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Entropy And Enthalpy

Jarmila Oremusová, Zuzana Vitková, Anton Vitko, Marián Tárník, Eva Miklovičová, Oľga Ivánková, Ján Murgaš, Daniel Krchňák
The paper analyses influences of the temperature and hydrophilic groups on micellar properties of ionic surfactants with 12-carbonic hydrophobic chains. The aim is to assess the impact of hydrophilic groups and temperature on thermodynamic parameters and micellization. This knowledge is indispensable for the formulation of new dosage forms. The method uses conductometric measurements. The following hydrophilic groups are analyzed: trimethylammonium bromide, trimethylammonium chloride, ethyldimethylammonium bromide, didodecyldimethylammonium bromide, pyridinium chloride, benzyldimethyl-ammonium chloride, methylephedrinium bromide, cis and trans-[(2-benzyloxy)-cyclohexyl-methyl]-N, N-dimethylammonium bromide, sodium sulphate and lithium sulphate...
February 12, 2019: Molecules: a Journal of Synthetic Chemistry and Natural Product Chemistry
Zsombor Miskolczy, Mónika Megyesi, Orsolya Toke, László Biczók
The inclusion of protonated (-)-tetrahydropalmatine (THP+) and dehydrocorydaline (DHC+), natural alkaloids, in the cavity of cucurbit[7]uril was monitored in real time by a spectrofluorimetric method in water at various temperatures. Both guests produced 1 : 1 complexes in enthalpy controlled processes without any detectable intermediates. The tight entrance of CB7 imposed substantial steric hindrance for encapsulation making the entry into the host several orders of magnitude slower than diffusion. Despite the ∼6 kJ mol-1 lower activation enthalpy, the rate constant of THP+ ingression into CB7 was about 44-fold smaller at 298 K than that of DHC+ as a consequence of the considerably negative activation entropy of the former binding...
February 13, 2019: Physical Chemistry Chemical Physics: PCCP
Daniel Oliver, Monika Michaelis, Hendrik Heinz, Victor V Volkov, Carole C Perry
Polypeptide based biosilica composites show promise as next generation multi-functional nano-platforms for diagnostics and bio-catalytic applications. Following the identification of a strong silica binder (LDHSLHS) by phage display, we conduct structural analysis of the polypeptide at the interface with amorphous silica nanoparticles in an aqueous environment. Our approach relies on modelling infrared and Raman spectral responses using predictions of molecular dynamics simulations and quantum studies of the normal modes for several potential structures...
February 12, 2019: Physical Chemistry Chemical Physics: PCCP
Robin P Harkins, Christopher J Cramer, Wayne L Gladfelter
Hexamethylditin has been reported to be a more effective precursor compared to monotin analogs in hybrid molecular beam epitaxy depositions of perovskite oxides. To understand the differences, a library of 68 monotin- and ditin-containing molecules bearing hydrido and/or carbon-based ligands was generated, and their structures were optimized using density functional theory. On the basis of a modified W1-F12 composite thermochemical method, thermochemical data (enthalpy of formation, entropy, and heat capacity) were calculated for each structure over a range of temperatures (298-5000 K)...
February 12, 2019: Journal of Physical Chemistry. A
Tao Wang, Yangyang Liu, Yue Deng, Hongbo Fu, Liwu Zhang, Jianmin Chen
Despite the increased awareness of heterogeneous reactions of SO2 on mineral particles, the knowledge of how temperature influences the product species and kinetic parameters remain a crucially important part in atmospheric research. Here, we reported the formation of sulfur-containing species on hematite particles under various temperature and humidity conditions by mean of in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and ion chromatography (IC). High temperature is helpful in the ionization of H2 SO3 , making sulfite compounds occupy a great share among total products...
December 10, 2018: Science of the Total Environment
Reza Yekta, Gholamreza Dehghan, Samaneh Rashtbari, Leila Sadeghi, Behzad Baradaran, Nader Sheibani, Ali A Moosavi-Movahedi
Water molecules play a vital role in efficient drug binding to its target. Thiazolidinediones (TZDs), a class of anti-diabetic drugs, are widely used for treatment of type 2 diabetes mellitus. In the present study, the possible contribution of water molecules to the binding of TZDs to catalase, a potential target in the liver, was investigated by different experimental and theoretical methods. These studies indicated that TZDs could significantly improve the catalase catalytic function with a significant contribution from water molecules...
February 6, 2019: Archives of Biochemistry and Biophysics
Hankyul Lee, Francois Dehez, Christophe Chipot, Hyung Kyu Lim, Hyungjun Kim
Aromatic groups can engage in an interesting class of non-covalent interactions termed π-π interactions, which play a pivotal role in stabilizing a variety of molecular architectures, including nucleic acids, proteins and supramolecular assemblies. When the aromatic compounds interact with each other in an aqueous environment, their association is facilitated by the hydrophobic effect - the trend of non-polar solutes to aggregate in a polar solution. To develop an in-depth understanding of hydrophobic association, we investigate in the present work π-π interactions in water, employing as a paradigm the benzene dimer...
February 5, 2019: Journal of Chemical Theory and Computation
Nicolaj N Andersen, Kristina Eriksen, Micke Lisbjerg, Mille E Ottosen, Birgitte Olai Milhøj, Stephan P A Sauer, Michael Pittelkow
Binding of anions using macrocyclic structures with a non-polar interior using the CH···anion interaction as the recognition motif has gained popularity in the past few years, and such receptors often rely on a subtle interplay between enthalpy and entropic factors. For these types of receptors solvation of both the anion and the binding pocket of the macrocyclic host play important roles in the overall energetic picture of the binding event. Systematic chemical modifications of synthetic receptors that are able to bind anions in a variety of solvents is an important tool to gain understanding of the factors that determine the supramolecular chemistry of anions...
February 5, 2019: Journal of Organic Chemistry
Yue-Juan Zhang, Xiao-Long Liu, Wen-Ming Wang, Cheng Chen, Mu-Han Zhao, Ke-Wu Yang
Superbug infection caused by metallo-β-lactamases (MβLs) is a global public health threat. Previous studies reported that the thioesters specifically inhibited the B3 subclass MβL L1. In this work, nine amino acid thioesters 1-9 were synthesized, the activity evaluation revealed that all of these molecules exhibited broad-spectrum inhibitory efficacy against ImiS, IMP-1, NDM-1, and L1, with IC50 values range of 0.02-54.9 µM (except 5 and 7 on NDM-1), and 1 was found to be the best inhibitor with IC50 range of 0...
2019: Chemical & Pharmaceutical Bulletin
Deodatta Shinde, Stefan Fritze, Mattias Thuvander, Paulius Malinovskis, Lars Riekehr, Ulf Jansson, Krystyna Stiller
The microstructure and distribution of the elements have been studied in thin films of a near-equimolar CrNbTaTiW high entropy alloy (HEA) and films with 8 at.% carbon added to the alloy. The films were deposited by magnetron sputtering at 300°C. X-ray diffraction shows that the near-equimolar metallic film crystallizes in a single-phase body centered cubic (bcc) structure with a strong (110) texture. However, more detailed analyses with transmission electron microscopy (TEM) and atom probe tomography (APT) show a strong segregation of Ti to the grain boundaries forming a very thin Ti-Cr rich interfacial layer...
February 4, 2019: Microscopy and Microanalysis
Xiangyu Cao, Shuai Wang, Ruochen Bi, Siqi Tian, Yapeng Huo, Jianli Liu
Hexavalent chromium [Cr(VI)] is the main harmful component in the atmosphere released by chemical industry. The study was conducted to assess Cr(VI) inducing cardiovascular diseases (CVDs) in vitro by investigating the effects of Cr(VI) on bovine hemoglobin (BHb) and human umbilical vein endothelial cells (HUVECs). Multi-spectroscopic techniques and molecular docking method were used to determine the interaction of Cr(VI) and BHb. Fluorescence spectra results showed that the quenching constant (Ksv ) decreased with temperature raise, indicating that Cr(VI) quenches BHb fluorescence through static quenching mechanism...
January 24, 2019: Chemosphere
Pornkamon Nalakarn, Phansiri Boonnoy, Nililla Nisoh, Mikko Karttunen, Jirasak Wong-Ekkabut
It is well-known that fullerenes aggregate inside lipid membranes and that increasing the concentration may lead to (lethal) membrane rupture. It is not known, however, how aggregation and rupture depend on the lipid type, what physical mechanisms control this behavior and what experimental signatures detect such changes in membranes. In this paper, we attempt to answer these questions with molecular simulations, and we show that aggregation and membrane damage depend critically on the degree of saturation of the lipid acyl chains: unsaturated bonds, or "kinks", impose a subtle but crucial compartmentalization of the bilayer into core and surface regions leading to three distinct fullerene density maxima...
January 31, 2019: Scientific Reports
Qianru Wang, Yeqin Guan, Wenbo Gao, Jianping Guo, Ping Chen
Thermodynamic properties of alkali and alkaline earth metal amides are critical for their performances in hydrogen storage as well as catalytic ammonia synthesis. In this work, the equilibrium ammonia concentrations of LiNH2, KNH2 and Ba(NH2)2 under 10 bar of hydrogen pressure and different temperatures were measured by using a high-pressure gas-solid reaction system equipped with a conductivity meter. Hydrogenation of KNH2 gives the highest equilibrium ammonia concentration, followed by Ba(NH2)2 and LiNH2...
January 30, 2019: Chemphyschem: a European Journal of Chemical Physics and Physical Chemistry
Syed Saqib Ali, Mohammad Khalid Zia, ToobaSiddiqui, Haseeb Ahsan, Fahim Halim Khan
Alpha-2-macroglobulin (α2 M) is large glycoprotein present in the body fluids of vertebrates. It is an antiproteinase that inhibits a broad spectrum of proteases without the direct blockage of the protease active site. Curcumin, a yellow spice commonly used in India and several Asian countries, is reported to have anti-tumor and anti-inflammatory effects because of its antioxidant properties. In the present study, we have explored the interaction of curcumin with α2 M using various technique such as antiproteinase activity assay, spectroscopy...
January 25, 2019: International Journal of Biological Macromolecules
Abdelkader Labidi, Asier M Salaberria, Susana C M Fernandes, Jalel Labidi, Manef Abderrabba
Dyes are classified as one of the major pollutants of water. They have negative impacts not only on environment but also on human health. In fact, wastewater that contains these harmful substances requires many types of treatments. Therefore, alternative methods and adsorption agents are needed. Herein, we propose to evaluate the decolorization of methylene blue (MB) and methyl orange (MO) as two models of soluble dyes from water using chitin and chitosan-graft-polyacrylamide. Furthermore, the applicability of these biomacromolecules as alternative adsorption agents, their sticking probability and desorption were also examined...
January 24, 2019: Materials
Anjali Goel, Manu Chaudhary
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 of 9...
January 2019: Water Environment Research: a Research Publication of the Water Environment Federation
Hao Jiang, Xiao-Yu Hu, Stefanie Mosel, Christoph Hirschhäuser, Shirley K Knauer, Carsten Schmuck
Recently, branched and dendrimeric cationic peptides have shown increasing transfection efficiency compared to linear peptides owing to their superior capacity for DNA condensation. Herein, we design and synthesize two analogously guanidinocarbonylpyrrole (GCP)-substituted branched cationic tripeptides, which provide extremely strong electrostatic attraction with plasmid DNA. Both ligands 1 and 2 can bind to plasmid DNA and form condensed complexes owing to the branched structure and high positive charges, as demonstrated by isothermal titration calorimetry (ITC), Zeta-potential and atomic-force microscopy (AFM)...
January 25, 2019: Chembiochem: a European Journal of Chemical Biology
Toshiyuki Takamuku, Hiroyuki Sakurai, Akira Ogawa, Atsuya Tashiro, Masahiro Kawano, Yutaro Kawazu, Koichiro Sadakane, Hiroki Iwase, Kazuhiko Ozutsumi
In the room-temperature ionic liquid (IL) of 1-methyl-3-octylimidazolium bis(trifluoromethylsulfonyl)amide ([C8mim][TFSA]), the complex formation of Ni2+ with molecular liquids (MLs), dimethyl sulfoxide (DMSO), methanol (MeOH), and acetonitrile (AN), has been examined using ultraviolet (UV)-visible spectroscopy. The overall stability constants log βn, enthalpies , and entropies of the equilibria have been determined to elucidate the mechanism of complex formation. From a comparison of such thermodynamic parameters of the present [C8mim][TFSA] systems with those of the previous systems of 1-ethyl-3-methylimidazolium-based IL, [C2mim][TFSA], the effects of the octyl chain of the imidazolium cation, [C8mim]+, on the complex formation of Ni2+ with MLs have been demonstrated...
January 24, 2019: Physical Chemistry Chemical Physics: PCCP
A Paden King, Hendryck A Gellineau, Samantha N MacMillan, Justin J Wilson
Four cobalt(iii) complexes of the general formula [Co(Schiff base)(L)2]+, where L is ammonia (NH3) or 3-fluorobenzylamine (3F-BnNH2), were synthesized. The complexes were characterized by NMR spectroscopy, mass spectrometry, and X-ray crystallography. Their electrochemical properties, ligand substitution mechanisms, and ligand exchange rates in aqueous buffer were investigated. These physical properties were correlated to the cellular uptake and anticancer activities of the complexes. The complexes undergo sequential, dissociative ligand substitution, with the exchange rates depending heavily on the axial ligands...
January 23, 2019: Dalton Transactions: An International Journal of Inorganic Chemistry
Zhanyong Zhao, Peikang Bai, Liang Li, Jing Li, Liyun Wu, Pengcheng Huo, Le Tan
This research explored a novel chemical reduction of organic aluminum for plating Al on a graphene surface. The thermodynamics of the Al plating reaction process were studied. The Al plating process consisted of two stages: the first was to prepare (C₂H₅)₃Al. In this reaction, the ΔH(enthalpy) was 10.64 kcal/mol, the ΔG(Gibbs free energy) was 19.87 kcal/mol and the ΔS(entropy) was 30.9 cal/(mol·K); this was an endothermic reaction. In the second stage, the (C₂H₅)₃Al decomposed into Al atoms, which were gradually deposited on the surface of the graphene and the Al plating formed...
January 21, 2019: Materials
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