Chemical modification results in hyperactivation and thermostabilization ofFusarium solaniglucoamylase

2007 ◽  
Vol 53 (2) ◽  
pp. 177-185 ◽  
Author(s):  
Haq Nawaz Bhatti ◽  
M. Hamid Rashid ◽  
Muhammad Asgher ◽  
Rakhshanda Nawaz ◽  
A.M. Khalid ◽  
...  
Keyword(s):  
Thermal Stability ◽  
Chemical Modification ◽  
Soluble Starch ◽  
Water Soluble ◽  
Chemically Modified ◽  
Free Energy Of Activation ◽  
Enthalpy Of Activation ◽  
Specificity Constant ◽  
Modified Forms ◽  
Thermal Stability Of

Chemical modification of carboxyl groups of glucoamylase from a mesophilic fungus, Fusarium solani , was carried out using ethylenediamine as nucleophile in the presence of water-soluble 1-ethyl-3(3-dimethylaminopropyl)carbodiimide. Modification brought about a dramatic enhancement of catalytic activity and thermal stability of glucoamylase. Temperature and pH optima of ethylenediamine-coupled glucoamylase (ECG) increased as compared with those of native enzyme. The specificity constant (kcat/Km) of native, ECG-2, ECG-11, and ECG-17 was 136, 173, 225, and 170, respectively, at 55 °C. The enthalpy of activation (ΔH*) and free energy of activation (ΔG*) for soluble starch hydrolysis were lower for the chemically modified forms. All of the modified forms werestable at higher temperatures and possessed high ΔG* against thermal unfolding. The effects of α-chymotrypsin and subtilisin on the modified forms were activating as compared with native. Moreover, denaturation of ECG-2, ECG-11, and ECG-17 in urea at 4 mol·L–1also showed an activation trend. A possible explanation for the thermal denaturation of native and increased thermal stability of ECG-2, ECG-11, and ECG-17 at higher temperatures is also discussed.

scholarly journals Phosphated Avocado Seed: A Renewable Biomaterial for Preparing a Flame Retardant Biofiller

2021 ◽  
Author(s):  
DAVID Zuluaga-Parra ◽  
L.F Ramos-deValle ◽  
Saul Sanchez ◽  
J.R. Torres-Lubián ◽  
J.A. Rodríguez-Gonzalez ◽  
...  
Keyword(s):  
Thermal Stability ◽  
Chemical Modification ◽  
Flame Retardant ◽  
Photoelectron Spectroscopy ◽  
Morphological Changes ◽  
Ethylene Vinyl Acetate ◽  
Chemically Modified ◽  
Air Atmosphere ◽  
Thermal Stability Of ◽  
Avocado Seed

Abstract The cellulose and starch present in the avocado seed can be chemically modified to obtain biofillers with fire retarding characteristics. The resulting composites could be used as substitute of the corresponding halogenated composites. For this, the avocado seed was first washed, dehydrated and pulverized, and thereafter, chemically modified with phosphoric acid in the presence of urea. This was studied using infrared spectroscopy, nuclear magnetic resonance and X-Ray photoelectron spectroscopy, in order to determine the resulting chemical structure and confirm the presence of the proposed functional groups. In addition, scanning electron microscopy and elemental analysis were used, respectively, to establish the resulting morphological changes, as well as the elements present on the surface of the modified material. Thermogravimetric analysis was also carried out in order to establish the thermal stability of the material and predict the effect on the flame retardancy due to the mentioned chemical modification. Further tests established that the obtained modified structure and morphology of the avocado seed was highly dependent on the method used to dehydrate the pulverized avocado seed. It was also determined that chemical modification greatly increased the thermal stability of the avocado seed in air atmosphere. The flame-retardant effect of the modified avocado seed was assessed in polyethylene/ethylene-vinyl-acetate (PE/EVA) composites via cone calorimeter tests. These results showed that the modified avocado seed decreased the peak of the heat release rate (pHRR) by 50% and the total heat released (THR) by 15%. This phosphated avocado seed could be a good option as a renewable biofiller for polymer composites with enhanced flame-retardant properties.

scholarly journals Molecular Characterization of Cycloinulooligosaccharide Fructanotransferase from Bacillus macerans

2001 ◽  
Vol 67 (2) ◽  
pp. 995-1000 ◽  
Author(s):  
Hwa-Young Kim ◽  
Yong-Jin Choi
Keyword(s):  
Escherichia Coli ◽  
Thermal Stability ◽  
Striking Difference ◽  
Bacillus Macerans ◽  
Specific Manner ◽  
Specificity Constant ◽  
Processing Event ◽  
Hydrolysis Of ◽  
Thermal Stability Of

ABSTRACT Cycloinulooligosaccharide fructanotransferase (CFTase) converts inulin into cyclooligosaccharides of β-(2→1)-linkedd-fructofuranose by catalyzing an intramolecular transfructosylation reaction. The CFTase gene was cloned and characterized from Bacillus macerans CFC1. The CFTase gene encoded a polypeptide of 1,333 amino acids with a calculatedM r of 149,563. Western blot and zymography analyses revealed that the CFTase with a molecular mass of 150 kDa (CFT150) was processed (between Ser389 and Phe390 residue) to form a 107-kDa protein (CFT107) in the B. macerans CFC1 cells. The processed CFT107 was similar in its mass to the previously purified CFTase from B. macerans CFC1. The CFT107 enzyme was produced by B. macerans CFC1 but was not detected from the recombinant Escherichia coli cells, indicating that the processing event occurred in a host-specific manner. The two CFTases (CFT150 and CFT107) exhibited the same enzymatic properties, such as influences of pH and temperature on the enzyme activity, the intermolecular transfructosylation ability, and the ability of hydrolysis of cycloinulooligosaccharides produced by the cyclization reaction. However, the thermal stability of CFT107 was slightly higher than that of CFT150. The most striking difference between the two enzymes was observed in their Km values; the value for CFT150 (1.56 mM) was threefold lower than that for CFT107 (4.76 mM). Thus, the specificity constant (k cat/Km ) of CFT150 was about fourfold higher than that of CFT107. These results indicated that the N-terminal 358-residue region of CFT150 played a role in increasing the enzyme's binding affinity to the inulin substrate.

Thermo-physical behaviors of carbon nanofiber reinforced polylactic acid

2013 ◽  
Vol 1505 ◽  
Author(s):  
Ananta Raj Adhikari ◽  
Kamal Sarkar ◽  
Karen Lozano
Keyword(s):  
Thermal Stability ◽  
Polylactic Acid ◽  
Carbon Nanofiber ◽  
Water Soluble ◽  
Steady Increase ◽  
Future Technology ◽  
Large Numbers ◽  
Stage Crystallization ◽  
Thermo Physical Properties ◽  
Thermal Stability Of

ABSTRACT:Studies have demonstrated that the reinforcement of polymeric matrices using nanofiller can results with better thermo-physical properties of polymer. Carbon nanofiber (CNF) is a unique quasi-one dimensional nanostructure with large numbers of edges and defects compared to carbon nanotube (CNT). Further the availability in large quantity along with lower cost makes them an important nanomaterial for future technology. We have previously used CNF in different thermoplastic polymers. In this study CNFs were used with water soluble thermoplastic aliphatic polyster polylactic acid (PLA) and studied their thermal and mechanical properties. Thermal analysis using Thermogravimetric Analysis showed enhanced thermal stability of the polymer at higher nanotube loading (>1 wt%) and decrease of thermal stability at higher loading (>10 wt%). Crystallization thermogram of PLA was modified heavily with the addition of nanofibers changing clearly from one stage to two stage crystallization. In addition, CNF facilitates the crystallization of PLA resulting in an increase of its crystallization. The mechanical testing showed the steady increase of modulus of the composites with the nanofiber content within the range of study which can be regarded as due to the change in interface property of the composites.

scholarly journals Electrochemical properties and thermal stability of epoxy coatings electrodeposited on aluminium and modified aluminium surfaces

2001 ◽  
Vol 66 (11-12) ◽  
pp. 871-880 ◽  
Author(s):  
Vesna Miskovic-Stankovic ◽  
Zorica Lazarevic ◽  
Zorica Kacarevic-Popovic
Keyword(s):  
Thermal Stability ◽  
Electrochemical Impedance ◽  
Corrosion Behaviour ◽  
Charge Transfer Resistance ◽  
Epoxy Coatings ◽  
Transfer Resistance ◽  
Protective Properties ◽  
Chemically Modified ◽  
Thermal Stability Of

The corrosion behaviour of epoxy coatings electrodeposited on aluminium, as well as on electrochemically and chemically modified aluminium were investigated during exposure to 3 % NaCl. Electrochemical impedance spectroscopy (EIS) and thermogravimetric analysis (TGA) were used for the determination of the protective properties of epoxy coatings on aluminium, anodized aluminium, phosphatized and chromatized-phosphatized aluminium. The protective properties of epoxy coatings on anodized and chromatized-phosphatized aluminium are significantly improved with respect to the same epoxy coatings on aluminium and phosphatized aluminium: higher values of the pore resitance and charge-transfer resistance, lower values of the coating capacitance, double-layer capacitance and relative permittivity (from EIS) smaller amount of absorbed water inside the coating (From TGA). On the other hand, the lower values of the ipdt temperature indicate a lower thermal stability of the epoxy coatings on anodized and chromatized-phosphatized aluminium.

scholarly journals Thermal Stability of Gel Foams Stabilized by Xanthan Gum, Silica Nanoparticles and Surfactants

Gels ◽  
2021 ◽  
Vol 7 (4) ◽  
pp. 179
Author(s):  
Youjie Sheng ◽  
Canbin Yan ◽  
Yang Li ◽  
Yunchuan Peng ◽  
Li Ma ◽  
...  
Keyword(s):  
Thermal Stability ◽  
Surface Activity ◽  
Xanthan Gum ◽  
Foam Stability ◽  
Water Soluble ◽  
Water Soluble Polymer ◽  
Foaming Ability ◽  
Subtle Effect ◽  
Thermal Stability Of ◽  
Foam Drainage

The foams stabilized by nanoparticles (NPs), water-soluble polymers, and surfactants have potential application prospects in the development of new, environmentally friendly firefighting foams. In the present study, a gel foam containing a water-soluble polymer (xanthan gum, XG), hydrophilic silica NPs, hydrocarbon surfactant (SDS), and fluorocarbon surfactant (FS-50) were prepared. The surface activity, conductivity, viscosity, and foaming ability of foam dispersions were characterized. The gel foam stability under a radiation heat source and temperature distribution in the vertical foam layer were evaluated systematically. The results show that the addition of NPs and XG has a significant effect on the foaming ability, viscosity and foam thermal stability, but has a very subtle effect on the conductivity and surface activity. The foaming ability of the FS-50/SDS solution was enhanced by the addition of NPs, but decreased with increasing the XG concentration. The thermal stability of the foams stabilized by SDS/FS-50/NPs/XG increased with the addition of NPs and increasing XG concentration. Foam drainage and coarsening were significantly decelerated by the addition of NPs and XG. The slower foam drainage and coarsening are the main reason for the intensified foam thermal stability. The results obtained from this study can provide guidance for developing new firefighting foams.

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