Mechanism of oxidation of diazepam by Chloramine-B: A kinetic approach

The kinetics of the oxidation of diazepam (DZ) by Chloramine-B (CAB) has been studied in aqueous hydrochloric acid medium. The oxidation reaction follows the rate law: The dependence of the reaction rate on temperature is studied and activation parameters for the rate-determining step are evaluated. The dielectric constant of the medium has a small effect on the rate. Ionic strength and the reaction product benzenesulfonamide have no effect on the reaction rate. The solvent isotope effect is studied. A probable mechanism for the observed kinetic data is proposed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 605–611, 1998     

Smart Nanocarriers as an Emerging Platform for Cancer Therapy: A Review

Cancer is a group of disorders characterized by uncontrolled cell growth that affects around 11 million people each year globally. Nanocarrier-based systems are extensively used in cancer imaging, diagnostics as well as therapeutics; owing to their promising features and potential to augment therapeutic efficacy. The focal point of research remains to develop new-fangled smart nanocarriers that can selectively respond to cancer-specific conditions and deliver medications to target cells efficiently. Nanocarriers deliver loaded therapeutic cargos to the tumour site either in a passive or active mode, with the least drug elimination from the drug delivery systems. This review chiefly focuses on current advances allied to smart nanocarriers such as dendrimers, liposomes, mesoporous silica nanoparticles, quantum dots, micelles, superparamagnetic iron-oxide nanoparticles, gold nanoparticles and carbon nanotubes, to list a few. Exhaustive discussion on crucial topics like drug targeting, surface decorated smart-nanocarriers and stimuli-responsive cancer nanotherapeutics responding to temperature, enzyme, pH and redox stimuli have been covered.     

N‐bromosuccinimide oxidation of dipeptides and their amino acids: Synthesis,kinetics and mechanistic studies

Dipeptides (DP), namely valyl–glycine (Val–Gly), alanyl–proline (Ala–Pro), and valyl–proline (Val–Pro) were synthesized by classical solution phase methods and characterized. The kinetics of oxidation of amino acids (AA) and DP by N‐bromosuccinimide (NBS) was studied in the presence of perchlorate ions in acidic medium at 28°C. The reaction was followed spectrophotometrically at λ_max = 240 nm. The reactions follow identical kinetics, being first order each in [NBS], [AA], and [DP]. No effect on [H⁺], reduction product [succinimide], and ionic strength was observed. Effects of varying dielectric constant of the medium and addition of anions such as chloride and perchlorate were studied. Activation parameters have been computed. The oxidation products of the reaction were isolated and characterized. The proposed mechanism is consistent with the experimental results. An apparent correlation was noted between the rate of oxidation of AA and DP. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 376–385, 2006     

Mn(III) oxidation of peptides: A mechanistic investigation of kinetic variations in hydrophobic‐induced oxidation of tetrapeptides of elastin sequences

Four tetrapeptide analogues of elastin sequences, glycyl‐glycyl‐alanyl‐proline (GGAP), glycyl‐glycyl‐valyl‐proline (GGVP), glycyl‐glycyl‐isoleucyl‐proline (GGIP), and glycyl‐glycyl‐phenylalanyl‐proline (GGFP) were synthesized, based on their increasing order of hydrophobicity, by a classical solution phase method and were characterized. These tetrapeptides (TETPs) were oxidized using Mn(OAc)₃ in 25% acetic acid at 298 K, and the kinetics of the reaction was monitored spectrophotometrically at λ_max = 400 nm. A first‐order dependence of rate on each of [Mn(OAc)₃], [OAc^?], and substrate [TETP], an inverse order dependence on [H⁺], has been observed. The rate is independent of [Mn(II)]. However, an inverse order dependence on varying the dielectric constant using various percentages (v/v) of acetic acid has also been observed, and but addition of anions such as Cl^? and ClO₄^? has insignificant effect on the rate. Activation parameters have been evaluated using the Arrhenius and Erying plots. The oxidation products were isolated and characterized. Based on the results obtained, a plausible mechanism involving [Mn(OAc)₄]^? has been proposed. An apparent correlation was noted between the rate of oxidation of these TETPs by Mn(III) in the presence of sulfate ions in sulfuric acid medium and Mn(OAc)₃ in the acetic acid medium. The rate of oxidation with Mn(OAc)₃ was observed to be slower than with the former. The rate of oxidation of GGFP was found to be higher than GGIP, GGVP, and GGAP. This may be due to the presence of an aromatic side chain and/or because of the increased hydrophobicity. The overall order of rate of oxidation of TETPs is GGFP > GGIP > GGVP > GGAP, which also represents an increasing order of their hydrophobicity. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 115–123, 2006     

Photon interaction cross sections for some amino acids in the range 30–385 keV

Total attenuation cross sections for several amino acids have been measured for Ba¹³³ photons in a narrow beam good geometry setup, using a hyper pure germanium detector. These values are compared with the values calculated using the mixture rule based on the data of Hubbell for the individual elements and found to be in good agreement.     

A characterization of positive semidefinite operators on a Hilbert space

In this paper, we show that, under certain conditions, a Hilbert space operator is positive semidefinite whenever it is positive semidefinite plus on a closed convex cone and positive semidefinite on the polar cone (with respect to the operator). This result is a generalization of a result by Han and Mangasarian on matrices.This paper was presented at the 90th Annual Meeting of the American Mathematical Society, Louisville, Kentucky, January 25–28, 1984.     

Studies on the mixing of two non-axial plane jets in a confined passage: mean flow characteristics

The present study deals with the static pressure and mean velocity fields generated due to the mixing of two plane turbulent jets in a confined passage. Four different impingement angles, viz., 15, 30, 45 and 60 degrees, have been investigated. It is found that the inlet angle is the most important parameter governing the extent of the central recirculation zone, the wall recirculation zones, the position of the confluence point and the distance required for complete mixing. The rate of decay of the maximum velocity is very rapid for inlet angles exceeding 45 degrees.     

Anomalous scattering factors of some rare earth elements evaluated using photon interaction cross-sections

The real and imaginary parts,f’(E) and”(E) of the dispersion corrections to the forward Rayleigh scattering amplitude (also called anomalous scattering factors) for the elements La, Ce, Pr, Nd, Sm, Gd, Dy, Ho and Er, have been determined by a numerical evaluation of the dispersion integral that relates them through the optical theorem to the photoeffect cross-sections. The photoeffect cross-sections are derived from the total attenuation cross-section data set experimentally determined using high resolution high purity germanium detector in a narrow beam good geometry set-up for these elements in the photon energy range 5 to 1332 keV and reported earlier by the authors. Below 5 keV, Scofield’s photoeffect cross-sections compiled in XCOM program have been interpolated and used. Simple formulae forf” in terms of atomic number and energy have also been obtained. The data cover the energy region from 6 to 85 keV and atomic numberZ from 57–68. The results obtained are found to agree fairly well with the other available data.     

Electrical switching studies of lead-doped germanium telluride glasses

Samples of bulk Ge₂₀Te_80-xPb_x(2x8) glasses have been prepared by melt quenching and their electrical switching behavior has been investigated as a function of lead content and sample thickness. The samples are found to exhibit a threshold type of switching. The switching voltages are found to decrease with increase in lead content and they show an anomaly at the composition x=5 and a minimum at the composition x=7.5 respectively. The samples are found to withstand about 28 switching cycles, before latching permanently to the ON state. PACS 61.43.Dq; 61.43.Fs; 72.20.Ht; 72.80.Ng; 73.61.Jc; 84.32.Dd; 85.30.Fg     

Sodium N-chloro-p-nitrobenzenesulfonamide (chloramine-N) as a new redox titrant: I. The status of chloramine-N as a titrimetric reagent

The status of sodium N-chloro-p-nitrobenzenesulfonamide (chloramine-N) as a new redox titrant is examined. Analytical applications of CAN as a potential titrimetric reagent in the direct determination of diverse reducing agents such as glutathione, thioglycolic acid, thiourea, ascorbic acid, methionine, sulfite, and arsenite have been described. CAN has been synthesized and its structure elucidated from the spectral data and elemental analyses. The ultraviolet and infrared spectra and Fourier transform ¹H and ¹³C nuclear magnetic resonance spectral data have been presented.