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Me 6 trien = 1,1,4,7,10,10-hexamethyltriethylene tetramine} were synthesized and structurally characterized by spectroscopic techniques, X-ray crystallography, and variable-temperature magnetic measurements. In the complexes 1-3a, the ClO 4 -groups are counterions and the Ni 2+ centers are bridged by the azido ligands in an end-to-end bonding fashion. The coordination geometry around the Ni II ions is six-coordinate with a distorted octahedral environment achieved by the four N atoms of the tetradentate amines and two terminal N atoms of the azide groups. Complex 1 consists of dinuclear units with doubly bridged azido groups whereas in 2 and 3a, a polymeric 1D chain is formed in which the adjacent azido

Synthesis is reported of 2-amino-5-mercapto-5-methylhexanoic acid (2) as a bishomologue of penicillamine (1). In this synthesis, alkylation of diethyl acetamidomalonate gave ethyl 2-acetamido-2-carbethoxy-5-methyl-4-hexenoate (4). Addition of -toluenethiol to 4 using BF3-Et20 then gave ethyl 2-acetamido-2-carbethoxy-5-benzylthio-5-methylhex.anoate (6) in 63-74% yield; this reaction appears to be the first use of BFg-EtaO as a catalyst for effecting Markownikoff-type addition of a thiol to an alkene. The bishomologue 2 was obtained from 6 either by decarboxylation to the amide (5), debenzylation of 5 to 7, and hydrolysis, or (preferably) by decarboxylation and hydrolysis to the amino acid 8 in one step and debenzylation. The bishomologue 2 resisted hot strong acid. It reacts with formaldehyde, Fe(III), or Cu(II) much less readily than does 1 and therefore affords a promising means of probing biological properties of 1 where it is unclear whether these properties depend upon ring formation involving SH and NH2 or upon independent action of functional groups.

Glycerol binding and the radical-initiated hydrogen transfer by the coenzyme B(12)-independent glycerol dehydratase from Clostridium butyricum were investigated by using quantum mechanical/molecular mechanical (QM/MM) calculations based on the high-resolution crystal structure (PDB code: 1r9d). Our QM/MM calculations of enzyme catalysis considered the electrostatic coupling between the quantum-mechanical and molecular-mechanical subsystems and two alternative mechanisms. In addition to performing QM/MM calculations in the enzyme, we evaluated energetics along the same reaction pathway in aqueous solution modeled by the polarized dielectric and in the virtual enzyme site that included full steric component from the enzyme residues described by molecular mechanics but lacked the electrostatic contribution of these residues. In this way, we established significant enzyme catalytic effect with respect to reference reactions in both an aqueous solution and a nonpolar cavity. Structurally, four hydrogen bonds formed between glycerol and H164, S282, E435, and D447 anchor glycerol for hydrogen abstraction by thiyl radical on C433. These hydrogen-bond partners orient glycerol molecule to facilitate the formation of the transition state for hydrogen abstraction from carbon C1. This reaction then proceeds with the activation free energy of 6.3 kcal/mol and the reaction free energy of 6.1 kcal/mol. The polarization effects imposed by these hydrogen bonds represent a predominant contribution to a 7.5 kcal/mol enzyme catalytic effect. These results demonstrate the importance of electrostatic catalysis and hydrogen-bonding in enzyme-catalyzed radical reactions and advance our understanding of the catalytic mechanism of B(12)-independent glycerol dehydratases.

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Two thiocyanato-Cu(II) complexes including mononuclear dithiocyanato Cu(Me 3 dpt)(NCS) 2 (1) and the polymeric 1D [Cu(D,L-Ala)(l N,S -NCS)(H 2 O)] n (2) were synthesized and structurally characterized (Me 3 dpt = bis(N-methyl-3-propyl)methylamine, Ala = alaninate anion). The IR spectrum of complex 1 confirmed the N-bonding coordination mode of the thiocyanate groups, and its visible spectrum revealed the square pyramidal geometry around the central Cu 2? ion. Single X-ray crystallography of 1 showed that the Cu(II) center displays square pyramidal geometry with severe distortion toward trigonal bipyramidal environment. Complex 2 forms a 1-D polymeric chain with the NCS -acting as a l N,S -ligand. A distorted SP geometry around the Cu 2? centers was achieved by the O and N atoms of alaninato anion, the aqua ligand and by the N and S atoms of the bridging thiocyanate groups. Hydrogen bonds of the type N-HÁÁÁO, N-HÁÁÁS and O-HÁÁÁO are formed in this complex leading to the extension of the 1D chain to a supramolecular network.