Binding of the Oxo−Rhenium(V) Core to Methionine and to N-Terminal Histidine Dipeptides

Abstract

The ReOX(2)(met) compounds (X = Cl, Br) adopt a distorted octahedral structure in which a carboxylato oxygen lies trans to the Re=O bond, whereas the equatorial plane is occupied by two cis halides, an NH(2), and an SCH(3) group. Coordination of the SCH(3) unit creates an asymmetric center, leading to two diastereoisomers. X-ray diffraction studies reveal that the crystals of ReOBr(2)(d,l-met).1/2H(2)O and ReOBr(2)(d,l-met).1/2CH(3)OH contain only the syn isomer (S-CH(3) bond on the side of the Re=O bond), whereas ReOCl(2)(d-met) and ReOCl(2)(d,l-met) consist of the pure anti isomer. (1)H NMR spectroscopy shows that both isomers coexist in equilibrium in acetone (anti/syn ratio = 1:1 for X = Br, 3:1 for X = Cl). Exchange between these two isomers is fast above room temperature, but it slows down below 0 degrees C, and the sharp second-order spectra of both isomers at -20 degrees C were fully assigned. The coupling constants are consistent with the solid-state conformations being retained in solution. Complexes of the type [ReOX(2)(His-aa)]X (X = Cl, Br) are isolated with the dipeptides His-aa (aa = Gly, Ala, Leu, and Phe). X-ray diffraction work on [ReOBr(2)(His-Ala)]Br reveals the presence of distorted octahedral cations containing the Re=O(3+) core and a dipeptide coordinated through the histidine residue via the imidazole nitrogen, the terminal amino group, and the amide oxygen, the site trans to the Re=O bond being occupied by the oxygen. The alanine residue is ended by a protonated carboxylic group that does not participate in the coordination. The constant pattern of the(1)H NMR signals for the protons in the histidine residue confirms that the various dipeptides adopt a similar binding mode, consistent with the solid-state structure being retained in CD(3)OD solution.

Metal-ion induced transition from multi- to single-bilayer tubes in histidine bearing lipids and formation of monodisperse Au nanoparticles

“…This means the bond order of the CQO is decreased owing to the interaction with the metal ion. The similar IR changes have been reported by Aiba et al and Tiessier et al 38,39 Aiba et al have suggested that His-Gly and His-Gly-Gly bind to the copper(II) ion and they act as a tridentate ligand via an imidazole nitrogen, the NH 2 group, and the carbonyl oxygen. Furthermore, they indicated that the water molecule also binds to the copper(II) ion.…”

Re(CO)3 Complexes Synthesized via an Improved Preparation of Aqueous fac-[Re(CO)3(H2O)3]+ as an Aid in Assessing 99mTc Imaging Agents. Structural Characterization and Solution Behavior of Complexes with Thioether-Bearing Amino Acids as Tridentate Ligands

“…Amino acids (AAH) with a thioether group, such as S -methyl- l -cysteine (MECYSH) and methionine (METH), are good model compounds for this approach. However, only a few examples showing methionine or S -methylcysteine tridentate coordination in metal complexes have been reported; − moreover, reports of investigations into the coordination chemistry of metal carbonyl compounds made from MECYSH and METH are quite rare…”

12 Manganese, technetium and rhenium

“…Employing either the racemic D,L-Met or the pure L-Met results in the same coordination geometry. 49 A family of oxo-rhenium(V) complexes has been prepared by reaction of [Re V OCl 4 ] 2 with a series of ONN-tridentate and ONNO-tetradentate ligands. Thus in both octahedral [Re V O(L 15 )Cl 2 ] and [Re V O(L 16 )Cl] the oxo and phenolate O-donors are mutually trans; a variety of related complexes of this type were reported containing the same basic ligand chain.…”