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Entropy And Enthalpy

Jing Chang, Xiaolin Zhou, Ke Liu, Nina Ge
The present work aims to study the structural, elastic, mechanical and thermodynamic properties of the newly discovered orthorhombic Cmcm structure HfB4 (denoted as Cmcm -HfB4 hereafter) under pressure by the first-principles calculations. The obtained equilibrium structure parameters and ground-state mechanical properties were in excellent agreement with the other theoretical results. The calculated elastic constants and phonon dispersion spectra show that Cmcm -HfB4 is mechanically and dynamically stable up to 100 GPa and no phase transition was observed...
July 2018: Royal Society Open Science
Dan Zhou, Linlin Wang, Xiaopeng Chen, Xiaojie Wei, Jiezhen Liang, Dong Zhang, Guoxin Ding
Rosin esters are widely applied as masticatory substances and beverage stabilizers, while classical acid-catalysed processes will lead to metal residue or environmental issues. Super/subcritical CO2 -enriched high temperature liquid water (HTLW) as a green acid catalyst in the esterification reaction of rosin with glycerol was investigated. The pH of CO2 -H2 O binary system, as calculated based on gas-liquid equilibrium, charge balance and chemical equilibrium equations, ranged from 3.49 to 3.70 depending on the reaction conditions, indicating effective acid catalysis...
July 2018: Royal Society Open Science
Sikander Ali
In the present study, fungal biotransformation of synthetic levodopa to stable dopamine in an l-ascorbate-mediated thermophilic-aerobic biochemical reaction was investigated. A mutant strain of Aspergillus oryzae EMS-6 was used for the preparation of mycelial biomass. The mutant was previously developed through EMS-induced mutagenesis and repressed against l-cysteine HCl. Growth parameters such as rate of cultivation (48 h), initial pH (6) and incubation temperature (30 °C) supported 18.84 g/l biomass with 23 g/l glucose consumption...
August 2018: 3 Biotech
Indiran Muralisankar, Santhanam Agilan, Rajendran Selvakumar, Sundararajan Vairam
This study discusses the use of Co3 O4 impregnated graphene (CoOIG) as an efficient adsorbent for the removal of methyl violet (MV) dye from wastewater. CoOIG nanocomposites have been prepared by pyrolyzing paraffin wax with cobalt acetate. The synthesised nanocomposite was characterised by X-ray diffraction, field emission scanning electron microscope, transmission electron microscope, Fourier transform infrared spectroscope, Raman spectroscopy, and Brunauer-Emmett-Teller isotherm studies. The above studies indicate that the composites have cobalt oxide nanoparticles of size 51-58 nm embedded in the graphene nanoparticles...
September 2018: IET Nanobiotechnology
Sourav Das, Nikita Bora, Mostofa Ataur Rohman, Raju Sharma, Anupam Nath Jha, Atanu Singha Roy
The binding of two bio-active flavonoids, quercetin and rutin, with bovine hemoglobin (BHb) was investigated by multi-spectroscopic and computational (molecular docking and molecular dynamics simulation) studies. The two flavonoids were found to quench the intrinsic fluorescence of BHb through a static quenching mechanism. The binding constants at 288 K were observed to be (14.023 ± 0.73) × 104 M-1 and (7.848 ± 0.20) × 104 M-1, respectively for quercetin and rutin binding with BHb. Both rutin and quercetin were observed to increase the polarity around the Trp residues of BHb as indicated by synchronous and 3D spectral studies...
August 13, 2018: Physical Chemistry Chemical Physics: PCCP
Piotr Bonarek, Agnieszka Polit
In proteins, proton exchange is caused due to the changes in the proton affinity (pKa ) of ionizable groups that are engaged in conformational changes induced by the binding of a ligand. In addition, knowledge regarding the type and number of such ionizable groups is very important to understand the pH-dependent changes of the thermodynamic parameters. Therefore, in this study, we performed a comprehensive analysis of proton exchange by using beta lactoglobulin (Blg), a representative of the lipocalin family of proteins...
August 8, 2018: International Journal of Biological Macromolecules
R A Mansour, N M Aboeleneen, Nabil M AbdelMonem
The retention profile of methylene blue from aqueous solutions onto the solid adsorbent date pits has been investigated in a batch system. The characterization and adsorption efficiency for methylene blue was evaluated using date pits. Fourier Transform Infra-Red, Scanning Electron Microscope, Brunauer-Emmett-Teller analysis were performed to determine the characteristics of the material. The effect of contact time, initial dye concentration, adsorbent dosage, temperature, and solution pH were investigated...
August 24, 2018: International Journal of Phytoremediation
Michael D Ward, Christopher A Hunter, Nicholas H Williams
We describe here a family of coordination cages with interesting structural, guest-binding, and catalytic properties. Flexible bridging ligands containing two bidentate pyrazolylpyridine termini assemble with transition-metal dications to afford coordination cages containing a metal ion at each vertex, a bridging ligand spanning each edge, and a 2:3 metal:ligand ratio. This stoichiometry is expressed in structures ranging from M4 L6 tetrahedra to M16 L24 tetracapped truncated tetrahedra, which are stabilized by the formation of π-stacked arrays between electron-rich and electron-poor ligand segments that form around the cage periphery...
August 7, 2018: Accounts of Chemical Research
Maria Belén Camarada, Jeffrey Comer, Horacio Poblete, Azhagiya Singam Ettayapuram Ramaprasad, Valeria Márquez-Miranda, Cesar Morales-Verdejo, Fernando Danilo Gonzalez-Nilo
Dendrimers provide a means to control the synthesis of gold nanoparticles and stabilize their suspensions. However, design of improved dendrimers for this application is hindered by a lack of understanding how the dendrimers and synthesis conditions determine nanoparticle morphology and suspension stability. In the present work, we evaluate the effect of polyamidoamine (PAMAM) dendrimers terminated with different functional groups (-OH or -NH3+) and different synthesis conditions on the morphology of the resulting gold nanoparticles and their stability in solution...
August 3, 2018: Langmuir: the ACS Journal of Surfaces and Colloids
Yang Li, Xianwei Wang, Longlong Ren, Xuecheng Cao, Changge Ji, Fei Xia, John Zenghui Zhang
Amyloid aggregation initiates from a slow nucleation process, where the association of monomers is unfavorable in energetics. In principle, the enthalpy change for aggregation should compensate the entropy loss as new monomers attach to formed oligomers. However, the classical force fields with fixed point charges failed to yield the correct enthalpy change due to the lack of electrostatic polarization effect on amyloid aggregation. In this work, we performed molecular dynamics simulation for the full-length human islet amyloid using the polarized protein-specific charges and calculated the electrostatic interaction energy for amyloid oligomers...
August 1, 2018: Journal of Chemical Information and Modeling
Hasan Y Alniss
Understanding the thermodynamic and binding characteristics of DNA minor groove binders (MGBs) is important for the rational design and development of novel MGBs; however, there are contradicting results in the literature regarding the thermodynamic signature of MGBs. The expansion of the thermodynamic database for MGBs in the literature was encouraging to evaluate and critically test the previously reported hypothesis that MGB binding is mainly entropically driven. In this review, the thermodynamic data of a group of MGBs published in the literature were analyzed to better understand the factors that drive minor groove recognition...
July 30, 2018: Journal of Medicinal Chemistry
Andrzej Mianowski, Wojciech Urbańczyk
The thermodynamic aspects of the methods commonly used in thermogravimetric analysis, i.e., isothermal and dynamic, are presented. Models for isoconversional variants of dynamic methods are accepted. For the thermal dissociation of the solid phase, the free enthalpy of the system, called the Gibbs free energy state, and the stoichiometric principles according to de Donder's extent of reaction, were proposed as the starting point, binding the dissociative pressure in the gas phase with the rate of solid phase conversion...
July 30, 2018: Journal of Physical Chemistry. A
Bastiaan Molleman, Tjisse Hiemstra
Surface energy is a fundamental property of metallic nanoparticles (MeNPs), which plays a crucial role in nucleation and growth and has strong implications for the application and environmental impact of MeNPs. Surface energy (J m-2) can be size dependent, but experimental data on surface energy trends for MeNPs are inconclusive. Computational chemistry may resolve the issue, but the location and area of the surface used for scaling, which dramatically influences the outcome and interpretation, has not been properly investigated...
August 8, 2018: Physical Chemistry Chemical Physics: PCCP
Chao Feng, Amitava Roy, Carol Beth Post
Spleen tyrosine kinase (Syk) is an essential player in immune signaling through its ability to couple multiple classes of membrane immunoreceptors to intracellular signaling pathways. Ligand binding leads to the recruitment of Syk to a phosphorylated cytoplasmic region of the receptors called ITAM. Syk binds to ITAM with high-affinity (nanomolar Kd ) via its tandem pair of SH2 domains. The affinity between Syk and ITAM is allosterically regulated by phosphorylation at Y130 in a linker connecting the tandem SH2 domains; when Y130 is phosphorylated, the binding affinity decreases (micromolar Kd )...
July 27, 2018: Protein Science: a Publication of the Protein Society
Liliana R Teixeira, Joana M Dantas, Carlos A Salgueiro, Cristina M Cordas
Gene knock-out studies on Geobacter sulfurreducens have shown that the monoheme c-type cytochrome OmcF is essential for the extracellular electron transfer pathways involved in the reduction of iron and uranium oxy-hydroxides, as well as, on electricity production in microbial fuel cells. A detailed electrochemical characterization of OmcF was performed for the first time, allowing attaining kinetics and thermodynamic data. The heterogeneous electron transfer rate constant was determined at pH 7 (0.16 ± 0...
July 24, 2018: Biochimica et Biophysica Acta
Ning Liu, Chen Chen, Isaac Chang, Pengjie Zhou, Xiaojing Wang
To study the effect of alloy composition on phase selection in the CoCrCu0.1 FeMoNi high-entropy alloy (HEA), Mo was partially replaced by Co, Cr, Fe, and Ni. The microstructures and phase selection behaviors of the CoCrCu0.1 FeMoNi HEA system were investigated. Dendritic, inter-dendritic, and eutectic microstructures were observed in the as-solidified HEAs. A simple face centered cubic (FCC) single-phase solid solution was obtained when the molar ratio of Fe, Co, and Ni was increased to 1.7 at the expense of Mo, indicating that Fe, Co, and Ni stabilized the FCC structure...
July 25, 2018: Materials
Sonja Kunstmann, Ulrich Gohlke, Nina K Broeker, Yvette Roske, Udo Heinemann, Mark Santer, Stefanie Barbirz
The principles of protein-glycan binding are still not well understood on a molecular level. Attempts to link affinity and specificity of glycan recognition to structure suffer from the general lack of model systems for experimental studies and the difficulty to describe the influence of solvent. We have experimentally and computationally addressed energetic contributions of solvent in protein-glycan complex formation in the tailspike protein (TSP) of E. coli bacteriophage HK620. HK620TSP is a 230 kDa native trimer of right-handed, parallel beta-helices that provide extended, rigid binding sites for bacterial cell surface O-antigen polysaccharides...
August 9, 2018: Journal of the American Chemical Society
Zohreh Moradi, Mozhgan Khorasani-Motlagh, Ali Reza Rezvani, Meissam Noroozifar
In this study, fluorescence emission spectra, UV-Vis absorption spectra, Ethidium bromide (EB)-competition experiment, and iodide quenching experiment were used for the interaction study of the Fish salmon DNA (FS-DNA) with [Pr(dmp)2Cl3(OH2)] where dmp is 2,9-dimethyl 1,10-phenanthroline. The binding constant and the number of binding sites of the complex with FS-DNA were 6.09 ± 0.04 M-1 and 1.18, respectively. The free energy, enthalpy and entropy changes (ΔG°, ΔH° and ΔS°) in the binding process of the Pr(III) complex with FS-DNA were -8...
July 23, 2018: Journal of Biomolecular Structure & Dynamics
Bhargav R Patel, Kagan Kerman
Dye effluents are one of the main causes of water pollution. Azo dyes, the most widely applied colorants, are particularly difficult to degrade. Exposure of such dyes to the aquatic environment is hazardous to human health and biota due to their intrinsic harmful mutagenic and carcinogenic properties. Congo Red (CR) is an anionic and synthetic diazo dye, which is recalcitrant to the biodegradative process and metabolizes to produce a potential carcinogen. Research on the interaction of this toxic dye with serum albumin, as a transport protein, is of paramount significance because the physiological and toxicological behaviours of the dye in vivo are associated with its interactive characteristics with the proteins...
August 6, 2018: Analyst
Tayssir Hamieh
Inverse gas chromatography (IGC) at infinite dilution was used to characterize the surface and interfacial properties of polymers, oxides or polymers adsorbed on oxides. In this paper, the dispersive component of the surface energy of CA was calculated following the molecular models of the surface areas of n-alkanes proving the presence of two linear zones with two different slopes in the temperature intervals and indicating a change in the structure of CA groups. The acid-base properties in the Lewis terms of cellulose acrylate were determined...
July 17, 2018: Journal of Chromatography. A
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