Kinetics and mechanism of oxidation of l-ascorbic acid by peroxomonosulphate in acid perchlorate medium. Role of copper (II) as a trace metal-ion catalyst

The kinetics of oxidation of l-ascorbic acid by peroxomonosulphate (PMS) in presence and absence of Cu(II) catalyst has been studied. The stoichiometry of the reaction is represented by the following:

H₂A + HSO₅⁻ → A + HSO₄⁻ + H₂O     

Dynein-Inspired Multilane Exclusion Process with Open Boundary Conditions

Motivated by the sidewise motions of dynein motors shown in experiments, we use a variant of the exclusion process to model the multistep dynamics of dyneins on a cylinder with open ends. Due to the varied step sizes of the particles in a quasi-two-dimensional topology, we observe the emergence of a novel phase diagram depending on the various load conditions. Under high-load conditions, our numerical findings yield results similar to the TASEP model with the presence of all three standard TASEP phases, namely the low-density (LD), high-density (HD), and maximal-current (MC) phases. However, for medium- to low-load conditions, for all chosen influx and outflux rates, we only observe the LD and HD phases, and the maximal-current phase disappears. Further, we also measure the dynamics for a single dynein particle which is logarithmically slower than a TASEP particle with a shorter waiting time. Our results also confirm experimental observations of the dwell time distribution: The dwell time distribution for dyneins is exponential in less crowded conditions, whereas a double exponential emerges under overcrowded conditions.     

The influence of stop consonants' perceptual features on the Articulation Index model

Studies on consonant perception under noise conditions typically describe the average consonant error as exponential in the Articulation Index (AI). While this AI formula nicely fits the average error over all consonants, it does not fit the error for any consonant at the utterance level. This study analyzes the error patterns of six stop consonants /p, t, k, b, d, g/ with four vowels (/α/, /ε/, /I/, /ae/), at the individual consonant (i.e., utterance) level. The findings include that the utterance error is essentially zero for signal to noise ratios (SNRs) at least -2 dB, for >78% of the stop consonant utterances. For these utterances, the error is essentially a step function in the SNR at the utterance's detection threshold. This binary error dependence is consistent with the audibility of a single binary defining acoustic feature, having zero error above the feature's detection threshold. Also 11% of the sounds have high error, defined as ≥ 20% for SNRs greater than or equal to -2 dB. A grand average across many such sounds, having a natural distribution in thresholds, results in the error being exponential in the AI measure, as observed. A detailed analysis of the variance from the AI error is provided along with a Bernoulli-trials analysis of the statistical significance.     

Kinetics and mechanism of oxidation of l‐ascorbic acid by peroxomonophosphate in aqueous acid medium

The kinetics of oxidation of l ‐ascorbic acid (H₂A) by peroxomonophosphate in acid aqueous medium has been studied. The stoichiometry of the reaction corresponds to the reaction as represented by the equation (1) where A is dehydroascorbic acid. The reaction is second order versus first order with respect to each reactant. The rate is retarded by hydrogen ion concentration. A plausible reaction mechanism has been suggested. The derived rate law (2) from such a mechanism accounts for all experimental observations: (2) Such pH dependence is somewhat different from that observed in the case of metal ion oxidants. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 45: 41–16, 2013     

Strategic Substitution of −OH/−NR2 (R=Et,Me) Imparts Colorimetric Switching between F− and Hg2+ by Salicyaldehyde/Benzaldehyde-Quinoxaline Conjugates

We herein report two salicyaldehyde-quinoxaline ( HQS and HQSN ) conjugates and a benzaldehyde-quinoxaline ( QBN ) conjugate to fabricate selective chemosensors for F⁻ and Hg²⁺ in the micromolar range. This work demonstrates how sensing outcomes are affected by modulating proton acidity by introducing an electron donating group, −NEt₂, in the probe backbone. Interestingly, the un-substituted probe HQS can selectively detect F⁻, whereas HQSN and QBN are selective for Hg²⁺. In order to gain insights into the mechanism of sensing, geometry optimizations have been carried out on QS⁽⁻¹⁾ , QS⁽⁻¹⁾⋅⋅⋅HF , QSN⁽⁻¹⁾ and QSN⁽⁻¹⁾⋅⋅⋅HF and the experimental data are validated in terms of free energy and pK_a values. Detailed DFT and TD-DFT analyses provide ample support towards the mechanism of sensing of the analytes.     

Studies on α-glucosidase,aldose reductase and glycation inhibitory properties of sesquiterpenes and flavonoids of Zingiber zerumbet Smith

Eight known phytochemicals, four sesquiterpenes and four flavonoids of Zingiber zerumbet were screened against α-glucosidase enzyme, aldose reductase enzyme and antiglycation property under in vitro conditions. The results established kaempferol-3-O-methylether as a potent inhibitor of α-glucosidase enzyme with an IC₅₀ value of 7.88 μM. In aldose reductase enzyme inhibition assay, all the compounds except zerumbone epoxide showed good to excellent inhibition properties. Among these, the flavonoid compounds were found to be potent aldose reductase inhibitors compared with the four sesquiterpenes. In addition, compounds such as α-humulene, kaempferol, kaempferol-3-O-methylether and 3″,4″-O-diacetylafzelin displayed potent antiglycation properties. From overall results, we found that kaempferol and kaempferol-3-O-methylether are potent inhibitors of α-glucosidase enzyme, aldose reductase enzyme and glycation reaction, the three main targets of drugs for the treatment of diabetes and its complications.     

Oxidation of crotyl alcohol by N-chloro-4-methylbenzene sulphonamide in acidic medium and in alkaline media in the presence of os(VIII) catalyst-a kinetic pathway

The kinetic pathway of oxidation of crotyl alcohol by sodium salt of N -chloro-4-methylbenzene sulphonamide (chloramine-T) in acidic and alkaline medium has been studied. The speciation of chloramine-T has been made to suggest a proper and reasonable reaction mechanism. The thermodynamic quantities such as activation energy and activation entropy are evaluated in acidic as well as in catalysed alkaline medium. An anticipated reaction mechanism has been suggested.     

A Quinoxaline−Naphthaldehyde Conjugate for Colorimetric Determination of Copper Ion

This work facilitates detection of bivalent copper ion by a simple Schiff base probe QNH based on a quinoxaline−naphthaldehyde framework. The detailed study in absorption spectroscopy and theoretical aspects and crystal study of the probe and probe−copper complex has been discussed. The detection limit of the probe in the presence of Cu²⁺ is 0.45 µM in HEPES−buffer/acetonitrile (3/7, v/v) medium for absorption study. The reversibility of the probe−copper complex has been investigated by EDTA. The selective visual detection of copper has been established also in gel form.     

Kinetics and mechanism of oxidation of L-ascorbic acid by platinum(IV) in aqueous acid medium

The oxidation of l-ascorbic acid (H₂A) by platinum(IV) in aqueous acid medium exhibits overall second-order kinetics, being first order with respect to each reactant. Increasing both hydrogen and chloride ion concentrations inhibits the rate. The stoichiometry involves reaction of one platinum(IV) ion with H₂A to give dehydroascorbic acid. A reaction mechanism consistent with all the experimental observations is proposed.