Distribution Of Substituent Groups Research Articles

Impact of single and dual modifications on physicochemical properties of japonica and indica rice starches

The japonica (JR) and indica (IR) rice starches were modified by acetylation, hydroxypropylation, cross-linking, and dual modification (cross-linked acetylation and cross-linked hydroxypropylation) and the effects of single and dual chemical modifications of JR and WR on the physicochemical properties were investigated. The JR had a greater substitution degree of acetyl or hydroxypropyl groups than IR. The dual-modified JR showed broader gelatinization temperature range than corresponding single-modified starches, but narrower it in IR. The dual-modified JR and IR showed higher pasting temperature and lower breakdown than their corresponding single-modified starches. The dual modification with JR and IR induced significant increase in gel hardness as compared to the corresponding unmodified and single-modified starches. The dual-modified JR had a greater hardness, gumminess, and chewiness than the dual-modified IR. The different impact of single and dual modification with JR and IR on the physicochemical properties could be due to the differences in the location and distribution of substituent groups on the starch molecules.

Characteristics of carboxymethyl cellulose synthesized in two-phase medium C6H6(SINGLE BOND)C2H5OH. I. Distribution of substituent groups in the anhydroglucose unit

Carboxymethyl cellulose was synthesized in two-phase medium containing benzene, ethanol, and water. The distribution of substitution of hydroxyl group attached to Ck Carbons (k = 2, 3, and 6) in an anhydroglucose unit (AGU) was determined by 1H-NMR method. It showed that the sequence of distribution of carboxymethyl group of the products in AGU was C6 > C2 > C3; and when degree of substitution (DS) was low to 1.0, the approximate value of C2: C3: C6 was 1.45: 1: 2.15. When DS was higher than 1.0 and increased, the distribution of substitution tends to identical. Through analysis of X-ray diffraction and calculation of crystallinity and interplanar distance of CMC, the principle of distribution of the substituent had been explained. The influence of benzene on distribution of substituent of CMC was also investigated. It was found that distribution of substituent of CMC prepared in medium benzene-ethanol at C6 position was higher than that prepared in ethanol. © 1996 John Wiley & Sons, Inc.

Characteristics of carboxymethyl cellulose synthesized in two‐phase medium C6H6(SINGLE BOND)C2H5OH. I. Distribution of substituent groups in the anhydroglucose unit

Carboxymethyl cellulose was synthesized in two-phase medium containing benzene, ethanol, and water. The distribution of substitution of hydroxyl group attached to Ck Carbons (k = 2, 3, and 6) in an anhydroglucose unit (AGU) was determined by 1H-NMR method. It showed that the sequence of distribution of carboxymethyl group of the products in AGU was C6 > C2 > C3; and when degree of substitution (DS) was low to 1.0, the approximate value of C2: C3: C6 was 1.45: 1: 2.15. When DS was higher than 1.0 and increased, the distribution of substitution tends to identical. Through analysis of X-ray diffraction and calculation of crystallinity and interplanar distance of CMC, the principle of distribution of the substituent had been explained. The influence of benzene on distribution of substituent of CMC was also investigated. It was found that distribution of substituent of CMC prepared in medium benzene-ethanol at C6 position was higher than that prepared in ethanol. © 1996 John Wiley & Sons, Inc.

An explanation of the solubility behaviour of cellulose acetate in various solvents in terms of supermolecular structure formed by introduction of a substituent group into the glucopyranose unit

AbstractAn attempt is made to explain the solubility behaviour of cellulose derivatives with hydrophobic substituent groups towards several solvents in terms of supermolecular structure concepts, such as the degree of breakdown in intramolecular hydrogen bonds and conformational variety in the C1—O—C4 glucoside linkage, which depend on the total degree of substitution 〈〈F〈〈 and the distribution of substituent groups in the anhydroglucose (AHG) unit 〈〈fk〈〈 (k = 2, 3, and 6), and solvation.For this purpose, cellulose acetate (CA) samples with a wide range of 〈〈F〈〈 values were synthesized and the dependence of supermolecular structural parameters, including Xam(Ck) (k = 3, 6) (degree of breakdown in intramolecular hydrogen bond at Ck position) and Δ1/2(Ck)(k = 1,6) (half value width of Q. carbon NMR peak), on 〈〈F〈〈 or (〈fk〈〈 was investigated. It has been shown that a considerable breakdown in O3—H—O'5 hydrogen bond or allowance of wide variation in chain conformation around the C1—O—C'4 linkage is a minimum condition necessary for CA to dissolve in solvents, irrespective of type of solvent. Water‐solubility of CA is mainly governed by the supermolecular structure induced by the introduction of substituents at the C3 position and number of residual hydroxyl groups at the C6 position. Acetone‐solubility of CA is mainly governed by solvation of the side chain but an intramolecular interaction between acetyl groups and ring oxygen bonds tends to hinder its solubility at high values of 〈〈F〈〈. DMSO behaves as an amphoteric solvent solvating both hydroxyl and O‐acetyl groups in CA molecules.

13C NMR Study on the Distribution of Substituent Groups on Trihydric Alcohol Units in Cellulose Xanthate

An attempt was made to investigate 13C{1H} NMR spectra for cellulose xanthate (CX) in sodium hydroxide/D2O mixture and to assign NMR peaks of CX by applying the DEPT method and by inspecting the change in NMR spectra with ripening time. Based on NMR analysis a direct method is proposed for determining the probability of substitution at hydroxyl groups located at C2, C3, and C6 positions in trihydric glucopyranose unit « fk» (k=2, 3, and 6). The difference in « fk» between CXs prepared by the gas-solid (heterogeneous) and liquid-liquid (homogeneous) reactions was also examined. For the latter reactions an alkali-soluble cellulose was employed as starting material. As results, the substitution at C2 and C3 positions was greatly enhanced by the gas-solid reaction and the substitution at C6 was preferential in the liquid-liquid reaction. During ripening, xanthate groups at C2 and C3 positions decomposed first and after complete decomposition of these groups xanthate group at C6 position decomposes very gradually.

Roles of Molecular Characteristics in Blood Anticoagulant Activity and Acute Toxicity of Sodium Cellulose Sulfate

An attempt was made to establish correlations among molecular characteristics, blood anticoagulant activity, and acute toxicity of sodium cellulose sulfate (NaCS). For this purpose, 25 NaCS samples ranging in number-average molecular weights Mn from 800 to 36.8×104 and in total degree of substitutions ‹‹F›› from 0.5 to 2.75 were prepared. The distribution of substituent groups on three carbon positions (C2, C3, and C6) in a glucopyranose unit ‹‹fk›› (k=2, 3, and 6) of NaCS was determined by the NMR method. The anticoagulant activity of NaCS to the whole blood was evaluated by the methods of Lee-White, Imai, and the Commentary of Japanese Pharmacopoeia. Acute toxicity, as measured by LD50 (vein injection), of NaCS for rats was determined by the Probit method. Inhibitory action of NaCS on blood coagulation was estimated using a coagulation factor deficient substrate plasma and a sample plasma from normal blood. It was found that the sum ‹‹f2››+‹‹f3›› is a predominant factor for the anticoagulant activity of NaCS, but Mn is only a minor factor. LD50 of NaCS was found to be intricatedly influenced by ‹‹f2››+‹‹f3›› and Mn. The inhibitory action of NaCS towards coagulation factor VIII was found to be much more intensive than heparin. An anatomical study showed that after injection of NaCS, no abnormality occurred in live rats but a state of anemia appeared in the liver of dead rats and congestive and blood shots occurred in their lungs.

Conformational specificity in a biological sugar transport system.

The ‘carrier’ system in the surface of the human erythrocyte, facilitating passage of monosaccharides through the cell membrane, reacts preferentially with those sugars in which the pyranose ring tends to assume the particular ‘chair’ shape designated by Reeves as the ‘C1’ conformation. This novel type of steric specificity was revealed in a comparative study of fourteen aldoses (6 pentoses, 5 hexoses, and 3 deoxyhexoses), in which the dissociation constants of the carrier-sugar complexes were derived from the kinetics of the transfer process and of the competitive inhibition by phloretin. The sequence of increasing affinities thus determined paralleled the sequence of increasing relative stability in the C1 conformation as dictated by the distribution of substituent groups between axial and equatorial positions on the ring. Sugars predominantly stable in the other chair conformation (1C) showed extremely low affinity. Since no instance of biological utilization of the latter sugars has apparently yet been found, it is suggested that the necessity for the C1 ring-shape is basic in all enzymic reactions with pyranoses. However, most systems show further special requirements for particular side-group arrangements, which are superimposed on the primary ring specificity seen in the red cell's sugar transport system.

Influence of Inhibitors on the Oxidation of Rubber Solutions

Abstract 1. The nature and distribution of substituent groups (NH2, N(CH3)2, CH3, OCH3, COOH) influences the relative activity of amines as rubber antioxidants. 2. Azo compounds fall in the following order of their inhibiting action on rubber oxidation: p-aminoazobenzene, dimethylaminoazobenzene-o-carboxylic acid, dimethylaminoazobenzene, azobenzene. 3. Phenylsemicarbazide is a more effective antioxidant than Neozone D. 4. Diazoaminobenzene and diphenylthiocarbazone do not inhibit the oxidation of rubber, but initiate it quite rapidly. 5. Sudan I and III inhibit the oxidation of rubber solutions, but less than does 2-naphthol.