Sample records for accurate molecular weight

  1. Role of viscosity in the accurate prediction of source-terms for high molecular weight substances

    E-print Network

    Shaikh, Irfan Yusuf

    1999-01-01

    ROLE OF VISCOSITY IN THE ACCURATE PREDICTION OF SOURCE-TERMS FOR HIGH MOLECULAR WEIGHT SUBSTANCES A Thesis by IRFAN YUSUF SHAIKH Submitted to the Office of Graduate Studies of Texas ARM University in partial fulfillment of the requirements... for the degree of MASTER OF SCIENCE August 1999 Major Subject: Chemical Fngineering ROLE OF VISCOSITY IN THE ACCURATE PREDICTION OF SOURCE-TERMS FOR HIGH MOLECULAR WEIGHT SUBSTANCES A Thesis by IRFAN YUSUF SHAIKH Submitted to the Office of Graduate...

  2. RAPID AND ACCURATE METHOD FOR ESTIMATING MOLECULAR WEIGHTS OF ORGANIC COMPOUNDS FROM LOW RESOLUTION MASS SPECTRA

    EPA Science Inventory

    An improved method of estimating molecular weights of volatile organic compounds from their mass spectra has been developed and evaluated for accuracy. his technique can be implemented with a user friendly expert system on a personal computer. he method is based on a pattern reco...

  3. A modified ELISA accurately measures secretion of high molecular weight hyaluronan (HA) by Graves' disease orbital cells.

    PubMed

    Krieger, Christine C; Gershengorn, Marvin C

    2014-02-01

    Excess production of hyaluronan (hyaluronic acid [HA]) in the retro-orbital space is a major component of Graves' ophthalmopathy, and regulation of HA production by orbital cells is a major research area. In most previous studies, HA was measured by ELISAs that used HA-binding proteins for detection and rooster comb HA as standards. We show that the binding efficiency of HA-binding protein in the ELISA is a function of HA polymer size. Using gel electrophoresis, we show that HA secreted from orbital cells is primarily comprised of polymers more than 500 000. We modified a commercially available ELISA by using 1 million molecular weight HA as standard to accurately measure HA of this size. We demonstrated that IL-1?-stimulated HA secretion is at least 2-fold greater than previously reported, and activation of the TSH receptor by an activating antibody M22 from a patient with Graves' disease led to more than 3-fold increase in HA production in both fibroblasts/preadipocytes and adipocytes. These effects were not consistently detected with the commercial ELISA using rooster comb HA as standard and suggest that fibroblasts/preadipocytes may play a more prominent role in HA remodeling in Graves' ophthalmopathy than previously appreciated. PMID:24302624

  4. Laser desorption/ionization on porous silicon mass spectrometry for accurately determining the molecular weight distribution of polymers evaluated using a certified polystyrene standard.

    PubMed

    Seino, Teruyuki; Sato, Hiroaki; Torimura, Masaki; Shimada, Kazue; Yamamoto, Atsushi; Tao, Hiroaki

    2005-05-01

    Desorption/ionization on porous silicon-mass spectrometry (DIOS-MS) is a novel soft ionization MS technique that does not require any matrix reagent, ideally resulting in fewer obstructive peaks in the lower mass region. In this study, the etching conditions of porous silicon spots as an ionization platform of DIOS-MS were investigated for determining the molecular weight distribution (MWD) of polymers. To evaluate the accuracy of DIOS mass spectra observed using porous silicon spots prepared under various etching conditions, a certified polystyrene (PS) standard sample with an average molecular weight of ca. 2400 was used as a model sample. By optimizing the etching conditions, the MWD of the PS sample could be accurately observed by DIOS-MS using both p-type and n-type porous silicon spots. Especially, in the case of a suitable n-type spot, an accurate peak distribution with very fewer obstructive background peaks could be observed using the minimum laser power, comparable to the conventional matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS). PMID:15913133

  5. Accurate determination of the molecular weight of the major surface layer protein isolated from Clostridium thermosaccharolyticum by time-of-flight mass spectrometry.

    PubMed Central

    Allmaier, G; Schäffer, C; Messner, P; Rapp, U; Mayer-Posner, F J

    1995-01-01

    Matrix-assisted laser desorption with concomitant ionization, in combination with a linear time-of-flight mass spectrometer, was used to analyze underivatized and hard-to-solubilize surface layer proteins and glycoproteins by depositing them on top of a microcrystalline layer of the matrix alpha-cyano-4-hydroxycinnamic acid. Use of this special sample preparation technique allowed the first successful desorption-ionization of intact surface layer proteins and accurate determination of their molecular weights by mass spectrometry. The molecular mass of the monomeric subunit of the major surface layer protein isolated from Clostridium thermosaccharolyticum E207-71 was determined to be 75,621 +/- 81 Da. The obtainable mass accuracy of the technique is conservatively considered to be within +/- 0.2%. This result deviates from that given by sodium dodecyl sulfate-polyacrylamide gel electrophoresis by approximately 7.4 kDa because this method is strongly affected and biased by the three-dimensional structure of this type of surface protein. With the apparent advantages of unsurpassed mass accuracy, low dependence on the physicochemical properties of the surface layer proteins, and high sensitivity, it can be concluded that a linear time-of-flight instrument combined with UV matrix-assisted laser desorption with concomitant ionization is better suited for molecular weight determination than is gel electrophoresis. PMID:7868619

  6. Calculating Molecular Weight

    NSDL National Science Digital Library

    This video and online calculator show how to calculate the molecular weight of a substance from the atomic weights given on the periodic table. Use the molecular weight to convert between the macroscopic scale (grams of a substance) and the microscopic scale (number of molecules of that substance).

  7. Molecular Weight and Molecular Weight Distributions in Synthetic Polymers.

    ERIC Educational Resources Information Center

    Ward, Thomas Carl

    1981-01-01

    Focuses on molecular weight and molecular weight distributions (MWD) and models for predicting MWD in a pedagogical way. In addition, instrumental methods used to characterize MWD are reviewed with emphasis on physical chemistry of each, including end-group determination, osmometry, light scattering, solution viscosity, fractionation, and…

  8. Apparatus for molecular weight separation

    DOEpatents

    Smith, Richard D. (Richland, WA); Liu, Chuanliang (Haverhill, MA)

    2001-01-01

    The present invention relates generally to an apparatus and method for separating high molecular weight molecules from low molecular weight molecules. More specifically, the invention relates to the use of microdialysis for removal of the salt (low molecular weight molecules) from a nucleotide sample (high molecular weight molecules) for ESI-MS analysis. The dialysis or separation performance of the present invention is improved by (1) increasing dialysis temperature thereby increasing desalting efficiency and improving spectrum quality; (2) adding piperidine and imidazole to the dialysis buffer solution and reducing charge states and further increasing detection sensitivity for DNA; (3) using low concentrations (0-2.5 mM NH4OAc) of dialysis buffer and shifting the DNA negative ions to higher charge states, producing a nearly 10-fold increase in detection sensitivity and a slightly decreased desalting efficiency, (4) conducting a two-stage separation or (5) any combination of (1), (2), (3) and (4).

  9. Application of [superscript 1]H DOSY for Facile Measurement of Polymer Molecular Weights

    E-print Network

    Li, Weibin

    To address the practical issues of polymer molecular weight determination, the first accurate polymer weight-average molecular weight determination method in diverse living/controlled polymerization via DOSY (diffusion-ordered ...

  10. Molecular Weight & Energy Transport 7 September 2011

    E-print Network

    Militzer, Burkhard

    Molecular Weight & Energy Transport 7 September 2011 Goals · Review mean molecular weight · Practice working with diffusion Mean Molecular Weight 1. We will frequently use µ, µe, and µI (the mean molecular weight per particle, per free electron, and per ion, respectively). Let's practice computing

  11. Learning Weighted Naive Bayes with Accurate Ranking Harry Zhang

    E-print Network

    Zhang, Huajie "Harry"

    Learning Weighted Naive Bayes with Accurate Ranking Harry Zhang Faculty of Computer Science Bayes is one of most effective classification algo- rithms. In many applications, however, a ranking of exam- ples are more desirable than just classification. How to ex- tend naive Bayes to improve its

  12. The Molecular Weight Distribution of Polymer Samples

    ERIC Educational Resources Information Center

    Horta, Arturo; Pastoriza, M. Alejandra

    2007-01-01

    Various methods for the determination of the molecular weight distribution (MWD) of different polymer samples are presented. The study shows that the molecular weight averages and distribution of a polymerization completely depend on the characteristics of the reaction itself.

  13. Ultrahigh molecular weight aromatic siloxane polymers

    NASA Technical Reports Server (NTRS)

    Ludwick, L. M.

    1982-01-01

    The condensation of a diol with a silane in toluene yields a silphenylene-siloxane polymer. The reaction of stiochiometric amounts of the diol and silane produced products with molecular weights in the range 2.0 - 6.0 x 10 to the 5th power. The molecular weight of the product was greatly increased by a multistep technique. The methodology for synthesis of high molecular weight polymers using a two step procedure was refined. Polymers with weight average molecular weights in excess of 1.0 x 10 to the 6th power produced by this method. Two more reactive silanes, bis(pyrrolidinyl)dimethylsilane and bis(gamma butyrolactam)dimethylsilane, are compared with the dimethyleminodimethylsilane in ability to advance the molecular weight of the prepolymer. The polymers produced are characterized by intrinsic viscosity in tetrahydrofuran. Weight and number average molecular weights and polydispersity are determined by gel permeation chromatography.

  14. Effect of molecular weight on polyphenylquinoxaline properties

    NASA Technical Reports Server (NTRS)

    Jensen, Brian J.

    1991-01-01

    A series of polyphenyl quinoxalines with different molecular weight and end-groups were prepared by varying monomer stoichiometry. Thus, 4,4'-oxydibenzil and 3,3'-diaminobenzidine were reacted in a 50/50 mixture of m-cresol and xylenes. Reaction concentration, temperature, and stir rate were studied and found to have an effect on polymer properties. Number and weight average molecular weights were determined and correlated well with viscosity data. Glass transition temperatures were determined and found to vary with molecular weight and end-groups. Mechanical properties of films from polymers with different molecular weights were essentially identical at room temperature but showed significant differences at 232 C. Diamine terminated polymers were found to be much less thermooxidatively stable than benzil terminated polymers when aged at 316 C even though dynamic thermogravimetric analysis revealed only slight differences. Lower molecular weight polymers exhibited better processability than higher molecular weight polymers.

  15. Soluble high molecular weight polyimide resins

    NASA Technical Reports Server (NTRS)

    Jones, R. J.; Lubowitz, H. R.

    1970-01-01

    High molecular weight polyimide resins have greater than 20 percent /by weight/ solubility in polar organic solvents. They permit fabrication into films, fibers, coatings, reinforced composite, and adhesive product forms. Characterization properties for one typical polyimide resin are given.

  16. Production of high molecular weight polylactic acid

    DOEpatents

    Bonsignore, Patrick V. (Joilet, IL)

    1995-01-01

    A degradable high molecular weight poly(lactic acid). A poly(lactic acid) has a terminal end group of one of carboxyl or hydroxyl groups with low molecular weight poly(lactic acid) units coupled with linking agents of di-isocyanates, bis-epoxides, bis-oxazolines and bis-ortho esters. The resulting high molecular weight poly(lactic acid) can be used for applications taking advantage of the improved physical properties.

  17. Production of high molecular weight polylactic acid

    DOEpatents

    Bonsignore, P.V.

    1995-11-28

    A degradable high molecular weight poly(lactic acid) is described. The poly(lactic acid) has a terminal end group of one of carboxyl or hydroxyl groups with low molecular weight poly(lactic acid) units coupled with linking agents of di-isocyanates, bis-epoxides, bis-oxazolines and bis-ortho esters. The resulting high molecular weight poly(lactic acid) can be used for applications taking advantage of the improved physical properties.

  18. Molecular Weight Dependence of Excluded Volume Effects

    E-print Network

    Kazumi Suematsu

    2014-01-26

    Molecular weight dependence of excluded volume effects is examined. The swollen-to-unperturbed coil transition point shifts to lower concentration range with increasing molecular weight (Mw). It is shown that in the limit of the infinite molecular weight, the excluded volume effects should vanish in all concentration range, except for the only one point, Co = 0. Quite in contrast, for short chains, the excluded volume effects never disappear even at the melt state.

  19. Molecular Weight Distribution of Wheat Proteins

    Microsoft Academic Search

    M. Southan; F. MacRitchie

    1999-01-01

    Cereal Chem. 76(6):827-836 The molecular weight distribution (MWD) of wheat proteins is becoming recognized as the main determinant of physical dough prop- erties. Studies of high polymers have shown that properties such as tensile strength are related to a fraction of polymer with molecular weight above a critical value and the MWD of this fraction. Elongation to break is treated

  20. Factors affecting molecular weight conversion of renin.

    PubMed

    Ikemoto, F; Kawamura, M; Takaori, K; Yamamoto, K

    1980-05-01

    Our recent findings on molecular weight conversion in the case of renin are summarized and reviewed herein. The molecular weight of renin extracted from isolated renin granules from dogs and rats is approximately 40,000. This renin reacts with a constituent of kidney extract to form a high molecular weight renin of approximately 60,000. This constituent was termed a renin binding substance. This substance is probably contained in the cytosol of kidney cortex, and its characteristics are (1) heat instability, (2) non-dialyzability, (3) loss of binding ability by acidification at pH 3.0 and (4) apparent molecular weight is over 47,000. The binding reaction is mediated in two different ways; thiol oxidation with sodium tetrathionate and exposure of the reaction mixture at 0 degrees C for several days without thiol oxidation. PMID:6993718

  1. Molecular weight characterization of advanced thermoplastic resins

    NASA Technical Reports Server (NTRS)

    Young, Philip R.; Davis, Judith R.; Chang, Alice C.

    1989-01-01

    Analytical techniques including low angle laser light scattering photometry (LALLS), differential viscometry (DV), gel permeation chromatography (GPC), GPC-LALLS and GPC-DV, were used to characterize the molecular weight and molecular weight distribution of several advanced thermoplastics. A discussion is presented of various molecular-weight-related parameters obtained by these techniques on an experimental polyimide and poly(arylene ether ketone) and a commercially available polysulfone. Where possible, these parameters are correlated with processability and selected mechanical properties. The molecular weight was found to vary during the thermal conversion of poly(amic acid) to polyimide. However, no change in composition of the polysulfone was noted in response to various processing procedures.

  2. Microdialysis unit for molecular weight separation

    SciTech Connect

    Smith, R.D.; Liu, C.

    1999-09-21

    The present invention relates generally to an apparatus and method for separating high molecular weight molecules from low molecular weight molecules. More specifically, the invention relates to the use of microdialysis for removal of the salt (low molecular weight molecules) from a nucleotide sample (high molecular weight molecules) for ESI-MS analysis. The dialysis or separation performance of the present invention is improved by (1) increasing dialysis temperature thereby increasing desalting efficiency and improving spectrum quality; (2) adding piperidine and imidazole to the dialysis buffer solution and reducing charge states and further increasing detection sensitivity for DNA; (3) using low concentrations of dialysis buffer and shifting the DNA negative ions to higher charge states, producing a nearly 10-fold increase in detection sensitivity and a slightly decreased desalting efficiency, or (4) any combination of (1), (2), and (3).

  3. Microdialysis unit for molecular weight separation

    DOEpatents

    Smith, Richard D. (Richland, WA); Liu, Chuanliang (Richland, WA)

    1999-01-01

    The present invention relates generally to an apparatus and method for separating high molecular weight molecules from low molecular weight molecules. More specifically, the invention relates to the use of microdialysis for removal of the salt (low molecular weight molecules) from a nucleotide sample (high molecular weight molecules) for ESI-MS analysis. The dialysis or separation performance of the present invention is improved by (1) increasing dialysis temperature thereby increasing desalting efficiency and improving spectrum quality; (2) adding piperidine and imidazole to the dialysis buffer solution and reducing charge states and further increasing detection sensitivity for DNA; (3) using low concentrations (0-2.5 mM NH4OAc) of dialysis buffer and shifting the DNA negative ions to higher charge states, producing a nearly 10-fold increase in detection sensitivity and a slightly decreased desalting efficiency, or (4) any combination of (1), (2), and (3).

  4. Effect of molecular weight on the antioxidant property of low molecular weight alginate from Laminaria japonica

    Microsoft Academic Search

    Xue Zhao; Bafang Li; Changhu Xue; Liping Sun

    In this study, three alginate fractions with different molecular weights and ratios of mannuronic acid (M) to guluronic acid\\u000a (G) were prepared by enzymatic hydrolysis and ultrafiltration to assess the antioxidant property of alginates from Laminaria japonica with molecular weight below 10 kDa. The antioxidant properties of different molecular weight alginates were evaluated by\\u000a determining the scavenging abilities on superoxide, hydroxyl,

  5. Accurate measure by weight of liquids in industry. Final report

    SciTech Connect

    Muller, M.R.

    1992-12-12

    This research`s focus was to build a prototype of a computerized liquid dispensing system. This liquid metering system is based on the concept of altering the representative volume to account for temperature changes in the liquid to be dispensed. This is actualized by using a measuring tank and a temperature compensating displacement plunger. By constantly monitoring the temperature of the liquid, the plunger can be used to increase or decrease the specified volume to more accurately dispense liquid with a specified mass. In order to put the device being developed into proper engineering perspective, an extensive literature review was undertaken on all areas of industrial metering of liquids with an emphasis on gravimetric methods.

  6. Accurate measure by weight of liquids in industry

    SciTech Connect

    Muller, M.R.

    1992-12-12

    This research's focus was to build a prototype of a computerized liquid dispensing system. This liquid metering system is based on the concept of altering the representative volume to account for temperature changes in the liquid to be dispensed. This is actualized by using a measuring tank and a temperature compensating displacement plunger. By constantly monitoring the temperature of the liquid, the plunger can be used to increase or decrease the specified volume to more accurately dispense liquid with a specified mass. In order to put the device being developed into proper engineering perspective, an extensive literature review was undertaken on all areas of industrial metering of liquids with an emphasis on gravimetric methods.

  7. Employing MALDI-MS on Poly(alkylthiophenes): Analysis of Molecular Weights, Molecular Weight Distributions, End-Group Structures, and

    E-print Network

    McCullough, Richard D.

    Employing MALDI-MS on Poly(alkylthiophenes): Analysis of Molecular Weights, Molecular Weight the molecular weights calculated by MALDI and GPC of all fractionated polymer samples showed that GPC calculated molecular weights are a factor of 1.2-2.3 times higher than MALDI. The polydispersities calculated by MALDI

  8. Polystyrene-equivalent molecular weight versus true molecular weight in size-exclusion chromatography

    Microsoft Academic Search

    Miloš Netopil??k; Pavel Kratochv??l

    2003-01-01

    The evaluation of the size-exclusion chromatography (SEC) concentration elution curves by means of a calibration dependence obtained in a given SEC set for a polymer different from the polymer to be analyzed results in an error in the determination of both molecular weight and molecular-weight distribution (MWD). The problem is analyzed assuming the validity of the universal-calibration concept. The differences

  9. Power laws and fractal behavior in nuclear stability, atomic weights and molecular weights

    E-print Network

    Pavin, Nenad

    Power laws and fractal behavior in nuclear stability, atomic weights and molecular weights V. Paar for the description of the line of stability of atomic nuclei, and for the description of atomic weights and molecular, a power law dependence on molecular weights was found experimentally for the interactions between

  10. Biodegradation of high molecular weight polylactic acid

    NASA Astrophysics Data System (ADS)

    Stloukal, Petr; Koutny, Marek; Sedlarik, Vladimir; Kucharczyk, Pavel

    2012-07-01

    Polylactid acid seems to be an appropriate replacement of conventional non-biodegradable synthetic polymer primarily due to comparable mechanical, thermal and processing properties in its high molecular weight form. Biodegradation of high molecular PLA was studied in compost for various forms differing in their specific surface area. The material proved its good biodegradability under composting conditions and all investigated forms showed to be acceptable for industrial composting. Despite expectations, no significant differences in resulting mineralizations were observed for fiber, film and powder sample forms with different specific surface areas. The clearly faster biodegradation was detected only for the thin coating on porous material with high specific surface area.

  11. Ultrahigh Molecular Weight Aromatic Siloxane Polymers

    NASA Technical Reports Server (NTRS)

    Ludwick, L. M.

    1983-01-01

    Silphenylene-siloxane polymers can be prepared by a condensation reaction of a diol 1,4-bis(hydroxydimethylsilyl)benzene and a silane bis(dimethylamino)dimethylsilane. Using a stepwise condensation technique, a polymer (R=CH3) with a molecular weight in excess of 1.0 x 1 million has been produced. The polymer exhibits increased thermal stability, compared to a methyl siloxane polymer without the aromatic phenyl ring in the backbone. The use of bis(dimethylamino)methylvinylsilane should allow for ready crosslinking at the vinyl sites (R=-CH=CH2) introduced into the backbone. However, under the conditions of the reaction system a high molecular weight polymer was not obtained or the polymer underwent a crosslinking process during the synthesis.

  12. Application of Molecular Rotors to the Determination of the Molecular Weight Dependence

    E-print Network

    Lee, James

    Application of Molecular Rotors to the Determination of the Molecular Weight Dependence molecular weight (M) of the polymer. These measure- ments can be compared with established theories molecular weight of a polymer by using a molecular weight series of poly- (propylene oxide) (PPOX) as model

  13. 8 Ultrahigh molecular weight polyethylene from slurry Insite TM technology

    Microsoft Academic Search

    Koichi Hasebe; Akio Fujiwara; Takashi Nozaki; Koichi Miyamoto; Harumi Watanabe

    2006-01-01

    Ultra-high molecular weight polyethylene (UHMWPE) homopolymer was prepared with the slurry INSITE™ technology and a Tebbe reagent. The molecular weight of the homopolymer was controlled from 2 million to 10 million of Mv by the concentration of the Tebbe reagent in the polymerization process. UHMWPE copolymer of ethylene and 1-hexene was also prepared. The molecular weight of the copolymer was

  14. Polymer Molecular Weight Analysis by [Superscript 1]H NMR Spectroscopy

    ERIC Educational Resources Information Center

    Izunobi, Josephat U.; Higginbotham, Clement L.

    2011-01-01

    The measurement and analysis of molecular weight and molecular weight distribution remain matters of fundamental importance for the characterization and physical properties of polymers. Gel permeation chromatography (GPC) is the most routinely used method for the molecular weight determination of polymers whereas matrix-assisted laser…

  15. Trends and Inferred Emissions of Atmospheric High Molecular Weight Perfluorocarbons

    E-print Network

    Trends and Inferred Emissions of Atmospheric High Molecular Weight Perfluorocarbons by Diane Jean and Planetary Sciences #12;2 #12;Trends and Inferred Emissions of Atmospheric High Molecular Weight- mates are presented for the five high molecular weight perfluorocarbons (PFCs): de- cafluorobutane (C4F

  16. Original article In vitro study of molecular weight, hydrophobicity

    E-print Network

    Boyer, Edmond

    Original article In vitro study of molecular weight, hydrophobicity and amino acid composition - The molecular weight, amino acid composition and hydrophobicity of the peptide residue produced by hydrolysis / aminopeptidases / peptides / hydrophobicity / molecular weight / amino acids Résumé ― Étude in vitro du

  17. RESEARCH Open Access Identification of low molecular weight nuclear

    E-print Network

    Paris-Sud XI, Université de

    RESEARCH Open Access Identification of low molecular weight nuclear complexes containing integrase of IN eluted within a high molecular weight complex competent for integration (IN complex I), IN was also detected in a low molecular weight complex devoid of full-length viral cDNA (IN complex II, ~440 KDa). At 6

  18. Molecular relaxation study of polystyrene: influence of temperature, draw rate and molecular weight

    E-print Network

    Pezolet, Michel

    Molecular relaxation study of polystyrene: influence of temperature, draw rate and molecular weight different polystyrene samples, four monodisperse of weight-average molecular weight ranging from 210 000 relaxation time (t1), which is of the order of seconds, is independent of average molecular weight (Mw

  19. An accurate molecular structure of phenyl, the simplest aryl radical.

    PubMed

    Martinez, Oscar; Crabtree, Kyle N; Gottlieb, Carl A; Stanton, John F; McCarthy, Michael C

    2015-02-01

    The phenyl radical (C6H5(·)) is the prototypical ?-type aryl radical and one of the most common aromatic building blocks for larger ring molecules. Using a combination of rotational spectroscopy of singly substituted isotopic species and vibrational corrections calculated theoretically, an extremely accurate molecular structure has been determined. Relative to benzene, the phenyl radical has a substantially larger C-Cipso-C bond angle [125.8(3)° vs. 120°], and a shorter distance [2.713(3)?Å vs. 2.783(2)?Å] between the ipso and para carbon atoms. PMID:25521111

  20. Effect of molecular weight on fibrous PVA produced by electrospinning

    Microsoft Academic Search

    A. Koski; K. Yim; S. Shivkumar

    2004-01-01

    The effects of polymer weight average molecular weight (MW) on the fiber structure of electrospun polyvinylalcohol (PVA) have been studied. PVA with a degree of hydrolysis of 98–99% and with molecular weights ranging from 9000 to 186,000 g\\/mol was dissolved in water. The concentration (C) of the polymer in the solution was varied depending on the molecular weight. The solution

  1. Determinations of molecular weight and molecular weight distribution of high polymers by the rheological properties

    NASA Technical Reports Server (NTRS)

    Huang, J. Y.; Hou, T. H.; Tiwari, S. N.

    1989-01-01

    Several methods are reviewed by which the molecular weight (MW) and the molecular weight distribution (MWD) of polymeric material were determined from the rheological properties. A poly(arylene ether) polymer with six different molecular weights was used in this investigation. Experimentally measured MW and MWD were conducted by GPC/LALLS (gel permeation chromatography/low angle laser light scattering), and the rheological properties of the melts were measured by a Rheometric System Four rheometer. It was found that qualitative information of the MW and MWD of these polymers could be derived from the viscoelastic properties, with the methods proposed by Zeichner and Patel, and by Dormier et al., by shifting the master curves of the dynamic storage modulus, G', and the loss modulus, G'', along the frequency axis. Efforts were also made to calculate quantitative profiles of MW and MWD for these polymers from their rheological properties. The technique recently proposed by Wu was evaluated. It was found that satisfactory results could only be obtained for polymers with single modal distribution in the molecular weight.

  2. The influence of molecular weight on plasticizer retention

    E-print Network

    The influence of molecular weight on plasticizer retention A key change to specification PGI-ll 04, which requires an average plasticizer molecular weight greater than or equal to 400 to ensure long- cizer are retained by the PYC material after mi- gration ifa minimum mol- ecular weight is used

  3. Towards Accurate Molecular Modeling of Plastic Bonded Explosives

    NASA Astrophysics Data System (ADS)

    Chantawansri, T. L.; Andzelm, J.; Taylor, D.; Byrd, E.; Rice, B.

    2010-03-01

    There is substantial interest in identifying the controlling factors that influence the susceptibility of polymer bonded explosives (PBXs) to accidental initiation. Numerous Molecular Dynamics (MD) simulations of PBXs using the COMPASS force field have been reported in recent years, where the validity of the force field in modeling the solid EM fill has been judged solely on its ability to reproduce lattice parameters, which is an insufficient metric. Performance of the COMPASS force field in modeling EMs and the polymeric binder has been assessed by calculating structural, thermal, and mechanical properties, where only fair agreement with experimental data is obtained. We performed MD simulations using the COMPASS force field for the polymer binder hydroxyl-terminated polybutadiene and five EMs: cyclotrimethylenetrinitramine, 1,3,5,7-tetranitro-1,3,5,7-tetra-azacyclo-octane, 2,4,6,8,10,12-hexantirohexaazazisowurzitane, 2,4,6-trinitro-1,3,5-benzenetriamine, and pentaerythritol tetranitate. Predicted EM crystallographic and molecular structural parameters, as well as calculated properties for the binder will be compared with experimental results for different simulation conditions. We also present novel simulation protocols, which improve agreement between experimental and computation results thus leading to the accurate modeling of PBXs.

  4. Molecular Weight Effects on the Viscoelastic Response of a Polyimide

    NASA Technical Reports Server (NTRS)

    Nicholson, Lee M.; Whitley, Karen S.; Gates, Thomas S.

    2000-01-01

    The effect of molecular weight on the viscoelastic performance of an advanced polymer (LaRC -SI) was investigated through the use of creep compliance tests. Testing consisted of short-term isothermal creep and recovery with the creep segments performed under constant load. The tests were conducted at three temperatures below the glass transition temperature of each material with different molecular weight. Through the use of time-aging-time superposition procedures, the material constants, material master curves and aging-related parameters were evaluated at each temperature for a given molecular weight. The time-temperature superposition technique helped to describe the effect of temperature on the timescale of the viscoelastic response of each molecular weight. It was shown that the low molecular weight materials have increased creep compliance and creep compliance rate, and are more sensitive to temperature than the high molecular weight materials. Furthermore, a critical molecular weight transition was observed to occur at a weight-average molecular weight of approximately 25000 g/mol below which, the temperature sensitivity of the time-temperature superposition shift factor increases rapidly.

  5. STANDARD OPERATING PROCEDURE LOW MOLECULAR WEIGHT ORGANIC ACIDS (selected)

    E-print Network

    Pawlowski, Wojtek

    (s): ___________________________________________________ Chemical(s): formic acid, lactic acid, acetic acid, propionic acid, butyric acid, valeric acid, and other12.1 STANDARD OPERATING PROCEDURE for LOW MOLECULAR WEIGHT ORGANIC ACIDS (selected) Location low molecular weight organic acids Specific Hazards: Causes severe burns to mucous membranes. Causes

  6. New molecular weight forms of arabinogalactan from Larix occidentalis

    Microsoft Academic Search

    James H. Prescott; Ernest V. Groman; Gyongyi Gulyas

    1997-01-01

    Arabinogalactan fractions with narrow molecular weight distributions were obtained from a crude extract of Larix occidentalis by gel-filtration chromatography. Molecular weight distributions of the fractions were determined by a combination of gel filtration chromatography (GFC) with intensity (Rayleigh) light scattering. Two distinct distributions were observed, with the fractions in the lower distribution as small as 3 kDa. A sensitive immunoassay

  7. Dendrimers: The First High Molecular Weight Newtonian Polymers?

    NASA Astrophysics Data System (ADS)

    Dvornic, Petar R.

    1997-03-01

    Rheological behavior of the first seven generations of polyamidoamine (PAMAM) dendrimers has been investigated under a variety of testing conditions including: (a) steady-state, oscillatory and "creep"-type shearing; (b) dendrimer solutions in a good solvent and neat dendrimers; and (c) a wide range of molecular weights, solution concentrations and temperatures. The results obtained indicate typical Newtonian flow behavior even for the highest examined molecular weight dendrimers. These results will be compared with the results obtained from the linear and randomly branched polyamidoamines of the corresponding molecular weights. It will be proposed that Newtonian flow may represent a characteristic physical property of dendrimers which (a) sets them apart from all other known types of macromolecular architecture and (b) makes them candidates for a "missing link" between the small molecular weight compounds of classical organic chemistry and truly high molecular weight macromolecules of polymer science.

  8. The low-molecular-weight glutenin subunits of wheat gluten

    Microsoft Academic Search

    Renato D'Ovidio; Stefania Masci

    2004-01-01

    Low-molecular-weight glutenin subunits (LMW-GS) are polymeric protein components of wheat endosperm and like all seed storage proteins, are digested to provide nutrients for the embryo during seed germination and seedling growth. Due to their structural characteristics, they exhibit features important for the technological properties of wheat flour. Their ability to form inter-molecular disulphide bonds with each other and\\/or with high-molecular-weight

  9. Molecular Weight Dependence of the Viscosity of Polyethylene Macrocycles

    NASA Astrophysics Data System (ADS)

    Wang, Jian; McKenna, Gregory; Benitez, Diego; Gorodetskaya, Irina; Grubbs, Robert

    2005-03-01

    The Grubbs group at Caltech is using a new method of synthesis for the production of macrocycles that avoids the problems of sample contamination with long chain linear molecules. They have produced macrocyclic polyethylenes having molecular weights as high as 400,000 g/mole. At Texas Tech University rheological measurements are being made using both the Plazek Magnetic Bearing Torsional Creep Apparatus and a Paar Physica controlled stress rheometer. Because the samples are polydisperse, with Mw/Mn values of 1.6-1-9, we here report only the results of the viscosity as a function of molecular weight. Surprisingly, unlike reports in the literature for polystyrene rings or polybutadiene rings, the viscosities of the polyethylene rings are larger than those for equivalent molecular weight linear polyethylenes and the viscosity increases approximately exponentially with weight average molecular weight. Further results will be reported at the meeting.

  10. Free volume model for molecular weights of polymers

    NASA Technical Reports Server (NTRS)

    Singh, J. J.; Eftekhari, A.

    1992-01-01

    A free volume model has been developed for determining molecular weights of linear polymers. It is based on the size of free volume cells in two geometries of poly(arylene ether ketone)s. Free volume cell sizes in test samples were measured using positron lifetime spectroscopy. The molecular weights computed from free volume cell sizes are in good agreement with the values measured by gel permeation chromatography, with a low angle laser light scattering photometer as the detector. The model has been further tested on two atactic polystyrene samples, where it predicted the ratio of their molecular weights with reasonable accuracy.

  11. Free volume variation with molecular weight of polymers

    NASA Technical Reports Server (NTRS)

    Singh, Jag J.; Eftekhari, Abe; Hinkley, Jeffrey A.; St.clair, Terry L.; Jensen, Brian J.

    1992-01-01

    Free volume measurements were made in several molecular weight fractions of two different geometries of poly(arylene ether ketone)s. Free volumes were measured using positron lifetime spectroscopy. It has been observed that the free volume cell size V(sub f) varies with the molecular weight M of the test samples according to an equation of the form V(sub f) = AM(B), where A and B are constants. The molecular weights computed from the free volume cell sizes are in good agreement with the values measured by gel permeation chromatography.

  12. Optimization of parameters for coverage of low molecular weight proteins

    E-print Network

    Muller, Stephan A.

    Proteins with molecular weights of <25 kDa are involved in major biological processes such as ribosome formation, stress adaption (e.g., temperature reduction) and cell cycle control. Despite their importance, the coverage ...

  13. A simplified electrophoretic system for determining molecular weights of proteins.

    PubMed Central

    Manwell, C

    1977-01-01

    Electrophoresis of 31 different proteins in commercially prepared polyacrylamide gradient gels, Gradipore, yields a linear relationship between a hypothetical limiting pore size (the reciprocal of a limiting gel concentration, GL) and the cube root of the mol.wt., over the range 13 500-9000 000. A regression analysis of these data reveals that 98.6% of all variability in 1/GL is explained by the molecular weight, and this degree of accuracy compares favourably with existing methods for the determination of molecular weight by retardation of mobility in polyacrylamide. This new procedure has the additional advantages that molecular-weight standards can be obtained from readily available body fluids or tissue extracts by localizing enzymes and other proteins by standard histochemical methods, and that the same electrophoretic system can be used in determining molecular weights as is used in routine surveys of populations for individual and species variation in protein heterogeneity. Images PLATE 1 PMID:921762

  14. Molecular-Weight-Controlled, End-Capped Polybenzimidazoles

    NASA Technical Reports Server (NTRS)

    Connell, John W.; Hergenrother, Paul M.; Smith, Joseph G., Jr.

    1993-01-01

    Novel molecular-weight-controlled end-capped poly(arylene ether benzimidazole)s (PAEBI's) prepared by nucleophilic displacement reaction of di(hydroxyl)benzimidazole monomers with activated aromatic dihalides. Polymers prepared at various molecular weights by upsetting stoichiometry of monomers and end-capped with monohydroxybenzimidazole. Exhibit favorable physical and mechanical properties, improved solubility in polar aprotic solvents and better compression moldability. Potential applications as adhesives, coatings, films, fibers, membranes, moldings, and composite matrix resins.

  15. Low molecular weight heparin in prevention of perioperative thrombosis

    Microsoft Academic Search

    A. Leizorovicz; M. C. Haugh; F. R. Chapuis; M. M. Samama; J. P. Boissel

    1992-01-01

    OBJECTIVE--To determine whether prophylactic treatment with low molecular weight heparin reduces the incidence of thrombosis in patients who have had general or orthopaedic surgery. DESIGN--Meta-analysis of results from 52 randomised, controlled clinical studies (29 in general surgery and 23 in orthopaedic surgery) in which low molecular weight heparin was compared with placebo, dextran, or unfractionated heparin. SUBJECTS--Patients who had had

  16. Molecular weight dependent structural regimes during the electrospinning of PVA

    Microsoft Academic Search

    Jing Tao; Satya Shivkumar

    2007-01-01

    The cumulative effects of molecular weight and concentration on the structural transitions in the electrospun polymer have been studied. Experiments have been conducted with water as the solvent for molecular weights of polyvinylalcohol (PVA) ranging from 9500 g\\/mol to 155,000 g\\/mol. The structural regimes for beads, beaded fibers, complete fibers and flat ribbons have been mapped. The development of a stable fiber

  17. Phase Behavior of Binary Blends of High Molecular Weight Diblock Copolymers with a Low Molecular Weight Triblock

    SciTech Connect

    Mickiewicz, Rafal A.; Ntoukas, Eleftherios; Avgeropoulos, Apostolos; Thomas, Edwin L. (MIT); (Ioannina)

    2009-08-26

    Binary blends of four different high molecular weight poly(styrene-b-isoprene) (SI) diblock copolymers with a lower molecular weight poly(styrene-b-isoprene-b-styrene) (SIS) triblock copolymer were prepared, and their morphology was characterized by transmission electron microscopy and ultra-small-angle X-ray scattering. All the neat block copolymers have nearly symmetric composition and exhibit the lamellar morphology. The SI diblock copolymers had number-average molecular weights, Mn, in the range 4.4 x 10{sup 5}--1.3 x 10{sup 6} g/mol and volume fractions of poly(styrene), {Phi}{sub PS}, in the range 0.43--0.49, and the SIS triblock had a molecular weight of Mn 6.2 x 10{sup 4} g/mol with {Phi}{sub PS} = 0.41. The high molecular weight diblock copolymers are very strongly segregating, with interaction parameter values, {chi}N, in the range 470--1410. A morphological phase diagram in the parameter space of molecular weight ratio (R = M{sub n}{sup diblock}/1/2M{sub n}{sup triblock}) and blend composition was constructed, with R values in the range between 14 and 43, which are higher than previously reported. The phase diagram revealed a large miscibility gap for the blends, with macrophase separation into two distinct types of microphase-separated domains for weight fractions of SI, w{sub SI} < 0.9, implying virtually no solubility of the much higher molecular weight diblocks in the lower molecular weight triblock. For certain blend compositions, above R 30, morphological transitions from the lamellar to cylindrical and bicontinuous structures were also observed.

  18. Evaluation of a Viscosity-Molecular Weight Relationship.

    ERIC Educational Resources Information Center

    Mathias, Lon J.

    1983-01-01

    Background information, procedures, and results are provided for a series of graduate/undergraduate polymer experiments. These include synthesis of poly(methylmethacrylate), viscosity experiment (indicating large effect even small amounts of a polymer may have on solution properties), and measurement of weight-average molecular weight by light…

  19. SEDFIT-MSTAR: Molecular weight and molecular weight distribution analysis of polymers by sedimentation equilibrium in the ultracentrifuge

    PubMed Central

    Schuck, Peter; Gillis, Richard B.; Besong, Tabot M.D.; Almutairi, Fahad; Adams, Gary G.; Rowe, Arthur J.; Harding, Stephen E.

    2014-01-01

    Sedimentation equilibrium (analytical ultracentrifugation) is one of the most inherently suitable methods for the determination of average molecular weights and molecular weight distributions of polymers, because of its absolute basis (no conformation assumptions) and inherent fractionation ability (without the need for columns or membranes and associated assumptions over inertness). With modern instrumentation it is also possible to run up to 21 samples simultaneously in a single run. Its application has been severely hampered because of difficulties in terms of baseline determination (incorporating estimation of the concentration at the air/solution meniscus) and complexity of the analysis procedures. We describe a new method for baseline determination based on a smart-smoothing principle and built into the highly popular platform SEDFIT for the analysis of the sedimentation behavior of natural and synthetic polymer materials. The SEDFIT-MSTAR procedure – which takes only a few minutes to perform - is tested with four synthetic data sets (including a significantly non-ideal system) a naturally occurring protein (human IgG1) and two naturally occurring carbohydrate polymers (pullulan and ?–carrageenan) in terms of (i) weight average molecular weight for the whole distribution of species in the sample (ii) the variation in “point” average molecular weight with local concentration in the ultracentrifuge cell and (iii) molecular weight distribution. PMID:24244936

  20. SEDFIT-MSTAR: molecular weight and molecular weight distribution analysis of polymers by sedimentation equilibrium in the ultracentrifuge.

    PubMed

    Schuck, Peter; Gillis, Richard B; Besong, Tabot M D; Almutairi, Fahad; Adams, Gary G; Rowe, Arthur J; Harding, Stephen E

    2014-01-01

    Sedimentation equilibrium (analytical ultracentrifugation) is one of the most inherently suitable methods for the determination of average molecular weights and molecular weight distributions of polymers, because of its absolute basis (no conformation assumptions) and inherent fractionation ability (without the need for columns or membranes and associated assumptions over inertness). With modern instrumentation it is also possible to run up to 21 samples simultaneously in a single run. Its application has been severely hampered because of difficulties in terms of baseline determination (incorporating estimation of the concentration at the air/solution meniscus) and complexity of the analysis procedures. We describe a new method for baseline determination based on a smart-smoothing principle and built into the highly popular platform SEDFIT for the analysis of the sedimentation behavior of natural and synthetic polymer materials. The SEDFIT-MSTAR procedure - which takes only a few minutes to perform - is tested with four synthetic data sets (including a significantly non-ideal system), a naturally occurring protein (human IgG1) and two naturally occurring carbohydrate polymers (pullulan and ?-carrageenan) in terms of (i) weight average molecular weight for the whole distribution of species in the sample (ii) the variation in "point" average molecular weight with local concentration in the ultracentrifuge cell and (iii) molecular weight distribution. PMID:24244936

  1. Molecular weight, polydispersity, and spectroscopic properties of aquatic humic substances

    USGS Publications Warehouse

    Chin, Y.-P.; Aiken, G.; O'Loughlin, E.

    1994-01-01

    The number- and weight-averaged molecular weights of a number of aquatic fulvic acids, a commercial humic acid, and unfractionated organic matter from four natural water samples were measured by high-pressure size exclusion chromatography (HPSEC). Molecular weights determined in this manner compared favorably with those values reported in the literature. Both recent literature values and our data indicate that these substances are smaller and less polydisperse than previously believed. Moreover, the molecular weights of the organic matter from three of the four natural water samples compared favorably to the fulvic acid samples extracted from similar environments. Bulk spectroscopic properties of the fulvic substances such as molar absorptivity at 280 nm and the E4/E6 ratio were also measured. A strong correlation was observed between molar absorptivity, total aromaticity, and the weight average molecular weights of all the humic substances. This observation suggests that bulk spectroscopic properties can be used to quickly estimate the size of humic substances and their aromatic contents. Both parameters are important with respect to understanding humic substance mobility and their propensity to react with both organic and inorganic pollutants. ?? 1994 American Chemical Society.

  2. Molecular weight dependent bimolecular recombination in organic solar cells.

    PubMed

    Philippa, Bronson; Stolterfoht, Martin; White, Ronald D; Velusamy, Marrapan; Burn, Paul L; Meredith, Paul; Pivrikas, Almantas

    2014-08-01

    Charge carrier recombination is studied in operational organic solar cells made from the polymer:fullerene system PCDTBT:PC71BM (poly[N-9''-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)]: [6,6]-phenyl-C70-butyric acid methyl ester). A newly developed technique High Intensity Resistance dependent PhotoVoltage is presented for reliably quantifying the bimolecular recombination coefficient independently of variations in experimental conditions, thereby resolving key limitations of previous experimental approaches. Experiments are performed on solar cells of varying thicknesses and varying polymeric molecular weights. It is shown that solar cells made from low molecular weight PCDTBT exhibit Langevin recombination, whereas suppressed (non-Langevin) recombination is found in solar cells made with high molecular weight PCDTBT. PMID:25106609

  3. Molecular weight dependent bimolecular recombination in organic solar cells

    NASA Astrophysics Data System (ADS)

    Philippa, Bronson; Stolterfoht, Martin; White, Ronald D.; Velusamy, Marrapan; Burn, Paul L.; Meredith, Paul; Pivrikas, Almantas

    2014-08-01

    Charge carrier recombination is studied in operational organic solar cells made from the polymer:fullerene system PCDTBT:PC71BM (poly[N-9''-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)]: [6,6]-phenyl-C70-butyric acid methyl ester). A newly developed technique High Intensity Resistance dependent PhotoVoltage is presented for reliably quantifying the bimolecular recombination coefficient independently of variations in experimental conditions, thereby resolving key limitations of previous experimental approaches. Experiments are performed on solar cells of varying thicknesses and varying polymeric molecular weights. It is shown that solar cells made from low molecular weight PCDTBT exhibit Langevin recombination, whereas suppressed (non-Langevin) recombination is found in solar cells made with high molecular weight PCDTBT.

  4. Microbial detection with low molecular weight RNA

    NASA Technical Reports Server (NTRS)

    Kourentzi, K. D.; Fox, G. E.; Willson, R. C.

    2001-01-01

    The need to monitor microorganisms in the environment has increased interest in assays based on hybridization probes that target nucleic acids (e.g., rRNA). We report the development of liquid-phase assays for specific bacterial 5S rRNA sequences or similarly sized artificial RNAs (aRNAs) using molecular beacon technology. These beacons fluoresce only in the presence of specific target sequences, rendering as much as a 27-fold fluorescence enhancement. The assays can be used with both crude cell lysates and purified total RNA preparations. Minimal sample preparation (e.g., heating to promote leakage from cells) is sufficient to detect many Gram-negative bacteria. Using this approach it was possible to detect an aRNA-labeled Escherichia coli strain in the presence of a large background of an otherwise identical E. coli strain. Finally, by using a longer wavelength carboxytetramethylrhodamine beacon it was possible to reduce the fraction of the signal due to cellular autofluorescence to below 0.5%.

  5. Molecular weights and molecular-weight distributions from ultracentrifugation of nonideal solutions.

    PubMed

    Wan, P J; Adams, E T

    1976-07-01

    Ultracentrifugation, membrane osmometry and capillary viscometry experiments have been performed on two dextran samples, which have molecular-weight distributions (MWDs) similar to those of dextrans used as blood plasma extenders. The manufacturer reported values of Mn and MW, determined by end group analysis and by light scattering, respectively. Our values of Mn, determined by osmometry, and MW, calculated from ultracentrifugal and viscometry experiments, agreed quite well with the manufacturer's results. Good agreement was obtained with values of MW and BLS (the light scattering second virial coefficient) obtained from sedimentation equilibrium experiments at different speeds using sector or nonsector-shaped centerpieces. Several ways of obtaining MW, MZ and BLS from sedimentation equilibrium experiments are presented. We have also shown how to obtain the speed-dependent term of the sedimentation equilibrium second virial coefficient. Both BLS and the speed-dependent nonideal terms could be used to correct the sedimentation equilibrium data, so that ideal values of d in c/d(r2) or dc/d(r2) could be estimated and used to obtain the MWDs of the dextran samples. Both Donnelly's and Scholte's methods were used with the sedimentation equilibrium data. With both methods, unimodal MWDs were encountered, which gave good agreement with the manufacturer's MWDs, obtained by a combination of analytical gel chromatography and light scattering. Uncorrected sedimentation equilibrium data gave MWDs quite different from the manufacturer's results. The MWD calculated from the differential distribution of sedimentation coefficients also gave a unimodal MWD, but this MWD did not give a good agreement with the sedimentation equilibrium results or with the manufacturer's results. PMID:963217

  6. RHEOLOGICAL PROPERTIES & MOLECULAR WEIGHT DISTRIBUTIONS OF FOUR PERFLUORINATED THERMOPLASTIC POLYMERS

    SciTech Connect

    Hoffman, D M; Shields, A L

    2009-02-24

    Dynamic viscosity measurements and molecular weight estimates have been made on four commercial, amorphous fluoropolymers with glass transitions (Tg) above 100 C: Teflon AF 1600, Hyflon AD 60, Cytop A and Cytop M. These polymers are of interest as binders for the insensitive high explosive 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) because of their high density and Tg above ambient, but within a suitable processing range of TATB. As part of this effort, the rheological properties and molecular weight distributions of these polymers were evaluated.

  7. Gelation behaviour of konjac glucomannan with different molecular weights.

    PubMed

    Zhang, H; Yoshimura, M; Nishinari, K; Williams, M A; Foster, T J; Norton, I T

    2001-07-01

    The deacetylation and gelation of konjac glucomannan (KGM) following alkali addition was investigated by Fourier transform infrared, while the rheological properties of KGM with different molecular weights were studied by dynamic viscoelastic measurements in shear mode and penetration force tests. It was found that gelation occurred after significant deacetylation had taken place. Rheometrical studies revealed that KGM with different molecular weights exhibited different gelation characteristics in small amplitude oscillatory shear flow. For the samples of fractionated KGM with lower molecular weights, a decrease in both the storage shear modulus (G') and loss shear modulus (G") was observed during gelation at temperatures above 75 degrees C. It is suggested that the decrease results from the wall slip between sample and measuring geometry owing to a rapid gelation process with syneresis and/or disentanglement of molecular chains adsorbed on the surface of parallel plates from those located in the bulk. Penetration force tests were employed to confirm the occurrence of slippage and thereby no decreases in rigidity of samples were observed during gelation. For the native KGM samples decreases in G' and G" during gelation were not observed, and it is suggested that this is due to the effect of the higher molecular weight and increased solution viscosity of these samples on the gelation kinetics. PMID:11343279

  8. Mean molecular weight and hydrogen abundance of Titan's atmosphere

    NASA Technical Reports Server (NTRS)

    Samuelson, R. E.; Hanel, R. A.; Kunde, V. G.; Maguire, W. C.

    1981-01-01

    The 200-600/cm continuum opacity in the troposphere and lower stratosphere of Titan is inferred from thermal emission spectra from the Voyager 1 IR spectrometer (IRIS). The surface temperature and mean molecular weight are between 94 and 97 K and between 28.3 and 29.2 AMU, respectively. The mole fraction of molecular hydrogen is 0.002 + or - 0.001, which is equivalent to an abundance of approximately 0.2 + or - 0.1 km amagat.

  9. Scale-invariant power law and fractality for molecular weights V. Paar a,*, N. Pavin a

    E-print Network

    Pavin, Nenad

    Scale-invariant power law and fractality for molecular weights V. Paar a,*, N. Pavin a , A. Rubcic of molecular weights of chemical compounds. A scale-invariant power law for molecular weights is introduced rights reserved. 1. Introduction Concepts of atomic and molecular weights are fundamental to chemistry

  10. POLYMER END-GROUP ANALYSIS: THE DETERMINATION OF AVERAGE MOLECULAR WEIGHT

    E-print Network

    Weston, Ken

    POLYMER END-GROUP ANALYSIS: THE DETERMINATION OF AVERAGE MOLECULAR WEIGHT Background reading form of macromolecules They are compounds of high molecular weight formed by combining a large number. Molecular Weight The physical properties of polymers depend heavily on their molecular weights, which vary

  11. During the past decades, the calculation of accurate free-energy differences from molecular

    E-print Network

    Simons, Jack

    ABSTRACT During the past decades, the calculation of accurate free-energy differences from), resulting in comparatively small free energy differences [4-10,12,16,20,24,29,31,32]. During the past decades, the calculation of accurate free-energy differences from molecular simulations has become

  12. Accurate Model Selection of Relaxed Molecular Clocks in Bayesian Phylogenetics

    PubMed Central

    Baele, Guy; Li, Wai Lok Sibon; Drummond, Alexei J.; Suchard, Marc A.; Lemey, Philippe

    2013-01-01

    Recent implementations of path sampling (PS) and stepping-stone sampling (SS) have been shown to outperform the harmonic mean estimator (HME) and a posterior simulation-based analog of Akaike’s information criterion through Markov chain Monte Carlo (AICM), in Bayesian model selection of demographic and molecular clock models. Almost simultaneously, a Bayesian model averaging approach was developed that avoids conditioning on a single model but averages over a set of relaxed clock models. This approach returns estimates of the posterior probability of each clock model through which one can estimate the Bayes factor in favor of the maximum a posteriori (MAP) clock model; however, this Bayes factor estimate may suffer when the posterior probability of the MAP model approaches 1. Here, we compare these two recent developments with the HME, stabilized/smoothed HME (sHME), and AICM, using both synthetic and empirical data. Our comparison shows reassuringly that MAP identification and its Bayes factor provide similar performance to PS and SS and that these approaches considerably outperform HME, sHME, and AICM in selecting the correct underlying clock model. We also illustrate the importance of using proper priors on a large set of empirical data sets. PMID:23090976

  13. Accurate model selection of relaxed molecular clocks in bayesian phylogenetics.

    PubMed

    Baele, Guy; Li, Wai Lok Sibon; Drummond, Alexei J; Suchard, Marc A; Lemey, Philippe

    2013-02-01

    Recent implementations of path sampling (PS) and stepping-stone sampling (SS) have been shown to outperform the harmonic mean estimator (HME) and a posterior simulation-based analog of Akaike's information criterion through Markov chain Monte Carlo (AICM), in bayesian model selection of demographic and molecular clock models. Almost simultaneously, a bayesian model averaging approach was developed that avoids conditioning on a single model but averages over a set of relaxed clock models. This approach returns estimates of the posterior probability of each clock model through which one can estimate the Bayes factor in favor of the maximum a posteriori (MAP) clock model; however, this Bayes factor estimate may suffer when the posterior probability of the MAP model approaches 1. Here, we compare these two recent developments with the HME, stabilized/smoothed HME (sHME), and AICM, using both synthetic and empirical data. Our comparison shows reassuringly that MAP identification and its Bayes factor provide similar performance to PS and SS and that these approaches considerably outperform HME, sHME, and AICM in selecting the correct underlying clock model. We also illustrate the importance of using proper priors on a large set of empirical data sets. PMID:23090976

  14. Molecular Weight Dependence of Polymersome Membrane Structure, Elasticity, and Stability

    E-print Network

    molecular weight Mh n, the hydrophobic core thickness for self- assembled bilayers of poly(ethylene oxide properties such as stability by forming vesicles from diblock copolymers of poly(ethylene oxide of PEO-PBD as well as PEO-poly(ethylethylene) was syn- thesized by standard living anionic

  15. Preparation of soybean oil polymers with high molecular weight

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The cationic polymerization of soybean oils was initiated by boron trifluoride diethyl etherate BF3.O(C2H5)2 in supercritical carbon dioxide (scCO2) medium. The resulting polymers had molecular weight ranging from 21,842 to 118,300 g/mol. Nuclear magnetic resonance spectroscopy (NMR) and gel perme...

  16. DETERMINATION OF MOLECULAR WEIGHT CITRUS PECTIN USING ION CHROMATOGRAPHY

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Objective was to investigate the use of ELS as a mass detector coupled with MALLS for determining the molecular weights of pectins and other polysaccharides under changing buffer concentrations using HPLC. This would permit the direct determination of the charge to size ratio of pectin which is imp...

  17. Nylon 6 nanocomposites: the effect of matrix molecular weight

    Microsoft Academic Search

    T. D. Fornes; P. J. Yoon; H. Keskkula; D. R. Paul

    2001-01-01

    Organoclay nanocomposites based on three different molecular weight grades of nylon 6 were prepared by melt processing using a twin screw extruder. Mechanical properties, transmission electron microscopy, wide-angle X-ray diffraction, and rheological measurements were used to characterize the three types of composites. Tensile modulus and yield strength were found to increase with increasing concentration of clay, while elongation at break

  18. Ultra-High-Molecular-Weight Silphenylene/Siloxane Polymers

    NASA Technical Reports Server (NTRS)

    Patterson, W. J.; Hundley, N. H.; Ludwick, L. M.

    1986-01-01

    Elastomers having molecular weights above 1 million made by twostage polymerization. Two-stage process proves far more successful than synthesis from reactive monomers. Process involves synthesis of silanolterminated prepolymer and subsequent extension of prepolymer chain with additional aminosilane monomer. Multistage method allows chain-extending monomer added in precise amounts between stages.

  19. Influence of intravascular molecular weight of hydroxyethyl starch on platelets.

    PubMed

    Treib, J; Haass, A; Pindur, G; Treib, W; Wenzel, E; Schimrigk, K

    1996-03-01

    Complications concerning the blood coagulation have been observed repeatedly after administration of highly substituted, high molecular weight hydroxyethyl starch (HES), but it has not been examined as to how intravascular molecular weight and degree of substitution of HES influence platelet number and volume after repeated administration. Thirty patients with cerebrovascular diseases were treated for 10 days with hemodilution. 500 to 1500 ml of HES 200/0.62(n=10), HES 200/0.5(n=10) or HES 40/0.5(n=10) were infused daily. During the first days, the number of platelets was not lowered beyond the dilution effect, but at the end of the therapy the number of platelets had increased in all 3 groups beyond the initial value. Platelet volume was lowered significantly in the 3 groups. HES 200/0.62 caused the largest drop in platelet volume (-10%, p<0.01). A possible explanation could be that HES macromolecules are attached to platelets or are phagocytized by them. The larger platelets are then broken down and, to compensate the loss, more thrombocytes are released. A correlation between the molecular weight of HES and the breakdown rate of the platelets can be suspected, because HES 200/0.62 has the highest intravascular mean molecular weight(121 kD) and the largest effect on platelet volume. PMID:8598237

  20. On high-order accurate weighted essentially non-oscillatory and discontinuous Galerkin schemes for compressible turbulence simulations.

    PubMed

    Shu, Chi-Wang

    2013-01-13

    In this article, we give a brief overview on high-order accurate shock capturing schemes with the aim of applications in compressible turbulence simulations. The emphasis is on the basic methodology and recent algorithm developments for two classes of high-order methods: the weighted essentially non-oscillatory and discontinuous Galerkin methods. PMID:23185054

  1. Structural determinants in a library of low molecular weight gelators.

    PubMed

    Morris, Kyle L; Chen, Lin; Rodger, Alison; Adams, Dave J; Serpell, Louise C

    2015-02-14

    Low molecular weight hydrogels are formed by molecules that form a matrix that immobilises water to form a self-supporting gel. Such gels have uses as biomaterials such as molecular scaffolds and structures for tissue engineering. One class of low molecular weight gelator (LMWG), naphthalene-conjugated dipeptides, has been shown to form hydrogels via self-assembly following a controlled drop in pH. A library of naphthalene-dipeptides has been generated previously although the relationship between the precursor sequence and the resulting self-assembled structures remained unclear. Here, we have investigated the structural details of a set of dipeptide sequences containing alanine (A) and valine (V) conjugated to naphthalene groups substituted with a Br, CN or H at the 6-position. Electron microscopy, circular dichroism and X-ray fibre diffraction shows that these LMWG may be structurally classified by their composition: the molecular packing is determined by the class of conjugate, whilst the chirality of the self-assemblies can be attributed to the dipeptide sequence. This provides insights into the relationship between the precursor sequence and the macromolecular and molecular structures of the fibres that make up the resulting hydrogels. PMID:25562785

  2. Recent Developments in Low Molecular Weight Complement Inhibitors

    PubMed Central

    Qu, Hongchang; Ricklin, Daniel; Lambris, John D.

    2009-01-01

    As a key part of the innate immune system, complement plays an important role not only in defending invading pathogens but also in many other biological processes. Inappropriate or excessive activation of complement has been linked to many autoimmune, inflammatory, and neurodegenerative diseases, as well as ischemia-reperfusion injury and cancer. A wide array of low molecular weight complement inhibitors has been developed to target various components of the complement cascade. Their efficacy has been demonstrated in numerous in vitro and in vivo experiments. Though none of these inhibitors has reached the market so far, some of them have entered clinical trials and displayed promising results. This review provides a brief overview of the currently developed low molecular weight complement inhibitors, including short peptides and synthetic small molecules, with an emphasis on those targeting components C1 and C3, and the anaphylatoxin receptors. PMID:19800693

  3. Liquid-phase oxidation of low-molecular weight olefins

    SciTech Connect

    Bulygin, M.G.; Boboleva, S.P.

    1982-01-01

    The use of various heterogeneous catalysts and variation of process conditions enable oxidation of low-molecular weight olefins to be carried out at the double bond either with the formation of oxides of glycols, or in the ..cap alpha..-position in relation to the double bond, with retention of the double bond and the formation of metacrolein (in the case of isobutylene). 8 references, 2 tables.

  4. Ultra-High-Molecular-Weight Silphenylene/Siloxane Elastomers

    NASA Technical Reports Server (NTRS)

    Hundley, N. H.; Patterson, W. J.

    1989-01-01

    Elastomers enhance thermal and mechancial properties. Capable of performing in extreme thermal/oxidative environments and having molecular weights above 10 to the sixth power prepared and analyzed in laboratory experiments. Made of methylvinylsilphenylene-siloxane terpolymers, new materials amenable to conventional silicone-processing technology. Similarly formulated commercial methyl-vinyl silicones, vulcanized elastomers exhibit enhance thermal/oxidative stability and equivalent or superior mechanical properties.

  5. High molecular weight polysaccharide that binds and inhibits virus

    DOEpatents

    Konowalchuk, Thomas W

    2014-01-14

    This invention provides a high molecular weight polysaccharide capable of binding to and inhibiting virus and related pharmaceutical formulations and methods on inhibiting viral infectivity and/or pathogenicity, as well as immunogenic compositions. The invention further methods of inhibiting the growth of cancer cells and of ameliorating a symptom of aging. Additionally, the invention provides methods of detecting and/or quantifying and/or isolating viruses.

  6. Low molecular weight protein tyrosine phosphatases: small, but smart

    Microsoft Academic Search

    G. Raugei; G. Ramponi; P. Chiarugi

    2002-01-01

    :   Low molecular weight protein tyrosine phosphatases (LMW-PTPs) are a family of 18-kDa enzymes involved in cell growth regulation.\\u000a Despite very limited sequence similarity to the PTP superfamily, they display a conserved signature motif in the catalytic\\u000a site. LMW-PTP associates and dephosphorylate many growth factor receptors, such as platelet-derived growth factor receptor\\u000a (PDGF-r), insulin receptor and ephrin receptor, thus downregulating

  7. Standard Heparin versus Low-Molecular-Weight Heparin

    Microsoft Academic Search

    Sergio Stefoni; Giuseppe Cianciolo; Gabriele Donati; Luigi Colì; Gaetano La Manna; Concettina Raimondi; Vittorio Dalmastri; Valentina Orlandi; Francesca D’Addio

    2002-01-01

    Background: To compare standard heparin (SH) and low molecular weight heparin (LMWH) in terms of anticoagulation, platelet activation and lipid metabolism, we selected 54 patients who had been on 4-hour hemodialysis three times weekly for at least 12 months, without bleeding disorders or dyslipidemic diseases. 28 were on hemodialysis with Polysulfone low-flux, 26 were on hemodiafiltration with Polysulfone high-flux. All

  8. Influence of Molecular Weight on the Mechanical Performance of a Thermoplastic Glassy Polyimide

    NASA Technical Reports Server (NTRS)

    Nicholson, Lee M.; Whitley, Karen S.; Gates, Thomas S.; Hinkley, Jeffrey A.

    1999-01-01

    Mechanical Testing of an advanced thermoplastic polyimide (LaRC-TM-SI) with known variations in molecular weight was performed over a range of temperatures below the glass transition temperature. The physical characterization, elastic properties and notched tensile strength were all determined as a function of molecular weight and test temperature. It was shown that notched tensile strength is a strong function of both temperature and molecular weight, whereas stiffness is only a strong function of temperature. A critical molecular weight (Mc) was observed to occur at a weight-average molecular weight (Mw) of approx. 22000 g/mol below which, the notched tensile strength decreases rapidly. This critical molecular weight transition is temperature-independent. Furthermore, inelastic analysis showed that low molecular weight materials tended to fail in a brittle manner, whereas high molecular weight materials exhibited ductile failure. The microstructural images supported these findings.

  9. Buckling in polymer monolayers: Molecular-weight dependence

    SciTech Connect

    Srivastava, S.; Basu, J.K.; (IIS)

    2010-11-12

    We present systematic investigations of buckling in Langmuir monolayers of polyvinyl acetate formed at the air-water interface. On compression the polymer monolayers are converted to a continuous membrane with a thickness of {approx}2-3 nm of well-defined periodicity, {lambda}{sub b}. Above a certain surface concentration the membrane undergoes a morphological transition buckling, leading to the formation of striped patterns. The periodicity seems to depend on molecular weight as per the predictions of the gravity-bending buckling formalism of Milner et al. for fluidlike films on water. However anomalously low values of bending rigidity and Young's modulus are obtained using this formalism. Hence we have considered an alternative model of buckling-based solidlike films on viscoelastic substrates. The values of bending rigidity and Young's modulus obtained by this method, although lower than expected, are closer to the bulk values. Remarkably, no buckling is found to occur above a certain molecular weight. We have tried to explain the observed molecular-weight dependence in terms of the variation in isothermal compressive modulus of the monolayers with surface concentration as well as provided possible explanations for the obtained low values of mechanical properties similar to that observed for ultrathin polymer films.

  10. Molecular Weight Dependence of Spreading Rates of Ultrathin Polymeric Films

    E-print Network

    M. P. Valignat; G. Oshanin; S. Villette; A. M. Cazabat; M. Moreau

    1998-04-24

    We study experimentally the molecular weight $M$ dependence of spreading rates of molecularly thin precursor films, growing at the bottom of droplets of polymer liquids. In accord with previous observations, we find that the radial extension R(t) of the film grows with time as R(t) = (D_{exp} t)^{1/2}. Our data substantiate the M-dependence of D_{exp}; we show that it follows D_{exp} \\sim M^{-\\gamma}, where the exponent \\gamma is dependent on the chemical composition of the solid surface, determining its frictional properties with respect to the molecular transport. In the specific case of hydrophilic substrates, the frictional properties can be modified by the change of the relative humidity (RH). We find that \\gamma \\approx 1 at low RH and tends to zero when RH gets progressively increased. We propose simple theoretical arguments which explain the observed behavior in the limits of low and high RH.

  11. 21 CFR 178.3750 - Polyethylene glycol (mean molecular weight 200-9,500).

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ...2011-04-01 2011-04-01 false Polyethylene glycol (mean molecular weight 200-9...and Production Aids § 178.3750 Polyethylene glycol (mean molecular weight 200-9,500). Polyethylene glycol identified in this...

  12. 21 CFR 178.3750 - Polyethylene glycol (mean molecular weight 200-9,500).

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ...2010-04-01 2009-04-01 true Polyethylene glycol (mean molecular weight 200-9...and Production Aids § 178.3750 Polyethylene glycol (mean molecular weight 200-9,500). Polyethylene glycol identified in this...

  13. 21 CFR 178.3750 - Polyethylene glycol (mean molecular weight 200-9,500).

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ...2012-04-01 2012-04-01 false Polyethylene glycol (mean molecular weight 200-9...and Production Aids § 178.3750 Polyethylene glycol (mean molecular weight 200-9,500). Polyethylene glycol identified in this...

  14. 21 CFR 178.3750 - Polyethylene glycol (mean molecular weight 200-9,500).

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ...2014-04-01 2014-04-01 false Polyethylene glycol (mean molecular weight 200-9...and Production Aids § 178.3750 Polyethylene glycol (mean molecular weight 200-9,500). Polyethylene glycol identified in this...

  15. 21 CFR 178.3750 - Polyethylene glycol (mean molecular weight 200-9,500).

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ...2013-04-01 2013-04-01 false Polyethylene glycol (mean molecular weight 200-9...and Production Aids § 178.3750 Polyethylene glycol (mean molecular weight 200-9,500). Polyethylene glycol identified in this...

  16. Drop formation and breakup of low viscosity elastic fluids: Effects of molecular weight and concentration

    E-print Network

    Drop formation and breakup of low viscosity elastic fluids: Effects of molecular weight of varying concentrations and molecular weights obtained from high speed imaging of the rate of change measurements. The effective relaxation times exhibit the expected scaling with molecular weight

  17. Capillary Modification by Noncovalent Polycation Adsorption: Effects of Polymer Molecular Weight

    E-print Network

    Dubin, Paul D.

    Capillary Modification by Noncovalent Polycation Adsorption: Effects of Polymer Molecular Weight was studied as a function of polymer molecular weight and coating ionic strength. By monitor- ing high molecular weight polycations at high ionic strength. Such capillaries can be used to elute

  18. ELSEVIER Marine Chemistry 56 (1997) 201-213 Photochemical production of low-molecular-weight carbonyl

    E-print Network

    1997-01-01

    ELSEVIER Marine Chemistry 56 (1997) 201-213 Photochemical production of low-molecular-weight a stainless steel screen, along with subsurface bulk seawater, and were analyzed for low-molecular-weight (LMW author.Present address: Wadsworth Center, Empire State Plaza/D514, Albany, NY 12201-0509, USA. Low-molecular-weight

  19. Dependence of Regioregular Poly(3-hexylthiophene) Film Morphology and Field-Effect Mobility on Molecular Weight

    E-print Network

    McGehee, Michael

    on Molecular Weight R. Joseph Kline, Michael D. McGehee,*, Ekaterina N. Kadnikova, Jinsong Liu, Jean M. J. Fre-average molecular weight (MW) of the conjugated polymer regioregular poly(3-hexylthiophene). Atomic force microscopy mobility of P3HT has been related to the regioregularity,18 number- average molecular weight (MW),19

  20. Using Protein Charge Ladders To Estimate the Effective Charges and Molecular Weights of

    E-print Network

    Gao, Jinming

    Using Protein Charge Ladders To Estimate the Effective Charges and Molecular Weights of Proteins electrophoresis (CE) and protein charge ladders to estimate values of effective charge (Z) and molecular weight to obtain by any other procedure. A secondary value of the method is to estimate values of molecular weight

  1. Facilitated Phospholipid Translocation across Vesicle Membranes Using Low-Molecular-Weight Synthetic

    E-print Network

    Smith, Bradley D.

    Facilitated Phospholipid Translocation across Vesicle Membranes Using Low-Molecular-Weight was reported by Moss, Ringsdorf, and co-workers,9 who showed that a high-molecular-weight, hydrophobically structures. Here, we report that the low-molecular- weight tris(aminoethyl)amine derivatives 1 and 2 (Scheme

  2. The Differential Effect of High and Low Molecular Weight Fucoidans on the Severity of

    E-print Network

    Lee, Won-Ha

    The Differential Effect of High and Low Molecular Weight Fucoidans on the Severity of Collagen studied.The effect of the treatment of high, medium and low molecular weight fucoidans (HMWF, MMWF are high-molecular-weight sulfated,fucose- rich polysaccharides, which are extracted from brown macroalgae

  3. Use of ultrasonic degradation to study the molecular weight influence of polymeric admixtures for mortars

    E-print Network

    Paris-Sud XI, Université de

    Use of ultrasonic degradation to study the molecular weight influence of polymeric admixtures to study the influence of the molecular weight of polysaccharidic admixtures on mortar properties. A wide range of admixtures with different molecular weight and constant structure was prepared. This has been

  4. Behavior of a Reverse Lamellar Phase in the Presence of Low Molecular Weight Triblock Molecules

    E-print Network

    Urbach, Wladimir

    Behavior of a Reverse Lamellar Phase in the Presence of Low Molecular Weight Triblock Molecules N molecular weight triblock molecules. So, we can wonder if these effects can also be induced by low molec lamellar phase upon the insertion of low molecular weight triblock molecules. Materials and Methods

  5. Author's personal copy Chemical and isotopic composition of high-molecular-weight dissolved organic

    E-print Network

    Guo, Laodong

    Author's personal copy Chemical and isotopic composition of high-molecular-weight dissolved organic of high-molecular-weight dissolved organic matter (HMW-DOM) in the mixing zone of the Mississippi River and transported in the high-molecular-weight (HMW) or colloidal phase

  6. Synthesis and biological activity of medium range molecular weight polymers containing

    E-print Network

    Theodorakis, Emmanuel

    Synthesis and biological activity of medium range molecular weight polymers containing exo-3®ed by FTIR, 1 H NMR and 13 C NMR spectroscopies. The apparent average molecular weights and polydispersity acid (ETCA); medium molecular weight; photopolymerization; in vitro cytotoxicity; in vivo antitumour

  7. Shifts in bacterial community structure associated with inputs of low molecular weight carbon compounds to soil

    E-print Network

    Minnesota, University of

    Shifts in bacterial community structure associated with inputs of low molecular weight carbon a c t Low molecular weight carbon (C) substrates are major drivers of bacterial activity and diversity in the soil environment. However, it is not well understood how specific low molecular weight C compounds

  8. Fluorescence spectroscopy and molecular weight distribution of extracellular polymers from full-scale activated sludge biomass

    Microsoft Academic Search

    M. Esparza-Soto; P. K. Westerhoff

    2001-01-01

    Two fractions of extracellular polymer substances (EPSs), soluble and readily extractable (RE), were characterised in terms of their molecular weight distributions (MWD) and 3-D excitation-emission- matrix (EEM) fluorescence spectroscopy signatures. The EPS fractions were different: the soluble EPSs were composed mainly of high molecular weight compounds, while the RE EPSs were composed of small molecular weight compounds. Contrary to previous

  9. Rapid isolation of metaphase chromosomes containing high molecular weight DNA

    PubMed Central

    1979-01-01

    Metaphase chromosomes with high molecular weight DNA were isolated from Chinese hamster ovary (CHO) cells in a neutral buffer containing polyamines and chelators. The individual, unfixed chromosomes retained their centromeric and secondary constrictions, distinct sister chromatids, and complex banding patterns. The DNA from these chromosomes was 100-fold larger (2 x 10(8) daltons) than DNA from chromosomes isolated by other procedures. These characteristics indicate preservation during isolation of considerable native structure. In contrast to chromosomes produced by other methods, these chromosomes were stable in storage and did not aggregate, thus providing useful material for studies of the structure and biochemistry of individual chromosomes. PMID:39081

  10. Accurate Parental Classification of Overweight Adolescents' Weight Status: Does It Matter?

    Microsoft Academic Search

    Dianne Neumark-Sztainer; Melanie Wall; Patricia van den Berg

    2010-01-01

    OBJECTIVE.Our goal was to explore whether parents of overweight adolescents who recognize that their children are overweight engage in behaviors that are likely to help their adolescents with long-term weight management. METHODS.The study population included overweight adolescents (BMI 85th percen- tile) who participated in Project EAT (Eating Among Teens) I (1999) and II (2004) and their parents who were interviewed

  11. Friction and Wear Behavior of Ultrahigh Molecular Weight Polyethylene as a Function of Crystallinity in the Presence of the

    E-print Network

    Lin, Zhiqun

    Friction and Wear Behavior of Ultrahigh Molecular Weight Polyethylene as a Function: In this study, the friction and wear behavior of ultrahigh molecular weight polyethylene (UHMWPE) were evaluated Words: ultrahigh molecular weight polyethylene (UHMWPE), crystallinity, friction, wear, phospholipid

  12. Mechanical Properties of LaRC(tm) SI Polymer for a Range of Molecular Weights

    NASA Technical Reports Server (NTRS)

    Whitley, Karen S.; Gates, Thomas S.; Hinkley, Jeffrey A.; Nicholson, Lee M.

    2000-01-01

    Mechanical testing of an advanced polyimide resin (LaRC(tm)-SI) with known variations in molecular weight was performed over a range of temperatures below the glass transition temperature. Elastic and inelastic properties were characterized as a function of molecular weight and test temperature. It was shown that notched tensile strength is a strong function of both temperature and molecular weight, whereas stiffness is only a strong function of temperature. The combined analysis of calculated yield stress and notched tensile strength indicated that low molecular weight materials tended to fail in a brittle manner, whereas high molecular weight materials exhibited ductile failure. The microphotographs of the failure surfaces also supported these findings.

  13. Controlling silk fibroin microspheres via molecular weight distribution.

    PubMed

    Zeng, Dong-Mei; Pan, Jue-Jing; Wang, Qun; Liu, Xin-Fang; Wang, Hui; Zhang, Ke-Qin

    2015-05-01

    Silk fibroin (SF) microspheres were produced by salting out SF solution via the addition of potassium phosphate buffer solution (K2HPO4-KH2PO4). The morphology, size and polydispersity of SF microspheres were adjusted by changing the molecular weight (MW) distribution and concentration of SF, as well as the ionic strength and pH of the buffer solution. Changing the conditions under which the SF fiber dissolved in the Lithium Boride (LiBr) solution resulted in altering the MW distribution of SF solution. Under optimal salting-out conditions (ionic strength>0.7M and pH>7) and using a smaller and narrower SF MW distribution, SF microspheres with smoother shapes and more uniform sizes were produced. Meanwhile, the size and polydispersity of the microspheres increased when the SF concentration was increased from 0.25mg/mL to 20mg/mL. The improved SF microspheres, obtained by altering the distribution of molecular weight, have potential in drug and gene delivery applications. PMID:25746265

  14. LARC-TPI 1500 series controlled molecular weight polyimide

    NASA Technical Reports Server (NTRS)

    Progar, Donald; St. Clair, Terry; Burks, Harold; Gautreaux, Carol; Yamaguchi, Akihiro

    1990-01-01

    LARC-TPI, a linear high temperature thermoplastic polyimide, was developed several years ago at NASA Langley Research Center. This material has been commercialized by Mitsui Toatsu Chemicals, Inc., Tokyo, Japan, as a varnish and powder. More recently, a melt-extruded film of a controlled molecular weight of this same polymer has been supplied to NASA Langley Research Center for evaluation. This new form, called LARC-TPI 1500 series, has been prepared in three molecular weights - high, medium and low flow polymers. The subject of this investigation deals with the rheological properties of the high and medium flow powders and the adhesive properties of the medium flow melt-extruded film. Rheological studies indicate that the high and medium flow forms of the polymer fall in the flow range of injection moldable materials. Adhesive data generated on the medium flow extruded film shows this form to be well suited for structural adhesive bonding. The data are as good or better than that for LARC-TPI data of previous studies.

  15. Effect of molecular weight on surface mobility of polystyrene films

    NASA Astrophysics Data System (ADS)

    Peng, Dongdong; Yang, Zhaohui; Tsui, Ophelia

    2011-03-01

    There have been mounting experimental results showing that a two-layer model is appropriate for describing the dynamics of polymer films. The model postulates that a surface mobile layer exists at the free surface and can modify the dynamics of the entire film. In a recent study, we measured the viscosity of unentangled, short-chain polystyrene (Mw=2.4kg/mol) films supported by silicon at different temperatures including the bulk Tg, and found that the data could be fully explained by assuming a surface mobile layer with a constant thickness exists and sits atop a bulk-like layer. In this talk, I will report the result we obtained by measuring the viscosity of polystyrene films with a wide range of molecular weights from 6.4 to 2316 kg/mol supported by silicon. Our result shows that the same two-layer model is applicable in describing the data if the mobility of the surface layer assumes a molecular weight dependence that differs from either the Rouse or Reptation model.

  16. Determination of molecular weight distributions in native and pretreated wood.

    PubMed

    Leskinen, Timo; Kelley, Stephen S; Argyropoulos, Dimitris S

    2015-03-30

    The analysis of native wood components by size-exclusion chromatography (SEC) is challenging. Isolation, derivatization and solubilization of wood polymers is required prior to the analysis. The present approach allowed the determination of molecular weight distributions of the carbohydrates and of lignin in native and processed woods, without preparative component isolation steps. For the first time a component selective SEC analysis of sawdust preparations was made possible by the combination of two selective derivatization methods, namely; ionic liquid assisted benzoylation of the carbohydrate fraction and acetobromination of the lignin in acetic acid media. These were optimized for wood samples. The developed method was thus used to examine changes in softwood samples after degradative mechanical and/or chemical treatments, such as ball milling, steam explosion, green liquor pulping, and chemical oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). The methodology can also be applied to examine changes in molecular weight and lignin-carbohydrate linkages that occur during wood-based biorefinery operations, such as pretreatments, and enzymatic saccharification. PMID:25563943

  17. Impact of molecular weight in four-branched star vectors with narrow molecular weight distribution on gene delivery efficiency.

    PubMed

    Nemoto, Yasushi; Borovkov, Alexey; Zhou, Yue-Min; Takewa, Yoshiaki; Tatsumi, Eisuke; Nakayama, Yasuhide

    2009-12-01

    A series of star-shaped cationic polymers, termed star vectors (SVs), has been developed as effective nonviral gene delivery carriers. In this study, we separated SVs into several fractions having different molecular weights with very narrow molecular weight distributions in order to examine in detail the influence of the molecular weight of the SVs on the gene transfection efficiency. As a model compound for several types of SVs, 4-branched poly(N,N-dimethylaminopropyl acrylamide) having a molecular weight (M(n)) of approximately 35 kDa and polydispersity of 1.6 was prepared by iniferter-based radical polymerization. The SVs were separated using size-exclusion chromatography to obtain seven fractions having M(n) ranging from 27 kDa to 73 kDa with polydispersity ranging from 1.1 to 1.2. All the fractionated SVs have similar pH of 10.2-10.4 and were able to interact with and condense luciferase-encoding plasmid deoxyribonucleic acid (DNA) to yield SV/DNA polyplexes. A water-soluble tetrazolium-1 (WST) assay showed that all SVs had minimal cellular cytotoxicity under an N/P charge ratio of 10. The critical micellar concentration decreased with an increase in the M(n) of the fractionated SVs; however, the particle size of the polyplexes, exclusion activity of ethidium bromide, and zeta-potential of the polyplexes increased. An in vitro evaluation using COS-1 cells at an N/P ratio of 10 showed that transfection activity increased almost linearly with M(n). The highest transfection activity was obtained for SVs with the highest M(n) (73 kDa), which was over 7 times that for the SVs with the lowest M(n) (27 kDa), the nonfractionated original SV, or PEI standard. The transfection efficiency was more correlated with the amphiphilicity or hydrophobicity of the SVs and the surface potential and condensate density of the polyplexes than with the particle size. PMID:19899789

  18. Molecular weight degradation and rheological properties of schizophyllan under ultrasonic treatment.

    PubMed

    Zhong, Kui; Zhang, Qi; Tong, Litao; Liu, Liya; Zhou, Xianrong; Zhou, Sumei

    2015-03-01

    Molecular weight degradation effects of schizophyllan (SPG) under ultrasonic treatments were investigated in this study. The degradation product was treated by alcohol fractional precipitation technology, and the molecular weight and rheological properties of ultrasonic-treated SPG (USPG) fractions were evaluated. Average molecular weight of SPG decreased significantly after ultrasonic treatments, and degradation product had more narrow distribution of molecular weight. The molecular weight degradation kinetics of SPG is adequately described by a second-order reaction. USPG fractions with different molecular weight were obtained by fractional precipitation for final alcohol concentration fractions 0-40%, 40-60% and 60-80%, respectively. USPG fractions had near-Newtonian flow behaviors, and USPG??% exhibited viscous responses over the entire accessible frequency range. Therefore, ultrasonic treatment is a viable modification technology for SPG and other polymer materials with high molecular weight. PMID:25263766

  19. Robust and accurate method for free-energy calculation of charged molecular systems

    NASA Astrophysics Data System (ADS)

    Anwar, Jamshed; Heyes, David M.

    2005-06-01

    A new approach is presented to eliminate the problem of creation and/or annihilation of atoms in free-energy calculations of charged molecular systems. The method employs a damping potential in the Ewald summation scheme, which is an exact solution of the electrostatics for three-dimensional periodic systems. The proposed method enables entire molecules to be mutated from a noninteracting (ideal) state in an efficient and robust way, thus providing a means by which accurate absolute free energies of structurally complex molecules can be determined. This methodology will enable chemical and phase equilibria to be determined for large molecular species with significant charge distributions, e.g., biomolecules and drugs.

  20. Detector response as a function of molecular weight and its effect on size exclusion chromatography molecular weight determination of polymer distributions

    Microsoft Academic Search

    Simon David Cook; Vicki S. Sible

    1997-01-01

    In size exclusion chromatography (SEC), if the response of the detector is not constant with molecular weight, the calculated molecular weights are not a true representation for the sample. Without response factors, or some other method of correcting the response for the specific polymer calibration standards used, the resulting distribution is biased. From literature references, it is known that polystyrene

  1. Tuning the superstructure of ultrahigh-molecular-weight polyethylene/low-molecular-weight polyethylene blend for artificial joint application.

    PubMed

    Xu, Ling; Chen, Chen; Zhong, Gan-Ji; Lei, Jun; Xu, Jia-Zhuang; Hsiao, Benjamin S; Li, Zhong-Ming

    2012-03-01

    An easy approach was reported to achieve high mechanical properties of ultrahigh-molecular-weight polyethylene (UHMWPE)-based polyethylene (PE) blend for artificial joint application without the sacrifice of the original excellent wear and fatigue behavior of UHMWPE. The PE blend with desirable fluidity was obtained by melt mixing UHMWPE and low molecular weight polyethylene (LMWPE), and then was processed by a modified injection molding technology-oscillatory shear injection molding (OSIM). Morphological observation of the OSIM PE blend showed LMWPE contained well-defined interlocking shish-kebab self-reinforced superstructure. Addition of a small amount of long chain polyethylene (2 wt %) to LMWPE greatly induced formation of rich shish-kebabs. The ultimate tensile strength considerably increased from 27.6 MPa for conventional compression molded UHMWPE up to 78.4 MPa for OSIM PE blend along the flow direction and up to 33.5 MPa in its transverse direction. The impact strength of OSIM PE blend was increased by 46% and 7% for OSIM PE blend in the direction parallel and vertical to the shear flow, respectively. Wear and fatigue resistance were comparable to conventional compression molded UHMWPE. The superb performance of the OSIM PE blend was originated from formation of rich interlocking shish-kebab superstructure while maintaining unique properties of UHMWPE. The present results suggested the OSIM PE blend has high potential for artificial joint application. PMID:22339721

  2. Preparation and characterization of water soluble high molecular weight ?-cyclodextrin-epichlorohydrin polymers

    Microsoft Academic Search

    E. Renard; A. Deratani; G. Volet; B. Sebille

    1997-01-01

    Water soluble ?-cyclodextrin polymers were prepared from ?-cyclodextrin crosslinked with epichlorohydrin under basic conditions. The influence of preparation conditions on the molecular weight distribution has been investigated. The knowledge of this relationship allows for the choice of reaction parameters according to the desired weight distribution of the ?-cyclodextrin polymer. A procedure was developed for the preparation of high molecular weight

  3. Variability of Low-Molecular-Weight, Heat-Modifiable Outer Membrane Proteins of Neisseria meningitidis

    PubMed Central

    Poolman, J. T.; De Marie, S.; Zanen, H. C.

    1980-01-01

    Analysis of major outer membrane protein (MOMP) profiles of various meningococci by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis (SDS-PAGE) revealed the presence of 0 to 2 low-molecular-weight, heat-modifiable MOMPs (molecular weight, 25,000 to 32,000) and 1 to 3 high-molecular-weight MOMPs (molecular weight, 32,000 to 46,000). Heat modifiability was investigated by comparing MOMP profiles after heating in SDS solutions at 100°C for 5 min or at 40°C for 1 h. Low-molecular-weight MOMPs shifted to higher apparent molecular weights after being heated at 100°C. Heat modifiability of high-molecular-weight MOMPs varied among strains; whenever modified these proteins shifted to lower apparent molecular weights after complete denaturation. Variability of low-molecular-weight, heat-modifiable MOMPs was demonstrated when MOMP profiles were compared of (i) isolates from index cases and associated cases and carriers among contacts, (ii) different isolates from the same individual, and (iii) isolates from a small epidemic caused by serogroup W-135. In some cases high-molecular-weight MOMPs revealed quantitative differences among related strains. The observed variability and quantitative differences indicate that MOMP serotyping and typing on the basis of SDS-PAGE profiles (PAGE typing) need careful reevaluation. ImagesFig. 1Fig. 2Fig. 3Fig. 4 PMID:6785230

  4. Apparatus and method of determining molecular weight of large molecules

    DOEpatents

    Fuerstenau, S.; Benner, W.H.; Madden, N.M.; Searles, W.

    1998-06-23

    A mass spectrometer determines the mass of multiply charged high molecular weight molecules. This spectrometer utilizes an ion detector which is capable of simultaneously measuring the charge z and transit time of a single ion as it passes through the detector. From this transit time, the velocity of the single ion may then be derived, thus providing the mass-to-charge ratio m/z for a single ion which has been accelerated through a known potential. Given z and m/z, the mass m of the single ion can then be calculated. Electrospray ions with masses in excess of 1 MDa and charge numbers greater than 425 e{sup {minus}} are readily detected. The on-axis single ion detection configuration enables a duty cycle of nearly 100% and extends the practical application of electrospray mass spectrometry to the analysis of very large molecules with relatively inexpensive instrumentation. 14 figs.

  5. Apparatus and method of determining molecular weight of large molecules

    DOEpatents

    Fuerstenau, Stephen (Montrose, CA); Benner, W. Henry (Danville, CA); Madden, Norman (Livermore, CA); Searles, William (Fremont, CA)

    1998-01-01

    A mass spectrometer determines the mass of multiply charged high molecular weight molecules. This spectrometer utilizes an ion detector which is capable of simultaneously measuring the charge z and transit time of a single ion as it passes through the detector. From this transit time, the velocity of the single ion may then be derived, thus providing the mass-to-charge ratio m/z for a single ion which has been accelerated through a known potential. Given z and m/z, the mass m of the single ion can then be calculated. Electrospray ions with masses in excess of 1 MDa and charge numbers greater than 425 e.sup.- are readily detected. The on-axis single ion detection configuration enables a duty cycle of nearly 100% and extends the practical application of electrospray mass spectrometry to the analysis of very large molecules with relatively inexpensive instrumentation.

  6. Molecular Weight Dependent Kernels in Generalized Mixing Rules

    E-print Network

    Wolfgang Thimm; Christian Friedrich; Tobias Roths; Josef Honerkamp

    2000-06-15

    In this paper, a model is proposed for the kernel in the generalized mixing rule recently formulated by Anderssen and Mead (1998). In order to derive such a model, it is necessary to take account of the rheological significance of the kernel in terms of the relaxation behaviour of the individual polymers involved. This leads naturally to consider a way how additional physical effects, which depend on the molecular weight distribution, can be included in the mixing rule. The advantage of this approach is that, without changing the generality derived by Anderssen and Mead (1998), the choice of the model proposed here for the kernel guarantees the enhanced physical and rheological significance of their mixing rule.

  7. Chemoenzymatic Synthesis of Homogeneous Ultralow Molecular Weight Heparins

    PubMed Central

    Xu, Yongmei; Masuko, Sayaka; Takieddin, Majde; Xu, Haoming; Liu, Renpeng; Jing, Juliana; Mousa, Shaker A.; Linhardt, Robert J.; Liu, Jian

    2012-01-01

    Ultralow molecular weight (ULMW) heparins are sulfated glycans that are clinically used to treat thrombotic disorders. ULMW heparins range from 1500 to 3000 daltons, corresponding from 5 to 10 saccharide units. The commercial drug Arixtra (fondaparinux sodium) is a structurally homogeneous ULMW heparin pentasaccharide that is synthesized through a lengthy chemical process. Here, we report 10- and 12-step chemoenzymatic syntheses of two structurally homogeneous ULMW heparins (MW = 1778.5 and 1816.5) in 45 and 37% overall yield, respectively, starting from a simple disaccharide. These ULMW heparins display excellent in vitro anticoagulant activity and comparable pharmacokinetic properties to Arixtra, as demonstrated in a rabbit model. The chemoenzymatic approach is scalable and shows promise for a more efficient route to synthesize this important class of medicinal agent. PMID:22034431

  8. Low-molecular-weight xylanase from Trichoderma viride

    SciTech Connect

    Ujiie, M.; Roy, C.; Yaguchi, M. (Inst. of Biological Sciences, Ottawa (Canada))

    1991-06-01

    An endo-1,4-{beta}-xylanase (1,4-{beta}-D-xylan xylanohydrolase, EC 3.2.1.8) has been isolated from a commercial proparation of Trichoderma viride. The molecular weight was 22,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and the pI value was 9.3. The xylanase was a true xylanase without cellulase activity. When the N-terminal amino acid sequence of thew first 50 residues was compared with that of a xylanase from Schizophyllum commune, strong evidence for homology was found, with more than 50% amino acid identity. T. viride xylanase also possessed extensive identity with a proposed amino-terminal consensus sequence of xylanases from bacteria.

  9. Excretion of low molecular weight heparin in human milk

    PubMed Central

    Richter, Christiane; Sitzmann, Jörg; Lang, Pierre; Weitzel, Hans; Huch, Albert; Huch, Renate

    2001-01-01

    Aims The excretion of low molecular weight heparin (LMWH) in breast milk was investigated in 15 lactating mothers after Caesarean section. Methods Blood and milk samples were collected before and 3–4 h after once daily routine subcutaneous injection of 2500 IU dalteparin. Anti-Xa activity was measured by an assay utilizing prolonged clotting times in plasma or breast milk as an index of LMWH activity. Results Plasma anti-Xa activities ranged from 0.074 to 0.308 IU ml?1 of plasma. Anti-Xa activities in breast milk ranged from < 0.005–0.037 IU ml?1 of milk. This is equivalent to a milk/plasma ratio of < 0.025–0.224. Conclusions Therefore, it appears highly unlikely that puerperal thromboprophylaxis with LMWH has any clinically relevant effect on the nursing infant. PMID:11736885

  10. Morphology of chemically crosslinked ultrahigh molecular weight polyethylene.

    PubMed

    Shen, F W; McKellop, H A; Salovey, R

    1998-07-01

    Morphological characterization of chemically crosslinked ultrahigh molecular weight polyethylene was performed by differential scanning calorimetry and scanning electron microscopy. The lamellar thickness of nascent UHMWPE inferred from DSC endotherms showed a very broad distribution, which was reduced significantly after melting and recrystallizing in DSC. Peroxide crosslinking further reduced the lamellar thickness distribution compared to uncrosslinked samples. After gamma-irradiation, a slowly cooled peroxide-free sample showed a greater increase in lamellar thickness distribution. Examination of the morphology of freeze-fractured surfaces by SEM showed that a slowly cooled peroxide-free UHMWPE exhibited a rougher fracture while chemically crosslinked samples showed a smoother fracture. After compression molding at 300 degrees C for 2 h, the grain boundaries between particles disappeared for all UHMWPE samples, indicating a complete fusion of the original flakes. PMID:9641626

  11. Ultra-high molecular weight silphenylene-siloxane polymers

    NASA Technical Reports Server (NTRS)

    Patterson, W. J.; Hundley, N. H.; Ludwick, L. M.

    1984-01-01

    Silphenylene-siloxane copolymers with molecular weights above one million were prepared using a two stage polymerization technique. The technique was successfully scaled up to produce 50 grams of this high polymer in a single run. The reactive monomer approach was also investigated using the following aminosilanes: bis(dimethylamino)dimethylsilane, N,N-bis(pyrrolidinyl)dimethylsilane and N,N-bis(gamma-butyrolactam)dimethylsilane). Thermal analyses were performed in both air and nitrogen. The experimental polymers decomposed at 540 to 562 C, as opposed to 408 to 426 C for commercial silicones. Differential scanning calorimetry showed a glass transition (Tg) at -50 to -55 C for the silphenylene-siloxane copolymer while the commercial silicones had Tg's at -96 to -112 C.

  12. Dairy Wastewater Treatment Using Low Molecular Weight Crab Shell Chitosan

    NASA Astrophysics Data System (ADS)

    Geetha Devi, M.; Dumaran, Joefel Jessica; Feroz, S.

    2012-08-01

    The investigation of possible use of low molecular weight crab shell chitosan (MW 20 kDa) in the treatment of dairy waste water was studied. Various experiments have been carried out using batch adsorption technique to study the effects of the process variables, which include contact time, stirring speed, pH and adsorbent dosage. Treated effluent characteristics at optimum condition showed that chitosan can be effectively used as adsorbent in the treatment of dairy wastewater. The optimum conditions for this study were at 150 mg/l of chitosan, pH 5 and 50 min of mixing time with 50 rpm of mixing speed. Chitosan showed the highest performance under these conditions with 79 % COD, 93 % turbidity and 73 % TSS reduction. The result showed that chitosan is an effective coagulant, which can reduce the level of COD, TSS and turbidity in dairy industry wastewater.

  13. Phosphorylation of a high molecular weight DNA polymerase. cap alpha

    SciTech Connect

    Donaldson, R.W.; Gerner, E.W.

    1987-02-01

    Anti-human DNA polymerase ..cap alpha.. murine IgG SJK-287-38 neutralized DNA polymerase ..cap alpha.. activity from rat embryonic fibroblasts infected with a temperature-sensitive transformation mutant of Rous sarcoma virus (tsLA24). After centrifugation of a crude cytosol fraction from log-phase cells in a 5-20% linear sucrose gradient, polypeptides of M/sub r/ approx. 185,000 and 220,000 were immunoprecipitated only from gradient fractions containing DNA polymerase ..cap alpha.. activity. When similar cultures were incubated in medium containing (/sup 32/P)orthophosphate, it was found that the M/sub r/ 220,000 protein was phosphorylated but that the other peptides specific for polymerase ..cap alpha.. activity did not contain detectable amounts of phosphate. Phospho amino acid analysis of the high molecular weight immunoprecipitable proteins indicated that the labeled amino acid was phosphoserine. Incubation of 2.5 units of crude DNA polymerase ..cap alpha.. with 4 units of agarose-immobilized alkaline phosphatase resulted in a nearly complete inhibition of DNA polymerase ..cap alpha.. activity. Subsequent incubation of this preparation with 5 or 50 ..mu..M ATP, but not the nonhydrolyzable analog adenosine 5'-(..gamma..-thio)triphosphate, restored the in vitro DNA polymerizing activity. These results demonstrate that a high molecular weight DNA polymerase ..cap alpha.. is phosphorylated in cultured cells and that this protein is a substrate for a serine kinase rather than the tyrosine-specific protein kinase of Rous sarcoma virus. The results suggest that phosphorylation/dephosphorylation reactions modulate the activity of this polymerase.

  14. [Anaphylactic reactions to low-molecular weight chemicals].

    PubMed

    Nowak, Daria; Panaszek, Bernard

    2015-01-01

    Low-molecular weight chemicals (haptens) include a large group of chemical compounds occurring in work environment, items of everyday use (cleaning products, clothing, footwear, gloves, furniture), jewelry (earrings, bracelets), drugs, especially in cosmetics. They cause type IV hypersensitive reactions. During the induction phase of delayed-type hypersensitivity, haptens form complexes with skin proteins. After internalization through antigen presenting cells, they are bound to MHC class II molecules. Next, they are exposed against specific T-lymphocytes, what triggers activation of Th1 cells mainly. After repeating exposition to that hapten, during effector phase, Th1 induce production of cytokines affecting non-specific inflammatory cells. Usually, it causes contact dermatitis. However, occasionally incidence of immediate generalized reactions after contact with some kinds of haptens is noticed. A question arises, how the hapten does induce symptoms which are typical for anaphylaxis, and what contributes to amplification of this mechanism. It seems that this phenomenon arises from pathomechanism occurring in contact urticaria syndrome in which an anaphylactic reaction may be caused either by contact of sensitized skin with protein antigens, high-molecular weight allergens, or haptens. One of the hypotheses indicates the leading role of basophiles in this process. Their contact with haptens, may cause to release mediators of immediate allergic reaction (histamine, eicosanoids) and to produce cytokines corresponding to Th2 cells profile. Furthermore, Th17 lymphocytes secreting pro-inflammatory interleukin-17 might be engaged into amplifying hypersensitivity into immediate reactions and regulatory T-cells may play role in the process, due to insufficient control of the activity of effector cells. PMID:25661919

  15. Successful use of low molecular weight heparin in intracardiac thrombus of an extremely low birth weight infant.

    PubMed

    Shin, Ji-hye; Kim, Gee-na; Kil, Hong-ryang; Chang, Mea-young

    2013-09-01

    The sick premature infants have high risk for thrombosis. Although therapeutic options include close observation, anticoagulation, thrombolytic therapy, and thrombectomy, guidelines for the management of neonatal arterial and venous thrombosis vary greatly among different centers. The authors report their experience using low molecular weight heparin (enoxaparin), with safe and successful resolution of right atrial thrombus, in an extremely low birth weight infant. PMID:22798281

  16. Molecular-weight-dependent mobilities in regioregular poly,,3-hexyl-thiophene... diodes

    E-print Network

    McGehee, Michael

    Molecular-weight-dependent mobilities in regioregular poly,,3-hexyl-thiophene... diodes Chiatzun as the molecular weight MW is increased from 3.2 to 31.1 kg/mol.10 The MW was found to affect the way chains pack in the direction perpendicular to the substrate of regioregular poly 3-hexyl-thiophene of different molecular

  17. High molecular weight coffee melanoidins are inhibitors for matrix metalloproteases.

    PubMed

    De Marco, Leticia Missagia; Fischer, Sarah; Henle, Thomas

    2011-11-01

    High molecular (above 10 kDa) melanoidins isolated from coffee beans of varying roasting degree were found to be efficient inhibitors for the zinc-containing matrix metalloproteases MMP-1, MMP-2, and MMP-9 with IC(50) values ranging between 0.2 and 1.1 mg/mL in vitro. The inhibitory potential increased with roasting degree. No or only slight inhibition of other zinc-containing peptidases closely related to MMPs, namely, Clostridium histolyticum collagenase and angiotensin converting enzyme, was found, indicating specific structural features of melanoidins to be responsible for the interaction with MMPs. A continuous increase on the apparent molecular weight of melanoidins as well as incorporation of phenolic substances into the melanoidin structure with progress of roasting was observed, concomitant with a significant increase in the carbon/nitrogen of the melanoidins. This suggests that the melanoidins are mainly formed by incorporation of carbohydrates and phenolic compounds onto a proteinaceous backbone. As MMP-1, MMP-2, and MMP-9 play a pivotal role in pathogenesis of colorectal cancer, studies on possible physiological effects of melanoidins are mandatory. PMID:21961901

  18. Distribution of molecular weight in glyceride polymerizates or aggregates of them after contact with lunar grains

    NASA Technical Reports Server (NTRS)

    Asunmaa, S. K.; Haack, R.

    1977-01-01

    An attempt is made to report on experiments in which a molecular-weight increase was determined in thin layers of triglyceride-containing glycerides after thin-layer contact for two years with lunar topsoil grains at 25 C without any thermal activation. It is noted that solidification was observed on both dielectric grains and metal-rich areas and that changes in viscosity and molecular weights were first detected by solidification of surface layers. Gel permeation chromatography is described which detected a general shift of the Gaussian distribution of the molecular-weight data toward generally higher molecular weights as well as an increase in mean molecular weight. Reaction mechanisms are considered, and results of spectrographic analysis are cited which support the interpretations of the molecular-weight data.

  19. Two-dimensional spatial coherence of excitons in semicrystalline polymeric semiconductors: The effect of molecular weight

    E-print Network

    Paquin, Francis; Hestand, Nicholas J; Sakowicz, Maciej; Bérubé, Nicolas; Côté, Michel; Reynolds, Luke X; Haque, Saif A; Stingelin, Natalie; Spano, Frank C; Silva, Carlos

    2013-01-01

    The electronic properties of macromolecular semiconductor thin films depend profoundly on their solid-state microstructure, which in turn is governed, among other things, by the processing conditions selected and the polymer chemical nature and molecular weight. Specifically, low-molecular-weight materials form crystalline domains of cofacially $\\pi$-stacked molecules, while the usually entangled nature of higher molecular-weight polymers leads to microstructures comprised of molecularly ordered crystallites interconnected by amorphous regions. Here, we examine the interplay between extended exciton states delocalized along the polymer backbones and across polymer chains within the $\\pi$-stack, depending on the structural development with molecular weight. We combine optical spectroscopies, thermal probes, and theoretical modeling, focusing on neat poly(3-hexylthiophene) (P3HT), one of the most extensively studied polymer semiconductors, of weight-average molecular weight of 3-450\\,kg/mol. The spatial coheren...

  20. Size and shape of soil humic acids estimated by viscosity and molecular weight

    Microsoft Academic Search

    Masayuki Kawahigashi; Hiroaki Sumida; Kazuhiko Yamamoto

    2005-01-01

    Ultrafiltration fractions of three soil humic acids were characterized by viscometry and high performance size-exclusion chromatography (HPSEC) in order to estimate shapes and hydrodynamic sizes. Intrinsic viscosities under given solute\\/solvent\\/temperature conditions were obtained by extrapolating the concentration dependence of reduced viscosities to zero concentration. Molecular mass (weight average molecular weight (M¯w) and number average molecular weight (M¯n)) and hydrodynamic radius

  1. Effects of molecular entanglements during electrospray of high molecular weight polymers

    Microsoft Academic Search

    Reinhard Festag; Spiro D. Alexandratos; David C. Joy; Bernhard Wunderlich; Brian Annis; Kelsey D. Cook

    1998-01-01

    Concentration-dependent bimodal size distributions (comprised of single-molecule particles and multimolecule clusters) observed\\u000a by microscopic examination of particles collected during electrospray (ES) of dilute solutions of high molecular weight polymers\\u000a suggest that chain entanglement can interfere with the droplet subdivisions believed to be intrinsic to the electrospray process.\\u000a The feasibility of such interference is discussed in the context of the spray

  2. Synthesis of a Low-Molecular-Weight Form of Exopolysaccharide by Bradyrhizobium japonicum USDA 110

    PubMed Central

    Louch, Heather A.; Miller, Karen J.

    2001-01-01

    A novel extracellular low-molecular-weight polysaccharide was detected as a contaminant within extracellular cyclic ?-1,6-?-1,3-glucan preparations from Bradyrhizobium japonicum USDA 110 cultures. Compositional analysis, methylation analysis, and nuclear magnetic resonance analysis revealed that this low-molecular-weight polysaccharide was composed of the same pentasaccharide repeating unit previously described for the high-molecular-weight form of the exopolysaccharide (EPS) synthesized by B. japonicum strains. Mass spectrometry analysis indicated that the size of this low-molecular-weight form of EPS was consistent with a dimeric form of the pentasaccharide repeating unit. PMID:11157281

  3. Molecular weight dependence of LB morphology of poly(n-hexyl isocyanate) (PHIC).

    PubMed

    Morioka, Takako; Shibata, Osamu; Kawaguchi, Masami

    2010-12-01

    The morphologies of Langmuir-Blodgett (LB) films of two fractionated poly(n-hexyl isocyanate) (PHIC) and those of their binary mixtures were observed by AFM, together with those of an unfractionated PHIC. The low molecular weight PHIC formed random packing of bundles consisting of rigid rods, while the high molecular weight PHIC formed random packing of bundles consisting of hairy rods. Bundle interpenetration was observed only for the latter in the semidilute regime. In the bilayer region, the area occupied by the PHIC bundles in the upper layer was obviously smaller for the high molecular weight PHIC than for the low molecular weight PHIC, suggesting that the bundles of high molecular weight PHIC more easily interpenetrate than those of low molecular weight PHIC. For the blended films composed of both low and high molecular weight PHICs, the characteristic morphologies of the respective PHIC samples were no longer present. Moreover, the morphologies of the blended films appeared to resemble each other at any molar fraction owing to the ideal miscibility of the low molecular weight and high molecular weight PHICs. The morphologies of the blended films were also similar to that of the unfractionated PHIC film in the dilute regime. In the semidilute regime, the blended films became rounded owing to an increase in bundles interpenetration between PHICs as compared to that in the dilute regime, whereas the morphology of unfractionated PHIC films remained unchanged as compared to that in the dilute regime. PMID:21028864

  4. Tissue integrity signals communicated by high-molecular weight hyaluronan and the resolution of inflammation

    PubMed Central

    Ruppert, S. M.; Hawn, T. R.; Arrigoni, A.; Wight, T. N.

    2014-01-01

    The extracellular matrix polysaccharide hyaluronan (HA) exerts size-dependent effects on leukocyte behavior. Low-molecular weight HA is abundant at sites of active tissue catabolism and promotes inflammation via effects on Toll-like receptor signaling. Conversely, high-molecular weight HA is prevalent in uninjured tissues and is anti-inflammatory. We propose that the ability of high-molecular weight but not low-molecular weight HA to cross-link CD44 functions as a novel form of pattern recognition that recognizes intact tissues and communicates “tissue integrity signals” that promote resolution of local immune responses. PMID:24614953

  5. Tissue integrity signals communicated by high-molecular weight hyaluronan and the resolution of inflammation.

    PubMed

    Ruppert, S M; Hawn, T R; Arrigoni, A; Wight, T N; Bollyky, P L

    2014-05-01

    The extracellular matrix polysaccharide hyaluronan (HA) exerts size-dependent effects on leukocyte behavior. Low-molecular weight HA is abundant at sites of active tissue catabolism and promotes inflammation via effects on Toll-like receptor signaling. Conversely, high-molecular weight HA is prevalent in uninjured tissues and is anti-inflammatory. We propose that the ability of high-molecular weight but not low-molecular weight HA to cross-link CD44 functions as a novel form of pattern recognition that recognizes intact tissues and communicates "tissue integrity signals" that promote resolution of local immune responses. PMID:24614953

  6. Application of the G-JF discrete-time thermostat for fast and accurate molecular simulations

    NASA Astrophysics Data System (ADS)

    Grønbech-Jensen, Niels; Hayre, Natha Robert; Farago, Oded

    2014-02-01

    A new Langevin-Verlet thermostat that preserves the fluctuation-dissipation relationship for discrete time steps is applied to molecular modeling and tested against several popular suites (AMBER, GROMACS, LAMMPS) using a small molecule as an example that can be easily simulated by all three packages. Contrary to existing methods, the new thermostat exhibits no detectable changes in the sampling statistics as the time step is varied in the entire numerical stability range. The simple form of the method, which we express in the three common forms (Velocity-Explicit, Störmer-Verlet, and Leap-Frog), allows for easy implementation within existing molecular simulation packages to achieve faster and more accurate results with no cost in either computing time or programming complexity.

  7. Cytoarchitecture of the mouse neocortex revealed by the low-molecular-weight neurofilament protein subunit.

    PubMed

    Paulussen, Melissa; Jacobs, Sandy; Van der Gucht, Estelle; Hof, Patrick R; Arckens, Lutgarde

    2011-09-01

    The expression patterns of the medium- and high-molecular-weight subunits of the neurofilament protein triplet have been extensively studied in several neuroanatomical studies. In the present study, we report the use of the low-molecular-weight neurofilament protein subunit (NF-L) as a reliable marker within the neurofilament protein family to reveal the regional architecture of mammalian neocortex. We document clearly its usefulness in anatomical parcellation studies and report unique expression patterns of NF-L throughout the mouse neocortex. NF-L was most abundant in the somatosensory cortex, the lateral secondary visual area, the granular insular cortex, and the motor cortex. Low NF-L staining intensity was observed in the agranular insular cortex, the prelimbic and infralimbic cortex, the anterior cingulate cortex, the visual rostromedial areas, the temporal association cortex, the ectorhinal cortex, and the lateral entorhinal cortex. NF-L immunoreactivity was present in the perikarya, dendrites, and proximal segment of axons primarily of pyramidal neurons, and was mainly located in layers II and III, and to a lesser extent in layers V and VI. Interestingly, Black-Gold myelin staining confirmed a close correlation between NF-L immunoreactivity and myelination patterns. The characteristic and distinctive distribution and laminar expression profiles of NF-L make it an excellent tool to assess accurately topographical boundaries among neocortical areas as illustrated herein in the adult mouse brain. PMID:21465412

  8. Optimization of parameters for coverage of low molecular weight proteins

    PubMed Central

    Müller, Stephan A.; Kohajda, Tibor; Findeiß, Sven; Stadler, Peter F.; Washietl, Stefan; Kellis, Manolis; von Bergen, Martin

    2010-01-01

    Proteins with molecular weights of <25 kDa are involved in major biological processes such as ribosome formation, stress adaption (e.g., temperature reduction) and cell cycle control. Despite their importance, the coverage of smaller proteins in standard proteome studies is rather sparse. Here we investigated biochemical and mass spectrometric parameters that influence coverage and validity of identification. The underrepresentation of low molecular weight (LMW) proteins may be attributed to the low numbers of proteolytic peptides formed by tryptic digestion as well as their tendency to be lost in protein separation and concentration/desalting procedures. In a systematic investigation of the LMW proteome of Escherichia coli, a total of 455 LMW proteins (27% of the 1672 listed in the SwissProt protein database) were identified, corresponding to a coverage of 62% of the known cytosolic LMW proteins. Of these proteins, 93 had not yet been functionally classified, and five had not previously been confirmed at the protein level. In this study, the influences of protein extraction (either urea or TFA), proteolytic digestion (solely, and the combined usage of trypsin and AspN as endoproteases) and protein separation (gel- or non-gel-based) were investigated. Compared to the standard procedure based solely on the use of urea lysis buffer, in-gel separation and tryptic digestion, the complementary use of TFA for extraction or endoprotease AspN for proteolysis permits the identification of an extra 72 (32%) and 51 proteins (23%), respectively. Regarding mass spectrometry analysis with an LTQ Orbitrap mass spectrometer, collision-induced fragmentation (CID and HCD) and electron transfer dissociation using the linear ion trap (IT) or the Orbitrap as the analyzer were compared. IT-CID was found to yield the best identification rate, whereas IT-ETD provided almost comparable results in terms of LMW proteome coverage. The high overlap between the proteins identified with IT-CID and IT-ETD allowed the validation of 75% of the identified proteins using this orthogonal fragmentation technique. Furthermore, a new approach to evaluating and improving the completeness of protein databases that utilizes the program RNAcode was introduced and examined. Electronic supplementary material The online version of this article (doi:10.1007/s00216-010-4093-x) contains supplementary material, which is available to authorized users. PMID:20803007

  9. Characterization and analysis of the molecular weight of lignin for biorefining studies

    SciTech Connect

    Tolbert, Allison [Georgia Institute of Technology, Atlanta] [Georgia Institute of Technology, Atlanta; Akinosho, Hannah [Georgia Institute of Technology, Atlanta] [Georgia Institute of Technology, Atlanta; Khunsupat, Taya Ratayakorn [ORNL] [ORNL; Naskar, Amit K [ORNL] [ORNL; Ragauskas, Arthur [Georgia Institute of Technology, Atlanta] [Georgia Institute of Technology, Atlanta

    2014-01-01

    The molecular weight of lignin is a fundamental property that infl uences the recalcitrance of biomass and the valorization of lignin. The determination of the molecular weight of lignin in native biomass is dependent on the bioresources used and the isolation and purifi cation procedures employed. The three most commonly employed isolation methods are milled wood lignin (MWL), cellulolytic enzyme lignin (CEL), and enzymatic mild acidolysis lignin (EMAL). Common characterization techniques for determining the molecular weight of lignin will be addressed, with an emphasis on gel permeation chromatography (GPC). This review also examines the mechanisms behind several biological, physical, and chemical pre-treatments and their impact on the molecular weight of lignin. The number average molecular weight (Mn), weight average molecular weight (Mw) and polydispersity index (D) all vary in magnitude depending on the biomass source, pre-treatment conditions, and isolation method. Additionally, there is a growing body of literature that supports changes in the molecular weight of lignin in response to genetic modifi cations in the lignin biosynthetic pathways. This review summarizes different procedures for obtaining the molecular weight of lignin that have been used in recent years and highlight future opportunities for applications of lignin.

  10. Photochemical Preparation of a Novel Low Molecular Weight Heparin

    PubMed Central

    Higashi, Kyohei; Hosoyama, Saori; Ohno, Asami; Masuko, Sayaka; Yang, Bo; Sterner, Eric; Wang, Zhenyu; Linhardt, Robert J.; Toida, Toshihiko

    2011-01-01

    Commercial low molecular weight heparins (LMWHs) are prepared by several methods including peroxidative cleavage, nitrous acid cleavage, chemical ß-elimination, and enzymatic ?-elimination. The disadvantages of these methods are that strong reaction conditions or harsh chemicals are used and these can result in decomposition or modification of saccharide units within the polysaccharide backbone. These side-reactions reduce product quality and yield. Here we show the partial photolysis of unfractionated heparin can be performed in distillated water using titanium dioxide (TiO2). TiO2 is a catalyst that can be easily removed by centrifugation or filtration after the photochemical reaction takes place, resulting in highly pure products. The anticoagulant activity of photodegraded LMWH (pLMWH) is comparable to the most common commercially available LMWHs (i.e., Enoxaparin and Dalteparin). 1H NMR spectra obtained show that pLMWH maintains the same core structure as unfractionated heparin. This photochemical reaction was investigated using liquid chromatography/mass spectrometry (LC/MS) and unlike other processes commonly used to prepare LMWHs, photochemically preparation affords polysaccharide chains of reduced length having both odd and even of saccharide residues. PMID:22205826

  11. Association between Cationic Liposomes and Low Molecular Weight Hyaluronic Acid.

    PubMed

    Gasperini, Antonio A M; Puentes-Martinez, Ximena E; Balbino, Tiago Albertini; de Paula Rigoletto, Thais; de Sá Cavalcanti Corrêa, Gabriela; Cassago, Alexandre; Portugal, Rodrigo Villares; de La Torre, Lucimara Gaziola; Cavalcanti, Leide P

    2015-03-24

    This work presents a study of the association between low molecular weight hyaluronic acid (16 kDa HA) and cationic liposomes composed of egg phosphatidylcholine (EPC), 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE), and 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP). The cationic liposome/HA complexes were evaluated to determine their mesoscopic structure, average size, zeta potential, and morphology as a function of the amount of HA in the system. Small angle X-ray scattering results revealed that neighboring cationic liposomes either stick together after a partial coating of low concentration HA or disperse completely in excess of HA, but they never assemble as multilamellar vesicles. Cryo-transmission electron microscopy images confirm the existence of unilamellar vesicles and large aggregates of unilamellar vesicles for HA fractions up to 80% (w/w). High concentrations of HA (> 20% w/w) proved to be efficient for coating extruded liposomes, leading to particle complexes with sizes in the nanoscale range and a negative zeta potential. PMID:25730494

  12. Photoelectrical characterization of a new low molecular weight compound

    NASA Astrophysics Data System (ADS)

    Siderov, V.; Dobrikov, G. H.; Zhivkov, I.; Dobrikov, G. M.; Georgiev, Y.; Yordanov, R.; Honova, J.; Weiter, M.

    2014-12-01

    Photoelectrical characterization of a newly synthesized low molecular weight compound was carried out. 1,8-naphtalimide (chemical formula C32H34N4O5S) was originally synthesized and analyzed by NMR spectroscopy. Thin films were deposited in vacuum on commercially pre-patterned ITO covered glass substrates and the samples were prepared in clean room environment. The films deposited were characterized by SEM. Photoelectrical characteristics of the samples prepared were estimated by dark current-voltage measurement, spectral dependence of the photoconductivity and measurement under exposure with light, produced by solar simulator. Finally electroluminescence measurements were performed. It was found that the samples exhibit diode behaviour. The low values characterizing photovoltaic parameters obtained could be connected with the relative higher series resistance (Rseries). The predominant influence of Rseries is assumed as the relative high photoluminescence, measured from solution should be related to a relatively strong charge carrier photogeneration. This result is supported by electroluminescent measurement. Another reason for the low values of the photovoltaic parameters measured could be the non-optimized film thickness leading to a non-optimal light absorption and increased charge carrier recombination. The assumption for the predominant influence of Rseries is supported by the electroluminescent measurements.

  13. Molecular Weight Dependence of Polymersome Membrane Elasticity and Stability

    E-print Network

    Harry Bermudez; Aaron K. Brannan; Daniel A. Hammer; Frank S. Bates; Dennis E. Discher

    2002-02-22

    Vesicles prepared in water from a series of diblock copolymers and termed "polymersomes" are physically characterized. With increasing molecular weight $\\bar{M}_n$, the hydrophobic core thickness $d$ for the self-assembled bilayers of polyethyleneoxide - polybutadiene (PEO-PBD) increases up to 20 $nm$ - considerably greater than any previously studied lipid system. The mechanical responses of these membranes, specifically, the area elastic modulus $K_a$ and maximal areal strain $\\alpha_c$ are measured by micromanipulation. As expected for interface-dominated elasticity, $K_a$ ($\\simeq$ 100 $pN/nm$) is found to be independent of $\\bar{M}_n$. Related mean-field ideas also predict a limiting value for $\\alpha_c$ which is universal and about 10-fold above that typical of lipids. Experiments indeed show $\\alpha_c$ generally increases with $\\bar{M}_n$, coming close to the theoretical limit before stress relaxation is opposed by what might be chain entanglements at the highest $\\bar{M}_n$. The results highlight the interfacial limits of self-assemblies at the nano-scale.

  14. Method for determination of polyethylene glycol molecular weight.

    PubMed

    Pihlasalo, Sari; Hänninen, Pekka; Härmä, Harri

    2015-04-01

    A method utilizing competitive adsorption between polyethylene glycols (PEGs) and labeled protein to nanoparticles was developed for the determination of PEG molecular weight (MW) in a microtiter plate format. Two mix-and-measure systems, time-resolved luminescence resonance energy transfer (TR-LRET) with donor europium(III) polystyrene nanoparticles and acceptor-labeled protein and quenching with quencher gold nanoparticles and fluorescently labeled protein were compared for their performance. MW is estimated from the PEG MW dependent changes in the competitive adsorption properties, which are presented as the luminescence signal vs PEG mass concentration. The curves obtained with the TR-LRET system overlapped for PEGs larger than 400 g/mol providing no information on MW. Distinctly different curves were obtained with the quenching system enabling the assessment of PEG MW within a broad dynamic range. The data was processed with and without prior knowledge of the PEG concentration to measure PEGs over a MW range from 62 to 35?000 g/mol. The demonstration of the measurement independent of the PEG concentration suggests that the estimation of MW is possible with quenching nanoparticle system for neutrally charged and relatively hydrophilic polymeric molecules widening the applicability of the simple and cost-effective nanoparticle-based methods. PMID:25783500

  15. High molecular weight plant heteropolysaccharides stimulate fibroblasts but inhibit keratinocytes.

    PubMed

    Shahbuddin, Munira; Shahbuddin, Dahlia; Bullock, Anthony J; Ibrahim, Halijah; Rimmer, Stephen; MacNeil, Sheila

    2013-06-28

    Konjac glucomannan (KGM) is a natural polysaccharide of ?(1-4)-D-glucomannopyranosyl backbone of D-mannose and D-glucose derived from the tuber of Amorphophallus konjac C. Koch. KGM has been reported to have a wide range of activities including wound healing. In this study we examined KGM extracts prepared from five plant species, (Amorphophallus konjac Koch, Amorphophallus oncophyllus, Amorphophallus prainii, Amorphophallus paeoniifolius and Amorphophallus elegans) for their effects on cultured human keratinocytes and fibroblasts. Extracts from A. konjac Koch, A. oncophyllus and A. prainii (but not from A. paeoniifolius or A. elegans) stimulated fibroblast proliferation both in the absence and presence of serum. However, these materials inhibited keratinocyte proliferation. The fibroblast stimulatory activity was associated with high molecular weight fractions of KGM and was lost following ethanol extraction or enzyme digestion with ?-mannanase. It was also reduced by the addition of concanavalin A but not mannose suggesting that these heteropolysaccharides are acting on lectins but not via receptors specific to mannose. The most dramatic effect of KGM was seen in its ability to support fibroblasts for 3weeks under conditions of deliberate media starvation. This effect did not extend to supporting keratinocytes under conditions of media starvation but KGM did significantly help support adipose derived stem cells under media starvation conditions. PMID:23694709

  16. High molecular weight glutenin subunit in durum wheat (T. durum).

    PubMed

    Branlard, G; Autran, J C; Monneveux, P

    1989-09-01

    The diversity of high molecular weight (HMW) glutenin subunits of 502 varieties of durum wheat (Triticum durum) from 23 countries was studied using sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). Twenty-nine types of patterns were observed with 18 mobility bands. A total of 18 alleles were identified by comparing the mobilities of their subunits to those previously found in hexaploid wheat (T. aestivum) and in Triticum turgidum var. dicoccum. Five new alleles were detected: two on the Glu A1 and three on the Glu B1 locus. Comparison of the frequency of alleles in the three species T. aestivum, T. dicoccum and T. durum was investigated. Significant differences exist between each of these species on the basis of the frequency distributions of their three and four common alleles at the Glu A1 and Glu B1 locus, respectively. The Glu B1c allele occuring very frequently in hexaploid wheats was not found in the two tetraploid species. More than 83% of the T. durum analysed were found to have the Glu A1c (null) allele. PMID:24227241

  17. Delamination toughness of ultra high molecular weight polyethylene (UHMWPE) composites

    NASA Astrophysics Data System (ADS)

    Porras, A.; Tellez, J.; Casas-Rodriguez, J. P.

    2012-08-01

    Ultra high molecular weight polyethylene (UHMWPE) fibre reinforced composites are an important group of material for armours solutions, where their unique combination of properties could be utilized. A commonly observed failure mode in this kind of unidirectional laminated composites under impact ballistic is delamination between the composite layers. In the present study, an investigation on the delamination toughness behaviour exhibited by UHMWPE composites laminated was made. The interlaminar Mode II critical strain energy release rates of (UHMWPE) fibre reinforced composites were characterized using the End Notch Flexural (ENF) test. Critical strain energy release rate was obtained from the load - deflection test data using the beam theory expression. It was found that the energy release rate of the composite exhibited a very low value of around 60J/m2 using a moulding pressure of approximately 1200 psi. In order to analyse the delamination resistance of composite, the effects of changing the manufacture process variables and the use of a thermoplastic adhesive film in the composites were investigated. The composite laminates were produced by hot compressing moulding using a film-stacking procedure. It was found that the damage resistance of the UHMWPE composite was influenced by the manufacture method, which affects the Mode II interlaminar fracture toughness and the ballistic response of composites.

  18. Ultra High Molecular Weight Polyethylene: Mechanics, Morphology, and Clinical Behavior

    PubMed Central

    Sobieraj, MC; Rimnac, CM

    2013-01-01

    Ultra high molecular weight polyethylene (UHMWPE) is a semicrystalline polymer that has been used for over four decades as a bearing surface in total joint replacements. The mechanical properties and wear properties of UHMWPE are of interest with respect to the in vivo performance of UHMWPE joint replacement components. The mechanical properties of the polymer are dependent on both its crystalline and amorphous phases. Altering either phase (i.e., changing overall crystallinity, crystalline morphology, or crosslinking the amorphous phase) can affect the mechanical behavior of the material. There is also evidence that the morphology of UHMWPE, and, hence, its mechanical properties evolve with loading. UHMWPE has also been shown to be susceptible to oxidative degradation following gamma radiation sterilization with subsequent loss of mechanical properties. Contemporary UHMWPE sterilization methods have been developed to reduce or eliminate oxidative degradation. Also, crosslinking of UHMWPE has been pursued to improve the wear resistance of UHMWPE joint components. The 1st generation of highly crosslinked UHMWPEs have resulted in clinically reduced wear; however, the mechanical properties of these materials, such as ductility and fracture toughness, are reduced when compared to the virgin material. Therefore, a 2nd generation of highly crosslinked UHMWPEs are being introduced to preserve the wear resistance of the 1st generation while also seeking to provide oxidative stability and improved mechanical properties. PMID:19627849

  19. Reactions of allylic radicals that impact molecular weight growth kinetics.

    PubMed

    Wang, Kun; Villano, Stephanie M; Dean, Anthony M

    2015-02-18

    The reactions of allylic radicals have the potential to play a critical role in molecular weight growth (MWG) kinetics during hydrocarbon oxidation and/or pyrolysis. Due to their stability (when compared to alkyl radicals), they can accumulate to relatively high concentrations. Thus, even though the rate coefficients for their various reactions are small, the rates of these reactions may be significant. In this work, we use electronic structure calculations to examine the recombination, addition, and abstraction reactions of allylic radicals. For the recombination reaction of allyl radicals, we assign a high pressure rate rule that is based on experimental data. Once formed, the recombination product can potentially undergo an H-atom abstraction reaction followed by unimolecular cyclization and ?-scission reactions. Depending upon the conditions (e.g., higher pressures) these pathways can lead to the formation of stable MWG species. The addition of allylic radicals to olefins can also lead to MWG species formation. Once again, cyclization of the adduct followed by ?-scission is an important energy accessible route. Since the recombination and addition reactions produce chemically-activated adducts, we have explored the pressure- and temperature-dependence of the overall rate constants as well as that for the multiple product channels. We describe a strategy for estimating these pressure-dependencies for systems where detailed electronic structure information is not available. We also derive generic rate rules for hydrogen abstraction reactions from olefins and diolefins by methyl and allyl radicals. PMID:25648200

  20. [Thromboembolism prophylaxis with low molecular weight heparin in abdominal surgery].

    PubMed

    Adolf, J; Knee, H; Roder, J D; van de Flierdt, E; Siewert, J R

    1989-01-13

    The effect of low-molecular weight (LMW) heparin fragment (one injection of 1500 aPTT [activated partial thromboplastin time]-U/24 h)--group 1--was compared with unfractionated (UF) heparin (3 x 5000 IU/24 h)--group 2--in a randomized prospective double-blind trial of 404 patients (202 patients in each group), aged 50 years or older, undergoing abdominal surgery. The two groups were well matched for thromboembolic risk factors. The first subcutaneous injection was made two hours preoperatively; postoperative injections continued for at least seven days. The radiofibrinogen test served as the test criterion. If positive, phlebography and lung sequence scanning were performed. On complete prophylaxis the thrombosis rate was nearly identical in the two groups--10.8% vs 11.4%. No pulmonary emboli were detected in either group if correctly treated. There was no significant difference between the two groups with respect to peroperative blood loss, re-operation rate and wound haematoma rate. But there was a significantly higher number of injection haematomas in group 2. These results suggest that a single daily injection of 1500 aPTT-U LMW heparin provides effective prophylaxis against postoperative venous thromboembolism. PMID:2535983

  1. Purification of a Low Molecular Weight Fucoidan for SPECT Molecular Imaging of Myocardial Infarction

    PubMed Central

    Saboural, Pierre; Chaubet, Frédéric; Rouzet, Francois; Al-Shoukr, Faisal; Ben Azzouna, Rana; Bouchemal, Nadia; Picton, Luc; Louedec, Liliane; Maire, Murielle; Rolland, Lydia; Potier, Guy; Le Guludec, Dominique; Letourneur, Didier; Chauvierre, Cédric

    2014-01-01

    Fucoidans constitute a large family of sulfated polysaccharides with several biochemical properties. A commercial fucoidan from brown algae, containing low molecular weight polysaccharidic species constituted of l-fucose, uronic acids and sulfate groups, was simply treated here with calcium acetate solution. This treatment led to a purified fraction with a yield of 45%. The physicochemical characterizations of the purified fucoidan using colorimetric assay, MALLS, dRI, FT-IR, NMR, exhibited molecular weight distributions and chemical profiles similar for both fucoidans whereas the sulfate and l-fucose contents increased by 16% and 71%, respectively. The biodistribution study in rat of both compounds labeled with 99mTc evidenced a predominant renal elimination of the purified fucoidan, but the crude fucoidan was mainly retained in liver and spleen. In rat myocardial ischemia-reperfusion, we then demonstrated the better efficiency of the purified fucoidan. This purified sulfated polysaccharide appears promising for the development of molecular imaging in acute coronary syndrome. PMID:25251032

  2. Molecular imprinted polymer-coated optical fiber sensor for the identification of low molecular weight molecules.

    PubMed

    Lépinay, Sandrine; Ianoul, Anatoli; Albert, Jacques

    2014-10-01

    A biomimetic optical probe for detecting low molecular weight molecules (maltol, 3-hydroxy-2-methyl-4H-pyran-4-one, molecular weight of 126.11 g/mol), was designed, fabricated, and characterized. The sensor couples a molecular imprinted polymer (MIP) and the Bragg grating refractometry technology into an optical fiber. The probe is fabricated first by inscribing tilted grating planes in the core of the fiber, and then by photopolymerization to immobilize a maltol imprinted MIP on the fiber cladding surface over the Bragg grating. The sensor response to the presence of maltol in different media is obtained by spectral interrogation of the fiber transmission signal. The results showed that the limit of detection of the sensor reached 1 ng/mL in pure water with a sensitivity of 6.3 × 10(8)pm/M. The selectivity of the sensor against other compounds and its reusability were also studied experimentally. Finally, the unambiguous detection of concentrations as little as 10nM of maltol in complex media (real food samples) by the MIP-coated tilted fiber Bragg grating sensor was demonstrated. PMID:25059178

  3. Purification of a low molecular weight fucoidan for SPECT molecular imaging of myocardial infarction.

    PubMed

    Saboural, Pierre; Chaubet, Frédéric; Rouzet, Francois; Al-Shoukr, Faisal; Azzouna, Rana Ben; Bouchemal, Nadia; Picton, Luc; Louedec, Liliane; Maire, Murielle; Rolland, Lydia; Potier, Guy; Guludec, Dominique Le; Letourneur, Didier; Chauvierre, Cédric

    2014-09-01

    Fucoidans constitute a large family of sulfated polysaccharides with several biochemical properties. A commercial fucoidan from brown algae, containing low molecular weight polysaccharidic species constituted of l-fucose, uronic acids and sulfate groups, was simply treated here with calcium acetate solution. This treatment led to a purified fraction with a yield of 45%. The physicochemical characterizations of the purified fucoidan using colorimetric assay, MALLS, dRI, FT-IR, NMR, exhibited molecular weight distributions and chemical profiles similar for both fucoidans whereas the sulfate and l-fucose contents increased by 16% and 71%, respectively. The biodistribution study in rat of both compounds labeled with 99mTc evidenced a predominant renal elimination of the purified fucoidan, but the crude fucoidan was mainly retained in liver and spleen. In rat myocardial ischemia-reperfusion, we then demonstrated the better efficiency of the purified fucoidan. This purified sulfated polysaccharide appears promising for the development of molecular imaging in acute coronary syndrome. PMID:25251032

  4. Formation of high molecular weight products from benzene during boundary lubrication

    NASA Technical Reports Server (NTRS)

    Morales, W.

    1985-01-01

    High molecular weight products were detected on the wear track of an iron disk at the end of a sliding friction and wear test using benzene as a lubricant. Size exclusion chromagography in conjunction with UV analysis gave evidence that the high molecular weight products are polyphenyl ether type substances. Organic electrochemistry was used to elucidate the possible surface reaction mechanisms.

  5. High-molecular-weight renin converting enzyme from dog kidney: detection and fractionation.

    PubMed

    Tanaka, M; Iwao, H; Ikemoto, F; Yamamoto, K

    1985-03-25

    Renal cortical high-molecular-weight renin (Mw:60,000) of the dog is a complex of renin (low-molecular-weight renin; Mw:40,000) and a renin binding protein. We detected an enzyme-like substance that catalyzes the conversion from high- into low-molecular-weight renin. When the renal cortical extract was added to the high-molecular-weight renin and the preparation incubated at 37 degrees C for 30 min, the high-molecular-weight renin was converted into the low-molecular-weight form. No such conversion occurred in the case of renal medullary extract. This converting substance was fractionated using concanavalin A Sepharose, 70% ammonium sulfate saturation and DEAE-cellulose chromatography. The converting activity was inhibited by potassium tetrathionate, N-ethylmaleimide and 5,5'-dithiobis-(2-nitrobenzoic acid). These events suggest that this substance is an enzyme possessing sulfhydryl moieties. However, a cathepsin B inhibitor leupeptin did not affect the activity. Accordingly, the high-molecular-weight renin converting enzyme, which is sensitive to sulfhydryl oxidation, may explain the mechanism of interconversion between high- and low-molecular-weight renin involving the oxidation-reduction of tissue sulfhydryl groups. PMID:3884947

  6. Molecular Weight Determination by an Improved Temperature-Monitored Vapor-Density Method.

    ERIC Educational Resources Information Center

    Grider, Douglas J.; And Others

    1988-01-01

    Recommends determining molecular weights of liquids by use of a thermocouple. Utilizing a mathematical gas equation, the molecular weight can be determined from the measurement of the vapor temperature upon complete evaporation. Lists benefits as reduced time and cost, and improved safety factors. (ML)

  7. An evaluation of field-flow fractionation for molecular weight characterization of polymeric materials

    SciTech Connect

    Fuller, E.N.

    1992-08-01

    An evaluation has been made of field-flow fractionation for potential polymer molecular weight characterization applications at Allied- Signal Inc., Kansas City Division. The data obtained show that the technique can provide useful information regarding polymer molecular weights which are analogous to those obtained by gel permeation chromatography. 13 refs., 21 figs., 4 tabs.

  8. An evaluation of field-flow fractionation for molecular weight characterization of polymeric materials. Final report

    SciTech Connect

    Fuller, E.N.

    1992-08-01

    An evaluation has been made of field-flow fractionation for potential polymer molecular weight characterization applications at Allied- Signal Inc., Kansas City Division. The data obtained show that the technique can provide useful information regarding polymer molecular weights which are analogous to those obtained by gel permeation chromatography. 13 refs., 21 figs., 4 tabs.

  9. The effect of whey protein hydrolyzate average molecular weight on the lactic acid fermentation

    Microsoft Academic Search

    Mel Berezny Leh; Marvin Charles

    1989-01-01

    Summary The batch fermentation of whey permeate to lactic acid was improved by supplementing the broth with enzyme-hydrolyzed whey protein. Hydrolyzates prepared with endoprotease were more stimulatory to acid production rates than were those prepared with exo\\/endo protease. The effect of hydrolyzate average molecular weight on acid production is presented. Results show that the hydrolyzate having an average molecular weight

  10. Light scattering polydispersity analysis of molecular diffusion by Laplace transform inversion in weighted spaces

    E-print Network

    Bertero, Mario

    scattering polydispersity analysis of molecular diffusion by Laplace transform inversion in weighted spaces MLight scattering polydispersity analysis of molecular diffusion by Laplace transform inversion in weighted spaces M. Bertero, P. Brianzi, E. R. Pike, G. de Villiers, K. H. Lan@f@f et al. Citation: J. Chem

  11. A Simple, Inexpensive Molecular Weight Measurement for Water-Soluble Polymers Using Microemulsions.

    ERIC Educational Resources Information Center

    Mathias, Lon J.; Moore, D. Roger

    1985-01-01

    Describes an experiment involving use of a microemulsion and its characteristic thermal phase change to determine molecular weights of polyoxyethylene samples. The experiment provides students with background information on polymers and organized media and with experience in evaluating polymer molecular weight by using a unique property of a…

  12. High-Molecular-Weight Polyethylene Glycol Prevents Lethal Sepsis Due to Intestinal Pseudomonas aeruginosa

    E-print Network

    Lee, Ka Yee C.

    High-Molecular-Weight Polyethylene Glycol Prevents Lethal Sepsis Due to Intestinal Pseudomonas of this study were to test the ability of a high-molecular- weight polyethylene glycol compound, polyethylene: The ability of polyethylene glycol 15­20 to protect the intestinal epi- thelium against the opportunistic

  13. Isolation of low-molecular-weight heparin/heparan sulfate from marine sources.

    PubMed

    Saravanan, Ramachandran

    2014-01-01

    The glycosaminoglycan (heparin and heparan sulfate) are polyanionic sulfated polysaccharides mostly recognized for its anticoagulant activity. In many countries, low-molecular-weight heparins have replaced the unfractionated heparin, owing to its high bioavailability, half-life, and less adverse effect. The low-molecular-weight heparins differ in mode of preparation (chemical or enzymatic synthesis and chromatography fractionations) and as a consequence in molecular weight distribution, chemical structure, and pharmacological activities. Bovine and porcine body parts are at present used for manufacturing of commercial heparins, and the appearance of mad cow disease and Creutzfeldt-Jakob disease in humans has limited the use of bovine heparin. Consequently, marine organisms come across the new resource for the production of low-molecular-weight heparin and heparan sulfate. The importance of this chapter suggests that the low-molecular-weight heparin and heparan sulfate from marine species could be alternative sources for commercial heparin. PMID:25081076

  14. Considerations in the use of high-pressure size exclusion chromatography (HPSEC) for determining molecular weights of aquatic humic substances

    Microsoft Academic Search

    Qunhui Zhou; Stephen E. Cabaniss; Patricia A. Maurice

    2000-01-01

    High-pressure size exclusion chromatography (HPSEC) is a powerful technique for determining molecular weight (MW) distributions of aquatic humic substances (HS). Previous researchers have shown that HPSEC can provide values of weight average molecular weight (Mw), number average molecular weight (Mn), and polydispersity (?) that are comparable to values determined by other techniques such as vapor pressure osmometry and field flow

  15. Respiratory clearance of aerosolized radioactive solutes of varying molecular weight

    SciTech Connect

    Huchon, G.J.; Montgomery, A.B.; Lipavsky, A.; Hoeffel, J.M.; Murray, J.F.

    1987-05-01

    To determine the influence of varying molecular weight (mol wt) on respiratory clearance of aerosolized solutes, we studied eight radiopharmaceuticals, each administered to four dogs: sodium /sup 99m/Tc pertechnetate (TcO4), /sup 99m/Tc glucoheptonate ((/sup 99m/Tc)GH), 51Cr-ethylenedinitrotetraacetate ((51Cr)EDTA), /sup 99m/Tc diethylenetriaminepentaacetate ((99mTc) DTPA), /sup 111/In diethylenetriaminepentaacetate ((/sup 111/In)DTPA), /sup 67/Ga desferoxaminemesylate ((/sup 67/Ga)DFOM), /sup 99m/Tc dextran ((/sup 99m/Tc)DX) and /sup 111/In transferrin ((/sup 111/In)TF). After aerosolization (0.8 m MMD, 2.4 GSD), clearance was determined for 30 min and then corrected by intravenous injection for nonairspace radioactivity. In-TF clearance (0.11 +/- 0.10%/min) was lower than TcO4 (6.32 +/- 0.62%/min), (/sup 99m/Tc)GH (1.50 +/- 0.37%/min), (/sup 51/Cr)EDTA (2.38 +/- 1.02%/min), (/sup 99m/Tc)DTPA (3.51 +/- 0.40%/min), (/sup 111/In)DTPA (2.35 +/- 0.42%/min), (/sup 67/Ga) DFOM (1.99 +/- 0.49%/min) and (/sup 99m/Tc)DX (1.81 +/- 0.75%/min) clearances (p less than 0.001). TcO4 clearance was higher than others (p less than 0.001). Technetium binding to DX was unsatisfactory; aerosolization caused unbinding from DTPA. We conclude that respiratory clearance of large mol wt solutes within 30 min is negligible and, that clearance of molecules between 347-5099 daltons differs greatly, suggesting that binding and/or intrapulmonary retention affect transfer.

  16. High Molecular Weight Dimer Esters in ?-Pinene Secondary Organic Aerosol

    NASA Astrophysics Data System (ADS)

    Kristensen, Kasper; Cui, Tianqu; Zhang, Haofei; Gold, Avram; Glasius, Marianne; Surratt, Jason D.

    2014-05-01

    Monoterpenes, such as ?-pinene, constitute an important group of biogenic volatile organic compounds (BVOC). Once emitted into the atmosphere ?-pinene is removed by oxidization by the hydroxyl radical (OH), reactions with ozone (O3), and with nitrate radicals (NO3) resulting in the formation of first-generation oxidation products, such as semi-volatile carboxylic acids. In addition, higher molecular weight dimer esters originating from the oxidation of ?-pinene have been observed in both laboratory-generated and ambient secondary organic aerosols (SOA). While recent studies suggest that the dimers are formed through esterification between carboxylic acids in the particle phase, the formation mechanism of the dimer esters is still ambiguous. In this work, we present the results of a series of smog chamber experiments to assess the formation of dimer esters formed from the oxidation of ?-pinene. Experiments were conducted in the University of North Carolina (UNC) dual outdoor smog chamber facility to investigate the effect of oxidant species (OH versus O3), relative humidity (RH), and seed aerosol acidity in order to obtain a better understanding of the conditions leading to the formation of the dimer esters and how these parameters may affect the formation and chemical composition of SOA. The chemical composition of ?-pinene SOA was investigated by ultra-performance liquid chromatography/electrospray ionization high-resolution quadrupole time-of-flight mass spectrometry (UPLC/ESI-HR-Q-TOFMS), and a total of eight carboxylic acids and four dimer esters were identified, constituting between 8 and 12 % of the total ?-pinene SOA mass.

  17. Atlantic Ocean Measurements of Low Molecular Weight Alkyl Nitrates

    NASA Astrophysics Data System (ADS)

    Dahl, E. E.; Saltzman, E. S.

    2003-12-01

    The surface oceans appear to be a source of low molecular weight alkyl nitrates to the atmosphere. These compounds are converted by photolysis to NOx, and may contribute to ozone production in remote regions. The mechanism(s) of production of oceanic alkyl nitrates in surface seawater are currently unknown. Laboratory studies suggest that the reaction of peroxy radicals with nitric oxide in seawater may provide a near-surface source of these compounds. These precursors originate from the photolysis of dissolved organic matter and nitrite. Depth profiles of alkyl nitrates in the North Atlantic Ocean (Chuck et al. 2002) show elevated concentrations of alkyl nitrates below the photic zone, suggesting that non-photochemical mechanisms are also likely. We have recently completed a series of alkyl nitrate (C1-C3) depth profiles and shipboard incubation experiments in the north Atlantic, on a cruise track from Reykjavik, Iceland to Natal, Brazil (A16N2003; R/V Brown). The northernmost stations (45-50N), exhibited alkyl nitrate maxima in the mixed layer, and a positive correlation between alkyl nitrates and nitrite. In the tropics and subtropics, alkyl nitrate maxima were below the mixed layer, and alkyl nitrates correlated with nitrate. Shipboard deck irradiation studies demonstrated photochemical production of alkyl nitrates in waters that correlated with the initial nitrite concentration. Addition of nitrite stimulated production to extremely high levels, suggesting that NO, rather than peroxy radicals, is the limiting reactant in these waters. Overall, the distribution of alkyl nitrates suggests that both photochemical and microbial sources of alkyl nitrate may occur.

  18. Qualitative and quantitative analysis of low molecular weight phenols by high pressure liquid chromatography

    E-print Network

    Hahn, David Henry

    1981-01-01

    ) and Hatch-6488 (Polyphenols of Sorghum). TABLE OF CONTENTS INTRODUCTION REVIEW OF LITERATURE Low Molecular Weight Phenols Disease Resistance Insect Res1stance . Sorghum Grain Molds Locat1on of Low Molecular We1ght Phenols Extract1on Methods Separat.... Finally, apply the extract1on and separation schemes developed to several varieties of sorghum with vary1ng degrees of resistance to grain molding and weather1ng fungi . REVIEW OF LITERATVRE Low molecular Weight Phenols Phenolic compounds occur...

  19. Simple, rapid and accurate molecular diagnosis of acute promyelocytic leukemia by loop mediated amplification technology

    PubMed Central

    Spinelli, Orietta; Rambaldi, Alessandro; Rigo, Francesca; Zanghì, Pamela; D'Agostini, Elena; Amicarelli, Giulia; Colotta, Francesco; Divona, Mariadomenica; Ciardi, Claudia; Coco, Francesco Lo; Minnucci, Giulia

    2015-01-01

    The diagnostic work-up of acute promyelocytic leukemia (APL) includes the cytogenetic demonstration of the t(15;17) translocation and/or the PML-RARA chimeric transcript by RQ-PCR or RT-PCR. This latter assays provide suitable results in 3-6 hours. We describe here two new, rapid and specific assays that detect PML-RARA transcripts, based on the RT-QLAMP (Reverse Transcription-Quenching Loop-mediated Isothermal Amplification) technology in which RNA retrotranscription and cDNA amplification are carried out in a single tube with one enzyme at one temperature, in fluorescence and real time format. A single tube triplex assay detects bcr1 and bcr3 PML-RARA transcripts along with GUS housekeeping gene. A single tube duplex assay detects bcr2 and GUSB. In 73 APL cases, these assays detected in 16 minutes bcr1, bcr2 and bcr3 transcripts. All 81 non-APL samples were negative by RT-QLAMP for chimeric transcripts whereas GUSB was detectable. In 11 APL patients in which RT-PCR yielded equivocal breakpoint type results, RT-QLAMP assays unequivocally and accurately defined the breakpoint type (as confirmed by sequencing). Furthermore, RT-QLAMP could amplify two bcr2 transcripts with particularly extended PML exon 6 deletions not amplified by RQ-PCR. RT-QLAMP reproducible sensitivity is 10?3 for bcr1 and bcr3 and 10?2 for bcr2 thus making this assay particularly attractive at diagnosis and leaving RQ-PCR for the molecular monitoring of minimal residual disease during the follow up. In conclusion, PML-RARA RT-QLAMP compared to RT-PCR or RQ-PCR is a valid improvement to perform rapid, simple and accurate molecular diagnosis of APL.

  20. Thermomechanical analysis of ultra-high molecular weight polyethylene-metal hip prostheses.

    PubMed

    Rocchi, M; Affatato, S; Falasca, G; Viceconti, M

    2007-08-01

    In order to predict the frictional heating and the contact stresses between the polyethylene cup and the metallic ball-head forming the articulation of a hip prosthesis a three-dimensional finite element model was developed and calculated. The non-linear model includes a fully coupled thermomechanical formulation of the mechanical properties of the ultra-high-molecular-weight polyethylene, and a large-sliding Coulomb frictional contact between the two components. The model predicts the temperature of the polyethylene with an accuracy that was tested by comparing the model predictions with the temperature measurements. The temperature measurements were taken by thermocouples placed on the cup surface, the head surface and the inside of the thermostatic bath, during a complete test within a hip joint wear simulator. The model was found to be very accurate, predicting the measured temperatures with an accuracy better than 2 per cent. The temperature peak (51 degrees C) was predicted at the contact surface. The model results indicate that frictional heat is mostly dissipated through the metallic ball-head. The full coupling between the thermal and the mechanical conditions used in this study appears to be necessary if accurate predictions of the polyethylene deformation are required. PMID:17937196

  1. Molecular chaperone properties of the high molecular weight aggregate from aged lens

    NASA Technical Reports Server (NTRS)

    Takemoto, L.; Boyle, D.; Spooner, B. S. (Principal Investigator)

    1994-01-01

    The high molecular weight aggregate (HMWA) fraction was isolated from the water soluble proteins of aged bovine lenses. Its composition and ability to inhibit heat-induced denaturation and aggregation were compared with the lower molecular weight, oligomeric fraction of alpha isolated from the same lens. Although the major components of both fractions were the alpha-A and alpha-B chains, the HMWA fraction possessed a decreased ability to protect other proteins against heat-induced denaturation and aggregation. Immunoelectron microscopy of both fractions demonstrated that alpha particles from the HMWA fraction contained increased amounts of beta and gamma crystallins, bound to a central region of the supramolecular complex. Together, these results demonstrate that alpha crystallins found in the HMWA fraction possess a decreased ability to protect against heat-induced denaturation and aggregation, and suggest that at least part of this decrease could be due to the increased presence of beta and gamma crystallins complexed to the putative chaperone receptor site of the alpha particles.

  2. Weighted integration of visual position information Center for Molecular and Behavioral Neuroscience,

    E-print Network

    Krekelberg, Bart

    Weighted integration of visual position information Center for Molecular and Behavioral for Molecular and Behavioral Neuroscience, Rutgers, The State University of New Jersey, Newark, NJ, USAAdam P. Morris Center for Molecular and Behavioral Neuroscience, Rutgers, The State University of New Jersey

  3. Compression molding simulation of ultra high molecular weight polyethylene

    NASA Astrophysics Data System (ADS)

    Parasnis, Narasinha Chandrakant

    Experimental investigation based on design of experiments approach was conducted for studying the effect of different processing variables on mechanical and physical properties of compression molded Ultra High Molecular Weight Polyethylene (UHMWPE). Soak times at melt and at crystallization temperatures, cooling rate from molten state and pressures applied during the molding cycle were most significant processing variables. Based on the preliminary experiments, further detailed investigation into the effect of pressure on the mechanical and physical properties of the molded part was conducted. The study revealed that for highest crystallinity and modulus, the pressure applied at melt should be ˜15 MPa and that at crystallization temperature it should be ˜77 MPa. Studies on non-isothermal crystallization of UHMWPE showed differences in ultimate crystallinity (˜11%) as the cooling rate was changed from 1°C/min to 22°C/min. The changes in crystallinity were more significant at lower cooling rates (<6°C/min) than at higher cooling rates (6 to 22°C/min). A compression molding simulation including crystallization kinetics and temperature dependent polymer properties was implemented. Three different processing cycles capable of producing different crystallinity distributions were modeled and verified. The model showed that a compression molding cycle with soak at crystallization produced high crystallinity (˜48%) parts. The model was modified to account for the effect of pressure on crystallization. The perfect contact assumed in the finite element model at all the interfaces led to low predictions of pressure within the polymer. Pressure-volume-temperature analysis was conducted at high pressures (20 to 160 MPa) to access the effect of pressure. The change in onset, peak and end crystallization temperatures was linearly related to the applied pressure with every 1 MPa increase in pressure accounting for an increase of 0.3$C in the crystallization temperatures. The temperature predictions from the finite element model were used in a residual stress model to predict residual stresses within compression molded parts. The model predicted that for a cycle with soak at crystallization the residual stresses would be low (˜-1 to 0.8 MPa) since the temperature and cooling rate gradients at the end of the crystallization are nonexistent.

  4. Low molecular weight carboxylic acids in oxidizing porphyry copper tailings.

    PubMed

    Dold, Bernhard; Blowes, David W; Dickhout, Ralph; Spangenberg, Jorge E; Pfeifer, Hans-Rudolf

    2005-04-15

    The distribution of low molecular weight carboxylic acids (LMWCA) was investigated in pore water profiles from two porphyry copper tailings impoundments in Chile (Piuquenes at La Andina and Cauquenes at El Teniente mine). The objectives of this study were (1) to determine the distribution of LMWCA, which are interpreted to be the metabolic byproducts of the autotroph microbial community in this low organic carbon system, and (2) to infer the potential role of these acids in cycling of Fe and other elements in the tailings impoundments. The speciation and mobility of iron, and potential for the release of H+ via hydrolysis of the ferric iron, are key factors in the formation of acid mine drainage in sulfidic mine wastes. In the low-pH oxidation zone of the Piuquenes tailings, Fe(III) is the dominant iron species and shows high mobility. LMWCA, which occur mainly between the oxidation front down to 300 cm below the tailings surface at both locations (e.g., max concentrations of 0.12 mmol/L formate, 0.17 mmol/L acetate, and 0.01 mmol/L pyruvate at Piuquenes and 0.14 mmol/L formate, 0.14 mmol/L acetate, and 0.006 mmol/L pyruvate at Cauquenes), are observed at the same location as high Fe concentrations (up to 71.2 mmol/L Fe(II) and 16.1 mmol/L Fe(III), respectively). In this zone, secondary Fe(III) hydroxides are depleted. Our data suggest that LMWCA may influence the mobility of iron in two ways. First, complexation of Fe(III), through formation of bidentate Fe(III)-LMWCA complexes (e.g., pyruvate, oxalate), may enhance the dissolution of Fe(III) (oxy)hydroxides or may prevent precipitation of Fe(III) (oxy)hydroxides. Soluble Fe(III) chelate complexes which may be mobilized downward and convert to Fe(II) by Fe(III) reducing bacteria. Second, monodentate LMWCA (e.g., acetate and formate) can be used by iron-reducing bacteria as electron donors (e.g., Acidophilum spp.), with ferric iron as the electron acceptor. These processes may, in part, explain the low abundances of secondary Fe(III) hydroxide precipitates below the oxidation front and the high concentrations of Fe(II) observed in the pore waters of some low-sulfide systems. The reduction of Fe(III) and the subsequent increase of iron mobility and potential acidity transfer (Fe(II) oxidation can result in the release of H+ in an oxic environment) should be taken in account in mine waste management strategies. PMID:15884343

  5. Preparation of low molecular weight fucoidan by gamma-irradiation and its anticancer activity.

    PubMed

    Choi, Jong-il; Kim, Hyun-Joo

    2013-09-12

    Fucoidan is a marine sulfated polysaccharide with a wide variety of biological activities. Recently, it has been reported that low molecular weight fucoidan has the enhanced antioxidant and anticoagulative activities. However, degradation techniques such as enzymolysis and acid hydrolysis for obtaining low molecular weight fucoidan, have the disadvantages such as narrow substrate specificity and unfavorable hydrolysis of side groups, respectively. In this study, low molecular weight fucoidan was prepared by gamma-irradiation. When fucoidan was gamma-irradiated, the molecular weight rapidly dropped to 38 kDa when the sample was irradiated at 10 kGy, then gradually dropped to 7 kDa without the significant elimination of the sulfate groups. Low molecular weight fucoidan had higher cytotoxicity than native fucoidan in cancer cells, such as AGS, MCF-7, and HepG-2. In addition, low molecular weight fucoidan showed higher inhibitory activity of cell transformation, which resulted in higher anticarcinogenicity. This result suggests that low molecular weight fucoidan with enhanced biological activities can be produced by a simple irradiation method without changing the functional groups. PMID:23911457

  6. Perchlorate-induced combustion of organic matter with variable molecular weights: Implications for Mars missions

    NASA Astrophysics Data System (ADS)

    Sephton, Mark A.; Lewis, James M. T.; Watson, Jonathan S.; Montgomery, Wren; Garnier, Carole

    2014-11-01

    Instruments on the Viking landers and Curiosity rover analyzed samples of Mars and detected carbon dioxide and organic compounds of uncertain origin. Mineral-assisted reactions are leading to uncertainty, particularly those involving perchlorate minerals which thermally decompose to produce chlorine and oxygen which can then react with organic matter to generate organochlorine compounds and carbon dioxide. Although generally considered a problem for interpretation, the release profiles of generated gases can indicate the type of organic matter present. We have performed a set of experiments with perchlorate and organic matter of variable molecular weights. Results indicate that organic susceptibility to thermal degradation and mineral-assisted reactions is related to molecular weight. Low molecular weight organic matter reacts at lower temperatures than its high molecular weight counterparts. The natural occurrence and association of organic matter with differing molecular weights helps to discriminate between contamination (usually low molecular weight organic matter only) and indigenous carbon (commonly low and high molecular weight organic matter together). Our results can be used to provide insights into data returning from Mars.

  7. Low-molecular-weight heparin for the treatment of deep vein thrombosis.

    PubMed

    Thompson-Ford, J K

    1998-01-01

    Low-molecular-weight heparin has been studied for the treatment of deep vein thrombosis in the inpatient setting and more recently in the outpatient setting. It is as safe and effective as unfractionated heparin and is effective when administered subcutaneously once or twice a day. Its bioavailability nears 100% and it has a longer half-life than unfractionated heparin, resulting in a prolonged anticoagulant effect. A reduction in thrombocytopenia and bleeding complications with low-molecular-weight heparin has been reported. Laboratory monitoring is unnecessary. Low-molecular-weight heparin provides the opportunity for home therapy. PMID:9692649

  8. High molecular weight first generation PMR polyimides for 343 C applications

    NASA Technical Reports Server (NTRS)

    Malarik, D. C.; Vannucci, R. D.

    1992-01-01

    The effect of molecular weight on 343 C thermo-oxidative stability (TOS), mechanical properties, and processability, of the first generation PMR polyimides was studied. Graphite fiber reinforced PMR-15, PMR-30, PMR-50, and PMR-75 composites (corresponding to formulated molecular weights of 1500, 3000, 5000, and 7500, respectively) were fabricated using a simulated autoclave process. The data reveal that while alternate autoclave cure schedules are required for the high molecular weight resins, low void laminates can be fabricated which have significantly improved TDS over PMR-15, with only a small sacrifice in mechanical properties.

  9. Effect of sterilization irradiation on friction and wear of ultrahigh-molecular-weight polyethylene

    NASA Technical Reports Server (NTRS)

    Jones, W. R., Jr.; Hady, W. F.; Crugnola, A.

    1979-01-01

    The effect of sterilization gamma irradiation on the friction and wear properties of ultrahigh molecular weight polyethylene (UHMWPE) sliding against 316L stainless steel in dry air at 23 C was determined. A pin-on-disk apparatus was used. Experimental conditions included a 1-kilogram load, a 0.061- to 0.27-meter-per-second sliding velocity, and a 32000- to 578000-meter sliding distance. Although sterilization doses of 2.5 and 5.0 megarads greatly altered the average molecular weight and the molecular weight distribution, the friction and wear properties of the polymer were not significantly changed.

  10. High molecular weight first generation PMR polyimides for 343 C applications

    NASA Technical Reports Server (NTRS)

    Malarik, Diane C.; Vannucci, Raymond D.

    1991-01-01

    The effect of molecular weight on 343 C thermo-oxidative stability (TOS), mechanical properties, and processability, of the first generation PMR polyimides was studied. Graphite fiber reinforced PMR-15, PMR-30, PMR-50, and PMR-75 composites (corresponding to formulated molecular weights of 1500, 3000, 5000, and 7500, respectively) were fabricated using a simulated autoclave process. The data reveals that while alternate autoclave cure schedules are required for the high molecular weight resins, low void laminates can be fabricated which have significantly improved TOS over PMR-15, with only a small sacrifice in mechanical properties.

  11. Improved low-volatile bituminous coal representation: incorporating the molecular-weight distribution

    SciTech Connect

    Marielle R. Narkiewicz; Jonathan P. Mathews [Pennsylvania State University, University Park, PA (United States). Department of Energy and Mineral Engineering, and the Earth and Mineral Sciences Energy Institute

    2008-09-15

    A large ({gt}22 000 atoms) molecular representation of Pocahontas No. 3 low-volatile bituminous coal was generated that contains 215 separate molecular entities, ranging between 78 and 3286 amu, creating a molecular-weight distribution. Data used in this construction were based on (1) the average molecular properties and the carboxylation-oxidation molecular-weight distribution, (2) aromatic 'raft' size evaluation via image analysis of lattice fringe high-resolution transmission electron microscopy images, (3) molecular-weight distribution through laser desorption mass spectrometry, and (4) physical characteristics (molecular orientation and helium density). The large-scale coal representation enabled the incorporation of molecular-weight diversity, which is an improvement to the structural modeling of coal. The large-scale model is necessary to conform to an appropriate molecular-weight distribution. A preferred orientation that is expected for a coal of this rank was imposed. The inclusion of these improvements will better enable the model to be used in application studies. 39 refs., 7 figs., 2 tabs.

  12. Electrospinning and characterization of medium-molecular-weight poly(vinyl alcohol)\\/high-molecular-weight poly(vinyl alcohol)\\/montmorillonite nanofibers

    Microsoft Academic Search

    Hyun Mi Ji; Hyun Woo Lee; Mohammad Rezaul Karim; In Woo Cheong; Eun A. Bae; Tae Hun Kim; Byung Chul Ji; Jeong Hyun Yeum

    2009-01-01

    Submicron fibers of medium-molecular-weight poly(vinyl alcohol) (MMW-PVA), high-molecular-weight poly(vinyl alcohol) (HMW-PVA),\\u000a and montmorillonite clay (MMT) in aqueous solutions were prepared by electrospinning technique. The effect of HMW-PVA and\\u000a MMT on the morphology and mechanical properties of the MMW-PVA\\/HMW-PVA\\/MMT nanofibers were investigated for the first time.\\u000a Scanning electron microscopy, viscometer, tensile strength testing machine, thermal gravimetric analyzer (TGA), and transmission\\u000a electron

  13. Modeling the relationship between body weight and energy intake: A molecular diffusion-based approach

    PubMed Central

    2012-01-01

    Background Body weight is at least partly controlled by the choices made by a human in response to external stimuli. Changes in body weight are mainly caused by energy intake. By analyzing the mechanisms involved in food intake, we considered that molecular diffusion plays an important role in body weight changes. We propose a model based on Fick's second law of diffusion to simulate the relationship between energy intake and body weight. Results This model was applied to food intake and body weight data recorded in humans; the model showed a good fit to the experimental data. This model was also effective in predicting future body weight. Conclusions In conclusion, this model based on molecular diffusion provides a new insight into the body weight mechanisms. Reviewers This article was reviewed by Dr. Cabral Balreira (nominated by Dr. Peter Olofsson), Prof. Yang Kuang and Dr. Chao Chen. PMID:22742862

  14. 21 CFR 177.1440 - 4,4?-Isopropylidenediphenol-epichlorohydrin resins minimum molecular weight 10,000.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ...4â²-Isopropylidenediphenol-epichlorohydrin resins minimum molecular weight 10...4,4?-Isopropylidenediphenol-epichlorohydrin resins minimum molecular weight 10...4?-isopropylidenediphenol and epichlorohydrin terminated with phenol, to...

  15. 21 CFR 177.1440 - 4,4?-Isopropylidenediphenol-epichlorohydrin resins minimum molecular weight 10,000.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ...4â²-Isopropylidenediphenol-epichlorohydrin resins minimum molecular weight 10...4,4?-Isopropylidenediphenol-epichlorohydrin resins minimum molecular weight 10...4?-isopropylidenediphenol and epichlorohydrin terminated with phenol, to...

  16. 21 CFR 177.1440 - 4,4?-Isopropylidenediphenol-epichlorohydrin resins minimum molecular weight 10,000.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ...4â²-Isopropylidenediphenol-epichlorohydrin resins minimum molecular weight 10...4,4?-Isopropylidenediphenol-epichlorohydrin resins minimum molecular weight 10...4?-isopropylidenediphenol and epichlorohydrin terminated with phenol, to...

  17. 21 CFR 177.1440 - 4,4?-Isopropylidenediphenol-epichlorohydrin resins minimum molecular weight 10,000.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ...4â²-Isopropylidenediphenol-epichlorohydrin resins minimum molecular weight 10...4,4?-Isopropylidenediphenol-epichlorohydrin resins minimum molecular weight 10...4?-isopropylidenediphenol and epichlorohydrin terminated with phenol, to...

  18. 21 CFR 177.1440 - 4,4?-Isopropylidenediphenol-epichlorohydrin resins minimum molecular weight 10,000.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ...4â²-Isopropylidenediphenol-epichlorohydrin resins minimum molecular weight 10...4,4?-Isopropylidenediphenol-epichlorohydrin resins minimum molecular weight 10...4?-isopropylidenediphenol and epichlorohydrin terminated with phenol, to...

  19. Accurate ensemble molecular dynamics binding free energy ranking of multidrug-resistant HIV-1 proteases.

    PubMed

    Sadiq, S Kashif; Wright, David W; Kenway, Owain A; Coveney, Peter V

    2010-05-24

    Accurate calculation of important thermodynamic properties, such as macromolecular binding free energies, is one of the principal goals of molecular dynamics simulations. However, single long simulation frequently produces incorrectly converged quantitative results due to inadequate sampling of conformational space in a feasible wall-clock time. Multiple short (ensemble) simulations have been shown to explore conformational space more effectively than single long simulations, but the two methods have not yet been thermodynamically compared. Here we show that, for end-state binding free energy determination methods, ensemble simulations exhibit significantly enhanced thermodynamic sampling over single long simulations and result in accurate and converged relative binding free energies that are reproducible to within 0.5 kcal/mol. Completely correct ranking is obtained for six HIV-1 protease variants bound to lopinavir with a correlation coefficient of 0.89 and a mean relative deviation from experiment of 0.9 kcal/mol. Multidrug resistance to lopinavir is enthalpically driven and increases through a decrease in the protein-ligand van der Waals interaction, principally due to the V82A/I84V mutation, and an increase in net electrostatic repulsion due to water-mediated disruption of protein-ligand interactions in the catalytic region. Furthermore, we correctly rank, to within 1 kcal/mol of experiment, the substantially increased chemical potency of lopinavir binding to the wild-type protease compared to saquinavir and show that lopinavir takes advantage of a decreased net electrostatic repulsion to confer enhanced binding. Our approach is dependent on the combined use of petascale computing resources and on an automated simulation workflow to attain the required level of sampling and turn around time to obtain the results, which can be as little as three days. This level of performance promotes integration of such methodology with clinical decision support systems for the optimization of patient-specific therapy. PMID:20384328

  20. High Molecular Weight Petrogenic and Pyrogenic Hydrocarbons in Aquatic Environments

    NASA Astrophysics Data System (ADS)

    Abrajano, T. A., Jr.; Yan, B.; O'Malley, V.

    2003-12-01

    Geochemistry is ultimately the study of sources, movement, and fate of chemicals in the geosphere at various spatial and temporal scales. Environmental organic geochemistry focuses such studies on organic compounds of toxicological and ecological concern (e.g., Schwarzenbach et al., 1993, 1998; Eganhouse, 1997). This field emphasizes not only those compounds with potential toxicological properties, but also the geological systems accessible to the biological receptors of those hazards. Hence, the examples presented in this chapter focus on hydrocarbons with known health and ecological concern in accessible shallow, primarily aquatic, environments.Modern society depends on oil for energy and a variety of other daily needs, with present mineral oil consumption throughout the 1990s exceeding 3×109 t yr-1 (NRC, 2002). In the USA, e.g., ˜40% of energy consumed and 97% of transportation fuels are derived from oil. In the process of extraction, refinement, transport, use, and waste production, a small but environmentally significant fraction of raw oil materials, processed products, and waste are released inadvertently or purposefully into the environment. Because their presence and concentration in the shallow environments are often the result of human activities, these organic materials are generally referred to as "environmental contaminants." Although such reference connotes some form of toxicological or ecological hazard, specific health or ecological effects of many organic "environmental contaminants" remain to be demonstrated. Some are, in fact, likely innocuous at the levels that they are found in many systems, and simply adds to the milieu of biogenic organic compounds that naturally cycle through the shallow environment. Indeed, virtually all compounds in crude oil and processed petroleum products have been introduced naturally to the shallow environments as oil and gas seepage for millions of years ( NRC, 2002). Even high molecular weight (HMW) polyaromatic compounds were introduced to shallow environments through forest fires and natural coking of crude oil ( Ballentine et al., 1996; O'Malley et al., 1997). The full development of natural microbial enzymatic systems that can utilize HMW hydrocarbons as carbon or energy source attests to the antiquity of hydrocarbon dispersal processes in the environment. The environmental concern is, therefore, primarily due to the rate and spatial scale by which petroleum products are released in modern times, particularly with respect to the environmental sensitivity of some ecosystems to these releases ( Schwarzenbach et al., 1993; Eganhouse, 1997; NRC, 2002).Crude oil is produced by diagenetic and thermal maturation of terrestrial and marine plant and animal materials in source rocks and petroleum reservoirs. Most of the petroleum in use today is produced by thermal and bacterial decomposition of phytoplankton material that once lived near the surface of the world's ocean, lake, and river waters (Tissot and Welte, 1984). Terrestrially derived organic matter can be regionally significant, and is the second major contributor to the worldwide oil inventory ( Tissot and Welte, 1984; Peters and Moldowan, 1993; Engel and Macko, 1993). The existing theories hold that the organic matter present in crude oil consists of unconverted original biopolymers and new compounds polymerized by reactions promoted by time and increasing temperature in deep geologic formations. The resulting oil can migrate from source to reservoir rocks where the new geochemical conditions may again lead to further transformation of the petrogenic compounds. Any subsequent changes in reservoir conditions brought about by uplift, interaction with aqueous fluids, or even direct human intervention (e.g., drilling, water washing) likewise could alter the geochemical makeup of the petrogenic compounds. Much of our understanding of environmental sources and fate of hydrocarbon compounds in shallow environments indeed borrowed from the extensive geochemical and analytical framework that was meticulo

  1. Capillary Electrophoretic Separation of DNA Restriction Fragments in Mixtures of Low-and High-Molecular-Weight

    E-print Network

    Barron, Annelise E.

    Capillary Electrophoretic Separation of DNA Restriction Fragments in Mixtures of Low- and High-Molecular-Weight separation by CE in HEC solutions is strongly influenced by the average HEC molecular weight as well of the effects of a mixture of low- and high-molecular weight HEC polymers, over a range of concentrations

  2. Self-assembly of an ultra-high-molecular-weight comb block copolymer at the airwater interface

    E-print Network

    Lin, Zhiqun

    Self-assembly of an ultra-high-molecular-weight comb block copolymer at the air­water interface Lei explored using the Langmuir­Blodgett (LB) technique. The CBCP had an ultra-high molecular weight (Mw ¼ 510 studies. To the best of our knowledge, this is the first study of self-assembly of ultra-high-molecular-weight

  3. Molecular weight and humification index as predictors of adsorption for plant-and manure-derived dissolved

    E-print Network

    Chorover, Jon

    Molecular weight and humification index as predictors of adsorption for plant- and manure molecular weight (MWAP) of the DOM was measured by high performance-size exclusion chromatography and ranged. Molecular weight analysis of the solution prior to and after sorption indicated that the DOM molecules

  4. The Influence of Polymer Molecular Weight in Lamellar Gels Based on Heidi E. Warriner,* S. L. Keller,#

    E-print Network

    Zasadzinski, Joseph A.

    The Influence of Polymer Molecular Weight in Lamellar Gels Based on PEG-Lipids Heidi E. Warriner very low-molecular-weight polymer-lipids (1212, 2689, and 5817 g/mole), shows lamellar order, high-molecular-weight poly- (ethylene oxide) [(PEO, (OCH2CH2)N)], which has a low immunogenicity

  5. Friction and wear behavior of ultra-high molecular weight polyethylene as a function of polymer crystallinity

    E-print Network

    Lin, Zhiqun

    Friction and wear behavior of ultra-high molecular weight polyethylene as a function of polymer-grade ultra-high molecular weight polyethylene (UHMWPE) (GUR 1050 resin) were evaluated as a function replacements; Ultra-high molecular weight polyethylene (UHMWPE); Crystallinity; Friction; Wear 1. Introduction

  6. Low molecular weight thiols in arsenic hyperaccumulator Pteris vittata upon exposure to arsenic and other trace elements

    E-print Network

    Ma, Lena

    Low molecular weight thiols in arsenic hyperaccumulator Pteris vittata upon exposure to arsenic; accepted 25 September 2003 ``Capsule'': Arsenic induces synthesis of low molecular weight thiols in the arsenic hyperaccumulator Pteris vittata. Abstract Low molecular weight thiol-containing compounds have

  7. Effect of protein molecular weight on the mass transfer in protein mixing

    NASA Astrophysics Data System (ADS)

    Asad, Ahmed; Chai, Chuan; Wu, JiangTao

    2012-03-01

    The mixing of protein solutions with that of precipitating agents is very important in protein crystallization experiments. In this work, the interferometry images were recorded during the mixing of two proteins with different molecular weights: lysozyme of ˜14.6 kDa, trypsin of ˜23.3 kDa and pepsin of ˜34.8 kDa were placed in a Mach-Zehnder interferometer. The protein molecular weight dependence on the competition of the transport process and kinetics at the interface was studied. The concentration profiles of protein solutions were calculated to analyze the mass transfer during the mixing process. It was observed that the mass transfer process is more efficient during the mixing of proteins with higher molecular weights. In addition, the more rapid concentration changes above the interface suggest that convection may dominate the diffusion. The phenomenon of convection is higher in the protein solutions with higher molecular weight.

  8. Improved performance of ultra-high molecular weight polyethylene for orthopedic applications

    E-print Network

    Plumlee, Kevin Grant

    2009-05-15

    A considerable number of total-joint replacement devices used in orthopedic medicine involve articulation between a metallic alloy and ultra-high molecular weight polyethylene (UHMWPE). Though this polymer has excellent wear resistance, the wear...

  9. Methods for increasing the thermal conductivity of ultra-high molecular weight polyethylene (UHMWPE)

    E-print Network

    Miler, Josef L

    2006-01-01

    A two-part study was conducted to determine methods for producing ultra-high molecular weight polyethylene with high thermal conductivity by way of polymer chain orientation. The first portion of this report surveys current ...

  10. Unique Profile of Chicken Adiponectin, a Predominantly Heavy Molecular Weight Multimer,

    E-print Network

    Ramachandran, Ramesh

    Unique Profile of Chicken Adiponectin, a Predominantly Heavy Molecular Weight Multimer adiponectin levels in chickens, which are naturally hyperglycemic relative to mammals. Using gel filtration conditions, adiponectin in chicken plasma, and adipose tissue is predominantly a multimeric HMW isoform

  11. The influence of gamma radiation on the molecular weight and glass transition of PLLA and HAp/PLLA nanocomposite

    NASA Astrophysics Data System (ADS)

    Milicevic, D.; Trifunovic, S.; Dojcilovic, J.; Ignjatovic, N.; Suljovrujic, E.

    2010-09-01

    The influence of gamma radiation on the molecular weight and glass transition behaviour of poly- L-lactide (PLLA) and hydroxyapatite/poly- L-lactide (HAp/PLLA) nanocomposite has been studied. Since PLLA exposed to high-energy radiation in the presence of air is prone to chain scission reactions and large degradation, changes in molecular weight were obtained by gel permeation chromatography (GPC). Alterations in the glass transition behaviour were investigated by differential scanning calorimetry (DSC). The apparent activation energy (? H?) for glass transition was determined on the basis of the heating rate dependence of the glass transition temperature ( T g). Our findings support the fact that chain scission is the main reason for the decrease of T g and ? H? with the absorbed dose. Furthermore, more intensive chain scission degradation of PLLA was observed in HAp/PLLA and can only be ascribed to the presence of HAp nanoparticles. Consequently, initial differences in the glass transition temperature and/or apparent activation energy of PLLA and HAp/PLLA became more pronounced with absorbed dose. This study reveals that radiation-induced changes in molecular weight and glass transition temperature occur in a predictable and fairly accurate manner. Therefore, gamma radiation can be used not only for sterilization but also for tailoring desirable end-use properties of these biomaterials.

  12. Hydration free energies of cyanide and hydroxide ions from molecular dynamics simulations with accurate force fields

    USGS Publications Warehouse

    Lee, M.W.; Meuwly, M.

    2013-01-01

    The evaluation of hydration free energies is a sensitive test to assess force fields used in atomistic simulations. We showed recently that the vibrational relaxation times, 1D- and 2D-infrared spectroscopies for CN(-) in water can be quantitatively described from molecular dynamics (MD) simulations with multipolar force fields and slightly enlarged van der Waals radii for the C- and N-atoms. To validate such an approach, the present work investigates the solvation free energy of cyanide in water using MD simulations with accurate multipolar electrostatics. It is found that larger van der Waals radii are indeed necessary to obtain results close to the experimental values when a multipolar force field is used. For CN(-), the van der Waals ranges refined in our previous work yield hydration free energy between -72.0 and -77.2 kcal mol(-1), which is in excellent agreement with the experimental data. In addition to the cyanide ion, we also study the hydroxide ion to show that the method used here is readily applicable to similar systems. Hydration free energies are found to sensitively depend on the intermolecular interactions, while bonded interactions are less important, as expected. We also investigate in the present work the possibility of applying the multipolar force field in scoring trajectories generated using computationally inexpensive methods, which should be useful in broader parametrization studies with reduced computational resources, as scoring is much faster than the generation of the trajectories.

  13. Effect of molecular weight on crystallization, melting behavior and morphology of poly(trimethylene terephalate)

    Microsoft Academic Search

    Xudong Chen; Gong Hou; Yujun Chen; Kun Yang; Yeping Dong; Hui Zhou

    2007-01-01

    The crystallization behavior of poly(trimethylene terephthalate) (PTT) as a function of molecular weight was investigated under non-isothermal and isothermal conditions using differential scanning calorimetry (DSC), temperature-modulated differential scanning analysis (TMDSC) and polarized light optical microscopy (PLOM). The overall rate of bulk crystallization decreased with increasing molecular weight. The enthalpy for non-isothermal cold crystallization (?Hc), the melting enthalpy (?Hm), the melting

  14. Low-molecular-weight heparin during instability in coronary artery disease

    Microsoft Academic Search

    1996-01-01

    SummaryBackground Intravenous heparin is at least as effective as aspirin in preventing new cardiac events after an episode of unstable coronary artery disease (CAD), though the benefits are short-lived. Low-molecular-weight heparin has similar antithrombotic properties but can be given subcutaneously and is therefore suitable for long-term treatment. We have investigated whether subcutaneous low-molecular-weight heparin, in addition to aspirin and antianginal

  15. Enhancement of molecular weight build up in polyimides using ether solvents

    NASA Technical Reports Server (NTRS)

    Egli, Annemarie H.; St. Clair, Terry L.

    1985-01-01

    Two linear polyimides were prepared in various ether and amide solvents. The inherent viscosity was then monitored as a function of time. The polymers made in the ether solvents consistently gave higher inherent viscosities, and thus molecular weights, than the same polymers made in the amide solvents. This molecular weight buildup is attributed to the unique solvation mechanism of the ether solvents which enhances the basicity of the amines via hydrogen bonding.

  16. Corner rounding in EUV photoresist: tuning through molecular weight, PAG size, and development time

    SciTech Connect

    Anderson, Christopher; Daggett, Joe; Naulleau, Patrick

    2009-12-31

    In this paper, the corner rounding bias of a commercially available extreme ultraviolet photoresist is monitored as molecular weight, photoacid generator (PAG) size, and development time are varied. These experiments show that PAG size influences corner biasing while molecular weight and development time do not. Large PAGs are shown to exhibit less corner biasing, and in some cases, lower corner rounding, than small PAGs. In addition, heavier resist polymers are shown to exhibit less corner rounding than lighter ones.

  17. Molecular weight effects on solution rheology of pullulan and mechanical properties of its films

    Microsoft Academic Search

    Athina Lazaridou; Costas G Biliaderis; Vassilis Kontogiorgos

    2003-01-01

    The effects of molecular weight on solution rheology of pullulan, and on thermomechanichal properties of sorbitol and\\/or water-plasticized pullulan specimens, prepared by either hot pressing or casting of aqueous solutions, were studied. Pullulan samples differing in molecular weight were characterized by 13C NMR spectroscopy and size exclusion chromatography combined with a multiangle laser light scattering and a refractive index detector.

  18. Citrate compared to low molecular weight heparin anticoagulation in chronic hemodialysis patients

    Microsoft Academic Search

    Martien J F M Janssen; Jeroen K Deegens; Theodoor H Kapinga; Johan R Beukhof; Peter C Huijgens; Arie C van Loenen; Jan van der Meulen

    1996-01-01

    Citrate compared to low molecular weight heparin anticoagulation in chronic hemodialysis patients. Citrate and nadroparin calcium, a low molecular weight heparin (LMWH), were compared in a randomized cross-over trial in 21 chronic hemodialysis patients regarding anticoagulation, calcium and magnesium kinetics, biocompatibility, dialysis efficiency, and aluminum contamination. Citrate was infused into the arterial line at a minimum rate of 0.68 mmol\\/min,

  19. Peptide containing microspheres from low molecular weight and hydrophilic poly( d, l-lactide-co-glycolide)

    Microsoft Academic Search

    Rahul C. Mehta; B. C. Thanoo; Patrick P. Deluca

    1996-01-01

    Biodegradable poly(d,l-lactide-co-glycolide) (PLGA) polymers of molecular weight lower than 30 000 Da and free terminal carboxylic acid end groups were evaluated for incorporation of a peptide. These low molecular weight hydrophilic polymers require characterization for carboxylic acid content and fraction of water soluble polymer, both of which significantly affected the structure and peptide incorporation. The polymers from different suppliers have

  20. Degradation of high molecular weight poly( l-lactide) in alkaline medium

    Microsoft Academic Search

    Darinn Cam; Suong-hyu Hyon; Yoshito Ikada

    1995-01-01

    To study the effect of molecular weight and morphology on hydrolytic degradation, four poly(l-lactide)s (PLLAs) with average molecular weight of 3.0 × 105, 4.5 x 105, 6.5 × 105 and 3 × 106 were used. PLLA films with different morphologies were obtained by solution casting. Degradation of the films was performed at 37 °C in 0.01 n NaOH solution and

  1. Synthesis and Characterization of Low Molecular Weight Azido Polymers as High Energetic Plasticizers

    Microsoft Academic Search

    Y. Murali Mohan; K. Mohana Raju

    2004-01-01

    The present work describes a convenient process for the preparation of low molecular weight hydroxyl-terminated glycidyl azide polymers. The facile route involves the formation of glycidyl azide polymer in a single step. The polymerization of epichlorohydrin was carried out in dipolar aprotic solvent N,N-dimethylformamide (DMF) medium using diols as initiators in the presence of sodium azide. Various low molecular weight

  2. Portable Compression Device and Low-Molecular-Weight Heparin Compared With Low-Molecular-Weight Heparin for Thromboprophylaxis After Total Joint Arthroplasty

    Microsoft Academic Search

    John Z. Edwards; Pamela A. Pulido; Kace A. Ezzet; Steven N. Copp; Richard H. Walker; Clifford W. Colwell

    2008-01-01

    This preliminary prospective study to determine the rate of deep venous thrombosis (DVT) examined 277 patients undergoing total knee or total hip arthroplasty (TKA or THA) who were randomized to use a portable, continuous enhanced circulation therapy (CECT) compression device and low-molecular-weight heparin (LMWH) or to receive LMWH alone. Patients were screened for DVT using duplex ultrasound at hospital discharge

  3. Sulphydryl oxidation in the mechanism of molecular-weight conversion of renin in dog kidney.

    PubMed

    Ikemoto, F; Takaori, K; Iwao, H; Yamamoto, K

    1982-02-01

    1. A high-molecular-weight renin (M(r) 60 000) was formed by the reaction of a low-molecular-weight renin (M(r) 40 000) with a renin-binding substance in canine renal cortical extract in the presence of the sulphydryl (SH) group oxidizing agent potassium tetrathionate; thus the reaction required SH oxidation. 2. Renin extracted from isolate renin granules was adsorbed on to thiopropyl Sepharose 6B, and then liberated with dithiothreitol (50 mmol/1), indicating that it possessed on SH moiety(s). 3. However, the renin was capable of reaction with the renin-binding substance even after its SH moiety (or moieties) was protected with 5,5'- dithiobis-(2-nitrobenzoic acid). 4. The high-molecular-weight renin was converted into the low-molecular-weight renin by incubation (37 degrees C, 15 min) with cytosol (soluble fraction) of renal cortex and liver. Such converting ability was diminished after the cytosol was treated with perchloric acid or potassium tetrathionate. 5. These results suggest that the reaction of renin with the renin-binding substances does not require disulphide bond(s) and that an enzyme-like substance which is sensitive to SH oxidation is involved in the conversion from the high molecular-weight renin into the low-molecular weight renin. PMID:7032805

  4. Molecular weight dependent vertical composition profiles of PCDTBT:PC??BM blends for organic photovoltaics.

    PubMed

    Kingsley, James W; Marchisio, Pier Paolo; Yi, Hunan; Iraqi, Ahmed; Kinane, Christy J; Langridge, Sean; Thompson, Richard L; Cadby, Ashley J; Pearson, Andrew J; Lidzey, David G; Jones, Richard A L; Parnell, Andrew J

    2014-01-01

    We have used Soxhlet solvent purification to fractionate a broad molecular weight distribution of the polycarbazole polymer PCDTBT into three lower polydispersity molecular weight fractions. Organic photovoltaic devices were made using a blend of the fullerene acceptor PC??BM with the molecular weight fractions. An average power conversion efficiency of 5.89% (peak efficiency of 6.15%) was measured for PCDTBT blend devices with a number average molecular weight of Mn = 25.5 kDa. There was significant variation between the molecular weight fractions with low (Mn = 15.0 kDa) and high (Mn = 34.9 kDa) fractions producing devices with average efficiencies of 5.02% and 3.70% respectively. Neutron reflectivity measurements on these polymer:PC??BM blend layers showed that larger molecular weights leads to an increase in the polymer enrichment layer thickness at the anode interface, this improves efficiency up to a limiting point where the polymer solubility causes a reduction of the PCDTBT concentration in the active layer. PMID:24924096

  5. Molecular weight dependent vertical composition profiles of PCDTBT:PC71BM blends for organic photovoltaics

    NASA Astrophysics Data System (ADS)

    Kingsley, James W.; Marchisio, Pier Paolo; Yi, Hunan; Iraqi, Ahmed; Kinane, Christy J.; Langridge, Sean; Thompson, Richard L.; Cadby, Ashley J.; Pearson, Andrew J.; Lidzey, David G.; Jones, Richard A. L.; Parnell, Andrew J.

    2014-06-01

    We have used Soxhlet solvent purification to fractionate a broad molecular weight distribution of the polycarbazole polymer PCDTBT into three lower polydispersity molecular weight fractions. Organic photovoltaic devices were made using a blend of the fullerene acceptor PC71BM with the molecular weight fractions. An average power conversion efficiency of 5.89% (peak efficiency of 6.15%) was measured for PCDTBT blend devices with a number average molecular weight of Mn = 25.5 kDa. There was significant variation between the molecular weight fractions with low (Mn = 15.0 kDa) and high (Mn = 34.9 kDa) fractions producing devices with average efficiencies of 5.02% and 3.70% respectively. Neutron reflectivity measurements on these polymer:PC71BM blend layers showed that larger molecular weights leads to an increase in the polymer enrichment layer thickness at the anode interface, this improves efficiency up to a limiting point where the polymer solubility causes a reduction of the PCDTBT concentration in the active layer.

  6. Molecular weight dependent vertical composition profiles of PCDTBT:PC71BM blends for organic photovoltaics

    PubMed Central

    Kingsley, James W.; Marchisio, Pier Paolo; Yi, Hunan; Iraqi, Ahmed; Kinane, Christy J.; Langridge, Sean; Thompson, Richard L.; Cadby, Ashley J.; Pearson, Andrew J.; Lidzey, David G.; Jones, Richard A. L.; Parnell, Andrew J.

    2014-01-01

    We have used Soxhlet solvent purification to fractionate a broad molecular weight distribution of the polycarbazole polymer PCDTBT into three lower polydispersity molecular weight fractions. Organic photovoltaic devices were made using a blend of the fullerene acceptor PC71BM with the molecular weight fractions. An average power conversion efficiency of 5.89% (peak efficiency of 6.15%) was measured for PCDTBT blend devices with a number average molecular weight of Mn = 25.5?kDa. There was significant variation between the molecular weight fractions with low (Mn = 15.0?kDa) and high (Mn = 34.9?kDa) fractions producing devices with average efficiencies of 5.02% and 3.70% respectively. Neutron reflectivity measurements on these polymer:PC71BM blend layers showed that larger molecular weights leads to an increase in the polymer enrichment layer thickness at the anode interface, this improves efficiency up to a limiting point where the polymer solubility causes a reduction of the PCDTBT concentration in the active layer. PMID:24924096

  7. [Purification and properties of low molecular weight endoglucanase of the cellulase complex from Trichoderma koningii].

    PubMed

    Churilova, I V; Maksimov, V I; Klesov, A A

    1980-04-01

    A homogenous low molecular weight 1,4-beta-glucan glucanohydrolase (endoglucanase) has been isolated from a crude commercial preparation of cellokoningine P10X of T. koningii origin. The molecular weight of the enzyme as determined by polyacrylamide gel electrophoresis is 13 000. The endoglucanase was obtained as a lyophylized preparation free of the cellobiase activity. It was shown that cellobiose or methylcellobioside activate the effect of the low molecular weight endoglucanase (measured by the viscometric technique with respect to CMC hydrolysis) and at the same time almost completely suppress the activity of high molecular weight endoglucanases from the sane source. A detailed kinetic study of the effects showed that the low molecular weight enzyme is activated by a transglycosylation mechanism, where cellobiose acts as an added nucleophile. The activation is 6-fold at saturating concentrations of cellobiose (Ks = 15 mM). It was shown that diverse kinetic behaviour of cellobiose which can act both as activatory and inhibitor for endoglucanases from different sources can be explained, firstly, by different ratios of low to high molecular weight endoglucanases in the cellulase complexes, and, secondly, by their ability to catalyze transglycosylation reactions, which, in turn, results in a transfer of reducing end groups of the reaction products onto cellobiose as an added nucleophile. PMID:7189672

  8. Changes in the molecular weight distribution of dissolved organic carbon within a Precambrian shield stream

    Microsoft Academic Search

    D. N. Kothawala; R. D. Evans; P. J. Dillon

    2006-01-01

    Dissolved organic carbon (DOC) is of environmental and biological significance to Precambrian shield streams. Our objective was to determine the extent of transformations to the concentration and molecular weight distribution (MWD) of DOC along the length of Harp 4A stream, from the headwater swamp to the outflow into Harp Lake. The average MWD shifted to a smaller weight by 0.48

  9. Scientific note A scientific note on the preparation of high molecular weight DNA

    E-print Network

    Paris-Sud XI, Université de

    electrophoresis (PFGE). Various meth- ods have been described for the isolation of DNA suitable for PFGE analysis on dissection of specific tissues from insects. Since very large amounts of high molec- ular weight DNA most of the insect body. High molecular weight DNA could be obtained from larvae and pupae but not from

  10. Two-dimensional spatial coherence of excitons in semicrystalline polymeric semiconductors: Effect of molecular weight

    NASA Astrophysics Data System (ADS)

    Paquin, Francis; Yamagata, Hajime; Hestand, Nicholas J.; Sakowicz, Maciej; Bérubé, Nicolas; Côté, Michel; Reynolds, Luke X.; Haque, Saif A.; Stingelin, Natalie; Spano, Frank C.; Silva, Carlos

    2013-10-01

    The electronic properties of macromolecular semiconductor thin films depend profoundly on their solid-state microstructure, which in turn is governed, among other things, by the processing conditions selected and the polymer's chemical nature and molecular weight. Specifically, low-molecular-weight materials form crystalline domains of cofacially ?-stacked molecules, while the usually entangled nature of higher-molecular-weight polymers leads to microstructures comprised of molecularly ordered crystallites interconnected by amorphous regions. Here, we examine the interplay between extended exciton states delocalized along the polymer backbones and across polymer chains within the ? stack, depending on the structural development with molecular weight. Such two-dimensional excitations can be considered as Frenkel excitons in the limit of weak intersite coupling. We combine optical spectroscopies, thermal probes, and theoretical modeling, focusing on neat poly(3-hexylthiophene) (P3HT)—one of the most extensively studied polymeric semiconductors—of weight-average molecular weight (Mw) of 3-450 kg/mol. In thin-film structures of high-molecular-weight materials (Mw > 50 kg/mol), a balance of intramolecular and intermolecular excitonic coupling results in high exciton coherence lengths along chains (˜4.5 thiophene units), with interchain coherence limited to ˜2 chains. In contrast, for structures of low-Mw P3HT (<50 kg/mol), the interchain exciton coherence is dominant (˜30% higher than in architectures formed by high-molecular-weight materials). In addition, the spatial coherence within the chain is significantly reduced (by nearly 25%). These observations give valuable structural information; they suggest that the macromolecules in aggregated regions of high-molecular-weight P3HT adopt a more planar conformation compared to low-molecular-weight materials. This results in the observed increase in intrachain exciton coherence. In contrast, shorter chains seem to lead to torsionally more disordered architectures. A rigorous, fundamental description of primary photoexcitations in ?-conjugated polymers is hence developed: two-dimensional excitons are defined by the chain-length dependent molecular arrangement and interconnectivity of the conjugated macromolecules, leading to interplay between intramolecular and intermolecular spatial coherence.

  11. Effects of Dextran Molecular Weight on Red Blood Cell Aggregation

    PubMed Central

    Neu, Björn; Wenby, Rosalinda; Meiselman, Herbert J.

    2008-01-01

    The reversible aggregation of human red blood cells (RBC) by proteins or polymers continues to be of biologic and biophysical interest, yet the mechanistic details governing the process are still being explored. Although a depletion model with osmotic attractive forces due to polymer depletion near the RBC surface has been proposed for aggregation by the neutral polyglucose dextran, its applicability at high molecular mass has not been established. In this study, RBC aggregation was measured over a wide range of dextran molecular mass (70 kDa to 28 MDa) at concentrations ?2 g/dL. Our results indicate that aggregation does not monotonically increase with polymer size; instead, it demonstrates an optimum dextran molecular mass around 200-500 kDa. We used a model for depletion-mediated RBC aggregation to calculate the expected depletion energies. This model was found to be consistent with the experimental results and thus provides new insight into polymer-RBC interactions. PMID:18586848

  12. Unified wear model for highly crosslinked ultra-high molecular weight polyethylenes (UHMWPE)

    Microsoft Academic Search

    Orhun K. Muratoglu; Charles R. Bragdon; Daniel O. O’Connor; Murali Jasty; William H. Harris; Rizwan Gul; Fred McGarry

    1999-01-01

    Crosslinking has been shown to improve the wear resistance of ultra-high molecular weight polyethylene in both in vitro and clinical in vivo studies. The molecular mechanisms and material properties that are responsible for this marked improvement in wear resistance are still not well understood. In fact, following crosslinking a number of mechanical properties of UHMWPE are decreased including toughness, modulus,

  13. Use of Kinematic Viscosity Data for the Evaluation of the Molecular Weight of Petroleum Oils

    ERIC Educational Resources Information Center

    Maroto, J. A.; Quesada-Perez, M.; Ortiz-Hernandez, A. J.

    2010-01-01

    A new laboratory procedure for the evaluation of the mean molecular weight (mean relative molecular mass) of petroleum oils with high accuracy is described. The density and dynamic viscosity of three commercial petroleum oils are measured at different temperatures. These experimental data are used to calculate the kinematic viscosity as a function…

  14. Tailoring a low-molecular weight protein tyrosine phosphatase into an efficient reporting protein

    SciTech Connect

    Liu, Xiao-Yan; Li, Lan-Fen [The National Laboratory of Protein Engineering and Plant Genetic Engineering, College of Life Science, Peking University, Beijing 100871 (China)] [The National Laboratory of Protein Engineering and Plant Genetic Engineering, College of Life Science, Peking University, Beijing 100871 (China); Su, Xiao-Dong, E-mail: xdsu@pku.edu.cn [The National Laboratory of Protein Engineering and Plant Genetic Engineering, College of Life Science, Peking University, Beijing 100871 (China) [The National Laboratory of Protein Engineering and Plant Genetic Engineering, College of Life Science, Peking University, Beijing 100871 (China); Shenzhen Graduate School of Peking University, Shenzhen 518055 (China)

    2009-05-15

    Fusion reporter methods are important tools for biology and biotechnology. An ideal reporter protein in a fusion system should have little effects on its fusion partner and provide an easy and accurate readout. Therefore, a small monomeric protein with high activity for detection assays often has advantages as a reporter protein. For this purpose, we have tailored the human B-form low-molecular-weight phosphotyrosyl phosphatase (HPTP-B) to increase its general applicability as a potent reporter protein. With the aim to eliminate interference from cysteine residues in the native HPTP-B, combined with a systematic survey of N- and C-terminal truncated variants, a series of cysteine to serine mutations were introduced, which allowed isolation of an engineered soluble protein with suitable biophysical properties. When we deleted both the first six residues and the last two residues, we still obtained a soluble mutant protein with correct folding and similar activity with wild-type protein. This mutant with two cysteine to serine mutations, HPTP-B{sup N{sub {Delta}}6-C{sub {Delta}}2-C90S-C109S}, has good potential as an optimal reporter.

  15. Determination of molecular weights of humic substances by analytical (UV scanning) ultracentrifugation

    NASA Astrophysics Data System (ADS)

    Reid, Patrick M.; Wilkinson, Alan E.; Tipping, Edward; Jones, Malcolm N.

    1990-01-01

    Samples of peat humic acid (PHA) and surface water humic (WBHA) and fulvic (WBFA) acids have been extracted from Whitray Beck in North Yorkshire, U.K. The molecular weights of the extracts have been investigated by sedimentation equilibrium using an analytical ultracentrifuge equipped with a UV scanning system. The system allows measurements to be made at low concentrations of humic substances, comparable to those existing in natural humic-rich water. A method is described for correcting UV scanning data for changes in the optical properties of the materials with changing molecular weight. Measurements have also been made on reference samples of Suwannee river humic (SRHA) and fulvic (SRFA) acids from the International Humic Substances Society (IHSS). The weight-average molecular weights of the extracted samples range from approximately 2000 to 17000 and follow a series PHA > WBHA > WBFA. Apparent specific volumes of these materials were in a range from 0.45 to 0.58 cm 3 g -1 as measured by digital densimetry. All the samples studied were analysed by gel filtration, but the molecular weights determined by this method based on a globular protein calibration are not in good accord with the absolute determinations by the sedimentation-equilibrium technique. The molecular weight of the SRHA determined by sedimentation equilibrium is in good agreement with that reported by BECKETT (1987) et al., based on flow field-flow fractionation.

  16. Polymerization of Kraft lignin via ultrasonication for high-molecular-weight applications.

    PubMed

    Wells, Tyrone; Kosa, Matyas; Ragauskas, Arthur J

    2013-11-01

    Kraft lignin is an inexpensive and abundant byproduct of pulp mills that can be used in the synthesis of adhesives and carbon fibers along with energy production. Some of these material applications favor the utilization of high molecular weight (HMW) lignin. This study investigates the use of ultrasonics as a means to increase the degree of polymerization (DP) of highly purified Kraft lignin. Treated samples were characterized by gel permeation chromatography (GPC), Fourier transform infrared (FTIR) spectroscopy, (13)C and (31)P nuclear magnetic resonance (NMR). After 15 min of sustained cavitation, ultrasonicated lignin generated a high molecular-weight fraction (~35%) that had a weight-average molecular weight (Mw) over 450-fold greater than the initial Kraft lignin sample. (13)C-NMR and (31)P-NMR analysis indicated that the highly-polymerized fraction was enriched with C5 condensed phenolic structures. PMID:23714331

  17. Profiling of the Molecular Weight and Structural Isomer Abundance of Macroalgae-Derived Phlorotannins

    PubMed Central

    Heffernan, Natalie; Brunton, Nigel P.; FitzGerald, Richard J.; Smyth, Thomas J.

    2015-01-01

    Phlorotannins are a group of complex polymers of phloroglucinol (1,3,5-trihydroxybenzene) unique to macroalgae. These phenolic compounds are integral structural components of the cell wall in brown algae, but also play many secondary ecological roles such as protection from UV radiation and defense against grazing. This study employed Ultra Performance Liquid Chromatography (UPLC) with tandem mass spectrometry to investigate isomeric complexity and observed differences in phlorotannins derived from macroalgae harvested off the Irish coast (Fucus serratus, Fucus vesiculosus, Himanthalia elongata and Cystoseira nodicaulis). Antioxidant activity and total phenolic content assays were used as an index for producing phlorotannin fractions, enriched using molecular weight cut-off dialysis with subsequent flash chromatography to profile phlorotannin isomers in these macroalgae. These fractions were profiled using UPLC-MS with multiple reaction monitoring (MRM) and the level of isomerization for specific molecular weight phlorotannins between 3 and 16 monomers were determined. The majority of the low molecular weight (LMW) phlorotannins were found to have a molecular weight range equivalent to 4–12 monomers of phloroglucinol. The level of isomerization within the individual macroalgal species differed, resulting in substantially different numbers of phlorotannin isomers for particular molecular weights. F. vesiculosus had the highest number of isomers of 61 at one specific molecular mass, corresponding to 12 phloroglucinol units (PGUs). These results highlight the complex nature of these extracts and emphasize the challenges involved in structural elucidation of these compounds. PMID:25603345

  18. Malignant hypertension: a syndrome accompanied by plasmatic diminution of low and high molecular weight kininogens.

    PubMed

    Ribeiro, A B; Schwarzwalder, S R; Saragoça, M A; Almeida, F A; Voos, A; Stella, R C; Ramos, O L

    1983-01-01

    Total kininogen (Kgn), kallikrein, and prekallikrein were measured in patients with malignant hypertension (MH), essential hypertension (EH), normotensive control (NC), and hypertension and chronic renal failure (HRF). These components of the kallikrein-kinin system were related to the levels of creatinine and fibrinogen. High molecular weight Kgn and low molecular weight Kgn were also measured in blood samples from a peripheral vein, arterial blood, and suprahepatic vein in NC, EH, and MH. Results showed that total Kgn levels were diminished in MH and this diminution could not be ascribed to decreases in renal function, hematocrit, or fibrinogen levels. Appropriate antihypertensive treatment for over 1 year did not normalize Kgn levels in 10 of 11 patients. High molecular weight Kgn and low molecular weight Kgn were both diminished in MH (0.26 +/- 0.04 nmol bradykinin/ml and 0.93 +/- 0.12 nmol lysyl-bradykinin/ml, respectively) as compared to NC (0.39 +/- 0.07 and 1.92 +/- 0.16) and EH (0.51 +/- 0.07 and 1.65 +/- 0.13). Higher concentrations of high molecular weight Kgn were demonstrated in the suprahepatic vein as compared to arterial blood, demonstrating its synthesis by the liver. However, patients with MH had a diminished capacity to synthetize high molecular weight Kgn. A decrease in synthesis of high molecular weight Kgn may be a partial explanation for low levels of total Kgn. It is suggested that a lack of Kgn may play a role in the pathogenesis of MH. PMID:6558004

  19. Adsorption of dissolved organics in lake water by aluminum oxide. Effect of molecular weight

    USGS Publications Warehouse

    Davis, J.A.; Gloor, R.

    1981-01-01

    Dissolved organic compounds in a Swiss lake were fractionated into three molecular size classes by gel exclusion chromatography, and adsorption of each fraction on colloidal alumina was studied as a function of pH. Organic compounds with molecular weight (Mr) greater than 1000 formed strong complexes with the alumina surface, but low molecular weight compounds were weakly adsorbed. Electrophoretic mobility measurements indicated that alumina particles suspended in the original lake water were highly negatively charged because of adsorbed organic matter. Most of the adsorbed organic compounds were in the Mr range 1000 < Mr < 3000. Adsorption of these compounds during the treatment of drinking water by alum coagulation may be responsible for the preferential removal of trihalomethane precursors. Adsorption may also influence the molecular-weight distribution of dissolved organic material in lakes. surface, the present work will focus on the influence of molecular size and pH on the adsorption behavior of dissolved organic material of a Swiss lake. From a geochemical point of view, it is important to know the molecular-weight distribution of adsorbed organic matter so that we may better assess its reactivity with trace elements. The study also serves as a first step in quantifying the role of adsorption in the geochemical cycle of organic carbon in lacustrine environments. For water-treatment practice, we need to determine whether molecular weight fractionation occurs during adsorption by aluminum oxide. Such a fractionation could be significant in the light of recent reports that chloroform and other organochlorine compounds are preferentially produced by particular molecular-weight fractions (25-27). ?? 1981 American Chemical Society.

  20. The Role of Molecular Weight and Temperature on the Elastic and Viscoelastic Properties of a Glassy Thermoplastic Polyimide

    NASA Technical Reports Server (NTRS)

    Nicholson, Lee M.; Whitley, Karen S.; Gates, Thomas S.

    2001-01-01

    Mechanical testing of the elastic and viscoelastic response of an advanced thermoplastic polyimide (LaRC-SI) with known variations in molecular weight was performed over a range of temperatures below the glass transition temperature. The notched tensile strength was shown to be a strong function of both molecular weight and temperature, whereas stiffness was only a strong function of temperature. A critical molecular weight was observed to occur at a weight average molecular weight of M, approx. 22,000 g/mol below which, the notched tensile strength decreases rapidly. This critical molecular weight transition is temperature-independent. Low, molecular weight materials tended to fail in a brittle manner, whereas high molecular weight materials exhibited ductile failure. Furthermore, low molecular weight materials have increased creep compliance and creep compliance rate, and are more sensitive to temperature than the high molecular weight materials. At long timescales (less than 1100 hours) physical aging serves to significantly decrease the creep compliance and creep rate of all the materials tested. Low molecular weight materials are less influenced by the effects of physical aging.

  1. Determination of molecular weights of humic substances by analytical (UV scanning) ultracentrifugation

    SciTech Connect

    Reid, P.M.; Wilkinson, A.E.; Tipping, E.; Jones, M.N. (Univ. of Manchester (England) Freshwater Biological Association, Ambleside, Cumbria (England))

    1990-01-01

    Samples of peat humic acid (PHA) and surface water humic (WBHA) and fulvic (WBFA) acids have been extracted from Whitray Beck in North Yorkshire, U.K. The molecular weights of the extracts have been investigated by sedimentation equilibrium using an analytical ultracentrifuge equipped with a UV scanning system. The system allows measurements to be made at low concentrations of humic substances, comparable to those existing in natural humic-rich water. A method is described for correcting UV scanning data for changes in the optical properties of the materials with changing molecular weight. Measurements have also been made on reference samples of Suwannee river humic (SRHA) and fulvic (SRFA) acids from the International Humic Substances Society (IHSS). The weight-average moleuclar weights of the extracted samples range from approximately 2,000 to 17,000 and follow a series PHA > WBHA > WBFA. Apparent specific volumes of these materials were in a range from 0.45 to 0.58 cm{sup 3} g{sup {minus}1} as measured by digital densimetry. Al the samples studied were analysed by gel filtration, but the molecular weights determined by this method based on a globular protein calibration are not in good accord with the absolute determinations by the sedimentation-equilibrium technique. The molecular weight of the SRHA determined by sedimentation equilibrium is in good agreement with that reported by BECKETT (1987) et al., based on flow field-flow fractionation.

  2. Different molecular weight hyaluronic acid effects on human macrophage interleukin 1? production.

    PubMed

    Baeva, Larissa F; Lyle, Daniel B; Rios, Maria; Langone, John J; Lightfoote, Marilyn M

    2014-02-01

    This study examined the effect of hyaluronan (HA) molecular weight on immune response. HA with molecular weights ranging from the unitary disaccharide unit (400 Da) up to 1.7 × 10(6) Da and with very low endotoxin contamination level (less than 0.03 EU/mg) was used. Primary human monocyte/macrophage cultures were assayed for IL-1? production under a variety of inflammatory conditions with or without HA. Under the highest inflammatory states, production of interleukin 1? (IL-1?) was suppressed in the presence of high molecular weight hyaluronan (HMW-HA) and in the presence of low molecular weight hyaluronan (LMW-HA) at mg/mL concentrations. There was variability in the sensitivity of the response to HA fragments with MW below 5000 Da at micromolar concentrations. There was variability in IL-1? cytokine productions from donor to donor in unstimulated human cell cultures. This study supplements our previous published study that investigated the immunogenic effect of HA molecular weights using murine cell line RAW264.6, rat splenocytes, and rat adherent differentiated primary macrophages. These data support the hypothesis that if the amount of endotoxin is reduced to an extremely low level, LMW-HA may not directly provoke normal tissue macrophage-mediated inflammatory reactions. PMID:23533059

  3. Influence of polymer molecular weight in osteoinductive composites for bone tissue regeneration.

    PubMed

    Barbieri, Davide; Yuan, Huipin; Luo, Xiaoman; Farè, Silvia; Grijpma, Dirk W; de Bruijn, Joost D

    2013-12-01

    In bone tissue regeneration, certain polymer and calcium-phosphate-based composites have been reported to enhance some biological surface phenomena, facilitating osteoinduction. Although the crucial role of inorganic fillers in heterotopic bone formation by such materials has been shown, no reports have been published on the potential effects the polymer phase may have. The present work starts from the assumption that the polymer molecular weight regulates the fluid uptake, which determines the hydrolysis rate and the occurrence of biological surface processes. Here, two composites were prepared by extruding two different molecular weight L/D,L-lactide copolymers with calcium phosphate apatite. The lower molecular weight copolymer allowed larger fluid uptake in the composite thereof, which was correlated with a higher capacity to adsorb proteins in vitro. Further, the large fluid absorption led to a quicker composite degradation that generated rougher surfaces and enhanced ion release. Following intramuscular implantation in sheep, only the composite with the lower molecular weight polymer could induce heterotopic bone formation. Besides influencing the biological potential of composites, the molecular weight also regulated their viscoelastic behaviour under cyclic stresses. The results lead to the conclusion that designing biomaterials with appropriate physico-chemical characteristics is crucial for bone tissue regeneration in mechanical load-bearing sites. PMID:23917043

  4. How Accurate is Web-Based Self-Reported Height, Weight, and Body Mass Index in Young Adults?

    PubMed Central

    2014-01-01

    Background Web-based approaches are an effective and convenient medium to deliver eHealth interventions. However, few studies have attempted to evaluate the accuracy of online self-reported weight, and only one has assessed the accuracy of online self-reported height and body mass index (BMI). Objective This study aimed to validate online self-reported height, weight, and calculated BMI against objectively measured data in young Australian adults. Methods Participants aged 18-35 years were recruited via advertisements on social media sites and reported their current height and weight as part of an online survey. They then subsequently had the same measures objectively assessed by a trained researcher. Results Self-reported height was significantly overestimated by a mean of 1.36 cm (SD 1.93; P<.001), while self-reported weight was significantly underestimated by –0.55 kg (SD 2.03; P<.001). Calculated BMI was also underestimated by –0.56 kg/m2 (SD 0.08; P<.001). The discrepancy in reporting resulted in the misclassification of the BMI category of three participants. Measured and self-reported data were strongly positively correlated (height: r=.98, weight: r=.99, BMI: r=.99; P<.001). When accuracy was evaluated by BMI category and gender, weight remained significantly underreported by females (P=.002) and overweight/obese participants (P=.02). Conclusions There was moderate to high agreement between self-reported and measured anthropometric data. Findings suggest that online self-reported height and weight can be a valid method of collecting anthropometric data. PMID:24398335

  5. Phase and orientational ordering of low molecular weight rod molecules in a quenched liquid crystalline polymer matrix with mobile side

    E-print Network

    Cao, Jianshu

    Phase and orientational ordering of low molecular weight rod molecules in a quenched liquid interaction among the host and the low molecular weight guest. Control and manipulation of properties of the short LC molecular rods is crucial for practical applications.1 Below we review theoretical

  6. Syndiotactic polystyrene nanofibrils in silica nanotube reactors: understanding of synthesis with ultrahigh molecular weight.

    PubMed

    Choi, Kyu Yong; Han, Joong Jin; He, Bo; Lee, Sang Bok

    2008-03-26

    Nanofibrils of ultrahigh molecular weight syndiotactic polystyrene (sPS) have been synthesized in a silica nanotube reactor (SNTR) using a metallocene catalyst in conjunction with methylaluminoxane cocatalyst. Very thin sPS nanofibrils (<10 nm) grown at the catalytic sites on the pore walls aggregate to form intertwined, rope-like nanofibrils with 30-50 nm diameters, which further intertwine into even larger 200 nm diameter polymer nanofibrils. The extrusion of nanofibrils synthesized inside the SNTR was directly observed by scanning electron microscopy, and the individual SNTR containing a single polymer nanofibril was separated and observed by transmission electron microscopy. The sPS synthesized in the SNTR has ultrahigh molecular weight (Mw = 928,000 g/mol) with a large fraction of 2 000,000-5,000,000 g/mol molecular weight polymers. PMID:18303889

  7. Molecular weight of DNA from four entomopoxviruses determined by electron microscopy.

    PubMed Central

    Langridge, W H; Roberts, D W

    1977-01-01

    DNA was isolated from entomopoxviruses infected Amsacta moorei and Euxoa auxiliaris (Lepidoptera), Goeldichironomus holoprasinus (Diptera), and Othnonius batesi (Coleoptera) and compared with vertebrate virus DNA (vaccinia). After incubation in Pronase, sodium lauryl sulfate, and deoxycholate, poxvirus preparations shadowed with platinum and palladium revealed subcore particles 45 to 60 nm in diameter. Continued incubation in Pronase resulted in the gradual release of DNA from the particles. Metal-shadowed DNA molecules were photographed in the electron microscope and measured, and the average molecular weights were calculated. Lepidopteran poxvirus DNA (135 X 10(6)) was approximately equal to vaccinia DNA (131.7 X 10(6)) in molecular weight. The molecular weight of dipteran and coleopteran poxvirus DNA (200 X 10(6) to 251 X 10(6)) was approximately 50% greater than vaccinia DNA. Based on the concentration of DNA and protein per virion, Amsacta entomopoxvirus contained 5.7 to 7.7% DNA. Images PMID:833926

  8. Molecular weight of DNA from four entomopoxviruses determined by electron microscopy.

    PubMed

    Langridge, W H; Roberts, D W

    1977-01-01

    DNA was isolated from entomopoxviruses infected Amsacta moorei and Euxoa auxiliaris (Lepidoptera), Goeldichironomus holoprasinus (Diptera), and Othnonius batesi (Coleoptera) and compared with vertebrate virus DNA (vaccinia). After incubation in Pronase, sodium lauryl sulfate, and deoxycholate, poxvirus preparations shadowed with platinum and palladium revealed subcore particles 45 to 60 nm in diameter. Continued incubation in Pronase resulted in the gradual release of DNA from the particles. Metal-shadowed DNA molecules were photographed in the electron microscope and measured, and the average molecular weights were calculated. Lepidopteran poxvirus DNA (135 X 10(6)) was approximately equal to vaccinia DNA (131.7 X 10(6)) in molecular weight. The molecular weight of dipteran and coleopteran poxvirus DNA (200 X 10(6) to 251 X 10(6)) was approximately 50% greater than vaccinia DNA. Based on the concentration of DNA and protein per virion, Amsacta entomopoxvirus contained 5.7 to 7.7% DNA. PMID:833926

  9. Low molecular weight chitosan-insulin polyelectrolyte complex: characterization and stability studies.

    PubMed

    Al-Kurdi, Zakieh I; Chowdhry, Babur Z; Leharne, Stephen A; Al Omari, Mahmoud M H; Badwan, Adnan A

    2015-01-01

    The aim of the work reported herein was to investigate the effect of various low molecular weight chitosans (LMWCs) on the stability of insulin using USP HPLC methods. Insulin was found to be stable in a polyelectrolyte complex (PEC) consisting of insulin and LMWC in the presence of a Tris-buffer at pH 6.5. In the presence of LMWC, the stability of insulin increased with decreasing molecular weight of LMWC; 13 kDa LMWC was the most efficient molecular weight for enhancing the physical and chemical stability of insulin. Solubilization of insulin-LMWC polyelectrolyte complex (I-LMWC PEC) in a reverse micelle (RM) system, administered to diabetic rats, results in an oral delivery system for insulin with acceptable bioactivity. PMID:25830681

  10. Granulocyte elastase cleaves human high molecular weight kininogen and destroys its clot-promoting activity

    PubMed Central

    1988-01-01

    Purified human granulocyte elastase cleaved purified human high molecular weight (HMW) kininogen into multiple low molecular weight fragments, and destroyed the clot-promoting activity of the HMW kininogen. Elastase digestion did not release kinin or destroy the bradykinin portion of the HMW kininogen molecule; kallikrein could release kinin from the elastase-induced low molecular weight digestion products of HMW kininogen. Purified alpha 1-antitrypsin prevented the destruction of the clot-promoting activity of HMW kininogen by elastase; it also delayed the clotting of normal plasma. Elastase may play a significant role in altered hemostasis as well as fibrinolysis, in areas of inflammation to which polymorphonuclear leukocytes have been attracted. PMID:3260266

  11. The development of low-molecular weight hydrogels for applications in cancer therapy

    NASA Astrophysics Data System (ADS)

    Tian, Ran; Chen, Jin; Niu, Runfang

    2014-03-01

    To improve the anti-cancer efficacy and to counteract the side effects of chemotherapy, a variety of drug delivery systems have been invented in past decades, but few of these systems have succeeded in clinical trials due to their respective inherent shortcomings. Recently, low-molecular weight hydrogels of peptides that self-assemble via non-covalent interactions have attracted considerable attention due to their good biocompatibility, low toxicity, inherent biodegradability as well as their convenience of design. Low-molecular weight hydrogels have already shown promise in biomedical applications as diverse as 3D-cell culture, enzyme immobilization, controllable MSC differentiation, wound healing, drug delivery etc. Here we review the recent development in the use of low-molecular weight hydrogels for cancer therapy, which may be helpful in the design of soft materials for drug delivery.

  12. Isolation and function of a low molecular weight protein of mung bean embryonic axes.

    PubMed

    Manickam, A; Carlier, A R

    1980-08-01

    A low molecular weight protein from dry mung bean (Vigna radiata) embryonic axes has been purified to near homogeneity by chromatography on DEAE-cellulose and hydroxylapatite. It shows a molecular weight of about 12,000 in sodium dodecyl sulfate-polyacrylamide gels and a sedimentation coefficient of about 2 S in sucrose gradients. This protein occurs in greater amounts in dry axes than in dry cotyledons, and it dramatically disappears during early germination of the seed. Affinity chromatography tests do not indicate it as a trypsin inhibitor or as a glycoprotein. It is a water-soluble cytoplasmic protein exhibiting an amino acid composition characteristic of storage proteins with a high content of glutamic acid/glutamine. We suggest that it is a low molecular weight storage albumin. PMID:24306292

  13. Influence of refractive index and molecular weight of alcohol agents on skin optical clearing effect

    NASA Astrophysics Data System (ADS)

    Mao, Zhongzhen; Zheng, Ying; Hu, Yating; Lu, Wei; Luo, Qingming; Zhu, Dan

    2007-02-01

    In order to discuss the relative factors affecting the optical clearing effect of agents on skin tissues, six hydroxy-terminated and saturated alcohols with different refractive index and molecular weight were chosen as the optical clearing agents (OCAs). After being treated by different OCAs, the change of transmitted intensity of porcine skins in vitro was measured by single integrating sphere system. The results showed the optical clearing effects of six OCAs, i.e., glycerol, PEG400, PEG200, 1,3-propylene glycol, 1,4-butanediol and 1-butanol, arranged in the descending order. Based on the above results, the refractive index and molecular weight was further discussed. The optical clearing effect of alcohols has been deduced to have negative correlation with refractive index (r=-0.608), but no correlation with molecular weight (r= 0.008).

  14. Low molecular-weight phenols in Tannat wines made by alternative winemaking procedures.

    PubMed

    Favre, Guzmán; Peña-Neira, Álvaro; Baldi, Cecilia; Hernández, Natalia; Traverso, Sofía; Gil, Graciela; González-Neves, Gustavo

    2014-09-01

    Low molecular weight phenols of Tannat red wines produced by Traditional Maceration (TM), Prefermentative Cold Maceration (PCM), Maceration Enzyme (ENZ) and grape-Seed Tannins additions (ST), were performed and discussed. Alternatives to TM increased wine phenolic contents but unequally, ST increased mainly smaller flavans-3-ol, PCM anthocyanins and ENZ proanthocyanidins (up to 2250 mg/L). However low molecular weight flavan-3-ols remained below 9 mg/L in all wines, showing that there is not necessarily a correspondence between wine richness in total tannins and flavan-3-ols contents at low molecular weight. PCM wines had particularly high concentrations of tyrosol and tryptophol, yeast metabolism derived compounds. The use of grape-seed enological tannins did not increase grape seed derived phenolic compounds such as gallic acid. Caftaric acid was found in concentrations much higher than those reported in other grape varieties. Wine phenolic content and composition was considerably affected by the winemaking procedures tested. PMID:24731376

  15. Application of computer-assisted molecular modeling (CAMM) for immunoassay of low molecular weight food contaminants: A review

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Immunoassay for low molecular weight food contaminants, such as pesticides, veterinary drugs, and mycotoxins is now a well-established technique which meets the demands for a rapid, reliable, and cost-effective analytical method. However, due to limited understanding of the fundamental aspects of i...

  16. Molecular simulations with solvent competition quantify water displaceability and provide accurate interaction maps of protein binding sites.

    PubMed

    Alvarez-Garcia, Daniel; Barril, Xavier

    2014-10-23

    Binding sites present well-defined interaction patterns that putative ligands must meet. Knowing them is essential to guide structure-based drug discovery projects. However, complex aspects of molecular recognition-such as protein flexibility or the effect of aqueous solvation-hinder accurate predictions. This is particularly true for polar contacts, which are heavily influenced by the local environment and the behavior of discrete water molecules. Here we present and validate MDmix (Molecular Dynamics simulations with mixed solvents) as a method that provides much more accurate interaction maps than ordinary potentials (e.g., GRID). Additionally, MDmix also affords water displaceability predictions, with advantages over methods that use pure water as solvent (e.g., inhomogeneous fluid solvation theory). With current MD software and hardware solutions, predictions can be obtained in a matter of hours and visualized in a very intuitive manner. Thus, MDmix is an ideal complement in everyday structure-based drug discovery projects. PMID:25275946

  17. A log-normal distribution model for the molecular weight of aquatic fulvic acids

    USGS Publications Warehouse

    Cabaniss, S.E.; Zhou, Q.; Maurice, P.A.; Chin, Y.-P.; Aiken, G.R.

    2000-01-01

    The molecular weight of humic substances influences their proton and metal binding, organic pollutant partitioning, adsorption onto minerals and activated carbon, and behavior during water treatment. We propose a lognormal model for the molecular weight distribution in aquatic fulvic acids to provide a conceptual framework for studying these size effects. The normal curve mean and standard deviation are readily calculated from measured M(n) and M(w) and vary from 2.7 to 3 for the means and from 0.28 to 0.37 for the standard deviations for typical aquatic fulvic acids. The model is consistent with several types of molecular weight data, including the shapes of high- pressure size-exclusion chromatography (HP-SEC) peaks. Applications of the model to electrostatic interactions, pollutant solubilization, and adsorption are explored in illustrative calculations.The molecular weight of humic substances influences their proton and metal binding, organic pollutant partitioning, adsorption onto minerals and activated carbon, and behavior during water treatment. We propose a log-normal model for the molecular weight distribution in aquatic fulvic acids to provide a conceptual framework for studying these size effects. The normal curve mean and standard deviation are readily calculated from measured Mn and Mw and vary from 2.7 to 3 for the means and from 0.28 to 0.37 for the standard deviations for typical aquatic fulvic acids. The model is consistent with several type's of molecular weight data, including the shapes of high-pressure size-exclusion chromatography (HP-SEC) peaks. Applications of the model to electrostatic interactions, pollutant solubilization, and adsorption are explored in illustrative calculations.

  18. Molecular weight of barley ?-glucan does not influence satiety or energy intake in healthy male subjects.

    PubMed

    Clegg, Miriam E; Thondre, Pariyarath S

    2014-12-01

    Previous studies have shown the ability of high molecular weight barley ?-glucan with increased viscosity to attenuate glycemic response, gastric emptying and in vitro starch digestion. The main objective of this study was to investigate the effect of molecular weight of barley ?-glucan in a semisolid meal on energy intake and subjective feelings of hunger, fullness, desire to eat and prospective food consumption in healthy male subjects. In a randomised, controlled, crossover trial, 23 healthy male subjects (BMI 24.2?±?2.5?kg/m(2)) tested soups equivalent to 25?g available carbohydrate containing high or low molecular weight barley ?-glucan (~3?g) as preload after a standard breakfast. The viscosity of soup with high molecular weight ?-glucan was 350?Pa·s whereas the soup with low molecular weight ?-glucan had a viscosity of 100?Pa·s. Appetite ratings before and for two hours after consumption of ?-glucan soups and subsequent ad libitum energy intake at lunch were recorded and compared with a control soup with no ?-glucan. There was no significant difference in food intake at the ad libitum meal or for the remainder of the day following consumption of the three test foods (p?>?0.05). Similarly, there were no significant differences (p?>?0.05) in hunger, fullness, desire to eat or prospective food consumption following ?-glucan soups. The current study provides evidence that the molecular weight of barley ?-glucan may not impact on perceived feelings of hunger or food intake at the current dose and viscosity. PMID:25106092

  19. Low molecular weight heparin and prevention of postoperative thrombosis in abdominal surgery.

    PubMed

    Koppenhagen, K; Adolf, J; Matthes, M; Tröster, E; Roder, J D; Hass, S; Fritsche, H M; Wolf, H

    1992-06-01

    In a prospective, double-blind, randomized multicenter trial the efficacy and safety of low molecular weight heparin and unfractionated heparin were compared for the prevention of postoperative deep vein thrombosis in patients undergoing abdominal surgery. Six hundred and seventy-three patients were randomly allocated to the two prophylaxis groups; 20 of these, however, did not undergo surgery and did not receive any prophylaxis. Of the remaining 653 patients 323 received one subcutaneous injection of 3,000 anti-Xa units of low molecular weight heparin and 330 received subcutaneously 5,000 U heparin three times a day. Treatment was initiated 2 h preoperatively and continued for 7 to 10 days. The occurrence of DVT was determined by the 125I-labelled fibrinogen uptake test and phlebography. Venous thrombosis was diagnosed in 24 of 323 patients (7.4%) treated with low molecular weight heparin and in 26 of 330 patients (7.9%) treated with low-dose heparin. DVT of proximal veins was detected in four patients of the low molecular weight heparin group and in three patients of the low-dose heparin group. During the observation period three pulmonary emboli - one fatal and two non-fatal - occurred in patients receiving prophylaxis with low-dose heparin. No pulmonary embolism was found in patients treated with low molecular weight heparin. Both prophylactic schemes were well tolerated. Intra- and postoperative blood loss, incidence of wound hematoma, frequency and volume of intra- and postoperative blood transfusion were similar in both groups with a slight advantage for the low molecular weight heparin group.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:1324534

  20. Synthesis of Ultrahigh Weight Average Molecular Mass of Poly-L-lactide

    Microsoft Academic Search

    Z. H. Zhou; X. P. Liu; L. H. Liu

    2008-01-01

    High purity in high yield L-lactide was prepared using a new purification method, and poly-L-lactide (PLLA) with ultra-high weight average molecular mass and narrow polydispersity index was synthesized by ring-opening polymerization. The effects of the purification method on the purity and yield of L-lactide were investigated, and the influences of initiator concentration, polymerization temperature and polymerization time on the weight

  1. The Combined Influence of Molecular Weight and Temperature on the Aging and Viscoelastic Response of a Glassy Thermoplastic Polyimide

    NASA Technical Reports Server (NTRS)

    Nicholson, Lee M.; Whitley, Karen S.; Gates, Thomas S.

    2000-01-01

    The effect of molecular weight on the viscoelastic performance of an advanced polymer (LaRC-SI) was investigated through the use of creep compliance tests. Testing consisted of short-term isothermal creep and recovery with the creep segments performed under constant load. The tests were conducted at three temperatures below the glass transition temperature of five materials of different molecular weight. Through the use of time-aging-time superposition procedures, the material constants, material master curves and aging-related parameters were evaluated at each temperature for a given molecular weight. The time-temperature superposition technique helped to describe the effect of temperature on the timescale of the viscoelastic response of each molecular weight. It was shown that the low molecular weight materials have higher creep compliance and creep rate, and are more sensitive to temperature than the high molecular weight materials. Furthermore, a critical molecular weight transition was observed to occur at a weight-average molecular weight of M (bar) (sub w) 25000 g/mol below which, the temperature sensitivity of the time-temperature superposition shift factor increases rapidly. The short-term creep compliance data were used in association with Struik's effective time theory to predict the long-term creep compliance behavior for the different molecular weights. At long timescales, physical aging serves to significantly decrease the creep compliance and creep rate of all the materials tested.

  2. A low cost, colour coded, hand held spring scale accurately categorises birth weight in low resource settings

    Microsoft Academic Search

    L C Mullany; G L Darmstadt; P Coffey; S K Khatry; S C LeClerq; J M Tielsch

    2006-01-01

    Aims: To determine the accuracy of a low cost, spring calibrated, hand held scale in classifying newborns into three weight categories (?2500 g, 2000–2499 g, <2000 g).Methods: The test device was compared to a gold standard digital baby scale with precision to 2 g. In Sarlahi district, Nepal, 1890 newborns were eligible for the study. Measurements were collected for both

  3. Potential antioxidant and anticoagulant capacity of low molecular weight fucoidan fractions extracted from Laminaria japonica.

    PubMed

    Wang, Jing; Zhang, Quanbin; Zhang, Zhongshan; Song, Houfang; Li, Pengcheng

    2010-01-01

    A low molecular weight fucoidan (DFPS), obtained from the brown seaweed Laminaria japonica, was separated into three fractions by anion-exchange column chromatography. All three fractions (DF1, DF2, DF3) predominantly contained variety fucose, galactose and sulfate group. The antioxidant and anticoagulant activities of these fractions were investigated. The results showed that all fractions possessed considerable antioxidant activities, DF1 was most active. All samples inhibited coagulant in APTT, TT and PT assays obviously. Available data presented the content of sulfate group, the molar ratio of sulfate/fucose and sulfate/total sugar, and the molecular weight played an important role on antioxidant and anticoagulant activity. PMID:19883681

  4. Adsorption of proteins by chrysotile and crocidolite: role of molecular weight and charge density

    SciTech Connect

    Valerio, F.; Balducci, D.; Lazzarotto, A.

    1987-12-01

    Transferrin ..gamma..-globulin, fibrinogen, aldolase, albumin, and cytochrome c at concentration of 0.45 ..mu..Mole/liter were treated with chrysotile and crocidolite fibers. Specific adsorption for each protein and correlations between protein molecular weight and charge density in experimental conditions were evaluated. Chrysotile showed the highest adsorption capability, particularly toward albumin and cytochrome c. Affinity for fibers was poorly linked to protein molecular weight; on the contrary, a good correlation with protein charge density was found. The sign of charge on fibers and proteins seemed to play a minor role in adsorption.

  5. Formulation/cure technology for ultrahigh molecular weight silphenylene-siloxane polymers

    NASA Technical Reports Server (NTRS)

    Hundley, N. H.; Patterson, W. J.

    1985-01-01

    Molecular weights above one million were achieved for methylvinylsilphenylene-siloxane terpolymers using a two-stage polymerization technique which was successfully scaled up to 200 grams. The resulting polymer was vulcanized by two different formulations and compared to an identically formulated commercial methylvinyl silicone on the basis of ultimate strength, Young's modulus, percent elongation at failure, and tear strength. Relative thermal/oxidative stabilities of the elastomers were assessed by gradient and isothermal thermogravimetric analyses performed in both air and nitrogen. The experimental elastomer exhibited enhanced thermal/oxidative stability and possed equivalent or superior mechanical properties. The effect of variations in prepolymer molecular weight on mechanical properties was also investigated.

  6. Small molecular weight protein-protein interaction antagonists: an insurmountable challenge?

    PubMed

    Dömling, Alexander

    2008-06-01

    Several years ago small molecular weight protein-protein interaction (PPI) antagonists were considered as the Mount Everest in drug discovery and generally regarded as too difficult to be targeted. However, recent industrial and academic research has produced a great number of new antagonists of diverse PPIs. This review structurally analyses small molecular weight PPI antagonists and their particular targets as well as tools to discover such compounds. Besides general discussions there will be a focus on the PPI p53/mdm2. PMID:18501203

  7. Removal of higher molecular weight organic compounds by the granular activated carbon adsorption unit process.

    PubMed

    Stevens, A A; Seeger, D R; DeMarco, J; Moore, L

    1987-01-01

    The granular activated carbon adsorption unit process in drinking water treatment typically removes purgeable organic compounds for time periods on the order of a few weeks. Experimental evidence indicates that less volatile compounds of generally higher molecular weight than the purgeable fraction, but still detectable by gas chromatography, are efficiently removed for longer periods. Field data substantiate this. Explanatory mechanisms may include stronger adsorption affinities or biodegradation. Non-gas chromatographable, higher molecular weight materials such as humic acids, as measured by Total Organic Carbon (TOC) or trihalomethane formation potential, revert to lower removal efficiencies. Biodegradation may be responsible for a continued long term removal of a fraction of these materials. PMID:3694484

  8. Low molecular weight thermostable .beta.-D-glucosidase from acidothermus cellulolyticus

    DOEpatents

    Himmel, Michael E. (Littleton, CO); Tucker, Melvin P. (Lakewood, CO); Adney, William S. (Golden, CO); Nieves, Rafael A. (Lakewood, CO)

    1995-01-01

    A purified low molecular weight .beta.-D-glucosidase is produced from Acidothermus cellulolyticus ATCC 43068. The enzyme is water soluble, possesses activity against pNP-.beta.-D-glucopyranoside, has a high of degree of stability toward heat, exhibits optimal temperature activity at about 65.degree. C. at a pH range of from about 2 to about 7, has an inactivation temperature of about 80.degree. C. at a pH range of from about 2 to about 7 and has a molecular weight of about 50.5-54.5 kD as determineded by SDS-PAGE.

  9. Effect of molecular weight on the electrophoretic deposition of carbon black nanoparticles in moderately viscous systems.

    PubMed

    Modi, Satyam; Panwar, Artee; Mead, Joey L; Barry, Carol M F

    2013-08-01

    Electrophoretic deposition from viscous media has the potential to produce in-mold assembly of nanoparticles onto three-dimensional parts in high-rate, polymer melt-based processes like injection molding. The effects of the media's molecular weight on deposition behavior were investigated using a model system of carbon black and polystyrene in tetrahydrofuran. Increases in molecular weight reduced the electrophoretic deposition of the carbon black particles due to increases in suspension viscosity and preferential adsorption of the longer polystyrene chains on the carbon black particles. At low deposition times (?5 s), only carbon black deposited onto the electrodes, but the deposition decreased with increasing molecular weight and the resultant increases in suspension viscosity. For longer deposition times, polystyrene codeposited with the carbon black, with the amount of polystyrene increasing with molecular weight and decreasing with greater charge on the polystyrene molecules. This deposition behavior suggests that use of lower molecular polymers and control of electrical properties will permit electrophoretic deposition of nanoparticles from polymer melts for high-rate, one-step fabrication of nano-optical devices, biochemical sensors, and nanoelectronics. PMID:23848316

  10. Seven Golden Rules for heuristic filtering of molecular formulas obtained by accurate mass spectrometry

    Microsoft Academic Search

    Tobias Kind; Oliver Fiehn

    2007-01-01

    Background: Structure elucidation of unknown small molecules by mass spectrometry is a challenge despite advances in instrumentation. The first crucial step is to obtain correct elemental compositions. In order to automatically constrain the thousands of possible candidate structures, rules need to be developed to select the most likely and chemically correct molecular formulas. Results: An algorithm for filtering molecular formulas

  11. Characterization and antioxidant activity of two low-molecular-weight polysaccharides purified from the fruiting bodies of Ganoderma lucidum

    Microsoft Academic Search

    Wei Liu; Hengyu Wang; Xiubing Pang; Wenbing Yao; Xiangdong Gao

    2010-01-01

    Two low-molecular-weight polysaccharides, GLPL1 and GLPL2, purified from a crude Ganoderma lucidum polysaccharide preparation GLPP were investigated for their physicochemical properties, structure characterization and antioxidant activities. The results indicated that GLPL1 was a glucan with an average molecular weight of 5.2kDa, while GLPL2 was composed of glucose, galactose and mannose in a ratio of 29:1.8:1.0 with the average molecular weight

  12. Novel High-Molecular Weight Fucosylated Milk Oligosaccharides Identified in Dairy Streams

    PubMed Central

    Mehra, Raj; Barile, Daniela; Marotta, Mariarosaria; Lebrilla, Carlito B.; Chu, Caroline; German, J. Bruce

    2014-01-01

    Oligosaccharides are the third largest component in human milk. This abundance is remarkable because oligosaccharides are not digestible by the newborn, and yet they have been conserved and amplified during evolution. In addition to encouraging the growth of a protective microbiota dominated by bifidobacteria, oligosaccharides have anti-infective activity, preventing pathogens from binding to intestinal cells. Although it would be advantageous adding these valuable molecules to infant milk formula, the technologies to reproduce the variety and complexity of human milk oligosaccharides by enzymatic/organic synthesis are not yet mature. Consequently, there is an enormous interest in alternative sources of these valuable oligosaccharides. Recent research has demonstrated that bovine milk and whey permeate also contain oligosaccharides. Thus, a thorough characterization of oligosaccharides in bovine dairy streams is an important step towards fully assessing their specific functionalities. In this study, bovine milk oligosaccharides (BMOs) were concentrated by membrane filtration from a readily available dairy stream called “mother liquor”, and analyzed by high accuracy MALDI FT-ICR mass spectrometry. The combination of HPLC and accurate mass spectrometry allowed the identification of ideal processing conditions leading to the production of Kg amount of BMO enriched powders. Among the BMOs identified, 18 have high-molecular weight and corresponded in size to the most abundant oligosaccharides present in human milk. Notably 6 oligosaccharides contained fucose, a sugar monomer that is highly abundant in human milk, but is rarely observed in bovine milk. This work shows that dairy streams represent a potential source of complex milk oligosaccharides for commercial development of unique dairy ingredients in functional foods that reproduce the benefits of human milk. PMID:24810963

  13. Novel high-molecular weight fucosylated milk oligosaccharides identified in dairy streams.

    PubMed

    Mehra, Raj; Barile, Daniela; Marotta, Mariarosaria; Lebrilla, Carlito B; Chu, Caroline; German, J Bruce

    2014-01-01

    Oligosaccharides are the third largest component in human milk. This abundance is remarkable because oligosaccharides are not digestible by the newborn, and yet they have been conserved and amplified during evolution. In addition to encouraging the growth of a protective microbiota dominated by bifidobacteria, oligosaccharides have anti-infective activity, preventing pathogens from binding to intestinal cells. Although it would be advantageous adding these valuable molecules to infant milk formula, the technologies to reproduce the variety and complexity of human milk oligosaccharides by enzymatic/organic synthesis are not yet mature. Consequently, there is an enormous interest in alternative sources of these valuable oligosaccharides. Recent research has demonstrated that bovine milk and whey permeate also contain oligosaccharides. Thus, a thorough characterization of oligosaccharides in bovine dairy streams is an important step towards fully assessing their specific functionalities. In this study, bovine milk oligosaccharides (BMOs) were concentrated by membrane filtration from a readily available dairy stream called "mother liquor", and analyzed by high accuracy MALDI FT-ICR mass spectrometry. The combination of HPLC and accurate mass spectrometry allowed the identification of ideal processing conditions leading to the production of Kg amount of BMO enriched powders. Among the BMOs identified, 18 have high-molecular weight and corresponded in size to the most abundant oligosaccharides present in human milk. Notably 6 oligosaccharides contained fucose, a sugar monomer that is highly abundant in human milk, but is rarely observed in bovine milk. This work shows that dairy streams represent a potential source of complex milk oligosaccharides for commercial development of unique dairy ingredients in functional foods that reproduce the benefits of human milk. PMID:24810963

  14. PK/PD modelling of comb-shaped PEGylated salmon calcitonin conjugates of differing molecular weights.

    PubMed

    Ryan, Sinéad M; Frías, Jesús M; Wang, Xuexuan; Sayers, Claire T; Haddleton, David M; Brayden, David J

    2011-01-20

    Salmon calcitonin (sCT) was conjugated via cysteine-1 to novel comb-shaped end-functionalised (poly(PEG) methyl ether methacrylate) (sCT-P) polymers, to yield conjugates of total molecular weights (MW) inclusive of sCT: 6.5, 9.5, 23 and 40kDa. The conjugates were characterised by HPLC and their in vitro and in vivo bioactivity was measured by cAMP assay on human T47D cells and following intravenous (i.v.) injection to rats, respectively. Stability against endopeptidases, rat serum and liver homogenates was assessed. There were linear and exponential relationships between conjugate MW with potency and efficacy respectively, however the largest MW conjugate still retained 70% of E(max) and an EC(50) of 3.7nM. In vivo, while free sCT and the conjugates reduced serum [calcium] to a maximum of 15-30% over 240 min, the half-life (T(1/2)) was increased and the area under the curve (AUC) was extended in proportion to conjugate MW. Likewise, the polymer conferred protection on sCT against attack by trypsin, chymotrypsin, elastase, rat serum and liver homogenates, with the best protection afforded by sCT-P (40kDa). Mathematical modelling accurately predicted the MW relationships to in vitro efficacy, potency, in vivo PK and enzymatic stability. With a significant increase in T(1/2) for sCT, the 40kDa MW comb-shaped PEG conjugate of sCT may have potential as a long-acting injectable formulation. PMID:20946924

  15. A digitally controlled AGC loop circuitry for GNSS receiver chip with a binary weighted accurate dB-linear PGA

    NASA Astrophysics Data System (ADS)

    Gang, Jin; Yiqi, Zhuang; Yue, Yin; Miao, Cui

    2015-03-01

    A novel digitally controlled automatic gain control (AGC) loop circuitry for the global navigation satellite system (GNSS) receiver chip is presented. The entire AGC loop contains a programmable gain amplifier (PGA), an AGC circuit and an analog-to-digital converter (ADC), which is implemented in a 0.18 ?m complementary metal-oxide-semiconductor (CMOS) process and measured. A binary-weighted approach is proposed in the PGA to achieve wide dB-linear gain control with small gain error. With binary-weighted cascaded amplifiers for coarse gain control, and parallel binary-weighted trans-conductance amplifier array for fine gain control, the PGA can provide a 64 dB dynamic range from ?4 to 60 dB in 1.14 dB gain steps with a less than 0.15 dB gain error. Based on the Gaussian noise statistic characteristic of the GNSS signal, a digital AGC circuit is also proposed with low area and fast settling. The feed-backward AGC loop occupies an area of 0.27 mm2 and settles within less than 165 ?s while consuming an average current of 1.92 mA at 1.8 V.

  16. Accurate description of phase diagram of clathrate hydrates at the molecular level

    Microsoft Academic Search

    Rodion V. Belosudov; Oleg S. Subbotin; Hiroshi Mizuseki; Yoshiyuki Kawazoe; Vladimir R. Belosludov

    2009-01-01

    In order to accurately estimate the thermodynamic properties of hydrogen clathrate hydrates, we developed a method based on the solid solution theory of van der Waals and Platteeuw. This model allows one to take into account the influence of guest molecules on the host lattice and guest-guest interactions-especially when more than one guest molecule occupies a cage. The free energies,

  17. Effect of chitosan molecular weight on rheological behavious of chitosan modified nanoclay at highly hydrated state

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Effect of chitosan molecular weight (M(cs)) on the rheological properties of chitosan modified clay (CMCs) at highly hydrated state was investigated. With special emphasis on its effect on the thixotropy of CMCs, the structure recovery at rest after underwent a pre-shearing process was further perfo...

  18. Ultrafiltration processes for removing humic substances: effect of molecular weight fractions and PAC treatment

    Microsoft Academic Search

    Cheng-Fang Lin; Yuh-Jay Huang; Oliver J Hao

    1999-01-01

    The role of humic substances in general and different molecular weight fractions of humic substances in particular on the membrane performance in terms of quality (chlorination byproducts) and quantity (permeate flux) is unclear. One of the goals of the present study is to evaluate the effect of fractionated humic substances on the ultrafiltration (UF) performance. A commercial humic solution was

  19. Infiltration and Erosion in Soils Treated with Dry PAM of Two Molecular Weights and Phosphogypsum

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Soil surface application of dissolved linear polyacrylamide (PAM) of high molecular weight (MW) can mitigate seal formation, runoff and erosion, especially when added with a source of electrolytes (e.g., gypsum). Practical difficulties associated with PAM solution application prohibited commercial u...

  20. Polyacrylamide molecular weight and phosphogypsum effects on infiltration and erosion in semi-arid soils

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Seal formation at the surface of semi-arid soils during rainstorms reduces soil infiltration rate (IR) and causes runoff and erosion. Surface application of dry anionic polyacrylamide (PAM) with high molecular weight (MW) has been found to be effective in stabilizing soil aggregates, and decreasing ...

  1. Polyacrylamide Molecular Weight and Phosphogypsum Effects on Infiltration and Erosion in Semi-Arid Soils

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Seal formation at the surface of semi-arid soils during rainstorms reduces soil infiltration rate (IR) and causes runoff and erosion. Surface application of dry anionic polyacrylamide (PAM) with high molecular weight (MW) has been found to be effective in stabilizing soil aggregates, and decreasing ...

  2. Diffusion of small molecular weight drugs in radiation-crosslinked poly(ethylene oxide) hydrogels

    Microsoft Academic Search

    Jennifer L. Stringer; Nikolaos A. Peppas

    1996-01-01

    Poly(ethylene oxide) (PEO) hydrogels were formed by crosslinking of aqueous PEO solutions of Mn = 35 000, 900 000 and 5 000 000 in concentrations of 5–50% using ?-irradiation with 3–10 Mrad. The hydrogels were characterized by equilibrium swelling experiments. The average interjunction molecular weight, Mc, varied from 3500 to 32 000, whereas the mesh size, ?, varied from 120

  3. Incorporation of high-molecular-weight glutenin subunits into doughs using 2 gram mixograph and extensigraphs

    Technology Transfer Automated Retrieval System (TEKTRAN)

    To study the contributions of high-molecular-weight glutenin subunits (HMW-GS) to the gluten macropolymer and dough properties, wheat HMW-GS (x- and y-types) are synthesized in a bacterial expression system. These subunits are then purified and used to supplement dough mixing and extensigraph exper...

  4. The Effects of Molecular Weight and Temperature on the Kinetic Friction of Silicone Rubbers

    E-print Network

    Chaudhury, Manoj K.

    The Effects of Molecular Weight and Temperature on the Kinetic Friction of Silicone Rubbers is estimated to be 25 kJ/mol, which is larger than the activation energy of viscous flow of silicone fluids rubber products were performed for the sole purpose of tabulating properties for consumers

  5. TOXICOLOGICAL HIGHLIGHT (REDOX REDUX: A CLOSER LOOK AT CONCEPTAL LOW MOLECULAR WEIGHT THIOLS)

    EPA Science Inventory

    Glutathione (GSH) is present as the most abundant low molecular weight thiol (LMWT) in virtually all mitochondria-bearing eucaryotic cells, often at millimolar concentrations (Meister, 1988). Functions of GSH include roles in DNA and protein synthesis, maintenance of cell membra...

  6. SMALL AND MIDDLE MOLECULAR WEIGHT SOLUTE CLEARANCE IN NOCTURNAL INTERMITTENT PERITONEAL DIALYSIS

    Microsoft Academic Search

    Donald F. Brophy; Kevin M. Sowinski; Michael A. Kraus; Sharon M. Moe; James E. Klaunig; Bruce A. Mueller

    ? ? ? ? ? Objectives: To determine the dialysate-to-plasma (D\\/P) concentration ratios and peritoneal dialytic clearance (ClD) of substances with a wide range of molecular weights in subjects receiving a simulated nocturnal intermittent peri- toneal dialysis (NIPD) session. ? ? ? ? ? Design: Open-label single-dose study. ? ? ? ? ? Subjects: Six end-stage renal disease patients under-

  7. Mechanisms of Dynamic Deformation and Failure in Ultra-High Molecular Weight Polyethylene Fiber-Polymer

    E-print Network

    Wadley, Haydn

    of Philosophy Material Science and Engineering Mark R. O'Masta May 2014 #12;APPROVAL SHEET The dissertation for the School of Engineering and Applied Science: James H. Aylor, Dean School of Engineering and Applied ScienceMechanisms of Dynamic Deformation and Failure in Ultra- High Molecular Weight Polyethylene Fiber

  8. Morphology Evolution of Molecular Weight Dependent P3HT: PCBM Solar Cells

    NASA Astrophysics Data System (ADS)

    Liu, Feng; Chen, Dian; Briseno, Alejandro; Russell, Thomas

    2011-03-01

    Effective strategies to maximize the performance of bulk heterojunction (BHJ) photovoltaic devices have to be developed and understood to realize their full potential. In BHJ solar cells, the morphology of the active layer is a critical issue to improve device efficiency. In this work, we choose poly(3-hexyl-thiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) system to study the morphology evolution. Different molecular weight P3HTs were synthesized by using Grignard Metathesis (GRIM) method. In device optimization, polymer with a molecular weight between 20k-30k shows the highest efficiency. It was observed that the as-spun P3HT: PCBM (1:1) blends do not have high order by GISAXS. Within a few seconds of thermal annealing at 150 ^o the crystallinity of P3HT increaased substantially and the polymer chains adopted an edge-on orientation. An-bicontinous morphology was also developed within this short thermal treatment. The in situ GISAXS experiment showed that P3HT of high molecular weight was more easily crystallized from a slowly evaporated chlorobenzene solution and their edge-on orientation is much more obvious than for the lower molecular weight P3HTs. DSC was used to study the thermal properties of P3HTs and P3HT: PCBM blend. The ? of P3HT-PCBM was also calculated by using melting point depression method.

  9. Determination of low molecular weight thiols using monobromobimane fluorescent labeling and high-performance liquid chromatography

    NASA Technical Reports Server (NTRS)

    Fahey, Robert C.; Newton, Gerald L.

    1988-01-01

    Methods are described for the preparation and high-performance liquid chromatography (HPLC) analysis of monobromobimane derivatives of low molecular weight thiols in extracts of biological samples. Typical problems encountered in the development and application of these methods are discussed. Analysis of mung bean extract is used as an example.

  10. Influence of plasticizer molecular weight on plasticizer retention in PVC geomembranes

    E-print Network

    PROOFS Influence of plasticizer molecular weight on plasticizer retention in PVC geomembranes T. D, accepted 31 October 2004 ABSTRACT: Plasticizers are used to make PVC flexible so it can be used as a geomembrane. Plasticizers can migrate from PVC geomembranes over time because of contact with air, liquid, and

  11. Methanol-induced chain termination in poly(3-hydroxybutyrate) biopolymers: molecular weight control

    Technology Transfer Automated Retrieval System (TEKTRAN)

    A systematic study was performed to demonstrate the impact of methanol (MeOH) on poly(3-hydroxybutyrate) (PHB) synthesis and molecular weight (MW) control. Glycerine (init. conc. = 1.0%; w/v), was used as the primary carbon source in batch-culture fermentations with varying concentrations (0 to 0.85...

  12. IMPROVED METHOD FOR ESTIMATING MOLECULAR WEIGHTS OF VOLATILE ORGANIC COMPOUNDS FROM LOW RESOLUTION MASS SPECTRA

    EPA Science Inventory

    An improved method of estimating molecular weights of volatile organic compound from their mass spectra has been developed and implemented with an expert system. he method is based on the strong correlation of MAXMASS, the highest mass with an intensity of 5% of the base peak in ...

  13. EVAPORATIVE LIGHT SCATTERING DETECTOR AS A MASS DETECTOR WITH MALLS FOR DETERMINATION OF PECTIN MOLECULAR WEIGHT

    Technology Transfer Automated Retrieval System (TEKTRAN)

    A method to calibrate and use an evaporative light scattering detector (ELS) as a mass detector for molecular weight determination of polysaccharides using a multi-angle laser light scattering detector (MALLS) is shown. The calibration of the ELS was performed under isocratic conditions using conce...

  14. Intestinal Absorption of Low Molecular Weight Heparin in Animals and Human Subjects

    Microsoft Academic Search

    Aviram Nissan; Ehud Ziv; Miriam Kidron; Hanoch Bar-On; Gideon Friedman; Esther Hyam; Amiram Eldor

    2000-01-01

    Introduction: We had previously shown that the use of bile salts, which act as surfactants, facilitates the intestinal absorption of large molecules such as those of heparin and insulin. However, the bioavailability of unfractionated heparin (UFH) administered through the large intestine was low. The aim of the present study was to evaluate the absorption of low molecular weight heparin (LMWH)

  15. Antibacterial activity of chitosans and chitosan oligomers with different molecular weights

    Microsoft Academic Search

    Hong Kyoon No; Na Young Park; Shin Ho Lee; Samuel P Meyers

    2002-01-01

    Antibacterial activities of six chitosans and six chitosan oligomers with different molecular weights (Mws) were examined against four gram-negative (Escherichia coli, Pseudomonas fluorescens, Salmonella typhimurium, and Vibrio parahaemolyticus) and seven gram-positive bacteria (Listeria monocytogenes, Bacillus megaterium, B. cereus, Staphylococcus aureus, Lactobacillus plantarum, L. brevis, and L. bulgaricus). Chitosans showed higher antibacterial activities than chitosan oligomers and markedly inhibited growth of

  16. Determination of molecular weight of heparin by size exclusion chromatography with universal calibration

    E-print Network

    Dubin, Paul D.

    Determination of molecular weight of heparin by size exclusion chromatography with universal chromatography using ``universal cali- bration.'' A universal calibration curve was constructed for Superose 12 chromatography (SEC).1 * Corresponding author. Fax: 1-317-274-6879. E-mail address: dubin@chem.iupui.edu (P

  17. Lubrication and wear of ultra-high molecular weight polyethylene in total joint replacements

    Microsoft Academic Search

    A Wang; A Essner; V. K Polineni; C Stark; J. H Dumbleton

    1998-01-01

    This paper reviews recent advances in the tribology of artificial joints. Emphasis is placed on the latest developments in understanding wear mechanisms and in wear testing of ultra-high molecular weight polyethylene (UHMWPE) materials and components. Two major advances have been made. One is the discovery and recognition of the importance of multidirectional motion in wear mechanisms and wear testing of

  18. SAMPLING AND ANALYSIS FOR HIGH-MOLECULAR-WEIGHT POLAR ORGANIC COMPOUNDS

    EPA Science Inventory

    The report gives results of preliminary investigations into the determination of high-molecular-weight polar organic compounds from wood-combustion residues. It is intended as a reference to be used by laboratories that are developing methods for the identification and quantifica...

  19. Holographic recording medium employing a photoconductive layer and a low molecular weight microcrystalline polymeric layer

    NASA Technical Reports Server (NTRS)

    Gange, Robert Allen (Inventor)

    1977-01-01

    A holographic recording medium comprising a conductive substrate, a photoconductive layer and an electrically alterable layer of a linear, low molecular weight hydrocarbon polymer has improved fatigue resistance. An acrylic barrier layer can be interposed between the photoconductive and electrically alterable layers.

  20. Incorporation of high-molecular-weight glutenin subunits into doughs using 2 gram mixograph and extensigraphs

    Technology Transfer Automated Retrieval System (TEKTRAN)

    To study the contributions of high-molecular-weight glutenin subunits (HMW-GS) to the gluten macropolymer and dough properties, wheat HMW-GS (x- and y-types) are synthesized in a bacterial expression system. These subunits are then purified and used to supplement dough mixing and extensigraph experi...

  1. Characterization of Different Molecular Weight Fractions Separated from Utah Maltenes by Gel Permeation Chromatography

    Microsoft Academic Search

    J. R. Woods; L. S. Kollyar; D. S. Montgomery; B. D. Sparks; J. A. Ripmeester

    1990-01-01

    Maltenes derived from Utah bitumens were separated by gel permeation chromatography ( OPC) into fractions having number average molecular weights ( MW) in the range from 300 to 11985. The fractions were examined by vapor pressure osmometry, absorption spectrometry in the visible region as well as proton and carbon -13 NMR. The results are reported in comparison with those for

  2. Variant high-molecular-weight glutenin subunits arising from biolistic transformation of wheat

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Genetic transformation via the biolistic method has been used to introduce genes encoding natural and novel high-molecular-weight glutenin subunits (HMW-GS) into wheat. The appearance of new seed proteins of sizes not predicted by the transgene coding sequences has been noted in some of these exper...

  3. High molecular weight caldesmon positive stromal cells in the capsule of hepatocellular carcinomas

    Microsoft Academic Search

    H Nakayama; H Enzan; M Yamamoto; E Miyazaki; W Yasui

    2004-01-01

    Aims: To investigate the smooth muscle nature of the stromal cells in the capsule of hepatocellular carcinomas.Methods: Immunohistochemical analysis using monoclonal antibody to high molecular weight caldesmon (HCD), a highly specific marker for smooth muscle cells, was performed in 33 encapsulated hepatocellular carcinomas and adjacent hepatic tissues.Results: HCD positive stromal cells were detected in the capsule of 21 of the

  4. Effect of high molecular weight glutenin subunit allelic composition on wheat flour tortilla quality

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Wheat cultivars possessing quality attributes needed to produce optimum quality tortillas have not been identified. This study investigated the effect of variations in high molecular weight glutenin subunits encoded at the Glu-1 loci (Glu-A1, Glu-B1, Glu-D1) on dough properties and tortilla quality....

  5. Microfluidics Meets Dilute Solution Viscometry: An Undergraduate Laboratory to Determine Polymer Molecular Weight Using a Microviscometer

    ERIC Educational Resources Information Center

    Pety, Stephen J.; Lu, Hang; Thio, Yonathan S.

    2011-01-01

    This paper describes a student laboratory experiment to determine the molecular weight of a polymer sample by measuring the viscosity of dilute polymer solutions in a PDMS microfluidic viscometer. Sample data are given for aqueous solutions of poly(ethylene oxide) (PEO). A demonstration of shear thinning behavior using the microviscometer is…

  6. Effects of molecular weight on the diffusion coefficient of aquatic dissolved organic matter and humic substances.

    PubMed

    Balch, J; Guéguen, C

    2015-01-01

    In situ measurements of labile metal species using diffusive gradients in thin films (DGT) passive samplers are based on the diffusion rates of individual species. Although most studies have dealt with chemically isolated humic substances, the diffusion of dissolved organic matter (DOM) across the hydrogel is not well understood. In this study, the diffusion coefficient (D) and molecular weight (MW) of 11 aquatic DOM and 4 humic substances (HS) were determined. Natural, unaltered aquatic DOM was capable of diffusing across the diffusive gel membrane with D values ranging from 2.48×10(-6) to 5.31×10(-6) cm(2) s(-1). Humic substances had diffusion coefficient values ranging from 3.48×10(-6) to 6.05×10(-6) cm(2) s(-1), congruent with previous studies. Molecular weight of aquatic DOM and HS samples (?500-1750 Da) measured using asymmetrical flow field-flow fractionation (AF4) strongly influenced D, with larger molecular weight DOM having lower D values. No noticeable changes in DOM size properties were observed during the diffusion process, suggesting that DOM remains intact following diffusion across the diffusive gel. The influence of molecular weight on DOM mobility will assist in further understanding and development of the DGT technique and the uptake and mobility of contaminants associated with DOM in aquatic environments. PMID:25112575

  7. Small molecular weight organic thin-film photodetectors and solar cells

    Microsoft Academic Search

    Peter Peumans; Aharon Yakimov; Stephen R. Forrest

    2003-01-01

    In this review, we discuss the physics underlying the operation of single and multiple heterojunction, vacuum-deposited organic solar cells based on small molecular weight thin films. For single heterojunction cells, we find that the need for direct contact between the deposited electrode and the active organics leads to quenching of excitons. An improved device architecture, the double heterojunction, is shown

  8. EXPERT SYSTEM FOR ESTIMATING MOLECULAR WEIGHTS OF VOLATILE ORGANIC COMPOUNDS FROM LOW RESOLUTION MASS SPECTRA

    EPA Science Inventory

    MAXMASS, the highest mass with an intensity of 5% of the base peak in a low resolution mass spectrum, has been found to be linearly correlated with the true molecular weights of 400 randomly selected spectra, yielding a family of parallel lines. imple exert system using MAXMASS h...

  9. LARGE SCALE EVALUATION OF A PATTERN RECOGNITION/EXPERT SYSTEM FOR MASS SPECTRAL MOLECULAR WEIGHT ESTIMATION

    EPA Science Inventory

    A fast, personal-computer based method of estimating molecular weights of organic compounds from low resolution mass I spectra has been thoroughly evaluated. he method is based on a rule-based pattern,recognition/expert system approach which uses empirical linear corrections whic...

  10. Method for Characterization of Low Molecular Weight Organic Acids in Atmospheric Aerosols Using Ion Chromatography Mass

    E-print Network

    Dickerson, Russell R.

    Method for Characterization of Low Molecular Weight Organic Acids in Atmospheric Aerosols Using Ion in the atmosphere is usually divided by the analysis of organic carbon, black (also called elemental) carbon, mecha- nisms of formation, and the ability to model their fate and transport. The composition

  11. Anomalous Molecular Weight Dependence of Chain Dynamics in Unentangled Polymer Blends with Strong Dynamic Asymmetry

    E-print Network

    Silvia Arrese-Igor; Angel Alegria; Angel J. Moreno; Juan Colmenero

    2012-02-23

    We address the general question of how the molecular weight dependence of chain dynamics in unentangled polymers is modified by blending. By dielectric spectroscopy we measure the normal mode relaxation of polyisoprene in blends with a slow matrix of poly(ter-butylstyrene). Unentangled polyisoprene in the blend exhibits strong deviations from Rouse scaling, approaching 'entangled-like' behavior at low temperatures in concomitance with the increase of the dynamic asymmetry in the blend. The obtained results are discussed in the framework of the generalized Langevin equation formalism. On this basis, a non trivial relationship between the molecular weight dependence of the longest chain relaxation time and the nonexponentiality of the corresponding Rouse correlator is found. This result is confirmed by molecular dynamics simulations.

  12. Surfactant-aided electrospraying of low molecular weight carbohydrate polymers from aqueous solutions.

    PubMed

    Pérez-Masiá, Rocío; Lagaron, Jose M; López-Rubio, Amparo

    2014-01-30

    In this work it is demonstrated, for the first time, that it is feasible to develop, using the electrospraying technique, low molecular weight carbohydrate-based capsule morphologies from aqueous solutions through the rational use of surfactants. Two different low molecular weight carbohydrate polymers were used, a maltodextrin and a commercial resistant starch. The solution properties and subsequent high voltage sprayability was evaluated upon addition of non-ionic (Tween20, and Span20) and zwitterionic (lecithin) surfactants. The morphology and molecular organization of the structures obtained was characterized and related to the solution properties. Results showed that, while unstable jetting and dropping occurred from the pure carbohydrate solutions without surfactant, the addition of some surface active molecules above their critical micelle concentration facilitated capsule formation. Higher surfactant concentrations led to smaller and more homogeneous capsule morphologies, related to lower surface tension and higher conductivity of the solutions. PMID:24299771

  13. How accurate is Born-Oppenheimer molecular dynamics for crossings of potential surfaces ?

    E-print Network

    Hakon Hoel; Ashraful Kadir; Petr Plechac; Mattias Sandberg; Anders Szepessy

    2014-06-13

    The difference of the value of observables for the time-independent Schr\\"odinger equation, with matrix valued potentials, and the values of observables for ab initio Born-Oppenheimer molecular dynamics, of the ground state, depends on the probability to be in excited states and the electron/nuclei mass ratio. The paper first proves an error estimate (depending on the electron/nuclei mass ratio and the probability to be in excited states) for this difference of observables, assuming that molecular dynamics space-time averages converge, with a rate related to the maximal Lyapunov exponent. The analysis does not assume a uniform lower bound on the spectral gap and consequently the probability to be in excited states can be large. A numerical method to determine the probability to be in excited states is then presented, based on Ehrenfest molecular dynamics and stability analysis of a perturbed eigenvalue problem.

  14. An Efficient and Accurate Car-Parrinello-like Approach to Born-Oppenheimer Molecular Dynamics

    E-print Network

    Thomas D. Kühne; Matthias Krack; Fawzi R. Mohamed; Michele Parrinello

    2006-12-20

    We present a new method which combines Car-Parrinello and Born-Oppenheimer molecular dynamics in order to accelerate density functional theory based ab-initio simulations. Depending on the system a gain in efficiency of one to two orders of magnitude has been observed, which allows ab-initio molecular dynamics of much larger time and length scales than previously thought feasible. It will be demonstrated that the dynamics is correctly reproduced and that high accuracy can be maintained throughout for systems ranging from insulators to semiconductors and even to metals in condensed phases. This development considerably extends the scope of ab-initio simulations.

  15. Accurate displacement measurement via a self-adaptive digital image correlation method based on a weighted ZNSSD criterion

    NASA Astrophysics Data System (ADS)

    Yuan, Yuan; Huang, Jianyong; Peng, Xiaoling; Xiong, Chunyang; Fang, Jing; Yuan, Fan

    2014-01-01

    Digital image correlation (DIC) technique has been increasingly employed to implement surface deformation measurements in many engineering fields. Practically, it has been demonstrated that the choice of subset sizes exerts a strong influence on measurement results of DIC, especially when there exists locally larger deformation over the subsets involved. This paper proposes a novel subpixel registration algorithm with Gaussian windows to implicitly optimize the subset sizes by adjusting the shape of Gaussian windows in a self-adaptive fashion with the aid of a so-called weighted zero-normalized sum-of-squared difference correlation criterion. The feasibility and effectiveness of the self-adaptive algorithm are carefully verified through a set of well-designed synthetic speckle images, which indicates that the presented algorithm is able to greatly enhance the accuracy and precision of displacement measurements as compared with the traditional subpixel registration methods.

  16. In situ analysis of melt-drawing behavior of ultrahigh molecular weight polyethylene films with different molecular weights: roles of entanglements on oriented crystallization.

    PubMed

    Kato, Satomi; Tanaka, Hidekazu; Yamanobe, Takeshi; Uehara, Hiroki

    2015-04-16

    Ultrahigh molecular weight polyethylene (UHMW-PE) films having different molecular weights (MWs) were melt-drawn at 150 °C. The stress-strain curve for higher-MW film exhibits higher stress on the characteristic plateau region and a subsequent steeper increase of stress due to strain hardening. Structural changes during such melt-drawing were analyzed using in situ wide-angle X-ray diffraction measurements. Hexagonal crystallization occurs at the beginning of the plateau region, independent of the sample MW. Once this hexagonal reflection intensity is saturated, it remains constant even at the later stage of draw. In contrast, orthorhombic reflection intensities gradually increase with increasing draw strain. Both of these oriented crystallizations into plateau hexagonal and increasing orthorhombic forms are accelerated with increasing MW. Correspondingly, the higher amount of extended chain crystals (ECCs) was confirmed from morphological observation for the resultant melt-drawn films of the higher-MW sample. Deep entanglements can effectively transmit the applied stress; thus, the oriented amorphous melts induce rapid hexagonal crystallization with disentangling shallow entanglements, which subsequently transforms into orthorhombic form. Such hexagonal crystallization plays the role of a thermodynamic pathway for growing such ECCs, where the stable orthorhombic form gradually accumulates with increasing draw strain. PMID:25785561

  17. Effects of Molecular Weight on poly( -pentadecalactone) Mechanical and Thermal Properties

    SciTech Connect

    Cai, J.; Liu, C; Cai, M; Zhu, J; Zuo, F; Hsiao, B; Gross, R

    2010-01-01

    A series of poly({omega}-pentadecalactone) (PPDL) samples, synthesized by lipase catalysis, were prepared by systematic variation of reaction time and water content. These samples possessed weight-average molecular weights (M{sub w}), determined by multi-angle laser light scattering (MALLS), from 2.5 x 10{sup 4} to 48.1 x 10{sup 4}. Cold-drawing tensile tests at room temperature of PPDL samples with M{sub W} between 4.5 x 10{sup 4} and 8.1 x 10{sup 4} showed a brittle-to-ductile transition. For PPDL with M{sub W} of 8.1 x 10{sup 4}, inter-fibrillar slippage dominates during deformation until fracture. Increasing M{sub W} above 18.9 x 10{sup 4} resulted in enhanced entanglement network strength and strain-hardening. The high M{sub W} samples also exhibited tough properties with elongation at break about 650% and tensile strength about 60.8 MPa, comparable to linear high density polyethylene (HDPE). Relationships among molecular weight, Young's modulus, stress, strain at yield, melting and crystallization enthalpy (by differential scanning calorimetry, DSC) and crystallinity (from wide-angle X-ray diffraction, WAXD) were correlated for PPDL samples. Similarities and differences of linear HDPE and PPDL molecular weight dependence on their mechanical and thermal properties were also compared.

  18. Molecular weight distribution characterization of hydrophobe-modified hydroxyethyl cellulose by size-exclusion chromatography.

    PubMed

    Li, Yongfu; Meunier, David M; Partain, Emmett M

    2014-09-12

    Size-exclusion chromatography (SEC) of hydrophobe-modified hydroxyethyl cellulose (HmHEC) is challenging because polymer chains are not isolated in solution due to association of hydrophobic groups and hydrophobic interaction with column packing materials. An approach to neutralize these hydrophobic interactions was developed by adding ?-cyclodextrin (?-CD) to the aqueous eluent. SEC mass recovery, especially for the higher molecular weight chains, increased with increasing concentration of ?-CD in the eluent. A ?-CD concentration of 0.75wt% in the eluent was determined to be optimal for the HmHEC polymers studied. These conditions enabled precise determinations of apparent molecular weight distributions exhibiting less than 2% relative standard deviation in the measured weight-average molecular weight (MW) for five injections on three studied samples and showed no significant differences in MW determined on two different days. The developed technology was shown to be very robust for characterizing HmHEC having MW from 500kg/mol to 2000kg/mol, and it can be potentially applied to other hydrophobe-modified polymers. PMID:25092594

  19. Synthesis of PCEC Copolymers with Controlled Molecular Weight Using Full Factorial Methodology

    PubMed Central

    Barghi, Leila; Asgari, Davoud; Barar, Jaleh; Valizadeh, Hadi

    2015-01-01

    Purpose: Polycaprolactone (PCL) is a biodegradable polyester and has attracted attention as a suitable carrier for development of controlled drug delivery due to its non-toxicity and biocompatibility. It has been reported that the biodegradability of PCL can be enhanced by copolymerization with PEG. Molecular weight (Mw) and CL block lengths optimization in a series of synthesized PCEC copolymers was the main purpose of this study. Methods: The composition of copolymers was designed using full factorial methodology. Molecular weight of used PEG (4 levels) and weight ratio of epsilon-caprolactone/PEG (3 levels) were selected as independent variables. The PCEC copolymers were synthesized by ring opening polymerization. Formation of copolymers was confirmed by FT-IR spectroscopy as well as H-NMR. The Mn of PCEC copolymers was calculated from HNMR spectra. The thermal behavior of copolymers was characterized on differential scanning calorimeter. Results: Molecular weight of twelve synthesized copolymers was ranged from 1782 to 9264. In order to evaluate the effect of selected variables on the copolymers composition and Mw, a mathematical model for each response parameter with p-value less than 0.001were obtained. Average percent error for prediction of total Mn of copolymers and Mn of CL blocks were 13.81% and 14.88% respectively. Conclusion: In conclusion, the proposed model is significantly valid due to obtained low percent error in Mn prediction of test sets. PMID:25789219

  20. Poly (?-caprolactone)\\/hydroxyapatite composites: effects of particle size, molecular weight distribution and irradiation on interfacial interaction and properties

    Microsoft Academic Search

    Biqiong Chen; Kang Sun

    2005-01-01

    Hydroxyapatite reinforced poly(?-caprolactone) composites with different particle sizes and molecular weight distributions were prepared using a simple melt-processing method. Some composites were modified by electron beam irradiation. Dynamic viscoelastic properties were investigated using dynamic mechanical thermal analysis (DMTA) and an advanced rheometric expansion system. The results showed that the composite with narrower molecular weight distribution and smaller particle sizes had

  1. Low molecular weight heparin versus regular heparin or aspirin in the treatment of unstable angina and silent ischemia

    Microsoft Academic Search

    Enrique P. Gurfinkel; Eustaquio J. Manos; Ricardo I. Mejaíl; Miguel A. Cerdá; Ernesto A. Duronto; Claudio N. García; Ana M. Daroca; Branco Mautner

    1995-01-01

    Objectives. This study was designed to test the hypothesis that low molecular weight heparin may lessen the severity of ischemic events in patients with unstable angina.Background. Unstable angina is a thrombotic process that requires intensive medical treatment Although current treatments can reduce the number of complications, serious bleeding continues to occur. Nadroparin calcium, a low molecular weight heparin, seems to

  2. Polyelectrolyte-Micelle Coacervation: Effects of Micelle Surface Charge Density, Polymer Molecular Weight, and Polymer/Surfactant Ratio

    E-print Network

    Dubin, Paul D.

    to 4.28 × 105 were obtained, and coacervate volume fraction as a function of polymer molecular weightPolyelectrolyte-Micelle Coacervation: Effects of Micelle Surface Charge Density, Polymer Molecular Weight, and Polymer/Surfactant Ratio Yilin Wang, Kozue Kimura, and Paul L. Dubin* Department of Chemistry

  3. Macromonomers having different molecular weights of polyethylene glycol and end group functionalities in dispersion polymerization of styrene

    Microsoft Academic Search

    So Yeun Kim; Kangseok Lee; Hyejun Jung; Sang Eun Shim; Byung H. Lee; Soonja Choe

    2005-01-01

    Bifunctional polyurethane-based macromonomers (BPUM) were synthesized from various molecular weights of polyethylene glycol (PEG) and hexamethylene diisocyanate (HDI) with different end group functionalities. The synthesized BPUMs were applied to the dispersion polymerization of styrene in ethanol. Structures of various macromonomers and PS particles were investigated using 1H NMR. Molecular weights of PEG 1000, 2000, 4000, and 8000 were able to

  4. Effect of molecular weight of polymeric additives on formation, permeation properties and hypochlorite treatment of asymmetric polyacrylonitrile membranes

    Microsoft Academic Search

    Bumsuk Jung; Joon Ki Yoon; Bokyung Kim; Hee-Woo Rhee

    2004-01-01

    Asymmetric polyacrylonitrile membranes were prepared via phase inversion process from casting solution composed of synthesized polyacrylonitrile (PAN), dimethylsulfoxide (DMSO), and poly(vinylpyrrolidone) (PVP) of different molecular weights. The effect of molecular weight of PVP in the casting solution on the morphology, water flux was investigated. The effect of hypochlorite treatment on PVP which was entrapped in pore was investigated. As the

  5. Bioremediation of high molecular weight polycyclic aromatic hydrocarbons: a review of the microbial degradation of benzo[ a]pyrene

    Microsoft Academic Search

    Albert L. Juhasz; Ravendra Naidu

    2000-01-01

    Over the past 30 years, research on the microbial degradation of polycyclic aromatic hydrocarbons (PAHs) has resulted in the isolation of numerous genera of bacteria, fungi and algae capable of degrading low molecular weight PAHs (compounds containing three or less fused benzene rings). High molecular weight PAHs (compounds containing four or more fused benzene rings) are generally recalcitrant to microbial

  6. Low molecular weight oligomers of amyloid peptides display ?-barrel conformations: A replica exchange molecular dynamics study in explicit solvent

    NASA Astrophysics Data System (ADS)

    De Simone, Alfonso; Derreumaux, Philippe

    2010-04-01

    The self-assembly of proteins and peptides into amyloid fibrils is connected to over 40 pathological conditions including neurodegenerative diseases and systemic amyloidosis. Diffusible, low molecular weight protein and peptide oligomers that form in the early steps of aggregation appear to be the harmful cytotoxic species in the molecular etiology of these diseases. So far, the structural characterization of these oligomers has remained elusive owing to their transient and dynamic features. We here address, by means of full atomistic replica exchange molecular dynamics simulations, the energy landscape of heptamers of the amyloidogenic peptide NHVTLSQ from the beta-2 microglobulin protein. The simulations totaling 5 ?s show that low molecular weight oligomers in explicit solvent consist of ?-barrels in equilibrium with amorphous states and fibril-like assemblies. The results, also accounting for the influence of the pH on the conformational properties, provide a strong evidence of the formation of transient ?-barrel assemblies in the early aggregation steps of amyloid-forming systems. Our findings are discussed in terms of oligomers cytotoxicity.

  7. Utilizing fast multipole expansions for efficient and accurate quantum-classical molecular dynamics simulations.

    PubMed

    Schwörer, Magnus; Lorenzen, Konstantin; Mathias, Gerald; Tavan, Paul

    2015-03-14

    Recently, a novel approach to hybrid quantum mechanics/molecular mechanics (QM/MM) molecular dynamics (MD) simulations has been suggested [Schwörer et al., J. Chem. Phys. 138, 244103 (2013)]. Here, the forces acting on the atoms are calculated by grid-based density functional theory (DFT) for a solute molecule and by a polarizable molecular mechanics (PMM) force field for a large solvent environment composed of several 10(3)-10(5) molecules as negative gradients of a DFT/PMM hybrid Hamiltonian. The electrostatic interactions are efficiently described by a hierarchical fast multipole method (FMM). Adopting recent progress of this FMM technique [Lorenzen et al., J. Chem. Theory Comput. 10, 3244 (2014)], which particularly entails a strictly linear scaling of the computational effort with the system size, and adapting this revised FMM approach to the computation of the interactions between the DFT and PMM fragments of a simulation system, here, we show how one can further enhance the efficiency and accuracy of such DFT/PMM-MD simulations. The resulting gain of total performance, as measured for alanine dipeptide (DFT) embedded in water (PMM) by the product of the gains in efficiency and accuracy, amounts to about one order of magnitude. We also demonstrate that the jointly parallelized implementation of the DFT and PMM-MD parts of the computation enables the efficient use of high-performance computing systems. The associated software is available online. PMID:25770527

  8. Utilizing fast multipole expansions for efficient and accurate quantum-classical molecular dynamics simulations

    NASA Astrophysics Data System (ADS)

    Schwörer, Magnus; Lorenzen, Konstantin; Mathias, Gerald; Tavan, Paul

    2015-03-01

    Recently, a novel approach to hybrid quantum mechanics/molecular mechanics (QM/MM) molecular dynamics (MD) simulations has been suggested [Schwörer et al., J. Chem. Phys. 138, 244103 (2013)]. Here, the forces acting on the atoms are calculated by grid-based density functional theory (DFT) for a solute molecule and by a polarizable molecular mechanics (PMM) force field for a large solvent environment composed of several 103-105 molecules as negative gradients of a DFT/PMM hybrid Hamiltonian. The electrostatic interactions are efficiently described by a hierarchical fast multipole method (FMM). Adopting recent progress of this FMM technique [Lorenzen et al., J. Chem. Theory Comput. 10, 3244 (2014)], which particularly entails a strictly linear scaling of the computational effort with the system size, and adapting this revised FMM approach to the computation of the interactions between the DFT and PMM fragments of a simulation system, here, we show how one can further enhance the efficiency and accuracy of such DFT/PMM-MD simulations. The resulting gain of total performance, as measured for alanine dipeptide (DFT) embedded in water (PMM) by the product of the gains in efficiency and accuracy, amounts to about one order of magnitude. We also demonstrate that the jointly parallelized implementation of the DFT and PMM-MD parts of the computation enables the efficient use of high-performance computing systems. The associated software is available online.

  9. Seven Golden Rules for heuristic filtering of molecular formulas obtained by accurate mass spectrometry

    PubMed Central

    Kind, Tobias; Fiehn, Oliver

    2007-01-01

    Background Structure elucidation of unknown small molecules by mass spectrometry is a challenge despite advances in instrumentation. The first crucial step is to obtain correct elemental compositions. In order to automatically constrain the thousands of possible candidate structures, rules need to be developed to select the most likely and chemically correct molecular formulas. Results An algorithm for filtering molecular formulas is derived from seven heuristic rules: (1) restrictions for the number of elements, (2) LEWIS and SENIOR chemical rules, (3) isotopic patterns, (4) hydrogen/carbon ratios, (5) element ratio of nitrogen, oxygen, phosphor, and sulphur versus carbon, (6) element ratio probabilities and (7) presence of trimethylsilylated compounds. Formulas are ranked according to their isotopic patterns and subsequently constrained by presence in public chemical databases. The seven rules were developed on 68,237 existing molecular formulas and were validated in four experiments. First, 432,968 formulas covering five million PubChem database entries were checked for consistency. Only 0.6% of these compounds did not pass all rules. Next, the rules were shown to effectively reducing the complement all eight billion theoretically possible C, H, N, S, O, P-formulas up to 2000 Da to only 623 million most probable elemental compositions. Thirdly 6,000 pharmaceutical, toxic and natural compounds were selected from DrugBank, TSCA and DNP databases. The correct formulas were retrieved as top hit at 80–99% probability when assuming data acquisition with complete resolution of unique compounds and 5% absolute isotope ratio deviation and 3 ppm mass accuracy. Last, some exemplary compounds were analyzed by Fourier transform ion cyclotron resonance mass spectrometry and by gas chromatography-time of flight mass spectrometry. In each case, the correct formula was ranked as top hit when combining the seven rules with database queries. Conclusion The seven rules enable an automatic exclusion of molecular formulas which are either wrong or which contain unlikely high or low number of elements. The correct molecular formula is assigned with a probability of 98% if the formula exists in a compound database. For truly novel compounds that are not present in databases, the correct formula is found in the first three hits with a probability of 65–81%. Corresponding software and supplemental data are available for downloads from the authors' website. PMID:17389044

  10. Raman study of uniaxial deformation of single-crystal mats of ultrahigh molecular weight linear polyethylene

    NASA Astrophysics Data System (ADS)

    Zavgorodnev, Yu V.; Chvalun, S. N.; Nikolaeva, G. Yu; Sagitova, E. A.; Pashinin, P. P.; Gordeyev, S. A.; Prokhorov, K. A.

    2015-03-01

    We present for the first time a Raman spectroscopic study of the deformation process of solution-crystallized single-crystal mats of ultrahigh molecular weight linear polyethylene (UHMW PE). We study the deformed regions of the films, drawn only until the formation of the neck, and the films of much higher draw ratios, just before rupture starts. For comparison, we have also carried out Raman investigations of films produced by compression of UHMW PE powder. We have found that the uniaxial molecular orientation in the neck region of the single-crystal mat films develops more slowly as compared to the films, prepared by compression of the UHMW PE powder.

  11. Accurate vibrational spectra via molecular tailoring approach: a case study of water clusters at MP2 level.

    PubMed

    Sahu, Nityananda; Gadre, Shridhar R

    2015-01-01

    In spite of the recent advents in parallel algorithms and computer hardware, high-level calculation of vibrational spectra of large molecules is still an uphill task. To overcome this, significant effort has been devoted to the development of new algorithms based on fragmentation methods. The present work provides the details of an efficient and accurate procedure for computing the vibrational spectra of large clusters employing molecular tailoring approach (MTA). The errors in the Hessian matrix elements and dipole derivatives arising due to the approximation nature of MTA are reduced by grafting the corrections from a smaller basis set. The algorithm has been tested out for obtaining vibrational spectra of neutral and charged water clusters at Møller-Plesset second order level of theory, and benchmarking them against the respective full calculation (FC) and/or experimental results. For (H2O)16 clusters, the estimated vibrational frequencies are found to differ by a maximum of 2 cm(-1) with reference to the corresponding FC values. Unlike the FC, the MTA-based calculations including grafting procedure can be performed on a limited hardware, yet take a fraction of the FC time. The present methodology, thus, opens a possibility of the accurate estimation of the vibrational spectra of large molecular systems, which is otherwise impossible or formidable. PMID:25573553

  12. Accurate vibrational spectra via molecular tailoring approach: A case study of water clusters at MP2 level

    NASA Astrophysics Data System (ADS)

    Sahu, Nityananda; Gadre, Shridhar R.

    2015-01-01

    In spite of the recent advents in parallel algorithms and computer hardware, high-level calculation of vibrational spectra of large molecules is still an uphill task. To overcome this, significant effort has been devoted to the development of new algorithms based on fragmentation methods. The present work provides the details of an efficient and accurate procedure for computing the vibrational spectra of large clusters employing molecular tailoring approach (MTA). The errors in the Hessian matrix elements and dipole derivatives arising due to the approximation nature of MTA are reduced by grafting the corrections from a smaller basis set. The algorithm has been tested out for obtaining vibrational spectra of neutral and charged water clusters at Møller-Plesset second order level of theory, and benchmarking them against the respective full calculation (FC) and/or experimental results. For (H2O)16 clusters, the estimated vibrational frequencies are found to differ by a maximum of 2 cm-1 with reference to the corresponding FC values. Unlike the FC, the MTA-based calculations including grafting procedure can be performed on a limited hardware, yet take a fraction of the FC time. The present methodology, thus, opens a possibility of the accurate estimation of the vibrational spectra of large molecular systems, which is otherwise impossible or formidable.

  13. An alternative accurate tracer of molecular clouds: the `XCI-factor'

    NASA Astrophysics Data System (ADS)

    Offner, Stella S. R.; Bisbas, Thomas G.; Bell, Tom A.; Viti, Serena

    2014-05-01

    We explore the utility of CI as an alternative high-fidelity gas-mass tracer for galactic molecular clouds. We evaluate the `XCI-factor' for the 609 ?m carbon line, the analogue of the CO `X-factor', which is the ratio of the H2 column density to the integrated 12CO(1-0) line intensity. We use 3D-PDR to post-process hydrodynamic simulations of turbulent, star-forming clouds. We compare the emission of CI and CO for model clouds irradiated by 1 and 10 times the average background and demonstrate that CI is a comparable or superior tracer of the molecular gas distribution for column densities up to 6 × 1023 cm-2. Our results hold for both reduced and full chemical networks. For our fiducial Galactic cloud, we derive an average XCO of 3.0 × 1020 cm-2 K-1 km-1 s and XCI of 1.1 × 1021 cm-2 K-1 km-1 s. L1

  14. Secondary Organic Aerosol Formation by Molecular-Weight Building Reactions of Biogenic Oxidation Products

    NASA Astrophysics Data System (ADS)

    Barsanti, K.; Guenther, A.; Matsunaga, S.; Smith, J.

    2006-12-01

    Understanding the chemical composition of atmospheric organic aerosols (OA) remains one of the significant challenges to accurately representing OA in air quality and climate models. Meeting this challenge will require further understanding of secondary organic aerosols (SOA), of which biogenic emissions are thought to be major precursors. Of recent interest is the significance of higher-molecular weight (MW) compounds (i.e., "oligomers"). Theoretical, laboratory, and field study results suggest that relatively volatile oxidation products may contribute to SOA formation through multi-phase MW- building reactions. The significance of such reactions for biogenic SOA formation, including for newly considered precursors such as isoprene, is explored in this work. Theoretical and field studies are employed to: 1) identify MW-building reactions that may contribute to SOA formation in the atmosphere, 2) identify MW-building reaction products in ambient samples, and 3) parameterize atmospheric SOA formation by MW-building reactions of biogenic oxidation products. Likely reactions of biogenic oxidation products include ester, amide, and peroxyhemiacetal formation. Each of the proposed reactions involves known oxidation productions of biogenic precursors (e.g., carboxylic acids and aldehydes) reacting with one another and/or other atmospheric constituents (e.g., sulfuric acid and ammonia) to form higher-MW/lower-volatility products that can condense to form SOA. It has been suggested that products of MW-building reactions can revert to the parent reactants during sampling and analysis. Thus, relatively volatile compounds detected in ambient particle samples in fact may be decomposition products of higher-MW products. The contribution of relatively volatile biogenic oxidation products to SOA via ester, amide, and peroxyhemiacetal formation, as determined by studies based on fundamental thermodynamics and gas/particle partitioning theory, will be discussed; in addition to evidence for such reactions based on field measurements. Finally, while the role of MW-building reactions in contributing to existing SOA has been considered previously, the role of such reactions in OA nucleation events also will be addressed.

  15. Role of Laccase and Low Molecular Weight Metabolites from Trametes versicolor in Dye Decolorization

    PubMed Central

    Moldes, Diego; Fernández-Fernández, María; Sanromán, M. Ángeles

    2012-01-01

    The studies regarding decolorization of dyes by laccase may not only inform about the possible application of this enzyme for environmental purposes, but also may provide important information about its reaction mechanism and the influence of several factors that could be involved. In this paper, decolorization of crystal violet and phenol red was carried out with different fractions of extracellular liquids from Trametes versicolor cultures, in order to describe the role of laccase in this reaction. Moreover, the possible role of the low molecular weight metabolites (LMWMs) also produced by the fungus was evaluated. The results confirm the existence of a nonenzymatic decolorization factor, since the nonprotein fraction of the extracellular liquids from cultures of T. versicolor has shown decolorization capability. Several experiments were performed in order to identify the main compounds related to this ability, which are probably low molecular weight peroxide compounds. PMID:22566767

  16. Temperature, Molecular Weight, and Concentration Dependences of Thermal Diffusion for Ethylene Glycol Oligomers and Crown Ethers

    NASA Astrophysics Data System (ADS)

    Maeda, Kousaku; Kita, Rio; Shinyashiki, Naoki; Yagihara, Shin

    The Soret coefficient ST of ethylene glycol oligomers (EGOs) and crown ethers (CEs) in water were obtained by thermal diffusion forced Rayleigh scattering by changing the temperature, molecular weight, and concentration. The effect of a hydroxyl group on the EGOs and the effect of the cyclic structure of CEs on the thermal diffusion were determined systematically by changing the molecular weights of the EGOs and CEs. For dilute aqueous solutions, EGOs and CEs, except EG, show positive ST values that decrease with increasing temperature, which is similar to the results of previous studies on mixtures of water and organic solvents. The temperature dependence of ST changes its behavior from negative to positive with decreasing number of repeating units of EGOs. This behavior is related to the increase in the number density of the hydroxyl group. The ST values of EG show two different concentration regions, namely, the low concentration (0-2 wt %) and high concentration (2-100 wt %) regions.

  17. Role of laccase and low molecular weight metabolites from Trametes versicolor in dye decolorization.

    PubMed

    Moldes, Diego; Fernández-Fernández, María; Sanromán, M Ángeles

    2012-01-01

    The studies regarding decolorization of dyes by laccase may not only inform about the possible application of this enzyme for environmental purposes, but also may provide important information about its reaction mechanism and the influence of several factors that could be involved. In this paper, decolorization of crystal violet and phenol red was carried out with different fractions of extracellular liquids from Trametes versicolor cultures, in order to describe the role of laccase in this reaction. Moreover, the possible role of the low molecular weight metabolites (LMWMs) also produced by the fungus was evaluated. The results confirm the existence of a nonenzymatic decolorization factor, since the nonprotein fraction of the extracellular liquids from cultures of T. versicolor has shown decolorization capability. Several experiments were performed in order to identify the main compounds related to this ability, which are probably low molecular weight peroxide compounds. PMID:22566767

  18. Simulated dynamic response of a multi-stage compressor with variable molecular weight flow medium

    NASA Technical Reports Server (NTRS)

    Babcock, Dale A.

    1995-01-01

    A mathematical model of a multi-stage compressor with variable molecular weight flow medium is derived. The modeled system consists of a five stage, six cylinder, double acting, piston type compressor. Each stage is followed by a water cooled heat exchanger which serves to transfer the heat of compression from the gas. A high molecular weight gas (CFC-12) mixed with air in varying proportions is introduced to the suction of the compressor. Condensation of the heavy gas may occur in the upper stage heat exchangers. The state equations for the system are integrated using the Advanced Continuous Simulation Language (ACSL) for determining the system's dynamic and steady state characteristics under varying operating conditions.

  19. Friction and wear of polyethylene oxide polymer having a range of molecular weights

    NASA Technical Reports Server (NTRS)

    Buckley, D. H.

    1978-01-01

    Sliding friction and wear experiments were conducted at light loads (25 to 250 g) with various molecular weights of the polyethylene oxide polymer sliding on itself and iron. Results of the experimental investigation indicate that: (1) the coefficient of friction for the polymer decreases with increasing molecular weight; (2) friction coefficient is higher for the polymer sliding on itself than it is for the polymer sliding on iron; (3) at sufficiently high loads localized surface melting occurs and the friction coefficient is the same for the polymer sliding on itself and iron; (4) fracture cracks develop in the sliding wear track at higher but not lower sliding velocities, reflecting a strain rate sensitivity to crack initiation, and (5) the friction coefficient for the polymer sliding on iron increases with the formation of a polymer film on the iron surface.

  20. Isolation, purification and characterisation of low molecular weight xylanase from Bacillus pumilus SSP-34.

    PubMed

    Subramaniyan, S

    2012-04-01

    Low molecular weight endo-xylanase from Bacillus pumilus SSP-34 was purified to homogeneity using ion exchange and size exclusion chromatographies. Xylanases were isolated by novel purification protocol which includes the use of anion exchange matrix such as DEAE Sepharose CL 6B with less affinity towards enzyme protein. The purified B. pumilus SSP-34 have a molecular weight of 20 kDa, with optimum pH and temperature at 6.0 and 50 °C, respectively. The enzyme was stable at 50 °C for 30 min. It showed remarkable stability at pH values ranging from 4.5 to 9 when the reaction was carried out at 50 °C. K (m) and V (max) values, determined with oats spelts xylan were 6.5 mg ml?¹ and 1,233 ?mol min?¹ mg?¹ protein, respectively, and the specific activity was 1,723 U mg?¹. PMID:22350873

  1. Sulfated, Low Molecular Weight Lignins Inhibit a Select Group of Heparin-Binding Serine Proteases

    PubMed Central

    Henry, Brian L.; Thakkar, Jay N.; Liang, Aiye; Desai, Umesh R.

    2012-01-01

    Sulfated low molecular weight lignins (LMWLs), designed as oligomeric mimetics of low molecular weight heparins (LMWHs), have been found to bind in exosite II of thrombin (Abdel Aziz et al. Biochem. Biophys. Res. Commun. 413 (2011) 348–352). To assess whether sulfated LMWLs recognize other heparin-binding proteins, we studied their effect on serine proteases of the coagulation, inflammatory and digestive systems. Using chromogenic substrate hydrolysis assay, sulfated LMWLs were found to potently inhibit coagulation factor XIa and human leukocyte elastase, moderately inhibit cathepsin G and not inhibit coagulation factors VIIa, IXa, and XIIa, plasma kallikrein, activated protein C, trypsin, and chymotrypsin. Competition studies show that UFH competes with sulfated LMWLs for binding to factors Xa and XIa. These results further advance the heparin-mimicking property of sulfated LMWLs and will aid the design of anticoagulants based on their novel scaffold. PMID:22155248

  2. High molecular weight bioemulsifiers, main properties and potential environmental and biomedical applications.

    PubMed

    Mnif, Inès; Ghribi, Dhouha

    2015-05-01

    High molecular weight bioemulsifiers are amphipathic polysaccharides, proteins, lipopolysaccharides, lipoproteins, or complex mixtures of these biopolymers, produced by a wide variety of microorganisms. They are characterized by highly structural diversity and have the ability to decrease the surface and interfacial tension at the surface and interface respectively and/or emulsify hydrophobic compounds. Emulsan, fatty acids, phospholipids, neutral lipids, exopolysaccharides, vesicles and fimbriae are among the most popular high molecular weight bioemulsifiers. They have great physic-chemical properties like tolerance to extreme conditions of pH, temperature and salinity, low toxicity and biodegradability. Owing their emulsion forming and breaking capacities, solubilization, mobilization and dispersion activities and their viscosity reduction activity; they possess great environmental application as enhancer of hydrocarbon biodegradation and for microbial enhanced oil recovery. Besides, they are applied in biomedical fields for their antimicrobial and anti-adhesive activities and involvement in immune responses. PMID:25739564

  3. Interactions among Hageman factor, plasma prekallikrein, high molecular weight kininogen, and plasma thromboplastin antecedent.

    PubMed Central

    Ratnoff, O D; Saito, H

    1979-01-01

    To investigate the earliest steps of the intrinsic clotting pathway, Hageman factor (Factor XII) was exposed to Sephadex gels to which ellagic acid had been adsorbed; Hageman factor was then separated from the gels and studied in the fluid phase. Sephadex-ellagic acid-exposed Hageman factor, whether purified or in plasma, activated plasma thromboplastin antecedent, but only when high molecular weight kininogen was presnet. In the absence of plasma prekallikrein, maximal activation of plasma thromboplastin antecedent was slightly delayed in plasma, a delay not observed with similarly treated purified Hageman factor. Thus, high molecular weight kininogen was needed for expression of Hageman factor's clot-promoting properties and plasma prekallikrein played a minor role in the interaction of ellagic acid-treated Hageman factor and plasma thromboplastin antecedent. PMID:284420

  4. High molecular weight acidic polysaccharides from Malva sylvestris and Alcea rosea.

    PubMed

    Classen, B; Blaschek, W

    1998-10-01

    Leaves and flowers of Malva sylvestris and Alcea rosea (Malvaceae) were compared by determination of the swelling index as well as the content and viscosity of their mucilages. The investigations showed mucilage from flowers of Alcea to be superior to mucilages from leaves or flowers from Malva. High molecular weight acidic polysaccharides (HMWAPs) were isolated from the mucilages of leaves and flowers of both species. The molecular weight of all HMWAPs was in a range of 1.3 to 1.6 x 10(6) D. HMWAP-content in mucilage from flowers of Alcea was highest compared to content in mucilages from leaves or flowers from Malva. HMWAPs were found to be composed mainly of glucuronic acid, galacturonic acid, rhamnose and galactose. Methylation analysis of the carboxyl-reduced and deuterium labeled sugar derivatives of HMWAPs from flowers of Malva sylvestris ssp. mauritiana and Alcea rosea enabled elucidation of the principal structural features of both polysaccharides. PMID:9810269

  5. Participation of low molecular weight electron carriers in oxidative protein folding.

    PubMed

    Margittai, Eva; Csala, Miklós; Mandl, József; Bánhegyi, Gábor

    2009-03-01

    Oxidative protein folding is mediated by a proteinaceous electron relay system, in which the concerted action of protein disulfide isomerase and Ero1 delivers the electrons from thiol groups to the final acceptor. Oxygen appears to be the final oxidant in aerobic living organisms, although the existence of alternative electron acceptors, e.g. fumarate or nitrate, cannot be excluded. Whilst the protein components of the system are well-known, less attention has been turned to the role of low molecular weight electron carriers in the process. The function of ascorbate, tocopherol and vitamin K has been raised recently. In vitro and in vivo evidence suggests that these redox-active compounds can contribute to the functioning of oxidative folding. This review focuses on the participation of small molecular weight redox compounds in oxidative protein folding. PMID:19399252

  6. Influence of molecular weight on the resistance of polylactide fibers by radiation sterilization

    SciTech Connect

    Horacek, I.; Kudlacek, L. (Univ. of Chemical Technology Pardubice (Czechoslovakia). Dept. of Fibres and Textile Chemistry)

    1993-10-05

    The mechanical properties and in vitro degradability of poly(L-lactide) fibers with different average molecular weights, prepared by a dry spinning-hot drawing process from CHCl[sub 3] solutions, were studied in relation to the [gamma]-irradiation dose. In the range of molecular weight of 1.6--3.6 [times] 10[sup 5], no differences were found in the relative decrease of tensile strength after irradiation of 25 kGy. Changes of the elongation at break are discussed in terms of a network solution theory. In vitro degradation of the fibers is also discussed in network solution theory terms. Regardless of the courses of degradation curves, it may be stated that all prepared fibers could be sterilized by [gamma]-rays and the rate of degradation was not affected by the irradiation dose.

  7. Cyclic compressive loading results in fatigue cracks in ultra high molecular weight polyethylene.

    PubMed

    Pruitt, L; Koo, J; Rimnac, C M; Suresh, S; Wright, T M

    1995-01-01

    Wear damage to the articulating surfaces of total joint components made of ultra high molecular weight polyethylene is associated with a fatigue fracture mechanism, despite the fact that these surfaces are subjected to primarily compressive and compressive-tensile cyclic stresses. The question arises as to whether fatigue cracks will form under such loading conditions. In this study, we experimentally demonstrated that fatigue cracks could be initiated and propagated in notched ultra high molecular weight polyethylene specimens subjected to fully compressive and compressive-tensile cyclic loading. Under these loading conditions, growth of fatigue cracks was limited: the cracks arrested without catastrophic failure of the test specimens. The final length of the crack was dependent on the load ratio of the fatigue cycle; fatigue cracks propagated to greater lengths as the load ratio was increased. PMID:7853097

  8. Binding of pyrene to aquatic and commercial humic substances: The role of molecular weight and aromaticity

    USGS Publications Warehouse

    Chin, Y.-P.; Aiken, G.R.; Danielsen, K.M.

    1997-01-01

    The binding of pyrene to a number of humic substances isolated from various aquatic sources and a commercial humic acid was measured using the solubility enhancement method. The humic materials used in this study were characterized by various spectroscopic and liquid chromatography methods. A strong correlation was observed between the pyrene binding coefficient, K(doc), and the molecular weights, molar absorptivities at 280 nm, and aromaticity of the aquatic humic substances. Binding of pyrene to the commercial humic acid, however, was significantly stronger and did not obey the relationships observed between K(doc) and the chemical properties of the aquatic humic substrates. These results suggest that the molecular weight and the aromatic content of the humic substrates exert influences on the binding of nonpolar and planar aromatic molecules and that the physicochemical properties of both humic materials and organic solutes are important in controlling the speciation of nonpolar organic contaminants in natural waters.

  9. MOLECULAR WEIGHT, ELECTROCHEMICAL AND BIOLOGICAL PROPERTIES OF TUBERCULIN PROTEIN AND POLYSACCHARIDE MOLECULES

    PubMed Central

    Seibert, Florence B.; Pedersen, Kai O.; Tiselius, Arne

    1938-01-01

    Studies have been made by means of sedimentation in the ultracentrifuge, and by diffusion and electrophoresis, to determine the molecular weights and homogeneity of the tuberculin protein and polysaccharide molecules as found in their natural state in the unchanged filtrates from culture media after growth of tubercle bacilli. These results have been compared with data obtained on fractions isolated by chemical procedures from them or from old tuberculin. By means of electrophoresis in the Tiselius apparatus it was possible to separate the protein from the polysaccharide, as these two fractions occur naturally in the original culture medium filtrates of acid-fast bacilli. The protein from the bovine strain of bacillus proved to be homogeneous in sedimentation (S20 = 1.6), diffusion (D20 = 12.0) and electrophoresis, with a molecular weight of about 10,000. The tuberculin polysaccharide isolated in electrophoresis appeared to be practically the same in sedimentation and in precipitin reaction as the polysaccharide isolated by chemical procedure. The latter proved to be homogeneous in sedimentation (S20 = 1.6) and diffusion (D20 = 11.0) with a molecular weight of about 9000. A practically homogeneous protein was isolated from the culture filtrate of the human tubercle bacillus H 37 by fractional ammonium sulfate precipitation, with a molecular weight of 32,000 (S20 = 3.3; D20 = 8.2). It was electrochemically homogeneous, with an isoelectric point at pH 4.3 and an isoionic point at pH 4.7. It could be dried or frozen with no loss in homogeneity. It was highly antigenic in the precipitin reaction and produced the anaphylactic type of local skin reaction in tuberculous guinea pigs, in contrast to the true tuberculin type of reaction caused by a purified PPD fraction. Furthermore death resulted in tuberculous guinea pigs from intracutaneous injection of exceptionally small amounts. A protein with molecular weight of about 17,000 was isolated from the filtrate from cultures of the timothy bacillus. The nucleic acid originally occurring in old tuberculin (OT) seems to be responsible for the high electrochemical mobility observed. From OT and the PPD made from it, potent but non-antigenic molecules of 16,000 and 9000 weight and with a low content of nucleic acid were isolated. With increase in size these deviated much from the normal compact spherical shape, and aggregation was evident from the tendency toward gel formation. The smallest molecule (9000) was homogeneous (S20 = 1.0; D20 = 10.0) and had lost some tuberculin potency. PMID:19870796

  10. Removal of low molecular weight phenols from olive oil mill wastewater using microalgae.

    PubMed

    Pinto, Gabriele; Pollio, Antonino; Previtera, Lucio; Stanzione, Maria; Temussi, Fabio

    2003-10-01

    The treatment of olive oil mill wastewater (OMW) with two phenol resistant algae, Ankistrodesmus braunii and Scenedesmus quadricauda, showed a limited reduction of phenol content after 5 d of treatment, irrespective of algal concentration. Otherwise, cultures of both algae, grown in the dark, degraded over 50% of the low molecular weight phenols contained in OMW, but they were not completely removed, but were biotransformed into other non-identified, aromatic compounds. PMID:14584924

  11. Characterization of Rhizobial Isolates of Phaseolus vulgaris by Staircase Electrophoresis of Low-Molecular-Weight RNA

    PubMed Central

    Velázquez, Encarna; Martínez-Romero, Esperanza; Rodríguez-Navarro, Dulce Nombre; Trujillo, Martha E.; Daza, Antonio; Mateos, Pedro F.; Martínez-Molina, Eustoquio; van Berkum, Peter

    2001-01-01

    Low-molecular-weight (LMW) RNA molecules were analyzed to characterize rhizobial isolates that nodulate the common bean growing in Spain. Since LMW RNA profiles, determined by staircase electrophoresis, varied across the rhizobial species nodulating beans, we demonstrated that bean isolates recovered from Spanish soils presumptively could be characterized as Rhizobium etli, Rhizobium gallicum, Rhizobium giardinii, Rhizobium leguminosarum bv. viciae and bv. trifolii, and Sinorhizobium fredii. PMID:11157280

  12. Regulation of high molecular weight bovine brain neutral protease by phospholipids in vitro

    Microsoft Academic Search

    V. Chauhan; A. M. Sheikh; A. Chauhan; W. D. Spivack; M. D. Fenko; M. N. Malik

    2005-01-01

    The activity of the heat stable, glycosylated high molecular weight bovine brain neutral protease (HMW protease) is differentially regulated by phospholipids. While phosphatidylcholine (PC), phosphatidylserine (PS) and phosphatidic acid (PA) had only marginal stimulatory effect (40–75%) on the activity of HMW protease, lysophoshatidylcholine (lysoPC) and lysophosphatidic acid (lysoPA) activated the enzyme by more than two-fold. Both lysoPC and lysoPA exhibited

  13. Desmocalmin: a calmodulin-binding high molecular weight protein isolated from desmosomes

    Microsoft Academic Search

    SACHIKO TSUKITA; SHOICHIRO TSUKITA

    1985-01-01

    A unique high molecular weight protein (240,000 mol wt) has been purified from isolated desmosomes of bovine muzzle epidermis, using low-salt extraction at pH 9.5-10.5 and gel-filtration followed by calmodulin-affinity column chromatography. This protein was shown to bind to calmodulin in a Ca2+-dependent manner, so we called it desmocalmin here. Desmocalmin also bound to the reconstituted keratin filaments in vitro

  14. Molecular weight variations in the diversity of phospholipase A2 forms in reptile venoms.

    PubMed

    DuBourdieu, D J; Kawaguchi, H; Shier, W T

    1987-01-01

    Reptile venoms exhibit a wide diversity of phospholipase A2 forms when examined by electrophoretic and chromatographic techniques which separate on the basis of net charge. In principle, diversity in charge among the enzyme forms could result from two types of structural modifications: (i) pretranslational modifications, such as differences in amino acid sequences; (ii) post-translational modifications, such as partial proteolysis or hydrolysis of amide functions of asparagine and glutamine residues. Some types of modifications alter both charge and molecular weight. A radiolabeling technique has been developed which allows detection of phospholipase A2 enzymes after electrophoretic separation on the basis of molecular weight in polyacrylamide gels containing sodium dodecylsulfate. Venom preparations were radiolabeled by incubation with p-dodecylphenacylbromide, which was prepared radiolabeled to high specific activity with tritium. The labeling agent was dispersed in phosphatidylcholine liposomes and incubated with venom preparations under conditions of optimal enzyme activity. The preparations were then extracted with ether and hexane to remove substrate and unbound label and subjected to polyacrylamide gel electrophoresis under standard conditions. Protein-bound radiolabel was detected by fluorography and autoradiography. Patterns of labeled species obtained by gel electrophoresis of selected venoms using separation on the basis of charge were similar to the patterns of phospholipase A2 variants obtained under the same electrophoretic conditions using enzymatic detection in phosphatidylcholine-containing gels. Examination of a variety of snake and lizard venoms using this technique revealed the presence of multiple molecular weight forms of labeled enzymes, but the extent of diversity was less than that observed with the same venoms using separation of phospholipase electrophoretic variants on the basis of charge. The results are consistent with diversity in reptile venom phospholipase A2 forms being derived from differences in both molecular weight and charge. PMID:3590214

  15. Low molecular weight heparin (bemiparin sodium) and the coagulation profile of patients with heart failure

    Microsoft Academic Search

    Ferruccio De Lorenzo; Douglas Newberry; Mike Scully; Zibgniew Kadziola; Gloria Dawson; Nancy Ranlall; Neelam Saba; Ali Noorani; Shaharam Kashani; Rene' Williams; Vijay Vir Kakkar

    2002-01-01

    Background Congestive heart failure (CHF) is associated with a hypercoagulable state. Patients and Methods A single-center, randomized, double-blind, placebo-controlled trial was performed to test the hypothesis that a prophylactic dose of low molecular weight heparin (bemiparin sodium 3500 IU\\/daily subcutaneously) will modify a hypercoagulable state in CHF. This study included 100 patients with CHF (New York Heart Association classification II

  16. Studies of low density lipoprotein molecular weight in human beings with coronary artery disease

    Microsoft Academic Search

    John R. Crouse; Johns S. Parks; Harry M. Schey; Frederic R. Kahl

    Low density lipoprotein molecular weight (LDL MW) correlates positively with coronary artery disease in cho- lesterol-fed nonhuman primates. To evaluate this in human beings with coronary artery disease (CAD) we measured LDL MW in 93 volunteers undergoing coronary angiography (47 controls and 46 CAD patients). LDL MW of CAD patients was less than that of controls (patients, 2.79 * 0.17

  17. Treatment of mobile right heart thrombi with low-molecular-weight heparin

    PubMed Central

    Lampropoulos, Konstantinos M; Bonou, Maria; Theocharis, Constantinos; Barbetseas, John

    2013-01-01

    Treatment of choice in patients with mobile thrombi in the right heart chambers is still controversial owing to the increased risk of recurrent pulmonary embolism (PE). Thrombolysis and surgical or catheter embolectomy are the preferred options. We present a case of an elderly patient with PE and free-floating atrial thrombi who was treated successfully with low-molecular-weight heparin (LMWH). PMID:23531929

  18. Molecular weight dependence of polyethylene glycol penetration across acetone-disrupted permeability barrier

    Microsoft Academic Search

    J. C. Tsai; P. L. Hung; H. M. Sheu

    2001-01-01

    \\u000a Abstract Previous studies have demonstrated that permeability barrier disruption by acetone treatment significantly enhances skin\\u000a permeability to both hydrophilic and amphipathic compounds, but not to highly lipophilic compounds. The purpose of the present\\u000a study was to investigate the dependence of permeability on molecular weight (MW) in acetone-disrupted hairless mouse skin\\u000a in contrast to normal skin. Penetration of polyethylene glycol (PEG)

  19. Sorption and permeation of low molecular weight volatile compounds in polypropylene

    E-print Network

    Vidal, Antonio Ramiro Santiago

    1991-01-01

    there is no interaction between the polymer and the penetrant molecules. The permeability coefficient is the combination of the diffusion coefficient (D) and solubility coefficient (S). They are 8 related as follows: P DS The diffusion coefficient is associated... with the velocity of propagation of the permeant molecules, and the solubility coefficient reflects the degree of affinity between the permeant molecules and the polymer. 9 The list of factors influencing sorption and permeation of low molecular weight organic...

  20. Low-molecular-weight triacylglycerols of the seed oil of Artemisia absinthium

    Microsoft Academic Search

    N. T. Ul'chenko; E. I. Gigienova; A. U. Umarov; U. A. Abdullaev

    1981-01-01

    Low-molecular-weight triacylglycerols have been isolated from the seed oil ofArtemisia absinthown in which one acyl radical is derived from ethanoic, propanoic, butanoic, pentanoic, hexanoic, heptanoic, octanoic, or nonanoic acid. Their main representatives are the ethanoyl and propanoyl derivatives, position 2 being occupied mainly by the ethanoyl radical. The isomers with a short acyl radical in position 2 make up 75%

  1. Low-Molecular-Weight Fucoidan Promotes Therapeutic Revascularization in a Rat Model of Critical Hindlimb Ischemia

    Microsoft Academic Search

    CHARLES-EDOUARD LUYT; ANNE MEDDAHI-PELL ´ E; BENOIT HO-TIN-NOE; SYLVIA COLLIEC-JOUAULT; JEAN GUEZENNEC; LILIANE LOUEDEC; HERV ´ E PRATS; MARIE-PAULE JACOB; MARY OSBORNE-PELLEGRIN; DIDIER LETOURNEUR; JEAN-BAPTISTE MICHEL; CHU X. Bichat

    2003-01-01

    The therapeutic potential of low-molecular-weight (LMW) fu- coidan, a sulfated polysaccharide extracted from brown sea- weed devoid of direct antithrombin effect, was investigated in vitro and in a model of critical hindlimb ischemia in rat. In vitro results showed that LMW fucoidan enhanced fibroblast growth factor (FGF)-2-induced ( 3 H)thymidine incorporation in cultured rat smooth muscle cells. Intravenous injection in

  2. The Nerve Growth Factor: Purification as a 30,000-Molecular-Weight Protein

    Microsoft Academic Search

    Vincenzo Bocchini; Pietro U. Angeletti

    1969-01-01

    The nerve growth factor protein was purified over 100-fold from adult mouse salivary glands. The first step was a gel filtration on Sephadex G-100 at pH 7.5 of the aqueous gland extract. After gel filtration, most of the NGF activity was eluted in the 80,000-90,000-molecular-weight region (G-100 pool). The G-100 pool was dialyzed at pH 5.0 and fractionated by CM52

  3. Chemistry and properties of controlled molecular weight end-capped LaRC-CPI

    NASA Technical Reports Server (NTRS)

    Hergenrother, Paul M.; Havens, Stephen J.

    1991-01-01

    As part of a program on structural resins for high temperature aerospace applications, a controlled molecular weight end-capped semi-crystalline polyimide, designated LaRC-CPI, was evaluated. Neat resin moldings, adhesive specimens and composites were fabricated at temperatures of 365-375 C under pressures of 200-500 psi. Adhesive and composite specimens provided good mechanical properties at temperatures as high as 232 C.

  4. Structural and genetical studies on the high-molecular-weight subunits of wheat glutenin

    Microsoft Academic Search

    P. I. Payne; L. M. Holt; C. N. Law

    1981-01-01

    Summary  The high-molecular-weight (HMW) subunits of glutenin from about 185 varieties were fractionated by sodium dodecyl sulphate\\u000a polyacrylamide gel electrophoresis (SDS-PAGE). About 20 different, major subunits were distinguished by this technique although\\u000a each variety contained, with only a few exceptions, between 3 and 5 subunits. Further inter-varietal substitution lines to\\u000a those already described (Payne et al. 1980) were analysed and the

  5. Rapid cycling of high-molecular-weight dissolved organic matter in the ocean

    Microsoft Academic Search

    Rainer M. W. Amon; Ronald Benner

    1994-01-01

    DISSOLVED organic matter (DOM) in the ocean is one of the largest active reservoirs of organic carbon on Earth. It is important to understand the processes by which DOM is recycled, particularly as changes in the oceanic DOM pool could affect atmospheric carbon dioxide concentrations on timescales of 1,000 to 10,000 years (ref. 1). It is commonly believed that low-molecular-weight

  6. Orientation softening in the deformation and wear of ultra-high molecular weight polyethylene

    Microsoft Academic Search

    A. Wang; D. C. Sun; S.-S. Yau; B. Edwards; M. Sokol; A. Essner; V. K. Polineni; C. Stark; J. H. Dumbleton

    1997-01-01

    Stress-induced anisotropy is an important phenomenon in the plastic deformation of semi-crystalline linear high polymers. The significance of this phenomenon in the wear of ultra-high molecular weight polyethylene (UHMWPE) bearing surfaces in total joint-replacement prostheses is studied in this investigation. Both linear and crosslinked UHMWPE materials were studied by means of a sequential biaxial tensile test and a hip-joint simulator

  7. Polyethylene glycol-induced mammalian cell hybridization: Effect of polyethylene glycol molecular weight and concentration

    Microsoft Academic Search

    Richard L. Davidson; Kathleen A. O'Malley; Thomas B. Wheeler

    1976-01-01

    The effects of polyethylene glycol (PEG) molecular weight and concentration on mammalian cell hybridization were studied. The peak hybridization-inducing activity with all grades of PEG from 400–6000 was found to occur in the concentration range of 50–55%. However, changes in concentration were seen to have different quantitative effects with different grades of PEG. For monolayer fusions, PEG 1000 at 50%

  8. Low-molecular-weight iron complexes and oxygen radical reactions in idiopathic haemochromatosis.

    PubMed

    Gutteridge, J M; Rowley, D A; Griffiths, E; Halliwell, B

    1985-04-01

    The sera of patients with idiopathic haemochromatosis and iron-overload have been found to contain low-molecular-weight iron complexes detectable in the 'bleomycin assay'. These complexes stimulate both the peroxidation of membrane lipids and the formation of the highly reactive and damaging hydroxyl radical. The iron chelator desferrioxamine interferes with these reactions. We suggest that oxygen radical reactions stimulated by iron salts are important in the pathology of idiopathic haemochromatosis. PMID:2578915

  9. Effect of cryogrinding on the molecular weight of samples of polyisobutylene

    SciTech Connect

    Waters, P.F. (American Univ., Washington, DC); Hadermann, A.F.; Trippe, J.C.

    1983-01-01

    Three different molecular weight samples of isobutylene are ground and dissolved in isooctane. Also, unground samples are dissolved for comparison. The viscosity and height-at-break in ductless siphon are measured. Small quantities of macromolecules dissolved in fuels impede the aerosolization of the fuels (the purpose of antimisting additives). Mathematical formulas for the intrinsic viscosity and height-at-break are derived from the data.

  10. Effect of molecular weight of PEG on membrane morphology and transport properties

    Microsoft Academic Search

    B. Chakrabarty; A. K. Ghoshal; M. K. Purkait

    2008-01-01

    Flat sheet asymmetric polymeric membranes were prepared from homogeneous solution of polysulfone (PSf) by phase inversion method. N-methyl-2-pyrrolidone (NMP) and dimethyl acetamide (DMAc) were used as solvents separately. Polyethylene glycol (PEG) of three different molecular weights (400Da, 6000Da and 20000Da, respectively) were used as the polymeric additives in the casting solution. The morphology and structure of the resulting membranes were

  11. Development of an extremely wear-resistant ultra high molecular weight polyethylene for total hip replacements.

    PubMed

    McKellop, H; Shen, F W; Lu, B; Campbell, P; Salovey, R

    1999-03-01

    Osteolysis induced by ultra high molecular weight polyethylene wear debris is one of the primary factors limiting the lifespan of total hip replacements. Crosslinking polyethylene is known to improve its wear resistance in certain industrial applications, and crosslinked polyethylene acetabular cups have shown improved wear resistance in two clinical studies. In the present study, crosslinked polyethylene cups were produced by two methods. Chemically crosslinked cups were produced by mixing a peroxide with ultra high molecular weight polyethylene powder and then molding the cups directly to shape. Radiation-crosslinked cups were produced by exposing conventional extruded ultra high molecular weight polyethylene bar stock to gamma radiation at various doses from 3.3 to 100 Mrad (1 Mrad = 10 kGy), remelting the bars to extinguish residual free radicals (i.e., to minimize long-term oxidation), and then machining the cups by conventional techniques. In hip-joint simulator tests lasting as long as 5 million cycles, both types of cross-linked cups exhibited dramatically improved resistance to wear. Artificial aging of the cups by heating for 30 days in air at 80 degrees C induced oxidation of the chemically crosslinked cups. However, a chemically crosslinked cup that was aged 2.7 years at room temperature had very little oxidation. Thus, whether substantial oxidation of chemically crosslinked polyethylene would occur at body temperature remains unclear. The radiation-crosslinked remelted cups exhibited excellent resistance to oxidation. Because crosslinking can reduce the ultimate tensile strength, fatigue strength, and elongation to failure of ultra high molecular weight polyethylene, the optimal crosslinking dose provides a balance between these physical properties and the wear resistance of the implant and might substantially reduce the incidence of wear-induced osteolysis with total hip replacements. PMID:10221831

  12. Influence of polymerization conditions on the molecular weight and polydispersity of polyepichlorohydrin

    Microsoft Academic Search

    D. Guanaes; E. Bittencourt; M. N. Eberlin; A. A. Sabino

    2007-01-01

    The influence of the relevant reaction conditions on the molecular weight and polydispersity during the cationic ring-opening polymerization of epichlorohydrin has been studied using an experimental design. The polymerization was conducted in the presence of an alcohol (diol and triol), a Lewis acid at two temperatures (5°C and 25°C), and with two monomer addition rates. FT-IR spectra were used for

  13. Effects of a Low-Molecular-Weight CCR3 Antagonist on Chronic Experimental Asthma

    Microsoft Academic Search

    Michael Wegmann; Rolf Goggel; Sarper Sel; Serdar Sel; Klaus J. Erb; Frank Kalkbrenner; Harald Renz; Holger Garn

    Eosinophils represent one of the main effector cell populations of allergic airway inflammation and allergic bronchial asthma. Their infiltration correlates with many characteristics of the disease, in- cluding airway hyperresponsiveness (AHR) and increased mucus production. CCR-3 is the principle chemokine receptor involved in eosinophil attraction into inflamed tissue. Therefore, antagonizing CCR-3couldbeanovelpromisingapproachtowardasthmatherapy. Weinvestigatedtheeffectofalow-molecular-weightCCR-3antago- nistonestablishedairwayinflammationinachronicmodelofexper- imental bronchial asthma. For this purpose, BALB\\/c

  14. Pre-analytical operating procedures for serum Low Molecular Weight protein profiling

    Microsoft Academic Search

    Francesco Di Girolamo; Jhessica Alessandroni; Paolo Somma; Fiorella Guadagni

    2010-01-01

    Biological specimen collection and storage are an integral component of serum proteomics research. Although many efforts have been posed to address the effects of pre-analytical procedures, standardized protocols for collection and storage of samples for Low Molecular Weight (LMW) proteome profiling are still needed.Here we report a systematic analysis on the influence of pre-analytical factors [clotting times, temperature and time

  15. Efficient bulk heterojunction photovoltaic cells using small-molecular-weight organic thin films

    Microsoft Academic Search

    Peter Peumans; Soichi Uchida; Stephen R. Forrest

    2003-01-01

    The power conversion efficiency of small-molecular-weight and polymer organic photovoltaic cells has increased steadily over the past decade. This progress is chiefly attributable to the introduction of the donor-acceptor heterojunction that functions as a dissociation site for the strongly bound photogenerated excitons. Further progress was realized in polymer devices through use of blends of the donor and acceptor materials: phase

  16. Clinical efficacy of low molecular weight heparin in postoperative thrombosis prophylaxis

    Microsoft Academic Search

    U. Schmitz-Huebner; H. Bfinte; G. Freise; B. Reers; C. Rfischemeyer; R. Scherer; H. Schulte; J. van de Loo

    1984-01-01

    Summary In a randomized controlled clinical trial, the efficacy and safety of two low molecular weight heparin (LMWH) fractions in the prophylaxis of deep vein thrombosis (DVT) were assessed. One hundred twenty-six patients undergoing major abdominal surgery received alternatively 2,500 APTT units b.i.d. of two LMWH fractions or 5,000 APTT units b.i.d. of an unfractionated sodium mucosal heparin (UFH). LMWH

  17. Fluid absorption study in ultra-high molecular weight polyethylene (UHMWPE) sterilized and unsterilized acetabular cups.

    PubMed

    Affatato, S; Vandelli, C; Bordini, B; Toni, A

    2001-01-01

    The weight gain due to fluid absorption was measured in gamma-sterilized, ethylene oxide (ETO) gas-sterilized, and unsterilized ultra-high molecular weight (UHMW) polyethylene acetabular cups. After about 2 months the total average fluid absorption gain of the polyethylene cups was: 1.76 +/- 0.45 mg (average +/- standard deviation) for the unsterilized polyethylene cups, 2.81 +/- 0.95 mg for the gamma-sterilized polyethylene cups and 1.51 +/- 0.34 for the ETO gas-sterilized polyethylene cups. There was little difference in fluid absorption between the sterilized and unsterilized specimens. In particular, the gamma-sterilized acetabular cups absorbed more than the ETO gas-sterilized and the unsterilized cups. However, the weight gain was higher in serum compared with that in water. PMID:11323978

  18. Towards More Accurate Measurements of the Ionization Energy of Molecular Hydrogen

    NASA Astrophysics Data System (ADS)

    Sprecher, D.; Beyer, M.; Liu, J.; Merkt, F.; Salumbides, E.; Eikema, K. S. E.; Ubachs, W.; Jungen, Ch.

    2013-06-01

    With two electrons and two protons, molecular hydrogen is the simplest molecule displaying all features of a chemical bond. H_2 is therefore a fundamental system for testing molecular quantum mechanics and quantum electrodynamics in molecules. The test can be performed by comparing measured and calculated intervals between different rovibronic states of H_2. Two further quantities that can be used for this test are the dissociation and ionization energies of H_2, and considerable efforts have been invested over more than 80 years to improve the precision and accuracy of experimental and theoretical determination of these two quantities. The current status of the comparison is that the theoretical and experimental values of the ionization and dissociation energies of H_2 agree within the combined uncertainty of 30 MHz (see also). The factors currently limiting the precision of the experimental determination will be discussed and the strategies that are being implemented towards overcoming these limitations will be presented. A long-term goal is to achieve a precision of better than 15 kHz, which is the ultimate limit imposed on the accuracy of the theoretical determination by the current uncertainty of the proton-to-electron mass ratio. E. J. Salumbides, G. D. Dickenson, T. I. Ivanov and W. Ubachs, {Phys. Rev. Lett.} 107 (4), 043005 (2011). K. Piszczatowski, G. Lach, M. Przybytek, J. Komasa, K. Pachuckiand and B. Jeziorski, {J. Chem. Theory Comput.} 5 (11), 3039 (2009). J. Liu, E. J. Salumbides, U. Hollenstein, J. C. J. Koelemeij, K. S. E. Eikema, W. Ubachs and F. Merkt, {J. Chem. Phys.} 130 (17), 174306 (2009). D. Sprecher, Ch. Jungen, W. Ubachs and F. Merkt, {Faraday Discuss.} 150, 51 (2011).

  19. INFLUENCE OF POLYMER MOLECULAR WEIGHT, TEMPERATURE, AND STRAIN RATE ON THE MECHANICAL PROPERTIES OF PBX 9501

    SciTech Connect

    D. J. IDAR; D. G. THOMPSON; ET AL

    2001-06-01

    Compression and tensile measurements were conducted on newly formulated (baseline) and lower molecular weight (virtually-aged) plastic-bonded explosive PBX 9501. The PBX 9501 binder system is composed of nitroplasticized Estane 5703, TM a polyester polyurethane copolymer. The molecular weight of polyester urethanes can degrade with time as a function of hydrolysis, affecting the mechanical behavior of the polymer or a polymer composite material of high explosives, i.e. PBXs. The molecular weight of Estane 5703{trademark} was degraded by exposure to high temperature and humidity for different periods of time, and then formulated to produce ''virtually-aged'' PBX 9501 specimens. Quasi-static and dynamic compression tests were conducted on the baseline and virtually-aged PBX 9501 as a function of temperature and strain rate. Quasi-static tensile tests were also conducted as a function of temperature and test rate. Rate and temperature dependence was exhibited during both compression and tensile loading. Results also show significant differences between the baseline and virtually-aged specimens for the dynamic compression tests at -15 C, and for the quasi-static compression tests at -15 C, 22 C, and 50 C.

  20. Analysis of low molecular weight compounds by MALDI-FTICR-MS.

    PubMed

    Wang, Hao-Yang; Chu, Xu; Zhao, Zhi-Xiong; He, Xiao-Shuang; Guo, Yin-Long

    2011-05-15

    This review focuses on recent applications of matrix-assisted laser desorption ionization-Fourier-transform ion cyclotron resonance mass spectrometry (MALDI-FTICR-MS) in qualitative and quantitative analysis of low molecular weight compounds. The scope of the work includes amino acids, small peptides, mono and oligosaccharides, lipids, metabolic compounds, small molecule phytochemicals from medicinal herbs and even the volatile organic compounds from tobacco. We discuss both direct analysis and analysis following derivatization. In addition we review sample preparation strategies to reduce interferences in the low m/z range and to improve sensitivities by derivatization with charge tags. We also present coupling of head space techniques with MALDI-FTICR-MS. Furthermore, omics analyses based on MALDI-FTICR-MS were also discussed, including proteomics, metabolomics and lipidomics, as well as the relative MS imaging for bio-active low molecular weight compounds. Finally, we discussed the investigations on dissociation/rearrangement processes of low molecular weight compounds by MALDI-FTICR-MS. PMID:21482202

  1. Optimization of Glutamine Peptide Production from Soybean Meal and Analysis of Molecular Weight Distribution of Hydrolysates

    PubMed Central

    Xie, Yanli; Liang, Xinhong; Wei, Min; Zhao, Wenhong; He, Baoshan; Lu, Qiyu; Huo, Quangong; Ma, Chengye

    2012-01-01

    The process parameters of enzymatic hydrolysis and molecular weight distribution of glutamine (Gln) peptides from soybean meal were investigated. The Protamex® hydrolysis pH of 6.10, temperature of 56.78 °C, enzyme to substrate ratio (E/S) of 1.90 and hydrolysis time of 10.72 h were found to be the optimal conditions by response surface methodology (RSM) for a maximal degree of hydrolysis (DH) value of 16.63% and Gln peptides content at 5.95 mmol/L. The soybean meal was hydrolyzed by a combination of Protamex® and trypsinase so that DH and Gln peptides would reach 22.02% and 6.05 mmol/mL, respectively. The results of size exclusion chromatography indicated that the relative proportion of the molecular weight <1000 Da fraction increased with DH values from 6.76%, 11.13%, 17.89% to 22.02%, most notably the 132–500 Da fractions of hydrolysates were 42.14%, 46.57%, 58.44% and 69.65%. High DH values did not lead to high Gln peptides content of the hydrolysate but to the low molecular weight Gln peptides. PMID:22837706

  2. Stable, concentrated solutions of high molecular weight polyaniline and articles therefrom

    DOEpatents

    Mattes, Benjamin R. (Sante Fe, NM); Wang, Hsing-Lin (Los Alamos, NM)

    2000-01-01

    Stable, concentrated solutions of high molecular weight polyaniline. In order to process high quality fibers and other articles possessing good mechanical properties, it is known that solution concentrations of the chosen polymer should be in the range from 15-30% (w/w). Moreover, it is desirable to use the highest molecular weight consistent with the solubility properties of the polymer. However, such solutions are inherently unstable, forming gels before processing can be achieved. The present invention describes the addition gel inhibitors (GIs) to the polymer solution, thereby permitting high concentrations (>15% (w/w)) of high molecular weight ((M.sub.w)>120,000, and (M.sub.n)>30,000) emeraldine base (EB) polyaniline to be dissolved. Secondary amines have been used for this purpose in concentrations which are small compared to those which might otherwise be used in a cosolvent role therefor. The resulting solutions are useful for generating excellent fibers, films, coatings and other objects, since the solutions are stable for significant time periods, and the GIs are present in too small concentrations to cause polymer deterioration. It is demonstrated that the GIs found to be useful do not act as cosolvents, and that gelation times of the solutions are directly proportional to the concentration of GI. In particular, there is a preferred concentration of GI, which if exceeded causes structural and electrical conductivity degradation of resulting articles. Heating of the solutions significantly improves solubility.

  3. Stable, concentrated solutions of high molecular weight polyaniline and articles therefrom

    DOEpatents

    Mattes, Benjamin R. (Santa Fe, NM); Wang, Hsing-Lin (Los Alamos, NM)

    1999-11-09

    Stable, concentrated solutions of high molecular weight polyaniline. In order to process high quality fibers and other articles possessing good mechanical properties, it is known that solution concentrations of the chosen polymer should be in the range from 15-30% (w/w). Moreover, it is desirable to use the highest molecular weight consistent with the solubility properties of the polymer. However, such solutions are inherently unstable, forming gels before processing can be achieved. The present invention describes the addition gel inhibitors (GIs) to the polymer solution, thereby permitting high concentrations (between 15% and 30% (w/w)) of high molecular weight ((M.sub.w)>120,000, and (M.sub.n)>30,000) emeraldine base (EB) polyaniline to be dissolved. Secondary amines have been used for this purpose in concentrations which are small compared to those which might otherwise be used in a cosolvent role therefor. The resulting solutions are useful for generating excellent fibers, films, coatings and other objects, since the solutions are stable for significant time periods, and the GIs are present in too small concentrations to cause polymer deterioration. It is demonstrated that the GIs found to be useful do not act as cosolvents, and that gelation times of the solutions are directly proportional to the concentration of GI. In particular, there is a preferred concentration of GI, which if exceeded causes structural and electrical conductivity degradation of resulting articles. Heating of the solutions significantly improves solubility.

  4. Influence of molecular weight on in vitro immunostimulatory properties of instant coffee.

    PubMed

    Passos, Cláudia P; Cepeda, Márcio R; Ferreira, Sónia S; Nunes, Fernando M; Evtuguin, Dmitry V; Madureira, Pedro; Vilanova, Manuel; Coimbra, Manuel A

    2014-10-15

    Instant coffee was prepared and fractionated into higher (>100kDa), medium (5-10, 10-30, 30-100kDa) and lower (1-5, <1kDa) molecular weight fractions. Sugars and linkage composition characteristics of arabinogalactans and galactomannans were recovered in all fractions. Also, amino acid analysis performed after hydrolysis showed similar compositions in all fractions. On the contrary, free chlorogenic acids and caffeine were only detected in the lowest molecular weight fraction (<1kDa). A direct relationship between the melanoidins browning index and the molecular weight was observed. The fractions obtained were incubated in vitro with murine spleen lymphocytes in order to evaluate their possible immunostimulatory abilities. The surface expression of CD69 (early activation marker) on different lymphocyte sub-populations showed that the fraction with 1-5kDa was able to induce activation of B-lymphocytes. This was the only fraction to induce B-lymphocyte activation, since all the other fractions failed, even when higher concentrations were used. PMID:24837922

  5. Ionic Conductivity of Nanostructured Block Copolymer Electrolytes in the Low Molecular Weight Limit

    NASA Astrophysics Data System (ADS)

    Teran, Alexander; Yuan, Rodger; Gurevitch, Inna; Balsara, Nitash

    2013-03-01

    Nanostructured block copolymer electrolytes containing an ion-conducting block and a modulus-strengthening block are of interest for applications in solid-state lithium metal batteries. Previous work using symmetric polystyrene-block-poly(ethylene oxide) mixed with a lithium salt has demonstrated that the ionic conductivity increases with increasing molecular weight of the poly(ethylene oxide) block in the high molecular weight regime due to an increase in the width of the conducting channel. Our current study extends the previous work to the low molecular weight limit. Small angle X-ray scattering, differential scanning calorimetry, and ac impedance spectroscopy experiments help identify the opposing forces influencing the conductivity in these materials. We also examine the annealing process for these materials, whose ion transport characteristics are well known to be influenced by sample preparation and thermal history. The conductivity appears to be influenced by the conductive channel width as well as the glass transition temperature of the insulating block, which also plays an important role in the annealing process.

  6. Methanol-induced chain termination in poly(3-hydroxybutyrate) biopolymers: Molecular weight control.

    PubMed

    Ashby, Richard D; Solaiman, Daniel K Y; Strahan, Gary D; Levine, Alex C; Nomura, Christopher T

    2015-03-01

    A systematic study was performed to demonstrate the impact of methanol (MeOH) on poly(3-hydroxybutyrate) (PHB) synthesis and molecular weight (MW). Glycerine was used as the primary carbon source with varying concentrations of MeOH. Methanol retarded but did not completely inhibit growth and PHB production in Pseudomonas oleovorans. Proton NMR analysis revealed that the PHB polymers were end-capped with methoxy chemical groups causing MW reductions. The MW decreases were contingent upon the initial MeOH media concentration and the duration of the fermentations. The largest impact occurred at an initial MeOH concentration of 0.10% (w/v) where the number average molecular weights (Mn) decreased by 39%, 55%, and 72% in the 48, 72 and 96h cultures, respectively. Diffusion ordered NMR spectroscopy revealed a diffusivity (D) increase in the smaller molecular weight polymers with the PHB synthesized in the presence of 0.85% MeOH (72h post-inoculation) having a D value of 0.66×10(-10)m(2)/s. Diffusivity increases indicate a reduction in hydrodynamic radii (Rhz) consistent with shorter chain-lengths. Crude glycerine from the biodiesel production process has been used as an inexpensive fermentation feedstock for polyhydroxyalkanoate (PHA) synthesis but its composition is facility-dependent. This information will be vital to tailor PHA properties to specific applications. PMID:25542165

  7. Influence of the polymer molecular weight on the microstructure of hybrid materials prepared by ?-irradiation

    NASA Astrophysics Data System (ADS)

    Lancastre, Joana J. H.; Falcão, António N.; Margaça, Fernanda M. A.; Ferreira, Luís M.; Miranda Salvado, Isabel M.; Casimiro, Maria H.; Almásy, László; Meiszterics, Anikó

    2015-01-01

    Hybrid materials have been the object of intense research due to their potential for biomedical applications as well as in other fields. They are usually prepared by sol-gel but the method of gamma irradiation of the precursors is an alternative avoiding the addition of any other chemicals. The study of the hybrids prepared by this method has been progressing to understand the impact of different variables on the microstructure. In this work, the influence of the polymer?s molecular weight on the microstructure of the materials is investigated. Hybrids were obtained from a mixture of polydimethylsiloxane (PDMS) silanol terminated, tetraethylorthosilicate (TEOS) and zirconium propoxide (PrZr) in the wt% composition 20PDMS-73TEOS-7PrZr varying only the PDMS molecular weight. The obtained materials are homogeneous, transparent and flexible and their microstructure was analysed by Scanning Electron Microscopy (SEM) and Small-Angle Neutron Scattering (SANS). It was found that different microstructures were obtained, depending on the polymer molecular weight.

  8. Phase Behavior of Weakly Ordered Diblock Copolymers in the High Molecular Weight Limit

    NASA Astrophysics Data System (ADS)

    Patel, Amish; Balsara, Nitash

    2004-03-01

    Poly(tert-butylstyrene-block-polydiene) (TBS-D) diblock copolymers with molecular weights ranging from 10 kg/mol to 500 kg/mol have been synthesized. The dienes studied thus far are 1-4 polyisoprene and 1-2 polybutadiene. The Flory-Huggins interaction parameters (kii) between TBS and D chains are negative at room temperature. Thus, the mean field theory of polymer blends predicts that TBS-D diblock copolymers must be disordered, regardless of their molecular weight. With increasing temperature, kii increases, and we thus expect the formation of ordered phases. The nature of these transitions can be also predicted by mean-field theory. We are conducting small-angle X-ray scattering and optical birefringence experiments on the TBS-D block copolymers to test the applicability of the mean-field theory. This enables a test of the mean-field theory of block copolymers over an unprecedented range of molecular weights. The results of these tests will be presented at the meeting.

  9. Developmental co-expression of small molecular weight apolipoprotein B synthesis and triacylglycerol secretion

    SciTech Connect

    Coleman, R.A.; Haynes, E.B.; Sand, T.M.; Davis, R.A.

    1987-05-01

    The development of the liver's ability to coordinately express the synthesis and secretion of the two major components of very low density lipoproteins (VLDL): triacylglycerol (TG) and apolipoprotein B (apo B) was examined in cultured hepatocytes obtained from fetal, suckling and adult rats. Hepatocytes from fetal and suckling rats synthesized and secreted TG at rates lower than that displayed by adult cells. When TG synthesis was equalized by adding oleic acid to the culture medium, fetal cells still secreted only 39% as much TG as did adult cells. To determine the basis for the apparent defect in VLDL assembly/secretion displayed by fetal cells, the synthesis and secretion of (TVS)methionine-labeled apo B was quantified by immunoprecipitation. Although adult and fetal cells synthesized and secreted large molecular weight apo B at similar rates, the synthesis and secretion of small molecular weight apo B was 2-fold greater in adult cells. These data suggest that the ability to assemble/secrete VLDL triacylglycerol varies in parallel with the developmental expression of small molecular weight apo B. Furthermore, these studies show the usefulness of the cultured rat hepatocyte model for examining the ontogeny and regulation of VLDL assembly/secretion.

  10. The effects of high molecular weight hydroxyethyl starch solutions on platelets.

    PubMed

    Deusch, Engelbert; Thaler, Ulrich; Kozek-Langenecker, Sibylle A

    2004-09-01

    Physicochemical characteristics of hydroxyethyl starch (HES) molecules determine their side effects on hemostasis. Our aim in the present experiments was to test the antiplatelet effect of novel high molecular weight HES. Citrated whole blood was hemodiluted in vitro (0% and 20%) with either HES 550 (Hextend), HES 600 (6%Hetastarch-Baxter), HES 200 (Elohäst), or the solvent of Hextend in its commercially available solution. The availability of glycoprotein IIb-IIIa was assessed on nonstimulated and on agonist-induced platelets using flow cytometry. Glycoprotein IIb-IIIa availability increased significantly after hemodilution with Hextend and its solvent by 23% and 24%, respectively, but decreased in the presence of 6% Hetastarch-Baxter and Elohäst by 18% and 15%, respectively, with no significant difference between the latter two colloids. This study shows that Hextend does not inhibit platelet function as anticipated by its high molecular weight and degree of substitution. The unexpected platelet stimulating effect of Hextend is unique among the currently available HES preparations and may, at least in part, be induced by its solvent containing calcium chloride dihydrate (2.5 mmol/L). The platelet-inhibiting effect of 6%Hetastarch-Baxter was not significantly different from that of medium molecular weight HES 200. PMID:15333389

  11. Zwitterionic polymerization to generate high molecular weight cyclic poly(carbosiloxane)s.

    PubMed

    Brown, Hayley A; Chang, Young A; Waymouth, Robert M

    2013-12-18

    The zwitterionic ring-opening of 2,2,5,5-tetramethyl-2,5-disila-1-oxacyclopentane (TMOSC) with N-heterocyclic carbenes generates high molecular weight cyclic p(TMOSC). The NHC-mediated polymerization of TMOSC with 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes, 1) generates the poly(carbosiloxane) p(TMOSC) with molecular weights from 27,000 < Mn < 80,000 Da (1.4 < Mw/Mn < 2.2) within 30 min at room temp. With the more nucleophilic carbene 1,3,4,5-tetramethyl-imidazol-2-ylidene (4), the ring-opening polymerization occurs within minutes at room temperature to generate cyclic p(TMOSC) with molecular weights up to Mn = 940,000 Da (Mw/Mn = 3.2). The resulting p(TMOSC)s are predominantly cyclic as evidenced by dilute solution viscosity studies and MALDI-TOF MS. DFT calculations provide support for both zwitterionic and neutral, cyclic intermediates. PMID:24308512

  12. Low molecular weight DNA replication intermediates in Escherichia coli: mechanism of formation and strand specificity

    PubMed Central

    Amado, Luciana; Kuzminov, Andrei

    2013-01-01

    Chromosomal DNA replication intermediates, revealed in ligase-deficient conditions in vivo, are of low molecular weight independently of the organism, suggesting discontinuous replication of both the leading and the lagging DNA strands. Yet, in vitro experiments with purified enzymes replicating sigma-structured substrates show continuous synthesis of the leading DNA strand in complete absence of ligase, supporting the textbook model of semi-discontinuous DNA replication. The discrepancy between the in vivo and in vitro results is rationalized by proposing that various excision repair events nick continuously-synthesized leading strands after synthesis, producing the observed low molecular weight intermediates. Here we show that, in an E. coli ligase-deficient strain with all known excision repair pathways inactivated, new DNA is still synthesized discontinuously. Furthermore, hybridization to strand-specific targets demonstrates that the low molecular weight replication intermediates come from both the lagging and the leading strands. These results support the model of discontinuous leading strand synthesis in E. coli. PMID:23876705

  13. The Effect of Molecular Weight on the Composite Properties of Cured Phenylethynyl Terminated Imide Oligomers

    NASA Technical Reports Server (NTRS)

    Smith, J. G., Jr.; Connell, J. W.; Hergenrother, P. M.

    1997-01-01

    As part of a program to develop high temperature/high performance structural resins for aeronautical applications, imide oligomers containing terminal phenylethynyl groups with calculated number average molecular weights of 1250, 2500 and 5000 g/mol were prepared, characterized, and evaluated as adhesives and composite matrix resins. The goal of this work was to develop resin systems that are processable using conventional processing equipment into void free composites that exhibit high mechanical properties with long term high temperature durability, and are not affected by exposure to common aircraft fluids. The imide oligomers containing terminal phenylethynyl groups were fabricated into titanium adhesive specimens and IM-7 carbon fiber laminates under 0.1 - 1.4 MPa for 1 hr at 350-371 C. The lower molecular weight oligomers exhibited higher cured Tg, better processability, and better retention of mechanical properties at elevated temperature without significantly sacrificing toughness or damage tolerance than the higher molecular weight oligomer. The neat resin, adhesive and composite properties of the cured polymers will be presented.

  14. Purification of two high molecular weight toxins of Clostridium difficile which are antigenically related.

    PubMed

    von Eichel-Streiber, C; Harperath, U; Bosse, D; Hadding, U

    1987-05-01

    Two Cl. difficile toxins were isolated from cultures of Cl. difficile strain VPI 10463. A purification procedure to prepare homogenous Cl. difficile toxins is given. This procedure allows purification of high molecular weight toxins A and B without using immunaffinity chromatography. The main step of the purification is the separation of a partially purified toxin preparation over a FPLC-Mono Q column by anion exchange chromatography. The experimental conditions for a rechromatography were determined to prepare the two major toxic activities as homogenous high molecular weight proteins. Our toxin A has a molecular weight (Mr) of ca. 300 kDa and an IP of 4.7. The Mr of our toxin B is ca. 250 kDa, the isoelectric focusing gives rise to two bands one at 4.7 and the other at 4.8. The two bands represent charge isomers as have been described for other bacterial toxins. Both toxins differ in cytotoxicity testing by a factor of 1000 but have the same activity when tested in vivo. Toxin specific monoclonal antibodies (mabs) were elicited by separate immunization of mice either with toxin A or toxin B, respectively. All of our mabs cross react with pure toxin A and toxin B when tested by ELISA or Western Blotting. Some mabs strongly cross react indicating that both toxins have major epitopes in common. A hypothesis for the structural and possible functional relatedness between the two toxins is discussed. PMID:2467163

  15. High molecular weight adiponectin correlates positively with myeloperoxidase in patients with type 2 diabetes mellitus.

    PubMed

    Bobbert, P; Rauch, U; Stratmann, B; Goldin-Lang, P; Antoniak, S; Bobbert, T; Schultheiss, H P; Tschoepe, D

    2008-11-01

    Adiponectin (APN) is present in human plasma as a low molecular weight (LMW), a middle molecular weight (MMW) and a high molecular weight form (HMW). As a support to determine properties such as anti-atherogenic or atherogenic effects, recent clinical studies suppose to determine the ratio of each APN multimer to total APN but not the absolute plasma concentration of APN. In the present study, the correlation of APN and its multimers with myeloperoxidase (MPO), an enzyme with pro-inflammatory properties, was examined in patients with type 2 diabetes mellitus. MPO and APN serum levels were assessed in 49 patients with type 2 diabetes mellitus at the beginning and at the end of an anti-diabetic treatment. After treatment a significant increase in the ratio of HMW to total APN (from 0.43+/-0.16 to 0.59+/-0.14, p<0.05) was found. Before treatment, HMW-APN was correlated positively with MPO (r=0.314, p<0.05). Moreover, a positive correlation was observed between the increased HMW ratio and MPO during treatment (r=0.304, p<0.05). HMW-APN correlates positively with MPO in patients with type 2 diabetes. Therefore, HMW-APN may exert possible pro-inflammatory effects in type 2 diabetes. PMID:18778866

  16. Influence of Polymer Molecular Weight, Temperature, and Strain Rate on the Mechanical Properties of PBX 9501

    NASA Astrophysics Data System (ADS)

    Idar, D. J.; Thompson, D. G.; Gray, G. T., III; Blumenthal, W. R.; Cady, C. M.; Peterson, P. D.; Roemer, E. L.; Wright, W. J.; Jacquez, B. J.

    2002-07-01

    Compression and tensile measurements were conducted on newly formulated (baseline) and lower molecular weight (virtually-aged) plastic-bonded explosive PBX 9501. The PBX 9501 binder system is composed of nitroplasticized Estane 5703,trademark a polyester polyurethane copolymer. The molecular weight of polyester urethanes can degrade with time as a function of hydrolysis, affecting the mechanical behavior of the polymer or a polymer composite material of high explosives, i.e. PBXs. The molecular weight of Estane 5703trademark was degraded by exposure to high temperature and humidity for different periods of time, and then formulated to produce "virtually-aged" PBX 9501 specimens. Quasi-static and dynamic compression tests were conducted on the baseline and virtually-aged PBX 9501 as a function of temperature and strain rate. Quasi-static tensile tests were also conducted as a function of temperature and test rate. Rate and temperature dependence was exhibited during both compression and tensile loading. Results also show significant differences between the baseline and virtually-aged specimens for the dynamic compression tests at -15degC, and for the quasi-static compression tests at -15degC, 22degC, and 50degC.

  17. Accurate description of phase diagram of clathrate hydrates at the molecular level.

    PubMed

    Belosudov, Rodion V; Subbotin, Oleg S; Mizuseki, Hiroshi; Kawazoe, Yoshiyuki; Belosludov, Vladimir R

    2009-12-28

    In order to accurately estimate the thermodynamic properties of hydrogen clathrate hydrates, we developed a method based on the solid solution theory of van der Waals and Platteeuw. This model allows one to take into account the influence of guest molecules on the host lattice and guest-guest interactions--especially when more than one guest molecule occupies a cage. The free energies, equations of state, and chemical potentials of hydrogen and mixed propane-hydrogen clathrate hydrates of cubic structure II with different cage fillings have been estimated using this approach. Moreover, the proposed theory has been used for construction p-T phase diagrams of hydrogen hydrate and mixed hydrogen-propane hydrates in a wide range of pressures and temperatures. For the systems with well defined interactions the calculated curves of "guest gas-hydrate-ice I(h)" equilibrium agree with the available experimental data. We also believe that the present model allows one not only to calculate the hydrogen storage ability of known hydrogen hydrate but also predict this value for structures that have not yet been realized by experiment. PMID:20059082

  18. Hypoglycemic effect of polysaccharides with different molecular weight of Pseudostellaria heterophylla

    PubMed Central

    2013-01-01

    Abstracts Background The aims of this study were to evaluate the antidiabetic activity and to detect molecular size of Pseudostellaria heterophylla polysaccharide (PHP). Pseudostellaria heterophylla is a medicine extensively used in traditional Chinese medicine formulas to treat diabetes and its complications. Methods Molecular weight of PHP was determined by gel permeation chromatography combined with phenol-sulphuric acid method and the monosaccharides composition was determined by HPLC with a precolumn derivatization. Four polysaccharides with different molecular weight were compared for hypoglycemic active on two animal models both high does alloxan induced type1 diabetic mellitus (T1DM) and high-fat/lower does streptozotocin induced type2 diabetic mellitus (T2DM). Blood sugar, glucose tolerance, and insulin tolerance were detected. Rat serum IL-1?, IL-2, IL-10, Leptin, TNF-?, Acrp30 and CRP were also analyzed by sandwich-ELISA approaches to preliminary probe the hypoglycemic mechanism of PHP. Results The hypoglycemic effects related to molecular size of polysaccharide were more effective against T2DM than T1DM. PHP comprise four monosaccharides of galacturonic acid, glucose, galactose and arabinos. T2DM rats daily receiving oral dose of polysaccharide(100?~?400 mg/kg) with 50?~?210 kDa molecular weight (PF40) could not only significantly lower blood sugar but also reduce total triglyceride level in serum. PF40 improves in insulin tolerance inhibited the expression of some biomarkers including inflammatory cytokine TNF-? and elevated anti-inflammatory cytokine IL-10, regulated adiponectin Acrp30 and leptin. Conclusions PF40 prevent the cascade of inflammatory events in the treatment of T2DM to block overweight progresses to obesity. PMID:24131482

  19. Molecular Characterization and Diagnostic Value of Taenia solium Low-Molecular-Weight Antigen Genes

    Microsoft Academic Search

    YASUHITO SAKO; MINORU NAKAO; TAKASHI IKEJIMA; XIAN ZHI PIAO; KAZUHIRO NAKAYA; AKIRA ITO

    2000-01-01

    Neurocysticercosis (NCC) caused by infection with the larvae of Taenia solium is an important cause of neurological disease worldwide. In order to establish an enzyme-linked immunosorbent assay (ELISA) for this infection using recombinant proteins, we carried out molecular cloning and identified four candidates as diagnostic antigens (designated Ag1, Ag1V1, Ag2, and Ag2V1). Except for Ag2V1, these clones could encode a

  20. Controlled Release of High Molecular Weight Hyaluronic Acid from Molecularly Imprinted Hydrogel Contact Lenses

    Microsoft Academic Search

    Maryam Ali; Mark E. Byrne

    2009-01-01

    Purpose  Current dry eye treatment includes delivering comfort agents to the eye via drops, but low bioavailability and multiple administration\\u000a continues to be a barrier to effective treatment. There exists a significant unmet need for devices to treat dry eye and for\\u000a more comfortable contact lenses.\\u000a \\u000a \\u000a \\u000a Methods  Using molecular imprinting strategies with an analysis of biology, we have rationally designed and synthesized

  1. The Effects of Low Molecular Weight Dicarboxylic Acids on Cloud Formation Anthony J. Prenni,* Paul J. DeMott, Sonia M. Kreidenweis, and D. Eli Sherman

    E-print Network

    Russell, Lynn

    The Effects of Low Molecular Weight Dicarboxylic Acids on Cloud Formation Anthony J. Prenni,* Paul prevalent dicarboxylic acid, followed by malonic and succinic acids. Low molecular weight dicarboxylic acids

  2. pH response and molecular recognition in a low molecular weight peptide hydrogel.

    PubMed

    Lange, Stefanie C; Unsleber, Jan; Drücker, Patrick; Galla, Hans-Joachim; Waller, Mark P; Ravoo, Bart Jan

    2015-01-14

    In this article we report the preparation and characterization of a peptide-based hydrogel, which possesses characteristic rheological properties, is pH responsive and can be functionalized at its thiol function. The tripeptide N-(fluorenyl-9-methoxycarbonyl)-L-Cys(acetamidomethyl)-L-His-L-Cys-OH 1 forms stable supramolecular aggregates in water leading to hydrogels above 1.5 wt%. Rheological analysis of the hydrogel revealed visco-elastic and shear thinning properties of samples containing 1.5 wt% of peptide 1. The hydrogel reversibly responds to pH changes. Below and above pH 6, electrostatic repulsion of the peptide results in a weakening of the three-dimensional gel network. Based on atomic force microscopy, small angle X-ray scattering and molecular dynamics simulations, it is proposed that the peptide assembles into nanostructures that tend to entangle at higher concentrations in water. The development of functional materials based on the peptide assemblies was possible via thiol-ene-click chemistry of the free thiol function at the C-terminal cysteine unit. As a proof of concept, the functionalization with adamantyl units to give 1-Ad was shown by molecular recognition of ?-cyclodextrin vesicles. These vesicles were used as supramolecular cross-linkers of the assemblies of peptide 1 mixed with peptide 1-Ad leading to gel networks at a reduced peptide concentration. PMID:25379633

  3. Repeatability and reproducibility of thermal field-flow fractionation in molecular weight determination of processed natural rubber.

    PubMed

    Kim, Won-Suk; Eum, Chul Hun; Molnár, Attila; Yu, Jong-Sung; Lee, Seungho

    2006-03-01

    The purpose of this study is (1) to determine the repeatability and reproducibility of thermal field-flow fractionation (ThFFF) in measuring the molecular weight of compounded natural rubber, and (2) to examine the correlation between the molecular weights obtained from ThFFF and the rheological data. 8 batches of compounded natural rubber were obtained from a thermo-mechanical mastication process, and were analyzed by ThFFF in a designed testing sequence. ThFFF analysis showed the compounded natural rubbers range in weight-average molecular weight (M(w)) from 143,000 to 360,000. By taking into account both the short term variability (repeatability) as well as the long term variability (reproducibility) of the instrument, ThFFF was shown to be able to distinguish between samples differing by as little as 21,000 in M(w) and 15,600 in number-average molecular weight, M(n) (based on cis-polyisoprene calibration); and thus is a useful tool for the molecular weight analysis of natural rubber-related materials. It was also found that the rheological data (G' and tan delta) measured on both the virgin and the compounded natural rubber correlated well with the molecular weights obtained from ThFFF when normalized. PMID:16496053

  4. Heparin and low-molecular-weight heparin in the treatment of venous thromboembolism.

    PubMed

    Pineo, G F; Hull, R D

    1998-09-01

    Venous thromboembolism (deep vein thrombosis and pulmonary embolism) continues to constitute a major clinical challenge. Effective and safe prophylactic measures against venous thromboembolism are now available for most high risk patients. In spite of this, pulmonary embolism is responsible for approximately 150,000 to 200,000 deaths per year in the United States alone. Over the past 20 years, based on a number of high quality (Level I) clinical trials, patterns of practice with respect to the treatment of venous thromboembolism have changed dramatically. The standard treatment of venous thromboembolism has been the use of unfractionated heparin by continuous intravenous infusion, with laboratory monitoring using the activated partial thromboplastin time (APTT), with warfarin starting on day 1 or 2 and continued for 3 months. Unfractionated heparin has withstood the test of time and has been shown to be safe and effective in preventing recurrent venous thromboembolism and death in numerous clinical trials. The response of individual patients to heparin is highly variable, requiring frequent laboratory monitoring. Heparin has a number of other troublesome side effects including bleeding, heparin-induced thrombocytopenia and osteoporosis. The low-molecular-weight heparins have a number of advantages over unfractionated heparin. In particular, their increased bio-availability and prolonged half-life permit once daily subcutaneous injections and their predictable antithrombotic response based on body weight permits treatment without laboratory monitoring. Low-molecular-weight heparin in therapeutic doses causes less bleeding than unfractionated heparin and evidence is accumulating that the incidence of heparin-induced thrombocytopenia and osteoporosis are decreased as well. In individual clinical trials and meta-analyses, low-molecular-weight heparin treatment results in decreased recurrent thromboembolism, major bleeding and death when compared with unfractionated heparin in the treatment of deep vein thrombosis and pulmonary embolism. These agents have also been shown to be both effective and safe for the out-of-hospital treatment of venous thrombosis. Therefore, in many countries, low-molecular-weight heparin has replaced unfractionated heparin for the treatment of venous thromboembolism. PMID:10331096

  5. Effects of molecular weight and ratio of guluronic acid to mannuronic acid on the antioxidant properties of sodium alginate fractions prepared by radiation-induced degradation

    Microsoft Academic Search

    Murat ?en

    2011-01-01

    In this study, the effects of the molecular weight and ratio of guluronic acid (G) to mannuronic acid (M), G\\/M, of some sodium alginate (NaAlg) fractions on their antioxidative properties were investigated. Low-molecular-weight-fractions with various G\\/M were prepared by gamma radiation-induced degradation of NaAlg. Change in their molecular weight was monitored. Antioxidant properties of the fractions with various molecular weight

  6. Low-molecular-weight heparin for the treatment of venous thromboembolism in the elderly.

    PubMed

    Pineo, Graham F; Hull, Russell D

    2005-01-01

    Venous thromboembolism (deep vein thrombosis and/or pulmonary embolism) is a common problem in the elderly population. Indeed, increasing age is a significant risk factor for venous thromboembolism. The treatment of venous thromboembolism in the elderly population presents certain unique problems related to aging, such as decreasing body weight, increasing renal insufficiency and numerous comorbid conditions, which complicate therapy. Treatment of venous thromboembolism in the elderly has been complicated by an increased incidence of bleeding, particularly with the use of warfarin. The risk of bleeding may be substantially reduced by carefully adjusting the warfarin dose to maintain a therapeutic INR and for this purpose anticoagulant management clinics have been shown to be useful. The low-molecular-weight heparins have been shown to be efficacious and safe for the treatment of venous thromboembolism in several clinical trials, including many patients in the older age brackets. Furthermore, these agents can safely be used in the out-of-hospital setting. Long-term use of low-molecular-weight heparin is an alternative to the use of oral anticoagulant therapy, particularly in patients with cancer or recurrent venous thromboembolism. PMID:15678269

  7. Effect of gamma irradiation on the friction and wear of ultrahigh molecular weight polyethylene

    NASA Technical Reports Server (NTRS)

    Jones, W. R.; Hady, W. F.; Crugnola, A.

    1981-01-01

    The effect of sterilization gamma irradiation on the friction and wear properties of ultrahigh molecular weight polyethylene (UHMWPE) sliding against stainless steel 316L in dry air at 23 C is investigated, the results to be used in the development of artificial joints which are to surgically replace diseased human joints. A pin-on-disk sliding friction apparatus is used, a constant sliding speed in the range 0.061-0.27 m/s is maintained, a normal load of 1 kgf is applied with dead weight, and the irradiation dose levels are: 0, 2.5, and 5.0 Mrad. Wear and friction data and conditions for each of the ten tests are summarized, and include: (1) wear volume as a function of the sliding distance for the irradiation levels, (2) incremental wear rate, and (3) coefficient of friction as a function of the sliding distance. It is shown that (1) the friction and wear properties of UHMWPE are not significantly changed by the irradiation doses of 2.5 and 5.0 Mrad, (2) the irradiation increases the amount of insoluble gel as well as the amount of low molecular weight material, and (3) after run-in the wear rate is either steady or gradually decreases as a function of the sliding distance.

  8. New and rapid procedure for the isolation of ultra-high molecular weight eukaryotic DNA

    SciTech Connect

    Longmire, J.L.; Lewis, A.; Meincke, L.J.; Hildebrand, C.E.

    1986-05-01

    The authors have developed a novel procedure that permits the rapid extraction and isolation of ultra-high molecular weight DNA from avian or mammalian cells using dialysis against a solution of polyethylene glycol (PEG). Cells harvested by centrifugation and washed twice in ice-cold Ca/sup + +/- and Mg/sup + +/-free phosphate buffered saline were resuspended in 5 ml 0.01 M Tris-Cl (pH 8.0); 0.001 M EDTA (TE); sodium dodecyl sulfate and proteinase K were added to final concentrations of 0.1% and 0.1 mg/ml, respectively. After incubation at 37/sup 0/C overnight, the viscous solution was transferred to a mini-collodian bag and concentrated by dialysis against 4-5 changes of 20% PEG in TE over a period of 5 hours at RT. Concentrated samples were desalted by dialysis against fresh TE for two 15 minute intervals. DNA obtained using this procedure gives A/sub 260//A/sub 280/ consistently >1.8. Analysis of DNA size using pulsed field gel electrophoresis revealed a distribution of fragments >500 Kb in length. Further measurements examined were (1) restriction enzyme digestibility, (2) ligation efficiency of restricted DNA, and (3) cloning efficiency using the lambda vector Ch21A. This novel methodology offers a valuable alternative protocol for rapid purification of ultrahigh molecular weight DNA for various applications in molecular biology.

  9. the role of molecular weight and polydispersity of the PNI-PAAM on the pore size due to LCST of polymer.

    E-print Network

    Cao, Guozhong

    the role of molecular weight and polydispersity of the PNI- PAAM on the pore size due to LCST±silica membranes with various molecular weights of PEG have demonstrated that PNIPAAM molecules dispersed in the hy alcohol (Aaper), crystal violet (Fischer Scientific), PEG of polymer standard grade with molecular weights

  10. Gamma Irradiation Effects on Molecular Weight and in Vitro Degradation of Poly(D,L-Lactide- CO -Glycolide) Microparticles

    Microsoft Academic Search

    Angela G. Hausberger; Richard A. Kenley; Patrick P. DeLuca

    1995-01-01

    Purpose. The objective of the reported work was to quantitatively establish ?-irradiation dose effects on initial molecular weight distributions and in vitro degradation rates of a candidate credible biopolymeric delivery system.

  11. Enzymatic polymerization of high molecular weight DNA amphiphiles that self-assemble into star-like micelles.

    PubMed

    Tang, Lei; Tjong, Vinalia; Li, Nan; Yingling, Yaroslava G; Chilkoti, Ashutosh; Zauscher, Stefan

    2014-05-21

    High molecular weight ssDNA amphiphiles are synthesized by enzymatic polymerization. These highly asymmetric diblock DNA copolymers self-assemble into "hairy", star-like micelles, shown in the AFM image and the DPD snapshot. PMID:24497034

  12. Accurate static and dynamic properties of liquid electrolytes for Li-ion batteries from ab initio molecular dynamics

    SciTech Connect

    Ganesh, P.; Jiang, D.; Kent, P.R.C.

    2011-01-01

    Lithium-ion batteries have the potential to revolutionize the transportation industry, as they did for wireless communication. A judicious choice of the liquid electrolytes used in these systems is required to achieve a good balance among high-energy storage, long cycle life and stability, and fast charging. Ethylene-carbonate (EC) and propylene-carbonate (PC) are popular electrolytes. However, to date, almost all molecular-dynamics simulations of these fluids rely on classical force fields, while a complete description of the functionality of Li-ion batteries will eventually require quantum mechanics. We perform accurate ab initio molecular-dynamics simulations of ethylene- and propylene-carbonate with LiPF6 at experimental concentrations to build solvation models which explain available neutron scattering and nuclear magnetic resonance (NMR) results and to compute Li-ion solvation energies and diffusion constants. Our results suggest some similarities between the two liquids as well as some important differences. Simulations also provide useful insights into formation of solid-electrolyte interphases in the presence of electrodes in conventional Li-ion batteries.

  13. Effects of branching and molecular weight of surface-bound poly(ethylene oxide) on protein rejection

    Microsoft Academic Search

    Karin Beroström; Eva Österberg; Krister Holmberg; Allan S. Hoffman; Thomas P. Schuman; Antoni Kozlowski; J. Milton Harris

    1995-01-01

    To understand better the origin of protein rejection observed with surface-bound poly(ethylene oxide) (or PEO), we have measured fibrinogen adsorption for a series of linear and branched, low-molecular-weight PEOs bound to solid polystyrene surfaces. The results show that a dependence on molecular weight is found below 1500 g mol for linear PEO. Branched PEOs are less effective at protein rejection

  14. Study of the inclusion compounds formed between ?-cyclodextrin and high molecular weight poly(ethylene oxide) and poly(?-caprolactone)

    Microsoft Academic Search

    Lei Huang; Emily Allen; Alan E. Tonelli

    1998-01-01

    We report the formation of high molecular weight polymer inclusion compounds (ICs) between ?-cyclodextrin and poly(ethylene oxide) (PEO) (Mn = 100 kg mol?1), and poly(?-caprolactone) (PCL) (Mn = 40 kg mol?1). Both high molecular weight polymer ICs were successfully made by ultrasonic and heating techniques. Dsc, tga, X-ray diffraction, FT i.r. and solid state 13C n.m.r. were utilized to observe

  15. Improved section adhesion for immunocytochemistry using high molecular weight polymers of l-lysine as a slide coating

    Microsoft Academic Search

    W. M. Huang; S. J. Gibson; P. Facer; J. Gu; J. M. Polak

    1983-01-01

    Poly-l-lysine (PPL) has been used to coat glass slides in the preparation of tissue sections for immunocytochemical staining. The adhesive properties of different molecular weight (m.w.) polymers of l-lysine have been tested on pre-fixed cryostat sections which were subjected to a 3 day washing treatment. It has been found that the higher the molecular weight of the polymer, the greater

  16. Molecular weight distribution and structural characteristics of polymers obtained from acid soluble lignin treated by oxidative enzymes

    Microsoft Academic Search

    Anderson Guerra; André Ferraz

    2001-01-01

    Brown precipitates were obtained by polymerization of low molecular weight lignin fragments contained in a model effluent. Polymerization reactions were initiated by potato-polyphenoloxidase (PPO) or horseradish peroxidase\\/H2O2 system (HRP\\/H2O2). The insolubilization processes occurred after a molecular weight increase of the lignin, as shown by gel permeation chromatography (GPC). The effect of reaction time, pH and amount of soluble lignin per

  17. Neutrophil-Activating Protein Mediates Adhesion of Helicobacter pylori to Sulfated Carbohydrates on High-Molecular-Weight Salivary Mucin

    Microsoft Academic Search

    FERRY NAMAVAR; MARION SPARRIUS; ENNO C. I. VEERMAN; BEN J. APPELMELK

    1998-01-01

    The in vitro binding of surface-exposed material and outer membrane proteins of Helicobacter pylori to high-molecular-weight salivary mucin was studied. We identified a 16-kDa surface protein which adhered to high-molecular-weight salivary mucin. This protein binds specifically to sulfated oligosaccharide structures such as sulfo-Lewis a, sulfogalactose and sulfo-N-acetyl-glucosamine on mucin. Sequence analysis of the pro- tein proved that it was identical

  18. Effect of reaction temperature and reaction time on the preparation of low-molecular-weight chitosan using phosphoric acid

    Microsoft Academic Search

    Zhishen Jia; Dongfeng Shen

    2002-01-01

    Low-molecular-weight chitosan were prepared using 85% phosphoric acid at different reaction temperatures and reaction time. At room temperature, the viscosity average-molecular weights (Mv) of chitosan decreased to 7.1×104 from 21.4×104 after 35 days treatment. The degradation rate decreased with increasing hydrolysis time. The yields of chitosan also continuously decreased from 68.4 to 40.2% after 35 days. At 40, 60 and

  19. Evidence favoring the existence of two high molecular weight precursor forms of dog kidney renin.

    PubMed

    Potter, D M; Dunn, P M; McDonald, W J

    1979-08-01

    Extraction of canine renal cortical tissue at pH 7.4 in the presence of the protease inhibitors diisopropylfluorophosphate (0.2 mM), Na2EDTA (7.8 mM), sodium tetrathionate (7.8 mM). N-ethyl maleimide (7.8 mM) yielded renin activity in two high molecular weight (HMW) forms, 65,000 (65K) and 55,000 (55K). Serial gel filtration chromatography of such extracts stored at 4 C showed that over the course of 2 days, activity at both 65,000 and 55,000 decreased almost entirely, while low molecular weight (LMW) activity at 41,000 (41K), not present immediately after extraction, had appeared in the extracts, The renin activity of the extract doubled over the first 24 h of storage and remained stable over the next 24 h. The activity of all three renin forms was comparably inhibited by antirenin antibodies. Our results support the concept that HMW renin(s) is a biological precursor of 41K renin. The new finding of a renin form intermediate in apparent molecular weight between 65K and 41K renin suggests that proteolytic processing of HMW to LMW renin may involve more than one step. The fact that in vitro conversion of HMW to LMW renin will occur under these conditions but takes place slowly may provide a technique for the future study of the precise manner in which HMW is converted to LMW renin. PMID:456314

  20. Manifestation of sub-Rouse modes in flow at the surface of low molecular weight polystyrene

    E-print Network

    K. L. Ngai; S. Capaccioli; Daniele Prevosto; Luigi Grassia

    2014-10-17

    The presence of a viscoelastic mechanism distinctly different from the segmental a-relaxation and the Rouse modes within the glass-rubber transition zone of polymers had been justified by theoretical considerations, and subsequently experimentally verified in different bulk polymers by various techniques, and in several laboratories. Referred to in the literature as the sub-Rouse modes, they were also found in polymer thin films by the creep compliance measurements of McKenna and co-workers Established by experiment and theoretical considerations is the enhanced mobility of sub-Rouse modes in thin PS films by the combination of effect from the free surface, finite size, and induced chain orientations, concomitant with the segmental a-relaxation. Induced chain orientations effect is present only when h is less than the end-to-end distance of the high molecular weight polymer chains. In this paper, the proven enhanced mobility of sub-Rouse modes at the surface of polymers is used to explain recent experimental investigations of viscous flow at the surface of low molecular weight PS by Chai et al. [Science, 343, 994 (2014)], and by Yang et al. [Science, 328, 1676 (2010).]. Viscous flow of polymers is by global chain motion, therefore the observed large reduction of viscosity at the surface of low molecular weight PS originates from the sub-Rouse modes, and not the segmental a-relaxation. This distinction is not commonly recognized in the current literature. The accerleration of the sub-Rouse modes at the surface explains the experimental findings.

  1. An investigation of the preparation of high molecular weight perfluorocarbon polyethers

    NASA Technical Reports Server (NTRS)

    Watts, R. O.; Tarrant, P.

    1972-01-01

    High molecular weight perfluorocarbon polyether gums were obtained by photolysis of perfluorodienes and discyl fluorides containing a perfluorocarbon polyether backbond. The materials obtained are represented by chemical formulas. A method was developed whereby reactive acyl fluoride and trifluorovinyl end groups are converted into inert structures. In order to investigate the possible preparation of difunctional molecules which may be useful in polymer synthesis, the reactions of hexafluoropropene oxide (HFPO) with Grignard and organolithium reagents have been studied. Reactions of various nucleophilic reagents with HFPO were also investigated.

  2. Metal-UHWMPE (Ultra High Molecular Weight Polyethylene) wear: experimental testing.

    PubMed

    Affatato, S; Terzi, S; Nardi, D; Toni, A; Cianci, R

    1997-01-01

    Testing conducted on a hip joint simulator verified the Charnley hypothesis that the diameter of the prosthetic head is proportional to wear. The study was conducted by pairing heads in Ortinox TM with acetabular cups in polyethylene at high molecular weight (UHMWPE). A comparison between the different sizes of the heads (26 and 30 mm in diameter) showed a different trend in the wear rate; in particular, the head with a smaller diameter behaves better tribologically than the head with a larger diameter. PMID:9618977

  3. Radiation cross-linking in ultra-high molecular weight polyethylene for orthopaedic applications

    PubMed Central

    Oral, Ebru; Muratoglu, Orhun K.

    2007-01-01

    The motivation for radiation cross-linking of ultra-high molecular weight polyethylene (UHMWPE) is to increase its wear resistance to be used as bearing surfaces for total joint arthroplasty. However, radiation also leaves behind long-lived residual free radicals in this polymer, the reactions of which can detrimentally affect mechanical properties. In this review, we focus on the radiation cross-linking and oxidative stability of first and second generation highly cross-linked UHMWPEs developed in our laboratory. PMID:19050735

  4. Birefringence measurement of liquid single crystal elastomer swollen with low molecular weight liquid crystal

    NASA Astrophysics Data System (ADS)

    Yusuf, Yusril; Sumisaki, Yusuke; Kai, Shoichi

    2003-11-01

    We experimentally measured the birefringence of a liquid single crystal elastomer (LSCE) swollen with a low molecular weight liquid crystal (LMWLC), 5CB, by polarizing microscopy as a function of temperature. The optical intensity of swollen LSCE shows significant intensity changes at temperatures TNI, TA and TB that indicates a variety of different transitions. A temperature TNI is known as the apparent nematic-isotropic transition for outside LMWLC, TA and TB are interpreted as the nematic-isotropic transition for LMWLC inside the LSCE and for the swollen LSCE, respectively.

  5. Hystereses of volume changes in liquid single crystal elastomers swollen with low molecular weight liquid crystal

    NASA Astrophysics Data System (ADS)

    Yusuf, Yusril; Cladis, P. E.; Brand, Helmut R.; Finkelmann, Heino; Kai, Shoichi

    2004-05-01

    The hystereses of volume changes in liquid single crystal elastomers (LSCEs) swollen with a low molecular weight liquid crystal (LMWLC), 5CB, are studied as a function of temperature. The swollen LSCE shows significant hystereses in the volume changes at temperatures TNI and TA during the processes on heating and on cooling, where the temperature TNI is the apparent nematic-isotropic transition for outside LMWLC and TA the nematic-isotropic transition for LMWLC inside the LSCE. No significant hysteresis at TB however can be observed which is the nematic-isotropic phase transition temperature for equilibrium shape of the swollen LSCE (networks).

  6. Effect of molecular weights of polyethyleneimine on the polyplex formation with calf thymus DNA

    Microsoft Academic Search

    Jungho Han; Seog K. Kim; Tae-Sub Cho; Jae-Cheol Lee

    2004-01-01

    In this study we investigated the spectral properties, including electric absorption, circular and linear dichroism (CD and\\u000a LD), and fluorescence emission, of DNA in a DNA-branched polyethyleneimine (BPEI) polyplex at various polymer molecular weights\\u000a (M\\u000a \\u000a w\\u000a ) and BPEI-amine-to-DNA-phosphate ratios (N\\/P ratios). All BPEIs exhibited a common N\\/P dependence in their absorption and\\u000a CD spectra. At N\\/P ratios < 1.0,

  7. On the origins of the androgen receptor low molecular weight species

    PubMed Central

    Mudryj, Maria; Tepper, Clifford G.

    2015-01-01

    Prostate cancer (CaP), a commonly diagnosed malignancy, is readily treated by androgen ablation. This treatment temporarily halts the disease, but castrate resistant neoplasms that are refractory to current therapies emerge. There are multiple mechanisms by which CaP cells circumvent androgen ablation therapies, but this review focuses on the emergence of low molecular weight androgen receptor species that are missing the ligand binding domain and function independently of ligand to drive proliferation. The etiology, biological activity, unique feature, predictive value and therapeutic implication of these androgen receptor isoforms are discussed in depth. PMID:23860689

  8. A low molecular weight cut-off polymer–silicate membrane for microfluidic applications

    Microsoft Academic Search

    Gwendoline M. Toh; Naoki Yanagisawa; Robert C. Corcoran; Debashis Dutta

    2010-01-01

    In this article, we report a novel approach to fabricating a low molecular weight cut-off membrane that could readily be employed\\u000a for several microfluidic applications. The reported structure was created by selectively retaining a precursor solution [5%\\u000a (w\\/v) maleic anhydride, 21% (v\\/v) (37:1) acrylamide\\/bisacrylamide, and 0.2% (w\\/v) VA-086 photoinitiator] in a chosen location\\u000a of a microfluidic network via capillary forces

  9. Size-exclusion chromatography study of the molecular-weight distribution of gamma-irradiated pullulan.

    PubMed

    Shingel, K I; Tsarenkov, V M; Petrov, P T

    2000-03-10

    The polyelectrolyte behavior of gamma-irradiated pullulan in aqueous solutions leads to secondary effects of adsorption on a Shodex OHPak KB 806 column gel during size-exclusion chromatography. Suppression of the polyelectrolyte properties of gamma-irradiated pullulan is achieved by using a 0.05 M aqueous solution of NaH2PO4 (pH 4.95) as the mobile phase. Under these conditions, adequate molecular-weight distributions of gamma-irradiated pullulan samples are obtained. PMID:10744337

  10. O-acetylation of low-molecular-weight polysaccharide from Enteromorpha linza with antioxidant activity.

    PubMed

    Zhang, Zhongshan; Wang, Xiaomei; Zhao, Mingxing; Qi, Huimin

    2014-08-01

    Polysaccharide extracted from green algae Enteromorpha linza (EP) is a sulfated polysaccharide, which possesses excellent antioxidant activities. In present study, the acetylated derivatives of low-molecular-weight polysaccharide (LEP) was prepared with the method of response surface quadratic model. And then the antioxidant activities of the derivatives were investigated including scavenging effects of superoxide and hydroxyl radicals. The results of chemical analysis and FT-IR spectrum showed the acetylation was successful. And in addition, certain derivative with different degree of substitution (DS) exhibited different antioxidant activity. PMID:24854210

  11. High molecular weight lipids from the trilaminar outer wall (TLS)-containing microalgae Chlorella emersonii, Scenedesmus conmmunis and Tetraedron minimum.

    PubMed

    Allard, B; Templier, J

    2001-06-01

    High molecular weight lipids were isolated from Chlorella emersonii, Scenedesmus communis and Tetraedron minimum, thin trilaminar outer wall (TLS)-containing freshwater microalgae producing an insoluble non-hydrolysable biopolymer (i.e. algaenan). Molecular weight determination by gel permeation chromatography indicated that their molecular weights range from ca. 400 to 2000 Da. Flash pyrolysis with in situ methylation using tetramethylammonium hydroxide (TMAH) and alkaline hydrolysis showed that the high molecular weight lipids isolated from C. emersonii and S. communis are mainly composed of saturated n-C26 and n-C28 fatty acids and alcohols and of saturated n-C30 and n-C32 alpha,omega-diols and omega-hydroxy acids. In contrast the high molecular weight lipids isolated from T. minimum are predominantly composed of long-chain fatty acids and omega-hydroxy acids. Aromatic moieties were also identified in small amounts in the thermochemolysate and in the hydrolysate. Chemical structural models containing long-chain mono- and polyesters were proposed for the high molecular weight lipids isolated from the three microalgae in agreement with analytical and spectroscopic data. Structural similarity between the outer cell wall of these microalgae and the cuticular membrane of higher plants is suggested. PMID:11393527

  12. Bio-Based Bisfuran: Synthesis, Crystal Structure and Low Molecular Weight Amorphous Polyester.

    PubMed

    Gaitonde, Vishwanath; Lee, Kyunghee; Kirschbaum, Kristin; Sucheck, Steven J

    2014-07-23

    Discovery of renewable monomer feedstocks for fabrication of polymeric demand is critical in achieving sustainable materials. In the present work we have synthesized bisfuran diol (BFD) monomer from furfural, over four steps. BFD was examined via X-ray crystallography to understand the molecular arrangement in space, hydrogen bonding and packing of the molecules. This data was further used to compare BFD with structurally related Bisphenol A (BPA), and its known derivatives to predict the potential estrogenic or anti-estrogenic activities in BFD. Further, BFD was reacted with succinic acid to generate polyester material, bisfuran polyester (BFPE-1). MALDI characterization of BFPE-1 indicates low molecular weight polyester and thermal analysis reveals amorphous nature of the material. PMID:25045189

  13. 'All-supramolecular' nanocapsules from low-molecular weight ureas through interfacial addition reaction in miniemulsion.

    PubMed

    Groison, Emilie; Adjili, Salim; Ferrand, Alice; Lortie, Frédéric; Portinha, Daniel; Sintes-Zydowicz, Nathalie

    2011-03-16

    This contribution presents a new strategy for preparing nanocapsules with a shell made of a supramolecular polymer which repeating units are held together by reversible interactions rather than covalent bonds. These nanocapsules were prepared in classical miniemulsion through interfacial addition reaction of a diisocyanate (IPDI) and a monoamine (iBA), forming low-molecular weight bis-ureas moieties which are strong self-complementary interacting molecules through hydrogen-bonding. The nanocapsules present a diameter around 100 nm, and MALDI-TOF MS and (1)H NMR analyses confirm the expected molecular characteristics for the shell. This strategy opens the scope of a new type of nanomaterials exhibiting stimuli-responsiveness due to the reversible interaction linking the repeating units. PMID:21433204

  14. Dragline silk: a fiber assembled with low-molecular-weight cysteine-rich proteins.

    PubMed

    Pham, Thanh; Chuang, Tyler; Lin, Albert; Joo, Hyun; Tsai, Jerry; Crawford, Taylor; Zhao, Liang; Williams, Caroline; Hsia, Yang; Vierra, Craig

    2014-11-10

    Dragline silk has been proposed to contain two main protein constituents, MaSp1 and MaSp2. However, the mechanical properties of synthetic spider silks spun from recombinant MaSp1 and MaSp2 proteins have yet to approach natural fibers, implying the natural spinning dope is missing critical factors. Here we report the discovery of novel molecular constituents within the spinning dope that are extruded into dragline silk. Protein studies of the liquid spinning dope from the major ampullate gland, coupled with the analysis of dragline silk fibers using mass spectrometry, demonstrate the presence of a new family of low-molecular-weight cysteine-rich proteins (CRPs) that colocalize with the MA fibroins. Expression of the CRP family members is linked to dragline silk production, specifically MaSp1 and MaSp2 mRNA synthesis. Biochemical data support that CRP molecules are secreted into the spinning dope and assembled into macromolecular complexes via disulfide bond linkages. Sequence analysis supports that CRP molecules share similarities to members that belong to the cystine slipknot superfamily, suggesting that these factors may have evolved to increase fiber toughness by serving as molecular hubs that dissipate large amounts of energy under stress. Collectively, our findings provide molecular details about the components of dragline silk, providing new insight that will advance materials development of synthetic spider silk for industrial applications. PMID:25259849

  15. Removal of low-molecular weight DBPs and inorganic ions for characterization of high-molecular weight DBPs in drinking water.

    PubMed

    Zhang, Xiangru; Minear, Roger A

    2006-03-01

    High-molecular weight (MW) halogenated disinfection byproducts (DBPs) may cause adverse health effects. In this work several issues related to the better separation and characterization of the high MW halogenated DBPs (MW>500Da) were studied. Ultra-filtration (UF) coupled with a nominal 500-Da membrane was employed to flush out low MW DBPs and inorganic ions. Two procedures, intermittent UF and continuous UF, were used and compared. The results demonstrate that haloacetic acids, chloride and sodium ions could be effectively flushed out, and most of phosphate ions could be flushed out for a given dilution number or sufficient Milli-Q water. The size exclusion chromatograms indicate that haloacetic acids and trihalomethanes were not bound to Suwannee River fulvic acid (SRFA); 2,4,6-trichlorophenol might form some binding with SRFA, but it appeared to be very weak and readily broken up when passing along the size exclusion column. The octanol-water partition coefficients of low MW DBPs and the properties of humic substances seem to play key roles in determining the formation of possible bindings between low MW DBPs and humic substances. PMID:16490231

  16. Gas separation properties of carbon molecular sieve membranes derived from polyimide\\/polyvinylpyrrolidone blends: effect of the molecular weight of polyvinylpyrrolidone

    Microsoft Academic Search

    Youn Kook Kim; Ho Bum Park; Young Moo Lee

    2005-01-01

    Carbon molecular sieve (CMS) membranes were prepared using aromatic polyimide (PI) and polyvinylpyrrolidone (PVP) polymer blends. The characteristics of the carbon structures and the gas permeation properties of the CMS membranes pyrolyzed at 500 and 700°C were investigated in terms of the molecular weight of PVP (the thermally labile polymer). The PI\\/PVP blend showed two separate thermal decomposition steps. In

  17. Hyaluronic acid-coated chitosan nanoparticles: molecular weight-dependent effects on morphology and hyaluronic acid presentation.

    PubMed

    Almalik, Abdulaziz; Donno, Roberto; Cadman, Christopher J; Cellesi, Francesco; Day, Philip J; Tirelli, Nicola

    2013-12-28

    Chitosan nanoparticles are popular carriers for the delivery of macromolecular payloads, e.g. nucleic acids. In this study, nanoparticles were prepared via complexation with triphosphate (TPP) anions and were successively coated with hyaluronic acid (HA). Key variables of the preparative process (e.g. chitosan and HA molecular weight) were optimised in view of the maximisation of loading with DNA, of the Zeta potential and of the dimensional stability, and the resulting particles showed excellent storage stability. We have focused on the influence of chitosan molecular weight on nanoparticle properties. Larger molecular weight increased their porosity (=decreased cross-link density), and this caused also larger dimensional changes in response to variations in osmotic pressure or upon drying. The dependency of nanoparticle porosity on chitosan molecular weight had a profound effect on the adsorption of HA on the nanoparticles; HA was apparently able to penetrate deeply into the more porous high molecular weight (684 kDa) chitosan nanoparticles, while it formed a corona around those composed of more densely cross-linked low molecular weight (25 kDa) chitosan. Atomic Force Microscopy (AFM) allowed not only to highlight the presence of this corona, but also to estimate its apparent thickness to about 20-30 nm (in a dry state). The different morphology has a significant effect on the way HA is presented to biomolecules, and this has specific relevance in relation to interactions with HA receptors (e.g. CD44) that influence kinetics and mechanism of nanoparticle uptake. Finally, it is worth to mention that chitosan molecular weight did not appear to greatly affect the efficiency of nanoparticle loading with DNA, but significantly influenced its chitosanase-triggered release, with high molecular chitosan nanoparticles seemingly more prone to degradation by this enzyme. PMID:24103813

  18. Preparation and application of low molecular weight poly(vinyl chloride). III mechanical properties of blended poly(vinyl chloride)

    SciTech Connect

    Yamamoto, Kikuo; Maehala, Takashi; Mitani, Katsuo; Mizutani, Yukio (Tokuyama Soda Co., Ltd., Tokuyama-city (Japan))

    1993-11-05

    The blending effect of poly(vinyl chloride) with relatively higher molecular weight (HMW-PVC) and relatively lower molecular weight (LMW-PVC) has been investigated by measuring various mechanical properties: melt properties, tensile strength, tensile modulus, and impact strength. The blended PVC has slightly improved melt properties in comparison with the HMW-PVC used. The tensile strength of the blended PVC is related to the weight-average polymerization degree (Pw) of LMW-PVC and the LMW-PVC content. At the LMW-PVC content of 20%, the tensile strength of blended PVC is a maximum: approximately 58 MPa.

  19. [Spectroscopic characteristics of different molecular weight dissolved organic matter in water from Yangtze River estuary].

    PubMed

    Huang, Wen-Dan; Zhou, Li-Min; Zheng, Xiang-Min; Huang, Jing; Chen, Shi-Ji

    2013-04-01

    Cross flow ultrafiltration systems and three dimensional fluorescence spectrum were used to investigate the fluorescence characterization of different molecular weight dissolved organic matter in water of wet season and dry season from Yangtze River estuary, in order to find out the sources and influencing factors. The results showed that four types of dissolved organic carbon (DOM) fluorescence peaks were observed in the water: humic-like fluorescence peak A and C, and protein-like fluorescence peak B and D. Fluorescent substances mainly existed in the truly dissolved organic matter (UOM, < 1 kDa), secondly in low and medium molecular weight of colloidal organic matter (1-500 kDa). Protein of DOM in water mainly originated from anthropogenic sources, then from autochthonous sources. Compared to protein, humic acid of DOM in wet season was both terrigenous and autochthonous sources, while in dry season mainly from terrestrial organic matter. In addition, humic acid in UOM was mainly derived from biological decomposition, however, in colloidal organic matter (COM) came from terrestrial organic matter and was affected by resuspension effects. There was linear correlation between fluorescence intensity and environmental parameters. It was revealed that the complex environmental conditions would influence the fluorescent substance of DOM in water from Yangtze River estuary. PMID:23841416

  20. Extraction conditions of Antheraea mylitta sericin with high yields and minimum molecular weight degradation.

    PubMed

    Yun, Haesung; Oh, Hanjin; Kim, Moo Kon; Kwak, Hyo Won; Lee, Jeong Yun; Um, In Chul; Vootla, Shyam Kumar; Lee, Ki Hoon

    2013-01-01

    Although the technique for extracting the Bombyx mori sericin has been extensively known, the extraction of sericin from wild-silkworm cocoons is not yet standardized. The aim of this study was to find the optimal conditions for the extraction of sericin from Antheraea mylitta cocoons, with high yields and minimum degradation. We attempted to apply various protocols for the extraction of the A. mylitta sericin (AmS). Among these, we found that the extraction of AmS with a sodium carbonate solution exhibited the highest yield except the conventional soap-alkali extraction. To find the optimal conditions for the AmS extraction with the sodium carbonate, we changed the concentration of sodium carbonate and the treatment time. With an increase in the sodium carbonate concentration and the extraction time, the yield of AmS increased, but the molecular weight (MW) of AmS decreased. Considering the yield, molecular weight distribution (MWD) and amino acid composition of AmS, we suggest that the optimal conditions for the AmS extraction require treatment with 0.02 M sodium carbonate and boiling for 60 min. PMID:23026092

  1. Low-molecular-weight hydroxyacids in marine atmospheric aerosol: evidence of a marine microbial origin

    NASA Astrophysics Data System (ADS)

    Miyazaki, Y.; Sawano, M.; Kawamura, K.

    2014-04-01

    Lactic acid (LA) and glycolic acid (GA), which are low-molecular-weight hydroxyacids, were identified in the particle and gas phases within the marine atmospheric boundary layer over the western subarctic North Pacific. Major portion of LA (81%) and GA (57%) were present in the particulate phase, which is consistent with the presence of a hydroxyl group in these molecules leading to the low volatility of the compounds. The average concentration of LA in more biologically influenced marine aerosols (average 33 ± 58 ng m-3) was substantially higher than that in less biologically influenced aerosols (average 11 ± 12 ng m-3). Over the oceacnic region of phytoplankton blooms, the concentration of aerosol LA was comparable to that of oxalic acid, which was the most abundant diacid during the study period. A positive correlation was found between the LA concentrations in more biologically influenced aerosols and chlorophyll a in seawater (r2 = 0.56), suggesting an important production of aerosol LA possibly associated with microbial (e.g., lactobacillus) activity in seawater and/or aerosols. Our finding provides a new insight into the poorly quantified microbial sources of marine organic aerosols (OA) because such low-molecular-weight hydroxyacids are key intermediates for OA formation.

  2. Low-molecular-weight hydroxyacids in marine atmospheric aerosol: evidence of a marine microbial origin

    NASA Astrophysics Data System (ADS)

    Miyazaki, Y.; Sawano, M.; Kawamura, K.

    2014-08-01

    Lactic acid (LA) and glycolic acid (GA), which are low-molecular-weight hydroxyacids, were identified in the particle and gas phases within the marine atmospheric boundary layer over the western subarctic North Pacific. A major portion of LA (81%) and GA (57%) was present in the particulate phase, which is consistent with the presence of a hydroxyl group in these molecules leading to the low volatility of the compounds. The average concentration (±SD) of LA in more biologically influenced marine aerosols (33 ± 58 ng m-3) was substantially higher than that in less biologically influenced aerosols (11 ± 12 ng m-3). Over the oceanic region of phytoplankton blooms, the concentration of aerosol LA was comparable to that of oxalic acid, which was the most abundant diacid during the study period. A positive correlation was found between the LA concentrations in more biologically influenced aerosols and chlorophyll a in seawater (r2 = 0.56), suggesting an important production of aerosol LA possibly associated with microbial (e.g., lactobacillus) activity in seawater and/or aerosols. Our finding provides a new insight into the poorly quantified microbial sources of marine organic aerosols (OAs) because such low-molecular-weight hydroxyacids are key intermediates for OA formation.

  3. UV curable lens production using molecular weight controlled PEEK based acrylic oligomer (Ac-PEEK).

    PubMed

    ?nan, Tulay Y; Y?ld?z, Emel; Karaca, Birsen; Dogan, Hacer; Vatansever, Alican; Nalbant, Muhammed; Eken, Koray

    2014-08-01

    We produced UV curable lenses with properties blocking short wave UV light. In the UV-curable formulations, we used an oligomer (Ac-PEEK) with another urethan oligomer (Mw = 2000). Radically active, molecular weight controlled Ac-PEEK was obtained by reacting 2-hydroxyl ethyl methacrylate with molecular- weight- controlled and isocyanate terminated PEEK (Mn = 4500). We characterized all synthesized monomer, oligomer and optical materials with UV/Vis spectrophotometer with interferogram, elemental analyser, mass spectrophotometer, proton nuclear magnetic resonance, Fourier transform infrared spectroscopy, thermal gravimetric analyzer, differential scanning calorimeter, scanning electron microscopy and gas chromatography. Results suggested that newly synthesized oligomer with the structure of PEEK absorbs short wave UV-light. Ageing tests [ISO 11979-5, Ophthalmic implants-intraocular lenses (IOL)-Part 5: Biocompatibility] performed on the IOL materials were successful. High contact angle of the obtained lenses suggests that all lenses were hydrophobic and SEM results revealed that lenses are morphologically homogeneous. Based on all positive properties just mentioned, we safely conclude that the lenses produced in this study are very promising for IOL production. PMID:24796625

  4. Impact of Molecular Weight on Lymphatic Drainage of a Biopolymer-Based Imaging Agent

    PubMed Central

    Bagby, Taryn R.; Cai, Shuang; Duan, Shaofeng; Thati, Sharadvi; Aires, Daniel J.; Forrest, Laird

    2012-01-01

    New lymphatic imaging technologies are needed to better assess immune function and cancer progression and treatment. Lymphatic uptake depends mainly on particle size (10–100 nm) and charge. The size of carriers for imaging and drug delivery can be optimized to maximize lymphatic uptake, localize chemotherapy to lymphatic metastases, and enable visualization of treatment deposition. Toward this end, female BALB/c mice were injected subcutaneously in the hind footpad or forearm with a series of six different molecular weight hyaluronan (HA) near-infrared dye (HA-IR820) conjugates (ca. 5–200 nm). Mice were imaged using whole body fluorescent imaging over two weeks. HA-IR820 fluorescence was clearly visualized in the draining lymphatic capillaries, and in the popliteal and iliac or axillary lymph nodes. The 74-kDa HA-IR820 had the largest lymph node area-under-the-curve. In contrast to prior reports, mice bearing limb tumors exhibited three-fold longer retention of 74-kDa HA-IR820 in the popliteal node compared to mice without tumors. HA conjugate kinetics and disposition can be specifically tailored by altering their molecular weight. The specific lymphatic uptake and increased nodal retention of HA conjugates indicate significant potential for development as a natural biopolymer for intralymphatic drug delivery and imaging. PMID:24300232

  5. Assembly and Characterization ofWell-DefinedHigh-Molecular-Weight Poly(p-phenylene) Polymer Brushes

    SciTech Connect

    Chen, Jihua [ORNL; Dadmun, Mark D [ORNL; Mays, Jimmy [ORNL; Messman, Jamie M [ORNL; Hong, Kunlun [ORNL; Britt, Phillip F [ORNL; Sumpter, Bobby G [ORNL; Alonzo Calderon, Jose E [ORNL; Kilbey, II, S Michael [ORNL; Ankner, John Francis [ORNL; Bredas, Jean-Luc E [ORNL; Malagoli, Massimo [ORNL; Deng, Suxiang [ORNL; Swader, Onome A [ORNL; Yu, Xiang [ORNL

    2011-01-01

    The assembly and characterization of well-de ned, end-tethered poly- (p-phenylene) (PPP) brushes having high molecular weight, low polydispersity and high 1,4-stereoregularity are presented. The PPP brushes are formed using a precursor route that relies on either self-assembly or spin coating of high molecular weight (degrees of poly- merizations 54, 146, and 238) end-functionalized poly(1,3-cyclohexadiene) (PCHD) chains from benzene solutions onto silicon or quartz substrates, followed by aromatization of the end-attached PCHD chains on the surface. The approach allows the thickness (grafting density) of the brushes to be easily varied. The dry brushes before and after aromatization are characterized by ellipsometry, atomic force microscopy, grazing angle attenuated total re ectance Fourier transform infrared spectroscopy, and UV-Vis spectros- copy. The properties of the PPP brushes are compared with those of lms made using oligo- paraphenylenes and with ab initio density functional theory simulations of optical proper- ties. Our results suggest conversion to fully aromatized, end-tetheredPPPpolymerbrusheshaving eective conjugation lengths of 5 phenyl units.

  6. Assembly and Characterization of Well Defined High Molecular Weight Poly(p-phenylene) Polymer Brushes

    SciTech Connect

    Alonzo Calderon, Jose E [ORNL; Kilbey, II, S Michael [ORNL; Ankner, John Francis [ORNL; Britt, Phillip F [ORNL; Chen, Jihua [ORNL; Dadmun, Mark D [ORNL; Deng, Suxiang [ORNL; Hong, Kunlun [ORNL; Mays, Jimmy [ORNL; Messman, Jamie M [ORNL; Sumpter, Bobby [ORNL; Swader, Onome A [ORNL; Yu, Xiang [ORNL; Bredas, Jean-Luc E [ORNL; Malagoli, Massimo [ORNL

    2011-01-01

    The assembly and characterization of well-defined, end-tethered poly(p-phenylene) (PPP) brushes having high molecular weight, low polydispersity and high 1,4-stereoregularity are presented. The PPP brushes are formed using a precursor route that relies on either self-assembly or spin coating of high molecular weight (degrees of polymerizations 54, 146, and 238) end-functionalized poly(1,3-cyclohexadiene) (PCHD) chains from benzene solutions onto silicon or quartz substrates, followed by aromatization of the end-attached PCHD chains on the surface. The approach allows the thickness (grafting density) of the brushes to be easily varied. The dry brushes before and after aromatization are characterized by ellipsometry, atomic force microscopy, grazing angle attenuated total reflectance Fourier transform infrared spectroscopy, and UV-Vis spectroscopy. The properties of the PPP brushes are compared with those of films made using oligo-paraphenylenes and with ab initio density functional theory simulations of optical properties. Our results suggest conversion to fully aromatized, end-tethered PPP polymer brushes having effective conjugation lengths of 5 phenyl units.

  7. Insights into the Toxicological Properties of a Low Molecular Weight Fraction from Zoanthus sociatus (Cnidaria)

    PubMed Central

    Domínguez-Pérez, Dany; Diaz-Garcia, Carlos Manlio; García-Delgado, Neivys; Sierra-Gómez, Yusvel; Castañeda, Olga; Antunes, Agostinho

    2013-01-01

    The phylum Cnidaria is an ancient group of venomous animals, specialized in the production and delivery of toxins. Many species belonging to the class Anthozoa have been studied and their venoms often contain a group of peptides, less than 10 kDa, that act upon ion channels. These peptides and their targets interact with high affinity producing neurotoxic and cardiotoxic effects, and even death, depending on the dose and the administration pathway. Zoanthiniaria is an order of the Subclass Hexacorallia, class Anthozoa, and unlike sea anemone (order Actiniaria), neither its diversity of toxins nor the in vivo effects of the venoms has been exhaustively explored. In this study we assessed some toxicological tests on mice with a low molecular weight fraction obtained by gel filtration in Sephadex G-50 from Zoanthus sociatus crude extract. The gel filtration chromatogram at 280 nm revealed two major peaks, the highest absorbance corresponding to the low molecular weight fraction. The toxicological effects seem to be mostly autonomic and cardiotoxic, causing death in a dose dependent manner with a LD50 of 792 ?g/kg. Moreover, at a dose of 600 ?g/kg the active fraction accelerated the KCl-induced lethality in mice. PMID:23945599

  8. Ultrastructure, glutathione and low molecular weight proteins of Penicillium brevicompactum in response to cobalt.

    PubMed

    Farrag, Rasha M

    2009-01-01

    Penicillium brevicompactum highly tolerated cobalt concentrations of 50, 200, 800 and 1000 ppm both through cell wall and intracellular sequestration- immobilization of the metal on/within the cell wall, cell wall thickness, presence of electron-dense deposits inside vacuoles (thiol peptides sequestering cobalt) and in the cytoplasm (cobalt), and presence of matrixed electron-dense deposits, only at 800 and 1000 ppm, were observed. Increased vacuole formation and plasmolysis were also observed. Fraction number 9 of the cell free extract showed maximum cobalt uptake for all the investigated cobalt concentrations. In this fraction, glutathione was only induced at 500, 800 and 1000 ppm. Maximum glutathione concentration supported maximum cobalt uptake at 800 ppm. Low molecular weight protein profiles of fraction number 9 revealed that the presence of cobalt induced the appearance of new proteins that were not detected in the same fraction of the control. These low molecular weight peptides (12-5 KDa) suggest the production of Co-metallothioneins. This is the first report of cobalt-induced glutathione by P. brevicompactum and suggests the possible production of phytochelatins. PMID:20380143

  9. Antiadhesion and antibiofilm activities of high molecular weight coffee components against Streptococcus mutans.

    PubMed

    Stauder, Monica; Papetti, Adele; Mascherpa, Dora; Schito, Anna Maria; Gazzani, Gabriella; Pruzzo, Carla; Daglia, Maria

    2010-11-24

    In previous studies we demonstrated that green and roasted coffee contains low molecular weight (LMW) compounds capable of inhibiting the ability of Streptococcus mutans, the major causative agent of human dental caries, to adhere to hydroxyapatite (HA) beads. This study addressed the ability of the whole high molecular weight coffee fraction (cHMW) and of its melanoidin and non-melanoidin components (GFC1-5), applied at concentrations that occur in coffee beverages, to (i) inhibit S. mutans growth; (ii) affect S. mutans sucrose-dependent adhesion to and detachment from saliva-coated HA beads (sHA); and (iii) inhibit biofilm development on microtiter plates. The results indicated that only cHMW is endowed with antimicrobial activity. The cHMW fraction and each of the five GFC components inhibited S. mutans adhesion, the strongest effect being exerted by cHMW (91%) and GFC1 (88%). S. mutans detachment from sHA was four times greater (?20%) with cHMW and the GFC1 and GFC4 melanoidins than with controls. Finally, biofilm production by S. mutans was completely abolished by cHMW and was reduced by 20% by the melanoidin components GFC2 and GFC4 and by the non-melanoidin component GFC5 compared with controls. Altogether these findings show that coffee beverage contains both LMW compounds and HMW melanoidin and non-melanoidin components with a strong ability to interfere in vitro with the S. mutans traits relevant for cariogenesis. PMID:21038921

  10. Bemiparin, an effective and safe low molecular weight heparin: a review.

    PubMed

    Ciccone, Marco Matteo; Cortese, Francesca; Corbo, Filomena; Corrales, Noel Ernesto; Al-Momen, Abdul Kareem; Silva, Antonio; Zito, Annapaola; Pinto, Mariangela; Gesualdo, Michele; Scicchitano, Pietro

    2014-07-01

    Bemiparin is a low molecular weight heparin (LMWH) indicated for the acute treatment of deep vein thrombosis with or without pulmonary embolism, for the prophylaxis of venous thromboembolism in surgical and non-surgical patients and for the prevention of clotting in the extracorporeal circuit during hemodialysis. Due to its excellent pharmacological profile-the second-generation LMWH with the lowest molecular weight, the longest half-life and the highest anti-Factor Xa/anti-Factor IIa activity ratio-it can be safely used in special categories of patients (children, elderly, patients with renal impairment and congestive heart failure). Several studies demonstrated its safety and efficacy, while cost analyses show the economic benefits of bemiparin treatment as compared to other heparins. Recent evidences suggested the application of bemiparin even in the management of diabetic foot ulcers. The aim of this narrative review was to evaluate literature according to results coming from studies involving bemiparin administration in various clinical conditions. PMID:24657810

  11. Gene Targeted Ablation of High Molecular Weight Fibroblast Growth Factor-2

    PubMed Central

    Azhar, Mohamad; Yin, Moying; Zhou, Ming; Li, Hongqi; Mustafa, Marwan; Nusyr, Eyad; Keenan, Jack B.; Chen, Hwudaurw; Pawlosky, Sharon; Gard, Connie; Grisham, Christina; Sanford, L. Philip; Doetschman, Tom

    2009-01-01

    Fibroblast growth factor-2 (FGF2) is produced as high molecular weight isoforms (HMW) and a low molecular weight isoform (LMW) via alternative usage of translation start sites in a single Fgf2mRNA. Although the physiological function of FGF2 and FGF2 LMW has been investigated in myocardial capillarogenesis during normal cardiac growth, the role of FGF2 HMW has not been determined. Here we report the generation of FGF2 HMW-deficient mice in which FGF2 HMW isoforms are ablated by the Tag-and-Exchange gene targeting technique. These mice are normal and fertile with normal fecundity, and have a normal life span. Histological, immunohistochemical and morphometric analyses indicate normal myocardial architecture, blood vessel and cardiac capillary density in young adult FGF2 HMW-deficient mice. These mice along with the FGF2- and FGF2 LMW-deficient mice that we have generated previously will be very useful for elucidating the differential functions of FGF2 isoforms in patho-physiology of cardiovascular diseases. PMID:19105223

  12. What lies beyond the eye: the molecular mechanisms regulating tomato fruit weight and shape

    PubMed Central

    van der Knaap, Esther; Chakrabarti, Manohar; Chu, Yi Hsuan; Clevenger, Josh P.; Illa-Berenguer, Eudald; Huang, Zejun; Keyhaninejad, Neda; Mu, Qi; Sun, Liang; Wang, Yanping; Wu, Shan

    2014-01-01

    Domestication of fruit and vegetables resulted in a huge diversity of shapes and sizes of the produce. Selections that took place over thousands of years of alleles that increased fruit weight and altered shape for specific culinary uses provide a wealth of resources to study the molecular bases of this diversity. Tomato (Solanum lycopersicum) evolved from a wild ancestor (S. pimpinellifolium) bearing small and round edible fruit. Molecular genetic studies led to the identification of two genes selected for fruit weight: FW2.2 encoding a member of the Cell Number Regulator family; and FW3.2 encoding a P450 enzyme and the ortholog of KLUH. Four genes were identified that were selected for fruit shape: SUN encoding a member of the IQD family of calmodulin-binding proteins leading to fruit elongation; OVATE encoding a member of the OVATE family proteins involved in transcriptional repression leading to fruit elongation; LC encoding most likely the ortholog of WUSCHEL controlling meristem size and locule number; FAS encoding a member in the YABBY family controlling locule number leading to flat or oxheart shape. For this article, we will provide an overview of the putative function of the known genes, when during floral and fruit development they are hypothesized to act and their potential importance in regulating morphological diversity in other fruit and vegetable crops. PMID:24904622

  13. Effects of high-molecular-weight cryoprotectants on platelets and the coagulation system.

    PubMed

    Bakaltcheva, I; Ganong, J P; Holtz, B L; Peat, R A; Reid, T

    2000-06-01

    The objective of this study is to examine the effects of the most widely used high-molecular-weight cryoprotectants on the coagulation system. Dextran, hydryoxyethyl starch (HES), polyvinyl pyrrolidone (PVP), polyethylene glycol (PEG), and albumin were added at different concentrations in the range between 0.01-1% (w/v) to solvent/detergent-treated plasma. Using a STA/STA Compact coagulation analyzer the following clotting tests were performed: prothrombin time (PT), activated partial thromboplastin time (APTT), thrombin time (TT), Factor V, and Factor VIII percentage of activity. PVP and PEG caused a significant increase in APTT, a decrease in Factor VIII percentage of activity, and a slight decrease in TT, while PT and Factor V percentage of activity remained unchanged. Dextran, HES, and albumin did not effect the clotting tests. The effect of high-molecular-weight cryoprotectants on platelets was assessed by platelet-induced clot retraction (PICR) and aggregation with thrombin and agglutination with ristocetin. Platelet aggregation and agglutination were unaffected by all cryoprotectants tested; however, PICR was significantly reduced in the presence of PVP or PEG. Possible mechanisms by which PVP and PEG interfere with the coagulation system are discussed. We also raise issues concerning the development of one-step blood cryopreservation techniques which do not require cryoprotectant removal prior to transfusion. PMID:10924260

  14. A sulfuric-lactic acid process for efficient purification of fungal chitosan with intact molecular weight.

    PubMed

    Naghdi, Mitra; Zamani, Akram; Karimi, Keikhosro

    2014-02-01

    The most recent method of fungal chitosan purification, i.e., two steps of dilute sulfuric acid treatment, pretreatment of cell wall at room temperature for phosphate removal and extraction of chitosan from the phosphate free cell wall at high temperature, significantly reduces the chitosan molecular weight. This study was aimed at improvement of this method. In the pretreatment step, to choose the best conditions, cell wall of Rhizopus oryzae, containing 9% phosphate, 10% glucosamine, and 21% N-acetyl glucosamine, was treated with sulfuric, lactic, acetic, nitric, or hydrochloric acid, at room temperature. Sulfuric acid showed the best performance in phosphate removal (90%) and cell wall recovery (89%). To avoid depolymerisation of chitosan, hot sulfuric acid extraction was replaced with lactic acid treatment at room temperature, and a pure fungal chitosan was obtained (0.12 g/g cell wall). Similar pretreatment and extraction processes were conducted on pure shrimp chitosan and resulted in a chitosan recovery of higher than 87% while the reduction of chitosan viscosity was less than 15%. Therefore, the sulfuric-lactic acid method purified the fungal chitosan without significant molecular weight manipulation. PMID:24211428

  15. Low molecular weight protamine (LMWP): a nontoxic protamine substitute and an effective cell-penetrating peptide.

    PubMed

    He, Huining; Ye, Junxiao; Liu, Ergang; Liang, Qiuling; Liu, Quan; Yang, Victor C

    2014-11-10

    Low molecular weight protamine (LMWP) is a peptide fragment produced in our laboratory from enzymatic digestion of native protamine. More than 30 papers studying the properties and applications of LMWP have been published by our group in various journals since its initial discovery in 1999. Results have shown that LMWP could completely neutralize the anticoagulant functions of both heparin and low molecular weight heparin (LMWH), with reduced antigenicity and cross-reactivity toward the mice-derived anti-protamine antibodies. Aside from its potential as a heparin/LMWH antagonist, LMWP also shows the ability to retard insulin adsorption by the formation of an insoluble complex, making it a less toxic long-lasting insulin product than the conventional neutral protamine Hagedorn (NPH) insulin for diabetic control. Importantly, LMWP (Sequence: VSRRRRRRGGRRRR), with 10 arginine residues in its structure, could function as a cell-penetrating peptide (CPP), also termed protein transduction domain (PTD), to achieve effective intracellular protein or gene delivery in clinical practice. In this paper, we present a thorough review of our work related to LMWP, with the aim of providing readers an insight into its potential to be a clinical protamine substitute as well as a non-toxic cell penetrating peptide applicable to achieve intracellular protein and gene delivery. PMID:24943246

  16. The integrity of welded interfaces in ultra-high molecular weight polyethylene: Part 2--interface toughness.

    PubMed

    Haughie, David W; Buckley, C Paul; Wu, Junjie

    2006-07-01

    In Part 2 of a study of welding of ultra-high molecular weight polyethylene (UHMWPE), experiments were conducted to measure the interfacial fracture energy of butt welds, for various welding times and temperatures above the melting point. Their toughness was investigated at 37 degrees C in terms of their fracture energy, obtained by adapting the essential work of fracture (EWF) method. However, a proportion of the welded samples (generally decreasing with increasing welding time or temperature) failed in dual ductile/brittle mode, hence invalidating the EWF test. Even those failing in purely ductile mode showed a measurable interface work of fracture only for the highest weld temperature and time: 188 degrees C and 90 min. Results from the model presented in Part 1 show that this corresponds to the maximum reptated molecular weight reaching close to the peak in the molar mass distribution. Hence this work provides the first experimental evidence that the slow rate of self-diffusion in UHMWPE leads to welded interfaces acting as low-toughness crack paths. Since such interfaces exist around every powder particle in processed UHMWPE this problem cannot be avoided, and it must be accommodated in design of hip and knee bearing surfaces made from this polymer. PMID:16574221

  17. What lies beyond the eye: the molecular mechanisms regulating tomato fruit weight and shape.

    PubMed

    van der Knaap, Esther; Chakrabarti, Manohar; Chu, Yi Hsuan; Clevenger, Josh P; Illa-Berenguer, Eudald; Huang, Zejun; Keyhaninejad, Neda; Mu, Qi; Sun, Liang; Wang, Yanping; Wu, Shan

    2014-01-01

    Domestication of fruit and vegetables resulted in a huge diversity of shapes and sizes of the produce. Selections that took place over thousands of years of alleles that increased fruit weight and altered shape for specific culinary uses provide a wealth of resources to study the molecular bases of this diversity. Tomato (Solanum lycopersicum) evolved from a wild ancestor (S. pimpinellifolium) bearing small and round edible fruit. Molecular genetic studies led to the identification of two genes selected for fruit weight: FW2.2 encoding a member of the Cell Number Regulator family; and FW3.2 encoding a P450 enzyme and the ortholog of KLUH. Four genes were identified that were selected for fruit shape: SUN encoding a member of the IQD family of calmodulin-binding proteins leading to fruit elongation; OVATE encoding a member of the OVATE family proteins involved in transcriptional repression leading to fruit elongation; LC encoding most likely the ortholog of WUSCHEL controlling meristem size and locule number; FAS encoding a member in the YABBY family controlling locule number leading to flat or oxheart shape. For this article, we will provide an overview of the putative function of the known genes, when during floral and fruit development they are hypothesized to act and their potential importance in regulating morphological diversity in other fruit and vegetable crops. PMID:24904622

  18. Anti-HIV-1 activity of low molecular weight sulfated chitooligosaccharides.

    PubMed

    Artan, Murat; Karadeniz, Fatih; Karagozlu, Mustafa Zafer; Kim, Moon-Moo; Kim, Se-Kwon

    2010-03-30

    Chitooligosaccharides are nontoxic and water-soluble compounds obtained by enzymatic degradation of chitosan, which is derived from chitin by a deacetylation process. Chitooligosaccharides possess broad range of activities such as antitumour, antifungal, antibacterial activities. Sulfated chitooligosaccharides (SCOSs) with different molecular weights were synthesized by a random sulfation reaction. In the present study, anti-HIV-1 properties of SCOSs and the impact of molecular weight on their inhibitory activity were investigated. SCOS III (MW 3-5 kDa) was found to be the most effective compound to inhibit HIV-1 replication. At nontoxic concentrations, SCOS III exhibited remarkable inhibitory activities on HIV-1-induced syncytia formation (EC(50) 2.19 microg/ml), lytic effect (EC(50) 1.43 microg/ml), and p24 antigen production (EC(50) 4.33 microg/ml and 7.76 microg/ml for HIV-1(RF) and HIV-1(Ba-L), respectively). In contrast, unsulfated chitooligosaccharides showed no activity against HIV-1. Furthermore, it was found that SCOS III blocked viral entry and virus-cell fusion probably via disrupting the binding of HIV-1 gp120 to CD4 cell surface receptor. These results suggest that sulfated chitooligosaccharides represent novel candidates for the development of anti-HIV-1 agent. PMID:20117763

  19. Subcutaneous low molecular weight heparin for management of anticoagulation in infants on excor ventricular assist device.

    PubMed

    Ghez, Olivier; Liesner, Ri; Karimova, Ann; Ng, Cho; Goldman, Allan; van Doorn, Carin

    2006-01-01

    Anticoagulation in infants and children on a ventricular assist device presents particular challenges. Unfractionated heparin has poor bioavailability; it can be difficult to achieve a stable anticoagulant effect; and, in the long-term, there is a risk of osteopenia. Long-term warfarin can be difficult to manage in infants on formula milk with vitamin K supplementation. We review our recent experience with subcutaneous low molecular weight heparin. Two patients received a left ventricular assist device (Excor, Berlin Heart AG) as a bridge to transplantation. Initial anticoagulation consisted of unfractionated heparin infusion beginning 6 hours after implantation to maintain an activated partial thromboplastin time of 70 seconds, checked every 4 to 6 hours. Platelet count (aim >80,000/microl) and thromboelastography were assessed daily. Antithrombin required substitution to maintain levels >70 IU/dl. To optimize anticoagulation, both infants were switched to subcutaneous low molecular weight heparin twice daily aiming for an anti-Xa activity between 0.5 and 1.0 IU/ml. Aspirin was added on day 4, checking platelet aggregation every 2 to 4 days, aiming at arachidonic acid stimulated aggregation 10% to 30% of baseline, collagen 100% of baseline. Dipyridamole was added once stability was reached if platelets count exceeded 150,000/microl. There were no clinical thromboembolic or bleeding events. Both patients had successful transplantation. PMID:17117062

  20. Occupational asthma: new low-molecular-weight causal agents, 2000-2010.

    PubMed

    Pralong, J A; Cartier, A; Vandenplas, O; Labrecque, M

    2012-01-01

    Background. More than 400 agents have been documented as causing occupational asthma (OA). The list of low-molecular-weight (LMW) agents that have been identified as potential causes of OA is constantly expanding, emphasizing the need to continually update our knowledge by reviewing the literature. Objective. The objective of this paper was to identify all new LMW agents causing occupational asthma reported during the period 2000-2010. Methods. A Medline search was performed using the keywords occupational asthma, new allergens, new causes, and low-molecular-weight agents. Results. We found 39 publications describing 41 new LMW causal agents, which belonged to the following categories: drugs (n = 12), wood dust (n = 11), chemicals (n = 8), metals (n = 4), biocides (n = 3), and miscellaneous (n = 3). The diagnosis of OA was confirmed through SIC for 35 of 41 agents, peak expiratory flow monitoring for three (3) agents, and the clinical history alone for three (3) agents. Immunological tests provided evidence supporting an IgE-mediated mechanism for eight (8) (20%) of the newly described agents. Conclusion. This paper highlights the importance of being alert to the occurrence of new LMW sensitizers, which can elicit OA. The immunological mechanism is explained by a type I hypersensitivity reaction in 20% of all newly described LMW agents. PMID:22548090

  1. Occupational Asthma: New Low-Molecular-Weight Causal Agents, 2000–2010

    PubMed Central

    Pralong, J. A.; Cartier, A.; Vandenplas, O.; Labrecque, M.

    2012-01-01

    Background. More than 400 agents have been documented as causing occupational asthma (OA). The list of low-molecular-weight (LMW) agents that have been identified as potential causes of OA is constantly expanding, emphasizing the need to continually update our knowledge by reviewing the literature. Objective. The objective of this paper was to identify all new LMW agents causing occupational asthma reported during the period 2000–2010. Methods. A Medline search was performed using the keywords occupational asthma, new allergens, new causes, and low-molecular-weight agents. Results. We found 39 publications describing 41 new LMW causal agents, which belonged to the following categories: drugs (n = 12), wood dust (n = 11), chemicals (n = 8), metals (n = 4), biocides (n = 3), and miscellaneous (n = 3). The diagnosis of OA was confirmed through SIC for 35 of 41 agents, peak expiratory flow monitoring for three (3) agents, and the clinical history alone for three (3) agents. Immunological tests provided evidence supporting an IgE-mediated mechanism for eight (8) (20%) of the newly described agents. Conclusion. This paper highlights the importance of being alert to the occurrence of new LMW sensitizers, which can elicit OA. The immunological mechanism is explained by a type I hypersensitivity reaction in 20% of all newly described LMW agents. PMID:22548090

  2. Changes in Molecular Weight of Cellulose in the Pea Epicotyl during Growth 1

    PubMed Central

    Spencer, F. S.; Maclachlan, G. A.

    1972-01-01

    A procedure is described for preparing cellulose nitrate from pea tissues (Pisum sativum L. var. Alaska) in quantitative yield, undegraded and uncontaminated by other polysaccharides. The average degree of polymerization of this product, estimated from viscosity measurements, increased during cell growth and development from a value of about 5000 glucose units in the apical meristem (plumule plus hook) to values near 8000 in fully grown maturing tissues (>20 mm from apex). The cellulose content per cell also increased (approximately 10-fold) during growth in these tissues, as did particulate glucan synthetase activity (3-fold rise). Since the yield of soluble cellulase activity is known to decrease from high values in the meristem to barely detectable amounts in mature tissues, it is suggested that the relative levels and properties of these hydrolytic and synthetic enzyme activities control the amount and degree of polymerization of cellulose formed during cell expansion in the pea epicotyl. Degree of polymerization distribution patterns showed that a low molecular weight component of cellulose (degree of polymerization < 500) was prominent in young tissues whereas high molecular weight components (degree of polymerization > 7000) predominated in mature tissues. Also, cellulose which was formed from radioactive sucrose during 30 minutes of incubation showed a remarkably similar degree of polymerization distribution to cellulose which was present in the tissue at the time of synthesis. It is concluded that new and old parts of the epicotyl cellulose framework are subject to constant modification and equilibration by cellulose-metabolizing enzymes. PMID:16657897

  3. Thrombin generation assay identifies individual variability in responses to low molecular weight heparin in pregnancy: implications for anticoagulant monitoring.

    PubMed

    Chowdary, Pratima; Adamidou, Despoina; Riddell, Anne; Aghighi, Saman; Griffioen, Anja; Priest, Paul; Moghadam, Lida; Kelaher, Nicholas; Huq, Farah Y; Kadir, Rezan A; Tuddenham, Edward G; Gatt, Alex

    2015-03-01

    Low molecular weight heparin (LMWH) given to inhibit coagulation and reduce the risk of thrombosis, is typically monitored by anti-Xa assay. However, anti-Xa levels may not necessarily provide an accurate measure of coagulation inhibition. Moreover, pregnancy is associated with hypercoagulability, which may compromise the efficacy of LMWH. We looked at the association between anti-Xa levels and parameters of thrombin generation assay [TGA; area under the curve (AUC), peak height (PH) and time to peak (ttP)] using samples from 41 pregnant women receiving LMWH and 40 normal pregnant women controls. TGA results confirmed the physiological hypercoagulability of normal pregnancy (mean normalised values: AUC 119%; PH 157%; ttP 72%). Although anti-Xa measures correlated with all three TGA parameters, this group correlation masked significant inter-individual variability, demonstrated by the R(2) value or coefficient of determination. Anti-Xa levels contributed to 74% of variation in AUC values, 63% of variation in PH values and only 53% of variation in ttP values. The remainder reflects the contribution of patients' intrinsic coagulation status. Hence, some patients with 'safe' anti-Xa levels may potentially be under-anticoagulated, particularly in pregnancy. Measuring coagulability directly with TGA may lower the risk of adverse events due to under-anticoagulation in selected patients. PMID:25351814

  4. Dexamethasone-conjugated low molecular weight polyethylenimine as a nucleus-targeting lipopolymer gene carrier.

    PubMed

    Mi Bae, Yun; Choi, Hye; Lee, Seungah; Ho Kang, Seong; Tae Kim, Young; Nam, Kihoon; Sang Park, Jong; Lee, Minhyung; Sig Choi, Joon

    2007-01-01

    Dexamethasone, a glucocorticoid steroid, can dilate the nuclear pore complexes and translocate into the nucleus when it is bound to its glucocorticoid receptor, suggesting that the transport of DNA into the nucleus may be facilitated by the reagent. In this research, dexamethasone was conjugated to low molecular weight polyethylenimine (2 kDa) for efficient translocation of the polymer/DNA complex into the nucleus. Polyethylenimine (PEI)-dexamethasone (PEI-Dexa) was synthesized by one-step reaction using the Traut's reagent. In gel retardation assay, the PEI-Dexa/DNA complex was completely retarded at or above 0.3/1 weight ratio (polymer/DNA). The average size distributions and zeta-potential values of the complexes were measured at various weight ratios. In vitro transfection assay showed that the PEI-Dexa/DNA complex had higher gene delivery efficiency compared to PEI 2kDa/DNA complex. The localization of PEI-Dexa/plasmid DNA complexes in the nucleus was confirmed by using total internal reflection fluorescence and Nomarski differential interference contrast microscope as well as confocal microscope. Therefore, with efficient nuclear translocation and low cytotoxicity, PEI-Dexa may be useful for nonviral gene therapy. PMID:17850108

  5. Probing the molecular weight distributions of non-boiling petroleum fractions by Ag+ electrospray ionization mass spectrometry.

    PubMed

    Roussis, Stilianos G; Proulx, Richard

    2004-01-01

    This work explores the possibility of Ag+ electrospray ionization mass spectrometry (ESI-MS) to determine the molecular weight distributions of non-boiling petroleum fractions. Information about the molecular weight distributions is needed for fundamental studies on the nature of heavy crude oils and bitumens and for the development of novel recovery and processing methods. The method does not depend on thermal processes for the introduction of the fractions into the gas phase of the mass spectrometer, which is a considerable advantage over most other ionization methods. The Ag+ electrospray mass spectra of the fractions analyzed by using a toluene/methanol/cyclohexane (60:28:12%) solvent system display bimodal distributions in the ranges m/z approximately 300 to approximately 3000 and m/z 3000 to approximately 20,000. The abundances of the high molecular weight peak distributions can be reduced by in-source collisional activation experiments. Comparisons with the results obtained for model heteroatom-containing compounds (molecular weight < 600 Da) and high molecular weight polystyrene standards (up to one million Da) indicate that the majority of the structures in the saturate, naphthenoaromatic and polar aromatic fractions, and a significant portion of the asphaltenes, are small molecules. However, a considerable portion of the asphaltenes and some portion of the other fractions contain high molecular weight structures bound by covalent or strong non-covalent bonds. The results obtained by the Ag+ ESI method in this study for the saturate, aromatic, and polar fractions in a bitumen are in qualitative agreement with published molecular weight average results obtained for Cold Lake bitumen fractions analyzed by conventional gel permeation chromatography and field desorption mass spectrometry. Further work is needed to study the nature of the bonds and the interactions of the molecules in the asphaltene fractions by Ag+ ESI-MS. PMID:15282776

  6. Fluorescence imaging of macromolecule transport in high molecular weight cut-off microdialysis.

    PubMed

    Chu, Jiangtao; Koudriavtsev, Vitali; Hjort, Klas; Dahlin, Andreas P

    2014-11-01

    When microdialysis (MD) membrane exceeds molecular weight cut-off (MWCO) of 100 kDa, the fluid mechanics are in the ultrafiltration regime. Consequently, fluidic mass transport of macromolecules in the perfusate over the membrane may reduce the biological relevance of the sampling and cause an inflammatory response in the test subject. Therefore, a method to investigate the molecular transport of high MWCO MD is presented. An in vitro test chamber was fabricated to facilitate the fluorescent imaging of the MD sampling process, using fluoresceinylisothiocyanate (FITC) dextran and fluorescence microscopy. Qualitative studies on dextran behavior inside and outside the membrane were performed. Semiquantitative results showed clear dextran leakage from both 40 and 250 kDa dextran when 100 kDa MWCO membranes were used. Dextran 40 kDa leaked out with an order of magnitude higher concentration and the leakage pattern resembled more of a convective flow pattern compared with dextran 250 kDa, where the leakage pattern was more diffusion based. No leakage was observed when dextran 500 kDa was used as a colloid osmotic agent. The results in this study suggest that fluorescence imaging could be used as a method for qualitative and semiquantitative molecular transport and fluid dynamics studies of MD membranes and other hollow fiber catheter membranes. PMID:25286875

  7. Synthesis and characterization of sugar based low molecular weight gelators and the preparation of chiral sulfinamides

    NASA Astrophysics Data System (ADS)

    Mangunuru, Hari Prasad Reddy

    Low molecular weight gelators (LMWGs) have received considerable attention in the field of chemistry from last few decades. These compounds form self-assembled fibrous networks like micelles, cylindrical, sheets, fibers, layers and so on. The fibrous network entraps the solvent and forms gel, because of the self-assembly phenomenon and their demonstrated potential uses in a variety of areas, ranging from environmental to medicinal applications. Sugars are good starting materials to synthesize the new class of LMWG's, because these are different from some expensive materials, these are natural products. We have synthesized and characterized the LMGS's based on D-glucose and D-glucosamine. D-glucosamine is the versatile starting material to make different peptoids and triazoles. Several series of compounds were synthesized using compounds 1-3 as starting material and studied the gelation behavior all the compounds. We have studied the self-assembling properties of a new class of tripeptoids, synthesized by one-pot Ugi reaction from simple starting materials. Among the focused library of tripeptoids synthesized, we found that several efficient low molecular weight organogelators were obtained for aqueous DMSO and ethanol mixtures. We have also synthesized and characterized a series of monosaccharide triazole derivatives. These compounds were synthesized from N-acetyl glucosamine and D-glucose via a Cu(I) catalyzed azide/alkyne cycloaddition reaction (CuAAc). The compounds have been screened for their gelation properties and several efficient low molecular weight organo/hydro gelators were obtained, among these compounds, five per-acetyl glucosamine derivatives and one peracetyl glucose derivative were able to form gels in water. These new molecules are expected to be useful in drug delivery and tissue engineering.*. Asymmetric synthesis of chiral amines is a challenging in synthetic organic chemistry. The development of new catalysts for asymmetric organic transformations is a very important research goal in modern synthetic organic chemistry. We have synthesized a new class of chiral oxathiozinone from chiral amino phenol. From this synthesized chiral sulfinamides, ketimines followed by reducing the ketimines synthesized the highly hindered chiral amines. *Please refer to dissertation for diagrams.

  8. Low-Molecular-Weight Heparin and Unfractionated Heparin Decrease Th-1, 2, and 17 Expressions

    PubMed Central

    Huang, Jing-Ning; Tsai, Ming-Chin; Fang, Shun-Lung; Chang, Margaret Dah-Tsyr; Wu, Yu-Rou; Tsai, Jaw-Ji; Fu, Lin-Shien; Lin, Heng-Kuei; Chen, Yi-Jun; Li, Tsai-Wei

    2014-01-01

    Background We evaluated the effects of T helper cell differentiation in a mite-allergic animal model treated with inhaled heparins of different molecular weight. Method BALB/c mice were divided into four groups: 1. Control, 2. Mite intratracheal (mIT), 3. Inhaled heparin (hIN), 4. Inhaled low-molecular-weight heparin (lmwhIN). Groups 2, 3, and 4 were sensitized twice with Der p allergen subcutaneously on day 1 and day 8. Der p allergen was administered intratracheally on day 15. Groups 3 and 4 were treated with heparin or low-molecular-weight (lmw) heparin intranasally from day 1 to 22. Splenocytes from sacrificed mice stimulated with 16 µg/ml of Der p were cultured for 72 hours. Supernatants of splenocyte were collected to analyze the effect of Interleukin (IL)17-A/F, Interferon(IFN)-?, IL-4, IL-13, and IL-10. Serum was also collected for Der P-specific IgE level on day 23. Total RNA was extracted from spleen tissue for mRNA expression. Gene expression of Foxp3, IL-10 IFN-?, GATA3, IL-5, and ROR?t were analyzed. Results Both hIN and lmwhIN groups had lower serum IgE level than that of the mIT group (both p<0.0001). Both hIN and lmwhIN groups showed significantly decreased transcripts of GATA-3, IFN-?, IL-5, and ROR?t mRNA in their spleen. Regarding the supernatant of splenocyte culture stimulated with Der p, compared with the mIT group, there were significant decreases in IL-17A/F, IFN-?, IL-4, IL-13, and IL-10 secretion in inhaled hIN and lmwhIN groups. Conclusions From this balb/c mice study, the analyses of mRNA and cytokines revealed that both intranasal heparin and lmw heparin treatment decreased the expression of Th1, Th2, and Th17 in spleen. The underlying mechanism(s) warrant further studies. PMID:25364825

  9. Factors that affect molecular weight distribution of Suwannee river fulvic acid as determined by electrospray ionization/mass spectrometry

    USGS Publications Warehouse

    Rostad, C.E.; Leenheer, J.A.

    2004-01-01

    Effects of methylation, molar response, multiple charging, solvents, and positive and negative ionization on molecular weight distributions of aquatic fulvic acid were investigated by electrospray ionization/mass spectrometry. After preliminary analysis by positive and negative modes, samples and mixtures of standards were derivatized by methylation to minimize ionization sites and reanalyzed.Positive ionization was less effective and produced more complex spectra than negative ionization. Ionization in methanol/water produced greater response than in acetonitrile/water. Molar response varied widely for the selected free acid standards when analyzed individually and in a mixture, but after methylation this range decreased. After methylation, the number average molecular weight of the Suwannee River fulvic acid remained the same while the weight average molecular weight decreased. These differences are probably indicative of disaggregation of large aggregated ions during methylation. Since the weight average molecular weight decreased, it is likely that aggregate formation in the fulvic acid was present prior to derivatization, rather than multiple charging in the mass spectra. ?? 2004 Elsevier B.V. All rights reserved.

  10. Preparation and characterization of molecular weight fractions of glycosaminoglycan from sea cucumber Thelenata ananas using free radical depolymerization.

    PubMed

    Wu, Mingyi; Xu, Shimin; Zhao, Jinhua; Kang, Hui; Ding, Hui

    2010-03-30

    A glycosaminoglycan from sea cucumber Thelenata anana (THG) was isolated as a polymer of molecular weight of around 70 kDa. Its low molecular weight derivatives were first prepared by free radical depolymerization with hydrogen peroxide in the presence of copper(II) ion. The parameters of the process were investigated by a high-performance gel permeation chromatography. Analyses of chemical composition and molecular weight distribution indicated that the fragmentation of the main-chain of THG occurred randomly, obeyed pseudo first-order kinetics, and produced species with rather narrow and unimodal distribution of molar mass. The characterization of different molecular weight fractions was investigated by using viscometry and atomic force microscopy (AFM). Analysis of molecular weight and intrinsic viscosity in terms of the known theories for unperturbed wormlike cylinder yielded 1201+/-110 nm(-1), 15.3+/-1.5 nm, and 1.5+/-0.3 nm for molar mass per unit contour length M(L), persistence length q, and diameter d, respectively. The M(L) and d values were approximately consistent with those observed by AFM. The present data suggest that THG may dissolve in 0.1M aqueous NaCl as single-stranded helical chains. PMID:20117762

  11. Aqueous geochemistry of low molecular weight hydrocarbons at elevated temperatures and pressures: constraints from mineral buffered laboratory experiments

    NASA Astrophysics Data System (ADS)

    Seewald, Jeffrey S.

    2001-05-01

    Organic matter, water, and minerals coexist at elevated temperatures and pressures in sedimentary basins and participate in a wide range of geochemical processes that includes the generation of oil and natural gas. A series of laboratory experiments were conducted at 300 to 350°C and 350 bars to examine chemical interactions involving low molecular weight aqueous hydrocarbons with water and Fe-bearing minerals under hydrothermal conditions. Mineral buffers composed of hematite-magnetite-pyrite, hematite-magnetite, and pyrite-pyrrhotite-magnetite were added to each experiment to fix the redox state of the fluid and the activity of reduced sulfur species. During each experiment the chemical system was externally modified by addition of ethene, ethane, propene, 1-butene, or n-heptane, and variations in the abundance of aqueous organic species were monitored as a function of time and temperature. Results of the experiments indicate that decomposition of aqueous n-alkanes proceeds through a series of oxidation and hydration reactions that sequentially produce alkenes, alcohols, ketones, and organic acids as reaction intermediaries. Organic acids subsequently undergo decarboxylation and/or oxidation reactions to form carbon dioxide and shorter chain saturated hydrocarbons. This alteration assemblage is compositionally distinct from that produced by thermal cracking under anhydrous conditions, indicating that the presence of water and minerals provide alternative reaction pathways for the decomposition of hydrocarbons. The rate of hydrocarbon oxidation decreases substantially under reducing conditions and in the absence of catalytically active aqueous sulfur species. These results represent compelling evidence that the stability of aqueous hydrocarbons at elevated temperatures in natural environments is not a simple function of time and temperature alone. Under the appropriate geochemical conditions, stepwise oxidation represents a mechanism for the decomposition of low molecular weight hydrocarbons and the production of methane-rich ("dry") natural gas. Evaluation of aqueous reaction products generated during the experiments within a thermodynamic framework indicates that alkane-alkene, alkene-ketone, and alkene-alcohol reactions attained metastable thermodynamic equilibrium states. This equilibrium included water and iron-bearing minerals, demonstrating the direct involvement of inorganic species as reactants during organic transformations. The high reactivity of water and iron-bearing minerals suggests that they represent abundant sources of hydrogen and oxygen available for the formation of hydrocarbons and oxygenated alteration products. Thus, variations in elemental kerogen composition may not accurately reflect the timing and extent of hydrocarbon, carbon dioxide, and organic acid generation in sedimentary basins. This study demonstrates that the stabilities of aqueous hydrocarbons are strongly influenced by inorganic sediment composition at elevated temperatures. Incorporation of such interactions into geochemical models will greatly improve prediction of the occurrence of hydrocarbons in natural environments over geologic time.

  12. Surface engineering on mesoporous silica chips for enriching low molecular weight phosphorylated proteins

    NASA Astrophysics Data System (ADS)

    Hu, Ye; Peng, Yang; Lin, Kevin; Shen, Haifa; Brousseau, Louis C., III; Sakamoto, Jason; Sun, Tong; Ferrari, Mauro

    2011-02-01

    Phosphorylated peptides and proteins play an important role in normal cellular activities, e.g., gene expression, mitosis, differentiation, proliferation, and apoptosis, as well as tumor initiation, progression and metastasis. However, technical hurdles hinder the use of common fractionation methods to capture phosphopeptides from complex biological fluids such as human sera. Herein, we present the development of a dual strategy material that offers enhanced capture of low molecular weight phosphoproteins: mesoporous silica thin films with precisely engineered pore sizes that sterically select for molecular size combined with chemically selective surface modifications (i.e. Ga3+, Ti4+ and Zr4+) that target phosphoroproteins. These materials provide high reproducibility (CV = 18%) and increase the stability of the captured proteins by excluding degrading enzymes, such as trypsin. The chemical and physical properties of the composite mesoporous thin films were characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy and ellipsometry. Using mass spectroscopy and biostatistics analysis, the enrichment efficiency of different metal ions immobilized on mesoporous silica chips was investigated. The novel technology reported provides a platform capable of efficiently profiling the serum proteome for biomarker discovery, forensic sampling, and routine diagnostic applications.Phosphorylated peptides and proteins play an important role in normal cellular activities, e.g., gene expression, mitosis, differentiation, proliferation, and apoptosis, as well as tumor initiation, progression and metastasis. However, technical hurdles hinder the use of common fractionation methods to capture phosphopeptides from complex biological fluids such as human sera. Herein, we present the development of a dual strategy material that offers enhanced capture of low molecular weight phosphoproteins: mesoporous silica thin films with precisely engineered pore sizes that sterically select for molecular size combined with chemically selective surface modifications (i.e. Ga3+, Ti4+ and Zr4+) that target phosphoroproteins. These materials provide high reproducibility (CV = 18%) and increase the stability of the captured proteins by excluding degrading enzymes, such as trypsin. The chemical and physical properties of the composite mesoporous thin films were characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy and ellipsometry. Using mass spectroscopy and biostatistics analysis, the enrichment efficiency of different metal ions immobilized on mesoporous silica chips was investigated. The novel technology reported provides a platform capable of efficiently profiling the serum proteome for biomarker discovery, forensic sampling, and routine diagnostic applications. Electronic supplementary information (ESI) available. See DOI: 10.1039/c0nr00720j

  13. Cold atmospheric pressure gas plasma enhances the wear performance of ultra-high molecular weight polyethylene.

    PubMed

    Perni, Stefano; Kong, Michael G; Prokopovich, Polina

    2012-03-01

    Ultra-high molecular weight polyethylene (UHMWPE) is frequently employed in joint replacements because of its high biocompatibility; however, this material does not exhibit particularly strong wear performance, thus potentially reducing the longevity of such devices. Numerous techniques have been investigated to increase the resistance to wear of UHMWPE, but they are all based on expensive machinery and require a high level of safety precautions. Cold atmospheric pressure gas plasma treatment is an inexpensive process that has been used as a surface modification method and as a sterilization technique. We demonstrate for the first time that a helium/oxygen cold atmospheric pressure gas plasma can be used to enhance the wear performance of UHMWPE without affecting the cytocompatibility of the material. The exposure to a cold atmospheric pressure gas plasma results in a greater level of crosslinking of the polyethylene chains. As a consequence of the higher crosslinking, the material stiffness of the treated surface is increased. PMID:22202910

  14. Thermal Behaviour of W+C Ion Implanted Ultra High Molecular Weight Polyethylene (UHMWPE)

    SciTech Connect

    Urkac, E. Sokullu; Oztarhan, A. [Bioengineering Department, Ege University, Bornova, Izmir 35100 (Turkey); Tihminlioglu, F. [Chemical Engineering Department, Izmir Institute of High Technology, Gulbahcekoyu Urla, Izmir (Turkey); Ila, D.; Chhay, B.; Muntele, C. [Center for Irradiation of Materials, Alabama A and M University, Normal, Huntsville AL 35762 (United States); Budak, S. [Department of Electrical Engineering, Alabama A and M University, Normal, AL 35762 (United States); Oks, E.; Nikolaev, A. [High Current Electrnonics, Institute, Tomsk (Russian Federation)

    2009-03-10

    The aim of this work was to examine thermal behavior of the surface modified Ultra High Molecular Weight Poly Ethylene (UHMWPE ) in order to understand the effect of ion implantation on the properties of this polymer which is widely used especially for biomedical applications. UHMWPE samples were Tungsten and Carbon (W+C) hybrid ion implanted by using Metal Vapour Vacuum Arc (MEVVA) ion implantation technique with a fluence of 10 17 ions/cm2 and extraction voltage of 30 kV. Untreated and surface-treated samples were investigated by Rutherford Back Scattering (RBS) Analysis, Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) Spectrometry, Thermo Gravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC). This study has shown that ion implantation represents a powerful tool on modifying thermal properties of UHMWPE surfaces. This combination of properties can make implanted UHMWPE a preferred material for biomedical applications.

  15. Bioassay-guided isolation of a low molecular weight PHB from Burkholderia sp. with phytotoxic activity.

    PubMed

    Petta, Tânia; Raichardt, Leandro; Melo, Itamar S; Moraes, Luiz A B

    2013-08-01

    This work reports on the bioassay-guided isolation and identification of the macrocyclic pentolide 1, a cyclic polyhydroxybutyrate (PHB) with low molecular weight. This metabolite is produced by Burkholderia sp. and it exhibited phytotoxic activity in a Lemna minor bioassay. Its structure was determined by (1)H and (13)C NMR, heteronuclear multiple quantum correlation, heteronuclear multiple bond correlation, IR, and electrospray ionization tandem mass spectrometry analyses. The period for maximum production of the pentolide was optimized and determined on the basis of multiple reaction monitoring experiments at 15 days. The potential of Burkholderia sp. as a producer of higher biopolymers of PHB was also investigated. The methodology employed here accelerated the isolation and characterization of a phytotoxic metabolite whose structure can serve as a model for the synthesis of new classes of herbicides. PMID:23722946

  16. Spontaneous Hemocholecyst in an End-Stage Renal Failure Patient on Low Molecular Weight Heparin Hemodialysis

    PubMed Central

    Blouhos, Konstantinos; Boulas, Konstantinos A.; Tselios, Dimitrios G.; Hatzigeorgiadis, Anestis

    2012-01-01

    The present paper describes a case of spontaneous hemocholecyst in a patient with end-stage renal failure on low molecular weight heparin hemodialysis. The patient presented with acute right upper quadrant pain. An initial ultrasound scan demonstrated a distended gallbladder containing echogenic bile without stones. During hospitalization the patient became febrile, and jaundiced, developed leukocytosis, and had an elevation in serum bilirubin, transaminases, and alkaline phosphatase. A new ultrasound demonstrated a thick-walled gallbladder containing echogenic bile and pericholecystic fluid. MRI depicted a distended gallbladder containing material of mixed signal intensity and a normal biliary tract. Open cholecystectomy revealed a gallbladder filled with blood and clots, and transcystic common bile duct exploration flushed blood clots out of the bile duct. To our knowledge this is the second case of spontaneous hemocholecyst reported in the literature as a consequence of uremic bleeding and LMWH hemodialysis in the absence of other pathology. PMID:23304616

  17. Tribological behavior of ultra-high molecular weight polyethylene in a hip joint simulator

    NASA Astrophysics Data System (ADS)

    Mohamad Raffi, N.; Kanagarajan, D.; Srinivasan, V.

    2012-12-01

    In this paper effects of various injection molding parameters on tribological properties of ultra-high molecular weight polyethylene (UHMWPE) were investigated. The tribological properties like coefficient of friction and wear rate were obtained from the experimental results of hip simulator which was designed and fabricated in the laboratory. Bovine serum was used as a lubricant in this study. In addition, the hardness of the specimen was also investigated as well. The injection molding parameters that varied for this study are melt temperature, injection velocity and compaction time. The results show that contact loads and melt temperature were mostly influenced the tribological behavior of UHMWPE. A wear mechanism map was developed to study the dominant wear mechanism that influences the wear behavior of UHMWPE. SEM was employed to study the worn out morphologies of UHMWPE. The dominant wear mechanisms that are dominated through our study are ironing, scratching, ploughing, plastic deformation, and fatigue wear.

  18. Exploring the role of low-molecular-weight heparins in pregnancy.

    PubMed

    Greer, Ian A

    2002-08-01

    Thromboembolic complications are leading causes of both maternal and fetal morbidity and mortality. To reduce the incidence of venous thromboembolism (VTE) in pregnancy and improve outcomes, a wider understanding of the risk factors involved and better identification of women at risk of thrombosis are required. Optimal management of thromboembolic disease, both to prevent VTE and to avoid recurrence of pregnancy complications such as miscarriage, centers on the use of low-molecular-weight heparin (LMWH). LMWHs, such as enoxaparin and dalteparin, have clinical and practical advantages compared with unfractionated heparin in terms of improved safety (significantly lower incidence of osteoporosis, thrombocytopenia, and possibly allergic skin reactions) and the potential for outpatient treatment of acute VTE. However, many unanswered questions remain, including who to treat, how to treat them, and when to treat in the case of patients with thrombophilia and a history of previous pregnancy complications. PMID:12232820

  19. Mechanical characterization of ultra-high molecular weight polyethylene-hydroxyapatite nanocomposites.

    PubMed

    Crowley, J; Chalivendra, V B

    2008-01-01

    An experimental study of Ultra-High Molecular Weight Polyethylene (UHMWPE) and hydroxyapatite (HAP) nanocomposites for the purpose of joint prosthesis is investigated under quasi-static and dynamic loading conditions. By employing compression mold process, five different volume fractions of hydroxyapatite nanoparticle reinforced nanocomposites are made. Quasi-static tension and compression tests are performed using ASTM test methods. Dynamic compression characterization is performed using split Hopkinson pressure bar technique. The nanocomposite performance as a function of volume fraction under a typical loading rate is investigated. The results of the fabricated nanocomposites are compared with currently employed UHMWPE in the joint implants. For comparison purposes, separate sets of tests are performed on currently employed UHMWPE. This comparison provides a valid measure to identify the optimum volume fraction of hydroxyapatite that can be used without compromising the integrity of the UHMPWPE in joint prosthesis. PMID:18725695

  20. Binding assay for low molecular weight analytes based on reflectometry of absorbing molecules in porous substrates.

    PubMed

    Stephan, Milena; Kramer, Corinna; Steinem, Claudia; Janshoff, Andreas

    2014-04-21

    Small molecule sensing is of great importance in pharmaceutical research. While there exist well established screening methods such as EMSA (electrophoretic motility shift assay) or biointeraction chromatography to report on successful binding interactions, there are only a few techniques that allow studying and quantifying the interaction of low molecular weight analytes with a binding partner directly. We report on a binding assay for small molecules based on the reflectivity change of a porous transparent film upon immobilisation of an absorbing substance on the pore walls. The porous matrix acts as a thin optical transparent film to produce interference fringes and accumulates molecules at the inner wall to amplify the sensor response. The benefits and limits of the assay are demonstrated by investigating the binding of biotin labelled with an atto dye to avidin physisorbed within an anodic aluminium oxide membrane. PMID:24599267

  1. Fluid-bicontinuous gels stabilized by interfacial colloids: low and high molecular weight fluids

    E-print Network

    P. S. Clegg

    2008-02-22

    Carefully tuned composite materials can have properties wholly unlike their separate constituents. We review the development of one example: colloid-stabilized emulsions with bicontinuous liquid domains. These non-equilibrium structures resemble the sponge mesophase of surfactants; however, in the colloid-stabilized case the interface separating the liquid domains is itself semi-solid. The arrangement of domains is created by arresting liquid-liquid phase separation via spinodal decomposition. Dispersed colloids exhibiting partial wettability become trapped on the newly created interface and jam together as the domains coarsen. Similar structures have been created in polymer blends stabilized using either interfacial nanoparticles or clay platelets. Here it has been possible to create the domain arrangement either by phase separation or by direct mixing of the melt. The low molecular-weight liquid and polymer based structures have been developed independently and much can be learnt by comparing the two.

  2. High-Flow, High-Molecular-Weight, Addition-Curing Polyimides

    NASA Technical Reports Server (NTRS)

    Chuang, Kathy C.; Vannucci, Raymond D.

    1993-01-01

    In developed series of high-flow PMR-type polyimide resins, 2, 2'-bis(trifluoromethyl)-4, 4'-diaminobiphenyl (BTDB) substituted for 1, 4-pheylenediamine in PMR-II formulation. Polyimides designated either as PMR-12F when nadic ester (NE) end caps used, or as V-CAP-12F when p-aminostyrene end caps used. High-molecular-weight, addition-curing polyimides based on BTBD and HFDE highly processable high-temperature matrix resins used to make composite materials with excellent retention of properties during long-term exposure to air at 650 degrees F or higher temperature. Furthermore, 12F addition-curing polyimides useful for electronic applications; fluorinated rigid-rod polyimides known to exhibit low thermal expansion coefficients as well as low absorption of moisture.

  3. Molecular weight: Property relationships of high performance polymers used for adhesives and composites

    NASA Technical Reports Server (NTRS)

    Kranbuehl, D.

    1975-01-01

    Degradation of high performance polyimide precursor resins was investigated by measuring the molecular weight of the polymers in solution, using a membrane osmometer. It was found that polyimide precursor resins composed of BTDA and ODPA combined with DABP and MDA were unstable in DMAC. The degradation rate was found to depend upon the chemical nature of the isomeric diamine and the geometric structure about the amide linkage. The polymers of DABP were less susceptible to degradation than those of MDA and p,p'-compounds were more stable than m,m'-compounds. These results suggest that degradation is correlated with the basicity of the diamine. That is, the rate of the degradation reaction increases with the basicity of the diamine group in the polyimide precursor resin. The presence of water and a higher temperature increased the degradation rate of the polymers.

  4. Friction, wear, transfer, and wear surface morphology of ultrahigh-molecular-weight polyethylene

    NASA Technical Reports Server (NTRS)

    Fusaro, R. L.

    1985-01-01

    Tribological studies at 25 C in a 50-percent-relative-humidity air atmosphere were conducted using hemispherically tipped 440 C HT (high temperature) stainless steel pins sliding against ultra-high-molecular-weight polyethylene (UHMWPE) disks. The results indicate that sliding speed, sliding distance, contact stress and specimen geometry can markedly affect friction, UHMWPE wear, UHMWPE transfer and the type of wear mechanisms that occur. Adhesion appears to be the predominant wear mechanism; but after long sliding distances at slow speeds, heavy ridges of transfer result which can induce fatigue-like wear on the UHMWPE disk wear track. In one instance, abrasive wear to the metallic pin was observed. This was caused by a hard particle embedded in the UHMWPE disk wear track.

  5. Friction, wear, transfer and wear surface morphology of ultra-high-molecular-weight polyethylene

    NASA Technical Reports Server (NTRS)

    Fusaro, R. L.

    1983-01-01

    Tribological studies at 25 C in a 50-percent-relative-humidity air atmosphere were conducted using hemispherically tipped 440 C HT (high temperature) stainless steel pins sliding against ultra-high-molecular-weight polyethylene (UHMWPE) disks. The results indicate that sliding speed, sliding distance, contact stress and specimen geometry can markedly affect friction, UHMWPE wear, UHMWPE transfer and the type of wear mechanisms that occur. Adhesion appears to be the predominant wear mechanism; but after long sliding distances at slow speeds, heavy ridges of transfer result which can induce fatigue-like wear on the UHMWPE disk wear track. In one instance, abrasive wear to the metallic pin was observed. This was caused by a hard particle embedded in the UHMWPE disk wear track.

  6. Effect of radiation sterilization and aging on ultrahigh molecular weight polyethylene

    SciTech Connect

    Roe, R.J.; Grood, E.S.; Shastri, R.; Gosselin, C.A.; Noyes, F.R.

    1981-03-01

    The mechanical properties of polyethylene components used in prosthesis are altered after fabrication by the sterilization procedure and by the environmental and mechanical aging which occurs after implantation. To assess the importance and extent of these alterations, ultrahigh molecular weight polyethylenes from two sources, Hercules 1900 and RCH 1000C, were subjected to gamma-ray irradiation and aging in serum and argon environments. Changes induced by these treatments in the structural and mechanical parameters have been determined by a variety of experimental techniques. The effect of irradiation is to introduce crosslinks and to increase the degree of crystallinity resulting in changes in the tensile properties in the direction of higher stiffness and reduced ductility. Aging for six months produced similar changes with subtle differences. The results suggest that the initially low degree of crystallinity which results from the sluggish mobility of the very long chain molecules offers the opportunity for significant changes in the properties during use in the long run.

  7. Recording of Surface Relief in Azobenzene Containing Low Molecular Weight Organic Glasses

    NASA Astrophysics Data System (ADS)

    Klismeta, K.; Teteris, J.

    2015-03-01

    One of the used methods to induce mass motion on the surface of azopolymer films is holographic recording using laser wavelength corresponding to the absorption band of the azo compound. The sinusoidal light interference pattern on the surface of the sample leads to a sinusoidal surface patterning – a stable surface relief grating (SRG). As confirmed by atomic force microscopy (AFM), these gratings are found to be very large, with depth up to hundreds of nanometres and they diffract light very efficiently. In this work azobenzene containing low molecular weight organic glass K-RJ-8 was experimentally studied. The compound absorbs at the visible spectrum, holographic recording in this range using different polarization states of the recording beams was done. Diffraction efficiency was measured during the recording of the SRG. The relationship between formation of SRG and photoinduced birefringence is discussed.

  8. Skin: Major target organ of allergic reactions to small molecular weight compounds

    SciTech Connect

    Merk, Hans F. [Department of Dermatology and Allergology, Univ.-Hospital, RWTH Aachen, Pauwelsstr. 30, D-52074 Aachen (Germany)], E-mail: hans.merk@post.rwth-aachen.de; Baron, Jens M.; Neis, Mark M.; Obrigkeit, Daniela Hoeller [Department of Dermatology and Allergology, Univ.-Hospital, RWTH Aachen, Pauwelsstr. 30, D-52074 Aachen (Germany); Karlberg, Ann-Therese [Dermatochemistry and Skin Allergy, Department of Chemistry, Goeteborg University, SE-412 96 Goeteborg (Sweden)

    2007-11-01

    Skin is a major target organ for allergic reactions to small molecular weight compounds. Drug allergic reactions may be life-threatening such as in the case of anaphylactic reactions or bullous drug reactions and occur in about 5% of all hospitalized patients. Allergic contact dermatitis has an enormous influence on the social life of the patient because it is the most frequent reason for occupational skin diseases and the treatment and prevention of this disease cost approximately Euro 3 billion per year in Germany. The different proposed pathophysiological pathways leading to a drug eruption are discussed in this paper. All major enzymes which are involved in the metabolism of xenobiotica were shown to be present in skin. Evidence supporting the role of metabolism in the development of drug allergy and allergic contact dermatitis is demonstrated in the example of sulphonamides and fragrances.

  9. Mesoscale simulation of the rheology of high molecular weight polymer gels

    NASA Astrophysics Data System (ADS)

    Sliozberg, Yelena; Brennan, John; Sirk, Timothy; Andzelm, Jan

    2011-03-01

    Polymer gels are comprised of physically or chemically cross-linked polymers that are highly swollen with solvent. The rheology of these gels depends on their morphological properties, such as the number of bridging chains and trapped entanglements. The prediction of structural and mechanical properties of gels using computational approaches is challenging and requires advanced particle-based mesoscale methodologies. Recently, we have implemented an approach to predict mechanical properties of high molecular weight block copolymers by allowing for chain entanglement behavior within the dissipative particle dynamics (DPD) methodology. Diffusion coefficients have been evaluated to locate the crossover from the Rouse to reptation dynamics. In this talk, we will demonstrate that including a segmental repulsive potential in addition to the usual DPD framework can prevent chain crossings and leads to an improved representation of mechanical and structural properties of polymer gels.

  10. Molecular Weight Distribution of Proteins Synthesized in Single, Identified Neurons of Aplysia

    PubMed Central

    Wilson, David L.

    1971-01-01

    Parietovisceral ganglia from Aplysia californica were incubated in medium containing leucine-3H. Single, identified nerve cell somas were isolated from the ganglia, and their proteins extracted and separated by electrophoresis on 5% SDS-polyacrylamide gels. The distribution of total or newly synthesized proteins from the single neurons was determined by staining or slicing and liquid scintillation counting of the gels. Experiments showed that: (a) a number of proteins were being synthesized in abundance in the nerve cells; (b) different, identified neurons showed reproducibly different labeling patterns in the gels; (c) cells R2 and R15, which showed different distributions of radioactivity in the gels, had similar staining patterns; and (d) there was significant incorporation into material of high (>75,000) molecular weight in most of the cells. PMID:4099509

  11. Characterization of low molecular weight organic acids from beech wood treated in supercritical water.

    PubMed

    Yoshida, Kei; Kusaki, Junko; Ehara, Katsunobu; Saka, Shiro

    2005-01-01

    Japanese beech (Fagus crenata Blume), its cell wall components, and model compounds were treated by supercritical water (380 degrees C, 100 MPa) for 5 s using a batch-type reactor to investigate the production behavior of low molecular weight organic acids. It was found that cellulose and hemicellulose were decomposed to formic acid, pyruvic acid, glycolic acid, acetic acid, and lactic acid, whereas lignin was barely decomposed to such organic acids under the given conditions. However, after prolonged treatment (380 degrees C, 100 MPa, 4 min) of lignin, some organic acids were recovered owing perhaps to the decomposition of the propyl side chain of lignin. It was additionally revealed that the predominant organic acid recovered was acetic acid, which might be derived from the acetyl group of hemicellulose in Japanese beech. PMID:15930559

  12. Low molecular weight carbohydrates in pine nuts from Pinus pinea L.

    PubMed

    Ruiz-Aceituno, L; Ramos, L; Martinez-Castro, I; Sanz, M L

    2012-05-16

    Low molecular weight carbohydrates in pine nuts from Pinus pinea L. (n = 7) have been studied by gas chromatography-mass spectrometry as their trimethylsilyl oximes. Besides previously reported components, such as glucose, fructose, sucrose, and raffinose, several soluble carbohydrates have been identified for the first time in this product, including saccharides (galactose, maltose, and planteose) and cyclitols (pinitol, galactinol, galactopinitol A1, fagopyritol B1, and other glycosyl-inositols). Most abundant cyclitols were chiro-inositol, fagopyritol B1, and pinitol, with concentrations ranging from 126.7 to 222.1 mg (100 g)(-1), 94.2 to 177.1 mg (100 g)(-1), and 51.2 to 282.8 mg (100 g)(-1), respectively. PMID:22533651

  13. The Potency of Hyaluronan of Different Molecular Weights in the Stimulation of Blood Phagocytes

    PubMed Central

    Safrankova, Barbora; Gajdova, Silvie; Kubala, Lukas

    2010-01-01

    The regulatory functions of glycosaminoglycan hyaluronan (HA) are suggested to be dependent on its molecular weight (MW). Proinflammatory and stimulatory effects are proposed mainly for the low MW HA. However, the complex response of blood phagocytes to HA of different MW is unclear. Herein, the effects of highly purified HA of precisely defined MW (52, 250, and 970?kDa) on human blood phagocytes were tested. All MW HA activated blood phagocytes, including the spontaneous production of ROS, degranulation, and the production of tumor necrosis factor alpha, with low MW HA 52?kDa having the highest potency and high MW HA 970?kDa having the lowest potency. Interestingly, HA inhibited ROS production stimulated by opsonized zymosan particles and, in contrast, potentiated starch-activated ROS production, mostly independent of MW. Data showed a significant effect of HA of different MW on blood phagocytes, including high MW HA. PMID:21403830

  14. Surface structure of nascent particles of ultrahigh molecular weight poly(ethylene) reactor powders

    NASA Astrophysics Data System (ADS)

    Lebedev, D. V.; Ivan'kova, E. M.; Marikhin, V. A.; Myasnikova, L. P.; Seydewitz, V.

    2009-08-01

    A comparative investigation of the surface structure of three ultrahigh molecular weight poly(eth-ylene) (UHMWPE) reactor powders that differ by their ability to be processed to high-performance fibers is carried out with a JEOL 6300 scanning electron microscope and a nanoluminograph, which makes it possible to study thermoluminescence of ultrathin near-surface layers of solids. The activation energies of relaxation processes in near-surface layers of nascent particles and the sizes of kinetic units of motion, for which the mobility is defrozen in the temperature range of the corresponding transitions, are calculated from the glow curves. The possible location of kinetic units in supermolecular formations resolved in micrographs and their influence on the dissolution of the reactor powder are discussed.

  15. Surface free energy of ultra-high molecular weight polyethylene modified by electron and gamma irradiation

    NASA Astrophysics Data System (ADS)

    Abdul-Kader, A. M.; Turos, A.; Radwan, R. M.; Kelany, A. M.

    2009-06-01

    Surface free energy of biocompatible polymers is important factor which affects the surface properties such as wetting, adhesion and biocompatibility. In the present work, the change in the surface free energy of ultra-high molecular weight polyethylene (UHMWPE) samples, which is produced by electron beam and gamma ray irradiation were, investigated. Mechanism of the changes in surface free energy induced by irradiations of doses ranging from 25 to 500 kGy was studied. FTIR technique was applied for sample analysis. Contact angle measurements showed that wettability and surface free energy of samples have increased with increasing the irradiation dose, where the values of droplet contact angle of the samples decrease gradually with increasing the radiation dose. The increase in the wettability and surface free energy of the irradiated samples are attributed to formation of hydrophilic groups on the polymer surface by the oxidation, which apparently occurs by exposure of irradiated samples to the air.

  16. Surface modification of ultra high molecular weight polyethylene fibers via the sequential photoinduced graft polymerization

    NASA Astrophysics Data System (ADS)

    Li, Zhi; Zhang, Wei; Wang, Xinwei; Mai, Yongyi; Zhang, Yumei

    2011-06-01

    In this study, a sequential photoinduced graft polymerization process was proposed to improve the poor interfacial bonding property of ultra high molecular weight polyethylene (UHMWPE) fibers. The polymerization was initiated by dormant semipinacol (SP) groups and carried out in a thin liquid layer. Methacrylic acid (MAA) and acryl amide (AM) were grafted stepwise onto the surface of UHMWPE fibers. Attenuated total reflectance infrared spectroscopy (ATR-IR) and thermo gravimetric analysis (TGA) confirmed the grafting. The analysis result of pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) indicated the structure of grafted chains. Scanning electron microscopy (SEM) images and atomic force microscopy (AFM) images revealed the apparent morphology changing, and the grafted layers were observed. Interfacial shear stress (IFSS) test of the modified fibers showed an extensively improved interfacial bonding property. The active groups grafted onto the fibers would supply enough anchor points for the chemical bonding with various resins or further reactions.

  17. Effect of soil sieving on respiration induced by low-molecular-weight substrates

    NASA Astrophysics Data System (ADS)

    Datta, Rahul; Vranová, Valerie; Pavelka, Marian; Rejšek, Klement; Formánek, Pavel

    2014-03-01

    The mesh size of sieves has a significant impact upon soil disturbance, affecting pore structure, fungal hyphae, proportion of fungi to bacteria, and organic matter fractions. The effects are dependent upon soil type and plant coverage. Sieving through a 2 mm mesh increases mineralization of exogenously supplied carbohydrates and phenolics compared to a 5 mm mesh and the effect is significant (p<0.05), especially in organic horizons, due to increased microbial metabolism and alteration of other soil properties. Finer mesh size particularly increases arabinose, mannose, galactose, ferulic and pthalic acid metabolism, whereas maltose mineralization is less affected. Sieving through a 5 mm mesh size is suggested for all type of experiments where enhanced mineralization of low-molecular-weight organic compounds needs to be minimalized.

  18. [Galactosylated derivatives of low-molecular-weight chitosan: production and properties].

    PubMed

    Il'ina, A V; Varlamov, V P

    2007-01-01

    Chitosan, a binary heteropolysaccharide consisting of 2-acetamide-2-deoxy-beta-D-glucopyranose and 2-amino-2-deoxy-beta-D-glucopyranose residues linked in different proportions via beta-glycosidic bonds. The presence of a primary amino group in the chitosan structure allows for the synthesis of various derivatives. The procedure of obtaining activated N-hydroxysuccinimide esters with the use of lactobionic acid was applied to obtain galactosylated derivatives of low-molecular-weight chitosan with a substitution degree varying from 8 to 23%. The properties of these derivatives (viscosity, solubility, and biodegradability) were studied. These derivatives are well soluble at pH values greater than the acidity constant of amino groups of chitosan (6.5). Broadening the pH range towards increase and the presence of galactose residues allows these derivatives to be used in working with biological objects. PMID:17345864

  19. Organic molecules in the atmosphere of Jupiter. [low molecular weight hydrocarbons

    NASA Technical Reports Server (NTRS)

    Ponnamperuma, C. A.

    1978-01-01

    Organic synthesis in the primitive solar system was simulated by Fischer Tropsch type experiments. Particular attention was given to the formation of lower molecular weight hydrocarbons. In a gas flow experiment, a gas mixture of H2 and CO was introduced into a heated reaction tube at a constant flow rate and passed through a catalyst (powdered Canyon Diablo). The products that emerged were directly analyzed by gas chromatography. The results of 21 runs under various gas mixing rations, reaction temperatures, and gas-catalyst contact times showed the predominance of the saturated hydrocarbon formation at C sub 4 and C sub 5 over the unsaturated ones. Saturate/unsaturate ratios were mostly less than 0.4 and none showed over 0.7.

  20. Immune-enhancing activities of low molecular weight ?-glucan depolymerized by gamma irradiation

    NASA Astrophysics Data System (ADS)

    Sung, Nak-Yun; Byun, Eui-Hong; Kwon, Sun-Kyu; Song, Beom-Seok; Choi, Jong-il; Kim, Jae-Hun; Byun, Myung-Woo; Yoo, Young-Choon; Kim, Mee-Ree; Lee, Ju-Woon

    2009-07-01

    ?-glucans are structural cell wall polymers of many microorganisms and cereals which possess immunomodulatory properties and have been used in the food, cosmetic and medical industry. In our previous study, ?-glucan was depolymerized by gamma irradiation and leads to improve the solubility and viscosity. This study was carried out to evaluate the functional properties, mainly immune-enhancing activities of low molecular weight ?-glucan fragmented by gamma irradiation. The results showed that RAW 264.7 macrophage cell stimulation activities of irradiated ?-glucan were higher than that of non-irradiated ?-glucan. In addition, the oral administration of gamma-irradiated ?-glucan significantly increased the proliferation and cytokine (IFN-? and IL-2) release of spleen and Peyer's patch cells compared with non-irradiated ?-glucan. In conclusion, gamma irradiation could be used as an effective method for the production of depolymerized ?-glucan improved functional property such as immunomodulatory activity.