Thermal Degradation and Kinetics of Alginate Polyurethane Hybrid Material Prepared from Alginic Acid as a Polyol

Abstract Alginate polyurethane hybrid materials are prepared by varying mole ratio of 2, 4-TDI as a di-isocyanate and alginic acid as a polyol in presence of dimethyl sulfoxide (DMSO) as a solvent. FT-IR and 13 C onedimensional (1D) solid state NMR (SSNMR) spectroscopy indicates that alginic acid is converted into alginate-polyurethane hybrid material via urethane linkage. Surface morphology of alginate-polyurethane hybrids changes by varying alginic acid: TDI ratio. The peak at near 221°C in DSC thermogram of alginic acid (Alg) is shifted to higher temperature in alginate-polyurethane hybrid (Algpu1 and Algpu2). TGA study shows that alginate-polyurethane hybrid prepared using alginic acid: TDI = 1:1 (Algpu2) is more stable than alginic acid: TDI = 1:0.5 (Algpu1) at 300°C. Kinetic analysis was performed to fit with TGA data, where the entire degradation process has been considered as three consecutive 1st order reactions. This study shows that thermal stability of alginate-polyurethane hybrid material was increased by adjusting mole ratio of 2, 4-TDI and alginic acid

Resonance Raman studies on enzymatic intermediates of heme proteins and model compounds

The essential goal of HRP and catalase research is to gain an understanding of the conformations and mechanisms of enzymatic reactions in which the protein matrix regulates heme reactivity. A doubly oxidized heme (metalloporphyrin) has been proposed as a reactive intermediate in the catalytic cycles of peroxidases and catalases, and it has been suggested to be a free radical porphyrin species. The major accomplishments of this research were summarized as follows: (1) The RR spectra for HRP I was obtained by low power laser excitation and microdroplet stream. $\nu$(Fe-O) was located at 737 cm\sp{-1} and is 39 cm\sp{-1} downshift from HRP II. The high frequency spectra confirms the A\sb{\rm 2u} ground state of HRP I. (2) The RR spectra of Cat I and II were obtained with excitation by 406.7 nm laser line. $\nu$(Fe-O) of Cat II was located at 797 cm\sp{-1} and Cat I at 805 cm\sp{-1}. $\Delta\nu$ between Cat I and Cat II is +8 cm\sp{-1}. The high frequency spectra of Cat II shows low spin ferryl heme and Cat I is A\sb{\rm 1u} ground state. (3) The RR spectra of $\pi$ cation radical complexes of Fe(TMP) was obtained in $-$78\sp\circC. The photodegradation of cation radical species in presence of methanol was studied. The new intermediate was found at reaction between ferryl cation radical species and substrates. (4) An effective mixing method which originally suggested by Clegg et. al. has been modified and characterized

Electrochemical and Spectroscopic Studies of Iron Porphyrin Nitrosyls and their Reduction Products

The enzymatic reduction of nitrate to ammonia is catalyzed by a class of enzymes called the assimilatory nitrite reductases. These enzymes, commonly found in plants, contain siroheme and a 4Fe-4S cluster in their native form. Sulfite reductases, which are also able to carry out the reduction of nitrite to ammonia, are large, complex enzymes, but they can be dissociated into a functioning subunit that has a single siroheme and a 4Fe-4S cluster. The catalytic reduction of nitrite proceeds via the formation of a siroheme-nitrosyl complex, which is then reduced to ammonia. The nitrosyl complex has been observed experimentally and is the major species present during turnover. While no other intermediates have been observed in the operating enzyme, hydroxylamine can be reduced by the enzyme, though at a slower rate than nitrite, and is thought to be an intermediate in the reduction. The details of the reduction are not known, and it has been the aim of several research groups to characterize intermediates in the reduction and to elucidate the reduction mechanism using model porphyrin complexes

Electrochemical and Spectroscopic Studies of Iron Porphyrin Nitrosyls and their Reduction Products

The enzymatic reduction of nitrate to ammonia is catalyzed by a class of enzymes called the assimilatory nitrite reductases. These enzymes, commonly found in plants, contain siroheme and a 4Fe-4S cluster in their native form. Sulfite reductases, which are also able to carry out the reduction of nitrite to ammonia, are large, complex enzymes, but they can be dissociated into a functioning subunit that has a single siroheme and a 4Fe-4S cluster. The catalytic reduction of nitrite proceeds via the formation of a siroheme-nitrosyl complex, which is then reduced to ammonia. The nitrosyl complex has been observed experimentally and is the major species present during turnover. While no other intermediates have been observed in the operating enzyme, hydroxylamine can be reduced by the enzyme, though at a slower rate than nitrite, and is thought to be an intermediate in the reduction. The details of the reduction are not known, and it has been the aim of several research groups to characterize intermediates in the reduction and to elucidate the reduction mechanism using model porphyrin complexes

Exploration of Zero-Valent Iron Stabilized Calcium–Silicate–Alginate Beads’ Catalytic Activity and Stability for Perchlorate Degradation

Perchlorate contamination in groundwater poses a serious threat to human health, owing to its interference with thyroid function. The high solubility and poor adsorption of perchlorate ions make perchlorate degradation a necessary technology in groundwater contaminant removal. Here, we demonstrate the perchlorate degradation by employing nano zero-valent iron (nZVI) embedded in biocompatible silica alginate hybrid beads fabricated using calcium chloride (1 wt%) as a crosslinker. The concentration of precursors (sodium alginate, sodium silicate) for bead formation was standardized by evaluating the thermal stability of beads prepared at different sodium silicate and alginate concentrations. Thermal degradation of silica alginate hybrid samples showed a stepwise weight loss during the thermal sweep, indicating different types of reactions that occur during the degradation process. The formation of the silica alginate hybrid structure was confirmed by FT-IR spectroscopy. Scanning electron microscopy (SEM) data revealed the surface morphology of silica alginate hybrid changes by varying sodium silicate and alginate concentrations. nZVI-loaded alginate–silicate polymer bead (nZVI-ASB) exhibited excellent perchlorate degradation efficiency by degrading 20 ppm of perchlorate within 4 h. Our study also showed the perchlorate degradation efficiency of nZVI-ASB is maximum at neutral pH conditions