Phase Transfer Catalysis Preparation of Aryl Thioethers

Phase transfer catalyzed displacement of halogen from activated aromatic rings by thiophenoxide ion has formed aryl thioethers in good yield.     

Effect of viscous dissipation on the mixed convection heat transfer from an exponentially stretching surface

The mixed convection flow and heat transfer from an exponentially stretching vertical surface in a quiescent fluid is analyzed using similarity solution technique. Wall temperature and stretching velocity are assumed to have specific exponential function forms. The influence of buoyancy along with viscous dissipation on the convective transport in the boundary layer region is analyzed in both aiding and opposing flow situations. The flow is governed by the mixed convection parameter Gr/Re². The velocity and temperature inside the boundary layer are observed to be influenced by the parameters like Prandtl number Pr, Gebhart number Gb. Significant changes are observed in non-dimensional skin friction and heat transfer coefficients due to viscous dissipation in the medium. The flow and temperature distributions inside the boundary layer are analyzed and the results for non-dimensional skin friction and heat transfer coefficients are discussed through computer generated plots.     

Sequential adsorption of bacteriophage T4 lysozyme stability variants at solid–water interfaces

The sequential adsorption of the wild type T4 lysozyme and one of its structural stability variants was studied, using ellipsometry and ¹²⁵I radioisotope labeling techniques. The mutant lysozyme was produced by substitution of the isoleucine residue at position 3 in the wild type with a tryptophan residue, resulting in a protein with lower structural stability. The mutant protein was more resistant to surfactant-mediated elution, and apparently adsorbed at the interfaces with a greater interfacial area/molecule than the wild typeT4 lysozyme. However, the results of each type of experiment suggested that sequential adsorption and exchange of proteins occurred only in the case of the less stable mutant followed by the wild type. This suggests that, in these exchange reactions, properties of the adsorbing protein (e.g. its ability to adsorb when a relatively small amount of unoccupied area is present) were more important than the apparent binding strength of the adsorbed protein molecules.     

A mild and chemoselective method for the deprotection of tert-butyldimethylsilyl (TBDMS) ethers using iron(III) tosylate as a catalyst

The most common method for the deprotection of TBDMS ethers utilizes stoichiometric amounts of tetrabutylammonium fluoride, n-Bu₄N⁺F⁻ (TBAF), which is highly corrosive and toxic. We have developed a mild and chemoselective method for the deprotection of TBDMS, TES, and TIPS ethers using iron(III) tosylate as a catalyst. Phenolic TBDMS ethers, TBDPS ethers and the BOC group are not affected under these conditions. Iron(III) tosylate is an inexpensive, commercially available, and non-corrosive reagent.     

Bioorthogonal profiling of protein methylation using azido derivative of S-adenosyl-L-methionine

Protein methyltransferases (PMTs) play critical roles in multiple biological processes. Because PMTs often function in vivo through forming multimeric protein complexes, dissecting their activities in the native contexts is challenging but relevant. To address such a need, we envisioned a Bioorthogonal Profiling of Protein Methylation (BPPM) technology, in which a SAM analogue cofactor can be utilized by multiple rationally engineered PMTs to label substrates of the corresponding native PMTs. Here, 4-azidobut-2-enyl derivative of S-adenosyl-L-methionine (Ab-SAM) was reported as a suitable BPPM cofactor. The resultant cofactor-enzyme pairs were implemented to label specifically the substrates of closely related PMTs (e.g., EuHMT1 and EuHMT2) in a complex cellular mixture. The BPPM approach, coupled with mass spectrometric analysis, enables the identification of the nonhistone targets of EuHMT1/2. Comparison of EuHMT1/2's methylomes indicates that the two human PMTs, although similar in terms of their primary sequences, can act on the distinct sets of nonhistone targets. Given the conserved active sites of PMTs, Ab-SAM and its use in BPPM are expected to be transferable to other PMTs for target identification.     

Adsorption of Thermomonospora fusca E5 and Trichoderma reesei cellobiohydrolase I cellulases on synthetic surfaces

The interfacial behavior of Thermomonosporafusca E5 and Trichoderma reesei cellobiohydrolase I (CBHI) cellulases were studied at synthetic surfaces. For this purpose, colloidal silica and polystyrene particles were used to prepare cellulase-particle suspensions that could be analyzed by solution-phase techniques. Circular dichroism spectroscopy of each cellulase, alone as well as in suspension with silica, was used to determine whether structural changes occurred on adsorption. Changes in spectra were observed for CBHI, but not for E5. Gel-permeation chromatography of the cellulase-particle suspensions showed that neither cellulase binds to silica, suggesting that changes in spectra for CBHI were a result of solution-phase phenomena. Microfiltration of cellulase-polystyrene suspensions showed that both cellulases bind to polystyrene. However, circular dichroism experiments with polysterene proved unworkable, owing to excessive light absorption by the polystyrene. Adsorption kinetics of each cellulase were recorded, in situ, at hydrophilic and silanized, hydrophobic silica surfaces using ellipsometry. Ellipsometric data recorded for each cellulase at hydrophilic silica showed insignificant adsorption. Binding did occur between each cellulase and silanized silica, most likely mediated through hydrophobic associations. Adsorption in this case was irreversible to dilution.     

Growth morphology of zinc tris(thiourea) sulphate crystals

The growth morphology of crystals of zinc tris(thiourea) sulphate (ZTS) is investigated experimentally, and computed using the Hartman-Perdok approach. Attachment energies of the observed habit faces are calculated for determining their relative morphological importance. A computer code is developed for carrying out these calculations. A special procedure is adopted for computing the cohesive energy of a slice of the structure parallel to any rational crystallographic plane. For estimating the cohesive energies, formal charges on the experimentally determined atomic positions in the molecules of ZTS are calculated by ab initio molecular-orbital computations, with wave functions obtained by the Hartree-Fock procedure. Fairly good agreement with the observed crystal morphology is obtained for a model of growth mechanism in which ZTS is assumed to exist in solution sa szinc tris(thiourea) ions and sulphate ions.