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David B. Marshall - One of the best experts on this subject based on the ideXlab platform.
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Analysis of 1st‐Order Rate Constant Spectra With Regularized Least‐Squares and ExpectationMaximization: 1. Theory and Numerical Characterization
Analytical Chemistry, 1993Co-Authors: Brett J. Stanley, Stephen E. Bialkowski, David B. MarshallAbstract:Analysis of parallel, first-Order Rate processes by deconvolution of single-exponential kernels from experimental data is performed with regularized least squares and the method of expectation maximization (EM). These methods may be used in general for the unbiased numerical analysis of linear Fredholm integrals of the first kind with optimal results. Regularized least squares is performed using a smoothing regularizor with an adaptive choice for the regularization parameter (CONTIN) and by ridge regression using the generalized cross-validation choice for the regularization parameter (GCV)
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analysis of 1st Order Rate Constant spectra with regularized least squares and expectationmaximization 1 theory and numerical characterization
Analytical Chemistry, 1993Co-Authors: Brett J. Stanley, Stephen E. Bialkowski, David B. MarshallAbstract:Analysis of parallel, first-Order Rate processes by deconvolution of single-exponential kernels from experimental data is performed with regularized least squares and the method of expectation maximization (EM). These methods may be used in general for the unbiased numerical analysis of linear Fredholm integrals of the first kind with optimal results. Regularized least squares is performed using a smoothing regularizor with an adaptive choice for the regularization parameter (CONTIN) and by ridge regression using the generalized cross-validation choice for the regularization parameter (GCV)
Adedayo A Fodeke - One of the best experts on this subject based on the ideXlab platform.
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reversible reaction of 5 5 dithiobis 2 nitrobenzoate with the hemoglobins of the domestic cat acetylation of nh3 terminal group of the β chain transforms the complex ph dependence of the forward apparent second Order Rate Constant to a simple form
Biophysical Chemistry, 2006Co-Authors: Kehinde O Okonjo, Adedayo A FodekeAbstract:We demonstRate kinetically that the reaction of 5,5V-dithiobis(2-nitrobenzoate) with the CysF9[93]h sulfhydryl group of domestic cat hemoglobins is a reversible process. In the major hemoglobin, in which the NH3 + terminal group of GlyNA1[1]h is free, kf, the apparent forward second Order Rate Constant, has a complex pH dependence profile. In the minor hemoglobin, the NH3 + terminal group of SerNA1[1]h is acetylated, and the pH dependence profile of kf is simple. These results support the proposal that the positively charged groups at the organic phosphate binding site are electrostatically linked to CysF9[93]h. Quantitative analyses of the complex profiles enabled us to estimate pKa so f 7.47 T0.3; 6.53 T0.03 and 8.49 T0.3 for GlyNA1[1]h, HisH21[143]h and other histidines within 2 nm of the sulfhydryl, and CysF9[93]h, respectively, of the major hemoglobin. Analyses of the simple profiles gave pKas of 6.33 T0.17 and 8.54 T0.5 for HisH21[143]h and other histidines within a distance of 2 nm of the sulfhydryl, and CysF9[93]h of the minor hemoglobin, respectively. D 2005 Elsevier B.V. All rights reserved.
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Reversible reaction of 5,5′-dithiobis(2-nitrobenzoate) with the hemoglobins of the domestic cat: Acetylation of NH3+ terminal group of the β chain transforms the complex pH dependence of the forward apparent second Order Rate Constant to a simple for
Biophysical chemistry, 2005Co-Authors: Kehinde O Okonjo, Adedayo A FodekeAbstract:We demonstRate kinetically that the reaction of 5,5V-dithiobis(2-nitrobenzoate) with the CysF9[93]h sulfhydryl group of domestic cat hemoglobins is a reversible process. In the major hemoglobin, in which the NH3 + terminal group of GlyNA1[1]h is free, kf, the apparent forward second Order Rate Constant, has a complex pH dependence profile. In the minor hemoglobin, the NH3 + terminal group of SerNA1[1]h is acetylated, and the pH dependence profile of kf is simple. These results support the proposal that the positively charged groups at the organic phosphate binding site are electrostatically linked to CysF9[93]h. Quantitative analyses of the complex profiles enabled us to estimate pKa so f 7.47 T0.3; 6.53 T0.03 and 8.49 T0.3 for GlyNA1[1]h, HisH21[143]h and other histidines within 2 nm of the sulfhydryl, and CysF9[93]h, respectively, of the major hemoglobin. Analyses of the simple profiles gave pKas of 6.33 T0.17 and 8.54 T0.5 for HisH21[143]h and other histidines within a distance of 2 nm of the sulfhydryl, and CysF9[93]h of the minor hemoglobin, respectively. D 2005 Elsevier B.V. All rights reserved.
Urs Jans - One of the best experts on this subject based on the ideXlab platform.
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Degradation of naled and dichlorvos promoted by reduced sulfur species in well-defined anoxic aqueous solutions
Environmental science & technology, 2006Co-Authors: Qiu Gan, Raphael M. Singh, Urs JansAbstract:This work examines the reaction of reduced sulfur species (e.g., bisulfide, thiosulfate, thiophenolate) with naled, a registered insecticide, in well-defined anoxic aqueous solutions at 5 degrees C. High concentrations of reduced sulfur species can occur in the porewater of sediments and in anoxic subregions of estuaries. The dominanttransformation product from the reaction of naled with reduced sulfur species is dichlorvos, which indicates that debromination is the major reaction pathway. Dichlorvos is also a registered insecticide which is more toxic than naled. The second-Order Rate Constants for reaction of naled with bisulfide and thiophenolate at 5 degrees C are 10.2 +/- 0.4 M(-1) s(-1) and 27.3 +/- 0.9 M(-1) s(-1), respectively, while the second-Order Rate Constant for the reaction of naled with hydrogen sulfide and thiophenol are not significantly different from zero. The second-Order Rate Constant of the reaction of naled with thiosulfate at 5 degrees C is 5.0 +/- 0.3 M(-1) s(-1). In contrast, the second-Order Rate Constant of the reaction of dichlorvos with bisulfide at 25 degrees C is (3.3 +/- 0.1) x 10(-3) M(-1) s(-1). The activation parameters of the reaction of naled with bisulfide were also determined from the measured second-Order Rate Constants over a temperature range. The results indicate that reduced sulfur species can play a very important role in the transformation of naled and dichlorvos in the coastal marine environment. It can be expected that in the presence of reduced sulfur species, naled is almost immediately transformed into the more toxic dichlorvos, which has an expected half-life of 4 days to weeks.
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Nucleophilic substitution reactions of chlorpyrifos-methyl with sulfur species
Environmental science & technology, 2006Co-Authors: Urs JansAbstract:Chlorpyrifos-methyl is widely used in the control of insects on certain stored grain, including wheat, barley, oats, rice, and sorghum. The reactions of chlorpyrifos-methyl with hydrogensulfide/bisulfide (H2S/HS-), polysulfides (Sn(2-)), thiophenolate (PhS-), and thiosulfate (S2O3(2-)) were examined in well-defined aqueous solutions over a pH range from 5 to 9. The Rates are first-Order in the concentration of the different reduced sulfur species. The resulting data indicate that chlorpyrifos-methyl undergoes a S(N)2 reaction with the reduced sulfur species. The transformation products indicate that the nucleophilic substitution of reduced sulfur species occurs at the carbon atom of a methoxy group to form the desmethyl chlorpyrifos-methyl. The formation of trichloropyridinol, a minor degradation product, could be attributed entirelyto hydrolysis. The reaction of chlorpyrifos-methyl with thiophenolate leads to the formation of the corresponding methylated sulfur compound. The resulting pseudo-first-Order Rate Constant for chlorpyrifos-methyl with bisulfide yielded a second-Order Rate Constant of 2.2 (+/- 0.1) x 10(-3) M(-1) s(-1). The determined second-Order Rate Constants show that the reaction of chlorpyrifos-methyl with HS- is of the same Order of magnitude as the reaction of chlorpyrifos-methyl with S2O3(2-) with a second-Order Rate Constant of 1.0 (+/- 0.1) x 10(-3) M(-1) s(-1). The second-Order Rate Constant for chlorpyrifos-methyl with polysulfides (3.1 (+/- 0.3) x 10(-2) M(-1) s(-1)) is of the same Order of magnitude as the one with thiophenolate (2.1 (+/- 0.2) x 10(-2) M(-1) s(-1)). The second-Order Rate Constant for the reaction of polysulfides is approximately 1 Order of magnitude greater than that for the reaction with HS-. When the determined second-Order Rate Constants are multiplied by the concentration of HS-, polysulfides and thiosulfate reported in salt marshes and porewaters, predicted half-lives show that the inorganic reduced sulfur species present at environmentally relevant concentrations may represent an important sink for phosphorothionate triesters in coastal marine environments.
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Reaction of chlorpyrifos-methyl in aqueous hydrogen sulfide/bisulfide solutions.
Journal of Agricultural and Food Chemistry, 2003Co-Authors: Urs Jans, M. Hasan MiahAbstract:The kinetics of the reactions of chlorpyrifos-methyl, an organophosphorus insecticide, with hydrogen sulfide (H2S) and bisulfide (HS-) were determined in well-defined aqueous solutions. The resulting pseudo-first-Order Rate Constant for chlorpyrifos-methyl with bisulfide yielded a second-Order Rate Constant of (2.1 ± 0.3) × 10-3 M-1 s-1. The second-Order Rate Constant for chlorpyrifos-methyl with hydrogen sulfide is significantly slower than the second-Order Rate Constant with bisulfide. The contribution of H2S to the observed degradation Rate Constant of chlorpyrifos-methyl at concentrations of up to 4 mM H2S is not significant. The second-Order Rate Constant of chlorpyrifos-methyl with H2S was too low to be measured in this study. The results indicate that HS- present at environmentally relevant concentrations may represent an important sink for phosphorothionate triesters in a coastal marine environment, while H2S reacts too slowly to be environmentally relevant (pH 6−9). Trichloropyridinol, the major ...
Shunichi Fukuzumi - One of the best experts on this subject based on the ideXlab platform.
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proton promoted oxygen atom transfer vs proton coupled electron transfer of a non heme iron iv oxo complex
Journal of the American Chemical Society, 2012Co-Authors: Jiyun Park, Yuma Morimoto, Yongmin Lee, Wonwoo Nam, Shunichi FukuzumiAbstract:Sulfoxidation of thioanisoles by a non-heme iron(IV)–oxo complex, [(N4Py)FeIV(O)]2+ (N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine), was remarkably enhanced by perchloric acid (70% HClO4). The observed second-Order Rate Constant (kobs) of sulfoxidation of thioaniosoles by [(N4Py)FeIV(O)]2+ increases linearly with increasing concentration of HClO4 (70%) in acetonitrile (MeCN)at 298 K. In contrast to sulfoxidation of thioanisoles by [(N4Py)FeIV(O)]2+, the observed second-Order Rate Constant (ket) of electron transfer from one-electron reductants such as [FeII(Me2bpy)3]2+ (Me2bpy = 4,4-dimehtyl-2,2′-bipyridine) to [(N4Py)FeIV(O)]2+ increases with increasing concentration of HClO4, exhibiting second-Order dependence on HClO4 concentration. This indicates that the proton-coupled electron transfer (PCET) involves two protons associated with electron transfer from [FeII(Me2bpy)3]2+ to [(N4Py)FeIV(O)]2+ to yield [FeIII(Me2bpy)3]3+ and [(N4Py)FeIII(OH2)]3+. The one-electron reduction potential (Ered)...
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scandium ion promoted photoinduced electron transfer oxidation of fullerenes and derivatives by p chloranil and p benzoquinone
Journal of the American Chemical Society, 2001Co-Authors: Shunichi Fukuzumi, Hisahiro Mori, Hiroshi Imahori, Tomoyoshi Suenobu, Yasuyuki Araki, Osamu Ito, Karl M KadishAbstract:In the presence of scandium triflate, an efficient photoinduced electron transfer from the triplet excited state of C60 to p-chloranil occurs to produce C60 radical cation which has a diagnostic NIR (near-infrared) absorption band at 980 nm, whereas no photoinduced electron transfer occurs from the triplet excited state of C60 (3C60*) to p-chloranil in the absence of scandium ion in benzonitrile. The electron-transfer Rate obeys pseudo-first-Order kinetics and the pseudo-first-Order Rate Constant increases linearly with increasing p-chloranil concentration. The observed second-Order Rate Constant of electron transfer (ket) increases linearly with increasing scandium ion concentration. In contrast to the case of the C60/p-chloranil/Sc3+ system, the ket value for electron transfer from 3C60* to p-benzoquinone increases with an increase in Sc3+ concentration ([Sc3+]) to exhibit a first-Order dependence on [Sc3+], changing to a second-Order dependence at the high concentrations. Such a mixture of first-Order ...
Brett J. Stanley - One of the best experts on this subject based on the ideXlab platform.
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Analysis of 1st‐Order Rate Constant Spectra With Regularized Least‐Squares and ExpectationMaximization: 1. Theory and Numerical Characterization
Analytical Chemistry, 1993Co-Authors: Brett J. Stanley, Stephen E. Bialkowski, David B. MarshallAbstract:Analysis of parallel, first-Order Rate processes by deconvolution of single-exponential kernels from experimental data is performed with regularized least squares and the method of expectation maximization (EM). These methods may be used in general for the unbiased numerical analysis of linear Fredholm integrals of the first kind with optimal results. Regularized least squares is performed using a smoothing regularizor with an adaptive choice for the regularization parameter (CONTIN) and by ridge regression using the generalized cross-validation choice for the regularization parameter (GCV)
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analysis of 1st Order Rate Constant spectra with regularized least squares and expectationmaximization 1 theory and numerical characterization
Analytical Chemistry, 1993Co-Authors: Brett J. Stanley, Stephen E. Bialkowski, David B. MarshallAbstract:Analysis of parallel, first-Order Rate processes by deconvolution of single-exponential kernels from experimental data is performed with regularized least squares and the method of expectation maximization (EM). These methods may be used in general for the unbiased numerical analysis of linear Fredholm integrals of the first kind with optimal results. Regularized least squares is performed using a smoothing regularizor with an adaptive choice for the regularization parameter (CONTIN) and by ridge regression using the generalized cross-validation choice for the regularization parameter (GCV)
