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1

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...

2

Rapid and accurate method for estimating molecular weights of organic compounds from low resolution mass spectra  

Microsoft Academic Search

An improved method of estimating molecular weights of volatile organic compounds from their mass spectra has been developed and evaluated for accuracy. This technique can be implemented with a user friendly expert system on a personal computer. The method is based on a pattern recognition based classifier and empirically derived rules from a set of toxic and related organic compounds.

D Scott

1992-01-01

3

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).

2013-06-17

4

Using Second-derivative Filters to Assist in Width Estimations of Size Exclusion Chromatography Signal Peaks with Static Light-scattering Detections to Obtain More Accurate Molecular Weight.  

PubMed

Static light-scattering (LS) detection can determine the molecular weight (MW) of polymers eluted with size-exclusion chromatography (SEC) without using any standards when the differential refraction index (RI) of solutes are obtained. On the other hand, the noisy chromatographic signal peak acquired using a static LS detector often causes difficulty in peak-width recognition. This disadvantage limits the determination accuracy and precision of the MW values. This study developed one second-order derivative filtering procedure by convolving the original LS chromatogram against the second-derivative curve of one artificial Gaussian-shape chromatographic peak to suppress the noises and to correct the baseline of the chromatogram. More accurate estimations of the chromatographic peak widths of pullulan samples were achieved to improve the MW determination accuracy. For noisy original chromatography peaks of pullulan 5 k (SNR of approximately 10), the non-ideal determination accuracy of the MW values (9.3%) is improved to -1.3% with the assistance of the filtering procedures. PMID:25382042

Chen, Po-Ting; Chen, Hsiao-Ping; Hung, Chia-Hung; Wang, Shau-Chun

2014-01-01

5

Molecular Weight and Molecular Weight Distributions in Synthetic Polymers.  

ERIC Educational Resources Information Center

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…

Ward, Thomas Carl

1981-01-01

6

Apparatus for molecular weight separation  

DOEpatents

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).

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

2001-01-01

7

Molecular Weight & Energy Transport 7 September 2011  

E-print Network

't transport the bulk of the energy in the sun. #12;Molecular Weight & Energy Transport 7 September 2011 Goals · Review mean molecular weight this intuitively before looking back at your quantitative results. #12;molecular weight & energy transport 2 Energy

Militzer, Burkhard

8

Molecular Weight & Energy Transport 7 September 2011  

E-print Network

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

Militzer, Burkhard

9

Ultradrawing gel films of blends of ultrahigh molecular weight polyethylene and low molecular weight polyethylenes with different molecular weights  

Microsoft Academic Search

The ultradrawing behavior of five series of gel films prepared from the blends of one ultrahigh molecular weight polyethylene (UHMWPE) and five other low molecular weight polyethylene (LMWPE) resins with varying molecular weight is reported. The critical draw ratio (?c) of each of the five UHMWPE\\/LMWPE gel film series were found to depend significantly upon the amount of LMWPE present

Jen-Taut Yeh; Sheng-Shang Chang

2000-01-01

10

Ultrahigh molecular weight aromatic siloxane polymers  

NASA Technical Reports Server (NTRS)

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.

Ludwick, L. M.

1982-01-01

11

Whale High-Molecular-Weight and Low-Molecular-Weight Kininogens  

Microsoft Academic Search

The expression of high-molecular-weight and low-molecular-weight kininogen mRNAs in the whale liver was examined by reverse transcription-polymerase chain reaction. The nucleotide sequences of the high-molecular-weight and low-molecular-weight kininogen cDNAs were analyzed and deduced to the amino acid sequences. The high-molecular-weight kininogen composed of 609 amino acid residues with 18 signal peptides possessed the consensus sequences of the cysteine protease inhibitor

Umeko Semba; Yoko Shibuya; Hiroaki Okabe; Izumi Hayashi; Tetsuro Yamamoto

2000-01-01

12

Mechanical properties of mammalian and fish gelatins based on their weight average molecular weight and molecular weight distribution  

Microsoft Academic Search

Acid porcine skin gelatins (type A), lime bone gelatins (type B) and gelatin from different cold water fish species were compared on the basis of low deformation mechanical properties, Bloom value, weight average molecular weight, molecular weight distribution and isoelectric point. The dynamic storage modulus and Bloom value for all types of gelatin increased with increasing weight average molecular weight.

Jonhard Eysturskarð; Ingvild J. Haug; Ann-Sissel Ulset; Kurt I. Draget

2009-01-01

13

Production of high molecular weight polylactic acid  

SciTech Connect

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.

Bonsignore, Patrick V. (Joilet, IL)

1995-01-01

14

Production of high molecular weight polylactic acid  

DOEpatents

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.

Bonsignore, P.V.

1995-11-28

15

Power ENO methods: A fth order accurate Weighted Power ENO method  

E-print Network

Power ENO methods: A #12;fth order accurate Weighted Power ENO method Susana Serna University@uv.es December 2, 2002 Abstract In this paper we introduce a new class of ENO reconstruction pro- cedures, the Power ENO methods, to design high order accurate shock capturing methods for hyperbolic conservation

Soatto, Stefano

16

Accurate Evaluation Method of Molecular Binding Affinity from Fluctuation Frequency  

NASA Astrophysics Data System (ADS)

Exact estimation of the molecular binding affinity is significantly important for drug discovery. The energy calculation is a direct method to compute the strength of the interaction between two molecules. This energetic approach is, however, not accurate enough to evaluate a slight difference in binding affinity when distinguishing a prospective substance from dozens of candidates for medicine. Hence more accurate estimation of drug efficacy in a computer is currently demanded. Previously we proposed a concept of estimating molecular binding affinity, focusing on the fluctuation at an interface between two molecules. The aim of this paper is to demonstrate the compatibility between the proposed computational technique and experimental measurements, through several examples for computer simulations of an association of human immunodeficiency virus type-1 (HIV-1) protease and its inhibitor (an example for a drug-enzyme binding), a complexation of an antigen and its antibody (an example for a protein-protein binding), and a combination of estrogen receptor and its ligand chemicals (an example for a ligand-receptor binding). The proposed affinity estimation has proven to be a promising technique in the advanced stage of the discovery and the design of drugs.

Hoshino, Tyuji; Iwamoto, Koji; Ode, Hirotaka; Ohdomari, Iwao

2008-05-01

17

Biodegradation of high molecular weight polylactic acid  

NASA Astrophysics Data System (ADS)

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.

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

2012-07-01

18

Effects of Multiple Pulping Variables on the Molecular Weight and Molecular Weight Distribution of Kraft Lignin  

Microsoft Academic Search

The effects of pulping variables on the molecular weight and molecular weight distribution of dissolved lignin have been studied. Kraft lignins were prepared by cooking Slash pine (Pinus caribaea) wood chips in a pilot-scale batch circulation digester. Four pulping variables, effective alkali, sulfidity, cooking temperature, and time-at-temperature. were arranged in a very broad input space under a central composite experimental

Daojie Dong; Arthur L. Fricke

1995-01-01

19

Ultrahigh Molecular Weight Aromatic Siloxane Polymers  

NASA Technical Reports Server (NTRS)

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.

Ludwick, L. M.

1983-01-01

20

Towards Accurate Molecular Modeling of Plastic Bonded Explosives  

NASA Astrophysics Data System (ADS)

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.

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

2010-03-01

21

Accurate Measurement of Body Weight and Food Intake in Environmentally Enriched Male Wistar Rats  

Microsoft Academic Search

Laboratory animals are crucial in the study of energy homeostasis. In particular, rats are used to study alterations in food intake and body weight. To accurately record food intake or energy expenditure it is necessary to house rats individually, which can be stressful for social animals. Environmental enrichment may reduce stress and improve welfare in laboratory rodents. However, the effect

Kylie E. L. Beale; Kevin G. Murphy; Eleanor K. Harrison; Angela J. Kerton; Mohammad A. Ghatei; Stephen R. Bloom; Kirsty L. Smith

2011-01-01

22

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

E-print Network

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

Pezolet, Michel

23

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

NASA Technical Reports Server (NTRS)

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.

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

1989-01-01

24

Insight into hyaluronic acid molecular weight control.  

PubMed

Hyaluronic acid (HA) is a ubiquitous polysaccharide found in humans, animals, bacteria, algae and molluscs. Simple yet sophisticated, HA demonstrates unique and valuable rheological properties. In solution, HA behaves as a stiffened random coil and the resultant behaviour, even at low concentrations, is far from Newtonian or 'ideal'. These rheological properties are heavily influenced by molecular weight (MW), so it is not surprising that many of the biological functions of HA are dependent on molecular size. The current billion dollar market for HA continues to grow rapidly, both in gross production and the number of applications for its use. Increasing demand, in conjunction with a reticence to use animal-derived HA, has revitalised the market for HA produced by bacterial fermentation. Although the genes and pathways involved in bacterial production of HA are well characterised, the mechanisms that underlie HA MW control are less well understood. By performing a thorough analysis of the proposed mechanisms of MW control in bacterial fermentation, this mini-review tries to elucidate the challenges and future directions for bacterial HA biosynthesis. PMID:24957250

Marcellin, Esteban; Steen, Jennifer A; Nielsen, Lars K

2014-08-01

25

Low molecular weight heparins and heparinoids.  

PubMed

Several low molecular weight (LMW) heparin preparations, including dalteparin, enoxaparin and nadroparin, as well as the heparinoid danaparoid sodium, are approved for use in Australia. LMW heparins are replacing unfractionated heparin for the prevention and treatment of venous thromboembolism and the treatment of non-ST-segment-elevation acute coronary syndromes. The advantages of LMW heparins over unfractionated heparin include a longer half-life (allowing once-daily or twice-daily subcutaneous dosing), high bioavailability and predictable anticoagulant response (avoiding the need for dose adjustment or laboratory monitoring in most patients), and a low risk of heparin-induced thrombocytopenia and osteoporosis. Laboratory monitoring of LMW heparin therapy should be considered in newborns and children, patients with renal impairment, those who are pregnant, and those at the extremes of bodyweight (eg, < 40 kg or > 100 kg). LMW heparins should: be avoided or used with caution in patients undergoing neuraxial anaesthesia, owing to the potential for epidural haematoma formation; not be used (ie, are contraindicated) in patients with immune heparin-induced thrombocytopenia, as they may cross-react with anti-heparin antibodies. Conventional unfractionated heparin retains a role in the management of patients at high risk of bleeding, undergoing invasive procedures, and patients with renal failure owing to its shorter half-life, reversibility with protamine sulfate, and extrarenal metabolism. The heparinoid danaparoid sodium is effective for the treatment of heparin-induced thrombocytopenia. PMID:12358583

Eikelboom, John W; Hankey, Graeme J

2002-10-01

26

New molecular weight forms of arabinogalactan from Larix occidentalis  

Microsoft Academic Search

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

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

1997-01-01

27

Towards Accurate Molecular Modeling of Plastic Bonded Explosives  

Microsoft Academic Search

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

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

2010-01-01

28

Power ENO methods: a fifth-order accurate Weighted Power ENO method  

NASA Astrophysics Data System (ADS)

In this paper we introduce a new class of ENO reconstruction procedures, the Power ENO methods, to design high-order accurate shock capturing methods for hyperbolic conservation laws, based on an extended class of limiters, improving the behavior near discontinuities with respect to the classical ENO methods. Power ENO methods are defined as a correction of classical ENO methods [J. Comput. Phys. 71 (1987) 231], by applying the new limiters on second-order differences or higher. The new class of limiters includes as a particular case the minmod limiter and the harmonic limiter used for the design of the PHM methods [see SIAM J. Sci. Comput. 15 (1994) 892]. The main features of these new ENO methods are the substantially reduced smearing near discontinuities and the good resolution of corners and local extrema. We design a new fifth-order accurate Weighted Power ENO method that improves the behavior of Jiang-Shu WENO5 [J. Comput. Phys. 126 (1996) 202]. We present several one- and two-dimensional numerical experiments for scalar and systems of conservation laws, including linear advections and one- and two-dimensional Riemann problems for the Euler equations of gas dynamics, comparing our methods with the classical and weighted ENO methods, showing the advantages and disadvantages.

Serna, Susana; Marquina, Antonio

2004-03-01

29

Molecular weight of aquatic fulvic acids by vapor pressure osmometry  

USGS Publications Warehouse

The molecular weights of aquatic fulvic acids extracted from five rivers were determined by vapor pressure osmometry with water and tetrahydrofuran as solvents. The values obtained ranged from 500 to 950 dallons, indicating that the molecular weights of aquatic fulvic acids are not as great as has been suggested in some other molecular weight studies. The samples were shown to be relatively monodisperse from radii of gyration measurements determined by small angle x-ray scattering. THF affords greater precision and accuracy than H2O in VPO measurements, and was found to be a suitable solvent for the determination of molecular weight of aquatic fulvic acid because it obviates the dissociation problem. An inverse correlation was observed with these samples between the concentration of Ca++ and Mg++ in the river water and the radii of gyration and molecular weights of the corresponding fulvic acid samples. ?? 1987.

Aiken, G.R.; Malcolm, R.L.

1987-01-01

30

The low-molecular-weight glutenin subunits of wheat gluten  

Microsoft Academic Search

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

Renato D'Ovidio; Stefania Masci

2004-01-01

31

Delayed hypersensitivity to one low-molecular-weight heparin with tolerance of other low-molecular-weight heparins.  

PubMed

We report a patient who developed infiltrated plaques at the sites of subcutaneous injection of a low-molecular-weight heparin. Skin tests and a lymphocyte transformation test revealed hypersensitivity to sandoparin and heparin sodium. The low-molecular-weight heparins nadroparin and dalteparin were subsequently tolerated without adverse effects. Possible risk factors for sensitization are discussed. PMID:7718467

Bircher, A J; Itin, P H; Tsakiris, D A; Surber, C

1995-03-01

32

Molecular Weight Dependence of the Viscosity of Polyethylene Macrocycles  

NASA Astrophysics Data System (ADS)

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.

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

2005-03-01

33

Low molecular weight IgM in primary biliary cirrhosis.  

PubMed Central

Low molecular weight IgM is the monomeric subunit of pentameric IgM and is not generally found in the blood of healthy individuals. Using a sensitive immunoblotting technique, low molecular weight IgM was detected in all 17 patients with primary biliary cirrhosis and constituted up to 5% of the total circulating IgM. This low molecular weight IgM moiety correlated significantly with total IgM (p less than 0.01) but not with the specific biliary cirrhosis mitochondrial autoantibody anti-M2. Furthermore it was not possible to show that a partially purified sample of low molecular weight IgM contained M2 binding activity. Mitogen stimulated peripheral blood mononuclear cells from two of four patients were observed to secrete low molecular weight IgM in vitro, a finding seen in only one of six healthy subjects. Immunoblot analysis of patients sera revealed the presence of other oligomers of IgM in addition to low molecular weight IgM. In conclusion this study suggests that during the enhanced IgM synthesis observed in primary biliary cirrhosis a defect occurs in the assembly of the IgM pentamer with release of monomeric and oligomeric IgM into the circulation. The pathogenic significance of these circulating low molecular weight IgM species is unknown. Images Figure 1 PMID:2318435

Roberts-Thomson, P J; Shepherd, K

1990-01-01

34

Free volume model for molecular weights of polymers  

NASA Technical Reports Server (NTRS)

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.

Singh, J. J.; Eftekhari, A.

1992-01-01

35

Free volume model for molecular weights of polymers  

NASA Astrophysics Data System (ADS)

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.

Singh, J. J.; Eftekhari, A.

1992-03-01

36

A Weight-Averaged Interpolation Method for Coupling Time-Accurate Rarefied and Continuum Flows  

NASA Astrophysics Data System (ADS)

A novel approach to coupling rarefied and continuum flow regimes as a single, hybrid model is introduced. The method borrows from techniques used in the simulation of spray flows to interpolate Lagrangian point-particles onto an Eulerian grid in a weight-averaged sense. A brief overview of traditional methods for modeling both rarefied and continuum domains is given, and a review of the literature regarding rarefied/continuum flow coupling is presented. Details of the theoretical development of the method of weighted interpolation are then described. The method evaluates macroscopic properties at the nodes of a CFD grid via the weighted interpolation of all simulated molecules in a set surrounding the node. The weight factor applied to each simulated molecule is the inverse of the linear distance between it and the given node. During development, the method was applied to several preliminary cases, including supersonic flow over an airfoil, subsonic flow over tandem airfoils, and supersonic flow over a backward facing step; all at low Knudsen numbers. The main thrust of the research centered on the time-accurate expansion of a rocket plume into a near-vacuum. The method proves flexible enough to be used with various flow solvers, demonstrated by the use of Fluent as the continuum solver for the preliminary cases and a NASA-developed Large Eddy Simulation research code, WRLES, for the full lunar model. The method is applicable to a wide range of Mach numbers and is completely grid independent, allowing the rarefied and continuum solvers to be optimized for their respective domains without consideration of the other. The work presented demonstrates the validity, and flexibility of the method of weighted interpolation as a novel concept in the field of hybrid flow coupling. The method marks a significant divergence from current practices in the coupling of rarefied and continuum flow domains and offers a kernel on which to base an ongoing field of research. It has the potential to significantly increase the flexibility of hybrid rarefied/continuum flow analyses.

Diaz, Steven William

37

Trends and inferred emissions of atmospheric high molecular weight perfluorocarbons  

E-print Network

Atmospheric observations and atmospheric observation-based global emission estimates are presented for the five high molecular weight perfluorocarbons (PFCs): decafluorobutane (C 4 F 1 0 ), dodecafluoropentane (C5 F1 2 ), ...

Ivy, Diane Jean

2012-01-01

38

Optimization of parameters for coverage of low molecular weight proteins  

E-print Network

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 ...

Muller, Stephan A.

39

Biosynthesis of low molecular weight (7S) and high molecular weight (19S) immunoglobulin M  

PubMed Central

The class of immunoglobulin M (IgM) characterized by high molecular weight proteins with a sedimentation coefficient of 19S, includes a smaller molecular form with an S20,[unk] of approximately 7. The synthetic origin of the 7S IgM was investigated by biosynthetic studies on bone marrow cells from three patients with macroglobulinemia whose sera contained 7S IgM and 19S IgM. Labeled 7S IgM and 19S IgM were identified in extracellular culture fluids by radioimmunochemical techniques. The separation of the two molecular forms of IgM by density-gradient ultracentrifugation of the culture fluids before radioimmunochemical analyses permitted the identification of both the labeled 7S IgM and 19S IgM. One patient's serum contained two separate and distinct 19S IgM proteins as well as 7S IgM. The use of specific isolated carrier IgM proteins permitted the radioimmunochemical detection of labeled 7S IgM and both 19S IgM proteins. The introduction of cycloheximide into a culture system effects the cessation of protein synthesis. The analyses of culture fluids harvested at timed intervals after the addition of cycloheximide revealed not only the stability of 19S IgM to intracellular proteolysis, but also provided evidence for a possible precursor-product relationship between the 7S IgM and the 19S IgM. The demonstration that the labeled 7S IgM is neither an in vitro breakdown product of 19S IgM nor a resultant of 19S IgM intracellular catabolism substantiated the synthetic origin of 7S IgM in human sera. Images PMID:4982899

Solomon, Alan; McLaughlin, Carla L.

1970-01-01

40

Molecular weight induced peak doubling in liquid chromatography  

E-print Network

of certain blocked high-molecular weight amino acids and peptides on silica gel using high pressure liquid chromatography with an isopropanol-methylene chloride solvent system. The peak doubling appears to be a combination of molecular weight... considerations and protic solvent interactions within the system, and can be prevented by the use of aprotic solvent systems such as acetonitrile-methylene chloride or toluene-ethyl acetate. iv DEDICATION This work is dedicated to Dr. Sherrel C. Smith, whose...

Fickling, John Mebane

2012-06-07

41

Molecular-Weight-Controlled, End-Capped Polybenzimidazoles  

NASA Technical Reports Server (NTRS)

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.

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

1993-01-01

42

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

SciTech Connect

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.

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

2009-08-26

43

Identification of the High Molecular Weight Isoform of Phostensin  

PubMed Central

Phostensin is encoded by KIAA1949. 5?-RACEanalysis has been used to identify the translation start site of phostensin mRNA, indicating that it encodes 165 amino acids with an apparent molecular weight of 26 kDa on SDS-PAGE. This low-molecular-weight phostensin is present in human peripheral blood mononuclear cells and many leukemic cell lines. Phostensin is a protein phosphatase-1(PP1) binding protein. It also contains one actin-binding motif at its C-terminal region and binds to the pointed ends of actin filaments, modulating actin dynamics. In the current study, a high-molecular-weight phostensin is identified by using immunoprecipitationin combination with a proteomic approach. This new species of phostensin is also encoded by KIAA1949 and consists of 613 amino acids with an apparent molecular weight of 110 kDa on SDS-PAGE. The low-molecular-weight and high-molecular-weight phostensins were named as phostensin-? and phostensin-?, respectively. Although phostensin-? is the C-terminal region of phostensin-?, it is not degraded from phostensin-?. Phostensin-? is capable of associating with PP1 and actin filaments, and is present in many cell lines. PMID:24434620

Lin, Yu-Shan; Huang, Hsien-Lu; Liu, Wei-Ting; Lin, Ta-Hsien; Huang, Hsien-Bin

2014-01-01

44

Evaluation of a Viscosity-Molecular Weight Relationship.  

ERIC Educational Resources Information Center

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…

Mathias, Lon J.

1983-01-01

45

Effect of Weight Loss on High-Molecular Weight Adiponectin in Obese Children  

Microsoft Academic Search

Our aim was to determine the influence of weight reduction on total (T-) and high-molecular weight (HMW-) adiponectin in obese (OB) prepubertal children. Seventy OB prepubertal white patients were followed for 18 months and studied after reducing their BMI by 1 (n = 51) and 2 standard deviation scores (SDS) (n = 21) under conservative treatment, and 6 months after

Gabriel Á. Martos-Moreno; Vicente Barrios; Guillermo Martínez; Federico Hawkins; Jesús Argente

2010-01-01

46

Utilization of low-molecular-weight heparin prophylaxis in pediatric and adolescent trauma patients.  

PubMed

The objective of this study was to use trauma registry data to describe the number and characteristics of patients 21 years or younger receiving thromboprophylaxis with low-molecular-weight heparin at 2 pediatric and 2 adult level 1 trauma centers. Among 706 patients, the average age was 18.5 years, and 94.6% were hospitalized at adult centers. The most common injuries were lower extremity fractures (35.6%) and head injuries (20.4%). Major bleeding was reported in 3 patients (0.4%), and thrombotic events were reported in 15 patients (2.1%). Despite a lack of scientific evidence, low-molecular-weight heparin prophylaxis is being used in young trauma patients (primarily those 14 years or older). Prospective multicenter studies are needed to accurately describe the risks and benefits of low-molecular-weight heparin prophylaxis in young trauma patients, thereby identifying those who truly benefit from this intervention. PMID:22673081

O'Brien, Sarah H; Klima, Jennifer; Gaines, Barbara A; Betz, Sally; Zenati, Mazen S

2012-01-01

47

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

PubMed

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

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

2014-01-01

48

Microbial detection with low molecular weight RNA  

NASA Technical Reports Server (NTRS)

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%.

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

2001-01-01

49

Polyarginine Molecular Weight Determines Transfection Efficiency of Calcium Condensed Complexes  

PubMed Central

Cell penetrating peptides (CPPs) have been extensively studied in polyelectrolyte complexes as a means to enhance the transfection efficiency of plasmid DNA (pDNA). Increasing the molecular weight of CPPs often enhances gene expression, but poses a risk of increased cytotoxicity and immunogenicity compared to low molecular weight CCPs. Conversely, low molecular weight CPPs typically have low transfection efficiency due to large complex size. Complexes made using low molecular weight CPPs were found to be condensed to a small size by adding calcium. In this study, complexes of low molecular weight polyarginine and pDNA were condensed with calcium. These complexes showed high transfection efficiency and low cytotoxicity in A549 carcinomic human alveolar basal epithelial cells. The relationship between transfection efficiency and polyarginine size (5, 7, 9 or 11 amino acids), polyarginine/pDNA charge ratios, and calcium concentrations were studied. Polyarginine 7 was significantly more effective than other polyarginines under most formulation conditions suggesting a link between cell penetration ability and transfection efficiency. PMID:23534410

Alhakamy, Nabil A.; Berkland, Cory J.

2014-01-01

50

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

USGS Publications Warehouse

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.

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

1994-01-01

51

Molecular weight dependent bimolecular recombination in organic solar cells  

NASA Astrophysics Data System (ADS)

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.

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

2014-08-01

52

Molecular weight dependent bimolecular recombination in organic solar cells.  

PubMed

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

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

2014-08-01

53

Scedosporium and Pseudallescheria low molecular weight metabolites revealed by database search.  

PubMed

The potential of mMass software search tool with new compound libraries was demonstrated on metabolomics of Scedosporium prolificans, S. apiospermum and Pseudallescheria boydii sensu stricto. Cyclic peptides pseudacyclins, small molecular weight tyroscherin analogues and various lipids were annotated by public software tool (http://www.mmass.org) utilising accurate matrix-assisted laser desorption/ionisation mass spectral data of intact fungal spores. Electrospray ionisation combined with tandem mass spectrometry was used for monohexosylceramide characterisation in fungal extracts. PMID:21995661

Krasny, Lukas; Strohalm, Martin; Bouchara, Jean-Philippe; Sulc, Miroslav; Lemr, Karel; Barreto-Bergter, Eliana; Havlicek, Vladimir

2011-10-01

54

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

E-print Network

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

Weston, Ken

55

Study on antimicrobial activity of chitosan with different molecular weights  

Microsoft Academic Search

E. coli and Staphylococcus aureus are used to study the antimicrobial activity of chitosan of different molecular weights (MW). The effect of the concentration and MW of chitosan were investigated, respectively, and the antimicrobial mechanism was discussed. For chitosan with MW below 300 kDa, the antimicrobial effect on S. aureus was strengthened as the MW increased. In contrast, the effect

Lian-Ying Zheng; Jiang-Feng Zhu

2003-01-01

56

Standardisation of unfractionated and low-molecular-weight heparin.  

PubMed

Unfractionated and low-molecular-weight heparins are complex biologicals. Standardisation and global harmonisation of units and methods of measurement are essential for safety and efficacy of this important class of anticoagulants. This chapter describes the traceability of the international unit and current status of the relationship between the international and pharmacopoeial standards, together with a review on current pharmacopoeial assay methods. PMID:22566221

Gray, Elaine

2012-01-01

57

Perioperative low molecular weight heparin for infrageniculate bypass  

Microsoft Academic Search

Purpose: Recent studies suggest that subcutaneous low molecular weight heparin (LMWH) is a safe, effective alternative to intravenous heparin (IVH) for deep venous thrombosis. LMWH may also be a safe, effective alternative to IVH when necessary for lower extremity bypass procedures performed with polytetrafluoroethylene (PTFE) grafts. The purpose of this study was to compare subcutaneous LMWH with IVH for perioperative

William D. McMillan; Walter J. McCarthy; Samuel J. Lin; Jon S. Matsumura; William H. Pearce; James S. T. Yao

1997-01-01

58

Ultra-High-Molecular-Weight Silphenylene/Siloxane Polymers  

NASA Technical Reports Server (NTRS)

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.

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

1986-01-01

59

Is Accurate Perception of Body Image Associated with Appropriate Weight-Control Behavior among Adolescents of the Seychelles.  

PubMed

Background. We examined body image perception and its association with reported weight-control behavior among adolescents in the Seychelles. Methods. We conducted a school-based survey of 1432 students aging 11-17 years in the Seychelles. Perception of body image was assessed using both a closed-ended question (CEQ) and Stunkard's pictorial silhouettes (SPS). Voluntary attempts to change weight were also assessed. Results. A substantial proportion of the overweight students did not consider themselves as overweight (SPS: 24%, CEQ: 34%), and a substantial proportion of the normal-weight students considered themselves as too thin (SPS: 29%, CEQ: 15%). Logistic regression analysis showed that students with an accurate weight perception were more likely to have appropriate weight-control behavior. Conclusions. We found that substantial proportions of students had an inaccurate perception of their weight and that weight perception was associated with weight-control behavior. These findings point to forces that can drive the upwards overweight trends. PMID:21603277

Alwan, Heba; Viswanathan, Bharathi; Paccaud, Fred; Bovet, Pascal

2011-01-01

60

Recent Developments in Low Molecular Weight Complement Inhibitors  

PubMed Central

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

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

2009-01-01

61

Mothers' and Fathers' Perceptions of Their Adolescent Daughters' Shape, Weight, and Body Esteem: Are They Accurate?  

ERIC Educational Resources Information Center

Examined parents' awareness of their daughters' attitudes, beliefs, and feelings about their bodies. Sixty-six adolescent daughters completed an eating disorder scale, a body figure rating scale, and made ratings of their shape and weight. Greater discrepancies between parents' estimates of daughters' body esteem and daughters' self-reported body…

Geller, Josie; Srikameswaran, Suja; Zaitsoff, Shannon L.; Cockell, Sarah J.; Poole, Gary D.

2003-01-01

62

Accurate computation of weights in classical Gauss-Christoffel quadrature rules  

SciTech Connect

For many classical Gauss-Christoffel quadrature rules there does not exist a method which guarantees a uniform level of accuracy for the Gaussian quadrature weights at all quadrature nodes unless the nodes are known exactly. More disturbing, some algebraic expressions for these weights exhibit an excessive sensitivity to even the smallest perturbations in the node location. This sensitivity rapidly increases with high order quadrature rules. Current uses of very high order quadratures are common with the advent of more powerful computers, and a loss of accuracy in the weights has become a problem and must be addressed. A simple but efficient and general method for improving the accuracy of the computation of the quadrature weights even though the nodes may carry a significant large error. In addition, a highly efficient root-finding iterative technique with superlinear converging rates for computing the nodes is developed. It uses solely the quadrature polynomials and their first derivatives. A comparison of this method with the eigenvalue method of Golub and Welsh implemented in most standard software libraries is made. The proposed method outperforms the latter from the point of view of both accuracy and efficiency. The Legendre, Lobatto, Radau, Hermite, and Laguerre quadrature rules are examined. 22 refs., 7 figs., 5 tabs.

Yakimiw, E. [Recherche en Prevision Numerique, Dorval, Quebec (Canada)] [Recherche en Prevision Numerique, Dorval, Quebec (Canada)

1996-12-01

63

Homogeneous low-molecular-weight heparins with reversible anticoagulant activity.  

PubMed

Low-molecular-weight heparins (LMWHs) are carbohydrate-based anticoagulants clinically used to treat thrombotic disorders, but impurities, structural heterogeneity or functional irreversibility can limit treatment options. We report a series of synthetic LMWHs prepared by cost-effective chemoenzymatic methods. The high activity of one defined synthetic LMWH against human factor Xa (FXa) was reversible in vitro and in vivo using protamine, demonstrating that synthetically accessible constructs can have a critical role in the next generation of LMWHs. PMID:24561662

Xu, Yongmei; Cai, Chao; Chandarajoti, Kasemsiri; Hsieh, Po-Hung; Li, Lingyun; Pham, Truong Q; Sparkenbaugh, Erica M; Sheng, Juzheng; Key, Nigel S; Pawlinski, Rafal; Harris, Edward N; Linhardt, Robert J; Liu, Jian

2014-04-01

64

Low-Molecular-Weight Protein Tyrosine Phosphatases of Bacillus subtilis  

Microsoft Academic Search

In gram-negative organisms, enzymes belonging to the low-molecular-weight protein tyrosine phosphatase (LMPTP) family are involved in the regulation of important physiological functions, including stress resistance and synthesis of the polysaccharide capsule. LMPTPs have been identified also in gram-positive bacteria, but their functions in these organisms are presently unknown. We cloned two putative LMPTPs from Bacillus subtilis, YfkJ and YwlE, which

Lucia Musumeci; Cristina Bongiorni; Lutz Tautz; Robert A. Edwards; Andrei Osterman; Marta Perego; Tomas Mustelin; Nunzio Bottini

2005-01-01

65

Synthesis and Characterization of Low Molecular Weight Polylactic Acid  

Microsoft Academic Search

The polymerization of (D, L)-lactic acid in the absence of catalysts was studied. Azeotropic distillation using xylene, gave poly(lactic acid) with very low molecular weight, which however, was further increased by post-curing in an air oven. Moreover degradation phenomena and residual xylene were observed, with this procedure. Polycondensation of lactic acid at temperatures up to 180 C under vacuum, resulted

C. S. Proikakis; P. A. Tarantili; A. G. Andreopoulos

2002-01-01

66

Production of chemicals from methanol. I. Low molecular weight olefins  

SciTech Connect

Methanol has been converted to water and hydrocarbons, with up to 70% selectivity to C/sub 2/-C/sub 4/ olefins, at 100% conversion, over ZSM-5 class zeolite catalysts modified with phosphorus compounds. Ethylene is proposed as the initial hydrocarbon produced. Evidence for the alkylation of olefins with methanol or methyl ether over these catalysts to produce higher molecular weight olefins is presented. 2 figures, 5 tables.

Kaeding, W.W.; Butter, S.A.

1980-01-01

67

Ultra-High-Molecular-Weight Silphenylene/Siloxane Elastomers  

NASA Technical Reports Server (NTRS)

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.

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

1989-01-01

68

Buckling in polymer monolayers: Molecular-weight dependence  

SciTech Connect

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.

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

2010-11-12

69

Impact resistance and fractography in ultra high molecular weight polyethylenes.  

PubMed

Highly crosslinked ultra high molecular weight polyethylenes (UHMWPE) stabilized by a remelting process or by the addition of an antioxidant are highly wear resistant and chemically stable. However, these polyethylenes currently used in total joint replacements suffer a loss of mechanical properties, especially in terms of fracture toughness. In this study we analyze the impact behavior of different polyethylenes using an instrumented double notch Izod test. The materials studied are three resins: GUR1050, GUR1020 with 0.1wt% of vitamin E, and MG003 with 0.1wt% of vitamin E. These resins were gamma irradiated at 90kGy, and pre and post-irradiation remelting processes were applied to GUR1050 for two different time periods. Microstructural data were determined by means of differential scanning calorimetry and transmission electron microscopy. Fractography carried out on the impact fracture surfaces and images obtained by scanning electron microscopy after etching indicated the existence of a fringe structure formed by consecutive ductile-brittle and brittle-ductile transitions, which is related to the appearance of discontinuities in the load-deflection curves. A correlation has been made of the macroscopic impact strength results and the molecular chain and microstructural characteristics of these aforementioned materials, with a view to designing future resins with improved impact resistance. The use of UHMWPE resins with low molecular weight or the application of a remelting treatment could contribute to obtain a better impact strength behavior. PMID:24275347

Puértolas, J A; Pascual, F J; Martínez-Morlanes, M J

2014-02-01

70

Accurate quadrupolar NMR relaxation rates of aqueous cations from classical molecular dynamics.  

PubMed

Nuclear magnetic resonance (NMR) relaxation rates encode information about the collective and local dynamics around nuclei. Provided a suitable microscopic model is available, this allows investigating, e.g., the solvation shell dynamics around aqueous ions. Previous attempts with molecular dynamics simulations faced the double challenge of calculating accurately the microscopic properties governing the relaxation process, such as the electric field gradient (EFG) at the nucleus, and of sampling the trajectories over sufficiently long times. Here we show how to compute the NMR relaxation rate from classical molecular dynamics simulations. We use a recently derived force field parametrized on ab initio calculations and show that the EFG predicted by this force field can be used to accurately estimate the one computed by DFT using the PAW method where the electronic structure is described explicitly. The predicted relaxation rates for aqueous alkaline and alkaline Earth cations are in good agreement with experimental data. Our approach opens the way to the quantitative interpretation of these rates with molecular simulation. PMID:25340813

Carof, Antoine; Salanne, Mathieu; Charpentier, Thibault; Rotenberg, Benjamin

2014-11-20

71

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

Code of Federal Regulations, 2011 CFR

...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...

2011-04-01

72

The Influence of molecular weight on nanoporous polymer films  

NASA Astrophysics Data System (ADS)

Asymmetric diblock copolymers of poly(styrene) and poly(methyl methacrylate), P(S-b-MMA), having cylindrical domains of PMMA, provide a model system to produce nanoporous thin films. Using either controlling interfacial interaction or applying an external electric field, cylinder domains can be oriented normal to the surface. Exposing the film to deep UV radiation may degrade the PMMA and crosslink the styrene matrix. After washing a porous film is obtained. By changing the molecular weight, smooth porous films with pore diameters ranging from 13 to 50nm are obtained where the pores are closely hexagonal packed.

Xu, Ting; Kim, Ho-Cheol; Derouchey, Jason; Seney, Chevey; Levesque, Cathy; Martin, Paul; Stafford, Chris; Russell, Thomas

2001-03-01

73

Pharmacological and Clinical Differences Between Low-Molecular-Weight Heparins  

PubMed Central

Thanks to their predictable pharmacokinetics and ease of use, low-molecular-weight heparins (LMWHs) have established uses in the prevention and treatment of thrombotic diseases and as a replacement for unfractionated heparin (UFH). Although LMWHs as a class have similar antithrombotic effects, they comprise a diverse group of agents with distinct biochemical and pharmacological profiles. In light of the ongoing pressure to contain pharmacy costs, the diversity among the LMWHs and their benefits over UFH are important considerations in clinical practice. PMID:20221326

Merli, Geno J.; Groce, James B.

2010-01-01

74

Structure and molecular weight of the dynein ATPase  

PubMed Central

Dynein has been examined by scanning transmission electron microscopy (STEM). Samples of 30S dynein from tetrahymena cilia were applied to carbon films and either were freeze- dried and examined as unstained, unfixed specimens, or were negatively stained with uranyl sulfate. A totally new image of the dynein molecule was revealed showing three globular heads connected by three separate strands to a common base. Two of the heads appeared to be identical and exhibited a diameter of 10 nm while the third head was somewhat larger (approximately 12 nm). The overall length of the particle was 35 nm. Mass analysis, based upon the integration of electron scattering intensities for unstained particles, gave a molecular weight of 1.95 (+/-)0.24) megadaltons. Mass per unit length analysis was performed using bovine brain microtubules decorated with dynein under conditions where the dynein shows a linear repeat of 24 nm with seven dynein molecules surrounding a microtubule made up of 14 protofilaments. Undecorated microtubules gave a molecular weight per unit length of 21,000+/-1,900 daltons/A, compared to a value of 84,400+/-2,200 daltons/A for the fully decorated microtubules. Taken together, these data give a molecular weight of 2.17 (+/- 0.14) megadaltons per dynein molecule, in agreement with measurements on the isolated particles. Mass analysis of individual globular heads observed in isolated particles gave a molecular weight distribution with a mean of 416+/- 76 kdaltons. These data could also be viewed as the sum of two populations of head with two-thirds of the heads at approximately 400 kdaltons and one-third at approximately 550 kdaltons, although more precise data will be required to distinguish two classes of heads with confidence. The mass of the dynein-microtubule complex as a function of distance from the midline of the particle was analysed to distinguish which end of the dynein molecule was bound to the microtubule. The projected mass distribution was consistent with a model where the three dynein heads were oriented toward the microtubule and clearly not consistent with the opposite orientation. These data indicate that the three globular heads form the ATP-sensitive site in this heterologous dynein-microtubule system and suggest that the rootlike base of the dynein molecule forms the structural attachment site to the A-subfiber of the outer doublet in cilia and flagella. The structure and function of the dynein are dicussed in terms of these new results. PMID:6220019

Johnson, KA; Wall, JS

1983-01-01

75

Absolute molecular weight distribution of low-molecular-weight heparins by size-exclusion chromatography with multiangle laser light scattering detection.  

PubMed

The absolute molecular weight (M(r)) distribution of seven low-molecular-weight (LMW) heparin products was determined by size-exclusion chromatography (SEC) coupled with multiangle laser light scattering (MALLS) detection. The SEC/MALLS technique does not rely on relative M(r) standards for column calibration and yields absolute M(r) estimates directly from the angular dependence of scattered light intensity as a function of concentration, as formulated by light scattering theory. The SEC/MALLS method we describe is rapid, precise, and accurate. In 1 h it yields results from triplicate injections that agree well with the manufacturers' own independent analyses and that exhibit coefficients of variation of approximately 1%. By eliminating the requirement for finite quantities of highly purified, well-characterized M(r) standards derived from heparin, the present procedure represents a clear improvement over relative methods of M(r) determination. Thus, it is concluded that the SEC/MALLS method is ideally suited to routine quality control of commercial LMW-heparin products. PMID:9056218

Knobloch, J E; Shaklee, P N

1997-02-15

76

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

E-print Network

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 by working with panels of commercial admixtures of the same family and different molecular weights

Paris-Sud XI, Université de

77

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

Code of Federal Regulations, 2013 CFR

... Polyethylene glycol (mean molecular weight 200-9,500). 178.3750 Section... Polyethylene glycol (mean molecular weight 200-9,500). Polyethylene glycol...oxide and water with a mean molecular weight of 200 to 9,500. (b) It...

2013-04-01

78

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

... Polyethylene glycol (mean molecular weight 200-9,500). 178.3750 Section... Polyethylene glycol (mean molecular weight 200-9,500). Polyethylene glycol...oxide and water with a mean molecular weight of 200 to 9,500. (b) It...

2014-04-01

79

21 CFR 172.820 - Polyethylene glycol (mean molecular weight 200-9,500).  

Code of Federal Regulations, 2012 CFR

... Polyethylene glycol (mean molecular weight 200-9,500). 172.820 Section... Polyethylene glycol (mean molecular weight 200-9,500). Polyethylene glycol...ethylene oxide and water with a mean molecular weight of 200 to 9,500. (2) It...

2012-04-01

80

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

E-print Network

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

Dubin, Paul D.

81

21 CFR 172.820 - Polyethylene glycol (mean molecular weight 200-9,500).  

Code of Federal Regulations, 2013 CFR

... Polyethylene glycol (mean molecular weight 200-9,500). 172.820 Section... Polyethylene glycol (mean molecular weight 200-9,500). Polyethylene glycol...ethylene oxide and water with a mean molecular weight of 200 to 9,500. (2) It...

2013-04-01

82

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

Code of Federal Regulations, 2012 CFR

... Polyethylene glycol (mean molecular weight 200-9,500). 178.3750 Section... Polyethylene glycol (mean molecular weight 200-9,500). Polyethylene glycol...oxide and water with a mean molecular weight of 200 to 9,500. (b) It...

2012-04-01

83

Structural comparisons between chicken low molecular weight immunoglobulin heavy chains and human ? chains  

Microsoft Academic Search

Comparisons between chicken low molecular weight immunoglobulin (LMW Ig) and human ? heavy chains as to molecular weights, amino acid compositions, tryptic peptide maps, and CHO-peptide sequences revealed significant differences. The molecular weight of the chicken heavy chain, 60,000, is approximately 10,000 more than that for human ?, indicating up to 100 more amino acids, including three more cysteine residues.

James C. Travis; Bob G. Sanders

1973-01-01

84

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

NASA Astrophysics Data System (ADS)

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.

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

2014-02-01

85

Preoperative core needle biopsy is accurate in determining molecular subtypes in invasive breast cancer  

PubMed Central

Background Estrogen receptor (ER), progesterone receptor (PgR), HER2, and Ki67 have been increasingly evaluated by core needle biopsy (CNB) and are recommended for classifying breast cancer into molecular subtypes. However, the concordance rate between CNB and open excision biopsy (OEB) has not been well documented. Methods Patients with paired CNB and OEB samples from Oct. 2009 to Feb. 2012 in Ruijin Hospital were included. ER, PgR, HER2, and Ki67 were determined by immunohistochemistry (IHC). Patients with HER2 IHC 2+ were further examined by FISH. Cutoff value for Ki67 high expression was 14%. Molecular subtypes were constructed as follows: Luminal A, Luminal B, Triple Negative, and HER2 positive. Results There were 298 invasive breast cancer patients analyzed. Concordance rates for ER, PgR, and HER2 were 93.6%, 85.9%, and 96.3%, respectively. Ki67 expression was slightly higher in OEB than in CNB samples (29.3% vs. 26.8%, P?=?0.046). Good agreement (??=?0.658) was demonstrated in evaluating molecular subtypes between CNB and OEB, with a concordance rate of 77.2%. We also used a different Ki67 cutoff value (20%) for determining Luminal A and B subtypes in HR (hormone receptor) +/HER2- diseases and the overall concordance rate was 79.2%. However, using a cut-point of Ki67 either 14% or 20% for both specimens, there will be about 14% of HR+/HER2- specimens that are called Luminal A on CNB and Luminal B on OEB. Conclusion CNB was accurate in determining ER, PgR, and HER2 status as well as non-Luminal molecular subtypes in invasive breast cancer. Ki67 should be retested on OEB samples in HR+/HER2- patients to accurately distinguish Luminal A from B tumors. PMID:23957561

2013-01-01

86

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

Code of Federal Regulations, 2010 CFR

...more than 0.2 percent total by weight of ethylene and diethylene glycols if its mean molecular weight is 350 or higher...more than 0.5 percent total by weight of ethylene and diethylene glycols if its mean molecular weight is below...

2010-04-01

87

Shear creep compliance of polyoxymethylene copolymers with different molecular weights  

NASA Astrophysics Data System (ADS)

Polyoxymethylene copolymer (POM) is considered a high performance engineering polymer with many applications due to its good chemical resistance and very good mechanical properties. It is known that mechanical properties of polymers are greatly influenced by their average molecular weight (Mw). This paper presents the shear creep compliance of new POM copolymers with a broad range of average molecular weights (10240 to 204400 g/mol). Master curves of creep compliance were constructed using the time-temperature superposition principle. It was observed that at short time (t = 0.25 s), creep compliance is independent of Mw. As the time increases (t = 3.16×108 s ˜ 10 years) shear compliance decreases as a power function of Mw, but only up to a critical Mw of approximately 92300 g/mol. After this critical Mw creep compliance becomes again independent of Mw. These results in combination with finite element analysis could be used for selecting a specific Mw according to suit the requirements of certain application.

Gonzalez-Gutierrez, Joamin; Megen, Zerihun Mellese; von Bernstorff, Bernd Steffen; Emri, Igor

2014-05-01

88

Degradation rate of ultra-high molecular weight polyethylene.  

PubMed

Ultra-high molecular weight polyethylene components for total joint replacement chemically degrade before and after implantation, and the degradation is associated with an increase in density. The goal of this study was to determine the average rate of density change in these components following sterilization by gamma radiation in air as a function of shelf age and implantation time. Using the density gradient column method, density profiles were obtained through the thickness from loaded and unloaded regions of 10 retrieved Insall-Burstein/Posterior-Stabilized II tibial components and one operating-room inventory component for which the initial density profile and patient history (if applicable) were known. The average density of the components increased at a constant rate of 0.000186 g/cc/month during the first 50 months after sterilization (r2 = 0.54) but was not significantly affected by loading (p > 0.05). The quantitative degradation rates may be useful to help verify kinetic models to predict bulk degradative changes on the basis of micro-structural and chemical processes. This research also suggests the hypothesis that degradation of ultra-high molecular weight polyethylene can be modeled in terms of changes in bulk or average properties. PMID:9066527

Kurtz, S M; Rimnac, C M; Bartel, D L

1997-01-01

89

Ice Nucleation by High Molecular Weight Organic Compounds  

NASA Astrophysics Data System (ADS)

Deep convection in the tropics is frequently associated with biomass burning. Recent work has suggested that the size of ice crystals in the anvils of tropical cumulonimbus clouds may be affected by biomass burning, though the mechanism for such an effect is uncertain (Sherwood, 2002). We will present results of an investigation of the role that high molecular weight organic compounds, known to be produced in biomass burning (Elias et al., 1999), may play in tropical cirrus anvils through heterogeneous nucleation of ice. In particular, we examine the mechanisms underlying heterogeneous nucleation of ice by films of long chain alcohols by studying the interaction of the alcohols and water/ice using temperature controlled, Attenuated Total Reflection - Fourier Transform Infrared spectroscopy. The mechanisms are interpreted in the context of recent criticisms of some aspects of classical nucleation theory (Seeley and Seidler, 2001; Oxtoby, 1998). References V. Elias, B. Simoneit, A. Pereira, J. Cabral, and J. Cardoso, Detection of high molecular weight organic tracers in vegetation smoke samples by high-temperature gas chromatography-mass spectrometry. Environ. Sci. Tecnol., 33, 2369-2376, 1999. D. Oxtoby, Nucleation of first-order phase transitions. Acc. Chem. Res., 31, 91-97, 1998. L. Seeley and G. Seidler, Preactivation in the nucleation of ice by Langmuir films of aliphatic alcohols. J. Chem. Phys., 114, 10464-10470, 2001. S. Sherwood, Aerosols and ice particle size in tropical cumulonimbus. J. Climate, 15, 1051-1063, 2002.

Cantrell, W.

2003-12-01

90

Molecular and Pharmacologic Profile of Tinzaparin and A Comparable Low-Molecular-Weight Bacterial Sulfaminoheparosan  

Microsoft Academic Search

Low-molecular-weight heparins (LMWH) represent depolymerized porcine mucosal heparin derivatives, which are commonly used for the management of thrombotic disorders. Because of their widespread usage, the supplies of the raw material namely unfractionated heparin are nearly exhausted. Porcine mucosal tissue is almost exclusively used for the preparation of these agents. Thus, there is a timely need for the production of heparin

Jyothi Maddineni; Qing Ma; Debra A. Hoppensteadt; Muzaffer Demir; Marco Manoni; Umberto Cornelli; Jawed Fareed

2004-01-01

91

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

NASA Technical Reports Server (NTRS)

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.

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

2000-01-01

92

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

PubMed

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

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

2012-03-01

93

On the efficient and accurate short-ranged simulations of uniform polar molecular liquids  

E-print Network

We show that spherical truncations of the 1/r interactions in models for water and acetonitrile yield very accurate results in bulk simulations for all site-site pair correlation functions as well as dipole-dipole correlation functions. This good performance in bulk simulations contrasts with the generally poor results found with the use of such truncations in nonuniform molecular systems. We argue that Local Molecular Field (LMF) theory provides a general theoretical framework that gives the necessary corrections to simple truncations in most nonuniform environments and explains the accuracy of spherical truncations in uniform environments by showing that these corrections are very small. LMF theory is derived from the exact Yvon-Born-Green (YBG) hierarchy by making physically-motivated and well-founded approximations. New and technically interesting derivations of both the YBG hierarchy and LMF theory for a variety of site-site molecular models are presented in appendices. The main paper focuses on understanding the accuracy of these spherical truncations in uniform systems both phenomenologically and quantitatively using LMF theory.

Jocelyn M. Rodgers; Zhonghan Hu; John D. Weeks

2010-12-01

94

A Large Catalog of Accurate Distances to Molecular Clouds from PS1 Photometry  

NASA Astrophysics Data System (ADS)

Distance measurements to molecular clouds are important but are often made separately for each cloud of interest, employing very different data and techniques. We present a large, homogeneous catalog of distances to molecular clouds, most of which are of unprecedented accuracy. We determine distances using optical photometry of stars along lines of sight toward these clouds, obtained from PanSTARRS-1. We simultaneously infer the reddenings and distances to these stars, tracking the full probability distribution function using a technique presented in Green et al. We fit these star-by-star measurements using a simple dust screen model to find the distance to each cloud. We thus estimate the distances to almost all of the clouds in the Magnani et al. catalog, as well as many other well-studied clouds, including Orion, Perseus, Taurus, Cepheus, Polaris, California, and Monoceros R2, avoiding only the inner Galaxy. Typical statistical uncertainties in the distances are 5%, though the systematic uncertainty stemming from the quality of our stellar models is about 10%. The resulting catalog is the largest catalog of accurate, directly measured distances to molecular clouds. Our distance estimates are generally consistent with available distance estimates from the literature, though in some cases the literature estimates are off by a factor of more than two.

Schlafly, E. F.; Green, G.; Finkbeiner, D. P.; Rix, H.-W.; Bell, E. F.; Burgett, W. S.; Chambers, K. C.; Draper, P. W.; Hodapp, K. W.; Kaiser, N.; Magnier, E. A.; Martin, N. F.; Metcalfe, N.; Price, P. A.; Tonry, J. L.

2014-05-01

95

Dairy Wastewater Treatment Using Low Molecular Weight Crab Shell Chitosan  

NASA Astrophysics Data System (ADS)

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.

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

2012-08-01

96

Low-molecular-weight xylanase from Trichoderma viride  

SciTech Connect

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.

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

1991-06-01

97

Lipid solubility and molecular weight: whose idea was that.  

PubMed

Gene Cooper was a bright theoretician, a skilled product developer, and a motivational leader who applied his talents to the skin science area early in his career. His work led to the development of finite dose skin absorption models, chemical penetration enhancer technologies and quantitative structure-penetration relationships for chemicals contacting human skin. His ideas regarding the impact of molecular weight and lipid solubility on skin transport catalyzed the later development by Potts and Guy of the first successful skin permeability model. But Gene's most important contribution to the field was as a scientific role model and an inspirational leader who launched the careers of several young scientists, including the author of this article. PMID:23921116

Kasting, G B

2013-01-01

98

Apparatus and method of determining molecular weight of large molecules  

DOEpatents

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.

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

1998-01-01

99

Apparatus and method of determining molecular weight of large molecules  

DOEpatents

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.

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

1998-06-23

100

Ultra-high molecular weight silphenylene-siloxane polymers  

NASA Technical Reports Server (NTRS)

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.

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

1984-01-01

101

Fast and Accurate Quantum Molecular Dynamics of Dense Plasmas Across Temperature Regimes  

NASA Astrophysics Data System (ADS)

We develop and implement a new quantum molecular dynamics approximation that allows fast and accurate simulations of dense plasmas from cold to hot conditions. The method is based on a carefully designed orbital-free implementation of density functional theory. The results for hydrogen and aluminum are in very good agreement with Kohn-Sham (orbital-based) density functional theory and path integral Monte Carlo calculations for microscopic features such as the electron density as well as the equation of state. The present approach does not scale with temperature and hence extends to higher temperatures than is accessible in the Kohn-Sham method and lower temperatures than is accessible by path integral Monte Carlo calculations, while being significantly less computationally expensive than either of those two methods.

Sjostrom, Travis; Daligault, Jérôme

2014-10-01

102

Fast and accurate quantum molecular dynamics of dense plasmas across temperature regimes  

E-print Network

We have developed and implemented a new quantum molecular dynamics approximation that allows fast and accurate simulations of dense plasmas from cold to hot conditions. The method is based on a carefully designed orbital-free implementation of density functional theory (DFT). The results for hydrogen and aluminum are in very good agreement with Kohn-Sham (orbital-based) DFT and path integral Monte Carlo (PIMC) for microscopic features such as the electron density as well as equation of state. The present approach does not scale with temperature and hence extends to higher temperatures than is accessible in Kohn-Sham method and lower temperatures than is accessible by PIMC, while being significantly less computationally expensive than either of those two methods

Sjostrom, Travis

2014-01-01

103

Human neutrophils contain and bind high molecular weight kininogen.  

PubMed

Because plasma kallikrein activates human neutrophils, and in plasma prekallikrein (PK) circulates complexed with high molecular weight kininogen (HMWK), we determined whether HMWK could mediate kallikrein's association with neutrophils. HMWK antigen (237 +/- 61 ng HMWK/10(8) neutrophils) was present in lysates of washed human neutrophils. Little if any plasma HMWK was tightly bound and nonexchangeable with the neutrophil surface. Human neutrophils were found to possess surface membrane-binding sites for HMWK but no internalization was detected at 37 degrees C. 125I-HMWK binding to neutrophils was dependent upon Zn2+. Binding of 125I-HMWK to neutrophils was specific and 90% reversible. 125I-HMWK binding to neutrophils was saturable with an apparent Kd of 9-18 nM and 40,000-70,000 sites per cell. Upon binding to neutrophils, 125I-HMWK was proteolyzed by human neutrophil elastase (HNE) into lower relative molecular mass derivatives. Furthermore, HMWK found in neutrophils also served as a cofactor for HNE secretion because neutrophils deficient in HMWK have reduced HNE secretion when stimulated in plasma deficient in HMWK or with purified kallikrein. These studies indicate that human neutrophils contain a binding site for HMWK that could serve to localize plasma or neutrophil HMWK on their surface to possibly serve as a receptor for kallikrein and to participate in HNE secretion by this enzyme. PMID:2738152

Gustafson, E J; Schmaier, A H; Wachtfogel, Y T; Kaufman, N; Kucich, U; Colman, R W

1989-07-01

104

Human neutrophils contain and bind high molecular weight kininogen.  

PubMed Central

Because plasma kallikrein activates human neutrophils, and in plasma prekallikrein (PK) circulates complexed with high molecular weight kininogen (HMWK), we determined whether HMWK could mediate kallikrein's association with neutrophils. HMWK antigen (237 +/- 61 ng HMWK/10(8) neutrophils) was present in lysates of washed human neutrophils. Little if any plasma HMWK was tightly bound and nonexchangeable with the neutrophil surface. Human neutrophils were found to possess surface membrane-binding sites for HMWK but no internalization was detected at 37 degrees C. 125I-HMWK binding to neutrophils was dependent upon Zn2+. Binding of 125I-HMWK to neutrophils was specific and 90% reversible. 125I-HMWK binding to neutrophils was saturable with an apparent Kd of 9-18 nM and 40,000-70,000 sites per cell. Upon binding to neutrophils, 125I-HMWK was proteolyzed by human neutrophil elastase (HNE) into lower relative molecular mass derivatives. Furthermore, HMWK found in neutrophils also served as a cofactor for HNE secretion because neutrophils deficient in HMWK have reduced HNE secretion when stimulated in plasma deficient in HMWK or with purified kallikrein. These studies indicate that human neutrophils contain a binding site for HMWK that could serve to localize plasma or neutrophil HMWK on their surface to possibly serve as a receptor for kallikrein and to participate in HNE secretion by this enzyme. Images PMID:2738152

Gustafson, E J; Schmaier, A H; Wachtfogel, Y T; Kaufman, N; Kucich, U; Colman, R W

1989-01-01

105

Low-molecular-weight heparin in pediatric patients.  

PubMed

The incidence of thromboembolic events (TEs) in childhood is greatly underestimated. Two age groups account for approximately 70% of TEs in childhood: infants and teenagers. There are several predisposing risk factors for newborns such as small vessels, high hematocrit, and a unique neonatal hemostatic system. Central venous lines contribute to 80% of deep vein thrombosis in newborns. Other risk factors for all children are shock syndromes, trauma, surgery, heart and kidney disease, and acquired or hereditary thrombophilias. The best prophylaxis is to recognize, avoid, and remove risk factors if possible. This is particularly relevant in childhood, where risk factors can be found in the majority of TEs. The serious sequelae of TEs (mortality, and short- and long-term morbidity) require therapeutic intervention. Unfractionated heparin (UFH) has the following disadvantages: age-dependent unpredictable pharmacokinetics, the need for intravenous access for therapy and monitoring, delays in achieving therapeutic ranges, bleeding risk, the risk of heparin-induced thrombocytopenia, and osteoporosis with long-term use. Oral anticoagulants, in addition to some of these disadvantages, show considerable variation by diet (especially if there is a change from breast to bottle feeding), medication, and intercurrent illness. Review of case reports and cohort studies on 728 children treated with low-molecular-weight heparin (LMWH) indicate the following advantages over UFH: minimal monitoring, ease of administration (subcutaneous), and possibly equivalent efficacy and safety. Dose recommendations for pediatric patients cannot be directly extrapolated from those for adult patients. If dosages are calculated according to body weight, infants < 3 months (or < 5 kg) need approximately 50% more LMWH than older children or adults to reach prophylactic or therapeutic anti-factor Xa levels. Further studies are necessary to address the following: the importance of risk factors, the necessity of screening for hereditary thrombophilia, the efficacy and safety of treatment, and side effects and duration of treatment. Thromboembolic events (TEs) are considered to be rare in children. However, recent surveys reveal that TEs in children occur more often than suspected. The incidence is greatly underestimated because TEs are usually overlooked. Retrospective surveys in children treated for acute lymphoblastic leukemia with corticosteroids and asparaginase revealed clinically symptomatic TE in only 2 to 12% of patients. However, in prospective studies with routine imaging, the incidence was more than 20%. The objectives of this article are to update the present knowledge on TEs in children, including incidence, predominant age groups, risk factors, diagnosis, and indications for prophylaxis and therapy; and to discuss the use of low-molecular-weight heparin (LMWH) in children. PMID:15085464

Sutor, Anton Heinz; Chan, Anthony K C; Massicotte, Patricia

2004-02-01

106

In situ reinforced polymers using low molecular weight compounds  

NASA Astrophysics Data System (ADS)

The primary objective of this research is to generate reinforcing domains in situ during the processing of polymers by using phase separation techniques. Low molecular weight compounds were mixed with polymers where the process viscosity is reduced at process temperatures and mechanical properties are improved once the material system is cooled or reacted. Thermally induced phase separation and thermotropic phase transformation of low molar mass compounds were used in isotactic polypropylene (iPP) and poly(ether ether ketone) (PEEK) resins. Reaction induced phase separation was utilized in thermosets to generate anisotropic reinforcements. A new strategy to increase fracture toughness of materials was introduced. Simultaneously, enhancement in stiffness and reduction in process viscosity were also attained. Materials with improved rheological and mechanical properties were prepared by using thermotropic phase transformations of metal soaps in polymers (calcium stearate/iPP). Morphology and thermal properties were studied using WAXS, DSC and SEM. Mechanical and rheological investigation showed significant reduction in process viscosity and substantial improvement in fracture toughness were attained. Effects of molecular architecture of metal soaps were investigated in PEEK (calcium stearate/PEEK and sodium stearate/PEEK). The selected compounds reduced the process viscosity due to the high temperature co-continuous morphology of metal soaps. Unlike the iPP system that incorporates spherical particles, interaction between PEEK and metal soaps resulted in two discrete and co-continuous phases of PEEK and the metal stearates. DMA and melt rheology exhibited that sodium stearate/PEEK composites are stiffer. Effective moduli of secondary metal stearate phase were calculated using different composite theories, which suggested bicontinuous morphology to the metal soaps in PEEK. Use of low molecular weight crystallizable solvents was investigated in reactive systems. Formation of anisotropic reinforcements was evaluated using dimethyl sulfone (DMS) as the crystallizable diluent and diglycidyl ether of bisphenol-A (DGEBA)/m-phenylene diamine (mPDA) material system as the epoxy thermoset. Miscible blends of DMS and DGEBA/mPDA form homogenous mixtures that undergo polymerization induced phase separation, once the DGEBA oligomers react with mPDA. The effect of the competition between the crystallization and phase separation of DMS resulted in nano-wires to micro-scale fiber-like crystals that were generated by adjusting the reaction temperature and DMS concentration.

Yordem, Onur Sinan

107

A simple capillary electrophoresis method for the rapid separation and determination of intact low molecular weight and unfractionated heparins  

Microsoft Academic Search

A simple, selective and accurate capillary electrophoresis (CE) method has been developed for the rapid separation and identification of various low molecular weight heparins (LMWHs) and unfractionated heparin. Separation and operational parameters were investigated using dalteparin sodium as the test LMWH. The developed method used a 70cm fused silica capillary (50?m i.d.) with a detection window 8.5cm from the distal

Rahul P. Patel; Christian Narkowicz; Joseph P. Hutchinson; Emily F. Hilder; Glenn A. Jacobson

2008-01-01

108

Classical Heisenberg model of magnetic molecular ring clusters: Accurate approximants for correlation functions and susceptibility  

NASA Astrophysics Data System (ADS)

We show that the measured magnetic susceptibility of molecular ring clusters can be accurately reproduced, for all but low temperatures T, by a classical Heisenberg model of N identical spins S on a ring that interact with isotropic nearest-neighbor interactions. While exact expressions for the two-spin correlation function, CN(n,T), and the zero-field magnetic susceptibility, ?N(T), are known for the classical Heisenberg ring, their evaluation involves summing infinite series of modified spherical Bessel functions. By contrast, the formula CN(n,T)=(un+uN-n)/(1+uN), where u(K)=coth K-K-1 is the Langevin function and K=JS(S+1)/(kBT) is the nearest-neighbor dimensionless coupling constant, provides an excellent approximation if N?6 for the regime |K|<3. This choice of approximant combines the expected exponential decay of correlations for increasing yet small values of n, with the cyclic boundary condition for a finite ring, CN(n,T)=CN(N-n,T). By way of illustration, we show that, for T>50 K, the associated approximant for the susceptibility derived from the approximate correlation function is virtually indistinguishable from both the exact theoretical susceptibility and the experimental data for the "ferric wheel" molecular cluster ([Fe(OCH3)2(O2CCH2Cl)]10), which contains N=10 interacting Fe3+ ions, each of spin S=5/2, that are symmetrically positioned in a nearly planar ring.

Luscombe, James H.; Luban, Marshall; Borsa, Ferdinando

1998-05-01

109

Kinetics of Formation of Molecular Weight Distribution of Epoxy Composite  

NASA Astrophysics Data System (ADS)

Curing of epoxy matrix prepreg in free space environment is a complex problem. A simulation of the chemical reaction, evaporation and radiation effects in the matrix is a way to understand and predict the curing process. We have developed a mathematical apparatus of the epoxy resin kinetics in term of molecular weight distribution (MWD), which includes the polymerization mechanism of bifunctional epoxy and sixfunctional triethylenetetraamine (TETA) molecules. The mathematical model for a number of molecules with the mass m at time t is based on the following equation $ beta(t,m)=m_{am} / m sum(6}_{i=0) alpha(am) _i (t,m)+ m_{ep} / m sum(2}_{i=0) alpha(ep) _i (t,m), where m_{am} and m_{ep} are the masses of one amine block and one epoxy block, respectively; alpha^{am}_i (t,m) is the MWD near the TETA blocks with the chemical bonds i at time t for the mass values m>0; alpha_i^{ep}(t,m) is the MWD parameters of the epoxy blocks with chemical bonds i at time t for the mass values m>0. For the distribution densities alpha^{am}_i (t,m) and alpha_i^{ep}(t,m), we propose the differential system of equations, which has been solved by applying boundary conditions which are based on the results of chromatography and infrared spectroscopy measurements of the epoxy matrix having different concentration of the hardener. For the initial MWD we accept a Gaussian distribution with parameters alpha^{am}_0 (t,m_1) =146 amu, alpha_0^{ep}(t,m_1) =340 amu and alpha_1^{ep}(t,m_1) =624 amu. Dispersion of the molecular weight for the initial distribution equals to 25 amu. A portion of TETA molecules in the fraction was 25%, and the portion of epoxy molecules with i=0 and i=1 was 67.5% and 7.5%$, respectively. Solutions were obtained at mass step equals to 5 amu and at time step equals to 0.25 min over the interval from 0 to 500 min. The model gives a full kinetic of MWD during the curing reaction. The study is supported by the RFBR (grants N 12-08-00970-a and N 14-08-96011-r-ural-a).

Komar, Lyudmila A.; Kondyurin, Alexey; Svistkov, Alexander L.

110

Product Individuality of Commercially Available Low-Molecular-Weight Heparins and Their Generic Versions: Therapeutic Implications  

Microsoft Academic Search

The currently available brand-name low-molecular-weight heparins (LMWHs) in the United States include dalteparin (Pfizer), enoxaparin (Aventis), and tinzaparin (Pharmion). Other products available, in Europe, include certoparin (Novartis), reviparin (Abbott), nadroparin (GlaxoSmithkline), and parnaparin (Alpha-Wasserman). Each of these LMWHs has a characteristic molecular weight profile and biological activity in terms of an anti-FXa and anti-FIIa potency. The mean molecular weight of

Jyothi Maddineni; Jeanine M. Walenga; Walter P. Jeske; Debra A. Hoppensteadt; Jawed Fareed; Rakesh Wahi; Rodger L. Bick

2006-01-01

111

Accurate Molecular Classification of Renal Tumors Using MicroRNA Expression  

PubMed Central

Subtypes of renal tumors have different genetic backgrounds, prognoses, and responses to surgical and medical treatment, and their differential diagnosis is a frequent challenge for pathologists. New biomarkers can help improve the diagnosis and hence the management of renal cancer patients. We extracted RNA from 71 formalin-fixed paraffin-embedded (FFPE) renal tumor samples and measured expression of more than 900 microRNAs using custom microarrays. Clustering revealed similarity in microRNA expression between oncocytoma and chromophobe subtypes as well as between conventional (clear-cell) and papillary tumors. By basing a classification algorithm on this structure, we followed inherent biological correlations and could achieve accurate classification using few microRNAs markers. We defined a two-step decision-tree classifier that uses expression levels of six microRNAs: the first step uses expression levels of hsa-miR-210 and hsa-miR-221 to distinguish between the two pairs of subtypes; the second step uses either hsa-miR-200c with hsa-miR-139-5p to identify oncocytoma from chromophobe, or hsa-miR-31 with hsa-miR-126 to identify conventional from papillary tumors. The classifier was tested on an independent set of FFPE tumor samples from 54 additional patients, and identified correctly 93% of the cases. Validation on qRT-PCR platform demonstrated high correlation with microarray results and accurate classification. MicroRNA expression profiling is a very effective molecular bioassay for classification of renal tumors and can offer a quantitative standardized complement to current methods of tumor classification. PMID:20595629

Fridman, Eddie; Dotan, Zohar; Barshack, Iris; David, Miriam Ben; Dov, Avital; Tabak, Sarit; Zion, Orit; Benjamin, Sima; Benjamin, Hila; Kuker, Hagit; Avivi, Camila; Rosenblatt, Kinneret; Polak-Charcon, Sylvie; Ramon, Jacob; Rosenfeld, Nitzan; Spector, Yael

2010-01-01

112

A genetic determinant of the phenotypic variance of the molecular weight of low density lipoprotein.  

PubMed

The molecular weight of monodisperse human plasma low densitylipoprotein has been measured in 69 individuals and found to vary over the range of 2.4 to 3.9 X 10-6. By contrast, the molecular weight of low density lipoprotein measured on two separate occasions for specific individuals shows a mean difference of 0.07 X 10-6 and a standard deviation of 0.08 X 10-6; hence low density lipoprotein differing in molecular weight by greater than 0.2 X 10-6 may be considered different macomolecules. The distribution of the molecular weight of low density lipoprotein does not differ as a function of age or sex. Hyperlipemic subjects having monodisperse low density lipoprotein show similar molecular weight distribution to normal subjects, as do subjects with premature coronary artery disease. Family studies reveal a correlation coefficient of 0.82 between average molecular weights of parents and offspring, with significance at 0.01. In order to assess the influence of environment on molecular weight of low density lipoprotein, the correlation coefficient between the fathers' and mothers' low density lipoprotein was measured and no statistically significant correlation was found. These data are interpreted as strong evidence for a genetic determination of molecular weight of low density lipoprotein. A study of individuals in five families yields molecular weight data consistent with a single gene locus genetic mode of inheritance without dominance. The regression coefficient of the mean low denisty lipoprotein parental molecular weight on the offspring molecular weight is 0.30. If the variability of molecular weight is considered as an expression of phenotypic variance, then the regression analysis identified 30% of this phenotypic variance as arising from additive gene action presumably at a single locus. Segregation in the family data is consistent. Since the differences in molecular weight of low density lipoprotein arise from differences in the amount of lipid bound to the apoprotein, it is likely that an additional portion of the phenotypic variance of the molecular weight results from individual variations in the metabolism of low density lipoprotein, which yield differences in lipid content. The individual variation in molecular weight is only approximately 5%; hence those metabolic sequences that influence molecular weight of low density lipoproteins must be precisely controlled. PMID:166386

Fisher, W R; Hammond, M G; Mengel, M C; Warmke, G L

1975-06-01

113

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

PubMed Central

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

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

2014-01-01

114

Regulatory considerations for generic or biosimilar low molecular weight heparins.  

PubMed

The aim of the present paper is to address the legal aspects, technical requirements and possible conditions of use associated to low molecular weight heparin generics and biosimilars that are arriving to the market in United States and the European Union, respectively. To this end the concept of "similar biological medicinal product" that was coined in 2003 by the pharmaceutical legislation of the European Union is compared to the concept of generic in the United States and the concept of generic in the European Union. This different legal basis determines directly the technical requirements to obtain a marketing authorisation. Therefore, the chemical/biological, non-clinical and clinical requirements to demonstrate therapeutic equivalence are different in these two Regulatory Authorities, FDA and EMA. Consequently, the possible conditions of use are different. In the United States the products approved as generics by the FDA are considered interchangeable to the Reference Listed Drug. In contrast, the EMA legislation only deals with the approvability or prescribability of the medicines and it is a national / regional decision of the member States to consider these biosimilar products as interchangeable or not. PMID:21838658

García-Arieta, Alfredo; Blázquez, Antonio

2012-06-01

115

Can we differentiate the low-molecular-weight heparins?  

PubMed

The low-molecular-weight heparins (LMWHs) have a number of therapeutic advantages, relative to standard unfractionated heparin (UFH). They are readily bioavailable when injected subcutaneously and can be given in fixed doses, allowing for far simpler administration. Several LMWHs are now commercially available, each demonstrating different physical and chemical properties and different activities in animal models of anticoagulation or hemorrhage. In clinical comparisons with placebo in the treatment of unstable coronary artery disease (UCAD), the LMWHs dalteparin sodium and nadroparin calcium have demonstrated good anticoagulant efficacy. In comparisons with UFH, on the other hand, only enoxaparin has shown superior anticoagulant activity, as reported in the results of the Efficacy and Safety of Subcutaneous Enoxaparin in Non-Q-wave Coronary Events (ESSENCE) and Thrombolysis In Myocardial Infarction (TIMI) 11B trials. However, close scrutiny of the methodology of the clinical trials in UCAD reveals considerable differences in study designs, dosage regimens, duration of administration of active treatments, and the timing and definition of endpoints. Therefore, it would not be scientifically sound to compare results with the different LMWHs based on the current available studies. It is also not possible to draw any conclusions with regard to the relative efficacy of the different LMWHs, since there are no properly-sized comparative data between dalteparin sodium, enoxaparin sodium, and nadroparin calcium. PMID:10680037

Turpie, A G

2000-01-01

116

[Intracellular calci-proteins of low molecular weight].  

PubMed

The role of calcium as an intracellular second messenger is now widely recognized. Upon stimulation of a eukaryotic cell, its cytosolic concentration increases 100 fold from pCa 7 to pCa 5. Calcium effects within the cell are mostly mediated through binding of the ion to low molecular weight proteins that form an evolutionary family including parvalbumin, calmodulin, troponin C, the alkali and regulatory light chains of myosin, the S-100 protein and the vitamin D-dependent intestinal calcium-binding protein. The structural, evolutionary and functional unit of each of these proteins is the calcium-binding domain, made of a 12-residue binding loop flanked on each side by a ca 12-residue long alpha-helix. Calcium binding proteins differ in the number of domains and in the Ca2+-binding properties of the domains. Parvalbumin exhibits two high affinity Ca2+-Mg2+-binding sites involved in the relaxation phase of fast skeletal muscle. In contrast, calmodulin and troponin C exhibit low affinity Ca2+-specific sites that trigger Ca2+-dependent effects. Calcium binding to calmodulin is sequential and ordered and results in a conformational change that enables the protein to interact through a hydrophobic patch with the numerous calmodulin-dependent enzymes. Calmodulin is highly conserved, ubiquitous and multifunctional. It is responsible for the Ca2+ control of cell motility, of energy production through the glycogenolytic pathway, and of the modulation of messengers, amongst which are Ca2+ itself, cAMP and neurotransmitters. PMID:7133987

Demaille, J G

1982-01-01

117

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

NASA Astrophysics Data System (ADS)

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.

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

2012-08-01

118

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

PubMed Central

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

Sobieraj, MC; Rimnac, CM

2013-01-01

119

Adsorption of low molecular weight halocarbons by montmorillonite  

SciTech Connect

Montmorillonite clay from Clay Spur, WY, was found to adsorb several low molecular weight, hydrophobic halocarbons from aqueous solution at sub-parts-per-million levels. The halocarbons studied were trichloroethylene, tetrachloroethylene, hexachloroethane, and dibromochloropropane. When the montmorillonite was treated with sodium citrate-bicarbonate-dithionite (CBD), it adsorbed higher levels of halocarbons than the untreated clay. In addition, the CBD-treated clay exhibited a maximum in halocarbon adsorption around pH 4, while untreated clay showed little variation in adsorption over the pH range 2-10. Adsorption of trichloroethylene was inhibited by low concentrations of sodium chloride (0.01 M or greater) in solution. Aging the CBD-treated clay in water decreased its capacity to adsorb trichloroethylene. Desorption studies showed that the sorption of tetrachloroethylene to CBD-treated clay is an irreversible process when compared to sorption by fumed silica. The ability of montmorillonite to adsorb halocarbons and the instability of the clay in water are postulated to involve changes in the oxide surface coating on the clay.

Estes, T.J.; Shah, R.V.; Vilker, V.L. (Univ. of California, Los Angeles (USA))

1988-04-01

120

Photochemical Preparation of a Novel Low Molecular Weight Heparin  

PubMed Central

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

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

2011-01-01

121

Classical Heisenberg model of magnetic molecular ring clusters: Accurate approximants for correlation functions and susceptibility  

SciTech Connect

We show that the measured magnetic susceptibility of molecular ring clusters can be accurately reproduced, for all but low temperatures T, by a classical Heisenberg model of N identical spins S on a ring that interact with isotropic nearest-neighbor interactions. While exact expressions for the two-spin correlation function, C{sub N}(n,T), and the zero-field magnetic susceptibility, {chi}{sub N}(T), are known for the classical Heisenberg ring, their evaluation involves summing infinite series of modified spherical Bessel functions. By contrast, the formula C{sub N}(n,T)=(u{sup n}+u{sup N{minus}n})/(1+u{sup N}), where u(K)=cothK{minus}K{sup {minus}1} is the Langevin function and K=JS(S+1)/(k{sub B}T) is the nearest-neighbor dimensionless coupling constant, provides an excellent approximation if N{ge}6 for the regime {vert_bar}K{vert_bar}{lt}3. This choice of approximant combines the expected exponential decay of correlations for increasing yet small values of n, with the cyclic boundary condition for a finite ring, C{sub N}(n,T)=C{sub N}(N{minus}n,T). By way of illustration, we show that, for T{gt}50K, the associated approximant for the susceptibility derived from the approximate correlation function is virtually indistinguishable from both the exact theoretical susceptibility and the experimental data for the {open_quotes}ferric wheel{close_quotes} molecular cluster ([Fe(OCH{sub 3}){sub 2}(O{sub 2}CCH{sub 2}Cl)]{sub 10}), which contains N=10 interacting Fe{sup 3+} ions, each of spin S=5/2, that are symmetrically positioned in a nearly planar ring. {copyright} {ital 1998 American Institute of Physics.}

Luscombe, J.H. [Department of Physics, Naval Postgraduate School, Monterey, California93943 (United States)] [Department of Physics, Naval Postgraduate School, Monterey, California93943 (United States); Luban, M.; Borsa, F. [Ames Laboratory and Department of Physics and Astronomy, Iowa State University, Ames, Iowa50011 (United States)] [Ames Laboratory and Department of Physics and Astronomy, Iowa State University, Ames, Iowa50011 (United States)

1998-05-01

122

Accurate measurement of the molecular thickness of thin organic shells on small inorganic cores using dynamic light scattering.  

PubMed

Dynamic light scattering (DLS) has become a primary nanoparticle characterization technique with applications from material characterization to biological and environmental detection. With the expansion in DLS use from homogeneous spheres to more complicated nanostructures comes a decrease in accuracy. Much research has been performed to develop different diffusion models that account for the vastly different structures, but little attention has been given to the effect on the light scattering properties in relation to DLS. In this work, small (core size < 5 nm) core-shell nanoparticles were used as a case study to measure the capping thickness of a layer of dodecanethiol (DDT) on Au and ZnO nanoparticles by DLS. We find that the DDT shell has very little effect on the scattering properties of the inorganic core and, hence, can be ignored to a first approximation. However, this results in conventional DLS analysis overestimating the hydrodynamic size in the volume- and number-weighted distributions. With the introduction of a simple correction formula that more accurately yields hydrodynamic size distributions, a more precise determination of the molecular shell thickness is obtained. With this correction, the measured thickness of the DDT shell was found to be 7.3 ± 0.3 Å, much less than the extended chain length of 16 Å. This organic layer thickness suggests that, on small nanoparticles, the DDT monolayer adopts a compact disordered structure rather than an open ordered structure on both ZnO and Au nanoparticle surfaces. These observations are in agreement with published molecular dynamics results. PMID:24386968

Shortell, Matthew P; Fernando, Joseph F S; Jaatinen, Esa A; Waclawik, Eric R

2014-01-21

123

Kinetics of enzymatic starch liquefaction: simulation of the high molecular weight product distribution  

SciTech Connect

Enzymatic corn starch liquefaction with alpha-amylase was carried out. Molecular weight distributions of the resulting hydrolysates are presented using aqueous size exclusion chromatographic techniques. It is demonstrated that despite the fact that the enzyme employed reacts in a random endoacting manner, the product distributions are nonrandom. The results are explained in part by a multimerization process whereby the polymeric substrate molecules preferentially associate, forming intermolecular aggregates. These aggregates are either a consequence of the manner in which the material is deposited into the native granular structure of starch or due to intrinsic physical chemical properties of the polysaccharide. In the latter case, the results are shown to correspond to known multimerized amylose, although complete characterization of the polysaccharide is currently not available. The results presented are used to develop a simplified kinetic model of starch liquefaction and shown to simulate the product distributions accurately. 44 references.

Rollings, J.E.; Thompson, R.W.

1984-12-01

124

Absolute Molecular Weight Distribution of Low-Molecular-Weight Heparins by Size-Exclusion Chromatography with Multiangle Laser Light Scattering Detection  

Microsoft Academic Search

The absolute molecular weight (Mr) distribution of seven low-molecular-weight (LMW) heparin products was determined by size-exclusion chromatography (SEC) coupled with multiangle laser light scattering (MALLS) detection. The SEC\\/MALLS technique does not rely on relativeMrstandards for column calibration and yields absoluteMrestimates directly from the angular dependence of scattered light intensity as a function of concentration, as formulated by light scattering theory.

James E. Knobloch; Patrick N. Shaklee

1997-01-01

125

Low molecular weight protamine (LMWP) as nontoxic heparin\\/low molecular weight heparin antidote (II): In vitro evaluation of efficacy and toxicity  

Microsoft Academic Search

Patients undergoing anticoagulation with heparin or low molecular weight heparin (LMWH) require a superior antidote that possesses\\u000a more selective biological actions and a better safety profile than protamine. We had previously developed 2 low molecular\\u000a weight protamine (LMWP) fractions (TDSP4 and TDSP5) from thermolysin-digested protamine as potential nontoxie, heparin-neutralizing\\u000a agents. In this, the second article in this series, studies focused

Li-Chien Chang; Jun Feng Liang; Hsiao-Feng Lee; Lai Ming Lee; Victor C. Yang

2001-01-01

126

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

USGS Publications Warehouse

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.

Lee, M.W.; Meuwly, M.

2013-01-01

127

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

PubMed Central

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

Saboural, Pierre; Chaubet, Frederic; 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, Cedric

2014-01-01

128

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

PubMed

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

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

129

Molecular dynamics study of the molecular weight dependence of surface tensions of normal alkanes and methyl methacrylate oligomers.  

PubMed

Surface tensions (gamma) of normal alkanes and methyl methacrylate (MMA) oligomers at various molecular weights in the low molecular weight range were computed using a newly proposed molecular dynamics (MD) simulation strategy which was developed based on the definition of gamma = ( partial differential U/ partial differential sigma)n,V,S. The MD simulations, even with the use of a generic force field, reproduced the experimentally observed molecular weight dependence of gamma (i.e., gamma proportional Mn(-2/3), where Mn is the number-average molecular weight) for both series of oligomers. Analysis of the data reveals that solvent accessible surface area, one of the key input variables used for the calculation of gamma, exhibits an Mn(2/3) (rather than Mn(1)) dependence. The reason for such dependence is that solvent accessible surface area formed by the chainlike small molecules depends, to a larger extent, on their orientations rather than their size. However, this is not the case for high molecular weight molecules as solvent accessible surface area of such surfaces are determined by the orientations of their segments which are determined by the conformations of the molecules. This may explain why surface tension of polymers experimentally exhibits an Mn(-1) dependence. It is inferred that the corresponding molecular weight dependence of the entropy changes associated with molecules in the low and high molecular weight ranges would be different. PMID:16570996

Li, Chunli; Choi, Phillip

2006-04-01

130

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

E-print Network

predictions, and vapor cloud dispersion. Dedicated to my parents, Razia and Yusuf Shaikh ACKNOWLEDGEMENTS I would like to acknowledge the members of my committee for their suggestions in this work; Dr. M. Sam Mannan for his continued support as my... to thank my parents, Razia and Vusuf Shaikh for the myriad of ways they have supported my efforts throughout my college career. TABLE OF CONTENTS Page ABSTRACT . DEDICATION . lv ACKNOWLEDGEMENTS . TABLE OF CONTENTS v vt LIST OF FIGURES vt 1 1...

Shaikh, Irfan Yusuf

2012-06-07

131

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

SciTech Connect

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.

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

132

Low molecular weight heparin loaded pH-sensitive microparticles.  

PubMed

Low molecular weight heparins (LMWH) have shown efficacy in the treatment of inflammatory bowel disease after parenteral administration however risking severe hemorrhagic adverse effects. Therefore, an oral colonic targeted heparin dosage form allowing the release of LMWH directly in the inflamed tissue would be of major interest. Enoxaparin was entrapped into pH-sensitive microspheres using Eudragit P4135F that dissolves at pH>7.2. Particle preparation was based on a double emulsion technique with either solvent extraction or evaporation. In order to increase the entrapment efficacy several preparation parameters were optimized, such as inner phase volume, polymer concentration, stabilization of the internal interface by surfactants. Solvent evaporation led to higher entrapment rates (evaporation: 70.1+/-9.9%; extraction: 46.5+/-6.4%). When increasing the volume of the inner aqueous heparin phase, lower encapsulation rates and larger microspheres ( approximately 100-400 microm) were obtained. Sorbitan monostearate (1.75-28% of the total particle mass) had a stabilizing effect on the primary water/oil emulsion. Indeed, higher encapsulation rates (7%: 78.2+/-3.5%; 14%: 76.4+/-10.1%) and smaller particles ( approximately 120-160 microm) were obtained whereas hexadecyltrimethylammonium bromide destabilized the primary emulsion. Interfacial tension studies at a simulated internal water/oil interface confirmed these results. As expected, in vitro drug release was found to be strongly pH-dependent; LMWH was retained in microspheres at pH<6 (<20% release within 4h) whereas a fast drug release was obtained at pH 7.4. The developed microspheres exhibited a particle size adapted to the needs of inflammatory bowel disease therapy, an efficient LMWH encapsulation, and a pH-controlled drug release. These microspheres represent a promising tool for the selective oral delivery of heparin to the colon, especially interesting in the treatment of inflammatory bowel disease. PMID:17150317

Meissner, Yvette; Ubrich, Nathalie; El Ghazouani, Fatima; Maincent, Philippe; Lamprecht, Alf

2007-04-20

133

High molecular weight polyethylene nanospheres: synthesis physical and mechanical properties.  

PubMed

The high molecular weight (MW) polyethylene (PE) particles of particle size varied from macro to micron to nanometer were synthesized by Grignard reagent. The microscopy analysis (scanning electron microscope, SEM; transmission electron microscope, TEM; and atomic force microscope, AFM) shows the spherical shape of PE particles. The effects of particle size, varies from macro to nanometer scale on crystal structure, crystallinity (chic), glass transition temperature (Tg), melting temperature (Tm), surface roughness and mechanical properties were studied. Differential scanning calorimetry (DSC) experiments show that the nanoparticles of PE are highly crystalline (chic approximately equal 72%). The crystal length of PE nanoparticles is found to be approximately 14 A. Although the Gibbs-Thomson equation is explained the depression of melting temperature (DeltaTm) by 5 degrees C, the impervious results of Tg are still not fully understood. The low roughness value (2 A) proves the presence of "atomic-scale-chain" folding at the surface of PE nanoparticles. A novel protocol is developed, and the elastic modulus of individual nanospherical PE particles is computed from 'force-distance' mapping curves of AFM. Hemispherical tungsten (W) tip was fabricated from focused ion beam and used as an indenter to measure the mechanical properties. It is found that the nano sized PE particles have higher elastic modulus (E = 1.2-1.4 GPa) compared to the bulk or macro sized PE (E = 0.6-0.7 GPa). The results corroborate the robustness of our experiments, since, the analogous results for macro sized particles match well with the literature. PMID:18681057

Paik, Pradip; Kar, Kamal K

2008-06-01

134

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

NASA Astrophysics Data System (ADS)

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.

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

2014-05-01

135

Influence of Polymer Molecular Weight, Temperature, and Strain Rate on the Mechanical Properties of PBX 9501  

Microsoft Academic Search

Compression and tensile measurements were conducted on newly formulated (baseline) and lower molecular weight (virtually-aged) specimens of plastic-bonded explosive PBX 9501. The PBX 9501 binder system is composed of nitroplasticized Estane 5703, a polyester urethane 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

D. J. Idar; D. G. Thompson; G. T. Gray III; W. R. Blumenthal; C. D. Cady; P. D. Peterson; B. J. Jacquez; E. L. Roemer; W. J. Wright

2001-01-01

136

Short communication Improved reproducibility in the determination of the molecular weight  

E-print Network

Short communication Improved reproducibility in the determination of the molecular weight characterization of chitosan being reported by Wu and coworkers in 1976, who devised a protocol involving injection, UV, detection were employed and molecular weights were determined relative to dextran standards (Wu

Buschmann, Michael

137

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

ERIC Educational Resources Information Center

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)

Grider, Douglas J.; And Others

1988-01-01

138

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

SciTech Connect

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.

Fuller, E.N.

1992-08-01

139

Molecular weight dependence of coexistence curve of polystyrene/Poly(2-chloro styrene) blends  

NASA Astrophysics Data System (ADS)

Phase diagrams of polystyrene (PS)/Poly(2-chloro styrene) (P2-ClS) blend systems were determined by differential scanning calorimetry (DSC) measurements in order to investigate the molecular weight dependence. The temperature-concentration region where the two phase state is stable increased with increasing PS molecular weight showing the tendensy to increase the incompatibility.

Takahashi, Masato; Orino, Daisuke; Saito, Masahito; Kobayashi, Hideyuki; Yamaguchi, Hiroaki; Matsuda, Hideomi

1999-04-01

140

Formation of high molecular weight products from benzene during boundary lubrication  

NASA Technical Reports Server (NTRS)

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.

Morales, W.

1985-01-01

141

Are All Low Molecular Weight Heparins Equivalent in the Management of Venous Thromboembolism?  

Microsoft Academic Search

Low molecular weight heparins are replacing unfractionated heparin in a number of clinical indications because of their improved subcutaneous bioavailability and more predictable antithrombotic response. Clinical trials have demonstrated that low molecular weight heparins are at least as safe and effective as unfractionated heparin for the initial treatment of venous thromboembolism, and unfractionated heparin and warfarin for primary and secondary

Jawed Fareed; Walter Jeske; Daniel Fareed; Melaine Clark; Rakesh Wahi; Cafer Adiguzel; Debra Hoppensteadt

2008-01-01

142

Correlation between gas molecular weight, heating value and sonic speed under variable compositions of natural gas  

Microsoft Academic Search

A simulation study of likely uncertainties in molecular weight and heating value of the gas mixture as predicted from measured or calculated sonic speed. The sonic speed, molecular weight and heating value of natural gas were studied as a function of random fluctuation of the gas fractions. A method of sonic speed prediction was developed and used for over 50,000

L. Burstein; D. Ingman; Y. Michlin

1999-01-01

143

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

E-print Network

High-Molecular-Weight Polyethylene Glycol Prevents Lethal Sepsis Due to Intestinal Pseudomonas: During stress, erosion of protective intestinal mucus occurs in association with adherence of this study were to test the ability of a high-molecular- weight polyethylene glycol compound, polyethylene

Lee, Ka Yee C.

144

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

PubMed

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

Saravanan, Ramachandran

2014-01-01

145

Two-Phase Thermodynamic Model for Efficient and Accurate Absolute Entropy of Water from Molecular Dynamics Simulations  

E-print Network

to study the properties of water under various physical and chemical environments around biological mol properties from MD simulations. 1. Introduction The thermodynamic properties of water (especially the energyTwo-Phase Thermodynamic Model for Efficient and Accurate Absolute Entropy of Water from Molecular

Goddard III, William A.

146

Bacterial degradation of high molecular-weight polynuclear aromatic hydrocarbons  

SciTech Connect

The ability of Pseudomonas paucimobilis, strain EPA 505 (a soil bacterium capable of utilizing fluoranthene as the sole source of carbon and energy for growth) to metabolize a variety of high molecular-weight polynuclear aromatic hydrocarbons (PAHs) was investigated. After 16 hours of incubation with 10 ppm of a PAH, a resting cell suspension (1 mg wet cells/ml) of P. paucimobilis grown on fluoranthene degraded 80.0, 72.9, 31.5, 33.3, 12.5, and 7.8% of pyrene, benz[a]anthracene (B[a]A), chrysene, benzo[a]pyrene (B[a]P), benzo[b]fluoranthene (B[b]F), and dibenz[a,h]anthracene (DB[a,h]A), respectively. No degradation of dibenz[a,1]pyrene was detected under these conditions. Studies with [7-{sup 14}C]B[a]P and [5,6,11,12-{sup 14}C]chrysene showed that after 48 hours of incubation, the cells degraded nearly 28 and 42% of {sup 14}C-B[a]P and {sup 14}C-chrysene to {sup 14} C0{sub 2}, respectively, suggesting that the bacterium is able to metabolize B[a]P and chrysene via ring cleavage. No evolution of {sup 14}CO{sub 2} was detected from cultures incubated with [4,5,9,10{sup 14}C]pyrene or [1,2,3,4,4a,4bU-{sup 14}C]dibenz[a,1]pyrene. The degradation of B[a]P with P. paucimobilis significantly reduced the mutagenic activity associated with the hydrocarbon. The addition of 5 ppm of B[a]A, chrysene, fluoranthene, or DB[a,h]A to the incubation medium containing 5 ppm B[a]P had no effect on the degradation of B[a]P by P. paucimobilis. The data suggest that P. paucimobilis, strain EPA 505 may be useful for remediation of PAH-contaminated sites.

Ye, D.; Siddiqi, A.; Kumar, S.; Sikka, H.C. [State Univ. of New York, Buffalo, NY (United States)

1995-12-31

147

Structural elucidation of Argonne premium coals: Molecular weights, heteroatom distributions and linkages between clusters  

SciTech Connect

The objective of this study is to create a statistically accurate picture of important structural features for a group of coals representing a broad rank range. Mass spectrometric techniques are used to study coals, coal extracts and chemically modified coals and extracts. Laser desorption mass spectrometry is used to determine molecular weight distributions. Desorption chemical ionization high resolution mass spectrometry provides detailed molecular information on compound classes of molecules is obtained using tandem mass spectrometry. These results are correlated with other direct studies on these samples such as solid NMR, XPS and X-ray absorption spectroscopy. From the complex sets of data, several general trends are emerging especially for heteroatom containing species. From a statistical point of view, heteroatoms must play important roles in the reactivity of all coals. Direct characterization of sulfur containing species in the Argonne coals has been reported from XANES analysis. Indirect methods used include: TG-FTIR and HRMS which rely on thermal desorption and pyrolysis to vaporize the samples. Both XANES and XPS data on nitrogen has been reported, but at this time, the XPS information is probably more reliable. Results from HRMS are discussed in this paper. Most other information on nitrogen is limited to analysis of liquefaction products. However, nitrogen can be important in influencing characteristics of coal liquids and as a source of NO{sub x}`s in coal combustion.

Winans, R.E.,; Kim, Y.; Hunt, J.E.; McBeth, R.L.

1995-12-31

148

How Does the Preparation of Rye Porridge Affect Molecular Weight Distribution of Extractable Dietary Fibers?  

PubMed Central

Extractable dietary fiber (DF) plays an important role in nutrition. This study on porridge making with whole grain rye investigated the effect of rest time of flour slurries at room temperature before cooking and amount of flour and salt in the recipe on the content of DF components and molecular weight distribution of extractable fructan, mixed linkage (1?3)(1?4)-?-d-glucan (?-glucan) and arabinoxylan (AX) in the porridge. The content of total DF was increased (from about 20% to 23% of dry matter) during porridge making due to formation of insoluble resistant starch. A small but significant increase in the extractability of ?-glucan (P = 0.016) and AX (P = 0.002) due to rest time was also noted. The molecular weight of extractable fructan and AX remained stable during porridge making. However, incubation of the rye flour slurries at increased temperature resulted in a significant decrease in extractable AX molecular weight. The molecular weight of extractable ?-glucan decreased greatly during a rest time before cooking, most likely by the action of endogenous enzymes. The amount of salt and flour used in the recipe had small but significant effects on the molecular weight of ?-glucan. These results show that whole grain rye porridge made without a rest time before cooking contains extractable DF components maintaining high molecular weights. High molecular weight is most likely of nutritional importance. PMID:21686191

Rakha, Allah; Aman, Per; Andersson, Roger

2011-01-01

149

Effect of molecular weight distribution on e-beam exposure properties of polystyrene  

NASA Astrophysics Data System (ADS)

Polystyrene is a negative electron beam resist whose exposure properties can be tuned simply by using different molecular weights (Mw). Most previous studies have used monodisperse polystyrene with a polydispersity index (PDI) of less than 1.1 in order to avoid any uncertainties. Here we show that despite the fact that polystyrene’s sensitivity is inversely proportional to its Mw, no noticeable effect of very broad molecular weight distribution on sensitivity, contrast and achievable resolution is observed. It is thus unnecessary to use the costly monodisperse polystyrene for electron beam lithography. Since the polydispersity is unknown for general purpose polystyrene, we simulated a high PDI polystyrene by mixing in a 1:1 weight ratio two polystyrene samples with Mw of 170 and 900 kg mol-1 for the high Mw range, and 2.5 and 13 kg mol-1 for the low Mw range. The exposure property of the mixture resembles that of a monodisperse polystyrene with similar number averaged molecular weight \\overline{{Mn}}, which indicates that it is \\overline{{Mn}} rather than \\overline{{Mw}} (weight averaged molecular weight) that dominates the exposure properties of polystyrene resist. This also implies that polystyrene of a certain molecular weight can be simulated by a mixture of two polystyrenes having different molecular weights.

Dey, Ripon Kumar; Cui, Bo

2013-06-01

150

High Molecular Weight Petrogenic and Pyrogenic Hydrocarbons in Aquatic Environments  

NASA Astrophysics Data System (ADS)

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

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

2003-12-01

151

Heparin and low-molecular-weight heparin therapy for venous thromboembolism. The twilight of anticoagulant monitoring.  

PubMed

Recent improvements in the methods of clinical trials and the use of accurate objective tests to detect venous thromboembolism have made possible a series of randomized trials to evaluate various treatments for venous thromboembolism. The results of these trials have resolved many of the uncertainties a clinician confronts in selecting an appropriate course of anticoagulant therapy. These trials have shown that the intensity of both initial heparin treatment and long-term anticoagulant therapy must be sufficient to prevent unacceptable rates of recurrence of venous thromboembolism. Patients with proximal deep vein thrombosis who receive inadequate anticoagulant therapy have a risk of clinically evident, objectively documented recurrent venous thromboembolism that approaches 20% to 25%. The need for therapy with heparin and the importance of monitoring blood levels of the effect of heparin have been established. The importance of achieving adequate heparinization was suggested by a nonrandomized trial in 1972 and randomized trials in the 1980s have confirmed this finding. Furthermore, randomized trials have demonstrated the importance of achieving adequate heparinization early in the course of therapy. Unfractionated intravenous heparin has provided an effective therapy for more than half a century, but the need to monitor therapy and establish therapeutic levels is a fundamental problem. It is evident that validated heparin protocols are more successful in establishing adequate heparinization than intuitive ordering by the clinician. However, even with the best of care using a heparin protocol, some patients treated with intravenous heparin will receive subtherapy. In this context, subtherapy reflects a practical limitation of the use of unfractionated heparin, rather than a poor standard of care. Furthermore, it is recognized that the practical difficulties associated with heparin administration are compounded by the substantive practical difficulties of standardizing APTT testing and the therapeutic range. Our findings emphasize the confounding effect that initial heparin treatment has on long-term outcome. In future trials of longterm therapy, it is imperative that the initial therapy is of adequate intensity and duration; failure to administer adequate initial treatment may lead to a poor outcome that is falsely attributed to the long-term therapy under evaluation. Therapy with low-molecular-weight heparin, which does not require monitoring and dose finding, is the likely practical solution to these dilemmas. Based on the experience of difficulties achieving adequate therapy with subcutaneous unfractionated heparin dosing, we administered a low-molecular-weight heparin formulation in a single daily dose, rather than splitting the treatment into 2 equal doses. The initial intensity of therapy was thereby maximized. Therapy with low-molecular-weight heparin proved to be better than therapy with unfractionated heparin. PMID:10204652

Hull, R D; Pineo, G F; Stein, P

1998-12-01

152

High molecular weight first generation PMR polyimides for 343 C applications  

NASA Technical Reports Server (NTRS)

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.

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

1992-01-01

153

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

NASA Technical Reports Server (NTRS)

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.

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

1979-01-01

154

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

Microsoft Academic Search

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

Tobias Kind; Oliver Fiehn

2007-01-01

155

Critical Analysis and Review of Flash Points of High Molecular Weight Poly-functional C, H, N, O Compounds  

E-print Network

The research focuses on the critical review and prediction of flash points of high molecular weight compounds used mainly in the specialty chemical area. Thus far this area of high molecular weight specialty chemicals has not been thoroughly...

Thomas, Derrick

2011-08-08

156

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

PubMed

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

Alvarez-Garcia, Daniel; Barril, Xavier

2014-10-23

157

Molecular weight, chain profile of rice amylopectin and starch pasting properties.  

PubMed

Differences in fine structure, average molecular size of amylopectin (AP) as well as clarity of the AP solution from indica waxy rice and high amylose (HAM) rice were examined. Despite similar amylose content (AM), rice starches displayed different pasting properties. Waxy APs had higher values of both number-average and weight-average molecular weight (Mn¯ and Mw¯) but lower values of intrinsic viscosity [?], compared to HAM APs. HAM APs had higher values of average chain length (CL¯), average external chain length (ECL¯), and a proportion of DP ? 37. Statistical correlations of mol proportions of debranched AP, branching parameters, and molecular weight of AP were calculated. The study showed that starch pasting properties and clarity of AP solutions were influenced by molecular weight and branching characteristics of AP. PMID:24751267

Kowittaya, Chutarat; Lumdubwong, Namfone

2014-08-01

158

PolyPEGA with predetermined molecular weights from enzyme-mediated radical polymerization in water.  

PubMed

The preparation of acrylic polymers with predetermined molecular weights using metalloenzymes as catalysts, ascorbic acid as reducing agent and alkyl halides as initiators is reported. The mechanism of polymerization resembles an ARGET ATRP process. PMID:21552589

Ng, Yeap-Hung; di Lena, Fabio; Chai, Christina L L

2011-06-14

159

21 CFR 172.820 - Polyethylene glycol (mean molecular weight 200-9,500).  

Code of Federal Regulations, 2011 CFR

...polymer of ethylene oxide and water with a mean molecular weight...glycol: Commercial grade. Purify if necessary, by distillation...glycol: Commercial grade. Purify, if necessary, by distillation...glycol and diethylene glycol in water. Suitable...

2011-04-01

160

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

E-print Network

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 ...

Miler, Josef L

2006-01-01

161

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

Microsoft Academic Search

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,

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

162

Sorption and permeation of low molecular weight volatile compounds in polypropylene  

E-print Network

SORPTION AND PERMEATION OP LOW MOLECULAR WEIGHT VOLATILE COMPOUNDS IN POLYPROPYLENE A Thesis by ANTONIO RAMIRO SANTIAGO VIDAL JUNIOR Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment... of the requirements for the degree of MASTER OF SCIENCE August 1991 Major Subject: Mechanical Engineering SORPTION AND PERMEATION OF LOW MOLECULAR WEIGHT VOLATILE COMPOUNDS IN POLYPROPYLENE A Thesis by ANTONIO RAMIRO SANTIAGO VIDAL JUNIOR Approved...

Vidal, Antonio Ramiro Santiago

2012-06-07

163

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

SciTech Connect

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.

Anderson, Christopher; Daggett, Joe; Naulleau, Patrick

2009-12-31

164

Study on Enzymatic Hydrolysis of Gadus morrhua Skin Collagen and Molecular Weight Distribution of Hydrolysates  

Microsoft Academic Search

Process parameters on enzymatic hydrolysis and molecular weight (MW) distribution of collagen hydrolysates from Gadus morrhua skin were investigated. The optimal process parameters were obtained by the single-factor and orthogonal experiments. The molecular weight distribution of hydrolysates was determined using both Sephadex G25 partition and high speed liquid chromatography electricity spray mass spectrum (HPLC-ESI-MS). Collagen hydrolysates were first gained by

Jian-xin HUO; Zheng ZHAO

2009-01-01

165

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

E-print Network

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

Ma, Lena

166

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

...Isopropylidenediphenol-epichlorohydrin resins minimum molecular weight 10,000. 177.1440 Section 177...Isopropylidenediphenol-epichlorohydrin resins minimum molecular weight 10,000. 4,4?-Isopropylidenediphenol-epichlo-rohydrin resins having a minimum molecular weight of 10,000 may be safely used...

2014-04-01

167

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

PubMed Central

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

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

168

Preparation of polysaccharides in different molecular weights from Ulva pertusa Kjellm (Chorophyta)  

NASA Astrophysics Data System (ADS)

As molecular weight controls the biological activities of polysaccharides, screening the optimal molecular weight of polysaccharides is important in drug research and application. In this study, hydrogen peroxide was employed as oxidant, and temperature, reaction time, and concentration of polysaccharides and hydrogen peroxide were examined for their effects on the preparation of polysaccharides in different molecular weights from Ulva pertusa. Our experiment suggested that the optimal degradation concentrations for polysaccharides and hydrogen peroxide were 2.5% (w/v) and 8.0% (v/v), respectively. The range of degradation measured by relative viscosity was mainly controlled by temperature and time. Results revealed that 35°C was the optimal temperature for obtaining low-degradation samples, and 50°C was the most favorable temperature to accelerate the reaction to yield highly-degraded samples. Four samples in different molecular weights A, B, C and D were finally prepared. The controllability was evaluated by the relative standard deviation (RSD) of relative viscosity, and the peak molecular weights and the polydispersity indexes (Mw/Mn) of molecular weights were measured by high performance gel permeation chromatography (HPGPC).

Yu, Pengzhan; Zhang, Quanbin; Zhang, Hong; Niu, Xizhen; Li, Zhien

2004-12-01

169

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

PubMed

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

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

170

Accurate physical laws can permit new standard units: The two laws F?=ma? and the proportionality of weight to mass  

NASA Astrophysics Data System (ADS)

Three common approaches to F?=ma? are: (1) as an exactly true definition of force F? in terms of measured inertial mass m and measured acceleration a?; (2) as an exactly true axiom relating measured values of a?, F? and m; and (3) as an imperfect but accurately true physical law relating measured a? to measured F?, with m an experimentally determined, matter-dependent constant, in the spirit of the resistance R in Ohm's law. In the third case, the natural units are those of a? and F?, where a? is normally specified using distance and time as standard units, and F? from a spring scale as a standard unit; thus mass units are derived from force, distance, and time units such as newtons, meters, and seconds. The present work develops the third approach when one includes a second physical law (again, imperfect but accurate)—that balance-scale weight W is proportional to m—and the fact that balance-scale measurements of relative weight are more accurate than those of absolute force. When distance and time also are more accurately measurable than absolute force, this second physical law permits a shift to standards of mass, distance, and time units, such as kilograms, meters, and seconds, with the unit of force—the newton—a derived unit. However, were force and distance more accurately measurable than time (e.g., time measured with an hourglass), this second physical law would permit a shift to standards of force, mass, and distance units such as newtons, kilograms, and meters, with the unit of time—the second—a derived unit. Therefore, the choice of the most accurate standard units depends both on what is most accurately measurable and on the accuracy of physical law.

Saslow, Wayne M.

2014-04-01

171

Influence of molecular weight on the thermal decomposition of hydroxyl terminated polybutadiene  

Microsoft Academic Search

Thermogravimetric analysis of hydroxyl terminated polybutadiene (HTPB) and its fractions of different molecular weights separated by preparative GPC shows two major stages of weight loss of different nature in a nitrogen atmosphere. The first stage is primarily depolymerisation, cyclisation and crosslinking of molecules and the second stage is mainly the decomposition of the residue from the first stage. The kinetic

Sreelatha S. Panicker; K. N. Ninan

1997-01-01

172

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

E-print Network

). In addi- tion, weight reduction by calorie restriction or gastric bypass sur- ISSN Print 0013-7227 ISSNUnique Profile of Chicken Adiponectin, a Predominantly Heavy Molecular Weight Multimer, and Relationship to Visceral Adiposity Gilbert L. Hendricks III,* Jill A. Hadley,* Susan M. Krzysik-Walker, K

Ramachandran, Ramesh

173

Intrinsic viscoelasticity in thin high-molecular-weight polymer films  

NASA Astrophysics Data System (ADS)

The rheology of 44-75-nm-thick polystyrene films were probed by destabilization in an electric field. The non-cross-linked films showed the hallmark of viscoelasiticy; they exhibited elastic behavior at high shear rates and viscous rheology at low shear rates for stationary applied fields. These results are interpreted in terms of surface adhesion of chain segments in contact with the substrate surface, which substantially reduces reptative molecular motion of nearly all chains within the film.

Sheng, Xiaoyuan; Wintzenrieth, Frédéric; Thomas, Katherine R.; Steiner, Ullrich

2014-06-01

174

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

Microsoft Academic Search

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,

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

1999-01-01

175

Molecular weight determination from light scattering and refraction in solutions. A new and coherent theoretical equation  

Microsoft Academic Search

The classical theoretical equation allowing for the determination of the solute's molecular weight (M2) from light scattering (LS) and refractive measurements in diluted solutions is reexamined. Serious theoretical and practical defects in its derivation and application are pointed out, especially about the refraction increment dndc. A new theoretical equation is deduced from a more consistent application of the basic molecular

M. Hérail; M. Le Guennec; D. Le Goff; A. Proutière

1996-01-01

176

From high molecular weight precursor polyrotaxanes to supramolecular sliding networks. The ‘sliding gels’  

Microsoft Academic Search

This paper presents the synthesis and characterization of an original class of supramolecular networks, the ‘sliding’ gels. In this new class of network materials the crosslink points are not fixed but sliding. The molecular structure is based on intermolecularly crosslinked ?-cyclodextrins\\/poly(ethylene-glycol) precursor polyrotaxanes. A synthetic method was developed to obtain various high molecular weight precursor polyrotaxanes with various amounts of

Guillaume Fleury; Guy Schlatter; Cyril Brochon; Georges Hadziioannou

2005-01-01

177

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

ERIC Educational Resources Information Center

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…

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

2010-01-01

178

Identification of high molecular weight serine-proteases in Loxosceles intermedia (brown spider) venom  

Microsoft Academic Search

High molecular weight serine-proteases have been identified in Loxosceles intermedia (brown spider) venom. The mechanism by which Loxosceles spp venoms cause dermonecrotic injury (a hallmark of loxoscelism) is currently under investigation, but it seems to be molecularly complex and in some instance proteases might be expected to play a role in this skin lesion. In the present investigation, when we

Silvio S. Veiga; Rafael B. da Silveira; Juliana L. Dreyfuss; Juliana Haoach; Aline M. Pereira; Oldemir C. Mangili; Waldemiro Gremski

2000-01-01

179

Synthesis of the low molecular weight heat shock proteins in plants  

Microsoft Academic Search

Heat shock of living tissue induces the synthesis of a unique group of proteins, the heat shock proteins. In plants, the major group of heat shock proteins has a molecular mass of 15 to 25 kilodaltons. Accumulation to these proteins to stainable levels has been reported in only a few species. To examine accumulation of the low molecular weight heat

M. A. Mansfield; J. L. Key

1987-01-01

180

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

E-print Network

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.

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

2006-10-19

181

Accurate predictions for molecular magnetisabilities and rotational g tensors using a simple and efficient DFT approach  

Microsoft Academic Search

In a recent paper, we applied a simple but highly efficient density functional theory (DFT) method which appeared to correct for the deficiencies in the virtual Kohn–Sham (KS) orbitals and eigenvalues of the prediction of nuclear shielding parameters. We now report the performance of this new DFT approach to the prediction of molecular magnetisabilities and rotational g tensors. For comparison,

P. J Wilson; R. D Amos; N. C Handy

2000-01-01

182

Molecular weight distribution analysis by ultracentrifugation: adaptation of a new approach for mucins.  

PubMed

Mucins are the key macromolecular component of mucus, nature's natural lubricant, and one of the most important physical properties is their molecular weight distribution. A new approach for polydisperse polymers was recently published based on sedimentation velocity in the analytical ultracentrifuge and converts a distribution of sedimentation coefficient g(s) vs. s plot into a distribution of molecular weight utilising the power-law or scaling relationship between the sedimentation coefficient and molecular weight, s=?sMw(b) where s is the sedimentation coefficient, Mw is the weight average molecular weight and ?s and b are characteristic coefficients related to conformation. We investigate the possibility of using a large database of previously published values of s an M to define ?s and b for both aqueous solution and aqueous solution supplemented by 6M guanidine hydrochloride (a solvent which helps to minimise sample degradation). These values are then applied to a study of the molecular weight distributions of preparations of human gastric mucin in the different solvents and at different stages of purification. PMID:23465917

Gillis, Richard B; Adams, Gary G; Wolf, Bettina; Berry, Monica; Besong, Tabot M D; Corfield, Anthony; Kök, Samil M; Sidebottom, Ray; Lafond, David; Rowe, Arthur J; Harding, Stephen E

2013-03-01

183

Molecular weight changes induced in an anionic polydimethylsiloxane by gamma irradiation in vacuum  

NASA Astrophysics Data System (ADS)

An anionic almost monodisperse linear polydimethylsiloxane (PDMS) was subjected to gamma irradiation under vacuum at room temperature. The molecular weight changes induced by the radiation process have been investigated using size exclusion chromatography (SEC) with refraction index (RI) and multi angle laser light scattering (MALLS) detectors, to obtain the number and weight average molecular weights of the irradiated samples. The analysis of the data indicates that crosslinking reactions predominated over scission reactions. The results obtained by an SEC-RI have confirmed the presence of small, but measurable amounts of scission. A previously developed mathematical model of the irradiation process that accounts for simultaneous scission and crosslinking and allows for both H- and Y-crosslinks, fitted well the measured molecular weight data. This prediction is in accordance with the experimental data obtained by 29Si-Nuclear Magnetic Resonance spectroscopy (NMR) and previously reported data for commercial linear PDMS ( Satti et al., 2008).

Satti, Angel J.; Andreucetti, Noemí A.; Ciolino, Andrés E.; Vitale, Cristian; Sarmoria, Claudia; Vallés, Enrique M.

2010-11-01

184

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

USGS Publications Warehouse

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.

Davis, J. A.; Gloor, R.

1981-01-01

185

A Large Catalog of Accurate Distances to Molecular Clouds from PS1 Photometry  

E-print Network

Distance measurements to molecular clouds are important, but are often made separately for each cloud of interest, employing very different different data and techniques. We present a large, homogeneous catalog of distances to molecular clouds, most of which are of unprecedented accuracy. We determine distances using optical photometry of stars along lines of sight toward these clouds, obtained from PanSTARRS-1. We simultaneously infer the reddenings and distances to these stars, tracking the full probability distribution function using a technique presented in Green et al. (2014). We fit these star-by-star measurements using a simple dust screen model to find the distance to each cloud. We thus estimate the distances to almost all of the clouds in the Magnani et al. (1985) catalog, as well as many other well-studied clouds, including Orion, Perseus, Taurus, Cepheus, Polaris, California, and Monoceros R2, avoiding only the inner Galaxy. Typical statistical uncertainties in the distances are 5%, though the sys...

Schlafly, E F; Finkbeiner, D P; Rix, H -W; Bell, E F; Burgett, W S; Chambers, K C; Draper, P W; Hodapp, K W; Kaiser, N; Magnier, E A; Martin, N F; Metcalfe, N; Price, P A; Tonry, J L

2014-01-01

186

Low-molecular-weight polyethylenimine as a non-viral vector for DNA delivery: comparison of physicochemical properties, transfection efficiency and in vivo distribution with high-molecular-weight polyethylenimine  

Microsoft Academic Search

Low-molecular-weight polyethylenimine (LMW-PEI) was synthesized by the acid-catalyzed, ring-opening polymerization of aziridine and compared with commercially available high-molecular-weight PEI (HMW-PEI) of 25 kDa. Molecular weights were determined by size-exclusion chromatography in combination with multi-angle laser light scattering. The weight average molecular weight (Mw) of synthesized LMW-PEI was determined as 5.4±0.5 kDa, whereas commercial HMW-PEI showed a Mw of 48±2 kDa.

Klaus Kunath; Anke von Harpe; Dagmar Fischer; Holger Petersen; Ulrich Bickel; Karlheinz Voigt; Thomas Kissel

2003-01-01

187

Antihyperlipidemic effects of different molecular weight sulfated polysaccharides from Ulva pertusa (Chlorophyta).  

PubMed

Ulvan, a sulfated polysaccharide from Ulva pertusa, was degraded to yield two low molecular weight fractions U1 and U2. The molecular weights of ulvan and its fractions were determined and varied from 151.6 to 28.2 kDa. They were fed to rats on a hypercholesterolemic diet for 21 days to evaluate and compare the antihyperlipidemic actions. Ulvan-based diet significantly lowered the levels of serum total cholesterol (-45.2%, P<0.05) and low density lipoprotein cholesterol (LDL-cholesterol, -54.1%, P<0.05). While U1- and U2-based diets significantly elevated the levels of serum high density lipoprotein cholesterol (HDL-cholesterol, +22.0% for U1, not significant; +61.0% for U2; P<0.05) and reduced triglyceride (TG, -82.4% for U1, -77.7% for U2; P<0.05) in rats as compared to control diet. In addition, consumptions of various ulvans significantly increased fecal bile acid excrement. The results indicated that ulvans with different molecular weights exhibited diverse effects on lipid metabolism. The high molecular weight ulvan was effective in serum total and LDL-cholesterol, whereas low molecular weight fractions were in TG and HDL-cholesterol. The fractions were considered to be more beneficial to hyperlipidemia associated with diabetes over ulvan. PMID:14527817

Pengzhan, Yu; Ning, Li; Xiguang, Liu; Gefei, Zhou; Quanbin, Zhang; Pengcheng, Li

2003-12-01

188

Methodology for preservation of high molecular-weight RNA in paraffin-embedded tissue: application for laser-capture microdissection.  

PubMed

Laser-capture microdissection techniques have enhanced the ability to perform molecular studies of pure-cell populations. Although many technical factors affect the outcome of the procedure, none is more critical than the appropriate handling of the tissue. Because extraction of intact RNA from paraffin-embedded tissue is a difficult and inconsistent process, frozen sections with their attendant problems are used for this purpose. The major limitation of frozen section is its inferior morphologic quality compared with paraffin-embedded sections that may complicate accurate identification of cells during microdissection. We have developed a procedure that provides both high-quality histomorphology and RNA preservation in paraffin-embedded tissue. It is based on the use of a methanol-based fixative coupled with microwave-assisted rapid tissue processing. This technology in conjunction with a modified hematoxylin-eosin stain and a RNA extraction method allows isolation of high molecular-weight RNA from laser-capture microdissected, hematoxylin and eosin-stained paraffin sections. The high quality of the extracted RNA was confirmed by capillary electrophoresis and RT-PCR. The combination of a methanol-based fixative, rapid microwave tissue processing, and a modified hematoxylin and eosin stain produces paraffin sections that yield high molecular-weight RNA upon microdissection. This methodology opens the door for a wide range of gene expression analyses using paraffin-embedded tissue. PMID:16106192

Vincek, Vladimir; Nassiri, Mehdi; Block, Norman; Welsh, Catherine F; Nadji, Mehrdad; Morales, Azorides R

2005-09-01

189

Coupling density functional theory to polarizable force fields for efficient and accurate Hamiltonian molecular dynamics simulations  

NASA Astrophysics Data System (ADS)

Hybrid molecular dynamics (MD) simulations, in which 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, pose a challenge. A corresponding computational approach should guarantee energy conservation, exclude artificial distortions of the electron density at the interface between the DFT and PMM fragments, and should treat the long-range electrostatic interactions within the hybrid simulation system in a linearly scaling fashion. Here we describe a corresponding Hamiltonian DFT/(P)MM implementation, which accounts for inducible atomic dipoles of a PMM environment in a joint DFT/PMM self-consistency iteration. The long-range parts of the electrostatics are treated by hierarchically nested fast multipole expansions up to a maximum distance dictated by the minimum image convention of toroidal boundary conditions and, beyond that distance, by a reaction field approach such that the computation scales linearly with the number of PMM atoms. Short-range over-polarization artifacts are excluded by using Gaussian inducible dipoles throughout the system and Gaussian partial charges in the PMM region close to the DFT fragment. The Hamiltonian character, the stability, and efficiency of the implementation are investigated by hybrid DFT/PMM-MD simulations treating one molecule of the water dimer and of bulk water by DFT and the respective remainder by PMM.

Schwörer, Magnus; Breitenfeld, Benedikt; Tröster, Philipp; Bauer, Sebastian; Lorenzen, Konstantin; Tavan, Paul; Mathias, Gerald

2013-06-01

190

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

NASA Astrophysics Data System (ADS)

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.

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

2014-01-01

191

Preparation and gel properties of low molecular weight curdlan by hydrolysis of curdlan with commercial ?-amylase.  

PubMed

Low molecular weight curdlan (LMWC) was prepared by hydrolysis of curdlan with commercial ?-amylase. The hydrolysis reaction was conducted using 31.94mg ?-amylase per 500mL reaction mixture, which contained 5g curdlan. The hydrolysis was performed at pH 5.98 and 55.92°C for 10min. The molecular weight and structure of LMWC were characterized by high-performance liquid chromatography and Fourier transform infrared spectroscopy, respectively. Generally, LMWC showed lower gel strength than high molecular weight curdlan (HMWC). Unlike HMWC, LMWC could form into a gel at 50°C. By contrast, HMWC could form into a gel at pH 11, but LMWC gel failed to form at this pH level. The strength of LMWC and HMWC gels increased with increasing temperature and decreased with increasing pH level. PMID:25256495

Chen, Yi-Feng; Zhu, Qin; Wu, Sheng-Jun

2014-11-26

192

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

PubMed

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

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

2014-09-01

193

Albumin-bound low molecular weight thiols analysis in plasma and carotid plaques by CE.  

PubMed

We describe a new method for the quantification of low molecular weight thiols, as homocysteine, cysteine, cysteinylglycine, glutamylcysteine and glutathione bound to human plasma albumin. After albumin isolation and purification by SDS-PAGE, thiols were freed from protein with tri-n-butylphosphine and successively derivatized with 5-iodoacetamidofluorescein. Samples were then injected and quantified in about 18 min by CE with laser induced fluorescence detection. Precision tests indicate a good repeatability of the method both for migration times (RSD<0.63%) and areas (RSD<2.98%). The method allows to measure all five low molecular weight thiols released from just 3 microg of albumin thus improving the other described methods in which only three or four thiols were detected. Due to the elevated sensitivity (LOD of 0.3 pM for all thiols), also low molecular weight thiols bound to albumin filtered in tissues could be quantified. PMID:19950356

Zinellu, Angelo; Lepedda, Antonio; Sotgia, Salvatore; Zinellu, Elisabetta; Marongiu, Giommaria; Usai, Maria Franca; Gaspa, Leonardo; De Muro, Pierina; Formato, Marilena; Deiana, Luca; Carru, Ciriaco

2010-01-01

194

The antineoplastic effect of low-molecular-weight heparins – a literature review  

PubMed Central

There is some evidence for the antitumor effect of heparins, especially the low-molecular-weight ones. The authors discuss the potential mechanism of this antineoplastic effect and present results from several in vitro and in vivo experiments. The clinical trials concerning the impact of low-molecular-weight heparins on the tumor and on the patients’ survival are described. The objective was to find out if heparins could be administered as an antitumor drug, independently of their anticoagulatory properties. The antitumor role of tissue factor, heparinase, chemokines, stromal proteins, cellular interactions as well as angiogenesis and immunology seems certain. The results of the available studies seem promising but large clinical trials are necessary in order to confirm the antineoplastic effect of the low-molecular-weight heparins and to approve them for standard anticancer treatment. It could be a breakthrough in modern oncology. PMID:23788954

Püsküllüo?lu, Miros?awa; Krzemieniecki, Krzysztof

2013-01-01

195

Pharmacological effects and clinical applications of ultra low molecular weight heparins.  

PubMed

Heparin, one of the common anticoagulants, is clinically used to prevent and treat venous thromboembolism (VTE). Though it has been the drug of choice for many advanced medical and surgical procedures with a long history, the adverse events, such as bleeding, heparin-induced thrombocytopenia (HIT), allergic reactions, follow. Therefore, low molecular weight heparins (LMWHs) and ultra low molecular weight heparins (ULMWHs), with lower molecular weights, higher anti-FXa activity, longer half-life times and lower incidence of adverse events than unfractionated heparin (UFH), were researched and developed. Fondaparinux, a chemically synthesized ULMWH of pentasaccharide, has the same antithrombin III (AT-III)-binding sequence as found in UFH and LMWH. In addition, AVE5026 and RO-14, another two ULMWHs, are obtained by selective chemical depolymerization. In this paper, we review the preparation process, pharmacological effects and clinical applications of fondaparinux, AVE5026 and RO-14. PMID:24647152

Liu, Zhang; Ji, Shengli; Sheng, Juzheng; Wang, Fengshan

2014-02-01

196

Properties of different molecular weight sodium lignosulfonate fractions as dispersant of coal-water slurry  

SciTech Connect

Four purified sodium lignosulfonate (SL) samples with different molecular weights were prepared by fractionation using ultrafiltration. The effect of the molecular weights of SL on the apparent viscosity of coal-water slurry (CWS) was investigated by studying the adsorption amounts and the zeta potentials in the coal-water interface. The results show that the adsorption behavior of the dispersants in the coal-water interface is the key factor to affect the dispersing effect, that the higher adsorption amount and compact adsorption film help reduce the viscosity reduction of CWS, and that the zeta potential is also an important factor influenced by the sulfonic group and carboxy contents of the lignosulfonate molecule. Furthermore, SL with a molecular weight ranging from 10000 to 50000 has both a higher adsorbed amount and zeta potential on the coal surface and the best effect on reducing the viscosity of the coal-water slurry.

Zhou, M.S.; Qiu, X.Q.; Yang, D.J.; Lou, H.M. [South China University of Technology, Guangzhou (China). School for Chemical & Energy Engineering

2006-07-01

197

Molecular weight effects upon the adhesive bonding of a mussel mimetic polymer.  

PubMed

Characterization of marine biological adhesives are teaching us how nature makes materials and providing new ideas for synthetic systems. One of the most widely studied adhering animals is the marine mussel. This mollusk bonds to wet rocks by producing an adhesive from cross-linked proteins. Several laboratories are now making synthetic mimics of mussel adhesive proteins, with 3,4-dihydroxyphenylalanine (DOPA) or similar molecules pendant from polymer chains. In select cases, appreciable bulk bonding results, with strengths as high as commercial glues. Polymer molecular weight is amongst several parameters that need to be examined in order to both understand biomimetic adhesion as well as to maximize performance. Experiments presented here explore how the bulk adhesion of a mussel mimetic polymer varies as a function of molecular weight. Systematic structure-function studies were carried out both with and without the presence of an oxidative cross-linker. Without cross-linking, higher molecular weights generally afforded higher adhesion. When a [N(C4H9)4](IO4) cross-linker was added, adhesion peaked at molecular weights of ~50,000-65,000 g/mol. These data help to illustrate how changes to the balance of cohesion versus adhesion influence bulk bonding. Mussel adhesive plaques achieve this balance by incorporating several proteins with molecular weights ranging from 6000 to 110,000 g/mol. To mimic these varied proteins we made a blend of polymers containing a range of molecular weights. Interestingly, this blend adhered more strongly than any of the individual polymers when cross-linked with [N(C4H9)4](IO4). These results are helping us to both understand the origins of biological materials as well as design high performance polymers. PMID:23668520

Jenkins, Courtney L; Meredith, Heather J; Wilker, Jonathan J

2013-06-12

198

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

USGS Publications Warehouse

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.

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

2000-01-01

199

Low-Molecular-Weight Heparin (Fragmin) During Instability in Coronary Artery Disease (FRISC)  

Microsoft Academic Search

This study evaluated whether the low-molecular-weight (LMW) heparin dalteparin sodium (Fragmin) had protective effects against cardiac events in aspirin-treated patients with unstable coronary artery syndromes. Patients (n = 1,506) with unstable angina or non-Q-wave myocardial infarction were randomized to double-blind, placebo-controlled treatment with LMW heparin. The treatment was given as subcutaneous injections: 120 U\\/kg body weight\\/12 hours during the first

1997-01-01

200

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

PubMed

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

Dömling, Alexander

2008-06-01

201

Modification of Low Molecular Weight Polysaccharides from Tremella Fuciformis and Their Antioxidant Activity in Vitro  

PubMed Central

In this study, sulfated low molecular-weight Tremella fuciformis polysaccharides (SLTP) with different sulfate contents were synthesized and their antioxidant activities, including superoxide anion radical, 1,1-diphenyl-2-picryl-hydrazyl (DPPH) radical and hydroxyl radical scavenging activities were investigated. The results indicated that, compared to natural Tremella fuciformis polysaccharide (TP) and low molecular weight Tremella fuciformis polysaccharide (LTP), sulfated LTP (SLTP) exhibited stronger scavenging activity towards superoxide anion, DPPH and hydroxyl radicals. In all the cases the effect was found to be dose dependent. The scavenging activity of SLTP was found to be in parallel with the degree of sulfation of SLTP.

Wu, Qiong; Zheng, Cheng; Ning, Zheng-Xiang; Yang, Bao

2007-01-01

202

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

NASA Technical Reports Server (NTRS)

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.

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

1985-01-01

203

Accurate Thermodynamics for Short-Ranged Truncations of Coulomb Interactions in Site-Site Molecular Models  

E-print Network

Coulomb interactions are present in a wide variety of all-atom force fields. Spherical truncations of these interactions permit fast simulations but are problematic due to their incorrect thermodynamics. Herein we demonstrate that simple analytical corrections for the thermodynamics of uniform truncated systems are possible. In particular results for the SPC/E water model treated with spherically-truncated Coulomb interactions suggested by local molecular field theory [Proc. Nat. Acad. Sci. USA 105, 19136 (2008)] are presented. We extend results developed by Chandler [J. Chem. Phys. 65, 2925 (1976)] so that we may treat the thermodynamics of mixtures of flexible charged and uncharged molecules simulated with spherical truncations. We show that the energy and pressure of spherically-truncated bulk SPC/E water are easily corrected using exact second-moment-like conditions on long-ranged structure. Furthermore, applying the pressure correction as an external pressure removes the density errors observed by other research groups in NPT simulations of spherically-truncated bulk species.

Jocelyn M. Rodgers; John D. Weeks

2009-11-14

204

Affine-response model of molecular solvation of ions: Accurate predictions of asymmetric charging free energies.  

PubMed

Two mechanisms have been proposed to drive asymmetric solvent response to a solute charge: a static potential contribution similar to the liquid-vapor potential, and a steric contribution associated with a water molecule's structure and charge distribution. In this work, we use free-energy perturbation molecular-dynamics calculations in explicit water to show that these mechanisms act in complementary regimes; the large static potential (?44 kJ/mol/e) dominates asymmetric response for deeply buried charges, and the steric contribution dominates for charges near the solute-solvent interface. Therefore, both mechanisms must be included in order to fully account for asymmetric solvation in general. Our calculations suggest that the steric contribution leads to a remarkable deviation from the popular "linear response" model in which the reaction potential changes linearly as a function of charge. In fact, the potential varies in a piecewise-linear fashion, i.e., with different proportionality constants depending on the sign of the charge. This discrepancy is significant even when the charge is completely buried, and holds for solutes larger than single atoms. Together, these mechanisms suggest that implicit-solvent models can be improved using a combination of affine response (an offset due to the static potential) and piecewise-linear response (due to the steric contribution). PMID:23020318

Bardhan, Jaydeep P; Jungwirth, Pavel; Makowski, Lee

2012-09-28

205

Synthesis of the low molecular weight heat shock proteins in plants  

SciTech Connect

Heat shock of living tissue induces the synthesis of a unique group of proteins, the heat shock proteins. In plants, the major group of heat shock proteins has a molecular mass of 15 to 25 kilodaltons. Accumulation to these proteins to stainable levels has been reported in only a few species. To examine accumulation of the low molecular weight heat shock proteins in a broader range of species, two-dimensional electrophoresis was used to resolve total protein from the following species: soybean (Glycine max L. Merr., var Wayne), pea (Pisum sativum L., var Early Alaska), sunflower (Helianthus annuus L.), wheat (Triticum asetivum L.), rice (Oryza sativa L., cv IR-36), maize (Zea mays L.), pearl millet (Pennisetum americanum L. Leeke, line 23DB), and Panicum miliaceum L. When identified by both silver staining and incorporation of radiolabel, a diverse array of low molecular weight heat shock proteins was synthesized in each of these species. These proteins accumulated to significant levels after three hours of heat shock but exhibited considerable heterogeneity in isoelectric point, molecular weight, stainability, and radiolabel incorporation. Although most appeared to be synthesized only during heat shock, some were detectable at low levels in control tissue. Compared to the monocots, a higher proportion of low molecular weight heat shock proteins was detectable in control tissues from dicots.

Mansfield, M.A.; Key, J.L. (Univ., of Georgia, Athens (USA))

1987-08-01

206

Synthesis of the low molecular weight heat shock proteins in plants.  

PubMed

Heat shock of living tissue induces the synthesis of a unique group of proteins, the heat shock proteins. In plants, the major group of heat shock proteins has a molecular mass of 15 to 25 kilodaltons. Accumulation of these proteins to stainable levels has been reported in only a few species. To examine accumulation of the low molecular weight heat shock proteins in a broader range of species, two-dimensional electrophoresis was used to resolve total protein from the following species: soybean (Glycine max L. Merr., var Wayne), pea (Pisum sativum L., var Early Alaska), sunflower (Helianthus annuus L.), wheat (Triticum aestivum L.), rice (Oryza sativa L., cv IR-36), maize (Zea mays L.), pearl millet (Pennisetum americanum L. Leeke, line 23DB), and Panicum miliaceum L. When identified by both silver staining and incorporation of radiolabel, a diverse array of low molecular weight heat shock proteins was synthesized in each of these species. These proteins accumulated to significant levels after three hours of heat shock but exhibited considerable heterogeneity in isoelectric point, molecular weight, stainability, and radiolabel incorporation. Although most appeared to be synthesized only during heat shock, some were detectable at low levels in control tissue. Compared to the monocots, a higher proportion of low molecular weight heat shock proteins was detectable in control tissues from dicots. PMID:16665553

Mansfield, M A; Key, J L

1987-08-01

207

A Simple Karl Fischer Titration Technique for Measuring the Silanol Content of High Molecular Weight Polysiloxanes  

Microsoft Academic Search

This article presents a simple technique for measuring the silanol (SiOH) content of polysiloxanes having molecular weights of 26,000 amu or more. It extends an earlier procedure, in which 50°C methanol converts each silanol group into a methoxy group (SiOCH3) and the resulting water is measured by Karl Fischer titration. Unlike previous work, however, the present technique dissolves the high molecular

Louis A. Bloomfield

2012-01-01

208

Asphaltene Molecular Size and Weight by Time-Resolved Fluorescence Depolarization  

Microsoft Academic Search

The most important attribute of any chemical compound is its elemental constituents. There is, fortunately, no uncertainty\\u000a about the elemental composition of asphaltenes. The second most important attribute of any chemical compound is its molecular\\u000a structure and, as a prerequisite to that information, molecular weight. Although the set of structures of individual chemical\\u000a units constituting asphaltene, such as the number

Henning Groenzin; Oliver C. Mullins

209

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

NASA Technical Reports Server (NTRS)

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.

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

2000-01-01

210

Effect of cyclic strain on the mechanical behavior of virgin ultra-high molecular weight polyethylene.  

PubMed

Ultra High Molecular Weight Polyethylene (UHMWPE) is a polymeric material employed in critical biomedical applications. Knowledge of its mechanical behavior is essential in order to obtain accurate prediction of stresses and deformations in real components, in particular when cyclic loading is considered. In the present research the effects of alternating and pulsating cyclic strain on the mechanical response of UHMWPE were studied by means of an experimental procedure based on tests carried out in strain control at different mean cyclic strain levels. During the tests the temperature increase due to hysteretic heating was controlled by means of a compressed air cooling apparatus specifically devised. By taking advantage of the possibility to control and stabilize temperature, cyclic steady-state mechanical response was investigated at room temperature and at 37 and 50 °C, comparing the effects of alternating and pulsating loading cycles. A transient thermal analysis using the finite element method (FEM) was also carried out to analyze temperature distribution within the specimen. UHMWPE exhibited cyclic softening as a result of a thermal contribution due to temperature increase and of a mechanical contribution related to the effects of applied load on the microstructure. The material exhibited different peak stress percent reductions for pulsating and alternating loading and during tensile and compressive loading phases. For pulsating tests significant cyclic mean stress relaxation was also observed. Based on the experimental procedure described the cyclic curve was determined as a function of temperature and fitted with a Ramberg-Osgood type constitutive equation, in which material parameters are temperature dependent. In this way the combined effects of temperature rises, such as those that might occur in biological environments or due to frictional heating, and mechanical loads could effectively be taken into account for constitutive modeling purposes of cyclic mechanical behavior of UHMWPE. PMID:21783133

Avanzini, A

2011-10-01

211

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

PubMed

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

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

2014-01-01

212

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

PubMed Central

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

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

2014-01-01

213

Localization of small heat shock proteins to the higher plant endomembrane system. [Low-molecular-weight heat shock proteins  

SciTech Connect

Most eukaryotic cells respond to high temperature and other stresses with the production of heat shock proteins, which aid in cell survival. There are four major classes of heat shock proteins HSP90, HSP70, HSP60 and low-molecular weight HSP. The data from this research indicate that members of the low-molecular weight heat shock proteins are most likely resident endoplasmic reticulum (ER) proteins and may be similar in function to related low-molecular weight heat shock proteins in the cytoplasm. The low-molecular weight heat shock proteins, the HSP90 and the HSP70 all appear to localize to the endoplasmic reticulum. Since the ER-localized low-molecular weight heat shock proteins are physically separated from their counterparts in other cell compartments, investigations of the ER-localized heat shock proteins provides a simplified model system for determining the functions of low-molecular weight heat shock proteins in eukaryotes.

Helm, K.W.; Vierling, E. (Univ. of Arizona, Tucson (United States)); LaFayette, P.R.; Nagao, R.T.; Key, J.L. (Univ. of Georgia, Athens (United States))

1993-01-01

214

Neutron Scattering of Solution-Grown Polymer Crystals: Molecular Dimensions Are Insensitive to Molecular Weight  

Microsoft Academic Search

Neutron scattering gives information on molecular conformations in solid solutions of polymers of one isotope in another. Results on crystals of polyethylene grown from solution show a molecular dimension (in the form of a radius of gyration) that is almost invariant with the length of the chain. It is proposed that certain lengths of folded chains fold back onto themselves

D. M. Sadler; A. Keller

1979-01-01

215

Water activity and mobility in solutions of glycerol and small molecular weight sugars: Implication for cryo- and lyopreservation  

NASA Astrophysics Data System (ADS)

In this study, the free volume models, originally developed for large molecular weight polymer-solvent systems, were used to study the water activity and mobility in solutions of four small molecular weight cryo-/lyoprotectants, viz., glycerol, a monosaccharide (fructose), and two disaccharides (sucrose and trehalose). The free volume model parameters were determined by fitting the models to available experimental data using a nonlinear optimization procedure. It was found that free volume models could accurately predict the available experimental data, which suggests that the free volume models might be generally applicable to aqueous solutions of small molecular weight cryo-/lyoprotectants. Furthermore, several models for estimating the mutual diffusion coefficient were tested using available experimental data for aqueous solutions of glycerol and a better method to estimate the mutual diffusion coefficient was proposed. Free volume models were used to predict and analyze the water activity and mobility in solutions of four cryo-/lyoprotectants under conditions frequently encountered in cryo-/lyopreservation applications. It was found that the water mobility in the glassy state of the above four solutions is essentially negligible in the case of cryopreservation with storage temperature lower than -110°C. However, the water mobility in a glass at higher temperature (>-80°C) may be significant. As a result, a subcooling of up to 50°C may be necessary for the long-term cryo-/lyopreservation of biomaterials depending on the water content and the type of cryo-/lyoprotectants. It was further shown that trehalose might be the best of the four protectants studied for lyopreservation (water mass fraction ?0.1) when the storage temperature is above the room temperature. The results from this study might be useful for the development of more effective protocols for both cryopreservation and lyopreservation of living cells and other biomaterials.

He, Xiaoming; Fowler, Alex; Toner, Mehmet

2006-10-01

216

Oversulfated Chondroitin Sulfate: Impact of a Heparin Impurity, Associated with Adverse Clinical Events, on Low-Molecular-Weight Heparin Preparation  

PubMed Central

Heparin, a widely used anticoagulant, is being rapidly displaced by low-molecular-weight heparins. Recently, certain lots of heparin have been associated with anaphylactoid-type reactions resulting from contamination with oversulfated chondroitin sulfate. This impurity has also contaminated low-molecular-weight heparins obtained by chemical and enzymatic depolymerization of heparin. The sensitivity of oversulfated chondroitin sulfate to five different depolymerization processes similar to ones used in preparing low-molecular-weight heparins is reported. PMID:18754653

Zhang, Zhenqing; Weiwer, Michel; Li, Boyangzi; Kemp, Melissa M.; Daman, Tyler H.; Linhardt, Robert J.

2009-01-01

217

Mechanistic and clinical aspects of fatigue of ultrahigh molecular weight polyethylene  

Microsoft Academic Search

Ultrahigh molecular weight polyethylene (UHMWPE) is a tough semi-crystalline polymer employed widely as a bearing material in total joint replacements. While UHMWPE has been tremendously successful in this application, debris generated due to frictional contact may lead ultimately to an adverse biological reaction and failure of the implant. Radiation cross-linking of the polymer has been undertaken in order to improve

Jevan Furmanski

2008-01-01

218

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

NASA Technical Reports Server (NTRS)

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.

Fahey, Robert C.; Newton, Gerald L.

1988-01-01

219

Efficient access to the non-reducing end of low molecular weight heparin for fluorescent labeling.  

PubMed

A novel thiol fluorophore was synthesized to be selectively attached to the non-reducing end of low molecular weight heparin (LMWH) via a Michael addition. Double labeling of LMWH was demonstrated to be a feasible approach for the determination of heparinase II activity by FRET. PMID:24846618

Wang, Zongqiang; Shi, Chen; Wu, Xuri; Chen, Yijun

2014-07-01

220

[Role of low molecular weight heparins for treating non-massive pulmonary embolism].  

PubMed

Pulmonary revascularization after submassive pulmonary embolism can be achieved within 14 days in 50% of the patients treated with intravenous heparin then oral anticoagulants. Recurrence is estimated at 5% and risk of severe haemorrhage at 5 to 6%. For deep vein thrombosis, low-molecular weight heparins are at least as effective as unfractionated heparin and have a comparable or lower rate of complications. For submassive pulmonary embolism, two low-molecular weight heparins (calcium nadroparin and sodium dalteparin) have been compared with unfractionated heparin. Pulmonary revascularization on day 8 was about 68% for all treatment regimens. No cases of recurrent embolism were recorded and no severe haemorrhage occurred in patients given low-molecular weight heparin but did occur in 6% of those given unfractionated heparin. These early results, together with easy subcutaneous administration and the absence of daily dose adaptation requirement, suggest that low-molecular weight heparins could play a major role in treating submassive pulmonary embolism and thromboembolism in general. PMID:7899306

Charbonnier, B; Pacouret, G

1994-12-10

221

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 ...

222

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...

223

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...

224

Molecular weight distribution of Pinus radiata kraft mill wastewater treated by anaerobic digestion  

Microsoft Academic Search

Kraft mill is responsible for massive discharge of highly polluted effluents. The main characteristics of this effluent are high toxicity and low biodegradability due to tannin, lignin and chlorophenol compounds. The composition may vary dramatically depending, for instance, on the utilised feedstock and process. The purpose of this work was to investigate the molecular weight distribution of Pinus radiata kraft

G Vidal; S Videla; M. C Diez

2001-01-01

225

Biopolymer Mimicry with Polymeric Wormlike Micelles: Molecular Weight Scaled Flexibility, Locked-in Curvature,  

E-print Network

Biopolymer Mimicry with Polymeric Wormlike Micelles: Molecular Weight Scaled Flexibility, Locked micelles formed in water from a series of poly(ethylene oxide) (PEO)-based diblock copolymer amphiphiles (lP) of wormlike micelles scaled as lP d2.8 , consistent with a fluid aggregate ( d3 ) rather than

226

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

227

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

NASA Technical Reports Server (NTRS)

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.

Gange, Robert Allen (Inventor)

1977-01-01

228

IR-MALDI OF LOW MOLECULAR WEIGHT COMPOUNDS USING A FREE ELECTRON LASER.  

EPA Science Inventory

Initial experiments on infrared matrix-assisted laser desorption/ionization mass spectrometry (IR-MALDI) using a free electron laser in the analysis of low-molecular-weight compounds are reported. Mass spectra from samples of ethylenediaminetetraacetic acid (EDTA), nitrilotriacet...

229

Ultra-High Molecular-Weight Polyethylene Composites: Structure, Properties and Ballistic Response  

E-print Network

Ultra-High Molecular-Weight Polyethylene Composites: Structure, Properties and Ballistic Response, the sails of racing ships and ballistic impact protection systems. In this study, three commercially and the HB26 laminate was investigated in a ballistic loading scenario. X-ray and thermal analysis have

Wadley, Haydn

230

Synthesis and biological activity of medium molecular weight polymers of camptothecin  

E-print Network

Synthesis and biological activity of medium molecular weight polymers of camptothecin Neung-Ju Lee. Keywords: 3,6-Endo-methylene-1,2,3,6-tetrahydrophthalimidohaxanoylcamptothecin; Camptothecin; Poly,10], neocarzinostatin [11], podophyllotoxin [12] and camptothecin (CPT) [13­16]. Among these compounds the CPT

Theodorakis, Emmanuel

231

Effect of consolidation on adhesive and abrasive wear of ultra high molecular weight polyethylene  

Microsoft Academic Search

Total hip replacement (THR) is widely performed to recover hip joint functions lost by trauma or disease and to relieve pain. The major cause of failure in THR is the wear of the ultra high molecular weight polyethylene (UHMWPE) component. The dominant wear mechanism in THR occurs through adhesion and abrasion. While poor consolidation of UHMWPE is known to increase

Rizwan M. Gul; Frederick J. McGarry; Charles R. Bragdon; Orhun K. Muratoglu; William H. Harris

2003-01-01

232

COMPARISON OF HIGH MOLECULAR WEIGHT ORGANICS ISOLATED FROM DRINKING WATER IN FIVE CITIES  

EPA Science Inventory

Since the previously unidentifiable non-volatile fraction of the chlorinated organics in drinking water is of significant health concern, the physical and chemical characteristics of the high molecular weight organics isolated from drinking water in five cities (New Orleans, Phil...

233

Antithrombotic Activity of Orally Administered Low Molecular Weight Heparin (Logiparin) in a Rat Model  

Microsoft Academic Search

Previous studies in rats demonstrated that orally administered, unfractionated bovine lung heparin is absorbed and has a dose-dependent antithrombotic effect. The objective of this study was to determine if an oral low molecular weight heparin had a similar antithrombotic effect in the same model. Thrombosis was induced in rats by application of 10% formalin in 65% methanol to the exposed

Linda M. Hiebert; Tilly Ping; Sandra M. Wice

2000-01-01

234

Small molecular weight organic thin-film photodetectors and solar cells  

Microsoft Academic Search

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

Peter Peumans; Aharon Yakimov; Stephen R. Forrest

2003-01-01

235

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

E-print Network

The Differential Effect of High and Low Molecular Weight Fucoidans on the Severity of Collagen and LMWF, respectively) on the pro- gression of collagen-induced arthritis (CIA) was tested. A daily oral and the levels of collagen-specific antibodies, while LMWF reduced the severity of arthritis and the levels of Th

Lee, Won-Ha

236

Molecular weight dependence of reductions in the glass transition temperature of thin, freely standing polymer films  

E-print Network

Molecular weight dependence of reductions in the glass transition temperature of thin, freely suggests the possibility of finite size effects; changes in the glass transition temperature and dynamics using calorimetric techniques to mea- sure the glass transition temperature Tg of glass forming or

Dutcher, John

237

Bounds for molecular weights of organic compounds from low resolution mass spectra  

Microsoft Academic Search

Simple empirical rules for determining the upper and lower limits to the molecular weight of organic compounds from low resolution mass spectra have been established and evaluated. The rules are based on the average of two easily determined spectral features, Maxmass and Himax1. The lower limit is this average less 5 Da and the upper limit is the average plus

Donald R. Scott

1995-01-01

238

A simple capillary electrophoresis method for the rapid separation and determination of intact low molecular weight and unfractionated heparins.  

PubMed

A simple, selective and accurate capillary electrophoresis (CE) method has been developed for the rapid separation and identification of various low molecular weight heparins (LMWHs) and unfractionated heparin. Separation and operational parameters were investigated using dalteparin sodium as the test LMWH. The developed method used a 70 cm fused silica capillary (50 microm i.d.) with a detection window 8.5 cm from the distal end. Phosphate electrolyte (pH 3.5; 50 mM), an applied voltage of -30 k V, UV detection at 230 nm and sample injection at 20 mbar for 5s were used. The method performance was assessed in terms of linearity, selectivity, intra- and inter-day precision and accuracy. The method was successfully applied to the European Pharmacopeia LMWH standard, dalteparin sodium, enoxaparin sodium and heparin sodium with a significant reduction in the run time and increased resolution compared with previously reported CE methods. Different CE separation profiles were obtained for various LMWHs and unfractionated heparin showing significant structural diversity. The current methodology was sensitive enough to reveal minor constituent differences between two different batches of enoxaparin sodium. This CE method also clearly showed chemical changes that occurred to LMWHs under different stress conditions. The sensitivity, selectivity and simplicity of the developed method allow its application in research or manufacturing for the identification, stability analysis, characterization and monitoring of batch-to-batch consistency of different low molecular weight and unfractionated heparins. PMID:18024047

Patel, Rahul P; Narkowicz, Christian; Hutchinson, Joseph P; Hilder, Emily F; Jacobson, Glenn A

2008-01-01

239

Neutron scattering of solution-grown polymer crystals: molecular dimensions are insensitive to molecular weight.  

PubMed

Neutron scattering gives information on molecular conformations in solid solutions of polymers of one isotope in another. Results on crystals of polyethylene grown from solution show a molecular dimension (in the form of a radius of gyration) that is almost invariant with the length of the chain. It is proposed that certain lengths of folded chains fold back onto themselves to form stacks of chain-folded ribbons ("superfolding"). PMID:17738998

Sadler, D M; Keller, A

1979-01-19

240

Molecular Weight Changes and Crosslinking Kinetics in Glassy and Elastomeric Thin Films  

NASA Astrophysics Data System (ADS)

The quantitative and qualitative kinetics of molecular bridging through hydrogen extraction from the tertiary carbon in Polymer backbones are explored through HPLC with MALLS in 300nm films of Polystyrene, Poly(n-butyl acrylate), and other polymers above and below the glass transition temperature. Changes in molecular weight distribution and the appearance of peaks at double and triple the original molecular weight allow the study of the initial stages of network formation. The relative merits of multiple bridging molecules are explored, as well as their effects on kinetics and distribution. When our compounds are mixed into a polymer and exposed to UV radiation, they abstract hydrogen atoms from any chains in proximity, thereby initiating a cascade of free radical reactions that include several mechanisms that can lead to covalent polymer crosslinking.

Carbone, Nicholas; Ene, Mada; Lancaster, Jeffrey; Koberstein, Jeffrey

2010-03-01

241

Low-molecular-weight heparin prophylaxis: preoperative versus postoperative initiation in patients undergoing elective hip surgery.  

PubMed

Administration of low-molecular-weight heparin prophylaxis in elective hip implant patients commonly begins 12 h preoperatively in European practices to optimize effectiveness, and 12 to 24 h postoperatively in North American practices to optimize safety. A meta-analysis comparing these two treatment regimes revealed that preoperative initiation demonstrated greater efficacy and superior safety for patients (10.0% rate of total deep-vein thrombosis vs. 15.3%, P = .023). In addition to the pre/postsurgical debate, proximity of initiation of low-molecular-weight heparin in relation to surgery is an issue of critical importance. Recent studies revealed that beginning therapy immediately within 2 h preoperatively or 6 h postoperatively dramatically decreased the risk of venous thrombosis. An investigation of low-molecular-weight heparin prophylaxis initiated 2 h before elective hip surgery or approximately 6 h after surgery compared with warfarin sodium revealed that total and proximal deep-vein thrombosis rates were reduced in patients receiving low-molecular-weight heparin compared with warfarin. The frequencies of deep-vein thrombosis for patients receiving preoperative and postoperative dalteparin vs. warfarin for all deep-vein thrombosis were 36 of 337 (10.7%, P < .001) and 44 of 336 (13.1%, P < .001) vs. 81 of 338 (24.0%); and for proximal deep-vein thrombosis were 3 of 354 (0.8%, P = .035) and 3 of 358 (0.8%, P = .033) vs. 11 of 363 (3.0%). Relative risk reductions for the dalteparin groups vs. warfarin ranged from 45% to 72%. In this case, low-molecular-weight heparin administered in close proximity to surgery provided superior efficacy over warfarin. Major bleeding was significantly increased with the preoperative regimen but not the postoperative regimen. PMID:11342095

Hull, R D; Pineo, G F; MacIsaac, S

2001-01-01

242

The statistical estimation of molecular weights from normal and difference ultracentrifuge boundaries  

PubMed Central

1. To determine molecular weights from boundary data taken from a sedimentation velocity experiment in an ultracentrifuge, the parameter s/D must be estimated. This can be obtained by using non-linear statistical methods to fit a mathematical model [the Fujita & MacCosham (1959) equation] to the results. 2. The statistical method chosen was the simplex method of Nelder & Mead (1965), which was found to be ideal for this problem. Internal errors were calculated at the end of the search for the minimum in the residuals, but in general these errors were found to not represent the overall true error of the experiment. 3. Calculations of molecular weights of myoglobin showed that instabilities at low concentrations of protein (less than 0.8mg/ml) disturbed the calculation of s/D. If 1% (w/v) sucrose was included in the solvent, these instabilities were decreased, and extrapolating to infinite time the linear function of s versus 1/(time) gave an acceptable value for s with an error of ±4.8%. The estimates of the molecular weights were less well-defined and the mean value was low by 8%, with an estimated error of the mean of ±3%. The conclusion was that vibration was responsible for the instabilities without sucrose. 4. The Fujita–MacCosham equation can be extended to make it possible to estimate ratios of sedimentation and molecular weights for difference boundaries. Tests using two solutions of orosomucoid in which a 2% decrease in velocity of one boundary was achieved by adding a calculated quantity of sucrose showed that the analysis gave realistic values for the two ratios, and the error for the ratio of sedimentation coefficients was ±10%. The error was larger for the estimated ratio of the molecular weights, but the analysis gave the expected value for the ratio. PMID:5084797

McCallum, Margaret A.; Spragg, S. P.

1972-01-01

243

Effects of High Molecular Weight Species on Shear-Induced Orientation and Crystallization of Isotactic Polypropylene  

SciTech Connect

In situ rheo-SAXS (small-angle X-ray scattering) and rheo-WAXD (wide-angle X-ray diffraction) techniques were used to investigate the role of high molecular weight species on the evolution of oriented microstructure in isotactic polypropylene (iPP) melt under shear flow. The two iPP samples, designated as PP-A and PP-B, respectively, had the same number-average (M{sub n}) but different weight-average (M{sub w}) and Z-average (M{sub z}) molecular weights. Molecular weight distribution (MWD) of PP-A and PP-B was such that for MW<10{sup 5} the MWD curves overlapped; whereas in the high MW tail region, the amount of high molecular weight species was higher in PP-B than PP-A. Both samples were subjected to an identical shear condition (rate=60 s{sup -1}, duration=5 s, T=155 degC). In situ 2D SAXS and WAXD images allowed the tracking of shear-induced oriented structures in the melt. It was found that the shish structures evolved much earlier, and the degree of crystal orientation and oriented crystal fractions were higher in PP-B than PP-A. Moreover, PP-B exhibited faster crystallization kinetics than PP-A. These results, along with the predictions of double reptation models of chain motion and experimental studies of chain conformation dynamics in dilute solutions under flow, suggest the following: When a polymer melt that consists of entangled chains of different lengths is deformed, the chain segments aligned with the flow eigenvector can undergo the abrupt coil-stretch-like transition, while other segments would remain in the coiled state. Since, flow-induced orientation decays much more slowly for long chains than for short chains, oriented high molecular weight species play a prominent role in formation of the stretched sections, where shish originates. Our experimental results are strong evidence of the hypothesis that even a small increase in the concentration of high molecular weight species causes a significant increase in the formation, stability and concentration of the flow-induced oriented microstructure.

Somani,R.; Yang, L.; Hsiao, B.

2006-01-01

244

A Method of Measuring the Critical Shear Stress of Molten High-Density Polyethylene (HDPE) and the Relationship between the Critical Shear Stress and Molecular Weight or Molecular Weight Distribution  

Microsoft Academic Search

The flow curve of molten high-density polyethylene (HDPE) has the discontinuous point characterized by the critical shear stress. In this paper we propose a method for measuring the critical shear stress and discusse the relationship between the critical shear stress and molecular weight or molecular weight distribution of HDPE. During the experiment at a constant shear rate, the pressure increases

Takatoshi Shimura; Eiichi Takatori; Takeshi Yamamoto

2010-01-01

245

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

SciTech Connect

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.

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

2010-01-01

246

Antifungal effects of chitosan with different molecular weights on in vitro development of Rhizopus stolonifer (Ehrenb.:Fr.) Vuill  

Microsoft Academic Search

Determination of the molecular weight of three types of chitosan was carried out by HPSEC-RI. The effect of low, medium and high molecular weight chitosan was evaluated on development of three isolates of Rhizopus stolonifer. Image analysis and electronic microscopy observations were done in spores of this fungus. Germination of R. stolonifer in potato dextrose broth with chitosan was also

A. N. Hernández-Lauzardo; S. Bautista-Baños; M. G. Velázquez-del Valle; M. G. Méndez-Montealvo; M. M. Sánchez-Rivera; L. A. Bello-Pérez

2008-01-01

247

Effect of the Molecular Weight of Dispersant to the Slurry for Lead-Free Transparent Dielectric Films  

Microsoft Academic Search

To manufacture a green sheet for the lead-free PDP transparent dielectric by tape casting method, the dispersion characteristics of the slurry prepared by different molecular weight of polymeric dispersant have been studied. The dispersion stability was enhanced as the molecular weight of a dispersant was lower. Rapid particle agglomeration occurred by bonding among of long polymer chains and it effected

Byung-Yong Wang; Dae-Soon Lim; Young-Jei Oh

2009-01-01

248

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

Microsoft Academic Search

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

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

249

Effect of Molecular Weight on the Mechanical and Optical Properties of Triacetyl Cellulose Films for LCD Applications  

Microsoft Academic Search

Physical and optical properties of a series of TAC films with different molecular weight synthesized by acetylation of cotton linter have been investigated. The synthesized TACs had fully acetylated structure in which acetic acid contents was about 62%. Dimensional stability, thermal stability, modulus, tensile strength and elongation at break of TAC film were influenced by the molecular weight of base

Myeong Hee Kim; Hyeong Tae Kim; Seong Hun Kim; Kwang-Sik Choi; Kyung Youl Baek; Soon Man Hong; Chong Min Koo

2009-01-01

250

Molecular Characterization and Diagnostic Value of Taenia solium Low-Molecular-Weight Antigen Genes  

Microsoft Academic Search

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

YASUHITO SAKO; MINORU NAKAO; TAKASHI IKEJIMA; XIAN ZHI PIAO; KAZUHIRO NAKAYA; AKIRA ITO

2000-01-01

251

Characteristics of precipitation-formed polyethylene glycol microgels are controlled by molecular weight of reactants.  

PubMed

This work describes the formation of poly(ethylene glycol) (PEG) microgels via a photopolymerized precipitation reaction. Precipitation reactions offer several advantages over traditional microsphere fabrication techniques. Contrary to emulsion, suspension, and dispersion techniques, microgels formed by precipitation are of uniform shape and size, i.e. low polydispersity index, without the use of organic solvents or stabilizers. The mild conditions of the precipitation reaction, customizable properties of the microgels, and low viscosity for injections make them applicable for in vivo purposes. Unlike other fabrication techniques, microgel characteristics can be modified by changing the starting polymer molecular weight. Increasing the starting PEG molecular weight increased microgel diameter and swelling ratio. Further modifications are suggested such as encapsulating molecules during microgel crosslinking. Simple adaptations to the PEG microgel building blocks are explored for future applications of microgels as drug delivery vehicles and tissue engineering scaffolds. PMID:24378988

Thompson, Susan; Stukel, Jessica; AlNiemi, Abrar; Willits, Rebecca Kuntz

2013-01-01

252

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

NASA Technical Reports Server (NTRS)

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.

Buckley, D. H.

1978-01-01

253

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

PubMed

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

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

2012-01-01

254

Determination of molecular weight distributions of large water soluble macromolecules using dynamic light scattering  

SciTech Connect

Characterization of polymer molecular weight is an extremely important aspect of polymer research, and a vast number of analytical techniques has been used to determine molecular weights. One method is dynamic light scattering (DLS). DLS is also referred to as photon correlation spectroscopy (PCS), quasi-elastic light scattering (QLS), and may other appellations. The phenomenon that gives rise to the DLS technique was first observed in the early 1930's. In the mid 1950's, measurement techniques similar to modern dynamic light scattering were developed. Two major technical developments have greatly enhanced the use of DLS. The first was the development of the laser. This provided a light source with very high intensity at a single frequency. Also, major advances in digital electronics have allowed better data acquisition and faster data analysis than were previously available.

Mettille, M.J.; Hester, R.D.

1988-05-01

255

Binding of pyrene to aquatic and commercial humic substances: The role of molecular weight and aromaticity  

USGS Publications Warehouse

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.

Chin, Y. -P.; Aiken, G. R.; Danielsen, K. M.

1997-01-01

256

Evaluating nephrotoxicity of high-molecular-weight organic compounds in drinking water from lignite aquifers  

USGS Publications Warehouse

High-molecular-weight organic compounds such as humic acids and/or fulvic acids that are naturally mobilized from lignite beds into untreated drinking-water supplies were suggested as one possible cause of Balkan endemic nephropathy (BEN) and cancer of the renal pelvis. A lab investigation was undertaken in order to assess the nephrotoxic potential of such organic compounds using an in vitro tissue culture model. Because of the infeasibility of exposing kidney tissue to low concentrations of organics for years in the lab, tangential flow ultrafiltration was employed to hyperconcentrate samples suitable for discerning effects in the short time frames necessitated by tissue culture systems. Effects on HK-2 kidney cells were measured using two different cell proliferation assays (MTT and alamarBlue). Results demonstrated that exposure of kidney tissue to high-molecular-weight organics produced excess cell death or proliferation depending on concentration and duration of exposure. Copyright ?? Taylor & Francis Group, LLC.

Bunnell, J.E.; Tatu, C.A.; Lerch, H.E.; Orem, W.H.; Pavlovic, N.

2007-01-01

257

Low molecular weight measles immunoglobulin M in subacute sclerosing panencephalitis and acute measles.  

PubMed Central

Thirty eight patients with subacute sclerosing panencephalitis (SSPE) were investigated. Five patients who previously had measles immunoglobulin M (IgM) detected in unfractionated serum and cerebrospinal fluid (CSF) had measles IgM exclusively in the low molecular weight (LMW) fractions of serum and CSF. Measles IgM had previously not been found in unfractionated serum from 33 patients but was detected exclusively in the LMW fractions of serum from 30 patients. Seven children with acute measles had the expected high molecular weight (HMW) measles IgM in serum but 5 also had LMW measles IgM. Four young adults who had had measles in childhood had neither HMW nor LMW measles IgM in their sera. PMID:4022875

Connolly, J. H.; Simpson, D. M.; Trudgett, A.; Hopkins, A. P.

1985-01-01

258

High molecular weight acidic polysaccharides from Malva sylvestris and Alcea rosea.  

PubMed

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

Classen, B; Blaschek, W

1998-10-01

259

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

NASA Technical Reports Server (NTRS)

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.

Babcock, Dale A.

1995-01-01

260

Polyethylene glycol interferes with protein molecular weight determinations by gel filtration.  

PubMed

Gel filtration studies on Sephadex G-75 demonstrate markedly increased elution volumes for proteins chromatographed with polyethylene glycol. As little as 5% (w/v) polyethylene glycol in the applied protein sample can reduce apparent molecular weight estimates by gel filtration as much as 55%. Furthermore, gel filtration columns equilibrated with polyethylene glycol are not size-separating columns. Consequently, caution must be exercised when performing and interpreting gel filtration studies of proteins previously treated or precipitated with polyethylene glycol. PMID:6731837

Yan, S B; Tuason, D A; Tuason, V B; Frey, W H

1984-04-01

261

Effects of low-molecular-weight aluminum complexes on brain tissue calcium homeostasis  

Microsoft Academic Search

The in vitro effects of low-molecular-weight aluminum complexes (citrate, lactate, and ATP complex) on the Ca2+ uptake and aluminum-induced lipid peroxidation of brain tissue show that the modification of the calcium homeostasis is determined\\u000a by the nature of the ligand and that there is no correlation between the aluminum-induced lipid peroxidation and the Ca2+ uptake. The same characteristics have been

Leopold J. Anghileri; Pierre Thouvenot; Alain Bertrand

1998-01-01

262

Effect of molecular weight on non-isothermal decomposition kinetics of hydroxyl terminated polybutadiene  

Microsoft Academic Search

Hydroxyl terminated polybutadiene prepared by free radical polymerization was fractionated by a solvent-nonsolvent precipitation method. The fractions were characterized by gel permeation chromatography for their molecular weight averages (¯Mn,¯Mw and¯Mz) and dispersities. The kinetic parameters, viz., energy of activationE and preexponential factorA for the thermal decomposition of the fractions were computed from their TG data, using four nonisothermal integral equations.

K. N. Ninan; K. B. Catherine; K. Krishnan

1990-01-01

263

In vivo antitumor and immunomodulation activities of different molecular weight lambda-carrageenans from Chondrus ocellatus  

Microsoft Academic Search

?-Carrageenan is a sulfated galactan isolated from some red algae and have been reported to have many kinds of biological activities. ?-Carrageenan from Chondrus ocellatus, an important economic alga in China and many other parts of the world, was degraded by microwave, and obtained five products that have different molecular weight: 650, 240, 140, 15, 9.3kDa. Analytical results confirmed that

Gefei Zhou; YuePing Sun; Hua Xin; Yuna Zhang; Zhien Li; Zuhong Xu

2004-01-01

264

Determination of water-soluble low-molecular-weight organic acids in soils by ion chromatography  

Microsoft Academic Search

Low-molecular-weight organic acids (LOAs) widely occur in soils and affect the soil properties and processes. We developed a simplified and relatively rapid method to identify and quantify the water-soluble LOAs in soils by using ion chromatography with an exclusive column for organic acids, an ion exchange column for anions, and an electric conductivity detector. These combinations enabled to separate more

Masayuki Tani; Kayoko Shinjo Shida; Kiyoshi Tsutsuki; Renzo Kondo

2001-01-01

265

The effect of ?-irradiation on ultra-high molecular weight polyethylene recrystallized under different cooling conditions  

Microsoft Academic Search

The effect of ?-irradiation on the thermal and mechanical properties of ultra-high molecular weight polyethylene (UHMWPE) used in orthopedic implants was investigated. UHMWPE was recrystallized with different cooling conditions for the purpose of enhancing the crosslinking extent of the polymer after ?-irradiation. UHMWPE was irradiated with ?-ray to a dosage of 10–500kGy in air and nitrogen atmosphere. Differential scanning calorimetry,

Phil Hyun Kang; Young Chang Nho

2001-01-01

266

Evaluation of number-average molecular weight of poly(tetrafluoroethylene) irradiated with. gamma. rays  

Microsoft Academic Search

The number-average molecular weight of poly(tetrafluoroethylene) (PTFE) irradiated from a ⁶°Co source in air at room temperature has been estimated from the experimental results of tensile creep measurements and electron microscopy. The viscoelastic method which makes use of the maximum relaxation time was used for samples with low radiation doses. The mean chain length of highly irradiated samples, which can

M. Takenaga; K. Yamagata

1981-01-01

267

The effect of substrate on the molecular weight ofpoly-?-hydroxybutyrate produced by Azotobacter vinelandii UWD  

Microsoft Academic Search

Summary Azotobacter vinelandii UWD produced very high molecular weight (MW) (approx. 4 million Daltons) poly-ß-hydroxybutyrate (PHB) when grown in 5% w\\/v beet molasses medium. The polymer MW decreased as the beet molasses concentration was increased. Similar results were obtained in equivalent concentrations of sucrose (as raw sugar), but the polymer MW was not greater than 1.6 million. This difference was

Guo-Qiang Chen; William J. Page

1994-01-01

268

Efficient bulk heterojunction photovoltaic cells using small-molecular-weight organic thin films  

Microsoft Academic Search

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

Peter Peumans; Soichi Uchida; Stephen R. Forrest

2003-01-01

269

Low-Molecular-Weight Heparin Prophylaxis: Preoperative Versus Postoperative Initiation in Patients Undergoing Elective Hip Surgery  

Microsoft Academic Search

Administration of low-molecular-weight heparin prophylaxis in elective hip implant patients commonly begins 12 h preoperatively in European practices to optimize effectiveness, and 12 to 24 h postoperatively in North American practices to optimize safety. A meta-analysis comparing these two treatment regimes revealed that preoperative initiation demonstrated greater efficacy and superior safety for patients (10.0% rate of total deep-vein thrombosis vs.

Russell D. Hull; Graham F. Pineo; Susan MacIsaac

2001-01-01

270

Mechanisms of occupational asthma caused by low-molecular-weight chemicals  

Microsoft Academic Search

\\u000a Understanding the pathogenesis and working mechanisms of occupational asthma (OA) is crucial towards optimizing prevention\\u000a and management of the disease. The study of the sensitizing and asthma-inducing properties of low-molecular-weight (LMW) agents\\u000a is evolving quickly. So far, experimental research has shown that OA caused by sensitization to LMW agents does not completely\\u000a fit the pathways of the traditional allergic model,

Vanessa De Vooght; Valérie Hox; Benoit Nemery; Jeroen A. J. Vanoirbeek

271

Low molecular weight Neutral Boron Dipyrromethene (Bodipy) dyads for fluorescence-based neural imaging  

NASA Astrophysics Data System (ADS)

The neutral low molecular weight julolidine-based borondipyrromethene (Bodipy) dyads JULBD and MJULBD were used for fast voltage-sensitive dye imaging of neurons in the crab stomatogastric ganglion. The fluorescence modulation of the dyads mirrors alterations in the membrane potential of the imaged neurons. The toxicity of the dyes towards the neurons is related to their structure in that methyl groups at the 3,5 positions results in reduced toxic effects.

Bai, Dan; Benniston, Andrew C.; Clift, Sophie; Baisch, Ulrich; Steyn, Jannetta; Everitt, Nicola; Andras, Peter

2014-05-01

272

Solubility and molecular weight of hemicelluloses from Alnus incana and Alnus glutinosa. Effect of tree age  

Microsoft Academic Search

The xylems of Alnus incana Moench. and Alnus glutinosa Gaertn. 8-15-year-old trees were subjected to comparative studies regarding the molecular weight (MW) of hemicelluloses. Extraction of hemicelluloses according to the sequence 1% NaOH-10% KOH-18% NaOH, followed by direct analysis of each extract using the SEC\\/UV method, was applied aiming at simultaneous quantitative and MW analysis. Both the tree age and

Tatiana Bikova; Arnis Treimanis

2002-01-01

273

Low-molecular-weight triacylglycerols of the seed oil of Artemisia absinthium  

Microsoft Academic Search

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%

N. T. Ul'chenko; E. I. Gigienova; A. U. Umarov; U. A. Abdullaev

1981-01-01

274

High Molecular Weight (HMW) Glutenin Subunit Composition of Some Nordic and Middle European Wheats  

Microsoft Academic Search

A collection of 123 winter and 106 spring wheat (Triticum aestivum L.) cultivars and breeding lines commonly grown in Nordic and Middle European countries were characterised for the composition of high-molecular-weight (HMW) glutenin subunits on the ground of data from literature and experiments of author. HMW glutenin subunit composition was determined by one-dimensional sodium dodecyl sulphatepolyacrylamide gel electrophoresis (SDS-PAGE). The

M. Tohver

2007-01-01

275

Studies of low density lipoprotein molecular weight in human beings with coronary artery disease  

Microsoft Academic Search

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

John R. Crouse; Johns S. Parks; Harry M. Schey; Frederic R. Kahl

276

Low molecular weight PEIs modified by hydrazone-based crosslinker and betaine as improved gene carriers.  

PubMed

Low-molecular-weight polyethyleneimine (LMW PEI) exhibits poorer transfection efficiency but lower cytotoxicity compared to high-molecular-weight polyethyleneimine (such as PEI 25kDa). To enhance the gene transfection performance of LMW PEI, we herein demonstrate a new strategy for modifying LMW PEI. A crosslinker containing an acid-labile hydrazone bond (hydrazone-based crosslinker) was synthesized and used to crosslink PEI 1.8kDa and convert it into higher-molecular-weight polycations. And the crosslinked polycations were further modified by incorporating a betaine monomer [N,N-dimethyl(acrylamidopropyl)ammonium propane sulfonate, DMAAPS] onto their surfaces. The molar percentages of the incorporated betaine molecules to amino groups on the polycations were determined as 21.2%, 36.0% and 77.2%, respectively. Molecular weights of the modified polycations were measured using capillary viscometry at pH 7.4 and 5.0, respectively, and the degradation of the polymers in acidic solution was confirmed. The PEIs modified with hydrazone and betaine (PEI-Hdz-DMAAPS) exhibit much lower cytotoxicity than PEI 25K, and they also show no or little hemolytic effect with their hemolysis rates around 5%. PEI-Hdz-DMAAPS21.2%/DNA and PEI-Hdz-DMAAPS36.0%/DNA complexes exhibit high transfection efficiencies, which are comparable to or higher than that of PEI 25K/DNA complex in the absence or presence of 10% serum. With these improved gene delivery properties, the PEI-Hdz-DMAAPS samples have great potential for serving as efficient gene carriers. This strategy may provide some insights for constructing some other biocompatible materials. PMID:25092585

Fang, Gang; Zeng, Fang; Yu, Changmin; Wu, Shuizhu

2014-10-01

277

Characterization of Rhizobial Isolates of Phaseolus vulgaris by Staircase Electrophoresis of Low-Molecular-Weight RNA  

PubMed Central

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

Velazquez, Encarna; Martinez-Romero, Esperanza; Rodriguez-Navarro, Dulce Nombre; Trujillo, Martha E.; Daza, Antonio; Mateos, Pedro F.; Martinez-Molina, Eustoquio; van Berkum, Peter

2001-01-01

278

Length variation of i-type low-molecular-weight glutenin subunit genes in diploid wheats  

Microsoft Academic Search

Allelic variation of the low-molecular-weight glutenin subunit (LMW-GS) is associated with the significant differences of\\u000a dough quality in bread and durum wheat, and has been widely evaluated at protein level in wheat and its relatives. In this\\u000a study, a PCR primer set, targeting the high variable repetitive domains, was employed to assay the length variation of i-type\\u000a LMW-GS genes in

H. Long; Z. Huang; Y.-M. Wei; Z.-H. Yan; Z.-C. Ma; Y.-L. Zheng

2008-01-01

279

Comparative Study on the in vitro and in vivo Activities of Seven Low-Molecular-Weight Heparins  

Microsoft Academic Search

Different low-molecular-weight (LMW) heparins are produced by fractionation, enzymatic and chemical methods. Although the manufacturer’s assigned molecular weights of these agents are similar (around 5,000 daltons), they exhibit considerable molecular structural heterogeneity due to the variations in the manufacturing process. In vitro standardization of these LMW heparins produces highly variable results due to the variability of assay specificity. In a

J. Fareed; J. M. Walenga; D. Hoppensteadt; X. Huan; A. Racanelli

1988-01-01

280

Predictive model for tensile true stress-strain behavior of chemically and mechanically degraded ultrahigh molecular weight polyethylene.  

PubMed

The gamma radiation sterilization of ultrahigh molecular weight polyethylene (UHMWPE) components in air generates long-lived free radicals that oxidize slowly over time during shelf storage and after implantation. To investigate the combined effects of chemical and mechanical degradation on the mechanical behavior of UHMWPE, sterilized tensile specimens were immersed in 0.5% hydrogen peroxide solution at 37 degrees C for up to 9 months and concurrently subjected to cyclic stress levels of 0 (control), 0 to 5, and 0 to 10 MPa. After chemical and mechanical preconditioning, specimen density was measured using the density gradient column technique. The true stress-strain behavior was measured up to 0.12 true strain and characterized using a multilinear material model, the parameters of which were found to vary linearly with density and cyclic stress history. The mechanical behavior of as-irradiated and degraded UHMWPE was accurately predicted by an analytical composite beam model of the tensile specimens. The results of this study support the hypothesis that chemical and mechanical degradation affect the true stress-strain behavior of UHMWPE. In the future, the material model data presented in this study will enable more accurate prediction of the stresses and strains in UHMWPE components following gamma sterilization in air and subsequent in vivo degradation. PMID:9730061

Kurtz, S M; Rimnac, C M; Bartel, D L

1998-01-01

281

Radiation and chemical crosslinking promote strain hardening behavior and molecular alignment in ultra high molecular weight polyethylene during multi-axial loading conditions  

Microsoft Academic Search

The mechanical behavior and evolution of crystalline morphology during large deformation of eight types of virgin and crosslinked ultra high molecular weight polyethylene (UHMWPE) were studied using the small punch test and transmission electron microscopy (TEM). We investigated the hypothesis that both radiation and chemical crosslinking hinder molecular mobility at large deformations, and hence promote strain hardening and molecular alignment

Steven M. Kurtz; Lisa A. Pruitt; Charles W. Jewett; Jude R. Foulds; Avram A. Edidin

1999-01-01

282

Influence of molecular weight on in vitro immunostimulatory properties of instant coffee.  

PubMed

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

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

283

Optimization of Glutamine Peptide Production from Soybean Meal and Analysis of Molecular Weight Distribution of Hydrolysates  

PubMed Central

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

Xie, Yanli; Liang, Xinhong; Wei, Min; Zhao, Wenhong; He, Baoshan; Lu, Qiyu; Huo, Quangong; Ma, Chengye

2012-01-01

284

Determination of dextrose equivalent value and number average molecular weight of maltodextrin by osmometry.  

PubMed

Dextrose equivalent (DE) value is the most common parameter used to characterize the molecular weight of maltodextrins. Its theoretical value is inversely proportional to number average molecular weight (M(n)), providing a theoretical basis for correlations with physical properties important to food manufacturing, such as: hygroscopicity, the glass transition temperature, and colligative properties. The use of freezing point osmometry to measure DE and M(n) was assessed. Measurements were made on a homologous series of malto-oligomers as well as a variety of commercially available maltodextrin products with DE values ranging from 5 to 18. Results on malto-oligomer samples confirmed that freezing point osmometry provided a linear response with number average molecular weight. However, noncarbohydrate species in some commercial maltodextrin products were found to be in high enough concentration to interfere appreciably with DE measurement. Energy dispersive spectroscopy showed that sodium and chloride were the major ions present in most commercial samples. Osmolality was successfully corrected using conductivity measurements to estimate ion concentrations. The conductivity correction factor appeared to be dependent on the concentration of maltodextrin. Equations were developed to calculate corrected values of DE and M(n) based on measurements of osmolality, conductivity, and maltodextrin concentration. This study builds upon previously reported results through the identification of the major interfering ions and provides an osmolality correction factor that successfully accounts for the influence of maltodextrin concentration on the conductivity measurement. The resulting technique was found to be rapid, robust, and required no reagents. PMID:19200083

Rong, Y; Sillick, M; Gregson, C M

2009-01-01

285

High Molecular Weight Isoforms of Growth Hormone In Cells of the Immune System  

PubMed Central

A substantial body of research exists to support the idea that cells of the immune system produce growth hormone (GH). However, the structure and mechanism of action of lymphocyte-derived GH continues to remain largely unknown. Here we present the results of Western analysis of whole cell extracts showing that different molecular weight isoforms of GH of approximately 100 kDa, 65 kDa, and 48 kDa can be detected in primary mouse cells of the immune system and in the mouse EL4 cell line. The identity of the 65 kDa and 48 kDa isoforms of GH were confirmed by mass spectrometry. The various isoforms were detected in both enriched T and B spleen cell populations. The large molecular weight isoform appears to reside primarily in the cytoplasm whereas the lower molecular weight 65 kDa and 48 kDa isoforms were detected primarily in the nucleus. These results also suggest that GH isoforms are induced by oxidative stress. In EL4 cells overexpressing GH, the expression of luciferase controlled by a promoter containing the antioxidant response element is increased almost three-fold above control. The data suggest that the induction of isoforms of the GH molecule in cells of the immune system may be an important mechanism of adaptation and/or protection of lymphoid cells under conditions of oxidative stress. PMID:21741628

Weigent, Douglas A.

2013-01-01

286

Ionic Conductivity of Nanostructured Block Copolymer Electrolytes in the Low Molecular Weight Limit  

NASA Astrophysics Data System (ADS)

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.

Teran, Alexander; Yuan, Rodger; Gurevitch, Inna; Balsara, Nitash

2013-03-01

287

Developmental co-expression of small molecular weight apolipoprotein B synthesis and triacylglycerol secretion  

SciTech Connect

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.

Coleman, R.A.; Haynes, E.B.; Sand, T.M.; Davis, R.A.

1987-05-01

288

The Effect of PEG Molecular Weights on Dissolution Behavior of Simvastatin in Solid Dispersions  

PubMed Central

The purpose of the present study was to investigate the effect of polyethylene glycol (PEG) molecular weights (6000, 12000 and 20000) as solid dispersion (SD) carriers on the dissolution behavior of simvastatin. SDs with various drug : carrier ratios were prepared by solvent method and evaluated for dissolution rate. Differential scanning calorimetry (DSC), X-ray diffraction (XRD), infrared spectroscopy and solubility studies were also performed on the optimum SD formulation. Samples prepared with all three types of PEG showed improved drug dissolution compared to intact drug and corresponding physical mixtures. Meanwhile, the best result was obtained by PEG 12000 with drug : carrier ratio of 1:7 which showed a 3-fold increase in dissolution rate compared to the intact drug. Based on DSC and XRD, no crystalline change occurred during the sample preparation. Solubility studies revealed that increasing the PEG molecular weight resulted in higher phase solubility of drug. In addition, saturated solubility of the optimum SD was significantly higher than that of intact drug and the related physical mixture (24.83, 8.74 and 8.88 ?g/mL, respectively) that could be due to the decreased particle size and aggregation. The results confirmed the influence of PEG molecular weight on drug dissolution rate from solid dispersion systems. PMID:24250667

Bolourchian, Noushin; Mahboobian, Mohammad Mehdi; Dadashzadeh, Simin

2013-01-01

289

Low molecular weight DNA replication intermediates in Escherichia coli: mechanism of formation and strand specificity  

PubMed Central

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

Amado, Luciana; Kuzminov, Andrei

2013-01-01

290

Isolation of low molecular weight metal binding proteins from growth plate chondrocytes  

SciTech Connect

Matrix vesicles (MV), cell derived structures responsible for the induction of mineral formation in the extracellular matrix of cartilage and other calcified tissues have previously been shown to contain high concentrations of zinc. In the present study, the intracellular source of MV Zn was investigated. Crude homogenates of chicken epiphyseal growth plates were centrifuged at 100,000 g and the supernatant fractionated by ultrafiltration. The high molecular weight fraction was found to contain 53% of the total An and 80% of the protein. However, the low molecular weight fraction had the highest specific Zn content. Since Zn was not detected in expressed extracellular fluid, the soluble Zn-binding proteins must be derived from the chondrocyte cytosol. Cytosolic proteins obtained from isolated chondrocytes were fractionated on a Sephedex G-75 column. At least two proteins showing low absorbance at 280 nm and high Zn content were observed in the low molecular weight fractions. The results suggest that metallothionein-like proteins are important in the cellular metabolism of metals essential to the normal mineralization of calcified tissues.

Sauer, G.R.; Wuthier, R.E. (Univ. of South Carolina, Columbia (United States))

1991-03-11

291

Sizing of PDADMAC/PSS complex aggregates by polyelectrolyte and salt concentration and PSS molecular weight.  

PubMed

Herein we report on the influence of salt and polyelectrolyte (PEL) concentration, molecular weight, and mixing ratio on the size and size distribution of polyelectrolyte complex (PEC) particles composed of cationic poly(diallyldimethylammonium chloride) and anionic poly(styrene sulfonic acid). The unusual salt concentration dependence of PEC particle sizes was observed. This behavior was explained by competition of two processes both related to the charge screening: swelling/shrinking of the outer shell formed by the excess PEL molecules and increasing/decreasing of the aggregation rate of colloidal PEC particles. The results on the size regulation of PEC particles by varying PEL concentration reflect both competitive processes as well. The regulation of the mixing ratio of PEL allows producing PEC particles with different charges, and it does not affect significantly the PEC particle size regulation by salt concentration. The PEC size dependence on the molecular weight of polymer was shown to be power and an exponent value of ? ? 0.13 was obtained for the spherical PEC particles. This value is lower than one for polymer particles with a compact globular structure with exponent values of ? = 0.33. However, the molecular weight of only one polymer component of a two-component PEC particle was varied. PMID:23190399

Starchenko, Vitaliy; Müller, Martin; Lebovka, Nikolai

2012-12-27

292

Low molecular weight EPS II of Rhizobium meliloti allows nodule invasion in Medicago sativa.  

PubMed Central

Effective invasion of alfalfa by Rhizobium meliloti Rm1021 normally requires the presence of succinoglycan, an exopolysaccharide (EPS) produced by the bacterium. However, Rm1021 has the ability to produce a second EPS (EPS II) that can suppress the symbiotic defects of succinoglycan-deficient strains. EPS II is a polymer of modified glucose-(beta-1,3)-galactose subunits and is produced by Rm1021 derivatives carrying either an expR101 or mucR mutation. If the ability to synthesize succinoglycan is blocked genetically, expR101 derivatives of Rm1021 are nodulation-proficient, whereas mucR derivatives of Rm1021 are not. The difference in nodulation proficiency between these two classes of EPS II-producing strains is due to the specific production of a low molecular weight form of EPS II by expR101 strains. A low molecular weight EPS II fraction consisting of 15-20 EPS II disaccharide subunits efficiently allows nodule invasion by noninfective strains when present in amounts as low as 7 pmol per plant, suggesting that low molecular weight EPS II may act as a symbiotic signal during infection. Images Fig. 1 Fig. 2 PMID:8710923

Gonzalez, J E; Reuhs, B L; Walker, G C

1996-01-01

293

Absorption spectroscopy of the rubidium dimer in an overheated vapor: An accurate check of molecular structure and dynamics  

SciTech Connect

Experimental studies of the absorption spectrum of the Rb{sub 2} dimer are performed in the 600-1100 nm wavelength range for temperatures between 615 and 745 K. The reduced absorption coefficient is measured by spatially resolved white light absorption in overheated rubidium vapor with a radial temperature gradient, which enables simultaneous measurements at different temperatures. Semiclassical and quantum spectral simulations are obtained by taking into account all possible transitions involving the potential curves stemming from the 5 {sup 2}S+5 {sup 2}S and 5 {sup 2}S+5 {sup 2}P asymptotes. The most accurate experimental potential curves are used where available, and newly calculated potential curves and transition dipole moments otherwise. The overall consistency of the theoretical model with the experimental interpretation is obtained only if the radial dependence of both the calculated transition dipole moments and the spin-orbit coupling is taken into account. This highlights the low-resolution absorption spectroscopy as a valuable tool for checking the accuracy of molecular electronic structure calculations.

Beuc, R.; Movre, M.; Horvatic, V.; Vadla, C. [Institute of Physics, Bijenicka 46, 10000 Zagreb (Croatia); Dulieu, O.; Aymar, M. [Laboratoire Aime Cotton, CNRS, Campus d'Orsay, 91405 Orsay Cedex (France)

2007-03-15

294

High-molecular weight protein toxins of marine invertebrates and their elaborate modes of action.  

PubMed

High-molecular weight protein toxins significantly contribute to envenomations by certain marine invertebrates, e.g., jellyfish and fire corals. Toxic proteins frequently evolved from enzymes meant to be employed primarily for digestive purposes. The cellular intermediates produced by such enzymatic activity, e.g., reactive oxygen species or lysophospholipids, rapidly and effectively mediate cell death by disrupting cellular integrity. Membrane integrity may also be disrupted by pore-forming toxins that do not exert inherent enzymatic activity. When targeted to specific pharmacologically relevant sites in tissues or cells of the natural enemy or prey, toxic enzymes or pore-forming toxins even may provoke fast and severe systemic reactions. Since toxin-encoding genes constitute "hot spots" of molecular evolution, continuous variation and acquirement of new pharmacological properties are guaranteed. This also makes individual properties and specificities of complex proteinaceous venoms highly diverse and inconstant. In the present chapter we portray high-molecular weight constituents of venoms present in box jellyfish, sea anemones, sea hares, fire corals and the crown-of-thorns starfish. The focus lies on the latest achievements in the attempt to elucidate their molecular modes of action. PMID:20358685

Butzke, Daniel; Luch, Andreas

2010-01-01

295

Mass spectrometric techniques for characterizing low-molecular-weight resins used as paint varnishes.  

PubMed

The molecular structure of three low-molecular-weight resins used as paint varnishes has been characterized by use of an approach based on three different mass spectrometric techniques. We investigated the ketone resin MS2A, the aldehyde resin Laropal A81, and the hydrocarbon resin Regalrez 1094, now commonly used in restoration. To date, the molecular structures of these resins have not been completely elucidated. To improve current knowledge of the chemical composition of these materials, information obtained by gas chromatography-mass spectrometry (GC/MS), pyrolysis-gas chromatography-mass spectrometry (Py/GC/MS), and electrospray ionization mass spectrometry (ESI-Q-ToF) was combined. Analysis, in solution, of the whole polymeric fraction of the resins by flow-injection ESI-Q-ToF, and of the non-polymeric fraction by GC-MS, enabled us to identify previously unreported features of the polymer structures. In addition, the Py-GC/MS profiles that we obtained will help to enhance the databases currently available in the literature. The proposed approach can be extended to other low-molecular-weight resins used as varnishes in conservation. PMID:23151653

Bonaduce, I; Colombini, M P; Degano, I; Di Girolamo, F; La Nasa, J; Modugno, F; Orsini, S

2013-01-01

296

Characterization of currently marketed heparin products: analysis of molecular weight and heparinase-I digest patterns.  

PubMed

We evaluated polyacrylamide gel electrophoresis (PAGE) and size exclusion chromatography coupled with multi-angle laser light scattering (SEC-MALLS) approaches to determine weight-average molecular weight (M(w)) and polydispersity (PD) of heparins. A set of unfractionated heparin sodium (UFH) and low-molecular-weight heparin (LMWH) samples obtained from nine manufacturers which supply the US market were assessed. For SEC-MALLS, we measured values for water content, refractive index increment (dn/dc), and the second virial coefficient (A(2)) for each sample prior to molecular weight assessment. For UFH, a mean ± standard deviation value for M(w) of 16,773 ± 797 was observed with a range of 15,620 to 18,363 (n = 20, run in triplicate). For LMWHs by SEC-MALLS, we measured mean M(w) values for dalteparin, tinzaparin, and enoxaparin of 6,717 ± 71 (n = 4), 6,670 ± 417 (n = 3), and 3,959 ± 145 (n = 3), respectively. PAGE analysis of the same UFH, dalteparin, tinzaparin, and enoxaparin samples showed values of 16,135 ± 643 (n = 20), 5,845 ± 45 (n = 4), 6,049 ± 95 (n = 3), and 4,772 ± 69 (n = 3), respectively. These orthogonal measurements are the first M(w) results obtained with a large heparin sample set on product being marketed after the heparin crisis of 2008 changed the level of scrutiny of this drug class. In this study, we compare our new data set to samples analyzed over 10 years earlier. In addition, we found that the PAGE analysis of heparinase digested UFH and neat LMWH samples yield characteristic patterns that provide a facile approach for identification and assessment of drug quality and uniformity. PMID:21901459

Sommers, Cynthia D; Ye, Hongping; Kolinski, Richard E; Nasr, Moheb; Buhse, Lucinda F; Al-Hakim, Ali; Keire, David A

2011-11-01

297

Effect of gamma irradiation on the friction and wear of ultrahigh molecular weight polyethylene  

NASA Technical Reports Server (NTRS)

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.

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

1981-01-01

298

Molecular Size and Weight of Asphaltene and Asphaltene Solubility Fractions from Coals, Crude Oils and Bitumen  

SciTech Connect

The molecular weight of asphaltenes has been a controversy for several decades. In recent years, several techniques have converged on the size of the fused ring system; indicating that chromophores in virgin crude oil asphaltenes typically have 4-10 fused rings. Consequently, the molecular weight debate is equivalent to determining whether asphaltenes are monomeric (one fused-ring system per molecule) or whether they are polymeric. Time-resolved fluorescence depolarization (FD) is employed here to interrogate the absolute size of asphaltene molecules and to determine the relation of the size of the fused ring system to that of the corresponding molecule. Coal, petroleum and bitumen asphaltenes are compared. Molecular size of coal asphaltenes obtained here by FD-determined rotational diffusion match closely with Taylor-dispersion-derived translational diffusion measurements with UV absorption. Coal asphaltenes are smaller than petroleum asphaltenes. N-methyl pyrrolidinone (NMP) soluble and insoluble fractions are examined. NMP soluble and insoluble fractions of asphaltenes are monomeric. It is suggested that the 'giant' asphaltene molecules reported from SEC studies using NMP as the eluting solvent may actually be the expected flocs of asphaltene which are not soluble in NMP. Data is presented that intramolecular electronic relaxation in asphaltenes does not perturb FD results.

Badre,S.; Goncalves, C.; Norinaga, K.; Gustavson, G.; Mullins, O.

2005-01-01

299

High molecular weight hyaluronan mediates the cancer resistance of the naked mole-rat  

PubMed Central

The naked mole-rat displays exceptional longevity, with a maximum lifespan exceeding 30 years1–3. This is the longest reported lifespan for a rodent species and is especially striking considering the small body mass of the naked mole-rat. In comparison, a similarly sized house mouse has a maximum lifespan of 4 years4,5. In addition to their longevity, naked mole-rats show an unusual resistance to cancer. Multi-year observations of large naked mole-rat colonies did not detect a single incidence of cancer2,6. Here we identify a mechanism responsible for the naked mole-rat’s cancer resistance. We found that naked mole-rat fibroblasts secrete extremely high molecular weight hyaluronan (HA), which is over five times larger than human or mouse HA. This high molecular weight HA accumulates abundantly in naked mole rat tissues due to the decreased activity of HA-degrading enzymes and a unique sequence of hyaluronan synthase 2 (HAS2). Furthermore, the naked mole-rat cells are more sensitive to HA signaling, as the naked mole rat cells have a higher affinity to HA than the mouse or human cells. Perturbation of the signaling pathways sufficient for malignant transformation of mouse fibroblasts fails to transform naked mole-rat cells. However, once high molecular weight HA is removed by either knocking down HAS2 or overexpressing the HA-degrading enzyme, Hyal2, naked mole-rat cells become susceptible to malignant transformation and readily form tumors in mice. We speculate that naked mole-rats have evolved a higher concentration of HA in the skin to provide skin elasticity needed for life in underground tunnels. This trait may have then been co-opted to provide cancer resistance and longevity to this species. PMID:23783513

Tian, Xiao; Azpurua, Jorge; Hine, Christopher; Vaidya, Amita; Myakishev-Rempel, Max; Ablaeva, Julia; Mao, Zhiyong; Nevo, Eviatar; Gorbunova, Vera; Seluanov, Andrei

2013-01-01

300

Manifestation of sub-Rouse modes in flow at the surface of low molecular weight polystyrene  

E-print Network

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.

K. L. Ngai; S. Capaccioli; Daniele Prevosto; Luigi Grassia

2014-10-17

301

'All-supramolecular' nanocapsules from low-molecular weight ureas through interfacial addition reaction in miniemulsion.  

PubMed

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

Groison, Emilie; Adjili, Salim; Ferrand, Alice; Lortie, Frédéric; Portinha, Daniel; Sintes-Zydowicz, Nathalie

2011-03-16

302

Antioxidant properties of different molecular weight polysaccharides from Athyrium multidentatum (Doll.) Ching.  

PubMed

Different molecular weight polysaccharides were prepared by degradation of polysaccharides extracted from Athyrium multidentatum (Doll.) Ching rhizome (CPA) with hydrogen peroxide and ascorbic acid. Four low molecular polysaccharides derivatives (CPA-1, CPA-2, CPA-3 and CPA-4) were successfully obtained and had their antioxidant activities investigated employing various established in vitro systems. All CPA derivatives showed pronounced antioxidant activity, and had stronger antioxidant ability than CPA in certain tests. CPA-1 exhibited the strongest scavenging ability on 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical among all samples, and the IC50 value was 25 ?g/mL. CPA-2 possessed the highest scavenging ability against superoxide radical at 200 ?g/mL. The scavenging activity of CPA-4 on hydroxyl radical was higher than CPA from 120 to 200 ?g/mL. The mechanism on influence the antioxidant activity of CPA and its degraded derivatives was indicated. PMID:24751245

Sheng, Jiwen; Sun, Yanlong

2014-08-01

303

An investigation of the preparation of high molecular weight perfluorocarbon polyethers  

NASA Technical Reports Server (NTRS)

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.

Watts, R. O.; Tarrant, P.

1972-01-01

304

Study on Different Molecular Weights of Chitosan as an Immobilization Matrix for a Glucose Biosensor  

PubMed Central

Two chitosan samples (medium molecular weight (MMCHI) and low molecular weight (LMCHI)) were investigated as an enzyme immobilization matrix for the fabrication of a glucose biosensor. Chitosan membranes prepared from acetic acid were flexible, transparent, smooth and quick-drying. The FTIR spectra showed the existence of intermolecular interactions between chitosan and glucose oxidase (GOD). Higher catalytic activities were observed on for GOD-MMCHI than GOD-LMCHI and for those crosslinked with glutaraldehyde than using the adsorption technique. Enzyme loading greater than 0.6 mg decreased the activity. Under optimum conditions (pH 6.0, 35°C and applied potential of 0.6 V) response times of 85 s and 65 s were observed for medium molecular weight chitosan glucose biosensor (GOD-MMCHI/PT) and low molecular weight chitosan glucose biosensor (GOD-LMCHI/PT), respectively. The apparent Michaelis-Menten constant () was found to be 12.737 mM for GOD-MMCHI/PT and 17.692 mM for GOD-LMCHI/PT. This indicated that GOD-MMCHI/PT had greater affinity for the enzyme. Moreover, GOD-MMCHI/PT showed higher sensitivity (52.3666 nA/mM glucose) when compared with GOD-LMCHI/PT (9.8579 nA/mM glucose) at S/N>3. Better repeatability and reproducibility were achieved with GOD-MMCHI/PT than GOD-LMCHI/PT regarding glucose measurement. GOD-MMCHI/PT was found to give the highest enzymatic activity among the electrodes under investigation. The extent of interference encountered by GOD-MMCHI/PT and GOD-LMCHI/PT was not significantly different. Although the Nafion coated biosensor significantly reduced the signal due to the interferents under study, it also significantly reduced the response to glucose. The performance of the biosensors in the determination of glucose in rat serum was evaluated. Comparatively better accuracy and recovery results were obtained for GOD-MMCHI/PT. Hence, GOD-MMCHI/PT showed a better performance when compared with GOD-LMCHI/PT. In conclusion, chitosan membranes shave the potential to be a suitable matrix for the development of glucose biosensors. PMID:23940599

Ang, Lee Fung; Por, Lip Yee; Yam, Mun Fei

2013-01-01

305

Radiation cross-linking in ultra-high molecular weight polyethylene for orthopaedic applications  

PubMed Central

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

Oral, Ebru; Muratoglu, Orhun K.

2007-01-01

306

Total internal reflection ellipsometry and SPR detection of low molecular weight environmental toxins  

NASA Astrophysics Data System (ADS)

The environmental toxins, such as herbicides simazine and atrazine, and T2 mycotoxin were registered with the optical methods of surface plasmon resonance (SPR) and recently developed total internal reflection ellipsometry (TIRE). The immune assay approach was exploited for in situ registration of the above low molecular weight toxins with specific antibodies immobilised onto the gold surface via (poly)allylamine hydrochloride layer using electrostatic self-assembly (ESA) technique. The comparison of two methods of SPR and TIRE shows a higher sensitivity of the latter.

Nabok, A. V.; Tsargorodskaya, A.; Hassan, A. K.; Starodub, N. F.

2005-06-01

307

Antioxidation activities of low-molecular-weight gelatin hydrolysate isolated from the sea cucumber Stichopus japonicus  

Microsoft Academic Search

Gelatin extracted from the body wall of the sea cucumber (Stichopus japonicus) was hydrolyzed with flavourzyme. Low-molecular-weight gelatin hydrolysate (LMW-GH) of 700–1700 Da was produced using an\\u000a ultrafiltration membrane bioreactor system. Chemiluminescence analysis revealed that LMW-GH scavenges high free radicals in\\u000a a concentration-dependent manner; IC50 value for superoxide and hydroxyl radicals was 442 and 285 ?g mL?1, respectively. LMW-GH exhibited

Jingfeng Wang; Yuming Wang; Qingjuan Tang; Yi Wang; Yaoguang Chang; Qin Zhao; Changhu Xue

2010-01-01

308

Dragline silk: a fiber assembled with low-molecular-weight cysteine-rich proteins.  

PubMed

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

Pham, Thanh; Chuang, Tyler; Lin, Albert; Joo, Hyun; Tsai, Jerry; Crawford, Taylor; Zhao, Liang; Williams, Caroline; Hsia, Yang; Vierra, Craig

2014-11-10

309

Is glucose tolerance factor an artifact produced by acid hydrolysis of low-molecular-weight chromium-binding substance?  

Microsoft Academic Search

A low-molecular-weight chromium-binding substance (LMWCr) has been isolated and purified from porcine kidney and porcine kidney powder and characterized. The oligopeptide is biologically active, has a molecular weight ofca 1500 daltons, and is comprised of cysteine, glycine, glutamate, aspartate, and CrIII. Porcine kidney LMWRCr is also susceptible to hydrolysis, especially under the conditions for the acid hydrolysis used in the

K. Heather Sumrall; John B. Vincent

1997-01-01

310

Conductive Fibre Prepared From UltraHigh Molecular Weight Polyaniline for Smart Fabric and Interactive Textile Applications  

Microsoft Academic Search

Panion™ fibre is prepared from a high molecular weight version of chlorine and defect free polyaniline (PANI). It is processed into textile fibre by continuous wet spinning techniques. The room temperature DC conductivity for unstretched and stretched (5x at 373K) high molecular weight samples was 72 and 725??1cm?1, respectively. Resistivity measurements of Panion™, from 4 to 350K, indicate that the

D. Bowman; B. R. Mattes

2005-01-01

311

Thickness effects on fracture toughness of ultra-high-molecular- weight polyethylene via the J-integral  

E-print Network

THICKNESS EFFECTS ON FRACTURE TOUGHNESS OF ULTRA-HIGH-MOLECULAR-WEIGHT POLYETHYLENE VIA THE J-INTEGRAL A Thesis by JARVIS CRAIG LEHMANN Submitted to the Office of Graduate Studies of Texas ARM University in partial fulfillment... of the requirements for the degree of MASTER OF SCIENCE December t 992 Major Subject: Mechanical Engineering THICKNESS EFFECTS ON FRACTURE TOUGHNESS OF ULTRA-HIGH-MOLECULAR-WEIGHT POLYETHYLENE VIA THE J-INTEGRAL A Thesis by JARVIS CRAIG LEHMANN Approved...

Lehmann, Jarvis Craig

2012-06-07

312

Binding and molecular weight properties of the insulin receptor from omental and subcutaneous adipocytes in human obesity  

Microsoft Academic Search

Summary  The insulin binding properties and the molecular weights of the insulin receptor and its insulin binding subunit were studied in omental and subcutaneous adipocytes prepared from obese- and normal-weight subjects. Insulin binding by such adipocytes was decreased in obesity when the binding activity was expressed per unit of cell surface area. No significant difference from the lean controls was evident,

J. N. Livingston; K. M. Lerea; J. Bolinder; L. Kager; L. Backrnan; P. Arner

1984-01-01

313

High and Low Molecular Weight Hyaluronic Acid Differentially Regulate Human Fibrocyte Differentiation  

PubMed Central

Background Following tissue injury, monocytes can enter the tissue and differentiate into fibroblast-like cells called fibrocytes, but little is known about what regulates this differentiation. Extracellular matrix contains high molecular weight hyaluronic acid (HMWHA; ?2×106 Da). During injury, HMWHA breaks down to low molecular weight hyaluronic acid (LMWHA; ?0.8–8×105 Da). Methods and Findings In this report, we show that HMWHA potentiates the differentiation of human monocytes into fibrocytes, while LMWHA inhibits fibrocyte differentiation. Digestion of HMWHA with hyaluronidase produces small hyaluronic acid fragments, and these fragments inhibit fibrocyte differentiation. Monocytes internalize HMWHA and LMWHA equally well, suggesting that the opposing effects on fibrocyte differentiation are not due to differential internalization of HMWHA or LMWHA. Adding HMWHA to PBMC does not appear to affect the levels of the hyaluronic acid receptor CD44, whereas adding LMWHA decreases CD44 levels. The addition of anti-CD44 antibodies potentiates fibrocyte differentiation, suggesting that CD44 mediates at least some of the effect of hyaluronic acid on fibrocyte differentiation. The fibrocyte differentiation-inhibiting factor serum amyloid P (SAP) inhibits HMWHA-induced fibrocyte differentiation and potentiates LMWHA-induced inhibition. Conversely, LMWHA inhibits the ability of HMWHA, interleukin-4 (IL-4), or interleukin-13 (IL-13) to promote fibrocyte differentiation. Conclusions We hypothesize that hyaluronic acid signals at least in part through CD44 to regulate fibrocyte differentiation, with a dominance hierarchy of SAP>LMWHA?HMWHA>IL-4 or IL-13. PMID:22022512

Maharjan, Anu S.; Pilling, Darrell; Gomer, Richard H.

2011-01-01

314

Comparative wear tests of ultra-high molecular weight polyethylene and cross-linked polyethylene.  

PubMed

Wear particle-induced osteolysis is a major concern in hip implant failure. Therefore, recent research work has focussed on wear-resistant materials, one of the most important of which is cross-linked polyethylene. In view of this, the objective of this study was to compare the in vitro wear performance of cross-linked polyethylene to traditional ultra-high molecular weight polyethylene. In order to mimic appropriate in vivo conditions, a novel high-capacity wear tester called a circularly translating pin-on-disc was used. The results of this in vitro study demonstrated that the wear rate for cross-linked polyethylene was about 80% lower than that of conventional ultra-high molecular weight polyethylene. This difference closely matches in vivo results reported in the literature for total hip replacements that use the two biopolymers. The in vitro results were also verified against ASTM F732-00 (standard test method for wear testing of polymeric materials for use in total joint prostheses). The 50-station circularly translating pin-on-disc proved to be a reliable device for in vitro wear studies of orthopaedic biopolymers. PMID:23637270

Harsha, A P; Joyce, Tom J

2013-05-01

315

Structural Characterization of the Symbiotically Important Low-Molecular-Weight Succinoglycan of Sinorhizobium meliloti  

PubMed Central

The production of succinoglycan by Sinorhizobium meliloti Rm1021 is required for successful nodule invasion by the bacterium of its host plant, alfalfa. Rm1021 produces succinoglycan, an acidic exopolysaccharide composed of an octasaccharide repeating unit modified with acetyl, succinyl, and pyruvyl moieties, in both low- and high-molecular-weight forms. Low-molecular-weight (LMW) succinoglycan, previously thought to consist of monomers, trimers, and tetramers of the repeating unit, has been reported as being capable of promoting the formation of nitrogen-fixing nodules by succinoglycan-deficient derivatives of strain Rm1021. We have determined that the three size classes of LMW succinoglycan species are in fact monomers, dimers, and trimers of the repeating unit and that the trimer is the species active in promoting nodule invasion. A detailed structural analysis of the components of LMW succinoglycan by using various chromatographic techniques, along with nuclear magnetic resonance analyses, has revealed that there is considerable heterogeneity within the LMW succinoglycan oligomers in terms of noncarbohydrate substitutions, and we have determined the structural basis of this heterogeneity. PMID:10542182

Wang, Lai-Xi; Wang, Ying; Pellock, Brett; Walker, Graham C.

1999-01-01

316

Impact of molecular weight on lymphatic drainage of a biopolymer-based imaging agent.  

PubMed

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

Bagby, Taryn R; Cai, Shuang; Duan, Shaofeng; Thati, Sharadvi; Aires, Daniel J; Forrest, Laird

2012-01-01

317

Seasonal Variations of Low Molecular Weight Dicarboxylic Acids in Atmospheric Aerosols at Okinawa Islands, Japan  

NASA Astrophysics Data System (ADS)

Low molecular weight dicarboxylic acids are major fraction of water soluble organic compounds in the atmospheric aerosols. Recently, economy of East Asia grows up remarkably, and atmospheric aerosols discharged from this area have been transported to Japan. In this study, we collected aerosol at Cape Hedo (CH) and University of the Ryukyus(UR), and studied the distribution and origin of low molecule dicarboxylic acid. Aerosols were collected on a quartz filter with a high volume air sampler. Low molecular weight dicarboxylic acids extracted by pure water were derivatized to dibutyl esters by reactions with BF3/butanol and were measured by GC-FID. In many samples, oxalic acid showed the highest concentration. Concentration of oxalic acid, malonic acid, succinic acid and malic acid were strongly correlated between the two sampling sites. Oxalic acid occupied on the average 83% and 76% of all the dicarboxylic acid measured for CH samples and UR samples. It is suggested that the aerosols in Okinawa were affected by secondary photochemical reactions, not by the primary emissions from local sources. The seasonal variation of the dicarboxylic acids concentrations in CH and UR showed higher in spring and fall, and a lower in summer. From the back trajectory analysis, dicarboxylic acids concentrations showed higher when an air mass came from East Asia area, and showed lower when it came from Pacific Ocean.

Nakaema, F.; Handa, D.; Tanahara, A.; Arakaki, T.

2009-04-01

318

Impact of Molecular Weight on Lymphatic Drainage of a Biopolymer-Based Imaging Agent  

PubMed Central

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

Bagby, Taryn R.; Cai, Shuang; Duan, Shaofeng; Thati, Sharadvi; Aires, Daniel J.; Forrest, Laird

2012-01-01

319

Molecular Weight Dependence of the Morphology in P3HT:PCBM Solar Cells.  

PubMed

In polymer-based photovoltaic devices, optimizing and controlling the active layer morphology is important to enhancing the device efficiency. Using poly(3-hexylthiophene) (P3HT) with well-defined molecular weights (MWs), synthesized by the Grignard metathesis (GRIM) method, we show that the morphology of the photovoltaic active layer and the absorption and crystal structure of P3HT are dependent on the MW. Differential scanning calorimetry showed that the crystallinity of P3HT reached a maximum for intermediate MWs. Grazing-incidence wide-angle X-ray diffraction showed that the spacing of the (100) planes of P3HT increased with increasing MW, while the crystal size decreased. Nonlinear crystal lattice expansions were found for both the (100) and (020) lattice planes, with an unusual ?-?-stacking enhancement observed between 50 and 100 °C. The melting point depression for P3HT, when mixed with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), and, hence, the Flory-Huggins interaction parameter depended on the MW. PCBM was found to perturb the ordering of P3HT chains. In photovoltaic devices, P3HT with a MW of ?20K showed the best device performance. The morphologies of these blends were studied by grazing-incidence small-angle X-ray scattering (GISAXS) and resonant soft X-ray scattering. In GISAXS, we observed that the low-molecular-weight P3HT more readily crystallizes, promoting a phase-separated morphology. PMID:25350382

Liu, Feng; Chen, Dian; Wang, Cheng; Luo, Kaiyuan; Gu, Weiyin; Briseno, Alejandro L; Hsu, Julia W P; Russell, Thomas P

2014-11-26

320

Occupational Asthma: New Low-Molecular-Weight Causal Agents, 2000-2010  

PubMed Central

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

Pralong, J. A.; Cartier, A.; Vandenplas, O.; Labrecque, M.

2012-01-01

321

Polyvinylpyrrolidone molecular weight controls silica shell thickness on Au nanoparticles with diglycerylsilane as precursor.  

PubMed

Several strategies have been described for the preparation of silica-encapsulated gold nanoparticles (SiO(2)-AuNP), which typically suffer from an initial interface between gold and silica that is difficult to control, and layer thicknesses that are very sensitive to minor changes in silane concentration and incubation time. The silica shell thicknesses are normally equal to or larger than the gold particles themselves, which is disadvantageous when the particles are to be used for biodiagnostic applications. We present a facile and reproducible method to produce very thin silica shells (3-5 nm) on gold nanoparticles: the process is highly tolerant to changes in reaction conditions. The method utilized polyvinylpyrrolidone (PVP) of specific molecular weights to form the interface between gold and silica. The method further requires a nontraditional silica precursor, diglycerylsilane, which efficiently undergoes sol-gel processing at neutrality. Under these conditions, higher molecular weight PVP leads to thicker silica shells: PVP acts as the locus for silica growth into an interpenetrating organic-inorganic hybrid structure. PMID:22767525

Vanderkooy, Alan; Brook, Michael A

2012-08-01

322

Assembly and Characterization ofWell-DefinedHigh-Molecular-Weight Poly(p-phenylene) Polymer Brushes  

SciTech Connect

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.

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

323

Assembly and Characterization of Well Defined High Molecular Weight Poly(p-phenylene) Polymer Brushes  

SciTech Connect

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.

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

324

Controllable production of low molecular weight heparins by combinations of heparinase I/II/III.  

PubMed

Enzymatic depolymerization of heparin by heparinases is promising for production of low molecular weight heparins (LMWHs) as anticoagulants, due to its mild reaction conditions and high selectivity. Here, different heparinase combinations were used to depolymerize heparin. Heparinase I and heparinase II can depolymerize heparin more efficiently than heparinase III, respectively, but heparinase III was the best able to protect the anticoagulant activities of LMWHs. Heparinase III and heparinase I/II combinations were able to efficiently depolymerize heparin to LMWHs with higher anticoagulant activity than the LMWHs produced by the respective heparinase I and heparinase II. HepIII and HepI is the best combination for maintaining high anti-IIa activity (75.7 ± 4.21 IU/mg) at the same Mw value. Furthermore, considering both the changes in molecular weight and anticoagulant activity, the action patterns of heparinase I and heparinase II were found not to follow the exolytic and processive depolymerizing mechanism from the reducing end of heparin. PMID:24299802

Wu, Jingjun; Zhang, Chong; Mei, Xiang; Li, Ye; Xing, Xin-Hui

2014-01-30

325

Investigations on the high molecular weight foaming fractions of espresso coffee.  

PubMed

The target of the present work was the chemical, technological, and sensorial characterization of the brown polymers (foaming fractions) of freshly prepared espresso coffee. The total foaming fraction (TFF) was precipitated with ammonium sulfate from the defatted freshly prepared beverage and then subfractionated by adding 2-propanol/water to give an insoluble fraction (foaming fraction A, FFA) and a soluble fraction (foaming fraction B, FFB). The former is almost colorless, has a higher molecular weight and a lower nitrogen content, and contains mostly polysaccharides, whereas the latter has a lower molecular weight and a higher protein/melanoidin content, which results in a darker color. FFB showed greater foaming capability, but FFA contributed to the stability of the foam. FFB was further fractionated with solid-phase extraction and characterized by different analytical methods (size exclusion chromatography, UV, HPLC-DAD, 1H NMR). All of the melanoidin-rich fractions showed antioxidant properties with the 2,2-diphenyl-1-picrylhydrazyl hydrate method. PMID:15537326

D'Agostina, Alessandra; Boschin, Giovanna; Bacchini, Francesca; Arnoldi, Anna

2004-11-17

326

A sulfuric-lactic acid process for efficient purification of fungal chitosan with intact molecular weight.  

PubMed

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

Naghdi, Mitra; Zamani, Akram; Karimi, Keikhosro

2014-02-01

327

Commercialization of low molecular weight guayule rubber in environmentally friendly coatings  

SciTech Connect

Guayule (Parthenium Argentatum Gray), a shrub growing in the southwest United States and Mexico, is a promising domestic source of natural rubber. Low molecular weight guayule rubber (LMWGR) is one of four major coproducts obtained during the processing of the guayule shrub and this work describes our recent efforts directed to the derivation of value-added LMWGR derivatives; in particular chlorinated hydroxylated LMWGR and acrylated chlorinated LMWGR. Both products are useful as raw materials for the formulation of low volatile organic compound (VOC) coating formulations. Chlorinated hydroxylated LMWGR was synthesized via the chlorination of partially hydroxylated LMWGR whose structure was confirmed by {sup 1}H and {sup 13}C NMR spectroscopy, elemental analysis, and fourier transform infrared spectroscopy (FTIR). We have used chlorinated hydroxylated LMWGR as a reactive, primary alcohol in high solids polyurethane tough, of high gloss, and resistant to water, selected solvents, acids, and bases. Acrylated chlorinated low molecular weight rubber (ACLMWGR) was synthesized via reacting chlorinated hydroxylated LMWGR and acryloyl chloride. ACLMWGR is a useful prepolymer in 100% solids, UV cure coating formulations. The coatings cure readily when exposed to ultraviolet light giving films with excellent adhesion, good chemical resistance, ease of sanding, and water and solvent resistance. The cured finishes are hard, attractive, of high gloss, and possess excellent adhesion as well as superb water and solvent resistance.

Thames, S.F.; He, Z.A. [Univ. of Southern Mississippi, Hattiesburg, MS (United States)

1993-12-31

328

Update on the clinical use of the low-molecular-weight heparin, parnaparin  

PubMed Central

Parnaparin is a low-molecular-weight heparin that has widely shown its efficacy and safety in prevention of venous thromboembolism, in the treatment of chronic venous disorders, and in the treatment of venous and arterial (stable and unstable angina, acute ST-segment elevation myocardial infarction) thrombosis. Parnaparin at the respective dosages of 3200, 4250, 6400, or 12800 IUaXa for a period ranging from 3 to 5 days to 6 months, is usually administered subcutaneously by means of once-daily regimen and is better tolerated than unfractionated heparin at the injection site. In the variety of commercially available low-molecular-weight heparins, parnaparin represents a useful therapeutic option, even though little evidence is available comparing the superiority or the equivalent efficacy and safety of parnaparin to that of the unfractionated heparin or placebo. This review summarizes the available literature on the use of parnaparin in different settings of cardiovascular diseases, including papers published during the past year and ongoing studies. PMID:19851520

Camporese, Giuseppe; Bernardi, Enrico; Noventa, Franco

2009-01-01

329

High molecular weight peptide with corticotropin-releasing factor activity from porcine hypothalami.  

PubMed

The presence of a corticotropin-releasing factor (CRF) behaving as a peptide with a molecular weight of about 5000 was established after purification of porcine hypothalamic extracts by gel filtration on Sephadex G-25 and then on Sephadex G-50. Purified CRF stimulated the release of corticotropin (ACTH) in three in vitro systems: isolated rat pituitary quarters, monolayer cultures of dispersed pituitary cells, and superfused pituitary cells on a column. A linear logarithmic dose-response relationship existed between 50 and 200 micrograms of CRF preparations per ml and the total amount of ACTH released by the superfused pituitary cells. The pituitary ACTH response to CRF in the pituitary quarters system was also approximately linearly related to the logarithm of the dose of CRF. CRF also stimulated in vivo release of ACTH in rats pretreated with chlorpromazine, morphine, and Nembutal. CRF activity was labile to digestion with trypsin and chymotrypsin and was partially destroyed by pepsin. The evidence indicates that CRF of porcine origin is a polypeptide of a higher molecular weight than previously assumed. PMID:6975479

Schally, A V; Chang, R C; Arimura, A; Redding, T W; Fishback, J B; Vigh, S

1981-08-01

330

Low-molecular-weight hydroxyacids in marine atmospheric aerosol: evidence of a marine microbial origin  

NASA Astrophysics Data System (ADS)

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.

Miyazaki, Y.; Sawano, M.; Kawamura, K.

2014-04-01

331

Determination of low-molecular-weight heparin by Heptest on the automated coagulation laboratory system.  

PubMed

The manual Heptest for measuring low-molecular-weight heparin fractions was applied to a fully automated, coagulation-dedicated analyzer, the Automated Coagulation Laboratory 300 Plus. The clot-based assay mode of the instrument was used, which operates on the principle of light scattering. Undiluted plasmas and the original reagents of the Heptest kit were used. Also, the 2-minute incubation time of the manual procedure was maintained. Automation reduced plasma and reagent volumes by about one half. As a result of the high precision of the automated procedure, single determinations suffice, and 18 plasma samples can be analyzed in about 8 minutes. Coefficients of variation were 1.0% to 3.2% for within-run and 1.9% to 6.0% for inter-run analyses. Analytical recovery was 98% to 104%. Comparisons of 132 samples between the two procedures yielded an R value of 0.974 for activity expression in seconds and 0.945 for U/mL. Several low-molecular-weight heparin fractions were tested. PMID:8438788

Ozawa, T; Domagalski, J; Mammen, E F

1993-02-01

332

UV curable lens production using molecular weight controlled PEEK based acrylic oligomer (Ac-PEEK).  

PubMed

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

?nan, Tulay Y; Y?ld?z, Emel; Karaca, Birsen; Dogan, Hacer; Vatansever, Alican; Nalbant, Muhammed; Eken, Koray

2014-08-01

333

Low-molecular-weight compounds having neurotrophic activity in cultured PC12 cells and neurons.  

PubMed

Recent reports have indicated that some low-molecular-weight compounds mimic neurotrophic factors inducing neurite outgrowth and neuroprotection. Carnosic acid (CA) promotes neurite outgrowth through the activation of Nrf2 in PC12 cells. CA also protects neurons via the keap/Nrf2 transcriptional pathway from oxidative stress. Forskolin-induced neurite outgrowth is mediated by activation of the PKA signalling pathway and this PKA-mediated neurite outgrowth is achieved by the expression of nur77 in PC12 cells. In addition, forskolin at its low concentration is closely related to the cAMP-induced protective function against L-DOPA-induced cytotoxicity in PC12 cells. A HDAC inhibitor trichostatin A (TSA) increases neurite length via p53 acetylation in rat cultured cerebellar granule neurons and in cerebral cortical neurons, and also protects neurons against glutathione depletion-induced oxidative stress. Recently, it was revealed that Nrf2 and p53 bind to CBP/p300 directly, and Nur77 is acetylated in vivo and in vitro by CBP/p300. Acetylation of Nrf2, p53 and Nur77 by CBP/p300 may constitute a novel similar regulatory mechanism for low-molecular-weight compounds with neurotrophic activities. PMID:21908547

Maruoka, Hiroki; Sasaya, Harue; Sugihara, Kensuke; Shimoke, Koji; Ikeuchi, Toshihiko

2011-11-01

334

Isolation and characterization of cDNA clones encoding a low molecular weight nonmuscle tropomyosin isoform.  

PubMed

cDNA clones encoding rat fibroblast tropomyosin 4 (TM-4) were isolated and characterized. DNA sequence analysis was carried out to determine the sequence of the protein. The derived amino acid sequence revealed that rat fibroblast TM-4 was found to contain 248 amino acids. The amino acid sequence of rat fibroblast TM-4 was compared with two other low molecular weight TM isoforms, equine platelet beta-TM and a human fibroblast TM. Rat TM-4 exhibited 98% sequence identity with the equine platelet TM but only 75% identity with the human fibroblast TM isoform. The high degree of conservation between the rat and equine proteins indicates that they belong to the same isotype of TM. Comparison of the amino acid sequences of the three low molecular TM isoforms along the length of the proteins reveals regions that are strongly conserved and regions that have considerably diverged. In the regions from amino acid residues 1 to 148 and 176 to 221, amino acid substitutes are moderate. The most variant regions in the sequence are in the middle part of the proteins from amino acids 149 to 175 and at the carboxyl-terminal region of the proteins from amino acids 222 to 248. The differences in the sequence of the rat and platelet TMs compared to the human TM may define distinct functional domains among the low molecular weight TMs. In addition, expression of tropomyosin was studied in a variety of tissues and transformed cells. We also demonstrate that at least three separate genes encode tropomyosins expressed in rat fibroblasts. PMID:3611091

Yamawaki-Kataoka, Y; Helfman, D M

1987-08-01

335

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

PubMed

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, ultimate tensile strength, yield strength, and hardness. In general, these changes would be expected to constitute a precursor for lower wear resistance, presenting a paradox in that wear resistance increases with crosslinking. In order to understand better and to analyze this paradoxical behaviour of crosslinked UHMWPE, we investigated the wear behavior of (i) radiation-crosslinked GUR 1050 resin, (ii) peroxide-crosslinked GUR 1050 resin and (iii) peroxide-crosslinked Himont 1900 resin using a bi-directional pin-on-disk (POD) machine. Wear behavior was analyzed as a function of crystallinity, ultimate tensile strength (UTS), yield strength (YS), and molecular weight between crosslinks (Mc). The crosslink density increased with increasing radiation dose level and initial peroxide content. The UTS, YS, and crystallinity decreased with increasing crosslink density. While these variations followed the same trend, the absolute changes as a function of crosslink density were different for the three types of crosslinked UHMWPE studied. There was no unified correlation for the wear behavior of the three types of crosslinked UHMWPE with the crystallinity, UTS and YS. However, the POD wear rate showed the identical linear dependence on Mc with all three types of crosslinked UHMWPEs studied. Therefore, we have strong evidence to propose that Mc or crosslink density is a fundamental material property that governs the lubricated adhesive and abrasive wear mechanisms of crosslinked UHMWPEs, overriding the possible effects of other material properties such as UTS, YS and crystallinity on the wear behavior. PMID:10458559

Muratoglu, O K; Bragdon, C R; O'Connor, D O; Jasty, M; Harris, W H; Gul, R; McGarry, F

1999-08-01

336

High-molecular weight hyaluronan reduced renal PKC activation in genetically diabetic mice.  

PubMed

The cluster determinant (CD44) seems to play a key role in tissues injured by diabetes type 2. CD44 stimulation activates the protein kinase C (PKC) family which in turn activates the transcriptional nuclear factor kappa B (NF-?B) responsible for the expression of the inflammation mediators such as tumor necrosis factor alpha (TNF-?), interleukin-6 (IL-6), interleukin-18 (IL-18), inducible nitric oxide synthase (iNOS), and matrix metalloproteinases (MMPs). Regulation of CD44 interaction with its ligands depends greatly upon PKC. We investigated the effect of the treatment with high-molecular weight hyaluronan (HA) on diabetic nephropathy in genetically diabetic mice. BKS.Cg-m+/+Lepr(db) mice had elevated plasma insulin from 15 days of age and high blood sugar levels at 4 weeks. The severe nephropathy that developed was characterized by a marked increased in CD44 receptors, protein kinase C betaI, betaII, and epsilon (PKC(?I), PKC(?II), and PKC?) mRNA expression and the related protein products in kidney tissue. High levels of mRNA and related protein levels were also detected in the damaged kidney for NF-?B, TNF-?, IL-6, IL-18, MMP-7, and iNOS. Chronic daily administration of high-molecular mass HA for 2 weeks significantly reduced CD44, PKC(?I), PKC(?II), and PKC? gene expression and the related protein production in kidney tissue and TNF-?, IL-6, IL-18, MMP-7, and iNOS expression and levels also decreased. Histological analysis confirmed the biochemical data. However, blood parameters of diabetes were unchanged. These results suggest that the CD44 and PKC play an important role in diabetes and interaction of high-molecular weight HA with these proteins may reduce inflammation and secondary pathologies due to this disease. PMID:20713153

Campo, Giuseppe M; Avenoso, Angela; Micali, Antonio; Nastasi, Giancarlo; Squadrito, Francesco; Altavilla, Domenica; Bitto, Alessandra; Polito, Francesca; Rinaldi, Maria Grazia; Calatroni, Alberto; D'Ascola, Angela; Campo, Salvatore

2010-11-01

337

Preparation and application of low molecular weight poly(vinyl chloride). III mechanical properties of blended poly(vinyl chloride)  

SciTech Connect

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.

Yamamoto, Kikuo; Maehala, Takashi; Mitani, Katsuo; Mizutani, Yukio (Tokuyama Soda Co., Ltd., Tokuyama-city (Japan))

1993-11-05

338

Development of solvent-free offset ink using vegetable oil esters and high molecular-weight resin.  

PubMed

In the development of solvent-free offset ink, the roles of resin molecular weight and used solvent on the ink performance were evaluated by examining the relationship between the various properties of resin and solvent and print quality. To find the best performing resin, the soy-oil fatty acid methyl ester (FAME) was applied to the five modified-phenolic resins having different molecular weights. It is found from the experimental results that the ink made of higher molecular weight and better solubility resin gives better printability and print quality. It is because larger molecular weight resin with better solubility gives higher rate of ink transfer. From the ink application of different esters to high molecular weight resin, the best printing performance was yielded from the soy-oil fatty acid butyl ester (FABE). It is due to its high kinematic viscosity resulting in the smallest change of ink transfer weight upon multiple number of printing, which improves the stability of ink quality. PMID:23728325

Park, Jung Min; Kim, Young Han; Kim, Sung Bin

2013-01-01

339

Probing the molecular weight distributions of non-boiling petroleum fractions by Ag+ electrospray ionization mass spectrometry.  

PubMed

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

Roussis, Stilianos G; Proulx, Richard

2004-01-01

340

Identification of low molecular weight proteins isolated by 2-D liquid separations.  

PubMed

Proteins with molecular mass (M(r)) <20 kDa are often poorly separated in 2-D sodium dodecyl sulfate polyacrylamide gel electrophoresis. In addition, low-M(r) proteins may not be readily identified using peptide mass fingerprinting (PMF) owing to the small number of peptides generated in tryptic digestion. In this work, we used a 2-D liquid separation method based on chromatofocusing and non-porous silica reversed-phase high-performance liquid chromatography to purify proteins for matrix-assisted laser desorption/ionization time-of-flight mass spectrometric (MALDI-TOFMS) analysis and protein identification. Several proteins were identified using the PMF method where the result was supported using an accurate M(r) value obtained from electrospray ionization TOFMS. However, many proteins were not identified owing to an insufficient number of peptides observed in the MALDI-TOF experiments. The small number of peptides detected in MALDI-TOFMS can result from internal fragmentation, the few arginines in its sequence and incomplete tryptic digestion. MALDI-QTOFMS/MS can be used to identify many of these proteins. The accurate experimental M(r) and pI confirm identification and aid in identifying post-translational modifications such as truncations and acetylations. In some cases, high-quality MS/MS data obtained from the MALDI-QTOF spectrometer overcome preferential cleavages and result in protein identification. PMID:15282756

Zhu, Kan; Miller, Fred R; Barder, Timothy J; Lubman, David M

2004-07-01

341

Widespread presence of large molecular weight adrenocorticotropin-like substances in normal rat extrapituitary tissues.  

PubMed

ACTH activity in glacial acetic acid extracts of normal rat tissues was studied by both ACTH RIA and a sensitive in vitro bioassay. ACTH immunoactivity was found in all tissues: brain, 278 +/- 54 (mean +/- SE; picograms per mg protein); stomach, 59 +/- 4; kidney, 47 +/- 3; colon, 40 +/- 4; small intestine, 37 +/- 4; liver, 18 +/- 2; and heart, 16 +/- 3. Tissue ACTH showed parallelism with ACTH standard in the RIA. No correlation existed between tissue ACTH and plasma ACTH in normal rats. Dexamethasone treatment (0.4 mg/day for 5 days) suppressed plasma ACTH, but did not affect tissue ACTH levels. When tissue extracts were passed through Sephadex G-75-SF columns, ACTH immunoactivity was exclusively eluted in the portion of bigger molecular weight than ACTH standard, except in the brain. Based on this column chromatography, the molecular weight of the main peak of activity was estimated as 26,000. Tissue ACTH-like material contained no detectable biological activity (less than 2 pg/100 ng tissue). However, biological activity was easily detectable after exposure of the tissue extracts to trypsin. When studied by immunoassay and bioassay, this 26,000 mol wt ACTH was digested and cleaved to 4,500 mol wt and biologically active ACTH with trypsin treatment. Tissue ACTH immunoactivity does not seem to be the result of artifacts: 1) extracts were adjusted to pH 8.0 and a common osmolality (150 mosmol/liter) before assay; 2) protein contents in RIA tubes were only 0.1-1.6 mg; 3) tissue extracts incubated with [125I]iodo-ACTH for 48 h produced less than 5% damage of labeled hormone, as assessed by moderate excess of antibody binding; 4) enzyme inhibitors did not modify tissue ACTH levels; and 5) ACTH immunoactivity of tissue extracts was absorbed by anti-ACTH immunocolumns. We conclude that high molecular weight ACTH-like materials are widespread in normal rat extrapituitary tissues and are probably a precursor form of 4500 mol wt ACTH. PMID:6307659

Saito, E; Iwasa, S; Odell, W D

1983-09-01

342

Effect of high molecular weight plasticizers on the gelatinization of starch under static and shear conditions.  

PubMed

Starch gelatinization in the presence of high molecular weight polyol plasticizers and water was studied under static and dynamic conditions and was compared to a glycerol reference. For static gelatinization, glycerol, sorbitol, diglycerol and polyglycerol were examined using polarized light microscopy and differential scanning calorimetry. A wide range of starch/water/plasticizer compositions were prepared to explore the gelatinization regime for each plasticizer. The plasticizers show that the onset and conclusion temperatures for sorbitol and glycerol are in the same range and are lower than the other two plasticizers. On the other hand, polyglycerol shows a higher gelatinization temperature than diglycerol because of its higher molecular weight and viscosity. The results indicate that in the case of all plasticizers, increasing the water content tends to decrease the gelatinization temperature and, except for polyglycerol, increasing the plasticizer content increases the gelatinization temperature. In the case of polyglycerol, however, increasing the plasticizer content had the opposite effect and this was found to be related to the borderline solubility of polyglycerol in water. When the polyglycerol/water solubility was increased by increasing the temperature of the water/plasticizer/starch slurry, the gelatinization temperature dependence was found to be similar to the other polyols. A rheological technique was developed to study the dynamic gelatinization process by tracking the influence of shear on the complex viscosity in a couette flow system. Glycerol, diglycerol and sorbitol were subjected to different dynamic gelatinization treatments and the results were compared with static gelatinization. It is quantitatively shown that shear has a major effect on the gelatinization process. The conclusion temperature of gelatinization is significantly diminished (up to 21 °C) in the presence of shear whereas the onset temperature of gelatinization remains virtually unchanged as compared to static conditions. By comparing glycerol, diglycerol and sorbitol data, it is shown that the molecular weight or structure did not qualitatively affect the changes shear imposed on dynamic gelatinization. Shear had a relatively more pronounced effect on diglycerol as the plasticizer with less hydrogen bonding ability. PMID:23399222

Taghizadeh, Ata; Favis, Basil D

2013-02-15

343

Low-Molecular-Weight Heparin and Unfractionated Heparin Decrease Th-1, 2, and 17 Expressions  

PubMed Central

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

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

344

Surface engineering on mesoporous silica chips for enriching low molecular weight phosphorylated proteins  

NASA Astrophysics Data System (ADS)

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

Hu, Ye; Peng, Yang; Lin, Kevin; Shen, Haifa; Brousseau, Louis C., III; Sakamoto, Jason; Sun, Tong; Ferrari, Mauro

2011-02-01

345

Effect of soil sieving on respiration induced by low-molecular-weight substrates  

NASA Astrophysics Data System (ADS)

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.

Datta, Rahul; Vranová, Valerie; Pavelka, Marian; Rejšek, Klement; Formánek, Pavel

2014-03-01

346

Post-cardiac catheterization access site complications and low-molecular -weight heparin following cardiac catheterization.  

PubMed

The low molecular weight heparin enoxaparin is often administered to patients on long-term anticoagulation regimens who temporarily discontinue warfarin prior to undergoing invasive procedures. The clinical outcome of all enoxaparin-treated patients who underwent cardiac catheterization or coronary artery interventional procedures (n = 119) was evaluated. A total of 5 patients (4.2%) requiring anticoagulation (3 with chronic atrial fibrillation and 2 with ventricular thrombi) developed severe late enoxaparin-associated hemorrhagic or vascular complications at the femoral arterial puncture site between 3 and 11 days post-procedure. Complications included development of femoral arterial pseudoaneurysm (n = 3), hypotension (systolic blood pressure < 90 mmHg) (n = 2), acute decrease in hemoglobin levels to < 8.5 mg/dl (n = 4) and cardiac arrest (n = 1). In patients receiving standard dose enoxaparin after percutaneous invasive cardiac procedures, there is the potential for delayed and severe access site hemorrhagic and vascular complications. PMID:12556615

MacDonald, Lee A; Meyers, Sheridan; Bennett, Charles L; Fintel, Dan; Grosshans, Neal; Syegco, Raffy; Davidson, Charles J

2003-02-01

347

Bioassay-guided isolation of a low molecular weight PHB from Burkholderia sp. with phytotoxic activity.  

PubMed

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

Petta, Tânia; Raichardt, Leandro; Melo, Itamar S; Moraes, Luiz A B

2013-08-01

348

Antioxidation activities of low-molecular-weight gelatin hydrolysate isolated from the sea cucumber Stichopus japonicus  

NASA Astrophysics Data System (ADS)

Gelatin extracted from the body wall of the sea cucumber ( Stichopus japonicus) was hydrolyzed with flavourzyme. Low-molecular-weight gelatin hydrolysate (LMW-GH) of 700-1700 Da was produced using an ultrafiltration membrane bioreactor system. Chemiluminescence analysis revealed that LMW-GH scavenges high free radicals in a concentration-dependent manner; IC50 value for superoxide and hydroxyl radicals was 442 and 285 ?g mL-1, respectively. LMW-GH exhibited excellent inhibitory characteristics against melanin synthesis and tyrosinase activity in B16 cells. Furthermore, LMW-GH notably increased intracellular glutathione (GSH), which in turn suppressed melanogenesis. LMW-GH performs antioxidation activity, holding the potential of being used as a valuable ingredient in function foods, cosmetics and pharmaceuticals or nutriceuticals.

Wang, Jingfeng; Wang, Yuming; Tang, Qingjuan; Wang, Yi; Chang, Yaoguang; Zhao, Qin; Xue, Changhu

2010-03-01

349

Synthesis of a high molecular weight thyroglobulin dimer by two ovine thyroid cell lines: the OVNIS.  

PubMed

The OVNIS 6H and 5H thyroid cells, 2 permanent cell lines isolated 3 years ago from ovine tissue, synthesize a high molecular weight glycosylated protein, immunologically related to ovine thyroglobulin, which is similar to the prothyroid hormone dimer (17-19) S: thyroglobulin. Using sucrose gradient centrifugation and cell labelling with [14C]Leu or [3H]GlNH2, radioactivity was observed in proteins purified from cell layers and from cell culture media. Addition of thyrotropin to or removal from the media resulted respectively in an increase (+773%) or decrease (-1090%) of the total radioactivity detected in the (17-19)S thyroglobulin fraction. Estimation of thyroglobulin by RIA gave similar though less pronounced effects. These experiments prove (1) that thyroglobulin is still expressed in these OVNIS thyroid cell lines even after 3 years of permanent culture, (2) that TSH modulates the level of this protein through a TSH-receptor functional system. PMID:3709961

Hovsépian, S; Aouani, A; Fayet, G

1986-05-01

350

Postoperative Suprachoroidal Hemorrhage in a Glaucoma Patient on Low Molecular Weight Heparin  

PubMed Central

Suprachoroidal hemorrhage is a complication associated with intraocular surgery that can occur both intraoperatively and postoperatively. Several intraoperative or postoperative risk factors have been indentified. The use of low-molecular weight heparin (LMWH) is considered one of the risk factors in surgical cases (ocular or non ocular) and non-surgical cases. Here we present a case of suprachoroidal hemorrhage in a glaucoma patient that occurred after preoperative prophylactic LMWH for deep venous thrombosis. The use of LMWH has been reported to cause suprachoroidal hemorrhage even in patients without any risk factors. The use of LMWH continues to increase, hence it is important to be aware of the possibility of suprachoroidal hemorrhage and to determine the risk/benefit ratio, especially in patients with other risk factors. PMID:23741139

AlHarkan, Dora H.; AlJadaan, Ibrahim A.

2013-01-01

351

Organic molecules in the atmosphere of Jupiter. [low molecular weight hydrocarbons  

NASA Technical Reports Server (NTRS)

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.

Ponnamperuma, C. A.

1978-01-01

352

Absorption and effectiveness of orally administered low molecular weight collagen hydrolysate in rats.  

PubMed

Collagen, a major extracellular matrix macromolecule, is widely used for biomedical purposes. We investigated the absorption mechanism of low molecular weight collagen hydrolysate (LMW-CH) and its effects on osteoporosis in rats. When administered to Wistar rats with either [(14)C]proline (Pro group) or glycyl-[(14)C]prolyl-hydroxyproline (CTp group), LMW-CH rapidly increased plasma radioactivity. LMW-CH was absorbed into the blood of Wistar rats in the peptide form. Glycyl-prolyl-hydroxyproline tripeptide remained in the plasma and accumulated in the kidney. In both groups, radioactivity was retained at a high level in the skin until 14 days after administration. Additionally, the administration of LMW-CH to ovariectomized stroke-prone spontaneously hypertensive rats increased the organic substance content and decreased the water content of the left femur. Our findings show that LMW-CH exerts a beneficial effect on osteoporosis by increasing the organic substance content of bone. PMID:19957932

Watanabe-Kamiyama, Mari; Shimizu, Muneshige; Kamiyama, Shin; Taguchi, Yasuki; Sone, Hideyuki; Morimatsu, Fumiki; Shirakawa, Hitoshi; Furukawa, Yuji; Komai, Michio

2010-01-27

353

HYSCORE and Davies ENDOR study of irradiated ultra high molecular weight polyethylene.  

PubMed

Ultra high molecular weight polyethylene (UHMWPE) has been studied with different magnetic resonance techniques to elicit information on the nature and the location of radicals generated during high energy irradiation. Field swept electron paramagnetic resonance, pulsed Davies electron nuclear double resonance and hyperfine sublevel correlation spectroscopic measurements allowed extracting for the first time the full (1) H hyperfine coupling tensors of the most abundant radical, i.e. a secondary alkyl radical and to ascertain the formation of allyl radicals in the first stages of the irradiation process. The (1) H hyperfine coupling tensors are analogous to those reported for single crystal irradiated polyethylene, suggesting that radicals generated in UHMWPE are located in the crystalline region of the polymer. PMID:22847885

Paganini, Maria Cristina; Brunella, Valentina; Chiesa, Mario

2012-09-01

354

The effect of a low molecular weight heparin on coagulation parameters in healthy cats.  

PubMed

The low molecular weight heparin (LMWH), dalteparin sodium, was administered subcutaneously (100 IU/kg) to 8 healthy cats twice daily for 13 doses. Anti-activated factor X (anti-Xa) activity was measured prior to administration (time 0), and 4, 6, 8, and 12 h after the 1st dose, 4 h after administration of the 3rd dose, and at 4, 6, 8, and 12 h after the last dose. Four cats developed measurable anti-Xa activity 4 h following a single dose, returning to baseline by 6 h. Anti-Xa activity was not detected at any time point in 4 cats. Prothrombin time (PT), activated partial thromboplastin time (APTT), and antithrombin (AT) concentrations were unaffected by LMWH administration. Dalteparin, at 100 IU/kg SC, did not achieve anti-Xa activity in 4 out of 8 cats and failed to maintain anti-Xa activity beyond 4 h in the other 4 healthy cats. PMID:19436582

Vargo, Cheryl L; Taylor, Susan M; Carr, Anthony; Jackson, Marion L

2009-04-01

355

Liquid alkanes with targeted molecular weights from biomass-derived carbohydrates.  

PubMed

Liquid transportation fuels must burn cleanly and have high energy densities, criteria that are currently fulfilled by petroleum, a non-renewable resource, the combustion of which leads to increasing levels of atmospheric CO(2). An attractive approach for the production of transportation fuels from renewable biomass resources is to convert carbohydrates into alkanes with targeted molecular weights, such as C(8)-C(15) for jet-fuel applications. Targeted n-alkanes can be produced directly from fructose by an integrated process involving first the dehydration of this C(6) sugar to form 5-hydroxymethylfurfural, followed by controlled formation of C-C bonds with acetone to form C(9) and C(15) compounds, and completed by hydrogenation and hydrodeoxygenation reactions to form the corresponding n-alkanes. Analogous reactions are demonstrated starting with 5-methylfurfural or 2-furaldehyde, with the latter leading to C(8) and C(13) n-alkanes. PMID:18702136

West, Ryan M; Liu, Zhen Y; Peter, Maximilian; Dumesic, James A

2008-01-01

356

Dispersion of titania nanoparticles in polydimethylsiloxane fluids using grafted low molecular weight polymers.  

SciTech Connect

Nanoparticle interactions and their impact on particle dispersion and rheology are well known to be functions of the interfacial structure between the particle and the fluid phase. The dispersion and flow properties of a titania nanopowder were evaluated in polydimethylsiloxane fluid using ''grafted to'' surface modification of the titania with short molecular weight PDMS polymers. The interaction energy between particles was modeled using analytical expressions as well as dynamic functional theory for polymer surface chains. Particle dynamics as a function of volume fraction were characterized using light scattering, acoustic spectroscopy, and shear and oscillatory measurements. Autophobic dewetting is a novel short range interaction in this system that may be impacting the maximum packing fraction of particles in a suspension.

Piech, Martin (United Technologies Corporation); Bell, Nelson Simmons; Frischknecht, Amalie Lucile

2008-06-01

357

Low Molecular Weight Opioid Peptide Esters Could be Developed as a New Class of Analgesics  

PubMed Central

Low molecular weight opioid peptide esters (OPE) could become a class of analgesics with different side effect profiles than current opiates. OPE may have sufficient plasma stability to cross the blood brain barrier (BBB), undergo ester hydrolysis and produce analgesia. OPE of dipeptides, tyr-pro and tyr-gly conjugated to ethanol have a structure similar to the anesthestic agent, etomidate. Based upon the analgesic activity of dipeptide opioids, Lipinski’s criteria, and permeability of select GABA esters to cross the BBB, opioid peptides (OP) conjugated to ethanol, cholesterol or 3-glucose are lead recommendations. Preliminary animal data suggests that tyr-pro-ethyl ester crosses the BBB and unexpectedly produces hyperalgesia. Currently, there are no approved OP analgesics available for clinical use. Clinical trials of good manufacturing practice OP administered to patients suffering from chronic pain with indwelling intrathecal pumps could resolve the issue that OP may be superior to opiates and may redirect research. PMID:21863129

Goldberg, Joel S.

2011-01-01

358

Skin: Major target organ of allergic reactions to small molecular weight compounds  

SciTech Connect

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.

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

359

Determination of nanoparticle size distribution together with density or molecular weight by 2D analytical ultracentrifugation  

PubMed Central

Nanoparticles are finding many research and industrial applications, yet their characterization remains a challenge. Their cores are often polydisperse and coated by a stabilizing shell that varies in size and composition. No single technique can characterize both the size distribution and the nature of the shell. Advances in analytical ultracentrifugation allow for the extraction of the sedimentation (s) and diffusion coefficients (D). Here we report an approach to transform the s and D distributions of nanoparticles in solution into precise molecular weight (M), density (?P) and particle diameter (dp) distributions. M for mixtures of discrete nanocrystals is found within 4% of the known quantities. The accuracy and the density information we achieve on nanoparticles are unparalleled. A single experimental run is sufficient for full nanoparticle characterization, without the need for standards or other auxiliary measurements. We believe that our method is of general applicability and we discuss its limitations. PMID:21654635

Carney, Randy P.; Kim, Jin Young; Qian, Huifeng; Jin, Rongchao; Mehenni, Hakim; Stellacci, Francesco; Bakr, Osman M.

2011-01-01

360

Production and characterization of low molecular weight sophorolipid under fed-batch culture.  

PubMed

The present study was designed for the production and optimization of the C12-C14 sophorolipid, using the yeast Candida bombicola ATCC-22214. The fermentation was carried under fed-batch culture conditions i.e., maintaining 15% coconut oil and 10% glucose as hydrophobic and hydrophilic carbon sources, respectively. A maximum yield 54.0 g/L (in 234 h) was achieved. A significant antimicrobial activity, surface activity, and emulsion ability were recorded. The native sophorolipid was found as enhancer of detergent efficacy of commercial detergent, tested on complex, smudge and oil contaminated clothes. Molecular weight of the C12 (605/623) and C14 (633/651) sophorolipids were determined by LC-MS which revealed it as diacetylated sophorolipid. This study is being important in terms of yield, which is better than the previously reported. PMID:23807367

Morya, V K; Park, Ji-ho; Kim, Tae Jung; Jeon, Sanggui; Kim, Eun-Ki

2013-09-01

361

Thermal Behaviour of W+C Ion Implanted Ultra High Molecular Weight Polyethylene (UHMWPE)  

NASA Astrophysics Data System (ADS)

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.

Urkac, E. Sokullu; Oztarhan, A.; Tihminlioglu, F.; Ila, D.; Budak, S.; Chhay, B.; Muntele, C.; Oks, E.; Nikolaev, A.

2009-03-01

362

Friction, wear, transfer, and wear surface morphology of ultrahigh-molecular-weight polyethylene  

NASA Technical Reports Server (NTRS)

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.

Fusaro, R. L.

1985-01-01

363

Surface modification of ultra high molecular weight polyethylene fibers via the sequential photoinduced graft polymerization  

NASA Astrophysics Data System (ADS)

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.

Li, Zhi; Zhang, Wei; Wang, Xinwei; Mai, Yongyi; Zhang, Yumei

2011-06-01

364

Surface free energy of ultra-high molecular weight polyethylene modified by electron and gamma irradiation  

NASA Astrophysics Data System (ADS)

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.

Abdul-Kader, A. M.; Turos, A.; Radwan, R. M.; Kelany, A. M.

2009-06-01

365

Surface structure of nascent particles of ultrahigh molecular weight poly(ethylene) reactor powders  

NASA Astrophysics Data System (ADS)

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.

Lebedev, D. V.; Ivan'kova, E. M.; Marikhin, V. A.; Myasnikova, L. P.; Seydewitz, V.

2009-08-01

366

Tribological behavior of ultra-high molecular weight polyethylene in a hip joint simulator  

NASA Astrophysics Data System (ADS)

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.

Mohamad Raffi, N.; Kanagarajan, D.; Srinivasan, V.

2012-12-01

367

Friction, wear, transfer and wear surface morphology of ultra-high-molecular-weight polyethylene  

NASA Technical Reports Server (NTRS)

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.

Fusaro, R. L.

1983-01-01

368

Atlantoaxial transarticular screw fixation and posterior fusion using ultra-high-molecular-weight polyethylene cable.  

PubMed

This article attempts to evaluate the effectiveness of the ultra-high-molecular-weight polyethylene (UHMW-PE) cable system in atlantoaxial transarticular screw fixation and posterior fusion through the clinical results of 10 postoperative patients with atlantoaxial subluxation secondary to rheumatoid arthritis. Among them, one patient with only one screw placed owing to an anomalous vertebral artery had the correction loss of the 3-mm atlas-dens interval after surgery. Another patient had a second operation to remove the screw and cable after 2 years 11 months because a unilateral transarticular screw had come to protrude through the lateral mass of the atlas ventrally. All patients had achieved C1-C2 osseous fusion without any complications associated with this cable system. The UHMW-PE cable is a very useful material as sublaminar wiring in atlantoaxial transarticular screw fixation and posterior fusion. PMID:16189448

Yonezawa, Ikuho; Arai, Yasuhisa; Tsuji, Takaaki; Takahashi, Masaki; Kurosawa, Hisashi

2005-10-01

369

Reversible masking using low-molecular-weight neutral lipids to achieve optimal-targeted delivery.  

PubMed

Intravenous injection of therapeutics is required to effectively treat or cure metastatic cancer, certain cardiovascular diseases, and other acquired or inherited diseases. Using this route of delivery allows potential uptake in all disease targets that are accessed by the bloodstream. However, normal tissues and organs also have the potential for uptake of therapeutic agents. Therefore, investigators have used targeted delivery to attempt delivery solely to the target cells; however, use of ligands on the surface of delivery vehicles to target specific cell surface receptors is not sufficient to avoid nonspecific uptake. PEGylation has been used for decades to try to avoid nonspecific uptake but suffers from many problems known as "The PEGylation Dilemma." We have solved this dilemma by replacing PEGylation with reversible masking using low-molecular-weight neutral lipids in order to achieve optimal-targeted delivery solely to target cells. Our paper will focus on this topic. PMID:22655199

Templeton, Nancy Smyth; Senzer, Neil

2012-01-01

370

Reversible Masking Using Low-Molecular-Weight Neutral Lipids to Achieve Optimal-Targeted Delivery  

PubMed Central

Intravenous injection of therapeutics is required to effectively treat or cure metastatic cancer, certain cardiovascular diseases, and other acquired or inherited diseases. Using this route of delivery allows potential uptake in all disease targets that are accessed by the bloodstream. However, normal tissues and organs also have the potential for uptake of therapeutic agents. Therefore, investigators have used targeted delivery to attempt delivery solely to the target cells; however, use of ligands on the surface of delivery vehicles to target specific cell surface receptors is not sufficient to avoid nonspecific uptake. PEGylation has been used for decades to try to avoid nonspecific uptake but suffers from many problems known as “The PEGylation Dilemma.” We have solved this dilemma by replacing PEGylation with reversible masking using low-molecular-weight neutral lipids in order to achieve optimal-targeted delivery solely to target cells. Our paper will focus on this topic. PMID:22655199

Templeton, Nancy Smyth; Senzer, Neil

2012-01-01

371

Low-molecular-weight heparin in the treatment of deep venous thrombosis.  

PubMed Central

Traditionally, acute deep venous thrombosis (DVT) is treated with intravenous heparin followed by oral anticoagulants. With the advent of the low-molecular-weight heparins (LMWHs), this strategy is changing dramatically. LMWHs are compounds derived from standard unfractionated heparin that offer distinct clinical advantages over unfractionated heparin, including better bioavailability, longer half-life, and a more predictable anticoagulant response that obviates the need for laboratory monitoring. The common side effects of unfractionated heparin, including bleeding, thrombocytopenia, and osteoporosis, may be less common with LMWH. For the treatment of established venous thromboembolism, LMWH is at least as safe and effective as unfractionated heparin. Recent studies demonstrate that home therapy of DVT with LMWH, compared with inpatient therapy with unfractionated heparin, produces comparable clinical outcomes and patient satisfaction, with dramatic cost savings. With careful patient selection, home therapy of venous thromboembolism is quickly becoming the new standard of care. PMID:9795594

Hauer, K E

1998-01-01

372

Degradation diagnosis of ultrahigh-molecular weight polyethylene with terahertz-time-domain spectroscopy  

SciTech Connect

We investigated ultrahigh-molecular-weight-polyethylene (UHMWPE) samples prepared by various conditions with terahertz-time-domain spectroscopy (THz-TDS). Degradation of the virgin UHMWPE samples by {gamma} irradiation induced a drastic increase of the absorption ranging continuously over the THz region. The increase of the absorption continuum is interpreted to originate in the oxidation of the amorphous region within the sample. Only slight THz spectral changes induced by the {gamma} irradiation were, however, observed for the UHMWPE samples doped with 0.1 and 0.3 wt % vitamin E. This result agrees with the earlier indication that vitamin E has an antidegradation effect on UHMWPE. The present result shows that the THz-TDS can be used for the quality control of UHMWPE by monitoring the absorption continuum in the THz region.

Yamamoto, Kohji; Yamaguchi, Mariko; Tani, Masahiko; Hangyo, Masanori; Teramura, Satoshi; Isu, Toshiro; Tomita, Naohide [Institute of Laser Engineering, Osaka University, 2-6 Yamadaoka, Suita, Osaka, 565-0871 (Japan); Graduate School of Material Science, Nara Institute of Science and Technology (NAIST), 8916-5, Takayama, Ikoma, Nara, 630-0101 (Japan); International Innovation Center, Kyoto University, Yoshida-Hon-machi, Sakyo-ku, Kyoto, 606-8501 (Japan)

2004-11-29

373

Tribological properties of ultra-high molecular weight polyethylene at ultra-low temperature  

NASA Astrophysics Data System (ADS)

The hardness, compression properties, creep resistance and tribological properties of ultra-high molecular weight polyethylene at ultra-low temperature were researched in this paper, and the feasibility of its use in low temperature components was explored. Studies had shown that the UHMWPE sample at ultra-low temperature had a brittle tendency, and its compression curve was similar to the brittle material, for which the brittle fracture occurred in the 20% compression. Besides, the creep resistance of the sample at low temperature got worse, and its hardness showed an increasing tendency. With the increased experimental load, the friction coefficient varied seriously, and during the same load, the friction coefficient at low temperature was higher than that at room temperature. According to the worn morphology, the sample at low temperature showed a typical feature of fatigue wear and abrasive wear, while at room temperature it mainly for abrasive wear.

Liu, Hongtao; Ji, Hongmin; Wang, Xuemei

2013-12-01

374

Multidomain hybrid hydrogels: spatially resolved photopatterned synthetic nanomaterials combining polymer and low-molecular-weight gelators.  

PubMed

A simple approach to a patterned multidomain gel is reported, combining a pH-responsive low-molecular-weight gelator (LMWG) and a photoinducible polymer gelator (PG). Using SEM (scanning electron microscopy), NMR spectroscopy, and CD, we demonstrate that self-assembly of the LMWG network occurs in the presence of the PG network, but that the PG has an influence on LMWG assembly kinetics and morphology. The application of a mask during photoirradiation allows patterning of the PG network; we define the resulting system as a "multidomain gel"-one domain consists of a LMWG, whereas the patterned region contains both LMWG and PG networks. The different domains have different properties with regard to diffusion of small molecules, and both gelator networks can control diffusion rates to give systems capable of controlled release. Such materials may have future applications in multikinetic control of drug release, or as patterned scaffolds for directed tissue engineering. PMID:25146876

Cornwell, Daniel J; Okesola, Babatunde O; Smith, David K

2014-11-10

375

Effects of concentration, degree of deacetylation and molecular weight on emulsifying properties of chitosan.  

PubMed

Chitosan has excellent emulsifying properties. Emulsifying activity and stability of chitosan were determined by integrated light scattering technique and turbidimetric method. The effects of concentration, degree of deacetylation and molecular weight on emulsifying properties of chitosan were systematically studied in the paper. Emulsifying activity of chitosan initially increased, arrived at the peak at 0.75% and then declined, while emulsifying stability continuously increased with a rise of chitosan concentration from 0.25% to 1.25%. Emulsifying activity and stability of chitosan initially decreased and reached the minimum, then increased with the rise of degree of deacetylation. Chitosan with DD 60.5% and 86.1% showed superior emulsifying activity and stability. Chitosan with low Mw exhibited better emulsifying activity than those with high Mw. Chitosan with Mw 410 kDa and 600 kDa showed superior emulsifying activity in the test range. Emulsifying stability of chitosan increased with a rise of Mw. PMID:21382402

Li, Xingke; Xia, Wenshui

2011-06-01

376

Molecular weight: Property relationships of high performance polymers used for adhesives and composites  

NASA Technical Reports Server (NTRS)

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.

Kranbuehl, D.

1975-01-01

377

The scaling of the dielectric and electric relaxation in two low molecular weight glass forming liquids  

NASA Astrophysics Data System (ADS)

The scaling of the dielectric and electric relaxation in two low molecular weight glass forming systems (PDE=Phenolphtalein-dimethylether and KDE=Kresolphtalein-di-methylether) is studied in the frequency regime from 10 -3 Hz to 10 9 Hz by use of broadband dielectric spectroscopy. For both the dielectric ?-relaxation and the dc-conductivity the temperature dependence is characterised by a crossover (at a temperature TA) from an Arrhenius to a Vogel-Fulcher-Tammann law. Above TA the dc-conductivity (reflecting translational diffusion of mobile charge carriers) and the ?-relaxation have the same temperature dependence. Below TA a decoupling is found in agreement with recent tracer diffusion experiments (M. Lohfink and H. Sillescu, in: Proc. of the 1st Tohwa University Int. Symp., Fukuoka, Japan, 4-8.11.1991, Am. Inst. Phys. Conf. Series). For the ?-relaxation, the relaxation time distribution shows a pronounced temperature dependence below TA, while it is only weakly varying with temperature above TA.

Stickel, F.; Kremer, F.; Fischer, E. W.

1993-12-01

378

Direct evidence for methylation of arginine residues in high molecular weight forms of basic fibroblast growth factor.  

PubMed Central

Basic fibroblast growth factor (bFGF) is a heparin-binding angiogenic polypeptide mitogen. Protein sequence analysis of bFGF isolated from tissue sources initially established that it is composed of 146 amino acids (apparent Mr 18,000). More recently larger apparent molecular weight forms have been identified and partially characterized. In addition, these high molecular weight forms (apparent Mr 22,000 and 25,000) have been shown to localize preferentially to nuclear fractions of transfected cells. In this report we demonstrate that the higher molecular weight, amino terminally extended forms of bFGF contain methylated arginine residues. The demonstration is based on 1) amino acid sequence analysis of a protein known to contain methylated arginine (myelin basic protein) and a comparison with amino acid sequence analysis of trypsin-derived fragments of the high molecular weight bFGF purified from guinea pig brain and 2) the ability to label in vivo the high molecular weight forms of bFGF with S-adenosyl-L-(methyl-3H)-methionine, the substrate of arginine-protein methylase I. These results are suggestive of a role of arginine methylation in directing nuclear localization of certain forms of bFGF. Images PMID:1713785

Burgess, W H; Bizik, J; Mehlman, T; Quarto, N; Rifkin, D B

1991-01-01

379

Thromboprophylaxis with low-molecular-weight heparin in medical patients with cancer  

PubMed Central

Venous thromboembolism (VTE) is a frequent complication of cancer and cancer treatment and is associated with multiple clinical consequences including recurrent VTE, bleeding and an increase in risk of death. While the risks associated with VTE has been well recognized in surgical cancer patients, there is also considerable and increasing risk in medical cancer patients. VTE risk factors in medical cancer patients include the type and stage of cancer, major comorbid illnesses, current hospitalization, active chemotherapy, hormonal therapy, and antiangiogenic agents. Low-molecular-weight heparins (LMWHs) are commonly recommended for the prevention of VTE in hospitalized cancer patients and higher-risk ambulatory cancer patients due to their favorable risk-to-benefit profile. These agents have been shown to be effective in both the primary and secondary prevention of VTE in medical cancer patients. Extended-duration anticoagulant therapy is often recommended to reduce the risk of VTE recurrence in patients with cancer. LMWHs are often utilized for long-term prophylaxis due to a reduced need for coagulation monitoring, few major bleeding episodes, and once-daily dosing. Despite clinical and practical benefits, a substantial proportion of medical cancer patients do not receive VTE prophylaxis. To improve the appropriate prevention and treatment of VTE in cancer patients, guidelines have been published recently by the American Society of Clinical Oncology and the National Comprehensive Cancer Network. Widespread dissemination and application of these guidelines are encouraged to improve the appropriate use of these agents and improve clinical outcomes in medical cancer patients at risk for VTE and its complications. Condensed abstract To improve appropriate prevention of venous thromboembolism in cancer patients and clinical outcomes widespread dissemination and utilization of evidence-based guidelines such as those from the American Society of Clinical Oncology and the National Comprehensive Cancer Network are needed. Low-molecular-weight heparins are commonly recommended for the prevention of venous thromboembolism in hospitalized cancer patients and higher-risk ambulatory cancer patients. PMID:19827150

Lyman, Gary H.

2009-01-01

380

Metabolic engineering of Pichia pastoris for production of hyaluronic acid with high molecular weight.  

PubMed

The high molecular weight (>1 MDa) of hyaluronic acid (HA) is important for its biological functions. The reported limiting factors for the production of HA with high molecular weight (MW) by microbial fermentation are the insufficient HA precursor pool and cell growth inhibition. To overcome these issues, the Xenopus laevis xhasA2 and xhasB genes encoding hyaluronan synthase 2 (xhasA2) and UDP-glucose dehydrogenase (xhasB), were expressed in Pichia pastoris widely used for production of heterologous proteins. In this study, expression vectors containing various combination cassettes of HA pathway genes including xhasA2 and xhasB from X. laevis as well as UDP-glucose pyrophosphorylase (hasC), UDP-N-acetylglucosamine pyrophosphorylase (hasD) and phosphoglucose isomerase (hasE) from P. pastoris were constructed and tested. First, HA pathway genes were overexpressed using pAO815 and pGAPZB vectors, resulting in the production of 1.2 MDa HA polymers. Second, in order to decrease hyaluronan synthase expression a strong AOX1 promoter in the xhasA2 gene was replaced by a weak AOX2 promoter which increased the mean MW of HA to 2.1 MDa. Finally, the MW of HA polymer was further increased to 2.5 MDa by low-temperature cultivation (26 °C) which reduced cell growth inhibition. The yield of HA production by the P. pastoris recombinant strains in 1L of fermentation culture was 0.8-1.7 g/L. PMID:24892811

Jeong, Euijoon; Shim, Woo Yong; Kim, Jung Hoe

2014-09-20

381

Low-Molecular Weight Heparin Increases Circulating sFlt-1 Levels and Enhances Urinary Elimination  

PubMed Central

Rationale Preeclampsia is a devastating medical complication of pregnancy which leads to maternal and fetal morbidity and mortality. While the etiology of preeclampsia is unclear, human and animal studies suggest that excessive circulating levels of soluble fms-like tyrosine-kinase-1 (sFlt-1), an alternatively spliced variant of VEGF-receptor1, contribute to the signs and symptoms of preeclampsia. Since sFlt-1 binds to heparin and heparan sulfate proteoglycans, we hypothesized that the anticoagulant heparin, which is often used in pregnancy, may interfere with the levels, distribution and elimination of sFlt-1 in vivo. Objective We systematically determined serum and urine levels of angiogenic factors in preeclamptic women before and after administration of low molecular weight heparin and further characterized the interaction with heparin in biochemical studies. Methods and Results Serum and urine samples were used to measure sFlt-1 levels before and after heparin administration. Serum levels of sFlt-1 increased by 25% after heparin administration in pregnant women. The magnitude of the increase in circulating sFlt-1 correlated with initial sFlt-1 serum levels. Urinary sFlt-1 levels were also elevated following heparin administration and levels of elimination were dependent on the underlying integrity of the glomerular filtration barrier. Biochemical binding studies employing cation exchange chromatography revealed that heparin bound sFlt-1 had decreased affinity to negatively charged surfaces when compared to sFlt-1 alone. Conclusion Low molecular weight heparin administration increased circulating sFlt1 levels and enhanced renal elimination. We provide evidence that both effects may be due to heparin binding to sFlt1 and masking the positive charges on sFlt1 protein. PMID:24465515

Belaidi, Abdel Ali; Fridman, Alexander; Karumanchi, S. Ananth; Thadhani, Ravi; Schermer, Bernhard; Mallmann, Peter; Schwarz, Guenter; Benzing, Thomas; Brinkkoetter, Paul T.

2014-01-01

382

A low molecular weight proteome comparison of fertile and male sterile 8 anthers of Zea mays  

PubMed Central

Summary During maize anther development, somatic locular cells differentiate to support meiosis in the pollen mother cells. Meiosis is an important event during anther growth and is essential for plant fertility as pollen contains the haploid sperm. A subset of maize male sterile mutants exhibit meiotic failure, including ms8 (male sterile 8) in which meiocytes arrest as dyads and the locular somatic cells exhibit multiple defects. Systematic proteomic profiles were analysed in biological triplicates plus technical triplicates comparing ms8 anthers with fertile sibling samples at both the premeiotic and meiotic stages; proteins from 3.5 to 20 kDa were fractionated by 1-D PAGE, cleaved with Lys-C and then sequenced using a LTQ Orbitrap Velos MS paradigm. Three hundred and 59proteins were identified with two or more assigned peptides in which each of those peptides were counted at least two or more times (0.4% peptide false discovery rate (FDR) and 0.2% protein FDR); 2761 proteins were identified with one or more assigned peptides (0.4% peptide FDR and 7.6% protein FDR). Stage-specific protein expression provides candidate stage markers for early anther development, and proteins specifically expressed in fertile compared to sterile anthers provide important clues about the regulation of meiosis. 49% of the proteins detected by this study are new to an independent whole anther proteome, and many small proteins missed by automated maize genome annotation were validated; these outcomes indicate the value of focusing on low molecular weight proteins. The roles of distinctive expressed proteins and methods for mass spectrometry of low molecular weight proteins are discussed. PMID:22748129

Wang, Dongxue; Adams, Christopher M.; Fernandes, John F.; Egger, Rachel L.; Walbot, Virginia

2014-01-01

383

Improvement of toughness by stereocomplex crystal formation in optically pure polylactides of high molecular weight.  

PubMed

A solution casting method followed by thermal homogenization was performed for the preparation of 1:1 blends and non-blended films from poly(d-lactide) (PDLA) and poly(l-lactide) (PLLA) of three different molecular weights, and their thermal and mechanical properties were determined via differential scanning calorimetry (DSC) and tensile tests. According to the literature, when Mw is below 1.0×10(5)g/mol only stereocomplex crystallization takes place, and when it is higher, both homocrystallites and stereocomplex crystallites co-exist. In order to promote crystallization as a homocrystal in neat polylactides and to promote the stereoselective crystallization as stereocomplex in the case of non-blended films, and in turn, to achieve different degrees of crystallinity, several thermal treatments of annealing were carried out in this work. Highly stereocomplexed blends were found by the stereospecific thermal treatments. As a consequence, the toughness of 1:1 blends was found significantly enhanced over those of non-blended films, irrespective of molecular weight. For instance, in B2-5050 stereocomplexed blend having poly(l-lactide) and poly(d-lactide) of Mw=1.2×10(5)g/mol, tensile strength increased from 44.0±2.1MPa to 65.1±6.1MPa, and the elongation at break from 10.8±2.5% to 33.1±8.1% with respect to its non-blended poly(l-lactide) counterpart crystallized as homocrystal. This improvement in mechanical properties in stereocomplexed blends is not attributed to the inherent properties of the type of crystal polymorph but to the presence of a higher density of intercrystalline connections through a mobile amorphous phase, i.e. tie chains in the stereocomplexed supramolecular spherulitic entities that provide in the stereocomplexed samples enhanced strength and elongation at break at the same time. PMID:24951928

López-Rodríguez, N; Martínez de Arenaza, I; Meaurio, E; Sarasua, J R

2014-09-01

384

Extended Fujita Approach to the Molecular Weight Distribution of Polysaccharides and other Polymeric Systems  

PubMed Central

In 1962 H. Fujita (Mathematical Theory of Sedimentation Analysis, Academic Press, New York, pp. 182–192) examined the possibility of transforming a quasi-continuous distribution g(s) of sedimentation coefficient s into a distribution f(M) of molecular weight M for linear polymers using the relation f(M) = g(s).(ds/dM) and showed that this could be done if information about the relation between s and M is available from other sources. Fujita provided the transformation based on the scaling relation s = ?M0.5, where ? is taken as a constant for that particular polymer and the exponent 0.5 essentially corresponds to a randomly coiled polymer under ideal conditions. This method was successfully applied to mucus glycoproteins (S.E. Harding, Adv. Carbohyd. Chem. Biochem. 47 (1989), 345–381). We now describe an extension of the method to general conformation types via the scaling relation s = ?Mb, where b = 0.4–0.5 for a coil, ~0.15–0.2 for a rod and ~0.67 for a sphere. We give examples of distributions f(M) vs M obtained for polysaccharides from SEDFIT derived least squares g(s) vs s profiles (P. Schuck, Biophys. J. 78 (2000) 1606–1619) and the analytical derivative for ds/dM performed with Microcal ORIGIN. We also describe a more direct route from a direct numerical solution of the integral equation describing the molecular weight distribution problem. Both routes give identical distributions although the latter offers the advantage of being incorporated completely within SEDFIT. The method currently assumes that solutions behave ideally: sedimentation velocity has the major advantage over sedimentation equilibrium in that concentrations less than 0.2 mg/ml can be employed, and for many systems non-ideality effects can be reasonably ignored. For large, non-globular polymer systems, diffusive contributions are also likely to be small. PMID:21276851

Harding, Stephen E.; Schuck, Peter; Abdelhameed, Ali Saber; Adams, Gary; Kok, M. Samil; Morris, Gordon A.

2011-01-01

385

Effects of molecular weight distribution and chemical properties of natural organic matter on gold nanoparticle aggregation.  

PubMed

The complexity of natural organic matter (NOM) motivates determination of how specific components in a NOM mixture interact with and affect nanoparticle (NP) behavior. The effects of two Suwannee River NOM fractions (separated by a 100,000 g/mol ultrafiltration membrane) on gold NP aggregation are compared. The weight-average molecular weight, Mw, for the unfractionated NOM was 23,300 g/mol, determined by size exclusion chromatography with multiangle light scattering. The NOM was comprised of ~1.8 wt % of >100,000 g/mol retentate (NOMr, Mw = 691,000 g/mol) and 98 wt % of filtrate (NOMf, Mw = 12,800 g/mol). Ten ppm of NOMr provided significantly better NP stability against aggregation than 10 ppm of NOMf in 100 mM NaCl due to steric effects. In the unfractionated NOM, the relative importance of the two components was concentration-dependent. For a low concentration of unfractionated NOM (10 ppm), both fractions contributed to the NOM effects; for a high concentration (560 ppm), NP stability was controlled by the small amount (10 ppm) of NOMr present, rather than the higher amount (550 ppm) of NOMf. Therefore, large humic aggregates in a heterogeneous NOM sample can have disproportionately strong effects, and characterization of Mw distributions (rather than average Mw) may be required to explain NOM effects on NP behavior. PMID:23550560

Louie, Stacey M; Tilton, Robert D; Lowry, Gregory V

2013-05-01

386

Ultradrawing novel ultra-high molecular weight polyethylene fibers filled with bacterial cellulose nanofibers.  

PubMed

Novel ultrahigh molecular weight polyethylene (UHMWPE)/bacterial cellulose (BC) (F100BCy) and UHMWPE/modified bacterial cellulose (MBC) (F100MBCx-y) as-prepared fibers were prepared and ultra-drawn. The achievable draw ratio (Dra) values of each F100MBCx-y as-prepared fiber series specimens approached a maximum value as their MBC contents reached the optimal value at 0.0625phr. In which, the maximum Dra value obtained for F100MBCx-0.0625 as-prepared fiber specimen prepared at the optimal MBC content reached another maximum value at 347 as the weight ratio of maleic anhydride grafted polyethylene to BC approach an optimal value at 10. In contrast, no significant improvement in Dra values was found for F100BCy as-prepared fiber specimens. To understand these interesting ultradrawing properties described above, Fourier transform infra-red, specific surface areas, and transmission electron microcopic analyses of original and modified BC nanofibers together with the thermal, orientation and tensile properties of F100BCy and F100MBCx-y fiber specimens were performed. PMID:24299742

Yeh, Jen-Taut; Tsai, Chih-Chen; Wang, Chuen-Kai; Shao, Jhih-Wun; Xiao, Ming-Zheng; Chen, Su-Chen

2014-01-30

387

A low molecular weight artificial RNA of unique size with multiple probe target regions  

NASA Technical Reports Server (NTRS)

Artificial RNAs (aRNAs) containing novel sequence segments embedded in a deletion mutant of Vibrio proteolyticus 5S rRNA have previously been shown to be expressed from a plasmid borne growth rate regulated promoter in E. coli. These aRNAs accumulate to high levels and their detection is a promising tool for studies in molecular microbial ecology and in environmental monitoring. Herein a new construct is described which illustrates the versatility of detection that is possible with aRNAs. This 3xPen aRNA construct carries a 72 nucleotide insert with three copies of a unique 17 base probe target sequence. This aRNA is 160 nucleotides in length and again accumulates to high levels in the E. coli cytoplasm without incorporating into ribosomes. The 3xPen aRNA illustrates two improvements in detection. First, by appropriate selection of insert size, we obtained an aRNA which provides a unique and hence, easily quantifiable peak, on a high resolution gel profile of low molecular weight RNAs. Second, the existence of multiple probe targets results in a nearly commensurate increase in signal when detection is by hybridization. These aRNAs are naturally amplified and carry sequence segments that are not found in known rRNA sequences. It thus may be possible to detect them directly. An experimental step involving RT-PCR or PCR amplification of the gene could therefore be avoided.

Pitulle, C.; Dsouza, L.; Fox, G. E.

1997-01-01

388

Exposure to low molecular weight isocyanates and formaldehyde in foundries using hot box core binders.  

PubMed

Emissions from a chemical core binder system (Hot Box) based on a formaldehyde-carbamide resin have been investigated. The binder is used in some Swedish die-casting foundries. During core-making and casting, low molecular monoisocyanates, in particular methyl isocyanate (MIC) and isocyanic acid (ICA), were identified. Exposure to air concentrations of MIC, ICA and formaldehyde were subsequently determined in all Swedish foundries using the Hot Box binder, and involved three brass and one grey iron foundry. The survey was carried out in the winter period of 2001, and involved core-makers, casters and fettlers in the brass foundries, whereas only core-makers were included in the grey iron foundry. For each worker, four to five short-term samples of isocyanates (n = 298) and one 8 h sample of formaldehyde (n = 64) were collected during one shift for 15 die-casters, 39 core-makers and 10 other workers in the foundry. The air concentrations of the MIC short-term samples varied between <4 and 68 microg m(-3), with corresponding ICA levels between <4 and 280 microg m(-3). Calculated 8 h time weighted average air concentrations of MIC, based on short-term samples for each individual, varied between <4 and 31 microg m(-3); for ICA the corresponding levels varied from <4 to 190 microg m(-3). The formaldehyde time weighted average concentration levels ranged from 14 to 1600 microg m(-3), and the Swedish occupational exposure limit (600 microg m(-3)) was exceeded only in 3% of the samples. In general, the core-makers were exposed to higher average formaldehyde levels compared to the casters, the latter being more exposed to monoisocyanates. During core-making and die-casting, low molecular monoisocyanates, in particular MIC and ICA, were identified. Compared to the American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit value-time weighted average (TLV-TWA) for MIC, the exposures were low. The lack of toxicological and human data for ICA and the relatively high air concentrations call for medical examination and preventive measures in production, ventilation and the use of personal safety equipment in the investigated foundries. PMID:16126762

Westberg, Håkan; Löfstedt, Håkan; Seldén, Anders; Lilja, Bengt-Gunnar; Nayström, Peter

2005-11-01

389

Low Molecular Weight Hydrocarbon Production at the Lost City Hydrothermal Field  

NASA Astrophysics Data System (ADS)

Here we present concentration, and stable and radiocarbon isotope data from hydrocarbons dissolved in hydrogen-rich fluids venting at the ultramafic-hosted Lost City Hydrothermal Field. The cool (<90°C) fluids venting from the spectacular carbonate chimneys at Lost City contain abundant low molecular weight hydrocarbons. A log-linear relationship (Schulz-Flory distriubution) between methane (mmol/kg), ethane (?mol/kg), propane (?mol/kg), and butane (nmol/kg) concentrations indicates synchronous production that is compatible with abiogenic formation such as Fischer-Tropsch type (FTT) genesis. However, a Schulz-Flory distribution of low-molecular weight hydrocarbons is commonly observed in the formation of petroleum via the pyrolysis of organic matter. Radiocarbon isotopic evidence suggests that the carbon source to Lost City hydrocarbons is carbon found in the host rocks, with no contribution from seawater bicarbonate. The underlying ultramafic host rocks contain <600 ppm non-carbonate carbon, most likely as a graphite found along grain boundaries, however a macro-molecular organic carbon source has not been eliminated (Delacour et al., 2004). While the absence of a large organic matter source argues for an abiogenic formation mechanism, a thermogenic source cannot yet be completely ruled out. The forthcoming carbon and hydrogen stable isotope analysis of Lost City hydrocarbons is expected to shed light on the formation mechanism. Both abiogenic FTT reactions and thermogenic formation imprint distinctive trends in the carbon isotopes of C1-C4 alkanes (Sherwood Lollar et al., 2002). Our initial findings, pending isotopic confirmation, illustrate the simple minimum requirements for extensive hydrocarbon production in nature: ultramafic rocks and water. Delacour, A. et al., 2004. Fluid-Rock Interaction in the Basement of the Lost City Vent Field: Insights from Stable and Radiogenic Isotopes. Eos, Transactions, American Geophysical Union, 85(47): Abstract B13A-0198. Sherwood Lollar, B., Westgate, T.D., Ward, J.A., Slater, G.F. and Lacrampe, C.G., 2002. Abiogenic formation of alkanes in the Earth's crust as a minor source for global hydrocarbon reservoirs. Nature (London), 416(6880): 522-524.

Proskurowski, G.; Lilley, M.; Olson, E.; Kelley, D.; Frueh-Green, G.

2005-12-01

390

Effect of alcohol on the properties of micellar systems. Part 1. Critical micellization concentration, micelle molecular weight and ionization degree  

SciTech Connect

Additions of alcohols of medium chain length (butanol to hexanol) to micellar solutions result in a decrease of critical micelle concentration and micelle molecular weight, and an increase of the micelle ionization degree. Moreover, the micelle molecular weight (or surfactant aggregation number) at a given alcohol concentration increases with the surfactant concentration and may reach values larger than in the absence of alcohol. Striking differences have been found in the changes of molecular weight of TTAB micelles in H/sub 2/O-pentanol mixtures in the presence of 0.1 M KBr and in the absence of salt. These various results have been explained by considering the effect of the micelle solubilized alcohol on the micelle surface charge density and on the dielectric constant of the palisade layer. 48 references.

Zana, R.; Yiv, S.; Strazielle, C.; Lianos, P.

1981-03-01

391

Eczematous plaques related to unfractionated and low-molecular-weight heparin in pregnancy: cross-reaction with danaparoid sodium.  

PubMed

The use of low-molecular-weight heparin has been expanded to prevent pregnancy complications such as pregnancy loss, intra-uterine growth restriction and severe early-onset pre-eclampsia in high-risk patients with evidence of acquired or congenital thrombophilia. Therefore, the number of patients with side effects from low-molecular-weight heparin is expected to increase. We describe two women with infiltrating patchy plaques that developed in reaction to low-molecular-weight heparin during pregnancy. In the first patient, a switch to other formulations of heparin and heparinoid failed; the second patient, however, did well when enoxaparin was replaced with dalteparin. This report confirms the risk of skin reactions to enoxaparin and dalteparin, and reports on a skin reaction associated with danaparoid sodium in a pregnant woman. PMID:14614358

Blickstein, Dorith; Hod, Moshe; Bar, Jacob

2003-12-01

392

Differential effects of fucoidans with low and high molecular weight on the viability and function of spleen cells.  

PubMed

Fucoidan is an edible sulfated polysaccharide purified from brown algae that has multiple biological activities. However, the effects of fucoidans of different molecular weights on immune cells have not been determined. Thus, we treated spleen cells with low- and high-molecular-weight fucoidans (LMF and HMF, respectively). Viability assays demonstrated that HMF enhanced the viability and prevented the death of spleen cells. Furthermore, functional analysis revealed that HMF significantly increased the production of interferon-? and nitric oxide. In contrast, LMF had low activity and was relatively toxic to spleen cells. Taken together, these results indicate that HMF makes the greatest contribution to the immunostimulatory activity of fucoidan mixtures. Additionally, fucoidans with different molecular weights may have different effects on the viability and function of immune cells. This study increases our understanding of fucoidans, and may broaden their use in the basic research and clinical fields. PMID:24681238

Jang, Ji-Young; Moon, Sun-Young; Joo, Hong-Gu

2014-06-01

393

Determining the molecular weight distribution of Pocahontas No. 3 low-volatile bituminous coal utilizing HRTEM and laser desorption ionization mass spectra data  

Microsoft Academic Search

Knowledge of the molecular weight distribution is important for rationalizing coal behavior. While many analytical approaches generate average data, inclusion of coal’s inherent structural diversity would improve molecular representations of coal and their usefulness. The molecular weight distribution of Pocahontas No. 3 coal was estimated based on a new approach coupling HRTEM lattice fringe image data and laser desorption ionization

Jonathan P. Mathews; Victor Fernandez-Also; A. Daniel Jones; Harold H. Schobert

2010-01-01

394

Synthesis of fluorene- and anthracene-based ?-conjugated polymers and dependence of emission range and luminous efficiency on molecular weight  

Microsoft Academic Search

In the present work poly[9,9-dioctylfluorene-co-2-pentyl-9,10-bis(4-vinylphenyl)anthracene], a fluorene- and anthracene-based copolymer, is synthesized through a Heck coupling reaction. In order to synthesize polymers with high-molecular weight, DMF (P1), DMF\\/p-Xylene=1\\/1 (P2), p-Xylene (P3), and 1,4-Dioxane (P4) are used as solvents, which are an important factor in the synthesis process. The number of average molecular weights (Mn) of the synthesized polymers P1–P4 do

Jang Yong Lee; Min Hee Choi; Doo Kyung Moon; Jung Rim Haw

2010-01-01

395

A low molecular weight isoform of hyaluronidase: purification from Indian cobra (Naja naja) venom and partial characterization.  

PubMed

A low molecular weight isoform of hyaluronidase (NNH2) has been isolated from Indian cobra (Naja naja) venom by successive chromatography on Sephadex G-75 and CM-Sephadex C-25 columns. The apparent molecular weight determined by SDS-PAGE is 52 kD, and the pI value is 9.7. NNH2 is an endoglycosidase and exhibits in vitro absolute specificity for hyaluronan; it also hydrolyzed hyaluronan in human skin sections. NNH2 is nontoxic, but it indirectly potentiates the hemorrhagic activity of hemorrhagic complex-I. Curcumin, indomethacin, and tannic acid inhibited dose dependently the degradation of hyaluronan by NNH2. PMID:16038614

Girish, K S; Kemparaju, K

2005-06-01

396

Thermomechanical behavior of virgin and highly crosslinked ultra-high molecular weight polyethylene used in total joint replacements.  

PubMed

Three series of uniaxial tension and compression tests were conducted on two conventional and two highly crosslinked ultra-high molecular weight polyethylenes (UHMWPEs) all prepared from the same lot of medical grade GUR 1050. The conventional materials were unirradiated (control) and gamma irradiated in nitrogen with a dose of 30 kGy. The highly crosslinked UHMWPEs were gamma irradiated at room temperature with 100 kGy and then thermally processed by either annealing below the melt transition at 100 degrees C or by remelting above the melt transition at 150 degrees C. The true stress-strain behavior of the four UHMWPE materials was characterized as a function of strain rate (between 0.02 and 0.10 s(-1)) and test temperature (20-60 degrees C). Although annealing and remelting of UHMWPE are primarily considered as methods of improving oxidation resistance, thermal processing was found to significantly impact the crystallinity, and hence the mechanical behavior, of the highly crosslinked UHMWPE. The crystallinity and radiation dose were key predictors of the uniaxial yielding, plastic flow, and failure properties of conventional and highly crosslinked UHMWPEs. The thermomechanical behavior of UHMWPE was accurately predicted using an Arrhenius model, and the associated activation energies for thermal softening were related to the crystallinity of the polymers. The conventional and highly crosslinked UHMWPEs exhibited low strain rate dependence in power law relationships, comparable to metals. In light of the unifying trends observed in the true stress-strain curves of the four materials investigated in this study, both crosslinking (governed by the gamma radiation dose) and crystallinity (governed by the thermal processing) were found to be useful predictors of the mechanical behavior of UHMWPE for a wide range of test temperatures and rates. The data collected in this study will be used to develop constitutive models based on the physics of polymer systems for predicting the thermomechanical behavior of conventional and crosslinked UHMWPE used in total joint replacements. PMID:12109694

Kurtz, S M; Villarraga, M L; Herr, M P; Bergström, J S; Rimnac, C M; Edidin, A A

2002-09-01

397

Accurate and Scalable O(N) Algorithm for First-Principles Molecular-Dynamics Computations on Large Parallel Computers  

NASA Astrophysics Data System (ADS)

We present the first truly scalable first-principles molecular dynamics algorithm with O(N) complexity and controllable accuracy, capable of simulating systems with finite band gaps of sizes that were previously impossible with this degree of accuracy. By avoiding global communications, we provide a practical computational scheme capable of extreme scalability. Accuracy is controlled by the mesh spacing of the finite difference discretization, the size of the localization regions in which the electronic wave functions are confined, and a cutoff beyond which the components of the overlap matrix can be omitted when computing selected elements of its inverse. We demonstrate the algorithm's excellent parallel scaling for up to 101 952 atoms on 23 328 processors, with a wall-clock time of the order of 1 min per molecular dynamics time step and numerical error on the forces of less than 7×10-4 Ha/Bohr.

Osei-Kuffuor, Daniel; Fattebert, Jean-Luc

2014-01-01

398

Toward Accurate Reaction Energetics for Molecular Line Growth at Surface: Quantum Monte Carlo and Density Functional Theory Calculations  

SciTech Connect

We revisit the molecular line growth mechanism of styrene on the hydrogenated Si(001) 2x1 surface. In particular, we investigate the energetics of the radical chain reaction mechanism by means of diffusion quantum Monte Carlo (QMC) and density functional theory (DFT) calculations. For the exchange correlation (XC) functional we use the non-empirical generalized-gradient approximation (GGA) and meta-GGA. We find that the QMC result also predicts the intra dimer-row growth of the molecular line over the inter dimer-row growth, supporting the conclusion based on DFT results. However, the absolute magnitudes of the adsorption and reaction energies, and the heights of the energy barriers differ considerably between the QMC and DFT with the GGA/meta-GGA XC functionals.

Kanai, Y; Takeuchi, N

2009-10-14

399

Basis-set extrapolation techniques for the accurate calculation of molecular equilibrium geometries using coupled-cluster theory  

Microsoft Academic Search

To reduce remaining basis-set errors in the determination of molecular equilibrium geometries, a basis-set extrapolation (BSE) scheme is suggested for the forces used in geometry optimizations. The proposed BSE scheme is based on separating the Hartree-Fock and electron-correlation contributions and uses expressions obtained by straightforward differentiation of well established extrapolation formulas for energies when using basis sets from Dunning's hierarchy

Miriam Heckert; Mihály Kállay; David P. Tew; Wim Klopper; Jürgen Gauss

2006-01-01

400

Evidence for high molecular weight Na-Ca exchange in cardiac sarcolemmal vesicles.  

PubMed

Cardiac sarcolemma (SL) vesicles were subjected to irradiation inactivation-target sizing analyses and gel permeation high performance liquid chromatography (HPLC) to ascertain the weight range of native Na-Ca exchange. Frozen SL vesicle preparations were irradiated by electron bombardment and assayed for Na-Ca exchange activity. When applied to classical target sizing theory, the results yielded a minimum molecular weight (Mr) of approximately 226,000 +/- 20,000 SD (n = 6). SL vesicle proteins were solubilized in 6% sodium cholate in the presence of exogenous phospholipid and fractionated by size on a TSK 30XL HPLC column. Eluted proteins were mixed 1:1 with mobile phase buffer containing 50 mg/ml soybean phospholipid and reconstituted by detergent dilution. The resulting proteoliposomes were assayed for Na-Ca exchange activity. Na-Ca exchange activity eluted in early fractions containing larger proteins as revealed by SDS-PAGE. Recovery of total protein and Na-Ca exchange activity were 91 +/- 7 and 68 +/- 11%, respectively. In the peak fraction, Na-Ca exchange specific activity increased two- to threefold compared to reconstituted controls. Compared to the elution profile of protein standards under identical column conditions, sodium cholate solubilized exchange activity had a minimum Mr of 224,000 Da. Specific 45Ca2+-binding SL proteins with Mr of 234,000, 112,000, and 90,000 Da were detected by autoradiography of proteins transferred electrophoretically to nitrocellulose. These data suggest that native cardiac Na-Ca exchange is approximately 225,000 Da or larger. The exact identification and purification of cardiac Na-Ca exchange protein(s) remains incomplete. PMID:3244156

Hale, C C; Kleiboeker, S B; Carlton, C G; Rovetto, M J; Jung, C; Kim, H D

1988-12-01

401

Low-molecular-weight heparin (Fragmin) during instability in coronary artery disease (FRISC). FRISC Study Group.  

PubMed

This study evaluated whether the low-molecular-weight (LMW) heparin dalteparin sodium (Fragmin) had protective effects against cardiac events in aspirin-treated patients with unstable coronary artery syndromes. Patients (n = 1,506) with unstable angina or non-Q-wave myocardial infarction were randomized to double-blind, placebo-controlled treatment with LMW heparin. The treatment was given as subcutaneous injections: 120 U/kg body weight/12 hours during the first 5-7 days and 7,500 U once daily during the following 35-45 days. The primary endpoint, death or myocardial infarction after 6 days, showed a 3% (4.7%-1.7%) absolute and a 65% relative reduction in the LMW heparin group. There was a 6.8% (15.5%-8.7%) absolute and a 47% relative reduction of urgent revascularization or need for heparin or nitroglycerin infusions in combination with the primary endpoint. After 40 days there was an absolute reduction of death or myocardial infarction of 2.8% (10.7%-7.9%) and its combination with incapacitating angina was reduced by 5.9% (30.7%-24.8%). The survival analysis indicated a reactivation of the instability soon after lowering the dose at 5-7 days. With long-term follow-up, 3-4 months after termination of LMW heparin, the differences between groups were no longer statistically significant. However, the cumulative reduction in death, myocardial infarction, and revascularization because of incapacitating angina of 5.1% (25.3%-20.4%) was maintained. No cerebral and few major bleeds occurred. Compliance was adequate. Thus, subcutaneous LMW heparin protects against cardiac events in the acute phase of unstable coronary artery disease. The subcutaneous regimen also allows prolongation of treatment in the outpatient setting, which might maintain the initial benefits over a longer period. PMID:9296466

Swahn, E; Wallentin, L

1997-09-01

402

Hypervelocity Impact Experiments on Epoxy/Ultra-High Molecular Weight Polyethylene Composite Panels Reinforced with Nanotubes  

NASA Technical Reports Server (NTRS)

Advanced composites with multi-functional capabilities are of great interest to the designers of aerospace structures. Polymer matrix composites (PMCs) reinforced with high strength fibers provide a lightweight and high strength alternative to metals and metal alloys conventionally used in aerospace architectures. Novel reinforcements such as nanofillers offer potential to improve the mechanical properties and add multi-functionality such as radiation resistance and sensing capabilities to the PMCs. This paper reports the hypervelocity impact (HVI) test results on ultra-high molecular weight polyethylene (UHMWPE) fiber composites reinforced with single-walled carbon nanotubes (SWCNT) and boron nitride nanotubes (BNNT). Woven UHMWPE fabrics, in addition to providing excellent impact properties and high strength, also offer radiation resistance due to inherent high hydrogen content. SWCNT have exceptional mechanical and electrical properties. BNNT (figure 1) have high neutron cross section and good mechanical properties that add multi-functionality to this system. In this project, epoxy based UHMWPE composites containing SWCNT and BNNT are assessed for their use as bumper shields and as intermediate plates in a Whipple Shield for HVI resistance. Three composite systems are prepared to compare against one another: (I) Epoxy/UHMWPE, (II) Epoxy/UHMWPE/SWCNT and (III) Epoxy/UHMWPE/SWCNT/BNNT. Each composite is a 10.0 by 10.0 by 0.11 cm3 panel, consisting of 4 layers of fabrics arranged in cross-ply orientation. Both SWCNT and BNNT are 0.5 weight % of the fabric preform. Hypervelocity impact tests are performed using a two-stage light gas gun at Rice University

Khatiwada, Suman; Laughman, Jay W.; Armada, Carlos A.; Christiansen, Eric L.; Barrera, Enrique V.

2012-01-01

403

Relationship between chemical structure and the occupational asthma hazard of low molecular weight organic compounds  

PubMed Central

Aims: To investigate quantitatively, relationships between chemical structure and reported occupational asthma hazard for low molecular weight (LMW) organic compounds; to develop and validate a model linking asthma hazard with chemical substructure; and to generate mechanistic hypotheses that might explain the relationships. Methods: A learning dataset used 78 LMW chemical asthmagens reported in the literature before 1995, and 301 control compounds with recognised occupational exposures and hazards other than respiratory sensitisation. The chemical structures of the asthmagens and control compounds were characterised by the presence of chemical substructure fragments. Odds ratios were calculated for these fragments to determine which were associated with a likelihood of being reported as an occupational asthmagen. Logistic regression modelling was used to identify the independent contribution of these substructures. A post-1995 set of 21 asthmagens and 77 controls were selected to externally validate the model. Results: Nitrogen or oxygen containing functional groups such as isocyanate, amine, acid anhydride, and carbonyl were associated with an occupational asthma hazard, particularly when the functional group was present twice or more in the same molecule. A logistic regression model using only statistically significant independent variables for occupational asthma hazard correctly assigned 90% of the model development set. The external validation showed a sensitivity of 86% and specificity of 99%. Conclusions: Although a wide variety of chemical structures are associated with occupational asthma, bifunctional reactivity is strongly associated with occupational asthma hazard across a range of chemical substructures. This suggests that chemical cross-linking is an important molecular mechanism leading to the development of occupational asthma. The logistic regression model is freely available on the internet and may offer a useful but inexpensive adjunct to the prediction of occupational asthma hazard. PMID:15778257

Jarvis, J; Seed, M; Elton, R; Sawyer, L; Agius, R

2005-01-01

404

Identification and Characterization of High-Molecular-Weight Glutenin Subunits from Agropyron intermedium  

PubMed Central

High-molecular-weight glutenin subunit (HMW-GS) is a primary determinant of processing quality of wheat. Considerable progress has been made in understanding the structure, function and genetic regulation of HMW-GS in wheat and some of its related species, but less is known about their orthologs in Agropyron intermedium, a useful related species for wheat improvement. Here seven HMW-GSs in Ag. intermedium were identified using SDS-PAGE and Western blotting experiments. Subsequently, the seven genes (Glu-1Aix1?4 and Glu-1Aiy1?3) encoding the seven HMW-GSs were isolated using PCR technique with degenerate primers, and confirmed by bacterial expression and Western blotting. Sequence analysis indicated that the seven Ag. intermedium HMW-GSs shared high similarity in primary structure to those of wheat, but four of the seven subunits were unusually small compared to the representatives of HMW-GS from wheat and two of them possessed extra cysteine residues. The alignment and clustering analysis of deduced amino acid sequences revealed that 1Aix1 and 1Aiy1 subunits had special molecular structure, belonging to the hybrid type compounding between typical x- and y-type subunit. The xy-type subunit 1Aix1 is composed of the N-terminal of x-type and C-terminal of y-type, whereas yx-type subunit 1Aiy1 comprises the N-terminal of y-type and C-terminal of x-type. This result strongly supported the hypothesis of unequal crossover mechanism that might generate the novel coding sequence for the hybrid type of HMW-GSs. In addition to the aforementioned, the other novel characteristics of the seven subunits were also discussed. Finally, phylogenetic analysis based on HMW-GS genes was carried out and provided new insights into the evolutionary biology of Ag. intermedium. PMID:24503781

Cao, Shuanghe; Li, Zhixin; Gong, Caiyan; Xu, Hong; Yang, Ran; Hao, Shanting; Wang, Xianping; Wang, Daowen; Zhang, Xiangqi

2014-01-01

405

Effects of the sample preparation temperature on the nanostructure of compression moulded ultrahigh molecular weight polyethylene.  

PubMed

In this study, the effects of the sample sectioning temperature on the surface nanostructure and mechanical response of compression moulded ultrahigh molecular weight polyethylene (UHMWPE) at a nanometer scale (nanomechanical properties) have been characterized. The primary focus of this work was to determine if the sample sectioning temperature significantly changed the nanostructure of UHMWPE, while the secondary focus was to characterize the effect on the mechanical response due to the changes in the sectioned surface nanostructure. The goals of this study were: (a) to investigate the potential possibility of creating surface artefacts by the sample preparation technique by sectioning at different temperatures relative to the published range of glass transition temperatures, Tg, for PE (-12, -80 and -25 degrees C); (b) to determine the possibility of molecular orientation induced by plastic deformation of the UHMWPE sample during the process of sample preparation; (c) to measure the relative difference in nanomechanical properties owing to evolution of different nanostructures as a function of sample sectioning temperature. Field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM) and nanoindentation were used to demonstrate that the sectioning temperature caused a change in nanostructure of the compression moulded UHMWPE sectioned surface, explaining the change in mechanical response to indentation at a nanoscale. In this study, it was demonstrated that significant plastic deformation occurs when a shear stress is applied between the glass or diamond blade and the UHMWPE during sample preparation under ambient conditions at a temperature of 22 degrees C. These results also suggest that an optimum sample sectioning temperature should definitely be below the measured Tg of the polymer. PMID:12022419

Ho, S P; Riester, L; Drews, M; Boland, T; LaBerge, M

2002-01-01

406

High-molecular-weight protein hydrodynamics studied with a long-lifetime metal-ligand complex.  

PubMed

[Ru(2,2'-bipyridine)(2)(4,4'-dicarboxy-2,2'-bipyridine)](2+) (RuBDc) is a very photostable probe that possesses favorable photophysical properties including long lifetime, high quantum yield, large Stokes' shift, and highly polarized emission. In the present study, we demonstrated the usefulness of this probe for monitoring the rotational diffusion of high-molecular-weight (MW) proteins. Using frequency-domain fluorometry with a high-intensity, blue light-emitting diode (LED) as the modulated light source, we compared the intensity and anisotropy decays of RuBDc conjugated to immunoglobulin G (IgG) and immunoglobulin M (IgM), which show a six-fold difference in MW We obtained slightly longer lifetimes for IgM (=428 ns in buffer) than IgG (=422 ns in buffer) in the absence and presence of glycerol, suggesting somewhat more efficient shielding of RuBDc from water in IgM than in IgG. The anisotropy decay data showed longer rotational correlation times for IgM (1623 and 65.7 ns in buffer) as compared to IgG (264 and 42.5 ns in buffer). Importantly, the ratio of the long rotational correlation times of IgM to IgG in buffer was 6.2, which is very close to that of MW of IgM to IgG (6.0). The shorter correlation times are most likely to be associated with domain motions within the proteins. The anisotropy decays reflect both the molecular size and shape of the immunoglobulins, as well as the viscosity. These results show that RuBDc can have numerous applications in studies of high-MW protein hydrodynamics and in fluorescence polarization immunoassays (FPI) of high-MW analytes. PMID:12044900

Kang, Jung Sook; Piszczek, Grzegorz; Lakowicz, Joseph R

2002-06-01

407

Effects of protein molecular weight on the intrinsic material properties and release kinetics of wet spun polymeric microfiber delivery systems.  

PubMed

Wet spun microfibers have great potential for the design of multifunctional controlled release scaffolds. Understanding aspects of drug delivery and mechanical strength, specific to protein molecular weight, may aid in the optimization and development of wet spun fiber platforms. This study investigated the intrinsic material properties and release kinetics of poly(l-lactic acid) (PLLA) and poly(lactic-co-glycolic acid) (PLGA) wet spun microfibers encapsulating proteins with varying molecular weights. A cryogenic emulsion technique developed in our laboratory was used to encapsulate insulin (5.8 kDa), lysozyme (14.3 kDa) and bovine serum albumin (BSA, 66.0 kDa) within wet spun microfibers (~100 ?m). Protein loading was found to significantly influence mechanical strength and drug release kinetics of PLGA and PLLA microfibers in a molecular-weight-dependent manner. BSA encapsulation resulted in the most significant decrease in strength and ductility for both PLGA and PLLA microfibers. Interestingly, BSA-loaded PLGA microfibers had a twofold increase (8±2 MPa to 16±1 MPa) in tensile strength and a fourfold increase (3±1% to 12±6%) in elongation until failure in comparison to PLLA microfibers. PLGA and PLLA microfibers exhibited prolonged protein release up to 63 days in vitro. Further analysis with the Korsmeyer-Peppas kinetic model determined that the mechanism of protein release was dependent on Fickian diffusion. These results emphasize the critical role protein molecular weight has on the properties of wet spun filaments, highlighting the importance of designing small molecular analogues to replace growth factors with large molecular weights. PMID:22902813

Lavin, Danya M; Zhang, Linda; Furtado, Stacia; Hopkins, Richard A; Mathiowitz, Edith

2013-01-01

408

On the use of hydroxyl radical kinetics to assess the number-average molecular weight of dissolved organic matter.  

PubMed

Dissolved organic matter (DOM) is involved in numerous environmental processes, and its molecular size is important in many of these processes, such as DOM bioavailability, DOM sorptive capacity, and the formation of disinfection byproducts during water treatment. The size and size distribution of the molecules composing DOM remains an open question. In this contribution, an indirect method to assess the average size of DOM is described, which is based on the reaction of hydroxyl radical (HO(•)) quenching by DOM. HO(•) is often assumed to be relatively unselective, reacting with nearly all organic molecules with similar rate constants. Literature values for HO(•) reaction with organic molecules were surveyed to assess the unselectivity of DOM and to determine a representative quenching rate constant (krep = 5.6 × 10(9) M(-1) s(-1)). This value was used to assess the average molecular weight of various humic and fulvic acid isolates as model DOM, using literature HO(•) quenching constants, kC,DOM. The results obtained by this method were compared with previous estimates of average molecular weight. The average molecular weight (Mn) values obtained with this approach are lower than the Mn measured by other techniques such as size exclusion chromatography (SEC), vapor pressure osmometry (VPO), and flow field fractionation (FFF). This suggests that DOM is an especially good quencher for HO(•), reacting at rates close to the diffusion-control limit. It was further observed that humic acids generally react faster than fulvic acids. The high reactivity of humic acids toward HO(•) is in line with the antioxidant properties of DOM. The benefit of this method is that it provides a firm upper bound on the average molecular weight of DOM, based on the kinetic limits of the HO(•) reaction. The results indicate low average molecular weight values, which is most consistent with the recent understanding of DOM. A possible DOM size distribution is discussed to reconcile the small nature of DOM with the large-molecule behavior observed in other studies. PMID:25222517

Appiani, Elena; Page, Sarah E; McNeill, Kristopher

2014-10-21

409

A large molecular size fraction of riverine high molecular weight dissolved organic matter (HMW DOM) stimulates growth of the harmful dinoflagellate Alexandrium minutum  

Microsoft Academic Search

An increase in the concentration of riverine dissolved organic matter (DOM) has been observed during the last decades, and this material can stimulate marine plankton in coastal waters with significant freshwater input. We studied the effect of two size fractions of riverine high molecular weight dissolved organic matter (HMW DOM), isolated with tangential ultrafiltration, on the harmful dinoflagellate Alexandrium minutum

Tony Fagerberg; Per Carlsson; Mikael Lundgren

2009-01-01

410

Molecular weight dependency on the production of the TNF stimulated by fractions of rye (1-->3),(1-->4)-beta-D-glucan.  

PubMed

Mixed-linkage (1-->3),(1-->4)-beta-D-glucan with a weight average molecular weight varying between 79,800 and 13,900 was purified from rye. These fractions were used for stimulation of human monocytes to produce tumour necrosis factor (TNF). A mixed-linkage beta-glucan with a weight average molecular weight of 18,900 was found to be the most potent immunostimulator. PMID:11119264

Roubroeks, J P; Skjåk-Braek, G; Ryan, L; Christensen, B E

2000-12-01

411

Effects of Deletions of High Molecular Weight Glutenin Subunit Alleles on Dough Properties and Wheat Flour Tortilla Quality  

E-print Network

In wheat (Triticum aestivum L), high molecular weight glutenin subunits (HMW -GS) are synthesized by the loci Glu-A1, Glu-B1, and Glu-D1 on the long arm of group 1 chromosome, and their variants play a significant role in the functional properties...

Tuncil, Yunus

2012-10-19

412

PII S0016-7037(01)00830-4 Chemical characterization of high molecular weight dissolved organic matter in fresh and  

E-print Network

matter in fresh and marine waters DANIEL J. REPETA* TRACY M. QUAN, LIHINI I. ALUWIHARE and AMYMARIE characteristics of fresh water and marine DOM presumably arise from differences in the organic matter sources molecular weight fraction of dissolved organic matter in a suite of lakes, rivers, seawater, and marine

Aluwihare, Lihini

413

Enhanced Gene Delivery Mediated by Low Molecular Weight Chitosan/DNA Complexes: Effect of pH and Serum  

E-print Network

RESEARCH Enhanced Gene Delivery Mediated by Low Molecular Weight Chitosan/DNA Complexes: Effect for 8­24 h to maximize uptake and then the media was changed to pH 7.4 with 10% serum for an additional on non-viral vectors has gained momentum as they offer several advantages, including stability, safety

Buschmann, Michael

414

Carbon ion implantation of ultra-high molecular weight polyethylene using filtered cathodic vacuum arc with substrate pulse biasing  

Microsoft Academic Search

This paper discusses the results of an investigation that has been carried out to improve the nano-hardness and tribological properties of ultra-high molecular weight polyethylene (UHMWPE) using a filtered cathodic arc source with substrate pulse biasing. The filtered cathodic arc source generated highly ionized carbon plasma and ions were accelerated towards the substrate by the negative substrate pulse voltage. Graphitization,

J. Y. Sze; B. K. Tay

2006-01-01

415

A MURINE MODEL FOR LOW MOLECULAR WEIGHT CHEMICALS: DIFFERENTIATION OF RESPIRATORY SENSITIZERS (TMA) FROM CONTACT SENSITIZERS (DNFB)  

EPA Science Inventory

Exposure to low molecular weight (LMW) chemicals contributes to both dermal and respiratory sensitization and is an important occupational health problem. Our goal was to establish an in vivo murine model for hazard identification of LMW chemicals that have the potential to indu...

416

Carrier DNA For Yeast Transformation Preparation of high molecular weight single stranded carrier DNA for yeast transformations.  

E-print Network

with an equal volume of phenol:CHCl3. Centrifuge for 5 minutes to separate layers. 6. Precipitate DNA. Add 1Carrier DNA For Yeast Transformation Preparation of high molecular weight single stranded carrier DNA for yeast transformations. 1. Dissolve 100 mg DNA in 10 ml TE, pH 8 in a sterile 50 ml plastic

Aris, John P.

417

Serious adverse incidents with the usage of low molecular weight heparins in patients with chronic kidney disease  

Microsoft Academic Search

Background: The aim of the study is to describe serious adverse events in patients with renal insufficiency administered low molecular weight heparins (LMWHs). Methods: Systematic case note review from July 2002 to March 2003, Hope Hospital, Salford, UK, was used. Results: Ten patients experienced an adverse incident on LMWH therapy. Five patients were on maintenance hemodialysis therapy, and 1 patient

Vasim Farooq; Janet Hegarty; Thangavelu Chandrasekar; Elizabeth H. Lamerton; Sandip Mitra; John B. Houghton; Philip A. Kalra; Stephen Waldek; Donal J. O’Donoghue; Grahame N. Wood

2004-01-01

418

Degradation of high molecular weight compounds of Kraft pulp mill effluents by a combined treatment with fungi and bacteria  

Microsoft Academic Search

Pretreatment of Kraft pulp mill effluents by mycelial pellets or extracellular ligninolytic liquid from Phanerochaete chrysosporium enhanced the anaerobic degradation of high molecular weight (HMW) compounds up to 79% and 72% respectively, against 45% when only anaerobic digestion was considered. Decolourization was obtained only after fungal pretreatment, since both anaerobic digestion and ligninolytic liquid pretreatment of Kraft effluent slightly increased

G. Feijoo; G. Vidal; M. T. Moreira; R. Méndez; J. M. Lema

1995-01-01

419

Advances in the understanding of low molecular weight silicon formation and implications for control by AMC filters  

Microsoft Academic Search

Trimethylsilanol (TMS) is a low molecular weight \\/ low boiling point silicon-containing, airborne contaminant that has received increased interest over the past few years as an important cause for contamination of optical surfaces in lithography equipment. TMS is not captured well by carbon-based filters, and hexamethyldisiloxane (HMDSO), even though captured well, can be converted to TMS when using acidic filter

Jürgen M. Lobert; Philip W. Cate; David J. Ruede; Joseph R. Wildgoose; Charles M. Miller; John C. Gaudreau

2010-01-01

420

Isolation and characterization of five novel high molecular weight subunit of glutenin genes from Triticum timopheevi and Aegilops cylindrica  

Microsoft Academic Search

Analysis by SDS-PAGE of total protein fractions from single seeds of Aegilops cylindrica (genomes C and D) and Triticum timopheevi (genomes A and G) showed the presence of three bands corresponding to high molecular weight subunits of glutenin (HMW subunits) in the former and two major bands and a minor band corresponding to HMW subunits in the latter. Three Ae.

Y. Wan; D. Wang; P. R. Shewry; N. G. Halford

2002-01-01

421

Mixed molecular weight copolymer nanoparticles for the treatment of drug-resistant tumors: formulation development and cytotoxicity.  

PubMed

Nanoparticles composed of both high- and low-molecular-weight methoxy poly(ethylene glycol)-block-poly(caprolactone) (MePEG-b-PCL) diblock copolymers (termed "mixed molecular weight nanoparticles") were investigated for the encapsulation and delivery of the taxane drugs paclitaxel (PTX) and docetaxel (DTX). These nanoparticles were prepared using nanoprecipitation and emulsion methods. These 80 nm nanoparticles were prepared with high yields, efficiently solubilized PTX and DTX up to 500 and 1300 ?g/mL, respectively, and demonstrated controlled release of these drugs over 14 days. The taxane-sensitive (MDCKII) and taxane-resistant [P-glycoprotein (P-gp) overexpressing] MDCKII-MDR cell lines were used to establish the cytotoxic profiles of these nanoparticles. Because of the coencapsulation of the previously demonstrated P-gp inhibitor, a low-molecular-weight MePEG-b-PCL copolymer (MePEG17 -b-PCL5 ), these drug-loaded mixed molecular weight nanoparticles dramatically reduced the viability of P-gp overexpressing MDCKII-MDR cells and restored sensitivity to taxane drugs in these cells. © 2014 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 103:3966-3976, 2014. PMID:25318668

Wan, Chung Ping Leon; Letchford, Kevin; Leung, Donna; Jackson, John K; Burt, Helen M

2014-12-01

422

Deep blue light-emitting diode based on high molecular weight poly(9,9-dioctylfluorene) with high efficiency  

E-print Network

/green emitter as the dopants [1,2]. Deep blue PLED is more essential than the sky blue one in making white lightDeep blue light-emitting diode based on high molecular weight poly(9,9-dioctylfluorene) with high November 2007 Available online 18 December 2007 Abstract A highly efficient deep blue polymer light

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