Protonation, binary and ternary Cu(II) complex formation constants of N-methyl-L-histidine (N-MH) and N-a-methyl-L-histidine (N-a-MH) have been measured through potentiometric titrations. UV/VIS spectra have been recorded for both the binary systems; the Cu(II)/N-a-MH complexes have been investigated by means of Fast Atom Bombardment mass spectroscopy as well. The data on protonation equilibria of N-MH and N-a-MH show the existence of a difference in basicity between the respective nitrogen atoms, thus giving information on the tautomerism involving the imidazole residue of L-histidine (L-His) in the physiological pH range. The complexation behaviour of N-MH is quite similar to that of underivatized L-His: the same species are formed and their log beta values are very close. On the contrary, the presence of a methyl substituent on the N alpha atom deeply affects the complexing properties of the ligand. N-a-MH cannot act as a tridentate ligand for steric reasons and tends to form polynuclear complexes.

Binary and ternary Cu(II) complexes of Ntau- and Npi-methyl-L-histidine in aqueous solution

REMELLI, Maurizio;PULIDORI, Fernando
1994

Abstract

Protonation, binary and ternary Cu(II) complex formation constants of N-methyl-L-histidine (N-MH) and N-a-methyl-L-histidine (N-a-MH) have been measured through potentiometric titrations. UV/VIS spectra have been recorded for both the binary systems; the Cu(II)/N-a-MH complexes have been investigated by means of Fast Atom Bombardment mass spectroscopy as well. The data on protonation equilibria of N-MH and N-a-MH show the existence of a difference in basicity between the respective nitrogen atoms, thus giving information on the tautomerism involving the imidazole residue of L-histidine (L-His) in the physiological pH range. The complexation behaviour of N-MH is quite similar to that of underivatized L-His: the same species are formed and their log beta values are very close. On the contrary, the presence of a methyl substituent on the N alpha atom deeply affects the complexing properties of the ligand. N-a-MH cannot act as a tridentate ligand for steric reasons and tends to form polynuclear complexes.
1994
Remelli, Maurizio; Munerato, C.; Pulidori, Fernando
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11392/462937
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