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Ionization Equilibrium (ionization + equilibrium)

Distribution by Scientific Domains

Chemistry	40%

Selected Abstracts

Ionization equilibrium and Mott transition in an excited semiconductor, phase diagram

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2009
F. Richter
Abstract The thermodynamic properties of an electron,hole plasma in a highly excited semiconductor are investigated. Special attention is directed to the influence of many-particle effects like screening, lowering of the ionization energy, and Mott effect on the ionization equilibrium. In particular, the Mott effect limits the region of existence of excitons and, therefore, of a possible Bose,Einstein condensate at low temperatures. Results for the chemical potential and the degree of ionization are presented for cuprous oxide. A possible window for the occurrence of a BEC of excitons taking into account the Mott effect is shown. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Inductive effect of uncharged groups: dependence on electronegativity

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 7 2006
Otto Exner
Abstract Substituent effects in rigid non-conjugated systems were followed on the series of 3-substituted 1-fluoro-bicyclo[1.1.1]pentanes and 2-substituted 1-fluoroethanes in the fixed ap conformation. Their energies were calculated within the framework of the density functional theory at the B3LYP/6-311++G(3df,3pd)//B3LYP/6-311++G(3df,3pd) level and the substituent effects were expressed in terms of isodesmic homodesmotic reactions. The results were confirmed by the energies of 1,4-disubstituted bicyclo[2.2.2]octanes reported in the literature and calculated at a lower level. Interaction of two common substituents of low or medium polarity cannot be described as the classical inductive effect by one term, proportional in all series, but an additional parameter is necessary, which depends only on the first atom of the substituent and may be identified with its electronegativity. The second term decreases with the distance more steeply than the first term and is always much less important. Nevertheless its statistical significance was proved by several sensitive tests at the highest level used in statistics. When one of the substituents is charged (or at least strongly polar as NO2 or CN), the first term is much increased and the second becomes less significant or insignificant. Therefore, the standard definition of the inductive effect with a uniform, universally valid constant can be retained as far as one treats only the ionization equilibria, both in solution and in the gas phase, or kinetics with a strongly polar transition state. In contrast to the firm statistical proofs, the physical meaning of the electronegativity term was not established. Any relation to various group electronegativities does not exist, similarity to the 13C NMR shifts is merely qualitative. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Micellar Effects on the Reaction between an Arenediazonium Ion and the Antioxidants Gallic Acid and Octyl Gallate

HELVETICA CHIMICA ACTA, Issue 1 2008
Losada Barreiro, Sonia
Abstract The effect of sodium dodecyl sulfate (SDS) micelles on the reaction between the 3-methylbenzenediazonium (3MBD) ion and either the hydrophilic antioxidant gallic acid (GA) or the hydrophobic analogue octyl gallate (OG) have been investigated as a function of pH. Titration of GA in the absence and presence of SDS micelles showed that the micelles do not alter the first ionization equilibrium of GA. Analysis of the dependence of the observed rate constant (kobs) with pH shows that the reactive species are GA2, and OG,. Kinetics results in the absence and presence of SDS micelles suggest that SDS aggregates do not alter the expected reaction pathway. SDS Micelles inhibit the spontaneous decomposition of 3MBD as well as the reaction between 3MBD and either GA or OG, and upon increasing the SDS concentration, with kobs approaching the value for the thermal decomposition of 3MBD in the presence of SDS. Our results are consistent with the prediction of the pseudophase model and show that the origin of the inhibition for the reaction with GA is different to that for the reaction with OG; in the former case, the observed inhibition can be rationalized in terms of the micelle-induced electrostatic separation of reactants in the micellar Stern layer, whereas the observed inhibition in the reaction with OG is a consequence of the dilution effect caused by increasing SDS concentration, decreasing the local OG, concentration in the Stern layer. [source]

Spectroscopic Investigations on the Binding of the Photosensitizer Chlorin p6 with Amine-modified Silica Nanoparticles in Aqueous Media

PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2009
Beena Jain
Absorption and emission properties of the amphiphilic photosensitizer Chlorin p6 were investigated in aqueous medium in the presence of silica nanoparticles (SiNPs) having positively charged amino groups. The results of these studies reveal that the acid,base ionization equilibrium of Chlorin p6 in aqueous medium is significantly affected as a result of strong electrostatic binding between the negatively charged drug and SiNP. The spectroscopic signature of the drug bound to SiNPs suggests that the tri-anionic form of the drug remains bound to the positively charged SiNPs at pH 8.0. As the pH is progressively decreased the formation of hydrophobic aggregates is disrupted significantly due to the presence of electrostatic binding force, which competes with intermolecular hydrophobic forces. The interplay of hydrophobic and electrostatic forces in the drug,nanoparticle binding process might affect the relative uptake and photodynamic efficacy of the free drug and the drug,nanoparticle complex in cancer cells. [source]