The bioinorganic chemistry of N2S2 metal complexes: reactivity and ligating ability

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Title: The bioinorganic chemistry of N2S2 metal complexes: reactivity and ligating ability
Author: Golden, Melissa Lynn
Abstract: [N ,N ? ? -bis - (mercaptoethyl ) -1 ,5 -diazacyclooctanato]NiII , Ni -1 , is known to undergo metallation reactions with numerous metals . [N ,N ? ? -bis - (mercaptoethyl ) -1 ,5 -diazacycloheptanato]NiII , (bme -dach )Ni or Ni -1 ? ? , differs from Ni -1 by one less carbon in its diazacycle backbone ring producing subtle differences in N2S2Ni geometry . Metallation of Ni -1 ? ? with PdCl2 , Pd (NO3 )2 , and NiBr2 produced three structural forms : Ni2Pd basket , Ni4Pd2 C4 -paddlewheel , and Ni3 slant chair . In attempts to provide a rationale for the heterogeneity in the active site of Acetyl coA Synthase , metal ion capture studies of Ni -1 in methanol found a qualitative ranking of metal ion preference : Zn2+ < Ni2+ < Cu+ . Formation constants for metal ion capture of Ni -1 ? ? in water were determined for Pb2+ , Ni2+ , Zn2+ , Cu+ , and Ag+ . A quantitative estimate places copper some 15 orders of magnitude above nickel or zinc in binding affinity . Sulfur dioxide uptake by Ni -1 ? ? is characterized by significant color change , improved adduct solubility , and reversible binding of two equivalents of SO2 . These combined properties establish Ni -1 ? ? as a suitable model for gas uptake at nickel thiolate sites and as a possibly useful chemical sensor for this poisonous gas . Comparisons of molecular structures , & #61472 ; & #957 ; (SO ) stretching frequencies , and thermal gravimetric analyses are made to reported adducts including the diazacyclooctane derivative , Ni -1 & #903 ;2SO2 . Visual SO2 detection limits of Ni -1 and Ni -1 ? ? are established at 25 ppm and 100 ppm , respectively . Structural studies of products resulting from reaction at the nucleophilic S -sites of (bme -dach )Ni and [ (bme -dach )Zn]2 included acetyl chloride and sodium iodoacetate as electrophiles are shown . The acetyl group is a natural electrophile important to the citric acid cycle . Acetylation of (bme -dach )Ni produces a five coordinate , paramagnetic species . Iodoacetate is a cysteine modification agent known to inhibit enzymatic activity . The reaction of (bme -dach )Ni and sodium iodoacetate yields a blue , six coordinate nickel complex in a N2S2O2 donor environment . The bismercaptodiazacycloheptane ligand binds lead (II ) forming an unprecedented structural form of N2S2M dimers , in which Pb2+ is largely bound to sulfur in a highly distorted trigonal geometry . Its unusual structure is described in comparison to other derivatives of the bme -daco ligand . The synthesis and structural characterization of square pyramidal (bme -dach )GaCl are also given and compared to the analogous (bme -daco )GaCl .
URI: http : / /hdl .handle .net /1969 .1 /2198
Date: 2005-08-29

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The bioinorganic chemistry of N2S2 metal complexes: reactivity and ligating ability. Available electronically from http : / /hdl .handle .net /1969 .1 /2198 .

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