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Molar Volume (molar + volume)
Kinds of Molar Volume Selected AbstractsDensity, Surface Tension, and Viscosity of PbO-B2O3 -SiO2 Glass MeltsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2004Shigeru Fujino The density, surface tension, and viscosity of the melts from the PbO-B2O3 -SiO2 system have been measured at temperatures in the range 1073,1473 K. The effect of composition on these properties was also investigated. The density of the melt was found to increase linearly with increasing PbO content. Molar volume was derived from the density data, and its deviation from the additivity of partial molar volumes was calculated. These deviations in molar volume from those obtained from additivity rules have been used along with the ratio of various coordination numbers of boron (as reported by Bray) to discuss the structure of the melts. The surface tension was found to decrease with decreasing SiO2/B2O3 ratio, and to increase in the range of the PbO content between 30 and 60 mol%, showing a maximum at ,60 mol% PbO, and then decreased with further additions. This result suggested that the surface tension would be affected primarily by the B2O3 content in the range of the PbO content between 30,60 mol%, and mainly by the PbO content in the range of the PbO content >60 mol%, respectively. The viscosity of the melt was found to decrease linearly with increasing PbO content. The results obtained indicate that the increase in viscosity with B2O3 was half that of SiO2 (on a molar basis), and an empirical equation has been proposed for the viscosity as a function of mole fraction. [source] Properties of 2,2,2-Trifluoroethanol/Water Mixtures: Acidity, Basicity, and DipolarityHELVETICA CHIMICA ACTA, Issue 2 2005Paz Sevilla, Sierra In this report, we focus our attention on the characterization of 2,2,2-trifluoroethanol(TFE)/H2O mixtures and describe their intrinsic parameters; i.e., solvent acidity (SA), solvent basicity (SB), and solvent dipolarity/polarizability (SPP), by the probe/homomorph-couple method for a range of mixtures from 0,100% (v/v) TFE. Variation of these parameters is not linear and has a singular and unpredictable behavior depending on the precise composition of the mixture. Based on these parameters, we describe the TFE-induced changes in some physical properties; i.e., viscosity (,), partial molar volume (V,), density (,), dielectric constant (,), vapor pressure (pv), and spectroscopic properties; i.e., NMR chemical shifts (,(1H)) of TFE Me group for all molar fractions studied. In addition, by means of CD studies, we report that formation of the secondary structure, as percentage of helical content, ,, of a polypeptide, poly(L -lysine), in several TFE/H2O mixtures is adequately described by these mixture parameters. SA, SB, and SPP of TFE/H2O mixtures provide an excellent tool for the interpretation of formation and stability of intramolecular H-bonds, and, thus, of secondary structures in polypeptides. [source] Contrast analysis of the composition of ribosomes extracted with different purification proceduresJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 4 2000Giuseppe Briganti The composition and hydration of E. coli ribosomes isolated with different purification protocols has been analysed by combining two experimental techniques: measurements of small-angle neutron scattering (SANS), for two different isotopic solvent compositions, and refractive index (RI) increments. From the contrast between the solvent and solute scattering densities and the molar polarizability, determined experimentally with SANS and RI measurements, three independent equations are obtained and three unknown quantities are determined: (i) the volume of the solute hydrated skeleton Vs, (ii) the material contained in it, namely the biological components, intrinsic (rRNA and proteins) and extrinsic, such as aminoacylsynthetase and elongation factors, (iii) the number of water molecules structurally bound to the ribosome and non-exchangeable with the solvent. From the form factor at infinite contrast, a second definition of the solute volume is obtained, , which represents the volume within the contour surface of the ribosome. This value is generally larger than Vs and can include a certain amount of water molecules, i.e. those inside the volume (,Vs). Considering the molar volume of this water to be equal to that of the bulk water, it is possible to evaluate its amount. The particle density calculated from the ribosome components in , including proteins, RNA, bound and unbound water molecules, corresponds to the buoyant density measured for E. coli 70S particles. The two ribosomal preparations display different performances in protein synthesis; hence the results indicate that the optimal condition corresponds to a wider skeleton and contour volume but containing a smaller amount of segregated water molecules. It is believed that the method provides a reliable technique to determine the composition of ribosomes under various experimental conditions. [source] Investigation of the molecular surface area and volume: Defined and calculated by the molecular face theoryJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 11 2010Li-Dong Gong Abstract Based on the molecular face (MF) theory, the molecular face surface area (MFSA) and molecular face volume (MFV) are defined. For a variety of organic molecules and several inorganic molecules, the MFSA and MFV have been studied and calculated in terms of an algorithm of our own via the Matlab package. The MFV shows a very good linear relationship with the experimentally measured critical molar volume. It is also found that the MFSA and MFV have significant linear correlations with those of the commonly used hard-sphere model and the electron density isosurface. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010 [source] Solvent effects in the hydrodechlorination of 2,4-dichlorophenol over Pd/Al2O3AICHE JOURNAL, Issue 3 2010Santiago Gómez-Quero Abstract Solvent effects in the liquid phase (0.1 MPa; 303 K) hydrodechlorination (HDC) of 2,4-dichlorophenol have been established over Pd/Al2O3. In the absence of secondary reactions, catalyst deactivation, and transport limitations, a stepwise HDC yields 2-chlorophenol and phenol, where product selectivity was insensitive to the nature of the solvent. In contrast, the initial HDC rates exhibited a marked dependence on the reaction medium and increased in the order: benzene < THF < n -hexane < cyclohexane < alcohols < water. Higher rates result from the concomitant effect of an increase in the dielectric constant (,) and a decrease in the molar volume ( ) of the solvent, where the major (ca. 80%) contribution is due to ,. We attribute this response to the increased solvent capacity to stabilize the arenium intermediate at higher/lower ,/, an effect that extends to reaction in water + organic combinations. We provide, for the first time, a reliable quantification of solvent effects that can be potentially applied to other catalytic hydrogenolysis systems. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Using estimated thermodynamic properties to model accessory phases: the case of tourmalineJOURNAL OF METAMORPHIC GEOLOGY, Issue 7 2007V. J. VAN HINSBERG Abstract Accessory phases and minor components in minerals are commonly ignored in thermodynamic modelling. Such an approach seems unwarranted, as accessory phases can represent a significant element reservoir and minor components can substantially change their host mineral's stability field. However, a lack of thermodynamic data prohibits assessment of these effects. In this contribution, the polyhedron method is used to estimate the thermodynamic properties of tourmaline, a common and widespread accessory phase, stable over a range of P,T,X conditions. The polyhedron method allows ,H, S, V, CP and Vm(T,P) properties to be estimated from a linear stoichiometric summation over the fractional properties of its polyhedron constituents. To allow for estimates of tourmaline, fractional thermodynamic properties for BIII and BIV polyhedra were derived. Mixing contributions to molar volume were evaluated and symmetrical mixing parameters derived for Al-Mg, Al-Fe and Al-Li interaction on tourmaline's Y-site and T-site Al-Si interaction. Evaluation of the estimated properties using experimental and natural equilibria between tourmaline and melts, minerals and hydrothermal fluids, shows that reliable semi-quantitative results are obtained. The boron contents in fluids coexisting with tourmaline are calculated to within an order of magnitude of measured content, and where anchor-points are available, agreement improves to within a factor of 2. Including tourmaline in petrogenetic modelling of metamorphic rocks indicates that its presence leads to disappearance of staurolite and garnet, among others, and modifies the XMg of coexisting phases, in line with observations on natural rocks. [source] A new method to calculate end-member thermodynamic properties of minerals from their constituent polyhedra I: enthalpy, entropy and molar volumeJOURNAL OF METAMORPHIC GEOLOGY, Issue 3 2005V. J. VAN HINSBERG Abstract The thermodynamic properties of silicate minerals can be described as a linear combination of the fractional properties of their constituent polyhedra. In contrast, given the thermodynamic properties of these polyhedra, the thermodynamic properties of minerals can be estimated, where only the crystallography of the mineral needs to be known. Such estimates are especially powerful for hypothetical mineral end-members or for minerals where experimental determination of their thermodynamic properties is difficult. In this contribution the fractional enthalpy, entropy and molar volume for 35 polyhedra have been determined using weighted multiple linear regression analysis on a data set of published mineral thermodynamic properties. The large number of polyhedra determined, allows calculation of a much larger variety of phases than was previously possible and the larger set of minerals used provides more confident fractional properties. The OH-bearing minerals have been described by partial and total hydroxide coordinated components, which gives better results than previous models and precludes the need of a S,V term to improve estimates of entropy. However, the fractional thermodynamic properties only give adequate results for silicate minerals and double oxides, and should therefore not be used to estimate the properties of other minerals. The thermodynamic properties of ,new' minerals are calculated from a linear stoichiometric combination of their constituent polyhedra, resulting in estimates generally with associated uncertainty of <5%. The quality of such data appears to be of sufficient accuracy for thermodynamic modelling as shown for meta-bauxites from the Alps and the Aegean, where the effect of Zn on the P,T stability of staurolite can be both qualitatively and quantitatively reproduced. [source] Primary carbonate/CO2 inclusions in sapphirine-bearing granulites from central Sri LankaJOURNAL OF METAMORPHIC GEOLOGY, Issue 3 2000Bolder-Schrijver High-density CO2 -rich fluid inclusions from a sapphirine-bearing granulite (Hakurutale, Sri Lanka) have been studied by microthermometry, Raman spectrometry and SEM analysis. Based on textural evidence, two groups of inclusions can be identified: primary, negative crystal shaped inclusions (group I) and pseudo-secondary inclusions, which experienced a local, limited post-trapping modification (group II). Both groups contain magnesite as a daughter mineral, occurring in a relatively constant fluid/solid inclusion volume ratio (volsolid =0.15 total volume). CO2 densities for group I and II differ only slightly. Both groups contain a fluid, which was initially trapped at peak metamorphic conditions as a homogeneous (CO2+MgCO3) mixture. Thermodynamic calculations suggest that such a fluid (CO2+15 vol% MgCO3) is stable under granulite facies conditions. After trapping, magnesite separated upon cooling, while the remaining CO2 density suffered minor re-adjustments. A model isochore based on the integration of the magnesite molar volume in the CO2 fluid passes about 1.5,2 kbar below peak metamorphic conditions. This remaining discrepancy can be explained by the possible role of a small quantity of additional water. [source] PSRK method for gas hydrate equilibria: I. Simple and mixed hydratesAICHE JOURNAL, Issue 1 2004Ji-Ho Yoon Abstract A thermodynamic model using the predictive Soave-Redlich-Kwong (PSRK) group contribution method to calculate the fugacities of all components in the vapor and liquid phases in equilibrium with the coexisting hydrate phase is proposed. Since the PSRK method together with the UNIFAC model takes the gas,gas interaction in the vapor and liquid phases into account, the phase equilibria of mixed gas hydrates can be successfully reproduced. This approach greatly improves upon the accuracy of the modified Huron-Vidal second-order (MHV2) model, especially for three-guest hydrate systems. Based on experimentally determined X-ray data, an accurate representation for the molar volume of the structure I (sI) hydrate is provided and used for predicting the equilibrium dissociation of methane hydrate at high pressures. Using this correlation, it is possible to reduce noticeable errors in dissociation predictions of high-pressure hydrate formers. Complete phase behavior, including a new quadruple point, which is predicted to be 272.6 K and 7.55 MPa, for cyclopropane hydrate, is presented by the proposed model calculation. © 2004 American Institute of Chemical Engineers AIChE J, 50: 203,214, 2004 [source] Volume-translated equations of state: Empirical approach and physical relevanceAICHE JOURNAL, Issue 6 2003Leonid V. Yelash The volume translation technique is widely applied in chemical engineering modeling of phase behavior and thermodynamic properties. This empirical correction of the molar volume improves the correlation of liquid densities when cubic equations of state are employed. Based on a recently proposed method of analyzing equations of state, the influence of the volume translation on the properties obtained from an equation of state, such as virial coefficients, as well as on the phase behavior, critical properties, the isobaric thermal expansion coefficient, and the heat capacities of pure substances is investigated. The influence of different kinds of temperature-dependent volume translations is investigated and compared to approaches that originate from theoretical considerations. The investigation shows that empirical as well as theoretical approaches for the development of equations of state can exhibit nonphysical behavior. However, the understanding of the reasons for such problems can help to develop reliable equations of state based on both kinds of method. [source] Calculation of densities from cubic equations of stateAICHE JOURNAL, Issue 4 2002Ulrich K. Deiters Some cubic equations of state can eventually have unphysical solutions for the molar volume. The conditions for this phenomenon are discussed. The computational accuracy and computing time requirements of the analytical root finding method (Cardano's formula) are investigated. A new, faster iterative root finder for cubic polynomials is proposed. [source] Differences in the interaction between aryl propionic acid derivatives and poly(vinylpyrrolidone) K30: A multi-methodological approachJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 11 2009Zehadin Gashi Abstract The present work aims at the application of several methods to explain differences in the physical interaction of some aryl propionic acid derivatives (ibuprofen [IBP], ketoprofen [KET], flurbiprofen [FLU], naproxen [NAP], fenbufen [FEN]) with poly(vinylpyrrolidone) (PVP) K30, stored together at 298,±,0.5 K and 22% RH. X-ray powder diffractometry and 13C-solid state NMR demonstrated that IBP was able to strongly interact with the polymer, while weak interaction was observed for KET, FLU, NAP, and the least for FEN. The interaction of comelted drug and PVP was studied by differential scanning calorimetry by applying the Gordon,Taylor equation, which revealed that small molar drug volumes may favour the drug diffusion through the PVP amorphous chains increasing the polymer free volume and decreasing the mixture Tg. The molecular docking study revealed that intermolecular energy is mainly due to the contribution of van der Waals energy component, causing the differences among the drugs, and is related to the drug,PVP surface contact area in the complex formed. Solid-state kinetic study demonstrated that IBP molecules are involved in a three-dimensional diffusion mechanism within the polymer favoured by its low molar volume that reduces molecular hindrance, and by the weakness of its crystal lattice, which facilitates crystallinity loss and stabilisation of the amorphous phase. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:4216,4228, 2009 [source] Informatic calibration of a materials properties database for predictive assessment of mechanically activated disordering potential for small molecule organic solidsJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 8 2009Yannan Lin Abstract The potential for small molecule organic crystalline materials to become disordered as a result of high shear mechanical processing was investigated. A data-driven model was generated from a database of critical materials properties, which were expected to correlate with the potential of a small molecule organic crystalline solid to become fully disordered by the application of mechanical energy. The model was compared with a previously published disordering model based on fundamental thermodynamic relationships. Samples of 23 crystalline solids were subjected to extensive comminution under controlled temperature conditions; powder X-ray diffraction (PXRD) and differential scanning calorimetry (DSC) were used to confirm disordering. Logistic regression was used to investigate the significance of each materials property with respect to the prediction of disordering potential. Seven materials properties (glass transition temperature, melting temperature, heat of fusion, crystallographic density, Young's modulus, molar volume and attachment energy) were identified as having a significant correlation with the potential for material disordering. Stepwise multivariate logistic regression was used to further assess the correlation between disordering potential and each of the seven properties. A linear probability model based on two materials properties (glass transition temperature and molar volume) was developed for the prediction of disordering potential. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:2696,2708, 2009 [source] Density, Surface Tension, and Viscosity of PbO-B2O3 -SiO2 Glass MeltsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2004Shigeru Fujino The density, surface tension, and viscosity of the melts from the PbO-B2O3 -SiO2 system have been measured at temperatures in the range 1073,1473 K. The effect of composition on these properties was also investigated. The density of the melt was found to increase linearly with increasing PbO content. Molar volume was derived from the density data, and its deviation from the additivity of partial molar volumes was calculated. These deviations in molar volume from those obtained from additivity rules have been used along with the ratio of various coordination numbers of boron (as reported by Bray) to discuss the structure of the melts. The surface tension was found to decrease with decreasing SiO2/B2O3 ratio, and to increase in the range of the PbO content between 30 and 60 mol%, showing a maximum at ,60 mol% PbO, and then decreased with further additions. This result suggested that the surface tension would be affected primarily by the B2O3 content in the range of the PbO content between 30,60 mol%, and mainly by the PbO content in the range of the PbO content >60 mol%, respectively. The viscosity of the melt was found to decrease linearly with increasing PbO content. The results obtained indicate that the increase in viscosity with B2O3 was half that of SiO2 (on a molar basis), and an empirical equation has been proposed for the viscosity as a function of mole fraction. [source] Independent Effects of Nitrogen Substitution for Oxygen and Yttrium Substitution for Magnesium on the Properties of Mg-Y-Si-Al-O-N GlassesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2003Michael J. Pomeroy Glasses of composition (in equivalent percent) (28 ,x)Mg:xY:56Si:16Al:(100 ,y)O:yN, with x= 0, 14, or 28 for y= 0 and 15 and with x= 0, 7, 14, 21, or 28 for y= 10, were prepared by melting and casting. For glasses where the nitrogen content was varied for a constant cationic ratio, the glass molar volume (MV), compactness (C), Young's modulus (E), glass-transition temperature (Tg), and dilatometric-softening temperature (Tds) varied linearly as the nitrogen content increased, with MV decreasing and the other properties increasing. From the incremental changes in these properties with nitrogen content, for glasses with x= 0, 14, and 28, good linear fits (R2 > 0.99) were obtained, and best-fit slopes are reported here. The property changes and their linearity were consistent with the increased cross-linking of the glass network by tricoordinated nitrogen. The replacement of magnesium by yttrium led to a nonlinear decrease in glass compactness and to nonlinear increases in MV, Tg, and Tds. However, linear correlations were found for MV and ionic volume and for Tg, Tds, and the coordination of (Si,Al)(O,N) tetrahedra of the glass structural units to the modifier cations not involved in charge compensating aluminum ions in fourfold coordination. The replacement of magnesium by yttrium had little effect on Young's modulus, and this result was related to similar changes in the compactness, C. The present results showed that the effects of substituting nitrogen for oxygen and yttrium for magnesium are independent and additive; thus, no synergistic effects of anion and cation substitutions were observed. [source] Sorption and Swelling of Poly(D,L-lactic acid) and Poly(lactic-co-glycolic acid) in Supercritical CO2MACROMOLECULAR SYMPOSIA, Issue 1 2007Ronny Pini Abstract Summary: The equilibrium sorption and swelling behavior in supercritical CO2 of poly(D,L-lactic acid) and poly(lactic-co-glycolic acid) has been studied at a temperature of 35,°C and at pressures up to 200 bar. Sorption was measured through a gravimetric technique and swelling by visualization. From these data, the behavior of the different polymers can be compared. In terms of partial molar volume of CO2 in the polymer matrix, all the polymers exhibit a behavior typical of rubbery systems. The experimental results have been modeled using the Sanchez-Lacombe equation of state, which is able to represent the actual behavior of the polymer-CO2 systems with reasonable accuracy. [source] On Lindemann's Melting CriterionMATERIALWISSENSCHAFT UND WERKSTOFFTECHNIK, Issue 2 2004H.-J. Hoffmann Schmelzen; Schmelztemperatur; Schmelzkriterium; Lindemann-Kriterium Abstract Lindemann's empirical melting criterion is applied using data of the solid chemical elements. The respective expression which depends on the melting temperature, the molar mass and the molar volume correlates fairly well with the Debye temperatures. However, it seems incapable to predict inversely the melting temperatures with the other parameters given. Thus, Lindemann's criterion has no empirical relevance in addition to its scientific deficits. Über das Schmelzkriterium von Lindemann Das empirische Schmelzkriterium nach Lindemann wird an Hand von Daten der festen chemischen Elemente geprüft. Der betreffende Ausdruck, der von Schmelztemperatur, Molmasse und Molvolumen abhängt, korreliert recht gut mit der Debye-Temperatur. Es gelingt jedoch nicht mit befriedigender Genauigkeit, die Schmelztemperaturen aus der Umkehrung dieses Ausdrucks bei gegebenen anderen Parametern vorherzusagen. Neben den anderen bekannten Mängeln hat das Lindemann-Kriterium somit auch keine empirische Vorhersagekraft. [source] Non-adiabatic small polaron hopping conduction in sodium borate tungstate glassesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 2 2003A. Al-Shahrani Abstract The dc electrical conductivity of (100,x)Na2B4O7,xWO3 (x = 5, 15, 20 and 30 mol%) glasses is reported in the temperature range 323,473 K. The density and molar volume for these glasses are consistent with the ionic size, atomic weight and amount of different elements in the glasses. At high temperatures the Mott model of phonon-assisted small polaron hopping between nearest neighbours is consistent with conductivity data, while at intermediate temperatures the Greaves variable-range hopping model is found to be appropriate. The estimated model parameters such as number of ions per unit volume, hopping distance, polaron radius and activation energy are found to be consistent with the formation of localized states in these glasses. The electrical conduction of these glasses is confirmed to be that of non-adiabatic small polaron hopping. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Analysis of phase transition and expansion behaviour of Al2(WO4)3 by temperature-regulated X-ray diffractionPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 11 2008Takuya Hashimoto Abstract X-ray diffraction measurements of Al2(WO4)3 were carried out under various temperatures from 123 K to 373 K. Diffraction patterns above 273 K and below 253 K could be successfully explained as orthorhombic Pbcn (No. 60) and monoclinic P21/n (No. 14) with superstructure, respectively, which were in agreement with the results of convergent-beam electron diffraction. Thermal expansion of low-temperature monoclinic phase and slight shrinkage of high-temperature orthorhombic phase were observed from the temperature dependence of lattice constants and molar volume, showing agreement with the result of dilatometry. It is revealed that abrupt expansion of Al2(WO4)3 at the structural phase transition is attributed to an abrupt increase of the c -axis, which is parallel to the 21 screw axis and perpendicular to the n-glide plane. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Environmental stress cracking behavior of bottle and fiber grade poly(ethylene terephthalate) in contact with aqueous amine solutionsPOLYMER ENGINEERING & SCIENCE, Issue 10 2008Nadir de B. Sanches The environmental stress cracking (ESC) resistance of commercial virgin bottle and fiber grade poly(ethylene terephthalate) (PET) in contact with aqueous amine solutions was investigated. The ESC resistance, in terms of time to failure, was evaluated taking into account some factors, such as test temperature, molar volume (Vo) of the ESC agent, and molecular weight and degree of crystallinity (Xc) of PET. The specimens were tested in flexural mode using a constant load flexural creep test apparatus and also in tensile mode using a dynamometer. After the creep tests, the specimens were photographed with a digital camera and analyzed by scanning electron microscopy (SEM). It was found that ESC resistance was higher with the increase of ESC agent molar volume as well as with the increase of molecular weight and degree of crystallinity of PET. The highest temperature (60°C) lowered the ESC resistance of the specimens, except for the crystalline specimens in n -butylamine that exhibited a higher ESC resistance at 60°C, which can probably be attributed to the induced crystallization of the remaining amorphous phase by the plasticizing effect of n -butylamine. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers [source] Anisotropic crystal structure distortion of the monoclinic polymorph of acetaminophen at high hydrostatic pressuresACTA CRYSTALLOGRAPHICA SECTION B, Issue 2 2000E. V. Boldyreva The anisotropy of structural distortion of the monoclinic polymorph of acetaminophen induced by hydrostatic pressure up to 4.0,GPa was studied by single-crystal X-ray diffraction in a Merrill,Bassett diamond anvil cell (DAC). The space group (P21/n) and the general structural pattern remained unchanged with pressure. Despite the overall decrease in the molar volume with pressure, the structure expanded in particular crystallographic directions. One of the linear cell parameters (c) passed through a minimum as the pressure increased. The intramolecular bond lengths changed only slightly with pressure, but the changes in the dihedral and torsion angles were very large. The compressibility of the intermolecular hydrogen bonds NH,O and OH,O was measured. NH,O bonds were shown to be slightly more compressible than OH,O bonds. The anisotropy of structural distortion was analysed in detail in relation to the pressure-induced changes in the molecular conformations, to the compression of the hydrogen-bond network, and to the changes in the orientation of molecules with respect to each other in the pleated sheets in the structure. Dirichlet domains were calculated in order to analyse the relative shifts of the centroids of the hydrogen-bonded cycles and of the centroids of the benzene rings with pressure. [source] True and Apparent Temperature Dependence of Protein Adsorption Equilibrium in Reversed-Phase HPLCBIOTECHNOLOGY PROGRESS, Issue 6 2002Szabelski The adsorption behavior of bovine insulin on a C8 -bonded silica stationary phase was investigated at different column pressures and temperatures in isocratic reversed-phase HPLC. Changes in the molar volume of insulin (, Vm) upon adsorption were derived from the pressure dependence of the isothermal retention factor ( k,). The values of , Vm were found to be practically independent of the temperature between 25 and 50 °C at ,96 mL/mol and to increase with increasing temperature, up to ,108 mL/mol reached at 50 °C. This trend was confirmed by two separate series of measurements of the thermal dependence of ln( k,). In the first series the average column pressure was kept constant. The second series involved measurements of ln( k,) under constant mobile-phase flow rate, the average column pressure varying with the temperature. In both cases, a parabolic shape relationship was observed between ln( k,) and the temperature, but the values obtained for ln k, were higher in the first than in the second case. The relative difference in ln( k,), caused by the change in pressure drop induced by the temperature, is equivalent to a systematic error in the estimate of the Gibbs free energy of 12%. Thus, a substantial error is made in the estimates of the enthalpy and entropy of adsorption when neglecting the pressure effects associated with the change in the molar volume of insulin. This work proves that the average column pressure must be kept constant during thermodynamic measurements of protein adsorption constants, especially in RPLC and HIC. Our results show also that there is a critical temperature, Tc , 53 °C, at which ln( k,) is maximum and the insulin adsorption process changes from an exothermic to an endothermic one. This temperature determines also the transition point in the molecular mechanism of insulin adsorption that involves successive unfolding of the protein chain. [source] A theoretical study on the structures and energetics of hypothetical TiM(NCN)3 compounds of the 3d transition metalsJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 11 2005Maxence Launay Abstract Quasi-ternary cyanamides and carbodiimides of general formula AB(NCN)3 with A , B have neither been predicted nor synthesized. Thus, hypothetical compounds of that kind containing 3d transition metals were considered (A = Ti, B = Mn, Fe, Co, Ni, Cu) by means of density-functional calculations on 34 structural models, most of which were derived from chemically related phases. After performing structure optimizations based on the local-density approximation, the relative energetic orderings are rationalized in terms of geometrical factors such as molar volumes and polyhedral connections. Total-energy generalized-gradient calculations evidence that the most stable models are enthalpically favored with respect to the elements. Even at ambient temperatures, the ternary phases are predicted as being thermodynamically stable in terms of their Gibbs free formation energies, especially if energetically competing and low-lying binaries (TiC, TiN) can be excluded by a kinetic reaction control. The best models are characterized by low-spin magnetic transition metals found in octahedral coordination, and the TiN6 and MN6 polyhedra either share faces or edges. © 2005 Wiley Periodicals, Inc. J Comput Chem 26: 1180,1188, 2005 [source] Molecular simulation of ammonia absorption in the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([emim][Tf2N])AICHE JOURNAL, Issue 9 2009Wei Shi Isotherms for ammonia absorption in the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([emim][Tf2N]) are computed at temperatures ranging from 298 K to 348 K using osmotic ensemble Monte Carlo simulations. The results agree well with previous experimental measurements. Activity coefficients vary from 0.5 to 0.8, indicating negative deviations from Raoult's Law. The computed enthalpy of mixing ranges from ,2 to ,11 kJ/mol. Computed partial molar volumes are on the order of 25,30 cm3/mol. Energy and radial distribution analyses indicate that ammonia interacts more strongly with the cation than the anion, in contrast to observations made of other gases in ionic liquids such as CO2. The reason for this behavior is that ammonia forms a strong hydrogen bond with the ring hydrogen atoms of the cation. The simulations predict that strategies aimed at changing the solubility of ammonia should focus on altering the hydrogen bond donating ability of the cation, and that altering the anion will have more modest effects. It is shown that this hypothesis is consistent with available experimental data. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Density, Surface Tension, and Viscosity of PbO-B2O3 -SiO2 Glass MeltsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2004Shigeru Fujino The density, surface tension, and viscosity of the melts from the PbO-B2O3 -SiO2 system have been measured at temperatures in the range 1073,1473 K. The effect of composition on these properties was also investigated. The density of the melt was found to increase linearly with increasing PbO content. Molar volume was derived from the density data, and its deviation from the additivity of partial molar volumes was calculated. These deviations in molar volume from those obtained from additivity rules have been used along with the ratio of various coordination numbers of boron (as reported by Bray) to discuss the structure of the melts. The surface tension was found to decrease with decreasing SiO2/B2O3 ratio, and to increase in the range of the PbO content between 30 and 60 mol%, showing a maximum at ,60 mol% PbO, and then decreased with further additions. This result suggested that the surface tension would be affected primarily by the B2O3 content in the range of the PbO content between 30,60 mol%, and mainly by the PbO content in the range of the PbO content >60 mol%, respectively. The viscosity of the melt was found to decrease linearly with increasing PbO content. The results obtained indicate that the increase in viscosity with B2O3 was half that of SiO2 (on a molar basis), and an empirical equation has been proposed for the viscosity as a function of mole fraction. [source] Urea interactions with protein groups: A volumetric study,BIOPOLYMERS, Issue 10 2010Soyoung Lee Abstract We determined the partial molar volumes and adiabatic compressibilities of N -acetyl amino acid amides, N -acetyl amino acid methylamides, N -acetyl amino acids, and short oligoglycines as a function of urea concentration. We analyze these data within the framework of a statistical thermodynamic formalism to determine the association constants for the reaction in which urea binds to the glycyl unit and each of the naturally occurring amino acid side chains replacing two waters of hydration. Our determined association constants, k, range from 0.04 to 0.39M. We derive a general equation that links k with changes in free energy, ,Gtr, accompanying the transfer of functional groups from water to urea. In this equation, ,Gtr is the sum of a change in the free energy of cavity formation, ,,GC, and the differential free energy of solute,solvent interactions, ,,GI, in urea and water. The observed range of affinity coefficients, k, corresponds to the values of ,,GI ranging from highly favorable to slightly unfavorable. Taken together, our data support a direct interaction model in which urea denatures a protein by concerted action via favorable interactions with a wide range of protein groups. Our derived equation linking k to ,Gtr suggests that ,,GI and, hence, the net transfer free energy, ,Gtr, are both strongly influenced by the concentration of a solute used in the experiment. We emphasize the need to exercise caution when two solutes differing in solubility are compared to determine the ,Gtr contribution of a particular functional group. © 2010 Wiley Periodicals, Inc. Biopolymers 93: 866,879, 2010. [source] | ||||||||||||||||