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 [ML_p(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.

We investigated the effects of ultrasound-facilitated fixation on oral mucosal morphology. Bovine dorsal tongue and porcine buccal (cheek) mucosa were sonicated for 0, 5, 10 or 15 min in a modified methacarn fixative, then incubated at 25° C for 4 h. Initial mass, volume and density of each specimen were measured before and after treatment and fixation. Morphometric analysis of the scanning electron micrographs was used to quantify changes in mucosal structure and microtexture. Statistical methods were used to describe the relation between sonication time, tissue density and relative change in tissue density. Our results indicate a linear correlation between sonication time and density of the dorsal tongue specimens. The treatment caused contraction of the tongue tissue and expansion of the buccal mucosa. Differences between initial and final tongue densities and the relative change in tissue density of the tongue vs. buccal mucosa were statistically significant. Differences observed between initial and final buccal mucosa densities were not statistically significant. Changes in buccal mucosa density correlated inversely with sonication time by contrast to the tongue density, which was correlated directly with this factor. Our study illustrates that while preservation of mucosal morphology and biopolymers can be achieved by ultrasound-facilitated fixation, its effects on tissue density are both time-dependent and specific to certain regions of the mouth.