Direct quantification of mono- and di-D-α-tocopherol polyethylene glycol 1000 succinate by high performance liquid chromatography

A simple and direct reversed-phase high performance liquid chromatography (RP-HPLC) method with UV detection was developed and validated for the determination of mono- and di-D-α-tocopherol polyethylene glycol 1000 succinate (TPGS 1000) in TPGS mixture. Before the HPLC analysis, mono- and di-TPGS 1000 were separated by simulated moving bed (SMB) chromatography system and characterized by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). The mass spectrometric results confirmed that the molar mass distribution of TPGS prepared in our laboratory was very close to that of the product of Eastman Chemical Company with similar nˉ (average polymerization degree), M(n)ˉ (number-average molecular weight) and M(w)ˉ (weight-average molecular weight). The HPLC analysis was carried out on a C30 analytical column with mobile phases comprised of acetonitrile (A) and isopropanol (B) in gradient conditions. Validation of the analytical method was done on the following parameters: system suitability, linearity, limits of detection and quantification, accuracy and precision, method robustness and solution stability. The linearity of the calibration curves for mono- and di-TPGS 1000 from both sources was found to be good (r(2)>0.9996). The recovery values were from 94.6% to 103.3% for mono-TPGS, and 93.5% to 103.3% for di-TPGS. This method could be successfully used in the direct quantification of mono- and di-TPGS in TPGS 1000 mixture using TPGS standards with similar molecular mass distributions although derived from different sources.     

The effects of aspect ratio of inorganic fillers on the structure and property of composite ion-exchange membranes

A new type of nanocomposite ion-exchange membranes containing sulfonated polyethersulfone (sPES) polymer matrix and sulfonated surface-functionalized mesoporous silica (SS) inorganic fillers was prepared. Various characterizations revealed that the addition of inorganic fillers with different shapes had a significant influence on the membrane structure. The mesoporous inorganic fillers not only created extra pore and water channels, assisting the ionic migration and improving conductivity of the composites, but also provided additional fixed charge groups upon surface modification. This allows the Donnan exclusion to work effectively and thus improve the selectivity of membranes. It was proved that the incorporation of appropriate amount of SS additive could significantly improve the conductivity (up to 20 folds) and permselectivity (about 14%) of the sPES membranes. The performance of these newly developed membranes in desalination by electrodialysis was comparable with that of a commercial membrane (FKE).     

Probing the nature of the Co(III) ion in corrins: the structural and electronic properties of dicyano- and aquacyanocobyrinic acid heptamethyl ester and a stable yellow dicyano- and aquacyanocobyrinic acid heptamethyl ester

A stable yellow derivative of cobyrinic acid heptamethyl ester, (5R,6R)-Coα,Coβ-dicyano-5,6-dihydro-5-hydroxy-heptamethylcob(III)yrinate-c,6-lactone (DCSYCbs), was prepared from dicyanocobyrinic acid heptamethyl ester (DCCbs). The C5 carbon is oxidized and the c side chain cyclized to form a lactone at C6; the 13 atom, 14 π-e(-) delocalized system of corrins is interrupted, giving a triazamethine system with four conjugated double bonds between N22 and N24 and an isolated double bond between N21 and C4. Stable yellow aquacyanocobyrinic acid heptamethyl ester (ACSYCbs) was prepared by driving off HCN with N(2) in a methanol/acetic acid solution. The electronic spectra of DCCbs and DCSYCbs appear similar except that the bands in DCSYCbs are shifted to shorter wavelengths and the γ-band is much less intense. The experimental spectra were adequately modeled using TD-DFT at the PBE1PBE/6-311G(d,p) level of theory. DCSYCbs crystallizes in the space group P2(1)2(1)2(1) (R(1) = 6.08%) with Z = 4, including one methanol solvent molecule and one water molecule per cobester. The addition of a hydroxyl group at C5 causes loss of the double bond between C5 and C6 and elongation of the C5-C6 bond. From a combination of two-dimensional (1)H TOCSY and ROESY NMR spectra and (1)H/(13)C HSQC and HMBC data, the complete (1)H and (13)C NMR assignments of DCSYCbs were possible, except for two of the ester methyl groups and the (13)C resonances of the two axial cyanide ligands. The latter were assigned using relative chemical shifts calculated by GIAO-DFT methods. The (59)Co resonance of DCCbs was observed at 4074 ppm while that of DCSYCbs is shifted downfield to 4298 ppm. Comparison with available (59)Co data of analogous systems suggests that the more π-conjugated corrin of DCCbs interacts more strongly with the metal than the less extensively conjugated macrocycle of DCSYCbs. As the strength of the interaction between Co(III) and an equatorial macrocycle increases, ν(CN) of axially coordinated CN(-) shifts to lower frequency; in DCSYCbs and DCCbs ν(CN) occurs at 2138 and 2123 cm(-1), respectively. Hence the corrin ligand in DCCbs interacts more strongly with the metal than the stable yellow corrin ligand, with its diminished conjugation. The UV-vis spectral data and DFT-calculated MOs are consistent with greater overlap between the corrin and the metal orbitals in DCCbs relative to DCSYCbs, which gives the metal in the former a softer, more covalent character.     

Interactions of single-stranded DNA on microcantilevers

The microcantilever approach has attracted considerable attention in recent years as a means of label-free detection of a variety of biomolecular and chemical reactions. The underlying physics of the intermolecular interactions that result in mechanical motions is yet to be fully explored, but it seems both rich in science and of technological importance. This paper presents an overview of experiments and theories related to interactions of single-stranded DNA immobilized on microcantilevers. Experiments and theories show that, at high grafting density, hydration forces are the dominant factor determining cantilever deflections, not electrostatics or conformational entropy.     

Fullerenes without symmetry: crystallographic characterization of C1(30)-C90 and C1(32)-C90

Fullerenes are generally considered as highly symmetric, yet fullerene isomers with only C(1) symmetry, such as C(1)(30)-C(90) and C(1)(32)-C(90) whose structures are reported here, become increasingly numerous as fullerene size increases.     

L-arginine trifluoroacetate salt bridges in its solid state compound: the low-temperature three dimensional structural determination of L-arginine bis(trifluoroacetate) crystal and its vibrational spectral analysis

Structural varieties of L-arginine trifluoroacetate (abbreviated as LATF) and L-arginine bis(trifluoroacetate), LABTF, in the solid state compounds were observed and analyzed by the nuclear magnetic resonance (NMR) spectroscopy. The guanidinium-carboxylate interaction plays an important role involving in the crystal structure construction. Conformational changes of L-Arg(+) and L-Arg(2+) cations result from the intrinsic structural difference by hydrogen bonding and electrostatic interactions. The low-temperature structure of its crystalline salt, L-arginine bis(trifluoroacetate), was determined to describe the hydrogen bonding interactions. In comparison with the crystal structure at room temperature, the low-temperature L-Arg(2+) cations present tiny conformational difference and the rotational disorder of CF(3) group disappears. FT-IR and Raman spectra were investigated and hydrogen bonding interactions were analyzed on the basis of its vibrational spectra. Results indicate that this type interaction is greatly contributive to the structural features and vibrational spectral properties.     

Thermal behavior and thermal safety on 3,3-dinitroazetidinium salt of perchloric acid

3,3-Dinitroazetidinium (DNAZ) salt of perchloric acid (DNAZ·HClO₄) was prepared, it was characterized by the elemental analysis, IR, NMR, and a X-ray diffractometer. The thermal behavior and decomposition reaction kinetics of DNAZ·HClO₄ were investigated under a non-isothermal condition by DSC and TG/DTG techniques. The results show that the thermal decomposition process of DNAZ·HClO₄ has two mass loss stages. The kinetic model function in differential form, the value of apparent activation energy (E _a) and pre-exponential factor (A) of the exothermic decomposition reaction of DNAZ·HClO₄ are f(α) = (1 − α)⁻¹/2, 156.47 kJ mol⁻¹, and 10^15.12 s⁻¹, respectively. The critical temperature of thermal explosion is 188.5 °C. The values of ΔS ^≠, ΔH ^≠, and ΔG ^≠of this reaction are 42.26 J mol⁻¹ K⁻¹, 154.44 kJ mol⁻¹, and 135.42 kJ mol⁻¹, respectively. The specific heat capacity of DNAZ·HClO₄ was determined with a continuous C _p mode of microcalorimeter. Using the relationship between C _p and T and the thermal decomposition parameters, the time of the thermal decomposition from initiation to thermal explosion (adiabatic time-to-explosion) was evaluated as 14.2 s.