Mixed oxide supported hydrodesulfurization catalysts—a review

Support effects form important aspect of hydrodesulfurization (HDS) studies and mixed oxide supports received maximum attention in the last two decades. This review will focus attention on studies on mixed oxide supported Mo and W catalysts. For convenience of discussion, these are divided into Al₂O₃ containing mixed oxide supports, TiO₂ containing mixed oxide supports, ZrO₂ containing mixed oxide supports and other mixed oxide supports containing all the rest. TiO₂ containing mixed oxides received maximum attention, especially TiO₂–Al₂O₃ supported catalysts. A brief discussion about their prospects for application to ultradeep desulfurization is also included. An overview of the available literature with emphasis on research carried out in our laboratory form the contents of this publication.     

A backbone-reversed all-{beta} polypeptide (retro-CspA) folds and assembles into amyloid nanofibres

The backbone-reversed or ‘retro’, form of a modelall-ß-sheet protein, Escherichia coli CspA, was producedfrom a synthetic gene in E.coli in fusion with an N-terminalaffinity tag. Following purification under denaturing conditionsand dialysis-based removal of urea, the protein was found tofold into a soluble, poorly structured multimer. Upon concentration,this state readily transformed into amyloid nanofibres. CongoRed-binding amorphous forms were also observed. Since a ß-sheet-formingsequence is expected to retain high ß-sheet-formingpropensity even after backbone reversal and given the fact thatfolding of retro-CspA occurs only to a poorly structured form,we conclude that the increase effected in protein concentrationmay be responsible for the formation of intermolecular ß-sheets,facilitating the bleeding away of the protein’s conformationalequilibrium into aggregates that generate well-formed fibres.Since every molecule in these fibres contains a peptide tagfor binding Ni²⁺, the fibres may provide a template for depositionof nickel to generate novel materials. Received April 1, 2003; revised October 27, 2003; accepted October 30, 2003     

Synthesis and characterization of acidic properties of Al-SBA-15 materials with varying Si/Al ratios

Al-SBA-15 of varying Si/Al ratios in the range 11.4–78.4 was synthesized using tri-block copolymer P123. The calcined materials were examined by XRD, pore size distribution, surface area, ²⁷Al NMR spectroscopy. The acidity and acid strength distribution were studied using microcalorimetric adsorption of NH₃. The acidic properties were also examined by cumene cracking reaction as a function of Si/Al ratios. Systematic variation of acidity and activity was observed as a function of Si/Al ratio. The initial heats of NH₃ adsorption correlated well with activity indicate that acid sites with ΔH > 100 kJ/mole is responsible for cumene cracking activity. Linear correlations were obtained with total acidity and cumene cracking activities. The tetrahedral aluminum was found to be responsible for the observed acidities and catalytic activities.     

Effects of quinine on the mechanical frequency response of the cupula in the fish lateral line

Quinine induces changes in the motion of the cupula in the lateral line canal of the African knife-fish in response to sinusoidal water movements. Two different phases in the action of quinine on the cupular frequency response can be discerned. In the first phase the best frequency, i.e., the frequency at which the cupular vibratory displacement is maximal in response to constant-amplitude sinusoidal canal fluid displacement, shifts toward higher frequencies. During this phase, lasting about 70-100 min, the best frequency increases by a factor between 1.3 and 1.5. In the second phase, during roughly the following 90 min, the best frequency decreases gradually to a value 0.3-0.5 times that observed before the application of quinine.     

HLA-B27-restricted antigen presentation in the absence of tapasin reveals polymorphism in mechanisms of HLA class I peptide loading

Tapasin is a resident ER protein believed to be critical for antigen presentation by HLA class I molecules. We demonstrate that allelic variation in MHC class I molecules influences their dependence on tapasin for peptide loading and antigen presentation. HLA-B*2705 molecules achieve high levels of surface expression and present specific viral peptides in the absence of tapasin. In contrast, HLA-B*4402 molecules are highly dependent upon human tapasin for these functions, while HLA-B8 molecules are intermediate in this regard. Significantly, HLA-B*2705 like HLA-B*4402, requires tapasin to associate efficiently with TAP (transporters associated with antigen processing). The unusual ability of HLA-B*2705 to form peptide complexes without associating with TAP or tapasin confers flexibility in the repertoire of peptides presented by this molecule. We speculate that these properties might contribute to the role of HLA-B27 in conferring susceptibility to inflammatory spondyloarthropathies.     

Hexamethyl cyclotrisiloxane–styrene block copolymers and their chemical composition

Triblock copolymers of hexamethyl cyclotrisiloxane (D₃) and styrene were synthesized by first preparing “living” species of polystyrene dianion followed by polymerization of D₃. The chain lenght of polymeric blocks could be controlled in a predictable fashion leading to a central hard block of polystyrene and the two end segments of amorphous polydimethylsiloxane having narrow molecular weight distribution, were characterized by gel permeation chromatography. The chemical composition of block copolymers was determined by silicon analysis and infrared and nuclear magnetic resonance spectra. Thermal aging of block copolymers at 150, 200, and 300°C was also discussed.     

Cure characteristics,morphology, and mechanical properties of ethylene–propylene–diene–monomer rubber/acrylonitrile butadiene rubber blends

Blends based on ethylene–propylene–diene monomer rubber (EPDM) and acrylonitrile butadiene rubber (NBR) was prepared. Sulfur was used as the vulcanizing agent. The effects of blend ratio on the cure characteristics and mechanical properties, such as stress–strain behavior, tensile strength, elongation at break, hardness, rebound resilience, and abrasion resistance have been investigated. Tensile and tear strength showed synergism for the blend containing 30% of NBR, which has been explained in terms of morphology of the blends attested by scanning electron micrographs. A relatively cocontinuous morphology was observed for 70 : 30, EPDM/NBR blend system. The experimental results have been compared with the relevant theoretical models. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007