Macrocyclic Olefin Metathesis at High Concentrations by Using a Phase‐Separation Strategy

Macrocyclic olefin metathesis has seen advances in the areas of stereochemistry, chemoselectivity, and catalyst stability, but strategies aimed at controlling dilution effects in macrocyclizations are rare. Herein, a protocol to promote macrocyclic olefin metathesis, one of the most common synthetic tools used to prepare macrocycles, at relatively high concentrations (up to 60 mM ) is described by exploitation of a phase‐separation strategy. A variety of macrocyclic skeletons could be prepared having either different alkyl, aryl, or amino acids spacers.     

Biorefining of Waste Paper Biomass: Increasing the Concentration of Glucose by Optimising Enzymatic Hydrolysis

Waste copier paper is a potential substrate for the production of glucose relevant for manufacture of platform chemicals and intermediates, being composed of 51 % glucan. The yield and concentration of glucose arising from the enzymatic saccharification of solid ink-free copier paper as cellulosic substrate was studied using a range of commercial cellulase preparations. The results show that in all cellulase preparations examined, maximum hydrolysis was only achieved with the addition of beta-glucosidase, despite its presence in the enzyme mixtures. With the use of Accellerase® (cellulase), high substrate loading decreased conversion yield. However, this was overcome if the enzyme was added between 12.5 and 20 FPU g substrate^?1. Furthermore, this reaction condition facilitated continual stirring and enabled sequential additions (up to 50 % w/v) of paper to be made to the hydrolysis reaction, degrading nearly all (99 %) of the cellulose fibres and increasing the final concentration of glucose whilst simultaneously making high substrate concentrations achievable. Under optimal conditions (50 °C, pH 5.0, 72 h), digestions facilitate the production of glucose to much improved concentrations of up to 1.33 mol l^?1.     

Simultaneous chromatography and electrophoresis: two-dimensional planar separations

Single-dimension separations are routinely coupled in series to achieve two-dimensional separations, yet little has been done to simultaneously exploit multiple dimensions during separation. In this work, simultaneous chromatography and electrophoresis is introduced and evaluated for its potential to achieve two-dimensional separations. In simultaneous chromatography and electrophoresis, chromatography occurs via capillary action while an orthogonal electric field concurrently promotes electrophoresis in a second dimension. A novel apparatus with a dual solvent reservoir was designed to apply the concurrent electric field. Various compounds were used to characterize the apparatus and technique, i.e., vitamins, amino acids, and dyes. Improved separation is reported with equivalent analysis times in comparison to planar chromatography alone. The feasibility of simultaneously employing chromatography and electrophoresis in two dimensions is discussed.

A Comparison of the Stability and Reactivity of Diamido‐ and Diaminocarbene Copper Alkoxide and Hydride Complexes

The mononuclear N‐heterocyclic carbene (NHC) copper alkoxide complexes [(6‐NHC)CuOtBu] (6‐NHC=6‐MesDAC ( 1 ), 6‐Mes ( 2 )) have been prepared by addition of the free carbenes to the tetrameric tert‐butoxide precursor [Cu(OtBu)]₄, or by protonolysis of [(6‐NHC)CuMes] (6‐NHC=6‐MesDAC ( 3 ), 6‐Mes ( 4 )) with tBuOH. In contrast to the relatively stable diaminocarbene complex 2 , the diamidocarbene derivative 1 proved susceptible to both thermal and hydrolytic ring‐opening reactions, the latter affording [(6‐MesDAC)Cu(OC(O)CMe₂C(O)N(H)Mes)(CNMes)] ( 6 ). The intermediacy of [(6‐MesDAC)Cu(OH)] in this reaction was supported by the generation of Cu₂O as an additional product. Attempts to generate an isolable copper hydride complex of the type [(6‐MesDAC)CuH] by reaction of 1 with Et₃SiH resulted instead in migratory insertion to generate [(6‐MesDAC‐H)Cu(P(p‐tolyl)₃)] ( 9 ) upon trapping by P(p‐tolyl)₃. Migratory insertion was also observed during attempts to prepare [(6‐Mes)CuH], with [(6‐Mes‐H)Cu(6‐Mes)] ( 10 ) isolated, following a reaction that was significantly slower than in the 6‐MesDAC case. The longer lifetime of [(6‐Mes)CuH] allowed it to be trapped stoichiometrically by alkyne, and also employed in the catalytic semi‐reduction of alkynes and hydrosilylation of ketones.     

Photochemical Synthesis of Complex Carbazoles: Evaluation of Electronic Effects in Both UV‐ and Visible‐Light Methods in Continuous Flow

An evaluation of both a visible‐light‐ and UV‐light‐mediated synthesis of carbazoles from various triarylamines with differing electronic properties under continuous‐flow conditions has been conducted. In general, triarylamines bearing electron‐rich groups tend to produce higher yields than triarylamines possessing electron‐withdrawing groups. The incorporation of nitrogen‐based heterocycles, as well as halogen‐containing arenes in carbazole skeletons, was well tolerated, and often synthetically useful complementarity was observed between the UV‐light and visible‐light (photoredox) methods.     

Hydrogen binding in vacancy clusters in platinum

The binding of hydrogen in different vacancy complexes in platinum metal was investigated with atomic-scale sensitivity using perturbed angular correlations of gamma rays (PAC). Hydrogen was introduced by cathodic charging. Detrapping was monitored microscopically during desorption at 294 K by changes in site fractions of hydrogen-decorated and undecorated complexes. Analysis of desorption includes effects of retrapping of hydrogen at other sites. Assuming a trap concentration of 10^–3, binding enthalpies of 0.23(2), 0.28(1), 0.24(1) and >0.20 eV are obtained for hydrogen atoms in 1V to 4V complexes, respectively. The small differences between the binding enthalpies demonstrate that hydrogen binding is insensitive to the detailed geometrical structure of small vacancy complexes. However, the magnitudes found here are a factor of two smaller than in the literature.     

A Near-Quadratic Algorithm for Fence Design

A part feeder is a mechanism that receives a stream of identical parts in arbitrary orientations and outputs them oriented the same way. Various sensorless part feeders have been proposed in the literature. The feeder we consider consists of a sequence of fences that extend partway across a conveyor belt; a polygonal part P carried by the belt is reoriented by each fence it encounters. We present an O(m + n² log³n)-time algorithm to compute a sequence of fences that uniquely orients P, if one exists, where m is the total number of vertices and n is the number of stable edges of P. We reduce the problem to searching for a path in a state graph that has O(n³) edges. By exploiting various geometric properties of this graph, we show that it can be represented implicitly and that a desired path can be computed in O(m + n² log³n) time. We believe that our technique is quite general and could be applicable to other part-manipulation problems as well.     

Multishell conduction in multiwalled carbon nanotubes

The full electronic complexity of multiwalled carbon nanotubes may be explored by sequentially removing individual carbon shells. This technique is employed to directly measure the number of shells contributing to conduction at room temperature, as well as the contribution of each shell to the overall conductance. By exploring the gate dependence of the conductance, the random alternation between semiconducting and metallic shells can also be observed. Received: 31 August 2001 / Accepted: 3 December 2001 / Published online: 4 March 2002     

Spectroscopic characterization of porous nanohydroxyapatite synthesized by a novel amino acid soft solution freezing method

In this paper, we have reported a novel method to synthesize nanoporous hydroxyapatite (HAP) powders by freezing organic–inorganic soft solutions. The formation of porous and crystalline HAP nanopowder was achieved via calcining the samples at 600 °C followed by sintering at temperatures ranging from 900 °C to 1100 °C. The samples were analyzed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopic (SEM) techniques. The results showed the formation of a carbon free nanoporous hydroxyapatite powders due to the decomposition of organic template enclosing the precipitated HAP. It was also observed that the rapid grain growth with retainment of pores while the crystallinity of the HAP nanopowder increased with the increase in sintering temperature which is substantiated from the XRD and SEM results. Such organized porous materials can act as a better biomaterial for bone tissue engineering.     

Charge transfer model for quadrupole interactions and binding energies of point defects with111In/Cd probes in cubic metals

An overview of the experimental approaches to study weak interactions using traps is given. Both charged and neutral weak currents are considered.