Browsing by Author "Basu, Partha"
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Item Design, Synthesis, and Structure of Copper Dithione Complexes: Redox‐Dependent Charge Transfer(Wiley, 2019-12) Colston, Kyle J.; Dille, Sara A.; Mogesa, Benjamin; Astashkin, Andrei V.; Brant, Jacilynn A.; Zeller, Matthias; Basu, Partha; Chemistry and Chemical Biology, School of ScienceRedox‐active ligands impart versatility in transition metal complexes, which are attractive for photosensitizers, dye sensitized solar cells, photothermal therapy, etc. Dithiolene (Dt) ligands can transition between fully reduced and fully oxidized states. Herein, we report the syntheses, characterization, crystal structures and electronic properties of four [Cu(R2Dt0)2]+/2+ (R = Me, iPr) complexes, [Cu(iPr2Dt0)2][PF6] (1a), [Cu(iPr2Dt0)2][PF6]2 (1b), and [Cu(Me2Dt0)2][PF6] (2a), [Cu(Me2Dt0)2][PF6]2 (2b), where iPr2Dt0 = N,N′‐diisopropyl‐1,2‐piperazine dithione and Me2Dt0 = N,N′‐dimethyl‐1,2‐piperazine dithione. In addition, the molecular structure of [Cu(iPr2Dt0)2][BF4]2(1c) is also reported. Complexes 1a and 2a crystallized in the triclinic, P1 space group, and 1c crystallized in the monoclinic crystal system, space group C2/c. The single‐crystal X‐ray diffraction measurements show that the Cu(I) complexes have a distorted tetrahedral geometry, whereas the Cu(II) complex exhibits a true square‐planar geometry. Cu(I) complexes exhibit a low energy charge‐transfer band (450–650 nm), which are not observed in Cu(II) complexes. Electrochemical studies of these complexes show both ligand‐ and metal‐based redox couples.Item Interligand communication in a metal mediated LL′CT system – a case study(RSC, 2021) Dille, Sara A.; Colston, Kyle J.; Ratvasky, Stephen C.; Pu, Jingzhi; Basu, Partha; Chemistry and Chemical Biology, School of ScienceA series of oxo-Mo(IV) complexes, [MoO(Dt2−)(Dt0)] (where Dt2− = benzene-1,2-dithiol (bdt), toluene-3,4-dithiol (tdt), quinoxaline-2,3-dithiol (qdt), or 3,6-dichloro-benzene-1,2-dithiol (bdtCl2); Dt0 = N,N′-dimethylpiperazine-2,3-dithione (Me2Dt0) or N,N′-diisopropylpiperazine-2,3-dithione (iPr2Dt0)), possessing a fully oxidized and a fully reduced dithiolene ligand have been synthesized and characterized. The assigned oxidation states of coordinated dithiolene ligands are supported with spectral and crystallographic data. The molecular structure of [MoO(tdt)(iPr2Dt0)] (6) demonstrates a large ligand fold angle of 62.6° along the S⋯S vector of the Dt0 ligand. The electronic structure of this system is probed by density functional theory (DFT) calculations. The HOMO is largely localized on the Dt2− ligand while virtual orbitals are mostly Mo and Dt0 in character. Modeling the electronic spectrum of 6 with time dependent (TD) DFT calculations attributes the intense low energy transition at ∼18 000 cm−1 to a ligand-to-ligand charge transfer (LL′CT). The electron density difference map (EDDM) for the low energy transition depicts the electron rich Dt2− ligand donating charge density to the redox-active orbitals of the electron deficient Dt0 ligand. Electronic communication between dithiolene ligands is facilitated by a Mo-monooxo center and distortion about its primary coordination sphere.Item Kinetic consequences of the endogenous ligand to molybdenum in the DMSO reductase family: a case study with periplasmic nitrate reductase(Springer, 2021-02) Mintmier, Breeanna; McGarry, Jennifer M.; Bain, Daniel J.; Basu, Partha; Chemistry and Chemical Biology, School of ScienceThe molybdopterin enzyme family catalyzes a variety of substrates and plays a critical role in the cycling of carbon, nitrogen, arsenic, and selenium. The dimethyl sulfoxide reductase (DMSOR) subfamily is the most diverse family of molybdopterin enzymes and the members of this family catalyze a myriad of reactions that are important in microbial life processes. Enzymes in the DMSOR family can transform multiple substrates; however, quantitative information about the substrate preference is sparse, and, more importantly, the reasons for the substrate selectivity are not clear. Molybdenum coordination has long been proposed to impact the catalytic activity of the enzyme. Specifically, the molybdenum-coordinating residue may tune substrate preference. As such, molybdopterin enzyme periplasmic nitrate reductase (Nap) is utilized as a vehicle to understand the substrate preference and delineate the kinetic underpinning of the differences imposed by exchanging the molybdenum ligands. To this end, NapA from Campylobacter jejuni has been heterologously overexpressed, and a series of variants, where the molybdenum coordinating cysteine has been replaced with another amino acid, has been produced. The kinetic properties of these variants are discussed and compared with those of the native enzyme, providing quantitative information to understand the function of the molybdenum-coordinating residue.Item Methane, arsenic, selenium and the origins of the DMSO reductase family(Nature Publishing group, 2020-07-02) Wells, Michael; Kanmanii, Narthana Jeganathar; Al Zadjali, Al Muatasim; Janecka, Jan E.; Basu, Partha; Oremland, Ronald S.; Stolz, John F.; Chemistry and Chemical Biology, School of ScienceMononuclear molybdoenzymes of the dimethyl sulfoxide reductase (DMSOR) family catalyze a number of reactions essential to the carbon, nitrogen, sulfur, arsenic, and selenium biogeochemical cycles. These enzymes are also ancient, with many lineages likely predating the divergence of the last universal common ancestor into the Bacteria and Archaea domains. We have constructed rooted phylogenies for over 1,550 representatives of the DMSOR family using maximum likelihood methods to investigate the evolution of the arsenic biogeochemical cycle. The phylogenetic analysis provides compelling evidence that formylmethanofuran dehydrogenase B subunits, which catalyze the reduction of CO2 to formate during hydrogenotrophic methanogenesis, constitutes the most ancient lineage. Our analysis also provides robust support for selenocysteine as the ancestral ligand for the Mo/W atom. Finally, we demonstrate that anaerobic arsenite oxidase and respiratory arsenate reductase catalytic subunits represent a more ancient lineage of DMSORs compared to aerobic arsenite oxidase catalytic subunits, which evolved from the assimilatory nitrate reductase lineage. This provides substantial support for an active arsenic biogeochemical cycle on the anoxic Archean Earth. Our work emphasizes that the use of chalcophilic elements as substrates as well as the Mo/W ligand in DMSORs has indelibly shaped the diversification of these enzymes through deep time.Item Molecular cloning, expression and biochemical characterization of periplasmic nitrate reductase from Campylobacter jejuni(Oxford University Press, 2018-08-01) Mintmier, Breeanna; McGarry, Jennifer M.; Sparacino-Watkins, Courtney E.; Sallmen, Joseph; Fischer-Schrader, Katrin; Magalon, Axel; McCormick, Joseph R.; Stolz, John F.; Schwarz, Günter; Bain, Daniel J.; Basu, Partha; Chemistry and Chemical Biology, School of ScienceCampylobacter jejuni, a human gastrointestinal pathogen, uses nitrate for growth under microaerophilic conditions using periplasmic nitrate reductase (Nap). The catalytic subunit, NapA, contains two prosthetic groups, an iron sulfur cluster and a molybdenum cofactor. Here we describe the cloning, expression, purification, and Michaelis-Menten kinetics (kcat of 5.91 ± 0.18 s-1 and a KM (nitrate) of 3.40 ± 0.44 μM) in solution using methyl viologen as an electron donor. The data suggest that the high affinity of NapA for nitrate could support growth of C. jejuni on nitrate in the gastrointestinal tract. Site-directed mutagenesis was used and the codon for the molybdenum coordinating cysteine residue has been exchanged for serine. The resulting variant NapA is 4-fold less active than the native enzyme confirming the importance of this residue. The properties of the C. jejuni enzyme reported here represent the first isolation and characterization of an epsilonproteobacterial NapA. Therefore, the fundamental knowledge of Nap has been expanded.Item Molecular cloning, heterologous expression, and steady-state kinetics of camplyobacter jejuni periplasmic nitrate reductase(2020-08) Mintmier, Breeanna; Basu, Partha; Georgiadis, Millie; Deiss, Frédérique; Minto, RobertMononuclear molybdenum enzymes catalyze a variety of reactions that are essential in the cycling of nitrogen, carbon, arsenic, and sulfur. For decades, the structure and function of these crucial enzymes have been investigated to develop a fundamental knowledge for this vast family of enzymes and the chemistries they catalyze. The dimethyl sulfoxide reductase (DMSOR) family is the most diverse family of molybdoenzymes and, the members of this family catalyze a myriad of reactions that are important in microbial life processes. Periplasmic nitrate reductase (Nap) is an important member of the DMSO reductase family that catalyzes the reduction of nitrate (NO3-) to nitrite (NO2-), and yet the physiological role of Nap is not completely clear. Enzymes in this family can transform multiple substrates; however, quantitative information about the substrate preference is sparse and more importantly, the reasons for the substrate selectivity are not clear. Substrate specificity is proposed to be tuned by the ligands coordinating the molybdenum atom in the active site. As such, periplasmic nitrate reductase is utilized as a vehicle to understand the substrate preference and delineate the mechanistic underpinning of these differences. To this end, NapA from Campylobacter jejuni has been heterologously overexpressed, and a series of variants, where the molybdenum-coordinating cysteine has been replaced with another amino acid, has been produced. The kinetic and biochemical properties of these variants will be discussed and compared with those of the native enzyme, providing quantitative information to understand the function.Item Respiratory Selenite Reductase from Bacillus selenitireducens Strain MLS10(American Society for Microbiology, 2019-03-13) Wells, Michael; McGarry, Jennifer; Gaye, Maissa M.; Basu, Partha; Oremland, Ronald S.; Stolz, John F.; Chemistry and Chemical Biology, School of ScienceThe putative respiratory selenite [Se(IV)] reductase (Srr) from Bacillus selenitireducens MLS10 has been identified through a polyphasic approach involving genomics, proteomics, and enzymology. Nondenaturing gel assays were used to identify Srr in cell fractions, and the active band was shown to contain a single protein of 80 kDa. The protein was identified through liquid chromatography-tandem mass spectrometry (LC-MS/MS) as a homolog of the catalytic subunit of polysulfide reductase (PsrA). It was found to be encoded as part of an operon that contains six genes that we designated srrE, srrA, srrB, srrC, srrD, and srrF SrrA is the catalytic subunit (80 kDa), with a twin-arginine translocation (TAT) leader sequence indicative of a periplasmic protein and one putative 4Fe-4S binding site. SrrB is a small subunit (17 kDa) with four putative 4Fe-4S binding sites, SrrC (43 kDa) is an anchoring subunit, and SrrD (24 kDa) is a chaperon protein. Both SrrE (38 kDa) and SrrF (45 kDa) were annotated as rhodanese domain-containing proteins. Phylogenetic analysis revealed that SrrA belonged to the PsrA/PhsA clade but that it did not define a distinct subgroup, based on the putative homologs that were subsequently identified from other known selenite-respiring bacteria (e.g., Desulfurispirillum indicum and Pyrobaculum aerophilum). The enzyme appeared to be specific for Se(IV), showing no activity with selenate, arsenate, or thiosulfate, with a Km of 145 ± 53 μM, a V max of 23 ± 2.5 μM min-1, and a k cat of 23 ± 2.68 s-1 These results further our understanding of the mechanisms of selenium biotransformation and its biogeochemical cycle.IMPORTANCE Selenium is an essential element for life, with Se(IV) reduction a key step in its biogeochemical cycle. This report identifies for the first time a dissimilatory Se(IV) reductase, Srr, from a known selenite-respiring bacterium, the haloalkalophilic Bacillus selenitireducens strain MLS10. The work extends the versatility of the complex iron-sulfur molybdoenzyme (CISM) superfamily in electron transfer involving chalcogen substrates with different redox potentials. Further, it underscores the importance of biochemical and enzymological approaches in establishing the functionality of these enzymes.Item Understanding the Role of Ligand Oxidation State: Design, Synthesis, and Reactivity of Electronically Asymmetric Molybdenum Dithiolene Complexes(2019-08) Dille, Sara A.; Basu, Partha; Minto, Robert; Lei, Li; Pu, JingzhiMononuclear molybdopterin enzymes are a large class of enzymes that are present in all phyla of life. All pterin containing enzymes posses a molybdopterin cofactor made up of a molybdenum metal center coordinated directly by a dithiolene ligand, which is appended to a pyranopterin cofactor. The majority of these enzymes catalyze oxygen atom transfer reactions that are concomitant with a transfer of two-electrons. We are hypothesizing that by altering the oxidation states of the dithiolene, the reactivity of the cofactor can be tuned for different substrates. This investigation focuses on the synthesis and characterization of oxo-MoIV(dithiolene) complexes that possess a fully reduced dithiolene ligand (dithiolene) and a fully oxidized dithiolene ligand (dithione). These complexes are designed to represent the asymmetry of the dithiolene ligand that is observed in the crystal structures of the DMSO reductase family. Asymmetric oxo-MoIV(dithiolene) complexes exhibit a unique structural property, a large fold angle along the S•••S vector of the dithione ligand. These complexes also show a positive solvatochromic effect in a range of polar to nonpolar solvents. The rich electrochemical properties of these redox active complexes and other characterization details such as IR, and NMR studies will be presented. Effects on the reactivity of these complexes using biologically relevant substrates will be discussed. The oxygen atom transfer reactivity has been probed by mass spectrometry and NMR spectroscopy. The presented complexes aide in highlighting the effect redox state of the dithiolene ligand has in modulating reactivityItem Unraveling the inner workings of respiratory arsenate reductase(National Academy of Sciences, 2018-09-11) Stolz, John F.; Basu, Partha; Chemistry and Chemical Biology, School of Science