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Search Results: 1 - 10 of 3161 matches for " degree substitution. "
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Bactericidal Hydrogel Based on Sodium-Carboxymethylcellulose Contained Silver Nanoparticles: Obtaining and Properties  [PDF]
Yunusov Khaydar Ergashovich, arymsakov Abdushkur Abdukhalilovich, Rashidova Sayora Sharaphovna
Open Journal of Polymer Chemistry (OJPChem) , 2018, DOI: 10.4236/ojpchem.2018.84006
Abstract: Stable silver nanoparticles in a sodium-carboxymethylcellulose hydrogel with a substitution degree of 0.65 - 0.85 and polymerization degree of 200 - 600 have been synthesized. Physical, chemical properties and antimicrobial activity of sodium-carboxymethylcellulose hydrogels contained silver nanoparticles were studied. The shape, number and size of silver nanoparticles (SNP) incorporated into the structure of hydrogels of sodium-carboxymethylcellulose were studied by using UV-VIS spectroscopy, transmission electron and atomic force microscopy. It was found that the silver nitrate concentration increase in sodium-carboxymethylcellulose solutions, as well as photoirradiation of the hydrogel lead to the changes of the silver nanoparticles size and shape. The studies have shown that the spherical silver nanoparticles of 5 - 35 nm in the structure of sodium-carboxymethylcellulose hydrogel possess high bactericidal activity. Our results have shown that changing of size and shape of silver nanoparticles contributes to appearance of their biological activity.
Preparation and characterization of carboxymethylchitosan
Abreu, Fernanda R. de;Campana-Filho, Sérgio P.;
Polímeros , 2005, DOI: 10.1590/S0104-14282005000200004
Abstract: chitosan was reacted with monochloroacetic acid at room temperature for different reaction times (3h, 5h, 7h and 10h) and employing two chitosan/monochloroacetic acid molar ratios (1:4.3 or 1:8.6). the carboxymethylation of chitosan was confirmed by 1h nmr and 13c nmr spectroscopy. the carboxymethylchitosans had average degrees of substitution ranging from 0.52 to 1.44 as determined by potentiometric and conductimetric analysis. the occurrence of n,o-carboxymethylation was also observed in all cases.
Influência do grau de substitui??o e da distribui??o de substituintes sobre as propriedades de equilíbrio de carboximetilcelulose em solu??o aquosa
Caraschi, José Cláudio;Campana Filho, Sérgio P.;
Polímeros , 1999, DOI: 10.1590/S0104-14281999000200015
Abstract: samples of carboxymethylcellulose were prepared by the heterogeneous reaction of the soda/anthraquinone pulp obtained from sugar cane bagasse. the less substituted samples (ds<1,0) and the more substituted ones (ds> 1,0) showed different behaviors concerning to: i) the dependence of pkap on the degree of neutralization; ii) the agreement between ds values determined by titrations and by 1h nmr spectroscopy and iii) the agreement between the experimental values of transport coefficients (f) and the ones calculated by applying the manning theoretical approach. all samples showed a block distribution of substituents which, in the case of the less substituted samples, are short and well separated, favoring the occurrence of associative interactions and of aggregation. electrostatic excluded volume effects, which are more important for the more substituted samples, inhibit the aggregation and may explain the behavior of these samples.
Obtaining the Fluorescent Chitosan for Investigations in the Analytical Ultracentrifuge  [PDF]
Murodkhon R. Kodirkhonov
Advances in Biological Chemistry (ABC) , 2019, DOI: 10.4236/abc.2019.91002
Abstract: 1) In order to achieve the visibility of the chitosan macromolecule for the UV optical system of the analytical ultracentrifuge on investigation of the molecular characteristics and polymers interactions, the labeling of chitosan by a new fluorophore of fluorescein-5-isothiocyanat was carried out. 2) Samples of fluorescent chitosan with two different degrees of fluorophore substitution and various degrees of acetylation were obtained. 3) The labeled chitosans with the fluorescein-5-isothiocyanat allowed estimating the sedimentation coefficient and the molecular characteristic in the analytical ultracentrifuge. 4) The sensitivity of the UV-optical system of the analytical ultracentrifuge for the obtained fluorescent samples of chitosan relatively to the fixation of the meniscus and the influence of the wavelength and rotation speed were estimated.
Some aspects of acetylation of untreated and mercerized sisal cellulose
Ciacco, Gabriela T.;Morgado, Daniella Lury;Frollini, Elisabete;Possidonio, Shirley;El Seoud, Omar A.;
Journal of the Brazilian Chemical Society , 2010, DOI: 10.1590/S0103-50532010000100012
Abstract: we report here on some aspects of the acetylation in licl/n,n-dimethylacetamide, dmac, of untreated and mercerized sisal cellulose, hereafter designated as sisal and m-sisal, respectively. fiber mercerization by naoh solution has resulted in the following changes: 29.9% decrease in the index of crystallinity; 16.2% decrease in the degree of polymerization and 9.3% increase in α-cellulose content. a light scattering study of solutions of sisal, m-sisal, microcrystalline and cotton celluloses in licl/dmac has shown that they are present as aggregates, with (an apparent) average aggregation numbers of 5.2, 3.2, 9.8, and 35.3, respectively. the presence of these aggregates affects the accessibility of cellulose during its functionalization. a study of the evolution of the degree of substitution, ds, of cellulose acetate as a function of reaction time showed an increase up to 5 h, followed by a decrease at 7 h. possible reasons for this decrease are discussed. as expected, m-sisal gave a higher ds that its untreated counterpart.
Some intrinsic and extrinsic factors of acetylated starches: morphological, physicochemical and structural characteristics
Nú?ez-Santiago, M.C.;García-Suárez, F.J.;Gutierrez-Meraz, F.;Sánchez-Rivera, M.M.;Bello-Pérez, L.A.;
Revista mexicana de ingeniería química , 2011,
Abstract: degree substitution (ds), morphological characteristics, x-ray diffraction (xrd), pasting properties, thermal properties and amylopectin chain length distribution were used to study the effect of botanical source (potato starch, ps; and maize starch, ms) and reagent type (acetic anhydride and vinyl acetate) on starch acetyration. the reagent type produced a different effect depending on the botanical source: for ms, the reaction with acetic anhydride produced higher ds than ps, whereas that in the reaction with vinyl acetate resulted in an inverse pattern. in general, modified starches had a maltase cross, except for ps when acetylated with acetic anhydride. native ps had the highest crystallinity level and trie acetylated starches had a decreased amount of crystallinity (between 10% and 12 %) compared to the native starches. acetylation produced a decrease in pasting temperature, and changes in the pasting characteristics were more evident wish higher ds. structural changes in starch components due to the acetylation reaction produced a decrease in the temperature and enthalpy of gelatinization. in general, acetylated starches had minor retrogradation. regardless of reagent used, acetylated ms had higher retrogradation than acetylated ps. higher ds values resulted in greater amounts of short chains in both starches.
Analysis of the High Degree Myopia Surgical Correction Method Effectiveness
A.D. Chuprov,M.N. Duryagina
Sovremennye Tehnologii v Medicine , 2010,
Abstract: Aim of investigation is analysis of the high degree myopia surgical correction effectiveness with the photorefractive keratectomy (PhRK) (MAGEK) and the lens refractive substitution (LRS) methods.Materials and methods. 269 patients (507 eyes) are examined; 111 humans (210 eyes) of them with a myopia of 6.5 to 13 D are examined after the PhRK; 158 patients (297 eyes) with a myopia of 6.5 to 22 D — after the LRS. All the patients were divided into 5 groups. The PhRK (MAGEK) was accomplished in two groups at the MEL-70 and ESIRIS laser installations. The operations according to a phacoemulsification method were accomplished in three groups at the Millenium microsurgical system. A period of observation was 2 years.Results. The best vision acuity was in groups with the PhRK method intervention.Conclusion. A photorefractive keratectomy in the MAGEK modification is a selection method for correction of the high degree myopia at a sufficient thickness of cornea. A refractive substitution of a lens is effective method of correction for the patients with the contraindications to a keratorefractive surgery.
Enzymatic Synthesis of Sucrose Polyester as Food Emulsifier Compound
Sri Handayani,Ika Novianingsih,Awaliatul Barkah,Sumi Hudiyono
Makara Seri Sains , 2012,
Abstract: Sucrose polyester (SPE) is a carbohydrate ester compound that has diverse functions, from surfactant to low-calorie food products. Sucrose fatty acid ester with the degree of substitution 1-3 can be used as emulsifier in foods and cosmetics. The enzymatic synthesis of sucrose polyesters can be carried out using lipase in organic solvent and contain small amount of water. In these studies sucrose esters were synthesized by esterification reaction between sucrose with fatty acids from coconut and palm oil using Candida rugosa lipase in n-hexane. Optimization esterification reaction carried out for parameters of incubation time, temperature, and the ratio of the substrate. The optimum incubation time is at 18 hours for coconut oil and 12 hours palm oil, the optimum temperature is 30 oC for coconut and palm oil, and the mole ratio of fatty acid to sucrose is 40:1 for coconut oil and 64:1 for palm oil. Esterification products were characterized by FT-IR. The FT-IR spectrum showed the ester bond was formed as indicated by the wave number 1739.79/cm. Esterification products have 2 substitution degrees.
Optimization of Reaction Conditions for Preparing Carboxymethylcellulose
N.M. Ismail,A. Bono,A.C.R. Valintinus,S. Nilus
Journal of Applied Sciences , 2010,
Abstract: The cellulose powder was converted to carboxymethylcellulose (CMC) by etherification process using sodium monochloroacetate and sodium hydroxide. There are two reaction occur simultaneously during carboxymethylation that are the primary reaction which produces pure CMC and side reaction that produces undesired sodium glycolate. The carboxymethylation reaction was optimized against the reaction temperature, reaction time, SMCA concentration, NaOH concentration and the ratio solvent of ethanol:isopropanol. The Degree of Substitution (DS), viscosity and yield were analyzed with respect to the reaction conditions using response surface methodology. The method of analyzing the degree of substitution of CMC is back titration method. The produced CMC was identified by using Fourier Transform Infrared spectra (FTIR). The maximum DS obtained is 0.94, maximum yield is 22.0730 g and maximum viscosity 15.2 cP. After optimization of reaction conditions is carried out, the optimized DS obtained is 0.9424 and the optimized viscosity is 10.1 cP with yield is 22.1024 g.
Biomedical Activity of Chitin/Chitosan Based Materials—Influence of Physicochemical Properties Apart from Molecular Weight and Degree of N-Acetylation
Jolanta Kumirska,Mirko X. Weinhold,Jorg Th?ming,Piotr Stepnowski
Polymers , 2011, DOI: 10.3390/polym3041875
Abstract: The physicochemical nature of chitin and chitosan, which influences the biomedical activity of these compounds, is strongly related to the source of chitin and the conditions of the chitin/chitosan production process. Apart from widely described key factors such as weight-averaged molecular weight (M W) and degree of N-acetylation (DA), other physicochemical parameters like polydispersity (M W/M N), crystallinity or the pattern of acetylation ( P A) have to be taken into consideration. From the biological point of view, these parameters affect a very important factor—the solubility of chitin and chitosan in water and organic solvents. The physicochemical properties of chitosan solutions can be controlled by manipulating solution conditions (temperature, pH, ionic strength, concentration, solvent). The degree of substitution of the hydroxyl and the amino groups or the degree of quaternization of the amino groups also influence the mechanical and biological properties of chitosan samples. Finally, a considerable research effort has been directed towards developing safe and efficient chitin/chitosan-based products because many factors, like the size of nanoparticles, can determine the biomedical characteristics of medicinal products. The influence of these factors on the biomedical activity of chitin/chitosan-based products is presented in this report in more detail.
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