Dipeptides as potential anti-flammatory drugs for rheumatoid arthritis

Includes abstract.Includes bibliographical references.The H⁺ and Cu²⁺ equilibria of four glycine peptides (glycyl-glycine, glycyl-L-leucine, glycyl-L-phenylalanine and glycyl-L-histidine) and four sarcosine peptides (sarcosylglycine, sarcosyl-L-leucine, sarcosyl-L-phenylalanine and sarcosyl-L-histidine) have been studied using glass electrode potentiometry and isothermal titration calorimetry at 25 °C and an ionic strength 0.15 M (NaCl). The terminal amine of the sarcosine peptides is more basic than the glycine analogues. The methyl group on the terminal amine (for sarcosine peptides) does not affect the stability constants of the ML species, significantly. Log K for ML species for all the Cu(II)/peptides complexes ranged between 5.79 and 6.54, except for glycyl-L-histidine that showed log KML = 9.16. Heat accompanying the formation of ML for all the species ranged between -5.1 kcal mol⁻¹ and-6.6 kcal mol⁻¹, except for glycyl-L-histidine that showed ΔHML = -3.6 kcal.mol⁻¹. Structures for the different species in solution were postulated based on nuclear magnetic resonance and ultraviolet-visible spectrophotometry data. Molecular mechanics was used to investigate the possible structures. The minimum energy of the trans form of most the complexes was less than the cis form of the complexes