Open Access Publications

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Open access publications by faculty, postdocs, and graduate students in the Department of Chemistry and Biochemistry.


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    Synthesis, crystal and electronic structure of the Zintl phase Ba16Sb11. A case study uncovering greater structural complexity via monoclinic distortion of the tetragonal Ca16Sb11 structure type
    (Zeitschrift für anorganische und allgemeine Chemie | Journal of Inorganic and General Chemistry, 2023-09-14) Baranets, Sviatoslav; Ovchinnikov, Alexander; Samarakoon, S. M. Gayomi K.; Bobev, Svilen
    The binary Zintl phase Ba16Sb11 has been synthesized and structurally characterized. Detailed studies via single-crystal X-ray diffraction methods indicate that although Ba16Sb11 appears to crystallize in the tetragonal Ca16Sb11 structure type (space group Purn:x-wiley:00442313:media:zaac202300148:zaac202300148-math-0001 21m with a=13.5647(9) Å, c=12.4124(12) Å, Z=2, R1=3.14 %; wR2=4.77 %), there exists an extensive structural disorder. Some Ba16Sb11 crystals were found to be monoclinic and the structure was solved and refined in space group P21 (a=18.3929(12) Å, b=13.5233(8) Å, c=18.3978(12) Å, β=94.6600(10)°; Z=4, R1=5.84 %; wR2=9.58 %). The latter corresponds to a 2-fold superstructure of the tetragonal one, which provides a disorder-free structural model. In both descriptions, the disordered tetragonal and the ordered monoclinic superstructure, the basic building units that make up the structure of this Ba-rich compound are pairs of face-shared square antiprisms of Ba atoms, which are centered by Sb atoms. The dimerized antiprisms are linked into parallel chains via square prisms of Ba atoms, which are also centered by Sb atoms. The Zintl concept can be applied in a straightforward manner and as result, the structure of Ba32Sb22 (=2×Ba16Sb11) can be rationalized as (Ba2+)32(Sb3−)20[Sb2]4−. The partitioning of the valence electrons is done taking into an account the homoatomic Sb−Sb contacts (d=3.01 Å), which can be clearly distinguished in the lower symmetry space group. Electronic structure calculations of Ba16Sb11 are in good accordance with the Zintl rationalization and predict a semiconductor with a band gap of 0.77 eV.
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    HIV-1 mutants that escape the cytotoxic T-lymphocytes are defective in viral DNA integration
    (PNAS Nexus, 2022-05-20) Balasubramaniam, Muthukumar; Davids, Benem-Orom; Bryer, Alex; Xu, Chaoyi; Thapa, Santosh; Shi, Jiong; Aiken, Christopher; Pandhare, Jui; Perilla, Juan R.; Dash, Chandravanu
    HIV-1 replication is durably controlled without antiretroviral therapy (ART) in certain infected individuals called elite controllers (ECs). These individuals express specific human leukocyte antigens (HLA) that tag HIV-infected cells for elimination by presenting viral epitopes to CD8+ cytotoxic T-lymphocytes (CTL). In HIV-infected individuals expressing HLA-B27, CTLs primarily target the viral capsid protein (CA)-derived KK10 epitope. While selection of CA mutation R264K helps HIV-1 escape this potent CTL response, the accompanying fitness cost severely diminishes virus infectivity. Interestingly, selection of a compensatory CA mutation S173A restores HIV-1 replication. However, the molecular mechanism(s) underlying HIV-1 escape from this ART-free virus control by CTLs is not fully understood. Here, we report that the R264K mutation-associated infectivity defect arises primarily from impaired HIV-1 DNA integration, which is restored by the S173A mutation. Unexpectedly, the integration defect of the R264K variant was also restored upon depletion of the host cyclophilin A. These findings reveal a nuclear crosstalk between CA and HIV-1 integration as well as identify a previously unknown role of cyclophilin A in viral DNA integration. Finally, our study identifies a novel immune escape mechanism of an HIV-1 variant escaping a CA-directed CTL response.
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    Isocorrole-Loaded Polymer Nanoparticles for Photothermal Therapy under 980 nm Light Excitation
    (ACS Omega, 2022-10-18) Marek, Maximilian R. J.; Pham, Trong-Nhan; Wang, Jianxin; Cai, Qiuqi; Yap, Glenn P. A.; Day, Emily S.; Rosenthal, Joel
    Photothermal therapy (PTT) is a promising treatment option for diseases, including cancer, arthritis, and periodontitis. Typical photothermal agents (PTAs) absorb light in the near-infrared (NIR)-I region of 650–900 nm with a predominant focus around 800 nm, as these wavelengths are minimally absorbed by water and blood in the tissue. Recently, interest has grown in developing nanomaterials that offer more efficient photothermal conversion and that can be excited by light close to or within the NIR-II window of 1000–1700 nm, which offers less absorption by melanin. Herein, we report on the development of 5,5-diphenyl isocorrole (5-DPIC) complexes containing either Zn(II) or Pd(II) (Zn[5-DPIC] and Pd[5-DPIC], respectively) that absorb strongly across the 850–1000 nm window. We also show that poly(lactic-co-glycolic acid) (PLGA) nanoparticles loaded with these designer isocorroles exhibit low toxicity toward triple-negative breast cancer (TNBC) cells in the dark but enable efficient heat production and photothermal cell ablation upon excitation with 980 nm light. These materials represent an exciting new platform for 980 nm activated PTT and demonstrate the potential for designer isocorroles to serve as effective PTAs.
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    Selection Criteria for Small-Molecule Inhibitors in Area-Selective Atomic Layer Deposition: Fundamental Surface Chemistry Considerations
    (Accounts of Chemical Research, 2023-08-01) Mameli, Alfredo; Teplyakov, Andrew V.
    Conspectus Atomically precise and highly selective surface reactions are required for advancing microelectronics fabrication. Advanced atomic processing approaches make use of small molecule inhibitors (SMI) to enable selectivity between growth and nongrowth surfaces. The selectivity between growth and nongrowth substrates is eventually lost for any known combinations, because of defects, new defect formation, and simply because of a Boltzmann distribution of molecular reactivities on surfaces. The selectivity can then be restored by introducing etch-back correction steps. Most recent developments combine the design of highly selective combinations of growth and nongrowth substrates with atomically precise cycles of deposition and etching methods. At that point, a single additional step is often used to passivate the unwanted defects or selected surface chemical sites with SMI. This step is designed to chemically passivate the reactive groups and defects of the nongrowth substrates both before and/or during the deposition of material onto the growth substrate. This approach requires applications of the fundamental knowledge of surface chemistry and reactivity of small molecules to effectively block deposition on nongrowth substrates and to not substantially affect deposition on the growth surface. Thus, many of the concepts of classical surface chemistry that had been developed over several decades can be applied to design such small molecule inhibitors. This article will outline the approaches for such design. This is especially important now, since the ever-increasing number of applications of this concept still rely on trial-and-error approaches in selecting SMI. At the same time, there is a very substantial breadth of surface chemical reactivity analysis that can be put to use in this process that will relate the effectiveness of a potential SMI on any combination of surfaces with the following: selectivity; chemical stability of a molecule on a specific surface; volatility; steric hindrance, geometry, packing, and precursor of choice for material deposition; strength of adsorption as detailed by interdisplacement to determine the most stable SMI; fast attachment reaction kinetics; and minimal number of various binding modes. The down-selection of the SMI from the list of chemicals that satisfy the preliminary criteria will be decided based on optimal combinations of these requirements. Although the specifics of SMI selection are always affected by the complexity of the overall process and will depend drastically on the materials and devices that are or will be needed, this roadmap will assist in choosing the potential effective SMIs based on quite an exhaustive set of “SMI families” in connection with general types of target surfaces.
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    Cholesterol-substituted 3,4-ethylenedioxythiophene (EDOT-MA-cholesterol) and Poly(3,4-ethylenedioxythiophene) (PEDOT-MA-cholesterol)
    (Giant, 2023-05-23) Wu, Yuhang; Nagane, Samadhan S.; Baugh, Quintin; Lo, Chun-Yuan; Chhatre, Shrirang S.; Lee, Junghyun; Sitarik, Peter; Kayser, Laure V.; Martin, David C.
    Cholesterol is a rigid, crystalline, non-polar natural substance that exists in animal blood and cell membranes. Some of its derivatives are known to form ordered liquid crystalline mesophases under suitable conditions. In this work, we carefully examined the influence of cholesterol substitution on the characteristics of 3,4-ethylenedioxythiophene (EDOT-MA-cholesterol) and its corresponding polymer poly(3,4-ethylenedioxythiophene) (PEDOT-MA-cholesterol) synthesized by both chemical and electrochemical polymerization. We found evidence for an ordered lamellar (smectic-like) structure in the EDOT-MA-cholesterol monomer by differential scanning calorimetry (DSC), polarized optical microscopy (POM), and X-ray diffraction techniques. The ordered phase was observed to form on cooling from the isotropic melt at about 80 °C. Due to the insulating and bulky cholesterol side group on the EDOT monomer, we found that there was a maximum charge density for electrodeposition at ∼ 0.155−2. A series of electrodepositions were performed from 0 to 0.155−2 for probing the change of the charge transport with more charges used for the electrodeposition. We found that the impedance increased in the high-frequency range (above 104 Hz) and decreased in the low-frequency range (below 102 Hz). Three equivalent circuit models were proposed for fitting impedance data at different charge densities for a better understanding of the film growth process. The suppressed cyclic voltammogram (CV) of PEDOT-MA-cholesterol showed that the charge storage capability was essentially eliminated in the thickest films. The limited doping of the films was corroborated by their diminished electrochromic behavior, polaron-dominating absorption in UV-vis, overoxidized S 2p X-ray Photoelectron Spectroscopy (XPS) signal of electrodeposited films, and proton Nuclear Magnetic Resonance (1H NMR) of chemically polymerized samples. Dense film morphologies were confirmed by scanning electron microscopy (SEM). Grazing incident X-ray diffraction (GIWAXS) indicated the disrupted stacking of conjugated chains, which correlated with the decreased conductivity of the PEDOT-MA-cholesterol films. The measurement of the electrical conductivity gave a value of around 3.30 × 10−6−1 which is about six orders of magnitude lower than has been seen in PEDOT (∼3 Graphical abstract available at:
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    Electrochemically Enabled Total Syntheses of Natural Products
    (ChemElectroChem, 2023-06-01) Hatch, Chad E.; Chain, William J.
    Graphical Abstract available at: Electrochemical synthesis is a powerfully enabling technique for the formation of carbon-carbon and carbon-heteroatom bonds and has driven new developments in the total synthesis of complex bioactive natural products for 175 years. This review explores the unusual disconnections and operationally simple approaches to a diverse array of natural products. Abstract Electrochemical techniques have helped to enable the total synthesis of natural products since the pioneering work of Kolbe in the mid 1800’s. The electrochemical toolset grows every day and these new possibilities change the way chemists look at and think about natural products. This review provides a perspective on total syntheses wherein electrochemical techniques enabled the carbon-carbon bond formations in the skeletal assembly of important natural products, discussion of mechanistic details, and representative examples of the bond formations enabled over the last several decades. These bond formations are often distinctly different from those possible with conventional chemistries and allow assemblies complementary to other techniques.
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    A compendium of stable hotspots in the CHO genome
    (Biotechnology and Bioengineering, 2023-04-04) Hilliard, William; Lee, Kelvin H.
    The use of targeted integration for industrial CHO cell line development currently requires significant upfront effort to identify genomic loci capable of supporting multigram per liter therapeutic protein production from a limited number of transgene copies. To address this barrier to widespread adoption, we characterized transgene expression from thousands of stable hotspots in the CHO genome using the Thousands of Reporters Integrated in Parallel high-throughput screening method. This genome-scale data set was used to define a limited set of epigenetic properties of hotspot regions with sizes on the order of 10 kb. Cell lines with landing pad integrations at eight retargeted hotspot candidates consistently exhibited higher transgene mRNA expression than a commercially viable hotspot in equivalent culture conditions. Initial benchmarking of NISTmAb and trastuzumab productivity from one of these hotspots yielded mAb productivities of approximately 0.7–2 g/L (qP range: 2.9–8.2 pg/cell/day) in small-scale fed-batches. These findings indicate the list of hotspot candidates identified here will be a valuable resource for targeted integration platform development within the CHO community.
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    Synthesis and Crystal Structure of the Zintl Phases NaSrSb, NaBaSb and NaEuSb
    (Materials, 2023-02-08) Wang, Yi; Bobev, Svilen
    This work details the synthesis and the crystal structures of the ternary compounds NaSrSb, NaBaSb and NaEuSb. They are isostructural and adopt the hexagonal ZrNiAl-type structure (space group P6¯2m; Pearson code hP9). The structure determination in all three cases was performed using single-crystal X-ray diffraction methods. The structure features isolated Sb3– anions arranged in layers stacked along the crystallographic c-axis. In the interstices, alkali and alkaline-earth metal cations are found in tetrahedral and square pyramidal coordination environments, respectively. The formal partitioning of the valence electrons adheres to the valence rules, i.e., Na+Sr2+Sb3–, Na+Ba2+Sb3– and Na+Eu2+Sb3– can be considered as Zintl phases with intrinsic semiconductor behavior. Electronic band structure calculations conducted for NaBaSb are consistent with this notion and show a direct gap of approx. 0.9 eV. Additionally, the calculations hint at possible inverted Dirac cones, a feature that is reminiscent of topological quantum materials.
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    Dynamic bioinspired coculture model for probing ER+ breast cancer dormancy in the bone marrow niche
    (Science Advances, 2023-03-08) Pradhan, Lina; Moore, DeVonte; Ovadia, Elisa M.; Swedzinski, Samantha L.; Cossette, Travis; Sikes, Robert A.; van Golen, Kenneth; Kloxin, April M.
    Late recurrences of breast cancer are hypothesized to arise from disseminated tumor cells (DTCs) that reactivate after dormancy and occur most frequently with estrogen receptor–positive (ER+) breast cancer cells (BCCs) in bone marrow (BM). Interactions between the BM niche and BCCs are thought to play a pivotal role in recurrence, and relevant model systems are needed for mechanistic insights and improved treatments. We examined dormant DTCs in vivo and observed DTCs near bone lining cells and exhibiting autophagy. To study underlying cell-cell interactions, we established a well-defined, bioinspired dynamic indirect coculture model of ER+ BCCs with BM niche cells, human mesenchymal stem cells (hMSCs) and fetal osteoblasts (hFOBs). hMSCs promoted BCC growth, whereas hFOBs promoted dormancy and autophagy, regulated in part by tumor necrosis factor–α and monocyte chemoattractant protein 1 receptor signaling. This dormancy was reversible by dynamically changing the microenvironment or inhibiting autophagy, presenting further opportunities for mechanistic and targeting studies to prevent late recurrence.
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    Comparing spin injection in Fe75Co25/Bi2Te3 at GHz and optical excitations
    (Applied Physics Letters, 2023-02-13) Sharma, Vinay; Nepal, Rajeev; Wu, Weipeng; Pogue, E. A.; Kumar, Ravinder; Kolagani, Rajeswari; Gundlach, Lars; Jungfleisch, M. Benjamin; Budhani, Ramesh C.
    Spin-to-charge conversion (S2CC) processes in thin-film heterostructures have attracted much attention in recent years. Here, we describe the S2CC in a 3D topological insulator Bi2Te3 interfaced with an epitaxial film of Fe75Co25. The quantification of spin-to-charge conversion is made with two complementary techniques: ferromagnetic resonance based inverse spin Hall effect (ISHE) at GHz frequencies and femtosecond light-pulse induced emission of terahertz (THz) radiation. The role of spin rectification due to extrinsic effects like anisotropic magnetoresistance (AMR) and planar Hall effects (PHE) is pronounced at the GHz timescale, whereas the THz measurements do not show any detectible signal, which could be attributed to AMR or PHE. This result may be due to (i) homodyne rectification at GHz, which is absent in THz measurements and (ii) laser-induced thermal spin current generation and magnetic dipole radiation in THz measurements, which is completely absent in GHz range. The converted charge current has been analyzed using the spin diffusion model for the ISHE. We note that regardless of the differences in timescales, the spin diffusion length in the two cases is comparable. Our results aid in understanding the role of spin pumping timescales in the generation of ISHE signals.
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    The use of transmission electron microscopy with scanning mobility particle size spectrometry for an enhanced understanding of the physical characteristics of aerosol particles generated with a flow tube reactor
    (Aerosol Science and Technology, 2023-02-21) Tackman, Emma C.; Higgins, Devon N.; Kerecman, Devan E.; Ott, Emily-Jean; Johnston, Murray V.; Freedman, Miriam Arak
    Aerosol particles are found throughout the atmosphere with considerable variety in morphological characteristics and chemical composition. Identifying and characterizing these particle attributes is a significant step toward improving our understanding of atmospheric chemistry. Many methods exist for measuring the size and spreading of Aitken mode particles, but there are few studies rigorously comparing the results generated between approaches in this field. Here, we compare two methods for assessing aerosol particles – scanning mobility particle size spectrometry (SMPS) and transmission electron microscopy (TEM). Aitken mode particles consisting of salt seed particles and seed particles coated with α-pinene secondary organic material were produced in a flow tube reactor. The same populations of particles were analyzed using both techniques to facilitate direct comparison. For ammonium sulfate particles impacted onto carbon and Si TEM substrates, diameters increased by +0% to +30% when compared to the suspended electrical mobility diameters, an unexpectedly wide range for a single component system. Coated particles had unpredictable diameter differences, sometimes evaluated at larger and sometimes smaller sizes after impaction when compared to the corresponding SMPS electrical mobility diameter, from −34% to +60%. While all particles were generally round in shape, variation in particle morphology was also observed in coated samples. Between 0% and 98% of particles displayed obvious phase separation suggesting more population-level diversity than expected from these particle generation processes. Characterizing the differences between TEM and SMPS results better elucidates the role of a substrate where present and shows nonequivalence in particle size distributions obtained from different instruments.
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    Authentication of edible oils using an infrared spectral library and digital sample sets: A feasibility study
    (Journal of Chemometrics, 2023-03-19) Sota-Uba, Isio; White, Collin G.; Booksh, Karl; Lavine, Barry K.
    A potential method to determine whether two varieties of edible oils can be differentiated by Fourier transform infrared (FTIR) spectroscopy is proposed using digitally generated data of adulterated edible oils from an infrared (IR) spectral library. The first step is the evaluation of digitally blended data sets. Specifically, IR spectra of adulterated edible oils are computed from digitally blending experimental data of the IR spectra of an edible oil and the corresponding adulterant using the appropriate mixing coefficients to achieve the desired level of adulteration. To determine whether two edible oils can be differentiated by FTIR spectroscopy, pure IR spectra of the two edible oils are compared with IR spectra of two edible oils digitally mixed using a genetic algorithm for pattern recognition to solve a ternary classification problem. If the IR spectra of the two edible oils and their binary mixtures are differentiable from principal component plots of the spectral data, then differences between the IR spectra of these two edible oils are of sufficient magnitude to ensure that a reliable classification by FTIR spectroscopy can be obtained. Using this approach, the feasibility of authenticating edible oils such as extra virgin olive oil (EVOO) directly from library spectra is demonstrated. For this study, both digital and experimental data are combined to generate training and validation data sets to assess detection limits in FTIR spectroscopy for the adulterants.
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    Synthesis and Crystal Structure of the Zintl Phases Na2CaCdSb2, Na2SrCdSb2 and Na2EuCdSb2
    (Inorganics, 2022-12-18) Saparov, Bayram; Bobev, Svilen
    This work details the synthesis and the crystal structures of the quaternary Zintl phases Na2CaCdSb2, Na2SrCdSb2 and Na2EuCdSb2. They are isostructural and their noncentrosymmetric structure is with the space group Pmc21 (Pearson code oP12). All structural work is carried out via single-crystal X-ray diffraction methods. The structure features [CdSb2]4– layers of corner-shared CdSb4 tetrahedra, which are stacked along the b-crystallographic axis and are separated by cations. The results from the structure refinements suggest that in addition to full cation ordering, which is typical for this structure, there also exists a possibility for an accommodation of a small degree of cation disorder.
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    The Effect of Surface Terminations on the Initial Stages of TiO2 Deposition on Functionalized Silicon
    (ChemPhysChem, 2023-01-10) Parke, Tyler; Silva-Quinones, Dhamelyz; Wang, George T.; Teplyakov, Andrew V.
    As atomic layer deposition (ALD) emerges as a method to fabricate architectures with atomic precision, emphasis is placed on understanding surface reactions and nucleation mechanisms. ALD of titanium dioxide with TiCl4 and water has been used to investigate deposition processes in general, but the effect of surface termination on the initial TiO2 nucleation lacks needed mechanistic insights. This work examines the adsorption of TiCl4 on Cl−, H−, and HO− terminated Si(100) and Si(111) surfaces to elucidate the general role of different surface structures and defect types in manipulating surface reactivity of growth and non-growth substrates. The surface sites and their role in the initial stages of deposition are examined by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Density functional theory (DFT) computations of the local functionalized silicon surfaces suggest oxygen-containing defects are primary drivers of selectivity loss on these surfaces. Graphical Abstract available at: Deposition of TiO2 from TiCl4 and water dosing cycles onto H- and Cl-terminated silicon surfaces is defined by the interaction of the adsorbate molecule with defects on these surfaces. The nature of these defects and their effect on selectivity of deposition are investigated.
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    Anion Binding as a Strategy for the Synthesis of Porous Salts
    (Chemistry of Materials, 2022-12-27) Antonio, Alexandra M.; Dworzak, Michael R.; Korman, Kyle J.; Yap, Glenn P. A.; Bloch, Eric D.
    Porous salts have recently emerged as a promising new class of ultratunable permanently microporous solids. These adsorbents, which were first reported as ionic solids based on porous cations and anions, can be isolated from a wide variety of charged, permanently porous coordination cages. A challenge in realizing the full tunability of such systems, however, lies in the fact that the majority of coordination cages for which surface areas have been reported are comprised of charge-balanced inorganic and organic building blocks that result in neutral cages. As such, most reported permanently porous coordination cages cannot be used as reagents in the synthesis of porous salts. Here, we show that the facile reaction of TBAX (TBA+ = tetra-n-butylammonium; X = F– and Cl–) with molybdenum paddlewheel-based coordination cages of the M4L4 and M24L24 lantern and cuboctahedra structure types, respectively, affords charged cages by virtue of coordination of halide anions to the internal and/or external metal sites on these structures, as confirmed by single-crystal X-ray diffraction, X-ray photoelectron spectroscopy, and nuclear magnetic resonance (NMR) spectroscopy. At a practical level, the TBAX/cage reactions, which are fully reversible upon isolation of the cage with the appropriate solvent, solubilize otherwise rigorously insoluble cages. This method significantly increases the solution processability of these highly porous solids. Toward the formation of new porous salts, halide binding also serves to incorporate charge on neutral cages and make them amenable to simple salt metathesis reactions to afford new porous salts based on anions and cations with intrinsic porosity. A combination of diffraction methods and a suite of spectroscopic tools confirms speciation of the isolated solids, which represent a new class of highly tunable porous salts. Ultimately, this work represents a roadmap for the preparation of new porous solids and showcases the utility and broad applicability of anion binding as a strategy for the synthesis of porous salts.
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    Evolution of multiple spillover hydrogen species on anatase titanium dioxide
    (Cell Reports Physical Science, 2022-12-21) Liu, Kairui; Hou, Guangjin; Gao, Pan; Nie, Xuezhong; Bai, Shi; Janik, Michael J.; Zhang, Z. Conrad
    Hydrogen spillover is a widespread phenomenon on reducible metal oxide surfaces, with numerous observations confirming its occurrence. However, direct physical characterization of the spillover hydrogen species on an oxide catalyst support remains challenging. Differentiating the binding sites of specific spillover hydrogen species has been elusive. Herein, we vary temperature and reductive conditions, then quench and detect the physicochemical character of three distinct spillover hydrogen species on anatase titanium dioxide (TiO2-A) by deuterium magic-angle-spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy, aided by density functional theory. Fast cooling during the sample preparation is crucial in quenching the spillover deuterium species to enable MAS NMR detection. Energetically favorable spillover deuterium species evolve from deuteron to deuteride states with increasing reduction temperature. Prevailing deuteron species reside on the 2-fold-coordinated O2c site of the TiO2-A (101) surface at low reduction temperature. At high reduction temperature, deuterides residing at oxygen vacancies (Ti6c–D–Ti5c) are formed.
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    Attachment Chemistry of 4-Fluorophenylboronic Acid on TiO2 and Al2O3 Nanoparticles
    (Chemistry of Materials, 2022-12-13) Byron, Carly; Silva-Quinones, Dhamelyz; Sarkar, Sucharita; Brown, Scott C.; Bai, Shi; Quinn, Caitlin M.; Grzenda, Zachary; Chinn, Mitchell S.; Teplyakov, Andrew V.
    Surface modification of nanoparticulate TiO2 and Al2O3 materials with 4-fluorophenylboronic acid is investigated in order to both evaluate the novel surface modification schemes and develop spectroscopic labels for surface characterization. The chemistry of the modification is followed on all these surfaces using X-ray photoelectron spectroscopy, multinuclear (11B, 19F, and 13C) solid-state and solution NMR, and infrared spectroscopy to determine the binding modes of this compound using boron and fluorine as probe atoms. Density functional theory model calculations are utilized to visualize predicted surface species and to interpret the results of spectroscopic measurements. A comparison is made among TiO2 rutile, TiO2 anatase, and γ-Al2O3. On all three materials, the modification proceeds via the boronic functional groups, with metal oxide-controlled surface chemistry. The bonding configuration depends on the material and is dominated by a monodentate species for titania and by bidentate species for alumina. The surface structures determined to form on all the oxide semiconductors investigated suggest that sensitization or monolayer doping approaches with a well-defined chemical interaction via a boronic functionality can be developed.
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    Coupling Novel Probes with Molecular Localization Microscopy Reveals Cell Wall Homeostatic Mechanisms in Staphylococcus aureus
    (ACS Chemical Biology, 2022-11-22) Lund, Victoria A.; Gangotra, Haneesh; Zhao, Zhen; Sutton, Joshua A. F.; Wacnik, Katarzyna; DeMeester, Kristen; Liang, Hai; Santiago, Cintia; Grimes, Catherine Leimkuhler; Jones, Simon; Foster, Simon J.
    Bacterial cell wall peptidoglycan is essential for viability, and its synthesis is targeted by antibiotics, including penicillin. To determine how peptidoglycan homeostasis controls cell architecture, growth, and division, we have developed novel labeling approaches. These are compatible with super-resolution fluorescence microscopy to examine peptidoglycan synthesis, hydrolysis, and the localization of the enzymes required for its biosynthesis (penicillin binding proteins (PBPs)). Synthesis of a cephalosporin-based fluorescent probe revealed a pattern of PBPs at the septum during division, supporting a model of dispersed peptidoglycan synthesis. Metabolic and hydroxylamine-based probes respectively enabled the synthesis of glycan strands and associated reducing termini of the peptidoglycan to be mapped. Foci and arcs of reducing termini appear as a result of both synthesis of glycan strands and glucosaminidase activity of the major peptidoglycan hydrolase, SagB. Our studies provide molecular level details of how essential peptidoglycan dynamics are controlled during growth and division.
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    Enhanced thermoelectric performance in the zintl antimonides (Ca,RE)9Cd4Sb9 (RE = rare-earth metal). Synergy between increased structural complexity and drive towards optimized chemical bonding
    (Materials Today Advances, 2022-10-27) Ogunbunmi, M. O.; Baranets, S.; Bobev, S.
    The interplay of structural complexity, high carrier mobility, and high density of states effective mass can play a pivotal role in achieving enhanced thermoelectric (TE) performance in candidate materials. In this regard, the Zintl phases represent a class of compounds that are susceptible to harboring these key ingredients. This, in addition to their amenability to various forms of chemical substitution mechanisms makes them a good choice of systems to explore systematically. Here we demonstrate the role-play of these ingredients in achieving excellent TE properties on single-crystals of Ca9–xREyCd4+δSb9 (RE = Ce, Pr, Nd, Sm, Gd, Tb; x ≈ 0.5–0.8, y ≈ 0.5–0.7, δ ≈ 0.25). These phases represent a new addition to the “9–4–9” family with intricate chemical bonding arising from both a purposely introduced disorder on Ca sites and the inherent presence of interstitial Cd positions. Many of the newly synthesized and characterized phases show moderate values of the Seebeck coefficient, lying in the range of 71–116 μV/K at 600 K and evolving as degenerate semiconductors. Simultaneously, the electrical resistivity ρ(T) of the measured samples can be as low as 0.18 mΩ cm at this temperature. As a result, the observed TE power factors in the Ce-, Nd-, and Sm-samples are in the range 6–46 μW/cm.K2. For Ca9–xCexCd4+δSb9, the estimated thermoelectric quality factor B > 0.4 at 300 K, which corresponds to a figure of merit zT ≥ 1. Calculations based on the single parabolic band (SPB) model show that the optimum region for thermoelectric performance requires carrier concentration n = 2–6 × 1019 cm−3 thus providing for an open window to further tune the TE properties.
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    Recent Developments with Icetexane Natural Products
    (Chemistry and Biodiversity, 2022-10-10) Naeini, Ali Amiri; Ziegelmeier, Alexandre A.; Chain, William J.
    Icetexane diterpenoids are a diverse family of natural products sourced from several species of terrestrial plants. Icetexanes exhibit a broad array of biological activities and together with their complex 6-7-6 tricyclic scaffolds, they have piqued the interest of synthetic organic chemists, natural products chemists, and biological investigators over the past four decades and were reviewed 13 years ago. This review summarizes icetexane natural products isolated since 2009, provides an overview of new synthetic approaches to the icetexane problem, and proposes an additional classification of icetexanes based on novel structures that are unlike previously isolated materials.
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