Browsing by Author "Basu, Partha"
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Item Cervical cancer prevention and care in HIV clinics across sub-Saharan Africa: results of a facility-based survey(Wiley, 2024) Asangbeh-Kerman, Serra Lem; Davidović, Maša; Taghavi, Katayoun; Dhokotera, Tafadzwa; Manasyan, Albert; Sharma, Anjali; Jaquet, Antoine; Musick, Beverly; Twizere, Christella; Chimbetete, Cleophas; Murenzi, Gad; Tweya, Hannock; Muhairwe, Josephine; Wools-Kaloustian, Kara; Technau, Karl-Gunter; Anastos, Kathryn; Yotebieng, Marcel; Jousse, Marielle; Ezechi, Oliver; Orang’o, Omenge; Bosomprah, Samuel; Boni, Simon Pierre; Basu, Partha; Bohlius, Julia; IeDEA; Biostatistics and Health Data Science, Richard M. Fairbanks School of Public HealthIntroduction: To eliminate cervical cancer (CC), access to and quality of prevention and care services must be monitored, particularly for women living with HIV (WLHIV). We assessed implementation practices in HIV clinics across sub-Saharan Africa (SSA) to identify gaps in the care cascade and used aggregated patient data to populate cascades for WLHIV attending HIV clinics. Methods: Our facility-based survey was administered between November 2020 and July 2021 in 30 HIV clinics across SSA that participate in the International epidemiology Databases to Evaluate AIDS (IeDEA) consortium. We performed a qualitative site-level assessment of CC prevention and care services and analysed data from routine care of WLHIV in SSA. Results: Human papillomavirus (HPV) vaccination was offered in 33% of sites. Referral for CC diagnosis (42%) and treatment (70%) was common, but not free at about 50% of sites. Most sites had electronic health information systems (90%), but data to inform indicators to monitor global targets for CC elimination in WLHIV were not routinely collected in these sites. Data were collected routinely in only 36% of sites that offered HPV vaccination, 33% of sites that offered cervical screening and 20% of sites that offered pre-cancer and CC treatment. Conclusions: Though CC prevention and care services have long been available in some HIV clinics across SSA, patient and programme monitoring need to be improved. Countries should consider leveraging their existing health information systems and use monitoring tools provided by the World Health Organization to improve CC prevention programmes and access, and to track their progress towards the goal of eliminating CC.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 Dithione, the antipodal redox partner of ene-1,2-dithiol ligands and their metal complexes(Elsevier, 2020) Basu, Partha; Colston, Kyle J.; Mogesa, Benjamin; Chemistry and Chemical Biology, School of ScienceDefining the oxidation state of the central atom in a coordination compound is fundamental in understanding the electronic structure and provides a starting point for elucidating molecular properties. The presence of non-innocent ligand(s) can obscure the oxidation state of the central atom as the ligand contribution to the electronic structure is difficult to ascertain. Redox-active ligands, such as dithiolene ligands, are well known non-innocent ligands that can exist in both a fully reduced (Dt2−) and fully oxidized (Dt0) states. Complexes containing the fully oxidized dithione state of the ligand are uncommon and only a few have been completely characterized. Dithione ligands are of interest due to their electron-deficient nature and ability to act as an electron acceptor for more electron-rich moieties, such as other dithiolene ligands or metal centers. This article focuses the syntheses, structures, and metal coordination, particularly coordination compounds, of dithione ligands. Various examples of mono, bis, and tris dithione complexes are discussed.Item Influence of the Ligand-Field on EPR Parameters of cis- and trans-Isomers in MoV Systems Relevant to Molybdenum Enzymes: Experimental and Density Functional Theory Study(Elsevier, 2023) Nemykin, Victor N.; Sabin, Jared R.; Kail, Brian W.; Upadhyay, Anup; Hendrich, Michael P.; Basu, Partha; Chemistry and Chemical Biology, School of ScienceThe electron paramagnetic resonance (EPR) investigation of mononuclear cis- and trans-(L1O)MoOCl2 complexes [L1OH = bis(3,5-dimethylpyrazolyl)-3-tert-butyl-2-hydroxy-5-methylphenyl)methane] reveals a significant difference in their spin Hamiltonian parameters which reflect different equatorial and axial ligand fields created by the heteroscorpionate donor atoms. Density functional theory (DFT) was used to calculate the values of principal components and relative orientations of the g and A tensors, and the molecular framework in four pairs of isomeric mononuclear oxo‑molybdenum(V) complexes (cis- and trans-(L1O)MoOCl2, cis,cis- and cis,trans-(L-N2S2)MoOCl [L-N2S2H2 = N,N'-dimethyl-N,N'-bis(mercaptophenyl)ethylenediamine], cis,cis- and cis,trans-(L-N2S2)MoO(SCN), and cis- and trans-[(dt)2MoO(OMe)]2- [dtH2 = 2,3-dimercapto-2-butene]). Scalar relativistic DFT calculations were conducted using three different exchange-correlation functionals. It was found that the use of hybrid exchange-correlation functional with 25% of the Hartree-Fock exchange leads to the best quantitative agreement between theory and experiment. A simplified ligand-field approach was used to analyze the influence of the ligand fields in all cis- and trans-isomers on energies and contributions of molybdenum d-orbital manifold to g and A tensors and relative orientations. Specifically, contributions that originated from the spin-orbit coupling of the dxz, dyz, and dx2-y2 orbitals into the ground state have been discussed. The new findings are discussed in the context of the experimental data of mononuclear molybdoenzyme, DMSO reductase.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 Investigating the Photophysical Properties of Potential Organic Lead Sensors(2023) Quinones, Carlos; Basu, Partha; Deng, Yongming; Pu , JingzhiLeadGlow (LG) was reported in 2009 for its ability to both sensitively and selectively detect Pb2+ in aqueous solutions. Utilizing the synthetic approach of LG, it is possible to generate a class of novel fluorophores. A derivative of first-generation LG was synthesized and reported here for the first time, intuitively named LG2. Both compounds contain interesting photophysical properties that have not been extensively researched prior to this work. Because of this, photophysical properties of both LG and LG2 are unveiled here for the first time. These properties were investigated by determinations of quantum yield (QY), average fluorescence lifetime, and DFT calculations. LG was found to have a higher QY (0.057) than LG2 (0.011); however, LG2 displays an average fluorescence lifetime (3.186 ns) 5x greater than that of LG. Both LG and LG2 are synthesized via Hg2+-facilitated desulfurization of their respective thiocarbonyls, resulting in a turn-on fluorescence feature. The thiocarbonyl-containing fluorophores (SLG and SLG2) display quenched fluorescence compared to their oxo-derivatives (LG and LG2), this work attempts to investigate the mechanism(s) responsible. A whole class of LeadGlow compounds can be synthesized and could be potentially used as fluorescence-based sensors.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.