The Mechanism of Photochemical Release of Nitric Oxide from S-Nitrosoglutathione

Abstract— Laser flash photolysis of S-nitroso complexes of glutathione (GSNO) and bovine serum albumin (BSANO) via excitation at 355 nm has been used to investigate the photogeneration of nitric oxide (NO) and subsequent radical reactions. In the case of GSNO, liberation of NO was confirmed by its oxidation of oxyhemoglobin to met hemoglobin. Initial NO release is via homolytic cleavage of the S-N bond to produce the glutathione thiyl radical, GS, which can subsequently react with (a) ground-state GSNO (k= 1.7 × 10⁹M^?1/i> s^?1) to yield additional NO and oxidized glutathione, GSSG; and (b) oxygen (k= 3.0 × 10⁹M^?1 s^?1) to give the glutathione peroxy radical, GSOO, which subsequently reacts with ground-state GSNO (k= 3.8 × 10⁸M^?1 s^?1), also producing additional NO and GSSG. The relative concentrations of oxygen and GSNO in the system determine the major pathway for removal of G'. These secondary reactions occur at such high rates that they preclude radical recombination under low-intensity irradiation conditions. The quantum yield of overall loss of GSNO thus varies with both GSNO and oxygen concentrations; a value of 0.66 was determined for an aerated solution of GSNO (0.86 mM). In the case of GSNO, therefore, generation of NO is not due solely to homolysis of the S-N bond; secondary reactions of the radicals formed lead to further NO liberation. In rationalizing the known phototoxicity of GSNO, possible contributions from thiyl and thiyl-derived radicals should be considered. In contrast to GSNO, direct excitation of BSANO (containing one bound NO group per molecule) led to photodecomposition with a quantum yield of 0.09 but no evidence was obtained for liberation of NO into the bulk medium.     

Modeling of asymmetric membrane formation by dry-casting method

Many polymeric membranes are produced by phase inversion technique invented by Loeb and Sourirajan in 1962. The dry-casting method is one of the major phase inversion techniques in which a homogeneous polymer solution consisting of solvent(s) and nonsolvent(s) is cast on a support and then evaporation of the casting solution takes place under convective conditions. In this paper, we model membrane formation by the dry-casting method. The model takes into account film shrinkage, evaporative cooling, coupled heat, and mass transfer and incorporates practical and reliable diffusion theory as well as complex boundary conditions especially at the polymer solution/air interface. The predictions from the model provide composition paths, temperature, and thickness of the solution. By plotting the composition paths on the ternary phase diagram, we ascertain the general structural characteristics of the membranes prepared from particular casting conditions. The predictive ability of the model was evaluated by comparing the results with the experimental data obtained from gravimetric measurements for cellulose acetate (CA)–acetone–water system. In an attempt to illustrate the importance of diffusion formalism on the predictions, recently proposed multicomponent diffusion theory and its simplified forms were utilized in the model. The computational results show that the critical factor for capturing the accurate behavior of membrane formation is the diffusion formalism utilized in the model.     

Hydrolytic polycondensation of alkoxysilanes and modification of polymerization reactions

Polymers having oxide network chains are produced by hydrolytic polycondensation of metal alkoxides and alkoxysilanes. Molecular morphology and molecular size distribution of these inorganic polymers are strongly affected by certain nonchemical parameters. Included among these parameters is the molecular separation of interacting species during the polymerization. There is strong evidence that the molecular size expansion occurs by two distinct processes: initially by a gradual “growth” process, and later by “recombination” of high-molecular weight species. The later process often leads to a bi-modal molecular size distribution. The concentration of water-rich siloxane solutions leads to significant molecular size expansion by further oxide network formation. No similar polymer size growth occurs during the concentration of alcohol based solutions. This difference in the polymeric activities can be related to the difference in the terminal bond under the two different conditions.     

Natural and artificial radioactivity levels of greenhouse soils and relations with soil properties

Journal of Radioanalytical and Nuclear Chemistry - In this study, natural (226Ra, 232Th, 40K) and artificial (137Cs) radionuclide activity concentration levels of 63 greenhouse soils collected from...     

Effects of gamma irradiation on the shoot length of Cicer seeds

The effects of radiation on the shoot and root lengths of germinated seedling of irradiated seeds of Cicer species, i.e. three kabuli types and four desi types of cultivated chickpea (Cicer arietinum Ladiz.) and 2 annual wild types (C. reticulatum Ladiz. and C. bijugum K.H. Rech.) were investigated. The seeds were irradiated with a ⁶⁰Co gamma source using 0, 200, 300 and 400 Gy doses at 1.66 kGy h⁻¹. At 200 Gy minor effects could be observed, but at 400 Gy an obvious depression of shoot length was observed. The kabuli types were more affected than the desi ones. The critical dose that prevented the shoot and root elongation varied among species and also ranged from genotypes to genotype within species.     

Developing prospective teachers’ covariational reasoning through a model development sequence

Forming part of a wider research study, the current study investigated prospective middle school mathematics teachers’ ways of covariational reasoning on tasks involving simultaneously changing quantities. As the introductory theme of a larger unit on derivative, a model development sequence on covariational reasoning was designed and experimented with 20 participants in a mathematical modeling course offered to prospective teachers. The participants’ developing abilities of covariational reasoning were documented under three categories: (i) identifying the variables, (ii) ways of coordinating the variables, and (iii) ways of quantifying the rate of change. The results revealed significant improvement in the prospective teachers’ ways of identifying and coordinating the variables, and in quantifying the rate of change. Moreover, the results indicated that preference for a particular way of thinking in identifying and coordinating the variables determined the prospective teachers’ way of quantifying the rate of change and thereby their level of covariational reasoning.     

Technological significance of sol-gel process and process-induced variations in sol-gel materials and coatings

A significant aspect of sol-gel technology is the capability it provides to affect the substructure of materials by controlling the nature and the kinetics of chemical reactions. This capability allows us to produce novel materials, design unique molecular and pore morphologies, circumvent high-temperature reactions, and modify material properties. The modifications include strongly thermodynamic-dependent high-temperature properties such as sintering, crystallization, and viscosity in glass and ceramic materials. A particularly exciting area for investigation is the optical-electronic field, where a significant dependence of electro-optical properties and photosensitivity on process-induced molecular-structural variations occurs. Understanding the basis for the creation of structural variations in sol-gel processes should have significant impact on the technologies and systems that use these materials. In this article, some fundamental aspects of alkoxide-based, sol-gel processes and thermochemical bases for process-induced structural variates are discussed.