Modulation of stability properties of bovine trypsin after in vitro structural changes with a variety of chemical modifiers

Controlled chemical modification of enzymes, targeting groups not involved in the active site, can lead to modified catalysts that are intrinsically more efficient and resistant to heat and denaturing agents. Bovine pancreatic trypsin was covalently modified up to 75-85% with monomeric glutaraldehyde (MGA), polymeric glutaraldehyde (PGA), oxidized sucrose and oxidized sucrose polymers (OSP 70 and OSP 400). Virtually no loss in activity occurred upon modification. Temperature optima of trypsin shifts from 45-76 degrees C and T50 from 54-76 degrees C for the best modified sample made with OSP. The efficiency of the modifiers in stabilization was ranked in the order: OSP 400-T > OSP 70-T > PGA-T > MGA-T > Sucrose-T. Half-life of modified enzymes also followed the same trend. Both stabilization factor and t1/2 decreased with increasing temperatures. The free energy of activation for inactivation delta(deltaG*) varies from 12-20 kJ/mol and the activation enthalpy delta(deltaH*) of the modified trypsin by 80-120 kJ/mol indicating stabilization. Inactivation of modified trypsin by urea is less noticeable. The character of the two-step inactivation process of trypsin changes with the degree of stabilization in that the duration of phase I one increased noticeably as stabilization increases. Native trypsin fluoresces less intensely showing a red shift under the influence of denaturation. Such a fluorescence change is not so obvious for the modified enzymes indicating conformational stability acquired by modification.      

High Temperature Millimeter Wave Radiometric and Interferometric Measurements of Slag-Refractory Interaction for Application to Coal Gasifiers

Millimeter wave (MMW) radiometry can be used for simultaneous measurement of emissivity and temperature of materials under extreme environments such as in slagging coal gasifiers, where sensors have been identified as a key enabling technology need for process optimization. We present a dual-channel MMW heterodyne radiometer with active interferometric capability that allows simultaneous measurements of sample temperature, emissivity, and flow dynamics. Interferometric capability at 137 GHz is supplied via a probe signal originating from a local oscillator allowing monitoring of sample dynamics such as volume expansion and thickness change. This capability has been used to monitor characteristic behavior between refractories and slag such as slag infiltration, slag melting, viscous flow, foaming, and crucible corrosion by the molten slag. These results show the promise of the MMW system for extracting process parameters from operating slagging coal gasifiers, providing valuable information for process efficiency, control, and increased productivity.     

Induced crystallization of cellulose in never-dried cotton fibers

In the present investigation, we have made a systematic study of the induced crystallization in never-dried cotton fiber, by allowing it to desiccate under different conditions of humidity and temperature. The resulting structural changes have been followed using x-ray diffraction and infrared absorption techniques. A slow rate of drying coupled with a high temperature was more conducive for maximum crystallization. Analysis of the effect of temperature on the induced crystallization showed possible existence of a thermal transition in cellulose around 30°C. The induced crystallization brought about by slow drying as well as those produced using intercrystalline swelling agents, have been shown to be resulting from a proper channelization of the interfibrillar mobility existing in the never-dried fibers.     

Electrochemical etching of highT c superconducting materials

HighT _c superconductor materials of yttrium barium copper oxide (YBCO) have been etched by a new electrochemical technique. In this technique, acids like hydrochloric, nitric and phosphoric have been used as an electrolyte and etching has been achieved with acid dilutions as high as 1:200 with water. It is observed that rapid and controlled etching is possible by this technique.     

Mechanism of Ruthenium (III) Catalysis of Periodate Oxidation of Aldoses in Aqueous Alkaline Medium

The NO/H₂ reaction has been studied over a Ni loaded carbon film catalysts using in situ FTIR spectroscopy at the temperature range 25–350°C. On these catalysts, the differences in activity and selectivity were found depending on the nature of the surface functional groups. These differences were correlated with transient infrared spectral features which appeared during the reaction. It has been proved experimentally that the chemical character of the support is of vital importance during the process. The rise in NO conversion and N₂ selectivity was observed when the surface of the catalysts was changed by the NH₃ chemisorption. Amide and/or imide species formed due to the reduction of ammonium salts of carboxylic acids can play a significant role as active centers during the NO reduction.     

Crack stability in edge-notched clamped beam specimens: modeling and experiments

Stability of a fracture toughness testing geometry is important to determine the crack trajectory and R-curve behavior of the specimen. Few configurations provide for inherent geometric stability, especially when the specimen being tested is brittle. We propose a new geometrical construction called the single edge notched clamped bend specimen (SENCB), a modified form of three point bending, yielding stable cracking under load control. It is shown to be particularly suitable for small-scale structures which cannot be made free-standing, (e.g., thin films, coatings). The SENCB is elastically clamped at the two ends to its parent material. A notch is inserted at the bottom center and loaded in bending, to fracture. Numerical simulations are carried out through extended finite element method to derive the geometrical factor f(a/W) and \(\hbox {K}_{\mathrm{I}}\) for different beam dimensions. Experimental corroborations of the FEM results are carried out on both micro-scale and macro-scale brittle specimens. A plot of \(\hbox {K}_{\mathrm{I}}\) vs a/W, is shown to rise initially and fall off, beyond a critical a/W ratio. The difference between conventional SENB and SENCB is highlighted in terms of \(\hbox {K}_{\mathrm{I}}\) and FEM simulated stress contours across the beam cross-section. The \(\hbox {K}_{\mathrm{IC}}\) ’s of bulk NiAl and Si determined experimentally are shown to match closely with literature values. Crack stability and R-curve effect is demonstrated in a PtNiAl bond coat sample and compared with predicted crack trajectories from the simulations. The stability of SENCB is shown for a critical range of a/W ratios, proving that it can be used to get controlled crack growth even in brittle samples under load control.     

Chimeric constructs between human and rat equilibrative nucleoside transporters (hENT1 and rENT1) reveal hENT1 structural domains interacting with coronary vasoactive drugs

We have recently isolated cDNAs from human placenta and rat jejunum encoding the prototypic human and rat equilibrative nitrobenzylthioinosine (NBMPR)-sensitive nucleoside transporters hENT1 and rENT1. The two proteins (456 and 457 residues, Mr 50,000) are 78% identical in amino acid sequence and contain 11 potential transmembrane segments (TMs) with a large putative extracellular loop between TMs 1 and 2 and a large cytoplasmic loop between TMs 6 and 7. When expressed in Xenopus oocytes, recombinant hENT1 and rENT1 transport both purine and pyrimidine nucleosides, including adenosine, and are inhibited by nanomolar concentrations of NBMPR. hENT1 is also potently inhibited by coronary vasodilator drugs (dipyridamole, dilazep, and draflazine), whereas rENT1 is insensitive to inhibition by these compounds (dipyridamole IC50 values 190 nM (hENT1) and >/=10 microM (rENT1) at 10 microM uridine). In the present study, we have generated reciprocal chimeras between hENT1 and rENT1, using splice sites at residues 99 (end of TM 2) and 231 (end of TM 6), to identify structural domains of hENT1 responsible for transport inhibition by vasoactive compounds. Transplanting the amino-terminal half of hENT1 into rENT1 converted rENT1 into a dipyridamole/dilazep-sensitive transporter, whereas the amino-terminal half of rENT1 rendered hENT1 dipyridamole/dilazep-insensitive. Domain swaps within the amino-terminal halves of hENT1 and rENT1 identified residues 100-231 (incorporating TMs 3-6) of hENT1 as the major site of vasodilator interaction. Since these drugs function as competitive inhibitors of nucleoside transport and NBMPR binding, TMs 3-6 are likely to form part of the substrate-binding site.