Interaction of Dimethyltin(IV)²⁺ Cation with Gly-Gly, Gly-His, and Some Related Ligands. A New Case of a Metal Ion Able To Promote Peptide Nitrogen Deprotonation in Aqueous Solution

Abstract

Equilibrium (pH-metric) and spectroscopic (1H,13C, and 119Sn NMR and 119Sn Mössbauer) studies were performed to characterize the interaction of the dimethyltin(IV) cation with glycine, glycyl-glycine (Gly-Gly), imidazole-4-acetic acid, histamine, histidine, glycyl-histamine, glycyl-histidine (Gly-His), and β-alanyl-histidine (carnosine). For histamine and glycyl-histamine (having only nitrogen donor atoms) no complex formation was detected. The hydrolyzed species of the dimethyltin(IV) cation are always dominant over the complexes formed with the other ligands, except with Gly-Gly and Gly-His. For these two ligands, {COO-,N-,NH2} coordinated complexes are dominant in the neutral pH range with a trigonal bipyramidal structure, providing the first example that alkyltin(IV) cations are able to promote the deprotonation of the peptide-nitrogen in aqueous solutions, at unexpectedly low pH. In this process the carboxylate is the anchoring group (assisting by chelate formation), in contrast with any other metal ions which are known to coordinate to amide nitrogen. The metal coordination of the imidazole ring, which is suggested as binding site toward alkyltin(IV) cation in several proteins, was not observed for Gly-His under the conditions used; it is probably the case for the other ligands, too.

New Di- and Triorganotin(IV) Tyrosylalaninates as Models for Metal—Protein Interactions: Synthesis, Structural Characterization, and Potentiometric Studies of Tyrosylalanine, Glycyltyrosine, and Glycylisoleucine with Di- and Trimethyltin(IV) Moieties in Aqueous Medium

“…The hydrolysis constants of dimethyltin(IV) and trimethyltin(IV) cations reported earlier [33,41] have been taken into consideration during the evaluation of the pH-metric data. The composition and solution speciation of these species are very close to these reported earlier for the dimethyltin(IV)-Gly-Gly [42] and dimethyltin(IV)-Ala-Gly [43].…”

“…For this process the pK 2 values lie in the range 4.67 ± 0.20. The observed pK 2 values for MLH −1 species are nearly coincident with those reported for the corresponding dimethyltin(IV)-Gly-Gly [42] and dimethyltin(IV)-Ala-Gly [43]. In this process the deprotonation of the amide and amine nitrogen takes place in a cooperative manner with the removal of the coordinated hydroxyl group.…”

“…For this process the observed pK 1 values (see Table 7) are similar to each other in all the systems and may be attributed to the (i) deprotonation of a metal-bound water molecule forming hydroxo mixed-ligand complexes or (ii) metal-promoted deprotonation of −NH + 3 group present in zewitterionic form. The pK 1 values reported for dimethyltin(IV)-Gly-Gly [42] and-Ala-Gly [43] are 3.46 and 3.42, respectively, for which the formation of hydroxo mixed-ligand complexes was reported. In the present study the observed pK 1 (3.93-4.46) values also indicate a hydrolytic process takes place during the deprotonation of the carboxylate coordinated M(HL) complex species, forming a hydroxo mixed-ligand, M(HL)(OH) (i.e., COO − and OH − are coordinated) complex.…”

Thermodynamic and spectroscopic study for the interaction of dimethyltin(IV) with L–cysteine in aqueous solution

“…4 interaction of the organotin moieties with several biologically relevant compounds such as carbohydrates, amino acids, peptides, nucleic acids and DNA has been carried out mostly in the last decade [8][9][10][11][12][13][14][15][16][17][18][19][20][21]. From some of these cited studies, the interaction of dimethyltin (IV) and trialkyltin(IV) (with R = methylic, ethylic, and butylic groups) in aqueous solution, at physiological pH, with thiol groups of model molecules, as well as feline and rat haemoglobin, have been investigated by 119 Sn Mössbauer spectroscopy.…”

“…The proton chemical calculated assuming fast mutual exchange [12]. The heteronuclear couplings of the tin-bound methyl groups 2 J( 119 Sn-1 H) obtained in such a way were "converted" into C-Sn-C angles by using the published equation [31].…”