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Nucleic acid–solvent interactions: Temperature dependence of the heat of solution of thymine in water and ethanol
Author(s) -
Alvarez José,
Biltonen Rodney
Publication year - 1973
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.1973.360120809
Subject(s) - chemistry , thymine , hydrogen bond , nucleic acid , aqueous solution , solvent , solubility , macromolecule , ethanol , thermodynamics , hydrogen , organic chemistry , molecule , dna , biochemistry , physics
The heats of solution of thymine in water and ethanol have been determined calorimetrically as a function of temperature. These data, along with solubility data, have been used to calculate the thermodynamic quantities (Δ G t , Δ H t , Δ S t and Δ C p , t ) associated with the transfer of thymine from ethanol to water. Since Δ S t = −2 cal/mole deg and Δ C p , t = 0, it has been concluded that hydrophobic bonding does not play an important role in the thermocynamic stability of nucleic acids. However, large heat capacities of solution of thymine are observed in both solvents (Δ C ° p 2 = 45 ± 4 cal/mole deg). This is explained in terms of temperature variation in the degree of solvent–solute hydrogen bonding. It is our proposal that the components of macromolecules (i.e., nucleic acid bases and amino acids) do not make all possible hydrogen bonds with the solvent in the vicinity of room temperature. Thus the thermodynamic contribution of hydrogen bonding to the stability of macromolecules in aqueous solution must be reassessed.