Large Degree Of Polymerization Research Articles

Production and characterization of glucoamylase from fungus Aspergillus awamori expressed in yeast Saccharomyces cerevisiae using different carbon sources

Glucoamylase is widely used in the food industry to produce high glucose syrup, and also in fermentation processes for production beer and ethanol. In this work the productivity of the glucoamylase of Aspergillus awamori expressed by the yeast Saccharomyces cerevisiae, produced in submerged fermentation using different starches, was evaluated and characterized physico-chemically. The enzyme presented high specific activity, 13.8 U/mgprotein or 2.9 U/mgbiomass, after 48 h of fermentation using soluble starch as substrate. Glucoamylase presented optimum activity at temperature of 55°C, and, in the substratum absence, the thermostability was for 1h at 50°C. The optimum pH of activity was pH 3.5 - 4.0 and the pH stability between 5.0 and 7.0. The half life at 65°C was at 30.2 min, and the thermal energy of denaturation was 234.3 KJ mol(-1). The hydrolysis of different substrate showed the enzyme's preference for the substrate with a larger polymerization degree. The gelatinized corn starch was the substratum most susceptible to the enzymatic action.

Production and characterization of glucoamylase from fungus Aspergillus awamori expressed in yeast Saccharomyces cerevisiae using different carbon sources.

Glucoamylase is widely used in the food industry to produce high glucose syrup, and also in fermentation processes for production beer and ethanol. In this work the productivity of the glucoamylase of Aspergillus awamori expressed by the yeast Saccharomyces cerevisiae, produced in submerged fermentation using different starches, was evaluated and characterized physico-chemically. The enzyme presented high specific activity, 13.8 U/mgprotein or 2.9 U/mgbiomass, after 48 h of fermentation using soluble starch as substrate. Glucoamylase presented optimum activity at temperature of 55°C, and, in the substratum absence, the thermostability was for 1h at 50°C. The optimum pH of activity was pH 3.5 - 4.0 and the pH stability between 5.0 and 7.0. The half life at 65°C was at 30.2 min, and the thermal energy of denaturation was 234.3 KJ mol-1. The hydrolysis of different substrate showed the enzyme’s preference for the substrate with a larger polymerization degree. The gelatinized corn starch was the substratum most susceptible to the enzymatic action.

Polymer size in dilute solutions in the good-solvent regime

We determine the density expansion of the radius of gyration, of the hydrodynamic radius, and of the end-to-end distance for a monodisperse polymer solution in good-solvent conditions. We consider the scaling limit (large degree of polymerization), including the leading scaling corrections. Using the expected large-concentration behavior, we extrapolate these low-density expansions outside the dilute regime, obtaining a prediction for the radii for any concentration in the semidilute region. For the radius of gyration, comparison with field-theoretical predictions shows that the relative error should be at most 5% in the limit of very large polymer concentrations.

Bending Rigidity and Induced Persistence Length of Molecular Bottle Brushes: A Self-Consistent-Field Theory

The two-gradient version of the Scheutjens−Fleer self-consistent-field (SF-SCF) approach is employed for the analysis of the average conformations of side chains and corresponding contribution to the bending rigidity, or equivalently the induced persistence length, of molecular bottle brushes both under good and theta solvent conditions. This study is targeted to unravel conformational properties of poly(l-lysine)-graft-poly(ethylene glycol) copolymers in dilute aqueous solutions, where variation of temperature changes the solvent strength for poly(ethylene glycol) in a wide range. We focus on molecular brushes with moderate and high grafting density and large degree of polymerization of grafted chains. In this limit the predictions of an analytical mean-field theory for the dependences of the structural properties of the bottle brush on the architectural parameters are well confirmed. Both the induced persistence length and the ratio between the induced persistence length and the cross-sectional thickness of the bottle brush increase with increasing grafting density and/or increasing degree of polymerization of the grafted chains. However, in the range of moderate chain lengths and grafting densities this ratio remains small, which explains why the effects of the induced bending rigidity on the apparent persistence length have not been observed in earlier numerical experiments. We argue that only molecular bottle brushes with densely grafted long chains possess the potential for lyotropic ordering, both in solutions and at interfaces, due to the expected high effective segment asymmetry.

Benzyl Bromide Functionalized Poly(Phenyleneethynylene)s as Macroinitiators in the Atom Transfer Radical Polymerization of Methyl Methacrylate

The behavior of benzyl bromide functionalized poly(phenyleneethynylene)s as macroinitiators in the atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) was investigated. The 1H NMR observation of the ATRP using the exclusively para‐linked poly(phenyleneethynylene) macroinitiator PPE1A, and the low molecular weight initiator R‐BzBr, respectively, revealed lower reactivity for the macroinitiator. Comparison of graft copolymers, which were obtained from ATRP of MMA with PPE1A and the partially meta‐linked poly(phenyleneethynylene) PPE1B, showed higher reactivity in the case of PPE1B, expressed by a larger degree of polymerization in the PMMA side chains, as well as higher initiatior efficiency. This might be caused by better solubility of the less symmetric PPE1B. Investigation of the graft copolymers PPE2A and PPE2B was carried out by means of 1H NMR spectroscopy, gel permeation chromatography (GPC) as well as UV/vis spectroscopy. Impairment of the delocalized π‐electron system of the conjugated polymers during the ATRP was not detectable.

When tethered chains meet free ones; the stability of polymer wetting films on polymer brushes

AbstractWe present a combined experimental and theoretical self‐consistent field (SCF) investigation of the wetting behavior of a polystyrene melt (composed of chains with degree of polymerization P) on top of a polystyrene brush (composed of chains with length N) grafted onto a silica surface. The control variables are the grafting density σ of the brush chains and the length of mobile chains P. Experiments show in agreement with the theory that there is a window of complete wetting. Both at very low and at high grafting densities the system remains partial wet. At large degree of polymerization P, there is a difference between the experimental and theoretical results. Theory predicts partial wetting only, whereas the window of complete wetting persists in the experiments even when P >> N. This difference is attributed to the double‐well structure of the disjoining pressure as revealed by the SCF theory. With this type of disjoining pressure it is conceivable that a metastable zero contact angle remains present for very long times.

Star‐shaped polymers by Ru(II)‐catalyzed living radical polymerization. II. Effective reaction conditions and characterization by multi‐angle laser light scattering/size exclusion chromatography and small‐angle X‐ray scattering

AbstractStar poly(methyl methacrylate)s (P*) of various arm lengths and core sizes were synthesized in high yields by the polymer linking reaction in Ru(II)‐catalyzed living radical polymerization. The yields of the star polymers were strongly dependent on the reaction conditions and increased under the following conditions: (1) at a higher overall concentration of arm chains ([P*]), (2) with a larger degree of polymerization (DP) of the arm chains (arm length), and (3) with a larger ratio (r) of linking agents to P* (core size). In particular, the yields sharply increased in a short time at a higher temperature, in a polar solution, and at a higher complex concentration after the addition of linking agents. These star polymers were then analyzed by multi‐angle laser light scattering to determine the weight‐average molecular weight (3.8 × 103 to 1.5 × 106), the number of arm chains per molecule (f = 4–63), and the radius of gyration (Rz = 2–22 nm), which also depended on the reaction conditions (e.g., f and Rz increased as [P*], DP, and r increased). Small‐angle X‐ray scattering analyses of the star polymers showed that they consisted of spheres for which the radius of the microgel core was 2.7 nm. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2245–2255, 2002

Preparative fractionation and characterization of polycarbonate/eugenol-siloxane copolymers

Bisphenol-A polycarbonate/eugenol-siloxane copolymers were fractionated at the preparative scale by the continuous polymer fractionation (CPF) technique. It is the first example of copolymer fractionation by CPF. The distribution of siloxane species across the fractions was assessed for copolymers differing in initial siloxane concentration and block length. On- and off-line combinations of size exclusion chromatography and infrared spectroscopy were used to analyze chemical composition (CC) of the unfractionated samples across the molecular weight distribution enabling comparison with the fractions. A polycarbonate–siloxane copolymer containing 10 wt% of very short siloxane blocks (dp=2) was fractionated solely according to molecular weight (MW). By contrast, a copolymer containing 5 wt% siloxane blocks with a larger degree of polymerization (dp=23) was fractionated according to MW, as well as to CC. This ‘chemical drift’ effect for the larger siloxane block length can be ascribed to large solubility differences of low MW chains, which drastically vary in composition according to the (small) number of siloxane blocks they contain.

Inhibitory Effect of the Conformation of Amylose as a Function of I2 Concentration on Glucoamylase Activity.

In order to gain a better understanding of the adaptability of glucoamylase to the conformational change in the substrate related with the specificity of the enzyme action, the effect of the solution conformation of amylose (the substrate) as a function of the I2 concentration on enzyme activity was studied in the initial state by using amyloses with a wide range of average degree of polymerization (DP) in the presence of excess KI. The enzyme activity for the amylose oligomers in the DP range of 20 to 100 decreased monotonically with increasing I2 concentration. This inhibition of the enzyme activity is ascribed to the effect of the conformational change in amylose of the random coil or worm-like chain to a helix that is induced by the binding of I3 (-) ions responsible for inclusion complexation in combination with direct effect of free I3 (-) ions. In a rapidly mixed complex system for amylose with a large DP of 1,000, however, a significant two-step form of the inhibition of enzyme activity appeared with increasing I2 concentration, corresponding to the two-step conformational change of amylose in a random coil or worm-like chain to a helix and then to a rod-like compact structure.

Thermodynamic Interactions in Isotope Blends: Experiment and Theory

Small-angle neutron scattering (SANS) studies of binary mixtures provide χNS, a measure of thermodynamic interactions between dissimilar polymer chains, one of which is usually labeled with deuterium. For polymers differing only in isotopic substitution (isotope blends), χNS is seen to diverge strongly upward (or sometimes downward) at low concentrations of either blend component. This concentration dependence seems to vanish in the limit of large degree of polymerization N. Experimental results can be described by χNS(φ,N) = β + γ/Nφ(1 − φ), where φ is the volume fraction of deuterated polymer. For SANS from a series of blends with different φ it is shown that systematic errors in N and/or the static structure factor S(0) lead to precisely the same χNS(φ,N) when the Flory−Huggins interaction parameter χ is constant. While results for some isotope blend systems can be accounted for with reasonable error estimates, others appear to have a real dependence of χNS on φ and N. It is suggested that these “non-Flory−Huggins” effects stem from a modified entropy of mixing that is most evident in dilute blends. The concentration dependence of χNS(φ) has no practical effect on macroscopic phase behavior.

高重合度をもつ多核ヒドロキソアルミニウムイオンと膨潤性合成フッ素雲母との複合体生成

Synthetic expandable fluorine mica having layer charge of 0.5 [Na0.5Mg2.5Li0.5Si4O10F2] was reacted with concentrated hydroxoaluminum solution containing highly polymerized species of hydroxoaluminum polycations, which had six or eighteen times larger volumes than ordinary Al13-polycation having Keggin structure. Thermal durability of the complexes thus obtained from concentrated hydroxoaluminum solution was higher than that obtained from ordinary Ai13-polycation while microporous characters vanished for the former complexes, e., alumina pillared fluorine micas. The increase in thermal durability and vanishment of microporous characters probably resulted from the stuffed structure of intercalated bulky hydroxoaluminum polycations having larger polymerization degree as well as the highest value of intercalated Al-content of 2.30 mol/Si4O10.

High-affinity binding of a synthetic heptaglucoside and fungal glucan phytoalexin elicitors to soybean membranes

Soybean membranes possess high-affinity binding sites for fungal β-glucans that elicit phytoalexin synthesis. The ability of 1,3-1,6-β-glucans, released by acid hydrolysis from mycelial walls of Phytophthora megasperma f.sp. glycinea, to compete for the putative phytoalexin elicitor receptors increases with their average degree of polymerization (DP). The results suggest a function where the probability for glucan fragments of containing a structural determinant that is optimal for binding approaches 1 as the DP tends to infinity. Ligand displacement data obtained against a 125I-labeled glucan elicitor (average DP= 18) provided a theoretical minimum IC 50 (50% inhibitory concentration) for 1,3-1,6-β-glucans of 3 nM. The IC 50 value obtained for a synthetic hepta-β-glucoside having a known elicitor-active structure was 8 nM, remarkably close to the predicted value. Displacement of the 125I-glucan of large DP was uniform and complete showing that the heptaglucoside had access, with similar affinity, to all sites available to the radioligand. Further analysis using a 125I-labeled aminophenethylamine derivative of the heptaglucoside suggested that the putative glucan-elicitor receptors bind a basic structural determinant present in all elicitor-active glucans from the soybean pathogen P. megasperma.

ChemInform Abstract: THE ′OVERCONDENSATION′ OF PHOSPHATE IONS AND THE FORMATION OF CONJUGATE METAL OXIDE UPON THE THERMAL DEHYDRATION‐CONDENSATION OF HYDROGENORTHOPHOSPHATES

AbstractBei der thermischen Reaktion von H3PO4 oder NH4H4PO4 mit Metallsalzen wie Na2CO3 oder Mg(OH)2 erfolgt "Überkondensation" der Phosphatanionen (d. h. Bildung von Phosphaten höheren Kondensationsgrades als nach dem eingesetzten Molverhältnis [MO oder M2O]/[P2O5] zu erwarten wäre) und in einer konjugierten Reaktion Bildung des Metalloxids.

The “Overcondensation” of Phosphate Ions and the Formation of Conjugate Metal Oxide upon the Thermal Dehydration-condensation of Hydrogenorthophosphates

Abstract On the thermal reaction of H3PO4 or NH4H2PO4 with metal salts, such as Na2CO3 or Mg(OH)2, the “overcondensation” of the phosphate anions and the conjugate formation of metal oxide were observed. The “overcondensation” was defined as a formation reaction of the phosphate with a larger polymerization degree than that of the product to be expected from the [MO or M2O]/[P2O5] mole ratio of the starting mixtures. The “overcondensed” tetrametaphosphate and the conjugate oxide, magnesium oxide, were detected on the thermal condensation of MgHPO4·3H2O and of a mixture of NH4H2PO4 or H3PO4 and Mg(OH)2. The “overcondensed” tripoly- and trimeta-phosphate were found in the course of the formation reaction of Na pyrophosphate from a mixture of Na2CO3 and NH4H2PO4.

Computer simulation of successively solutional fractionation of macromolecules

AbstractThe successive solution fractionation (SSF) (i.e., the successive solvent extraction of coacervate) was simulated by using an electronic computer. A polymer having the most probable distribution of number average degree of polymerization, X0n = 150, and weight average degree of polymerization, X0w = 300, was hypothetically fractionated, on the basis of the generalized FLORY‐HUGGINS‐FUJISHIRO theory in which the concentration dependence of the polymer/solvent interaction parameter, expressed as p, was taken into account. As p is increased the composition of the fraction with a larger degree of polymerization (X), obtained by SSF, decreased, while the smaller X region remained almost constant. The composition of the fraction in the region of the smaller X is much smaller than that obtained from successive precipitation fractionation (SPF). The fractionation data (Xw and the amount of the fraction) were analyzed according to the treatment of SCHULZ and of KAMIDE et al. The results revealed that the first one is preferable to the second one in the case of SSF. The broadness of the molecular weight distribution in the fraction markedly decreased with decrease in the initial concentration of polymer, v0p, if v0p was higher than 0.1%. An asymtotic, limiting value for Xw/Xn of an extremely small fraction of polymer, separated by SSF, was appreciably larger than that from SPF, but the corresponding value for the standard deviation was zero. The molecular weight distribution of the fractions becomes narrower as their amount is smaller. This behaviour is in contrast to the case of SPF. In SSF, a decreasing in the relative amount of each fraction, besides that of an initial concentration, effectively enables fractions of narrow distribution to be obtained.

Über Vernetzte Makromolekulare Stoffe mit Inhomogener Netzwerkdichte

AbstractVisual swelling characteristics of crosslinked polyester resins in good swelling agents lead one to suppose that in these resins the crosslinks are not equally distributed. When polyester resins are cured by heat without added peroxide, the maximum conversion and therefore also the maximum crosslink density have been shown to depend on the initial radical concentration in the reaction medium. After the gelling point the conversion could not be enhanced by increasing the polymerization temperature. Obviously the primary network, which arises at the gelling point, predetermines the structure of the fully cured resin. Because of the relatively high functionality of the polyester molecules, the large degree of polymerization of the arising copolymer chains and their predominantly alternating structure, growing chain radicals are rapidly attached to the network. It must be assumed that after the gelling point the polymerization proceeds mainly at certain centers, the final number and extent of which depend on the special conditions of the polymerization reaction. The change of the reactivity ratios of the monomers, normally to be observed at high conversions, is explained by the restricted mobility of the still‐unsaturated polyester chains. The conversion at which this restriction appears depends on the structure of the primary network. Under special conditions popcorn formation takes place during polymerization of polyester resins. These popcorn polymers may be considered as an extreme case of a network with an unequal distribution of crosslinks. The composition of these popcorn‐containing polyester resins indicates that their existence is due to the reduction of the mobility and reactivity of the polyester chains at a very low conversion.