General Characteristics of the Changes in the Thermal Stability of Proteins and Enzymes After the Chemical Modification of Their Functional Groups

1984 ◽  
Vol 53 (11) ◽  
pp. 1078-1100 ◽  
Author(s):  
G D Kutuzova ◽  
N N Ugarova ◽  
Ilya V Berezin
Keyword(s):  
Thermal Stability ◽  
Chemical Modification ◽  
Functional Groups ◽  
Thermal Stability Of

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.

Thermal Stability of Oxygen-Containing Functional Groups on Activated Carbon Surfaces in a Thermal Oxidative Environment

2014 ◽  
Vol 47 (1) ◽  
pp. 21-27 ◽  
Author(s):  
Liqing Li ◽  
Xiaolong Yao ◽  
Hailong Li ◽  
Zheng Liu ◽  
Weiwu Ma ◽  
...  
Keyword(s):  
Thermal Stability ◽  
Activated Carbon ◽  
Functional Groups ◽  
Carbon Surfaces ◽  
Thermal Stability Of

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 FUNCTIONALIZATION OF CELLULOSE AND CHITOSAN IN IONIC LIQUIDS

2020 ◽  
Vol 54 (9-10) ◽  
pp. 857-868
Author(s):  
CRISTINA STEFANESCU ◽  
WILLIAM H. DALY ◽  
IOAN I. NEGULESCU
Keyword(s):  
Thermal Stability ◽  
Weight Loss ◽  
Ionic Liquid ◽  
Ionic Liquids ◽  
Functional Groups ◽  
Phthalic Anhydride ◽  
Reaction Products ◽  
Molar Ratios ◽  
Thermal Stability Of ◽  
Mechanisms Of Reactions

Chemistry of cellulose in ionic liquids has been briefly reviewed and, accordingly, the phthalation of chitosan in these ionic solvents has been investigated. Chitosan (K) has been reacted at 100 °C for 4 hours with phthalic anhydride (PA) in ionic liquids 1-butyl-3-methylimidazolium acetate (BMIMAc) and 1-butyl-3-methylimidazolium chloride (BMIMCl) in the presence of bases, pyridine and 1,4-diazobicyclo[2.2.2] octane (DABCO), or the phthalation has been catalyzed by N-bromosuccinimide (NBS). Depending on the nature of the reaction components, the samples were prepared with molar ratios of PA to anhydroglucose unit (PA:K) from 3:1 to 10:1, including molar ratios of bases or catalyst to chitosan, ranging also from 3:1 to 10:1. All the reaction products were soluble in dimethyl sulfoxide and dimethylformamide. Both functional groups of chitosan units, -OH and -NH2 , reacted, resulting in FTIR confirmed products containing esters, amide, and imide functional groups. Heating the isolated phthalated chitosan products to 200 °C led to cyclization with the formation of imide groups and elimination of water. When bases controlled the reactions, the highest degrees of substitution of DABCO product (DS = 0.80) was slightly higher than the highest DC of the reaction products obtained in the presence of pyridine (DS = 0.77). However, the presence of the Nbromosuccinimide catalyst in the system led to an increase of the degree of substitution of the functional groups of chitosan (DS = 1.75), compared with that listed above for the products resulted when the reactions were carried out in the presence of bases. The thermal stability of the chitosan derivatives obtained in the presence of a base depended primarily upon the nature of the counter ion of the ionic liquid. When the reaction was conducted in the acetate ionic liquid BMIMAc, the phthalated chitosan exhibited a lower thermal stability than that of chitosan, while when the chloride ionic liquid BMIMCl was used as solvent, the thermal stability of the phthalated chitosan increased, indicating an interference of the ionic solvents in the mechanisms of reactions. Nevertheless, the thermal behavior of the phthalated products obtained in reactions catalyzed by NBS may be correlated with the increasing degrees of substitution achieved with increased catalyst concentrations: a higher DS resulted in a higher weight loss at higher temperatures.

HYDROGENATED BUTADIENE-ACRYLONITRILE-BUTYLACRYLATE RUBBER AND ITS PROPERTIES

2013 ◽  
Vol 86 (2) ◽  
pp. 165-174
Author(s):  
Dongmei Yue ◽  
Xinpeng Wei ◽  
Xunzhang Wang ◽  
Weimin Wang ◽  
Liqun Zhang
Keyword(s):  
Thermal Stability ◽  
Chemical Modification ◽  
Reaction Times ◽  
Critical Factor ◽  
Ccd Camera ◽  
Proton Nuclear Magnetic Resonance ◽  
Resonance Spectroscopy ◽  
Modification Method ◽  
Thermal Stability Of ◽  
Ozone Resistance

ABSTRACT Butadiene-acrylonitrile-butylacrylate rubber (BNBR), which is synthesized by copolymerization of butadiene, acrylonitrile, and butyl acrylate, retains excellent properties of oil resistance and heat resistance because of the introduction of -CN, -COOR in the polymer. However, the presence of a lot of carbon-carbon double bonds (-C=C-) could lead to deterioration of material properties such as thermal stability and ozone resistance. To improve the properties of unsaturated elastomers, further chemical modification of diene-based polymers is very critical. Hydrogenation is a useful chemical modification method that can improve the thermal stability of diene-based polymer. BNBR was hydrogenated by homogenous hydrogenation using the Wilkinson catalyst RhCl(PPh3)3 in xylene. The effects of catalyst concentrations, reaction times, and hydrogen pressures on the conversion and product selectivity were discussed. The degree of hydrogenation was measured by proton nuclear magnetic resonance spectroscopy and Fourier transform infrared spectroscopy. The thermal stability of hydrogenated and nonhydrogenated copolymers was evaluated by thermogravimetric analysis (TGA). The CCD camera was used to characterize the ozone resistance of hydrogenated copolymer (HBNBR). The results obtained by TGA and the CCD camera show that the maximum saturation level is a critical factor for improvement of thermal stability and the ozone resistance of HBNBR.

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