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Thermodynamic Aspects (thermodynamic + aspect)

Distribution by Scientific Domains

Physics and Astronomy	50%

Selected Abstracts

Synthesis, pharmacology, crystal properties, and quantitative solvation studies from a drug transport perspective for three new 1,2,4-thiadiazoles

JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 9 2010
German L. Perlovich
Abstract A novel 1,2,4-thiadiazoles were synthesized. Crystal structures of these compounds were solved by X-ray diffraction experiments and comparative analysis of molecular conformational states, packing architecture, and hydrogen bonds networks were carried out. Thermodynamic aspects of sublimation processes of studied compounds were determined using temperature dependencies of vapor pressure. Thermophysical characteristics of the molecular crystals were obtained and compared with the sublimation and structural parameters. Solubility and solvation processes of 1,2,4-thiadiazoles in buffer, n -hexane and n -octanol were studied within the wide range of temperature intervals and thermodynamic functions were calculated. Specific and nonspecific interactions of molecules resolved in crystals and solvents were estimated and compared. Distribution processes of compounds in buffer/n -octanol and buffer/n -hexane systems (describing different types of membranes) were investigated. Analysis of transfer processes of studied molecules from the buffer to n -octanol/n -hexane phases was carried out by the diagram method with evaluation of the enthalpic and entropic terms. This approach allows us to design drug molecules with optimal passive transport properties. Calcium-blocking properties of the substances were evaluated. © 2010 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:3754,3768, 2010 [source]

Thermodynamic aspects of carbon incorporation into AlN epitaxial layers grown by MOVPE

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2005
J. Leitner
Abstract Thermodynamic aspects of carbon incorporation into AlN during the MOVPE growth are discussed. Under low potential in the gaseous phase, carbon dissolves in AlN substituting nitrogen atoms. A sublattice model has been proposed to describe the thermodynamic behavior of this pseudobinary solution AlN-C. When carbon potential increases, solid graphite is formed simultaneously to AlN. At V/III input ratio (V/III = x/x) lower than one, carbonitride Al5C3N as well carbide Al4C3 can be formed. The calculated results are compared with the composition of AlN layers growth by MOVPE. The serious discrepancies exist which can be explained by the crude nature of the solution model as well as by non-equilibrium conditions during the MOVPE growth and subsequent carbon supersaturation of the resulting layers. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Silicon Nanowires: A Review on Aspects of their Growth and their Electrical Properties

ADVANCED MATERIALS, Issue 25-26 2009
Volker Schmidt
Abstract This paper summarizes some of the essential aspects of silicon-nanowire growth and of their electrical properties. In the first part, a brief description of the different growth techniques is given, though the general focus of this work is on chemical vapor deposition of silicon nanowires. The advantages and disadvantages of the different catalyst materials for silicon-wire growth are discussed at length. Thereafter, in the second part, three thermodynamic aspects of silicon-wire growth via the vapor,liquid,solid mechanism are presented and discussed. These are the expansion of the base of epitaxially grown Si wires, a stability criterion regarding the surface tension of the catalyst droplet, and the consequences of the Gibbs,Thomson effect for the silicon wire growth velocity. The third part is dedicated to the electrical properties of silicon nanowires. First, different silicon nanowire doping techniques are discussed. Attention is then focused on the diameter dependence of dopant ionization and the influence of interface trap states on the charge carrier density in silicon nanowires. It is concluded by a section on charge carrier mobility and mobility measurements. [source]

Non-phenolic radical-trapping antioxidants

JOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 11 2009
Mario C. Foti
Abstract Objectives The aim of this review article is to introduce the reader to the mechanisms, rates and thermodynamic aspects of the processes involving the most biologically relevant non-phenolic radical-trapping antioxidants. Key findings Antioxidant defences in living organisms rely on a complex interplay between small molecules and enzymes, which cooperate in regulating the concentrations of potentially harmful oxidizing species within physiological limits. The noxious effects of an uncontrolled production of oxygen- and nitrogen-centered radicals are amplified by chain reactions (autoxidations), sustained mainly by peroxyl radicals (ROO,), that oxidize and alter essential biomolecules such as lipids, lipoproteins, proteins and nucleic acids. Summary Non-phenolic antioxidants represent an important and abundant class of radical scavengers in living organisms. These compounds react with peroxyl radicals through various mechanisms: (i) formal H-atom donation from weak X-H bonds (X = O, N, S), as in the case of ascorbic acid (vitamin C), uric acid, bilirubin and thiols; (ii) addition reactions to polyunsaturated systems with formation of C-radicals poorly reactive towards O2, for example ,-carotene and all carotenoids in general; (iii) co-oxidation processes characterized by fast cross-termination reactions, for example ,-terpinene; and (iv) catalytic quenching of superoxide (O2,,) with a superoxide dismutase-like mechanism, for example di-alkyl nitroxides and FeCl3. Kinetic data necessary to evaluate and rationalize the effects of these processes are reported. The mechanisms underlying the pro-oxidant effects of ascorbate and other reducing agents are also discussed. [source]

GaAs nanowires grown by MOVPE

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 6 2010
Jens Bauer
Abstract GaAs nanowire (NW) growth was studied by metal-organic vapour phase epitaxy (MOVPE). The vapour,liquid,solid (VLS) mechanism with gold-based alloy particles and the selective-area growth (SAG) mechanism on electron beam lithographically prepared SiNx/GaAs mask structures were applied. A special focus is set on thermodynamic aspects of the VLS process. The alloy particle formation and the influence of MOVPE growth parameters on the growth rate and the GaAs NW morphology are examined. Furthermore, the improvement of the real structure with particular interest on the twin formation is studied. Besides the commonly used continuous VLS growth mode also a pulsed VLS growth mode with alternating precursor supply is reported. Based on photoluminescence measurements the effect of strain in core/shell NW structures is confirmed. For the SAG mechanism the MOVPE growth parameters are determined and the real structure is described. [source]