Nucleic acid–solvent interactions: Temperature dependence of the heat of solution of thymine in water and ethanol

Abstract

synopsisThe 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 (AGt, A H , , ASt and AC,,J associated with the transfer of thymine from ethanol to water. Since A S t = -2 cal/mole deg and ACp,t = 0, it has been concluded that hydrophobic bonding does not play an important role in the thermodynamic stability of nucleic acids.However, large heat capacities of solution of thymine are observed in both solvents ( A C o p~ = 45 f 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.

Saturation molalities and standard molar enthalpies of solution of cytidine(cr), hypoxanthine(cr), thymidine(cr), thymine(cr), uridine(cr), and xanthine(cr) in H2O(l)

“…Thus, for cytidine(cr), Stern and Swanson [22] give D sol C p;m ¼ ð117 AE 33Þ J AE K À1 AE mol À1 . For thymine(cr), Alvarez and Biltonen [41] give D sol C p;m ¼ ð188 AE 17Þ J AE K À1 AE mol À1 , Kilday [23] gives D sol C p;m ¼ ð106 AE 26Þ J AE K À1 AE mol À1 , and Ahmed et al [43] give D sol C p;m ¼ ð170 AE 14Þ J AE K À1 AE mol À1 . For uridine(cr), Stern and Swanson [22] give D sol C p;m ¼ ð146 AE 33Þ J AE K À1 AE mol À1 .…”

“…Also, Kishore et al [46] report values of the standard partial molar heat capacity C p;2;m for aqueous solutions of thymidine, thymine, and uridine. Their [46] value for C p;2;m for thymine(aq), together with the value [41] of the standard molar heat capacity C p;m ¼ 151:4 J AE K À1 AE mol À1 for thymine(cr), gives D sol C p;m ¼ 90 J AE K À1 AE mol À1 . Values of C p;m for thymidine(cr) and uridine(cr) do not appear to have been reported in the literature.…”

Calorimetric studies of the polynucleotide analog poly(−)2‐[2‐(thymin‐1‐yl) propanamido]propenoic acid

“…It is not necessary that the maximum possible number of hydrogen bonds be present in order to arrive at a thermodynamically stable configuration relative to the random or unfolded structure. 12 Stability is accomplished by a summation of all contributing interaction forces.…”

Vapour pressures, molar enthalpies of sublimation and molar enthalpies of solution in water of five halogenated derivatives of uracil

“…(1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11) Our investigations of apparent molar volumes and heat capacities, enthalpies of solution and enthalpies of sublimation (4)(5)(6)(7)(8)(9)(10)(11) has focused on the interaction of these compounds with water. In this paper we report measurements on the halogenated derivatives of uracil including 5-fluorouracil, 5-chlorouracil, 6-chlorouracil, 5-bromouracil, and 5-iodouracil.…”