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Entropy And Enthalpy

Sourav Das, Santanu Santra, Mostofa Ataur Rohman, Mahuah Ray, Madhurima Jana, Atanu Singha Roy
The interaction of 6-Hydroxyflavone (6HF) with hen egg white lysozyme (HEWL) has been executed using multi-spectroscopic and computational methods. Steady state fluorescence studies indicated that static quenching mechanism is involved in the binding of 6HF with HEWL, which was further supported by excited state lifetime and UV-vis absorption studies. The binding constant (Kb ) of the HEWL-6HF complex was observed to be 6.44±0.09 ×104 M-1 at 293 K, which decreases with the increase in temperature. The calculation of the thermodynamic quantities showed that the binding is exothermic in nature with a negative enthalpy change (ΔH= -11...
October 12, 2018: Journal of Biomolecular Structure & Dynamics
Xiaogang Qu, Chuanqi Zhao, Hualong Song, Peter Scott, Andong Zhao, Jinsong Ren, Hisae Tateishi-Karimata, Naoki Sugimoto
DNA chirality is the fundamental issue for design of DNA-targeted chiral drugs and DNA-based chiral devices. Natural D-DNA and L-DNA are mirror-image counterparts. However, due to the inherent flexibility and conformation diversity of DNA, it is still not clear how enantiomeric compounds to recognize D-DNA and L-DNA. Are their recognitions following mirror-image dependence? Herein, taken quadruplex (G4 DNA) as an example which has diverse conformations and distinct biofunctions, 10 pairs of iron triplex metallohelices binding to D- and L-G4 DNA have been evaluated...
October 11, 2018: Angewandte Chemie
Mousumi Ghosh, Rohit Upadhyay, Dipendra Kumar Mahato, Hari Niwas Mishra
Blended sunflower (SO) (50-80%) and sesame oils (SEO) (20-50%) were evaluated for thermo-oxidative stability (induction period, IP), oxidation kinetics (rate constant, k), synergy and shelf-life (25 °C) (IP25 ) using Rancimat (100, 110, 120, and 130 °C). The Arrhenius equation (ln k vs. 1/T) and activated complex theory (ln k/T vs. 1/T) were used to estimate activation energies, activation enthalpies and entropies, which varied from 92.05 to 99.17 kJ/mol, 88.83 to 95.94 kJ/mol, -35.58 to -4.81 J/mol K, respectively (R2  > 0...
January 30, 2019: Food Chemistry
Liming Yuan, Yiting Cao, Qian Luo, Wenyu Yang, Xiaofeng Wu, Xiaoping Yang, Di Wu, Siyuan Tan, Ge Qin, Jia Zhou, Yue Zeng, Xinghua Chen, Xiaojun Tao, Qiufang Zhang
The nanomaterial composition of nanoparticles and their protein adsorption in the blood is of great significance in the design of drug-loaded nanoparticles. To explore the interaction between the different surface components of nanoparticles (NPs) and protein, we synthesized three kinds of pullulan NP polymers: cholesteric hydrophobically (CH) modified pullulan (CHP), CH-modified animated pullulan (CHAP), and CH-modified carboxylated pullulan (CHSP). Pullulan NPs were prepared by the dialysis method. Dynamic light scattering was used to determine the charge and size of the three NPs...
October 10, 2018: Nanoscale Research Letters
(no author information available yet)
In the present work the degradation of metanil yellow an azo dye by hexacyanoferrate(III) ions (oxidant) in the aqueous alkaline medium has been investigated by kinetic - spectrophotometric method at λmax 435 nm of the reaction mixture. The effect of various parameters such as the concentration of dye, oxidant and solution pH on the reaction rate has been determined. The results show that the rate of degradation increases linearly with the increase in concentrations of oxidant and dye at optimum pH 9.0 and constant temperature of 40 ± 0...
July 27, 2018: Water Environment Research: a Research Publication of the Water Environment Federation
Maik Otte, Andrea Schweinitz, Michele Bonus, Uta Enke, Christina Schumann, Holger Gohlke, Klaus Benndorf
Cyclic nucleotide-gated (CNG) and hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are tetrameric non-specific cation channels in the plasma membrane that are activated by either cAMP or cGMP binding to specific binding domains incorporated in each subunit. Typical apparent affinities of these channels for these cyclic nucleotides range from several hundred nanomolar to tens of micromolar. Here we synthesized and characterized novel cAMP and cGMP derivatives by substituting either hydrophobic alkyl chains or similar-sized more hydrophilic heteroalkyl chains to the 8-position of the purine ring with the aim to obtain full agonists of higher potency...
October 8, 2018: Scientific Reports
Zhuo Liu, Sara Lemmonds, Juan Huang, Madhusudan Tyagi, Liang Hong, Nitin Jain
The enhanced thermostability of thermophilic proteins with respect to their mesophilic counterparts is often attributed to the enthalpy effect, arising from strong interactions between protein residues. Intuitively, these strong interresidue interactions will rigidify the biomolecules. However, the present work utilizing neutron scattering and solution NMR spectroscopy measurements demonstrates a contrary example that the thermophilic cytochrome P450, CYP119, is much more flexible than its mesophilic counterpart, CYP101A1, something which is not apparent just from structural comparison of the two proteins...
October 8, 2018: Proceedings of the National Academy of Sciences of the United States of America
Loes M Stevers, Pim J de Vink, Christian Ottmann, Jurriaan Huskens, Luc Brunsveld
Protein-protein interactions (PPIs) are at the core of molecular control over cellular function. Multivalency in PPI formation, such as via proteins with multiple binding sites and different valencies, requires fundamental understanding to address correlated challenges in pathologies and drug development. Thermodynamic binding models are needed to provide frameworks for describing multivalent PPIs. We established a model based on ditopic host-guest systems featuring the effective molarity, a hallmark property of multivalency, as prime parameter governing the intramolecular binding in divalent interactions...
October 8, 2018: Journal of the American Chemical Society
Andrey N Pravdivtsev, Ivan Vladimirovich Skovpin, Alexandra I Svyatova, Nikita V Chukanov, Larisa M Kovtunova, Valerii I Bukhtiyarov, Eduard Y Chekmenev, Kirill V Kovtunov, Igor V Koptyug, Jan-Bernd Hovener
Signal Amplification By Reversible Exchange (SABRE) is a new and rapidly developing hyperpolarization technique. The recent discovery of Spin-Lock Induced Crossing SABRE (SLIC-SABRE) shows that high field hyperpolarization transfer techniques developed so far were optimized for singlet spin order that does not coincide with the experimentally produced spin state. Here, we investigate the SLIC-SABRE approach and the most advanced quantitative theoretical SABRE model. It is the goal to achieve the highest possible polarization with SLIC-SABRE at high field using the standard SABRE system, IrIMes catalyst with pyridine...
October 8, 2018: Journal of Physical Chemistry. A
Valeria Zai-Rose, Savannah J West, Wolfgang H Kramer, G Reid Bishop, Edwin A Lewis, John J Correia
The lower critical solution temperature (LCST) of the thermo-responsive engineered elastin-like polypeptide (ELP) biopolymer is being exploited for the thermal targeted delivery of doxorubicin (Dox) to solid tumors. We examine the impact of Dox labeling on the thermodynamic and hydrodynamic behavior of an ELP drug carrier and how Dox influences the liquid-liquid phase separation (LLPS). Turbidity, dynamic light scattering (DLS), and differential scanning calorimetry measurements show that ELP undergoes a cooperative liquid-liquid phase separation from a soluble to insoluble coacervated state that is enhanced by Dox labeling...
September 15, 2018: Biophysical Journal
Neetika Rawat, Aishwarya Kar, A Bhattacharyya, A K Yadav, D Bhattacharyya, S N Jha, P Kumar, S K Nayak, B S Tomar
The assessment of cucurbituril (CBn) for selective removal of actinides from nuclear waste streams requires comprehensive understanding of binding parameters and coordination of these complexes. The present work is the first experimental report on complexation of actinide ion with Cucurbit[5]uril (CB5) in solution. The thermodynamic parameters (ΔG, ΔH and ΔS) for complexation of CB5 with U(VI) in formic acid water medium were determined using microcalorimetry and UV-Vis spectroscopy. The enthalpy and entropy of complexation revealed the partial binding of U(VI) to CB5 portal...
September 19, 2018: Spectrochimica Acta. Part A, Molecular and Biomolecular Spectroscopy
Thomas Schmitt, Reinhard H H Neubert
This review is summarizing an important part of the state of the art in stratum corneum research. A complete overview on discoveries about the general biophysical and physicochemical properties of the known ceramide species' is provided. The ceramides are one of the three major components of the lipid matrix and mainly govern its properties and structure. They are shown to exhibit very little redundancy, despite the minor differences in their chemical structure. The results are discussed, compared to each other as well as the current base of knowledge...
October 3, 2018: Chemistry and Physics of Lipids
Amit Samanta, Jonathan L Belof
The first experimental insight into the nature of the liquid-solid interface occurred with the pioneering experiments of Turnbull, which simultaneously demonstrated both that metals could be deeply undercooled (and therefore had relatively large barriers to nucleation) and that the inferred interfacial free energy γ was linearly proportional to the enthalpy of fusion [D. Turnbull, J. Appl. Phys. 21 , 1022 (1950)]. By an atomistic simulation of a model face-centered cubic system via adiabatic free energy dynamics, we extend Turnbull's result to the realm of high pressure and demonstrate that the interfacial free energy, evaluated along the melting curve, remains linear with the bulk enthalpy of fusion, even up to 100 GPa...
September 28, 2018: Journal of Chemical Physics
Paul J Dauenhauer, Omar A Abdelrahman
Confinement of hydrocarbons in nanoscale pockets and pores provides tunable capability for controlling molecules in catalysts, sorbents, and membranes for reaction and separation applications. While computation of the enthalpic interactions of hydrocarbons in confined spaces has improved, understanding and predicting the entropy of confined molecules remains a challenge. Here we show, using a set of nine aluminosilicate zeolite frameworks with broad variation in pore and cavity structure, that the entropy of adsorption can be predicted as a linear combination of rotational and translational entropy...
September 26, 2018: ACS Central Science
Ghadah M Al-Senani, Foziah F Al-Fawzan
Wild herbs ( Origanum ( OR ) and Lavandula ( LV )) were used as environment-friendly adsorbents in this study. The adsorbents were used for adsorption of Cu and Ba from water. The adsorption of heavy metals onto OR and LV was dependent on particle size, dose, and solution pH. The diameter of adsorbent particles was less than 282.8 nm. The adsorption follows second-order kinetics. Langmuir and Freundlich models have been applied to describe the equilibrium data, and the thermodynamic parameters, the Gibbs free energy, ∆ G °, enthalpy, ∆ H °, and entropy, ∆ S °, have been determined...
2018: Bioinorganic Chemistry and Applications
Sladjana Slavkovic, Zachary R Churcher, Philip E Johnson
An unusual feature of the cocaine-binding aptamer is that it binds quinine much tighter than the ligand it was selected for, cocaine. Here we expand the repertoire of ligands that this aptamer binds to include the quinine-based antimalarial compounds amodiaquine, mefloquine, chloroquine and primaquine. Using isothermal titration calorimetry (ITC) we show that amodiaquine is bound by the cocaine-binding aptamer with an affinity of (7 ± 4) nM, one of the tightest aptamer-small molecule affinities currently known...
September 17, 2018: Bioorganic & Medicinal Chemistry
Michael J Cordon, James W Harris, Juan Carlos Vega-Vila, Jason S Bates, Sukhdeep Kaur, Mohit Gupta, Megan E Witzke, Evan C Wegener, Jeffrey T Miller, David W Flaherty, David D Hibbitts, Rajamani Gounder
Lewis acid sites in zeolites catalyze aqueous-phase sugar isomerization at higher turnover rates when confined within hydrophobic than within hydrophilic micropores; however, relative contributions of competitive water adsorption at active sites and preferential stabilization of isomerization transition states have remained unclear. Here, we employ a suite of experimental and theoretical techniques to elucidate the effects of co-adsorbed water on glucose isomerization reaction coordinate free energy landscapes...
September 28, 2018: Journal of the American Chemical Society
Sangtae Kim, Hyo Jin Gwon, Sung Wook Paek, Seong Keun Kim, Ji-Won Choi, Jin-Sang Kim, Jung-Hae Choi, Chong-Yun Kang, Seung-Hyub Baek
Despite the wide applicability of oxynitrides from photocatalysis to refractory coatings, our understanding of the materials has been limited in terms of their thermodynamics. The configurational entropy via randomly mixed O/N or via cation vacancies are known to stabilize oxynitrides, despite the positive formation enthalpies. Here, using tin oxynitrides as a model system, we show by ab initio computations that oxynitrides in seemingly charge-unbalanced composition stabilize by forming pernitrides among metal-(O,N)6 octahedra...
September 27, 2018: Scientific Reports
Daniel R Fröhlich, Carsten Koke, Martin M Maiwald, Claudia Chomyn, Johann Plank, Petra J Panak
The interaction between different trivalent lanthanides and a synthetic acrylate based PCE-superplasticizer (52IPEG4.5) is investigated by using a combination of laser- and synchrotron based spectroscopic techniques. Time-resolved laser fluorescence spectroscopy (TRLFS) is used to obtain thermodynamic data (stability constants (log β'(T)), reaction enthalpy (Δr H) and entropy(Δr S)) of the complexation reaction of Eu(III) and 52IPEG4.5 as a function of the temperature (20-80 °C) and ligand concentration (<2 g/kg) in 0...
September 18, 2018: Spectrochimica Acta. Part A, Molecular and Biomolecular Spectroscopy
Rui-Zhi Zhang, Francesco Gucci, Hongyu Zhu, Kan Chen, Michael J Reece
High-entropy compounds with compositional complexity can be designed as new thermoelectric materials. Here a data-driven model was developed, which chose suitable elements to reduce the enthalpy of formation and hence to increase the chance of single phase formation. Using this model, two high-entropy sulfides were designed, metallic Cu5 SnMgGeZnS9 and semiconducting Cu3 SnMgInZnS7 . They were then successfully fabricated as single-phase dense ceramics with homogeneously distributed cations, and their phase stability and atomic local structures were investigated using density functional theory calculations...
September 26, 2018: Inorganic Chemistry
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