Research and Publications - Department of Chemistry & Biochemistry

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1,2,3-Triazole-Heme Interactions in Cytochrome P450: Functionally Competent Triazole-Water-Heme Complexes
(American Chemical Society, 2012) Conner, Kip P.; Vennam, Preethi; Woods, Caleb M.; Krzyaniak, Matthew D.; Bowman, Michael K.; Atkins, William M.; University of Washington; University of Washington Seattle; University of Alabama Tuscaloosa
In comparison to imidazole (IMZ) and 1,2,4-triazole (1,2,4-TRZ), the isosteric 1,2,3-triazole (1,2,3-TRZ) is unrepresented among cytochrome P450 (CYP) inhibitors. This is surprising because 1,2,3-TRZs are easily obtained via "click" chemistry. To understand this underrepresentation of 1,2,3-TRZs among CYP inhibitors, thermodynamic and density functional theory computational studies were performed with unsubstituted IMZ, 1,2,4-TRZ, and 1,2,3-TRZ. The results indicate that the lower affinity of 1,2,3-TRZ for the heme iron includes a large unfavorable entropy term likely originating in solvent-1,2,3-TRZ interactions; the difference is not solely due to differences in the enthalpy of heme-ligand interactions. In addition, the 1,2,3-TRZ fragment was incorporated into a well-established CYP3A4 substrate and mechanism-based inactivator, 17-alpha-ethynylestradiol (17EE), via click chemistry. This derivative, 17-click, yielded optical spectra consistent with low-spin ferric heme iron (type II) in contrast to 17EE, which yields a high-spin complex (type I). Furthermore, the rate of CYP3A4-mediated metabolism of 17-click was comparable to that of 17EE, with a different regioselectivity. Surprisingly, continuous-wave electron paramagnetic resonance (EPR) and HYSCORE EPR spectroscopy indicate that 17-click does not displace water from the sixth axial ligand position of CYP3A4 as expected for a type II ligand. We propose a binding model in which 17-click pendant 1,2,3-TRZ hydrogen bonds with the sixth axial water ligand. The results demonstrate the potential for 1,2,3-TRZ to form metabolically labile water-bridged low-spin heme complexes, consistent with recent evidence that nitrogenous type II ligands of CYPs can be efficiently metabolized. The specific case of [CYP3A4 center dot 17-click] highlights the risk of interpreting CYP-ligand complex structure on the basis of optical spectra.
1-Propyl-4(5)-Methylimidazole Isomers for Temperature Swing Solvent Extraction
(MDPI, 2022) Qian, Shuai; Ward, Lauren M.; Rakers, Luke S.; Weinman, Steven T.; Bara, Jason E.; University of Alabama Tuscaloosa
Temperature swing solvent extraction (TSSE) utilizes an amine solvent with temperature-dependent water solubility to dissolve water at a lower temperature to concentrate or crystallize the brine and the phases are separated. Then, the water in solvent mixture is heated to reduce water solubility and cause phase separation between the solvent and water. The solvent and de-salted water phases are separated, and the regenerated solvent can be recycled. Issues with current TSSE solvents include the high solvent in water solubility and the high solvent volatility. This project used the highly tunable platform molecule imidazole to create two 1-butylimidazole isomers, specifically 1-propyl-4(5)-methylimidazole, to test their effectiveness for TSSE. The imidazoles take in more water than their current state-of-the-art counterparts, but do not desalinate the product water and dissolve in water at higher concentrations. Thus, while imidazoles make intriguing candidates for TSSE, further work is needed to understand how to design imidazoles that will be useful for TSSE applications.
3D Modeling of the Solidification Structure Evolution and of the Inter Layer/Track Voids Formation in Metallic Alloys Processed by Powder Bed Fusion Additive Manufacturing
(MDPI, 2022) Nastac, Laurentiu; University of Alabama Tuscaloosa
A fully transient discrete-source 3D Additive Manufacturing (AM) process model was coupled with a 3D stochastic solidification structure model to simulate the grain structure evolution quickly and efficiently in metallic alloys processed through Electron Beam Powder Bed Fusion (EBPBF) and Laser Powder Bed Fusion (LPBF) processes. The stochastic model was adapted to rapid solidification conditions of multicomponent alloys processed via multi-layer multi-track AM processes. The capabilities of the coupled model include studying the effects of process parameters (power input, speed, beam shape) and part geometry on solidification conditions and their impact on the resulting solidification structure and on the formation of inter layer/track voids. The multi-scale model assumes that the complex combination of the crystallographic requirements, isomorphism, epitaxy, changing direction of the melt pool motion and thermal gradient direction will produce the observed texture and grain morphology. Thus, grain size, morphology, and crystallographic orientation can be assessed, and the model can assist in achieving better control of the solidification microstructures and to establish trends in the solidification behavior in AM components. The coupled model was previously validated against single-layer laser remelting IN625 experiments performed and analyzed at National Institute of Standards and Technology (NIST) using LPBF systems. In this study, the model was applied to predict the solidification structure and inter layer/track voids formation in IN718 alloys processed by LPBF processes. This 3D modeling approach can also be used to predict the solidification structure of Ti-based alloys processes by EBPBF.
Abdominal segment reduction Development and evolution of a deeply fixed trait
(Landes Biocience, 2012) Yoder, John H.; University of Alabama Tuscaloosa
When a new student first begins to push flies, an immediate skill that must be learned is sorting the sexes. In Drosophila melanogaster several sexually dimorphic characters can be used to readily distinguish males from females including abdominal pigmentation, male sex combs and genital morphology. Another, often-overlooked, sexual dimorphism is adult abdominal segment number. Externally, adult Drosophila males possess one fewer abdominal segment than females; the terminal pregenital segment apparently either absent or fused with the next-most anterior segment. Beyond known roles for the homeotic protein Abdominal-B (Abd-B) and the sex-determining transcription factor Doublesex (Dsx) as key regulators of this trait, surprisingly little is known about either the morphogenetic processes or the downstream genetics responsible for patterning these events. We have explored both and found that rapid epithelial reorganization during pupation eliminates a nascent terminal male segment. We found this Abd-B-dependent process results from sex-and segment-specific regulation of diverse developmental targets including the wingless gene and surprisingly, dsx itself.(1,2) Here, I review our observations and discuss this trait as a model to explore both dynamics of epithelial morphogenesis as well as the evolution of developmental mechanisms.
Abiological catalysis by myoglobin mutant with a genetically incorporated unnatural amino acid
(Portland Press, 2021) Chand, Subhash; Ray, Sriparna; Yadav, Poonam; Samanta, Susruta; Pierce, Brad S.; Perera, Roshan; University of Texas Arlington; University of Nebraska Medical Center; Creighton University; University of Alabama Tuscaloosa
To inculcate biocatalytic activity in the oxygen-storage protein myoglobin (Mb), a genetically engineered myoglobin mutant H64DOPA (DOPA = L-3,4-dihydroxyphenylalanine) has been created. Incorporation of unnatural amino acids has already demonstrated their ability to accomplish many non-natural functions in proteins efficiently. Herein, the presence of redox-active DOPA residue in the active site of mutant Mb presumably stabilizes the compound I in the catalytic oxidation process by participating in an additional hydrogen bonding (H-bonding) as compared to the WT Mb. Specifically, a general acid-base catalytic pathway was achieved due to the availability of the hydroxyl moieties of DOPA. The reduction potential values of WT (E degrees = -260 mV) and mutant Mb (E degrees = -300 mV), w.r.t. Ag/AgCl reference electrode, in the presence of hydrogen peroxide, indicated an additional H-bonding in the mutant protein, which is responsible for the peroxidase activity of the mutant Mb. We observed that in the presence of 5 mM H2O2, H64DOPA Mb oxidizes thioanisole and benzaldehyde with a 10 and 54 folds higher rate, respectively, as opposed to WT Mb. Based on spectroscopic, kinetic, and electrochemical studies, we deduce that DOPA residue, when present within the distal pocket of mutant Mb, alone serves the role of His/Arg-pair of peroxidases.
Accelerating the insertion reactions of (NHC)Cu-H via remote ligand functionalization
(Royal Society of Chemistry, 2021) Speelman, Amy L.; Tran, Ba L.; Erickson, Jeremy D.; Vasiliu, Monica; Dixon, David A.; Bullock, R. Morris; United States Department of Energy (DOE); Pacific Northwest National Laboratory; University of Alabama Tuscaloosa
Most ligand designs for reactions catalyzed by (NHC)Cu-H (NHC = N-heterocyclic carbene ligand) have focused on introducing steric bulk near the Cu center. Here, we evaluate the effect of remote ligand modification in a series of [(NHC)CuH](2) in which the para substituent (R) on the N-aryl groups of the NHC is Me, Et, Bu-t, OMe or Cl. Although the R group is distant (6 bonds away) from the reactive Cu center, the complexes have different spectroscopic signatures. Kinetics studies of the insertion of ketone, aldimine, alkyne, and unactivated alpha-olefin substrates reveal that Cu-H complexes with bulky or electron-rich R groups undergo faster substrate insertion. The predominant cause of this phenomenon is destabilization of the [(NHC)CuH](2) dimer relative to the (NHC)Cu-H monomer, resulting in faster formation of Cu-H monomer. These findings indicate that remote functionalization of NHCs is a compelling strategy for accelerating the rate of substrate insertion with Cu-H species.
Achieving Excellence in Graduate Research: A Guide for New Graduate Students
(Wiley-Blackwell, 2015) Parker, Charles B.; Amsden, Jason J.; Peng, Qing; Stoner, Brian R.; Glass, Jeffrey T.; Duke University; University of Alabama Tuscaloosa; Research Triangle Institute
Acyclovir as an Ionic Liquid Cation or Anion Can Improve Aqueous Solubility
(American Chemical Society, 2017) Shamshina, Julia L.; Cojocaru, O. Andreea; Kelley, Steven P.; Bica, Katharina; Wallace, Sergey P.; Gurau, Gabriela; Rogers, Robin D.; University of Alabama Tuscaloosa; McGill University; Technische Universitat Wien; Tennessee Technological University
Six ionic liquid (IL)-forming ions (choline, tetrabutylphosphonium, tetrabutylammonium, and trimethyl-hexadecylammonium cations, and chloride and docusate anions) were paired with acyclovir as the counterion to form four low melting solid salts and two waxes; five of these compounds could be classified as ILs. All of the newly synthesized acyclovir ILs exhibited increased aqueous solubilities by at least 2 orders of magnitude when compared to that of neutral acyclovir. For three of the prepared compounds, the solubilities in simulated body fluids (phosphate-buffered saline, simulated gastric, and simulated intestinal fluids) were also greatly enhanced when compared to that of neutral acyclovir. Acyclovir in its anionic form was more water-or buffer-soluble than acyclovir in its cationic form, though this might be the effect of the particular ions, indicating that the solubilities can be finely tuned by proper choice of the cationic or anionic form of acyclovir and the counterion paired with it.
Alpha-Tocotrienol Prevents Oxidative Stress-Mediated Post-Translational Cleavage of Bcl-xL in Primary Hippocampal Neurons
(MDPI, 2020) Park, Han-A; Mnatsakanyan, Nelli; Broman, Katheryn; Davis, Abigail U.; May, Jordan; Licznerski, Pawel; Crowe-White, Kristi M.; Lackey, Kimberly H.; Jonas, Elizabeth A.; University of Alabama Tuscaloosa; Yale University
B-cell lymphoma-extra large (Bcl-xL) is an anti-apoptotic member of the Bcl2 family of proteins, which supports neurite outgrowth and neurotransmission by improving mitochondrial function. During excitotoxic stimulation, however, Bcl-xL undergoes post-translational cleavage to N-Bcl-xL, and accumulation of N-Bcl-xL causes mitochondrial dysfunction and neuronal death. In this study, we hypothesized that the generation of reactive oxygen species (ROS) during excitotoxicity leads to formation of N-Bcl-xL. We further proposed that the application of an antioxidant with neuroprotective properties such as alpha-tocotrienol (TCT) will prevent N-Bcl-xL-induced mitochondrial dysfunction via its antioxidant properties. Primary hippocampal neurons were treated with alpha-TCT, glutamate, or a combination of both. Glutamate challenge significantly increased cytosolic and mitochondrial ROS and N-Bcl-xL levels. N-Bcl-xL accumulation was accompanied by intracellular ATP depletion, loss of mitochondrial membrane potential, and cell death. alpha-TCT prevented loss of mitochondrial membrane potential in hippocampal neurons overexpressing N-Bcl-xL, suggesting that N-Bcl-xL caused the loss of mitochondrial function under excitotoxic conditions. Our data suggest that production of ROS is an important cause of N-Bcl-xL formation and that preventing ROS production may be an effective strategy to prevent N-Bcl-xL-mediated mitochondrial dysfunction and thus promote neuronal survival.
The Anionic Polymerization of a tert-Butyl-Carboxylate-Activated Aziridine
(MDPI, 2022) Giri, Chandan; Chang, Jen-Yu; Mbarushimana, Pierre Canisius; Rupar, Paul A.; University of Alabama Tuscaloosa
N-Sulfonyl-activated aziridines are known to undergo anionic-ring-opening polymerizations (AROP) to form polysulfonyllaziridines. However, the post-polymerization deprotection of the sulfonyl groups from polysulfonyllaziridines remains challenging. In this report, the polymerization of tert-butyl aziridine-1-carboxylate (BocAz) is reported. BocAz has an electron-withdrawing tert-butyloxycarbonyl (BOC) group on the aziridine nitrogen. The BOC group activates the aziridine for AROP and allows the synthesis of low-molecular-weight poly(BocAz) chains. A C-13 NMR spectroscopic analysis of poly(BocAz) suggested that the polymer is linear. The attainable molecular weight of poly(BocAz) is limited by the poor solubility of poly(BocAz) in AROP-compatible solvents. The deprotection of poly(BocAz) using trifluoroacetic acid (TFA) cleanly produces linear polyethyleneimine. Overall, these results suggest that carbonyl groups, such as BOC, can play a larger role in the in the activation of aziridines in anionic polymerization and in the synthesis of polyimines.
Anti-Apoptotic Effects of Carotenoids in Neurodegeneration
(MDPI, 2020) Park, Han-A; Hayden, Mary Margaret; Bannerman, Sydni; Jansen, Joseph; Crowe-White, Kristi M.; University of Alabama Tuscaloosa
Apoptosis, programmed cell death type I, is a critical part of neurodegeneration in cerebral ischemia, Parkinson's, and Alzheimer's disease. Apoptosis begins with activation of pro-death proteins Bax and Bak, release of cytochrome c and activation of caspases, loss of membrane integrity of intracellular organelles, and ultimately cell death. Approaches that block apoptotic pathways may prevent or delay neurodegenerative processes. Carotenoids are a group of pigments found in fruits, vegetables, and seaweeds that possess antioxidant properties. Over the last several decades, an increasing number of studies have demonstrated a protective role of carotenoids in neurodegenerative disease. In this review, we describe functions of commonly consumed carotenoids including lycopene, beta-carotene, lutein, astaxanthin, and fucoxanthin and their roles in neurodegenerative disease models. We also discuss the underlying cellular mechanisms of carotenoid-mediated neuroprotection, including their antioxidant properties, role as signaling molecules, and as gene regulators that alleviate apoptosis-associated brain cell death.
Antioxidant Activity in Supramolecular Carotenoid Complexes Favored by Nonpolar Environment and Disfavored by Hydrogen Bonding
(MDPI, 2020) Gao, Yunlong; Focsan, A. Ligia; Kispert, Lowell D.; Nanjing Agricultural University; University System of Georgia; Valdosta State University; University of Alabama Tuscaloosa
Carotenoids are well-known antioxidants. They have the ability to quench singlet oxygen and scavenge toxic free radicals preventing or reducing damage to living cells. We have found that carotenoids exhibit scavenging ability towards free radicals that increases nearly exponentially with increasing the carotenoid oxidation potential. With the oxidation potential being an important parameter in predicting antioxidant activity, we focus here on the different factors affecting it. This paper examines how the chain length and donor/acceptor substituents of carotenoids affect their oxidation potentials but, most importantly, presents the recent progress on the effect of polarity of the environment and orientation of the carotenoids on the oxidation potential in supramolecular complexes. The oxidation potential of a carotenoid in a nonpolar environment was found to be higher than in a polar environment. Moreover, in order to increase the photostability of the carotenoids in supramolecular complexes, a nonpolar environment is desired and the formation of hydrogen bonds should be avoided.
Arabidopsis Toxicos en Levadura 12 Modulates Salt Stress and ABA Responses in Arabidopsis thaliana
(MDPI, 2022) Kong, Feng; Ramonell, Katrina M.; University of Alabama Tuscaloosa; University of Georgia
Salt is one of the most common abiotic stresses, causing ionic and osmotic pressure changes that affect plant growth and development. In this work, we present molecular and genetic evidence that Arabidopsis Toxicos en Levadura 12 (ATL12) is involved in both salt stress and in the abscisic acid response to this stress. We demonstrate that ATL12 is highly induced in response to salt stress and that atl12 mutants have a lower germination rate, decreased root length, and lower survival rate compared to the Col-0 wild-type in response to salt stress. Overexpression of ATL12 increases expression of the salt stress-associated genes SOS1/2, and ABA-responsive gene RD29B. Additionally, higher levels of reactive oxygen species are detected when ATL12 is overexpressed, and qRT-PCR showed that ATL12 is involved in the AtRBOHD/F-mediated signaling. ATL12 expression is also highly induced by ABA treatment. Mutants of atl12 are hypersensitive to ABA and have a shorter root length. A decrease in water loss and reduced stomatal aperture were also observed in atl12 mutants in response to ABA. ABA-responsive genes RD29B and RAB18 were downregulated in atl12 mutants but were upregulated in the overexpression line of ATL12 in response to ABA. Taken together our results suggest that ATL12 modulates the response to salt stress and is involved in the ABA signaling pathway in Arabidopsis thaliana.
Asporin, an extracellular matrix protein, is a beneficial regulator of cardiac remodeling
(Elsevier, 2022) Huang, Chengqun; Sharma, Ankush; Thakur, Reetu; Rai, Deepika; Katiki, Madhusudhanarao; Germano, Juliana de Freitas; Song, Yang; Singh, Sakshi; Sin, Jon; Sengstock, David; Andres, Allen M.; Murali, Ramachandran; Mentzer, Robert M.; Gottlieb, Roberta A.; Piplani, Honit; Cedars Sinai Medical Center; University of Oslo; University of Alabama Tuscaloosa; Beaumont Health; Wayne State University
Heart failure is accompanied by adverse cardiac remodeling involving extracellular matrix (ECM). Cardiac ECM acts as a major reservoir for many proteins including growth factors, cytokines, collagens, and proteoglycans. Activated fibroblasts during cardiac injury can alter the composition and activity of these ECM proteins. Through unbiased analysis of a microarray dataset of human heart tissue comparing normal hearts (n = 135) to hearts with ischemic cardiomyopathy (n = 94), we identified Asporin (ASPN) as the top differentially regulated gene (DEG) in ischemic cardiomyopathy; its gene-ontology terms relate closely to fibrosis and cell death. ASPN is a Class I small leucine repeat protein member implicated in cancer, osteoarthritis, and periodontal ligament mineralization. However, its role in cardiac remodeling is still unknown. Here, we initially confirmed our big dataset analysis through cells, mice, and clinical atrial biopsy samples to demonstrate increased Aspn expression after pressure overload or cardiac ischemia/reperfusion injury. We tested the hypothesis that Aspn, being a TGFb1 inhibitor, can attenuate fibrosis in mouse models of cardiac injury. We found that Aspn is released by cardiac fibroblasts and attenuates TGFb signaling. Moreover, Aspn(-/-) mice displayed increased fibrosis and decreased cardiac function after pressure overload by transverse aortic constriction (TAC) in mice. In addition, Aspn protected cardiomyocytes from hypoxia/reoxygenation-induced cell death and regulated mitochondrial bioenergetics in cardiomyocytes. Increased infarct size after ischemia/reperfusion injury in Aspn(-/-) mice confirmed Aspn's contribution to cardiomyocyte viability. Echocardiography revealed greater reduction in left ventricular systolic function post-I/R in the Aspn(-/-) animals compared to wild type. Furthermore, we developed an ASPN-mimic peptide using molecular modeling and docking which when administered to mice prevented TAC-induced fibrosis and preserved heart function. The peptide also reduced infarct size after I/R in mice, demonstrating the translational potential of ASPN-based therapy. Thus, we establish the role of ASPN as a critical ECM molecule that regulates cardiac remodeling to preserve heart function. (C) 2022 Elsevier B.V. All rights reserved.
ATP Synthase c-Subunit Leak Causes Aberrant Cellular Metabolism in Fragile X Syndrome
(Cell Press, 2020) Licznerski, Pawel; Park, Han-A; Rolyan, Harshvardhan; Chen, Rongmin; Mnatsakanyan, Nelli; Miranda, Paige; Graham, Morven; Wu, Jing; Cruz-Reyes, Nicole; Mehta, Nikita; Sohail, Sana; Salcedo, Jorge; Song, Erin; Effman, Charles; Effman, Samuel; Brandao, Lucas; Xu, Gulan N.; Braker, Amber; Gribkoff, Valentin K.; Levy, Richard J.; Jonas, Elizabeth A.; Yale University; Columbia University; Marine Biological Laboratory - Woods Hole; University of Alabama Tuscaloosa; Clark University
Loss of the gene (Fmr1) encoding Fragile X mental retardation protein (FMRP) causes increased mRNA translation and aberrant synaptic development. We find neurons of the Fmr1(-/y) mouse have a mitochondrial inner membrane leak contributing to a "leak metabolism.'' In human Fragile X syndrome (FXS) fibroblasts and in Fmr1(-/y) mouse neurons, closure of the ATP synthase leak channel by mild depletion of its c-subunit or pharmacological inhibition normalizes stimulus-induced and constitutive mRNA translation rate, decreases lactate and key glycolytic and tricarboxylic acid (TCA) cycle enzyme levels, and triggers synapse maturation. FMRP regulates leak closure in wild-type (WT), but not FX synapses, by stimulus-dependent ATP synthase beta subunit translation; this increases the ratio of ATP synthase enzyme to its c-subunit, enhancing ATP production efficiency and synaptic growth. In contrast, in FXS, inability to close developmental c-subunit leak prevents stimulus-dependent synaptic maturation. Therefore, ATP synthase c-subunit leak closure encourages development and attenuates autistic behaviors.
beta-Carotene, a Potent Amyloid Aggregation Inhibitor, Promotes Disordered A beta Fibrillar Structure
(MDPI, 2023) Banerjee, Siddhartha; Baghel, Divya; Pacheco de Oliveira, Ana; Ghosh, Ayanjeet; University of Alabama Tuscaloosa
The aggregation of amyloid beta (Afi) into fibrillar aggregates is a key feature of Alzheimer's disease (AD) pathology. beta-carotene and related compounds have been shown to associate with amyloid aggregates and have direct impact on the formation of amyloid fibrils. However, the precise effect of beta-carotene on the structure of amyloid aggregates is not known, which poses a limitation towards developing it as a potential AD therapeutic. In this report, we use nanoscale AFM-IR spectroscopy to probe the structure of A beta oligomers and fibrils at the single aggregate level and demonstrate that the main effect of f beta-carotene towards modulating Afi aggregation is not to inhibit fibril formation but to alter the secondary structure of the fibrils and promote fibrils that lack the characteristic ordered beta structure.
Beta-Lactam Antibiotic Discrimination Using a Macromolecular Sensor in Water at Neutral pH
(MDPI, 2021) Xu, Yifei; Bonizzoni, Marco; University of Alabama Tuscaloosa
Penicillins and cephalosporins belong to the beta-lactam antibiotic family, which accounts for more than half of the world market for antibiotics. Misuse of antibiotics harms human health and the environment. Here, we describe an easy, fast, and sensitive optical method for the sensing and discrimination of two penicillin and five cephalosporin antibiotics in buffered water at pH 7.4, using fifth-generation poly (amidoamine) (PAMAM) dendrimers and calcein, a commercially available macromolecular polyelectrolyte and a fluorescent dye, respectively. In aqueous solution at pH 7.4, the dendrimer and dye self-assemble to form a sensor that interacts with carboxylate-containing antibiotics through electrostatic interaction, monitored through changes in the dye's spectroscopic properties. This response was captured through absorbance, fluorescence emission, and fluorescence anisotropy. The resulting data set was processed through linear discriminant analysis (LDA), a common pattern-base recognition method, for the differentiation of cephalosporins and penicillins. By pre-hydrolysis of the beta-lactam rings under basic conditions, we were able to increase the charge density of the analytes, allowing us to discriminate the seven analytes at a concentration of 5 mM, with a limit of discrimination of 1 mM.
The beta-latch structural element of the SufS cysteine desulfurase mediates active site accessibility and SufE transpersulfurase positioning
(Elsevier, 2023) Gogar, Rajleen K.; Carroll, Franki; Conte, Juliana, V; Nasef, Mohamed; Dunkle, Jack A.; Frantom, Patrick A.; University of Alabama Tuscaloosa
Under oxidative stress and iron starvation conditions, Escherichia coli uses the Suf pathway to assemble iron-sulfur clusters. The Suf pathway mobilizes sulfur via SufS, a type II cysteine desulfurase. SufS is a pyridoxal-5'-phosphate-depen-dent enzyme that uses cysteine to generate alanine and an active-site persulfide (C364-S-S-). The SufS persulfide is pro-tected from external oxidants/reductants and requires the transpersulfurase, SufE, to accept the persulfide to complete the SufS catalytic cycle. Recent reports on SufS identified a conserved "11-latch" structural element that includes the alpha 6 helix, a glycine-rich loop, a 11-hairpin, and a cis-proline residue. To identify a functional role for the 11-latch, we used site -directed mutagenesis to obtain the N99D and N99A SufS var-iants. N99 is a conserved residue that connects the alpha 6 helix to the backbone of the glycine-rich loop via hydrogen bonds. Our x-ray crystal structures for N99A and N99D SufS show a dis-torted beta-hairpin and glycine-rich loop, respectively, along with changes in the dimer geometry. The structural disruption of the N99 variants allowed the external reductant TCEP to react with the active-site C364-persulfide intermediate to complete the SufS catalytic cycle in the absence of SufE. The substitutions also appear to disrupt formation of a high -affinity, close approach SufS-SufE complex as measured with fluorescence polarization. Collectively, these findings demon-strate that the 11-latch does not affect the chemistry of persul-fide formation but does protect it from undesired reductants. The data also indicate the 11-latch plays an unexpected role in forming a close approach SufS-SufE complex to promote persulfide transfer.
Bimacrocyclic Effect in Anion Recognition by a Copper(II) Bicyclam Complex
(American Chemical Society, 2018) Invernici, Michele; Ciarrocchi, Carlo; Dondi, Daniele; Fabbrizzi, Luigi; Lazzaroni, Simone; Licchelli, Maurizio; Boiocchi, Massimo; Bonizzoni, Marco; University of Pavia; University of Alabama Tuscaloosa
The dicopper(II) complex of the bimacrocyclic ligand alpha,alpha' -bis(5,7-dimethyl-1,4,8,11-tetraazacyclotetradecan-6-yl)-o-xylene, 2, interacts with selected anions in dimethyl sulfoxide solution according to two different modes: (i) halides (Cl-, Br-, and I- ) and N(3)(- )coordinate the two metal centers at the same time between the two macrocyclic subunits that face each other and (ii) anionic species that do not fit the bridging coordination mode (e.g., NCO-, SCN-, CH3COO-, NO3-, and H2PO4-) interact with copper(II) ions only at the "external" positions or their interaction is too weak to be detected. Occurrence of the bridging interaction is demonstrated by X-ray crystallographic studies performed on the adduct formed by [Cu-2(2)](4+) with azide and by electron paramagnetic resonance investigation, as the anion coordination between the two copper(II) centers induces spin-spin coupling. Isothermal titration calorimetry experiments performed on [Cu-2(2)](4+) and, for comparison, on [(5,7-dimethyl-6-benzyl-1,4,8,11-tetraazacyclotetradecane)copper(II)], representing the mononuclear analogue, allowed determination of thermodynamic parameters (log K, Delta H, and T Delta S) associated with the considered complex/anion equilibria. Thermodynamic data showed that adducts formed by [Cu-2(2)](4+) with halides and azide benefit from an extra stability that can be explained on the basis of the anion advantage of simultaneously binding the two metal centers, i.e., in terms of the bimacrocyclic effect.
Bio-Based Admixture (Black Tea Extraction) for Better Performance of Metakaolin Blended Cement Mortars
(MDPI, 2022) Fang, Yi; Wang, Jialai; Wang, Xiaodong; Do Amaral, Monica Lages; Kniffin, Hannah; Reed, Miranda; Wang, Liang; Qian, Xin; University of Alabama Tuscaloosa; Anhui University of Science & Technology; Tongji University
With high pozzolanic reactivity, metakaolin (MK) is a popular supplementary cementitious material (SCM), which can be used to partially replace Portland cement in concretes. Due to its small particle size, however, MK can agglomerate, resulting in a nonuniform matrix and underperformance of the produced concrete. To address this issue, this paper exploits a low-cost, bio-based admixture-black tea extract (BTE)-to replace the traditional petroleum-based chemical admixture to enhance the dispersion and workability of MK blended cement mortars. Major biomolecules in the BTE such as caffeine, catechin, theanine, and theaflavin are rich in polyphenol, hydroxyl, and carboxylic acid groups, which can interact with cement particles and have profound effects on the hydration process and microstructure of the hydration products. Experimental studies showed that BTE does improve the workability of the MK blended cement mortar. More importantly, the BTE introduces significant change on the microstructure of the hardened pastes. Both the pores with size less than 50 nm and the total porosity of the hardened paste were significantly reduced, leading to a significant improvement in the micro- and macro-mechanical properties of the hardened paste. Experimental results suggest that up to 35% greater improvement in the compressive strength at 28 days was achieved using the proposed bio-admixture. Economic and environmental advantages of using the BTE as a renewable admixture were also illustrated through analyzing the cost-benefit, embodied carbon, and eco-efficiency of the MK blended mortars.

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