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https://www.readbyqxmd.com/read/28441485/new-insights-into-the-reaction-paths-of-4-carboxybenzophenone-triplet-with-oligopeptides-containing-n-and-c-terminal-methionine-residues
#1
Piotr Filipiak, Krzysztof Bobrowski, Gordon L Hug, Dariusz Pogocki, Christian Schoneich, Bronislaw Marciniak
The oxidation processes of L-Met-(Pro)n-L-Met peptides that contain two Met residues located on the N and C termini and separated by a defined number (n = 0 - 4) of proline residues were investigated in aqueous solutions using laser flash photolysis. The use of such peptides allowed for distance control between the sulfur atoms located in the side chains of the Met residues. Interactions between side chains of the Met residues were probed by the observation of transients with σ*-type 2c-3e (S∴S)(+), (S∴N)(+) and/or (S∴O)(+)-bonds as well as of α-(alkylthio)alkyl radicals (αS)...
April 25, 2017: Journal of Physical Chemistry. B
https://www.readbyqxmd.com/read/28441017/equilibration-of-micelle-polyelectrolyte-complexes-mechanistic-differences-between-static-and-annealed-charge-distributions
#2
Jennifer E Laaser, Michael McGovern, Yaming Jiang, Elise Lohmann, Theresa M Reineke, David C Morse, Kevin D Dorfman, Timothy P Lodge
The role of charge density and charge annealing in polyelectrolyte complexation was investigated through systematic comparison of two micelle-polyelectrolyte systems. First, poly(dimethylaminoethyl methacrylate)-block-poly(styrene) (PDMAEMA-b-PS) micelles were complexed with poly(styrenesulfonate) (PSS) at pH values above and below the pKa of PDMAEMA to investigate the role of charge annealing in the complexation process. Second, complexes of poly(DMAEMA-stat-oligo(ethylene glycol) methyl ether methacrylate)-block-poly(styrene) (P(DMAEMA-stat-OEGMA)-b-PS) micelles with the same PSS at low pH were used to investigate how the complexation process differs when the charged sites are in fixed positions along the polymer chains...
April 25, 2017: Journal of Physical Chemistry. B
https://www.readbyqxmd.com/read/28436660/efficient-charge-separation-of-cold-charge-transfer-states-in-organic-solar-cells-through-incoherent-hopping
#3
Stavros Athanasopoulos, Steffen Tscheuschner, Heinz Bässler, Anna Köhler
We demonstrate that efficient and nearly field-independent charge separation of electron-hole pairs in organic planar heterojunction solar cells can be described by an incoherent hopping mechanism. Using kinetic Monte Carlo simulations that include the effect of on-chain delocalization as well as entropic contributions, we simulate the dissociation of the charge-transfer state in polymer-fullerene bilayer solar cells. The model further explains experimental results of almost field independent charge separation in bilayers of molecular systems with fullerenes and provides important guidelines at the molecular level for maximizing the efficiencies of organic solar cells...
April 26, 2017: Journal of Physical Chemistry Letters
https://www.readbyqxmd.com/read/28433173/dye-adsorption-and-photo-induced-recycling-of-hydroxypropyl-cellulose-molybdenum-disulfide-composite-hydrogels
#4
Pengpeng Chen, Xiaoyan Liu, Rundong Jin, Wangyan Nie, Yifeng Zhou
A novel environmental friendly dye adsorbent composited of hydroxypropyl cellulose (HPC) and molybdenum disulfide (MoS2) were fabricated, which can be recycled and reused by illumination due to the photo-catalytic properties of MoS2. In order to promote a more homogeneous dispersion of MoS2 nanosheets in HPC, MoS2 was functionalized with HPC chains through esterification. The successful functionalization of MoS2 was confirmed by FTIR, XRD, XPS characterizations. The morphologies of the HPC and HPC-MoS2/HPC hydrogels were compared by SEM...
July 1, 2017: Carbohydrate Polymers
https://www.readbyqxmd.com/read/28433021/to-kink-or-not-a-search-for-long-chain-cumulenones-using-microwave-spectral-taxonomy
#5
Michael C McCarthy, Luyao Zou, Marie-Aline Martin-Drumel
A systematic search for carbon-chain cumulenones beyond H2C4O has been undertaken using microwave spectral taxonomy in combination with a pulsed jet discharge source. No evidence was found for the C2υ isomer of H2C5O or its longer derivatives, but HC(O)C4H, the longer variant of propynal, HC(O)CCH, was identified instead. Its rotational and leading centrifugal distortion constants have been derived to high accuracy from detection of both a- and b-type lines; those below 40 GHz were measured using a Fabry-Perot cavity, while lines between 40 and 72 GHz were recorded by double resonance techniques...
April 21, 2017: Journal of Chemical Physics
https://www.readbyqxmd.com/read/28426224/quantitative-analysis-of-polymer-brush-formation-kinetics-using-quartz-crystal-microbalance-viscoelasticity-of-polymer-brush
#6
Hirokazu Tanoue, Norifumi L Yamada, Kohzo Ito, Hideaki Yokoyama
Polymer brush formation kinetics was measured by quartz crystal microbalance (QCM). In the QCM measurement anomalous complex frequency shift as a function of graft density was observed: dissipation rate shift ΔΓ first increased, showed a peak and then decreased despite the graft density of the polymer brush was increasing monotonically. We calculated the shear modulus of the brush layer from the measured complex frequency shift and revealed that the peak of ΔΓ described the crossover from a viscous brush layer to elastic brush layer...
April 20, 2017: Langmuir: the ACS Journal of Surfaces and Colloids
https://www.readbyqxmd.com/read/28426214/calix-5-arene-through-the-annulus-threading-of-dialkylammonium-guests-weakly-paired-to-the-tfpb-anion
#7
Margherita De Rosa, Carmen Talotta, Carmine Gaeta, Annunziata Soriente, Placido Neri, Sebastiano Pappalardo, Giuseppe Gattuso, Anna Notti, Melchiorre F Parisi, Ilenia Pisagatti
The through-the-annulus threading of calix[5]arene penta-O-ethers by dialkylammonium cations coupled to the loosely coordinating superweak TFPB- anion has been successfully accomplished. 1H NMR titration data show that the preorganization of the calix[5]arene scaffold leads to great thermodynamic stability of the pseudorotaxane complexes as well as to a favorable kinetic of threading. Accordingly, calix[5]arene 1c, bearing tert-butyl groups at the wide rim, was threaded by all the cations under study (with the exception of the dibenzylammonium 2b+) more tightly than the other derivatives under investigation (Kas up to 2...
April 20, 2017: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28421451/mathematical-model-of-polymerase-chain-reaction-with-temperature-dependent-parameters
#8
D G Sochivko, A A Fedorov, Y I Alekseev, V E Kurochkin, M V Dubina
The course of the real-time polymerase chain reaction (PCR) is determined by the temperature dependence of the kinetics of the component reactions, particularly the DNA strand hybridization. To investigate the effect of thermal processes on the reaction behavior, a mathematical model in which the variable rate constant of dissociation of "primer-single strand" complexes depends on temperature was proposed. The reaction medium temperature, which depends on time, was also introduced into the model. The proposed model of real-time PCR makes it possible to analyze different aspects of the reaction, which are important for the development of instruments and reagents for PCR...
January 2017: Doklady. Biochemistry and Biophysics
https://www.readbyqxmd.com/read/28417361/methods-for-determining-glycosyltransferase-kinetics
#9
Maria Ngo, Michael D L Suits
Glycosyltransferases are a class of biosynthetic enzymes that transfer individual activated monosaccharide units to specific acceptors. Colorimetric assays using the detection of released products such as para-nitrophenol and coupled assays for inorganic phosphate detection allow for convenient and quantifiable kinetic characterization. These techniques may be applied to determine the enzymatic activity of glycosyltransferases by indirectly measuring the transfer of nucleotide-activated donor carbohydrate units to various cognate acceptor molecules...
2017: Methods in Molecular Biology
https://www.readbyqxmd.com/read/28417356/a-low-volume-parallel-copper-bicinchoninic-acid-bca-assay-for-glycoside-hydrolases
#10
Gregory Arnal, Mohamed A Attia, Jathavan Asohan, Harry Brumer
The quantitation of liberated reducing sugars by the copper-bicinchoninic acid (BCA) assay provides a highly sensitive method for the measurement of glycoside hydrolase (GH) activity, particularly on soluble polysaccharide substrates. Here, we describe a straightforward method adapted to low-volume polymerase chain reaction (PCR) tubes which enables the rapid, parallel determination of GH kinetics in applications ranging from initial activity screening and assay optimization, to precise Michaelis-Menten analysis...
2017: Methods in Molecular Biology
https://www.readbyqxmd.com/read/28415262/thermophoretic-force-on-nanocylinders-in-the-free-molecule-regime
#11
Jun Wang, Shuang Luo, Guodong Xia
We theoretically investigate the thermophoresis of nanocylinders in the free molecule regime, wherein the nonrigid-body effect is taken into account. The analytical formulas of the thermophoretic forces on cylinders suspended in both simple gases and binary gas mixtures are derived for the two limiting collision models, i.e., specular and diffuse scatterings, based on the gas kinetic theory. In the limit of the rigid-body collision, the expressions can be reduced to the theoretical results of Garcia-Ybarra and Rosner [AIChE J...
March 2017: Physical Review. E
https://www.readbyqxmd.com/read/28415183/fluctuations-in-hertz-chains-at-equilibrium
#12
Michelle Przedborski, Surajit Sen, Thad A Harroun
We examine the long-term behavior of nonintegrable, energy-conserved, one-dimensional systems of macroscopic grains interacting via a contact-only generalized Hertz potential and held between stationary walls. Such systems can be set up to have no phononic background excitation and represent examples of a sonic vacuum. Existing dynamical studies showed the absence of energy equipartitioning in such systems, hence their long-term dynamics was described as quasiequilibrium. Here we show that these systems do in fact reach thermal equilibrium at sufficiently long times, as indicated by the calculated heat capacity...
March 2017: Physical Review. E
https://www.readbyqxmd.com/read/28414110/rifampicin-as-a-novel-tyrosinase-inhibitor-inhibitory-activity-and-mechanism
#13
Wei-Ming Chai, Mei-Zhen Lin, Fang-Jun Song, Ying-Xia Wang, Kai-Li Xu, Jin-Xin Huang, Jian-Ping Fu, Yi-Yuan Peng
In this study, the inhibitory effect and mechanism of rifampicin on the activity of tyrosinase were investigated for developing a novel tyrosinase inhibitor. It was found to have a significant inhibition on the activity of tyrosinase (IC50=90±0.6μM). From the kinetics analysis, it was proved to be a reversible and noncompetitive type inhibitor of the enzyme with the KI value of 94±3.5μM. The results obtained from intrinsic fluorescence quenching indicated that rifampicin could interact with tyrosinase. In particular, the drastic decrease of fluorescence intensity was due to the formation of a rifampicin-enzyme complex in a static procedure which was mainly driven by hydrophobic forces and hydrogen bonding...
April 13, 2017: International Journal of Biological Macromolecules
https://www.readbyqxmd.com/read/28405646/half-sandwich-iridium-n-heterocyclic-carbene-anticancer-complexes
#14
Chuanlan Wang, Jinfeng Liu, Zhenzhen Tian, Meng Tian, Laijin Tian, Wenqian Zhao, Zhe Liu
Half-sandwich pseudo-octahedral pentamethylcyclopentadienyl Ir(III) complexes of the type [(η(5)-Cp(x))Ir(C^C)Cl]PF6, where Cp(x) is pentamethylcyclopentadienyl (Cp*), or its phenyl (Cp(xph) = C5Me4C6H5) or biphenyl (Cp(xbiph) = C5Me4C6H4C6H5) derivatives, and the C^C-chelating ligands are different N-heterocyclic carbene (NHC) ligands, have been synthesized and characterized. Three X-ray crystal structures have been determined. Except for Cp* complex 1A, the other eleven complexes 1B-4C all showed potent cytotoxicity, with IC50 values ranging from 2...
April 13, 2017: Dalton Transactions: An International Journal of Inorganic Chemistry
https://www.readbyqxmd.com/read/28404557/exercise-prescription-for-overhead-athletes-with-shoulder-pathology-a-systematic-review-with-best-evidence-synthesis
#15
REVIEW
Alexis A Wright, Eric J Hegedus, Daniel T Tarara, Samantha C Ray, Steven L Dischiavi
OBJECTIVE: To produce a best evidence synthesis of exercise prescription used when treating shoulder pathology in the overhead athlete. DESIGN: A systematic review of exercises used in overhead athletes including case studies and clinical commentaries. DATA SOURCES: MEDLINE, PubMed, SPORTDiscus and CINAHL from database inception through July 8, 2016. METHODS: We examined data from randomised controlled trials and prospective cohort (level I-IV evidence) studies that addressed exercise intervention in the rehabilitation of the overhead athlete with shoulder pathology...
April 12, 2017: British Journal of Sports Medicine
https://www.readbyqxmd.com/read/28403611/kot-bu-catalyzed-dehydrogenative-c-h-silylation-of-heteroaromatics-a-combined-experimental-and-computational-mechanistic-study
#16
Wen-Bo Liu, David P Schuman, Yun-Fang Yang, Anton Alexandrovich Toutov, Yong Liang, Hendrik F T Klare, Nasri Nesnas, Martin Oestreich, Donna G Blackmond, Scott C Virgil, Shibdas Banerjee, Richard N Zare, Robert H Grubbs, Kendall N Houk, Brian M Stoltz
We recently reported a new method for the direct dehydrogenative C-H silylation of heteroaromatics utilizing Earth-abundant potassium tert-butoxide. Herein we report a systematic experimental and computational mechanistic investigation of this transformation. Our experimental results are consistent with a radical chain mechanism. A trialkylsilyl radical may be initially generated by homolytic cleavage of a weakened Si-H bond of a hypercoordinated silicon species as detected by IR, or by traces of oxygen which can generate a reactive peroxide by reaction with (KOt-Bu)4 as indicated by density functional theory (DFT) calculations...
April 12, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28402870/long-chain-fatty-acid-feeding-frequency-in-anaerobic-codigestion-impacts-syntrophic-community-structure-and-biokinetics
#17
Ryan M Ziels, David A C Beck, H David Stensel
This study investigated the impacts of long-chain fatty acid (LCFA) feeding frequencies on microbial community structure, bioconversion kinetics, and process stability during anaerobic codigestion. Parallel laboratory-scale anaerobic codigesters fed with dairy cattle manure were either pulse-fed every two days or continuously-fed daily, respectively, with oleate (C18:1) in incremental step increases over 200 days up to 64% of the influent chemical oxygen demand (COD). The effluent acetate concentration exceeded 3000 mg/L in the continuous-fed codigester at the highest oleate loading rate, but remained below 100 mg/L in the pulse-fed codigester at the end of its 48-hr oleate feed cycle...
March 31, 2017: Water Research
https://www.readbyqxmd.com/read/28402665/kinetic-modeling-of-the-thermal-destruction-of-nitrogen-mustard-gas
#18
Juan-Carlos Lizardo-Huerta, Baptiste Sirjean, Laurent Verdier, René Fournet, Pierre-Alexandre Glaude
The destruction of stockpiles or unexploded ammunitions of nitrogen mustard (tris(2-chloroethyl)amine, HN-3) requires the development of safe processes. The thermal destruction of this kind of compound is one of the most efficient method of destruction. Because of the high-level of toxicity of this chemical, there is a considerable lack of knowledge on the chemical kinetics at high temperatures. In this study, a detailed chemical kinetic model for the pyrolysis of nitrogen mustard gas is developed based on a large number of thermokinetic parameters calculated with theoretical chemistry...
April 20, 2017: Journal of Physical Chemistry. A
https://www.readbyqxmd.com/read/28393155/the-influence-of-polymer-architectures-on-the-dewetting-behavior-of-thin-polymer-films-from-linear-chains-to-ring-chains
#19
Lina Wang, Lin Xu, Binyuan Liu, Tongfei Shi, Shichun Jiang, Lijia An
The dewetting behavior of ring polystyrene (RPS) film and linear polystyrene (LPS) film on silanized Si substrates with different grafting densities and PDMS substrate was investigated. Results showed that polymer architectures greatly influenced the dewetting behavior of the thin polymer film. On the silanized Si substrate with 69% grafting density, RPS chains exhibited stronger adsorption compared with LPS chains, and as a result the wetting layer formed more easily. For LPS films, with a decreased annealing temperature, the stability of the polymer film changed from non-slip dewetting via apparent slip dewetting to apparently stable...
April 10, 2017: Soft Matter
https://www.readbyqxmd.com/read/28391121/uptake-and-elimination-kinetics-of-perfluoroalkyl-substances-in-submerged-and-free-floating-aquatic-macrophytes-results-of-mesocosm-experiments-with-echinodorus-horemanii-and-eichhornia-crassipes
#20
N Pi, J Z Ng, B C Kelly
Studies investigating the bioaccumulation behavior of perfluoroalkyl substances (PFASs) in aquatic macrophytes are limited. The present study involved controlled mesocosm experiments to assess uptake and elimination rate constants (ku,ke), bioconcentration factors (BCFs) and translocation factors (TFs) of several perfluoroalkyl carboxylic acids (PFCAs) and perfluoroalkane sulfonic acids (PFSAs) in two aquatic plant species, including one submerged species (Echinodorus horemanii) and one free-floating species (Eichhornia crassipes)...
April 4, 2017: Water Research
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