Thermodynamics of the hydrophobic effect. I. Coupling of aggregation and pK(a) shifts in solutions of aliphatic amines.
Biophys Chem
; 93(1): 37-51, 2001 Oct 18.
Article
em En
| MEDLINE
| ID: mdl-11604215
ABSTRACT
Long aliphatic hydrocarbon chains aggregate in aqueous solution due to the hydrophobic effect, forming structures such as micelles and membranes, while amino groups titrate at basic pH. These two biologically important behaviors are linked in alkylamines, in which the pK(a) of the amino group is shifted downward by aggregation. In this paper we study the thermodynamics of these coupled processes, following aggregation by observing alkylamine pH titration behavior. The magnitude of the shift depended on the aliphatic chain length and on the concentration of alkylamine longer chains and higher concentrations lowered the pK(a) to a greater extent. Gibbs free energies of protonation and aggregation were calculated from the pK(a) shifts. Enthalpies, entropies, and heat capacities were estimated by van't Hoff analysis from the pK(a) shift dependencies on temperature. However, the results were less precise than the calorimetrically measured values, as described in the following article. A model to calculate titration curves, pK(a) shifts, and aggregation of uncharged alkylamines as a function of aliphatic chain length, concentration, and temperature is presented.
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Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Tensoativos
/
Termodinâmica
/
Aminas
/
Micelas
Idioma:
En
Revista:
Biophys Chem
Ano de publicação:
2001
Tipo de documento:
Article
País de afiliação:
Estados Unidos