Low Degree Of Branching Research Articles

The xylose-rich pectins from pea hulls

The hot acid extract of pea hull, HSP, was rich in galacturonic acid, arabinose and xylose. It was fractionated by copper precipitation followed by ion-exchange chromatography. The copper-soluble fraction represented 26% of HSP and was mostly composed of an arabinan with a low degree of branching, some heteroxylans and a glucan, probably starch. The copper-precipitate (74% of HSP) contained pectins and some residual arabinan, xylan, glucan and mannan. One of the pectic fractions was rich in terminal xylose and fucose; it could be partially degraded by endo-polygalacturonase but not by endo-xylanase and seemed to contain xylogalacturonans.

Differential prenatal toxicity of one straight-chain and five branched-chain primary alcohols in rats

One straight-chain alcohol ( n-octanol) and five branched-chain alcohols [2-ethylhexanol (2-EH), isodecanol, two types of isononanol and a C7-9-11 alcohol] were investigated for developmental effects in Wistar rats at equimolar dose levels (0, 1, 5 and 10 mmol/kg by gavage from gestation day 6 to 15; 10 animals per group). n-Octanol and both isononanols were also investigated in a supplementary experiment at 7.5 mmol/kg/day. Pronounced maternal but no developmental toxicity was achieved with n-octanol. C7-9-11 alcohol, which is a mixture of isomers mostly of a low degree of branching (α-methyl), showed no adverse effects at any dose levels. The two types of isononanols (typical mixtures of two different sets of isomers originating from two different production routes) exhibited a marked degree of maternal and foetal toxicity at 7.5 and 10 mmol/kg and slight foetal effects at 5 mmol/kg. Because of maternal toxicity in the top dose, a statistically significant increase in malformations was obtained only in the dose window of 7.5 mmol/kg in the supplementary experiment. Isodecanol (a mixture of different isomers) elicited maternal toxicity at 10 mmol/kg and caused a low incidence of retardations and rare malformations at that dose level. Some maternal signs but no foetal effects were observed at 5 mmol/kg. 2-EH showed strong maternal and also foetal toxicity at 10 mmol/kg and slight maternal and foetal toxicity at 5 mmol/kg. The differential responses to the test materials indicate that, at present, within this chemical class of alcohols, the potential for developmental toxicity has to be investigated case by case for each indvidual structure.

Strain-induced crystallization ofcis-1,4-polybutadiene containing dispersed 1,2-polybutadiene crystalline particles

Some grades of cis-1,4-polybutadiene contain dispersed crystalline particles made up of a block copolymer having amorphous cis-1,4- and crystalline 1,2 blocks. The particles are known to enhance the strain-induced crystallization of cis-1,4 matrix rubber. The deformational behavior was examined by dynamic shear measurements at small deformation and tensile stress–strain measurements at large deformation. In the shear measurements (linear behavior), the temperature dependence of the shift factor in the time-temperature superposition has been evaluated. The higher temperature dependence was observed for the lower crystalline particle content and higher degree of branching of the matrix rubber. The presence of the crystalline particles resulted in the viscosity enhancement like that expected from the dispersed particles. In the tensile measurements (non-linear behavior), the rubbers showed strain softening. The higher degree of strain softening was observed for the higher amount of the crystalline particles and lower degree of branching. The strain softening is a result of the crystalline particles facilitating the elongation. Because these particles posses the branches which are cis-1,4 chains of the block copolymer, the branches are lubricating the system during the stretching. The length of the branches must be short enough so as to produce no significant entanglement constraint. This observation is in accord with the previous one that a relatively long branch gives strain hardening, whereas a relatively short branch gives strain softening. The strain softening was found to enhance the strain-induced crystallization. This conclusion is opposite to what one might expect from the entanglement constraints by the long branches, forcing the orientation of the chains, and thus enhancing the strain-induced crystallization. © 1996 John Wiley & Sons, Inc.

Strain‐induced crystallization of cis‐1,4‐polybutadiene containing dispersed 1,2‐polybutadiene crystalline particles

Some grades of cis-1,4-polybutadiene contain dispersed crystalline particles made up of a block copolymer having amorphous cis-1,4- and crystalline 1,2 blocks. The particles are known to enhance the strain-induced crystallization of cis-1,4 matrix rubber. The deformational behavior was examined by dynamic shear measurements at small deformation and tensile stress–strain measurements at large deformation. In the shear measurements (linear behavior), the temperature dependence of the shift factor in the time-temperature superposition has been evaluated. The higher temperature dependence was observed for the lower crystalline particle content and higher degree of branching of the matrix rubber. The presence of the crystalline particles resulted in the viscosity enhancement like that expected from the dispersed particles. In the tensile measurements (non-linear behavior), the rubbers showed strain softening. The higher degree of strain softening was observed for the higher amount of the crystalline particles and lower degree of branching. The strain softening is a result of the crystalline particles facilitating the elongation. Because these particles posses the branches which are cis-1,4 chains of the block copolymer, the branches are lubricating the system during the stretching. The length of the branches must be short enough so as to produce no significant entanglement constraint. This observation is in accord with the previous one that a relatively long branch gives strain hardening, whereas a relatively short branch gives strain softening. The strain softening was found to enhance the strain-induced crystallization. This conclusion is opposite to what one might expect from the entanglement constraints by the long branches, forcing the orientation of the chains, and thus enhancing the strain-induced crystallization. © 1996 John Wiley & Sons, Inc.

Cell-Wall Polysaccharides of Developing Flax Plants.

Flax (Linum usitatissimum L.) fibers originate from procambial cells of the protophloem and develop in cortical bundles that encircle the vascular cylinder. We determined the polysaccharide composition of the cell walls from various organs of the developing flax plant, from fiber-rich strips peeled from the stem, and from the xylem. Ammonium oxalate-soluble polysaccharides from all tissues contained 5-linked arabinans with low degrees of branching, rhamnogalacturonans, and polygalacturonic acid. The fiber-rich peels contained, in addition, substantial amounts of a buffer-soluble, 4-linked galactan branched at the 0-2 and 0-3 positions with nonreducing terminal-galactosyl units. The cross-linking glycans from all tissues were (fucogalacto)xyloglucan, typical of type-I cell walls, xylans containing (1->)-[beta]-D-xylosyl units branched exclusively at the xylosyl O-2 with t-(4-O-methyl)-glucosyluronic acid units, and (galacto)glucomannans. Tissues containing predominantly primary cell wall contained a larger proportion of xyloglucan. The xylem cells were composed of about 60% 4-xylans, 32% cellulose, and small amounts of pectin and the other cross-linking polysaccharides. The noncellulosic polysaccharides of flax exhibit an uncommonly low degree of branching compared to similar polysaccharides from other flowering plants. Although the relative abundance of the various noncellulosic polysaccharides varies widely among the different cell types, the linkage structure and degree of branching of several of the noncellulosic polysaccharides are invariant.

Effects of Infection byPythiumspp. on Root System Morphology of Alfalfa Seedlings

Root system morphology of alfalfa seedlings infected by various Pythium spp. was evaluated in greenhouse experiments using morphometric and topological assessment methodologies. Infection of alfalfa seedlings by Pythium spp., particularly P. ultimum and P. irregulare, resulted in reductions in root system growth and changes in root system architecture. Reductions in root system morphological parameters, including total root system length and total numbers of root orders, as well as the topological parameters root system magnitude, altitude, and total exterior path length, indicated overall smaller root system size and complexity in infected plants compared with noninfected plants. Root system branching structure also was affected, with infected root systems developing with a lower degree of branching than noninfected root systems, as represented by fewer orders of branching and a more monopodial type of branching pattern. Although isolates of P. ultimum, P. irregulare, and P. sylvaticum all caused substantial pre- and postemergence damping-off, P. sylvaticum caused no measurable change in root system morphology. In contrast, P. ultimum caused severe reductions in root system size and branching complexity, and P. irregulare, which caused less-severe damping-off, also caused substantial changes in root system morphology. Isolates of P. dissotocum and P. torulosum had no effect on root system growth or morphology. Metalaxyl applied to the soil was effective in reducing the effects of these pathogens, whereas metalaxyl seed treatment was less effective. Use of architectural analysis methods enabled the quantitative assessment of the impact of root pathogens on root system branching structure for the first time

Structure of the principal non-starch polysaccharide from the cotyledons of Lupinus angustifolius (cultivar Gungurru)

Methylation analysis, selective enzymolysis ( O-glycosidases) and chemical degradation showed that the principal non-starch polysaccharide (NSP) in a 2% disodium ethylenediamine-tetraacetate (EDTA) extract (purified by ethanol precipitation) of lupin cotyledons ( Lupinus angustifolius cultivar Gungurru) has the backbone sequence of [ →4)-α- d-Gal p A-(1→2)-β- l-Rha p-(1→ ]. Side chains mainly consist of linear (1→4)-β- d-Gal p residues and shorter, highly branched (1→5)-α- l-Ara f residues are attached to the C-4 position of the rhamnosyl residues in the backbone. Some terminal β- d-Xyl p residues are linked to the galacturonosyl residues. 1H and 13C-NMR spectroscopy support the proposed partial structure of the in EDTA-soluble NSP, which has a sugar composition and gylcosidic linkages typical of those found in primary cell walls of dicots. The high proportion of neutral sugars, the almost equal ratio of galacturonic acid to rhamnose, with most of the latter substituted at the C-4 position, the low degree of branching of the (1→4)-linked galactan, and highly branched (1→5)-linked arabinosyl residues are the characteristic features of the lupin cotyledon pectic polysaccharides.

Antitumor activity of cell wall beta-1,3/1,6-glucans from Phytophthora species.

From the cell walls of various Phytophthora species (Oomycetes) different water-soluble beta-1,3/1,6-glucans were isolated and characterized. The glucans with relative molecular masses between 13 and 50 kd exhibited varying degrees of branching in the beta-1,3-linked glucan backbone ranging from 14 to 50%. The dose-dependent antitumor activity of the glucans against allogeneic sarcoma-180 was investigated. It could be demonstrated that beta-1,3/1,6-glucans with relative molecular masses below 50 kd can exhibit a prominent antitumor activity (inhibition rate up to 99%), being comparable to that of the high relative molecular mass (450 kd) beta-1,3/1,6-glucans. Biological activity of the glucans could be shown to be correlated with a low degree of branching. The most potent glucan with a degree of branching of 14% also was active against the syngeneic DBA/2-MC.SC-1 fibrosarcoma (inhibition rate up to 90%) and in combination with a suboptimum dose of diethylstilbestrol against Nobel-Nb prostate carcinoma (inhibition rate up to 90%).

Contribution of the side branches to rheological properties of pectins

The rheological properties of apple pectins with different degrees of side branches were investigated in terms of the zero-shear viscosity ( η 0), the shear rate dependence of viscosity and the superposability of rheological data to a variety of generalization curves such as η sp versus c[ η], η sp versus cM w, η η 0 versus γ ̇ γ ̇ 0·8 and η η 0 versus γ ( η 0 − η s) M w/ cRT. Increase in branching of pectins resulted in higher η 0 and increasing shear rate dependence of viscosity. The gradients of η sp.0 versus c [η] in the concentrated region ( c [η] > c ∗ [η] ) were dependent upon the degree of branching, i.e. the higher the branching, the higher the gradients, whereas there was no significant difference in the dilute region ( c [η] < c ∗ [η] ) irrespective of the degree of branching. Pectins with a low degree of branching displayed better superposition in η η 0 versus γ ̇ γ ̇ 0·8 and η η 0 versus γ ( η 0 − η s) M w/ cRT curves when compared to the sample with more branches. Circular dichroism (CD) studies of pectins showed that the conformation of pectin molecules was not affected by the degree of branching. It is concluded that side branches of pectins can result in significant entanglements in concentrated solutions.

Phenol—formaldehyde resins as a link to the understanding of the isothermal kinetic behavior of geopolymers (kerogens and coals)

Phenol-formaldehyde resins (Bakelites) were synthesized using various phenol: formaldehyde ratios and phenol:base (NaOH) ratios. Isothermal kinetic experiments indicated that the preparation ratios had a marked influence on the kinetic profile. Whereas most synthetic polymers studied previously showed a marked difference between their kinetic profiles in comparison with geopolymers, some of the resins studied here exhibited similarity to the geopolymers (kerogens, coals). The relations between the resin structures and their isothermal kinetic behavior were studied. It was found that highly branched (coral like) stereometric structures will yield a kinetic behavior which resembles that of geopolymers. Low degree of branching will yield a kinetic behavior similar to that of common synthetic polymers. Previously we have suggested a kinetic model which explains the kinetic behavior of geopolymers and the difference between the kinetic behavior of geo- and synthetic polymers. The results described in the present paper support this model.

Certain aspects of the formation of branched macromolecules during synthesis and heat-treatment of polymers such as polyphenylquinoxalines

Sedimentation, fractionation and viscometry have been used to study the laws governing the formation of branched macromolecules during the synthesis and heat treatment of a series of polyphenylquinoxalines specimens and the topology of the macromolecules has been studied. Under conditions of low-temperature polycondensation, chain propagation has been shown to occur with practically 100% closure of the quinoxaline ring not only in the case of linear but in the case of model branched polyphenylquinoxalines. In the case of low-temperature polycondensation of the polymer in the presence of a filler, namely, graphite, branched macromolecules are formed with low degrees of branching. the branching centres are thus imperfect fragments with incomplete closure of the quinoxaline ring, which leads to the formation of azomethine groups that are unstable in sulphuric acid. when linear or branched polyphenylquinoxalines are heat-treated at elevated temperatures, macromolecular branching processes occur in which the branching centres can be of various types.

熱帯産澱粉から得られたアミロースおよびアミロペクチンの分子特性

Four kinds of tropical starches were separated into four fractions, i. e., an amylose, two amylopectins, one of which precipitated and the other which did not precipitate in 66% ethanol solution and a C-fraction, which precipitated with thymol and did not precipitate in 10% 1-butanol. Potato and corn starches were used as controls. Iodine affinity, weight average molecular weight (MW), radius of gyration (RG), and intrinsic viscosity [η] were determined for each fraction. To determine MW and RG, one concentration approximation light scattering method was used. For amyloses, iodine affinities, MW, RG, and [η] were 19-21 I2 g/100g, 4 × 105 -2 × 106, 30 × 10-7 -97 × 10-7 cm, and 0.6-1.7 dl/g, respectively. Potato amylose had the highest MW, sago and corn amyloses had the lowest MW. Larger RG values were obtained for edible canna and corn than for others when compared in the same MW. Amylopectins (iodine affinities, 0.25-2 I2 g/100 g ; MW, 4 × 107-44 × 107 ; RG, 150 × 10-7-570 × 10-7 cm ; [η], 0.8-5 dl/g) were classified into three groups. The first one contained potato and edible canna amylopectins having medium MW in the three groups. It was thought that they might have the lowest degree of branching in the three groups. The second group contained arrowroot and cassava amylopectins having the highest MI. It was thought that they might have the highest degree of branching. The third group contained sago and corn amylopectins having the lowest MW. It was thought that they might have medium degree of branching. Six kinds of C-fraction (iodine affinities, 1.5-3.3 I2g/100 g ; MW, 3 × 107-6 × 107 ; RG, 150 × 10-7-270 × 10-7 cm ; [η], 0.8-2 dl/g) had similar Mw to the low Mw fractions in amylopectins, i. e, sago and corn amylopectins.

Solubility and IR studies of gamma-irradiated arabinoxylan

The structural and solubility changes of a water-insoluble arabinoxylan with a low degree of branching was studied after γ-irradiation by IR spectroscopy and chemical analysis of the polysaccharide and its polymeric fractions.

New soluble polyaniline: Synthesis, electrical properties and solution electronic spectrum

The reaction of aniline with copper(II) perchlorate in acetonitrile yields highly-electroconductive polyaniline perchlorate, [(-C 6H 4NH-)(ClO 4) m · nH 2O] x , which is soluble in dimethylsulfoxide (DMSO) and has low degrees of branching and/or crosslinking. The conductivity of a material with m = 0.43 is 3.1 S cm −1 at room temperature. The solution electronic spectrum of the perchlorate exhibits a strong band at 285 nm and a weak band at 445 nm; no band is observed in the region of 830 nm. In the solution electronic spectrum of the corresponding polymer base, strong bands are observed at 630 and 325 nm. When the solution of the polymer base is acidified, the 630 nm band disappears and a new band appears at 830 nm: the protonation of the polymer base by the acidification yields a spectrum that is different from that of the original polymer perchlorate. In the polymer chains of the perchlorate prepared by the present method, the majority of positive charges are centred on anilinium ion radicals (polarons) rather than on quinoneiminium ions (bipolarons).

Structural features of a rye-bran arabinoxylan with a low degree of branching

Two fractions (AX-1 and AX-II) of an l-arabino- d-xylan with a low degree of branching were isolated from rye bran by different extraction procedures with and without a chlorite-delignification step. The yields and compositions of AX-I and AX-II were similar, but the d.p. of AX-II was ∼100 units higher. AX-I was shown by partial hydrolysis, methylation analysis, and 13C-n.m.r. spectroscopy to contain a backbone of (1→4)-linked β- d-xylopyranosyl residues substituted with single α- l-arabinofuranosyl groups at position 3 of every sixth or seventh d-xylosyl residue.

Molecular weight distribution and conformational analysis of randomly branched poly(phenylene quinoxalines) of low branching degree

AbstractBy comparative investigations of solutions of randomly branched poly(phenylene quinoxalines) (PPQ) with low degree of branching and solutions of linear PPQ the hydrodynamic properties and polydispersity coefficient are shown to be sensitively affected by branching. The conformation of branched PPQ macromolecules in solution was found to deviate from Gaussian type. Additionally, differences between experimental and theoretical MWD were detected. Possible explanations of the observed desagreement are discussed.

The growth characteristics of Saccharomycopsis lipolytica: morphology and induction of mycelium formation

When Saccharomycopsis lipolytica was grown on minimal medium supplemented with glucose or n-hexadecane, all the cells of the culture remained in the yeast form. In complex medium, a mixed morphology of yeast and mycelial forms appeared. If the cells were grown on minimal medium supplemented with N-acetylglucosamine as the carbon source, a reproducible system for the production of mycelium was obtained. Neither temperature, pH, nor several other carbon sources were able to induce a reproducible yeast–mycelial transition. Mycelium formation is maximal after 12–15 h of incubation (in the presence of N-acetylglucosamine) and decreases with longer incubating times when N-acetylglucosamine is exhausted. During mycelium formation a considerable increase took place in dry weight; the cell numbers, however, remained almost constant between 12–15 h. Electron microscopy shows mycelium with a smooth surface, a great amount of mitochondria and a low degree of branching.

Structure of extracellular glucans synthesized by Streptococcus mutans of serotypes a-e in vitro.

Insoluble extracellular glucans synthesized by Streptococcus mutans in vitro were separated from bacterial cells by solubilization in potassium hydroxide. After neutralization of the alkaline solution only part of the glucans precipitated giving fraction AS-I. Another part was isolated from the neutralized solution by the addition of ethanol yielding fraction AS-II. Soluble glucans harvested from the culture supernatant were treated in the same manner giving fractions WS-I and WS-II, respectively. By methylation analysis it was shown that the insoluble glucans of fraction AS-I are characterized by a high percentage of α-1,3-linked glucosyl residues and a low degree of branching. In contrast to this, soluble glucans of fraction WS-II represent highly branched polysaccharides with a content of α-1,6-linkages between 40 and 60%. Glucans of fraction AS-II originally present in the insoluble complex are significantly different from both fractions mentioned with respect to their percentages of α-1,3- and α-1,6-linked glucosyl residues. The linkage patterns of glucans of fraction WS-I are similar to those of fraction AS-I. Thus, with respect to the linkage patterns three distinct fractions of glucan were isolated from streptococcal cultures. A comparison of the glucans of the five serotypes revealed that glucans of type b, c, and e form one group of polysaccharides characterized by a greater mean percentage of α-1,6-linkages and branching sites than the other group consisting of glucans of type a and d. Furthermore, strains of S. mutans seem to be capable of synthesizing an almost continuous series of glucans with variable proportions of different types of linkages.

Structural analysis of insoluble d-glucans by fourier-transform, infrared difference-spectrometry: correlation between structures of dextrans from strains of leuconostoc mesenteroides and of d-glucans from strains of streptococcus mutans

Fourier-transform infrared (F.t.-i.r.) difference-spectra have been recorded, relative to a water-soluble dextran of low degree of branching, for ( a) dextrans from Leuconostoc mesenteroides NRRL B-742 (the L fraction) and NRRL B-1149 (the A fraction), ( b) d-glucans from Streptococcus mutans KR-1 and OMA 176, and ( c) the controls of amylose, cellulose, nigeran, and pseudonigeran. Confirmation has been obtained for the presence, in the spectra of the relatively insoluble dextrans and d-glucans, of a previously recognized, characteristic absorbance at 822 cm −1, and the correlation of this band with contiguous, linearly (1 → 3)-linked, α- d-glucopyranosyl residues, to which polymer insolubility (and cariogenic properties) has been ascribed. This analytical method allows the mole percent of the contiguously linked 3-mono- O-substituted α- d-glucopyranosyl residues to be quickly and non-destructively established in solid-state samples, when employing weights of polysaccharides in the microgram range. The wavenumbers and intensities of other bands observed in the F.t.-i.r. difference-spectra of d-glucans containing (1→4)- d-linkages are also discussed.

Vinyl acetate polymerization initiated by alkylborane-oxidizer-type systems

A study has been made of vinyl acetate polymerization initiated by radicals emerging in the course of oxidization of triethyl, tri-n-butyl and tri-iso-butyl boranes. Under model conditions it is shown that the oxidation of alkylboranes by oxygen and by tert-butyl hydroperoxide is accompanied by the formation of alkyl and alkoxy radicals. It was found that the polyvinylacetate obtained is of high MW, and has a low degree of branching as regards the acetyl group. Crosslinking has been observed in vinyl acetate/polyvinylacetate reaction systems during the bulk polymerization in the presence of the above-specified initiating systems.