Study of the self‐association of methylated pyrimidines in aqueous solutions by ¹H NMR chemical shifts

Stacking Free Energies of All DNA and RNA Nucleoside Pairs and Dinucleoside-Monophosphates Computed Using Recently Revised AMBER Parameters and Compared with Experiment

“…Further support for the idea that the addition of a methyl group can increase self-association of nucleosides comes from a comparative microcalorimetry study of cytidine and 5-methylcytidine, with K stack values reported in that work (0.74 and 1.1 M –1 respectively) corresponding to a ΔΔ G stack 0.23 kcal/mol. Still another source of similar data comes from 1D NMR experiments (at 35 °C) which, for example, report K stack values of 0.091 and 0.165 M –1 for pyrimidine and 5-methylpyrimidine, respectively, again corresponding to a ΔΔ G stack of 0.35 kcal/mol . Finally, the same effect is apparent in larger nucleic acid systems: in thermal denaturation studies of a variety of double and triple helical systems, the 5-methyl group of T was shown to always provide a stabilizing effect …”

“…Still another source of similar data comes from 1D NMR experiments (at 35 °C) which, for example, report K stack values of 0.091 and 0.165 M −1 for pyrimidine and 5-methylpyrimidine, respectively, again corresponding to a ΔΔG stack of 0.35 kcal/mol. 43 Finally, the same effect is apparent in larger nucleic acid systems: in thermal denaturation studies of a variety of double and triple helical systems, the 5-methyl group of T was shown to always provide a stabilizing effect. 44 The second, more intriguing finding that emerges from a comparison of the DNA and RNA NS pairs is the anomalous behavior of the C+C system apparent in Figure 3B.…”

Observation of 18O solvent-induced isotope shifts in 19F NMR signals

“…Alternatively, for fluorouracil, upfield and downfield contributions to the 18 O-SIIS may more consistently balance than would seem to be the case in fluorouridine. Pyrimidine bases have been noted to weakly selfassociate in aqueous solution, 13 but with the relatively low concentrations used here the effect of this should be small (i.e. in the order of 0.1% of the molecules being associated, based on typical association constants 13 ).…”

“…Pyrimidine bases have been noted to weakly selfassociate in aqueous solution, 13 but with the relatively low concentrations used here the effect of this should be small (i.e. in the order of 0.1% of the molecules being associated, based on typical association constants 13 ).…”

Association between halothane and oxygenated solvents by 1H NMR spectroscopy

“…Since the work on association in the systems of chloroform with acetone or triethylamine (5) appeared, ' H NMR has often been applied to the study of association phenomena. Self-association has been studied in alcohols (6,7) and simple organic acids (8-1 1) as well as in complex organic molecules (12,13). Hetero-association has been investigated in systems of phenol with oxygenated solvents (14,15), amides (14), fluoroalkanes (16), and in systems of acetonitrile with amides (17,18).…”