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Articles 1 - 30 of 56
Full-Text Articles in Physical Sciences and Mathematics
Acrb Trimer Stability And Efflux Activity, Insight From Mutagenesis Studies, Linliang Yu, Wei Lu, Yinan Wei
Acrb Trimer Stability And Efflux Activity, Insight From Mutagenesis Studies, Linliang Yu, Wei Lu, Yinan Wei
Chemistry Faculty Publications
The multidrug transporter AcrB in Escherichia coli exists and functions as a homo-trimer. The assembly process of obligate membrane protein oligomers, including AcrB, remains poorly understood. In a previous study, we have shown that individual AcrB subunit is capable of folding independently, suggesting that trimerization of AcrB follows a three-stage pathway in which monomers first fold, and then assemble. Here we destabilized the AcrB trimer through mutating a single Pro (P223) in the protruding loop of AcrB, which drastically reduced the protein activity. We replaced P223 separately with five residues, including Ala, Val, Tyr, Asn, and Gly, and found that …
The Tetrafluoroborate Salt Of 4-Methoxybenzyl N-2-(Dimethylamino)Ethyl-N-Nitrosocarbamate: Synthesis, Crystal Structure And Dft Calculations, Helene Hedian, Vladimir Benin
The Tetrafluoroborate Salt Of 4-Methoxybenzyl N-2-(Dimethylamino)Ethyl-N-Nitrosocarbamate: Synthesis, Crystal Structure And Dft Calculations, Helene Hedian, Vladimir Benin
Chemistry Faculty Publications
The tetrafluoroborate salt of 4-methoxybenzyl N-2-(dimethylamino)ethyl-N-nitrosocarbamate was prepared in two steps, via the corresponding carbamate. Its crystal structure is monoclinic, space group P21/c. The unit cell dimensions are: a = 19.499(8) Å, b = 5.877(3) Å, c = 15.757(7) Å, α = 90°, β = 110.019(7)°, γ = 90°, V = 1696.5(12) Å3, Z = 4. The structure exhibits an unexpected, pseudo-gauche conformation with respect to the C2–C3 bond, due to a stabilizing hydrogen bond between the carbonyl oxygen (O1) and the hydrogen atom at the trialkylammonium center (H3n), with a distance between them of …
Maxwell's Equations, Part Iv, David W. Ball
Maxwell's Equations, Part Iv, David W. Ball
Chemistry Faculty Publications
In this column, we continue our explanation of Maxwell’s equations, the seminal classical explanation of electricity and magnetism (and, ultimately, light). For those of you new to the series, consider finding the last few appearances of this column to get caught up. Alternately, you should be able to find past columns on our website, www.spectroscopymag.com and look for “The Baseline” link. Words of warning: for my own reasons, the figures are being numbered sequentially through this series of columns, which is why the first figure in this column is numbered 26. Also, we’re going to get a bit mathematical. Unfortunately …
Analysis Of Volatile Organic Compounds In Virgin Coconut Oil And Their Sensory Attibutes, Fabian M. Dayrit, Jaclyn Elizabeth R. Santos, Bianca J. Villarino, Anthony R. Zosa
Analysis Of Volatile Organic Compounds In Virgin Coconut Oil And Their Sensory Attibutes, Fabian M. Dayrit, Jaclyn Elizabeth R. Santos, Bianca J. Villarino, Anthony R. Zosa
Chemistry Faculty Publications
The volatile compounds in the headspace of twenty-four commercial virgin coconut oil (VCO) samples prepared by different methods (i.e. expeller, centrifugation, and fermentation with and without heat) were analyzed by solid phase microextraction-gas chromatography mass spectrometry (SPME-GCMS). The following volatile organic compounds (VOCs) were identified: ethyl acetate, acetic acid, 2-pentanone, hexanal, n-octane, 2-heptanone, limonene, nonanal, octanoic acid, ethyl octanoate, δ-octalactone, ethyl decanoate, δ-decalactone, and dodecanoic acid. Fermentation-produced samples were found to have higher levels of acetic acid and free fatty acids in the headspace compared to VCO produced using the centrifuge and expeller methods. Descriptive sensory analysis of the VCO …
Opacity Of P(Mma-Maa)-Pmma Composite Latex System With Varying Maa Concentration, Gilbert U. Yu, Jerry T. Dy, Erwin P. Enriquez
Opacity Of P(Mma-Maa)-Pmma Composite Latex System With Varying Maa Concentration, Gilbert U. Yu, Jerry T. Dy, Erwin P. Enriquez
Chemistry Faculty Publications
Polymer composites of core-shell morphology are commonly used in the paint industry as opacity enhancer. These are usually made of block copolymer systems wherein the core is formed from a polymer that swells in the presence of a solvent and surrounded by a high glass transition polymeric shell. Thus, upon drying, the swollen regions turn into voids while leaving a hard shell. Here, composites based on poly(methyl methacrylate-butyl acrylate) [P(MMA-BuA)] (seed stage), poly(methyl methacrylate-methacrylic acid) [P(MMA-MAA)] (second stage), and poly(methyl methacrylate) [PMMA] (third stage) were synthesized through a multistage sequential emulsion polymerization and their opacity was investigated. The second stage …
Sweep, Step, Pulse, And Frequency-Based Techniques Applied To Protein Monolayer Electrochemistry At Nanoparticle Interfaces, Debbie S. Campbell-Rance, Tran T. Doan, Michael C. Leopold
Sweep, Step, Pulse, And Frequency-Based Techniques Applied To Protein Monolayer Electrochemistry At Nanoparticle Interfaces, Debbie S. Campbell-Rance, Tran T. Doan, Michael C. Leopold
Chemistry Faculty Publications
Protein monolayer electrochemistry (PME), a strategy using synthetic platforms to study the electron transfer (ET) properties of adsorbed proteins, has been successfully applied to proteins adsorbed at monolayer-protected gold cluster (MPCs) assembled films, an adsorption interface shown to be an effective alternative, compared to traditional self-assembled monolayer (SAM) films, for the immobilization and study of ET proteins. Within PME studies, cyclic voltammetry (CV) remains the most commonly applied electrochemical technique in spite of several limitations that occur when the sweep technique is used at either platform. In particular, CV for PME at MPC films results in analysis complications stemming from …
Synthesis And Antiproliferative Activity Of Some Steroidal Lactams, Yanmin Huang, Jianguo Cui, Sijing Chen, Chunfang Gan, Aimin Zhou
Synthesis And Antiproliferative Activity Of Some Steroidal Lactams, Yanmin Huang, Jianguo Cui, Sijing Chen, Chunfang Gan, Aimin Zhou
Chemistry Faculty Publications
Using cholesterol as starting material, a series of 6-substituted-3-aza-A-homo-3-oxycholestanes and 6-substituted-4-aza-A-homo-3-oxycholestanes were synthesized by the oxidation, reduction, oximation, Beckman rearrangement and condensation reaction. These synthesized compounds displayed a distinct cytotoxicity against MGC 7901, HeLa and SMMC 7404 cancer cells. Our results revealed that the structures of functional groups at position-6 on the steroidal ring are crucial for the IC50 value of antiproliferative activities of these compounds and the cytotoxic activity against MGC 7901 and SMMC 7404 cells was not significantly different between 4-N-lactams and 3-N-lactams when its 6-substituted group was a carbonyl or a hydroximino, but all 3-N-lactams showed a …
Templated Synthesis Of Glycoluril Hexamer And Monofunctionalized Cucurbit[6]Uril Derivatives, Derick Lucas, Tsuyoshi Minami, Greg Iannuzzi, Liping Cao, James B. Wittenberg, Pavel Anzenbacher Jr., Lyle Isaacs
Templated Synthesis Of Glycoluril Hexamer And Monofunctionalized Cucurbit[6]Uril Derivatives, Derick Lucas, Tsuyoshi Minami, Greg Iannuzzi, Liping Cao, James B. Wittenberg, Pavel Anzenbacher Jr., Lyle Isaacs
Chemistry Faculty Publications
We report that the p-xylylenediammonium ion (11) acts as a template in the cucurbit[n]uril forming reaction that biases the reaction toward the production of methylene bridged glycoluril hexamer (6C) and bis-nor-seco-CB [10]. Hexamer 6C is readily available on the gram scale by a one step synthetic procedure that avoids chromatography. Hexamer 6C undergoes macrocylization. with (substituted) phthalaldehydes 12,14,.15, and 18-in 9 M H2SO4 or concd HCl at room temperature to deliver monofunctionalized CB[6] derivatives 13,16,17, and 19 that are poised for further functionalization reactions: The kinetics of the macrocyclization reaction between hexamer and formaldehyde or phthalaldehyde depends on the presence …
Optical Properties Of Antiferroelectric Cs2nb4o11: Absorption Spectra And First-Principles Calculations, H. L. Liu, C. R. Huang, G. F. Luo, Wai-Ning Mei
Optical Properties Of Antiferroelectric Cs2nb4o11: Absorption Spectra And First-Principles Calculations, H. L. Liu, C. R. Huang, G. F. Luo, Wai-Ning Mei
Chemistry Faculty Publications
We report a joint experimental and theoretical investigation of the optical properties of Cs2Nb4O11. In room temperature optical absorption spectra, we found a direct gap about 3.5560.05 eV and charge transfer excitations at about 4.96 and 6.08 eV, which are in good agreement with the first-principles calculations. Upon passing through the 165 C antiferroelectric to paraelectric phase transition, the peak energies of two charge transfer bands display almost no temperature dependence, yet they become even broader and exhibit enhanced oscillator strength. We infer this intriguing behavior as the manifestation of Nb cation distortions due to the charge-lattice interaction.
Photoinduced Electron Transfer In Naphthalimide-Pyridine Systems: Effect Of Proton Transfer On Charge Recombination Efficiencies, Pavel Kucheryavy, Renat Khatmullin, Ekaterina Mirzakulova, Dapeng Zhou, Ksenija D. Glusac
Photoinduced Electron Transfer In Naphthalimide-Pyridine Systems: Effect Of Proton Transfer On Charge Recombination Efficiencies, Pavel Kucheryavy, Renat Khatmullin, Ekaterina Mirzakulova, Dapeng Zhou, Ksenija D. Glusac
Chemistry Faculty Publications
We studied the effect of proton-coupled electron transfer on lifetimes of the charge-separated radicals produced upon light irradiation of the thiomethyl-naphthalimide donor SMe-NI-H in the presence of nitro-cyano-pyridine acceptor (NO(2)-CN-PYR). The dynamics of electron and proton transfer were studied using femtosecond pump-probe spectroscopy in the UV/vis range. We find that the photoinduced electron transfer between excited SMe-NI-H and NO(2)-CN-PYR occurs with a rate of 1.1 x 10(9) s(-1) to produce radical ions SMe-NI-H(center dot+) and NO(2)-CN-PYR(center dot-). These initially produced radical ions in a solvent cage do not undergo a proton transfer, possibly due to unfavorable geometry between N-H proton …
Noncanonical Hydrogen Bonding In Nucleic Acids. Benchmark Evaluation Of Key Base-Phosphate Interactions In Folded Rna Molecules Using Quantum-Chemical Calculations And Molecular Dynamics Simulations, Marie Zgarbova, Petr Jurecka, Pavel Banas, Michal Otyepka, Judit E. Sponer, Neocles B. Leontis, Craig L. Zirbel, Jiri Sponer
Noncanonical Hydrogen Bonding In Nucleic Acids. Benchmark Evaluation Of Key Base-Phosphate Interactions In Folded Rna Molecules Using Quantum-Chemical Calculations And Molecular Dynamics Simulations, Marie Zgarbova, Petr Jurecka, Pavel Banas, Michal Otyepka, Judit E. Sponer, Neocles B. Leontis, Craig L. Zirbel, Jiri Sponer
Chemistry Faculty Publications
RNA molecules are stabilized by a wide range of non canonical interactions that are not present in DNA. Among them, the recently classified base phosphate (BPh) interactions belong to the most important ones. Twelve percent of nucleotides in the ribosomal crystal structures are involved in BPh interactions. BPh interactions are highly conserved and provide major constraints on RNA sequence evolution. Here we provide assessment of the energetics of BPh interactions using MP2 computations extrapolated to the complete basis set of atomic orbitals and corrected for higher-order electron correlation effects. The reference computations are compared with DFT-D and DFT-D3 approaches, the …
Optical And Electrochemical Properties Of Multi-Layer Polyelectrolyte Thin Films Incorporating Spherical, Gold Colloid Nanomaterials, Tran T. Doan, Robert W. Day, Michael C. Leopold
Optical And Electrochemical Properties Of Multi-Layer Polyelectrolyte Thin Films Incorporating Spherical, Gold Colloid Nanomaterials, Tran T. Doan, Robert W. Day, Michael C. Leopold
Chemistry Faculty Publications
Polyelectrolyte multilayer (PEM) films incorporating various types of spherical, gold nanomaterials (NMs) were investigated to assess the existence of electrochemical and/or optical signal enhancement effects directly attributable to embedded NMs and the relationship of these effects to film structure and composition. Specifically, electrostatically assembled films of cationic poly-L-lysine (PLL) and anionic poly(4-styrene sulfonate) (PSS) incorporating one of four types of spherical, gold colloid NMs were constructed on 3-(aminopropyl)trimethoxysilane (3-APTMS)-modified glass substrates for optical studies or 11-mercaptoundecanoic (MUA)-modified gold electrodes for electrochemical studies. The NMs inserted into the PEM films include citrate-stabilized gold nanoparticles, thioctic acid-stabilized gold nanoparticles (TAS-NPs), MUA-modified monolayer …
Exploring The Roles Of Nucleobase Desolvation And Shape Complementarity During The Misreplication Of O6-Methylguanine, Delia Chavarria, Andrea Ramos Serrano, Ichiro Hirao, Anthony J. Berdis
Exploring The Roles Of Nucleobase Desolvation And Shape Complementarity During The Misreplication Of O6-Methylguanine, Delia Chavarria, Andrea Ramos Serrano, Ichiro Hirao, Anthony J. Berdis
Chemistry Faculty Publications
O6-methylguanine is a miscoding DNA lesion arising from the alkylation of guanine. This report uses the bacteriophage T4 DNA polymerase as a model to probe the roles hydrogen-bonding interactions, shape/size, and nucleobase desolvation during the replication of this miscoding lesion. This was accomplished by using transient kinetic techniques to monitor the kinetic parameters for incorporating and extending natural and non-natural nucleotides. In general, the efficiency of nucleotide incorporation does not depend on the hydrogen-bonding potential of the incoming nucleotide. Instead, nucleobase hydrophobicity and shape complementarity appear to be the preeminent factors controlling nucleotide incorporation. In addition, shape complementarity plays a …
Design And Synthesis Of A Biotinylated Probe Of Cox-2 Inhibitor Nimesulide Analog Jcc76, Bo Zhong, Rati Lama, Kerri M. Smith, Yan Xu, Bin Su
Design And Synthesis Of A Biotinylated Probe Of Cox-2 Inhibitor Nimesulide Analog Jcc76, Bo Zhong, Rati Lama, Kerri M. Smith, Yan Xu, Bin Su
Chemistry Faculty Publications
JCC76 is a derivative of cyclooxygenase-2(COX-2) selective inhibitor nimesulide and exhibits potent anti-breast cancer activity. It selectively induces apoptosis of Her2 positive breast cancer cells. However, the specific molecular targets of JCC76 still remain unclear, which significantly withdraw the further drug development of JCC76. To identify the molecular targets of JCC76, a six carbon linker and biotin conjugated JCC76 probe was designed and synthesized. The anti-proliferation activity of the probe and its analogs was evaluated.
Synthesis Of N-Acyl-N,O-Acetals From N-Aryl Amides And Acetals In The Presence Of Tmsotf, C. Wade Downey, Alan S. Fleisher, James T. Rague, Chelsea L. Safran, Megan E. Venable, Robert D. Pike
Synthesis Of N-Acyl-N,O-Acetals From N-Aryl Amides And Acetals In The Presence Of Tmsotf, C. Wade Downey, Alan S. Fleisher, James T. Rague, Chelsea L. Safran, Megan E. Venable, Robert D. Pike
Chemistry Faculty Publications
Secondary amides undergo in situ silyl imidate formation mediated by TMSOTf and an amine base, followed by addition to acetal acceptors to provide N-acyl-N,O-acetals in good yields. An analogous, high-yielding reaction is observed with 2-mercaptothiazoline as the silyl imidate precursor. Competing reduction of the acetal to the corresponding methyl ether via transfer hydrogenation can be circumvented by the replacement of i-Pr2NEt with 2,6-lutidine under otherwise identical reaction conditions.
Energy Transfer From Fluorescent Proteins To Metal Nanoparticles, Suraj Saraswat, Anil Desireddy, Desheng Zheng, Lijun Guo, H. Peter Lu, Terry P. Bigioni, Dragan Isailovic
Energy Transfer From Fluorescent Proteins To Metal Nanoparticles, Suraj Saraswat, Anil Desireddy, Desheng Zheng, Lijun Guo, H. Peter Lu, Terry P. Bigioni, Dragan Isailovic
Chemistry Faculty Publications
Energy transfer plays a significant role in numerous chemical, physical, and biological processes. While the use of fluorescent proteins in Forster resonance energy transfer (FRET) studies of biomolecules is common, energy transfer between fluorescent proteins and inorganic nanoparticles has not been explored in detail. In this study, energy transfer from fluorescent phycobiliproteins to noble metal nanoparticles was analyzed. Solutions of B-phycoerythrin (B-PE) were mixed with colloidal Au and Ag nanoparticles and were characterized by steady-state and time-resolved fluorescence spectroscopy to determine the magnitude and mechanism of the energy transfer. It was found that the protein fluorescence was quenched after the …
Green Synthesis Of Polycyclic Benzimidazole Derivatives And Organic Semiconductors, Masashi Mamada, Cesar Perez-Bolivar, Pavel Anzenbacher Jr.
Green Synthesis Of Polycyclic Benzimidazole Derivatives And Organic Semiconductors, Masashi Mamada, Cesar Perez-Bolivar, Pavel Anzenbacher Jr.
Chemistry Faculty Publications
Polycyclic benzimidazole derivatives, an important class of compounds in organic electronics and photovoltaics, were prepared using a solvent-free "green" process based on heating carboxylic acid anhydrides and arylene diamines in the presence of zinc acetate in the solid state. Products were isolated and purified directly by train sublimation of the crude reaction mixtures. The reaction conditions were optimized using various carboxylic acid anhydrides. Optical and electrochemical properties of these materials are also described.
Probing Single-Molecule Enzyme Active-Site Conformational State Intermittent Coherence, Yufan He, Yue Li, Saptarshi Mukherjee, Yan Wu, Honggao Yan, H. Peter Lu
Probing Single-Molecule Enzyme Active-Site Conformational State Intermittent Coherence, Yufan He, Yue Li, Saptarshi Mukherjee, Yan Wu, Honggao Yan, H. Peter Lu
Chemistry Faculty Publications
The relationship between protein conformational dynamics and enzymatic reactions has been a fundamental focus in modern enzymology. Using single-molecule fluorescence resonance energy transfer (FRET) with a combined statistical data analysis approach, we have identified the intermittently appearing coherence of the enzymatic conformational state from the recorded single-molecule intensity-time trajectories of enzyme 6-hydroxymethyl-7,8-dihydropterin pyrophosphokinase (HPPK) in catalytic reaction. The coherent conformational state dynamics suggests that the enzymatic catalysis involves a multistep conformational motion along the coordinates of substrate-enzyme complex formation and product releasing, presenting as an extreme dynamic behavior intrinsically related to the time bunching effect that we have reported previously. …
Determination Of Hexamethylene Bisacetamide, An Antineoplastic Compound, In Mouse And Human Plasma By Lc–Ms/Ms, Kerri M. Smith, Wannarasmi Ketchart, Xiang Zhou, Monica M. Montano, Yan Xu
Determination Of Hexamethylene Bisacetamide, An Antineoplastic Compound, In Mouse And Human Plasma By Lc–Ms/Ms, Kerri M. Smith, Wannarasmi Ketchart, Xiang Zhou, Monica M. Montano, Yan Xu
Chemistry Faculty Publications
Hexamethylene bisacetamide (HMBA) is a polar compound which has recently been discovered to have antineoplastic activity by up-regulating the expression of an endogenous antiproliferative breast cancer protein, HEXIM1 (hexamethylene bisacetamide inducible protein 1) in vivo. HMBA has been shown in the past to induce terminal differentiation in multiple leukemia types at a concentration of 2–5 mM, but its phase I and II clinical trials were largely unsuccessful due to serious side effects (notably, thrombocytopenia) with dose escalation. In this work, a sensitive and simple LC–MS/MS method for direct determination of HMBA in mouse and human plasma is described. Plasma samples …
In Vitro And In Vivo Effects Of A Cyclooxygenase-2 Inhibitor Nimesulide Analog Jcc76 In Aromatase Inhibitors-Insensitive Breast Cancer Cells, Bo Zhong, Xiaohan Cai, Xing Yi, Aimin Zhou, Shiuan Chen, Bin Su
In Vitro And In Vivo Effects Of A Cyclooxygenase-2 Inhibitor Nimesulide Analog Jcc76 In Aromatase Inhibitors-Insensitive Breast Cancer Cells, Bo Zhong, Xiaohan Cai, Xing Yi, Aimin Zhou, Shiuan Chen, Bin Su
Chemistry Faculty Publications
Third generation aromatase inhibitors (AIs) are more effective than tamoxifen in the treatment of estrogen receptor (ER) positive breast cancer. However, long-term use of AIs commonly results in resistance. We examined whether compound JCC76{Cyclohexanecarboxylic acid [3-(2,5-dimethyl-benzyloxy)-4-(methanesulfonyl-methyl-amino)-phenyl]-amide}, an analog of Cyclooxygenase-2 (COX-2) inhibitor nimesulide, can inhibit the growth of AI-insensitive breast cancer cells and the mechanisms by which the compound affects cell proliferation. LTEDaro (long term estrogen deprived MCF-7aro cell) cells, which are a model for AI resistance, were used in this study. JCC76 effectively inhibited LTEDaro cell proliferation with an IC50 of 2.75 ± 0.31 μM. Further investigations reveal that …
Webfr3d-A Server For Finding, Aligning And Analyzing Recurrent Rna 3d Motifs, Craig L. Zirbel, Neocles B. Leontis, Anton I. Petrov
Webfr3d-A Server For Finding, Aligning And Analyzing Recurrent Rna 3d Motifs, Craig L. Zirbel, Neocles B. Leontis, Anton I. Petrov
Chemistry Faculty Publications
WebFR3D is the on-line version of 'Find RNA 3D' (FR3D), a program for annotating atomic-resolution RNA 3D structure files and searching them efficiently to locate and compare RNA 3D structural motifs. WebFR3D provides on-line access to the central features of FR3D, including geometric and symbolic search modes, without need for installing programs or downloading and maintaining 3D structure data locally. In geometric search mode, WebFR3D finds all motifs similar to a user-specified query structure. In symbolic search mode, WebFR3D finds all sets of nucleotides making user-specified interactions. In both modes, users can specify sequence, sequence-continuity, base pairing, base-stacking and other …
Negative Polaron And Triplet Exciton Diffusion In Organometallic "Molecular Wires", Julia M. Keller, Ksenija D. Glusac, Evgeny O. Danilov, Sean Mcilroy, Paiboon Sreearuothai, Andrew R. Cook, Hui Jiang, John R. Miller, Kirk S. Schanze
Negative Polaron And Triplet Exciton Diffusion In Organometallic "Molecular Wires", Julia M. Keller, Ksenija D. Glusac, Evgeny O. Danilov, Sean Mcilroy, Paiboon Sreearuothai, Andrew R. Cook, Hui Jiang, John R. Miller, Kirk S. Schanze
Chemistry Faculty Publications
The dynamics of negative polaron and triplet exciton transport within a series of monodisperse platinum (Pt) acetylide oligomers is reported. The oligomers consist of Pt-acetylide repeats, [PtL(2)-C C-ph-C C-](n) (where L = PBu(3) and Ph = 1,4-phenylene, n = 2, 3, 6, and 10), capped with naphthalene diimide (NDI) end groups. The Pt acetylide segments are electro- and photoactive, and they serve as conduits for transport of electrons (negative polaron) and triplet excitons. The NDI end groups are relatively strong acceptors, serving as traps for the carriers. Negative polaron transport is studied by using pulse radiolysis/transient absorption at the Brookhaven …
Wavepacket Motion Via A Conical Intersection In The Photochemistry Of Aqueous Transition-Metal Dianions, Igor L. Zheldakov, Mikhail N. Ryazantsev, Alexander N. Tarnovsky
Wavepacket Motion Via A Conical Intersection In The Photochemistry Of Aqueous Transition-Metal Dianions, Igor L. Zheldakov, Mikhail N. Ryazantsev, Alexander N. Tarnovsky
Chemistry Faculty Publications
The photochemical reaction paths in aqueous PtBr(6)(2-) and OsBr(6)(2-) have been studied by femtosecond broad-band pump probe spectroscopy supported by CASPT2 and DFT/TDDFT calculations. These paths lead to the separation of negative charges and propagate through distortions of nascent, penta-coordinated metal fragments caused by Jahn-Teller C(4v) and D(3h) conical intersections (CIs), respectively. Within 150 fs following 420 nm excitation of PtBr(6)(2-), the molecule undergoes internal conversion and intersystem crossing into the dissociative lowest triplet excited (3)T(1g) state, loses a ligand, and relaxes via the C(4v) CI to the nearly trigonal bipyramid (3)PtBr(5)(-) product in the triplet state. Direct 530 nm …
Application Of Raman Spectroscopy To Lubricants, Lubricated Surfaces And Lubrication Phenomena, David W. Johnson
Application Of Raman Spectroscopy To Lubricants, Lubricated Surfaces And Lubrication Phenomena, David W. Johnson
Chemistry Faculty Publications
Recent advances in lasers and detector technologies and the development of low-cost instruments and fiber-optic probes have brought about an explosion in the lubrication systems being studied by Raman spectroscopy. This article provides examples of the use of Raman spectroscopy in the study of lubrication phenomena, including the characterization of liquid lubricants, lubricant additives, and solid lubricants; the study of vapor-phase lubrication; and the use of coated nanoparticles as lubricants.
Maxwell's Equations, Part Ii, David W. Ball
Maxwell's Equations, Part Ii, David W. Ball
Chemistry Faculty Publications
This is the second part of a multi-part production on Maxwell’s equations of electromagnetism. The ultimate goal is a definitive explanation of these four equations; readers will be left to judge how definitive it is. A note: for certain reasons, figures are being numbered sequentially throughout this series, which is why the first figure in this column is numbered 8. I hope this does not cause confusion. Another note: this is going to get a bit mathematical. It can’t be helped: models of the physical universe, like Newton’s second law F = ma, are based in math. So are Maxwell’s …
Fast Excited-State Deactivation In N(5)-Ethyl-4a-Hydroxyfiavin Pseudobase, Dapeng Zhou, Ekaterina Mirzakulova, Renat Khatmullin, Igor Schapiro, Massimo Olivucci, Ksenija D. Glusac
Fast Excited-State Deactivation In N(5)-Ethyl-4a-Hydroxyfiavin Pseudobase, Dapeng Zhou, Ekaterina Mirzakulova, Renat Khatmullin, Igor Schapiro, Massimo Olivucci, Ksenija D. Glusac
Chemistry Faculty Publications
We present a study of the excited-state behavior of N(5)-ethyl-4a-hydroxyflavin (Et-FlOH), a model compound for bacterial bioluminescence. Using femtosecond pump-probe spectroscopy, we found that the Et-FlOH excited state exhibits multiexponential dynamics, with the dominant decay component having a 0.5 ps lifetime. Several possible mechanisms for fast excited-state decay in Et-FlOH were considered: (i) excited-state deprotonation of the -OH proton, (ii) thermal deactivation via (1)n,pi* -> (1)pi,pi* conical intersection, and (iii) excited-state release of OH(-) ion. These mechanisms were excluded based on transient absorption studies of two model compounds (N(5)-ethyl-4a-methoxyflavin, Et-FlOMe, and N(5)-ethyl-flavinium ion, Et-Fl(+)) and based on the results of …
Heteroepitaxial Growth Of Colloidal Nanocrystals Onto Substrate Films Via Hot-Injection Routes, Krishna P. Acharya, Elena Khon, Timothy O’Conner, Ian Nemitz, Anna Klinkova, Rony S. Khnayzer, Pavel Anzenbacher Jr., Mikhail Zamkov
Heteroepitaxial Growth Of Colloidal Nanocrystals Onto Substrate Films Via Hot-Injection Routes, Krishna P. Acharya, Elena Khon, Timothy O’Conner, Ian Nemitz, Anna Klinkova, Rony S. Khnayzer, Pavel Anzenbacher Jr., Mikhail Zamkov
Chemistry Faculty Publications
Hot-injection synthesis of colloidal nanocrystals (NCs) in a substrate-bound form is demonstrated. We show that polycrystalline films submerged into hot organic solvents can nucleate the heteroepitaxial growth of semiconductor NCs, for which the ensuing lattice quality and size distribution are on the par with those of isolated colloidal nanoparticles. This strategy is demonstrated by growing lead chalcogenide NCs directly onto solvent-submerged TiO(2) substrates. The resulting PbX/VTiO(2) (X = S, Se, Te) nanocomposites exhibit heteroepitaxial interfaces between lead chalcogenide and oxide domains and show an efficient separation of photoinduced charges, deployable for light-harvesting applications. The extendibility of the present method to …
Physico-Chemical And Microbiological Parameters In The Deterioration Of Virgin Coconut Oil, Ian Ken D. Dimzon, Melodina F. Valde, Jaclyn Elizabeth R. Santos, Mark Joseph Garrovillas, Henson M. Dejarme, Jo Margarette W. Remollo, Fabian M. Dayrit
Physico-Chemical And Microbiological Parameters In The Deterioration Of Virgin Coconut Oil, Ian Ken D. Dimzon, Melodina F. Valde, Jaclyn Elizabeth R. Santos, Mark Joseph Garrovillas, Henson M. Dejarme, Jo Margarette W. Remollo, Fabian M. Dayrit
Chemistry Faculty Publications
The deterioration of virgin coconut oil (VCO) due to physico-chemical oxidation and hydrolysis and microbiological processes was studied. The physico-chemical oxidation of VCO in the air at room temperature was negligible. Oxidation of VCO was observed only in the presence of air, UV radiation, ferric ion (Fe3+), and high free fatty acid (FFA) content. Chemical hydrolysis was performed at varying moisture levels and temperatures. The rate of hydrolysis to produce FFAs was measured using 31P NMR under conditions of saturated water (0.22%) and 80°C was found to be 0.066 µmol/g-hr (expressed as lauric acid). At 0.084% moisture and 80°C, the …
The Exonuclease Activity Of Hpmc2 Is Required For Transcriptional Regulation Of The Qr Gene And Repair Of Estrogen-Induced Abasic Sites, N. Krishnamurthy, C. R. Ngam, Anthony J. Berdis, M. M. Montano
The Exonuclease Activity Of Hpmc2 Is Required For Transcriptional Regulation Of The Qr Gene And Repair Of Estrogen-Induced Abasic Sites, N. Krishnamurthy, C. R. Ngam, Anthony J. Berdis, M. M. Montano
Chemistry Faculty Publications
We have previously reported that the expression of antioxidative stress enzymes is upregulated by trans-hydroxytamoxifen (TOT) in breast epithelial cell lines providing protection against estrogen-induced DNA damage. This regulation involves Estrogen Receptor β (ERβ) recruitment to the Electrophile Response Element (EpRE) and a novel protein, human homolog of Xenopus gene which Prevents Mitotic Catastrophe (hPMC2). We have also demonstrated that ERβ and hPMC2 are required for TOT-dependent recruitment of poly (ADP-ribose) polymerase 1 (PARP-1) and Topoisomerase IIβ (Topo IIβ) to the EpRE. Sequence analysis reveals that the C-terminus of hPMC2 encodes a putative exonuclease domain. Using in vitro kinetic assays, …
Profiling Sterols In Cerebrotendinous Xanthomatosis: Utility Of Girard Derivatization And High Resolution Exact Mass Lc-Esi-Msn Analysis, Andrea E. Debarber, Yana Sandlers, Anuradha S. Pappu, Louise S. Merkens, P. Barton Duell, Steven R. Lear, Sandra K. Erickson, Robert D. Steiner
Profiling Sterols In Cerebrotendinous Xanthomatosis: Utility Of Girard Derivatization And High Resolution Exact Mass Lc-Esi-Msn Analysis, Andrea E. Debarber, Yana Sandlers, Anuradha S. Pappu, Louise S. Merkens, P. Barton Duell, Steven R. Lear, Sandra K. Erickson, Robert D. Steiner
Chemistry Faculty Publications
In this study we profile free 3-oxo sterols present in plasma from patients affected with the neurodegenerative disorder of sterol and bile acid metabolism cerebrotendinous xanthomatosis (CTX), utilizing a combination of charge-tagging and LC-ESI-MSn performed with an LTQ-Orbitrap Discovery instrument. In addition, we profile sterols in plasma from 24-month-old cyp27A1 gene knockout mice lacking the enzyme defective in CTX. Charge-tagging was accomplished by reaction with cationic Girard's P (GP) reagent 1-(carboxymethyl) pyridinium chloride hydrazide, an approach uniquely suited to studying the 3-oxo sterols that accumulate in CTX, as Girard's reagent reacts with the sterol oxo moiety to form charged hydrazone …