Preparation, Spectrochemical, and Computational Analysis of L-Carnosine (2-[(3-Aminopropanoyl)amino]-3-(1H-imidazol-5-yl)propanoic Acid) and Its Ruthenium (II) Coordination Complexes in Aqueous Solution

Abstract

This study reports the synthesis and characterization of novel ruthenium (II) complexes with the polydentate dipeptide, L-carnosine (2-[(3-aminopropanoyl)amino]-3-(1H-imidazol-5-yl)propanoic acid). Mixed-ligand complexes with the general composition [MLp(Cl)q(H2O)r]·xH2O (M = Ru(II); L = L-carnosine; p = 3 − q; r = 0–1; and x = 1–3) were prepared by refluxing aqueous solutions of the ligand with equimolar amounts of ruthenium chloride (black-alpha form) at 60 °C for 36 h. Physical properties of the complexes were characterized by elemental analysis, DSC/TGA, and cyclic voltammetry. The molecular structures of the complexes were elucidated using UV-Vis, ATR-IR, and heteronuclear NMR spectroscopy, then confirmed by density function theory (DFT) calculations at the B3LYP/LANL2DZ level. Two-dimensional NMR experiments (1H COSY, 13C gHMBC, and 15N gHMBC) were also conducted for the assignment of chemical shifts and calculation of relative coordination-induced shifts (RCIS) by the complex formed. According to our results, the most probable coordination geometries of ruthenium in these compounds involve nitrogen (N1) from the imidazole ring and an oxygen atom from the carboxylic acid group of the ligand as donor atoms. Additional thermogravimetric and electrochemical data suggest that while the tetrahedral-monomer or octahedral-dimer are both possible structures of the formed complexes, the metal in either structure occurs in the (2+) oxidation state. Resulting RCIS values indicate that the amide-carbonyl, and the amino-terminus of the dipeptide are not involved in chelation and these observations correlate well with theoretical shift predictions by DFT.

Synthesis of L-Carnosine and its Applications in Biomedical Field

“…The UV-Vis absorbance spectra of carnosine, with absorbance bands observed at 266 nm and 213 nm which can be assigned to n-π* and π-π* of synthesized carnosine [19]. …”

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.…”

Solid-Phase Peptide Synthesis of Dipeptide (Histidine-β-Alanine) as a Chelating Agent by Using Trityl Chloride Resin, for Removal of Al3+, Cu2+, Hg2+and Pb2+: Experimental and Theoretical Study

“…6,7 ) have been studied. [8][9][10][11] In this paper, we report the synthesis of dipeptide histidine-β-alanine as a chelating agent with chemical method, solid-phase peptide synthesis. Molecular structure and chelating property of synthesized dipeptide were investigated.…”