The Partial Molar Volume and Heat Capacity of the Glycyl Group in Aqueous Solution at 25^C

The partial molar volumes, V₂ ^{^}, and the partial molar heat capacities, C_p,2 ^{^}, at infinite dilution have been determined for three new peptides of sequence seryl(glycyl)_xglycine, where x=0 to 2, in aqueous solution at 25^{^}C. Values for V₂ ^{^} at 25^°C have also been determined for two neutral peptide derivatives N-acetylglycylglycinamide and N-acetylglycylglycylglycinamide. These V₂ ^°; and C_p,2 ^°; results were used to estimate the partial molar volume and heat capacity of the backbone glycyl group, CH₂CONH, of proteins in aqueous solution at 25^°;C. The results obtained are compared with those calculated using partial molar data for alternative model compounds. The new glycyl group contributions are in excellent agreement with those currently used in our group additivity schemes for the calculation of the partial molar volumes and heat capacities of unfolded proteins.     

Retention study on silica gel in high-temperature liquid chromatography (HTLC)

Summary Retention volumes (V _N) of different kinds of test compound have been measured on silica gel as a function of column temperature (T) in the range 20 to 210°C.n-Heptane and mixtures ofn-heptane and polar modifiers were used as mobile phases. With nC7 and nC7-1,4-dioxane mixtures, there was a good linear relationship between InV _N and 1/T for column temperatures above 100 °C. When more polar modifiers such as butanol, ethanol and acetic acid were used, ‘N’-shaped curves were obtained for the plots of InV _N against 1/T. Possible explanations of this retention behavior have been proposed on the basis of related studies and common physical chemistry relationships. Column equilibration time after alteration of water content or column temperature is greatly reduced at elevated temperatures. This will benefit the application of LSC on silica gel.     

The Effect of the Molecular Size and Shape on the Volume Behavior of Binary Liquid Mixtures. Branched and Cyclic Alkanes in Heptane at 298.15 K

Excess molar volumes V ^E for 40 mixtures of heptane with a liquid alkane and apparent molar volumes in heptane for eight solid alkanes have been obtained at 298.15 K. They include five linear, 30 branched-chain, and 13 cyclic alkanes. Almost all systems exhibit negative V ^E values. For mixtures with open chain alkanes, V ^E increases from C5 to C7 and then decreases. A similar trend is shown by mixtures with cycloalkanes. V ^E values are compared with known H ^E data for mixtures with heptane and tetrachloromethane. Signs and trends of V ^E and H ^E are correlated with the free volume and interactional terms of the Flory theory. The partial molar volumes at infinite dilution in heptane, V°, have also been obtained and discussed together with literature data on other hydrocarbons and polar compounds. The calculated contributions to V° by CH₃, CH₂, CH and C groups are compared with previously determined contributions of polar groups. The lower contributions of the latter groups are explained with the volume contraction caused by dipole-induced dipole interaction. The volume effects associated with branching and cyclization have been evaluated and compared with the corresponding effects on solvation enthalpy. The branching effect, in the order of magnitude of few cm³·mol^?1, and the larger negative values of cyclization volumes, down to ?24 cm³·mol^?1, are discussed in terms of packing and solute–solvent interactions, in analogy to polar organic solutes either in heptane and tetrachloromethane. A negative cyclization effect is also exhibited by the solvation enthalpies.     

Densities and compressibilities of aqueous sodium carbonate and bicarbonate from 0 to 45°C

The densities and the sound speeds of aqueous NaHCO₃ and Na₂CO₃ solutions were measured from 0.05 to 1.0m and from 0 to 45°C. These data were fitted to functions of molality and temperature and were used to calculate the apparent molal volumes V_? and compressibilites κ_φ of these solutions. Polynomial expression for V_? and κ_φ as functions of molality and temperature have been determined. The partial molal volumes and compressibilities of these solutions and literature data have been used to determine the volume ΔV and compressibility Δκ changes for the ionization of carbonic acid in aqueous solutions. These values of ΔV and Δκ have been used to estimate the effect of pressure on the ionization constants for carbonic acid from 0 to 45°C. The calculated pressure coefficients are in good agreement with the measured values.     

Vanadium- and molybdenum-containing compositions prepared by mechanochemical and following thermal treatments of V2O5/(NH4)2Mo2O7 (V/Mo = 0.7/0.3)

X-ray powder diffraction, DTA, FT-IR spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), nitrogen adsorption, and mercury porometry were used to characterize samples prepared as a result of mechanochemical treatment (MCT) of a V₂O₅/(NH₄)₂Mo₂O₇ (V/Mo = 0.7/0.3) composition in water, ethanol, and air, as well as after calcining them at temperatures from the range 300–700°C. The MCT of nonporous powders in water yields porous materials with definite meso- and macropore sizes. Heat treatment in air at 300–450°C enhances the formation of a molybdenum substitutional solid solution in V₂O₅ and conserves rather high values of specific surface areas and pore volumes. An increase in heat treatment temperature is accompanied by the degradation of the solid solution and the formation of a V₂MoO₈ phase.     

New-phased metastable V(2) O(3) porous urchinlike micronanostructures: facile synthesis and application in aqueous lithium ion batteries

New‐phased metastable V₂O₃ porous urchinlike micronanostructures were first fabricated on a large scale by a simple top‐down strategy of pyrolyzing a vanadyl ethylene glycolated precursor in the absence of any templates or matrices. The pyrolysis mechanism was clearly revealed by synchrotron vacuum ultraviolet (VUV) photoionization mass spectra for the first time. The new‐phased metastable V₂O₃ exhibits a body‐centered cubic bixbyite structure and shows structural evolution from metastable cubic symmetry to thermodynamically stable rhombohedral symmetry V₂O₃ (R) above 510 °C. Furthermore, the prepared V₂O₃ porous urchinlike micronanostructures, as anode materials in aqueous lithium ion batteries, exhibit improved electrochemical properties with relatively high first discharge capacity and better cycle retention relative to thermodynamically stable V₂O₃ (R), which is derived from its unique microscopic crystal structure and macroscopic 3D framework with rigid morphology, porous structure, and high specific surface area.     

Appraisal of an Empirical Model for Simulation of Retention from Structure in Temperature-Programmed Gas Chromatography

The solvation parameter model and response surface methodology are evaluated for the prediction of retention in temperature-programmed gas chromatography. A large and varied group of compounds were separated at a constant flow rate on three columns of different selectivity (DB-1701, DB-210 and EC-Wax) with initial temperature in the range 60–120 °C and program rates of 1–15 °C min^?1. The solvation parameter model provides an acceptable fit to the experimental retention factors independent of column identity, initial temperature and program rate. The system coefficients of the solvation parameter model are shown to fit a second order program rate model of the form system coefficient = a_o + a₁ X + a₂ X ² where X is the program rate (°C min^?1) and a_o, a₁ and a₂ are fitting coefficients with no physical significance. Response surface methodology was used to derive empirical models to predict system coefficients with program rate and initial temperature as variables. These models explain the experimental data quite well but are local models that depend on the average properties of the solutes used for their derivation. Since they dependent on solute identity, these models are unsuitable for the general prediction of retention from structure, but may prove useful for estimating retention associated with variation in experimental variables for a defined group of compounds.     

Polybutadiene-coated zirconia packing materials in solvating gas chromatography using carbon dioxide as mobile phase

Summary In this paper, practical considerations of column efficiency, separation speed, thermal stability, and column polarity of capillary columns packed with polybutadiene-coated zirconia were investigated under solvating gas chromatography (SGC) conditions using carbon dioxide as mobile phase. When compared with results obtained from conventional porous octadecyl obtained from conventional porous octadecyl bonded silica (ODS) particles, PBD-zirconia particles produced greater change in mobile phase linear velocity with pressure than conventional ODS particles under the same conditions. The maximum plate number per second (N_t) obtained with a 30 cm PBD-zirconia column was approximately 1.5 times higher than that obtained with an ODS column at 100 °C. Therefore, the PBD-zirconia phase is more suitable for fast separations than conventional ODS particles in SGC. Maximum plate numbers per meter of 76,900 and 63,300 were obtained using a 57 cm×250 μm i.d. fused silica capillary column packed with 3 μm PBD-zirconia at 50 °C and 100 °C, respectively. The PBD-zirconia phase was stable at temperatures up to 320 °C under SGC conditions using carbon dioxide as mobile phase. Polarizable aromatic compounds and low molecular weight ketones and aldehydes were eluted with symmetrical peaks from a 10 cm column packed with 3 μm PBD-zirconia. Zirconia phases with greater inertness are required for the analysis of more polar compounds by SGC.     

Soluble aromatic polyamide and polyimides derived from di(aminophenyl) acetylenediurea

New aromatic polyamide and polyimides were prepared from di(aminophenyl)acetylenediurea. In addition, model compounds were synthesized and their IR spectra were in agreement with those of the corresponding polymers. The polymers were amorphous and readily soluble in polar aprotic solvents (DMF, NMP, DMSO) and certain acids (H₂SO₄, CCl₃COOH). The hydrophilicity of polyamide was estimated by measuring the isothermal water absorption. The polyamide softened at 260°C but no softening was observed for polyimides. The glass transition temperatures of polymers were determined by the TMA method and they were in the range of 235–310°C. The polymers were stable up to 359–404°C in N₂ or air and afforded char yields of 53–65% at 800°C in N₂. © 1996 John Wiley & Sons, Inc.     

Thermodynamic study of (heptane + amine) mixtures. II. Excess and partial molar volumes at 298.15 K

Excess molar volumes V^E at 298.15 K were determined by means of a vibrating tube densimeter for binary mixtures of heptane + primary n-alkyl (C₃ to C₁₀) and branched amines (iso-propyl-, iso-, sec-, and tert-butyl-, iso-, tert-pentyl-, and pentan-3-amine) in the whole composition range. The apparent molar volumes of solid dodecyl- and tetradecylamine in heptane dilute solution were also determined. The V^E values were found positive for mixtures involving C₃ to C₈ linear amines, with V^E decreasing with chain lengthening. Heptane + nonyl and decylamine showed s-shaped, markedly asymmetric, curves. Mixtures with branched C₃ to C₅ amines displayed positive V^E’s larger than those observed in the mixtures of the corresponding linear isomers. Partial molar volumes V° at infinite dilution in heptane were evaluated for the examined amines and compared with those of alkanes and alkanols taken from the literature. An additivity scheme, based on the intrinsic volume approach, was applied to estimate group (CH₃, CH₂, CH, C, NH₂, and OH) contributions to V°. The effect of branching on V° and the limiting slope of the apparent excess molar volumes were evaluated and discussed in terms of solute–solvent and solute–solute interactions.     

Progress in the syndiotactic polymerization of styrene with metallocene/mao catalysts

Metallocene/MAO catalysts are useful for the production of syndiotactic polystyrene - a new class of high performance polymers. The melting point of the obtained syndiotactic polystyrene depends on the metallocene used and can reach up to 275 °C. In the past, the most active catalysts in polymerization have been half-sandwich titanocenes such as CpTiCl₃ and Cp*TiCl₃. If the chlorinated compounds are changed into the fluorinated compounds as CpTiF₃ and Cp*TiF₃, the activity increases by a factor of 5 to 100. The fluorinated titanocenes are more stable at higher temperatures and need a lower MAO excess in order to obtain optimal activities. Polymers obtained with the unsubstituted CpTiF₃ show melting points which are 17 °C lower than those synthesized by pentamethylcyclopentadienyltitaniumtrifluoride. Especially Cp*TiF₃ shows a much higher activity and, compared with the chlorinated compound, gives polymers with a higher molecular weight. Substituted cyclopentadienyltitanocenes have even higher activities. Ethene/styrene copolymers can be obtained by catalysis with zirconocene compounds.     

The adsorption of H<Subscript>2</Subscript>O and D<Subscript>2</Subscript>O on porous polystyrene adsorbents

The adsorption of H₂O and D₂O on porous polymers, Chromosorb-102 (styrene-divinylbenzene copolymer) and MN-200 (supercross-linked polystyrene), was studied by gas chromatography. Test adsorbates used to study the properties of the surface of these polymers were n-alkanes (C₆-C₉), C₆H₆, and the polar compounds CHCl₃, CH₃NO₂, CH₃CN, (CH₃)₂CO, C₂H₅COOCH₃, and (C₂H₅)₂O. The experimental data on the retention of the sorbates were used to determine the contributions of dispersion and specific intermolecular interactions to the total energy of adsorption for the systems studied. The electron donor K _D and electron acceptor K _A characteristics of the surfaces of Chromosorb-102 and MN-200 were determined. The K _D and K _A values obtained allow these polymers to be classified as weakly specific adsorbents with the predominance of electron acceptor properties. The adsorption isotherms of H₂O and D₂O were measured at 55, 67, and 80°C. The dependences of the isosteric heats of adsorption Q _st on adsorption values were determined. The conclusion was drawn that H₂O interacted with the surface of the polymers by the adsorption mechanism, whereas absorption likely made a noticeable contribution to the retention of D₂O.     

High Performance Size Exclusion Chromatography Using Porous Glass Packing Materials

Abstract

Porous glass packing materials of average particle diameter 5 μm have been packed into a 7.2 mm i.d. x 25 cm column by viscousslurry packing parocedure. Average pore diameters of porous glasses were 170 Â, 500 Â, 1000 A, and 2000 A. The numbers of theoretical plates were between 7000 and 8000 per a column for porous glasses of pore diameters of 170, 500, and 1000 A, and 5000 for that of 2000 A. The retention volumes of narrow molecular weight-distribution polystyrene standards have been determined using tetrahydrofuran as mobile phase for the construction of calibration curves. Separations of polystyrene over molecular weight ranges of 1000 and 4,000,000 have been obtained by combining all four porous glass columns in series. Molecular weight averages of NBS 706 polystyrene have been measured and compared with the values determined with polystyrene gel columns. Both results were equivalent to the manufacturer's data. Porous glasses thus appear to be a useful packing materials for HPSEC.     

PVT properties of concentrated aqueous electrolytes: V. Densities and apparent molal volumes of the four major sea salts from dilute solution to saturation and from 0 to 100°C

The densities of the major sea salts (NaCl, Na₂SO₄, MgCl₂, and MgSO₄) have been measured from 25 to 95°C and to saturation. These results have been combined with literature data and fitted to equations of the form $$\Delta d = Am{\text{ }} + {\text{ }}Bm^{3/2} {\text{ }} + {\text{ }}Cm^2 {\text{ }} + {\text{ }}Dm^{5/2} $$ where Δd=d?d_o (d_o is the density of water) and A, B, and C, etc., are polynomial functions of temperature. The standard deviations of the fits were better than ±50×10^?6 g-cm^?3 for all the salts from 0 to 95°C and to saturation. The apparent molal volumes V_? of the salts have been fitted to the equations of Pitzer. The infinite dilution values of V_? were in good agreement with literature data, provided the results were not overfit. The large deviations of V_? for MgSO₄ from additivity as a function of concentration were attributed to the formation of MgSO₄ ion pairs.     

Three Copper(II) Coordination Polymers Constructed by Both Rigid and Flexible Ligands

Three new Copper(II) polymers coordinated by both rigid and flexible ligands, [Cu(bpy)(C₅H₆O₄)]_n ( 1 ), [Cu(bpy)(C₆H₈O₄)]_n ( 2 ), and [Cu₂(bpy)₂(C₆H₈O₄)₂]_n ( 3 ) (bpy = 4,4′‐bipyridine), have been hydrothermally synthesized and structurally characterized. Complex 1 features a box‐like bilayer motif of (4, 4) net. It crystallizes in triclinic space group with cell parameters: a = 8.1395(6) Å, b = 9.43 12(8) Å, c = 10.5473(8) Å, α = 112.1830(1)°, β = 92.423(2)°, γ = 104.752(2)°, V = 716.31(1) ų, Z = 2. Complex 2 crystallizes in triclinic space group with a = 8.8652(4) Å, b = 8.9429(4) Å, c = 10.6390(4) Å, α = 89.520(2)°, β = 69.123(2)°, γ = 75.2440(1)°, V = 758.92(6) ų, Z = 2. Complex 3 crystallizes in monoclinic space group Cc with a = 11.1521(1) Å, b = 15.3961(1) Å, c = 17.7419(1) Å, β = 105.715(3)°, V = 2932.4(5) ų, Z = 4. Complexes 2 and 3 are isomeric with different coordination modes of adipato ligand. Both of them possess the two‐fold interpenetrated 3‐D pcu topological net.     

Use of the Tóth and Unilan Equations for Chromatographic Testing of the Adsorption Properties of Active Carbon

The adsorption and chromatographic properties of active carbon samples obtained by adsorptive/desorptive modification have been studied by inverse gas chromatography to assess their suitability for adsorption of analytes from gas and liquid phases. This paper may help in the choice of an appropriate method for characterizing the surface of an active carbon with regard to particular analytes. Therefore, the specific, V _{g (T )}, and net, V _{S ( T )}, retention volumes were determined from the retention times of the peak maxima and centres of gravity of the peaks. A mathematical link between retention volume data and the monolayer capacity, a _m , was derived by use of a hyperbolic-type equation which enables the values of the terms of the Tóth and Unilan equations to be found. Adsorption second virial coefficients, B _{2 S} , calculated from the values of the terms of the Tóth and Unilan equations were used as a sensitive test of the accuracy of the calculated data. There were no significant differences between the isosteric enthalpies obtained by use of virial coefficients or retention volumes. It was shown experimentally there is substantial parallelism between the magnitudes of the differential isosteric enthalpy and the differential entropy for propane chromatographed on the adsorption systems tested. The cause of non-linear behaviour of plots of ln V _{g ( T )} against T ^?1 for different dynamic adsorption systems is discussed.     

Determination of volatile mercury species at the picogram level by low-temperature gas chromatography with cold-vapour atomic fluorescence detection

Alkylmercury compounds were preconcentrated from air on a Carbotrap (graphitized carbon black) column at room temperature. The species were then transferred by thermal desorption to a U-tube chromatographic column packed with 15% OV-3 on Chromosorb WAW-DMSC, held at ?196°C in liquid nitrogen. The compounds were clearly separated and eluted in order of increasing polarity using a simple, ramped heating step to 180°C over 20 min. After thermal decomposition of the eluant, the resultant mercury vapour was detected by cold-vapour atomic fluorescence spectrometry. The detection limits (as Hg) for the system were approximately 0.3 pg for mercury and dimethylmercury, 0.4 pg for diethylmercury, and 2.0 pg for methylmercury chloride. A study of the Long Island Sound atmosphere showed Hg⁰ to account for 95–100% of the total mercury present, with the remainder being monomethylmercury.     

Gas—liquid chromatography on phenyl-substituted polysiloxane stationary phases,alcohols and alcohol benzoyl derivatives

Retention indices of 54 alcohols and 55 alcohol benzoyl derivatives measured on short stainless steel columns (1 m × 2 mm i.d.) filled with Chromosorb G (AWDMCS (HP)) coated with 5% ($\text{w}\text{w}$) SE-30, OV-3, OV-7, OV-11, OV-17 or OV-25 stationary phases at 100°C, 120°C and 140°C, appear to be very accurate, provided that there is careful control of the Chromatographic process. Values of the temperature dependence of retention index of alcohols and benzoates, and variations of these values with the polarity of the phase used, are given.     

One-dimensional coordination polymers generated from an oxadiazole-containing N,N′-bipyridine-type ligand and inorganic salts

Three new one-dimensional coordination polymers have been prepared using Hg(II), Ag(I) and Zn(II) inorganic salts in combination with 2,5-bis(3-pyridyl)-1,3,4-oxadiazole (L6). The compounds were characterized by single crystal X-ray diffraction, IR spectroscopy, and elemental analysis. In the solid state, compounds 1 and 3 (1: monoclinic, P2₁/n, a=5.5373(3) Å, b=16.7839(9) Å, c=16.8120(9) Å, β=92.8610(10)°, V=1560.52(15) ų, Z=4; 3: monoclinic, P2₁/n, a=7.2958(4) Å, b=11.7214(6) Å, c=16.3979(9) Å, β=101.1150(10)°, V=1375.99(13) Å³, Z=4) feature novel one-dimensional helical chain motif. Compound 2, however, (2: monoclinic, P2₁/c, a=5.5506(4) Å, b=16.5895(12) Å, c=16.6871(11) Å, β=95.424(2)°, V=1529.70(19) ų, Z=4) exhibits one-dimensional zigzag chain motif, which result from the different conformations adopted by the L6 ligand and also the different metal coordination geometry. The luminescent properties of three new compounds were investigated in the solid state.     

Partial Molar Volumes of Cobalt(III) Complexes. Part 3: Homologous Series of Aminopentaamminecobalt(III) Complexes

Partial molar volumes (V ₂°) have been determined at infinite dilution in aqueous solution at 20 °C for a series of octahedral N₆-coordinated cobalt(III) species having five-coordinated ammonia ligands along with an N-coordinated linear alkyl amine whose alkyl chain was varied from ethylamine to octylamine. The experimental values for V ₂° are consistent with the relative sizes of the ligands but show increasing deviations from those predicted by computer modeling, as the size of the cation increases, presumably due to the void space of the cation that increases with the size of the amine ligand. The value of the partial molar volume at infinite dilution increased by about 16 mL⋅mol⁻¹ with each added methylene group.