Kamlet-Taft Solvent Parameters Research Articles

Solvatochromic studies on the hydrogen-bond donating and dipolarity/polarizability properties of the polyethylene oxide/silica interface

The polarity of the polyethylene oxide(PEO)/silica interface in 1,2-dichloroethane as solvent is classified by means of linear solvation energy (LSE) relationships . The properties of the bare silica particle surface and the silica/PEO interface is expressed by two terms: the dipolarity/polarizability (π*) of the interface and the hydrogen-bond donating ability (α) of the surface silanols. These terms can be defined by using the Kamlet–Taft solvent parameters α and π* as a reference system. The interfacial polarity parameters α and π* were calculated by means of correlation analyses of the energy of the UV/vis absorption maxima of the surface polarity indicators: di-cyano-bis(1,10-phenanthroline) iron II, bis-4,4′-(N,N-dimethylamino) benzophenone, and 2,6-diphenyl-4-(2,4,6-triphenyl-N-pyridino)phenolate when adsorbed onto the PEO/silica particle surface. The experimental values of the ET(30) parameter of the PEO/silica interface are compared with independently calculated values employing specific LSE relations derived for well-behaved regular solvents and functionalized silicas. PEO adsorption on silica causes a decrease in the value of the α parameter of the silica surface and an evident increase in the dipolarity/polarizability of the interface.

Solvent effects on diketopiperazine formation from N-terminal peptide residues

The kinetics of diketopiperazine formation from the peptide H-Ala-Pro-NH2 with the unprotected amino group in the form of its trifluoroacetate salt have been investigated in a large number of solvents, including aprotic and hydroxylic solvents. The first-order rate constant is considerably affected by the solvent properties, its value spanning more than three orders of magnitude. Moreover, alkylammonium carboxylate salts are efficient catalysts of the reaction. The correlation with Kamlet–Taft solvent parameters shows that the reaction rate is retarded by solvents with a high capacity to stabilise solutes that are charged or dipolar, and that are hydrogen donors and/or acceptors. Solvents with high cohesive energy density values significantly increase the reaction rate. These results are discussed in terms of a proton switch in the rate determining step and of solvation stabilisation of the initial state of the peptide and of the transition state of the rate-limiting step.

Influence of Hydrogen Bonding Solvents on the Infrared Absorption Band of the Carbonyl Group in Acetone

The IR absorption band position for the fundamental stretching mode of the carbonyl group in acetone was measured in twenty-three solvents using FTIR spectral methods. Eight of the solvents were hydrogen bond donor liquids. A quantitative reaction field model for the solvent-induced band shift is proposed which resolves the C=O frequency perturbation into a solvent polarity effect and a hydrogen bond donor acidity effect. That model reproduces the carbonyl band position within ?0.2 cm-1 in both aprotic and hydrogen bonding solvents by incorporating the appropriate Kamlet-Taft solvent parameters as the essential descriptors.