Conversion of methanol to hydrocarbons: how zeolite cavity and pore size controls product selectivity

Liquid hydrocarbon fuels play an essential part in the global energy chain, owing to their high energy density and easy transportability. Olefins play a similar role in the production of consumer goods. In a post-oil society, fuel and olefin production will rely on alternative carbon sources, such as biomass, coal, natural gas, and CO(2). The methanol-to-hydrocarbons (MTH) process is a key step in such routes, and can be tuned into production of gasoline-rich (methanol to gasoline; MTG) or olefin-rich (methanol to olefins; MTO) product mixtures by proper choice of catalyst and reaction conditions. This Review presents several commercial MTH projects that have recently been realized, and also fundamental research into the synthesis of microporous materials for the targeted variation of selectivity and lifetime of the catalysts.     

Temperature dependence of charge mobility in model discotic liquid crystals

We address the calculation of charge carrier mobility of liquid-crystalline columnar semiconductors, a very promising class of materials in the field of organic electronics. We employ a simple coarse-grained theoretical approach and study in particular the temperature dependence of the mobility of the well-known triphenylene family of compounds, combining a molecular-level simulation for reproducing the structural changes and the Miller-Abrahams model for the evaluation of the transfer rates within the hopping regime. The effects of electric field, positional and energetic disorder are also considered. Simulations predict a low energetic disorder (~0.05 eV), slightly decreasing with temperature within the crystal, columnar and isotropic phases, and fluctuations of the square transfer integral of the order of 0.003 eV(2). The shape of the temperature-dependent mobility curve is however dominated by the variation of the transfer integral and barely affected by the disorder. Overall, this model reproduces semi-quantitatively all the features of experimentally measured mobilities, on one hand reinforcing the correctness of the hopping transport picture and of its interplay with system morphology, and on the other suggesting future applications for off-lattice modeling of organic electronics devices.     

Understanding the different activities of highly promiscuous MbtI by computational methods

Salicylate synthase from Mycobacterium tuberculosis, MbtI, is a highly promiscuous Mg(2+) dependent enzyme with up to four distinct activities detected in vitro: isochorismate synthase (IS), isochorismate pyruvate lyase (IPL), salicylate synthase (SS) and chorismate mutase (CM). In this paper, Molecular Dynamic (MD) simulations employing hybrid quantum mechanics/molecular mechanics (QM/MM) potentials have been carried out to get a detailed knowledge of the IS and the IPL activities at the molecular level. According to our simulations, the architecture of the MbtI active site allows catalyzing the two reactions: the isochorismate formation, by means of a stepwise mechanism, and the salicylate production from isochorismate, that appears to be pericyclic in nature. Findings also explain the role of the magnesium cation and the pH dependence activity experimentally observed in MbtI. Mg(2+) would be polarizing and pre-organizing the substrate and active site, as well as shifting the pK(a) values of key active site residues.     

Influence of sintering on the structural and electronic properties of TiO2 nanoporous layers prepared via a non-sol–gel approach

In this work, a nonaqueous method is used to fabricate thin TiO₂ layers. In contrast to the common aqueous sol–gel approach, our method yields layers of anatase nanocrystallites already at low temperature. Raman spectroscopy, electron microscopy and charge extraction by linearly increasing voltage are employed to study the effect of sintering temperature on the structural and electronic properties of the nanocrystalline TiO₂ layer. Raising the sintering temperature from 120 to 600?°C is found to alter the chemical composition, the layer’s porosity and its surface but not the crystal phase. The room temperature mobility increases from 2?×?10^?6 to 3?×?10^?5?cm²/Vs when the sinter temperature is increased from 400 to 600?°C, which is explained by a better interparticle connectivity. Solar cells comprising such nanoporous TiO₂ layers and a soluble derivative of cyclohexylamino-poly(p-phenylene vinylene) were fabricated and studied with regard to their structural and photovoltaic properties. We found only weak polymer infiltration into the oxide layer for sintering temperatures up to 550?°C, while the polymer penetrated deeply into titania layers that were sintered at 600?°C. Best photovoltaic performance was reached with a nanoporous TiO₂ film sintered at 550?°C, which yielded a power conversion efficiency of 0.5?%. Noticeably, samples with the TiO₂ layer dried at 120?°C displayed short-circuit currents and open circuit voltages only about 15–20?% lower than for the most efficient devices, meaning that our nonaqueous route yields titania layers with reasonable transport properties even at low sintering temperatures.     

Advances in the investigation of dioxouranium(VI) complexes of interest for natural fluids

The interactions of dioxouranium(VI) cation with different organic and inorganic ligands of environmental and biological interest were carefully examined with the aim to draw a chemical speciation picture of this ion in natural aquatic ecosystems and in biological fluids. Since UO₂²⁺ ion shows a significant tendency to hydrolyze, particular attention was paid in considering the hydrolysis species formation both in the presence and in absence of ligands. The results reported in the literature show that formation of the hydrolytic species assumes a great importance in the complexation models for all the UO₂²⁺-ligand systems considered. In particular, the following ligands have been taken into account: (i) hydroxyl, chloride, fluoride, sulfate, carbonate and phosphate, as inorganic ligands, and (ii) carboxylates (with particular reference to oxalate and citrate), amines, amino acids, poly(amino carboxylates) (complexones), nucleotides, phosphonates, mercapto compounds and sulfonates, as organic ligands. In order to elucidate the speciation of uranyl in the presence of dissolved natural organic matter, the interactions with humic and fulvic acids were also considered. The strength of interaction in all the systems considered was expressed in terms of stability constants of complex species and, if available, of the relative thermodynamic stability parameters. When possible, if data reported in the literature were sufficiently homogeneous, trends of stability were found for the different ligands of the same class and for ligands of different classes. Moreover, relationships were derived for poly-functional ligands, such as poly-carboxylate, poly-amine and poly(amino carboxylate) ones, useful to predict the stability constants as a function of the number of binding sites per molecule, considering also, as in the case of amino acids, the contribution of the single functional groups to the whole stability of uranyl species formed. In addition, using the stability data collected for the uranyl-ligand systems considered, the sequestering capacity of some classes of ligands towards uranyl was calculated in terms of pL_0.5, i.e., the ligand concentration useful to bind at least 50% of the cation. A comparison of pL_0.5 of the most important classes of ligands considered was made to point out the different effectiveness in the UO₂²⁺ sequestration by the different ligands which can be present in multi-component solutions as natural waters and biological fluids. Finally, some considerations are reported about the different experimental techniques employed to study the complex formation in solution.     

New hyperbranched carbosiloxane–carbosilane polymers with aromatic units in the backbone

New hyperbranched polymers based on a carbosiloxane–carbosilane skeleton with aromatic units in the backbone have been prepared via one-pot hydrosilylation reaction using HSi(Me)₂–O–CH₂–C₆H₄–OSiMe–(CH₂)₄(C₃H₅)₂ as a novel AB₂ monomer. These polymers are easy to prepare, have narrow polydispersity values and present allyl groups on the surface which can be used as synthetic platforms for the introduction of different terminal groups like amine groups through hydrosilylation reactions, opening the door to functionalized polymers. The polymerization process was monitored using real-time ¹H NMR spectroscopy and the resulting hyperbranched polymers were characterized using ¹H NMR, ¹³C NMR, ²⁹Si NMR and SEC/MALLS. The degree of branching in these polymers was determined by quantitative ²⁹Si NMR spectroscopy and found to be very close to the theoretical value of 0.50 for AB₂ systems. The hydrolytic degradation of these polymers in protic solvents has been studied by ²⁹Si NMR.     

Novel access to carbodiphosphoranes in the coordination sphere of group 10 metals: template synthesis and protonation of PCP pincer carbodiphosphorane complexes of C(dppm)2

In a novel template synthesis of carbodiphosphoranes (CDPs), the phosphine functionalized CDP ligand C(dppm)(2) (dppm = Ph(2)PCH(2)PPh(2)) is formed in the coordination sphere of group 10 metals from CS(2) and 4 equivalents of dppm. The products are the PCP pincer complexes [M(Cl)(C(dppm)(2)-κ3P,C,P)]Cl (M = Ni, Pd, Pt) and 2 equivalents of dppmS. The compound C(dppm)(2), which is composed of a divalent carbon atom and two dppm subunits, represents a new PCP-type pincer ligand with the formally neutral carbon Lewis base of the CDP functionality as the central carbon. Treatment of [M(Cl)(C(dppm)(2)-κ3P,C,P)]Cl (M = Pd, Pt) with hydrochloric acid results in protonation at the CDP carbon atom and the formation of the PCP pincer complexes [M(Cl)(CH(dppm)(2)-κ3P,C,P)]Cl(2) (M = Pd, Pt). The PCP pincer ligand [CH(dppm)(2)](+) involves a formally cationic central carbon donor. The reaction of [Ni(Cl)(C(dppm)(2)-κ3P,C,P)]Cl with HCl leads to the extrusion of NiCl(2) and formation of the diprotonated CDP compound [CH(2)(dppm)(2)]Cl(2), from which the monoprotonated conjugate base [CH(dppm)(2)]Cl is obtained upon addition of bases, such as NH(3). The crystal structures of [M(Cl)(C(dppm)(2)-κ3P,C,P)]Cl (M = Ni, Pd, Pt), [Ni(Cl)(C(dppm)(2)-κ3P,C,P)](2)[NiCl(4)], [M(Cl)(CH(dppm)(2)-κ3P,C,P)]Cl(2) (M = Pd, Pt) as well as [CH(2)(dppm)(2)]Cl(2) and [CH(dppm)(2)]Cl are presented. A comparison of the solid state structures reveals interesting features, e.g. infinite supramolecular networks mediated by C-H···Cl hydrogen bond interactions and an unexpected loss of molecular symmetry upon protonation in the complexes [M(CH(dppm)(2)-κ3P,C,P)(Cl)]Cl(2) (M = Pd, Pt) as a result of the flexible ligand backbone. Additionally the new compounds were characterized comprehensively in solution by multinuclear (31)P, (13)C and (1)H NMR spectroscopy: Several spectroscopic parameters show a striking variability in particular regarding the carbodiphosphorane functionality. Furthermore the compound [Ni(Cl)(C(dppm)(2)-κ3P,C,P)]Cl was examined by cyclic voltammetry (CV) and could be shown to display quasi-reversible oxidative as well as reductive behaviour.     

Structure elucidation of fluorescent H1 antihistamines by ultraviolet resonance Raman spectroscopy: solvent structures of tripelennamine and mepyramine

Ultraviolet Resonance Raman (UVRR) spectroscopy—a Raman technique that combines high sensitivity with high selectivity and does not suffer from background fluorescence—is applied to the fluorescent H₁ antihistamines tripelennamine (TRP) and mepyramine (MEP) in aqueous solution to elucidate their molecular structure as a function of pH. In a previous investigation of these compounds (C. Tardioli, G. Gooijer G. van der Zwan, J. Phys. Chem. B, 113 , (2009), 6949), the presence of gauche conformers caused by intramolecular interaction of the protonated alkylamine tail with the pyridine nitrogen was assumed to explain the pH dependence of the fluorescence properties. In order to validate this assumption, use is made of the resonant excitation of the aminopyridine chromophore in TRP and MEP. In that way, structural information associated with the vibrations of that moiety can be obtained, and the changes it undergoes upon protonation can be monitored. Assignment of the vibrations was achieved with the help of a number of other compounds, and quantum chemical calculations. N,N‐Dimethylaminopyridine (2DMP) and its mono‐protonated form (2DMPH⁺) were investigated, since this molecule was shown to have optical properties closely resembling those of the aminopyridine moiety in TRP and MEP. Assignment of the vibrations of 2DMP was accomplished by comparison with the resonance Raman spectra of two other reference structures, 2‐aminopyridine and dimethylaniline—for which ordinary Raman data are available—and by Gaussian calculations. UVRR spectra of TRP and MEP could be readily interpreted on the basis of vibrational assignments of the parent chromophores, i.e. 2DMP and 2DMPH⁺. Vibrations of the aminopyridine chromophore in TRP and MEP at neutral pH, where the aminoalkyl chain is protonated, are modified when compared to the vibrational pattern recorded for a fully neutral molecule in alkaline solution. This implies an electronic redistribution in the ring originating from internal hydrogen bonding between the aminoalkyl tail and the aminopyridine chromophore. Copyright © 2010 John Wiley & Sons, Ltd.     

Acute and chronic MRI changes in the spine and spinal cord after surgical stem cell grafting in patients with definite amyotrophic lateral sclerosis: Post-infusion injuries are unrelated with clinical impairment

ObjectiveTo report MRI spinal changes after surgical infusion of bone marrow stem cells (BMSc) in ALS patients and assess their correlation with clinical events and functional performance.MethodsBMSc were surgically injected in the thoracic spinal cord of 11 ALS patients (6/5 male/female; median age 46 years). We performed first-week and third, sixth, ninth and twelfth post-surgical months spinal MRIs. The spinal changes in the postsurgical week and follow-up MRIs, as well as clinical events, functional scales and respiratory and electromyography data, were longitudinally monitored. Correlations between the imaging and clinical data were evaluated with the Spearman's test.ResultsTransient extradural fluid collections (100%), transient spinal cord T2 hyperintensity (81.8%), and chronic spinal cord deformities (63.6%) were the dominating MRI changes. Spinal cord hemorrhages (27.3%) and cystic myelomalacia (1/11 patients) were important although unusual findings. During the follow-up, minor adverse events of mild to moderate intensity eventually improved. Initial and follow-up imaging scores showed a strongly positive correlation (r 0.879, P < 0.001). The initial and delayed clinical scores did not correlate. There was no significant correlation between any of the imaging scores and clinical data.ConclusionsInfusion of BMSc produces a variety of spinal changes apparently unrelated with clinical events and disease worsening.     

MRI rotating frame relaxation measurements for articular cartilage assessment

In the present work we introduced two MRI rotating frame relaxation methods, namely adiabatic T_1ρ and Relaxation Along a Fictitious Field (RAFF), along with an inversion-prepared Magnetization Transfer (MT) protocol for assessment of articular cartilage. Given the inherent sensitivity of rotating frame relaxation methods to slow molecular motions that are relevant in cartilage, we hypothesized that adiabatic T_1ρ and RAFF would have higher sensitivity to articular cartilage degradation as compared to laboratory frame T₂ and MT. To test this hypothesis, a proteoglycan depletion model was used. Relaxation time measurements were performed at 0 and 48 h in 10 bovine patellar specimens, 5 of which were treated with trypsin and 5 untreated controls were stored under identical conditions in isotonic saline for 48 h. Relaxation times measured at 48 h were longer than those measured at 0 h in both groups. The changes in T₂ and MT relaxation times after 48 h were approximately 3 times larger in the trypsin treated specimens as compared to the untreated group, whereas increases of adiabatic T_1ρ and RAFF were 4 to 5 fold larger. Overall, these findings demonstrate a higher sensitivity of adiabatic T_1ρ and RAFF to the trypsin-induced changes in bovine patellar cartilage as compared to the commonly used T₂ and MT. Since adiabatic T_1ρ and RAFF are advantageous for human applications as compared to standard continuous-wave T_1ρ methods, adiabatic T_1ρ and RAFF are promising tools for assessing cartilage degradation in clinical settings.