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

Post- print / Lokaútgáfa höfundarAlkylation 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.Financial support by The Icelandic Centre of Research (Rannis) grant nr 152323 is gratefully acknowledged. SGS and GRR thank COST Action CM1105 for STSM Grant and Prof. Etelka Farkas for hosting the STMS at the early stages of this project. Dr Sigridur Jonsdottir is thanked for assistance with the collection of mass spectrometry data.Peer reviewe

Synthesis and characterization of asymmetric [Mo2O2(μ-S)2(S2)(L)] complexes (L = bipy, en, dien) and their heterogeneous reaction with propylene sulfide

Post-print (lokagerð höfundar)Crystalline and amorphous molybdenum sulfide “MoSx” catalysts are well established in sulfur removal from petrochemicals in heterogeneous reactions. Accessibility of sulfido ligands on the catalyst surface is generally accepted as pre-requisite for catalytic initiation. Interest in study of discrete molecules with similar active sites for sulfur transfer reactions in organic reactions prompted synthesis of the asymmetric dinuclear complexes, [Mo2O2(μ-S)2(S2)(L)] (1, L = bipyridine (bipy); 2, L = ethylene diamine (en), 3, L = diethylenediamine (dien)) in facile ligand exchange reaction. A single crystal of 1 was obtained from DMF/ether solution as dark red plates and analyzed by X-ray diffraction. The complexes remove sulfur from propylene sulfide in a heterogeneous reaction at ambient temperature on the NMR scale. Reactivity expected to reflect the donation properties of L with the largest LMCT contribution rendering the most reactive sulfido ligand yielded surprising results. DFT calculations of the optimized minimal energy structures of all three complexes were performed and several possible isomeric structures evaluated. The optimal energy form of 1 compared well with its crystal structure and results from calculated structures of 2 and 3 agree with spectroscopic observations. The modest reactivity is in agreement with poor access to the disulfide as inferred by DFT structures of the complexes and the crystal structure of 1 where strong SS interactions were found along its b-axis.Icelandic Centre for Research (173667)Peer reviewe