title: New monomeric cobalt(II) and zinc(II) complexes of a mixed N,S(alkylthiolate) ligand: model complexes of (His)(His)(Cys) metalloprotein active sites.
abstract: The new N(2)S(alkylthiolate) ligand 2-methyl-1-[methyl-(2-pyridin-2-ylethyl)amino]propane-2-thiolate, PATH (1), has been prepared and reacted with zinc(II) and cobalt(II) to give the monomeric complexes [(PATH)ZnBr] (2), [(PATH)ZnNCS] (3), [(PATH)CoBr] (4), and [(PATH)CoNCS] (5). The molecular structures of 4 and 5 have been determined by X-ray diffraction. Each complex displays a distorted tetrahedral geometry at the metal center, with the PATH ligand providing the N(2)S(alkylthiolate) donors. These complexes are close structural mimics of the active site of metalloproteins with a His(2)Cys-M(II) site such as that found in peptide deformylase. Complexes 4 and 5 are the first examples of crystallographically characterized Co(II) complexes with an N(2)SL (L not equal N,S) donor set. Only one diastereomer for 2-5 is observed in the solid state, and simple molecular mechanics (Chem3D) calculations suggest this isomer is stable because of a favorable ligand conformation. NMR studies in the case of Zn(II) and UV-vis studies in the case of Co(II) provide strong evidence that their solid-state structures are retained in solution. Cyclic voltammetry reveals processes for both the Co(II/I) (4, - 1.51 V; 5, - 1.49 V) and Co(III/II) (4, + 0.9 V; 5, + 0.9 V) couples. The UV-vis data for the cobalt complexes are consistent with a monomeric, four-coordinate geometry regardless of the nature of the solvent (i.e., donating (MeOH, CH(3)CN) vs nondonating (CH(2)Cl(2))) and are compared with other cobalt complexes as well as cobalt-substituted His(2)Cys metalloproteins (peptide deformylase and blue-copper proteins). In addition, reaction of the bromide complexes 2 and 4 with hydroxide anion leads to the formation of 1:1 hydroxide:M(II) complexes which have been characterized in situ by (1)H NMR and UV-vis spectroscopy, respectively.
authors.affiliation: Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218, USA.
authors.forename: SeChin
authors.initials: S
authors.lastname: Chang
authors.forename: Vivek V
authors.initials: VV
authors.lastname: Karambelkar
authors.forename: Roger D
authors.initials: RD
authors.lastname: Sommer
authors.forename: Arnold L
authors.initials: AL
authors.lastname: Rheingold
authors.forename: David P
authors.initials: DP
authors.lastname: Goldberg
mesh_terms: D000581:Amidohydrolases; D000626:Aminopeptidases / Q000737:chemistry; D001426:Bacterial Proteins / Q000737:chemistry; D001665:Binding Sites; D002384:Catalysis; D003035:Cobalt / Q000737:chemistry*; D003553:Cystine / Q000737:chemistry; D004563:Electrochemistry; D004926:Escherichia coli / Q000201:enzymology; D006639:Histidine / Q000737:chemistry; D006868:Hydrolysis; D007501:Iron / Q000737:chemistry; D008024:Ligands; D008667:Metalloproteins / Q000737:chemistry; D008956:Models, Chemical; D008968:Molecular Conformation; D015394:Molecular Structure; D019906:Nuclear Magnetic Resonance, Biomolecular; D009942:Organometallic Compounds / Q000737:chemistry*; D010455:Peptides / Q000737:chemistry; D011725:Pyridines / Q000138:chemical synthesis; D013053:Spectrophotometry; D013056:Spectrophotometry, Ultraviolet; D017550:Spectroscopy, Fourier Transform Infrared; D013329:Structure-Activity Relationship; D013438:Sulfhydryl Compounds / Q000737:chemistry; D015032:Zinc / Q000737:chemistry*
chemical_list: C511541:(2-methyl-1-(methyl-(2-pyridin-2-ylethyl)amino)propane-2-thiolate)zinc(II); C450799:2-methyl-1-(methyl(2-pyridin-2-ylmethyl)amino)propane-2-thiol; D001426:Bacterial Proteins; D008024:Ligands; D008667:Metalloproteins; D009942:Organometallic Compounds; D010455:Peptides; D011725:Pyridines; D013438:Sulfhydryl Compounds; C017079:mauC protein, Methylobacterium extorquens; D003035:Cobalt; D003553:Cystine; D006639:Histidine; D007501:Iron; D000626:Aminopeptidases; D000581:Amidohydrolases; C084507:peptide deformylase; D015032:Zinc