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Spectroscopy and chemistry of nickel metalloenzyme models

Gerard Joseph Colpas, University of Massachusetts Amherst

Abstract

The Ni K-edge x-ray absorption near edge structure (XANES) and extended x-ray absorption fine structure (EXAFS) of thirty-seven nickel (II) model complexes and eight nickel (III) model complexes were analyzed. The 1s $\to$ 3d peak areas were found to be indicative of each local geometry. The individual features were correlated with ligand type, local geometry, and oxidation state.^ The nickel-containing hydrogenase from the purple photosynthetic bacteria Thiocapsa roseopersicina was analyzed for both XANES and EXAFS. The enzyme was poised in the hydrogen-reduced, active form corresponding to nickel signal-C. The results are consistent with a mixed-donor, five-coordinate site having 3 $\pm$ 1 N,O-donors at 2.06 A, and 2 $\pm$ 1 S-donors at 2.21 A. Scattering from the second and third coordination sphere are consistent with Ni-Fe distances of 4.3 A, and 6.2 A, indicating the presence of a nearby iron-sulfur cluster.^ Four novel nickel (II) complexes were synthesized. The compounds include a dimeric nickel arylthiolate complex, (Ni(Me$\sb6$tren)Cl) $\sb2$ (Ni(S-p-$\rm C\sb6H\sb4Cl)\sb6$) (Me$\sb6$tren = 1,1,1-tris(2-dimethylaminoethyl)amine); a monomeric Ni(N$\sb2$S$\sb2$) complex with cis S-donors, Ni(dmpn) (dmpn = N,N$\sp\prime$-dimethyl-N,N$\sp\prime$-bis(2-mercaptoethyl)-1,$ 3$-propanediamine); a trimeric nickel complex with bridging thiolates, (Ni$\sb3$(dmpn)$\sb2$) (BF$\sb4)\sb2$; and a nickel-iron complex, $\{$ (Ni(dmpn)) $\sb3$Fe$\}$(ClO$\sb4)\sb2$. The spectroscopic and redox chemistry of these and other nickel-thiolate species were explored and compared with data available for nickel-containing hydrogenases. ^

Subject Area

Inorganic chemistry|Biophysics

Recommended Citation

Colpas, Gerard Joseph, "Spectroscopy and chemistry of nickel metalloenzyme models" (1991). Doctoral Dissertations Available from Proquest. AAI9207377.
https://scholarworks.umass.edu/dissertations/AAI9207377

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