Kinetics and mechanism of the oxidation of n-acetyl l-cysteine by 2,6-dichloroindophenol in methanol–water medium

The principal reactants interact in a molar ratio of 2:1 forming dihydroindophenol and the corresponding disulfide. The order of reaction is unity with respect to each reactant, namely, N-acetyl L-cysteine and indophenol. The rate shows an inverse linear relation with hydroxyl ions. It is not influenced by the variation in the initial concentration of indophenol. The rate increases on adding the salts possessing a cholinergic effect and the neutral electrolytes, as well as on increasing the dielectric constant of the medium. The products, namely, N-acetyl L-cystine (disulfide) and the leuco dye, do not influence the rate. A low energy and a highly negative entropy of activation (4.11 kcal/mol and -60.49 e.u., respectively) suggest the formation of an outer sphere complex as the rate-determining step.     

Lyoluminescence of sensitized glucose

Lyoluminescence studies have acquired considerable significance in recent years due to its potential as a cheap, convenient and versatile method for radiation dosimetry. It has advantages over other conventional techniques due to tissue equivalence of organic lyoluminescent materials and small size in which this type of dosimeter can be used. It is particularly attractive for therapeutic dosimetry. The paper reports the performance of glucose crystallised with known concentrations of sensitizer luminol. It also gives the relative performance of various lyoluminescence materials of similar type being studied currently.     

Propagation of sound pulses in a semiinfinite stratified medium

We consider the propagation of sound pulses due to a line source in the inhomogeneous, semi-infinite mediumy ≥ 0 with the boundary conditionφ=0 or?φ/(?y)=0 aty=0, whereφ is the acoustic velocity potential. We suppose that the velocity of wave propagation,c, is given byc ^?2=p ?qe ^?ay , wherep, q, α are real and positive andp>q. The method of dual integral transformation is used. The solution in terms of pulse propagation modes yields the diffracted pulse and the method of steepest descents gives the geometrical acoustic field.     

Kelvin Helmholtz Instability in a Magnetoplasma

Two dimensional transverse Kelvin-Helmholtz (K-H) instability has been studied at the interface between the two fluids (plasma medium) of finite thickness in relative motion to each other. The perturbations on the interface are assumed to be electromagnetic and a dispersion relation is obtained. The interface (boundary) has been found to be unstable for a wide range of perturbation wavelengths (wave numbers kx, ky). It is shown that the modification introduced by electromagnetic (quasi-electrostatic) perturbations in comparison to electrostatic one is to reduce the growth rate of perturbations. The growth rate maximizes when kx = ky. The applications of this study have been discussed to explain some of the observed ionospheric (auroral arc formation) and magnetospheric (unstable magnetopause boundary, hydromagnetic pulsations) phenomena.     

Raman and infrared spectra of tere-phthalaldehyde

The laser Raman spectrum of tere-phthalaldehyde powder has been recorded on a Jobin Yvonhg 2S spectrophotometer with a~100 mW Argon-Ion laser. The infrared spectrum of the solid substance has been recorded on a Perkin-Elmer 621 spectrophotometer in the region 300–4000 cm^-1 using KBr and nujol mull techniques. The observed frequencies have been assigned in terms of the fundamentals, overtones and combinations assumingD _2h point-group symmetry.     

Valence transition and magnetic ordering in Sn doped EuPd2Si2

The sharp, temperature induced, continuous valence transition in EuPd₂Si₂ is drastically changed by doping with Sn at the Si site upto 5 at. %. Only a first order valence transition occurs for a 3% Sn doped sample and the 2⁺ component which survives the valence transition orders magnetically at 4.2 K. No valence transition at all occurs for a 5% Sn doped sample right up to 1.9 K and magnetic ordering sets in around 30 K.     

The interplay of hydrophobic and electrostatic effects in the surfactant-induced aggregation/deaggregation of chlorin p6

The aggregation/deaggregation of chlorin p6 with the surfactants CTAB, SDS, and TX 100 have been studied by using absorption, fluorescence, and light scattering techniques. The ionic surfactants are found to cause aggregation of fluorophore at submicellar concentrations. The aggregates dissolve at higher surfactant concentrations to yield micellized monomers. This is rationalized by the interplay of electrostatic and hydrophobic effects. A prominent pH effect is observed in the ionic surfactant induced aggregation process as the charge on the fluorophore is controlled by the pH of the medium. Interestingly, the neutral TX-100 also induces aggregation of chlorin p6 at low concentrations, indicating that hydrophobic effects by themselves can cause aggregation unless there is a hindrance by repulsive electrostatic effects.     

Measurement of two-photon absorption cross-section in organic molecular salt with linear and circular polarized radiation

We report on the investigation of two-photon absorption (TPA) in 4-Diethylamino-N-Methyl-4-Stilbazolium Tosylate (DEST) with 40 picosecond, 1064 nm linear and circular polarization laser radiation. The TPA cross-section ₂ measured is larger for linear polarized radiation (948 GM) than that for the circular polarized radiation (840 GM). The large TPA cross-section of DEST facilitates highly directional and efficient TPA induced upconverted emission in the range of 590–640 nm even though the fluorescence efficiency of DEST is very low (0.5%). The net single pass efficiency of upconversion is 7%. PACS 42.65.-k; 42.70.Jk