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Entropy And Enthalpy

Panagiotis C Petris, Stefanos D Anogiannakis, Panagiotis-Nikolaos Tzounis, Doros N Theodorou
A complete thermodynamic analysis of mixtures consisting of molecules with complex chemical constitution can be rather demanding. Kirkwood-Buff theory of solutions allows the estimation of thermodynamic properties which cannot be directly extracted from atomistic simulations, such as the Gibbs energy of mixing (Δmix G). In this work we perform molecular dynamics simulations of n-hexane/ethanol binary mixtures in the liquid state under two temperature-pressure conditions and at various mole fractions. Based on the recently published methodology of Galata et al...
December 5, 2018: Journal of Physical Chemistry. B
Dmitry V Matyushov, Marshall D Newton
We present a thermodynamic analysis of the activation barrier for reactions which can be monitored through the difference in the energies of reactants and products defined as the reaction coordinate (electron and atom transfer, enzyme catalysis, etc). The free-energy surfaces along the reaction coordinate are separated into the enthalpy and entropy surfaces. For the Gaussian statistics of the reaction coordinate, the free-energy surfaces are parabolas, and the entropy surface is an inverted parabola. Its maximum coincides with the transition state for reactions with zero value of the reaction free energy...
December 4, 2018: Journal of Physical Chemistry. B
May Bakail, Silvia Rodriguez-Marin, Zsófia Hegedüs, Marie E Perrin, Françoise Ochsenbein, Andrew John Wilson
Inhibition of the histone H3-ASF1 (anti-silencing function 1) protein-protein interaction (PPI) represents a potential approach for treatment of numerous cancers. As an α-helix mediated PPI, constraint of the key histone H3 helix (residues 118-135) represents a strategy through which chemical probes might be elaborated to test this hypothesis. In this work variant H3118-135 peptides bearing pentenyl glycine residues at i and i + 4 positions were constrained by olefin metathesis. Biophysical analyses revealed that promotion of a bioactive helical conformation depends on the position at which the constraint is introduced, but that potency of binding towards ASF1 is unaffected by the constraint and instead that enthalpy-entropy compensation occurs...
December 4, 2018: Chembiochem: a European Journal of Chemical Biology
Douglas L Purnell, Joseph William Bozzelli
Thermochemical properties of fluorinated aldehydes are important for understanding their stability and reactions in the environment and in thermal processes. Structures and thermochemical properties of C1 to C3 fluorinated aldehydes are determined by use of computational chemistry. Standard enthalpies of formation for thirty C2- and C3- fluorinated aldehydes and thirty one radicals were calculated with eleven different ab initio and density functional theory methods: CBS-APNO, CBS-4M, CBS-QB3, M06-2X, ωB97X, B3LYP, G-2, G-3, G-4 and W1U via several series of isodesmic reactions...
December 4, 2018: Journal of Physical Chemistry. A
Xiongdiao Lan, LiXia Sun, Yaseen Muhammad, Zefen Wang, Haibo Liu, Jianhua Sun, Liqin Zhou, Xuezhen Feng, Dankui Liao, Shuangfei Wang
Angiotensin converting enzyme (ACE) inhibitory peptides derived from food protein exhibited antihypertensive effects by inhibiting ACE activity. In this work, the interaction between ACE inhibitory peptide GMKCAF (GF-6) and ACE was studied by isothermal titration calorimetry, molecular docking, UV absorption spectroscopy, fluorescence spectroscopy and circular dichroism spectroscopy. Experimental results revealed that the binding of GF-6 to ACE was a spontaneous exothermic process driven by both enthalpy and entropy...
December 4, 2018: Journal of Agricultural and Food Chemistry
Jesus Cantu, Diego F Gonzalez, Yvette Cantu, Tom Eubanks, J G Parsons
In the present study, pyrrhotite (Fe7 S8 ) was investigated for the removal of Pb2+ and Cu2+ ions from aqueous solution. The Fe7 S8 material was prepared through a solvothermal method and was characterized using XRD. The average particle size for the nanomaterial was determined to be 29.86 ± 0.87 nm using XRD analysis and Scherrer's equation. Batch studies were performed to investigate the effects of pH, time, temperature, interfering ions, and the binding capacity of Pb2+ and Cu2+ ions to the Fe7 S8 nanomaterial...
July 2018: Microchemical Journal, Devoted to the Application of Microtechniques in All Branches of Science
Asit Manna, Huaying Zhao, Junya Wada, Lakshmi Balagopalan, Harichandra D Tagad, Ettore Appella, Peter Schuck, Lawrence E Samelson
The T cell antigen receptor encounters foreign antigen during the immune response. Receptor engagement leads to activation of specific protein tyrosine kinases, which then phosphorylate multiple enzymes and adapter proteins. One such enzyme, phospholipase-Cγ1, is responsible for cleavage of a plasma membrane lipid substrate, a phosphoinositide, into two second messengers, diacylglycerol, which activates several enzymes including protein kinase C, and an inositol phosphate, which induces intracellular calcium elevation...
December 3, 2018: Proceedings of the National Academy of Sciences of the United States of America
Łukasz Szeleszczuk, Dariusz Maciej Pisklak, Tomasz Gubica, Klaudia Matjakowska, Sławomir Kaźmierski, Monika Zielińska-Pisklak
Piracetam, a popular nootropic drug, widely used in the treatment of age-associated mental decline and disorders of the nervous system such as Alzheimer's disease and dementia exists under normal pressure in three polymorphic forms (P1, P2 and P3) of different stability. In this work the relative stability of piracetam polymorphs depending on the temperature was studied using the ssNMR spectroscopy combined with ab initio DFT calculations. The ssNMR spectroscopy enabled the analysis of polymorphic phase transition in the case of pure active substance as well as polymorphic form identification in the analysis of the commercial solid dosage formulations...
November 22, 2018: Solid State Nuclear Magnetic Resonance
Neetu Singh, Anupama Kumari, Chandrajit Balomajumder
Biosorption is an effective treatment method for the removal of phenol and cyanide from aqueous solution by saw dust activated carbon (SDAC). Batch experiments were achieved as a function of several experimental parameters, i.e. influence of biosorbent dose (5-60 g/L) contact time (2-40 h), pH (4-12), initial phenol concentration (100-1000 mg/L) and initial cyanide concentration (10-100 mg/L) and temperature (20-40 °C). The biosorption capacities of the biosorbent were detected as 178.85 mg/g for phenol with 300 mg/L of initial concentration and 0...
November 2018: Saudi Journal of Biological Sciences
Xue Wang, Doudou Liu, Mingjie Wang, Zhiyun Chen, Tianxiang Yin, Weiguo Shen
The liquid-liquid phase equilibria of {water/PEG200/sodium bis(2-ethylhexyl)sulfosuccinate (AOT)/n-decane} with the molar ratio of water to AOT being 37.9 and various concentrations cPEG of PEG in water were measured in this study. The critical exponent β corresponding to the width of the coexistence curve was determined, which showed good agreement with the 3D-Ising value and supported the proposal of the pseudo binary droplet solution for these multiple microemulsions. A previously developed thermodynamic approach based on the Carnahan-Starling-van der Waals type equation was improved and used to analyze the coexistence curve data of {water/PEG200/AOT/n-decane} microemulsions to deduce the interaction properties between droplets and further to investigate the effect of the additive PEG200 on these interactions...
November 29, 2018: Soft Matter
Yeseul Choi, Andrew J Adamczyk
There are limited studies available that predict the properties of hydrogenated silicon-germanium (SiGe) clusters. For this purpose, we conducted a computational study of 46 hydrogenated SiGe clusters (SixGeyHz, 1<X+Y≤6) to predict the structural, thermochemical, and electronic properties. The optimized geometries of the SixGeyHz clusters were investigated using quantum chemical calculations and statistical thermodynamics. The clusters contained 6 to 9 fused Si-Si, Ge-Ge, or Si-Ge bonds, i.e., bonds participating in more than one 3- to 4-membered rings, and different degrees of hydrogenation, i...
November 28, 2018: Journal of Physical Chemistry. A
Zi-Xiang Cui, Ya-Nan Feng, Yong-Qiang Xue, Juan Zhang, Rong Zhang, Jie Hao, Jia-Yi Liu
Nanomaterials have excellent adsorption performance, which mainly depends on the adsorption thermodynamics that is related to the shape of the nanoparticles that make up the nanomaterial, but the effects of shape on the thermodynamics of adsorption are not fully clear. In this paper, theoretically, the general formulae of adsorption thermodynamic properties for nanoparticles with different shapes and different sizes were derived, and the influencing regularities and mechanisms on adsorption thermodynamic properties were discussed...
November 27, 2018: Physical Chemistry Chemical Physics: PCCP
Zhezhu Nan, Changchun Hao, Xiaoqi Ye, Ying Feng, Runguang Sun
Fluorescence quenching was used to elucidate the binding interaction mechanism between bovine serum albumin (BSA) and graphene oxide (GO). By analyzing the values of Stern-Volmer quenching constant (KSV ) and binding constant (KA ) which were affected by temperature, we supposed that the quenching process between GO and BSA was mainly determined by static quenching, combined with dynamic quenching. The study of thermodynamics showed that the values of enthalpy change (∆H), entropy change (∆S) and Free Energy (∆G) were all negative, which implied that the weak interaction of the molecular between BSA and GO was Van der Waals interaction or hydrogen bond, and the quenching process was exothermic and spontaneous...
November 13, 2018: Spectrochimica Acta. Part A, Molecular and Biomolecular Spectroscopy
Paweł Mateusz Nowak, Katarzyna Olesek, Michał Woźniakiewicz, Mariusz Mitoraj, Filip Sagan, Paweł Kościelniak
This paper shows that the acidity of substituted cathinones can change in a diversified and poorly predictable manner upon supramolecular interaction with cyclodextrins used as buffer additives in capillary electrophoresis. The direction and range of pKa shifts may be noticeably different for the particular cyclodextrins and cathinones, suggesting a strict correlation with structure. The most interesting results were observed for 2-hydroxyethyl-β-cyclodextrin, which is capable for inducing the large negative and enantioselective apparent pKa shifts for α-pyrrolidinovalerophenone and methylenedioxypyrovalerone, even much above -1...
December 14, 2018: Journal of Chromatography. A
A N Prusov, T A Smirnova, G Ya Kolomijtseva
We studied the thermodynamics of melting of isolated rat liver nuclei with different degrees of chromatin condensation determined by the concentration of polyamines (PA) and the solution ionic strength, as well as the effect of the antibiotic distamycin A (DM) on melting. Differential scanning calorimetry (DSC) profiles of nuclear preparations contained three peaks that reflected melting of three main chromatin domains. The number of peaks did not depend on the degree of condensation; however, nuclei with more condensed chromatin had a higher total enthalpy...
October 2018: Biochemistry. Biokhimii︠a︡
Hulya Yılmaz Ortak, Ebru Cubuk Demiralay
In this study, the thermodynamic dissociation constant (pKa ) values of tofacitinib in acetonitrile-water binary mixtures with of 25%, 30%, 35% and 45% (v/v) have been determined at 25-45 °C range of temperatures with reversed-phase liquid chromatography (RPLC). The chromatographic determination was achieved on a Kinetex Core-Shell EVO C18-Phenomenex (150 mm x 4.6 mm, 5 μm) analytical column. For each case pKa values and retention factors of tofacitinib by taking into account the effect of the activity coefficients in hydro-organic water-acetonitrile binary mixtures have been evaluated and which obtain by SOLVER algorithm of spreadsheet program Excel to fit experimental data to the nonlinear expression derived...
November 17, 2018: Journal of Pharmaceutical and Biomedical Analysis
Ke Chen, Liuliu Huang, Bin Shen
Nrf2 is a critical regulator of innate immune response and survival during sepsis, which is constitutively degraded through binding to the Keap1 adapter protein of E3 ubiquitin ligase. Two linear peptides DLG and ETG derived from, respectively, the low-affinity and high-affinity motifs of Nrf2 binding site exhibit self-binding affinity to Keap1 central hole (active pocket); they can be exploited as therapeutic self-inhibitory peptides to disrupt the Nrf2-Keap1 interaction. Molecular dynamics simulation and binding energetics decomposition reveal that the two peptides possess large flexibility and intrinsic disorder in unbound free state, and thus would incur a considerable entropy penalty upon binding to Keap1...
January 2019: Biophysical Chemistry
Gydo van Zundert, Brandi M Hudson, Saulo de Oliveira, Daniel A Keedy, Rasmus Fonseca, Amelie Heliou, Pooja Suresh, Kenneth Borrelli, Tyler Day, James Fraser, Henry van den Bedem
Proteins and ligands sample a conformational ensemble that governs molecular recognition, activity, and dissociation. In structure-based drug design, access to this conformational ensemble is critical to understand the balance between entropy and enthalpy in lead optimization. However, ligand conformational heterogeneity is currently severely underreported in crystal structures in the Protein Data Bank, owing in part to a lack of automated and unbiased procedures to model an ensemble of protein-ligand states into X-ray data...
November 20, 2018: Journal of Medicinal Chemistry
Gion Calzaferri
The influence of entropy in multiple chemical equilibria is investigated for systems with different types of sites for the condition that the binding enthalpy of the species is the same within each type of sites and independent of those species that are already bonded. This allows splitting of the free reaction enthalpy into the particle distribution term and all other contributions for each type of sites separately and, hence, to evaluate this entropy contribution to the free reaction enthalpy. The situations for which this applies can be chemically very different, e...
November 28, 2018: Physical Chemistry Chemical Physics: PCCP
E Igberase, A Ofomaja, P O Osifo
The multi-functional chitosan is important for the development of novel adsorbents which is needed for the effective removal of scavenging metal ions from water and wastewater. In this study the functionalized materials were characterize by FTIR, SEM/EDX, TGA/DTA, BET and XRD. Physicochemical parameters including pH, contact time, ionic strength and temperature were investigated in batch mode to optimize the conditions to be applied on a commercial scale for the maximum removal of metal ions using batch applications...
November 14, 2018: International Journal of Biological Macromolecules
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