A ¹H and ¹³C nuclear magnetic resonance study of carnosine

Abstract

The proton and carbon-13 resonance signals of carnosine (β-alanyl-L-histidine) were unambiguously assigned using a variety of nmr techniques including proton–carbon chemical shift correlations, titrations of nmr chemical shifts, coupling constants, and isotope shifts. From the 13C nmr titration, carnosine's three pKa values were estimated to be 2.7, 7.1, and 10.6, and it was found that the imidazole ring existed predominantly as the 3-H tautomer in basic solution. Conformational information about the Cα—Cβ bond and about the N—Cα bond was deduced from observed 3J(C,H) and 3J(H,H) values. The 13C nmr spectrum of carnosine in solution is also compared with that obtained for a solid sample.

Determination of microscopic acid?base parameters from NMR?pH titrations

“…Other complications arise from the N 1 -H and N 3 -H tautomerism of the imidazole ring (see 5 in Table 2). By using N-alkylated model compounds, tautomeric ratios have been determined for imidazole, histidine, and histamine derivatives including peptides and proteins by 1 H NMR titrations [122,123,124], 15 N NMR titrations [125,126,127], and 13 C NMR titrations in aqueous [122,128,129,130,131,132] and solid phases [132,133]. Microconstants of individual N 1 -H and N 3 -H tautomers of histidine derivatives have been estimated using model com- pounds [122] and directly from the 14 N NMR-pH titration of glycylhistamine and sarcosylhistamine [99].…”

CP/MAS spectroscopy in the determination of the tautomeric forms of gossypol, its Schiff bases and hydrazones in the solid state

“…[68,69] For the 15 N CP/MAS spectrum of S3, the 15 N resonances were assigned by a comparison with the δ N values in solution as well as with those from the 15 N CP/MAS spectra of the imidazole. [69] In the 15 N CP/MAS spectrum of S3, given in Fig.…”

A Model Study for Vanadium Protein Interactions: Synthesis, Characterization of Oxovanadium (IV and V) Complexes with L-carnosine

“…2H 2 O are given in Table 5 where the signals of L-carnosine are assigned as reported in the literature (Friedrich and Wasylishen, 1986) and chemical shifts of the complex are compared to those of free L-carnosine. 2H 2 O was recorded in the solid state to avoid dynamic ligand change of the complex in solution, particularly that of the imidazole moiety in the L-carnosine molecule which undergoes tautomeric change.…”