共查询到20条相似文献,搜索用时 15 毫秒
1.
Sitafloxacin (STFX) hydrate is a non-stoichiometric hydrate. The hydration state of STFX hydrate varies non-stoichiometrically depending on the relative humidity and temperature, though X-ray powder diffraction (XRPD) of STFX hydrate was not affected by storing at low and high relative humidities. The detailed properties of crystalline water of STFX hydrate were estimated in terms of hygroscopicity, thermal analysis combined with X-ray powder diffractometry, crystallography and density functional theory (DFT) calculation. STFX hydrate changed the water contents continuously and reversibly from an equivalent amount of dihydrate through that of sesquihydrate depending on the relative humidity at 25°C. Thermal analysis and X-ray powder diffraction (XRPD) simultaneous measurement also revealed that STFX hydrate dehydrated into a hydrated state equivalent to monohydrate by heating up to 100°C, whereas XRPD patterns were slightly affected. This indicated that the crystal structure of STFX hydrate was retained at the dehydration level of monohydrate. Single-crystal X-ray structural analysis showed that two STFX molecules and four water molecule sites were contained in an asymmetric unit. STFX molecules formed a channel structure where water molecules were included. At the partially dehydrated state, at least two of four water molecules were considered to be disordered in occupancy and/or coordinates. Insight into the crystal structure of STFX hydrate stored at low and high relative humidities and geometry of the hydrogen bond were helpful to estimate the origin of non-stoichiometric hydration of STFX hydrate. 相似文献
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V. R. Belosludov Yu. A. Dyadin G. N. Chekhova B. A. Kolesov S. I. Fadeev 《Journal of inclusion phenomena and macrocyclic chemistry》1985,3(3):243-260
The model of a clathrate solid solution, taking into account directed and nondirected guest-guest interactions, has been obtained using statistical thermodynamic methods in the approximation of the mean-field type for the general case (the formation of cavities of several types and the inclusion of different kinds of guest molecules by the host). Consideration of this interaction has been shown to improve the quantitative agreement between theory and experiment. When the guest-guest interaction is considerable in the case of guest molecules of the same type a phase transition (of a gas-liquid type) of the guest component may occur in the clathrate matrix. In the case of guests of two different types, the phase transition of the guest subsystem of the liquid-liquid type may also occur within one framework at the expense of a preferable interaction among guest molecules of the same type.We present the isothermal (20°C) section of the phase diagram of a hydroquinone-— formic acid — acetonitrile system. Clathrates, forming in the binary systems (with hydroquinone) produce restricted solid solutions (of type IV, according to Roozeboom). These and other experimental data are discussed in terms of the proposed theory.Dedicated to Professor H. M. Powell. 相似文献
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Mimura H Gato K Kitamura S Kitagawa T Kohda S 《Chemical & pharmaceutical bulletin》2002,50(6):766-770
This study clearly demonstrates that clathrated water molecules can contribute to both chemical stabilization and destabilization of clathrates. The solid-state stabilities for two isomorphic clathrates of cephalosporin, cefazolin sodium and FK041, were investigated in terms of the effects of water content. The isomorphic ranges of water content were estimated to be 3.5-5 mol/mol for alpha-form cefazolin sodium and 2-4 mol/mol for FK041 hydrate. Upon the isomorphic dehydration, alpha-form cefazolin sodium was destabilized as the water content decreased below 4.25 mol/mol owing to the disruption of hydrogen bonding network in lattice channels. In this case, the hydration of clathrated water up to 4.25 mol/mol contributed to the physical and chemical stability of the crystals. On the contrary, the isomorphic hydration in FK041 hydrate contributed to the chemical destabilization owing to the high water activity. The difference in water activity between alpha-form cefazolin sodium and FK041 hydrate could be attributed to the size of water channels. 相似文献
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Naohito Tsujii John H. Roudebush Catherine A. Cox-Uvarov Susan M. Kauzlarich 《Journal of solid state chemistry》2011,184(5):1293-1303
Phase stability of the type-I clathrate compound Ba8AlxSi46−x and the thermoelectric property dependence on chemical composition are presented. Polycrystalline samples were prepared by argon arc melting and annealing. Results of powder X-ray diffraction and electron microprobe analysis show that the type-I structure is formed without framework deficiency for 8≤x≤15. Lattice constant a increases linearly with the increase of x. Thermoelectric properties were measured for x=12, 14 and 15. The Seebeck coefficients are negative, with the absolute values increasing with x. The highest figure of merit zT=0.24 was observed for x=15 at T=1000 K, with carrier electron density n=3×1021 cm−3. A theoretical calculation based on the single parabolic band model reveals the optimum carrier concentration to be n∼4×1020 cm−3, where zT∼0.7 at T=1000 K is predicted. 相似文献
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A. J. Beysens G. H. Beuman J. J. van der Heijden K. E. J. Hoogtanders O. M. Steijger H. Lingeman 《Chromatographia》1994,39(7-8):490-496
Summary A sensitive and selective liquid chromatographic method, using precolumn derivatization with dansylhydrazine followed by fluorescence detection, has been developed for the determination of tacrolimus (FK 506) in whole blood. After haemolysis, whole blood samples are extracted with diethyl ether and derivatized. After on-line removal of excess dansylhydrazine on a C18 precolumn, the derivative is loaded on to a C18 clean-up column, and a heart cut is subsequently transferred to a graphitized carbon column, where the final separation takes place. The method requires 1 ml of sample and has a limit of quantitation of 3 ng/ml. At the 15 ng/ml level the precision isca 10%, and the response is linear from the limit of quantitation toca 200 ng/ml of FK 506 in whole blood. The capacity of the method is 50 samples/day and about 1000 1-ml samples can be analyzed without changing either clean-up or separation column. Finally, the applicability of the method for therapeutic drug monitoring is shown. 相似文献
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Molecular dynamics simulations of aqueous mixtures of methanol and sorbitol were performed over a wide range of binary composition, density (pressure), and temperature to study the equation of state and solvation of small apolar solutes. Experimentally, methanol is a canonical solubilizing agent for apolar solutes and a protein denaturant in mixed-aqueous solvents; sorbitol represents a canonical "salting-out" or protein-stabilizing cosolvent. The results reported here show increasing sorbitol concentration under isothermal, isobaric conditions results in monotonic increases in apolar solute excess chemical potential (mu2ex) over the range of experimentally relevant temperatures. For methanol at elevated temperatures, increasing cosolvent composition results in monotonically decreasing mu2ex. However, at lower temperatures mu2ex exhibits a maximum versus cosolvent concentration, as seen experimentally for Ar in ethanol-water solutions. Both density anomalies and hydrophobic effects--characterized by temperatures of density maxima and apolar solute solubility minima, respectively--are suppressed upon addition of either sorbitol or methanol at all temperatures and compositions simulated here. Thus, the contrasting effects of sorbitol and methanol on solute chemical potential cannot be explained by qualitative differences in their ability to enhance or suppress hydrophobic effects. Rather, we find mu2ex values across a broad range of temperatures and cosolvent composition can be quantitatively explained in terms of isobaric changes in solvent density--i.e., the equation of state--along with the corresponding packing fraction of the solvent. Analysis in terms of truncated preferential interaction parameters highlights that care must be taken in interpreting cosolvent effects on solvation in terms of local preferential hydration. 相似文献
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This paper reports the measured hydrate phase equilibria of simulated flue gas (12.6 vol% CO2, 80.5 vol% N2, 6.9 vol% O2) in the presence of tetra-n-butyl ammonium bromide (TBAB) or tri-n-butylphosphine oxide (TBPO), at (0, 5 and 26) wt%, respectively. The measurements of the phase boundary between (hydrate + liquid + vapor) (H + L + V) phases and (liquid + vapor) (L + V) phases were performed within the temperature range (275.97 to 293.99) K and pressure range (1.56 to 18.78) MPa with using the isochoric step-heating pressure search method. It was found that addition of TBAB or TBPO allowed the incipient equilibrium hydrate formation conditions for the flue gas to become milder. Compared to TBAB, TBPO was largely more effective in reducing the phase equilibrium pressure. 相似文献
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The solvation and transport properties of the sulfonate-hydronium ion pair have been studied in hydrated Nafion through molecular dynamics simulation. Explicit proton and charge delocalization of the excess proton transport, via the Grotthuss hopping mechanism, were treated using the self-consistent multistate empirical valence bond (SCI-MS-EVB) method. The nature of the sulfonate-hydronium ion pair was characterized through analysis of free-energy profiles. It was found that, in general, the excess proton is solvated between two water molecules of a Zundel moiety while in the contact ion pair position, but then it transitions to an Eigen-like configuration in the solvent-separated pair position. Furthermore, the positive charge associated with the excess proton passes between the contact and solvent-separated ion pair positions through the Grotthuss mechanism rather than simple vehicular diffusion. The total proton diffusion was decomposed into vehicular and Grotthuss components and were found to be of the same relative magnitude, but with a strong negative correlation resulting in a smaller overall diffusion. Correlated motions between the ion pair were examined through the distinct portion of the van Hove correlation function, and a characteristic time scale of approximately 425 ps was observed. Additionally, the association of the hydrated proton with the hydrophobic polymer backbone suggests its amphiphile-like behavior (see Acc. Chem. Res. 2006, 39, 143; Phys. Rev. 1954, 95, 249; J. Chem. Phys. 2005, 123, 084309). 相似文献
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Koichi Narita Takuya Kikuchi Kazuhiro Watanabe Dr. Toshiya Takizawa Dr. Takamasa Oguchi Dr. Kyosuke Kudo Keisuke Matsuhara Hideki Abe Dr. Takao Yamori Prof. Dr. Minoru Yoshida Prof. Dr. Tadashi Katoh Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(42):11174-11186
The bicyclic depsipeptide histone deacetylase (HDAC) inhibitors spiruchostatins A and B, 5′′‐epi‐spiruchostatin B and FK228 were efficiently synthesized in a convergent and unified manner. The synthetic method involved the following crucial steps: i) a Julia–Kocienski olefination of a 1,3‐propanediol‐derived sulfone and a L ‐ or D ‐malic acid‐derived aldehyde to access the most synthetically challenging unit, (3S or 3R,4E)‐3‐hydroxy‐7‐mercaptohept‐4‐enoic acid, present in a D ‐alanine‐ or D ‐valine‐containing segment; ii) a condensation of a D ‐valine‐D ‐cysteine‐ or D ‐allo‐isoleucine‐D ‐cysteine‐containing segment with a D ‐alanine‐ or D ‐valine‐containing segment to directly assemble the corresponding seco‐acids; and iii) a macrocyclization of a seco‐acid using the Shiina method or the Mitsunobu method to construct the requisite 15‐ or 16‐membered macrolactone. The present synthesis has established the C5′′ stereochemistry of spiruchostatin B. In addition, HDAC inhibitory assay and the cell‐growth inhibition analysis of the synthesized depsipeptides determined the order of their potency and revealed some novel aspects of structure–activity relationships. It was also found that unnatural 5′′‐epi‐spiruchostatin B shows extremely high selectivity (ca. 1600‐fold) for class I HDAC1 (IC50=2.4 nM ) over class II HDAC6 (IC50=3900 nM ) with potent cell‐growth‐inhibitory activity at nanomolar levels of IC50 values. 相似文献
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Prof. Dr. László Kótai Szabolcs Bálint István Gács Györgyi Lakatos András Angyal Prof. Dr. Raj. N. Mehrotra 《无机化学与普通化学杂志》2012,638(2):279-281
The minimal occupancy level (θmin) of the clathrate lattice of gas molecules is defined as the number of guest molecules in the host clathrate lattice, which can stabilize the thermodynamically unstable empty cage by covering the energy demand of the transformation of hexagonal ice into empty clathrate lattice (ΔHtrans). The θmin values for chlorine hydrate were determined from the n = f(p)T=const. relationship and the average molar intercalation heat of chlorine in the type I clathrate lattice was also calculated for both type of cavities. 相似文献
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Oostenbrink C Villa A Mark AE van Gunsteren WF 《Journal of computational chemistry》2004,25(13):1656-1676
Successive parameterizations of the GROMOS force field have been used successfully to simulate biomolecular systems over a long period of time. The continuing expansion of computational power with time makes it possible to compute ever more properties for an increasing variety of molecular systems with greater precision. This has led to recurrent parameterizations of the GROMOS force field all aimed at achieving better agreement with experimental data. Here we report the results of the latest, extensive reparameterization of the GROMOS force field. In contrast to the parameterization of other biomolecular force fields, this parameterization of the GROMOS force field is based primarily on reproducing the free enthalpies of hydration and apolar solvation for a range of compounds. This approach was chosen because the relative free enthalpy of solvation between polar and apolar environments is a key property in many biomolecular processes of interest, such as protein folding, biomolecular association, membrane formation, and transport over membranes. The newest parameter sets, 53A5 and 53A6, were optimized by first fitting to reproduce the thermodynamic properties of pure liquids of a range of small polar molecules and the solvation free enthalpies of amino acid analogs in cyclohexane (53A5). The partial charges were then adjusted to reproduce the hydration free enthalpies in water (53A6). Both parameter sets are fully documented, and the differences between these and previous parameter sets are discussed. 相似文献
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N. V. Vologdin P. V. Fabinskii V. A. Fedorov 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2016,90(6):1164-1167
Based on the scaled-particle theory, the Gibbs energy of the formation of cavities in the structure of water and some alcohols are calculated for the processes of dissolution of cobalt(III) and chromium(III) tris-acetylacetonates. The contribution from the hydrophobic hydration of the tris-acetylacetonate molecules in water is calculated. The location of the inversion area is clarified for a number of aqueous alcoholic solvents, and the effect the solvent’s macrophysical parameters have on the patterns of tris-acetylacetonate solvation is analyzed. 相似文献
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AbstractAn efficient and stereoselective procedure of oxidizing disulfide to thiosulfinate 2a using CHP as the oxidant and economically available Ti(O-i-Pr)4/L-DET/H2O as catalysts were developed. The reaction went smoothly under mild conditions with synthetic useful yield and the workup for obtaining the final product is quite convenient. 相似文献
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Calorimetric and thermogravimetric study of competitive clathration in theβ-[Ni(NCS)2(4-McPy)4] host
Janusz Lipkowski Anna Zielenkiewicz Jacek Hatt Wojciech Zielenkiewicz Toschitake Iwamoto 《Journal of inclusion phenomena and macrocyclic chemistry》1989,7(5):519-527
The stoichiometry of mixed guest clathrates of [Ni(NCS)2(4-methylpyridine)4] (host) with methanol/4-methylpyridine and acetone/4-methylpyridine as well as the enthalpies of clathration and the thermokinetic course of the processes were investigated. Two different mechanisms of molecular inclusion are proposed: (I) simple competition for the same type of absorption sites with two methanol molecules substituting one of 4-methylpyridine in the solid inclusion compound; and (II) competitive absorption for two types of absorption sites of acetone and 4-methylpyridine. Partial molar enthalpies of clathration of the individual guests are derived and discussed. The thermokinetic course of the processes is also given. The analytical thermogravimetric procedure is described and the solid products of thermal decomposition of the clathrates and of the host complex were identified by using X-ray powder diffractometry.Presented at the International Seminar on Inclusion Compounds, Jaszowiec, Poland, 24–26 September 1987. 相似文献
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Journal of Structural Chemistry - 相似文献
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Koch KR Burger MR Kramer J Westra AN 《Dalton transactions (Cambridge, England : 2003)》2006,(27):3277-3284
195Pt NMR together with DFT calculations and MD simulations, offer a powerful toolkit with which to probe the hydration shells of the [PtCl6]2- anions, which may lead to a more profound understanding of the solute-solvent interactions of such complexes. 相似文献