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Endothermic reactions

Ignacio Lizana, Eduardo J Delgado
The reaction between the antibiotic cefotaxime and the CTX-M-14 class A serine hydrolase is addressed from a theoretical point of view, by means of hybrid quantum mechanics/molecular mechanical (QM/MM) calculations, adopting a new approach that postulates that the residue Ser70 itself should play the role of the acid-base species required for the cefotaxime acylation. The proposed mechanism differs from earlier proposals existing in literature for other class A β-lactamases. The results confirm the hypothesis, and show that the reaction should occur via a concerted mechanism in which the acylation of the lactam carbonyl carbon, protonation of the N7 lactam atom, and opening of the β-lactam ring occurs simultaneously...
July 2017: Journal of Molecular Modeling
Jiajiang Lin, Mengqiang Sun, Xinwen Liu, Zuliang Chen
Kaolin supported nanoscale zero-valent iron (K-nZVI) is synthesized and applied as the Fenton-like oxidation catalyst to degrade a model azo dye, Direct Black G (DBG). The characterization of K-nZVI by the high resolution transmission electronmicroscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), Energy Diffraction Spectrum (EDS) and X-ray diffraction (XRD) show that kaolin as a support material not only reduces the aggregation of zero-valent iron (nZVI) but also facilitates the Fenton-like oxidation by increasing the local concentration of DBG in the vicinity of nZVI...
June 12, 2017: Chemosphere
Shumaila Afrin, Yusra Rahman, Tarique Sarwar, Mohammed Amir Husain, Abad Ali, Shamsuzzaman, Mohammad Tabish
Ticlopidine is an anti-platelet drug which belongs to the thienopyridine structural family and exerts its effect by functioning as an ADP receptor inhibitor. Ticlopidine inhibits the expression of TarO gene in S. aureus and may provide protection against MRSA. Groove binding agents are known to disrupt the transcription factor DNA complex and consequently inhibit gene expression. Understanding the mechanism of interaction of ticlopidine with DNA can prove useful in the development of a rational drug designing system...
June 11, 2017: Spectrochimica Acta. Part A, Molecular and Biomolecular Spectroscopy
P G Jambrina, M Menéndez, F J Aoiz
In spite of its importance in the Hg atmospheric chemistry, the dynamics of the Hg + Br2 → HgBr + Br reaction is poorly understood. In this article, we have carried out a comprehensive study of the reaction mechanism of this reaction by means of quasiclassical trajectories (QCTs) on an existing ab initio potential energy surface (PES). The reaction has a non trivial dynamics, as a consequence of its large endothermicity, the presence of a deep potential well, and the competition between the Br exchange and the collision induced dissociation processes...
June 13, 2017: Physical Chemistry Chemical Physics: PCCP
Di He, Jiuchuang Yuan, Maodu Chen
The non-adiabatic state-to-state dynamics of the Li(2p) + H2 → LiH + H reaction has been studied using the time-dependent wave packet method, based on a set of diabatic potential energy surfaces recently developed by our group. Integral cross sections (ICSs) can be increase more than an order of magnitude by the vibrational excitation of H2, whereas the ICSs are barely affected by the rotational excitation of H2. Moreover, ICSs of the title reaction with vibrationally excited H2 decrease rapidly with increasing collision energy, which is a typical feature of non-threshold reaction...
June 8, 2017: Scientific Reports
Nicholas S Shuman, Oscar Martinez, Shaun G Ard, Justin P Wiens, Nicholas R Keyes, Hua Guo, Albert A Viggiano
Rate constants and product branching fractions of reactions between diatomic interhalogens (ICl, ClF) and a series of anions (Br(-), I(-)) and cations (Ar(+), N2(+)) are measured using a selected ion flow tube apparatus and reported over the temperature range 200-500 K. The efficiency of both anion reactions with ICl is 2%-3% at 300 K to yield Cl(-), increasing with temperature in a manner consistent with the small endothermicities of the reactions. The anion reactions with ClF are 10%-20% efficient at 300 K to yield Cl(-) and also show a positive temperature dependence despite being highly exothermic...
June 7, 2017: Journal of Chemical Physics
Susan Azizi, Mahnaz Mahdavi Shahri, Rosfarizan Mohamad
In the present study, ZnO nanoparticles (NPs) were synthesized in zerumbone solution by a green approach and appraised for their ability to absorb Pb(II) ions from aqueous solution. The formation of as-synthesized NPs was established by X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), and UV-visible studies. The XRD and TEM analyses revealed high purity and wurtzite hexagonal structure of ZnO NPs with a mean size of 10.01 ± 2.6 nm. Batch experiments were performed to investigate the impact of process parameters viz...
June 8, 2017: Molecules: a Journal of Synthetic Chemistry and Natural Product Chemistry
Pierre Illien, Xi Zhao, Krishna K Dey, Peter J Butler, Ayusman Sen, Ramin Golestanian
Recent experiments have revealed that the diffusivity of exothermic and fast enzymes is enhanced when they are catalytically active, and different physical mechanisms have been explored and quantified to account for this observation. We perform measurements on the endothermic and relatively slow enzyme aldolase, which also shows substrate-induced enhanced diffusion. We propose a new physical paradigm, which reveals that the diffusion coefficient of a model enzyme hydrodynamically coupled to its environment increases significantly when undergoing changes in conformational fluctuations in a substrate concentration dependent manner, and is independent of the overall turnover rate of the underlying enzymatic reaction...
June 14, 2017: Nano Letters
A Kaushik, S Basu, K Singh, V S Batra, M Balakrishnan
This work investigates the value added utilization of two sugar-distillery wastes: (i) melanoidins, which are complex Maillard reaction products in molasses distillery wastewater, and (ii) unburnt carbon in sugarcane bagasse ash. Activated unburnt carbon (AUC), prepared by deashing and steam activation, had properties comparable to commercial activated carbon (CAC). Both carbons are suitable for melanoidins adsorption followed by desorption using 25% pyridine solution. For AUC, the equilibrium adsorption data is well described by Langmuir isotherm up to 35 °C while Freundlich model fits better at higher temperature...
May 24, 2017: Journal of Environmental Management
Dan Li, Xifen Zhu, Yin Zhong, Weilin Huang, Ping'an Peng
Recent studies showed that sulfidated nanoscale zerovalent iron (S-nZVI) is a better reducing agent than nanoscale zerovalen iron (nZVI) alone for reductive dechlorination of several organic solvents such as trichloroethylene (TCE) due to the catalytic role of iron sulfide (FeS). We measured the rates of transformation of hexabromocyclododecane (HBCD) by S-nZVI and compared them to those by FeS, nZVI, and reduced sulfur species. The results showed that: i) HBCD (20 mg L(-1)) was almost completely transformed by S-nZVI (0...
May 9, 2017: Water Research
Raja Mitra, Richard Goddard, Klaus-Richard Pörschke
As part of a comprehensive study of N-unsubstituted bispidines, the novel 9,9-difluorobispidine (D) has been synthesized. The compound crystallizes from pentane below 0 °C in the ordered-crystalline phase D-II and undergoes at 0-30 °C a stepwise endothermic phase transition to a dynamically disordered crystalline phase D-I; melting occurs at 227 °C. Single crystalline D-II has been subjected to X-ray structure analysis, revealing association of the molecules to form chains. Reaction of (1,5-hexadiene)PtCl2 with D affords {C7H10F2(NH)2}PtCl2 (D1), which can be converted by conventional routes to {C7H10F2(NH)2}Pt(cbdca)·5H2O (D2) and {C7H10F2(NH)2}Pt(C2O4) (D3)...
May 12, 2017: Inorganic Chemistry
D V Peron, S Fraga, F Antelo
The effect of temperature on the degradation of anthocyanins in juçara and "Italia" grape extracts was determined between 50 and 90°C. For both species, thermal degradation followed a first-order kinetic model. The decimal reduction time decreased with increasing temperature, and dependence on the thermodegradable factor was lower at higher temperatures. The anthocyanins from juçara degraded more slowly than those extracted from "Italia" grapes. The activation enthalpy and free energy of inactivation indicated an endothermic reaction, not spontaneous degradation, whereas the activation entropy suggested that the transition state has less structural freedom than that of the reactants...
October 1, 2017: Food Chemistry
Fang Zhu, Luwei Li, Wentao Ren, Xiaoqiang Deng, Tao Liu
Nano zero valent iron/Ni bimetal materials (nZVI/Ni) were prepared by borohydride reduction method to remediate toxic Cr(Ⅵ) contaminated in soil leachate. nZVI/Ni was characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS). Different factors including pH value of soil leachate, reaction time, temperature, humic acid and coexisting anions (SO4(2-), NO3(-), HCO3(-), CO3(2-)) were studied to analyze the reduction rate. Results showed that the reduction rate of Cr(Ⅵ) could reach 99...
August 2017: Environmental Pollution
Michael J Walt, Nancy Atwood, Stéphanie F Bernatchez, Bruce P Ekholm, Robert Asmus
Objective: To measure the skin temperature after application of a new skin protectant intended for incontinence-associated dermatitis (IAD), compared with a commercial product with an analogous cyanoacrylate-based chemistry. Approach: Twelve healthy human volunteers received an application of the new product on one thigh and of the comparator on the other thigh. An infrared camera using ThermaCAM™ software imaged the skin and measured the temperature at the skin surface over time to characterize the thermal cure profile induced by the products on the skin...
April 1, 2017: Advances in Wound Care
Mahendra Kumar Trivedi, Kalyan Kumar Sethi, Parthasarathi Panda, Snehasis Jana
OBJECTIVE: Zinc chloride is an important inorganic compound used as a source of zinc and has other numerous industrial applications. Unfortunately, it lacks reliable and accurate physicochemical, thermal, and spectral characterization information altogether. Hence, the authors tried to explore in-depth characterization of zinc chloride using the modern analytical technique. MATERIALS AND METHODS: The analysis of zinc chloride was performed using powder X-ray diffraction (PXRD), particle size distribution, differential scanning calorimetry (DSC), thermogravimetric analysis/differential thermogravimetric analysis (TGA/DTG), ultraviolet-visible spectroscopy (UV-vis), and Fourier transform-infrared (FT-IR) analytical techniques...
January 2017: International Journal of Pharmaceutical Investigation
M Takacs, S Ackermann, A Bonk, M Neises-von Puttkamer, Ph Haueter, J R Scheffe, U F Vogt, A Steinfeld
Thermochemical splitting of CO2 via a ceria-based redox cycle was performed in a solar-driven thermogravimetric analyzer. Overall reaction rates, including heat and mass transport, were determined under concentrated irradiation mimicking realistic operation of solar reactors. Reticulated porous ceramic (RPC) structures and fibers made of undoped and Zr(4+)-doped CeO2, were endothermally reduced under radiative fluxes of 1280 suns in the temperature range 1200-1950 K and subsequently re-oxidized with CO2 at 950-1400 K...
April 2017: AIChE Journal
Marcin Gronowski, Piotr Eluszkiewicz, Thomas Custer
Formyl cyanide has been detected toward Sgr B2 making this chemical and its potential isomers of astrophysical interest. We calculated the precise energies of the five most stable structural isomers of formyl cyanide and found that formyl isocyanide and 2H-azirin-2-one are less stable than formyl cyanide by 55 and 125 kJ/mol, respectively. We present our ab initio coupled cluster predictions of the spectroscopic parameters relevant to their gas-phase rotational and vibrational spectroscopy. Parameters include ground vibrational state rotational constants, centrifugal distortion parameters, equilibrium electric dipole moments, and nuclear quadrupole coupling constants...
May 4, 2017: Journal of Physical Chemistry. A
David L Swanson, Andrew E McKechnie, François Vézina
Adaptive explanations for both high and low body mass-independent basal metabolic rate (BMR) in endotherms are pervasive in evolutionary physiology, but arguments implying a direct adaptive benefit of high BMR are troublesome from an energetic standpoint. Here, we argue that conclusions about the adaptive benefit of BMR need to be interpreted, first and foremost, in terms of energetics, with particular attention to physiological traits on which natural selection is directly acting. We further argue from an energetic perspective that selection should always act to reduce BMR (i...
April 11, 2017: Journal of Comparative Physiology. B, Biochemical, Systemic, and Environmental Physiology
Peilin Liao, Rachel B Getman, Randall Q Snurr
Activation of the C-H bonds in ethane to form ethanol is a highly desirable, yet challenging, reaction. Metal-organic frameworks (MOFs) with open Fe sites are promising candidates for catalyzing this reaction. One advantage of MOFs is their modular construction from inorganic nodes and organic linkers, allowing for flexible design and detailed control of properties. In this work, we studied a series of single-metal atom Fe model systems with ligands that are commonly used as MOF linkers and tried to understand how one can design an optimal Fe catalyst...
April 10, 2017: ACS Applied Materials & Interfaces
Arush Sharma, Gaurav Sharma, Mu Naushad, Ayman A Ghfar, Deepak Pathania
The present study was attempted to ascertain the possible application of activated carbon as a cost-effective and eco-friendly adsorbent prepared via microwave-assisted chemical activation. The activated carbon was characterized using different techniques. The various adsorption parameters have been optimized to examine the viability of activated carbon as a plausible sorbent for the remediation of Congo red (CR) dye from the aquatic system. The equilibrium data adequately fitted to the Langmuir isotherm with better R(2) (0...
April 21, 2017: Environmental Technology
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