Nucleic acid components and their analogues. XVI. Dissociation constants of uracil, 6-azauracil, 5-azauracil and related compounds

Viscosimetry of Polymers and Polyelectrolytes

“…In the previous communication it was the dioxo member that deviated from the norm, in this case it is the diamino member. In this case, as previously, the most accessible chemical property that parallels this deviation in pairing behavior relative to the standard of the canonical nucleobases is the p K a value: although in the previous case a 2,4‐dioxotriazine (p K a of 6‐methyl‐2,4‐dioxo‐1,3,5‐triazine=7.219) is a distinctly stronger acid than a 2,4‐dioxopyrimidine (p K a of deoxyuridine=9.320), in the present case, a 5‐acylamino‐2,4‐diaminopyrimidine (p K a of the 5‐formylamino derivative=6.0321) is a stronger base than deoxyribofuranosyl‐2,6‐diaminopurine (p K a =4.422) or, for that matter, the canonical deoxyadenosine (p K a =3.823). Figure 4 juxtaposes the so‐far‐observed examples of normal versus deviating pairing behavior with the corresponding (known or estimated) p K a values of pairing partners.…”

Mapping the Landscape of Potentially Primordial Informational Oligomers: Oligodipeptides Tagged with 2,4‐Disubstituted 5‐Aminopyrimidines as Recognition Elements

“…In the previous communication it was the dioxo member that deviated from the norm, in this case it is the diamino member. In this case, as previously, the most accessible chemical property that parallels this deviation in pairing behavior relative to the standard of the canonical nucleobases is the pK a value: although in the previous case a 2,4-dioxotriazine (pK a of 6-methyl-2,4-dioxo-1,3,5-triazine = 7.2 [19] ) is a distinctly stronger acid than a 2,4-dioxopyrimidine (pK a of deoxyuridine = 9.3 [20] ), in the present case, a 5-acylamino-2,4-diaminopyrimidine (pK a of the 5-formylamino derivative = 6.03 [21] ) is a stronger base than deoxyribofuranosyl-2,6-diaminopurine (pK a = 4.4 [22] ) or, for that matter, the canonical deoxyadenosine (pK a = 3.8 [23] ). Figure 4 juxtaposes the so-far-observed examples of normal versus deviating pairing behavior with the corresponding (known or estimated) pK a values of pairing partners.…”

Luminescent and DFT Study of Keto–Enol Tautomers of 5-Fluorouracil and Its Derivatives in Aqueous Solutions

“…Second, tautomeric forms B – D are strong acids and they should be completely dissociated at pH 6.8. Indeed, since tautomers A – D have common anionic forms N1 and N3 (Figure ), it is obvious that the p K a of an arbitrary FU tautomer equals 8.0 – Δ G °/2.3 RT , where 8.0 is the p K a of tautomer A in aqueous solutions , and Δ G ° is the relative energy of tautomer X that equals G °( X ) – G °( A ) and is given in Table . Hence, it is easy to calculate that the p K a of rare forms lies in the range of 1–3, i.e., the molecular forms B – D are thermodynamically unstable at pH 6.8.…”