This review summarizes the multifaceted aspects of antioxidants and the basic kinetic models of inhibited autoxidation and analyzes the chemical principles of antioxidant capacity assays. Depending upon the reactions involved, these assays can roughly be classified into two types:  assays based on hydrogen atom transfer (HAT) reactions and assays based on electron transfer (ET). The majority of HAT-based assays apply a competitive reaction scheme, in which antioxidant and substrate compete for thermally generated peroxyl radicals through the decomposition of azo compounds. These assays include inhibition of induced low-density lipoprotein autoxidation, oxygen radical absorbance capacity (ORAC), total radical trapping antioxidant parameter (TRAP), and crocin bleaching assays. ET-based assays measure the capacity of an antioxidant in the reduction of an oxidant, which changes color when reduced. The degree of color change is correlated with the sample's antioxidant concentrations. ET-based assays include th...

The Chemistry behind Antioxidant Capacity Assays

This review compiles positively and negatively solvatochromic compounds which have been used to establish empirical scales of solvent polarity by means of UV/vis/near-IR spectroscopic measurements in solution-with particular emphasis on the E ~ ( 3 0 ) scale derived from negatively solvatochromic pyridinium N-phenolate betaine dyes. This requires a short discussion of the concept of solvent polarity and how empirical parameters of solvent polarity can be derived and understood in the framework of linear free-energy relationships. The preconditions for the occurrence of solvatochromism, and further requirements of solvatochromic compounds for them to be useful as solvent polarity indicators will be discussed. In addition to spectroscopically based single parameters of solvent polarity, multiparameter treatments of solvent effects by means of solvatochromic parameters will also be mentioned. The mutual interrelation between some of the more important W/vis/near-IR spectroscopically derived solvent scales, and their correlations with solvatochromic multiparameter equations will be exemplarily given.

Solvatochromic Dyes as Solvent Polarity Indicators

Scales of solute hydrogen-bonding: their construction and application to physicochemical and biochemical processes

Artificial Organic Host Molecules for Anions

Cross-coupling reactions of organoboranes: an easy way to construct C-C bonds (Nobel Lecture).

A scale of solute hydrogen-bond acidity has been constructed using equilibrium constants (as log K values) for complexation of series of acids (i) against a given base in dilute solution in tetrachloromethane, equation (A). Forty-five such equations have been solved to yield LB and DB, log Ki=LB log KAHI+DB(A) values characterising the base, and log KAH values that characterise the acid. In this analysis, use has been made of the novel observation that all the lines in equation (A) intersect at a given point where log K= log KAH=–1.1 with K on the molar scale. Some 190 log KAH values that constitute a reasonably general scale of solute hydrogen-bond acidity have been obtained. It is shown that there is no general connection between log KAH; and any proton-transfer quantities, although certain family dependences are obtained. A number of acid-base combinations are excluded from equation (A), and alternative log KAHE values have been determined for such cases. The general log KAH values may be transformed into α2H values suitable for use in multiple linear-regression analysis through the equation α2H=(log KAH+ 1.1)/4.636.

Hydrogen bonding. Part 10. A scale of solute hydrogen-bond basicity using log K values for complexation in tetrachloromethane

Solvent effects on a number of different processes have been surveyed, and results of the application of multiple linear regression analysis are discussed. The processes examined include examples o...

Solvent effects in organic chemistry — recent developments

On a evalue les effets de solvant sur un certain nombre de processus et on discute des resultats de l'application de l'analyse de regression lineaire multiple. Les processus etudies comportent des exemples de solubilite des gaz ou des vapeurs, des coefficients de distribution des solutes entre l'eau et une serie de solvants ainsi que des effets de solvant sur l'equilibre conformationel, sur la tautomerie ceto-enolique et sur les vitesses de reaction. On demontre que deux equations particulieres, celle de Koppel et Palm qui a ete etendue par Makitra et Pirig ainsi que celle d'Abraham, Kamlet et Taft, peuvent rendre compte d'une facon satisfaisante des effets de solvant sur ces divers processus. On note que l'interpretation des parametres obtenus a l'aide de ces equations qui impliquent des quantites macroscopiques comme le ΔG ou le ΔG 0 ne sont pas simples; des modeles sont necessaires pour interpreter ces quantites macroscopiques en fonction de quantites microscopiques qui peuvent caracteriser, par exemple, les interactions solute-solvant

Solvent effects in organic chemistry: recent developments

Olive oil–gas partition coefficients, Loil, have been determined for 80 solutes at 310 K using a gas chromatographic method in which olive oil is used as the stationary phase. Combination with other literature values has enabled a list of 140 log Loil values at 310 K to be constructed. Hexadecane–gas partition coefficients, Lhex, have similarly been determined for 140 solutes at 298 K. It is shown that olive oil–water partition coefficients, Poil, calculated indirectly from Loil and Lwater partition coefficients agree quite well with directly determined Poil values. Similarly, hexadecane–water partition coefficients, Phex, obtained from Lhex and Lwater agree with directly determined values. It is suggested that in the case of the two particular solvents, olive oil and hexadecane, mutual miscibility of the two phases is of little consequence, and that Poil and Phex values can conveniently be obtained by combining the respective solvent–gas and water–gas partition coefficients.

Determination of olive oil–gas and hexadecane–gas partition coefficients, and calculation of the corresponding olive oil–water and hexadecane–water partition coefficients

Priscilla L. Grellier

Papers

Hydrogen bonding. Part 10. A scale of solute hydrogen-bond basicity using log K values for complexation in tetrachloromethane

Solvent effects in organic chemistry — recent developments

Solvent effects in organic chemistry: recent developments

Determination of olive oil–gas and hexadecane–gas partition coefficients, and calculation of the corresponding olive oil–water and hexadecane–water partition coefficients

A general treatment of hydrogen bond complexation constants in tetrachloromethane