title: Synthesis and Speciation-Dependent Properties of a Multimetallic Model Complex of NiSOD That Exhibits Unique Hydrogen-Bonding.
abstract: The complex Na3[{NiII(nmp)}3S3BTAalk)] (1) (nmp2-= deprotonated form of N-(2-mercaptoethyl)picolinamide; H3S3BTAalk= N1,N3,N5-tris(2-mercaptoethyl)benzene-1,3,5-tricarboxamide, where H = dissociable protons), supported by the thiolate-benzenetricarboxamide scaffold (S3BTAalk), has been synthesized as a trimetallic model of nickel-containing superoxide dismutase (NiSOD). X-ray absorption spectroscopy (XAS) and1H NMR measurements on 1 indicate that the NiIIcenters are square-planar with N2S2coordination, and Ni-N and Ni-S distances of 1.95 and 2.16 Å, respectively. Additional evidence from IR indicates the presence of H-bonds in 1 from the approximately -200 cm-1shift in νNHfrom free ligand. The presence of H-bonds allows for speciation that is temperature-, concentration-, and solvent-dependent. In unbuffered water and at low temperature, a dimeric complex (1A; λ = 410 nm) that aggregates through intermolecular NH···O═C bonds of BTA units is observed. Dissolution of 1 in pH 7.4 buffer or in unbuffered water at temperatures above 50 °C results in monomeric complex (1M; λ = 367 nm) linked through intramolecular NH···S bonds. DFT computations indicate a low energy barrier between 1Aand 1Mwith nearly identical frontier MOs and Ni-ligand metrics. Notably, 1Aand 1Mexhibit remarkable stability in protic solvents such as MeOH and H2O, in stark contrast to monometallic [NiII(nmp)(SR)]-complexes. The reactivity of 1 with excess O2, H2O2, and O2•-is species-dependent. IR and UV-vis reveal that 1Ain MeOH reacts with excess O2to yield an S-bound sulfinate, but does not react with O2•-. In contrast, 1Mis stable to O2in pH 7.4 buffer, but reacts with O2•-to yield a putative [NiII(nmp)(O2)]-complex from release of the BTA-thiolate based on EPR.
authors.affiliation: Department of Chemistry and Center for Metalloenzyme Studies, The University of Georgia , 140 Cedar St, Athens, Georgia 30602, United States.
authors.forename: Ramsey A
authors.initials: RA
authors.lastname: Steiner
authors.affiliation: Departments of Pharmaceutical Sciences, and Biochemistry and Molecular Biology, Wayne State University , Detroit, Michigan 48201, United States.
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Dzul
authors.affiliation: Departments of Pharmaceutical Sciences, and Biochemistry and Molecular Biology, Wayne State University , Detroit, Michigan 48201, United States.
authors.forename: Timothy L
authors.initials: TL
authors.lastname: Stemmler
authors.affiliation: Department of Chemistry and Center for Metalloenzyme Studies, The University of Georgia , 140 Cedar St, Athens, Georgia 30602, United States.
authors.forename: Todd C
authors.identifier: http://orcid.org/0000-0002-6078-3997
authors.initials: TC
authors.lastname: Harrop