Minimum Molecular Weight Research Articles

Isothermal frontal polymerization: Confirmation of the isothermal nature of the process and the effect of oxygen and polymer seed molecular weight on front propagation

AbstractIsothermal frontal polymerization is a directional polymerization that utilizes the Norish‐Trommsdorff (gel) effect to produce optical gradient materials. When a solution of methyl methacrylate and thermal initiator contacts a polymer seed (a small piece of poly(methyl methacrylate), a viscous region is formed in which the polymerization rate is faster than in the bulk solution. We obtained definitive evidence of the isothermal nature of the process by placing thermocouples above the propagating front. Using the optical technique of laser line deflection (Weiner's method), we studied the front propagation to determine the induction period, and the maximum distance propagated as a function of the molecular weight of the seed. We determined that the polymer seed must have a minimum molecular weight to initiate a front. We also determined that oxygen would act as a bulk polymerization inhibitor and increase the front propagation distance, but after purging the monomer–initiator solution with oxygen for several hours, the distance was shortened. We ascribed this behavior to the formation of peroxy radicals from the slow decomposition of the initiator and subsequent reaction with oxygen. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3601–3608, 2006

Prediction of coil-stretch hysteresis for dilute polystyrene molecules in extensional flow

The existence of coil-stretch hysteresis in extensional flows of long-chain polymers in dilute solutions has recently been demonstrated using enormously long deoxyribonucleic acid (DNA) molecules [Schroeder et al., Science 301, 1515–1519 (2003)]; however, there is no demonstration of hysteresis for synthetic polymers of more modest molecular size. We here use Brownian dynamics simulations of bead-spring chains to predict that the minimum molecular weight of polystyrene in a dilute theta solvent that can show a “coil-stretch hysteresis” in a uniaxial extensional flow is around 0.5 million Daltons. We find that the threshold value of the ratio of effective drag coefficients in the stretched versus coiled states, ζstretch∕ζcoil, is about 4.5 for the occurrence of hysteresis, close to the value observed for DNA.

Purification of 5-aminolaevulinate synthase from liver mitochondria of chick embryo.

5-Aminolaevulinate synthase from chick-embryo liver mitochondria has, for the first time, been purified to homogeneity in its native non-degraded form by molecular sieve chromatography, chromatofocusing and affinity chromatography. The enzyme has a minimum molecular weight of 68000 as determined by sodium dodecylsulphate/polyacrylamide gel electrophoresis and a specific activity of 35000 units/mg of protein. This result conflicts with the previous report of Whiting, M.J. and Granick, G. [(1976) J. Biol. Chem. 251, 1340-1346] that the chick embryo enzyme has a molecular weight of 49000. We show here that the purified form can be degraded proteolytically to a smaller form of molecular weight around 50000 while retaining full enzymatic activity. It seem evident, therefore, that the enzyme isolated by Whiting & Granick (1976) was degraded. We have further established by pulse-labelling studies and immunoprecipitation that the enzyme isolated by our new and rapid procedure has the same minimum molecular weight as that which exists in vivo.

Shape Memory of Hydrogen-Bonded Polymer Network/Poly(ethylene glycol) Complexes

Because of a large difference in storage modulus below and above the glass transition temperature, poly(acrylic acid-co-methyl methacrylate)/poly(ethylene glycol) (P(AA-co-MMA)/PEG) complexes show shape memory properties with a recovery ratio of nearly reach 99%. Before the shape memory testing, it was necessary to determine the conformational changes of the P(AA-co-MMA) gel induced by complexation with linear PEG. It was found that both the concentration and molecular weight of PEG have a strong effect on the complexation with P(AA-co-MMA) gel. In such a system the minimum molecular weight of PEG required for the complex formation lowers to 1000.

The effect of molecular weight and temperature on tack properties of model polyisobutylenes

The effect of molecular weight and temperature on the tack of non-crosslinked soft polymers was investigated using blends of low and high molecular weight polyisobutylene as model systems. Molecular weight between entanglements M e was varied systematically by changing the mixing ratio. Video-optical imaging confirms that these model systems exhibit the characteristic debonding features of pressure-sensitive adhesives, including cavitation as well as formation and deformation of fibrils. The initial peak in the stress–strain diagram is a function of both the cohesive strength and ability to wet the probe. It contributes significantly to the work of adhesion at low molecular weight, low temperature and high contact force. Beyond a critical molecular weight, debonding is dominated by fibril deformation. In this regime, the work of adhesion is essentially independent of temperature, molecular weight and the details of the fibrillation pattern (more but thinner fibrils are observed as molecular weight increases). The minimum molecular weight needed for significant fibrillation is around 850 kg/mol (≈3 M e) both at −10°C and 25°C.

T lymphocyte dependence of the antibody response to 'T lymphocyte independent type 2' antigens.

With regard to their capacity for antibody induction, antigens can be classified as either T lymphocyte dependent (TD) or as T lymphocyte independent (TI).1 In the immune response to TD antigens, T lymphocyte help to B lymphocytes is essential for the regulation of B lymphocyte proliferation, production of immunoglobulins, immunoglobulin class switching, rescue of B lymphocytes from apoptotic death, germinal centre formation, and generation of B lymphocyte memory.2 In contrast to TD antigens, TI antigens induce antibody production without the help of T lymphocytes. TI antigens can be further divided into TI type 1 antigens (TI-1), which are polyclonal B lymphocyte activators (e.g. lipopolysaccharides), and TI type 2 (TI-2) antigens. TI-2 antigens are able to directly stimulate B lymphocytes. However, the antibody response to TI-2 antigens is somehow influenced by T lymphocytes.3 TI-2 antigens do not induce immunological memory and antibodies to TI-2 antigens in humans only develop after the age of 2 years.4,5 Generally, TI-2 antigens are antigens that consist of repetitive biochemical structures such as polymeric protein antigens, trinitrophenyl-ficoll (TNP-ficoll), and dinitrophenyl-ficoll (DNP-ficoll). A clinically important group among the TI-2 antigens are the bacterial capsular polysaccharides.6 Capsular polysaccharides of Streptococcus pneumoniae, Haemophilus influenzae and Neisseria meningitidis are responsible for the bacterial virulence and antibodies to capsular polysaccharides provide protection against invasive infections with these bacteria.7 The delay in antibody formation to encapsulated bacteria renders infants and young children highly susceptible to infections with encapsulated bacteria, especially from the ages of 4 to 6 months on, when the placentally derived maternal IgG is metabolized.5 Therefore, children younger than 2 years of age are more at risk for invasive infections caused by encapsulated micro-organisms.8 Children with a persisting defect in the production of antibodies specific for pneumococcal capsular antigens after this age have the so-called ‘specific antibody deficiency with normal immunoglobulins’ (SADNI). They suffer from recurrent pneumococcal infections, although their immunoglobulin and immunoglobulin subclass levels and responses to protein antigens are normal.9–12 It is estimated that 5–10% of the children referred for evaluation of recurrent infections have SADNI and it is therefore highly important to understand the immunological background of the antibody formation against TI-2 antigens.13 In this review we will summarize the current understanding of how T lymphocytes modulate the antibody response against TI-2 antigens.

Fifty Years Ago: DNA: the double helix

‘The chemical nature of the genes is unknown. They are probably proteins, because the nucleic acids consist of (few) blocks of tetranucleotides (Levene, 1930). This simple structure makes them unlikely candidates as carriers of the large information needed to act as genes.’ This view^strange as it may seem today ^ was shared by most biologists when I was preparing my exam in biology at the medical school in 1946. In a series of classical papers from 1906 on, Levene’s group and others had identi¢ed D-ribose and 2-deoxy-D-ribose as the sugars occurring in RNA and in DNA, respectively. They had also identi¢ed the purines and pyrimidines, localized the phosphodiester link between the sugars, and classi¢ed the linkage with the bases as glycosidic. Levene’s work culminated in the suggestion of a tetranucleotide structure for both RNA and DNA, i.e. that the nucleic acids are composed of an (unknown) number of building blocks, the tetranucleotides, each consisting of four sugars, four phosphates and one each of the four bases. In his words, ‘the tetranucleotide theory is the minimum molecular weight and the nucleic

Galactosylated chitosan (GC)-graft-poly(vinyl pyrrolidone) (PVP) as hepatocyte-targeting DNA carrier: Preparation and physicochemical characterization of GC-graft-PVP/DNA complex (1)

Galactosylated chitosan was conjugated with poly(vinyl pyrrolidone) (PVP) as a hydrophilic group. The complex formation of GC-graft-PVP (GCPVP)/DNA complexes was confirmed by agarose gel electrophoresis. The morphology of the complex observed by atomic force microscopy had a compact and spherical shape, around 40 nm particle sizes at a charge ratio of 3. The binding strength of GCPVP 10K/DNA complex measured by ethidium bromide binding assay was superior to that of the GCPVP 50K/DNA one, probably attributable to its higher flexibility due to the smaller size, whereas the DNase I protection of GCPVP 10K/DNA complex was inferior to that of the GCPVP 50K/DNA one. This indicated that effective complex formation required both higher binding strength and minimal molecular weight of polycation enough to induce the condensation of DNA. The DNA-binding property of GCPVP mainly depended on the molecular weight of chitosan and composition of PVP.

Influence of different polyesters and their molecular weight on the textural and electrooptical behavior of polymer‐dispersed liquid crystals

AbstractThe textural and electrooptical behavior of a nematic liquid crystal (LC) dispersed in a flexible and rigid polyester was studied. The dispersion of LC in the polymer matrix and light transmission through the polymer‐dispersed liquid crystal (PDLC) is governed by the nature of the polymer, its molecular weight, and the applied voltage. It was observed that the transmission of light and the dispersion of LC maximizes their respective values at the minimum molecular weight irrespective of the nature of the polymer and at the maximum voltage. The reason is the predominance of chain alignment over entanglement at the minimum molecular weight. As molecular weight increases, the transmission of light as well as the dispersion of LC in the polymer may increase or decrease depending on the predominance of chain entanglement or chain alignment. The alignment of LC droplets in the direction of the applied voltage is increased by an increase in the applied voltage, causing enhancement of the light transmission. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 284–289, 2003

Separation of an isoenzyme of polyphenol oxidase from Duranta plumieri by expanded bed chromatography.

Aqueous extracts of seeds of Duranta plumieri were found to be rich in polyphenol oxidase activity. The anion-exchange chromatography of the crude extract on Streamline DEAE resolved the activity into three fractions. The major fraction (77% of the total activity) was further purified by treating it with concanavalin A-agarose in the batch mode. The enzyme preparation eluting with alpha-methylmannoside showed a single band on SDS-PAGE. The minimum molecular weight corresponded to 14,000 Da. The K(m) and V(max) of this isoenzyme were found to be 7.1 mM and 73.5 U ml(-1) min(-1) respectively. The k(cat) of this isoenzyme was calculated to be 8235 s(-1). The isoenzyme also showed the phenomenon of latency and the activity could be enhanced by 196% on heating it at 55 degrees C for 30 min.

Molecular weight dependence of shear-induced structures in nematic semiflexible polymer solutions

The role of molecular weight in shear-induced structure transitions, such as striations during shear startup and banding during relaxation, was probed through small-angle light scattering and shear microscopy. The characteristic texture relaxation time for banding, τs, is molecular weight dependent. The minimum molecular weight for these shear-induced complex texture transitions to occur is estimated from τs as 27 000 for a 37 wt % poly(n-hexyl isocyanate) in 1,1,2,2-tetrachloroethane solution at room temperature. τs is independent of applied shear rate, implying that it is a material property. Thus, both of these structure transitions appear to occur only after shearing above a threshold Deborah number, γ̇τs|c, below which viscous forces would suppress these structure transitions. Both the strain dependence of the structure transitions during shear startup and the preshear rate dependence of the banding phenomenon exhibit little or no molecular weight dependence. Increasing molecular weight does appear to decrease the characteristic band correlation length and slow the decay rate of the bands.

Statistical Design Strategies To Optimize Properties in Emulsion Copolymerization of Methyl Methacrylate and Acrylonitrile

Emulsion copolymerization was performed by using (NH 4 ) 2 S 2 O 8 as an initiator in the presence of an emulsifier (sodium lauryl sulfate). The effect of changing the process variables {initiator concentration, emulsion concentration, feed ratio of monomer [acrylonitrile (AN)/methyl methacrylate (MMA)], and temperature} on the properties of the copolymer was monitored. The polymerization rate, particle size, molecular weight, and polydispersity index (of the polymer chain length) were determined for the polymerization conditions designed by the fractional factorial design method. Estimation of the effects on the polymerization rate through 2 4-1 1 fractional factorial design reveals that it depends on the AN/MMA ratio, surfactant concentration, and temperature. The surfactant concentration mainly influences the particle size and molecular weight, while the surfactant concentration and temperature are the key variables in influencing the polydispersity index. A regression equation relating the surfactant concentration, temperature, and polydispersity index is deduced, and the contour plot is made using that. A condition for obtaining the minimum molecular weight distribution was arrived statistically and verified by trial experiments. The minimum molecular weight polydispersity (<3.0) can be obtained at a surfactant concentration of 0.393 g/500 mL of solution and a reaction temperature of 54.6 °C.

Purification of phospholipase D from Dacus carota by three-phase partitioning and its characterization.

Phospholipase D from Dacus carota (carrot) was purified by subjecting it to three-phase partitioning. The single step of three phase partitioning led to 13-fold purification with an activity recovery of 72%. SDS-PAGE analysis showed a single band with minimum molecular weight corresponding to nearly 60 kDa. The purified enzyme had a pH optimum in the range of 6.0--6.5 and was unstable above 30 degrees C. Kinetic studies showed a K(m) value of 9.5 mM and a V(max) of 0.35 mL min(-1). The enzyme purified by three-phase partitioning was found to resolve into two isoenzymes on a DEAE-cellulose column.

Comparison of carboxylated and maleated polypropylene as reactive compatibilizers in polypropylene/polyamide-6,6 blends

Using reactive extrusion, polypropylene is functionalized with maleic anhydride and compared on an equimolar basis to polypropylene that is functionalized with an asymmetric, carboxylic acid containing peroxide. The grafting efficiency for the asymmetric peroxide is double that obtained for the maleic anhydride system. Moreover, the asymmetric peroxide yields a functionalized material with minimal molecular weight degradation and desirable mechanical properties, relative to maleic anhydride-grafted polypropylene. In compatibilized blends of polypropylene and nylon 6,6, the polypropylene that was functionalized with the asymmetric peroxide is found to be an improved compatibilizer compared to that of maleic anhydride-grafted polypropylene. The differences in mechanical properties of the two different functionalized polypropylene materials and their respective blends are rationalized on the basis of the grafting efficiency, molecular weight degradation during reactive extrusion, and effect of free functional species on the ability to form graft copolymers in compatibilized blends. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2398–2407, 2001

Formation of transparent exopolymer particles, TEP, from dissolved precursor material

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 192:1-11 (2000) - doi:10.3354/meps192001 Formation of transparent exopolymer particles, TEP, from dissolved precursor material Uta Passow* Marine Science Institute, University of California, Santa Barbara, California 93106, USA *E-mail: passow@lifesci.ucsb.edu ABSTRACT: Transparent exopolymer particles (TEP) form from polysaccharides released by many phytoplankton species, but this process by which dissolved organic matter becomes particulate is poorly understood. Here, the abiotic formation of TEP from precursors <0.2 µm and the minimum molecular weight (MW) of TEP-precursors were studied. In most samples TEP formed from material <0.2 µm (polycarbonate membrane filters, Poretics) when exposed to laminar shear in Couette flocculators. This result was unexpected as no TEP formed from material <0.45 µm (polycap capsules, Whatman) due to surface coagulation onto bubbles (Zhou et al. 1998; Limnol Oceanogr 43:1860-1871). Some TEP-precursors were able to pass through dialysis bags with a nominal pore size of 8 kDa (natural cellulose, Spektrum), although their MW is presumably 2 orders of magnitude larger, suggesting that TEP-precursors can be fibrillar. It is suggested that freshly released precursors are fibrillar and that these fibrillar precursors form larger colloids and eventually TEP within hours to days after their release. KEY WORDS: TEP · Particle formation · Exudation Full text in pdf format NextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 192. Publication date: January 31, 2000 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 2000 Inter-Research.

A carbonyl reductase-catalyzing reduction of N3-phenacyluridine in rabbit liver.

Carbonyl reductase activity for a novel hypnotic, N3-phenacyluridine, was mainly localized in the cytosol fraction of rabbit liver. The enzyme (N3-phenacyluridine reductase) which catalyzes the reduction of N3-phenacyluridine to N3-alpha-hydroxy-beta-phenethyluridine was purified from the cytosolic fraction of rabbit liver by various chromatographic techniques (DEAE-Sephacel, Red Sepharose CL-6B and hydroxylapatite). N3-Phenacyluridine reductase had a minimum molecular weight of 39kDa on sodium dodecyl sulfate polyacrylamide gel electrophoresis. This enzyme required reduced nicotinamide adenine dinucleotide phosphate (NADPH) as a cofactor and its optimal pH was 7.5. Flavonoids (quercetin and quercitrin) were potent inhibitors of the enzyme, but pyrazole or barbital had little effect. The apparent Km and Vmax values of the enzyme for the reduction of N3-phenacyluridine were 0.32 mM and 8.7 units/mg protein, respectively. A variety of carbonyl compounds, including N3-phenacyluridine, were effectively reduced by the enzyme. However, the enzyme purified from rabbit liver differs in several respects from known carbonyl reductases in rabbit liver.

Triple marker screening, Japanese experience

In order to provide evidence that a cytochrome P450 belonging to the IIB subfamily is expressed as a constitutive form in the guinea pig, we tried to purify an isozyme from liver microsomes of untreated guinea pigs by assessing its reactivity with anti-P450b antibody in the present study. One form of cytochrome P450, named P450GP-1, was obtained. The minimum molecular weight of this isozyme was estimated to be 52,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The amino terminal sequence up to the 33rd amino acid of P450GP-1 was determined. As expected, comparison of the amino acid sequence with those of cytochrome P450 isozymes from other species reported so far indicated that P450GP-1 was highly homologous to P450s categorized in the IIB subfamily; that is, 67% similarity to rat P450b, 82% to rabbit LM2, 76% to dog PBD-2, 70% to mouse pf 346, and 73% to human IIB1. On the other hand, P450GP-1 showed only low similarity, less than 41%, to other cytochrome P450s of the II subfamily and those of the I, III, and IV families. Affinity of P450GP-1 to anti-P450b immunoglobulin G was confirmed to be comparable with that of a principal antigen, P450b. Immunoblot analysis revealed that P450GP-1 in the guinea pig liver microsomes was induced by phenobarbital treatment, but the increase was not as large as in the rat. P450GP-1 efficiently catalyzed benzphetamine N-demethylation, strychnine 2-hydroxylation, and testosterone 16β-hydroxylation, all of which are also catalyzed by P450b. Based on these results, it was strongly suggested that the IIB-type of cytochrome P450 in guinea pigs, at least one of them, is a constitutive form which is moderately induced by phenobarbital.

Statistical experimental strategies approach to emulsion copolymerization of styrene andn-butyl acrylate

A batch emulsion copolymerization for the preparation of styrene-n-butylacrylate (St/BA) copolymer latexes is investigated. A series of n-butylacrylate-styrene copolymer latexes were obtained by emulsion copolymerization in the presence of K2S2O8 (KPS) as initiator and with/without emulsifier (sodium lauryl sulfate). The effect of such preparation conditions as initiator concentration, the St/BA ratio, reaction temperature, agitation rate, and emulsifier concentration on the polymerization rate, particle size of copolymer latex, and molecular weight distribution of the resulting copolymer (∼ 80% conversion), respectively, is systematically studied using fractional factorial design methodology. Fractional factorial analysis indicates that the effects of the St/BA ratio, reaction temperature, emulsifier concentration, as well as the two-factor interaction of temperature and emulsifier concentration, are the key variables influencing the polymerization rate. At ∼ 80% monomer conversion, statistical analysis clearly isolates emulsifier concentration as the dominant factor affecting average particle size of copolymer latex; results also indicate that the effects of the St/BA ratio, reaction temperature, and emulsifier concentration are major effects influencing the polydispersity of polymer molecular-weight distribution. For 7.30 g KPS/100 g monomer and 500 rpm agitation rate, the conditions for minimizing molecular-weight distribution (∼ 80% conversion) occur for a reaction temperature, St/BA ratio, and surfactant concentration of 70°C, ∼ 3.59/1, and ∼ 2.08 g/100 g monomer, respectively, generating a minimum molecular-weight polydispersity of ∼ 3.0. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 551–563, 1998

Structure of the extracellular hemoglobin of Biomphalaria glabrata

The hemoglobin of Biomphalaria glabrata was purified to homogeneity by gel filtration column followed by anion exchange chromatography. The dissociation products were analyzed by a 5–15% gradient polyacrylamide gel electrophoresis containing sodium dodecyl sulfate (SDS-PAGE) giving a band of 270 kDa and a band of 180 kDa after reduction with β-mercaptoethanol. The same profile was obtained in a 3.5% agarose gel electrophoresis containing SDS (SDS-AGE) but showed additional bands of higher molecular weight. These bands were proposed to be monomers, dimers and trimers, since they showed a good correlation in a plot of R f versus log M r. After partial reduction in a two-dimensional SDS-AGE, the proposed monomers and dimers produced two and four bands, respectively, likely indicating one to four chains crosslinked by disulfide bridges. Digestion with four different proteases yielded several equivalent fragments with molecular weights multiples of its minimum molecular weight (17.7 kDa). The circular dichroism spectrum of the protein showed a characteristic high α-helix content (∼70%). It was proposed that this hemoglobin is a pentamer with a molecular weight of aproximately 1.8×10 3 kDa, assembled by five 360-kDa subunits, each formed by two 180-kDa chains linked in pairs by disulfide bridges and each of these chains, in turn, comprised by ten heme binding domains linked in tandem. These data are compared to the published information for other planorbid extracellular hemoglobins.

Characterization of modified bismaleimide resin

A new high-temperature resin system based on methylene dianiline bismaleimide (MDA-BMI) chemistry is studied. This is a two-component resin system which is modified by 2,2′-methylene-bis[4-methyl-6-(2-propenyl)] phenol (MBMPP) and has excellent thermal mechanical properties and good toughness characteristics. This paper discusses in detail some of the characteristics of the prepolymer by reacting the two components in addition to the cured system's properties. The prepolymer has very good stability at 100–120°C with very minimal molecular weight increase. The reaction order for curing prepolymer is almost 1. The activation energy of the curing reaction is 74.12 KJ/mol. The flexural strength and modulus of the cured modified MDA-BMI and their retention at 250°C are 124 and 3774.6 MPa and 69 and 78%, respectively. © 1996 John Wiley & Sons, Inc.