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

Abstract

The followin g va lues we re obtained from measureme nl s of the e ntha lpy of solulion of a we ll c haracle ri zed sa mp le of crys ta lli ne ade nine in vari ous so lve nt s: nucleic acid bases; so lution calorimetry; th ermochemi stry.

Enthalpies of Solution of the Nucleic Acid Bases. 6. Guanine in Aqueous HCl and NaOH, and Guanine Hydrochlorides in Aqueous HCl

“…A plot similar to figure 3 was previously given for adenine [5]. I t showed no change of slope at rv 0.5 mol, L-I as shown in figure 3; the reason for this difference is not known.…”

“…Our earlier work [5] reported evidence of such a protonation for adenine in HCl solution at the concentration, rv 5 mol· L-I, with M/ = (7.9 ± 2.0) kJ· mol-I. Apparently a similar protonation for guanine occurs at the Hel concentration, 3.5 to 4 mol·L-1 (see fig.…”

“…This is the final paper in this series [1][2][3][4][5].1 It reports reo sults from an incomplete study of the enthalpies of solu tion of guanine (Gua) and guanine hydrochlorides (Gua' nHCl) in aqueous solutions of hydrochloric acid and of sodium hydroxide. Although there are still assumptions and unanswered questions, the results that were obtained are being published because the calorimetry is of high accuracy and considerable information is given characterizing the sam· pies used.…”

“…drochlorides in aqueous HCI solutions (0.3 to 6.0 mol, L-') were measured. Enthalpies at infinite dilution of protonation and of proton dissociation were calculated for guanine and compared with analogous values obtained for adenine [1,5], another purine base. The exact sites of the ionizations are somewhat uncertain.…”