Research and Publications - Department of Chemistry & Biochemistry

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    Synthesis and Characterization of Multifunctional Chitosan- MnFe2O4 Nanoparticles for Magnetic Hyperthermia and Drug Delivery
    (MDPI, 2010) Kim, Dong-Hyun; Nikles, David E.; Brazel, Christopher S.; University of Alabama Tuscaloosa
    Multifunctional nanoparticles composed of MnFe2O4 were encapsulated in chitosan for investigation of system to combine magnetically-triggered drug delivery and localized hyperthermia for cancer treatment with the previously published capacity of MnFe2O4 to be used as an efficient MRI contrast agent for cancer diagnosis. This paper focuses on the synthesis and characterization of magnetic MnFe2O4 nanoparticles, their dispersion in water and their incorporation in chitosan, which serves as a drug carrier. The surface of the MnFe2O4 nanoparticles was modified with meso-2,3-di-mercaptosuccinic acid (DMSA) to develop stable aqueous dispersions. The nanoparticles were coated with chitosan, and the magnetic properties, heat generation and hydrodynamic size of chitosan-coated MnFe2O4 were evaluated for various linker concentrations and in a range of pH conditions.
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    Biodegradable Orthopedic Magnesium-Calcium (MgCa) Alloys, Processing, and Corrosion Performance
    (MDPI, 2012) Salahshoor, Meisam; Guo, Yuebin; University of Alabama Tuscaloosa
    Magnesium-Calcium (Mg-Ca) alloy has received considerable attention as an emerging biodegradable implant material in orthopedic fixation applications. The biodegradable Mg-Ca alloys avoid stress shielding and secondary surgery inherent with permanent metallic implant materials. They also provide sufficient mechanical strength in load carrying applications as opposed to biopolymers. However, the key issue facing a biodegradable Mg-Ca implant is the fast corrosion in the human body environment. The ability to adjust degradation rate of Mg-Ca alloys is critical for the successful development of biodegradable orthopedic implants. This paper focuses on the functions and requirements of bone implants and critical issues of current implant biomaterials. Microstructures and mechanical properties of Mg-Ca alloys, and the unique properties of novel magnesium-calcium implant materials have been reviewed. Various manufacturing techniques to process Mg-Ca based alloys have been analyzed regarding their impacts on implant performance. Corrosion performance of Mg-Ca alloys processed by different manufacturing techniques was compared. In addition, the societal and economical impacts of developing biodegradable orthopedic implants have been emphasized.
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    Proteomic analysis of Staphylococcus aureus biofilm cells grown under physiologically relevant fluid shear stress conditions
    (BMC, 2014) Islam, Nazrul; Kim, Yonghyun; Ross, Julia M.; Marten, Mark R.; University of Maryland Baltimore County; University of Alabama Tuscaloosa
    Background: The biofilm forming bacterium Staphylococcus aureus is responsible for maladies ranging from severe skin infection to major diseases such as bacteremia, endocarditis and osteomyelitis. A flow displacement system was used to grow S. aureus biofilms in four physiologically relevant fluid shear rates (50, 100, 500 and 1000 s(-1)) to identify proteins that are associated with biofilm. Results: Global protein expressions from the membrane and cytosolic fractions of S. aureus biofilm cells grown under the above shear rate conditions are reported. Sixteen proteins in the membrane-enriched fraction and eight proteins in the cytosolic fraction showed significantly altered expression (p < 0.05) under increasing fluid shear. These 24 proteins were identified using nano-LC-ESI-MS/MS. They were found to be associated with various metabolic functions such as glycolysis / TCA pathways, protein synthesis and stress tolerance. Increased fluid shear stress did not influence the expression of two important surface binding proteins: fibronectin-binding and collagen-binding proteins. Conclusions: The reported data suggest that while the general metabolic function of the sessile bacteria is minimal under high fluid shear stress conditions, they seem to retain the binding capacity to initiate new infections.
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    Mechanistic and Bioinformatic Investigation of a Conserved Active Site Helix in alpha-Isopropylmalate Synthase from Mycobacterium tuberculosis, a Member of the DRE-TIM Metallolyase Superfarnily
    (American Chemical Society, 2014) Casey, Ashley K.; Hicks, Michael A.; Johnson, Jordyn L.; Babbitt, Patricia C.; Frantom, Patrick A.; University of Alabama Tuscaloosa; University of California San Francisco
    The characterization of functionally diverse enzyme superfamilies provides the opportunity to identify evolutionarily conserved catalytic strategies, as well as amino acid substitutions responsible for the evolution of new functions or specificities. Isopropylmalate synthase (IPMS) belongs to the DRE-TIM metallolyase superfamily. Members of this superfamily share common active site elements, including a conserved active site helix and an HXH divalent metal binding motif, associated with stabilization of a common enolate anion intermediate. These common elements are overlaid by variations in active site architecture resulting in the evolution of a diverse set of reactions that include condensation, lyase/aldolase, and carboxyl transfer activities. Here, using IPMS, an integrated biochemical and bioinformatics approach has been utilized to investigate the catalytic role of residues on an active site helix that is conserved across the superfamily. The construction of a sequence similarity network for the DRE-TIM metallolyase superfamily allows for the biochemical results obtained with IPMS variants to be compared across superfamily members and within other condensation-catalyzing enzymes related to IPMS. A comparison of our results with previous biochemical data indicates an active site arginine residue (R80 in IPMS) is strictly required for activity across the superfamily, suggesting that it plays a key role in catalysis, most likely through enolate stabilization. In contrast, differential results obtained from substitution of the C-terminal residue of the helix (Q84 in IPMS) suggest that this residue plays a role in reaction specificity within the superfamily.
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    Emergence of californium as the second transitional element in the actinide series
    (Nature Portfolio, 2015) Cary, Samantha K.; Vasiliu, Monica; Baumbach, Ryan E.; Stritzinger, Jared T.; Green, Thomas D.; Diefenbach, Kariem; Cross, Justin N.; Knappenberger, Kenneth L.; Liu, Guokui; Silver, Mark A.; DePrince, A. Eugene; Polinski, Matthew J.; Van Cleve, Shelley M.; House, Jane H.; Kikugawa, Naoki; Gallagher, Andrew; Arico, Alexandra A.; Dixon, David A.; Albrecht-Schmitt, Thomas E.; Florida State University; University of Alabama Tuscaloosa; United States Department of Energy (DOE); Argonne National Laboratory; Oak Ridge National Laboratory; National Institute for Materials Science
    A break in periodicity occurs in the actinide series between plutonium and americium as the result of the localization of 5f electrons. The subsequent chemistry of later actinides is thought to closely parallel lanthanides in that bonding is expected to be ionic and complexation should not substantially alter the electronic structure of the metal ions. Here we demonstrate that ligation of californium(III) by a pyridine derivative results in significant deviations in the properties of the resultant complex with respect to that predicted for the free ion. We expand on this by characterizing the americium and curium analogues for comparison, and show that these pronounced effects result from a second transition in periodicity in the actinide series that occurs, in part, because of the stabilization of the divalent oxidation state. The metastability of californium(II) is responsible for many of the unusual properties of californium including the green photoluminescence.
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    Palladium-Catalyzed Modification of Unprotected Nucleosides, Nucleotides, and Oligonucleotides
    (MDPI, 2015) Shaughnessy, Kevin H.; University of Alabama Tuscaloosa
    Synthetic modification of nucleoside structures provides access to molecules of interest as pharmaceuticals, biochemical probes, and models to study diseases. Covalent modification of the purine and pyrimidine bases is an important strategy for the synthesis of these adducts. Palladium-catalyzed cross-coupling is a powerful method to attach groups to the base heterocycles through the formation of new carbon-carbon and carbon-heteroatom bonds. In this review, approaches to palladium-catalyzed modification of unprotected nucleosides, nucleotides, and oligonucleotides are reviewed. Polar reaction media, such as water or polar aprotic solvents, allow reactions to be performed directly on the hydrophilic nucleosides and nucleotides without the need to use protecting groups. Homogeneous aqueous-phase coupling reactions catalyzed by palladium complexes of water-soluble ligands provide a general approach to the synthesis of modified nucleosides, nucleotides, and oligonucleotides.
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    Signatures of nonthermal melting
    (American Institute of Physics, 2015) Zier, Tobias; Zijlstra, Eeuwe S.; Kalitsov, Alan; Theodonis, Ioannis; Garcia, Martin E.; Universitat Kassel; University of Alabama Tuscaloosa; National Technical University of Athens
    Intense ultrashort laser pulses can melt crystals in less than a picosecond but, in spite of over thirty years of active research, for many materials it is not known to what extent thermal and nonthermal microscopic processes cause this ultrafast phenomenon. Here, we perform ab-initio molecular-dynamics simulations of silicon on a laser-excited potential-energy surface, exclusively revealing nonthermal signatures of laser-induced melting. From our simulated atomic trajectories, we compute the decay of five structure factors and the time-dependent structure function. We demonstrate how these quantities provide criteria to distinguish predominantly nonthermal from thermal melting. (C) 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.
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    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
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    Developmental and Reproductive Effects of Iron Oxide Nanoparticles in Arabidopsis thaliana
    (MDPI, 2015) Bombin, Sergey; LeFebvre, Mitchell; Sherwood, Jennifer; Xu, Yaolin; Bao, Yuping; Ramonell, Katrina M.; University of Alabama Tuscaloosa
    Increasing use of iron oxide nanoparticles in medicine and environmental remediation has led to concerns regarding exposure of these nanoparticles to the public. However, limited studies are available to evaluate their effects on the environment, in particular on plants and food crops. Here, we investigated the effects of positive (PC) and negative (NC) charged iron oxide (Fe2O3) nanoparticles (IONPs) on the physiology and reproductive capacity of Arabidopsis thaliana at concentrations of 3 and 25 mg/L. The 3 mg/L treated plants did not show evident effects on seeding and root length. However, the 25 mg/L treatment resulted in reduced seedling (positive-20% and negative-3.6%) and root (positive-48% and negative-negligible) length. Interestingly, treatment with polyethylenimine (PEI; IONP-PC coating) also resulted in reduced root length (39%) but no change was observed with polyacrylic acid (PAA; IONP-NC coating) treatment alone. However, treatment with IONPs at 3 mg/L did lead to an almost 5% increase in aborted pollen, a 2%-6% reduction in pollen viability and up to an 11% reduction in seed yield depending on the number of treatments. Interestingly, the treated plants did not show any observable phenotypic changes in overall size or general plant structure, indicating that environmental nanoparticle contamination could go dangerously unnoticed.
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    Short- and Long-Term Effects of Prenatal Exposure to Iron Oxide Nanoparticles: Influence of Surface Charge and Dose on Developmental and Reproductive Toxicity
    (MDPI, 2015) Di Bona, Kristin R.; Xu, Yaolin; Gray, Marquita; Fair, Douglas; Hayles, Hunter; Milad, Luckie; Montes, Alex; Sherwood, Jennifer; Bao, Yuping; Rasco, Jane F.; University of Alabama Tuscaloosa
    Iron oxide nanoparticles (NPs) are commonly utilized for biomedical, industrial, and commercial applications due to their unique properties and potential biocompatibility. However, little is known about how exposure to iron oxide NPs may affect susceptible populations such as pregnant women and developing fetuses. To examine the influence of NP surface-charge and dose on the developmental toxicity of iron oxide NPs, Crl:CD1(ICR) (CD-1) mice were exposed to a single, low (10 mg/kg) or high (100 mg/kg) dose of positively-charged polyethyleneimine-Fe2O3-NPs (PEI-NPs), or negatively-charged poly(acrylic acid)-Fe2O3-NPs (PAA-NPs) during critical windows of organogenesis (gestation day (GD) 8, 9, or 10). A low dose of NPs, regardless of charge, did not induce toxicity. However, a high exposure led to charge-dependent fetal loss as well as morphological alterations of the uteri (both charges) and testes (positive only) of surviving offspring. Positively-charged PEI-NPs given later in organogenesis resulted in a combination of short-term fetal loss (42%) and long-term alterations in reproduction, including increased fetal loss for second generation matings (mice exposed in utero). Alternatively, negatively-charged PAA-NPs induced fetal loss (22%) earlier in organogenesis to a lesser degree than PEI-NPs with only mild alterations in offspring uterine histology observed in the long-term.
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    The Synthesis, Characterization and Dehydrogenation of Sigma-Complexes of BN-Cyclohexanes
    (Wiley-VCH, 2016) Kumar, Amit; Ishibashi, Jacob S. A.; Hooper, Thomas N.; Mikulas, Tanya C.; Dixon, David A.; Liu, Shih-Yuan; Weller, Andrew S.; University of Oxford; Boston College; University of Alabama Tuscaloosa
    The coordination chemistry of the 1,2-BN-cyclohexanes 2,2-R-2-1,2-B,N-C4H10 (R-2=HH, MeH, Me-2) with Ir and Rh metal fragments has been studied. This led to the solution (NMR spectroscopy) and solid-state (X-ray diffraction) characterization of [Ir(PCy3)(2)(H)(2)(eta(2)eta(2)-H2BNR2C4H8)][BAr4F] (NR2=NH2, NMeH) and [Rh(iPr(2)PCH(2)CH(2)CH(2)PiPr(2))(eta(2)eta(2)-H2BNR2C4H8)][ BAr4F] (NR2=NH2, NMeH, NMe2). For NR2=NH2 subsequent metal-promoted, dehydrocoupling shows the eventual formation of the cyclic tricyclic borazine [BNC4H8](3), via amino-borane and, tentatively characterized using DFT/GIAO chemical shift calculations, cycloborazane intermediates. For NR2=NMeH the final product is the cyclic amino-borane HBNMeC4H8. The mechanism of dehydrogenation of 2,2-H,Me-1,2-B,N-C4H10 using the {Rh(iPr(2)PCH(2)CH(2)CH(2)PiPr(2))}+ catalyst has been probed. Catalytic experiments indicate the rapid formation of a dimeric species, [Rh-2(iPr(2)PCH(2)CH(2)CH(2)PiPr(2))(2)H-5][BAr4F]. Using the initial rate method starting from this dimer, a first-order relationship to [amine-borane], but half-order to [Rh] is established, which is suggested to be due to a rapid dimer-monomer equilibrium operating.
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    Programmatic conversion of crystal structures into 3D printable files using Jmol
    (Biomed Central, 2016) Scalfani, Vincent F.; Williams, Antony J.; Tkachenko, Valery; Karapetyan, Karen; Pshenichnov, Alexey; Hanson, Robert M.; Liddie, Jahred M.; Bara, Jason E.; University of Alabama Tuscaloosa; Saint Olaf College
    Background: Three-dimensional (3D) printed crystal structures are useful for chemistry teaching and research. Current manual methods of converting crystal structures into 3D printable files are time-consuming and tedious. To overcome this limitation, we developed a programmatic method that allows for facile conversion of thousands of crystal structures directly into 3D printable files. Results: A collection of over 30,000 crystal structures in crystallographic information file (CIF) format from the Crystallography Open Database (COD) were programmatically converted into 3D printable files (VRML format) using Jmol scripting. The resulting data file conversion of the 30,000 CIFs proceeded as expected, however some inconsistencies and unintended results were observed with co-crystallized structures, racemic mixtures, and structures with large counterions that led to 3D printable files not containing the desired chemical structure. Potential solutions to these challenges are considered and discussed. Further, a searchable Jmol 3D Print website was created that allows users to both discover the 3D file dataset created in this work and create custom 3D printable files for any structure in the COD. Conclusions: Over 30,000 crystal structures were programmatically converted into 3D printable files, allowing users to have quick access to a sizable collection of 3D printable crystal structures. Further, any crystal structure (> 350,000) in the COD can now be conveniently converted into 3D printable file formats using the Jmol 3D Print website created in this work. The 3D Print website also allows users to convert their own CIFs into 3D printable files. 3D file data, scripts, and the Jmol 3D Print website are provided openly to the community in an effort to promote discovery and use of 3D printable crystal structures. The 3D file dataset and Jmol 3D Print website will find wide use with researchers and educators seeking to 3D print chemical structures, while the scripts will be useful for programmatically converting large database collections of crystal structures into 3D printable files.
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    Short-Chain Chitin Oligomers: Promoters of Plant Growth
    (MDPI, 2017) Winkler, Alexander J.; Alfonso Dominguez-Nunez, Jose; Aranaz, Inmaculada; Poza-Carrion, Cesar; Ramonell, Katrina; Somerville, Shauna; Berrocal-Lobo, Marta; Universidad Politecnica de Madrid; University of Hamburg; Complutense University of Madrid; Consejo Superior de Investigaciones Cientificas (CSIC); CSIC - Centro Nacional de Biotecnologia (CNB); University of Alabama Tuscaloosa; Carnegie Institution for Science; Instituto Nacional Investigacion Tecnologia Agraria Alimentaria (INIA)
    Chitin is the second most abundant biopolymer in nature after cellulose, and it forms an integral part of insect exoskeletons, crustacean shells, krill and the cell walls of fungal spores, where it is present as a high-molecular-weight molecule. In this study, we showed that a chitin oligosaccharide of lower molecular weight (tetramer) induced genes in Arabidopsis that are principally related to vegetative growth, development and carbon and nitrogen metabolism. Based on plant responses to this chitin tetramer, a low-molecular-weight chitin mix (CHL) enriched to 92% with dimers (2mer), trimers (3mer) and tetramers (4mer) was produced for potential use in biotechnological processes. Compared with untreated plants, CHL-treated plants had increased in vitro fresh weight (10%), radicle length (25%) and total carbon and nitrogen content (6% and 8%, respectively). Our data show that low-molecular-weight forms of chitin might play a role in nature as bio-stimulators of plant growth, and they are also a known direct source of carbon and nitrogen for soil biomass. The biochemical properties of the CHL mix might make it useful as a non-contaminating bio-stimulant of plant growth and a soil restorer for greenhouses and fields.
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    Iridium and Ruthenium Complexes of N-Heterocyclic Carbene- and Pyridinol-Derived Chelates as Catalysts for Aqueous Carbon Dioxide Hydrogenation and Formic Acid Dehydrogenation: The Role of the Alkali Metal
    (American Chemical Society, 2017) Siek, Sopheavy; Burks, Dalton B.; Gerlach, Deidra L.; Liang, Guangchao; Tesh, Jamie M.; Thompson, Courtney R.; Qu, Fengrui; Shankwitz, Jennifer E.; Vasquez, Robert M.; Chambers, Nicole; Szulczewski, Gregory J.; Grotjahn, Douglas B.; Webster, Charles Edwin; Papish, Elizabeth T.; University of Alabama Tuscaloosa; Mississippi State University; San Diego State University
    Hydrogenation reactions can be used to store energy in chemical bonds, and if these reactions are reversible, that energy can be released on demand. Some of the most effective transition metal catalysts for CO, hydrogenation have featured pyridin-2-ol-based ligands (e.g., 6,6 '-dihydroxybipyridine (6,6 '-dhbp)) for both their proton-responsive features and for metal-ligand bifunctional catalysis. We aimed to compare bidentate pyridin-2-ol based ligands with a new scaffold featuring an N-heterocyclic carbene (NHC) bound to pyridin-2-ol. Toward this aim, we have synthesized a series of [Cp*Ir(NHC-py(OR))Cl]OTf complexes where R = Bu-t (1), H (2), or Me (3). For comparison, we tested analogous bipyderived iridium complexes as catalysts, specifically [Cp*Ir(6,6 '-dxbp)Cl]OTf, where x = hydroxy (4(Ir)) or methoxy (5(Ir)); 4(Ir) was reported previously, but 5(Ir) is new. The analogous ruthenium complexes were also tested using [(eta(6)-cymene)Ru(6,6 '-dxbp)CljOTf, where x = hydroxy (4(Ru)) or methoxy (5(Ru)); 4(Ru) and 5(Ru) were both reported previously. All new complexes were fully characterized by spectroscopic and analytical methods and by single-crystal X-ray diffraction for 1, 2, 3, 5(Ir), and for two [Ag(NHC-py(OR))(2)]OTf complexes 6 (R = Bu-t) and 7 (R = Me). The aqueous catalytic studies of both CO2 hydrogenation and formic acid dehydrogenation were performed with catalysts 1-5. In general, NHC-py(OR) complexes 1-3 were modest precatalysts for both reactions. NHC complexes 1-3 all underwent transformations under basic CO2 hydrogenation conditions, and for 3, we trapped a product of its transformation, 3(sp), which we, characterized crystallographically. For CO2 hydrogenation with base and dxbp-based catalysts, we observed that x = hydroxy (4(Ir)) is 5-8 times more active than x = methoxy (5(Ir)). Notably, ruthenium complex 4(Ru) showed 95% of the activity of 4(Ir). For formic acid dehydrogenation, the trends were quite different with catalytic activity showing 4(Ir) >> 4(Ru) and 4(Ir) approximate to 5(Ir). Secondary coordination sphere effects are important under basic hydrogenation conditions where the OH groups of 6,6 '-dhbp are deprotonated and alkali metals can bind and help to activate CO2. Computational DFT studies have confirmed these trends and have been used to study the mechanisms of both CO2, hydrogenation and formic acid dehydrogenation.
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    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.
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    Photo Protection of Haematococcus pluvialis Algae by Astaxanthin: Unique Properties of Astaxanthin Deduced by EPR, Optical and Electrochemical Studies
    (MDPI, 2017) Focsan, A. Ligia; Polyakov, Nikolay E.; Kispert, Lowell D.; Valdosta State University; Voevodsky Institute of Chemical Kinetics & Combustion SB RAS; University of Alabama Tuscaloosa
    The antioxidant astaxanthin is known to accumulate in Haematococcus pluvialis algae under unfavorable environmental conditions for normal cell growth. The accumulated astaxanthin functions as a protective agent against oxidative stress damage, and tolerance to excessive reactive oxygen species (ROS) is greater in astaxanthin-rich cells. The detailed mechanisms of protection have remained elusive, however, our Electron Paramagnetic Resonance (EPR), optical and electrochemical studies on carotenoids suggest that astaxanthin's efficiency as a protective agent could be related to its ability to form chelate complexes with metals and to be esterified, its inability to aggregate in the ester form, its high oxidation potential and the ability to form proton loss neutral radicals under high illumination in the presence of metal ions. The neutral radical species formed by deprotonation of the radical cations can be very effective quenchers of the excited states of chlorophyll under high irradiation.
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    Performance enhancement by vertical morphology alteration of the active layer in organic solar cells
    (Royal Society of Chemistry, 2018) Bi, Sheng; Ouyang, Zhongliang; Guo, Qinglei; Jiang, Chengming; Dalian University of Technology; University of Alabama Tuscaloosa; University of Illinois Urbana-Champaign
    Bulk heterojunction organic solar cells (OSCs) have attracted worldwide attention due to their great potential as a green, flexible and low-cost renewable energy source. A vertical configuration in the active layer due to the aggregation of donor and acceptor molecules and the influence on the performance of OSCs deserve an in-depth study. In this study, five different vertical configurations of the active layer in OSCs were built up. The absorbance and indexes of the devices were theoretically analyzed. It was found that the configuration with the donor and acceptor molecules distributed equally exhibits the highest power conversion efficiency, followed by the configuration with the donor closer to the anode and the acceptor closer to the cathode, which matches experimental results well. Further analyses present the recombination, resistance, quantum efficiency and current leakage of all the configurations. It is anticipated that our results will promote the better understanding and development of the OSC field.
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    Synthesis of Wurtzite Cu2ZnSnS4 Nanosheets with Exposed High-Energy (002) Facets for Fabrication of Efficient Pt-Free Solar Cell Counter Electrodes
    (Nature Portfolio, 2018) Zhang, Xiaoyan; Xu, You; Zhang, Junjie; Dong, Shuai; Shen, Liming; Gupta, Arunava; Bao, Ningzhong; Nanjing Tech University; Southeast University - China; University of Alabama Tuscaloosa
    Two-dimensional (2D) semiconducting nanomaterials have generated much interest both because of fundamental scientific interest and technological applications arising from the unique properties in two dimensions. However, the colloidal synthesis of 2D quaternary chalcogenide nanomaterials remains a great challenge owing to the lack of intrinsic driving force for its anisotropic growth. 2D wurtzite Cu2ZnSnS4 nanosheets (CZTS-NS) with high-energy (002) facets have been obtained for the first time via a simple one-pot thermal decomposition method. The CZTS-NS exhibits superior photoelectrochemical activity as compared to zero-dimensional CZTS nanospheres and comparable performance to Pt counter electrode for dye sensitized solar cells. The improved catalytic activity can be attributed to additional reactive catalytic sites and higher catalytic reactivity in high-energy (002) facets of 2D CZTS-NS. This is in accordance with the density functional theory (DFT) calculations, which indicates that the (002) facets of wurtzite CZTS-NS possess higher surface energy and exhibits remarkable reducibility for I-3(-) ions. The developed synthetic method and findings will be helpful for the design and synthesis of 2D semiconducting nanomaterials, especially eco-friendly copper chalcogenide nanocrystals for energy harvesting and photoelectric applications.
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    Explosive dissolution and trapping of block copolymer seed crystallites
    (Nature Portfolio, 2018) Guerin, Gerald; Rupar, Paul A.; Manners, Ian; Winnik, Mitchell A.; University of Toronto; University of Bristol; University of Alabama Tuscaloosa
    Enhanced control over crystallization-driven self-assembly (CDSA) of coil-crystalline block copolymers has led to the formation of intricate structures with well-defined morphology and dimensions. While approaches to build those sophisticated structures may strongly differ from each other, they all share a key cornerstone: a polymer crystallite. Here we report a trapping technique that enables tracking of the change in length of one-dimensional (1D) polymer crystallites as they are annealed in solution at different temperatures. Using the similarities between 1D polymeric micelles and bottle-brush polymers, we developed a model explaining how the dissolving crystallites reach a critical size independent of the annealing temperature, and then explode in a cooperative process involving the remaining polymer chains of the crystallites. This model also allows us to demonstrate the role of the distribution in seed core crystallinity on the dissolution of the crystallites.
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    Evolution of Grain Interfaces in Annealed Duplex Stainless Steel after Parallel Cross Rolling and Direct Rolling
    (MDPI, 2018) Wang, Ming; Li, Haoqing; Tian, Yujing; Guo, Hong; Fang, Xiaoying; Guo, Yuebin; Shandong University of Technology; University of Alabama Tuscaloosa
    Changes in various grain interfaces, including the grain boundary and phase boundary, are a strong indication of microstructural changes, particularly ultra-fined grains achieved by large strain deformation and subsequent annealing. After direct rolling and cross rolling with the same strain of epsilon = 2, the distributions of the interfaces in annealed UNS S32304 duplex stainless steel were investigated using electron backscatter diffraction (EBSD) in this study. The ferrite experienced continued recovery, and a high density of low-angle grain boundaries (LAGBs) was produced. The percentage and number of twin boundaries (TBs) and LAGBs varied within the austenite. TBs were frequently found within austenite, showing a deviation from the Kurdjumov-Sachs (K-S) orientation relationship (OR) with ferrite matrix. However, LAGBs usually occur in austenite, with the K-S OR in the ferrite matrix. LAGBs were prevalent in the precipitated austenite grains, and therefore a strong texture was introduced in the cross-rolled and annealed samples, in which the precipitated austenite readily maintained the K-S OR in the ferrite matrix. By contrast, more TBs and a less robust texture were found in the precipitated austenite in direct-rolled and annealed samples, deviating from the K-S OR.