Rate Constants For Trapping Research Articles

Predicting the reaction rates between flavonoids and methylglyoxal by combining molecular properties and machine learning

The kinetics of the reaction between methylglyoxal (MGO) and epigallocatechin gallate have been investigated at pH 7.4 and 37 °C, and the kinetic data were combined with previously obtained data of six other flavonoids to develop a model that allows to predict the trapping capacity of MGO based on the molecular properties of the seven flavonoids. The observed data were augmented by using synthetic minority oversampling technique forming a new data set that was used to create the predicting models for the trapping rate constant of MGO by flavonoids via principal component regression (PCR) and back-propagation neural network algorithm, respectively. The PCR model based on the first six principle components was robust and accurate comparing other created models, with an associated root-mean-square error value of 8.02 × 10−7 on the testing set. This work provides quantitative structure-activity models for rapid and accurate prediction of the trapping rate constant of MGO by flavonoids.

The influence of a trap state on the photoluminescence decay times under single pulse excitation

We numerically calculated the time-resolved photoluminescence spectra using the bimolecular trapping-detrapping model. The variations of carrier lifetimes are investigated by changing the carrier recombination and trapping rate constants, as well as the concentration of available trapping states.

Kinetic Modeling of 18F-(2S,4R)4-Fluoroglutamine in Mouse Models of Breast Cancer to Estimate Glutamine Pool Size as an Indicator of Tumor Glutamine Metabolism.

The PET radiotracer 18F-(2S,4R)4-fluoroglutamine (18F-Gln) reflects glutamine transport and can be used to infer glutamine metabolism. Mouse xenograft studies have demonstrated that 18F-Gln uptake correlates directly with glutamine pool size and is inversely related to glutamine metabolism through the glutaminase enzyme. To provide a framework for the analysis of 18F-Gln-PET, we have examined 18F-Gln uptake kinetics in mouse models of breast cancer at baseline and after inhibition of glutaminase. We describe results of the preclinical analysis and computer simulations with the goal of model validation and performance assessment in anticipation of human breast cancer patient studies. Methods: Triple-negative breast cancer and receptor-positive xenografts were implanted in athymic mice. PET mouse imaging was performed at baseline and after treatment with a glutaminase inhibitor or a vehicle solution for 4 mouse groups. Dynamic PET images were obtained for 1 h beginning at the time of intravenous injection of 18F-Gln. Kinetic analysis and computer simulations were performed on representative time-activity curves, testing 1- and 2-compartment models to describe kinetics. Results: Dynamic imaging for 1 h captured blood and tumor time-activity curves indicative of largely reversible uptake of 18F-Gln in tumors. Consistent with this observation, a 2-compartment model indicated a relatively low estimate of the rate constant of tracer trapping, suggesting that the 1-compartment model is preferable. Logan plot graphical analysis demonstrated late linearity, supporting reversible kinetics and modeling with a single compartment. Analysis of the mouse data and simulations suggests that estimates of glutamine pool size, specifically the distribution volume (VD) for 18F-Gln, were more reliable using the 1-compartment reversible model than the 2-compartment irreversible model. Tumor-to-blood ratios, a more practical potential proxy of VD, correlated well with volume of distribution from single-compartment models and Logan analyses. Conclusion: Kinetic analysis of dynamic 18F-Gln-PET images demonstrated the ability to measure VD to estimate glutamine pool size, a key indicator of cellular glutamine metabolism, by both a 1-compartment model and Logan analysis. Changes in VD with glutaminase inhibition support the ability to assess response to glutamine metabolism-targeted therapy. Concordance of kinetic measures with tumor-to-blood ratios provides a clinically feasible approach to human imaging.

Mechanistic investigation of water oxidation on hematite photoanodes using intensity-modulated photocurrent spectroscopy

Exploring the nature of photogenerated intermediates during the photoelectrochemical (PEC) oxidation of water is a crucial step to enhance the performance of PEC devices. In this work, the PEC water oxidation on different hematite photoanodes, either bare or modified with cobalt-based oxygen evolution co-catalyst, has been investigated using intensity-modulated photocurrent spectroscopy (IMPS) . The phenomenological rate constants for charge transfer and recombination have been determined at different bias potentials. Their potential dependence trends have been analyzed using a mechanistic model that combines the IMPS theory and the bulk characteristic of the semiconductor. Based on this model, the nature of the formed intermediates during water oxidation is explored. It is found that water oxidation takes place through the coupling of two mobile surface intermediates and two adjacent metal sites are involved in the process. The rate constants for the trapping of the photogenerated holes and the coupling of the mobile surface intermediates have been determined. All investigated photoanodes exhibit comparable rate constants for the trapping as well as for the coupling steps. The surface modification does not significantly influence the trapping and coupling rate constants but remarkably reduces the rate constant of recombination. These results indicate that the efficiency of hematite photoanode is limited by its intrinsic properties and the surface modification has a restricted impact on the overall performance.

Charge carrier injection and transport in QLED layer with dynamic equilibrium of trapping/de-trapping carriers

A theoretical analysis on carrier injection and transport through layers of quantum dot light emitting display (QLED) device was attempted assuming dynamic equilibrium of trapping and detrapping charge carriers. Assuming traps in exponential or Gaussian energy distribution, the effect of parameters on the current-voltage relationship for the device was investigated. The energy level and distribution of charge traps, a Schottky barrier, and the ratio of detrapping rate constant to the trapping rate constant were found to affect the current-voltage relationship significantly in the charge transport layer. The results suggest that the parameters must be modulated simultaneously in order to achieve a charge balance in the quantum dot layer of the QLED device.

Hydrogen permeation in 2205 duplex stainless steel under hydrostatic pressure and simulation by COMSOL

This article explores the effect of hydrostatic pressure on hydrogen diffusion process in 2205 duplex stainless steel. The experiments were performed in a homemade high pressure autoclave. The Fick's second law was modified and taken reversible traps into account. The apparent diffusion coefficient decreased by 74.85% when pressure increased from 0.1 to 7 MPa, both of forward and reverse trapping rate constants, apparent hydrogen concentration, and activation energy increased with higher hydrostatic pressure. Additionally, finite element method based on diffusion model was performed using COMSOL Multiphysics software and the trapping constants effects were analyzed, which can be used in ocean industry.

Radical scavenging properties of piperidine derivatives of fullerene C60/C70 and multi-walled carbon nanotubes

ABSTRACTDerivatives of C60/C70 fullerene and multi-walled carbon nanotubes (MWCNTs) with piperidine fragments were synthesized and their antioxidative activity was determined. The antioxidant activity of the investigated derivatives was studied by measuring the inhibition rate constants for their reaction with peroxy radicals in a model cumene initiated oxidation experiments and compared with that for commercial primary aromatic amine stabilizers. The inhibition rate constants for trapping of peroxy radicals by the MWCNTs amine derivatives were found to be higher than that of known aromatic amine antioxidants Neozone-D and Naugard 445. These novel compounds may be considered as promising broad-spectrum radical scavenging antioxidants.

Systematic trends in electron–hole pair trapping efficiency of rare earth doped YBO3 under vacuum ultraviolet excitation

Host-to-activator energy transfer efficiencies in rare-earth doped YBO3 under vacuum ultraviolet excitation have been estimated using excitation and reflectance spectroscopy. From these data, relative electron–hole pair (e–h) trapping rate constants have been calculated for seven different lanthanide dopants. In addition, the energies of activator electronic states relative to YBO3 band states were estimated using published empirical methods. From this, we find a correlation between e–h trapping efficiency and the energy of activator electronic states relative to YBO3 conduction and valence band energies.

Kinetic Evaluation of Spin Trapping Rate Constants of New CYPMPO-type Spin Traps for Superoxide and Other Free Radicals

Abstract CYPMPO (5-(2,2-dimethyl-1,3-propoxyl cyclophosphoryl)-5-methyl-1-pyrroline N-oxide) is a phosphorus containing spin trap that has been useful in aqueous media. Using a kinetic ESR spin trapping technique, we evaluated free radical trapping rate constants of two newly synthesized CYPMPO-type spin traps, including 2,2-dibutyl-substituted CYPMPO (DBCYP) and 5-phenyl-substituted CYPMPO (PhCYP). We investigated the spin trapping of five free radical species, i. e., superoxide, hydroxyl radical, alkoxyl radical, alkyl peroxyl radical and methyl radical. Other than superoxide, spin trapping rate constants of DBCYP and PhCYP are comparable to CYPMPO, ranging from 43.9% to 101% of CYPMPO's corresponding rate constants. However, PhCYP's spin-trapping rate constant against superoxide was 44% higher than that of CYPMPO. The results indicate that DBCYP and PhCYP may be the spin traps as useful as CYPMPO either in aqueous or non-aqueous medium.

Reactivities of substituted α-phenyl-N-tert-butyl nitrones.

In this work, a series of α-phenyl-N-tert-butyl nitrones bearing one, two, or three substituents on the tert-butyl group was synthesized. Cyclic voltammetry (CV) was used to investigate their electrochemical properties and showed a more pronounced substituent effect for oxidation than for reduction. Rate constants of superoxide radical (O2•–) reactions with nitrones were determined using a UV–vis stopped-flow method, and phenyl radical (Ph•) trapping rate constants were measured by EPR spectroscopy. The effect of N-tert-butyl substitution on the charge density and electron density localization of the nitronyl carbon as well as on the free energies of nitrone reactivity with O2•– and HO2• were computationally rationalized at the PCM/B3LYP/6-31+G**//B3LYP/6-31G* level of theory. Theoretical and experimental data showed that the rates of the reaction correlate with the nitronyl carbon charge density, suggesting a nucleophilic nature of O2•– and Ph• addition to the nitronyl carbon atom. Finally, the substituent effect was investigated in cell cultures exposed to hydrogen peroxide and a correlation between the cell viability and the oxidation potential of the nitrones was observed. Through a combination of computational methodologies and experimental methods, new insights into the reactivity of free radicals with nitrone derivatives have been proposed.

19.2: Distinguished Paper: Characterization of Electron‐Hole Pair Migration and Trapping in Rare Earth Doped YBO3 under Vacuum Ultraviolet Excitation

AbstractWe have measured host‐to‐activator energy transfer efficiencies in rare‐earth doped YBO3 under vacuum ultraviolet excitation. From these data, relative electron‐hole (e‐h) pair trapping rate constants can be estimated. Our analysis suggests a correlation between e‐h trapping efficiency and the energy of activator electronic states relative to the host conduction band.

Modeling hydrogen permeation through a thin titanium oxide film and palladium

Models that describe hydrogen permeation through a thin TiO2 film deposited on Pd have been developed based on a mass-balance equation consisting of diffusion, reversible hydrogen absorption/desorption, and irreversible hydrogen trapping. These models were numerically simulated by the finite element method. By comparing model simulations with experimental permeation curves, values of the parameters associated with permeation, such as diffusion coefficients, absorption and desorption rate constants, trapping rate constants, and saturation concentrations, can be evaluated. The TiO2 film noticeably impedes hydrogen permeation, essentially due to slow hydrogen transport in the oxide. The diffusion coefficient of hydrogen in TiO2 was found to be 10−13cm2/s, three orders of magnitude lower than that in Ti metal.

Image-Guided Po2 Probe Measurements Correlated with Parametric Images Derived from 18F-Fluoromisonidazole Small-Animal PET Data in Rats

(18)F-fluoromisonidazole PET, a noninvasive means of identifying hypoxia in tumors, has been widely applied but with mixed results, raising concerns about its accuracy. The objective of this study was to determine whether kinetic analysis of dynamic (18)F-fluoromisonidazole data provides better discrimination of tumor hypoxia than methods based on a simple tissue-to-plasma ratio. Eleven Dunning R3327-AT prostate tumor-bearing nude rats were immobilized in custom-fabricated whole-body molds, injected intravenously with (18)F-fluoromisonidazole, and imaged dynamically for 105 min. They were then transferred to a robotic system for image-guided measurement of intratumoral partial pressure of oxygen (Po(2)). The dynamic (18)F-fluoromisonidazole uptake data were fitted with 2 variants of a 2-compartment, 3-rate-constant model, one constrained to have K(1) equal to k(2) and the other unconstrained. Parametric images of the rate constants were generated. The Po(2) measurements were compared with spatially registered maps of kinetic rate constants and tumor-to-plasma ratios. The constrained pharmacokinetic model variant was shown to provide fits similar to that of the unconstrained model and did not introduce significant bias in the results. The trapping rate constant, k(3), of the constrained model provided a better discrimination of low Po(2) than the tissue-to-plasma ratio or the k(3) of the unconstrained model. The use of kinetic modeling on a voxelwise basis can identify tumor hypoxia with improved accuracy over simple tumor-to-plasma ratios. An effective means of controlling noise in the trapping rate constant, k(3), without introducing significant bias, is to constrain K(1) equal to k(2) during the fitting process.

Neutron Reflectivity Characterization of the Photoacid Reaction-Diffusion Latent and Developed Images of Molecular Resists for Extreme Ultraviolet Lithography

Lithographic feature size requirements have approached a few radius of gyration of photoresist polymers used in thin-film patterning. Furthermore, the feature dimensions are commensurate with the photoacid diffusion length that defines the underlying latent image. Smaller imaging building blocks may enable reduced feature sizes; however, resolution limits are also dependent upon the spatial extent of the photoacid-catalyzed reaction diffusion front and subsequent dissolution mechanism. The reaction-diffusion front was characterized by neutron reflectivity for ccc stereoisomer-purified, deuterium-labeled tert-butoxycarbonyloxy calix[4]resorcinarene molecular resists. The spatial extent of the reaction front exceeds the size of the molecular resist with an effective diffusion constant of (0.13 ± 0.06) nm(2)/s for reaction times longer than 60 s, with the maximum at shorter times. Comparison to a mean-field reaction-diffusion model shows that a photoacid trapping process provides bounds to the spatial and extent of reaction via a reaction-limited mechanism whereas the ratio of the reaction rate to trapping rate constants recovers the effective diffusion peak. Under the ideal step-exposure conditions, surface roughness was observed after either positive- or negative-tone development. However, negative-tone development follows a surface-restructuring mechanism rather than etch-like dissolution in positive-tone development.

ChemInform Abstract: Picosecond Radical Kinetics. Benzeneselenol as a Fast Radical Trapping Agent and Rate Constants for Ring Opening of the trans-(2- Phenylcyclopropyl)carbinyl Radical.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Antioxidant capacity of novel amine derivatives of buckminsterfullerene: Determination of inhibition rate constants in a model oxidation system

The radical scavenging efficiency of fullerenes can be significantly activated by means of a connection with hydrogen donating groups of antioxidants such as phenolic, amine and sulfhydryl. The developed system of conjugated σ–π bonds arranged in the fullerene molecule in a closed shape can promote a strong resonance effect on the grafted units and increase the hydrogen atom abstraction efficiency. In this case the known ability of fullerene to trap alkyl radicals might be combined with the strong chain breaking functionality to afford a new class of antioxidants with bimodal action. Explorations in the field of fullerene derivatives on their antioxidant performance provide novel information on the potential stabilization properties of this type of molecular structure. A series of amine derivatives of buckminsterfullerene (C 60) with tethered aliphatic chain, cycloaliphatic and aromatic fragments were synthesized and their antioxidant activity was determined. The antioxidant activity of the investigated derivatives was studied by measuring the inhibition rate constants for their reaction with alkyl and peroxy radicals in a model cumene initiated (2,2′-azobisisobutyronitrile, AIBN) oxidation experiments and compared to that recorded under identical experiments for buckminsterfullerene itself and commercial primary aromatic amine stabilizers. The results indicate that linking the amine moieties groups directly to the fullerene core gives rise to a new chain breaking antioxidant mode for the buckminsterfullerene while cyclic fragments containing the same but distant amine group do not reveal this ability. The inhibition rate constants for trapping of peroxy radicals by the amine derivatives were found to be higher than that of known aromatic amine antioxidants Neozone-D and Naugard 445. In addition the C 60 part of these molecules acts synergistically by trapping alkyl radicals with inhibition rate constants which exceed that of underivatised fullerene. The amine derivative containing sterically hindered piperidine and pyrrolidine fragments also heighten the inherent rate constant of buckminsterfullerene for scavenging alkyl radicals due to the additional antioxidant contribution promoted by the radical-quenching ability of the formed nitroxyl intermediates. These novel C 60–amine conjugates may be considered as promising molecules for broad-spectrum radical scavenging antioxidants.

Reactivity of Superoxide Radical Anion and Hydroperoxyl Radical with α-Phenyl-N-tert-butylnitrone (PBN) Derivatives

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.

Albumin Is the Main Nucleophilic Target of Human Plasma: A Protective Role Against Pro-atherogenic Electrophilic Reactive Carbonyl Species?

The aim of this work was to study the metabolic fate of 4-hydroxy- trans-2-nonenal (HNE) in human plasma, which represents the main vascular site of reactive carbonyl species (RCS) formation and where the main pro-atherogenic target proteins are formed. When HNE was spiked in human plasma, it rapidly disappeared (within 40 s) and no phase I metabolites were detected, suggesting that the main fate of HNE is due to an adduction mechanism. HNE consumption was then monitored in two plasma fractions: low molecular weight plasma protein fractions (<10 kDa; LMWF) and high molecular weight plasma protein fractions (>10 kDa; HMWF). HNE was almost stable in LMWF, while in HMWF it was consumed by almost 70% within 5 min. Proteomics identified albumin (HSA) as the main protein target, as further confirmed by a significantly reduced HNE quenching of dealbuminated plasma. LC-ESI-MS/MS analysis identified Cys34 and Lys199 as the most reactive adduction sites of HSA, through the formation of a Michael and Schiff base adducts, respectively. The rate constant of HNE trapping by albumin was 50.61 +/- 1.89 M (-1) s (-1) and that of Cys34 (29.37 M (-1) s (-1)) was 1 order of magnitude higher with respect to that of GSH (3.81 +/- 0.17 M (-1) s (-1)), as explained by molecular modeling studies. In conclusion, we suggest that albumin, through nucleophilic residues, and in particular Cys34, can act as an endogenous detoxifying agent of circulating RCS.

Effect of pH on superoxide/hydroperoxyl radical trapping by nitrones: an EPR/kinetic study

The pH dependence of the apparent rate constant kT ap for trapping by four nitrones was examined. In each case, kinetic curves were obtained after treatment of EPR spectra of the spin adduct formed using both singular value decomposition and pseudo-inverse deconvolution methods. Modelling these curves led to evaluate kT ap at various pH values. Analysis of the pH dependence of kT ap permitted the determination of the rate constants for the spin trapping of and of separately. Whatever the nitrone, our results clearly show that the EPR signals of the nitrone/superoxide spin adducts observed in aqueous media were essentially due to the trapping of the protonated species

Rate Constants for Reactions of Alkyl Radicals with Water and Methanol Complexes of Triethylborane

Reactions of secondary alkyl radicals with triethylborane and several of its complexes were studied. The H-atom transfer reactions from Et3B-OH2 and Et3B-OD2 were suppressed by addition of pyridine to the reaction mixture. Rate constants for reactions of secondary alkyl radicals with triethylborane and its complexes with water, deuterium oxide, methanol, and THF at ambient temperature were determined by radical clock methods. Cyclization of the 1-undecyl-5-hexenyl radical and ring opening of the 1-cyclobutyldodecyl radical were evaluated as clock reactions. The cyclobutylcarbinyl radical ring opening had the appropriate velocity for relatively precise determinations of the ratios of rate constants for H-atom transfer trapping and rearrangement, and these ratios combined with an estimated rate constant for the cyclobutylcarbinyl radical ring opening gave absolute values for the rate constants for the H-atom transfer reactions. For example, the triethylborane-water complex reacts with a secondary alkyl radical in benzene at 20 degrees C with a rate constant of 2 x 10(4) M(-1) s(-1). Variable temperature studies with the Et3B-CH3OH complex in toluene indicate that the hydrogen atom transfer reaction has unusually high entropic demand, which results in substantially more efficient hydrogen atom transfer trapping reactions in competition with radical ring opening and cyclization reactions at reduced temperatures.