An Improved Method for Site‐Specific End Modification of Zeolite L for the Formation of Zeolite L and Gold Nanoparticle Self‐Assembled Structures

The ability to site‐selectively modify micro‐ and nanosized particles has allowed for directed self‐assembly in two and three dimensions. Site‐selective modification of particles can be a complicated task requiring the pre‐organization of particles or enhanced particle fabrication methods. The aluminum silicate, zeolite L has been reported to undergo site‐specific modification at the zeolite channel entrances, post‐fabrication in a solution‐based method. The process by which the channel entrances are site selectively modified is explored here. The preliminary step of charging the zeolite channels with aqueous acid allows for catalysis of covalent bond formation at the channel entrances. Three new end‐specific modification reagents are described based on silanol and silyl ether functional groups. These reagents are purified by column chromatography and characterized by¹H NMR spectroscopy and high resolution mass spectrometry (HRMS); they provide for reliable end modification of zeolites L. Preferential reactivity at the channel entrances is also observed. The utility of the approach is demonstrated by modifying zeolite L with adamantane at the channel entrances. Site‐specific self‐assembly with β‐cyclodextrin coated gold nanoparticles can be triggered with a chemical stimulus. The resulting multivalent host‐guest interactions give gold clustered nanoparticles at the ends of the micrometer‐sized zeolites.     

Enantioselective methylalumination of α-olefins

The ability of various enantiopure zirconocenes to catalyze the asymmetric methylalumination of allylbenzene has been tested. The enantioselectivity of an ethylene(Ind)₂ZrCl₂/MAO system is the same as that of authentic methyl cation generated with Ph₃C⁺ from ethylene(Ind)₂ZrMe₂, confirming that the methyl cation is the active catalyst from ethylene(Ind)₂ZrCl₂/MAO.     

Zirconium-catalyzed carboalumination of α-olefins and chain growth of aluminum alkyls: kinetics and mechanism

A mechanism based on Michaelis-Menten kinetics with competitive inhibition is proposed for both the Zr-catalyzed carboalumination of α-olefins and the Zr-catalyzed chain growth of aluminum alkyls from ethylene. AlMe(3) binds to the active catalyst in a rapidly maintained equilibrium to form a Zr/Al heterobimetallic, which inhibits polymerization and transfers chains from Zr to Al. The kinetics of both carboalumination and chain growth have been studied when catalyzed by [(EBI)Zr(μ-Me)(2)AlMe(2)][B(C(6)F(5))(4)]. In accord with the proposed mechanism, both reactions are first-order in [olefin] and [catalyst] and inverse first-order in [AlR(3)]. The position of the equilibria between various Zr/Al heterobimetallics and the corresponding zirconium methyl cations has been quantified by use of a Dixon plot, yielding K = 1.1(3) × 10(-4) M, 4.7(5) × 10(-4) M, and 7.6(7) × 10(-4) M at 40 °C in benzene for the catalyst species [rac-(EBI)Zr(μ-Me)(2)AlMe(2)][B(C(6)F(5))(4)], [Cp(2)Zr(μ-Me)(2)AlMe(2)][B(C(6)F(5))(4)], and [Me(2)C(Cp)(2)Zr(μ-Me)(2)AlMe(2)][B(C(6)F(5))(4)] respectively. These equilibrium constants are consistent with the solution behavior observed for the [Cp(2)Zr(μ-Me)(2)AlMe(2)][B(C(6)F(5))(4)] system, where all relevant species are observable by (1)H NMR. Alternative mechanisms for the Zr-catalyzed carboalumination of olefins involving singly bridged Zr/Al adducts have been discounted on the basis of kinetics and/or (1)H NMR EXSY experiments.     

Efficient Synthesis of Novel Plasticizers by Direct Palladium-Catalyzed Di- or Multi-carbonylations

Diesters are of fundamental importance in the chemical industry and are used for many applications, e.g. as plasticizers, surfactants, emulsifiers, and lubricants. Herein, we present a straightforward and efficient method for the selective synthesis of diesters via palladium-catalyzed direct carbonylation of di- or polyols with readily available alkenes. Key-to-success is the use of a specific palladium catalyst with the “built-in-base” ligand L16 providing esterification of all alcohols and a high n/iso ratio. The synthesized diesters were evaluated as potential plasticizers in PVC films by measuring the glass transition temperature (T_g) via differential scanning calorimetry (DSC).     

Internal friction and vulnerability of mixed alkali glasses

Based on a hopping model we show how the mixed alkali effect in glasses can be understood if only a small fraction c(V) of the available sites for the mobile ions is vacant. In particular, we reproduce the peculiar behavior of the internal friction and the steep fall ("vulnerability") of the mobility of the majority ion upon small replacements by the minority ion. The single and mixed alkali internal friction peaks are caused by ion-vacancy and ion-ion exchange processes. If c(V) is small, they can become comparable in height even at small mixing ratios. The large vulnerability is explained by a trapping of vacancies induced by the minority ions. Reasonable choices of model parameters yield typical behaviors found in experiments.     

Negative field-dependent charge mobility in crystalline organic semiconductors with delocalized transport

Charge-carrier mobility has been investigated by time-of-flight (TOF) transient photocurrent in a lateral transport configuration in highly crystalline thin films of 2,7-dioctyl[1]benzothieno [3,2-b][1] benzothiophene (C₈-BTBT) grown by a zone-casting alignment technique. High TOF mobility has been revealed that it is consistent with the delocalized nature of the charge transport in this material, yet it featured a positive temperature dependence at \( T \ge 295\,{\text{K}} \). Moreover, the mobility was surprisingly found to decrease with electric field in the high-temperature region. These observations are not compatible with the conventional band-transport mechanism. We have elaborated an analytic model based on effective-medium approximation to rationalize the puzzling findings. The model considers the delocalized charge transport within the energy landscape formed by long-range transport band-edge variations in imperfect organic crystalline materials and accounts for the field-dependent effective dimensionality of charge transport percolative paths. The results of the model calculations are found to be in good agreement with experimental data.     

Effect of Microaerobic Fermentation in Preprocessing Fibrous Lignocellulosic Materials

Amending soil with organic matter is common in agricultural and logging practices. Such amendments have benefits to soil fertility and crop yields. These benefits may be increased if material is preprocessed before introduction into soil. We analyzed the efficiency of microaerobic fermentation (MF), also referred to as Bokashi, in preprocessing fibrous lignocellulosic (FLC) organic materials using varying produce amendments and leachate treatments. Adding produce amendments increased leachate production and fermentation rates and decreased the biological oxygen demand of the leachate. Continuously draining leachate without returning it to the fermentors led to acidification and decreased concentrations of polysaccharides (PS) in leachates. PS fragmentation and the production of soluble metabolites and gases stabilized in fermentors in about 2?C4?weeks. About 2?% of the carbon content was lost as CO₂. PS degradation rates, upon introduction of processed materials into soil, were similar to unfermented FLC. Our results indicate that MF is insufficient for adequate preprocessing of FLC material.     

Three‐Dimensionally Ordered Polypyrrole Electrode: Electrochemical Study on Capacity and Degradation Process

In this work we critically compare electrochemical stability and specific capacitance of the three‐dimensional (3D) polypyrrole membrane and the dense polypyrrole film fabricated at the same conditions. Herein, we concern about study the influence of the electrode morphology on the kinetics of diffusion process by analyzing voltammetry, coulometry and impedance response. This allows us to calculate well‐sustained values of the diffusion coefficient, specific capacitance and diffusion resistance, which summarize equilibrium parameters. The ultra‐thin walls, uniform porosity and well‐ordered structure called “inverse opal” ensure an efficient mass transport and fast charge exchange of the porous polypyrrole resulting in superior electrochemical performance. The calculated diffusion coefficient of anion doping process in 3D polypyrrole is more than two orders of magnitude higher comparing to the control sample. The improved electrochemical stability at high anodic potential is correlated with unique porous and dynamic structure of the polymer that is capable of handling volumetric changes upon electrode polarization. An effective diffusion length for the porous PPy remains unchanged during degradation process (overoxidation) and is significantly smaller in comparison to the dense polymer film, indicating that the degradation process for the porous system is somewhat hindered. This work provides an important insight for fast and scalable synthesis of 3D polymer electrode with improved electrochemical activity and stability for the future energy storage applications.     

Hydrogen-bonded networks based on manganese(II), nickel(II), copper(II) and zinc(II) complexes of N,N′-dimethylurea

A project related to the crystal engineering of hydrogen-bonded coordination complexes has been initiatied and some of our first results are presented here. The compounds [Mn(DMU)₆](ClO₄)₂ (1), [Ni(DMU)₆](ClO₄)₂ (2), [Cu(OClO₃)₂(DMU)₄] (3) and [Zn(DMU)₆](ClO₄)₂ (4) have all been prepared from the reaction of N,N-dimethylurea (DMU) and the appropriate hydrated metal perchlorate salt. Crystal structure determinations of the four compounds demonstrate the existence of [M(DMU)₆]²⁺ cations and ClO₄ ^– counterions in (1), (2) and (4), whereas in (3) monodentate coordination of the perchlorate groups leads to molecules. The [M(DMU)₆]²⁺ cations and ClO₄ ^– anions self-assemble to form a hydrogen-bonded one-dimensional (1D) architecture in (1) and different 2D hydrogen-bonded networks in (2) and (4). The hydrogen bonding functionalities on the molecules of (3) create a 2D structure. The complexes were also characterised by room-temperature effective magnetic moments and i.r. studies. The data are discussed in terms of the nature of bonding and the known structures.     

A structural model for the copper(II) site of Cu-Zn superoxide dismutase: preparation,crystal structure and properties of [Cu(Mebta)4(H2O)](ClO4)2·0.4EtOH (Mebta = 1-methylbenzotriazole)

Reaction of Cu(ClO₄)₂·6H₂O with 1-methylbenzotriazole (Mebta) in EtOH yields [Cu(Mebta)₄(H₂O)] (ClO₄)₂·0.4EtOH in ca. 75% yield. The structure of this salt has been determined by single-crystal X-ray crystallography. Mebta behaves as a monodentate ligand binding through N(3). The metal coordination geometry is best described as distorted square pyramidal with the H₂O ligand occupying the apical site. The complex was also characterized by molar conductivity, room-temperature effective magnetic moment and spectroscopic (i.r., far-i.r., u.v./vis, e.s.r.) studies. The data are discussed in terms of the nature of bonding and known structure. Comparison between the structural and spectroscopic properties of [Cu(Mebta)₄(H₂O)](ClO₄)₂·0.4EtOH and those of the Cu^II site of Cu–Zn superoxide dismutase shows that the former can be considered as a fairly good model for the latter.