Melemium Hydrogensulfate H3C6N7(NH2)3(HSO4)3 – the First Triple Protonation of Melem

We synthesized melemium hydrogensulfate H₃C₆N₇(NH₂)₃(HSO₄)₃ by reaction of melem with 70 % sulfuric acid. The crystal structure was elucidated by single‐crystal XRD (P2₁/n (no. 14), Z = 4, a = 10.277(2), b = 14.921(3), c = 11.771(2) Å, β = 99.24(3)°, V = 1781.5(6) Å³). H₃C₆N₇(NH₂)₃(HSO₄)₃ is the first compound displaying a triple protonation of melem., In this contribution an overview of accessible melemium sulfates depending on the concentration of sulfuric acid is given. Two additional melemium sulfates were identified this way.     

The influence of sulfonation degree on the thermal behaviour of sulfonated poly(arylene ethersulfone)s

Initial decomposition temperature (T_i), apparent activation energy of degradation (E_a) and glass transition temperature (T_g) of some low molar mass (M_n ≈ 8000 g mol⁻¹) sulfonated poly(arylene ethersulfone)s s-(PAES)s were determined to check their dependence on sulfonation degree (SD). The results obtained were compared with those for unsulfonated poly(arylene ethersulfone) PAES. In order to have an accurate control of the chemical structure, a pre-sulfonation route was followed for the preparation of sulfonated compounds. The thermal behaviour of the investigated s-(PAES)s as well as that of PAES appears not to be influenced by the environment (flowing nitrogen or static air atmosphere) of degradation. Both T_i and T_g values of s-(PAES)s were higher than those of PAES and increased quite linearly as a function of sulfonation degree. An analogous linear trend was observed for the apparent degradation energy of s-(PAES)s, but the values found were largely lower than those of unsulfonated homopolymer. The results are discussed and interpreted.     

Hydrolytic and microbial degradation of multi-block polyurethanes based on poly(?-caprolactone)/poly(ethylene glycol) segments

Biodegradable amphiphilic multi-block poly(ether-ester-urethane)s were prepared by one-step bulk polycondensation of PEG and PCL macro-diols and HMDI. For biomedical or environmental applications of the proposed materials, one of the critical steps is the study of the degradation characteristics under physiological or environmental conditions. Different ratios of PEG/PCL and molecular weights of the resultant copolymers allowed for tuning their hydrophilicity, as evaluated by water uptake measurements. The swelling results were further supported by microgravimetric measurements performed by QCM-D. In vitro hydrolytic biodegradation was carried out under different conditions (i.e., in phosphate buffer solution - with and without Lipase). Total mineralization in the presence of microorganisms from a sample of river water was observed to follow different kinetics, depending upon the composition and the molecular weight of the copolymer.     

Snx[BPO4]1−x composites as negative electrodes for lithium ion cells: Comparison with amorphous SnB0.6P0.4O2.9 and effect of composition

A comparative study of two Sn-based composite materials as negative electrode for Li-ion accumulators is presented. The former SnB_0.6P_0.4O_2.9 obtained by in-situ dispersion of SnO in an oxide matrix is shown to be an amorphous tin composite oxide (ATCO). The latter Sn_0.72[BPO₄]_0.28 obtained by ex-situ dispersion of Sn in a borophosphate matrix consists of Sn particles embedded in a crystalline BPO₄ matrix. The electrochemical responses of ATCO and Sn_0.72[BPO₄]_0.28 composite in galvanostatic mode show reversible capacities of about 450 and 530 mAh g⁻¹, respectively, with different irreversible capacities (60% and 29%). Analysis of these composite materials by ¹¹⁹Sn Mössbauer spectroscopy in transmission (TMS) and emission (CEMS) modes confirms that ATCO is an amorphous Sn^II composite oxide and shows that in the case of Sn_0.72[BPO₄]_0.28, the surface of the tin clusters is mainly formed by Sn^II in an amorphous interface whereas the bulk of the clusters is mainly formed by Sn⁰. The determination of the recoilless free fractions f (Lamb-Mössbauer factors) leads to the effective fraction of both Sn⁰ and Sn^II species in such composites. The influence of chemical composition and especially of the surface-to-bulk tin species ratio on the electrochemical behaviour has been analysed for several Sn_x[BPO₄]_1−x composite materials (0.17<x<0.91). The cell using the compound Sn_0.72[BPO₄]_0.28 as active material exhibits interesting electrochemical performances (reversible capacity of 500 mAh g⁻¹ at C/5 rate).     

The conductance and stability of fused dithia-heterocyclic compounds contacted with gold and platinum electrodes

The electronic transport properties of two kinds of fused dithia-heterocyclic compounds, 2,3,6,7-tetrahydrobenzo[1,2-b:4,5-b′]dithiophene (THBDT) and benzo[1,2-b:4,5-b]dithiophene (BDT), connected to gold and platinum electrodes are investigated using a self-consistent abinitio approach that combines the non-equilibrium Green’s function formalism with density functional theory. Our calculations show that the transmission at the Fermi level of the Au–THBDT–Au junction, where the THBDT molecule is connected to two gold electrodes through a gold adatom on each side, is 3.1 × 10⁻², in good agreement with the experimentally measured value (1.2 × 10⁻²). Replacement of the gold electrodes with platinum electrodes can improve the junction stability but cannot increase the zero-bias junction conductance. In contrast, due to the enhanced conjugation in BDT and the better molecule–electrode coupling, both the transmission and the stability of the Pt–BDT–Pt junction are improved significantly, demonstrating the close relation between the device performance and the device structure.     

Density functional theory and RRKM calculations of decompositions of the metastable E‐2,4‐pentadienal molecular ions

The potential energy profiles for the fragmentations that lead to [C₅H₅O]⁺ and [C₄H₆]^+? ions from the molecular ions [C₅H₆O]^+? of E‐2,4‐pentadienal were obtained from calculations at the UB3LYP/6‐311G + + (3df,3pd)//UB3LYP/6‐31G(d,p) level of theory. Kinetic barriers and harmonic frequencies obtained by the density functional method were then employed in Rice–Ramsperger–Kassel–Marcus calculations of individual rate coefficients for a large number of reaction steps. The pre‐equilibrium and rate‐controlling step approximations were applied to different regions of the complex potential energy surface, allowing the overall rate of decomposition to be calculated and discriminated between three rival pathways: C? H bond cleavage, decarbonylation and cyclization. These processes should have to compete for an equilibrated mixture of four conformers of the E‐2,4‐pentadienal ions. The direct dissociation, however, can only become important in the high‐energy regime. In contrast, loss of CO and cyclization are observable processes in the metastable kinetic window. The former involves a slow 1,2‐hydrogen shift from the carbonyl group that is immediately followed by the formation of an ion‐neutral complex which, in turn, decomposes rapidly to the s‐trans‐1,3‐butadiene ion [C₄H₆]^+?. The predominating metastable channel is the second one, that is, a multi‐step ring closure which starts with a rate‐limiting cis—trans isomerization. This process yields a mixture of interconverting pyran ions that dissociates to the pyrylium ions [C₅H₅O]⁺. These results can be used to rationalize the CID mass spectrum of E‐2,4‐pentadienal in a low‐energy regime. Copyright © 2010 John Wiley & Sons, Ltd.     

A first‐order system least‐squares finite element method for the Poisson‐Boltzmann equation

The Poisson‐Boltzmann equation is an important tool in modeling solvent in biomolecular systems. In this article, we focus on numerical approximations to the electrostatic potential expressed in the regularized linear Poisson‐Boltzmann equation. We expose the flux directly through a first‐order system form of the equation. Using this formulation, we propose a system that yields a tractable least‐squares finite element formulation and establish theory to support this approach. The least‐squares finite element approximation naturally provides an a posteriori error estimator and we present numerical evidence in support of the method. The computational results highlight optimality in the case of adaptive mesh refinement for a variety of molecular configurations. In particular, we show promising performance for the Born ion, Fasciculin 1, methanol, and a dipole, which highlights robustness of our approach. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010     

Intermittent simulated moving bed chromatography: 2. Separation of Tröger’s base enantiomers

The intermittent simulated moving bed (I-SMB) process is a modification of the conventional SMB process that has been recently analyzed theoretically [1]. Here, we present a comparative analysis of the two processes, each operated in a six column 1-2-2-1 configuration (one column in sections 1 and 4 and two columns in sections 2 and 3) and in a four-column 1-1-1-1 configuration. Experiments are carried out on a properly modified laboratory unit to separate racemic mixtures of the enantiomers of Tröger’s base in ethanol on ChiralPak AD at a total feed concentration of 1 g/L. Simulations are carried out for the same system using the equilibrium dispersive model and a bi-Langmuir isotherm, whose parameters have been preliminarily estimated from pulse and breakthrough experiments. Experiments and simulations are fully consistent and demonstrate that the four-column I-SMB process (but not the four-column SMB process) can separate the two enantiomers at very high purity and achieve a productivity twice as large as that of the six-column I-SMB and conventional SMB processes with the same solvent consumption.     

Synthesis and characterization of poly(thioether ether sulfone imide)s derived from isomeric bis(chlorophthalimide)s and bis(4-mercaptophenyl) sulfone

A series of isomeric bis(chlorophthalimide)s (BCPIs) were conveniently prepared from 3-chlorophthalic anhydride, 4-chlorophthalic anhydride, and mixtures thereof. Polymerization of BCPIs with bis(4-mercaptophenyl) sulfone (BMPS) proceeded smoothly in the presence of tributylamine, from which a class of isomeric poly(thioether ether sulfone imide)s (PTESIs) with inherent viscosities of 0.45-0.82 dL/g were obtained. The solubility, thermal stability, and mechanical properties of these polymers were characterized. Compared to the PTESIs derived from single BCPIs, i.e., 3,3′-, 3,4′-, or 4,4′-BCPIs, the PTESIs derived from mixed BCPIs showed better solubility and higher storage modulus. These PTESIs also demonstrated good thermal stability, giving only 5% weight loss at temperature of 490 °C in nitrogen atmosphere. The glass transition temperatures (T_gs) of these isomeric PTESIs were between 242 and 265 °C, and were increased with increasing of the ratio of 3-chlorophthalimide unit in the polymer backbone.     

Solid‐State NMR Characterization of Wilkinson’s Catalyst Immobilized in Mesoporous SBA‐3 Silica

The Wilkinson’s catalyst [RhCl(PPh₃)₃] has been immobilized inside the pores of amine functionalized mesoporous silica material SBA‐3 and The structure of the modified silica surface and the immobilized rhodium complex was determined by a combination of different solid‐state NMR methods. The successful modification of the silica surface was confirmed by ²⁹Si CP‐MAS NMR experiments. The presence of the T_n peaks confirms the successful functionalization of the support and shows the way of binding the organic groups to the surface of the mesopores. ³¹P‐³¹P J‐resolved 2D MAS NMR experiments were conducted in order to characterize the binding of the immobilized catalyst to the amine groups of the linkers attached to the silica surface. The pure catalyst exhibits a considerable ³¹P‐³¹P J‐coupling, well resolvable in 2D MAS NMR experiments. This J‐coupling was utilized to determine the binding mode of the catalyst to the linkers on the silica surface and the number of triphenylphosphine ligands that are replaced by coordination bonds to the amine groups. From the absence of any resolvable ³¹P‐³¹P J‐coupling in off‐magic‐angle‐spinning experiments, as well as slow‐spinning MAS experiments, it is concluded, that two triphenylphosphine ligands are replaced and that the catalyst is bonded to the silica surface through two linker molecules.