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Chemistry & Biochemistry Faculty Works

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Articles 1 - 30 of 125

Full-Text Articles in Physical Sciences and Mathematics

Water Spines And Networks In G-Quadruplex Structures, Kevin Li , '22, Liliya A. Yatsunyk, S. Neidle Jan 2021

Water Spines And Networks In G-Quadruplex Structures, Kevin Li , '22, Liliya A. Yatsunyk, S. Neidle

Chemistry & Biochemistry Faculty Works

Quadruplex DNAs can fold into a variety of distinct topologies, depending in part on loop types and orientations of individual strands, as shown by high-resolution crystal and NMR structures. Crystal structures also show associated water molecules. We report here on an analysis of the hydration arrangements around selected folded quadruplex DNAs, which has revealed several prominent features that re-occur in related structures. Many of the primary-sphere water molecules are found in the grooves and loop regions of these structures. At least one groove in anti-parallel and hybrid quadruplex structures is long and narrow and contains an extensive spine of linked …

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A Procedure For Computing Hydrocarbon Strain Energies Using Computational Group Equivalents, With Application To 66 Molecules, Paul R. Rablen Jan 2020

A Procedure For Computing Hydrocarbon Strain Energies Using Computational Group Equivalents, With Application To 66 Molecules, Paul R. Rablen

Chemistry & Biochemistry Faculty Works

A method is presented for the direct computation of hydrocarbon strain energies using computational group equivalents. Parameters are provided at several high levels of electronic structure theory: W1BD, G-4, CBS-APNO, CBS-QB3, and M062X/6-31+G(2df,p). As an illustration of the procedure, strain energies are computed for 66 hydrocarbons, most of them highly strained.

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Biophysical And X-Ray Structural Studies Of The (Gggtt)3ggg G-Quadruplex In Complex With N-Methyl Mesoporphyrin Ix, Linda Yingqi Lin , '20, S. Mccarthy, Barrett M. Powell , '18, Yanti Manurung , '20, Irene M. Xiang , '18, W. L. Dean, B. Chaires, Liliya A. Yatsunyk Jan 2020

Biophysical And X-Ray Structural Studies Of The (Gggtt)3ggg G-Quadruplex In Complex With N-Methyl Mesoporphyrin Ix, Linda Yingqi Lin , '20, S. Mccarthy, Barrett M. Powell , '18, Yanti Manurung , '20, Irene M. Xiang , '18, W. L. Dean, B. Chaires, Liliya A. Yatsunyk

Chemistry & Biochemistry Faculty Works

The G-quadruplex (GQ) is a well-studied non-canonical DNA structure formed by G-rich sequences found at telomeres and gene promoters. Biological studies suggest that GQs may play roles in regulating gene expression, DNA replication, and DNA repair. Small molecule ligands were shown to alter GQ structure and stability and thereby serve as novel therapies, particularly against cancer. In this work, we investigate the interaction of a G-rich sequence, 5’-GGGTTGGGTTGGGTTGGG-3’ (T1), with a water-soluble porphyrin, N-methyl mesoporphyrin IX (NMM) via biophysical and X-ray crystallographic studies. UV-vis and fluorescence titrations, as well as a Job plot, revealed a 1:1 binding stoichiometry with an …

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Aerobic C-C And C-O Bond Formation Reactions Mediated By High-Valent Nickel Species., Sofia Smith, Oriol Planas, Laura Gómez, Nigam Rath, Xavi Ribas, Liviu Mirica, Liviu Mirica Sep 2019

Aerobic C-C And C-O Bond Formation Reactions Mediated By High-Valent Nickel Species., Sofia Smith, Oriol Planas, Laura Gómez, Nigam Rath, Xavi Ribas, Liviu Mirica, Liviu Mirica

Chemistry & Biochemistry Faculty Works

Nickel complexes have been widely employed as catalysts in C–C and C–heteroatom bond formation reactions. While Ni(0), Ni(I), and Ni(II) intermediates are most relevant in these transformations, recently Ni(III) and Ni(IV) species have also been proposed to play a role in catalysis. Reported herein is the synthesis, detailed characterization, and reactivity of a series of Ni(II) and Ni(III) metallacycle complexes stabilized by tetradentate pyridinophane ligands with various N-substituents. Interestingly, while the oxidation of the Ni(II) complexes with various other oxidants led to exclusive C–C bond formation in very good yields, the use of O2 or H2O2 as oxidants led to …

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The Chemistry And Biology Of Cyclophostin, The Cyclipostins And Related Compounds, Christopher Spilling Jul 2019

The Chemistry And Biology Of Cyclophostin, The Cyclipostins And Related Compounds, Christopher Spilling

Chemistry & Biochemistry Faculty Works

Cyclophostin, the cyclipostins and the salinipostins are structurally related cyclic enolphosphate natural products. This mini review describes their isolation, synthesis and biological activities. In addition, the synthesis and biological activities of monocyclic enolphosphate and mono and bicyclic enolphosphonate analogs are presented.

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G-Quadruplex Dynamics Contribute To Regulation Of Mitochondrial Gene Expression, M. Falabella, J. E. Kolesar, C. Wallace, D. De Jesus, L. Sun, Y. V. Taguichi, C. Wang, T. Wang, Irene M. Xiang , '18, J. K. Alder, R. Maheshan, W. Horne, Joshua R. Turek-Herman , '16, P. J. Pagano, C. M. St. Croix, N. Sondheimer, Liliya A. Yatsunyk, F. B. Johnson, B. A. Kaufman Apr 2019

G-Quadruplex Dynamics Contribute To Regulation Of Mitochondrial Gene Expression, M. Falabella, J. E. Kolesar, C. Wallace, D. De Jesus, L. Sun, Y. V. Taguichi, C. Wang, T. Wang, Irene M. Xiang , '18, J. K. Alder, R. Maheshan, W. Horne, Joshua R. Turek-Herman , '16, P. J. Pagano, C. M. St. Croix, N. Sondheimer, Liliya A. Yatsunyk, F. B. Johnson, B. A. Kaufman

Chemistry & Biochemistry Faculty Works

Single-stranded DNA or RNA sequences rich in guanine (G) can adopt non-canonical structures known as G-quadruplexes (G4). Mitochondrial DNA (mtDNA) sequences that are predicted to form G4 are enriched on the heavy-strand and have been associated with formation of deletion breakpoints. Increasing evidence supports the ability of mtDNA to form G4 in cancer cells; however, the functional roles of G4 structures in regulating mitochondrial nucleic acid homeostasis in non-cancerous cells remain unclear. Here, we demonstrate by live cell imaging that the G4-ligand RHPS4 localizes primarily to mitochondria at low doses. We find that low doses of RHPS4 do not induce …

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Biosensor Applications Of Electrodeposited Nanostructures, Keith Stine Feb 2019

Biosensor Applications Of Electrodeposited Nanostructures, Keith Stine

Chemistry & Biochemistry Faculty Works

The development of biosensors for a range of analytes from small molecules to proteins to oligonucleotides is an intensely active field. Detection methods based on electrochemistry or on localized surface plasmon responses have advanced through using nanostructured electrodes prepared by electrodeposition, which is capable of preparing a wide range of different structures. Supported nanoparticles can be prepared by electrodeposition through applying fixed potentials, cycling potentials, and fixed current methods. Nanoparticle sizes, shapes, and surface densities can be controlled, and regular structures can be prepared by electrodeposition through templates. The incorporation of multiple nanomaterials into composite films can take advantage of …

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Ring Expansion Of Alkylidenecarbenes Derived From Lactams, Lactones, And Thiolactones Into Strained Heterocyclic Alkynes: A Theoretical Study, N. N. Thu Le, J. Just, J. M. Pankauski, Paul R. Rablen, D. M. Thamattoor Feb 2019

Ring Expansion Of Alkylidenecarbenes Derived From Lactams, Lactones, And Thiolactones Into Strained Heterocyclic Alkynes: A Theoretical Study, N. N. Thu Le, J. Just, J. M. Pankauski, Paul R. Rablen, D. M. Thamattoor

Chemistry & Biochemistry Faculty Works

Strained cycloalkynes are of considerable interest to theoreticians and experimentalists, and possess much synthetic value as well. Herein, a series of cyclic alkylidenecarbenes—formally obtained by replacing the carbonyl oxygen of four-, five-, and six-membered lactams, lactones, and thiolactones with a divalent carbon—were modeled at the CCSD(T)/cc-pVTZ//B3LYP/6-311+G** and CCSD(T)/cc-pVTZ//CCSD/6-311+G** levels of theory. The singlet carbenes were found to be more stable than the triplets. The strained heterocyclic alkynes formed by ring expansion of these singlet carbenes were also modeled. Interestingly, the C≡C bonds in the five-membered heterocycles, obtained from the rearrangement of β-lactam- and β-lactone-derived alkylidenecarbenes, displayed lengths intermediate between formal …

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Synthetic Ionophores As Non-Resistant Antibiotic Adjuvants, George Gokel, Mohit Patel, Evan Garrad, Joseph Meisel, Saeedeh Negin, Michael Gokel Jan 2019

Synthetic Ionophores As Non-Resistant Antibiotic Adjuvants, George Gokel, Mohit Patel, Evan Garrad, Joseph Meisel, Saeedeh Negin, Michael Gokel

Chemistry & Biochemistry Faculty Works

Antimicrobial resistance is a world-wide health care crisis. New antimicrobials must both exhibit potency and thwart the ability of bacteria to develop resistance to them. We report the use of synthetic ionophores as a new approach to developing non-resistant antimicrobials and adjuvants. Most studies involving amphiphilic antimicrobials have focused on either developing synthetic amphiphiles that show ion transport, or developing non-cytotoxic analogs of such peptidic amphiphiles as colistin. We have rationally designed, prepared, and evaluated crown ether-based synthetic ionophores (‘hydraphiles’) that show selective ion transport through bilayer membranes and are toxic to bacteria. We report here that hydraphiles exhibit a …

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N-Methyl Mesoporphyrin Ix As A Highly Selective Light-Up Probe For G-Quadruplex Dna, Ariana Yett , '21, Linda Yingqi Lin , '20, Dana Beseiso , '21, Joanne Miao , '22, Liliya A. Yatsunyk Jan 2019

N-Methyl Mesoporphyrin Ix As A Highly Selective Light-Up Probe For G-Quadruplex Dna, Ariana Yett , '21, Linda Yingqi Lin , '20, Dana Beseiso , '21, Joanne Miao , '22, Liliya A. Yatsunyk

Chemistry & Biochemistry Faculty Works

N-methyl mesoporphyrin IX (NMM) is a water-soluble, non-symmetric porphyrin with excellent optical properties and unparalleled selectivity for G-quadruplex (GQ) DNA. G-quadruplexes are non-canonical DNA structures formed by guanine-rich sequences. They are implicated in genomic stability, longevity, and cancer. The ability of NMM to selectively recognize GQ structures makes it a valuable scaffold for designing novel GQ binders. In this review, we survey the literature describing the GQ-binding properties of NMM as well as its wide utility in chemistry and biology. We start with the discovery of the GQ-binding properties of NMM and the development of NMM-binding aptamers. We then discuss …

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Mechanism For Copper(Ii)-Mediated Disaggregation Of A Porphyrin J-Aggregate, M. Trapani, I. G. Occhiuto, R. Zagami, G. De Luca, M. A. Castriciano, A. Romeo, L. M. Scolaro, Robert F. Pasternack Dec 2018

Mechanism For Copper(Ii)-Mediated Disaggregation Of A Porphyrin J-Aggregate, M. Trapani, I. G. Occhiuto, R. Zagami, G. De Luca, M. A. Castriciano, A. Romeo, L. M. Scolaro, Robert F. Pasternack

Chemistry & Biochemistry Faculty Works

J-aggregates of anionic meso-tetrakis(4-sulfonatophenyl)porphyrin form at intermediate pH (2.3–3.1) in the presence of NiSO₄ or ZnSO₄ (ionic strength, I.S. = 3.2 M). These aggregates convert to monomeric porphyrin units via metallation with copper(II) ions. The kinetics for the disassembly process, as monitored by UV/vis spectroscopy, exhibits zeroth-order behavior. The observed zeroth-order rate constants show a two-term dependence on copper(II) ion concentrations: linear and second order. Also observed is an inverse dependence on hydrogen ion concentration. Activation parameters have been determined for the disassembly process leading to ΔH^≠ = (+163 ± 15) kJ·mol⁻¹ and ΔS^≠ = (+136 ± 11) J·K⁻¹. A …

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Lipg A Bifunctional Phospholipase/Thioesterase Involved In Mycobacterial Envelope Remodeling, Christopher Spilling, Pierre Santucci, Vanessa Point, Isabelle Poncin, Alexandre Guy, Celine Crauste, Carole Serveau-Avesque, Jean Galano, Jean-Francois Cavalier, Stephane Canaan Dec 2018

Lipg A Bifunctional Phospholipase/Thioesterase Involved In Mycobacterial Envelope Remodeling, Christopher Spilling, Pierre Santucci, Vanessa Point, Isabelle Poncin, Alexandre Guy, Celine Crauste, Carole Serveau-Avesque, Jean Galano, Jean-Francois Cavalier, Stephane Canaan

Chemistry & Biochemistry Faculty Works

Tuberculosis caused by Mycobacterium tuberculosis is currently one of the leading causes of death from an infectious agent. The main difficulties encountered in eradicating this bacteria are mainly related to (i) a very complex lipid composition of the bacillus cell wall, (ii) its ability to hide from the immune system inside the granulomas, and (iii) the increasing number of resistant strains. In this context, we were interested in the Rv0646c (lipGMTB) gene located upstream to the mmaA cluster which is described as being crucial for the production of cell wall components and required for the bacilli adaptation and survival in …

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Generating High-Order Optical And Spin Harmonics From Ferromagnetic Monolayers, G.P. Zhang, M.S. Si, M. Murakami, Y.H. Bai, Thomas George Dec 2018

Generating High-Order Optical And Spin Harmonics From Ferromagnetic Monolayers, G.P. Zhang, M.S. Si, M. Murakami, Y.H. Bai, Thomas George

Chemistry & Biochemistry Faculty Works

High-order harmonic generation (HHG) in solids has entered a new phase of intensive research, with envisioned band-structure mapping on an ultrashort time scale. This partly benefits from a flurry of new HHG materials discovered, but so far has missed an important group. HHG in magnetic materials should have profound impact on future magnetic storage technology advances. Here we introduce and demonstrate HHG in ferromagnetic monolayers. We find that HHG carries spin information and sensitively depends on the relativistic spin–orbit coupling; and if they are dispersed into the crystal momentum k space, harmonics originating from real transitions can be k-resolved and …

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Interactions Between Spermine-Derivatized Tentacle Porphyrins And The Human Telomeric Dna G-Quadruplex, Navin C. Sabharwal , '14, Jessica Chen , '17, Joo Hyun Lee , '17, C. M. A. Gangemi, A. D'Urso, Liliya A. Yatsunyk Nov 2018

Interactions Between Spermine-Derivatized Tentacle Porphyrins And The Human Telomeric Dna G-Quadruplex, Navin C. Sabharwal , '14, Jessica Chen , '17, Joo Hyun Lee , '17, C. M. A. Gangemi, A. D'Urso, Liliya A. Yatsunyk

Chemistry & Biochemistry Faculty Works

G-rich DNA sequences have the potential to fold into non-canonical G-Quadruplex (GQ) structures implicated in aging and human diseases, notably cancers. Because stabilization of GQs at telomeres and oncogene promoters may prevent cancer, there is an interest in developing small molecules that selectively target GQs. Herein, we investigate the interactions of meso-tetrakis-(4-carboxysperminephenyl)porphyrin (TCPPSpm4) and its Zn(II) derivative (ZnTCPPSpm4) with human telomeric DNA (Tel22) via UV-Vis, circular dichroism (CD), and fluorescence spectroscopies, resonance light scattering (RLS), and fluorescence resonance energy transfer (FRET) assays. UV-Vis titrations reveal binding constants of 4.7 × 10⁶ and 1.4 × 10⁷ M⁻¹ and binding stoichiometry of …

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Laser-Induced Ultrafast Transport And Demagnetization At The Earliest Time: First-Principles And Real-Time Investigation, Thomas George, G.P. Zhang, Y. Bai, T. Jenkins Oct 2018

Laser-Induced Ultrafast Transport And Demagnetization At The Earliest Time: First-Principles And Real-Time Investigation, Thomas George, G.P. Zhang, Y. Bai, T. Jenkins

Chemistry & Biochemistry Faculty Works

It is generally believed that there are at least two ways to use an ultrafast laser pulse to demagnetize a magnetic sample. One is to directly photo-demagnetize the system through spin-orbit coupling (SOC), and the other is to utilize ultrafast hot electron transport without SOC. The challenge is that these two processes are entangled on the same time scale. While the experimental results have been inconclusive, theoretical investigations are even scarcer, beyond those earlier studies based on spin superdiffusion. For instance, we do not even know how fast electrons move under laser excitation and how far they move. Here we …

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Bis(Triphenylphosphine) Iminium Tetrafluoroborate Chloroform Monosolvate, Rachana Manandhar, Nigam Rath, Myron Jones Aug 2018

Bis(Triphenylphosphine) Iminium Tetrafluoroborate Chloroform Monosolvate, Rachana Manandhar, Nigam Rath, Myron Jones

Chemistry & Biochemistry Faculty Works

In the title compound, C36H30NP2+·BF4−·CHCl3 or [PPN]BF4·CHCl3, where [PPN] = [(Ph3P)2N]+, two tri­phenyl­phosphine units are attached to a central N atom. The P—N—P bond angle is 137.69 (11)°. The two P—N bonds are nearly equivalent, with lengths of 1.5834 (18) and 1.5798 (17) Å. Both the BF4− anion and the chloro­form solvent mol­ecule are disordered over two positions, with occupancy ratios of 0.872 (3):0.128 (3) and 0.9628 (9):0.0372 (9), respectively. In the crystal, C—H⋯F and C—H⋯Cl hydrogen bonds link the [PPN]+ cations, the BF4− anions, and the chloro­form solvent mol­ecules into an array which extends along the b-axis direction.

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Crystal Structures Of 2-Bromo-1,1,1,3,3,3-Hexa­Methyl-2-(Tri­Methyl­Sil­Yl)Tris­Ilane And 2-Bromo-1,1,1,3,3,3-Hexa­Isopropyl-2-(Triiso­Propyl­Sil­Yl)Tri­Silane, Eva Gulotty, Richard Staples, Shannon Biros, Peter Gaspar, Nigam Rath, William Winchester Aug 2018

Crystal Structures Of 2-Bromo-1,1,1,3,3,3-Hexa­Methyl-2-(Tri­Methyl­Sil­Yl)Tris­Ilane And 2-Bromo-1,1,1,3,3,3-Hexa­Isopropyl-2-(Triiso­Propyl­Sil­Yl)Tri­Silane, Eva Gulotty, Richard Staples, Shannon Biros, Peter Gaspar, Nigam Rath, William Winchester

Chemistry & Biochemistry Faculty Works

The synthesis and crystal structures of two tris­(tri­alkyl­sil­yl)silyl bromide compounds, C9H27BrSi4 (I, HypSiBr) and C27H63BrSi4 (II, TipSiBr), are described. Compound I was prepared in 85% yield by free-radical bromination of 1,1,1,3,3,3-hexa­methyl-2-(tri­methyl­sil­yl)tris­ilane using bromo­butane and 2,2′-azobis(2-methyl­propio­nitrile) as a radical initiator at 333 K. The mol­ecule possesses threefold rotational symmetry, with the central Si atom and the Br atom being located on the threefold rotation axis. The Si—Br bond distance is 2.2990 (12) Å and the Si—Si bond lengths are 2.3477 (8) Å. The Br—Si—Si bond angles are 104.83 (3)° and the Si—Si—Si bond angles are 113.69 (2)°, reflecting the steric hindrance …

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Conjugation Of Nanomaterials And Nematic Liquid Crystals For Futuristic Applications And Biosensors, Thomas George, Amit Choudhary, Guoqiang Li Jul 2018

Conjugation Of Nanomaterials And Nematic Liquid Crystals For Futuristic Applications And Biosensors, Thomas George, Amit Choudhary, Guoqiang Li

Chemistry & Biochemistry Faculty Works

The established role of nematic liquid crystals (NLCs) in the recent rapid development of displays has motivated researchers to modulate the electro-optical properties of LCs. Furthermore, adding nanomaterials into NLCs has led to enhancements of the properties of NLCs, like reduced threshold of the operating voltage, variation in pretilt angle, reduced switching time, etc. These enhanced properties, due to interfacial dynamics, are enabling wider applications of NLCs and nanomaterials. The recent literature of nanomaterial-doped NLCs is rich with various kinds of nanomaterials in a variety of NLCs. The light has been focused on the most widely used and studied gold …

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Quadruplexes In ‘Dicty’: Crystal Structure Of A Four-Quartet G-Quadruplex Formed By G-Rich Motif Found In The Dictyostelium Discoideum Genome, A. Guédin, Linda Yingqi Lin , '20, S. Armane, L. Lacroix, J.-L. Mergny, S. Thore, Liliya A. Yatsunyk Jun 2018

Quadruplexes In ‘Dicty’: Crystal Structure Of A Four-Quartet G-Quadruplex Formed By G-Rich Motif Found In The Dictyostelium Discoideum Genome, A. Guédin, Linda Yingqi Lin , '20, S. Armane, L. Lacroix, J.-L. Mergny, S. Thore, Liliya A. Yatsunyk

Chemistry & Biochemistry Faculty Works

Guanine-rich DNA has the potential to fold into non-canonical G-quadruplex (G4) structures. Analysis of the genome of the social amoeba Dictyostelium discoideum indicates a low number of sequences with G4-forming potential (249–1055). Therefore, D. discoideum is a perfect model organism to investigate the relationship between the presence of G4s and their biological functions. As a first step in this investigation, we crystallized the dGGGGGAGGGGTACAGGGGTACAGGGG sequence from the putative promoter region of two divergent genes in D. discoideum. According to the crystal structure, this sequence folds into a four-quartet intramolecular antiparallel G4 with two lateral and one diagonal loops. The G-quadruplex …

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Synthesis And Characterization Of (Pyno−)2gacl: A Redox-Active Gallium Complex, Jacob M. Kirsh , '17, Audra J. Woodside , '19, B. C. Manor, P. J. Carroll, Paul R. Rablen, Christopher R. Graves Jun 2018

Synthesis And Characterization Of (Pyno−)2gacl: A Redox-Active Gallium Complex, Jacob M. Kirsh , '17, Audra J. Woodside , '19, B. C. Manor, P. J. Carroll, Paul R. Rablen, Christopher R. Graves

Chemistry & Biochemistry Faculty Works

We report the synthesis of a gallium complex incorporating redox-active pyridyl nitroxide ligands. The (pyNO−)2GaCl complex was prepared in 85% yield via a salt metathesis route and was characterized by 1H and 13C NMR spectroscopies, X-ray diffraction, and theory. UV–Vis absorption spectroscopy and electrochemistry were used to access the optical and electrochemical properties of the complex, respectively. Our discussion focuses primarily on a comparison of the gallium complex to the corresponding aluminum derivative and shows that although the complexes are very similar, small differences in the electronic structure of the complexes can be correlated to the identity of the metal.

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The Spin-Forbidden A 4Σ−–X 2Π1/2 Transition Of Geh Detected In Absorption Using Intracavity Laser Spectroscopy, Jack Harms, Leah O’Brien, James O’Brien May 2018

The Spin-Forbidden A 4Σ−–X 2Π1/2 Transition Of Geh Detected In Absorption Using Intracavity Laser Spectroscopy, Jack Harms, Leah O’Brien, James O’Brien

Chemistry & Biochemistry Faculty Works

The a 4Σ−–X 2Π1/2 transition of GeH has been recorded in absorption for the first time using Intracavity Laser Spectroscopy (ILS). The GeH molecules were produced in a 0.40–0.60 A DC plasma discharge inside an aluminum hollow cathode, using 500 mTorr of Ar, 100 mTorr of H2, and 200 mTorr of GeH4. This cathode is located within the resonator cavity of a Coherent Verdi™ V-10 pumped dye laser. Effective path lengths for this series of measurements using the ILS method ranged from 2 to 7 km. Spectra were calibrated using the absorption spectrum of I2 collected from an extracavity cell, …

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The Spin-Forbidden A^4z-—X^2n(1/2) Transition Of Geh Detected In Absorption Using Intracavity Laser Spectroscopy, James O'Brien, L. O'Brien, L. Harms May 2018

The Spin-Forbidden A^4z-—X^2n(1/2) Transition Of Geh Detected In Absorption Using Intracavity Laser Spectroscopy, James O'Brien, L. O'Brien, L. Harms

Chemistry & Biochemistry Faculty Works

The a 4Σ--X 2Π1/2 transition of GeH has been recorded in absorption for the first time using Intracavity Laser Spectroscopy (ILS). The GeH molecules were produced in a 0.40-0.60 A DC plasma discharge inside an aluminum hollow cathode, using 500 mTorr of Ar, 100 mTorr of H2, and 200 mTorr of GeH4. This cathode is located within the resonator cavity of a Coherent Verdi™ V-10 pumped dye laser. Effective path lengths for this series of measurements using the ILS method ranged from 2 to 7 km. Spectra were calibrated using the absorption spectrum of I2 collected from an extracavity cell, …

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Shaping Light In Backward-Wave Nonlinear Hyperbolic Metamaterials, Thomas George, Alexander Popov, Sergey Myslivets, Vitaly Slabko, Victor Tkachenko Apr 2018

Shaping Light In Backward-Wave Nonlinear Hyperbolic Metamaterials, Thomas George, Alexander Popov, Sergey Myslivets, Vitaly Slabko, Victor Tkachenko

Chemistry & Biochemistry Faculty Works

Backward electromagnetic waves are extraordinary waves with contra-directed phase velocity and energy flux. Unusual properties of the coherent nonlinear optical coupling of the phase-matched ordinary and backward electromagnetic waves with contra-directed energy fluxes are described that enable greatly-enhanced frequency and propagation direction conversion, parametrical amplification, as well as control of shape of the light pulses. Extraordinary transient processes that emerge in such metamaterials in pulsed regimes are described. The results of the numerical simulation of particular plasmonic metamaterials with hyperbolic dispersion are presented, which prove the possibility to match phases of such coupled guided ordinary and backward electromagnetic waves. Particular …

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Preparation, Modification, Characterization, And Biosensing Application Of Nanoporous Gold Using Electrochemical Techniques, Jay Bhattarai, Dharmendra Neupane, Bishal Nepal, Vasilii Mikhaylov, Alexei Demchenko, Keith Stine Mar 2018

Preparation, Modification, Characterization, And Biosensing Application Of Nanoporous Gold Using Electrochemical Techniques, Jay Bhattarai, Dharmendra Neupane, Bishal Nepal, Vasilii Mikhaylov, Alexei Demchenko, Keith Stine

Chemistry & Biochemistry Faculty Works

Nanoporous gold (np-Au), because of its high surface area-to-volume ratio, excellent conductivity, chemical inertness, physical stability, biocompatibility, easily tunable pores, and plasmonic properties, has attracted much interested in the field of nanotechnology. It has promising applications in the fields of catalysis, bio/chemical sensing, drug delivery, biomolecules separation and purification, fuel cell development, surface-chemistry-driven actuation, and supercapacitor design. Many chemical and electrochemical procedures are known for the preparation of np-Au. Recently, researchers are focusing on easier and controlled ways to tune the pores and ligaments size of np-Au for its use in different applications. Electrochemical methods have good control over fine-tuning …

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Amide Neighbouring Group Effects In Peptides: Phenylalanine As Relay Amino Acid In Long‐Distance Electron Transfer, U. Wille, J. Nathanael, L. Gamon, M. Cordes, Paul R. Rablen, T. Bally, K. Fromm, B. Giese Feb 2018

Amide Neighbouring Group Effects In Peptides: Phenylalanine As Relay Amino Acid In Long‐Distance Electron Transfer, U. Wille, J. Nathanael, L. Gamon, M. Cordes, Paul R. Rablen, T. Bally, K. Fromm, B. Giese

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Nature uses proteins as medium for long‐distance electron transfer (ET) to carry out redox reactions in distant compartments. This ET occurs either by a single‐step superexchange or through a multi‐step charge hopping process, which uses side chains of amino acids as stepping stones. In this study we demonstrate that Phe can act as a relay amino acid for long‐distance electron hole transfer through peptides. The considerably increased susceptibility of the aromatic ring to oxidation is caused by the lone pairs of neighbouring amide carbonyl groups, which stabilize the Phe radical cation. This neighbouring amide group effect helps to better understand …

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Ruthenium Complexes Of The General Formula [Rucl 2 (Phox) 2 ] As Precatalysts In Propargylic Substitution Reactions, Negar Jourabchian, Kellsie Jurkowski, Eike Bauer Jan 2018

Ruthenium Complexes Of The General Formula [Rucl 2 (Phox) 2 ] As Precatalysts In Propargylic Substitution Reactions, Negar Jourabchian, Kellsie Jurkowski, Eike Bauer

Chemistry & Biochemistry Faculty Works

After activation by chloride abstraction utilizing NaBArF as an activator (BArF = tetrakis(3,5-bis(trifluoromethyl)phenyl)borate), a complex of the general formula [RuCl2 (PHOX)2 ] was utilized as a catalyst in propargylic substitution reactions, where PHOX is a phosphinooxazoline ligand. Oxygen and nitrogen-centered nucleophiles could be employed in the substitution of a propargylic acetate to obtain the corresponding propargylic substitution products in 87% to 9% isolated yields (45 °C, 16 h reaction time, toluene solvent, 1-2 mol% catalyst loading, 1-2 mol% activator).

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Identification Of 4-Isopropyl–Thiotropolone As A Novel Anti-Microbial: Regioselective Synthesis, Nmr Characterization, And Biological Evaluation, Mohamed Elagawany, Mohamed Elagawany, Lamees Hegazy, Feng Cao, Maureen Donlin, Nigam Rath, John Tavis, Bahaa Elgendy, Bahaa Elgendy Jan 2018

Identification Of 4-Isopropyl–Thiotropolone As A Novel Anti-Microbial: Regioselective Synthesis, Nmr Characterization, And Biological Evaluation, Mohamed Elagawany, Mohamed Elagawany, Lamees Hegazy, Feng Cao, Maureen Donlin, Nigam Rath, John Tavis, Bahaa Elgendy, Bahaa Elgendy

Chemistry & Biochemistry Faculty Works

We have synthesized and separated tosylated thujaplicin isomers for the first time, and elucidated their structures using 1D, 2D-NMR techniques and X-ray crystallography. The tosylated isomers were used to synthesize 4-isopropyl–thiotropolone and 6-isopropyl–thiotropolone in a regioselective manner. 1H and 13C Chemical shifts of synthesized isomers were fully assigned using several NMR experiments, and their isotropic magnetic shielding was calculated using the GIAO (Gauge Including Atomic Orbitals) method and the B3LYP def2-TZVPP level of theory. The calculated chemical shift values were in a good agreement with the experimental results. The biological activity of all synthesized compounds was evaluated against the fungal …

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First-Principles And Model Simulation Of All-Optical Spin Reversal, Thomas George, G.P. Zhang, Z. Babyak, Y. Xue, Y. Bai Oct 2017

First-Principles And Model Simulation Of All-Optical Spin Reversal, Thomas George, G.P. Zhang, Z. Babyak, Y. Xue, Y. Bai

Chemistry & Biochemistry Faculty Works

All-optical spin switching is a potential trailblazer for information storage and communication at an unprecedented fast rate free of magnetic fields. However, the current wisdom is largely based on semiempirical models of effective magnetic fields and heat pulses, so it is difficult to provide high-speed design protocols for actual devices. Here, we carry out a massively parallel first-principles and model calculation for 13 spin systems and magnetic layers, free of any effective field, to establish a simpler and alternative paradigm of laser-induced ultrafast spin reversal and to point out a path to a full-integrated photospintronic device. It is the interplay …

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Intramolecular Glycosylation, Alexei Demchenko, Xiao Jia Sep 2017

Intramolecular Glycosylation, Alexei Demchenko, Xiao Jia

Chemistry & Biochemistry Faculty Works

Carbohydrate oligomers remain challenging targets for chemists due to the requirement for elaborate protecting and leaving group manipulations, functionalization, tedious purification, and sophisticated characterization. Achieving high stereocontrol in glycosylation reactions is arguably the major hurdle that chemists experience. This review article overviews methods for intramolecular glycosylation reactions wherein the facial stereoselectivity is achieved by tethering of the glycosyl donor and acceptor counterparts.

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Is Perpendicular Magnetic Anisotropy Essential To All-Optical Ultrafast Spin Reversal In Ferromagnets?, Thomas George, Y. Bai, G.P. Zhang Sep 2017

Is Perpendicular Magnetic Anisotropy Essential To All-Optical Ultrafast Spin Reversal In Ferromagnets?, Thomas George, Y. Bai, G.P. Zhang

Chemistry & Biochemistry Faculty Works

All-optical spin reversal presents a new opportunity for spin manipulations, free of a magnetic field. Most of all-optical-spin-reversal ferromagnets are found to have a perpendicular magnetic anisotropy (PMA), but it has been unknown whether PMA is necessary for spin reversal. Here we theoretically investigate magnetic thin films with either PMA or in-plane magnetic anisotropy (IMA). Our results show that spin reversal in IMA systems is possible, but only with a longer laser pulse and within a narrow laser parameter region. Spin reversal does not show a strong helicity dependence where the left- and right-circularly polarized light lead to the identical …

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