Synthesis and characterization of pH‐ and salt‐responsive hydrogels based on etherificated sodium alginate

Hydrogels composed of etherificated sodium alginate (ESA), sodium acrylic acid (NaAA), and poly (vinyl alcohol) (PVA) were synthesized by aqueous solution polymerization. The effects of reaction variables such as terminal pH, ions, and ionic strength on hydrogel swelling ratio (SR) were determined and compared. SR was influenced strongly by pH and ionic strength. SR increased with increasing pH but tended to decrease with PVA content. At a given ionic strength, SR of ESA/NaAA/PVA hydrogel was dependent on the valence of anion; SR was higher in multivalent anion salt solution than in monovalent anion salt solution, i.e., SR_K2SO4 > SR_KCl and SR_Na2SO4 > SR_NaCl. The swelling kinetic of the hydrogels showed Fickian kinetic diffusion in acidic media and non‐Fickian behavior in alkaline media. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Using L‐Arginine‐Functionalized Gold Nanorods for Visible Detection of Mercury(II) Ions

A rapid and simple approach for visible determination of mercury ions (Hg²⁺) in aqueous solutions was developed based on surface plasmon resonance phenomenon using L‐arginine‐functionalized gold nanorods (AuNRs). At pH greater than 9, the deprotonated amine group of L‐arginine on the AuNRs bound with Hg²⁺ leading to the side‐by‐side assembly of AuNRs, which was verified by transmission electron microscopy images. Thus, when Hg²⁺ was present in the test solution, a blue shift of the typical longitudinal plasmon band of the AuNRs was observed in the ultra violet‐visible‐near infrared (UV‐Vis‐NIR) spectra, along with a change in the color of the solution, which occurred within 5 min. After carefully optimizing the potential factors affecting the performance, the L‐arginine/AuNRs sensing system was found to be highly sensitive to Hg²⁺, with the limit of detection of 5 nM (S/N = 3); it is also very selective and free of interference from 10 other metal ions (Ba²⁺, Ca²⁺, Cd²⁺, Co²⁺, Cs⁺, Cu²⁺, K⁺, Li⁺, Ni²⁺, Pb²⁺). The result suggests that the L‐arginine‐functionalized AuNRs can potentially serve as a rapid, sensitive, and easy‐to‐use colorimetric biosensor useful for determining Hg²⁺ in food and environmental samples.     

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.