The thermodynamic effects of exposing nucleic acid bases to water: Solubility measurements in water and organic solvents

Abstract

SynopsisIn order to examine the thermodynamic effects of exposing nucleic acid bases to water, we have measured the solubility of adenine, cytosine, and uracil in water and in organic solvents as a function of temperature. Transfer of a nucleic acid base from an organic environment into water is characterized by positive values for AH and for AS. We conclude from this result that the overall interaction between nucleic acid bases and water cannot be hydrophobic. If the effect we observe represents structure breaking in water by nucleic acid bases, this process would account for a major portion of the large, positive melting entropy of DNA, and would also con tribute substantially to the melting enthalpy.

Enthalpies of solution of the nucleic acid bases. 4. Uracil in water

“…From the solubility measureme nts of Scruggs, e t al. [5) we calculate the molal solubility at 298.15 K to be (0.0269 ± 0.0013) mol, kg-I, and fiCO = -RT in In = 9.0 ± 0.4 kJ· mol-I. Combining thi s with our value for the e nthalpy of solution we obtain…”

“…From the ir solubility measurements, Scruggs et al [5] calculate d fiH (37°C) = 6700 cal, mol-1 for the e nthalpy of so lution of urac il in water. Using the fiC p value determined in this work, we obtain 6536 cal, mol -lor 27.34 kJ· mol-1 at 298.15 K whic h is ne arl y 7 pe rcent less than our value but within the uncertaint y assigned.…”

“…A. Noms, Center for Anal yti cal C he mistry, Nati onal Measure me nt Laboratory, National Bureau of Standards. 5 By Mi cro Anal ysis, Inc. Wilmington , DE . …”

“…0 g ' L -I [5]2 a t 298 K; uracil sublimes a nd decomposes before melting. Onl y one value for 1 Figures in bracke ts ind icat e the lit erature refere nces at the e nJ of Ihi s pa per.…”

Enthalpies of solution of the nucleic acid bases. 5. Adenine in aqueous hydrochloric acid, aqueous sodium hydroxide, methanol, and ethanol

“…Scru ggs, Achte r, and Ross [9] measured the solubility of ade nine in methanol a t 277.8 K and 309.8 K. Assuming linearity between th ese tempe ratures, and the density of…”