) and (5) of this section by the indicated method of take and the indicated number of times (estimated...

50 CFR 218.102 - Permissible methods of taking.

Code of Federal Regulations, 2013 CFR

2013-10-01

... 50 Wildlife and Fisheries 10 2013-10-01 2013-10-01 false Permissible methods of taking. 218.102...) § 218.102 Permissible methods of taking. (a) Under Letters of Authorization issued pursuant to §§ 216... the indicated method of take and the indicated number of times (estimated based on the authorized...

50 CFR 216.272 - Permissible methods of taking.

Code of Federal Regulations, 2012 CFR

2012-10-01

... 50 Wildlife and Fisheries 10 2012-10-01 2012-10-01 false Permissible methods of taking. 216.272... (SOCAL Range Complex) § 216.272 Permissible methods of taking. (a) Under Letters of Authorization issued... species, by the indicated method of take and the indicated number of times: (1) Level B Harassment (±10...

50 CFR 218.122 - Permissible methods of taking.

Code of Federal Regulations, 2013 CFR

2013-10-01

... 50 Wildlife and Fisheries 10 2013-10-01 2013-10-01 false Permissible methods of taking. 218.122...) § 218.122 Permissible methods of taking. (a) Under Letters of Authorization issued pursuant to §§ 216... indicated method of take and the indicated number of times (estimated based on the authorized amounts of...

Linking quality indicators to clinical trials: an automated approach

PubMed Central

Coiera, Enrico; Choong, Miew Keen; Tsafnat, Guy; Hibbert, Peter; Runciman, William B.

2017-01-01

Abstract Objective Quality improvement of health care requires robust measurable indicators to track performance. However identifying which indicators are supported by strong clinical evidence, typically from clinical trials, is often laborious. This study tests a novel method for automatically linking indicators to clinical trial registrations. Design A set of 522 quality of care indicators for 22 common conditions drawn from the CareTrack study were automatically mapped to outcome measures reported in 13 971 trials from ClinicalTrials.gov. Intervention Text mining methods extracted phrases mentioning indicators and outcome phrases, and these were compared using the Levenshtein edit distance ratio to measure similarity. Main Outcome Measure Number of care indicators that mapped to outcome measures in clinical trials. Results While only 13% of the 522 CareTrack indicators were thought to have Level I or II evidence behind them, 353 (68%) could be directly linked to randomized controlled trials. Within these 522, 50 of 70 (71%) Level I and II evidence-based indicators, and 268 of 370 (72%) Level V (consensus-based) indicators could be linked to evidence. Of the indicators known to have evidence behind them, only 5.7% (4 of 70) were mentioned in the trial reports but were missed by our method. Conclusions We automatically linked indicators to clinical trial registrations with high precision. Whilst the majority of quality indicators studied could be directly linked to research evidence, a small portion could not and these require closer scrutiny. It is feasible to support the process of indicator development using automated methods to identify research evidence. PMID:28651340

Compression embedding

DOEpatents

Sandford, M.T. II; Handel, T.G.; Bradley, J.N.

1998-03-10

A method of embedding auxiliary information into the digital representation of host data created by a lossy compression technique is disclosed. The method applies to data compressed with lossy algorithms based on series expansion, quantization to a finite number of symbols, and entropy coding. Lossy compression methods represent the original data as integer indices having redundancy and uncertainty in value by one unit. Indices which are adjacent in value are manipulated to encode auxiliary data. By a substantially reverse process, the embedded auxiliary data can be retrieved easily by an authorized user. Lossy compression methods use loss-less compressions known also as entropy coding, to reduce to the final size the intermediate representation as indices. The efficiency of the compression entropy coding, known also as entropy coding is increased by manipulating the indices at the intermediate stage in the manner taught by the method. 11 figs.

Compression embedding

DOEpatents

Sandford, II, Maxwell T.; Handel, Theodore G.; Bradley, Jonathan N.

1998-01-01

A method of embedding auxiliary information into the digital representation of host data created by a lossy compression technique. The method applies to data compressed with lossy algorithms based on series expansion, quantization to a finite number of symbols, and entropy coding. Lossy compression methods represent the original data as integer indices having redundancy and uncertainty in value by one unit. Indices which are adjacent in value are manipulated to encode auxiliary data. By a substantially reverse process, the embedded auxiliary data can be retrieved easily by an authorized user. Lossy compression methods use loss-less compressions known also as entropy coding, to reduce to the final size the intermediate representation as indices. The efficiency of the compression entropy coding, known also as entropy coding is increased by manipulating the indices at the intermediate stage in the manner taught by the method.

Method and apparatus for reading meters from a video image

DOEpatents

Lewis, Trevor J.; Ferguson, Jeffrey J.

1997-01-01

A method and system to enable acquisition of data about an environment from one or more meters using video images. One or more meters are imaged by a video camera and the video signal is digitized. Then, each region of the digital image which corresponds to the indicator of the meter is calibrated and the video signal is analyzed to determine the value indicated by each meter indicator. Finally, from the value indicated by each meter indicator in the calibrated region, a meter reading is generated. The method and system offer the advantages of automatic data collection in a relatively non-intrusive manner without making any complicated or expensive electronic connections, and without requiring intensive manpower.

Spatial weighting approach in numerical method for disaggregation of MDGs indicators

NASA Astrophysics Data System (ADS)

Permai, S. D.; Mukhaiyar, U.; Satyaning PP, N. L. P.; Soleh, M.; Aini, Q.

2018-03-01

Disaggregation use to separate and classify the data based on certain characteristics or on administrative level. Disaggregated data is very important because some indicators not measured on all characteristics. Detailed disaggregation for development indicators is important to ensure that everyone benefits from development and support better development-related policymaking. This paper aims to explore different methods to disaggregate national employment-to-population ratio indicator to province- and city-level. Numerical approach applied to overcome the problem of disaggregation unavailability by constructing several spatial weight matrices based on the neighbourhood, Euclidean distance and correlation. These methods can potentially be used and further developed to disaggregate development indicators into lower spatial level even by several demographic characteristics.

Synthetic, Infrared, 1Hand 13CNMR Spectral Studies on N-(p-Substituted Phenyl)-p-Substituted Benzenesulphonamides, p-X'C6H4SO2NH- (p-XC6H4), where X' or X = H, CH3, C2H5, F, Cl or Br

NASA Astrophysics Data System (ADS)

Gowda, B. Thimme; Jayalakshmi, K. L.; Shetty, Mahesha

2004-05-01

Thirty N-(p-substituted phenyl)-p-substituted benzenesulphonamides of the general formula, p-X'C6H4SO2NH(p-XC6H4), where X' or X = H, CH3, C2H5, F, Cl or Br, are synthesised and their infrared spectra in the solid state and 1H and 13C NMR spectra in solution are measured. The N-H stretching vibrational frequencies, νN-H vary in the range 3334 - 3219 cm-1, while the asymmetric and symmetric SO2 vibrations appear in the ranges 1377 - 1311 cm-1 and 1182 - 1151 cm-1, respectively. The compounds exhibit S-N and C-N stretching vibrational absorptions in the ranges 937 - 898 cm-1 and 1310 - 1180 cm-1, respectively. There are no particular trends in the variation of these frequencies on substitution with either electron withdrawing or electron donating groups. The 1H and 13C chemical shifts of N-(p-substituted phenyl)-p-substituted benzenesulphonamides, are assigned to various protons and carbons of the two benzene rings. Further, incremental shifts of the ring protons and carbons due to -SO2NH(p-XC6H4) groups in the compounds of the formula, C6H5SO2NH(p-XC6H4), and p-X'C6H4SO2- and p-X'C6H4SO2NH- groups in the compounds of the formula, p-X'C6H4SO2NH(C6H5) are computed and used to calculate the 1H and 13C chemical shifts of the parallely substituted compounds of the general formula p-X'C6H4SO2NH(p-XC6H4). The computed values agree well with the observed chemical shifts. The above incremental shifts are found to correlate with the Hammett substituent parameters.

Tuning metal-to-metal charge transfer of mixed-valence complexes containing ferrocenylpyridine and rutheniumammines via solvent donicity and substituent effects.

PubMed

Chen, Y J; Kao, C H; Lin, S J; Tai, C C; Kwan, K S

2000-01-24

A homogeneous series of heterobimetallic complexes of [R-Fc(4-py)Ru(NH3)5](PF6)2 (R = H, Et, Br, acetyl; Fc(4-py) = 4-ferrocenylpyridine) have been prepared and characterized. The mixed-valence species generated in situ using ferrocenium hexafluorophosphate as the oxidant show class II behavior, and the oxidized sites are ruthenium centered. deltaE(1/2), E(1/2)(Fe(III)/Fe(II)) - E(1/2)(Ru(III)/Ru(II)), an upper limit for deltaGo that is an energetic difference between the donor and acceptor sites, changes sharply and linearly with Gutmann solvent donor number (DN) and Hammett substituent constants (sigma). The solvent-dependent and substituent-dependent intervalence transfer bands were found to vary almost exclusively with deltaE(1/2). The activation energy for the optical electron transfer versus deltaE(1/2) plot yields a common nuclear reorganization energy (lambda) of 0.74 +/- 0.04 eV for this series. The equation that allows one to incorporate the effect of both solvent donicity and substituents on optical electron transfer is Eop = lambda + deltaGo, where deltaGo = (deltaGo)intrinsic + (deltaGo)solvent donicity + (deltaGo)substituent effect (deltaGo )intinnsic with a numerical value of 0.083 +/- 0.045 eV was obtained from the intercept of the deltaE(1/2) of [H-Fc(4-py)Ru(NH3)5]2+,3+,4+ versus DN plot. (deltaGo)solvent donicity was obtained from the average slopes of the deltaE(1/2) of [R-Fc-(4-py)Ru(NH3)5]2+,3+,4+ versus DN plot, and (deltaGo)substituent effect was obtained from the average slopes of the corresponding deltaE(1/2) versus sigma plot. The empirical equation allows one to finely tune Eop of this series to Eop = 0.82 + 0.019(DN) + 0.44sigma eV at 298 K, and the discrepancy between the calculated and experimental data is less than 6%.

Human and rat liver phenol sulfotransferase: structure-activity relationships for phenolic substrates.

PubMed

Campbell, N R; Van Loon, J A; Sundaram, R S; Ames, M M; Hansch, C; Weinshilboum, R

1987-12-01

Phenol sulfotransferase (PST) catalyzes the sulfate conjugation of many phenolic drugs. Human liver contains thermostable (TS) and thermolabile forms of PST. Ion exchange chromatography shows that two isozymes of TS PST (peaks I and II) are present in human liver preparations. Rat liver contains four forms of PST that can be separated by ion exchange chromatography. Quantitative structure-activity relationship (QSAR) analysis was used to study phenolic substrates for both human and rat liver PST. Thirty-six substituted phenols were tested as substrates for partially purified human liver TS PST peak I. QSAR analysis resulted in derivation of the following equation: log 1/Km = 0.92 (+/- 0.18)log P - 1.48 (+/- 0.38)MR'4 - 0.64 (+/- 0.41)MR3 + 1.04 (+/- 0.63)MR2 + 0.67(+/- 0.44) sigma- + 4.03 (+/- 0.42). In this equation Km is the Michaelis constant, P is the octanol-water partition coefficient, MR is the molar refractivity of substituents at the 2-, 3-, and 4-positions, and sigma- is the Hammett constant. Values of log 1/Km calculated with this equation were highly correlated with log 1/Km values (r = 0.950) that were observed experimentally. Nine phenols were also tested as substrates for partially purified human liver TS PST peak II. Log 1/Km values for these compounds were significantly correlated for the two isozymes of TS PST (r = 0.992, p less than 0.001). QSAR analysis was also used to derive equations that described the behavior of phenolic substrates for rat liver PST forms I and II. These equations differed substantially from the equation derived for compounds tested with human liver TS PST peak I. Therefore, the characteristics of the active sites of human liver TS PST peak I and rat liver PST forms I and II appear to differ. Application of these equations may make it possible to predict Km values of phenolic substrates for human liver TS PST and for rat liver PST forms I and II.

Theory and Simulation of Rotational Shear Stabilization of Turbulence

NASA Astrophysics Data System (ADS)

Waltz, R. E.

1997-11-01

Stabilization of turbulence in tokamaks by E×B rotational shear is now thought to be a key mechanism leading to both L/H-edge and core transport barriers. Numerical simulations of ion temperature gradient (ITG) mode transport with gyrofluid flux tude codes first lead to the approximate rule that the critical E×B rotational shear rate γE = r/q partial (q v_E×B/r)/partialr ≈ γ_max the maximum of ballooning mode growth rates γ0 in the absence of the E×B shear.(R.E. Waltz, G.D. Kerbel, J Milovich, and G.W. Hammett, Phys. Plasmas 2) (1995) 2408; Phys. Plasmas 1 (1994) 2229. The present work revisits the (ρ arrow 0) flux tube simulations reformulated terms in of Floquet ballooning modes which convect in the ballooning mode angle θ0 arrow θ0 + γ_E/hats t. This formulation avoids linearly unstable and spurious ``box modes" which arise from discretizing in θ0 and illustrates the true nonlinear nature of the stabilization in toroidal geometry. The eigenmodes can be linearly stable(J.W. Connor, J.B. Taylor, and H.R Wilson, Phys. Rev. Lett. 70) (1993) 1803. at vanishingly small γE when θ_0-averaged γ_0(θ_0) <= 0, yet Floquet mode convective amplification with nonlinear coupling allows turbulence to persists unless γE ≈ γ_max. The rule seems to hold at vanishing magnetic shear hats. Going to finite ρ^* with diamagnetic velocities comparable to v_E× B, likely requires the total mode phase velocity shear (not just the v_E× B Doppler part) r/q partial (q v_mode/r)/partial r >= γ_max. ``Profile curvature" (x^2 profile variations in γ_0) works against stabilization from ``profile shear" (x-variation). From studies of global eigenmodes of the ``ballooning-Schrödinger equation,"(R.L. Dewar, Plasma Phys. and Control. Fusion 39) (1997) 437. the profile curvature is generally not important if ρ^* is typically small. Further studies of profile stabilization use the 2d full radius ITG code.(X. Garbet and R.E. Waltz, Phys. of Plasmas 3) (1996) 1898.

Magnetogenesis and magnetothermal equilibria in turbulent galaxy-cluster plasmas

NASA Astrophysics Data System (ADS)

Schekochihin, Alexander

2011-04-01

We do not know the exact mechanism of magnetic field generation in magnetised weakly collisional (or collisionless) turbulent plasma. We do know that large-scale MHD motions in such plasmas are subject to fast small-scale kinetic instabilities (mirror and firehose) triggered (at high beta) by pressure anisotropies and that these anisotropies will always arise in a turbulent plasma. Therefore, standard MHD equations cannot be used to describe the turbulent dynamo. I will argue that the likely scenario in such plasmas is explosively fast growth of magnetic fluctuations to dynamical levels. I will further argue that if an efficient turbulent dynamo is assumed, radiative cooling in such plasmas can be balanced in a thermally stable way by turbulent heating, whose rate is set by the condition that plasma locally remains in a marginal state with respect to the mirror and firehose instabilities. This thermal stability suggests that a cooling catastrophe is not inevitable, although whether this old problem is thus resolved depends on whether a number of assumptions about the nonlinear behaviour of the instabilities, strength of turbulence and efficiency of the dynamo are borne out by first- principles microphysical theory, simulations or plasma experiments.References:A. A. Schekochihin, M. Brueggen, L. Feretti, M. W. Kunz, and L. Rudnick, Space Sci. Rev., in preparation (2011)M. W. Kunz, A. A. Schekochihin, S. C. Cowley, J. J. Binney, and J. S. Sanders, Mon. Not. R. Astron. Soc., in press (2011) [e-print arXiv:1003.2719]M. S. Rosin, A. A. Schekochihin, F. Rincon, and S. C. Cowley, Mon. Not. R. Astron. Soc., in press (2011) [e-print arXiv:1002.4017]A. A. Schekochihin, S. C. Cowley, F. Rincon, and M. S. Rosin, Mon. Not. R. Astron. Soc. 405, 291 (2010) [e-print arXiv:0912.1359]A. A. Schekochihin, S. C. Cowley, R. M. Kulsrud, M. S. Rosin, and T. Heinemann, Phys. Rev. Lett. 100, 081301 (2008) [e-print arXiv:0709.3828]A. A. Schekochihin and S. C. Cowley, Phys. Plasmas 13, 056501 (2006) [e-print astro-ph/0601246]A. A. Schekochihin, S. C. Cowley, R. M. Kulsrud, G. W. Hammett, and P. Sharma, Astrophys. J. 629, 139 (2005) [e-print astro-ph/0501362

Strong Inhibition of O-Atom Transfer Reactivity for Mn(IV)(O)(π-Radical-Cation)(Lewis Acid) versus Mn(V)(O) Porphyrinoid Complexes.

PubMed

Zaragoza, Jan Paulo T; Baglia, Regina A; Siegler, Maxime A; Goldberg, David P

2015-05-27

The oxygen atom transfer (OAT) reactivity of two valence tautomers of a Mn(V)(O) porphyrinoid complex was compared. The OAT kinetics of Mn(V)(O)(TBP8Cz) (TBP8Cz = octakis(p-tert-butylphenyl)corrolazinato(3-)) reacting with a series of triarylphosphine (PAr3) substrates were monitored by stopped-flow UV-vis spectroscopy, and revealed second-order rate constants ranging from 16(1) to 1.43(6) × 10(4) M(-1) s(-1). Characterization of the OAT transition state analogues Mn(III)(OPPh3)(TBP8Cz) and Mn(III)(OP(o-tolyl)3)(TBP8Cz) was carried out by single-crystal X-ray diffraction (XRD). A valence tautomer of the closed-shell Mn(V)(O)(TBP8Cz) can be stabilized by the addition of Lewis and Brønsted acids, resulting in the open-shell Mn(IV)(O)(TBP8Cz(•+)):LA (LA = Zn(II), B(C6F5)3, H(+)) complexes. These Mn(IV)(O)(π-radical-cation) derivatives exhibit dramatically inhibited rates of OAT with the PAr3 substrates (k = 8.5(2) × 10(-3) - 8.7 M(-1) s(-1)), contrasting the previously observed rate increase of H-atom transfer (HAT) for Mn(IV)(O)(TBP8Cz(•+)):LA with phenols. A Hammett analysis showed that the OAT reactivity for Mn(IV)(O)(TBP8Cz(•+)):LA is influenced by the Lewis acid strength. Spectral redox titration of Mn(IV)(O)(TBP8Cz(•+)):Zn(II) gives Ered = 0.69 V vs SCE, which is nearly +700 mV above its valence tautomer Mn(V)(O)(TBP8Cz) (Ered = -0.05 V). These data suggest that the two-electron electrophilicity of the Mn(O) valence tautomers dominate OAT reactivity and do not follow the trend in one-electron redox potentials, which appear to dominate HAT reactivity. This study provides new fundamental insights regarding the relative OAT and HAT reactivity of valence tautomers such as M(V)(O)(porph) versus M(IV)(O)(porph(•+)) (M = Mn or Fe) found in heme enzymes.

Structures and properties of molecular torsion balances to decipher the nature of substituent effects on the aromatic edge-to-face interaction.

PubMed

Gardarsson, Haraldur; Schweizer, W Bernd; Trapp, Nils; Diederich, François

2014-04-14

Various recent computational studies initiated this systematic re-investigation of substituent effects on aromatic edge-to-face interactions. Five series of Tröger base derived molecular torsion balances (MTBs), initially introduced by Wilcox and co-workers, showing an aromatic edge-to-face interaction in the folded, but not in the unfolded form, were synthesized. A fluorine atom or a trifluoromethyl group was introduced onto the edge ring in ortho-, meta-, and para-positions to the C-H group interacting with the face component. The substituents on the face component were varied from electron-donating to electron-withdrawing. Extensive X-ray crystallographic data allowed for a discussion on the conformational behavior of the torsional balances in the solid state. While most systems adopt the folded conformation, some were found to form supramolecular intercalative dimers, lacking the intramolecular edge-to-face interaction, which is compensated by the gain of aromatic π-stacking interactions between four aryl rings of the two molecular components. This dimerization does not take place in solution. The folding free enthalpy ΔG(fold) of all torsion balances was determined by (1)H NMR measurements by using 10 mM solutions of samples in CDCl3 and C6D6. Only the ΔG(fold) values of balances bearing an edge-ring substituent in ortho-position to the interacting C-H show a steep linear correlation with the Hammett parameter (σ(meta)) of the face-component substituent. Thermodynamic analysis using van't Hoff plots revealed that the interaction is enthalpy-driven. The ΔG(fold) values of the balances, in addition to partial charge calculations, suggest that increasing the polarization of the interacting C-H group makes a favorable contribution to the edge-to-face interaction. The largest contribution, however, seems to originate from local direct interactions between the substituent in ortho-position to the edge-ring C-H and the substituted face ring. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Articles of protective clothing adapted for deflecting chemical permeation and methods therefor

DOEpatents

Vo-Dinh, Tuan

1996-01-01

Apparatus and methods for detecting the permeation of hazardous or toxic chemicals through protective clothing are disclosed. The hazardous or toxic chemicals of interest do not possess the spectral characteristic of luminescence. The apparatus and methods utilize a spectrochemical modification technique to detect the luminescence quenching of an indicator compound which upon permeation of the chemical through the protective clothing, the indicator is exposed to the chemical, thus indicating chemical permeation.

Community assessment techniques and the implications for rarefaction and extrapolation with Hill numbers.

PubMed

Cox, Kieran D; Black, Morgan J; Filip, Natalia; Miller, Matthew R; Mohns, Kayla; Mortimor, James; Freitas, Thaise R; Greiter Loerzer, Raquel; Gerwing, Travis G; Juanes, Francis; Dudas, Sarah E

2017-12-01

Diversity estimates play a key role in ecological assessments. Species richness and abundance are commonly used to generate complex diversity indices that are dependent on the quality of these estimates. As such, there is a long-standing interest in the development of monitoring techniques, their ability to adequately assess species diversity, and the implications for generated indices. To determine the ability of substratum community assessment methods to capture species diversity, we evaluated four methods: photo quadrat, point intercept, random subsampling, and full quadrat assessments. Species density, abundance, richness, Shannon diversity, and Simpson diversity were then calculated for each method. We then conducted a method validation at a subset of locations to serve as an indication for how well each method captured the totality of the diversity present. Density, richness, Shannon diversity, and Simpson diversity estimates varied between methods, despite assessments occurring at the same locations, with photo quadrats detecting the lowest estimates and full quadrat assessments the highest. Abundance estimates were consistent among methods. Sample-based rarefaction and extrapolation curves indicated that differences between Hill numbers (richness, Shannon diversity, and Simpson diversity) were significant in the majority of cases, and coverage-based rarefaction and extrapolation curves confirmed that these dissimilarities were due to differences between the methods, not the sample completeness. Method validation highlighted the inability of the tested methods to capture the totality of the diversity present, while further supporting the notion of extrapolating abundances. Our results highlight the need for consistency across research methods, the advantages of utilizing multiple diversity indices, and potential concerns and considerations when comparing data from multiple sources.

50 CFR 216.172 - Permissible methods of taking.

Code of Federal Regulations, 2012 CFR

2012-10-01

... 50 Wildlife and Fisheries 10 2012-10-01 2012-10-01 false Permissible methods of taking. 216.172... Permissible methods of taking. (a) Under Letters of Authorization issued pursuant to §§ 216.106 and 216.177... indicated method of take and the indicated number of times: (1) Level B Harassment (±10 percent of the...

50 CFR 216.172 - Permissible methods of taking.

Code of Federal Regulations, 2013 CFR

2013-10-01

... 50 Wildlife and Fisheries 10 2013-10-01 2013-10-01 false Permissible methods of taking. 216.172... Permissible methods of taking. (a) Under Letters of Authorization issued pursuant to §§ 216.106 and 216.177... indicated method of take and the indicated number of times: (1) Level B Harassment (±10 percent of the...

What is a good index? Problems with statistically based indicators and the Malmquist index as alternative

USDA-ARS?s Scientific Manuscript database

Conventional multivariate statistical methods have been used for decades to calculate environmental indicators. These methods generally work fine if they are used in a situation where the method can be tailored to the data. But there is some skepticism that the methods might fail in the context of s...

Comparison of nutritional status indicators according to feeding methods in patients with acute stroke.

PubMed

Kim, Sanghee; Byeon, Youngsoon

2014-04-01

Feeding methods for patients with acute stroke differ based on their ability to swallow; therefore, it is necessary to determine whether these methods deliver enough nourishment to these patients. Although nutrition could affect recovery from acute stroke, it is often overlooked. Indicators of nutritional status are important for the nutritional assessment of patients. The purpose of this study was to compare changes in nutritional indicators with various feeding methods in patients with acute stroke. Data on 261 patients with acute stroke who were admitted to a stroke unit in 2010 and met the inclusion criteria of the study were retrospectively analyzed. For comparative analysis, we investigated the participants' National Institutes of Health Stroke Scale score, feeding methods using the Modified Gugging Swallowing Screen, and indicators of nutritional status, such as body mass index, pre-albumin level, albumin level, total lymphocyte count, and total protein level. All nutritional indicators were compared at the time of admission to the stroke unit and at 7 days after admission. At the time of admission, indicators of nutritional status were within normal ranges in all feeding groups (tube, dysphagia, and general diet). At 7 days after admission, pre-albumin (P = 0.003), albumin (P = 0.001), and total protein (P = 0.000) values in the tube feeding group were below the normal range, and the pre-albumin value and total lymphocyte count were below the normal range in the dysphagia diet group (P = 0.027). The values for all nutritional indicators were within normal limits in the general diet group. Indicators of nutritional status change according to the swallowing ability of patients with acute stroke. At 7 days after admission to the stroke unit, patients with severe dysphagia had higher levels of indicators of malnutrition. Health care providers should consider whether the feeding method of each patient with stroke provides suitable nourishment. Additionally, it is important to know why these indicators vary based on swallowing abilities and what these patients require for adequate nutrition.

Gold in natural water: A method of determination by solvent extraction and electrothermal atomization

USGS Publications Warehouse

McHugh, J.B.

1984-01-01

A method has been developed using electrothermal atomization to effectively determine the amount of gold in natural water within the nanogram range. The method has four basic steps: (1) evaporating a 1-L sample; (2) putting it in hydrobromic acid-bromine solution; (3) extracting the sample with methyl-isobutyl-ketone; and (4) determining the amount of gold using an atomic absorption spectrophotometer. The limit of detection is 0.001 ??g gold per liter. Results from three studies indicate, respectively, that the method is precise, effective, and free of interference. Specifically, a precision study indicates that the method has a relative standard deviation of 16-18%; a recovery study indicates that the method recovers gold at an average of 93%; and an interference study indicates that the interference effects are eliminated with solvent extraction and background correction techniques. Application of the method to water samples collected from 41 sites throughout the Western United States and Alaska shows a gold concentration range of < 0.001 to 0.036 ??g gold per liter, with an average of 0.005 ??g/L. ?? 1984.

Articles of protective clothing adapted for deflecting chemical permeation and methods there for

DOEpatents

Vo-Dinh, T.

1996-02-27

Apparatus and methods for detecting the permeation of hazardous or toxic chemicals through protective clothing are disclosed. The hazardous or toxic chemicals of interest do not possess the spectral characteristic of luminescence. The apparatus and methods utilize a spectrochemical modification technique to detect the luminescence quenching of an indicator compound which upon permeation of the chemical through the protective clothing, the indicator is exposed to the chemical, thus indicating chemical permeation. 12 figs.

Method for characterization of the rate of movement of an oxidation front in cementitious materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Almond, Philip M.; Langton, Christine A.; Stefanko, David B.

2016-03-01

Disclosed are methods for determining the redox condition of cementitious materials. The methods are leaching methods that utilize a redox active transition metal indicator that is present in the cementitious material and exhibits variable solubility depending upon the oxidation state of the indicator. When the leaching process is carried out under anaerobic conditions, the presence or absence of the indicator in the leachate can be utilized to determine the redox condition of and location of the oxidation front in the material that has been subjected to the leaching process.

Method and apparatus for reading meters from a video image

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lewis, T.J.; Ferguson, J.J.

1995-12-31

A method and system enable acquisition of data about an environment from one or more meters using video images. One or more meters are imaged by a video camera and the video signal is digitized. Then, each region of the digital image which corresponds to the indicator of the meter is calibrated and the video signal is analyzed to determine the value indicated by each meter indicator. Finally, from the value indicated by each meter indicator in the calibrated region, a meter reading is generated. The method and system offer the advantages of automatic data collection in a relatively non-intrusivemore » manner without making any complicated or expensive electronic connections, and without requiring intensive manpower.« less

Method and apparatus for reading meters from a video image

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lewis, T.J.; Ferguson, J.J.

1997-09-30

A method and system to enable acquisition of data about an environment from one or more meters using video images. One or more meters are imaged by a video camera and the video signal is digitized. Then, each region of the digital image which corresponds to the indicator of the meter is calibrated and the video signal is analyzed to determine the value indicated by each meter indicator. Finally, from the value indicated by each meter indicator in the calibrated region, a meter reading is generated. The method and system offer the advantages of automatic data collection in a relativelymore » non-intrusive manner without making any complicated or expensive electronic connections, and without requiring intensive manpower. 1 fig.« less

Development and validation of a stability indicating HPLC method for determination of lisinopril, lisinopril degradation product and parabens in the lisinopril extemporaneous formulation.

PubMed

Beasley, Christopher A; Shaw, Jessica; Zhao, Zack; Reed, Robert A

2005-03-09

The purpose of the research described herein was to develop and validate a stability-indicating HPLC method for lisinopril, lisinopril degradation product (DKP), methyl paraben and propyl paraben in a lisinopril extemporaneous formulation. The method developed in this report is selective for the components listed above, in the presence of the complex and chromatographically rich matrix presented by the Bicitra and Ora-Sweet SF formulation diluents. The method was also shown to have adequate sensitivity with a detection limit of 0.0075 microg/mL (0.03% of lisinopril method concentration). The validation elements investigated showed that the method has acceptable specificity, recovery, linearity, solution stability, and method precision. Acceptable robustness indicates that the assay method remains unaffected by small but deliberate variations, which are described in ICH Q2A and Q2B guidelines.

National audit of continence care: laying the foundation.

PubMed

Mian, Sarah; Wagg, Adrian; Irwin, Penny; Lowe, Derek; Potter, Jonathan; Pearson, Michael

2005-12-01

National audit provides a basis for establishing performance against national standards, benchmarking against other service providers and improving standards of care. For effective audit, clinical indicators are required that are valid, feasible to apply and reliable. This study describes the methods used to develop clinical indicators of continence care in preparation for a national audit. To describe the methods used to develop and test clinical indicators of continence care with regard to validity, feasibility and reliability. A multidisciplinary working group developed clinical indicators that measured the structure, process and outcome of care as well as case-mix variables. Literature searching, consensus workshops and a Delphi process were used to develop the indicators. The indicators were tested in 15 secondary care sites, 15 primary care sites and 15 long-term care settings. The process of development produced indicators that received a high degree of consensus within the Delphi process. Testing of the indicators demonstrated an internal reliability of 0.7 and an external reliability of 0.6. Data collection required significant investment in terms of staff time and training. The method used produced indicators that achieved a high degree of acceptance from health care professionals. The reliability of data collection was high for this audit and was similar to the level seen in other successful national audits. Data collection for the indicators was feasible to collect, however, issues of time and staffing were identified as limitations to such data collection. The study has described a systematic method for developing clinical indicators for national audit. The indicators proved robust and reliable in primary and secondary care as well as long-term care settings.

Robustness of fit indices to outliers and leverage observations in structural equation modeling.

PubMed

Yuan, Ke-Hai; Zhong, Xiaoling

2013-06-01

Normal-distribution-based maximum likelihood (NML) is the most widely used method in structural equation modeling (SEM), although practical data tend to be nonnormally distributed. The effect of nonnormally distributed data or data contamination on the normal-distribution-based likelihood ratio (LR) statistic is well understood due to many analytical and empirical studies. In SEM, fit indices are used as widely as the LR statistic. In addition to NML, robust procedures have been developed for more efficient and less biased parameter estimates with practical data. This article studies the effect of outliers and leverage observations on fit indices following NML and two robust methods. Analysis and empirical results indicate that good leverage observations following NML and one of the robust methods lead most fit indices to give more support to the substantive model. While outliers tend to make a good model superficially bad according to many fit indices following NML, they have little effect on those following the two robust procedures. Implications of the results to data analysis are discussed, and recommendations are provided regarding the use of estimation methods and interpretation of fit indices. (PsycINFO Database Record (c) 2013 APA, all rights reserved).

Filling the gap in functional trait databases: use of ecological hypotheses to replace missing data.

PubMed

Taugourdeau, Simon; Villerd, Jean; Plantureux, Sylvain; Huguenin-Elie, Olivier; Amiaud, Bernard

2014-04-01

Functional trait databases are powerful tools in ecology, though most of them contain large amounts of missing values. The goal of this study was to test the effect of imputation methods on the evaluation of trait values at species level and on the subsequent calculation of functional diversity indices at community level using functional trait databases. Two simple imputation methods (average and median), two methods based on ecological hypotheses, and one multiple imputation method were tested using a large plant trait database, together with the influence of the percentage of missing data and differences between functional traits. At community level, the complete-case approach and three functional diversity indices calculated from grassland plant communities were included. At the species level, one of the methods based on ecological hypothesis was for all traits more accurate than imputation with average or median values, but the multiple imputation method was superior for most of the traits. The method based on functional proximity between species was the best method for traits with an unbalanced distribution, while the method based on the existence of relationships between traits was the best for traits with a balanced distribution. The ranking of the grassland communities for their functional diversity indices was not robust with the complete-case approach, even for low percentages of missing data. With the imputation methods based on ecological hypotheses, functional diversity indices could be computed with a maximum of 30% of missing data, without affecting the ranking between grassland communities. The multiple imputation method performed well, but not better than single imputation based on ecological hypothesis and adapted to the distribution of the trait values for the functional identity and range of the communities. Ecological studies using functional trait databases have to deal with missing data using imputation methods corresponding to their specific needs and making the most out of the information available in the databases. Within this framework, this study indicates the possibilities and limits of single imputation methods based on ecological hypothesis and concludes that they could be useful when studying the ranking of communities for their functional diversity indices.

Filling the gap in functional trait databases: use of ecological hypotheses to replace missing data

PubMed Central

Taugourdeau, Simon; Villerd, Jean; Plantureux, Sylvain; Huguenin-Elie, Olivier; Amiaud, Bernard

2014-01-01

Functional trait databases are powerful tools in ecology, though most of them contain large amounts of missing values. The goal of this study was to test the effect of imputation methods on the evaluation of trait values at species level and on the subsequent calculation of functional diversity indices at community level using functional trait databases. Two simple imputation methods (average and median), two methods based on ecological hypotheses, and one multiple imputation method were tested using a large plant trait database, together with the influence of the percentage of missing data and differences between functional traits. At community level, the complete-case approach and three functional diversity indices calculated from grassland plant communities were included. At the species level, one of the methods based on ecological hypothesis was for all traits more accurate than imputation with average or median values, but the multiple imputation method was superior for most of the traits. The method based on functional proximity between species was the best method for traits with an unbalanced distribution, while the method based on the existence of relationships between traits was the best for traits with a balanced distribution. The ranking of the grassland communities for their functional diversity indices was not robust with the complete-case approach, even for low percentages of missing data. With the imputation methods based on ecological hypotheses, functional diversity indices could be computed with a maximum of 30% of missing data, without affecting the ranking between grassland communities. The multiple imputation method performed well, but not better than single imputation based on ecological hypothesis and adapted to the distribution of the trait values for the functional identity and range of the communities. Ecological studies using functional trait databases have to deal with missing data using imputation methods corresponding to their specific needs and making the most out of the information available in the databases. Within this framework, this study indicates the possibilities and limits of single imputation methods based on ecological hypothesis and concludes that they could be useful when studying the ranking of communities for their functional diversity indices. PMID:24772273

Interferometric studies of the refractive indices of some fluorine compounds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Malik, Jim Gorden; Rogers, Max T.; Speirs, John L.

1954-08-01

It is the object of this investigation to construct an interferometer of the Rayleigh type and adapt it for two purposes; first, the measurement of the refractive indices of gases by an absolute method and, and second, the measurement of the refractive indices of very dilute solutions by the difference method.

Using Rapid Indicators for Enterococcus to assess the Risk of Illness after Exposure to Urban Runoff Contaminated Marine Water

EPA Science Inventory

BACKGROUND: Traditional fecal indicator bacteria (FIB) measurement is too slow (>18 h) for timely swimmer warnings. OBJECTIVES: Assess relationship of rapid indicator methods (qPCR) to illness at a marine beach impacted by urban runoff. METHODS: We measured baseline and two...

Systematic review: reliability of compendia methods for off-label oncology indications.

PubMed

Abernethy, Amy P; Raman, Gowri; Balk, Ethan M; Hammond, Julia M; Orlando, Lori A; Wheeler, Jane L; Lau, Joseph; McCrory, Douglas C

2009-03-03

The Centers for Medicare & Medicaid Services limit coverage of cancer drugs for off-label indications to indications listed in specified compendia. To assess whether compendia provide comprehensive, research-based, and timely information for off-label prescribing in oncology. 6 drug compendia, English-language literature searches of MEDLINE and the Cochrane Central Register of Controlled Trials from 2006 and 2008, and American Society of Clinical Oncology annual meeting abstracts from 2004 to 2007. Data Assessment: The compendia's stated methods, literature related to off-label indications of 14 cancer drugs in 2006, updated literature related to 1 off-label indication between 2006 and 2008, and completeness of compendia content and citations were assessed. The compendia's stated methods varied greatly from their actual practices. Compendia cited little of the available evidence, often neither the most recent nor that of highest methodological quality. Compendia differed in evidence cited, terminology, detail, presentation, and referencing. For the 14 off-label indications studied, the compendia differed in the indications included and whether and how they recommended particular agents for particular types of cancer. Update schedules varied, and documentation practices made it difficult to determine whether and when compendia content was updated. For 1 indication, compendia citations did not increase between 2006 and 2008 despite newly published articles. The 2006 analysis was limited to 14 off-label indications; the 2008 update examined 1 indication. Only off-label indications for cancer drugs were included, and results cannot be generalized to noncancer drugs or indications. Oncologists rely on compendia for up-to-date access to evidence and reimbursement information for off-label indications. Current compendia lack transparency, cite little current evidence, and lack systematic methods to review or update evidence.

Determination of suitable chemical extraction methods for the available iron content of brown forest soils in Turkey

NASA Astrophysics Data System (ADS)

Adiloglu, Aydin

2006-09-01

The aim of this research was to determine the available iron (Fe) content of brown forest soils of Edirne Province and the most suitable chemical extraction method. Eight chemical extraction methods (the 0.005 M DTPA + 0.01 M CaCl2 + 0.1 MTEA, 0.05 M HCl + 0.012 M H2SO4, 1 M NH4OAc (pH: 4.8), 0.01 M EDTA + 1 M NH4OAc, 1 M MgCl2, 0.01 M EDTA + 1 M (NH4)2CO3, 0.005 M DTPA + 1 M NH4HCO3, and 0.001 M EDDHA methods) and six biological indices (the dry matter yield, Fe concentration, Fe uptake, relative dry matter yield, relative Fe concentration, and relative Fe uptake) were compared. The biological indices were determined with barley (Hordeum vulgare L.) grown under greenhouse conditions. At the end of the experiment, the highest correlation coefficients (r) were determined to be between the 0.005 M DTPA + 0.01 M CaCl2 + 0.1 M TEA method and the biological indices and between the 0.005 M DTPA + 1 M NH4HCO3 method and the biological indices. The corresponding correlation coefficients (r) for the 0.005 M DTPA + 0.01 M CaCl2 + 0.1 M TEA method and the six biological indices were 0.621**, 0.823**, 0.810** 0.433**, 0.558**, and 0.640**, respectively. For the 0.005 M DTPA + 1 M NH4HCO3 method, these coefficients were equal to 0.618**, 0.520**, 0.679**, 0.521**, 0.492**, and 0.641**, respectively (** indicate the validity of the relationships at p < 0.01) These extraction methods, out of all the methods tested, were suggested for the determination of the available Fe content of the brown forest soils.

Apparatus and methods for detecting chemical permeation

DOEpatents

Vo-Dinh, T.

1994-12-27

Apparatus and methods for detecting the permeation of hazardous or toxic chemicals through protective clothing are disclosed. The hazardous or toxic chemicals of interest do not possess the spectral characteristic of luminescence. The apparatus and methods utilize a spectrochemical modification technique to detect the luminescence quenching of an indicator compound which upon permeation of the chemical through the protective clothing, the indicator is exposed to the chemical, thus indicating chemical permeation. The invention also relates to the fabrication of protective clothing materials. 13 figures.

Methods for specifying spatial boundaries of cities in the world: The impacts of delineation methods on city sustainability indices.

PubMed

Uchiyama, Yuta; Mori, Koichiro

2017-08-15

The purpose of this paper is to analyze how different definitions and methods for delineating the spatial boundaries of cities have an impact on the values of city sustainability indicators. It is necessary to distinguish the inside of cities from the outside when calculating the values of sustainability indicators that assess the impacts of human activities within cities on areas beyond their boundaries. For this purpose, spatial boundaries of cities should be practically detected on the basis of a relevant definition of a city. Although no definition of a city is commonly shared among academic fields, three practical methods for identifying urban areas are available in remote sensing science. Those practical methods are based on population density, landcover, and night-time lights. These methods are correlated, but non-negligible differences exist in their determination of urban extents and urban population. Furthermore, critical and statistically significant differences in some urban environmental sustainability indicators result from the three different urban detection methods. For example, the average values of CO 2 emissions per capita and PM 10 concentration in cities with more than 1 million residents are significantly different among the definitions. When analyzing city sustainability indicators and disseminating the implication of the results, the values based on the different definitions should be simultaneously investigated. It is necessary to carefully choose a relevant definition to analyze sustainability indicators for policy making. Otherwise, ineffective and inefficient policies will be developed. Copyright © 2017 Elsevier B.V. All rights reserved.

Balanced scorecard-based performance evaluation of Chinese county hospitals in underdeveloped areas.

PubMed

Gao, Hongda; Chen, He; Feng, Jun; Qin, Xianjing; Wang, Xuan; Liang, Shenglin; Zhao, Jinmin; Feng, Qiming

2018-05-01

Objective Since the Guangxi government implemented public county hospital reform in 2009, there have been no studies of county hospitals in this underdeveloped area of China. This study aimed to establish an evaluation indicator system for Guangxi county hospitals and to generate recommendations for hospital development and policymaking. Methods A performance evaluation indicator system was developed based on balanced scorecard theory. Opinions were elicited from 25 experts from administrative units, universities and hospitals and the Delphi method was used to modify the performance indicators. The indicator system and the Topsis method were used to evaluate the performance of five county hospitals randomly selected from the same batch of 2015 Guangxi reform pilots. Results There were 4 first-level indicators, 9 second-level indicators and 36 third-level indicators in the final performance evaluation indicator system that showed good consistency, validity and reliability. The performance rank of the hospitals was B > E > A > C > D. Conclusions The performance evaluation indicator system established using the balanced scorecard is practical and scientific. Analysis of the results based on this indicator system identified several factors affecting hospital performance, such as resource utilisation efficiency, medical service price, personnel structure and doctor-patient relationships.

Classification of Liss IV Imagery Using Decision Tree Methods

NASA Astrophysics Data System (ADS)

Verma, Amit Kumar; Garg, P. K.; Prasad, K. S. Hari; Dadhwal, V. K.

2016-06-01

Image classification is a compulsory step in any remote sensing research. Classification uses the spectral information represented by the digital numbers in one or more spectral bands and attempts to classify each individual pixel based on this spectral information. Crop classification is the main concern of remote sensing applications for developing sustainable agriculture system. Vegetation indices computed from satellite images gives a good indication of the presence of vegetation. It is an indicator that describes the greenness, density and health of vegetation. Texture is also an important characteristics which is used to identifying objects or region of interest is an image. This paper illustrate the use of decision tree method to classify the land in to crop land and non-crop land and to classify different crops. In this paper we evaluate the possibility of crop classification using an integrated approach methods based on texture property with different vegetation indices for single date LISS IV sensor 5.8 meter high spatial resolution data. Eleven vegetation indices (NDVI, DVI, GEMI, GNDVI, MSAVI2, NDWI, NG, NR, NNIR, OSAVI and VI green) has been generated using green, red and NIR band and then image is classified using decision tree method. The other approach is used integration of texture feature (mean, variance, kurtosis and skewness) with these vegetation indices. A comparison has been done between these two methods. The results indicate that inclusion of textural feature with vegetation indices can be effectively implemented to produce classifiedmaps with 8.33% higher accuracy for Indian satellite IRS-P6, LISS IV sensor images.

Comparison of gravimetric and a double-indicator dilution technique for assessment of extra-vascular lung water in endotoxaemia.

PubMed

Rossi, P; Oldner, A; Wanecek, M; Leksell, L G; Rudehill, A; Konrad, D; Weitzberg, E

2003-03-01

To compare a molecular double-indicator dilution technique with the gravimetrical reference method for measurement of extra-vascular lung water in porcine endotoxin shock. Open comparative experimental study. Animal research laboratory. In fourteen anaesthetised, mechanically ventilated landrace pigs, central and pulmonary haemodynamics as well as pulmonary gas exchange were measured. Extra-vascular lung water was quantitated gravimetrically as well as with a molecular double indicator dilution technique. Eight of these animals were subjected to endotoxaemia, the rest serving as sham controls. No difference in extra-vascular lung water was observed between the two methods in sham animals. Furthermore, extra-vascular lung water assessed with the molecular double-indicator dilution technique at the initiation of endotoxin infusion did not differ significantly from the corresponding values for sham animals. Endotoxaemia induced a hypodynamic shock with concurrent pulmonary hypertension and a pronounced deterioration in gas exchange. No increase in extra-vascular lung water was detected with the molecular double-indicator dilution technique in response to endotoxin, whereas this parameter was significantly higher when assessed with the gravimetric method. The molecular double-indicator dilution technique showed similar results as the gravimetrical method for assessment of extra-vascular lung water in non-endotoxaemic conditions. However, during endotoxin-induced lung injury the molecular double indicator dilution technique failed to detect the significant increase in extra-vascular lung water as measured by the gravimetric method. These data suggest that the molecular double indicator dilution technique may be of limited value during sepsis-induced lung injury.

Image portion identification methods, image parsing methods, image parsing systems, and articles of manufacture

DOEpatents

Lassahn, Gordon D.; Lancaster, Gregory D.; Apel, William A.; Thompson, Vicki S.

2013-01-08

Image portion identification methods, image parsing methods, image parsing systems, and articles of manufacture are described. According to one embodiment, an image portion identification method includes accessing data regarding an image depicting a plurality of biological substrates corresponding to at least one biological sample and indicating presence of at least one biological indicator within the biological sample and, using processing circuitry, automatically identifying a portion of the image depicting one of the biological substrates but not others of the biological substrates.

Indications, techniques, and outcomes of arthroscopic repair of scapholunate ligament and triangular fibrocartilage complex.

PubMed

Mathoulin, C L

2017-07-01

This review includes updated understanding of the roles of intrinsic and extrinsic carpal ligaments in scapholunate instability and details the author's experience of indications, arthroscopic repair methods, and outcomes of treating the instability. A classification on triangular fibrocartilage complex injuries is reviewed, followed by author's indications, methods, and outcomes of arthroscopic repair of triangular fibrocartilage complex injuries.

Using and Reporting the Delphi Method for Selecting Healthcare Quality Indicators: A Systematic Review

PubMed Central

Boulkedid, Rym; Abdoul, Hendy; Loustau, Marine; Sibony, Olivier; Alberti, Corinne

2011-01-01

Objective Delphi technique is a structured process commonly used to developed healthcare quality indicators, but there is a little recommendation for researchers who wish to use it. This study aimed 1) to describe reporting of the Delphi method to develop quality indicators, 2) to discuss specific methodological skills for quality indicators selection 3) to give guidance about this practice. Methodology and Main Finding Three electronic data bases were searched over a 30 years period (1978–2009). All articles that used the Delphi method to select quality indicators were identified. A standardized data extraction form was developed. Four domains (questionnaire preparation, expert panel, progress of the survey and Delphi results) were assessed. Of 80 included studies, quality of reporting varied significantly between items (9% for year's number of experience of the experts to 98% for the type of Delphi used). Reporting of methodological aspects needed to evaluate the reliability of the survey was insufficient: only 39% (31/80) of studies reported response rates for all rounds, 60% (48/80) that feedback was given between rounds, 77% (62/80) the method used to achieve consensus and 57% (48/80) listed quality indicators selected at the end of the survey. A modified Delphi procedure was used in 49/78 (63%) with a physical meeting of the panel members, usually between Delphi rounds. Median number of panel members was 17(Q1:11; Q3:31). In 40/70 (57%) studies, the panel included multiple stakeholders, who were healthcare professionals in 95% (38/40) of cases. Among 75 studies describing criteria to select quality indicators, 28 (37%) used validity and 17(23%) feasibility. Conclusion The use and reporting of the Delphi method for quality indicators selection need to be improved. We provide some guidance to the investigators to improve the using and reporting of the method in future surveys. PMID:21694759

Using and reporting the Delphi method for selecting healthcare quality indicators: a systematic review.

PubMed

Boulkedid, Rym; Abdoul, Hendy; Loustau, Marine; Sibony, Olivier; Alberti, Corinne

2011-01-01

Delphi technique is a structured process commonly used to developed healthcare quality indicators, but there is a little recommendation for researchers who wish to use it. This study aimed 1) to describe reporting of the Delphi method to develop quality indicators, 2) to discuss specific methodological skills for quality indicators selection 3) to give guidance about this practice. Three electronic data bases were searched over a 30 years period (1978-2009). All articles that used the Delphi method to select quality indicators were identified. A standardized data extraction form was developed. Four domains (questionnaire preparation, expert panel, progress of the survey and Delphi results) were assessed. Of 80 included studies, quality of reporting varied significantly between items (9% for year's number of experience of the experts to 98% for the type of Delphi used). Reporting of methodological aspects needed to evaluate the reliability of the survey was insufficient: only 39% (31/80) of studies reported response rates for all rounds, 60% (48/80) that feedback was given between rounds, 77% (62/80) the method used to achieve consensus and 57% (48/80) listed quality indicators selected at the end of the survey. A modified Delphi procedure was used in 49/78 (63%) with a physical meeting of the panel members, usually between Delphi rounds. Median number of panel members was 17(Q1:11; Q3:31). In 40/70 (57%) studies, the panel included multiple stakeholders, who were healthcare professionals in 95% (38/40) of cases. Among 75 studies describing criteria to select quality indicators, 28 (37%) used validity and 17(23%) feasibility. The use and reporting of the Delphi method for quality indicators selection need to be improved. We provide some guidance to the investigators to improve the using and reporting of the method in future surveys.

The Chace air indicator.

DOT National Transportation Integrated Search

1981-01-01

The study reported here has revealed very poor agreement between air contents determined by the Chace air indicator (CAI) and those by the pressure method. In tests of highway concretes the pressure method gave values typically 30% higher than antici...

Managing for resilience: an information theory-based ...

EPA Pesticide Factsheets

Ecosystems are complex and multivariate; hence, methods to assess the dynamics of ecosystems should have the capacity to evaluate multiple indicators simultaneously. Most research on identifying leading indicators of regime shifts has focused on univariate methods and simple models which have limited utility when evaluating real ecosystems, particularly because drivers are often unknown. We discuss some common univariate and multivariate approaches for detecting critical transitions in ecosystems and demonstrate their capabilities via case studies. Synthesis and applications. We illustrate the utility of an information theory-based index for assessing ecosystem dynamics. Trends in this index also provide a sentinel of both abrupt and gradual transitions in ecosystems. In response to the need to identify leading indicators of regime shifts in ecosystems, our research compares traditional indicators and Fisher information, an information theory based method, by examining four case study systems. Results demonstrate the utility of methods and offers great promise for quantifying and managing for resilience.

An Investigation of Agility Issues in Scrum Teams Using Agility Indicators

NASA Astrophysics Data System (ADS)

Pikkarainen, Minna; Wang, Xiaofeng

Agile software development methods have emerged and become increasingly popular in recent years; yet the issues encountered by software development teams that strive to achieve agility using agile methods are yet to be explored systematically. Built upon a previous study that has established a set of indicators of agility, this study investigates what issues are manifested in software development teams using agile methods. It is focussed on Scrum teams particularly. In other words, the goal of the chapter is to evaluate Scrum teams using agility indicators and therefore to further validate previously presented agility indicators within the additional cases. A multiple case study research method is employed. The findings of the study reveal that the teams using Scrum do not necessarily achieve agility in terms of team autonomy, sharing, stability and embraced uncertainty. The possible reasons include previous organizational plan-driven culture, resistance towards the Scrum roles and changing resources.

Regionalized rainfall-runoff model to estimate low flow indices

NASA Astrophysics Data System (ADS)

Garcia, Florine; Folton, Nathalie; Oudin, Ludovic

2016-04-01

Estimating low flow indices is of paramount importance to manage water resources and risk assessments. These indices are derived from river discharges which are measured at gauged stations. However, the lack of observations at ungauged sites bring the necessity of developing methods to estimate these low flow indices from observed discharges in neighboring catchments and from catchment characteristics. Different estimation methods exist. Regression or geostatistical methods performed on the low flow indices are the most common types of methods. Another less common method consists in regionalizing rainfall-runoff model parameters, from catchment characteristics or by spatial proximity, to estimate low flow indices from simulated hydrographs. Irstea developed GR2M-LoiEau, a conceptual monthly rainfall-runoff model, combined with a regionalized model of snow storage and melt. GR2M-LoiEau relies on only two parameters, which are regionalized and mapped throughout France. This model allows to cartography monthly reference low flow indices. The inputs data come from SAFRAN, the distributed mesoscale atmospheric analysis system, which provides daily solid and liquid precipitation and temperature data from everywhere in the French territory. To exploit fully these data and to estimate daily low flow indices, a new version of GR-LoiEau has been developed at a daily time step. The aim of this work is to develop and regionalize a GR-LoiEau model that can provide any daily, monthly or annual estimations of low flow indices, yet keeping only a few parameters, which is a major advantage to regionalize them. This work includes two parts. On the one hand, a daily conceptual rainfall-runoff model is developed with only three parameters in order to simulate daily and monthly low flow indices, mean annual runoff and seasonality. On the other hand, different regionalization methods, based on spatial proximity and similarity, are tested to estimate the model parameters and to simulate low flow indices in ungauged sites. The analysis is carried out on 691 French catchments that are representative of various hydro-meteorological behaviors. The results are validated with a cross-validation procedure and are compared with the ones obtained with GR4J, a conceptual rainfall-runoff model, which already provides daily estimations, but involves four parameters that cannot easily be regionalized.

A Novel Unsupervised Segmentation Quality Evaluation Method for Remote Sensing Images

PubMed Central

Tang, Yunwei; Jing, Linhai; Ding, Haifeng

2017-01-01

The segmentation of a high spatial resolution remote sensing image is a critical step in geographic object-based image analysis (GEOBIA). Evaluating the performance of segmentation without ground truth data, i.e., unsupervised evaluation, is important for the comparison of segmentation algorithms and the automatic selection of optimal parameters. This unsupervised strategy currently faces several challenges in practice, such as difficulties in designing effective indicators and limitations of the spectral values in the feature representation. This study proposes a novel unsupervised evaluation method to quantitatively measure the quality of segmentation results to overcome these problems. In this method, multiple spectral and spatial features of images are first extracted simultaneously and then integrated into a feature set to improve the quality of the feature representation of ground objects. The indicators designed for spatial stratified heterogeneity and spatial autocorrelation are included to estimate the properties of the segments in this integrated feature set. These two indicators are then combined into a global assessment metric as the final quality score. The trade-offs of the combined indicators are accounted for using a strategy based on the Mahalanobis distance, which can be exhibited geometrically. The method is tested on two segmentation algorithms and three testing images. The proposed method is compared with two existing unsupervised methods and a supervised method to confirm its capabilities. Through comparison and visual analysis, the results verified the effectiveness of the proposed method and demonstrated the reliability and improvements of this method with respect to other methods. PMID:29064416

Application of Biosphere Compatibility Indicator for Assessment of the Effectiveness of Environmental Protection Methods

NASA Astrophysics Data System (ADS)

Bakaeva, N. V.; Vorobyov, S. A.; Chernyaeva, I. V.

2017-11-01

The article is devoted to the issue of using the biosphere compatibility indicator to assess the effectiveness of environmental protection methods. The indicator biosphere compatibility was proposed by the vice-president of RAASN (Russian Academy of Architecture and Building Sciences), Doctor of Technical Sciences, Professor V.I. Ilyichev. This indicator allows one to assess not only qualitatively but also quantitatively the degree of urban areas development from the standpoint of preserving the biosphere in urban ecosystems while performing the city’s main functions. The integral biosphere compatibility indicator allows us to assess not only the current ecological situation in the territory under consideration but also to plan the forecast of its changes for the new construction projects implementation or for the reconstruction of the existing ones. The biosphere compatibility indicator, which is a mathematical expression of the tripartite balance (technosphere, biosphere and population of this area), allows us to quantify the effectiveness degree of different methods for environment protection to choose the most effective one under these conditions.

Rapid Methods for the Detection of General Fecal Indicators

EPA Science Inventory

Specified that EPA should develop: appropriate and effective indicators for improving detection in a timely manner of pathogens in coastal waters appropriate, accurate, expeditious and cost-effective methods for the timely detection of pathogens in coastal waters

Uncertainty assessment of PM2.5 contamination mapping using spatiotemporal sequential indicator simulations and multi-temporal monitoring data.

PubMed

Yang, Yong; Christakos, George; Huang, Wei; Lin, Chengda; Fu, Peihong; Mei, Yang

2016-04-12

Because of the rapid economic growth in China, many regions are subjected to severe particulate matter pollution. Thus, improving the methods of determining the spatiotemporal distribution and uncertainty of air pollution can provide considerable benefits when developing risk assessments and environmental policies. The uncertainty assessment methods currently in use include the sequential indicator simulation (SIS) and indicator kriging techniques. However, these methods cannot be employed to assess multi-temporal data. In this work, a spatiotemporal sequential indicator simulation (STSIS) based on a non-separable spatiotemporal semivariogram model was used to assimilate multi-temporal data in the mapping and uncertainty assessment of PM2.5 distributions in a contaminated atmosphere. PM2.5 concentrations recorded throughout 2014 in Shandong Province, China were used as the experimental dataset. Based on the number of STSIS procedures, we assessed various types of mapping uncertainties, including single-location uncertainties over one day and multiple days and multi-location uncertainties over one day and multiple days. A comparison of the STSIS technique with the SIS technique indicate that a better performance was obtained with the STSIS method.

Uncertainty assessment of PM2.5 contamination mapping using spatiotemporal sequential indicator simulations and multi-temporal monitoring data

NASA Astrophysics Data System (ADS)

Yang, Yong; Christakos, George; Huang, Wei; Lin, Chengda; Fu, Peihong; Mei, Yang

2016-04-01

Because of the rapid economic growth in China, many regions are subjected to severe particulate matter pollution. Thus, improving the methods of determining the spatiotemporal distribution and uncertainty of air pollution can provide considerable benefits when developing risk assessments and environmental policies. The uncertainty assessment methods currently in use include the sequential indicator simulation (SIS) and indicator kriging techniques. However, these methods cannot be employed to assess multi-temporal data. In this work, a spatiotemporal sequential indicator simulation (STSIS) based on a non-separable spatiotemporal semivariogram model was used to assimilate multi-temporal data in the mapping and uncertainty assessment of PM2.5 distributions in a contaminated atmosphere. PM2.5 concentrations recorded throughout 2014 in Shandong Province, China were used as the experimental dataset. Based on the number of STSIS procedures, we assessed various types of mapping uncertainties, including single-location uncertainties over one day and multiple days and multi-location uncertainties over one day and multiple days. A comparison of the STSIS technique with the SIS technique indicate that a better performance was obtained with the STSIS method.

Use of the method of biosphere compatibility for the assessment of environmental protection methods

NASA Astrophysics Data System (ADS)

Vorobyov, Sergey

2018-01-01

The article is devoted to the question of using the indicator of biosphere compatibility for assessing the effectiveness of environmental protection methods. The indicator of biosphere compatibility was proposed by the vice-president of RAASN (Russian Academy of Architecture and Building Sciences), Doctor of Technical Sciences, Professor V.I. Ilyichev. This indicator is allows not only qualitatively but also quantitatively to assess the degree of development of urban urban areas, from the standpoint of preserving the biosphere in urban ecosystems while realizing the city’s main functions. The integral indicator of biosphere compatibility is allows us to assess not only the current ecological situation in the territory under consideration, but also to plan the forecast of its changes for building the new construction projects, or for reconstructing existing ones. The indicator of biosphere compatibility, which is a mathematical expression of the tripartite balance (technosphere, biosphere and population of this area), is allows us to quantify the degree of effectiveness of different method of protecting the environment for choose the most effective for these conditions.

Method for warning of radiological and chemical agents using detection paints on a vehicle surface

DOEpatents

Farmer, Joseph C [Tracy, CA; Brunk, James L [Martinez, CA; Day, S Daniel [Danville, CA

2012-03-27

A paint that warns of radiological or chemical substances comprising a paint operatively connected to the surface, an indicator material carried by the paint that provides an indication of the radiological or chemical substances, and a thermo-activation material carried by the paint. In one embodiment, a method of warning of radiological or chemical substances comprising the steps of painting a surface with an indicator material, and monitoring the surface for indications of the radiological or chemical substances. In another embodiment, a paint is operatively connected to a vehicle and an indicator material is carried by the paint that provides an indication of the radiological or chemical substances.

Compensation of hospital-based physicians.

PubMed Central

Steinwald, B

1983-01-01

This study is concerned with methods of compensating hospital-based physicians (HBPs) in five medical specialties: anesthesiology, pathology, radiology, cardiology, and emergency medicine. Data on 2232 nonfederal, short-term general hospitals came from a mail questionnaire survey conducted in Fall 1979. The data indicate that numerous compensation methods exist but these methods, without much loss of precision, can be reduced to salary, percentage of department revenue, and fee-for-service. When HBPs are compensated by salary or percentage methods, most patient billing is conducted by the hospital. In contrast, most fee-for-service HBPs bill their patients directly. Determinants of HBP compensation methods are investigated via multinomial logit analysis. This analysis indicates that choice of HBP compensation methods are investigated via multinomial logit analysis. This analysis indicates that choice of HBP compensation methods is sensitive to a number of hospital characteristics and attributes of both the hospital and physicians' services markets. The empirical findings are discussed in light of past conceptual and empirical research on physician compensation, and current policy issues in the health services sector. PMID:6841112

Reading Comprehension and the Assessment and Acquisition of Word Knowledge. Technical Report No. 249.

ERIC Educational Resources Information Center

Anderson, Richard C.; Freebody, Peter

The "yes/no" method of vocabulary assessment requires students to indicate words they know from among a list of words and nonwords. Preliminary evidence gained from a study involving fifth grade students indicates that the method is superior in many ways to the multiple choice method of assessment. Analysis of "false alarms," cases in which…

Influence of the impact assessment method on the conclusions of a LCA study. Application to the case of a part made with virgin and recycled HDPE.

PubMed

Simões, Carla L; Xará, Susana M; Bernardo, C A

2011-10-01

Recent legislation has stressed the need to decide the best end-of-life (EoL) option for post-consumer products considering their full life-cycle and the corresponding overall environmental impacts. The life cycle assessment (LCA) technique has become a common tool to evaluate those impacts. The present study aimed to contribute to the better understanding of the application of this technique, by evaluating the influence of the selection of the life cycle impact assessment (LCIA) method in its results and conclusions. A specific case study was chosen, using previous information related to an anti-glare lamellae (AGL) for highway use, made with virgin and recycled high-density polyethylene (HDPE). Five distinct LCIA methods were used: Eco-indicator 99, CML 2 (2000), EPS 2000, Eco-indicator 95 and EDIP 97. Consistent results between these methods were obtained for the Climate change, Ozone layer depletion, Acidification and Eutrophication environmental indicators. Conversely, the Summer smog indicator showed large discrepancies between impact assessment methods. The work sheds light on the advantages inherent in using various LCIA methods when doing the LCA study of a specific product, thus evidencing complementary analysis perspectives.

Factors affecting the relationship between quantitative polymerase chain reaction (qPCR) and culture-based enumeration of Enterococcus in environmental waters.

PubMed

Raith, M R; Ebentier, D L; Cao, Y; Griffith, J F; Weisberg, S B

2014-03-01

To determine the extent to which discrepancies between qPCR and culture-based results in beach water quality monitoring can be attributed to: (i) within-method variability, (ii) between-method difference within each method class (qPCR or culture) and (iii) between-class difference. We analysed 306 samples using two culture-based (EPA1600 and Enterolert) and two qPCR (Taqman and Scorpion) methods, each in duplicate. Both qPCR methods correlated with EPA1600, but regression analyses indicated approximately 0·8 log10 unit overestimation by qPCR compared to culture methods. Differences between methods within a class were less than half of this and were minimal for between-replicate within a method. Using the 104 Enterococcus per 100 ml management decision threshold, Taqman qPCR indicated the same decisions as EPA1600 for 87% of the samples, but indicated beach posting for unhealthful water when EPA1600 did not for 12% of the samples. After accounting for within-method and within-class variability, 8% of the samples exhibited true between-class discrepancy where both qPCR methods indicated beach posting while both culture methods did not. Measurement target difference (DNA vs growth) accounted for the majority of the qPCR-vs-culture discrepancy, but its influence on monitoring application is outweighed by frequent incorrect posting with culture methods due to incubation time delay. This is the first study to quantify the frequency with which culture-vs-qPCR discrepancies can be attributed to target difference - vs - method variability. © 2013 The Society for Applied Microbiology.

How should hearing screening tests be offered?

PubMed

Koopman, Jan; Davey, Elizabeth; Thomas, Neil; Wittkop, Thomas; Verschuure, Hans

2008-05-01

This paper deals with the question of how the general public should be addressed when offering hearing screening. Postal-based questionnaires in the United Kingdom, Germany, and The Netherlands were sent to users of hearing devices, those that are in the process of obtaining one, or those that have indicated that they have special interest in hearing. Results of the survey indicated that respondents were enthusiastic about the idea of being able to carry out hearing self-screening tests via the internet, telephone, or questionnaires. A questionnaire as a method to screen on hearing was generally preferred above using the internet, which was preferred over using the telephone for the test. About 27% of the respondents indicated to use exclusively one method. Most respondents indicated that either method provided would be of interest (41%), 17% indicated not to be interested in conducting screening tests using the internet.

Assess and Predict Automatic Generation Control Performances for Thermal Power Generation Units Based on Modeling Techniques

NASA Astrophysics Data System (ADS)

Zhao, Yan; Yang, Zijiang; Gao, Song; Liu, Jinbiao

2018-02-01

Automatic generation control(AGC) is a key technology to maintain real time power generation and load balance, and to ensure the quality of power supply. Power grids require each power generation unit to have a satisfactory AGC performance, being specified in two detailed rules. The two rules provide a set of indices to measure the AGC performance of power generation unit. However, the commonly-used method to calculate these indices is based on particular data samples from AGC responses and will lead to incorrect results in practice. This paper proposes a new method to estimate the AGC performance indices via system identification techniques. In addition, a nonlinear regression model between performance indices and load command is built in order to predict the AGC performance indices. The effectiveness of the proposed method is validated through industrial case studies.

Comparison of Quantitative Antifungal Testing Methods for Textile Fabrics.

PubMed

Imoto, Yasuo; Seino, Satoshi; Nakagawa, Takashi; Yamamoto, Takao A

2017-01-01

　Quantitative antifungal testing methods for textile fabrics under growth-supportive conditions were studied. Fungal growth activities on unfinished textile fabrics and textile fabrics modified with Ag nanoparticles were investigated using the colony counting method and the luminescence method. Morphological changes of the fungi during incubation were investigated by microscopic observation. Comparison of the results indicated that the fungal growth activity values obtained with the colony counting method depended on the morphological state of the fungi on textile fabrics, whereas those obtained with the luminescence method did not. Our findings indicated that unique characteristics of each testing method must be taken into account for the proper evaluation of antifungal activity.

A novel sampling method for multiple multiscale targets from scattering amplitudes at a fixed frequency

NASA Astrophysics Data System (ADS)

Liu, Xiaodong

2017-08-01

A sampling method by using scattering amplitude is proposed for shape and location reconstruction in inverse acoustic scattering problems. Only matrix multiplication is involved in the computation, thus the novel sampling method is very easy and simple to implement. With the help of the factorization of the far field operator, we establish an inf-criterion for characterization of underlying scatterers. This result is then used to give a lower bound of the proposed indicator functional for sampling points inside the scatterers. While for the sampling points outside the scatterers, we show that the indicator functional decays like the bessel functions as the sampling point goes away from the boundary of the scatterers. We also show that the proposed indicator functional continuously depends on the scattering amplitude, this further implies that the novel sampling method is extremely stable with respect to errors in the data. Different to the classical sampling method such as the linear sampling method or the factorization method, from the numerical point of view, the novel indicator takes its maximum near the boundary of the underlying target and decays like the bessel functions as the sampling points go away from the boundary. The numerical simulations also show that the proposed sampling method can deal with multiple multiscale case, even the different components are close to each other.

Large-scale-system effectiveness analysis. Final report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Patton, A.D.; Ayoub, A.K.; Foster, J.W.

1979-11-01

Objective of the research project has been the investigation and development of methods for calculating system reliability indices which have absolute, and measurable, significance to consumers. Such indices are a necessary prerequisite to any scheme for system optimization which includes the economic consequences of consumer service interruptions. A further area of investigation has been joint consideration of generation and transmission in reliability studies. Methods for finding or estimating the probability distributions of some measures of reliability performance have been developed. The application of modern Monte Carlo simulation methods to compute reliability indices in generating systems has been studied.

A computerized method for automated identification of erect posteroanterior and supine anteroposterior chest radiographs

NASA Astrophysics Data System (ADS)

Kao, E.-Fong; Lin, Wei-Chen; Hsu, Jui-Sheng; Chou, Ming-Chung; Jaw, Twei-Shiun; Liu, Gin-Chung

2011-12-01

A computerized scheme was developed for automated identification of erect posteroanterior (PA) and supine anteroposterior (AP) chest radiographs. The method was based on three features, the tilt angle of the scapula superior border, the tilt angle of the clavicle and the extent of radiolucence in lung fields, to identify the view of a chest radiograph. The three indices Ascapula, Aclavicle and Clung were determined from a chest image for the three features. Linear discriminant analysis was used to classify PA and AP chest images based on the three indices. The performance of the method was evaluated by receiver operating characteristic analysis. The proposed method was evaluated using a database of 600 PA and 600 AP chest radiographs. The discriminant performances Az of Ascapula, Aclavicle and Clung were 0.878 ± 0.010, 0.683 ± 0.015 and 0.962 ± 0.006, respectively. The combination of the three indices obtained an Az value of 0.979 ± 0.004. The results indicate that the combination of the three indices could yield high discriminant performance. The proposed method could provide radiologists with information about the view of chest radiographs for interpretation or could be used as a preprocessing step for analyzing chest images.

Bond additivity corrections for quantum chemistry methods

DOE Office of Scientific and Technical Information (OSTI.GOV)

C. F. Melius; M. D. Allendorf

1999-04-01

In the 1980's, the authors developed a bond-additivity correction procedure for quantum chemical calculations called BAC-MP4, which has proven reliable in calculating the thermochemical properties of molecular species, including radicals as well as stable closed-shell species. New Bond Additivity Correction (BAC) methods have been developed for the G2 method, BAC-G2, as well as for a hybrid DFT/MP2 method, BAC-Hybrid. These BAC methods use a new form of BAC corrections, involving atomic, molecular, and bond-wise additive terms. These terms enable one to treat positive and negative ions as well as neutrals. The BAC-G2 method reduces errors in the G2 method duemore » to nearest-neighbor bonds. The parameters within the BAC-G2 method only depend on atom types. Thus the BAC-G2 method can be used to determine the parameters needed by BAC methods involving lower levels of theory, such as BAC-Hybrid and BAC-MP4. The BAC-Hybrid method should scale well for large molecules. The BAC-Hybrid method uses the differences between the DFT and MP2 as an indicator of the method's accuracy, while the BAC-G2 method uses its internal methods (G1 and G2MP2) to provide an indicator of its accuracy. Indications of the average error as well as worst cases are provided for each of the BAC methods.« less

Risk-based prioritization method for the classification of groundwater pesticide pollution from agricultural regions.

PubMed

Yang, Yu; Lian, Xin-Ying; Jiang, Yong-Hai; Xi, Bei-Dou; He, Xiao-Song

2017-11-01

Agricultural regions are a significant source of groundwater pesticide pollution. To ensure that agricultural regions with a significantly high risk of groundwater pesticide contamination are properly managed, a risk-based ranking method related to groundwater pesticide contamination is needed. In the present paper, a risk-based prioritization method for the classification of groundwater pesticide pollution from agricultural regions was established. The method encompasses 3 phases, including indicator selection, characterization, and classification. In the risk ranking index system employed here, 17 indicators involving the physicochemical properties, environmental behavior characteristics, pesticide application methods, and inherent vulnerability of groundwater in the agricultural region were selected. The boundary of each indicator was determined using K-means cluster analysis based on a survey of a typical agricultural region and the physical and chemical properties of 300 typical pesticides. The total risk characterization was calculated by multiplying the risk value of each indicator, which could effectively avoid the subjectivity of index weight calculation and identify the main factors associated with the risk. The results indicated that the risk for groundwater pesticide contamination from agriculture in a region could be ranked into 4 classes from low to high risk. This method was applied to an agricultural region in Jiangsu Province, China, and it showed that this region had a relatively high risk for groundwater contamination from pesticides, and that the pesticide application method was the primary factor contributing to the relatively high risk. The risk ranking method was determined to be feasible, valid, and able to provide reference data related to the risk management of groundwater pesticide pollution from agricultural regions. Integr Environ Assess Manag 2017;13:1052-1059. © 2017 SETAC. © 2017 SETAC.

Development and Validation of Stability-Indicating Derivative Spectrophotometric Methods for Determination of Dronedarone Hydrochloride

NASA Astrophysics Data System (ADS)

Chadha, R.; Bali, A.

2016-05-01

Rapid, sensitive, cost effective and reproducible stability-indicating derivative spectrophotometric methods have been developed for the estimation of dronedarone HCl employing peak-zero (P-0) and peak-peak (P-P) techniques, and their stability-indicating potential assessed in forced degraded solutions of the drug. The methods were validated with respect to linearity, accuracy, precision and robustness. Excellent linearity was observed in concentrations 2-40 μg/ml ( r 2 = 0.9986). LOD and LOQ values for the proposed methods ranged from 0.42-0.46 μg/ml and 1.21-1.27 μg/ml, respectively, and excellent recovery of the drug was obtained in the tablet samples (99.70 ± 0.84%).

Evaluation of the pulse-contour method of determining stroke volume in man.

NASA Technical Reports Server (NTRS)

Alderman, E. L.; Branzi, A.; Sanders, W.; Brown, B. W.; Harrison, D. C.

1972-01-01

The pulse-contour method for determining stroke volume has been employed as a continuous rapid method of monitoring the cardiovascular status of patients. Twenty-one patients with ischemic heart disease and 21 patients with mitral valve disease were subjected to a variety of hemodynamic interventions. The pulse-contour estimations, using three different formulas derived by Warner, Kouchoukos, and Herd, were compared with indicator-dilution outputs. A comparison of the results of the two methods for determining stroke volume yielded correlation coefficients ranging from 0.59 to 0.84. The better performing Warner formula yielded a coefficient of variation of about 20%. The type of hemodynamic interventions employed did not significantly affect the results using the pulse-contour method. Although the correlation of the pulse-contour and indicator-dilution stroke volumes is high, the coefficient of variation is such that small changes in stroke volume cannot be accurately assessed by the pulse-contour method. However, the simplicity and rapidity of this method compared to determination of cardiac output by Fick or indicator-dilution methods makes it a potentially useful adjunct for monitoring critically ill patients.

Stability-indicating RP-HPLC method for the simultaneous determination of escitalopram oxalate and clonazepam.

PubMed

Kakde, Rajendra B; Satone, Dinesh D; Gadapayale, Kamalesh K; Kakde, Megha G

2013-07-01

The objective of the current study was to develop a validated, specific stability-indicating reversed-phase liquid chromatographic (LC) method for the quantitative determination of escitalopram oxalate and clonazepam and their related substances in bulk drugs and pharmaceutical dosage forms in the presence of degradation products. Forced degradation studies were performed on the pure drugs of escitalopram oxalate and clonazepam, as per the stress conditions prescribed by the International Conference on Harmonization (ICH) using acid, base, oxidation, thermal stress and photolytic degradation to show the stability-indicating power of the method. Significant degradation was observed during acid and alkaline hydrolysis and no degradation was observed in other stress conditions. The chromatographic method was optimized using the samples generated from forced degradation studies. Good resolution between the peaks corresponded to the active pharmaceutical ingredients, escitalopram oxalate and clonazepam, and degradation products from the analyte were achieved on an ODS Hypersil C18 column (250 × 4.6 mm) using a mobile phase consisting of a mixture of acetonitrile-50 mM phosphate buffer + 10 mM triethylamine (70:30, v/v). The detection was conducted at 268 nm. The limit of detection and the limit of quantitation for escitalopram oxalate and clonazepam were established. The stress test solutions were assayed against the qualified working standards of escitalopram oxalate and clonazepam, which indicated that the developed LC method was stability-indicating. Validation of the developed LC method was conducted as per ICH requirements. The developed LC method was found to be suitable to check the quality of bulk samples of escitalopram oxalate and clonazepam.

City plants as ecological indicator of environment quality in St. Petersburg

NASA Astrophysics Data System (ADS)

Sapunov, Valentin; Glazyrina, Tatyana

2017-04-01

Under increase of natural hazard activity and anthropogenic pressure the effective and cheep monitoring methods become necessary. Majority of modern methods of monitoring, such as space and air, needs significant foundation. The simplest monitoring method is biological indication, basing on essay of variability, sex ration and sexual dimorphism. Such a method does not need long time efforts and may be realized by short observation. Urban plants are natural indicators of ecological pressure. Check or their state may give us significant information on area pollution by use of principles of phenogenic indication. Genetic and phenotypic variability of different organism have general principles and constants. The per cent of abnormal organisms and coefficient of variability are stable for majority of species under favorable state and increase under unfavorable conditions. The basis for indication is both state of adult trees and morphological variability of pollen grains. The part of dried threes and threes infected by parasites-xylophagous is correlated with toxic pollution. Float asymmetry of lives is measure of mutagenic pollution. Abnormal form of three (dichotomy, curved) is criteria of teratogenic pollution. Importance of such an indication is increased by such incidents as Chernobyl, Fucusima and so on. Algorithm for analyze of such a data is considered. The map of ecological pressure of St. Petersburg is presented.

[Evaluation of Organ Dose Estimation from Indices of CT Dose Using Dose Index Registry].

PubMed

Iriuchijima, Akiko; Fukushima, Yasuhiro; Ogura, Akio

Direct measurement of each patient organ dose from computed tomography (CT) is not possible. Most methods to estimate patient organ dose is using Monte Carlo simulation with dedicated software. However, dedicated software is too expensive for small scale hospitals. Not every hospital can estimate organ dose with dedicated software. The purpose of this study was to evaluate the simple method of organ dose estimation using some common indices of CT dose. The Monte Carlo simulation software Radimetrics (Bayer) was used for calculating organ dose and analysis relationship between indices of CT dose and organ dose. Multidetector CT scanners were compared with those from two manufactures (LightSpeed VCT, GE Healthcare; SOMATOM Definition Flash, Siemens Healthcare). Using stored patient data from Radimetrics, the relationships between indices of CT dose and organ dose were indicated as each formula for estimating organ dose. The accuracy of estimation method of organ dose was compared with the results of Monte Carlo simulation using the Bland-Altman plots. In the results, SSDE was the feasible index for estimation organ dose in almost organs because it reflected each patient size. The differences of organ dose between estimation and simulation were within 23%. In conclusion, our estimation method of organ dose using indices of CT dose is convenient for clinical with accuracy.

Biomonitoring of Environmental Status and Trends (BEST) Program: selected methods for monitoring chemical contaminants and their effects in aquatic ecosystems

USGS Publications Warehouse

Schmitt, Christopher J.; Dethloff, Gail M.

2000-01-01

This document describes the suite of biological methods of the U.S. Geological Survey- Biomonitoring of Environmental Status and Trends program for monitoring chemical contaminants and their effects on fish. The methods, which were selected by panels of experts, are being field-tested in rivers of the Mississippi River, Columbia River, and Rio Grande basins. General health biomarkers include a health assessment index based on gross observation; histopathological examination of selected organs and tissues; condition factor; and the heptosomatic and splenosomatic indices. Immune system indicators are plasma lysozyme activity and measures of splenic macrophage aggregates. Reproductive biomarkers include plasma concentrations of sex steroid hormones (17b-estradiol and 11-ketotestosterone) and vitellogenin, gonadal histopathology (including reproductive stage and, in females, gonadal atresia), and the gonadosomatic index. Indicators of exposure to polycyclic aromatic and polyhalogenated hydrocarbons are the H4IIE rat hepatoma cell bioassay (performed on solvent extracts of composite fish samples) and hepatic ethoxyresorufin-O-deethylase activity. Stable nitrogen isotope ratios are used to assess the trophic position of the fish and their exposure to sewage and other animal wastes. For each indicator we describe endpoint(s) and methods, and discuss the indicator?s value and limitations for contaminant monitoring and assessment.

Application of capability indices and control charts in the analytical method control strategy.

PubMed

Oliva, Alexis; Llabres Martinez, Matías

2017-08-01

In this study, we assessed the usefulness of control charts in combination with the process capability indices, C pm and C pk , in the control strategy of an analytical method. The traditional X-chart and moving range chart were used to monitor the analytical method over a 2-year period. The results confirmed that the analytical method is in-control and stable. Different criteria were used to establish the specifications limits (i.e. analyst requirements) for fixed method performance (i.e. method requirements). If the specification limits and control limits are equal in breadth, the method can be considered "capable" (C pm  = 1), but it does not satisfy the minimum method capability requirements proposed by Pearn and Shu (2003). Similar results were obtained using the C pk index. The method capability was also assessed as a function of method performance for fixed analyst requirements. The results indicate that the method does not meet the requirements of the analytical target approach. A real-example data of a SEC with light-scattering detection method was used as a model whereas previously published data were used to illustrate the applicability of the proposed approach. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Problemes et methodes de la lexicographie quebecoise (Problems and Methods of Quebec Lexicography).

ERIC Educational Resources Information Center

Cormier, Monique C., Ed.; Francoeur, Aline, Ed.

Papers on lexicographic research in Quebec (Canada) include: "Indications semantiques dans les dictionnaires bilingues" ("Semantic Indications in Bilingual Dictionaries) (Johanne Blais, Roda P. Roberts); "Definitions predictionnairiques de 'maison, batiment, et pavillon'" ("Pre-dictionary definitions of 'house,…

Managing for resilience: an information theory-based approach to assessing ecosystems

EPA Science Inventory

Ecosystems are complex and multivariate; hence, methods to assess the dynamics of ecosystems should have the capacity to evaluate multiple indicators simultaneously. Most research on identifying leading indicators of regime shifts has focused on univariate methods and simple mod...

A new four-step hierarchy method for combined assessment of groundwater quality and pollution.

PubMed

Zhu, Henghua; Ren, Xiaohua; Liu, Zhizheng

2017-12-28

A new four-step hierarchy method was constructed and applied to evaluate the groundwater quality and pollution of the Dagujia River Basin. The assessment index system is divided into four types: field test indices, common inorganic chemical indices, inorganic toxicology indices, and trace organic indices. Background values of common inorganic chemical indices and inorganic toxicology indices were estimated with the cumulative-probability curve method, and the results showed that the background values of Mg 2+ (51.1 mg L -1 ), total hardness (TH) (509.4 mg L -1 ), and NO 3 - (182.4 mg L -1 ) are all higher than the corresponding grade III values of Quality Standard for Groundwater, indicating that they were poor indicators and therefore were not included in the groundwater quality assessment. The quality assessment results displayed that the field test indices were mainly classified as grade II, accounting for 60.87% of wells sampled. The indices of common inorganic chemical and inorganic toxicology were both mostly in the range of grade III, whereas the trace organic indices were predominantly classified as grade I. The variabilities and excess ratios of the indices were also calculated and evaluated. Spatial distributions showed that the groundwater with poor quality indices was mainly located in the northeast of the basin, which was well-connected with seawater intrusion. Additionally, the pollution assessment revealed that groundwater in well 44 was classified as "moderately polluted," wells 5 and 8 were "lightly polluted," and other wells were classified as "unpolluted."

The Microbial Fecal Indicator Paradigm: Tools in the Toolbox Applications in Recreational Waters

EPA Science Inventory

Summary of ORD’s recent research to develop tools for assessing microbial water quality in recreational waters. Methods discussed include the development of health associations between microbial fecal indicators and the development of culture, and molecular methods for fec...

RAPID HEALTH-BASED METHOD FOR MEASURING MICROBIAL INDICATORS OF RECREATIONAL WATER QUALITY

EPA Science Inventory

Because the currently approved cultural methods for monitoring indicator bacteria in recreational water require 24 hours to produce results, the public may be exposed to potentially contaminated water before the water has been identified as hazardous. This project was initiated t...

Investigation of Current Methods to Identify Helicopter Gear Health

NASA Technical Reports Server (NTRS)

Dempsey, Paula J.; Lewicki, David G.; Le, Dy D.

2007-01-01

This paper provides an overview of current vibration methods used to identify the health of helicopter transmission gears. The gears are critical to the transmission system that provides propulsion, lift and maneuvering of the helicopter. This paper reviews techniques used to process vibration data to calculate conditions indicators (CI's), guidelines used by the government aviation authorities in developing and certifying the Health and Usage Monitoring System (HUMS), condition and health indicators used in commercial HUMS, and different methods used to set thresholds to detect damage. Initial assessment of a method to set thresholds for vibration based condition indicators applied to flight and test rig data by evaluating differences in distributions between comparable transmissions are also discussed. Gear condition indicator FM4 values are compared on an OH58 helicopter during 14 maneuvers and an OH58 transmission test stand during crack propagation tests. Preliminary results show the distributions between healthy helicopter and rig data are comparable and distributions between healthy and damaged gears show significant differences.

Investigation of Current Methods to Identify Helicopter Gear Health

NASA Technical Reports Server (NTRS)

Dempsey, Paula J.; Lewicki, David G.; Le, Dy D.

2007-01-01

This paper provides an overview of current vibration methods used to identify the health of helicopter transmission gears. The gears are critical to the transmission system that provides propulsion, lift and maneuvering of the helicopter. This paper reviews techniques used to process vibration data to calculate conditions indicators (CI s), guidelines used by the government aviation authorities in developing and certifying the Health and Usage Monitoring System (HUMS), condition and health indicators used in commercial HUMS, and different methods used to set thresholds to detect damage. Initial assessment of a method to set thresholds for vibration based condition indicators applied to flight and test rig data by evaluating differences in distributions between comparable transmissions are also discussed. Gear condition indicator FM4 values are compared on an OH58 helicopter during 14 maneuvers and an OH58 transmission test stand during crack propagation tests. Preliminary results show the distributions between healthy helicopter and rig data are comparable and distributions between healthy and damaged gears show significant differences.

Durability predictions of adhesively bonded composite structures using accelerated characterization methods

NASA Technical Reports Server (NTRS)

Brinson, H. F.

1985-01-01

The utilization of adhesive bonding for composite structures is briefly assessed. The need for a method to determine damage initiation and propagation for such joints is outlined. Methods currently in use to analyze both adhesive joints and fiber reinforced plastics is mentioned and it is indicated that all methods require the input of the mechanical properties of the polymeric adhesive and composite matrix material. The mechanical properties of polymers are indicated to be viscoelastic and sensitive to environmental effects. A method to analytically characterize environmentally dependent linear and nonlinear viscoelastic properties is given. It is indicated that the methodology can be used to extrapolate short term data to long term design lifetimes. That is, the method can be used for long term durability predictions. Experimental results for near adhesive resins, polymers used as composite matrices and unidirectional composite laminates is given. The data is fitted well with the analytical durability methodology. Finally, suggestions are outlined for the development of an analytical methodology for the durability predictions of adhesively bonded composite structures.

Effect of different cooking methods on minerals, vitamins and nutritional quality indices of kutum roach (Rutilus frisii kutum).

PubMed

Hosseini, Hedayat; Mahmoudzadeh, Maryam; Rezaei, Masoud; Mahmoudzadeh, Leila; Khaksar, Ramin; Khosroshahi, Nader Karimian; Babakhani, Aria

2014-04-01

In this study, the influence of four cooking methods (baking, boiling, microwaving and frying) was evaluated on the nutritional value of kutum roach. Proximate, fatty acid composition, vitamin and mineral contents and also nutritional quality indices (NQI) of kutum roach were investigated before and after cooking treatment. All treated samples showed increase in protein, ash and lipid contents and decrease in the content of total omega-3 fatty acids (n-3) in comparison to raw fish fillets (control group). Cooking methods had no significant effect on omega-6 fatty acids (n-6) except for frying that increased it. Nonetheless, all of the cooking methods reduced vitamin B1, A and D contents. Boiling significantly decreased mineral contents including Na, K, P and Zn. Considering the overall nutritional quality indices, vitamin and mineral contents, baking is the best cooking method among other applied methods. Copyright © 2013 Elsevier Ltd. All rights reserved.

Dynamic Assessment of Water Quality Based on a Variable Fuzzy Pattern Recognition Model

PubMed Central

Xu, Shiguo; Wang, Tianxiang; Hu, Suduan

2015-01-01

Water quality assessment is an important foundation of water resource protection and is affected by many indicators. The dynamic and fuzzy changes of water quality lead to problems for proper assessment. This paper explores a method which is in accordance with the water quality changes. The proposed method is based on the variable fuzzy pattern recognition (VFPR) model and combines the analytic hierarchy process (AHP) model with the entropy weight (EW) method. The proposed method was applied to dynamically assess the water quality of Biliuhe Reservoir (Dailan, China). The results show that the water quality level is between levels 2 and 3 and worse in August or September, caused by the increasing water temperature and rainfall. Weights and methods are compared and random errors of the values of indicators are analyzed. It is concluded that the proposed method has advantages of dynamism, fuzzification and stability by considering the interval influence of multiple indicators and using the average level characteristic values of four models as results. PMID:25689998

Dynamic assessment of water quality based on a variable fuzzy pattern recognition model.

PubMed

Xu, Shiguo; Wang, Tianxiang; Hu, Suduan

2015-02-16

Water quality assessment is an important foundation of water resource protection and is affected by many indicators. The dynamic and fuzzy changes of water quality lead to problems for proper assessment. This paper explores a method which is in accordance with the water quality changes. The proposed method is based on the variable fuzzy pattern recognition (VFPR) model and combines the analytic hierarchy process (AHP) model with the entropy weight (EW) method. The proposed method was applied to dynamically assess the water quality of Biliuhe Reservoir (Dailan, China). The results show that the water quality level is between levels 2 and 3 and worse in August or September, caused by the increasing water temperature and rainfall. Weights and methods are compared and random errors of the values of indicators are analyzed. It is concluded that the proposed method has advantages of dynamism, fuzzification and stability by considering the interval influence of multiple indicators and using the average level characteristic values of four models as results.

Risk-Based Prioritization Method for the Classification of Groundwater Pollution from Hazardous Waste Landfills.

PubMed

Yang, Yu; Jiang, Yong-Hai; Lian, Xin-Ying; Xi, Bei-Dou; Ma, Zhi-Fei; Xu, Xiang-Jian; An, Da

2016-12-01

Hazardous waste landfill sites are a significant source of groundwater pollution. To ensure that these landfills with a significantly high risk of groundwater contamination are properly managed, a risk-based ranking method related to groundwater contamination is needed. In this research, a risk-based prioritization method for the classification of groundwater pollution from hazardous waste landfills was established. The method encompasses five phases, including risk pre-screening, indicator selection, characterization, classification and, lastly, validation. In the risk ranking index system employed here, 14 indicators involving hazardous waste landfills and migration in the vadose zone as well as aquifer were selected. The boundary of each indicator was determined by K-means cluster analysis and the weight of each indicator was calculated by principal component analysis. These methods were applied to 37 hazardous waste landfills in China. The result showed that the risk for groundwater contamination from hazardous waste landfills could be ranked into three classes from low to high risk. In all, 62.2 % of the hazardous waste landfill sites were classified in the low and medium risk classes. The process simulation method and standardized anomalies were used to validate the result of risk ranking; the results were consistent with the simulated results related to the characteristics of contamination. The risk ranking method was feasible, valid and can provide reference data related to risk management for groundwater contamination at hazardous waste landfill sites.

[Object-oriented aquatic vegetation extracting approach based on visible vegetation indices.

PubMed

Jing, Ran; Deng, Lei; Zhao, Wen Ji; Gong, Zhao Ning

2016-05-01

Using the estimation of scale parameters (ESP) image segmentation tool to determine the ideal image segmentation scale, the optimal segmented image was created by the multi-scale segmentation method. Based on the visible vegetation indices derived from mini-UAV imaging data, we chose a set of optimal vegetation indices from a series of visible vegetation indices, and built up a decision tree rule. A membership function was used to automatically classify the study area and an aquatic vegetation map was generated. The results showed the overall accuracy of image classification using the supervised classification was 53.7%, and the overall accuracy of object-oriented image analysis (OBIA) was 91.7%. Compared with pixel-based supervised classification method, the OBIA method improved significantly the image classification result and further increased the accuracy of extracting the aquatic vegetation. The Kappa value of supervised classification was 0.4, and the Kappa value based OBIA was 0.9. The experimental results demonstrated that using visible vegetation indices derived from the mini-UAV data and OBIA method extracting the aquatic vegetation developed in this study was feasible and could be applied in other physically similar areas.

Development of a quality instrument for assessing the spontaneous reports of ADR/ADE using Delphi method in China.

PubMed

Chen, Lixun; Jiang, Ling; Shen, Aizong; Wei, Wei

2016-09-01

The frequently low quality of submitted spontaneous reports is of an increasing concern; to our knowledge, no validated instrument exists for assessing case reports' quality comprehensively enough. This work was conducted to develop such a quality instrument for assessing the spontaneous reports of adverse drug reaction (ADR)/adverse drug event (ADE) in China. Initial evaluation indicators were generated using systematic and literature data analysis. Final indicators and their weights were identified using Delphi method. The final quality instrument was developed by adopting the synthetic scoring method. A consensus was reached after four rounds of Delphi survey. The developed quality instrument consisted of 6 first-rank indicators, 18 second-rank indicators, and 115 third-rank indicators, and each rank indicator has been weighted. It evaluates the quality of spontaneous reports of ADR/ADE comprehensively and quantitatively on six parameters: authenticity, duplication, regulatory, completeness, vigilance level, and reporting time frame. The developed instrument was tested with good reliability and validity, which can be used to comprehensively and quantitatively assess the submitted spontaneous reports of ADR/ADE in China.

Technique for forming ITO films with a controlled refractive index

DOE Office of Scientific and Technical Information (OSTI.GOV)

Markov, L. K., E-mail: l.markov@mail.ioffe.ru; Smirnova, I. P.; Pavluchenko, A. S.

2016-07-15

A new method for fabricating transparent conducting coatings based on indium-tin oxide (ITO) with a controlled refractive index is proposed. This method implies the successive deposition of material by electron-beam evaporation and magnetron sputtering. Sputtered coatings with different densities (and, correspondingly, different refractive indices) can be obtained by varying the ratio of the mass fractions of material deposited by different methods. As an example, films with effective refractive indices of 1.2, 1.4, and 1.7 in the wavelength range of 440–460 nm are fabricated. Two-layer ITO coatings with controlled refractive indices of the layers are also formed by the proposed method.more » Thus, multilayer transparent conducting coatings with desired optical parameters can be produced.« less

Hypothesis analysis methods, hypothesis analysis devices, and articles of manufacture

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sanfilippo, Antonio P; Cowell, Andrew J; Gregory, Michelle L

Hypothesis analysis methods, hypothesis analysis devices, and articles of manufacture are described according to some aspects. In one aspect, a hypothesis analysis method includes providing a hypothesis, providing an indicator which at least one of supports and refutes the hypothesis, using the indicator, associating evidence with the hypothesis, weighting the association of the evidence with the hypothesis, and using the weighting, providing information regarding the accuracy of the hypothesis.

Differential Item Functioning Detection Using the Multiple Indicators, Multiple Causes Method with a Pure Short Anchor

ERIC Educational Resources Information Center

Shih, Ching-Lin; Wang, Wen-Chung

2009-01-01

The multiple indicators, multiple causes (MIMIC) method with a pure short anchor was proposed to detect differential item functioning (DIF). A simulation study showed that the MIMIC method with an anchor of 1, 2, 4, or 10 DIF-free items yielded a well-controlled Type I error rate even when such tests contained as many as 40% DIF items. In general,…

Validating activity indices from camera traps for commensal rodents and other wildlife in and around farm buildings.

PubMed

Lambert, Mark; Bellamy, Fiona; Budgey, Richard; Callaby, Rebecca; Coats, Julia; Talling, Janet

2018-01-01

Indices of rodent activity are used as indicators of population change during field evaluation of rodenticides. We investigated the potential for using camera traps to determine activity indices for commensal rodents living in and around farm buildings, and sought to compare these indices against previously calibrated survey methods. We recorded 41 263 images of 23 species, including Norway rats (Rattus norvegicus Berk.) and house mice (Mus musculus L.). We found a positive correlation between activity indices from camera traps and activity indices from a method (footprint tracking) previously shown to have a linear relationship with population size for Norway rats. Filtering the camera trap data to simulate a 30-s delay between camera trigger events removed 59.9% of data and did not adversely affect the correlation between activity indices from camera traps and footprint tracking. The relationship between activity indices from footprint tracking and Norway rat population size is known from a previous study; from this, we determined the relationship between activity indices from camera traps and population size for Norway rats living in and around farm buildings. Systematic use of camera traps was used to determine activity indices for Norway rats living in and around farm buildings; the activity indices were positively correlated with those derived from a method previously calibrated against known population size for this species in this context. © 2017 Crown copyright. Pest Management Science © 2017 Society of Chemical Industry. © 2017 Crown copyright. Pest Management Science © 2017 Society of Chemical Industry.

Identification of an updated set of prescribing-safety indicators for GPs

PubMed Central

Spencer, Rachel; Bell, Brian; Avery, Anthony J; Gookey, Gill; Campbell, Stephen M

2014-01-01

Background Medication error is an important contributor to patient morbidity and mortality and is associated with inadequate patient safety measures. However, prescribing-safety tools specifically designed for use in general practice are lacking. Aim To identify and update a set of prescribing-safety indicators for assessing the safety of prescribing in general practice, and to estimate the risk of harm to patients associated with each indicator. Design and setting RAND/UCLA consensus development of indicators in UK general practice. Method Prescribing indicators were identified from a systematic review and previous consensus exercise. The RAND Appropriateness Method was used to further identify and develop the indicators with an electronic-Delphi method used to rate the risk associated with them. Twelve GPs from all the countries of the UK participated in the RAND exercise, with 11 GPs rating risk using the electronic-Delphi approach. Results Fifty-six prescribing-safety indicators were considered appropriate for inclusion (overall panel median rating of 7–9, with agreement). These indicators cover hazardous prescribing across a range of therapeutic indications, hazardous drug–drug combinations and inadequate laboratory test monitoring. Twenty-three (41%) of these indicators were considered high risk or extreme risk by 80% or more of the participants. Conclusion This study identified a set of 56 indicators that were considered, by a panel of GPs, to be appropriate for assessing the safety of GP prescribing. Twenty-three of these indicators were considered to be associated with high or extreme risk to patients and should be the focus of efforts to improve patient safety. PMID:24686882

Quantitative Real-Time PCR Analysis of Total Propidium Monazide -Resistant Fecal Indicator Bacteria in Wastewater

EPA Science Inventory

A real-time quantitative PCR (qPCR) method and a modification of this method incorporating pretreatment of samples with propidium monoazide (PMA) were evaluated for respective analyses of total and presumptively viable Enterococcus and Bacteroidales fecal indicator bacteria. Thes...

A Comprehensive System of Energy Intensity Indicators for the U.S.: Methods, Data and Key Trends

DOE Office of Scientific and Technical Information (OSTI.GOV)

Belzer, D. B.

2014-08-01

This report describes a comprehensive system of energy intensity indicators for the United States that has been developed for the Department of Energy's Office of Energy Efficiency and Renewable Energy (EERE) over the past decade. This system of indicators is hierarchical in nature, beginning with detailed indexes of energy intensity for various sectors of the economy, which are ultimately aggregated to an overall energy intensity index for the economy as a whole. The aggregation of energy intensity indexes to higher levels in the hierarchy is performed with a version of the Log Mean Divisia index (LMDI) method. Based upon themore » data and methods in the system of indicators, the economy-wide energy intensity index shows a decline of about 14% in 2011 relative to a 1985 base year.« less

Differential evolution-based multi-objective optimization for the definition of a health indicator for fault diagnostics and prognostics

NASA Astrophysics Data System (ADS)

Baraldi, P.; Bonfanti, G.; Zio, E.

2018-03-01

The identification of the current degradation state of an industrial component and the prediction of its future evolution is a fundamental step for the development of condition-based and predictive maintenance approaches. The objective of the present work is to propose a general method for extracting a health indicator to measure the amount of component degradation from a set of signals measured during operation. The proposed method is based on the combined use of feature extraction techniques, such as Empirical Mode Decomposition and Auto-Associative Kernel Regression, and a multi-objective Binary Differential Evolution (BDE) algorithm for selecting the subset of features optimal for the definition of the health indicator. The objectives of the optimization are desired characteristics of the health indicator, such as monotonicity, trendability and prognosability. A case study is considered, concerning the prediction of the remaining useful life of turbofan engines. The obtained results confirm that the method is capable of extracting health indicators suitable for accurate prognostics.

A coloured oil level indicator detection method based on simple linear iterative clustering

NASA Astrophysics Data System (ADS)

Liu, Tianli; Li, Dongsong; Jiao, Zhiming; Liang, Tao; Zhou, Hao; Yang, Guoqing

2017-12-01

A detection method of coloured oil level indicator is put forward. The method is applied to inspection robot in substation, which realized the automatic inspection and recognition of oil level indicator. Firstly, the detected image of the oil level indicator is collected, and the detected image is clustered and segmented to obtain the label matrix of the image. Secondly, the detection image is processed by colour space transformation, and the feature matrix of the image is obtained. Finally, the label matrix and feature matrix are used to locate and segment the detected image, and the upper edge of the recognized region is obtained. If the upper limb line exceeds the preset oil level threshold, the alarm will alert the station staff. Through the above-mentioned image processing, the inspection robot can independently recognize the oil level of the oil level indicator, and instead of manual inspection. It embodies the automatic and intelligent level of unattended operation.

Prioritizing chemicals for environmental management in China based on screening of potential risks

NASA Astrophysics Data System (ADS)

Yu, Xiangyi; Mao, Yan; Sun, Jinye; Shen, Yingwa

2014-03-01

The rapid development of China's chemical industry has created increasing pressure to improve the environmental management of chemicals. To bridge the large gap between the use and safe management of chemicals, we performed a comprehensive review of the international methods used to prioritize chemicals for environmental management. By comparing domestic and foreign methods, we confirmed the presence of this gap and identified potential solutions. Based on our literature review, we developed an appropriate screening method that accounts for the unique characteristics of chemical use within China. The proposed method is based on an evaluation using nine indices of the potential hazard posed by a chemical: three environmental hazard indices (persistence, bioaccumulation, and eco-toxicity), four health hazard indices (acute toxicity, carcinogenicity, mutagenicity, and reproductive and developmental toxicity), and two environmental exposure hazard indices (chemical amount and utilization pattern). The results of our screening agree with results of previous efforts from around the world, confirming the validity of the new system. The classification method will help decisionmakers to prioritize and identify the chemicals with the highest environmental risk, thereby providing a basis for improving chemical management in China.

Relationship and Variation of qPCR and Culturable Enterococci Estimates in Ambient Surface Waters Are Predictable

EPA Science Inventory

The quantitative polymerase chain reaction (qPCR) method provides rapid estimates of fecal indicator bacteria densities that have been indicated to be useful in the assessment of water quality. Primarily because this method provides faster results than standard culture-based meth...

BOOTSTRAPPING AND MONTE CARLO METHODS OF POWER ANALYSIS USED TO ESTABLISH CONDITION CATEGORIES FOR BIOTIC INDICES

EPA Science Inventory

Biotic indices have been used ot assess biological condition by dividing index scores into condition categories. Historically the number of categories has been based on professional judgement. Alternatively, statistical methods such as power analysis can be used to determine the ...

RECREATIONAL WATER QUALITY AND SWIMMER HEALTH - CAN FASTER METHODS OF MEASURING RECREATIONAL WATER HELP PREVENT SWIMMING ASSOCIATED ILLNESS?

EPA Science Inventory

Evidence from various sources around the world indicate that there is a relationship between gastroenteritis in swimmers and the quality of the bathing water as measured with bacterial indicators of fecal contamination. Current EPA guidelines recommend the use of cultural method...

RAPID HEALTH-BASED METHOD FOR MEASURING MICROBIAL INDICATORS OF RECREATIONAL WATER QUALITY - 2006 EPA SCIENCE FORUM

EPA Science Inventory

Because the current approved cultural methods for monitoring indicator bacteria in recreational water require 24 hours to produce results, the public may be exposed to potentially contaminated water before the water has been identified as hazardous. This project was initiated to...

Text analysis methods, text analysis apparatuses, and articles of manufacture

DOEpatents

Whitney, Paul D; Willse, Alan R; Lopresti, Charles A; White, Amanda M

2014-10-28

Text analysis methods, text analysis apparatuses, and articles of manufacture are described according to some aspects. In one aspect, a text analysis method includes accessing information indicative of data content of a collection of text comprising a plurality of different topics, using a computing device, analyzing the information indicative of the data content, and using results of the analysis, identifying a presence of a new topic in the collection of text.

Web-Based Training Methods for Behavioral Health Providers: A Systematic Review.

PubMed

Jackson, Carrie B; Quetsch, Lauren B; Brabson, Laurel A; Herschell, Amy D

2018-07-01

There has been an increase in the use of web-based training methods to train behavioral health providers in evidence-based practices. This systematic review focuses solely on the efficacy of web-based training methods for training behavioral health providers. A literature search yielded 45 articles meeting inclusion criteria. Results indicated that the serial instruction training method was the most commonly studied web-based training method. While the current review has several notable limitations, findings indicate that participating in a web-based training may result in greater post-training knowledge and skill, in comparison to baseline scores. Implications and recommendations for future research on web-based training methods are discussed.

Characterization of System Status Signals for Multivariate Time Series Discretization Based on Frequency and Amplitude Variation

PubMed Central

2018-01-01

Many fault detection methods have been proposed for monitoring the health of various industrial systems. Characterizing the monitored signals is a prerequisite for selecting an appropriate detection method. However, fault detection methods tend to be decided with user’s subjective knowledge or their familiarity with the method, rather than following a predefined selection rule. This study investigates the performance sensitivity of two detection methods, with respect to status signal characteristics of given systems: abrupt variance, characteristic indicator, discernable frequency, and discernable index. Relation between key characteristics indicators from four different real-world systems and the performance of two fault detection methods using pattern recognition are evaluated. PMID:29316731

Tamper-indicating barcode and method

DOEpatents

Cummings, Eric B.; Even, Jr., William R.; Simmons, Blake A.; Dentinger, Paul Michael

2005-03-22

A novel tamper-indicating barcode methodology is disclosed that allows for detection of alteration to the barcode. The tamper-indicating methodology makes use of a tamper-indicating means that may be comprised of a particulate indicator, an optical indicator, a deformable substrate, and/or may be an integrated aspect of the barcode itself. This tamper-indicating information provides greater security for the contents of containers sealed with the tamper-indicating barcodes.

[Study on the optimization of monitoring indicators of drinking water quality during health supervision].

PubMed

Ye, Bixiong; E, Xueli; Zhang, Lan

2015-01-01

To optimize non-regular drinking water quality indices (except Giardia and Cryptosporidium) of urban drinking water. Several methods including drinking water quality exceed the standard, the risk of exceeding standard, the frequency of detecting concentrations below the detection limit, water quality comprehensive index evaluation method, and attribute reduction algorithm of rough set theory were applied, redundancy factor of water quality indicators were eliminated, control factors that play a leading role in drinking water safety were found. Optimization results showed in 62 unconventional water quality monitoring indicators of urban drinking water, 42 water quality indicators could be optimized reduction by comprehensively evaluation combined with attribute reduction of rough set. Optimization of the water quality monitoring indicators and reduction of monitoring indicators and monitoring frequency could ensure the safety of drinking water quality while lowering monitoring costs and reducing monitoring pressure of the sanitation supervision departments.

A New Method to Classify Injury Severity by Diagnosis: Validation using Workers' Compensation and Trauma Registry Data

PubMed Central

Sears, Jeanne M.; Bowman, Stephen M.; Rotert, Mary; Hogg-Johnson, Sheilah

2015-01-01

Purpose Acute work-related trauma is a leading cause of death and disability among U.S. workers. Existing methods to estimate injury severity have important limitations. This study assessed a severe injury indicator constructed from a list of severe traumatic injury diagnosis codes previously developed for surveillance purposes. Study objectives were to: (1) describe the degree to which the severe injury indicator predicts work disability and medical cost outcomes; (2) assess whether this indicator adequately substitutes for estimating Abbreviated Injury Scale (AIS)-based injury severity from workers' compensation (WC) billing data; and (3) assess concordance between indicators constructed from Washington State Trauma Registry (WTR) and WC data. Methods WC claims for workers injured in Washington State from 1998-2008 were linked to WTR records. Competing risks survival analysis was used to model work disability outcomes. Adjusted total medical costs were modeled using linear regression. Information content of the severe injury indicator and AIS-based injury severity measures were compared using Akaike Information Criterion and R2. Results Of 208,522 eligible WC claims, 5% were classified as severe. Among WC claims linked to the WTR, there was substantial agreement between WC-based and WTR-based indicators (kappa=0.75). Information content of the severe injury indicator was similar to some AIS-based measures. The severe injury indicator was a significant predictor of WTR inclusion, early hospitalization, compensated time loss, total permanent disability, and total medical costs. Conclusions Severe traumatic injuries can be directly identified when diagnosis codes are available. This method provides a simple and transparent alternative to AIS-based injury severity estimation. PMID:25900409

Semi-empirical proton binding constants for natural organic matter

NASA Astrophysics Data System (ADS)

Matynia, Anthony; Lenoir, Thomas; Causse, Benjamin; Spadini, Lorenzo; Jacquet, Thierry; Manceau, Alain

2010-03-01

Average proton binding constants ( KH,i) for structure models of humic (HA) and fulvic (FA) acids were estimated semi-empirically by breaking down the macromolecules into reactive structural units (RSUs), and calculating KH,i values of the RSUs using linear free energy relationships (LFER) of Hammett. Predicted log KH,COOH and log KH,Ph-OH are 3.73 ± 0.13 and 9.83 ± 0.23 for HA, and 3.80 ± 0.20 and 9.87 ± 0.31 for FA. The predicted constants for phenolic-type sites (Ph-OH) are generally higher than those derived from potentiometric titrations, but the difference may not be significant in view of the considerable uncertainty of the acidity constants determined from acid-base measurements at high pH. The predicted constants for carboxylic-type sites agree well with titration data analyzed with Model VI (4.10 ± 0.16 for HA, 3.20 ± 0.13 for FA; Tipping, 1998), the Impermeable Sphere model (3.50-4.50 for HA; Avena et al., 1999), and the Stockholm Humic Model (4.10 ± 0.20 for HA, 3.50 ± 0.40 for FA; Gustafsson, 2001), but differ by about one log unit from those obtained by Milne et al. (2001) with the NICA-Donnan model (3.09 ± 0.51 for HA, 2.65 ± 0.43 for FA), and used to derive recommended generic values. To clarify this ambiguity, 10 high-quality titration data from Milne et al. (2001) were re-analyzed with the new predicted equilibrium constants. The data are described equally well with the previous and new sets of values ( R2 ⩾ 0.98), not necessarily because the NICA-Donnan model is overparametrized, but because titration lacks the sensitivity needed to quantify the full binding properties of humic substances. Correlations between NICA-Donnan parameters are discussed, but general progress is impeded by the unknown number of independent parameters that can be varied during regression of a model fit to titration data. The high consistency between predicted and experimental KH,COOH values, excluding those of Milne et al. (2001), gives faith in the proposed semi-empirical structural approach, and its usefulness to assess the plausibility of proton stability constants derived from simulations of titration data.

Neighbouring group processes in the deamination of protonated phenylalanine derivatives.

PubMed

Lioe, Hadi; O'Hair, Richard A J

2005-10-21

The gas-phase fragmentation of protonated phenylalanine and a series of its derivatives (tyrosine, 4-methylphenylalanine, 4-aminophenylalanine, 4-methoxyphenylalanine, 4-tert-butylphenylalanine, 4-fluorophenylalanine, 4-chlorophenylalanine, 4-bromophenylalanine, 4-iodophenylalanine, 4-cyanophenylalanine, 4-nitrophenylalanine, 3-fluorophenylalanine, and 3,4-dichlorophenylalanine) were examined using a combination of low energy CID in a quadrupole ion trap mass spectrometer as well as DFT calculations and RRKM modelling. In particular, the relationship between the electron-donating ability of the substituent and the competitive losses of H2O + CO and NH3 were explored through the application of the Hammett equation. It was found that electron-donating substituents promote the loss of NH3, while electron-withdrawing substituents suppress the loss of NH3 and favour the H2O + CO loss fragmentation channel instead. These observations are consistent with a neighbouring group pathway operating for the loss of NH3. Molecular orbital calculation (at the B3LYP/6-31+G(d,p) level of theory) were also performed for a range of derivatives to compare the relative transition state energy barriers for three competing mechanisms: (i) the combined loss of H2O + CO, which is triggered by an initial intramolecular proton transfer from the ammonium group to hydroxyl OH, followed by the combined loss of H2O and CO to form an immonium ion; (ii) loss of NH3 via an aryl assisted neighbouring group pathway to yield a phenonium ion; (iii) loss of NH3 via a 1,2-hydride migration process, which results in the formation of a benzyl cation. The relative energy barriers for H2O + CO loss remain nearly constant, while that for both NH3 pathways increase as the substituent moves from electron-donating to electron-withdrawing. The relative transition state energy for loss of NH3 via the aryl assisted neighbouring group pathway is always lower than that of the 1,2-hydride migration process. RRKM modelling of the DFT predicted barrier heights suggest that the rate constants for H2O + CO loss are insensitive to the substituent on the ring, while the NH3 loss channels are greatly affected by the substituent. These theoretical results are consistent with the experimental observation of the relative yields of the competing fragmentation channels. Finally, comparisons with published gas phase and condensed phase studies on related systems are made.

Automated analysis of plethysmograms for functional studies of hemodynamics

NASA Astrophysics Data System (ADS)

Zatrudina, R. Sh.; Isupov, I. B.; Gribkov, V. Yu.

2018-04-01

The most promising method for the quantitative determination of cardiovascular tone indicators and of cerebral hemodynamics indicators is the method of impedance plethysmography. The accurate determination of these indicators requires the correct identification of the characteristic points in the thoracic impedance plethysmogram and the cranial impedance plethysmogram respectively. An algorithm for automatic analysis of these plethysmogram is presented. The algorithm is based on the hard temporal relationships between the phases of the cardiac cycle and the characteristic points of the plethysmogram. The proposed algorithm does not require estimation of initial data and selection of processing parameters. Use of the method on healthy subjects showed a very low detection error of characteristic points.

Finding a needle in a haystack: toward a psychologically informed method for aviation security screening.

PubMed

Ormerod, Thomas C; Dando, Coral J

2015-02-01

Current aviation security systems identify behavioral indicators of deception to assess risks to flights, but they lack a strong psychological basis or empirical validation. We present a new method that tests the veracity of passenger accounts. In an in vivo double-blind randomized-control trial conducted in international airports, security agents detected 66% of deceptive passengers using the veracity test method compared with less than 5% using behavioral indicator recognition. As well as revealing advantages of veracity testing over behavioral indicator identification, the study provides the highest levels to date of deception detection in a realistic setting where the known base rate of deceptive individuals is low.

Evaluation of different shadow detection and restoration methods and their impact on vegetation indices using UAV high-resolution imageries over vineyards

NASA Astrophysics Data System (ADS)

Aboutalebi, M.; Torres-Rua, A. F.; McKee, M.; Kustas, W. P.; Nieto, H.

2017-12-01

Shadows are an unavoidable component of high-resolution imagery. Although shadows can be a useful source of information about terrestrial features, they are a hindrance for image processing and lead to misclassification errors and increased uncertainty in defining surface reflectance properties. In precision agriculture activities, shadows may affect the performance of vegetation indices at pixel and plant scales. Thus, it becomes necessary to evaluate existing shadow detection and restoration methods, especially for applications that makes direct use of pixel information to estimate vegetation biomass, leaf area index (LAI), plant water use and stress, chlorophyll content, just to name a few. In this study, four high-resolution imageries captured by the Utah State University - AggieAir Unmanned Aerial Vehicle (UAV) system flown in 2014, 2015, and 2016 over a commercial vineyard located in the California for the USDA-Agricultural Research Service Grape Remote sensing Atmospheric Profile and Evapotranspiration Experiment (GRAPEX) Program are used for shadow detection and restoration. Four different methods for shadow detection are compared: (1) unsupervised classification, (2) supervised classification, (3) index-based method, and (4) physically-based method. Also, two different shadow restoration methods are evaluated: (1) linear correlation correction, and (2) gamma correction. The models' performance is evaluated over two vegetation indices: normalized difference vegetation index (NDVI) and LAI for both sunlit and shadowed pixels. Histogram and analysis of variance (ANOVA) are used as performance indicators. Results indicated that the performance of the supervised classification and the index-based method are better than other methods. In addition, there is a statistical difference between the average of NDVI and LAI on the sunlit and shadowed pixels. Among the shadow restoration methods, gamma correction visually works better than the linear correlation correction. Moreover, the statistical difference between sunlit and shadowed NDVI and LAI decreases after the application of the gamma restoration method. Potential effects of shadows on modeling surface energy balance and evapotranspiration using very high resolution UAV imagery over the GRAPEX vineyard will be discussed.

Statistical Approaches for Spatiotemporal Prediction of Low Flows

NASA Astrophysics Data System (ADS)

Fangmann, A.; Haberlandt, U.

2017-12-01

An adequate assessment of regional climate change impacts on streamflow requires the integration of various sources of information and modeling approaches. This study proposes simple statistical tools for inclusion into model ensembles, which are fast and straightforward in their application, yet able to yield accurate streamflow predictions in time and space. Target variables for all approaches are annual low flow indices derived from a data set of 51 records of average daily discharge for northwestern Germany. The models require input of climatic data in the form of meteorological drought indices, derived from observed daily climatic variables, averaged over the streamflow gauges' catchments areas. Four different modeling approaches are analyzed. Basis for all pose multiple linear regression models that estimate low flows as a function of a set of meteorological indices and/or physiographic and climatic catchment descriptors. For the first method, individual regression models are fitted at each station, predicting annual low flow values from a set of annual meteorological indices, which are subsequently regionalized using a set of catchment characteristics. The second method combines temporal and spatial prediction within a single panel data regression model, allowing estimation of annual low flow values from input of both annual meteorological indices and catchment descriptors. The third and fourth methods represent non-stationary low flow frequency analyses and require fitting of regional distribution functions. Method three is subject to a spatiotemporal prediction of an index value, method four to estimation of L-moments that adapt the regional frequency distribution to the at-site conditions. The results show that method two outperforms successive prediction in time and space. Method three also shows a high performance in the near future period, but since it relies on a stationary distribution, its application for prediction of far future changes may be problematic. Spatiotemporal prediction of L-moments appeared highly uncertain for higher-order moments resulting in unrealistic future low flow values. All in all, the results promote an inclusion of simple statistical methods in climate change impact assessment.

Beyond the false negative rate: development of quality indicators for sentinel lymph node biopsy in breast cancer.

PubMed

Quan, May Lynn; Wells, Bryan J; McCready, David; Wright, Frances C; Fraser, Novlette; Gagliardi, Anna R

2010-02-01

Sentinel lymph node biopsy (SNLB) has been adopted as the standard method of axillary staging for women with clinically node-negative early-stage breast cancer. The false negative rate as a quality indicator is impractical given the need for a completion axillary dissection to calculate. The objective of this study was to develop practical quality indicators for SLNB using an expert consensus method and to determine if they were feasible to measure. We used a modified Delphi consensus process to develop quality indicators for SLNB. A multidisciplinary expert panel reviewed potential indicators extracted from the medical literature to select quality indicators that were relevant and measurable. Feasibility was determined by abstracting the quality indicator variables from a retrospective chart review. The expert panel prioritized 11 quality indicators as benchmarks for assessing the quality of surgical care in SNLB. Nine of the indicators were measurable at the chart or institutional level. A systematic evidence- and consensus-based approach was used to develop measurable quality indicators that could be used by practicing surgeons and administrators to evaluate performance of SLNB in breast cancer.

Determination of the mechanical indices of composite materials by testing multilayered samples

NASA Astrophysics Data System (ADS)

Teregulov, I. G.; Kayumov, R. A.; Butenko, Yu. I.; Safiullin, D. Kh.

1996-09-01

The mechanical indices of materials such as composites reinforced by braids and ribbons are difficult to determine by standard methods. Moreover, the indices of such materials may be greatly altered when they are converted into various structures. It has been suggested that these indices be determined by analyzing the structure testing data. The determination of linear and nonlinear elastic, plastic, and viscoelastic parameters of reinforced materials is discussed. A very simple structure, namely, cylindrical shells made by symmetric winding, is studied as an example. Equilibrium conditions are used to obtain resolving equations relative to the mechanical indices. Convergence of iteration methods is examined. The effect of the scatter of experimental data on the calculated results is analyzed.

Pollution indices as useful tools for the comprehensive evaluation of the degree of soil contamination-A review.

PubMed

Kowalska, Joanna Beata; Mazurek, Ryszard; Gąsiorek, Michał; Zaleski, Tomasz

2018-04-05

The paper provides a complex, critical assessment of heavy metal soil pollution using different indices. Pollution indices are widely considered a useful tool for the comprehensive evaluation of the degree of contamination. Moreover, they can have a great importance in the assessment of soil quality and the prediction of future ecosystem sustainability, especially in the case of farmlands. Eighteen indices previously described by several authors (I geo , PI, EF, C f , PI sum , PI Nemerow , PLI, PI ave , PI Vector , PIN, MEC, CSI, MERMQ, C deg , RI, mCd and ExF) as well as the newly published Biogeochemical Index (BGI) were compared. The content, as determined by other authors, of the most widely investigated heavy metals (Cd, Pb and Zn) in farmland, forest and urban soils was used as a database for the calculation of all of the presented indices, and this shows, based on statistical methods, the similarities and differences between them. The indices were initially divided into two groups: individual and complex. In order to achieve a more precise classification, our study attempted to further split indices based on their purpose and method of calculation. The strengths and weaknesses of each index were assessed; in addition, a comprehensive method for pollution index choice is presented, in order to best interpret pollution in different soils (farmland, forest and urban). This critical review also contains an evaluation of various geochemical backgrounds (GBs) used in heavy metal soil pollution assessments. The authors propose a comprehensive method in order to assess soil quality, based on the application of local and reference GB.

Selection of vegetation indices for mapping the sugarcane condition around the oil and gas field of North West Java Basin, Indonesia

NASA Astrophysics Data System (ADS)

Muji Susantoro, Tri; Wikantika, Ketut; Saepuloh, Asep; Handoyo Harsolumakso, Agus

2018-05-01

Selection of vegetation indices in plant mapping is needed to provide the best information of plant conditions. The methods used in this research are the standard deviation and the linear regression. This research tried to determine the vegetation indices used for mapping the sugarcane conditions around oil and gas fields. The data used in this study is Landsat 8 OLI/TIRS. The standard deviation analysis on the 23 vegetation indices with 27 samples has resulted in the six highest standard deviations of vegetation indices, termed as GRVI, SR, NLI, SIPI, GEMI and LAI. The standard deviation values are 0.47; 0.43; 0.30; 0.17; 0.16 and 0.13. Regression correlation analysis on the 23 vegetation indices with 280 samples has resulted in the six vegetation indices, termed as NDVI, ENDVI, GDVI, VARI, LAI and SIPI. This was performed based on regression correlation with the lowest value R2 than 0,8. The combined analysis of the standard deviation and the regression correlation has obtained the five vegetation indices, termed as NDVI, ENDVI, GDVI, LAI and SIPI. The results of the analysis of both methods show that a combination of two methods needs to be done to produce a good analysis of sugarcane conditions. It has been clarified through field surveys and showed good results for the prediction of microseepages.