Potentiometric and spectroscopic studies of the complex formation between copper(II) and Gly-Leu-Phe or Sar-Leu-Phe tripeptides

Synthesis, Characterization, and Reaction Studies of Pd(II) Tripeptide Complexes

The aqueous synthesis of Pd(II) complexes with alkylated tripeptides led to the hydrolysis of the peptides at low pH values and mixtures of complexed peptides were formed. A non-aqueous synthetic route allowed the formation and isolation of single products and their characterization. Pd(II) complexes with α-Asp(OR)AlaGly(OR), β-Asp(OR)AlaGly(OR), and TrpAlaGly(OR) (R = H or alkyl) as tri and tetradentate chelates were characterized. The tridentate coordination mode was accompanied by a fourth monodentate ligand that was shown to participate in both ligand exchange reactions and a direct removal to form the tetradentate coordination mode. The tetradentate coordination revealed a rare a hemi labile carbonyl goup coordination mode to Pd(II). Reactivity with small molecules such as ethylene, acids, formate, and episulfide was investigated. Under acidic conditions and in the presence of ethylene; acetaldehyde was formed. The Pd(II) is a soft Lewis acid and thiophilic and the complexes abstract sulfur from episulfide at apparent modest catalytic rates. The complexes adopt a square planar geometry according to a spectroscopic analysis and DFT calculations that were employed to evaluate the most energetically favorable coordination geometry and compared with the observed infrared and NMR data.

Insights into metalloproteins and metallodrugs from electron paramagnetic resonance spectroscopy

Metal ions play an important role in diverse biological processes, and much of the basic knowledge derived from studying native bioinorganic systems are applied in the synthesis of new molecules with the aim of diagnosing and treating diseases. At first glance, metalloproteins and metallodrugs are very different systems, but metal ion coordination, redox chemistry and substrate binding play essential roles in advancing both of these research fields. In this article, we discuss recent metalloprotein and metallodrug studies where electron paramagnetic resonance spectroscopy served as a major tool to gain a better understanding of metal-based structures and their function.

Stability, Structure, and Permeability Studies of Copper Tripeptide Species in Aqueous Solution

The use of copper complexes to alleviate inflammation associated with rheumatoid arthritis (RA) is well known. This study focuses on designing a new drug that could be used to increase the bioavailability of copper and hence be more effective. The ligand chosen was sarcosyl-l-lysyl-l-lysine (Sar-Lys-Lys). The thermodynamic stability of H+, CuII, NiII, and ZnII complexes of Sar-Lys-Lys was measured in an aqueous solution at 298±0.01°C and an ionic strength of 0.15M (NaCl) using glass electrode potentiometry. UV-Vis, ESR, and 1H NMR spectroscopy was used to investigate the solution structures of the different species. At physiological pH, the ligand was found to coordinate via two amide nitrogens, the terminal amine, and the terminal carboxy group. The ε-amino group of lysine did not coordinate with the metal ion. Dermal absorption is the preferred method of administration and so this study used partition coefficients and tissue permeability studies to assess the bioavailability of the different complexes. Sar-Lys-Lys was found to increase the copper lipophilicity by a factor of 10 and increased tissue permeability by 30%.

Directed coordination study of [Pd(en)(H2O)2]2+ with hetero-tripeptides containing C-terminus methyl esters employing NMR spectroscopy

Alkylation of the C-terminus acids in small peptides allows direction to amine and amide coordination, while changing the peptide composition to form tetradentate κ⁴[n,5,5], where n = 5-, 6-, 7-, or 8-membered ring coordination geometries, can be achieved. The alkylated tripeptide ligands, TrpAlaGly(OMe), β-Asp(OtBu)AlaGly(OMe), Asp(OtBu)AlaGly(OMe), and the fully methylated GSH, γ-Glu(OMe)Cys(SMe)Gly(OMe), were synthesized and their coordination properties to [Pd(en)(H₂O)₂]²⁺ were studied. pH-dependent coordination was analyzed by NMR spectroscopy and the coordination to the alkylated tripeptides at selected pH values inferred from their NMR spectra. If selective coordination of amine/amide donors results in metal complexation, allowing for flexible and adjustable ligand frameworks, then this strategy could potentially be extended to other metal ions and peptide system.