Raman and IR spectroscopic investigation of zinc(II)-carnosine complexes

Abstract

The zinc(II)–L‐carnosine system was investigated at different pH and metal/ligand ratios by Raman and IR spectroscopy. The Raman and IR spectra present some marker bands useful to identify the sites involved in metal chelation at a specific pH value. In particular, the neutral imidazole group gives rise to some Raman bands, such as the νC4C5 band, that change in wave number, depending on whether the imidazole ring takes the tautomeric form I or II. Even if tautomer I is predominant in the free ligand, metal coordination can upset tautomeric preference and Nτ‐ and Nπ‐ligated complexes can be identified. Although weak compared to those of aromatic residues, these Raman marker bands may be useful in analyzing metal–histidine interaction in peptides and proteins. On the basis of the vibrational results, conclusions can be drawn on the species existing in the system. Depending on the available nitrogen atoms, various complexes can be formed and the prevalent form of the species depends mainly on the pH. At basic pH carnosine gives rise to two different neutral complexes: a water‐insoluble polymeric species, [ZnH−1L] 0italicn, and a dimer, [Zn2H−2L2]0. The first is predominant and involves the tautomeric I form of the imidazole ring in metal chelation; the second contains tautomer II and increases its percentage by going from a 2 to 0.25 metal/ligand ratio. Conversely, the dimeric species dominates at pH 7, whereas two charged species, [ZnHL]2+ and [ZnL]+, are formed under slightly acidic conditions. In the [ZnHL]2+ complex the imidazole ring takes part in the Zn(II) coordination in the tautomeric I form, whereas in [ZnL]+ the ring is protonated and not bound to the Zn(II) ion. In addition, the curve fitting analysis of the 1700–1530 cm−1 Raman region was helpful in indicating the predominant species at each pH. © 2000 John Wiley & Sons, Inc. Biopolymers (Biospectroscopy) 57: 352–364, 2000

Influence of metal ions on thermal aggregation of bovine serum albumin: Aggregation kinetics and structural changes

“…For this purpose, we used the fourth derivative spectra whose resolution is superior with respect to the second-derivative spectra, allowing detecting also some weak component bands. The structural assignments of the band components were carried out on the basis of the literature [44][45][46][47].…”

“…This band appears at different wavenumbers depending on the tautomeric form of His (tautomer I or II, also referred as N s -H or N p -H) and its involvement in coordination (Fig. S5) [47,[52][53][54]. Generally, free His gives rise to a band at about 1568 or 1583 cm À1 depending on the tautomeric form adopted by its imidazole ring (tautomer I or II, respectively) and the binding of a metal ion pushes up the C 4 @C 5 stretching wavenumbers by 10-20 cm À1 (Fig.…”

“…Generally, free His gives rise to a band at about 1568 or 1583 cm À1 depending on the tautomeric form adopted by its imidazole ring (tautomer I or II, respectively) and the binding of a metal ion pushes up the C 4 @C 5 stretching wavenumbers by 10-20 cm À1 (Fig. 8) [47,53,54]. In addition, this marker band shifts towards lower wavenumber (at about 1555 cm À1 ) when the anionic form of the His imidazole ring binds two different metal ions, making a metal-Im À -metal bridge (Fig.…”

Radical Damage Involving Sulfur-Containing Enzymes and Membrane Lipids

“…Tyr, Trp), on metal binding (e.g. His), oxidation or reduction state of a Cys sulphydryl group (SH), conformation geometry of disulfide bridges, hydrogen bonding and susceptibility of radical attack [43][44][45][46].…”

A vibrational spectroscopy study on anserine and its aqueous solutions

“…These studies have focused mostly on L-histidine [12][13][14], carnosine and its various metal complexes [15][16][17][18][19][20][21][22]. Surprisingly, the literature is sparse for anserine molecule, which is a methyl substituted derivative of carnosine.…”