Note: This page contains sample records for the topic accurate molecular weight from Science.gov.
While these samples are representative of the content of Science.gov,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of Science.gov
to obtain the most current and comprehensive results.
Last update: August 15, 2014.
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

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

3

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

4

Molecular Weight of Native Cellulose  

Microsoft Academic Search

THE molecular weight of cellulose is of great interest to cellulose chemistry, and many attempts have been made to determine it. The cellulose derivatives, esters and ethers, can in general be dissolved in simple organic solvents, and their molecular weights determined by the osmotic pressure method. It is questionable, however, if the derivatives can be prepared without degradation of the

Nils Gralén

1943-01-01

5

Accurate Molecular Polarizabilities Based on Continuum Electrostatics.  

PubMed

A novel approach for representing the intramolecular polarizability as a continuum dielectric is introduced to account for molecular electronic polarization. It is shown, using a finite-difference solution to the Poisson equation, that the Electronic Polarization from Internal Continuum (EPIC) model yields accurate gas-phase molecular polarizability tensors for a test set of 98 challenging molecules composed of heteroaromatics, alkanes and diatomics. The electronic polarization originates from a high intramolecular dielectric that produces polarizabilities consistent with B3LYP/aug-cc-pVTZ and experimental values when surrounded by vacuum dielectric. In contrast to other approaches to model electronic polarization, this simple model avoids the polarizability catastrophe and accurately calculates molecular anisotropy with the use of very few fitted parameters and without resorting to auxiliary sites or anisotropic atomic centers. On average, the unsigned error in the average polarizability and anisotropy compared to B3LYP are 2% and 5%, respectively. The correlation between the polarizability components from B3LYP and this approach lead to a R(2) of 0.990 and a slope of 0.999. Even the F2 anisotropy, shown to be a difficult case for existing polarizability models, can be reproduced within 2% error. In addition to providing new parameters for a rapid method directly applicable to the calculation of polarizabilities, this work extends the widely used Poisson equation to areas where accurate molecular polarizabilities matter. PMID:23646034

Truchon, Jean-François; Nicholls, Anthony; Iftimie, Radu I; Roux, Benoît; Bayly, Christopher I

2008-09-01

6

Accurate Molecular Polarizabilities Based on Continuum Electrostatics  

PubMed Central

A novel approach for representing the intramolecular polarizability as a continuum dielectric is introduced to account for molecular electronic polarization. It is shown, using a finite-difference solution to the Poisson equation, that the Electronic Polarization from Internal Continuum (EPIC) model yields accurate gas-phase molecular polarizability tensors for a test set of 98 challenging molecules composed of heteroaromatics, alkanes and diatomics. The electronic polarization originates from a high intramolecular dielectric that produces polarizabilities consistent with B3LYP/aug-cc-pVTZ and experimental values when surrounded by vacuum dielectric. In contrast to other approaches to model electronic polarization, this simple model avoids the polarizability catastrophe and accurately calculates molecular anisotropy with the use of very few fitted parameters and without resorting to auxiliary sites or anisotropic atomic centers. On average, the unsigned error in the average polarizability and anisotropy compared to B3LYP are 2% and 5%, respectively. The correlation between the polarizability components from B3LYP and this approach lead to a R2 of 0.990 and a slope of 0.999. Even the F2 anisotropy, shown to be a difficult case for existing polarizability models, can be reproduced within 2% error. In addition to providing new parameters for a rapid method directly applicable to the calculation of polarizabilities, this work extends the widely used Poisson equation to areas where accurate molecular polarizabilities matter.

Truchon, Jean-Francois; Nicholls, Anthony; Iftimie, Radu I.; Roux, Benoit; Bayly, Christopher I.

2013-01-01

7

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

8

Low molecular weight fuel additive  

US Patent & Trademark Office Database

The invention includes a method of improving the combustion efficiency of a fuel-burning device. The method includes the steps of adding a low molecular weight polymer to the fuel of the fuel-burning device and burning the fuel with the polymer in the fuel-burning device. The invention also includes fuel compositions containing such polymers.

2010-06-01

9

Accurate HLA type inference using a weighted similarity graph  

PubMed Central

Background The human leukocyte antigen system (HLA) contains many highly variable genes. HLA genes play an important role in the human immune system, and HLA gene matching is crucial for the success of human organ transplantations. Numerous studies have demonstrated that variation in HLA genes is associated with many autoimmune, inflammatory and infectious diseases. However, typing HLA genes by serology or PCR is time consuming and expensive, which limits large-scale studies involving HLA genes. Since it is much easier and cheaper to obtain single nucleotide polymorphism (SNP) genotype data, accurate computational algorithms to infer HLA gene types from SNP genotype data are in need. To infer HLA types from SNP genotypes, the first step is to infer SNP haplotypes from genotypes. However, for the same SNP genotype data set, the haplotype configurations inferred by different methods are usually inconsistent, and it is often difficult to decide which one is true. Results In this paper, we design an accurate HLA gene type inference algorithm by utilizing SNP genotype data from pedigrees, known HLA gene types of some individuals and the relationship between inferred SNP haplotypes and HLA gene types. Given a set of haplotypes inferred from the genotypes of a population consisting of many pedigrees, the algorithm first constructs a weighted similarity graph based on a new haplotype similarity measure and derives constraint edges from known HLA gene types. Based on the principle that different HLA gene alleles should have different background haplotypes, the algorithm searches for an optimal labeling of all the haplotypes with unknown HLA gene types such that the total weight among the same HLA gene types is maximized. To deal with ambiguous haplotype solutions, we use a genetic algorithm to select haplotype configurations that tend to maximize the same optimization criterion. Our experiments on a previously typed subset of the HapMap data show that the algorithm is highly accurate, achieving an accuracy of 96% for gene HLA-A, 95% for HLA-B, 97% for HLA-C, 84% for HLA-DRB1, 98% for HLA-DQA1 and 97% for HLA-DQB1 in a leave-one-out test. Conclusions Our algorithm can infer HLA gene types from neighboring SNP genotype data accurately. Compared with a recent approach on the same input data, our algorithm achieved a higher accuracy. The code of our algorithm is available to the public for free upon request to the corresponding authors.

2010-01-01

10

The Molecular Weight Distribution of Polymer Samples  

ERIC Educational Resources Information Center

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

Horta, Arturo; Pastoriza, M. Alejandra

2007-01-01

11

Effect of molecular weight on polymer processability  

SciTech Connect

Differences in rheological behavior due to the polymer molecular weight and molecular weight distribution have been shown with the MPT. SBR polymers having high molecular weight fractions develop higher stress relaxation time values due to the higher degree of polymer entanglements. Tests conducted at increasing temperatures show the diminishing influence of the polymer entanglements upon stress relaxation time. EPDM polymers show stress relaxation time and head pressure behavior which correlates with mill processability. As anticipated, compounded stock of EPDM have broad molecular weight distribution has higher stress relaxation time values than EPDM compounds with narrow molecular weight distribution.

Karg, R.F.

1983-01-01

12

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

13

Soluble high molecular weight polyimide resins  

NASA Technical Reports Server (NTRS)

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

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

1970-01-01

14

Production of high molecular weight polylactic acid  

SciTech Connect

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

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

16

Molecular weight determinations of biosolubilized coals  

SciTech Connect

We have compared several different methods for determining the molecular weight of biosolubilized coals: Aqueous gel permeation Chromatography (GPC), organic GPC, preparative GPC, dynamic laser light scattering (LLS), static LLS, static LLS, mass spectrometry, vapor phase osmometry (VPO) and ultrafiltration. We have found that careful consideration must be given to the molecular weight result obtained from each method. The average molecular weight and the molecular weight distribution were found to be dependent upon many factors, including the technique used; molecular weight standards, pH, and the percentage of sample analyzed. Weight average molecular weights, M{sub w}, obtained for biosolubilized leonardite range from 800,000 daltons for neutral pH aqueous GPC based on polyethylene glycol molecular weight standards to 570 daltons for pH 11.5 buffered aqueous GPC based on a fulvic acid standard. It is clear that the state of association of the biocoal analyte, as well as the interactions of sample with the separation matrix, can have large influence of the observed result, and these must be understood before reliable GPC measurements can be made. Furthermore, a uniform set of molecular weight standards for biodegraded coals is needed. 10 refs., 1 tab.

Linehan, J.C.; Clauss, S.; Bean, R.; Campbell, J.

1991-05-01

17

Molecular dynamics simulation by atomic mass weighting  

PubMed Central

A molecular dynamics-based simulation method in which atomic masses are weighted is described. Results from this method showed that the capability for conformation search in molecular dynamics simulation of a short peptide (FMRF-amide) is significantly increased by mass weighting.

Mao, Boryeu; Friedman, Alan R.

1990-01-01

18

Microdialysis unit 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, or (4) any combination of (1), (2), and (3).

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

1999-01-01

19

Fatigue characteristics of ultra high molecular weight polyethylene with different molecular weight for implant material  

Microsoft Academic Search

In order to investigate the effect of molecular weight on fatigue characteristics in the ultra high molecular weight polyethylene (UHMWPE), tension–tension fatigue tests of notched specimens were carried out in the present study. The effects of frequency and stress ratio on the fatigue characteristics were also investigated and fractography was discussed. The fatigue strength does not increase with increasing molecular

Mitsuo Niinomi; Lei Wang; Takumi Enjitsu; Kei-Ichi Fukunaga

2001-01-01

20

Dye-free protein molecular weight markers.  

PubMed

Protein molecular weight markers are widely used in sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting. Here, we describe novel protein molecular weight markers in which a prestaining procedure is no longer needed. Green fluorescent protein (GFP) is stable and resistant to denaturing agents/conditions. Various histidine-tagged GFP fusion proteins were overexpressed in Escherichia coli and purified by metal affinity chromatography. The minimal amount of each protein marker needed for analysis in SDS-PAGE and Western blot under visible light was 62.5 and 125 ng, respectively. Under ultraviolet (UV) ray, the minimal amount of each protein marker needed for analysis in SDS-PAGE and Western blot was half of those amounts used under visible light, respectively. Collectively, the accuracy, sensitivity, ease, economy, and flexibility of our strategy may reinforce the application of GFP in molecular biology. PMID:16041708

Chang, Microsugar; Hsu, Hsue-Yin; Lee, Han-Jung

2005-08-01

21

Molecular Weight Distribution of Gluten Proteins  

Microsoft Academic Search

Gluten confers on flour the ability to produce viscoelastic doughs. The molecular weight distribution (MWD) of gluten proteins\\u000a is one of the main determinants of physical dough properties. Size-exclusion high performance liquid chromatography (SE-HPLC)\\u000a is routinely used to evaluate this parameter. A proper, highly efficient solubilization protocol plays a vital role in the\\u000a determination of MWD. Coupling SE-HPLC with multi-angle

O. R. LARROQUE; P. Sharp; F. Bekes

22

A general, accurate procedure for calculating molecular interaction force.  

PubMed

The determination of molecular interaction forces, e.g., van der Waals force, between macroscopic bodies is of fundamental importance for understanding sintering, adhesion and fracture processes. In this paper, we develop an accurate, general procedure for van der Waals force calculation. This approach extends a surface formulation that converts a six-dimensional (6D) volume integral into a 4D surface integral for the force calculation. It uses non-uniform rational B-spline (NURBS) surfaces to represent object surfaces. Surface integrals are then done on the parametric domain of the NURBS surfaces. It has combined advantages of NURBS surface representation and surface formulation, including (1) molecular interactions between arbitrary-shaped objects can be represented and evaluated by the NURBS model further common geometries such as spheres, cones, planes can be represented exactly and interaction forces are thus calculated accurately; (2) calculation efficiency is improved by converting the volume integral to the surface integral. This approach is implemented and validated via its comparison with analytical solutions for simple geometries. Calculation of van der Waals force between complex geometries with surface roughness is also demonstrated. A tutorial on the NURBS approach is given in Appendix A. PMID:19596335

Yang, Pinghai; Qian, Xiaoping

2009-09-15

23

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

24

Application of 1H DOSY for Facile Measurement of Polymer Molecular Weights  

PubMed Central

To address the practical issues of polymer molecular weight determination, the first accurate polymer weight-average molecular weight determination method in diverse living/controlled polymerization via DOSY (diffusion-ordered NMR spectroscopy) is reported. Based on the linear correlation between the logarithm of diffusion coefficient (log D) and the molecular weights (log Mw), external calibration curves were created to give predictions of molecular weights of narrowly-dispersed polymers. This method was successfully applied to atom transfer radical polymerization (ATRP), reversible addition–fragmentation chain transfer (RAFT), and ring-opening metathesis polymerization (ROMP), with weight-average molecular weights given by this method closely correlated to those obtained from GPC measurement.

Li, Weibin; Chung, Hoyong; Daeffler, Christopher; Johnson, Jeremiah A.; Grubbs, Robert H.

2012-01-01

25

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

ERIC Educational Resources Information Center

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

Izunobi, Josephat U.; Higginbotham, Clement L.

2011-01-01

26

Molecular weight of aquatic fulvic acids by vapor pressure osmometry  

Microsoft Academic Search

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 form 500 to 950 daltons, 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

G. R. Aiken; R. L. Malcolm

1987-01-01

27

Accurate Photodissociation of UV-Irradiated Molecular Gas  

NASA Astrophysics Data System (ADS)

With the upcoming servicing of the HST and the installation of COS, a large number of molecular absorption and emission features will be observable in the visible and ultraviolet. These observations, and analysis of past ones, are expected to give new insights into our understanding of the evolution of a range of astronomical sources and the chemistry occuring in these environments. In particular, molecules are primarily destroyed in diffuse and translucent regions via photodissociation {PD} due to incident UV and optical radiation. The majority of astrochemical/spectral modeling codes available today use pre-computed exponentially-attenuated photorates based on dust scattering/absorption for an ``average" interstellar cloud. Since there is clearly a large scatter in the dust properties and local radiation field for various environments in the Galaxy and beyond, the adoption of such pre-computed photorates can lead to considerable errors in predicted abundances. We propose here to significantly improve current modeling capabilities by computing new rovibrationally-resolved PD cross sections for C_2, CN, and CS; constructing a publicly available database of available PD cross sections; implementating the PD cross sections into the spectral simulation code Cloudy for explicit computation of local photorates; and testing of the Cloudy implementation in diffuse and translucent cloud simulations and with photodissociation region benchmark models. The successful completion of the goals from this proposal will be important for obtaining accurate molecular abundances from HST observations of diffuse clouds, translucent clouds, and other UV-irradiated molecular regions and in inferring local grain properties.;

Stancil, Phillip

2008-07-01

28

A live weight-heart girth relationship for accurate dosing of east African shorthorn zebu cattle.  

PubMed

The accurate estimation of livestock weights is important for many aspects of livestock management including nutrition, production and appropriate dosing of pharmaceuticals. Subtherapeutic dosing has been shown to accelerate pathogen resistance which can have subsequent widespread impacts. There are a number of published models for the prediction of live weight from morphometric measurements of cattle, but many of these models use measurements difficult to gather and include complicated age, size and gender stratification. In this paper, we use data from the Infectious Diseases of East Africa calf cohort study and additional data collected at local markets in western Kenya to develop a simple model based on heart girth circumference to predict live weight of east African shorthorn zebu (SHZ) cattle. SHZ cattle are widespread throughout eastern and southern Africa and are economically important multipurpose animals. We demonstrate model accuracy by splitting the data into training and validation subsets and comparing fitted and predicted values. The final model is weight(0.262) = 0.95 + 0.022 × girth which has an R (2) value of 0.98 and 95 % prediction intervals that fall within the ± 20 % body weight error band regarded as acceptable when dosing livestock. This model provides a highly reliable and accurate method for predicting weights of SHZ cattle using a single heart girth measurement which can be easily obtained with a tape measure in the field setting. PMID:22923040

Lesosky, Maia; Dumas, Sarah; Conradie, Ilana; Handel, Ian Graham; Jennings, Amy; Thumbi, Samuel; Toye, Phillip; Bronsvoort, Barend Mark de Clare

2012-12-01

29

The viscosity–molecular weight relationships for diolic perfluoropolyethers  

Microsoft Academic Search

It is shown that for diolic perfluoropolyethers having short chain lengths the “anomalous” (non monotonic) relationship between isothermal melt viscosity and molecular weight, reported in recent papers, is not anomalous at all but fully explainable when one takes into account the fact that the glass transition of the samples Tg is itself a function of the molecular weight.For low molecular

G Ajroldi; G Marchionni; G Pezzin

1999-01-01

30

Accurate representations of general textures by a set of weighted grains  

SciTech Connect

The most compact way of describing general texture information is by way of a file of weighted discrete grains. When the textures are strong, this results in a great saving of necessary parameters. The most efficient way is a random file from which grains with low weights get discarded. This method is routine and independent of any preknowledge of the texture or even the symmetries. Typically, the order of 100 grains are sufficient for strong textures or fiber textures. Furthermore, these grains files are directly in the kind of format that is useful for computer simulation of current anisotropic properties or future texture development. For textures that are not very sharp, but nevertheless are not properly represented as random (which would imply isotropic properties), one may also use weighted-grains files, but here the number of grains needed may be large for an accurate representation. We have found that on the order of 1000 weighted grains are sufficient for most cases. When the symmetries are known, grains that are regularly (rather than randomly) arranged in orientation space are useful -- again better when they are weighted.

Kocks, U.F. (Los Alamos National Lab., NM (USA)); Kallend, J.S.; Biondo, A.C. (Illinois Inst. of Tech., Chicago, IL (USA). Dept. of Metallurgy and Materials Engineering)

1990-01-01

31

Recovery of petroleum with chemically treated high molecular weight polymers  

SciTech Connect

Plugging of reservoirs with high molecular weight polymers, e.g. Partially hydrolyzed polyacrylamide, is overcome by chemically treating a polymer having an excessively high average molecular weight prior to injection into a reservoir with an oxidizing chemical, e.g. sodium hypochlorite, and thereafter incorporating a reducing chemical, e.g., sodium sulfite, to stop degradation of the polymer when a desired lower average molecular weight and flooding characteristics are attained.

Gibb, C.L.; Rhudy, J.S.

1980-11-18

32

Molecular Weight Effects on the Viscoelastic Response of a 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 each material with different molecular weight. Through the use of time-aging-time superposition procedures, the material constants, material master curves and aging-related parameters were evaluated at each temperature for a given molecular weight. The time-temperature superposition technique helped to describe the effect of temperature on the timescale of the viscoelastic response of each molecular weight. It was shown that the low molecular weight materials have increased creep compliance and creep compliance rate, and are more sensitive to temperature than the high molecular weight materials. Furthermore, a critical molecular weight transition was observed to occur at a weight-average molecular weight of approximately 25000 g/mol below which, the temperature sensitivity of the time-temperature superposition shift factor increases rapidly.

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

2000-01-01

33

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

34

Low-molecular-weight heparins: pharmacologic profile and product differentiation  

Microsoft Academic Search

The interchangeability of low-molecular-weight heparins (LMWHs) has been the subject of discussion since these products were first introduced for the prophylaxis of deep vein thrombosis. Experimental evidence now exists to show that LMWHs differ from each other in a number of characteristics. Products have been differentiated on the basis of molecular weight and biologic properties, but only limited information derived

Jawed Fareed; Walter Jeske; Debra Hoppensteadt; Rana Clarizio; Jeanine M. Walenga

1998-01-01

35

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

36

Molecular weight of aquatic fulvic acids by vapor pressure osmometry  

SciTech Connect

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 form 500 to 950 daltons, 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 H/sub 2/O 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/sup + +/ and Mg/sup + +/ in the river water and the radii of gyration and molecular weights of the corresponding fulvic acid samples.

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

1987-08-01

37

Evaluation of ultrafiltration for determining molecular weight of fulvic acid  

USGS Publications Warehouse

Two commonly used ultrafiltration membranes are evaluated for the determination of molecular weights of humic substances. Polyacrylic acids of Mr 2000 and 5000 and two well-characterized fulvic acids are used as standards. Molecular size characteristics of standards, as determined by small-angle X-ray scattering, are presented. Great care in evaluating molecular weight data obtained by ultrafiltration is needed because of broad nominal cutoffs and membrane-solute interactions.

Aiken, G. R.

1984-01-01

38

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

39

Low molecular weight species in humic and fulvic fractions  

USGS Publications Warehouse

Fourier transform solution 1H nuclear magnetic resonance (NMR) spectrometry with homogated water peak irradiation is a useful method for detecting low molecular weight substances in humic extracts. Succinate, acetate, methanol, formate, lactate and some aryl methoxyl compounds have been detected in extracts from a wide range of sources. In view of the controversy over whether low molecular weight substances are contaminants in humic extracts introduced by the concentration procedure, we report that some of these materials are not contaminants since 1H-NMR can be used to follow their formation from higher molecular weight species. ?? 1988.

Wilson, M. A.; Collin, P. J.; Malcolm, R. L.; Perdue, E. M.; Cresswell, P.

1988-01-01

40

Apparatus for the Determination of Molecular Weights of Actinide Complexes.  

National Technical Information Service (NTIS)

This report describes the fabrication and standardisation of an apparatus called, 'Osmistor' for molecular weight determinations. The set up uses a matched pair of thermistors as temperature sensing device and is based on the principles of relative loweri...

M. S. Nagar M. R. Ponkshe M. S. Subramanian

1982-01-01

41

Low-Molecular-Weight Heparins in the Cardiac Catheterization Laboratory  

PubMed Central

We describe the unique properties of low-molecular-weight heparins and review studies of the use of these agents in the catheterization laboratory for percutaneous coronary intervention. Recent data regarding bedside monitoring of low-molecular-weight heparin activity are also discussed, as are ongoing and future studies that should be of assistance to clinicians as they consider expanding the use of this newer form of antithrombotic therapy.

Kadakia, Rajan A.; Baimeedi, Shravantika R.; Ferguson, James J.

2004-01-01

42

Accurate Model Selection of Relaxed Molecular Clocks in Bayesian Phylogenetics  

PubMed Central

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

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

2013-01-01

43

Accurate model selection of relaxed molecular clocks in bayesian phylogenetics.  

PubMed

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

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

2013-02-01

44

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

45

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.

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

2014-01-01

46

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

47

Microbial Detection with Low Molecular Weight RNA  

Microsoft Academic Search

The need to monitor microorganisms in the environment has increased interest in assays based on hybridization probes that\\u000a target nucleic acids (e.g., rRNA). We report the development of liquid-phase assays for specific bacterial 5S rRNA sequences\\u000a or similarly sized artificial RNAs (aRNAs) using molecular beacon technology. These beacons fluoresce only in the presence\\u000a of specific target sequences, rendering as much

Katerina D. Kourentzi; George E. Fox; Richard C. Willson

2001-01-01

48

Synthesis and characterization of high molecular weight poly(1,5-dioxepan-2-one) with narrow molecular weight distribution  

Microsoft Academic Search

Ring-opening polymerization of 1,5-dioxepan-2-one (DXO) initiated with aluminium isopropoxide in tetrahydrofuran (THF) solution and in bulk has been investigated. An improved monomer purification procedure is presented which makes it possible to synthesize high molecular weight poly(DXO) with a narrow molecular weight distribution. The kinetic dependence on parameters such as polymerization temperature, the presence of Lewis bases and water impurities is

Anders Löfgren; Ann-Christine Albertsson

1995-01-01

49

DSC of ? -irradiated ultra-high molecular weight polyethylene and high density polyethylene of normal molecular weight  

Microsoft Academic Search

The melting and the crystallization of?-irradiated (doses: 0–6Mrad) ultra-high molecular weight nascent polyethylene (UHMWPE) and high density nascent polyethylene with normal molecular weight (NMWPE) were investigated by DSC. The heat of melting of the nascent UHMWPE (DSC degree of crystallinity, respectively) increases up to a dose of 3 Mrad, after which it slightly decreases. The heat of the second melting

L. Minkova

1988-01-01

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

Importance of Accurate Charges in Molecular Docking: Quantum Mechanical/Molecular Mechanical (QM/MM) Approach  

PubMed Central

The extent to which accuracy of electric charges plays a role in protein-ligand docking is investigated through development of a docking algorithm, which incorporates quantum mechanical/molecular mechanical (QM/MM) calculations. In this algorithm, fixed charges of ligands obtained from force field parameterization are replaced by QM/MM calculations in the protein environment, treating only the ligands as the quantum region. The algorithm is tested on a set of 40 cocrystallized structures taken from the Protein Data Bank (PDB) and provides strong evidence that use of nonfixed charges is important. An algorithm, dubbed “Survival of the Fittest” (SOF) algorithm, is implemented to incorporate QM/MM charge calculations without any prior knowledge of native structures of the complexes. Using an iterative protocol, this algorithm is able in many cases to converge to a nativelike structure in systems where redocking of the ligand using a standard fixed charge force field exhibits nontrivial errors. The results demonstrate that polarization effects can play a significant role in determining the structures of protein-ligand complexes, and provide a promising start towards the development of more accurate docking methods for lead optimization applications.

CHO, ART E.; GUALLAR, VICTOR; BERNE, BRUCE J.; FRIESNER, RICHARD

2014-01-01

52

Molecular weight dependence of domain structure in silica-siloxane molecular composites  

Microsoft Academic Search

A detailed investigation of the molecular weight dependence of silica growth in in situ filled polydimethylsiloxane\\/tetraethylorthosilicate (PDMS\\/TEOS) materials was conducted using small angle neutron scattering (SANS). Composite materials were produced by using TEOS to simultaneously produce the glassy filler phase and to crosslink linear, hydroxyl terminated PDMS of variable molecular weight, M. Correlated domains of glassy filler were produced. The

T. A. Ulibarri; G. Beaucage; D. W. Schaefer; B. J. Olivier; R. A. Assink

1992-01-01

53

A weighted, multi-method approach for accurate basin-wide streamflow estimation in an ungauged watershed  

NASA Astrophysics Data System (ADS)

Decreased uncertainty with distributed, weighted, multi-method discharge estimates.High baseflow at upper elevations, while low elevations are mainly runoff driven.Scale-dependent river discharge suggests ergodic behavior in complex watersheds.Spatiotemporal discharge estimates necessary for accurate basin-wine partitioning.A single annual monsoonal event typically alters streambed characteristics.

Shope, Christopher L.; Bartsch, Svenja; Kim, Kiyong; Kim, Bomchul; Tenhunen, John; Peiffer, Stefan; Park, Ji-Hyung; Ok, Yong Sik; Fleckenstein, Jan; Koellner, Thomas

2013-06-01

54

RHEOLOGICAL PROPERTIES & MOLECULAR WEIGHT DISTRIBUTIONS OF FOUR PERFLUORINATED THERMOPLASTIC POLYMERS  

SciTech Connect

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

Hoffman, D M; Shields, A L

2009-02-24

55

Low-molecular-weight post-translationally modified microcins  

Microsoft Academic Search

Summary Microcins are a class of ribosomally synthesized anti- bacterial peptides produced by Enterobacteriaceae and active against closely related bacterial species. While some microcins are active as unmodified peptides, others are heavily modified by dedicated maturation enzymes. Low-molecular-weight micro- cins from the post-translationally modified group target essential molecular machines inside the cells. In this review, available structural and functional data

Konstantin Severinov; Ekaterina Semenova; Alexey Kazakov; Teymur Kazakov; Mikhail S. Gelfand

2007-01-01

56

Accurate and robust molecular crystal modeling using fragment-based electronic structure methods.  

PubMed

Accurately modeling molecular crystal polymorphism requires careful treatment of diverse intra- and intermolecular interactions which can be difficult to achieve without the use of high-level ab initio electronic structure techniques. Fragment-based methods like the hybrid many-body interaction QM/MM technique enable the application of accurate electronic structure models to chemically interesting molecular crystals. The theoretical underpinnings of this approach and the practical requirements for the QM and MM contributions are discussed. Benchmark results and representative applications to aspirin and oxalyl dihydrazide crystals are presented. PMID:24292635

Beran, Gregory J O; Wen, Shuhao; Nanda, Kaushik; Huang, Yuanhang; Heit, Yonaton

2014-01-01

57

Recommendations on biosimilar low-molecular-weight heparins  

Microsoft Academic Search

Summary. Based on the results of large clinical trials, several low-molecular-weight heparins (LMWHs) have been approved for prophylaxis and the treatment of venous and arterial thromboembolism. As a result of expiration or pending expiration of patent protection of the originator LMWHs, many generic or biosimilar LMWHs have been approved in some countries and more are likely to be approved elsewhere.

J. HARENBERG; A. KAKKAR; D. BERGQVIST; T. BARROWCLIFFE; B. CASU; J. FAREED; P. MISMETTI; F. A. OFOSU; W. RAAKE; M. SAMAMA; S. SCHULMAN

2009-01-01

58

Properties of crosslinked ultra-high-molecular-weight polyethylene  

Microsoft Academic Search

Substantially reducing the rate of generation of wear particles at the surfaces of ultra-high-molecular-weight polyethylene (UHMWPE) orthopedic implant bearing components, in vivo, is widely regarded as one of the most formidable challenges in modern arthroplasty. In the light of this, much research attention has been paid to the myriad of endogenous and exogenous factors that have been postulated to affect

Gladius Lewis

2001-01-01

59

Endogenous ethanol affects biopolyester molecular weight in recombinant Escherichia coli.  

PubMed

In biopolyester synthesis, polyhydroxyalkanoate (PHA) synthase (PhaC) catalyzes the polymerization of PHA in bacterial cells, followed by a chain transfer (CT) reaction in which the PHA polymer chain is transferred from PhaC to a CT agent. Accordingly, the frequency of CT reaction determines PHA molecular weight. Previous studies have shown that exogenous alcohols are effective CT agents. This study aimed to clarify the effect of endogenous ethanol as a CT agent for poly[(R)-3-hydroxybutyrate] [P(3HB)] synthesis in recombinant Escherichia coli, by comparing with that of exogenous ethanol. Ethanol supplementation to the culture medium reduced P(3HB) molecular weights by up to 56% due to ethanol-induced CT reaction. NMR analysis of P(3HB) polymers purified from the culture supplemented with (13)C-labeled ethanol showed the formation of a covalent bond between ethanol and P(3HB) chain at the carboxyl end. Cultivation without ethanol supplementation resulted in the reduction of P(3HB) molecular weight with increasing host-produced ethanol depending on culture aeration. On the other hand, production in recombinant BW25113(?adhE), an alcohol dehydrogenase deletion strain, resulted in a 77% increase in molecular weight. Analysis of five E. coli strains revealed that the estimated number of CT reactions was correlated with ethanol production. These results demonstrate that host-produced ethanol acts as an equally effective CT agent as exogenous ethanol, and the control of ethanol production is important to regulate the PHA molecular weight. PMID:24041146

Hiroe, Ayaka; Hyakutake, Manami; Thomson, Nicholas M; Sivaniah, Easan; Tsuge, Takeharu

2013-11-15

60

Low-molecular-weight post-translationally modified microcins.  

PubMed

Microcins are a class of ribosomally synthesized antibacterial peptides produced by Enterobacteriaceae and active against closely related bacterial species. While some microcins are active as unmodified peptides, others are heavily modified by dedicated maturation enzymes. Low-molecular-weight microcins from the post-translationally modified group target essential molecular machines inside the cells. In this review, available structural and functional data about three such microcins--microcin J25, microcin B17 and microcin C7-C51--are discussed. While all three low-molecular-weight post-translationally modified microcins are produced by Escherichia coli, inferences based on sequence and structural similarities with peptides encoded or produced by phylogenetically diverse bacteria are made whenever possible to put these compounds into a larger perspective. PMID:17711420

Severinov, Konstantin; Semenova, Ekaterina; Kazakov, Alexey; Kazakov, Teymur; Gelfand, Mikhail S

2007-09-01

61

Molecular weight dependence of domain structure in silica-siloxane molecular composites  

SciTech Connect

A detailed investigation of the molecular weight dependence of silica growth in in situ filled polydimethylsiloxane/tetraethylorthosilicate (PDMS/TEOS) materials was conducted using small angle neutron scattering (SANS). Composite materials were produced by using TEOS to simultaneously produce the glassy filler phase and to crosslink linear, hydroxyl terminated PDMS of variable molecular weight, M. Correlated domains of glassy filler were produced. The morphology of the in situ filled material showed a definite dependence on the molecular weight of the precursor polymer. The scale, R, of the glassy domains follows de Gennes` description of phase separation in a crosslinked system (R {alpha} M{sup 1/2}).

Ulibarri, T.A.; Beaucage, G.; Schaefer, D.W.; Olivier, B.J.; Assink, R.A.

1992-07-01

62

Molecular weight dependence of domain structure in silica-siloxane molecular composites  

SciTech Connect

A detailed investigation of the molecular weight dependence of silica growth in in situ filled polydimethylsiloxane/tetraethylorthosilicate (PDMS/TEOS) materials was conducted using small angle neutron scattering (SANS). Composite materials were produced by using TEOS to simultaneously produce the glassy filler phase and to crosslink linear, hydroxyl terminated PDMS of variable molecular weight, M. Correlated domains of glassy filler were produced. The morphology of the in situ filled material showed a definite dependence on the molecular weight of the precursor polymer. The scale, R, of the glassy domains follows de Gennes' description of phase separation in a crosslinked system (R {alpha} M{sup 1/2}).

Ulibarri, T.A.; Beaucage, G.; Schaefer, D.W.; Olivier, B.J.; Assink, R.A.

1992-01-01

63

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

64

Molecular weight dependence of domain structure in silica-siloxane molecular composites.  

National Technical Information Service (NTIS)

A detailed investigation of the molecular weight dependence of silica growth in in situ filled polydimethylsiloxane/tetraethylorthosilicate (PDMS/TEOS) materials was conducted using small angle neutron scattering (SANS). Composite materials were produced ...

T. A. Ulibarri G. Beaucage D. W. Schaefer B. J. Olivier R. A. Assink

1992-01-01

65

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

Microsoft Academic Search

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

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

2010-01-01

66

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.

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

2009-01-01

67

Mining the low molecular weight proteome of blood.  

PubMed

Serum and plasma are composed of highly complex protein/peptide mixtures resulting from the systemic monitoring of every biological process in a living organism. Some of these sentinel changes are extremely short-lived while others produce more stable by-products. In addition, since biological events occur simultaneously and with overlapping physiological demands, separating the desired ones from "background" changes is an exceptional challenge. In this review, we outline a definition of the "low molecular weight proteome" as a valuable subcomponent of the blood proteome. We make a case that this derivative proteome is as information rich and equally complex as the parent proteome. We discuss some of the technical challenges in the analysis of the low molecular weight proteome with an emphasis on MS-based analytical approaches. With specific example of several reported methodologies we attempt to frame the current state-of-the-art in study design as a guide to future efforts. PMID:21136732

Drake, Richard R; Cazares, Lisa; Semmes, O John

2007-08-01

68

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.

Merli, Geno J.; Groce, James B.

2010-01-01

69

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

70

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

71

Ultrafiltered Perfluoropolyether Lubricant under Molecular Weight Distribution Control  

Microsoft Academic Search

There are many problems to be overcome when storage devices are used at high-speed rotation and very small spacing between the head and disk. One of them is lubricant spin-off. Lubricant spin-off and lubricity have a close relation to the molecular weight distribution. The commercial Perfluoropolyether (PFPE), which is widely used as a lubricant for magnetic disks, has a wide

Takayuki Nakakawaji; Mina Ishida; Yutaka Ito; Hiroyuki Matsumoto; Hiroshi Tani; Heigo Ishihara

2000-01-01

72

High molecular weight functionalized poly(ethylene oxide)  

Microsoft Academic Search

Novel high molecular weight copolymers of ethylene oxide (EO) and glycidol or ethoxy ethyl glycidyl ether (EEGE) were obtained via suspension anionic coordination polymerization using calcium amide-alkoxide initiating system. 1H and 13C NMR spectroscopy were used for the structural characterization of the copolymers as well as for the determination of the molar content (up to 2mol%) of the functional monomers

Ph Dimitrov; E Hasan; St Rangelov; B Trzebicka; A Dworak; Ch. B Tsvetanov

2002-01-01

73

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

74

MEH-PPV:  Improved Synthetic Procedure and Molecular Weight Control  

Microsoft Academic Search

Mechanistic studies on the polymerization of R,R'-dibromo-2-methoxy-5-(2-ethylhexyloxy)- xylene have been performed. Polymerizations were initially carried out by adding potassium tert-butoxide to monomer in the presence of a chain transfer agent, anthracene. Anthracene showed little effect on the molecular weight of the resulting polymer, suggesting that the major polymerization route was not radically initiated. Polymerizations were also carried out by adding

C. J. Neef; J. P. Ferraris

2000-01-01

75

QSAR comparative study of Wiener descriptors for weighted molecular graphs.  

PubMed

Quantitative structure-property relationship (QSPR) and quantitative structure-activity relationship (QSAR) studies use statistical models to compute physical, chemical, or biological properties of a chemical substance from its molecular structure, encoded in a numerical form with the aid of various descriptors. Structural indices derived from molecular graph matrices represent an important group of descriptors used in QSPR and QSAR models; recently, their utilization was extended to molecular similarity and diversity, in database mining and virtual screening of combinatorial libraries. Initially defined from the distance matrix, the Wiener index W was the source of novel graph descriptors derived from recently proposed molecular matrices and of the Wiener graph operator. In this work we present a comparative study of several Wiener-type descriptors computed for vertex- and edge-weighted molecular graphs, corresponding to organic compounds with heteroatoms and multiple bonds. The acute toxicities toward Tetrahymena pyriformis of 47 nitrobenzenes are modeled with multilinear regression equations, using as structural descriptors the hydrophobicity (corrected for ionization) and various Wiener-type indices, with better results than a comparative molecular field analysis model. PMID:11128100

Ivanciuc, O

2000-01-01

76

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

NASA Technical Reports Server (NTRS)

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

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

1999-01-01

77

Accurate flux estimation during molecular beam epitaxy growth of vertical-cavity surface-emitting lasers  

Microsoft Academic Search

We report an in-situ method for accurate flux monitoring in gas-source molecular-beam epitaxy (GSMBE) growth of vertical-cavity surface-emitting lasers (VCSELs). The method uses a single reflectivity spectrum measurement on the incomplete structure to estimate the values of the effusion cell fluxes (and therefore the thickness and the composition of the different layers) used for the growth of the first part

L. Couturier; P. Grosse; A. Grouillet; A. Chenevas-Paule

1996-01-01

78

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

79

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

Code of Federal Regulations, 2010 CFR

...2009-04-01 2009-04-01 false Polyethylene glycol (mean molecular weight 200-9...Multipurpose Additives § 172.820 Polyethylene glycol (mean molecular weight 200-9,500). Polyethylene glycol identified in this...

2009-04-01

80

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

Code of Federal Regulations, 2010 CFR

...2010-01-01 2009-04-01 true Polyethylene glycol (mean molecular weight 200-9...Multipurpose Additives § 172.820 Polyethylene glycol (mean molecular weight 200-9,500). Polyethylene glycol identified in this...

2010-01-01

81

Synthesis of low molecular weight perfluoro oxymethylene vinyl ethers  

Microsoft Academic Search

Perfluoro oxymethylene vinyl ethers have been formed by a multi-step synthesis. The key intermediates are low molecular weight perfluoropolyether (PFPE) fluoroformates CF3O(CF2O)nCOF (I) n=1–6 obtained from the photo-oxidation of perfluoro propene (HFP) in perfluorohexane. Under certain conditions the light-mediated fluorination of PFPE fluoroformates (I) gives PFPE hypofluorites CF3O(CF2O)nCF2OF (II), which can be added to sym dichlorodifluoroethene to form the dichloro

G. Marchionni; U. De Patto; G. Spataro; Vito Tortelli

2003-01-01

82

High-molecular-weight rRNAs of cotton seeds  

Microsoft Academic Search

The electrophoretic mobilities of the 25S and 18S rRNAs of cotton seeds in polyacrylamide gel have been studied. A pyrimidyl-RNase\\u000a hydrolysate of the high-molecular-weight rRNAs was separated into isopleths containing up to decanucleotides. The mono-, di-,\\u000a and trinucleotide isopleths were separated, respectively, into CP and Up; ApCp, GpCp, ApUp, and GpUp; ApApCp, GpApCp, ApGpCp,\\u000a ApApUp, GpGpCp, ApGpUp + GpApUp, and

Kh. R. Nuriddinov; M. R. Nuriddinova; P. N. Nuriddinov

1982-01-01

83

Properties and Application of Low?Molecular?Weight High?Trans?1,4?Polyisoprene  

Microsoft Academic Search

A low?molecular?weight trans?1,4?polyisoprene (LMTPI) was synthesized with hydrogen as a molecular weight regulator. The effect of hydrogen pressure on the molecular weight of TPI was investigated. Increasing the H2 pressure effectively reduced the molecular weight of TPI. When LMTPI was used as plasticizer in styrene?butadiene rubber (SBR), the scorch time and optimum?curing time of the SBR compounds increased compared with

Aihua Du; Yongxian Zhao; Baochen Huang; Wei Yao

2008-01-01

84

Ignition and extinction of low molecular weight esters in nonpremixed flows  

Microsoft Academic Search

An experimental and kinetic modeling study is carried out to characterize combustion of low molecular weight esters in nonpremixed, nonuniform flows. An improved understanding of the combustion characteristics of low molecular weight esters will provide insights on combustion of high molecular weight esters and biodiesel. The fuels tested are methyl butanoate, methyl crotonate, ethyl propionate, biodiesel, and diesel. Two types

Ulrich Niemann; Reinhard Seiser; Kalyanasundaram Seshadri

2010-01-01

85

Impact fatigue response of ultra-high molecular weight linear polyethylene  

Microsoft Academic Search

The impact fatigue response of ultra-high molecular weight linear polyethylene (UHMW LPE), in a special test, has been examined and the results are presented in this paper. In an attempt to understand the influence of high molecular weight on impact strength, identical measurements were made on a normal molecular weight linear polyethylene (NMW LPE). UHMW LPE is found to have

S. K. Bhateja; J. K. Rieke; E. H. Andrews

1979-01-01

86

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

Code of Federal Regulations, 2010 CFR

...2009-04-01 true Polyethylene glycol (mean molecular weight 200-9,500). 178.3750...178.3750 Polyethylene glycol (mean molecular weight 200-9,500). Polyethylene...ethylene oxide and water with a mean molecular weight of 200 to 9,500....

2010-01-01

87

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

Code of Federal Regulations, 2010 CFR

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

2009-04-01

88

Calculating the molecular weight distribution from linear viscoelastic response of polymer melts  

Microsoft Academic Search

A method was developed for calculating the molecular weight distribution of a polymer melt from its rheology, specifically dynamic or relaxation moduli data. The molecular weight range covered by the solution is specified by the source data or the entanglement molecular weight, and the blending rule consistent with double reptation was used. The solutions for both the discrete relaxation spectrum

Scott H. Wasserman

1995-01-01

89

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

90

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

Code of Federal Regulations, 2013 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...

2013-04-01

91

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

92

Electrophoretic High Molecular Weight DNA Purification Enables Optical Mapping  

PubMed Central

Optical mapping generates an ordered restriction map from single, long DNA molecules. By overlapping restriction maps from multiple molecules, a physical map of entire chromosomes and genomes is constructed, greatly facilitating genome assembly in next generation sequencing projects, comparative genomics and strain typing. However, optical mapping relies on a method of preparing high quality DNA >250 kb in length, which can be challenging from some organisms and sample types. Here we demonstrate the ability of Boreal Genomics' Aurora instrument to provide pure, high molecular weight (HMW) DNA 250-1,100 kb in length, ideally suited for optical mapping. The Aurora performs electrophoretic DNA purification within an agarose gel in reusable cartridges, protecting long DNA molecules from shearing forces associated with liquid handling steps common to other purification methods. DNA can be purified directly from intact cells embedded and lysed within an agarose gel, preserving the highest molecular weight DNA possible while achieving exceptional levels of purity. The Aurora delivers DNA in a buffer solution, where DNA can be condensed and protected from shearing during recovery with a pipette. DNA is then returned to its regular coiled state by simple dilution prior to optical mapping. Here we present images showing HMW DNA purification taking place in the Aurora and subsequent images of single DNA molecules on OpGen's Argus® Optical Mapping System. Future work will focus on further optimizing Aurora HMW DNA purification to bias DNA recovery in favor of only the longest molecules in a sample, maximizing the benefits of optical mapping.

Maydan, Jason; Thomas, Matthew; Tabanfar, Leyla; Mai, Laura; Poon, Hau-Ling; Pe, Joel; Hahn, Kristen; Goji, Noriko; Amoako, Kingsley; Marziali, Andre; Hanson, Dan

2013-01-01

93

High molecular weight antigens present on human T cells.  

PubMed Central

A series of eight high molecular weight (140,000-220,000) glycoproteins on human peripheral T cells were recognized by radioimmunoprecipitation with a rabbit antiserum. The pattern of antigens present on each of eight human T cell lines studied was unique, and no line displayed the range of antigens present on peripheral T cells. The pattern of bands on peripheral T cells changed after allogeneic or lectin stimulation. Adsorption/elution experiments with antiserum showed that some of these proteins were antigenically related, and at least three different groups of proteins were present. Two of these groups could be partially distinguished by their ability to bind to ricin or lentil lectin and by their reactivity with two additional rabbit antisera. On some cell lines, it was found that proteins bound by lentil lectin but not ricin were precursors of higher molecular weight material recognized by ricin. Taken together, the data suggest that these proteins may be the products of a multigenic or multiallelic system, probably equivalent to the murine Ly 5 antigens. Images

Judd, W; Poodry, C A; Broder, S; Friedman, S M; Chess, L; Strominger, J L

1980-01-01

94

LARC-TPI 1500 series controlled molecular weight polyimide  

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

95

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

PubMed

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

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

2009-12-01

96

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

97

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

98

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

99

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

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

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

102

Soluble, High Molecular Weight Polysilsesquioxanes with Carboxylate Functionalities  

SciTech Connect

Trialkoxysilyl-containing monomers of the type (RO){sub 3}Si(CH{sub 2}){sub 3}C(O)OtBu (R = Me, Et) were prepared by hydrosilation of the corresponding vinylic tert-butyl esters CH{sub 3}CHCH{sub 2}C(O)OtBu. Acid- or base-catalyzed polymerization of the monomers leads to very high molecular weight polymers with relatively narrow polydispersities. The polymerization results in complete condensation of the alkoxy groups while the tert-butyl ester functionality remains fully intact. Partial or full deprotection of the tert-butyl group can easily be achieved to yield the corresponding carboxylic acid polymers. The ester and carboxylic acid functionalities of these new materials allow for their potential use in a variety of applications such as scavenging of heavy metals.

RAHIMIAN,KAMYAR; LOY,DOUGLAS A.; WHEELER,DAVID R.

2000-07-14

103

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

104

Receptor mediated cellular uptake of low molecular weight dendritic polyglycerols.  

PubMed

The development of effective polymer-based nanocarriers which are able to target diseased tissues still remains a great challenge in current research. Dendritic polyglycerols have emerged as novel polymeric scaffolds that have demonstrated a great potential for diverse biomedical applications. These architectures have already proven their usefulness in therapeutic approaches related to multivalency, given by the synergy between the nanosized dimensions combined with the high density of functional groups. However, a continuous effort is necessary to modify and tailor polyglycerol architectures to fit the future demands of biomedical applications. The present work deals with the development of a general synthetic strategy that allows the linkage of low molecular weight dendritic polyglycerols to fluorescent dyes and cell targeting ligands. The receptor mediated cellular uptake of the polyglycerol conjugates highlight their potential to acts as new targeted nanocarriers that should be able to decrease non-specific cellular uptake. PMID:24724501

Calderón, Marcelo; Reichert, Stephanie; Welker, Pia; Licha, Kai; Kratz, Felix; Haag, Rainer

2014-01-01

105

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

106

Molecular Weight and Charge Density Asymmetry in Polyelectrolyte Complexation  

NASA Astrophysics Data System (ADS)

We investigate the phase diagram of oppositely charged polymers in a good solvent using a field-theoretic model. Mean-field solutions fail to predict the experimentally observed macroscopic phase separation into a solvent-rich phase and a dense liquid aggregate of polymers - a ``complex coacervate.'' We therefore study the model within a one-loop approximation, which accounts for Gaussian fluctuations in electrostatic and chemical potentials. Our particular focus is the effect of molecular weight, ionic strength, and charge asymmetry on the phase envelope. A set of dimensionless parameters is identified that dictate the size and shape of the two-phase region. Our results should be helpful in guiding experimental studies of coacervation.

Audus, Debra; Fredrickson, Glenn; Duechs, Dominik

2009-03-01

107

Biological effects of high molecular weight lignin derivatives.  

PubMed

A number of high molecular weight (HMW) lignin derivatives possessing varied chemical properties were screened for their biological effects in order to obtain more information on the possible structural features of HMW lignin-related effects. The studied compounds were both commercial and in-house extracted lignin derivatives. Bioassays used include reverse electron transport (RET), Vibrio fischeri, Daphnia magna, and juvenile rainbow trout (Oncorhynchus mykiss) hepatocytes. The studied lignin derivatives inhibited the in vitro systems and luminescence of V. fischeri bacteria to some extent-daphnids were not affected. It seems that, at least in the RET assay, certain pH-dependent functional groups in lignin may be of importance regarding the biological effects. PMID:20494440

Pessala, Piia; Schultz, Eija; Kukkola, Jukka; Nakari, Tarja; Knuutinen, Juha; Herve, Sirpa; Paasivirta, Jaakko

2010-10-01

108

Phosphorylation of a high molecular weight DNA polymerase. cap alpha  

SciTech Connect

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

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

1987-02-01

109

Mechanistic information from analysis of molecular weight distributions of starch.  

PubMed

A methodology is developed for interpreting the molecular weight distributions of debranched amylopectin, based on techniques developed for quantitatively and qualitatively finding mechanistic information from the molecular weight distributions of synthetic polymers. If the only events occurring are random chain growth and stoppage (i.e., the rates are independent of degree of polymerization over the range in question), then the number of chains of degree of polymerization N, P(N), is linear in ln P(N) with a negative slope, where the slope gives the ratio of the stoppage and growth rates. This starting point suggests that mechanistic inferences can be made from a plot of lnP against N. Application to capillary electrophoresis data for the P(N) of debranched starch from across the major taxa, from bacteria (Escherichia coli), green algae (Chlamydomonas reinhardtii), mammals (Bos), and flowering plants (Oryza sativa, rice; Zea mays, maize; Triticum aestivum, wheat; Hordeum vulgare, barley; and Solanum tuberosum, potato), gives insights into the biosynthetic pathways, showing the differences and similarities of the alpha-1,4-glucans produced by the various species. Four characteristic regions for storage starch from the higher plants are revealed: (1) an initial increasing region corresponding to the formation of new branches, (2) a linear ln P region with negative slope, indicating random growth and stoppage, (3) a region corresponding to the formation of the crystalline lamellae and subsequent elongation of chains, and (4) a second linear ln P with negative slope region. Each region can be assigned to specific enzymatic processes in starch synthesis, including determining the ranges of degrees of polymerization which are subject to random and nonrandom processes. PMID:16004469

Castro, Jeffrey V; Dumas, Céline; Chiou, Herbert; Fitzgerald, Melissa A; Gilbert, Robert G

2005-01-01

110

High Molecular Weight Forms of Mammalian Respiratory Chain Complex II  

PubMed Central

Mitochondrial respiratory chain is organised into supramolecular structures that can be preserved in mild detergent solubilisates and resolved by native electrophoretic systems. Supercomplexes of respiratory complexes I, III and IV as well as multimeric forms of ATP synthase are well established. However, the involvement of complex II, linking respiratory chain with tricarboxylic acid cycle, in mitochondrial supercomplexes is questionable. Here we show that digitonin-solubilised complex II quantitatively forms high molecular weight structures (CIIhmw) that can be resolved by clear native electrophoresis. CIIhmw structures are enzymatically active and differ in electrophoretic mobility between tissues (500 – over 1000 kDa) and cultured cells (400–670 kDa). While their formation is unaffected by isolated defects in other respiratory chain complexes, they are destabilised in mtDNA-depleted, rho0 cells. Molecular interactions responsible for the assembly of CIIhmw are rather weak with the complexes being more stable in tissues than in cultured cells. While electrophoretic studies and immunoprecipitation experiments of CIIhmw do not indicate specific interactions with the respiratory chain complexes I, III or IV or enzymes of the tricarboxylic acid cycle, they point out to a specific interaction between CII and ATP synthase.

Nuskova, Hana; Holzerova, Eliska; Vrbacky, Marek; Pecina, Petr; Hejzlarova, Katerina; Kluckova, Katarina; Rohlena, Jakub; Neuzil, Jiri; Houstek, Josef

2013-01-01

111

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

112

The molecular weight of J chains derived from human immunoglobulin M  

PubMed Central

J chain was isolated from sulphonated human immunoglobulin M molecules by electrophoresis on polyacrylamide gels. When determined by electrophoresis in sodium dodecyl sulphate–polyacrylamide gels, the molecular weight of the protein was about 27000. After suspension in 5m-guanidine hydrochloride solution for 21 days, two groups of three bands appeared on the gels. Most of the protein dissociated to components of molecular weight 15000. The molecular weight of purified J chain was also determined by ultracentrifugation. In borate–saline solution the average weight-average molecular weight was about 29000. The molecular weight slowly decreased upon prolonged exposure to guanidine hydrochloride, and after 14 days the minimum molecular weight was about 15000. Some association between chains still existed. These data suggest that J chain derived from the paraprotein exists in borate–saline solution as dimers held by strong non-covalent forces. ImagesFig. 1.

Ricardo, Manuel J.; Brewer, John M.; Inman, Franklin P.

1974-01-01

113

Molecular weight averages as criteria for quality assessment of heated oils and fats  

Microsoft Academic Search

A simple method for quality assessment of heated oils and fats is described. The proposed method involves precise determination\\u000a of molecular weight averages (MWA)viz., the weight average molecular weight (\\u000a $$\\\\left( {\\\\bar {\\\\rm M}w} \\\\right)$$\\u000a ), the number average molecular weight (\\u000a $$\\\\left( {\\\\bar {\\\\rm M}n} \\\\right)$$\\u000a ) and the Z-average molecular weight (\\u000a $$\\\\left( {\\\\bar {\\\\rm M}z} \\\\right)$$\\u000a )

Sajid Husain; G. S. R. Sastry; N. Prasada Raju

1991-01-01

114

A hierarchical approach to accurate predictions of macroscopic thermodynamic behavior from quantum mechanics and molecular simulations  

NASA Astrophysics Data System (ADS)

The combination of molecular simulations and potentials obtained from quantum chemistry is shown to be able to provide reasonably accurate thermodynamic property predictions. Gibbs ensemble Monte Carlo simulations are used to understand the effects of small perturbations to various regions of the model Lennard-Jones 12-6 potential. However, when the phase behavior and second virial coefficient are scaled by the critical properties calculated for each potential, the results obey a corresponding states relation suggesting a non-uniqueness problem for interaction potentials fit to experimental phase behavior. Several variations of a procedure collectively referred to as quantum mechanical Hybrid Methods for Interaction Energies (HM-IE) are developed and used to accurately estimate interaction energies from CCSD(T) calculations with a large basis set in a computationally efficient manner for the neon-neon, acetylene-acetylene, and nitrogen-benzene systems. Using these results and methods, an ab initio, pairwise-additive, site-site potential for acetylene is determined and then improved using results from molecular simulations using this initial potential. The initial simulation results also indicate that a limited range of energies important for accurate phase behavior predictions. Second virial coefficients calculated from the improved potential indicate that one set of experimental data in the literature is likely erroneous. This prescription is then applied to methanethiol. Difficulties in modeling the effects of the lone pair electrons suggest that charges on the lone pair sites negatively impact the ability of the intermolecular potential to describe certain orientations, but that the lone pair sites may be necessary to reasonably duplicate the interaction energies for several orientations. Two possible methods for incorporating the effects of three-body interactions into simulations within the pairwise-additivity formulation are also developed. A low density approximation for the pair and three-body distribution functions is simpler to implement, but the results based on the numerical solution of the inhomogeneous Ornstein-Zernike equation using the Percus-Yevick closure are more accurate. Given the low temperatures for phase equilibria of the model system, neon, several approximations to estimate the quantum effects on the atomic nuclei are presented with reasonable success.

Garrison, Stephen L.

115

Hyaluronan Molecular Weight Is Controlled by UDP-N-acetylglucosamine Concentration in Streptococcus zooepidemicus*  

PubMed Central

The molecular weight of hyaluronan is important for its rheological and biological function. The molecular mechanisms underlying chain termination and hence molecular weight control remain poorly understood, not only for hyaluronan synthases but also for other ?-polysaccharide synthases, e.g. cellulose, chitin, and 1,3-betaglucan synthases. In this work, we manipulated metabolite concentrations in the hyaluronan pathway by overexpressing the five genes of the hyaluronan synthesis operon in Streptococcus equi subsp. zooepidemicus. Overexpression of genes involved in UDP-glucuronic acid biosynthesis decreased molecular weight, whereas overexpression of genes involved in UDP-N-acetylglucosamine biosynthesis increased molecular weight. The highest molecular mass observed was at 3.4 ± 0.1 MDa twice that observed in the wild-type strain, 1.8 ± 0.1 MDa. The data indicate that (a) high molecular weight is achieved when an appropriate balance of UDP-N-acetylglucosamine and UDP-glucuronic acid is achieved, (b) UDP-N-acetylglucosamine exerts the dominant effect on molecular weight, and (c) the wild-type strain has suboptimal levels of UDP-N-acetylglucosamine. Consistent herewith molecular weight correlated strongly (? = 0.84, p = 3 × 10?5) with the concentration of UDP-N-acetylglucosamine. Data presented in this paper represent the first model for hyaluronan molecular weight control based on the concentration of activated sugar precursors. These results can be used to engineer strains producing high molecular weight hyaluronan and may provide insight into similar polymerization mechanisms in other polysaccharides.

Chen, Wendy Yiting; Marcellin, Esteban; Hung, Jacky; Nielsen, Lars Keld

2009-01-01

116

Optimization of parameters for coverage of low molecular weight proteins  

PubMed Central

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

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

2010-01-01

117

Measurement of low molecular weight silicon AMC to protect UV optics in photo-lithography environments  

NASA Astrophysics Data System (ADS)

A new analytical method for semiconductor-specific applications is presented for the accurate measurement of low molecular weight, silicon-containing, organic compounds TMS, HMDSO and D3. Low molecular weight / low boiling point silicon-containing compounds are not captured for extended periods of time by traditional chemical filters but have the same potential to degrade exposure tool optical surfaces as their high molecular weight counterparts. Likewise, we show that capturing these compounds on sample traps that are commonly used for organic AMC analysis does not work for various reasons. Using the analytical method described here, TMS, HMDSO and D3 can be measured artifact-free, with at least a 50:1 peak-to-noise ratio at the method detection limit, determined through the Hubaux-Vos method and satisfying a conservative 99% statistical confidence. Method detection limits for the compounds are 1-6 ppt in air. We present calibration curve, capacity, capture efficiency, break-through and repeatability data to demonstrate robustness of method. Seventy-one real-world samples from 26 projects taken in several fab environments show that TMS is found in concentrations 100 times higher than those of HMDSO and D3. All compounds are found in all environments in concentrations ranging from zero to 12 ppm, but most concentrations were below 50 ppb. All compounds are noticeably higher in litho-bays than in sub-fabs and we found all three compounds inside of two exposure tools, suggesting cleanroom and/or tool-internal contamination sources.

Lobert, Jürgen M.; Miller, Charles M.; Grayfer, Anatoly; Tivin, Anne M.

2009-03-01

118

Interaction between perdeuterated dimyristoylphosphatidylcholine and low molecular weight pulmonary surfactant protein SPC  

Microsoft Academic Search

A low molecular weight hydrophobic protein was isolated from porcine lung lavage fluid using silicic acid and Sephadex LH-20 chromatography. The protein migrated with an apparent molecular weight of 5000-6000 on SDS-PAGE under reducing and nonreducing conditions. Gels run under reducing conditions also showed a minor band migrating with a molecular weight of 12,000. Amino acid compositional analysis and sequencing

G. A. Simatos; Kenneth B. Forward; M. R. Morrow; K. M. W. Keough

1990-01-01

119

Thermal characterization of Ag and Ag + N ion implanted ultra-high molecular weight polyethylene (UHMWPE)  

Microsoft Academic Search

Most of total hip joints are composed of ultra-high molecular weight polyethylene (UHMWPE ). However, as ultra-high molecular weight polyethylene is too stable in a body, wear debris may accumulate and cause biological response such as bone absorption and loosening of prosthesis. In this study, ultra-high molecular weight polyethylene samples were Ag and Ag+N hybrid ion implanted by using MEVVA

E. Sokullu Urkac; A. Oztarhan; F. Tihminlioglu; N. Kaya; D. Ila; C. Muntele; S. Budak; E. Oks; A. Nikolaev; A. Ezdesir; Z. Tek

2007-01-01

120

Preparation and anticoagulant activity of a low-molecular-weight sulfated chitosan  

Microsoft Academic Search

Synthesis of chitosan sulfates with low molecular weight (Mv 9000–35,000Da) was carried out by sulfation of low molecular weight chitosan (Mv 10,000–50,000Da). The oleum was used as sulfating agent and dimethylfornamide as medium. The chitosans were prepared by enzymatic and acidic hydrolysis of initial high molecular weight chitosan as well as by extrusion solid-state deacetylation of chitin. As was shown

G. Vikhoreva; G. Bannikova; P. Stolbushkina; A. Panov; N. Drozd; V. Makarov; V. Varlamov; L. Gal'braikh

2005-01-01

121

Exposure assessment of high molecular weight sensitisers: contribution to occupational epidemiology and disease prevention  

Microsoft Academic Search

An important group of sensitising agents are so called high molecular weight sensitisers--proteins or glycoproteins with molecular weights in the 5-70 kDa range that can provoke a specific IgE response in workers exposed to these agents. Exposure to high molecular weight sensitisers could only be evaluated indirectly in the recent past. Few measurement techniques existed that made it possible to

D. Heederik; Doekes de G; M. J. Nieuwenhuijsen

1999-01-01

122

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.

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

2011-01-01

123

Composition and molecular weight distribution of carob germ protein fractions.  

PubMed

Biochemical properties of carob germ proteins were analyzed using a combination of selective extraction, reversed-phase high-performance liquid chromatography (RP-HPLC), size exclusion chromatography (SEC) coupled with multiangle laser light scattering (SEC-MALS), and electrophoretic analysis. Using a modified Osborne extraction procedure, carob germ flour proteins were found to contain approximately 32% albumin and globulin and approximately 68% glutelin with no prolamins detected. The albumin and globulin fraction was found to contain low amounts of disulfide-bonded polymers with relatively low M(w) ranging up to 5 x 10(6) Da. The glutelin fraction, however, was found to contain large amounts of high molecular weight disulfide-bonded polymers with M(w) up to 8 x 10(7) Da. When extracted under nonreducing conditions and divided into soluble and insoluble proteins as typically done for wheat gluten, carob germ proteins were found to be almost entirely ( approximately 95%) in the soluble fraction with only ( approximately 5%) in the insoluble fraction. As in wheat, SEC-MALS analysis showed that the insoluble proteins had a greater M(w) than the soluble proteins and ranged up to 8 x 10(7) Da. The lower M(w) distribution of the polymeric proteins of carob germ flour may account for differences in functionality between wheat and carob germ flour. PMID:20557053

Smith, Brennan M; Bean, Scott R; Schober, Tilman J; Tilley, Michael; Herald, Thomas J; Aramouni, Fadi

2010-07-14

124

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

125

Antiaging activity of low molecular weight peptide from Paphia undulate  

NASA Astrophysics Data System (ADS)

Low molecular weight peptide (LMWP) was prepared from clam Paphia undulate and its antiaging effect on D-galactose-induced acute aging in rats, aged Kunming mice, ultraviolet-exposed rats, and thermally injured rats was investigated. P. undulate flesh was homogenized and digested using papain under optimal conditions, then subjected to Sephadex G-25 chromatography to isolate the LMWP. Administration of LMWP significantly reversed D-galactose-induced oxidative stress by increasing the activities of glutathione peroxidase (GPx) and catalase (CAT), and by decreasing the level of malondialdehyde (MDA). This process was accompanied by increased collagen synthesis. The LMWP prevented photoaging and promoted dermis recovery and remission of elastic fiber hyperplasia. Furthermore, treatment with the LMWP helped to regenerate elastic fibers and the collagen network, increased superoxide dismutase (SOD) in the serum and significantly decreased MDA. Thermal scald-induced inflammation and edema were also relieved by the LWMP, while wound healing in skin was promoted. These results suggest that the LMWP from P. undulate could serve as a new antiaging substance in cosmetics.

Chen, Xin; Cai, Bingna; Chen, Hua; Pan, Jianyu; Chen, Deke; Sun, Huili

2013-05-01

126

The Importance of Accurate Atomic and Molecular Line-lists for Characterizing Exoplanetary Atmospheres  

NASA Astrophysics Data System (ADS)

Recent advancements in exoplanet observations are placing unprecedented constraints on the physical and chemical properties of exoplanetary atmospheres. Statistically significant constraints have been placed on the abundances of atomic and molecular species, elemental abundance ratios, temperature profiles, energy circulation, presence of hazes/clouds, and non-equilibrium chemistry, in several exoplanetary atmospheres, including gas giants, ice giants, as well as super-Earths, over a wide temperature range. The chemical constraints have also motivated new paradigms for classifying exoplanets and new efforts to constraint their formation conditions. Central to all interpretations of exoplanet spectra, however, is the accuracy of fundamental inputs in the models, primarily, the atomic and molecular opacities, which are derived from laboratory experiments and/or ab initio numerical calculations. In this talk, we will review the state-of-the-art in atomic and molecular line-lists as applied to studies of exoplanetary atmospheres. We will discuss examples where advances in laboratory astrophysics, experimental and computational, have addressed important problems in the area of exoplanetary atmospheres, as well as outstanding questions requiring new experiments and/or theoretical calculations. For example, recent studies are suggesting that high-temperature line-lists of hydrocarbons (CH4, C2H2, HCN, etc.), and several metal hydrides, in addition to refined line-lists of several well-studied molecules, are important to accurately interpret exoplanetary spectra. We will highlight several fundamental questions in the area that require new efforts in laboratory astrophysics. Besides their importance in interpreting observations with current instruments, the refined parameters are also critical in the assessment of future facilities for exoplanet characterization, such as JWST, GMT, etc.

Madhusudhan, Nikku; Freedman, R.; Tennyson, J.

2013-06-01

127

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.

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

2014-01-01

128

High Molecular Weight (HMW) Dissolved Organic Matter (DOM) in Seawater: Chemical Structure, Sources and Cycling.  

National Technical Information Service (NTIS)

The goal of this thesis was to use high resolution analytical techniques coupled with molecular level analyses to chemically characterize high molecular weight (> 1 k Da (HMW)) dissolved organic matter (DOM) isolated from seawater in an attempt to provide...

L. I. Aluwihare

1999-01-01

129

Pecularities of the thermomechanical behaviour of ultra-high molecular weight linear polyethylene and its blends with linear polyethylene of normal molecular weight  

Microsoft Academic Search

Ultra-high molecular weight polyethylene UHMWPE (Mw=4 · 106,Is=O g\\/ 10 min), high density polyethylene of normal molecular weight NMWPE (Is= 4.8 g\\/10 min) and their blends have been investigated by means of thermomechanical loading in constant and impulse regime. It has been established that after melting, NMWPE passes to a viscous-liquid state. After melting at 138 °C UHMWPE passes to

M. Mihailov; L. Minkova

1987-01-01

130

Ultra-drawing of low molecular weight polyethylene — ultra-high molecular weight polyethylene blend films prepared by gelation\\/crystallization from semi-dilute solutions  

Microsoft Academic Search

Greatest drawability was studied for blend films with branched low molecular weight polyethylene (B-LMWPE) and ultra-high molecular weight polyethylene (UHMWPE) prepared by gelation\\/crystallization from solutions. The morphology of B-LMWPE–UHMWPE dry gel film and its deformation mechanism were mainly estimated by using differential scanning calorimeter, small-angle X-ray scattering, wide-angle X-ray diffraction and solid-state 13C NMR. The detailed analysis was carried out

Yuezhen Bin; Lin Ma; Reiko Adachi; Hiromichi Kurosu; Masaru Matsuo

2001-01-01

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

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

PubMed

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

Lépinay, Sandrine; Ianoul, Anatoli; Albert, Jacques

2014-10-01

133

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

Code of Federal Regulations, 2011 CFR

...Isopropylidenediphenol-epichlorohydrin resins minimum molecular weight 10,000. ...Isopropylidenediphenol-epichlorohydrin resins minimum molecular weight 10,000. ...Isopropylidenediphenol-epichlo-rohydrin resins having a minimum molecular...

2011-04-01

134

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

Code of Federal Regulations, 2012 CFR

...Isopropylidenediphenol-epichlorohydrin resins minimum molecular weight 10,000. ...Isopropylidenediphenol-epichlorohydrin resins minimum molecular weight 10,000. ...Isopropylidenediphenol-epichlo-rohydrin resins having a minimum molecular...

2012-04-01

135

Atlantic Ocean Measurements of Low Molecular Weight Alkyl Nitrates  

NASA Astrophysics Data System (ADS)

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

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

2003-12-01

136

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

137

Low-molecular-weight hydrophobic proteins from bovine pulmonary surfactant.  

PubMed

Pulmonary surfactant stabilizes the lung by reducing the surface tension in the terminal air spaces. Lipid extract surfactant contains approx. 1% (w/w) low-molecular-weight hydrophobic proteins SP-B (15 kDa: nonreduced) and SP-C (3.5 kDa) and with the remainder being mainly phospholipids. The hydrophobic proteins were purified from bovine lipid extract surfactant using delipidation by phospholipase C digestion followed by hydroxyapatite chromatography. The phospholipase C step removed most of phosphatidylcholine resulting in a 10-fold enrichment of hydrophobic proteins relative to phospholipid. Chromatography of this preparation on a hydroxyapatite column resulted in the elution of phospholipids followed by SP-C and then SP-B. The column chromatography was repeated to remove residual phospholipids and yield purified SP-B and SP-C. The final recovery of SP-B from the lipid extracts was about 15-20% and that of SP-C was 5-10%. The bovine surfactant proteins were reconstituted with phospholipids and examined for their ability to lower the surface tension with a pulsating bubble surfactometer. Reconstituted surfactant preparations containing SP-B and dipalmitoylphosphatidylcholine plus dioleoylphosphatidylglycerol were capable of reducing the surface tension to near zero values at minimum bubble radius while the reconstitutes with SP-C only lowered the surface tension to approx. 20 mN/m. A more rapid decrease in surface tension was observed with reconstituted samples containing both hydrophobic proteins. These results indicate that both SP-B and SP-C can promote the adsorption and spreading of surfactant lipids at the air/liquid interface. In addition, SP-B appears to facilitate the squeeze-out of unsaturated phospholipids leading to an enrichment of dipalmitoylphosphatidylcholine in the monolayer. PMID:2378907

Mathialagan, N; Possmayer, F

1990-07-16

138

Accurate conformation-dependent molecular electrostatic potentials for high-throughput in silico drug discovery.  

PubMed

The atom-centered partial charges-approximation is commonly used in current molecular modeling tools as a computationally inexpensive alternative to quantum mechanics for modeling electrostatics. Even today, the use of partial charges remains useful despite significant advances in improving the efficiency of ab initio methods. Here, we report on new parameters for the EEM and SFKEEM electronegativity equalization-based methods for rapidly determining partial charges that will accurately model the electrostatic potential of flexible molecules. The developed parameters cover most pharmaceutically relevant chemistries, and charges obtained using these parameters reproduce the B3LYP/cc-pVTZ reference electrostatic potential of a set of FDA-approved drug molecules at best to an average accuracy of 13 +/- 4 kJ mol(-1); thus, equipped with these parameters electronegativity equalization-based methods rival the current best non-quantum mechanical methods, such as AM1-BCC, in accuracy, yet incur a lower computational cost. Software implementations of EEM and SFKEEM, including the developed parameters, are included in the conformer-generation tool BALLOON, available free of charge at http://web.abo.fi/fak/mnf/bkf/research/johnson/software.php. PMID:20020481

Puranen, J Santeri; Vainio, Mikko J; Johnson, Mark S

2010-06-01

139

Non-Born-Oppenheimer potential energy curve: Hydrogen molecular ion with highly accurate free complement method  

NASA Astrophysics Data System (ADS)

Although the concept of a potential energy curve (PEC) originates from the outgrowth of the Born-Oppenheimer (BO) approximation, we propose the application of analysis methods for the physical PEC with non-Born-Oppenheimer (non-BO) wave functions. A numerical examination was performed with the highly accurate non-BO vibronic wave functions of hydrogen molecular ion, which were obtained in our previous studies with the free complement method. The reduced density function integrated over the electron coordinates plays an important role in understanding nuclear motion dynamics, since it corresponds to the wave function density of the vibrational and rotational motions. The maximum positions of this density indicate the high existence probability of nuclei and can be considered as a discrete representation of the PEC. Whereas an ordinary PEC with the BO approximation is obtained as a numeric curve after multiple electronic state calculations at fixed nuclear coordinates, we propose a new analytical expression of the PEC from a non-BO wave function.

Nakashima, Hiroyuki; Nakatsuji, Hiroshi

2013-08-01

140

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

141

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

PubMed

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. PMID:24170171

Lee, Myung Won; Meuwly, Markus

2013-12-14

142

A calorimetric study of normal high density and ultra-high molecular weight polyethylene blends  

Microsoft Academic Search

The melting and the crystallization of blends of ultra-high molecular weight polyethylene (UHMWPE) and polyethylene high density with normal molecular weight (NMWPE) are investigated by means of differential scanning calorimetry (DSC). Mixing the components at a temperature below the flow temperature of UHMWPE (215 °C) results in segregated melting and crystallization. The segregated melting and crystallization temperatures of both components

L. Minkova; M. Mihailov

1987-01-01

143

Degradation diagnosis of ultra-high-molecular weight polyethylene (UHMWPE) by terahertz-time-domain spectroscopy  

Microsoft Academic Search

We present that degradation of ultra-high-molecular-weight-polyethylene induces drastic absorption-increase ranging continuously over the THz region. This demonstrates the possibility that THz-TDS is applied to quality-control of ultra-high-molecular-weight polyethylene, which is widely utilized in medical implants.

K. Yamamoto; M. Yamagiichi; M. Tani; M. Hangyo; S. Teramura; T. Isu; N. Toraita

2004-01-01

144

Influences of polymer matrix melt viscosity and molecular weight on MWCNT agglomerate dispersion  

Microsoft Academic Search

In order to study the influence of melt viscosity and molecular weight on nanotube dispersion and electrical volume resistivity, three different polycarbonates (PCs) varying in molecular weight were melt compounded with 1 wt% multiwalled carbon nanotubes (MWCNTs, Baytubes® 150 HP) using a small-scale compounder. The experiments were performed at constant melt temperature but at varying mixing speeds, thereby applying different magnitudes

Gaurav R. Kasaliwal; Andreas Göldel; Petra Pötschke; Gert Heinrich

2011-01-01

145

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

ERIC Educational Resources Information Center

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

Mathias, Lon J.; Moore, D. Roger

1985-01-01

146

Calculating the molecular weight distribution from linear viscoelastic response of polymer melts  

SciTech Connect

A method was developed for calculating the molecular weight distribution of a polymer melt from its rheology, specifically dynamic or relaxation moduli data. The molecular weight range covered by the solution is specified by the source data or the entanglement molecular weight, and the blending rule consistent with double reptation was used. The solutions for both the discrete relaxation spectrum and final molecular weight distribution were obtained by Tikhonov regularization with the molecular weight distribution solution being particularly sensitive to the value of the regularization parameter {lambda}{sub {ital R}} used in the calculations. Here, {lambda}{sub {ital R}} was varied and patterns developed between the most appropriate values for an acceptable solution and the polydispersity of the corresponding samples. For relatively low {lambda}{sub {ital R}} values, the algorithm was precise enough to resolve individual components in nearly monodisperse, binary blend, and multimodal systems with as many as 13 components. Results for commercial materials of varying polydispersity generally agreed with the molecular weight distributions from chromatography with slightly higher {lambda}{sub {ital R}} values, particularly the location of peak molecular weights. Commercial polyolefins, which required still higher {lambda}{sub {ital R}} values, gave consistently poorer results due to restricted molecular weight ranges allowed by the source data.

Wasserman, S.H. [Department of Chemical Engineering, Princeton University, Princeton, New Jersey 08544 (United States)] [Department of Chemical Engineering, Princeton University, Princeton, New Jersey 08544 (United States)

1995-05-01

147

Effect of molecular weight and annealing temperature on the oxygen barrier properties of oriented PET film  

Microsoft Academic Search

The influence of molecular weight and annealing, or heat setting, temperature on the crystallinity and subsequent resistance to oxygen permeability was evaluated for biaxially oriented films of poly(ethylene terephthalate). Within the range investigated, molecular weight affected the amount of crystallinity developed at a given temperature, yet had little influence on oxygen permeability. Annealing temperature more directly influenced permeability than did

William Perkins

1988-01-01

148

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

149

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

Microsoft Academic Search

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. The authors 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

Stephen E. Cabaniss; Qunhui Zhou; Patricia A. Maurice; Yu-Ping Chin; George R. Aiken

2000-01-01

150

The renal handling of low molecular weight proteins  

PubMed Central

The present study was directed toward determining the role of the kidney in the metabolism of various classes of serum proteins and to define the urinary protein excretion patterns and the pathogenesis of disorders of protein metabolism in patients with proteinuria. To this end, the metabolic fates of a small protein, ?-L chain (mol wt 44,000), and a protein of intermediate size, IgG (mol wt 160,000), were studied in controls and patients with renal disease. Controls metabolized 0.28%/hr of circulating IgG and 22.3%/hr of circulating ?-L chain. All the IgG and 99% of the ?-L chain was catabolized with the remaining ?-L chain lost intact into the urine. The kidney was shown to be the major site of catabolism for small serum proteins. Three distinct disorders of protein metabolism were noted in patients with renal tubular disease and tubular proteinuria, glomerular disease (the nephrotic syndrome), and disease involving the entire nephrons (uremia), respectively. Patients with renal tubular disease had a 50-fold increase in the daily urinary excretion of 15-40,000 molecular weight proteins such as lysozyme and ?-L chains. Serum IgG and ?-L chain survivals were normal; however, the fraction of the over-all ?-L chain metabolism accounted for by proteinuria was increased 40-fold whereas endogenous catabolism was correspondingly decreased. Thus, tubular proteinuria results from a failure of proximal tubular uptake and catabolism of small proteins that are normally filtered through the glomerulus. Patients with the nephrotic syndrome had a slight increase in ?-L chain survival whereas IgG survival was decreased and the fraction of IgG lost in the urine was markedly increased. Here, abnormal glomerular permeability to proteins of intermediate size is the basic abnormality. Patients with uremia had a normal IgG survival but a four to 10-fold prolongation of ?-L chain survival due to loss of entire nephrons, the major site of metabolism of these proteins. This results in an increase (up to 10-fold) in the serum concentration of ?-L chain, lysozyme, and other small biologically active proteins, a phenomenon that may be of importance in causing some of the manifestations of the uremic syndrome. Images

Waldmann, Thomas A.; Strober, Warren; Mogielnicki, R. Peter

1972-01-01

151

Turbulent expansion flow of low molecular weight shear-thinning solutions  

Microsoft Academic Search

A Laser-Doppler anemometer and a pressure transducer were used to carry out detailed measurements of the mean and root mean square of the velocity and wall-pressure in an axisymmetric sudden expansion flow, with 0.4 and 0.5% by weight shear-thinning aqueous solutions of a low molecular weight polymer (6,000), after appropriate rheological characterisation. In spite of their very low molecular weight,

O. S. Castro; F. T. Pinho

1995-01-01

152

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

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

153

Immunochemical identity of the high and low molecular weight forms of Galapagos marine iguana hemoglobin.  

PubMed

1. Two forms of Galapagos marine iguana methemoglobin, with molecular weights of 140,000 and 70,000 daltons, were identified in iguana RBC lysates by Sephadex G-200 molecular sieve fractionation. 2. The 140,000 dalton ferric hemoglobin was isolated by DEAE-Sephadex A-50 ion-exchange chromatography and found to be pure by electrophoretic and immunological criteria. 3. Immunochemical analyses revealed the high and low molecular weight hemoglobins to be antigenically identical. PMID:122564

Higgins, P J

1978-01-01

154

Accurate staging of axillary lymph nodes from breast cancer patients using a novel molecular method  

PubMed Central

Background: The one-step nucleic acid amplification (OSNA) assay is a molecular-based lymph-node metastasis detection procedure that can assess a whole node and yields semi-quantitative results for the detection of clinically relevant nodal metastases. We aimed to determine the performance of the OSNA assay as an accurate nodal staging tool in comparison with routine histological examination. Methods: Subjects comprised 183 consecutive patients with pT1-2 breast cancer who underwent axillary dissection after positive sentinel-node (SN) biopsy with the OSNA assay. Of these, for non-SN evaluation, 119 patients underwent OSNA assay evaluation, whereas 64 had single-section histology. We compared the detection rates of non-SN metastasis and upstaging rates from the SN stage according to the American Joint Committee on Cancer staging between the OSNA and histology cohorts. Results: OSNA detected more cases of non-SN metastases than histology (OSNA 66/119, 55.5% vs histology 13/64, 20.3% P<0.001), particularly micrometastases (36/119, 30.3% vs 1/64, 1.6% P<0.001). Total upstaging rates were similar in both cohorts (20/119, 16.8% vs 9/64, 14.1%, P=0.79). Conclusion: OSNA detects a far greater proportion of non-SN micrometastases than routine histological examination. However, upstaging rates after axillary dissection were not significantly different between both cohorts. Follow-up of the OSNA cohort is required to determine its clinical relevance.

Osako, T; Iwase, T; Kimura, K; Yamashita, K; Horii, R; Akiyama, F

2011-01-01

155

[Effect of the molecular weight of chitosan on its antiviral activity in plants].  

PubMed

The effect of the molecular weight of chitosan on its ability to suppress systemic infection of bean mild mosaic virus in bean (Phasoleus vulgaris L.) plants was studied. The enzymatic hydrolysate of low-molecular-weight chitosan was successively fractionated by ultrafiltration through membranes with decreasing pore size. In total, four chitosan fractions with a weight-average molecular weight varying from 1.2 to 40.4 kDa were obtained. It was shown that the treatments of bean plants with these fractions (chitosan concentration, 10 or 100 microg/ml) inhibited virus accumulation and systemic propagation. The degree of chitosan-induced antiviral resistance increased as the molecular weight of chitosan decreased. The monomers comprising the chitosan molecule-glucosamine and N-acetylglucosamine--exhibited no antiviral activity. PMID:16761579

Kulikov, S N; Chirkov, S N; Il'ina, A V; Lopatin, S A; Varlamov, V P

2006-01-01

156

Time-dependent failure of amorphous poly-D,L-lactide: influence of molecular weight.  

PubMed

The specific time-dependent deformation response of amorphous poly(lactic acid) (PLA) is known to lead to rapid failure of these materials in load-bearing situations. We have investigated this phenomenon in uniaxial compression on P(L)DLLA samples with various molecular weights. The experiments revealed a strong dependence of the yield stress on the applied strain rate. Lower molecular weights showed identical deformation kinetics as higher molecular weights, albeit at lower stress values. This dependence on molecular weight was incorporated into an Eyring-equation by introducing mobility through a virtual temperature that is shifted by the deviation of the T(g) from T(g,?). Stress-dependent lifetime of polymer constructs was described by the use of this modified Eyring-equation, combined with a critical plastic strain. This model proves useful in predicting the molecular weight dependence of the time to failure, although it slightly overestimates life time at low stress levels for a material with very low molecular weight. The versatility of the model is demonstrated on e-beam sterilized PLDLLA, where the resulting reduction in molecular weight induces a substantial decrease in lifetime. A single T(g) measurement provides sufficient information to predict the decrease in lifetime. PMID:22842277

Söntjens, Serge H M; Engels, Tom A P; Smit, Theo H; Govaert, Leon E

2012-09-01

157

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

158

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

159

Biochemical method for molecular weight determinations of proteins and other macromolecules.  

PubMed

The invertase of Ricinus communis complexes with proteins, polyvinylpyrrolidone, polyethylene glycol, heparin and dextran sulfate. This association produces an increase of invertase activity. The minimal concentration of activator giving the maximal activation was attained at the same molarity for a given amount of enzyme for all macromolecules studied. These conditions are used for the molecular weight determination of the activating substance. The method may be used for the molecular weight determination of polymeric substances with a molecular weight in the range from 5000 to 1000,000 Da. PMID:3216089

Sampietro, A R; Prado, F E; Sayago, J E; Vattuone, M A

1988-10-01

160

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 reveals that while alternate autoclave cure schedules are required for the high molecular weight resins, low void laminates can be fabricated which have significantly improved TOS over PMR-15, with only a small sacrifice in mechanical properties.

Malarik, Diane C.; Vannucci, Raymond D.

1991-01-01

161

High-molecular-weight first-generation PMR polyimides for 343 C applications  

SciTech Connect

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

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

1991-12-01

162

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

163

Molecular Weight Determinations of Proteins by Californium Plasma Desorption Mass Spectrometry  

NASA Astrophysics Data System (ADS)

The plasma desorption mass spectrometry method is used to determine the molecular weights of larger molecules than before, to determine the molecular weights of proteins and peptides in mixtures, and to monitor protein modification reactions. Proteins up to molecular weight 25,000 can now be studied with a mass spectrometric technique. Protein-peptide mixtures that could not be resolved with conventional techniques were successfully analyzed by this technique. The precision of the method is good enough to permit one to follow the different steps in the conversion of porcine insulin to human insulin.

Sundqvist, B.; Roepstorff, Peter; Fohlman, J.; Hedin, A.; Hakansson, P.; Kamensky, I.; Lindberg, M.; Salehpour, M.; Sawe, G.

1984-11-01

164

Molecular weight determinations of proteins by californium plasma desorption mass spectrometry  

SciTech Connect

The plasma desorption mass spectrometry method is used to determine the molecular weights of larger molecules than before, to determine the molecular weights of proteins and peptides in mixtures, and to monitor protein modification reactions. Proteins up to molecular weight 25,000 can now be studied with a mass spectrometric technique. Protein-peptide mixtures that could not be resolved with conventional techniques were successfully analyzed by this technique. The precision of the method is good enough to permit one to follow the different steps in the conversion of porcine insulin to human insulin.

Sundqvist, B.; Roepstorff, P.; Fohlman, J.; Hedin, A.; Hakansson, P.; Kamensky, I.; Lindgerg, M.; Saehpour, M.; Saewe, G.

1984-11-09

165

Molecular dynamics simulations on the interactions of low molecular weight natural organic acids with C60.  

PubMed

As an important part of dissolved organic matter (DOM), low molecular weight organic acids (LOAs) may play a key role in the process for DOM stabilizing carbon nanomaterials (e.g. C60) suspensions in aquatic environment. In addition, both LOAs and C60 have been detected in the troposphere and therefore have a chance to interact with each other in the gaseous phase. However, the mechanism for LOAs-C60 interactions and their environmental implications need further investigations. In this study, molecular dynamics (MD) simulation was employed to investigate the interactions between both neutral and ionic LOAs with C60 in vacuum and water. The results showed that the adsorptions of all LOAs on C60 in energy are favorable, and the aromatic acids have stronger interactions with C60 than the aliphatic acids in vacuum and water. The interaction energies (Eint) of the LOA anions with C60 were weaker than those of their corresponding neutral LOA molecules. The models were also developed to predict and interpret Eint based on the results from MD simulations. Dispersion, induction and hydrophobic interactions were found to be the dominating factor in Eint. These findings indicate that cost-efficient MD simulation can be employed as an important tool to predict the adsorption behavior of LOAs on carbon nanomaterials. PMID:23411087

Sun, Qian; Xie, Hong-Bin; Chen, Jingwen; Li, Xuehua; Wang, Zhuang; Sheng, Lianxi

2013-07-01

166

Molecular characterization of novel low-molecular-weight glutenin genes in Aegilops longissima.  

PubMed

Extensive genetic variations of low-molecular-weight glutenin subunits (LMW-GS) and their coding genes were found in the wild diploid A- and D-genome donors of common wheat. In this study, we reported the isolation and characterization of 8 novel LMW-GS genes from Ae.longissima Schweinf. & Muschl., a species of the section Sitopsis of the genus Aegilops, which is closely related to the B genome of common wheat. Based on the N-terminal domain sequences, the 8 genes were divided into 3 groups. A consensus alignment of the extremely conserved domains with known gene groups and the subsequent cluster analysis showed that 2 out of the 3 groups of LMW-GS genes were closely related to those from the B genome, and the remaining was related to those from A and D genomes of wheat and Ae. tauschii. Using 3 sets of gene-group-specific primers, PCRs in diploid, tetraploid and hexaploid wheats and Ae. tauschii failed to obtain the expected products, indicating that the 3 groups of LMW-GS genes obtained in this study were new members of LMW-GS multi-gene families. These results suggested that the Sitopsis species of the genus Aegilops with novel gene variations could be used as valuable gene resources of LMW-GS. The 3 sets of group-specific primers could be utilized as molecular markers to investigate the introgression of novel alien LMW-GS genes from Ae. longissima into wheat. PMID:20145295

Huang, Z; Long, H; Jiang, Q-T; Wei, Y-M; Yan, Z-H; Zheng, Y-L

2010-01-01

167

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

PubMed Central

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

2014-01-01

168

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

169

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

170

Depolymerization behavior of thermoplastic poly(urethane) (TPU) and its dependence on initial molecular weight.  

PubMed

The quantitative and qualitative depolymerization behavior of thermoplastic poly(urethane) (TPU) consisting of 4,4'-methylenediphenyldiisocyanate (MDI), 1,6-hexanediol (HD) and 1-hexanol (HEX) was described using temperature-modulated differential scanning calorimetry and Fourier transform infrared (FT-IR) spectroscopy. The depolymerization behavior could be altered by lowering the starting molecular weight. This resulted not only in a higher ceiling temperature, but also in a faster decrease of the molecular weight as a function of temperature once the depolymerization has started. The increase in the ceiling temperature for low molecular weight TPUs is attributed to the lower entropy of polymerization for these compounds compared to high molecular weight TPUs. PMID:17983782

van Pelt, W W G J; Goossens, J G P

2007-11-26

171

High Molecular Weight First Generation Pmr Polyimides for 343 C Applications.  

National Technical Information Service (NTIS)

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...

D. C. Malarik R. D. Vannucci

1991-01-01

172

Evaluation of Ultra High Molecular Weight (UHMW) Polyethylene Panels for Aircraft Arresting Systems.  

National Technical Information Service (NTIS)

Ultra high molecular weight (UHMW) polyethylene panels for aircraft arresting systems have been used in the United States for approximately 15 years to provide better resistance to erosion of the pavement surface under arresting cables. When concrete or a...

E. R. Brown

2009-01-01

173

Deformation-Induced Structural Developments of Ultra-High Molecular Weight Polyethylene.  

National Technical Information Service (NTIS)

The deformation of ultrahigh molecular weight polyethylene (UHMW-PE) was investigated under various conditions in order to gain a better understanding of the deformation processes and the resulting structures and properties. X ray diffraction was used as ...

N. A. J. Vanaerle

1989-01-01

174

Ultra-High Molecular Weight Polyethylene Wear Particles Effects on Bioactivity.  

National Technical Information Service (NTIS)

Ultra-high molecular weight polyethylene (UHMWPE) wear particles have been recognized as one of the major causes of aseptic loosening in total joint replacements. Macrophage phagocytosis of wear particles induces human biological/physiological responses w...

H. W. Fang J. V. Sengers S. M. Hsu

2003-01-01

175

Friction, Wear, Transfer and Wear Surface Morphology of Ultra-High-Molecular-Weight Polyethylene.  

National Technical Information Service (NTIS)

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...

R. L. Fusaro

1983-01-01

176

Relationship Between Morphology and Mechanical Properties of Ultra High Molecular Weight Polyethylene.  

National Technical Information Service (NTIS)

Aspects of the morphology of the constituent particles of the raw ultra high molecular weight polyethylene (UHMWPE) used in this study have been examined using scanning electron microscopy. In addition differential scanning calorimetry has been used to de...

G. B. McKenna F. A. Khoury J. M. Crissman

1981-01-01

177

Dependence of Flow Properties of Polystyrene on Molecular Weight, Temperature and Shear.  

National Technical Information Service (NTIS)

The study is restricted to an interpretation of most of the publications, developed by about twenty groups, on the steady and dynamic flow behavior of undiluted, high molecular weight and linear polystyrenes at temperatures near 200C. Importantly, differe...

A. Casale J. F. Johnson R. S. Porter

1971-01-01

178

Study of the Catalytic Conversion of Synthesis Gas to Low-Molecular Weight Hydrocarbons.  

National Technical Information Service (NTIS)

The search for alternative sources of energy has provided the stage for the examination of catalytic reactions which can influence the supply of low molecular weight chemical feedstocks, such as ethylene, propylene, and butadiene. Synthesis gas produced f...

T. Y. Chan

1981-01-01

179

Oxidation reaction of high molecular weight carboxylic acids in supercritical water.  

PubMed

Stearic acid, being a model compound of high molecular weight carboxylic acids, was oxidized in a batch reactor by changing the oxygen supply with an insufficient oxygen supply at a constant reaction time at 420 degrees C. On the basis of the intermediate products identified by GC/MS, NMR, and HPLC analyses and the free-radical reaction mechanism, the oxidation pathways of high molecular weight carboxylic acids in supercritical water are discussed. The reaction of carboxylic acids in supercritical water proceeds with the consecutive oxidation of higher molecular weight carboxylic acids to lower molecular weight carboxylic acids through several major pathways. The attack of the hydroxyl radical occurs not only at the carbons in alpha-, beta-, gamma-positions to a --COOH group but also at the carbons ((omega-1)-carbon and/or omega-carbon) far in the alkyl chain from a --COOH group, which may lead to the formation of dicarboxylic acids. PMID:12901673

Jin, Fangming; Moriya, Takehiko; Enomoto, Heiji

2003-07-15

180

Molecular Weight Estimates of Vesicular Stomatitis Virus Ribonucleic Acids from Virions, Defective Particles, and Infected Cells.  

National Technical Information Service (NTIS)

Ribonucleic acid from vesicular stomatitis virus (VSV) virions (B particles), defective particles (T), and infected cells was examined by polyacrylamide gel electrophoresis, and apparent molecular weights were estimated. B particle RNA of 4,000,000 dalton...

F. L. Schaffer M. E. Soergel

1972-01-01

181

Novel low-molecular-weight-gelator-based microcapsules with controllable morphology and temperature responsiveness.  

PubMed

A new type of microcapsules with controllable morphology is presented. They are based on a low-molecular-weight gelator and can be switched from temperature-stable to temperature-responsive by simply modifying the preparation method. PMID:23239561

Patel, Ashok R; Remijn, Caroline; Heussen, Patricia C M; den Adel, Ruud; Velikov, Krassimir P

2013-02-01

182

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

183

The effect of chitosan molecular weight on the properties of alginate\\/ chitosan microparticles containing prednisolone  

Microsoft Academic Search

Purpose : The aim of the present study was to investigate the effect of chitosan molecular weight on size, size distribution, release rate, mucoadhesive properties and electrostatic bonding of alginate\\/chitosan microparticles containing prednisolone Method s: Three mucoadhesive alginate\\/chitosan microparticle formulations, f1, f2 and f3, were prepared using low, medium and high chitosan molecular weight (MW) chitosan, respectively, by directly spraying

Soheila Honary; Maryam Maleki; M Karami

184

Isolation and characterization of a high molecular weight actin-binding protein from Physarum polycephalum plasmodia  

Microsoft Academic Search

A high molecular weight actin-binding protein was isolated from the Physarum polycephalum plasmodia . The protein (HMWP) shares many properties with other high molecular weight actin-binding proteins such as spectrin, actin-binding protein from macro- phages, and filamin . It has a potent activity to cross-link F-actin into a gel-like structure . Its cross-linking activity does not depend on calcium concentrations

KAZUO SUTOH; MAKOTO IWANE; FUMIO MATSUZAKI; MASAKO KIKUCHI; ATSUSHI IKAI

1984-01-01

185

STUDY OF REACTIONS BETWEEN HIGHLY FUNCTIONALIZED LOW MOLECULAR WEIGHT POLYETHYLENE AND POLYAMINES TO PRODUCE THERMOSET MATERIALS  

Microsoft Academic Search

Low molecular weight functionalized polyolefins are mainly used as additives in adhesive formulations, compatibilizing agents and aqueous dispersions. However, the low viscosity and functionality they offer has never been explored to generate high molecular weight products that offer improved processing routes for polyolefins as well as wider applications.\\u000aThe aim of this thesis work was to investigate the preparation and

Tayyab Hameed

2012-01-01

186

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

187

Low molecular weight chitosan-based conjugate: A new platform for oral delivery of paclitaxel  

Microsoft Academic Search

A new platform for oral delivery of paclitaxel (PTX) was developed using a chemical conjugate system between PTX and low molecular weight chitosan (LMWC) having a narrow range of molecular weight (Mw). Three different Mws of chitosan (3k, 6k, and 9k) were used to prepare the conjugates. LMWC-PTX conjugates were synthesized by two step reactions: i) modification of PTX with

Eunhye Lee; Jinju Lee; Sangvong Jon

2006-01-01

188

Purification and Characterization of a Low Molecular Weight Endoxylanase from Mushroom Termitomyces clypeatus  

Microsoft Academic Search

A low molecular weight endo-xylanase (EC 3.2.1.8) was purified from an edible mushroom Termitomyces clypeatus grown in submerged medium with oat spelt xylan. Xylanase was purified to apparent homogeneity by ammonium sulfate fractionation\\u000a and gel filtration chromatography. Its molecular weight was determined by gel filtration chromatography and sodium dodecyl\\u000a sulfate-polyacrylamide gel electrophoresis to be 12 kDa. The enzyme was found to

Dhananjay Soren; Mohanlal Jana; Subhabrata Sengupta; Anil K. Ghosh

2010-01-01

189

High-molecular-weight first-generation PMR polyimides for 343 C applications  

Microsoft Academic Search

The effect of molecular weight on 343 C thermo-oxidative stability (TOS), mechanical properties, and processability, of the first generation PMR polyimides was studied. Graphite fiber reinforced PMR-15, PMR-30, PMR-50, and PMR-75 composites (corresponding to formulated molecular weights of 1500, 3000, 5000, and 7500, respectively) were fabricated using a simulated autoclave process. The data reveals that while alternate autoclave cure schedules

D. C. Malarik; R. D. Vannucci

1991-01-01

190

Orientation of plane strain-compressed ultra-high-molecular-weight polyethylene  

Microsoft Academic Search

Ultra-high-molecular-weight polyethylene (UHMWPE) samples of molecular weight 6million were compressed using a channel die and characterized by wide-angle and small-angle X-ray scattering. The results were compared to previous studies performed on high-density polyethylene (HDPE) under the same compression conditions. Most deformation mechanisms exhibited by UHMWPE were also observed in HDPE. However, the onset of crystallographic and morphological orientation occurred at

Y Boontongkong; R. E Cohen; M Spector; A Bellare

1998-01-01

191

Thermal degradation and melt viscosity of ultra-high-molecular-weight poly(ethylene terephthalate)  

Microsoft Academic Search

The thermal degradation and melt viscosity of ultra-high-molecular-weight poly(ethylene terephthalate) (UHMW-PET) with an intrinsic viscosity exceeding 2 dl g?1 were studied in the melt phase under a nitrogen atmosphere. The degradation rate increased with the molecular weight of the polymer. The high degradation rate of UHMW-PET could be interpreted by the differences in the terminal-end-group concentrations. The activation energy for

Susumu Tate; Haruhiko Narusawa

1996-01-01

192

The role of matrix molecular weight in rubber toughened nylon 6 blends: 1. Morphology  

Microsoft Academic Search

The effects of polyamide molecular weight on morphology generation in nylon 6 blends with maleated elastomers are described. The elastomers used include styrene—butadiene—styrene block copolymers with a hydrogenated mid-block, SEBS, and versions with X % grafted maleic anhydride, SEBS-g-MA-X%, and an ethylene\\/propylene copolymer, EPR, and a maleated version EPR-g-MA. The molecular weight of the nylon 6 phase governs the melt

A. J. Oshinski; H. Keskkula; D. R. Paul

1996-01-01

193

Sandwich microgravimetric immunoassay: sensitive and specific detection of low molecular weight analytes using piezoelectric quartz crystal  

Microsoft Academic Search

A multi-channel sandwich microgravimetric immunoassay (sMIA), using the quartz crystal microbalance (QCM) principle, has been developed to quantify low molecular weight substances in standard solutions. An antigen is sandwiched between two antigen-specific antibodies: the first antibody is coated on the quartz crystal surface and the second antibody is used for the detection of analyte. The concentration of low molecular weight

Satish Saha; Manoj Raje; C. Raman Suri

2002-01-01

194

Estimation of the Molecular Weight between Crosslinks of Crosslinked Semicrystalline Polyolefins  

NASA Astrophysics Data System (ADS)

The molecular weight between crosslinks (MXL) of crosslinked semicrystalline polyolefins, polyethylene in particular, has been estimated from uniaxial tensile tests in the melt state with the Sentmanat Extensional Rheometer (SER). Applying the Mooney-Rivlin equation to these stress-strain data resulted in the determination of an apparent molecular weight between crosslinks. This fast and convenient technique correlates well with the conventional approach where MXL is obtained via the plateau modulus from shear viscosity.

Mangnus, Marc A.; Karjala, Teresa P.; Gelfer, Mikhail M.; Hahn, Stephen F.

2008-07-01

195

21 CFR 177.1440 - 4,4â²-Isopropylidenediphenol-epichlorohydrin resins minimum molecular weight 10,000.  

Code of Federal Regulations, 2010 CFR

...Isopropylidenediphenol-epichlorohydrin resins minimum molecular weight 10,000. 177.1440 Section...Isopropylidenediphenol-epichlorohydrin resins minimum molecular weight 10,000. 4,4â²-Isopropylidenediphenol-epichlo-rohydrin resins having a minimum molecular weight of 10,000 may be...

2010-01-01

196

21 CFR 177.1440 - 4,4â²-Isopropylidenediphenol-epichlorohydrin resins minimum molecular weight 10,000.  

Code of Federal Regulations, 2010 CFR

...Isopropylidenediphenol-epichlorohydrin resins minimum molecular weight 10,000. 177.1440 Section...Isopropylidenediphenol-epichlorohydrin resins minimum molecular weight 10,000. 4,4â²-Isopropylidenediphenol-epichlo-rohydrin resins having a minimum molecular weight of 10,000 may be...

2009-04-01

197

[Molecular weight analysis of physiological proteinuria in newborn infants (author's transl)].  

PubMed

The physiological protien and glycoprotein excretions in the urine samples of a larger group of newborn infants were separated according to the molecular weights by SDS polyacrylamide gel electrophoresis and compared with the protein excretions of older children. We found higher proportions of albumin, of high molecular weight (MW = molecular weight greater than or equal to 150 000 dt) and of lower molecular weight (MW less than albumin 6800 dt) proteins in the first 24-h urine samples after birth. One week after birth the low molecular weight proteins predominated because there was a substantial decrease in the excretion of albumin and of high molecular weight proteins (MW greater than or equal to 150 000 dt). We compared the patterns of protein excretion of the newborn infants with those of children aged from 2 1/2 to 15 years. These urines samples showed a typical pattern of protein excretion not correlated to the age. These findings express a transitory immaturity of the glomerular filter and of the tubular protein reabsorbing system of the newborn kidney. Apparently, the tubular protein handling normalizes later than the glomerular filtration of proteins. PMID:449252

Thanner, F; Wartha, R; Gekle, D

1979-03-15

198

In vitro studies of PEG thin films with different molecular weights deposited by MAPLE  

NASA Astrophysics Data System (ADS)

In this work, polyethylene glycol (PEG) films were produced by Matrix Assisted Pulsed Laser Evaporation (MAPLE). The possibility to tailor the properties of the films by means of polymer molecular weight was explored. The films of PEG of average molecular weights 400 Da, 1450 Da, and 10000 Da (PEG400, PEG1450, and PEG10000) were investigated in vitro, in media similar with those inside the body (phosphate buffer saline PBS with pH 7.4 and blood). The mass of the polymer did not change during this treatment, but the polymer molecular weight was found to strongly influence the films properties and their behavior in vitro. Thus, immersion in PBS induced swelling of the PEG films, which was more pronounced for PEG polymers of higher molecular weight. Prior to immersion in PBS, the PEG films of higher molecular weight were more hydrophilic, the water contact angles decreasing from ˜66 grd for PEG400 to ˜41 grd for PEG1450 and to ˜15 grd for PEG10000. The same trend was observed during immersion of the PEG films in PBS. Before immersion in PBS, the refractive index of the films increased from ˜1.43 for PEG400 to ˜1.48 for PEG1450 and to ˜1.68 for PEG10000. During immersion in PBS the refractive index decreased gradually, but remained higher for the PEG molecules of higher mass. Finally, blood compatibility tests showed that the PEG films of higher molecular weight were most compatible with blood.

Paun, Irina Alexandra; Ion, Valentin; Luculescu, Catalin-Romeo; Dinescu, Maria; Canulescu, Stela; Schou, Jørgen

2012-10-01

199

Molecular weight dependent vertical composition profiles of PCDTBT:PC71BM 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 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

200

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.

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

201

Preparation of high molecular weight polyvinylalcohol by low temperature azoinitiator  

Microsoft Academic Search

Vinylacetate was bulk-polymerized at 30, 40, and 50 °C using a low temperature initiator, 2,2?-azobis(2,4-dimethylvaleronitrile) (ADMVN), and effects of polymerization temperature and initiator concentration were investigated in terms of polymerization behavior and molecular structures of polyvinylacetate (PVAc) and the corresponding polyvinylalcohol (PVA) obtained by saponifying with sodium hydroxide. Low polymerization temperature and low conversion by adopting ADMVN proved to be

Won Seok Lyoo; Byoung Chul Kim; Chul Joo Lee; Wan Shik Ha

1997-01-01

202

Preparation of ultra high molecular weight polyethylene with MgCl 2 \\/TiCl 4 catalyst: effect of internal and external donor on molecular weight and molecular weight distribution  

Microsoft Academic Search

Ultra high molecular weight polyethylene (UHMWPE) was prepared by using MgCl2-supported TiCl4 catalyst in conjunction with triethylaluminium (TEA) cocatalyst. The effects of internal and external donor on polydispersity\\u000a index (PDI) of UHMWPE were investigated. The catalyst activity with various kinds of internal donor decreased in the following\\u000a order: none > succinate > phthalate > diether, while the catalyst activity was less influenced by the structure of

He-xin Zhang; Young-jun Shin; Dong-ho Lee; Keun-Byoung Yoon

2011-01-01

203

Accurate molecular structures of chlorothiazide and hydrochlorothiazide by joint refinement against powder neutron and X-ray diffraction data.  

PubMed

The compounds chlorothiazide and hydrochlorothiazide (crystalline form II) have been studied in their fully hydrogenous forms by powder neutron diffraction on the GEM diffractometer. The results of joint Rietveld refinement of the structures against multi-bank neutron and single-bank X-ray powder data are reported and show that accurate and precise structural information can be obtained from polycrystalline molecular organic materials by this route. PMID:18204216

Leech, Charlotte K; Fabbiani, Francesca P A; Shankland, Kenneth; David, William I F; Ibberson, Richard M

2008-02-01

204

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

205

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

206

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

207

Impact of static pressure on transmembrane fluid exchange in high molecular weight cut off microdialysis.  

PubMed

With the interest of studying larger biomolecules by microdialysis (MD), this sampling technique has reached into the ultrafiltration region of fluid exchange, where fluid recovery (FR) has a strong dependence on pressure. Hence in this study, we focus on the fluid exchange across the high molecular weight cut off MD membrane under the influence of the static pressure in the sampling environment. A theoretical model is presented for MD with such membranes, where FR has a linear dependence upon the static pressure of the sample. Transmembrane (TM) osmotic pressure difference and MD perfusion rate decide how fast FR increases with increased static pressure. A test chamber for in vitro MD under static pressure was constructed and validated. It can hold four MD probes under controlled pressurized conditions. Comparison showed good agreement between experiment and theory. Moreover, test results showed that the fluid recovery of the test chamber MD can be set accurately via the chamber pressure, which is controlled by sample injection into the chamber at precise rate. This in vitro system is designed for modelling in vivo MD in cerebrospinal fluid and studies with biological samples in this system may be good models for in vivo MD. PMID:24370572

Chu, Jiangtao; Hjort, Klas; Larsson, Anders; Dahlin, Andreas P

2014-04-01

208

Microbial Synthesis and Physical Properties of Ultra-High-Molecular-Weight Poly[(R)-3-Hydroxybutyrate  

Microsoft Academic Search

Ultra-high-molecular-weight poly[(R)-3-hydroxybutyrate](P(3HB)) was biosynthesized from glucose by a recombinant Escherichia coli XL-1 Blue (pSYL105) harboring Alcaligenes eutrophus PHB biosynthesis phbCAB genes. Six kinds of P(3HB) samples with differ-ent weight-average molecular weight (Mw) from 1.1 × 10 to 11 × 10 measured by multi-angle laser light scattering were respectively produced at pH values of 7.0 to 6.5 in culture media. Solvent-cast

S. KUSAKA; T. IWATA; Y. DOI

1998-01-01

209

Molecular calipers for highly precise and accurate measurements of single-protein mechanics.  

PubMed

Single-molecule atomic force spectroscopy (AFM) has evolved into a powerful technique toward elucidating conformational changes in proteins when exposed to applied force. AFM technologies that are currently available allow for precise measurements of proteins length changes during conformational transitions. However, because of systematic errors in piezo calibration as well as errors originating from fitting experimental data using a worm-like chain model of polymer elasticity, high-precision measurements of length changes do not necessarily translate into highly accurate measurements of length changes, resulting in uncertainty in obtaining structural information about protein conformational changes. Actually achieving highly precise and accurate force spectroscopy measurements remains a challenge. Here, we report a protein caliper method that eliminates systematic errors that occur during single-protein force spectroscopy measurements, and thus achieves highly precise and accurate length change measurements in protein mechanics studies. To do this, a series of loop elongation variants of the small protein GB1, which differ by 2, 5, 10, 15, and 24 amino acid residues, were engineered. Differential measurements of amino acid residue length obtained from different AFM setups result in a precise measure of the length of a single amino acid residue, which varies within different AFM setups because of systematic error between individual AFM piezoelectric calibrations. The measured length of a single amino acid residue from a given AFM setup is then used as a caliper for the given setup to eliminate systematic error, leading to highly accurate and precise measurements of the number of amino acid residues that are involved in a conformation change of a polypeptide chain. We further developed a more precise, robust, and model-free method to determine the apparent size of single amino acid residues and conformational changes of proteins. This method improves the accuracy of single protein force spectroscopy measurements, providing an accurate means of measuring force-induced protein conformational changes. PMID:24555779

Wang, Yanyan; Hu, Xiaodong; Bu, Tianjia; Hu, Chunguang; Hu, Xiaotang; Li, Hongbin

2014-03-18

210

Effect of Molecular Weight of Surfactant in Nano Ceria Slurry on Shallow Trench Isolation Chemical Mechanical Polishing (CMP)  

NASA Astrophysics Data System (ADS)

We examined the effect of the molecular weight of surfactants in ceria slurry during chemical mechanical polishing (CMP) for shallow trench isolation (STI). We found that for a surfactant with a higher molecular weight, the oxide removal rate decreased drastically as the surfactant concentration increased, but in the case of a lower molecular weight, it only slightly decreased. In addition, slurries whose surfactants had lower molecular weights maintained a higher nitride removal rate with increasing surfactant concentration. The results showed that the molecular weight and surfactant concentration have complex effects on the oxide removal rate and the oxide-to-nitride removal selectivity.

Kang, Hyun-Goo; Katoh, Takeo; Lee, Myung-Yoon; Park, Hyung-Soon; Paik, Ungyu; Park, Jea-Gun

2004-08-01

211

High molecular weight hyaluronan for treatment of chronic shoulder pain associated with glenohumeral arthritis  

PubMed Central

Background There is insufficient evidence to determine whether intra-articular injections may be effective for treatment of glenohumeral osteoarthritis. Euflexxa® (high molecular weight hyaluronate), a bioengineered high molecular weight hyaluronan, has been shown to be a safe and effective treatment for patients with knee osteoarthritis. There is also support for the use of hyaluronate injection for the treatment of chronic shoulder pain associated with osteoarthritis or rotator cuff damage. This small-scale exploratory study was conducted to evaluate the safety and efficacy of high molecular weight hyaluronate for the treatment of chronic shoulder pain associated with osteoarthritis. Methods Subjects with glenohumeral osteoarthritis and chronic pain (n = 27) received one injection per week for 3 weeks of high molecular weight hyaluronate and were assessed for changes in pain (100 mm visual analog scale [VAS]), range of motion, and the subject’s and physician’s global assessment over 26 weeks. Subjects were also assessed for pain, stiffness, and physical functioning using the Western Ontario and McMaster Universities Arthritis Index (WOMAC). Finally, responses were evaluated using modified Outcome Measures in Rheumatoid Arthritis Clinical Trials (OMERACT)-Osteoarthritis Research Society International (OARSI) Proposition D criteria. Safety was assessed by recording adverse events. Results High molecular weight hyaluronate significantly improved pain (VAS, WOMAC), range of motion, stiffness, and physical functioning scores; 77.8% of subjects were rated as having an OMERACT-OARSI Proposition D high response. There were no serious adverse events, and none were considered to be related to treatment. Conclusion Treatment with high molecular weight hyaluronate improves pain, stiffness, and range of motion, and may have an acceptable safety and tolerability profile. A randomized, double-blind, placebo-controlled clinical trial may be warranted to investigate further the efficacy and safety of intra-articular high molecular weight hyaluronate for treatment of chronic shoulder pain in patients with glenohumeral osteoarthritis.

Weil, Arnold J

2011-01-01

212

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

213

Fast and accurate modeling of molecular atomization energies with machine learning.  

PubMed

We introduce a machine learning model to predict atomization energies of a diverse set of organic molecules, based on nuclear charges and atomic positions only. The problem of solving the molecular Schrödinger equation is mapped onto a nonlinear statistical regression problem of reduced complexity. Regression models are trained on and compared to atomization energies computed with hybrid density-functional theory. Cross validation over more than seven thousand organic molecules yields a mean absolute error of ?10??kcal/mol. Applicability is demonstrated for the prediction of molecular atomization potential energy curves. PMID:22400967

Rupp, Matthias; Tkatchenko, Alexandre; Müller, Klaus-Robert; von Lilienfeld, O Anatole

2012-02-01

214

Fast and Accurate Modeling of Molecular Atomization Energies with Machine Learning  

NASA Astrophysics Data System (ADS)

We introduce a machine learning model to predict atomization energies of a diverse set of organic molecules, based on nuclear charges and atomic positions only. The problem of solving the molecular Schrödinger equation is mapped onto a nonlinear statistical regression problem of reduced complexity. Regression models are trained on and compared to atomization energies computed with hybrid density-functional theory. Cross validation over more than seven thousand organic molecules yields a mean absolute error of ˜10kcal/mol. Applicability is demonstrated for the prediction of molecular atomization potential energy curves.

Rupp, Matthias; Tkatchenko, Alexandre; Müller, Klaus-Robert; von Lilienfeld, O. Anatole

2012-02-01

215

Molecular rearrangements in ultra high molecular weight polyethylene after irradiation and long-term storage in air  

Microsoft Academic Search

Molecular rearrangements and alterations in supermolecular structure of ultra high molecular weight polyethylene (UHMWPE) due to cross-linking and oxidation-induced chain scission following irradiation and subsequent storage in air at room temperature have been studied over a period of 29 months. The techniques that were used are: equilibrium swelling in decalin, differential scanning calorimetry (DSC), small angle X-ray scattering (SAXS), Fourier

A Bellare; E. W Merrill; M Jasty; W. H Harris

1999-01-01

216

Low molecular weight squash trypsin inhibitors from Sechium edule seeds.  

PubMed

Nine chromatographic components containing trypsin inhibitor activity were isolated from Sechium edule seeds by acetone fractionation, gel filtration, affinity chromatography and RP-HPLC in an overall yield of 46% of activity and 0.05% of protein. The components obtained with highest yield of total activity and highest specific activity were sequenced by Edman degradation and their molecular masses determined by mass spectrometry. The inhibitors contained 31, 32 and 27 residues per molecule and their sequences were: SETI-IIa, EDRKCPKILMRCKRDSDCLAKCTCQESGYCG; SETI-IIb, EEDRKCPKILMRCKRDSDCLAKCTCQESGYCG and SETI-V, CPRILMKCKLDTDCFPTCTCRPSGFCG. SETI-IIa and SETI-IIb, which differed by an amino-terminal E in the IIb form, were not separable under the conditions employed. The sequences are consistent with consensus sequences obtained from 37 other inhibitors: CPriI1meCk_DSDCla_C_C_G_CG, where capital letters are invariant amino acid residues and lower case letters are the most preserved in this position. SETI-II and SETI-V form complexes with trypsin with a 1:1 stoichiometry and have dissociation constants of 5.4x10(-11)M and 1.1x10(-9)M, respectively. PMID:16406091

Laure, Hélen J; Faça, Vítor M; Izumi, Clarice; Padovan, Júlio C; Greene, Lewis J

2006-02-01

217

The influence of molecular weight, crosslinking and counterface roughness on TNF-alpha production by macrophages in response to ultra high molecular weight polyethylene particles  

Microsoft Academic Search

The response of murine macrophages to clinically relevant polyethylene wear particles generated from different polyethylenes at various time points and volumetric doses in vitro was evaluated. Clinically relevant ultra high molecular weight polyethylene (UHMWPE) wear debris was generated in vitro in a lubricant of RPMI 1640 supplemented with 25% (v\\/v) foetal calf serum using a multi-directional pin-on-plate wear rig under

Joanne Helen Ingram; Martin Stone; John Fisher; Eileen Ingham

2004-01-01

218

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

SciTech Connect

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

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

1990-01-01

219

Antibody response to low-molecular-weight antigens of Aspergillus fumigatus in allergic bronchopulmonary aspergillosis.  

PubMed Central

Sera from patients with allergic bronchopulmonary aspergillosis (ABPA) or aspergilloma and normal sera were analyzed for specific antibodies by Western (immuno-) blotting with Aspergillus fumigatus antigens transferred electrophoretically onto polyvinylidene difluoride membranes. Western blot analysis demonstrated consistent reactivity of low-molecular-weight A. fumigatus antigens against ABPA sera but not against uncomplicated aspergilloma or normal sera. None of these low-molecular-weight components had any lectin-binding activity. Sera from patients with aspergilloma, however, frequently reacted with high-molecular-weight components of A. fumigatus. The majority of these high-molecular-weight antigenic components demonstrated concanavalin A-binding activity. The low-molecular-weight bands were discernible in Western blots with sera from all ABPA patients irrespective of disease activities, such as relapse, flare, or treatment. Antibodies detected by methods such as immunodiffusion or enzyme-linked immunosorbent assays demonstrated total antibody responses to most or all antigenic components, while Western blots demonstrated the reactivities of the individual components with the specific antibodies. Western blot analysis thus provided more information for immunodiagnosis of ABPA than other methods, especially when only crude antigens were available. Images

Kurup, V P; Greenberger, P A; Fink, J N

1989-01-01

220

Properties of the Syrian hamster phosphomannosyl receptor: an aggregate of low molecular weight proteins.  

PubMed Central

Phosphomannosyl receptor (PMR) isolated from Syrian hamster liver was purified to apparent homogeneity by affinity chromatography and one-dimensional PAGE. On one-dimensional PAGE, the receptor migrated with a Mr approximately equal to 215,000 as detected by a silver-staining reagent or by immunoblotting [utilizing antiPMR generated against purified hamster PMR (Mr 215,000) sequentially purified by affinity chromatography and NaDodSO4/PAGE]. On two-dimensional PAGE the receptor was partially dissociated into low-molecular weight components. The protein distribution on immunoblots of two-dimensional gels of hamster liver homogenates was nearly identical to that observed for purified hamster liver PMR. When liver homogenates were subjected to one-dimensional PAGE and immunoblotted under nonreducing conditions, an intensely labeled band that migrated with an apparent Mr of 43,000-49,000 was observed; under reducing conditions a single band with a Mr of 49,000 was observed. The low molecular weight compound was present in the soluble 130,000 X g supernatant but not in the particulate fraction of liver homogenates. An immunoreactive component of similar molecular weight was also present in hamster serum and plasma. These results suggest that PMR is either an aggregate comprised of small molecular weight components or, alternatively, that a number of small molecular weight components are tightly associated with PMR. Images

Maler, T; Rosenblum, B B; Jourdian, G W

1985-01-01

221

Kinetics of model high molecular weight organic compounds biodegradation in soil aquifer treatment.  

PubMed

Soil Aquifer Treatment (SAT) is a process where treated wastewater is purified during transport through unsaturated and saturated zones. Easily biodegradable compounds are rapidly removed in the unsaturated zone and the residual organic carbon is comprised of primarily high molecular weight compounds. This research focuses on flow in the saturated zone where flow conditions are predictable and high molecular weight compounds are degraded. Flow through the saturated zone was investigated with 4 reactors packed with 2 different particle sizes and operated at 4 different flow rates. The objective was to evaluate the kinetics of transformation for high molecular weight organics during SAT. Dextran was used as a model compound to eliminate the complexity associated with studying a mixture of high molecular weight organics. The hydrolysis products of dextran are easily degradable sugars. Batch experiments with media taken from the reactors were used to determine the distribution of microbial activity in the reactors. Zero-order kinetics were observed for the removal of dextran in batch experiments which is consistent with hydrolysis of high molecular weight organics where extracellular enzymes limit the substrate utilization rate. Biomass and microbial activity measurements demonstrated that the biomass was independent of position in the reactors. A Monod based substrate/biomass growth kinetic model predicted the performance of dextran removal in the reactors. The rate limiting step appears to be hydrolysis and the overall rate was not affected by surface area even though greater biomass accumulation occurred as the surface area decreased. PMID:21723581

Fox, Peter; Makam, Roshan

2011-10-01

222

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

NASA Technical Reports Server (NTRS)

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

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

2001-01-01

223

An FPGA Design to Achieve Fast and Accurate Results for Molecular Dynamics Simulations  

Microsoft Academic Search

A Molecular Dynamics (MD) system is defined by the position and momentum of particles and their interactions. The dynamics\\u000a of a system can be evaluated by an N-body problem and the simulation is continued until the energy reaches equilibrium. Thus,\\u000a solving the dynamics numerically and evaluating the interaction is computationally expensive even for a small number of particles\\u000a in the

Eunjung Cho; Anu G. Bourgeois; Feng Tan

2007-01-01

224

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

PubMed Central

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

Kind, Tobias; Fiehn, Oliver

2007-01-01

225

Thermal characterization of Ag and Ag + N ion implanted ultra-high molecular weight polyethylene (UHMWPE)  

NASA Astrophysics Data System (ADS)

Most of total hip joints are composed of ultra-high molecular weight polyethylene (UHMWPE ). However, as ultra-high molecular weight polyethylene is too stable in a body, wear debris may accumulate and cause biological response such as bone absorption and loosening of prosthesis. In this study, ultra-high molecular weight polyethylene samples were Ag and Ag + N hybrid ion implanted by using MEVVA ion implantation technique to improve its surface properties. Samples were implanted with a fluence of 10 17 ion/cm 2 and extraction voltage of 30 kV. Implanted and unimplanted samples were investigated by thermo-gravimetry analysis (TGA), differential scanning calorimetry (DSC), X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), optical microscopy (OM) and contact Angle measurement. Thermal characterization results showed that the ion bombardment induced an increase in the % crystallinity, onset and termination degradation temperatures of UHMWPE.

Sokullu Urkac, E.; Oztarhan, A.; Tihminlioglu, F.; Kaya, N.; Ila, D.; Muntele, C.; Budak, S.; Oks, E.; Nikolaev, A.; Ezdesir, A.; Tek, Z.

2007-08-01

226

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

227

Comparison of surface mobility on low and high molecular weight glasses  

NASA Astrophysics Data System (ADS)

The glass transition temperature of thin polymer films and the related issue of mobility at glass surfaces have attracted considerable interest in the last twenty years. We have recently conducted experiments on both polymeric and low molecular weight glass formers that provide information about mobility near the free surface. For several polymers, measurements of dye reorientation on freestanding films show a fast population that can be consistently assigned to the near-surface region. For indomethacin (a low molecular weight glass former), we have directly measured surface diffusion by following the decay of imprinted gratings of different periods. For both high and low molecular weight glassformers, we observed enhanced mobility near the free surface (by factors up to 10^4 and 10^7, respectively) relative to the bulk dynamics. In both cases, surface mobility has a substantially weaker temperature dependence than bulk mobility near the bulk Tg.

Ediger, Mark; Paeng, Keewook; Zhu, Lei; Yu, Lian

2012-02-01

228

High molecular weight first generation PMR polyimides for 343 C applications  

SciTech Connect

The polymers research effort at NASA Lewis Research Center, the lead NASA Center for aeropropulsion research, has primarily focused on the development of advanced polymers for aircraft engine applications. In order to improve engine performance, studies have emphasized the use of advanced, lightweight composite materials. The effect of molecular weight on 343 C. thermo-oxidative stability (TOS), mechanical properties, and processability, of the first generation PMR polymides was investigated. Graphite fiber reinforced PMR-15, PMR-30, PMR-50, and PMR-75 composites (corresponding to formulated molecular weights of 1,500, 3,000, 5,000, and 7,500, respectively) were fabricated utilizing a simulated autoclave process. The data reveals that, while alternate autoclave cure schedules are required for the high molecular weight resins, low void laminates can be fabricated which have significantly improved TOS over PMR-15, with only a small sacrifice in mechanical properties.

Malarik, D.C.; Vannucci, R.D. (NASA Lewis Research Center, Cleveland, OH (United States))

1992-07-01

229

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

NASA Astrophysics Data System (ADS)

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

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

2007-03-01

230

A microscale-molecular weight sensor: probing molecular diffusion between adjacent laminar flows by refractive index gradient detection.  

PubMed

A detection scheme that measures the refractive index gradient (RIG) between adjacent laminar flows in a microfluidic device has been used to develop a microscale-molecular weight sensor. The behavior of low Reynolds number flows has been well documented and shows that molecular transport (mixing) between adjacent laminar flows occurs by molecular diffusion between flow boundaries. A diode laser beam, incident upon and illuminating the entire width of a microchannel, measured the transverse concentration gradient at two different positions along a microchannel. The concentration gradient is impacted by the transverse diffusion from a flow with analyte into a flow initially without analyte. The RIG that forms as analyte diffuses from one adjacent flow to the other causes the laser beam, impinging orthogonal to the RIG through the microchannel, to be deflected. The angle of deflection is then monitored on a position-sensitive detector (PSD) at two different positions along the axis of flow to provide a measurement of analyte diffusion. The two positions are just after the flow initially without analyte merges with the flow initially containing all of the analyte (upstream) and then after the two streams have had more time to diffuse together (downstream). The ratio of the PSD signals obtained at the two positions along the flow, downstream signal divided by the upstream signal, is readily correlated to the analyte diffusion coefficient and, thus, the analyte molecular weight for a given class of compounds. The device was evaluated as a molecular weight sensor for poly(ethylene glycol) (PEG) solutions over a molar mass range from 106 to 22,800 g/mol. The ratio signal was found to be both independent of PEG concentration and sensitive to molecular weight changes for samples ranging from 960 to 22,800 g/mol. Independence of concentration is important for obtaining a reliable molecular weight measurement. The limit of detection for 11,840 g/mol PEG measured at the upstream detection position was determined to be 56 ppm, equivalent to 4.5 x 10(-6) RI (3sigma). This technique provides a much needed universal detection method, without requiring analyte derivatization chemistry (e.g., fluorescence), for microfluidic analyses that are becoming increasingly useful in monitoring chemical systems such as continuous-flow reactors or batch polymerization processes. Thus, the molecular weight determination capability is potentially applicable to other compound classes, such as DNA or proteins. PMID:12236369

Costin, Colin D; Synovec, Robert E

2002-09-01

231

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

232

Controlled functionalization of multiwalled carbon nanotubes with various molecular-weight poly(L-lactic acid).  

PubMed

Multiwalled carbon nanotubes (MWNT) were functionalized with poly(L-lactic acid) (PLLA) with different molecular weights using a "grafting to" technique. The oxidized MWNT (MWNT-COOH) were converted to the acyl-chloride-functionalized MWNT (MWNT-COCl) by treating them with thionyl chloride (SOCl2) and reacting them with PLLA to prepare the MWNT-g-PLLA. FTIR and Raman spectroscopy revealed that the PLLA was covalently attached to the MWNT, and the weight gain due to the functionalization was determined by thermogravimetric analyses (TGA). The Raman signals of the MWNT were greatly weakened as a result of the PLLA grafting. The morphology of the grafted PLLA was examined by using SEM and TEM. The amount of grafted PLLA depended on the molecular weight of the PLLA. The PLLA coated on the MWNT became thicker and more uniform with increasing PLLA molecular weight from 1000 to 3000. However, the amount of grafted PLLA became lower when the molecular weight of PLLA was further increased to 11,000 and 15,000, and the PLLA attached to the MWNT showed a squid leglike morphology forming blobs and leaving much of the MWNT surface bare. PMID:16853895

Chen, Guang-Xin; Kim, Hun-Sik; Park, Byung Hyun; Yoon, Jin-San

2005-12-01

233

Molecularly confirmed primary malignant rhabdoid tumor of the urinary bladder: implications of accurate diagnosis  

PubMed Central

Malignant rhabdoid tumors (MRTs) are well recognized in the kidney and extrarenal sites such as soft tissues, retroperitoneum, and bladder but are classified as atypical teratoid/rhabdoid tumors in the central nervous system. The unifying features of both extracranial MRT and atypical teratoid/rhabdoid tumors are the exon deletions/mutations of the SMARCB1 (SWI/SNF related, matrix associated, actin dependent regulator of chromatin, subfamily b, member 1) gene in 22q11.23 and resulting loss of SMARCB1/INI1 (integrase interactor 1) protein expression by immunohistochemistry. We herein report a case of extrarenal rhabdoid tumor confined to the bladder in a 3-year-old child, diagnosed by histopathology and confirmed by immunohistochemical and molecular studies. This is only the fourth molecularly proven primary MRT of the bladder to be reported. The patient’s peripheral blood was negative for the deletions observed in the tumor, thereby confirming a sporadic origin for the tumor. Given the possible dismal outcome, urgency for definitive diagnosis to institute intensive multimodality therapy, histopathologic differential diagnosis with rhabdomyosarcoma and urothelial carcinoma with rhabdoid features, and lack of consensus management guidelines, oncologists, urologists, and pathologists must be aware of this entity. Evaluation for a germ line SMARCB1 alteration may greatly aid risk stratification and family planning.

Savage, Natasha; Linn, Dan; McDonough, Colleen; Donohoe, Jeffrey M.; Franco, Arie; Reuter, Victor; Biddinger, Paul W.; Eaton, Katherine W.; Biegel, Jaclyn A.; Sharma, Suash

2012-01-01

234

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

235

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

PubMed

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 10(3)-10(5) 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. PMID:23822223

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

2013-06-28

236

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

237

Low molecular weight thermostable {beta}-D-glucosidase from Acidothermus cellulolyticus  

DOEpatents

A purified low molecular weight {beta}-D-glucosidase is produced from Acidothermus cellulolyticus ATCC 43068. The enzyme is water soluble, possesses activity against pNP-{beta}-D-glucopyranoside, has a high of degree of stability toward heat, exhibits optimal temperature activity at about 65 C at a pH range of from about 2 to about 7, has an inactivation temperature of about 80 C at a pH range of from about 2 to about 7 and has a molecular weight of about 50.5--54.5 kD as determined by SDS-PAGE. 6 figs.

Himmel, M.E.; Tucker, M.P.; Adney, W.S.; Nieves, R.A.

1995-07-11

238

High cell density perfusion culture of hybridoma cells recycling high molecular weight components.  

PubMed

We have developed a high cell density and high product concentration culture system recycling high molecular weight components. The production of monoclonal antibodies in high concentration was performed by this culture system with mouse human hybridoma H2 and V6 cells in serum-free defined media.The concentration of IgG after 48 days culture of H2 cells in ITES-eRDF reached 2 mg/ml and the purity of IgG in culture fluid was 61%. In addition, high molecular weight components in serum-free media, such as transferrin or BSA, could be reduced to 5% of the original concentration. PMID:22358569

Takazawa, Y; Tokashiki, M; Hamamoto, K; Murakami, H

1988-02-01

239

Photocuring of stimulus responsive membranes for controlled-release of drugs having different molecular weights  

NASA Astrophysics Data System (ADS)

Intelligent drug delivery membranes were prepared by photocuring poly(acrylic acid) coatings onto poly(2-hydroxyethyl methacrylate) membranes each with model drugs of different molecular weights being incorporated. pH-responsive release behaviours of the model drugs which included sodium salicylate, nicotinamide, nicotinic acid, methylene blue, brilliant green and crystal violet were investigated. Only the membrane with methylene blue incorporated showed a clear pH-responsive release and other drug-incorporated membranes showed no intelligent behaviour. These phenomena were explained in terms of the difference in diffusivity of drugs through polymer matrices of the membranes attributable to the difference in the molecular weights of drugs.

Ng, Loo-Teck; Nakayama, Hiroshi; Kaetsu, Isao; Uchida, Kumao

2005-06-01

240

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

241

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

SciTech Connect

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

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

1987-12-01

242

[Severe hemorrhagic complications during treatment with low molecular weight heparin. Apropos of 2 cases].  

PubMed

Two cases of fatal bleeding in patients treated with low molecular weight heparin for deep vein thrombosis are reported. Risk factors for bleeding were: severe underlying disease (cancer in one case, morbid obesity and cardiac failure in the other), age over 80 years and worsening of renal insufficiency in both cases, recent surgical procedure in one case. Anti-Xa activity was beyond the therapeutic range at the time of bleeding in both cases. The usefulness of biologically monitoring the treatment of deep vein thrombosis with low molecular weight heparin is discussed. PMID:9183451

Grateau, G; Chauvenet, L; Oudard, S; Bachmeyer, C; Capron, L; Horellou, M H; Samama, M M

1997-01-01

243

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

244

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

PubMed

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

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

2013-08-01

245

Low-molecular-weight inhibitors of NF-?B signalling pathways  

NASA Astrophysics Data System (ADS)

The nuclear factor ?B (NF-?B) is a transcription factor involved in inducible expression of cellular genes playing a key role in cardiovascular pathologies, carcinogenesis, inflammatory and viral diseases. The review describes the stimuli and processes inducing NF-?B activation and the components of a signalling cascade that could constitute targets for NF-?B inhibition. The molecular action and properties of various low-molecular weight inhibitors aiming to prevent NF-?B activity are summarised.

Dolinnaya, N. G.; Kubareva, Elena A.; Kazanova, E. V.; Zigangirova, N. A.; Naroditsky, B. S.; Gintsburg, A. L.; Oretskaya, Tat'yana S.

2008-11-01

246

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

247

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.

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

2014-01-01

248

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

PubMed

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

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

2011-01-20

249

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

NASA Astrophysics Data System (ADS)

In order to accurately estimate the thermodynamic properties of hydrogen clathrate hydrates, we developed a method based on the solid solution theory of van der Waals and Platteeuw. This model allows one to take into account the influence of guest molecules on the host lattice and guest-guest interactions-especially when more than one guest molecule occupies a cage. The free energies, equations of state, and chemical potentials of hydrogen and mixed propane-hydrogen clathrate hydrates of cubic structure II with different cage fillings have been estimated using this approach. Moreover, the proposed theory has been used for construction p-T phase diagrams of hydrogen hydrate and mixed hydrogen-propane hydrates in a wide range of pressures and temperatures. For the systems with well defined interactions the calculated curves of ``guest gas-hydrate-ice Ih'' equilibrium agree with the available experimental data. We also believe that the present model allows one not only to calculate the hydrogen storage ability of known hydrogen hydrate but also predict this value for structures that have not yet been realized by experiment.

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

2009-12-01

250

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

251

An agarose gel electrophoretic method for analysis of hyaluronan molecular weight distribution.  

PubMed

An electrophoretic method is described for determining the molecular weight distribution of hyaluronan (HA). The method involves separation of HA by electrophoresis on a 0.5% agarose gel, followed by detection of HA using the cationic dye Stains-All (3,3'-dimethyl-9-methyl-4,5,4'5'-dibenzothiacarbocyanine). The recommended sample load is 7 micrograms. Calibration of the method with HA standards of known molecular weight has established a linear relationship between electrophoretic mobility and the logarithm of the weight-average molecular weight over the range of approximately 0.2-6 x 10(6). The separated HA pattern may also be visualized after electrotransfer of HA from the agarose gel to a nylon membrane. The membrane may be stained with the dye alcian blue. Alternatively, specific detection of HA from impure samples can be achieved by probing the nylon membrane with biotin-labeled HA-binding protein and subsequent interaction with a streptavidin-linked gold reagent and silver staining for amplification. The electrophoretic method was used to analyze HA in two different liquid connective tissues. Normal human knee joint synovial fluid showed a narrow HA molecular weight distribution, with a peak at 6-7 x 10(6). Owl monkey vitreous HA also showed a narrow molecular weight distribution, with a peak at 5-6 x 10(6). These results agree well with available published data and indicate the applicability of the method to the analysis of impure HA samples which may be available in limited amounts. PMID:8080084

Lee, H G; Cowman, M K

1994-06-01

252

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

253

Accurate and efficient integration for molecular dynamics simulations at constant temperature and pressure.  

PubMed

In molecular dynamics simulations, control over temperature and pressure is typically achieved by augmenting the original system with additional dynamical variables to create a thermostat and a barostat, respectively. These variables generally evolve on timescales much longer than those of particle motion, but typical integrator implementations update the additional variables along with the particle positions and momenta at each time step. We present a framework that replaces the traditional integration procedure with separate barostat, thermostat, and Newtonian particle motion updates, allowing thermostat and barostat updates to be applied infrequently. Such infrequent updates provide a particularly substantial performance advantage for simulations parallelized across many computer processors, because thermostat and barostat updates typically require communication among all processors. Infrequent updates can also improve accuracy by alleviating certain sources of error associated with limited-precision arithmetic. In addition, separating the barostat, thermostat, and particle motion update steps reduces certain truncation errors, bringing the time-average pressure closer to its target value. Finally, this framework, which we have implemented on both general-purpose and special-purpose hardware, reduces software complexity and improves software modularity. PMID:24182003

Lippert, Ross A; Predescu, Cristian; Ierardi, Douglas J; Mackenzie, Kenneth M; Eastwood, Michael P; Dror, Ron O; Shaw, David E

2013-10-28

254

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

PubMed Central

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).

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

2012-01-01

255

The Sequential Appearance of Low and High-Molecular-Weight Forms of MAP2 in the Developing Cerebellum  

Microsoft Academic Search

Mammalian microtubule-associated protein 2 (MAPS) exists in high-molecular-weight (M, -280,000) and low-molecular- weight (M, -70,000) forms, with the latter protein being more abundant in embryonic brain homogenates than in prepa- rations from mature brain (Riederer and Matus, 1985). In the current study, we have shown that avian MAP2 also exists as both high- (M, -260,000) and low-molecular-weight (M, -65,000) forms

R. P. Tucker; L. I. Binder; C. Viereck; B. A. Hemmings; A. I. Matus

1999-01-01

256

Positively charged polyethylenimines enhance nasal absorption of the negatively charged drug, low molecular weight heparin  

Microsoft Academic Search

This study tests the hypothesis that positively charged polyethylenimines (PEIs) enhance nasal absorption of low molecular weight heparin (LMWH) by reducing the negative surface charge of the drug molecule. Physical interactions between PEIs and LMWH were studied by Fourier transform infrared (FTIR) spectroscopy, particle size analysis, conductivity measurements, zeta potential analysis, and azure A assay. The efficacy of PEIs in

Tianzhi Yang; Alamdar Hussain; Shuhua Bai; Ikramy A. Khalil; Hideyoshi Harashima; Fakhrul Ahsan

2006-01-01

257

Oral low molecular weight heparin delivery by microparticles from complex coacervation  

Microsoft Academic Search

As low molecular weight heparins exhibit limited oral absorption they usually have to be administered parenterally. Their strong negative charge appears to be one of the biggest hurdles to overcome in order to increase oral absorption. Complex coacervation has been proposed as a microencapsulation technique for increased oral drug absorption on the basis of charge compensation. Optimized tinzaparin\\/acacia gum mixture

Alf Lamprecht; Nathalie Ubrich; Philippe Maincent

2007-01-01

258

Study of the catalytic conversion of synthesis gas to low-molecular weight hydrocarbons. [Erionite  

Microsoft Academic Search

The search for alternative sources of energy has provided the stage for the examination of catalytic reactions which can influence the supply of low molecular weight chemical feedstocks, such as ethylene, propylene, and butadiene. Synthesis gas produced from partial oxidation of coal is considered the basic building block for all alternative chemical feedstock synthesis. However, the classical Fischer-Tropsch synthesis catalysts

Chan

1981-01-01

259

Effect of molecular weight on the flow-induced crystallization of isotactic poly(1-butene)  

Microsoft Academic Search

Turbidity measurements were used to characterize the effect of shear flow on the crystallization kinetics of several isotactic poly(1-butene) samples of different molecular weight (MW). Polymer melts were rapidly cooled below the nominal crystallization temperature, and subjected to a shear flow of varying shear rate but constant total deformation. While the quiescent crystallization was found to be essentially MW-independent, a

Stefano Acierno; Blandina Palomba; Henning H. Winter; Nino Grizzuti

2003-01-01

260

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

ERIC Educational Resources Information Center

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

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

2011-01-01

261

Kinetics of Toluene-Induced Leakage of Low Molecular Weight Solutes from Excised Sorghum Tissues 1  

PubMed Central

The relationship between toluene concentration and the rate of leakage of solutes from toluene-treated roots and leaves of Sorghum bicolor, L. Moench, was studied to determine the effect of toluene on plant cell membranes. A threshold concentration of 0.2% toluene was needed to induce leakage. Maximal leakage rates were obtained with 0.5% toluene. Low molecular weight solutes, such as amino acids, sugars, and inorganic ions, leaked from treated tissue, while macromolecules, such as protein were retained. The rates at which the low molecular weight solutes diffused from treated cells decreased with increasing molecular weight. At 25°C, treatment of roots and leaves with 0.5% toluene resulted in the quasi-quantitative leakage of solutes within 180 minutes. At 1°C, roots and leaves differed in their response to toluene. The rates of leakage from roots at 1°C were much lower and the total amounts much smaller than at 25°C, while in leaves the difference between the two temperatures was very small. The procedure of treating tissues with 0.5% toluene for 180 minutes at 25°C proved to be a rapid and simple technique for quantitative extraction of water-soluble, low molecular weight solutes from plant cells into the extracting medium while macromolecular constituents are retained inside the cells.

Weimberg, Ralph; Lerner, H. R.; Poljakoff-Mayber, A.

1981-01-01

262

The use of low molecular weight heparin in pediatric patients: A prospective cohort study  

Microsoft Academic Search

Objective: Low molecular weight heparins (LMWHs) offer several advantages over standard anticoagulant therapy (unfractionated heparin\\/warfarin) including predictable pharmacokinetics, minimal monitoring, and subcutaneous administration. Our objective was to determine the safety and efficacy of LMWHs in children.Methods: A prospective cohort of children treated with the LMWH enoxaparin (Rhone Poulenc Rorer) was monitored at the Hospital for Sick Children, Toronto, Canada, from

David Dix; Maureen Andrew; Velma Marzinotto; Karen Charpentier; Suzanne Bridge; Paul Monagle; Gabrielle deVeber; Michael Leaker; Anthony K. C Chan; M. Patricia Massicotte

2000-01-01

263

Prevention of deep vein thrombosis in patients with hip fractures: Low molecular weight heparin versus dextran  

Microsoft Academic Search

A randomized open trial was undertaken to compare the antithrombotic efficacy of a low molecular weight heparin (LMWH; Sandoparin®) with that of dextran 70 in patients undergoing surgery for hip fracture. One hundred thirteen patients received LMWH once daily subcutaneously at a fixed dosage while 103 patients received intravenous dextran 70. Postoperative deep vein thrombosis (DVT) was assessed by a

D. Oertli; P. Hess; M. D?rig; U. Laffer; R. Fridrich; K. Jaeger; R. Kaufmann; F. Harder

1992-01-01

264

Characterization of a novel low molecular weight sucrase from filamentous fungus Termitomyces clypeatus  

Microsoft Academic Search

An extracellular sucrase from the culture filtrate of filamentous basidiomycota Termitomyces clypeatus grown on high sucrose (5%, w\\/v) was purified by gel filtration chromatography, ion exchange chromatography and HPGPLC. The biochemical properties, molecular weight and conformation of sucrase produced were significantly different from the sucrase earlier purified from sucrose (1%, w\\/v) medium in the fungus. Purified sucrase was characterized as

Sudeshna Chowdhury; Shakuntala Ghorai; Samudra Prosad Banik; Swagata Pal; Soumen Basak; Suman Khowala

2009-01-01

265

High molecular weight first generation PMR polyimides for 343 C applications  

Microsoft Academic Search

The polymers research effort at NASA Lewis Research Center, the lead NASA Center for aeropropulsion research, has primarily focused on the development of advanced polymers for aircraft engine applications. In order to improve engine performance, studies have emphasized the use of advanced, lightweight composite materials. The effect of molecular weight on 343 C. thermo-oxidative stability (TOS), mechanical properties, and processability,

D. C. Malarik; R. D. Vannucci

1992-01-01

266

Mixed metal oxide catalyst for producing low molecular weight hydrocarbons from carbon monoxide and hydrogen  

Microsoft Academic Search

Low molecular weight hydrocarbons are produced by contacting carbon monoxide and hydrogen at elevated temperatures and pressures with a catalyst comprising oxides of chromium, molybdenum and\\/or tungsten, copper, thorium or uranium and at least one alkali or alkaline earth metal. Catalysts are provided which are prepared by the procedure of adding an alkali or alkaline earth metal carbonate to an

M. F. Lemanski; W. R. Kliewer

1984-01-01

267

Action of polyethylene glycols with linear structure and different molecular weights on rat liver lysosomes  

Microsoft Academic Search

The action of nonpolar detergents — polyethylene glycols with linear structure and differing in molecular weight from 700 to 15,000 — on rat liver lysosomes was studied. Triton X-100 was found to activate acid phosphatase of the total lysosome fraction more than the other polyethylene glycols. The action of polyethylene glycols on activation of acid phosphatase in lysosomal subfractions was

A. V. Tret'yakov; E. M. Ryazanov; A. S. Tarkov; N. K. Asinovskaya; V. A. Filov

1975-01-01

268

FERROELECTRIC SWITCHING LIQUID CRYSTAL POLYACRYLATES - THE CONTROL AND EFFECT OF MOLECULAR WEIGHT  

Microsoft Academic Search

The polymerisation of two liquid crystalline acrylate monomers is discussed with particular reference to control of the degree of polymerisation. Two series of liquid crystalline side chain polymers are produced, each with a broad smectic C phase and with a range of molecular weights. The electro-optic behaviour of the materials is discussed, and in one of the series ferroelectric response

Mark Verrall; David Beattie; David Coates; Ian Sage; Karl Lymer

1996-01-01

269

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

Microsoft Academic Search

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

Jennifer L. Stringer; Nikolaos A. Peppas

1996-01-01

270

Shaping of molecular weight distribution using B-spline based predictive probability density function control  

Microsoft Academic Search

Issues of modelling and control of molecular weight distributions (MWDs) of polymerization products have been studied under the recently developed framework of stochastic distribution control, where the purpose is to design the required control inputs that can effectively shape the output probability density functions (PDFs) of the dynamic stochastic systems. The B-spline neural network has been implemented to approximate the

Hong Yue; Jinfang Zhang; Hong Wang; Liulin Cao

2004-01-01

271

A study of the nanostructure and tensile properties of ultra-high molecular weight polyethylene  

Microsoft Academic Search

Ultra-high molecular weight polyethylene (UHMWPE) has gained worldwide acceptance as a bearing material used in orthopaedic implants. Despite its widespread use, inherent properties of the polymer continue to limit the wear resistance and the clinical lifespan of implanted knee and hip prosthetics containing UHMWPE components. The degree of crystallinity of UHMWPE is known to strongly influence several of its tensile

Mary Beth Turell; Anuj Bellare

2004-01-01

272

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

Microsoft Academic Search

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

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

1998-01-01

273

Dosimetric features and kinetic analysis of thermoluminescence from ultra-high molecular weight polyethylene  

Microsoft Academic Search

Thermoluminescence (TL) from beta irradiated ultra-high molecular weight polyethylene has been studied for measurements between 30 and 200 °C. An aliquot studied in this work produced TL glow curves consisting of two peaks, the main peak at 88 °C and a weaker intensity peak at 148 °C for heating at 1 °C s?1 following an excitation dose of 215 Gy.

M L Chithambo

2012-01-01

274

Powder compaction, sintering, and rolling of ultra high molecular weight polyethylene and its composites  

Microsoft Academic Search

The applicability of powder compaction and sintering techniques to the processing of ultra high molecular weight polyethylene (UHMWPE) powder is demonstrated. With proper processing procedure and type of UHMWPE powder, the mechanical properties obtained are nearly equivalent to those obtained by conventional melt processes. The properties were optimized by selection of a sintering temperature just above the melting point and

K. S. Han; J. F. Wallace; R. W. Truss; P. H. Geil

1981-01-01

275

Sliding wear behavior and mechanism of ultra-high molecular weight polyethylene  

Microsoft Academic Search

In this paper, the dry sliding wear behavior of ultra-high molecular weight polyethylene (UHMWPE) was tested on an MM200 rig. The effects of sliding speed and load on the sliding wear of UHMWPE were determined. Scanning electron microscopy (SEM) was employed to examine the worn surfaces. The SEM images showed that a series of ridges were formed on the UHMWPE

Y. Q. Wang; J. Li

1999-01-01

276

The microstructure of ultra-high molecular weight polyethylene used in total joint replacements  

Microsoft Academic Search

The microstructure of ultra-high molecular weight polyethylene (UHMWPE) has been studied using a range of techniques. Both the unprocessed base powder and ram-extruded polymer have been examined using optical microscopy, scanning and transmission electron microscopy and smallangle light scattering. By examining the microstructure of samples compression moulded at a range of temperatures, techniques have been developed to assess the degree

D. F. Farrar; A. A Brain

1997-01-01

277

A novel composite based on ultra-high-molecular-weight polyethylene  

Microsoft Academic Search

A novel composite material consisting of ultra-high-molecular-weight polyethylene (UHMWPE) fibers and matrix has been prepared, characterized and shown to possess unique properties, in particular an elongation of over 70% in the direction transverse to the fibers which induces transverse orientation of the matrix. This indicates that excellent adhesion between fibers and matrix has been achieved in this composite material which

Yachin Cohen; Dmitry M. Rein; Lev Vaykhansky

1997-01-01

278

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

Microsoft Academic Search

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

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

1999-01-01

279

Effectiveness of the membrane bioreactor in the biodegradation of high molecular weight compounds  

Microsoft Academic Search

This paper presents biological and physical performance data from a pilot-scale membrane bioreactor system fed with synthetic wastewater containing high molecular weight compounds. At steady state, high effluent quality was obtained and maintained for about 350days. The membrane was effective in retaining heterotrophic microorganisms and MS-2 viruses, eliminating the need for effluent disinfection. The flux through the membrane decreased rapidly

Nazim Cicek; Hans Winnen; Makram T. Suidan; Brian E. Wrenn; Vincent Urbain; Jacques Manem

1998-01-01

280

Effect of molecular weight heterogeneity on drug encapsulation efficiency of gelatin nano-particles  

Microsoft Academic Search

Influence of molecular weight heterogeneity and drug solubility, drug loading and hydrodynamic conditions on drug release kinetics from gelatin nanoparticles were investigated. Also to assess the ability of gelatin nanoparticles as a potential intravascular probe for diagnostic purposes and in improving the biodelivery of cycloheximide (CHX), which is being used as a representative drug. Comparative characterization of 75 Bloom (type

Anita Saxena; Kumar Sachin; H. B. Bohidar; Anita Kamra Verma

2005-01-01

281

High-Speed Spinning of Ultra-High Molecular Weight Polyethylene Fibres.  

National Technical Information Service (NTIS)

The aim of the thesis is to study and optimize the oriented crystallization of the ultra-high molecular weight polyethylene in the spinline, at high winding speeds, and obtain a strong polyethylene fibre in a one step process. Many variables influence the...

M. Roukema

1991-01-01

282

Molecular weight effects on the rheology of polymer\\/clay dispersions  

Microsoft Academic Search

We present rheological data on a model clay-polymer system, an aqueous dispersion of laponite RD with added polyethylene oxide (PEO), which is known to adsorb on the clay surfaces. We find that low to moderate molecular weight PEO significantly slows down gelation and decreases the complex viscosity and elastic modulus of the dispersion by several orders of magnitude. These somewhat

Hossein Baghdadi; Heidi Sardinha; Surita Bhatia

2004-01-01

283

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

EPA Science Inventory

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

284

Mass spectrometric study of dissociative ionization of low-molecular-weight models of aromatic polyamides  

SciTech Connect

Energetic characteristics of dissociative ionization processes of low-molecular-weight compounds modeling the chain fragments of aromatic polyamides were studied by mass spectrometric methods. Factors were determined that influence the radiation stability of molecules in this class of compounds. Mechanisms of radiational degradation of macromolecules of aromatic polyamides of different types were proposed.

Pozdnyakov, O.F.; Yudin, V.S.

1987-07-01

285

Molecular weight of nadp-dependent isocitrate dehydrogenase from rat brain cytosol under normoxia and hypoxia  

Microsoft Academic Search

The NADP-dependent isocitrate dehydrogenase obtained from brain cytosol of control and hypoxic animals was purified 36-fold by a combination of chromatography on DE-32 cellulose, CM cellulose, and DEAE-Sephadex and electrophoresis. Hypoxia did not change the molecular weight (about 165,000) of the enzyme, which was composed of two subunits of 80,000 daltons each.

Urszula Rafa?owska; Anna Pastuszko

1979-01-01

286

Effect of low molecular weight fluid on the hydrophobicity of silicone rubber  

Microsoft Academic Search

Silicone rubber (SIR) has good performance when used in outdoor insulators. The hydrophobicity of the surface is maintained in wet conditions as a result of the diffusion of the low molecular weight (LMW) fluid from the bulk to the surface. The amount of LMW fluid on the surface and in the bulk of the material determines the hydrophobicity during the

K. Iida; Y. Saitoh; R. Hackam

2008-01-01

287

The Molecular Weight Dependence of the Crystallization Rate for Linear Polyethylene Fractions.  

National Technical Information Service (NTIS)

This paper reports the experimental results, without a detailed analysis, of the strong influence of molecular weight on the crystallization rate for fractions of linear polyethylene encompassing the range 9 x 10 to the third power to 3.8 x 10 to the sixt...

L. Mandelkern J. G. Fatou K. Ohno

1968-01-01

288

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

Microsoft Academic Search

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

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

2005-01-01

289

Coagulation and nanofiltration: A hybrid system for the removal of lower molecular weight organic compounds (LMWOC)  

Microsoft Academic Search

The removal of lower molecular weight organic compounds (LMWOC) from water is of increasing concern. While, nano-filtration (NF) is a good option, it removes only a fraction of the LMWOC. In this paper, NF experiments were conducted to remove oxalic acid and diuron in combination with coagulation using poly-aluminum chloride (PAC) as the coagulant. The results showed that this hybrid

Yuanfang Wang; Li Shu; Veeriah Jegatheesan; Baoyu Gao

2009-01-01

290

Relation Between Colonic Inflammation Severity and Total Low-Molecular-Weight Antioxidant Profiles in Experimental Colitis  

Microsoft Academic Search

Tissue antioxidant status is altered as a response to oxidative stress. This oxidative stress, caused by reactive oxygen species, is associated with inflammatory bowel disease (IBD). Our aim was to examine the relationship between total tissue low-molecular-weight antioxidant (LMWA) profile and inflammation severity in dinitrobenzene sulfonic acid (DNBS) experimental colitis in the rat. Rats were treated with three doses of

Sigal Blau; Ron Kohen; Paul Bass; Abraham Rubinstein

2000-01-01

291

Determination of the molecular weight of barley ?-glucan using intrinsic viscosity measurements  

Microsoft Academic Search

Molecular weight (MW) of polysaccharides determines their solution properties such as intrinsic viscosity [?], flow and aggregation behavior. Determination of polysaccharide MW usually involves specialized equipment, extensive sample preparation and equipment calibration. Barley ?-glucan gum (BBG) was extracted at laboratory (LAB) and pilot plant (PP) scale. Its MW and critical concentration (c*) were determined using [?] at infinite dilution. Solutions

Zvonko Burkus; Feral Temelli

2003-01-01

292

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

EPA Science Inventory

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

293

Low molecular weight advanced glycation end products predict mortality in asymptomatic patients receiving chronic haemodialysis  

Microsoft Academic Search

Background. Advanced glycation end products (AGEs) have biological properties that may contribute to the premature cardiovascular mortality of haemo- dialysis patients. This study examines the hypothesis that low molecular weight forms of fluorescent AGEs (LMW fluorescence) predict mortality in haemodialy- sis patients. Methods. The LMW fluorescence was measured in 85 patients treated with chronic haemodialysis and prospectively followed for 4

Matthew A. Roberts; Merlin C. Thomas; Dharsh Fernando; Neil Macmillan; David A. Power; Francesco L. Ierino

2006-01-01

294

Modeling molecular weight development of gas-phase {alpha}-olefin copolymerization  

SciTech Connect

A comprehensive kinetic model developed for molecular weight calculations of ethylene and {alpha}-olefin copolymerizations in the context of a terminal model accounts for multiple-type active centers of the catalyst, detailed elementary chemical reactions, and catalyst composition. The moments of copolymer chain distributions are defined considering molecular weights of comonomer units so that copolymer molecular weight averages can be directly calculated for those moments. A double Z-transformation is introduced for the derivation of differential equations of the moments. Model simulations are carried out based on ethylene and 1-butene copolymerizations in a gas-phase fluidized-bed reactor. Polydispersity of accumulated copolymer depends on catalyst composition and kinetic characteristics of the catalyst. For a catalyst with specified kinetic characteristics, the polydispersity depends on the mole fraction of each type of active center. For a catalyst with two types of active centers; the maximum polydispersity of copolymer occurs at 50 wt.% of the total copolymer if polydispersities of the copolymers generated at each active site are the same. Polydispersity of accumulated copolymer is sensitive to propagation reactions and chain transfer to hydrogen reactions. Differences in chain transfer to cocatalyst and monomers and in spontaneous deactivation rates for different types of active centers may play minor roles in controlling molecular weight development in the presence of hydrogen. This model can be used for catalyst composition design, simulation of commercial olefin copolymerization processes, and kinetic parameter estimation.

Xie, T.; McAuley, K.B.; Hsu, J.C.C.; Bacon, D.W. [Queen`s Univ., Kingston, Ontario (Canada). Dept. of Chemical Engineering] [Queen`s Univ., Kingston, Ontario (Canada). Dept. of Chemical Engineering

1995-05-01

295

Operation mechanisms of organic electroluminescent diodes based on commonly used low-molecular-weight materials  

NASA Astrophysics Data System (ADS)

Optical and electrical characteristics of single- and double-layer organic electroluminescent (EL) diodes based on commonly used low-molecular weight materials of an aromatic diamine (TPD) and 8-hydroxyquinoline aluminum complex (Alq3) were investigated in order to compare their operation mechanisms.

Camaioni, Nadia; Kalinowski, Jan; di Marco, P.; Fattori, V.; Giro, Gabriele

1996-04-01

296

Weak alkali and alkaline earth metal complexes of low molecular weight ligands in aqueous solution  

Microsoft Academic Search

This work is aimed at reviewing the chemical literature dealing with thermodynamic aspects of the weak complex formation (species with logK values less than about 3) between alkali and alkaline earth metal ions with low molecular weight inorganic and organic ligands in aqueous solution. The following ligands (up to hexavalent anions) were examined in detail: (i) hydroxide, chloride, sulfate, carbonate

Pier G. Daniele; Claudia Foti; Antonio Gianguzza; Enrico Prenesti; Silvio Sammartano

2008-01-01

297

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...

298

Enhanced wear performance of ultra high molecular weight polyethylene crosslinked by organosilane  

Microsoft Academic Search

Ultra high molecular weight polyethylene (UHMWPE) crosslinked by organosilane was thermal compression molded. The organosilane used was the tri-ethyloxyl vinyl silane. Its gelation, melting behavior, crystallinity, mechanical and wear-resisting properties were systematically investigated. The results showed that the gel ratio of UHMWPE increases with the incorporation of organosilane. At a low content of organosilane, the melting point and crystallinity of

C. Y. Tang; X. L. Xie; X. C. Wu; R. K. Y. Li; Y. W. Mai

2002-01-01

299

An improved function for fitting sedimentation velocity data for low-molecular-weight solutes  

Microsoft Academic Search

Many traditional approaches to the analysis of sedimentation velocity data work poorly with data for low molecular weight solutes, which have sedimentation boundaries that are severely broadened by diffusion. An approach which has previously had some success is to directly fit these broad boundaries to approximate solutions of the Lamm equation which directly account for the high diffusion. However, none

John S. Philo

1997-01-01

300

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...

301

Towards more accurate molecular dynamics calculation of thermal conductivity: Case study of GaN bulk crystals  

NASA Astrophysics Data System (ADS)

Significant differences exist among literature for thermal conductivity of various systems computed using molecular dynamics simulation. In some cases, unphysical results, for example, negative thermal conductivity, have been found. Using GaN as an example case and the direct nonequilibrium method, extensive molecular dynamics simulations and Monte Carlo analysis of the results have been carried out to quantify the uncertainty level of the molecular dynamics methods and to identify the conditions that can yield sufficiently accurate calculations of thermal conductivity. We found that the errors of the calculations are mainly due to the statistical thermal fluctuations. Extrapolating results to the limit of an infinite-size system tend to magnify the errors and occasionally lead to unphysical results. The error in bulk estimates can be reduced by performing longer time averages using properly selected systems over a range of sample lengths. If the errors in the conductivity estimates associated with each of the sample lengths are kept below a certain threshold, the likelihood of obtaining unphysical bulk values becomes insignificant. Using a Monte Carlo approach developed here, we have determined the probability distributions for the bulk thermal conductivities obtained using the direct method. We also have observed a nonlinear effect that can become a source of significant errors. For the extremely accurate results presented here, we predict a [0001] GaN thermal conductivity of 185W/Km at 300 K, 102W/Km at 500 K, and 74W/Km at 800 K. Using the insights obtained in the work, we have achieved a corresponding error level (standard deviation) for the bulk (infinite sample length) GaN thermal conductivity of less than 10W/Km , 5W/Km , and 15W/Km at 300 K, 500 K, and 800 K, respectively.

Zhou, X. W.; Aubry, S.; Jones, R. E.; Greenstein, A.; Schelling, P. K.

2009-03-01

302

Ultra-drawing of gel films of ultra high molecular weight polyethylene\\/low molecular weight polymer blends containing BaTiO 3 nanoparticles  

Microsoft Academic Search

The ultra-drawing process of an ultra high molecular weight polyethylene (UHMWPE) gel film was examined by incorporating linear\\u000a low-density polyethylene (LLDPE) and BaTiO3 nanoparticles. The effects of LLDPE and the draw ratios on the morphological development and mechanical properties of the\\u000a nanocomposite membrane systems were investigated. By incorporating BaTiO3 nanoparticles in the UHMWPE\\/LLDPE blend systems, the ultra-drawing process provided a

Ho Sik Park; Jong Hoon Lee; Jae-Do Nam; Soo Jung Seo; Young Kwan Lee; Yong Soo Oh; Hyun-Chul Jung

2006-01-01

303

Isoleucine epimerization and amino acid composition in molecular-weight separations of Pleistocene Genyornis eggshell  

NASA Astrophysics Data System (ADS)

This study explores the geochronological utility and analytical reproducibility of separating the high-molecular-weight fraction (HMW) from eggshells of the extinct late Pleistocene ratite, Genyornis, using disposable, prepacked gel-filtration columns. The superior integrity of ratite eggshell for the retention of amino acids indicates that this biomineral is better suited for this type of investigation than previously studied molluscan shell. To evaluate the reproducibility of the gel-filtration technique, we analyzed triplicate subsamples of three eggshells of different ages. The reproducibility, based on the average intrashell variation (coefficient of variation; CV) in the extent of isoleucine epimerization (aIle/Ile) in the HMW (enriched in molecules ca. >10,000 MW) is 3%, well within the range appropriate for geochronological purposes. The average intrashell variation in the total amino acid concentration (?[aa]) of the HMW is 5%, somewhat better than for the total acid hydrolysate (TOTAL) of the same samples (7%). To evaluate the relation between molecular weight and the rate of isoleucine epimerization, three molecular-weight fractions were separated using gel filtration, plus the naturally hydrolyzed free fraction (FREE), for each of four fossil eggshells. AIle/Ile increases with decreasing molecular weight in all shells, with a ca. sixfold to ninefold difference in ratios between the HMW andFREE, and a ca. fivefold difference between the HMW andTOTAL. Although linear correlations between aIle/Ile measured in each molecular-weight fraction and in theTOTAL are all highly significant (r ? 0.951), the relation between the extent of epimerization in the HMW and in the TOTAL is best expressed as an exponential function (r = 0.951). This relation is consistent with the idea that, as the epimerization reaction approaches equilibrium in theTOTAL (ca. aIle/Ile > 1.1), its rate decreases beyond that of the HMW. The amino acid composition (relative percent of eight amino acids or combinations of amino acids) is more uniform in the HMW of the four samples compared to lower-molecular-weight fractions. The greater "compositional stability" of the HMW indicates that it contains a residuum of macromolecules that have not been affected by the diagenetically driven changes observed in lower-molecular-weight fractions.

Kaufman, Darrell S.; Miller, Gifford H.

1995-07-01

304

Intermolecular complexation of low-molecular-weight succinoglycans directs solubility enhancement of pindolol.  

PubMed

The low-molecular-weight succinoglycans isolated from Sinorhizobium meliloti are repeating octasaccharide units consisting of monomers, dimers, and trimers. Pindolol is a beta-blocker used to treat cardiovascular disorders. We investigated the formation of complexes between pindolol and low-molecular-weight succinoglycan monomers (SGs). Even though SGs have a linear structure, the solubility of pindolol in the presence of SGs was increased up to 7-fold compared with methyl-?-cyclodextrin reported as the best solubilizer of pindolol. Complexation of SGs with pindolol was confirmed by nuclear magnetic resonance, Fourier-transform infrared spectroscopy, differential scanning calorimetry, and scanning electron microscopy. Formation constants of complexes were determined from phase solubility diagrams. Conformation of complex was suggested based on a molecular docking study. The present study indicated that formation of pindolol/SGs complexes not only resulted in increased pindolol solubility but also could be useful for improving its clinical application as it did not affect cell viability. PMID:24721056

Kim, Kyoungtea; Cho, Eunae; Choi, Jae Min; Kim, Hwanhee; Jang, Ahri; Choi, Youngjin; Lee, Im Soon; Yu, Jae-Hyuk; Jung, Seunho

2014-06-15

305

High molecular weight polyethylene glycol cellular distribution and PEG-associated cytoplasmic vacuolation is molecular weight dependent and does not require conjugation to proteins.  

PubMed

Conjugation of therapeutic proteins with high molecular weight polyethylene glycols (HMW PEGs) is used to extend the half-life of biologics. To evaluate the effects of HMW PEGs in animals, we used an immunohistochemical procedure to study the tissue distribution and toxicity of unconjugated HMW PEGs in rats given 100 mg/kg (10K)PEG, (20K)PEG, or (40K)PEG intravenously. Both the PEG cellular distribution and the histology were different between groups. In (10K)PEG and (20K)PEG groups, PEG immunoreactivity was most prominent in the renal tubule epithelium and in alveolar macrophages and hepatic Kupffer cells and cellular vacuolation was absent. In contrast, rats given (40K)PEG had strong PEG immunoreactivity in splenic subcapsular red pulp macrophages, renal interstitial macrophages, and choroid plexus epithelial cells that was frequently associated with cytoplasmic vacuolation. While the vacuolation appeared to be an adaptive response, there was focal renal tubular epithelial degeneration associated with strong PEG immunoreactivity in one rat given (40K)PEG. These data indicate that both the tissue distribution and the vacuolation observed with unconjugated HMW PEGs are markedly influenced by the molecular weight of the PEG and that when vacuolation is observed it is likely an adaptive change that is associated with PEG cytoplasmic immunoreactivity. PMID:23788571

Rudmann, Daniel G; Alston, James T; Hanson, Jeffrey C; Heidel, Shawn

2013-01-01

306

Development of a bond-valence based interatomic potential for BiFeO3 for accurate molecular dynamics simulations.  

PubMed

We present an atomistic potential for BiFeO(3) based on the principles of bond-valence (BV) and bond-valence vector (BVV) conservation. The validity of this model potential is tested for both canonical ensemble (NVT) and isobaric-isothermal ensemble (NPT) molecular dynamics (MD) simulations. The model reproduces the ferroelectric-to-paraelectric phase transition in both NVT and NPT MD simulations and the temperature dependence of the local structure in BiFeO(3). The calculated domain wall energies for 71°, 109°and 180° walls agree well with density functional theory results. The success of our simple model potential for BiFeO(3) indicates that BV and BVV conservation provides a firm basis for the development of accurate atomistic potentials for complex oxides. PMID:23399759

Liu, Shi; Grinberg, Ilya; Rappe, Andrew M

2013-03-13

307

The potential benefits of low-molecular-weight heparins in cancer patients  

PubMed Central

Cancer patients are at increased risk of venous thromboembolism due to a range of factors directly related to their disease and its treatment. Given the high incidence of post-surgical venous thromboembolism in cancer patients and the poor outcomes associated with its development, thromboprophylaxis is warranted. A number of evidence-based guidelines delineate anticoagulation regimens for venous thromboembolism treatment, primary and secondary prophylaxis, and long-term anticoagulation in cancer patients. However, many give equal weight to several different drugs and do not make specific recommendations regarding duration of therapy. In terms of their efficacy and safety profiles, practicality of use, and cost-effectiveness the low-molecular-weight heparins are at least comparable to, and offer several advantages over, other available antithrombotics in cancer patients. In addition, data are emerging that the antithrombotics, and particularly low-molecular-weight heparins, may exert an antitumor effect which could contribute to improved survival in cancer patients when given for long-term prophylaxis. Such findings reinforce the importance of thromboprophylaxis with low-molecular-weight heparin in cancer patients.

2010-01-01

308

Molecular weight dependence of emission intensity and emitting sites distribution within single conjugated polymer molecules.  

PubMed

We investigated exciton migration, trapping and emission processes occurring within a single conjugated polymer molecule by means of superresolution fluorescence localization microscopy. This methodology allowed us to locate the spatial distribution of emitting sites within single chains with nanometre precision. The study was done on individual poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) molecules with average molecular weights ranging from 215,000 to 1,440,000 and with narrow weight distributions. We found that the mean emission intensity increases proportionally to the polymer molecular weight. The localization experiments suggest that the emitting sites are distributed nearly uniformly within a single chain and that the sites are on average 10 nm apart, irrespective of the molecular weight of the polymer. Furthermore, spatial contours formed by all the combined emitting sites within one chain show elongated shapes, in agreement with a rod-like structure of MEH-PPV in a collapsed state. PMID:21113536

Habuchi, Satoshi; Onda, Suguru; Vacha, Martin

2011-02-01

309

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

310

Species variations in the threshold molecular-weight factor for the biliary excretion of organic anions  

PubMed Central

1. The excretion in the bile and urine after intravenous injection of 16 organic anions having molecular weights between 355 and 752 was studied in female rats, guinea pigs and rabbits. 2. These compounds were mostly excreted unchanged, except for three of them, which were metabolized to a slight extent (<7% of dose). 3. The rat excreted all the compounds extensively (22–90% of dose) in the bile. 4. In guinea pigs four of the compounds with mol.wt. 355–403 were excreted in the bile to the extent of 7–16% of the dose, four with mol.wt. 407–465 to the extent of 25–44% and eight compounds with mol.wt. 479–752 to the extent of 44–100%. 5. In rabbits four compounds with mol.wt. 355–465 were excreted in the bile to the extent of 1–8% of the dose, two compounds with mol.wt. 479 and 495 to the extent of 24 and 22%, and six compounds with mol.wt. 505–752 to the extent of 31–94%. 6. These results, together with those of other investigations from this laboratory, are discussed and the conclusion is reached that there is a threshold molecular weight for appreciable biliary excretion (i.e. more than 10% of dose) of anions, which varies with species: about 325±50 for the rat, 400±50 for the guinea pig and 475±50 for the rabbit. 7. Anions with molecular weights greater than about 500 are extensively excreted in the bile of all three species. 8. That proportion of the dose of these compounds which is not excreted in the bile is excreted in the urine, and in the three species, bile and urine are complementary excretory pathways, urinary excretion being greatest for the compounds of lowest molecular weight and tending to decrease with increasing molecular weight. 9. Some implications of this interspecies variation in the molecular-weight requirement for extensive biliary excretion are discussed.

Hirom, P. C.; Millburn, P.; Smith, R. L.; Williams, R. T.

1972-01-01

311

Kinetics of nonisothermal crystallization and melting of normal high density and ultra-high molecular weight polyethylene blends  

Microsoft Academic Search

The kinetics of nonisothermal crystallization and melting of blends of ultra-high molecular weight polyethylene (UHMWPE) and polyethylene high density with normal molecular weight (NMWPE) are investigated by means of differential scanning calorimetry (DSC). Mixing the components at a temperature below the flow temperature of UHMWPE (215 °C) results in increased crystallization\\/melting rates of the individual components in the blends above

L. Minkova; M. Mihailov

1989-01-01

312

Influence of operational parameters on retention of ultra-high molecular weight polystyrenes in thermal field-flow fractionation  

Microsoft Academic Search

The influence of various parameters (concentration of the injected polymer solution, flow rate, temperature gradient, relaxation conditions) on the retention and shape of the fractogram of ultra-high molecular weight polystyrenes in thermal field-flow fractionation was investigated. Under the operating conditions adopted, reproducible oscillations in the peak shape are observed for molecular weights larger than a few millions, especially at relatively

J. Jan?a; M. Martin

1992-01-01

313

Effect of small amount of ultra high molecular weight component on the crystallization behaviors of bimodal high density polyethylene  

Microsoft Academic Search

In order to clarify the effect of high molecular weight component on the crystallization of bimodal high density polyethylene (HDPE), a commercial PE-100 pipe resin was blended with small loading of ultra high molecular weight polyethylene (UHMWPE). The isothermal crystallization kinetics and crystal morphology of HDPE\\/UHMWPE composites were studied by differential scanning calorimetry (DSC) and polarized optical microscopy (POM), respectively.

Shijie Song; Peiyi Wu; Minxing Ye; Jiachun Feng; Yuliang Yang

2008-01-01

314

Influence of Filler on the Pore Structure of Films of Ultra-High-Molecular-Weight Polyethylene Xerogels  

Microsoft Academic Search

The pore structure of filled films of xerogels of ultra-high-molecular-weight polyethylene prepared by gel-casting technique was studied by Fourier IR spectroscopy, attenuated total internal reflection spectroscopy, and optical microscopy. The influence of the filler nature, particle shape, and concentration on the pore structure formation of filled xerogels of ultra-high-molecular-weight polyethylene was examined.

P. M. Pakhomov; E. V. Nazarova; T. A. Anan'eva; Yu. N. Mikhailova; S. D. Khizhnyak

2003-01-01

315

Evidence from subunit molecular weight suggests hybridization was the source of the phosphoglucose isomerase gene duplication in Clarkia  

Microsoft Academic Search

The apparent molecular weight of cytosolic phosphoglucose isomerase (PGI) subunits was evaluated in 18 species of Clarkia which have or do not have duplicated genes specifying this glycolytic enzyme. Species that lack the duplication had subunits of 59,000 or 60,400 whereas species with the duplication generally possessed two types of PGI subunits with these or closely similar molecular weights. The

L. D. Gottlieb; R. C. Higgins

1984-01-01

316

Effect of high or low molecular weight of components of feed on transmembrane flux during forward osmosis  

Microsoft Academic Search

The possible mechanism of water transport from feed to osmotic agent side during forward osmosis in situation when feed contains high or low molecular weight compounds and their combination has been presented. The orientation of membrane was found to influence the transmembrane flux. When the feed contains mixture of low and high molecular weight compounds mode I (feed towards the

Chetan A. Nayak; Satya Sriram Valluri; Navin K. Rastogi

2011-01-01

317

A Method for Following Changes in Molecular Weight Distributions of Polymers on Degradation: Development and Comparison with Ultrasonic Degradation Experiments  

Microsoft Academic Search

When polymers are degraded by submitting them to shearing action, neither the probability of scission of a macromolecule, as a function of molecular weight (MW), nor the probability distribution of the lengths of the resulting fragments is known a priori. Information about these probabilities can be obtained by comparing observed changes in the molecular weight distributions (MWD) of degrading polymer

B. M. E. Van der hoff; C. E. Gall

1977-01-01

318

Synthesis, characterization and performance of asymmetric polyethersulfone (PES) ultrafiltration membranes with polyethylene glycol of different molecular weights as additives  

Microsoft Academic Search

This paper reports the performance of asymmetric polyethersulfone ultrafiltration flat sheet membranes with polyethylene glycol (PEG) of different molecular weight as additives. The membranes were prepared by phase inversion process from casting solution containing polyethersulfone (PES) as polymer, N,N-dimethylformamide (DMF) as solvent and PEG of different molecular weights namely as PEG 200, PEG 400 and PEG 600 as additives. The

Ani Idris; Norashikin Mat Zain; M. Y. Noordin

2007-01-01

319

The effect of high molecular weight dextran sulfate on the production of interleukin-8 in monocyte cell culture  

Microsoft Academic Search

It has been demonstrated that high molecular weight dextran sulfate (HMDS) is involved in the activation of immune cells. We have shown that HMDS increases the concentration of interleukin (IL)-8 in the medium of monocyte cell culture, in a dose-dependent fashion, whereas under the same conditions, low molecular weight dextran sulfate (LMDS) does not exhibit any effect on IL-8 biosynthesis.

P. P Jagodzi?ski; M Lewandowska; R Januchowski; K Franciszkiewicz; W. H Trzeciak

2002-01-01

320

Accurate Calculations of Intermolecular Interaction Energies Using Explicitly Correlated Coupled Cluster Wave Functions and a Dispersion-Weighted MP2 Method  

NASA Astrophysics Data System (ADS)

Explicitly correlated coupled-cluster calculations of intermolecular interaction energies for the S22 benchmark set of Jure?ka, \\vsponer, ?erný, and Hobza (Chem. Phys. Phys. Chem. 2006, 8, 1985) are presented. Results obtained with the recently proposed CCSD(T)-F12a method and augmented double-? basis sets are found to be in very close agreement with basis set extrapolated conventional CCSD(T) results. Furthermore, we propose a dispersion-weighted MP2 (DW-MP2) approximation that combines the good accuracy of MP2 for complexes with predominately electrostatic bonding and SCS-MP2 for dispersion-dominated ones. The MP2-F12 and SCS-MP2-F12 correlation energies are weighted by a switching function that depends on the relative HF and correlation contributions to the interaction energy. For the S22 set, this yields a mean absolute deviation of 0.2 kcal/mol from the CCSD(T)-F12a results. The method, which allows obtaining accurate results at low cost, is also tested for a number of dimers that are not in the training set.

Marchetti, Oliver; Werner, Hans-Joachim

2009-10-01

321

Accurate static and dynamic properties of liquid-electrolytes for Li-ion batteries from ab initio molecular dynamics  

SciTech Connect

Lithium-ion batteries have the potential to revolutionize the transportation industry, as they did for wireless communication. A judicious choice of the liquid electrolytes used in these systems is required to achieve a good balance among high-energy storage, long cycle life and stability, and fast charging. Ethylene-carbonate (EC) and propylene-carbonate (PC) are popular electrolytes. However, to date, almost all molecular-dynamics simulations of these fluids rely on classical force fields, while a complete description of the functionality of Li-ion batteries will eventually require quantum mechanics. We perform accurate ab initio molecular-dynamics simulations of ethylene- and propylene-carbonate with LiPF6 at experimental concentrations to build solvation models which explain available neutron scattering and nuclear magnetic resonance (NMR) results and to compute Li-ion solvation energies and diffusion constants. Our results suggest some similarities between the two liquids as well as some important differences. Simulations also provide useful insights into formation of solid-electrolyte interphases in the presence of electrodes in conventional Li-ion batteries.

Ganesh, Panchapakesan [ORNL; Jiang, Deen [ORNL; Kent, Paul R [ORNL

2011-01-01

322

Comparison between Airway Responses to High versus Low Molecular Weight Compounds in Occupational Asthma  

PubMed Central

Occupational asthma (OA) is a heterogeneous disease, and the characteristics of the sensitizer responsible for OA may induce different clinical, functional, and biological manifestations. We examined the characteristics of 74 patients with OA induced by low molecular weight compounds (LMWC) or by high molecular weight compounds (HMWC) and diagnosed by specific inhalation challenge (SIC). Patients with OA induced by LMWC had a longer occupational exposure before the beginning of symptoms, a lower sputum eosinophilia, and a higher prevalence of late airway response (LAR), in comparison with patients with OA induced by HMWC. Pulmonary function tended to be poorer and atopy tended to be less frequent in LMWC-induced OA than in HMWC-induced OA. These data confirm and extend previous observations showing that the characteristics of the specific sensitizer inducing OA may determine different clinical, functional, and biological features, probably related to the difference pathogenetic mechanisms underlying these different types of OA.

Talini, D.; Novelli, F.; Bacci, E.; Dente, F. L.; De Santis, M.; Di Franco, A.; Melosini, L.; Vagaggini, B.; Paggiaro, P. L.

2011-01-01

323

Comparison between Airway Responses to High versus Low Molecular Weight Compounds in Occupational Asthma.  

PubMed

Occupational asthma (OA) is a heterogeneous disease, and the characteristics of the sensitizer responsible for OA may induce different clinical, functional, and biological manifestations. We examined the characteristics of 74 patients with OA induced by low molecular weight compounds (LMWC) or by high molecular weight compounds (HMWC) and diagnosed by specific inhalation challenge (SIC). Patients with OA induced by LMWC had a longer occupational exposure before the beginning of symptoms, a lower sputum eosinophilia, and a higher prevalence of late airway response (LAR), in comparison with patients with OA induced by HMWC. Pulmonary function tended to be poorer and atopy tended to be less frequent in LMWC-induced OA than in HMWC-induced OA. These data confirm and extend previous observations showing that the characteristics of the specific sensitizer inducing OA may determine different clinical, functional, and biological features, probably related to the difference pathogenetic mechanisms underlying these different types of OA. PMID:21747871

Talini, D; Novelli, F; Bacci, E; Dente, F L; De Santis, M; Di Franco, A; Melosini, L; Vagaggini, B; Paggiaro, P L

2011-01-01

324

Managing cancer-related venous thromboembolic disease: low-molecular-weight heparins and beyond.  

PubMed

Venous thromboembolism is a major contributor to the morbidity and mortality of patients with cancer. For patients undergoing cancer surgery, several trials support the safety and efficacy of unfractionated heparin and of low-molecular-weight heparin for the prevention of venous thromboembolism, while data regarding the efficacy and safety of these agents in the setting of medical hospitalization is less definitive and must be extracted from trials including noncancer patients with different thrombotic risk factors. Randomized clinical studies confirm that patients with cancer who develop venous thromboembolism have superior outcomes when treated with long-term low-molecular-weight heparin as compared with warfarin. Novel anticoagulants that are orally bioavailable and function by directly inhibiting factor Xa or thrombin are entering the market. To date, data regarding the efficacy and safety of these novel anticoagulants as venous thromboembolism prophylaxis and treatment in cancer patients are not available and must be extracted from larger trials with heterogeneous patient populations. PMID:21082922

O'Connell, Casey L; Liebman, Howard A

2008-12-01

325

Identification of a high-molecular-weight (greater than 400 000) protein in hyaline cartilage.  

PubMed

A high-molecular-weight (greater than 400 000) non-collagenous protein has been identified in normal articular cartilage from several mammalian species and in bovine tracheal cartilage. This protein is reduced by 2-mercaptoethanol to subunits with a molecular weight of 116 000, which appear to constitute approx. 2-4% of the total protein detectable by the Lowry assay in 4 M guanidinium chloride extracts of normal bovine and canine articular cartilage. Antiserum to the 116 kDa subunit protein from bovine articular cartilage cross-reacts with the intact and subunit proteins from bovine trachea and from normal canine, porcine and human articular cartilage. This protein is not found in non-cartilagenous tissues, suggesting that it is a cartilage-specific protein. We conclude that the greater than 400 kDa protein and its subunit are ubiquitous and quantitatively significant proteins in hyaline cartilage. PMID:6095921

Fife, R S; Brandt, K D

1984-12-20

326

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

327

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

328

Synthesis and self-assembly of 1-deoxyglucose derivatives as low molecular weight organogelators  

PubMed Central

Summary Low molecular weight gelators are an important class of molecules. The supramolecular gels formed by carbohydrate derived low molecular weight gelators are interesting soft materials that show great potential for many applications. Previously, we have synthesized a series of methyl 4,6-O-benzylidene-?-D-glucopyranoside derivatives and found that several of them are good gelators for water, aqueous mixtures of DMSO, or aqueous mixtures of ethanol. The gelation efficiency of these glycolipid derivatives is dependent upon the structures of their acyl chains. In order to understand the influence of the anomeric position of the sugar headgroup towards self-assembly, we synthesized a series of 1-deoxyglucose analogs, and examined their gelation properties in several solvents. Several long chain esters, including diacetylene containing esters, and aryl esters exhibited gelation in ethanol, aqueous ethanol, or aqueous DMSO. The synthesis and characterization of these novel analogs are reported.

Yang, Hao; Cheuk, Sherwin; Coleman, Sherman

2011-01-01

329

Standard method for estimating apparent vapor pressures and molecular weights of lubricating oils  

SciTech Connect

This method provides a calculation procedure for converting data obtained by ASTM Method D 972, Test for Evaporation Loss of Lubricating Greases and Oils, to apparent vapor pressures and molecular weights. It has been demonstrated to be applicable to petroleum based and synthetic ester lubricating oils, at temperatures of 394 to 533 K (250 to 500/sup 0/F). However, its applicability to lubricating greases has not been established. The test is run at the selected temperature for a sufficient time to give the selected amount of evaporation, which is 5 +- 1 percent unless otherwise specified. This evaporation rate is compared with a standard value for pure m-terphenyl to yield the apparent vapor pressure and molecular weight of the lubricating oil.

Not Available

1980-01-01

330

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

331

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

332

Participation of low molecular weight electron carriers in oxidative protein folding.  

PubMed

Oxidative protein folding is mediated by a proteinaceous electron relay system, in which the concerted action of protein disulfide isomerase and Ero1 delivers the electrons from thiol groups to the final acceptor. Oxygen appears to be the final oxidant in aerobic living organisms, although the existence of alternative electron acceptors, e.g. fumarate or nitrate, cannot be excluded. Whilst the protein components of the system are well-known, less attention has been turned to the role of low molecular weight electron carriers in the process. The function of ascorbate, tocopherol and vitamin K has been raised recently. In vitro and in vivo evidence suggests that these redox-active compounds can contribute to the functioning of oxidative folding. This review focuses on the participation of small molecular weight redox compounds in oxidative protein folding. PMID:19399252

Margittai, Eva; Csala, Miklós; Mandl, József; Bánhegyi, Gábor

2009-03-01

333

Compressive deformation of phenol formaldehyde (PF) resin-impregnated wood related to the molecular weight of resin  

Microsoft Academic Search

The effects of molecular weight of PF resin on the deformation behaviour of NaClO2 treated resin-impregnated wood during compression were investigated. Blocks of Japanese cedar were subjected to 2% NaClO2 aqueous solution. This was repeated up to four times resulting in a weight loss of 28%. Treated and untreated samples were\\u000a impregnated with PF resin having different molecular weight. With

Hiroyuki Yano

2011-01-01

334

Chemically synthesized high molecular weight poly(2,2?-dithiodianiline) (PDTDA) as a cathode material for lithium rechargeable batteries  

Microsoft Academic Search

A high molecular weight poly(2,2?-dithiodianiline) (PDTDA) was chemically synthesized by simple solution polymerization method. The weight average molecular weight (M?w) was observed to be 420,000 by GPC analysis. The chemical structures of the undoped and the doped PDTDA were characterized by UV-Vis spectroscopy. It was confirmed that the S?S bonds within repeating units could be conserved well after polymerization and

Young-Gi Lee; Kwang Sun Ryu; Soon Ho Chang

2003-01-01

335

Evaluation of circulation profiles of liposomes coated with hydrophilic polymers having different molecular weights in rats  

Microsoft Academic Search

The purpose of this study was to evaluate the circulating properties of liposomes coated with modified polyvinyl alcohol (PVA-R) having different molecular weights (6000, 9000 and 20?000). The size controlled liposomes (egg phosphatidylcholine (or distearoylphosphatidylcholine):cholesterol=7:3 in a molar ratio) were prepared by the hydration method followed by sonication. Polymer coated liposomes were prepared by just mixing the resultant liposomal suspension

Hirofumi Takeuchi; Hiroyuki Kojima; Hiromitsu Yamamoto; Yoshiaki Kawashima

2001-01-01

336

Partial characterization of a non-proteinaceous, low molecular weight antigen of Eimeria tenella  

Microsoft Academic Search

A low molecular weight (LMW) antigen of Eimeria tenella, initially identified using a murine monoclonal antibody (mAb C34F1) raised against E. tenella sporozoites, was partially characterized using enzymatic degradation, solvent extraction, and immunization into various inbred\\u000a lines of mice. The LMW antigen could be isolated using Folch extraction (methanol\\/chloroform\\/water) and the epitope recognized\\u000a by mAb C34F1 was resistant to degradation

John R. Barta; Shan A. Tennyson; Marco L. Schito; Harry D. Danforth; Donald S. Martin

2000-01-01

337

Analytical Validation and Biological Evaluation of a High-Molecular-Weight Adiponectin ELISA  

Microsoft Academic Search

Background: Of the 3 circulating multimeric forms of adiponectin, the high-molecular-weight (HMW) form, as measured by size-exclusion and\\/or immunoblotting tech- niques, is a better index of insulin sensitivity for monitor- ing health and disease than is total adiponectin. We aimed to develop a simple ELISA to measure HMW adiponectin. Methods: We pretreated serum or plasma samples with digestion solution containing

Madhur K. Sinha; Traci Songer; Qiang Xiao; John H. Sloan; Jin Wang; Shaoquen Ji; William E. Alborn; Randy A. Davis; Michael M. Swarbrick; Kimber L. Stanhope; Bruce M. Wolfe; Peter J. Havel; Todd Schraw; Robert J. Konrad; Philipp E. Scherer; Jehangir S. Mistry

2007-01-01

338

In vitro phosphorylation of high molecular weight glutenin subunits from wheat endosperm  

Microsoft Academic Search

We have investigated the in vitro phosphorylation of high molecular weight glutenin subunits (HMW-GS), a group of non-soluble proteins present in wheat endosperm. Computer aided searches of potential biological sites in the known sequences of these proteins have evidenced the presence of sequence motifs specific for protein kinase C (PKC), calcium-dependent protein kinase from wheat, casein kinase II, tyrosine protein

Angelo M Facchiano; Giovanni Colonna; Emilio Chiosi; Gennaro Illiano; Annamaria Spina; Domenico Lafiandra; Francesco Buonocore

1999-01-01

339

Effect of molecular weight on the polymorphic transformation of isotactic poly(1-butene)  

Microsoft Academic Search

The effect of molecular weight on the polymorphic transformation of isotactic poly(1-butene)(iPB) under room temperature had been investigated by fourier transform infrared spectroscopy(FT-IR). The phase transformation time, phase transformation rate and phase transformation time difference between phase I and phase II at a given transformation degree were used to analysis the phase transformation kinetics of iPB aging at room temperature.

Aihua He; Chunsheng Xu; Huafeng Shao; Wei Yao; Baochen Huang

2010-01-01

340

Supramolecular association induced by Fe(III) in low molecular weight sodium polyacrylate  

Microsoft Academic Search

A supramolecular association between the sodium salt of a low molecular weight polyacrylic acid (PAA, Mw=1200) and Fe(III) is described and characterized using ultrafiltration (UF), gel permeation chromatography (GPC), dynamic light scattering (DLS), and infrared spectrometry (FTIR). The GPC and DLS experiments indicate the presence of massive and polydisperse aggregates of PAA linked by Fe(III) of ca. 100nm in size.

Roberto Baigorri; José María García-Mina; Gustavo González-Gaitano

2007-01-01

341

Conversion of proinsulin to insulin: involvement of a 31,500 molecular weight thiol protease.  

PubMed Central

A lysed crude secretory granule fraction from rat islets of Langerhans was shown to process endogenous proinsulin to insulin with a pH optimum of 5.0--6.0. The converting activity in the lysed fraction was not inhibited by serine protease inhibitors (diisopropyl fluorophosphate, soybean trypsin inhibitor, and aprotinin) or metalloprotease inhibitors (EDTA and o-phenanthroline) but was inhibited by some thiol protease reagents (p-chloromercuribenzenesulfonic acid, antipain, and leupeptin) but not by others (N-ethylmaleimide and iodoacetamide). N alpha-p-Tosyl-L-lysyl chloromethyl ketone only mildly inhibited at higher concentrations, whereas L-alanyl-L-lysyl-L-arginyl chloromethyl ketone was a powerful inhibitor. L-Alanyl-L-lysyl-L-arginyl chloromethyl ketone was [125I]iodotyrosylated and used as an affinity labeling agent for the converting activity. Because the crude granule preparation contained contaminating lysosomes the affinity labeling of the granule preparation proteins was compared with that in liver lysosomes purified from rats injected with Triton WR1339. In the crude granule fraction the affinity label bound in a cysteine-enhanced manner to a single 31,500 molecular weight protein, but in purified liver lysosomes the major affinity-labeled protein had a molecular weight of 25,000 and minor 31,500 and 35,000 molecular weight proteins were also labeled. Evidence suggests that these proteins are thiol proteases and that in islets the 31,500 molecular weight thiol protease is involved in the conversion of proinsulin to insulin. Images

Docherty, K; Carroll, R J; Steiner, D F

1982-01-01

342

Low Molecular Weight Soluble Starch and its Relationship with Sorghum Couscous Stickiness  

Microsoft Academic Search

Soluble carbohydrates from sorghum couscous were extracted with water and subjected to low-pressure, size-exclusion chromatography (SEC). Differences were observed in their amount and composition in couscous produced from different sorghum cultivars. When chromatographed on a high cut-off Sepharose CL-2B column, the soluble carbohydrates eluted at a molecular weight lower than that of amylose. Two distinct peaks were obtained when the

A Aboubacar; BR Hamaker

2000-01-01

343

The influence of the molecular weight of polyformaldehyde on some prcperties of the textured yarn  

Microsoft Academic Search

In this article the results are reported of an analysis of the influence of the molecular weight of polyformaldehyde (PF) on the crimpability of the filament after the relaxation of the deformation in the loose state immediately after stretching, and on certain physico-mechanical properties of the textured yarn. The experiments were carried out with copolymers of trioxane and 1,3-dioxalan (.the

I. I. Podkuiko; B. A. Egorov; A. V. Yudin

1975-01-01

344

Low-molecular-weight heparin in pediatric patients with thrombotic disease: A dose finding study  

Microsoft Academic Search

OBJECTIVE: To compare low-molecular-weight preparations of heparin (LMWH) with standard heparin in children requiring anticoagulant treatment for thromboembolic disease. METHODS: We treated 25 children who required heparin, but were at significant risk of bleeding, with LMWH (enoxaparin, Rhone-Poulenc Rorer). The median age was 4 years (range, newborn to 17 years), with nine infants less than 2 months of age. Fourteen

Patti Massicotte; Margaret Adams; Velma Marzinotto; Lu Ann Brooker; Maureen Andrew

1996-01-01

345

Exposure assessment of high molecular weight sensitisers: contribution to occupational epidemiology and disease prevention  

PubMed Central

An important group of sensitising agents are so called high molecular weight sensitisers--proteins or glycoproteins with molecular weights in the 5-70 kDa range that can provoke a specific IgE response in workers exposed to these agents. Exposure to high molecular weight sensitisers could only be evaluated indirectly in the recent past. Few measurement techniques existed that made it possible to measure the allergens directly. As a result, few studies focused on establishing exposure- response relations, and exposure standards have not been established for high molecular weight sensitisers, or those that have are of doubtful scientific basis. Recent use of immunoassays changed this perspective dramatically. Antibodies used in the assays can originate from human serum (sensitized workers), serum from sensitised animals (rabbits producing polyclonal antibodies), or animal derived cell cultures producing monoclonal antibodies. Although few comparative studies exist, the available evidence suggests that although the correlation of allergen concentrations obtained with different assays is good, large systematic differences occur. The use of conversion factors to make data from previously performed allergen measurements comparable or exchangeable is limited and thorough standardization of assays is preferred. Validation and comparison of different assays by comparisons between laboratories seem important issues that have not received the attention needed. Epidemiological studies in several industries that used immunoassay for the exposure characterisation have shown that risk of sensitisation increases with increasing exposure to allergens. Several studies have also shown that clear differences in potency seem to exist. Sensitisation to rat urinary allergens and fungal alpha-amylase occurred in the pg/m3 and ng/m3 range. The main research questions of the near future have to focus on the prevention of occupational sensitisation. Standard setting seems possible for some allergenson the basis of the available scientific evidence for the existence of exposure response relations. However, assays for characterising exposure to allergens have to be rigorously standardised before they can be used under field conditions.  

Heederik, D.; Doekes, G.; Nieuwenhuijsen, M. J.

1999-01-01

346

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

347

Low-molecular weight organic composition of acid water from coconut oil soapstock  

Microsoft Academic Search

Soapstock from alkaline refining of coconut oil was acidified, and the resulting acid water after neutralization was subjected\\u000a to gas chromatography, electron-ionization and chemical-ionization mass spectroscopy, and high-performance liquid chromatography.\\u000a The chief low-molecular weight organic components were C4?C18 fatty acids, hydroxylated acids, and sugar alcohols. The prevalence of acids and total absence of phosphate compounds make\\u000a coconut acid water different

Arunthathi Sivasothy; Peter J. Reilly

1996-01-01

348

Alkali-Degraded Cornea Generates a Low Molecular Weight Chemoattractant for Polymorphonuclear Leukocytes  

Microsoft Academic Search

Purpose. The current study was designed to determine if a polymorphonuclear leukocyte (PMN) chemoattractant is derived from alkali-degraded whole cornea and to establish a range for its molecular weight. Methods. We utilized a collagen gel-visual chemotactic assay to quantify the directional move- ment of PMN exposed to alkali-degraded corneas (30 min or 24 hi). In this experiment, the sample to

Roswell R. Pfister; Jeffrey L. Haddox; Charnell I. Sommers

349

Structural and mechanical properties of nitrogen ion implanted ultra high molecular weight polyethylene  

Microsoft Academic Search

The structural and mechanical properties have been studied for ultra high molecular weight polyethylene (UHMWPE) implanted by 80 keV N2+, (40 keV N+) with fluencies ranging from 1×1014 to 5×1015 ions\\/cm2. Elastic recoil detection (ERD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) have been employed to study the structural change of UHMWPE before and after implantation. ERD results show that

J. S. Chen; S. P. Lau; Z. Sun; B. K. Tay; G. Q. Yu; F. Y. Zhu; D. Z. Zhu; H. J. Xu

2001-01-01

350

Properties of self-reinforced ultra-high-molecular-weight polyethylene composites  

Microsoft Academic Search

The physical properties of ultra-high-molecular-weight polyethylene (UHMWPE) fibre\\/UHMWPE matrix composites have been characterized. It was found that the tensile strength and modulus, and creep resistance, were significantly increased after incorporating UHMWPE fibres into a UHMWPE matrix. The longitudinal tensile strength of the resulting self-reinforced composite increased with fibre content, according to the law of mixtures. The transverse strength did not

Meng Deng; Shalaby W. Shalaby

1997-01-01

351

Cracking and Impingement in Ultra–High-Molecular-Weight Polyethylene Acetabular Liners  

Microsoft Academic Search

The purpose of this study was to determine the prevalence of crack formation in conventional ultra–high-molecular-weight polyethylene cups and its association with rim impingement, oxidation, and time in situ. One hundred twenty acetabular cups were retrieved during revision total hip arthroplasty. In 40% (48\\/120) of the retrieved specimens, multiple subsurface cracks of several millimeters in length were revealed by transillumination.

Michael V. Birman; Philip C. Noble; Michael A. Conditt; Steve Li; Kenneth B. Mathis

2005-01-01

352

Quasi-static and dynamic nanoindentation studies on highly crosslinked ultra-high-molecular-weight polyethylene  

Microsoft Academic Search

In four separate studies, the effect of three methods used to highly crosslink ultra-high-molecular-weight polyethylene (UHMWPE) (gamma irradiation, electron beam irradiation, and peroxide treatment) on the polymer's stiffness was investigated using quasi-static and dynamic nanoindentation. From the quasi-static studies, it was found that (a) the highest value of the elastic modulus, E (2240±157MPa) was obtained from specimens prepared from direct

Sanjay Mishra; Gladius Lewis; Joe Losby; Zaifeng Fan; Joon B Park

2004-01-01

353

Orientation softening in the deformation and wear of ultra-high molecular weight polyethylene  

Microsoft Academic Search

Stress-induced anisotropy is an important phenomenon in the plastic deformation of semi-crystalline linear high polymers. The significance of this phenomenon in the wear of ultra-high molecular weight polyethylene (UHMWPE) bearing surfaces in total joint-replacement prostheses is studied in this investigation. Both linear and crosslinked UHMWPE materials were studied by means of a sequential biaxial tensile test and a hip-joint simulator

A. Wang; D. C. Sun; S.-S. Yau; B. Edwards; M. Sokol; A. Essner; V. K. Polineni; C. Stark; J. H. Dumbleton

1997-01-01

354

Ultra high molecular weight polyethylene—II. Thermal and photo-oxidation  

Microsoft Academic Search

Thermal- and photo-oxidation of ultra high molecular weight polyethylene (UHMWPE) has been studied using FTIR and derivatisation techniques. The species responsible for the initiation of the oxidative process are peroxides, produced by mechano-oxidative degradation, which evolve through a non-radical concerted mechanism and form ester and acid species. A second oxidative process takes place. It has an induction period and is

L. Costa; M. P. Luda; L. Trossarelli

1997-01-01

355

Low molecular weight protamine-functionalized nanoparticles for drug delivery to the brain after intranasal administration  

Microsoft Academic Search

The development of new strategies for enhancing drug delivery to the brain is of great importance in diagnostics and therapeutics of central nervous diseases. Low-molecular-weight protamine (LMWP) as a cell-penetrating peptide possesses distinct advantages including high cell translocation potency, absence of toxicity of peptide itself, and the feasibility as an efficient carrier for delivering therapeutics. Therefore, it was hypothesized that

Huimin Xia; Xiaoling Gao; Guangzhi Gu; Zhongyang Liu; Ni Zeng; Quanyin Hu; Qingxiang Song; Lei Yao; Zhiqing Pang; Xinguo Jiang; Jun Chen; Hongzhuan Chen

2011-01-01

356

High-speed tribology of PFPEs with different functional groups and molecular weights coated on DLC  

Microsoft Academic Search

In this article, we study the friction and wear durability of perfluoropolyether (PFPE) with different functional groups and molecular weights (MW) for a range of disk rotational speeds (500–7200 rpm or 1.2–17.33 m\\/s). A 4 mm diameter silicon nitride ball under a normal load of 4 g was employed as slider against PFPE lubricated diamond like carbon (DLC) film on magnetic hard disk. The

M. Minn; S. K. Sinha; S.-K. Lee; H. Kondo

2006-01-01

357

Assessment of Outpatient Treatment of Deep-Vein Thrombosis With Low-Molecular-Weight Heparin  

Microsoft Academic Search

Background: Low-molecular-weight (LMW) hepa- rins are safe and effective for out-of-hospital treatment of acute deep-vein thrombosis (DVT) in a clinical trial setting. We examined the efficacy, safety, and feasibility of home treatment with LMW heparin of consecutive eli- gible patients with acute DVT in a routine care setting. In addition, we report our experience with patient com- pliance, acceptance, and

Linda Harrison; Joanne McGinnis; Mark Crowther; Jeffrey Ginsberg; Jack Hirsh

1998-01-01

358

Molecular Weight-Dependent Lymphatic Transfer of Exogenous Macromolecules from Large Intestine of Renal Insufficiency Rats  

Microsoft Academic Search

To study the lymphatic delivery of exogenous macromolecules via the enteral route in renal insufficiency, we determined the transfer selectivity to the systemic blood and lymph of fluorescein isothiocyanate-labeled dextrans of different average molecular weight (10, 18, 39, and 69kD). The compounds were administered into the large intestinal lumen of rats with occluded renal circulation, with the aid of lipid-surfactant

Hiroshi Yoshikawa; Kanji Takada; Shozo Muranishi

1992-01-01

359

Is Impaired Renal Function a Contraindication to the Use of Low-Molecular-Weight Heparin?  

Microsoft Academic Search

Background: Because of the risk of accumulation of an- ticoagulant effect, it has been suggested that patients with a creatinine clearance of 30 mL\\/min or less (0.50 mL\\/s) should be excluded from treatment with low-molecular- weight (LMW) heparin, or have anti-factor Xa heparin level monitoring performed. Objective: To assess the appropriateness of this rec- ommendation. Methods: We performed a systematic

Jeff Nagge; Mark Crowther; Jack Hirsh

2002-01-01

360

Effect of hyaluronic acid molecular weight on the morphology of quantum dot–hyaluronic acid conjugates  

Microsoft Academic Search

The morphological analysis of novel quantum dot–hyaluronic acid (QDot-HA) conjugates was carried out with a transmission electron microscope (TEM). Adipic acid dihydrazide-modified HA (HA-ADH) was synthesized and conjugated to quantum dots (QDots) having carboxyl terminal ligands which were activated with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydroxysulfosuccinimide (sulfo-NHS). HA molecules with a molecular weight (MW) of 20K, 234K and 3000K were used

Jiseok Kim; Sei Kwang Hahn

2008-01-01

361

High and low molecular weight tracers for the electron microscopical detection of sialoglycoconjugates  

Microsoft Academic Search

Summary  Hydrazide-derivative tracers of different molecular weights have been synthesized for use in the electron microscopical detection of sodium periodate-oxidized sialyl residues of glycoconjugates in various tissues and cells. Haemundecapeptide hydrazide, horseradish peroxidase hydrazide, andLimulus polyphemus haemocyanin hydrazide were obtained by coupling adipic acid dihydrazide to the tracers with the aid of water-soluble carbodiimide. The enzymatic tracers thus prepared retained their

Virgil Mure?an; Nicolae Simionescu

1987-01-01

362

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

363

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

364

Tribology of ultra-high molecular weight polyethylene disks molded at different temperatures  

Microsoft Academic Search

Tribological characteristics of ultra-high molecular weight polyethylene (UHMW-PE) disks molded at 130–190°C were studied. The highest crystallinity was obtained for the sheet molded at 130°C, but crystallinity decreased with increasing molding temperature. Beyond 150°C, the resultant crystallinity reached a constant level. The dynamic friction coefficients of these UHMW-PE disks were measured using a ball-on-disk friction tester. The friction coefficient decreased

Taku Aoike; Daisuke Yokoyama; Hiroki Uehara; Takeshi Yamanobe; Tadashi Komoto

2007-01-01

365

Heparin-Induced Thrombocytopenia: Acknowledging Its Presence in Low-Molecular Weight Heparin Therapy  

Microsoft Academic Search

Low-molecular weight heparin (LMWH) is associated with a lower incidence of heparin-induced thrombocytopenia (HIT) than is\\u000a unfractionated heparin. We describe a 75-year-old woman who developed HIT with thrombotic manifestations following the use\\u000a of nadroparin calcium. Subsequent anticoagulation was achieved with warfarin. This case serves to highlight an important complication\\u000a that cannot be ignored despite its low incidence. The majority of

Heng Joo Ng; Lai Heng Lee

2003-01-01

366

Molecular weight dependence of polyethylene glycol penetration across acetone-disrupted permeability barrier  

Microsoft Academic Search

\\u000a Abstract Previous studies have demonstrated that permeability barrier disruption by acetone treatment significantly enhances skin\\u000a permeability to both hydrophilic and amphipathic compounds, but not to highly lipophilic compounds. The purpose of the present\\u000a study was to investigate the dependence of permeability on molecular weight (MW) in acetone-disrupted hairless mouse skin\\u000a in contrast to normal skin. Penetration of polyethylene glycol (PEG)

J. C. Tsai; P. L. Hung; H. M. Sheu

2001-01-01

367

Low-Molecular-Weight, Biologically Active Compounds from Marine Pseudoalteromonas Species  

Microsoft Academic Search

We have examined the ability of marine Proteobacteria from the Pseudoalteromonas genus and Alteromonas macleodii to produce low-molecular-weight, biologically active compounds with antimicrobial and surface-active properties. A new marine bacterium, Pseudoalteromonas issachenkonii, exhibited a high level of biological activity and produced antifungal and hemolytic compounds. A detailed spectroscopic investigation based on UV, IR, high-resolution mass spectrometry, and 2D 1H and

Nataliya I. Kalinovskaya; Elena P. Ivanova; Yulia V. Alexeeva; Nataliya M. Gorshkova; Tatyana A. Kuznetsova; Andrey S. Dmitrenok; Dan V. Nicolau

2004-01-01

368

Low-Molecular-Weight Glycoprotein from Cattle Blood Serum: Structure and Properties  

Microsoft Academic Search

The amino acid composition, structure, and physicochemical properties of a low-molecular-weight glycoprotein from cattle blood serum (SGP) were studied. The content of carbohydrates (represented by mannose-rich oligosaccharides) amounted to 45–50 wt %. The value of the specific partial heat of SGP, measured by differential scanning calorimetry (DSC), equaled 1.8 J\\/(g K), which is characteristic of unfolded proteins. Circular dichroic (CD)

I. A. Yamskov; A. A. Vinogradov; A. N. Danilenko; L. A. Maslova; E. Yu. Rybakova; V. P. Yamskova

2001-01-01

369

Isolation and characterization of a high molecular weight actin-binding protein from Physarum polycephalum plasmodia  

PubMed Central

A high molecular weight actin-binding protein was isolated from the Physarum polycephalum plasmodia. The protein ( HMWP ) shares many properties with other high molecular weight actin-binding proteins such as spectrin, actin-binding protein from macrophages, and filamin. It has a potent activity to cross-link F-actin into a gel-like structure. Its cross-linking activity does not depend on calcium concentrations. Hydrodynamic studies have revealed that the protein is in the monomeric state of a polypeptide chain with molecular weight of approximately 230,000 in a high ionic strength solvent, while it self-associates into a dimer under physiological ionic conditions. Electron microscopic examinations of HMWP have shown that the monomer particle observed in a high ionic strength solvent is rod shaped with the two-stranded morphology very similar to that of spectrin. On the other hand, under physiological ionic conditions, the HMWP dimer shows the dumb-bell shape with two globular domains connected with a thin flexible strand.

1984-01-01

370

Purification of two high molecular weight toxins of Clostridium difficile which are antigenically related.  

PubMed

Two Cl. difficile toxins were isolated from cultures of Cl. difficile strain VPI 10463. A purification procedure to prepare homogenous Cl. difficile toxins is given. This procedure allows purification of high molecular weight toxins A and B without using immunaffinity chromatography. The main step of the purification is the separation of a partially purified toxin preparation over a FPLC-Mono Q column by anion exchange chromatography. The experimental conditions for a rechromatography were determined to prepare the two major toxic activities as homogenous high molecular weight proteins. Our toxin A has a molecular weight (Mr) of ca. 300 kDa and an IP of 4.7. The Mr of our toxin B is ca. 250 kDa, the isoelectric focusing gives rise to two bands one at 4.7 and the other at 4.8. The two bands represent charge isomers as have been described for other bacterial toxins. Both toxins differ in cytotoxicity testing by a factor of 1000 but have the same activity when tested in vivo. Toxin specific monoclonal antibodies (mabs) were elicited by separate immunization of mice either with toxin A or toxin B, respectively. All of our mabs cross react with pure toxin A and toxin B when tested by ELISA or Western Blotting. Some mabs strongly cross react indicating that both toxins have major epitopes in common. A hypothesis for the structural and possible functional relatedness between the two toxins is discussed. PMID:2467163

von Eichel-Streiber, C; Harperath, U; Bosse, D; Hadding, U

1987-05-01

371

Hydroprocessing of narrow-boiling gas oil fractions; Dependence of reaction kinetics on molecular weight  

SciTech Connect

This paper discusses how a heavy gas oil, produced by thermal coking of Athabasca bitumen, was fractionated into six narrow-boiling cuts of nominal 50{degrees} C width and a high-boiling residue. The average molecular weights of the fractions ranged from 187 for the lightest fraction to 653 for the high-boiling residue. The six distillate fractions were catalytically hydroprocessed in a 150-mL CSTR with a commercial Ni/Mo catalyst. Removal of sulfur and nitrogen and conversion of aromatic carbon decreased with increasing average molecular weight (AMW) of the feed. The apparent activation energies for hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) increased with increasing feed AMW. The observed and intrinsic rate constants for HDS and HDN decreased logarithmically with increasing feed AMW and were fitted by a power-law equation. The intrinsic activation energy did not change significantly with increasing feed AMW. The estimated effectiveness factor increased with increasing feed AMW for both reactions and passed through a maximum at a molecular weight of 362 for the feed.

Trytten, L.C.; Gray, M.R. (Alberta Univ., Edmonton, AB (Canada). Dept. of Chemical Engineering); Sanford, E.C. (Syncrude Canada Ltd., Edmonton, AB (Canada))

1990-05-01

372

INFLUENCE OF POLYMER MOLECULAR WEIGHT, TEMPERATURE, AND STRAIN RATE ON THE MECHANICAL PROPERTIES OF PBX 9501  

SciTech Connect

Compression and tensile measurements were conducted on newly formulated (baseline) and lower molecular weight (virtually-aged) plastic-bonded explosive PBX 9501. The PBX 9501 binder system is composed of nitroplasticized Estane 5703, TM a polyester polyurethane copolymer. The molecular weight of polyester urethanes can degrade with time as a function of hydrolysis, affecting the mechanical behavior of the polymer or a polymer composite material of high explosives, i.e. PBXs. The molecular weight of Estane 5703{trademark} was degraded by exposure to high temperature and humidity for different periods of time, and then formulated to produce ''virtually-aged'' PBX 9501 specimens. Quasi-static and dynamic compression tests were conducted on the baseline and virtually-aged PBX 9501 as a function of temperature and strain rate. Quasi-static tensile tests were also conducted as a function of temperature and test rate. Rate and temperature dependence was exhibited during both compression and tensile loading. Results also show significant differences between the baseline and virtually-aged specimens for the dynamic compression tests at -15 C, and for the quasi-static compression tests at -15 C, 22 C, and 50 C.

D. J. IDAR; D. G. THOMPSON; ET AL

2001-06-01

373

Interfacial microgels formed by oppositely charged polyelectrolytes and surfactants. 1. Influence of polyelectrolyte molecular weight.  

PubMed

The synergistic adsorption and complexation of polystyrene sulfonate, PSS (a highly charged anionic polyelectrolyte), and dodecyltrimethylammonium bromide, C12TAB (a cationic surfactant), at the air-water interface can lead to interfacial gels that strongly influence foam-film drainage and stability. The formation and characteristics of these gels have been studied as a function of PSS molecular weight by combining surface tension, ellipsometry, and foam-film drainage experiments. Simultaneously the solution electromotive force has been measured to track the polymer-surfactant interactions in the bulk solution. It has been found that there is a critical molecular weight for surface gelation as well as for bulk precipitation and aggregation. Furthermore, we show that for the lowest molecular weights, PSS adsorbs with C12TAB in compact layers at the air-water interface. In particular, for mixtures of C12TAB with the monomer compound of the PSS repeat unit (e.g. Mw = 208), interfacial complexation is found to be similar to that of catanionic mixtures (mixtures of surfactants of opposite charge). PMID:15986674

Monteux, Cécile; Llauro, Marie-France; Baigl, Damien; Williams, Claudine E; Anthony, Olivier; Bergeron, Vance

2004-06-22

374

Post-translational modification and stability of low molecular weight cyclin E.  

PubMed

Our laboratory has previously described the presence of five tumor-specific low molecular weight isoforms of cyclin E in both tumor cell lines and breast cancer patient biopsies. We have also shown that one of these low forms arises from an alternate start site, whereas the other four appear as two sets of doublets following cleavage through an elastase-like enzyme. However, the origin of both sets of doublets was unknown. Here, we demonstrate that the larger isoform of each doublet is the result of phosphorylation at a key degradation site. Through site-directed mutagenesis of different phosphorylation sites within the cyclin E protein, we discovered that phosphorylation of threonine 395 is responsible for generating the larger isoform of each doublet. Because phosphorylation of threonine 395 has been linked to the proteasome-mediated degradation of full length cyclin E, we examined the stability of T395A phospho-mutants in both non-tumorigenic mammary epithelial cells and tumor cells. The results revealed that the low molecular weight isoforms appear to be stable in both a tumor cell line and a non-tumor forming cell line regardless of the presence of this critical phosphorylation site. The stability of low molecular weight cyclin E may have implications for both tumorigenesis and treatment of tumors expressing them. PMID:19561641

Mull, B B; Cox, J; Bui, T; Keyomarsi, K

2009-09-01

375

The Effect of Molecular Weight on the Composite Properties of Cured Phenylethynyl Terminated Imide Oligomers  

NASA Technical Reports Server (NTRS)

As part of a program to develop high temperature/high performance structural resins for aeronautical applications, imide oligomers containing terminal phenylethynyl groups with calculated number average molecular weights of 1250, 2500 and 5000 g/mol were prepared, characterized, and evaluated as adhesives and composite matrix resins. The goal of this work was to develop resin systems that are processable using conventional processing equipment into void free composites that exhibit high mechanical properties with long term high temperature durability, and are not affected by exposure to common aircraft fluids. The imide oligomers containing terminal phenylethynyl groups were fabricated into titanium adhesive specimens and IM-7 carbon fiber laminates under 0.1 - 1.4 MPa for 1 hr at 350-371 C. The lower molecular weight oligomers exhibited higher cured Tg, better processability, and better retention of mechanical properties at elevated temperature without significantly sacrificing toughness or damage tolerance than the higher molecular weight oligomer. The neat resin, adhesive and composite properties of the cured polymers will be presented.

Smith, J. G., Jr.; Connell, J. W.; Hergenrother, P. M.

1997-01-01

376

Stable, concentrated solutions of high molecular weight polyaniline and articles therefrom  

DOEpatents

Stable, concentrated solutions of high molecular weight polyaniline. In order to process high quality fibers and other articles possessing good mechanical properties, it is known that solution concentrations of the chosen polymer should be in the range from 15-30% (w/w). Moreover, it is desirable to use the highest molecular weight consistent with the solubility properties of the polymer. However, such solutions are inherently unstable, forming gels before processing can be achieved. The present invention describes the addition gel inhibitors (GIs) to the polymer solution, thereby permitting high concentrations (between 15% and 30% (w/w)) of high molecular weight ((M.sub.w)>120,000, and (M.sub.n)>30,000) emeraldine base (EB) polyaniline to be dissolved. Secondary amines have been used for this purpose in concentrations which are small compared to those which might otherwise be used in a cosolvent role therefor. The resulting solutions are useful for generating excellent fibers, films, coatings and other objects, since the solutions are stable for significant time periods, and the GIs are present in too small concentrations to cause polymer deterioration. It is demonstrated that the GIs found to be useful do not act as cosolvents, and that gelation times of the solutions are directly proportional to the concentration of GI. In particular, there is a preferred concentration of GI, which if exceeded causes structural and electrical conductivity degradation of resulting articles. Heating of the solutions significantly improves solubility.

Mattes, Benjamin R. (Santa Fe, NM); Wang, Hsing-Lin (Los Alamos, NM)

1999-11-09

377

Stable, concentrated solutions of high molecular weight polyaniline and articles therefrom  

DOEpatents

Stable, concentrated solutions of high molecular weight polyaniline. In order to process high quality fibers and other articles possessing good mechanical properties, it is known that solution concentrations of the chosen polymer should be in the range from 15-30% (w/w). Moreover, it is desirable to use the highest molecular weight consistent with the solubility properties of the polymer. However, such solutions are inherently unstable, forming gels before processing can be achieved. The present invention describes the addition gel inhibitors (GIs) to the polymer solution, thereby permitting high concentrations (>15% (w/w)) of high molecular weight ((M.sub.w)>120,000, and (M.sub.n)>30,000) emeraldine base (EB) polyaniline to be dissolved. Secondary amines have been used for this purpose in concentrations which are small compared to those which might otherwise be used in a cosolvent role therefor. The resulting solutions are useful for generating excellent fibers, films, coatings and other objects, since the solutions are stable for significant time periods, and the GIs are present in too small concentrations to cause polymer deterioration. It is demonstrated that the GIs found to be useful do not act as cosolvents, and that gelation times of the solutions are directly proportional to the concentration of GI. In particular, there is a preferred concentration of GI, which if exceeded causes structural and electrical conductivity degradation of resulting articles. Heating of the solutions significantly improves solubility.

Mattes, Benjamin R. (Sante Fe, NM); Wang, Hsing-Lin (Los Alamos, NM)

2000-01-01

378

High-molecular-weight polysaccharide antigen from Pseudomonas aeruginosa immunotype 2.  

PubMed Central

Previously, we isolated a high-molecular-weight immunogenic polysaccharide (designated PS) from Pseudomonas aeruginosa immunotype 1 (IT-1). The method which we used was modified to permit the isolation of a similar PS from P. aeruginosa IT-2. This antigen was composed primarily of carbohydrate, had a complex monosaccharide composition, including sugars not found in the lipopolysaccharide, and was nonpyrogenic in rabbits and nontoxic in mice at high doses. This material protected mice from challenges with live homologous cells. P. aeruginosa IT-2 PS gave a line of identity with the O side chain of the lipopolysaccharide, but different from this polysaccharide in molecular weight, chemical composition, and ability to immunize mice actively. Lipopolysaccharide from P. aeruginosa IT-2 contained an immunological determinant not found on P. aeruginosa IT-2 PS, which was detected due to its stability during treatment with dilute alkali. Thus, we recovered a high-molecular-weight PS antigen from P. aeruginosa IT-2, which was serologically identical to the lipopolysaccharide O side chain but was chemically and physically distinct. Also, like P. aeruginosa IT-1 strains, P. aeruginosa IT-2 contains an alkali-stable immunodeterminant on the lipopolysaccharide that may represent a core-like antigen.

Pier, G B; Sidberry, H F; Sadoff, J C

1981-01-01

379

Isolation and characterization of a high-molecular-weight polysaccharide from the slime of Pseudomonas aeruginosa.  

PubMed Central

A procedure is described for isolating a high-molecular-weight polysaccharide (PS) from the slime of Pseudomonas aeruginosa immunotype 1. The resultant material, obtained from the void volume of a Sephadex G-100 column, was composed of carbohydrate and water. No lipopolysaccharide (LPS), 2-keto-3-deoxyoctonoate, heptose, phosphate, or protein was detectable, and nucleic acid contamination was generally below 1%. The carbohydrate composition of the PS was glucose, rhamnose, galactose, arabinose, and mannose. PS had a molecular weight of between 100,000 and 350,000 and did not disaggregate when chromatographed in the presence of sodium deoxycholate. An antigen immunologically indistinguishable from PS could be obtained from LPS by either acetic acid hydrolysis and column chromatography or by allowing solutions of LPS to stand at room temperature for 3 days. Some of this LPS-associated polysaccharide eluted as the void volume of a G-100 column but differed from PS by its lack of galactose and arabinose. LPS also contained an immunodeterminant not shared with PS that was detected by its stability to dilute alkali treatment (0.1 N NaOH, 37 degrees C, 2 h). PS was destroyed by alkali treatment. PS appeared to represent a form of LPS polysaccharide side chain that contains galactose and arabinose and is of a high molecular weight. Images

Pier, G B; Sidberry, H F; Zolyomi, S; Sadoff, J C

1978-01-01

380

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

381

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

382

Letter: Oral contraception and increased formation of high molecular weight derivatives of fibrinogen.  

PubMed

Experiments conducted in the writers' laboratory on oral contraception and increased formation of high molecular weight derivatives of fibrinogen confirm results of a report by L.O. Pilgeram and others on an increased formation of soluble fibrin in patients taking oral contraceptives. 7 healthy women 17-35 years old were examined before and during a 4-12 week period of treatment with an oral contraceptive containing norgestrel .25 mg and ethinyl estradio. .05 mg. On Days 24 and 26 of the anovulatory menstrual cycles, citrated plasma was chromatographed on a Biogel-A-5m-column. Fibrinogen-related material in the eluates were titrated manually with the staphylococcal clumping test, and the mean concentrations before and during contraception were calculated for each fraction. The results indicated 1) an unchanged elution position of the quantitatively increased fibrinogen, 2) increased amounts of high molecular weight derivatives in the early fractions, and 3) the elution position of the main fraction of high molecular weight derivatives in the position calculated for the fibrinogen-fibrin-dimer. Mathematical processing of the data suggests that the polymers represent 5.6% of the total amount of the fibrinogen peak, which would correspond to a monomer concentration of 2%-3%, assuming that a 1:1 complex of fibrinogen and fibrin monomers is formed. PMID:4441885

Asbeck, F; Bebber, J; van de Loo, J

1974-12-28

383

Tubulin and high-molecular-weight polypeptides as Giardia lamblia antigens.  

PubMed Central

We determined the antigenic specificities of nine murine monoclonal antibodies to Giardia lamblia. Four distinct antibody reaction patterns were detected by immunofluorescence with G. lamblia trophozoites. Four monoclonal antibodies which reacted with the body but not the flagella of the whole trophozoites recognized two polypeptides of 170,000 and 155,000 molecular weights by immunoblotting. Two antibodies reacting with both the flagella and body also reacted with 170,000- and 155,000-molecular-weight antigens. An antibody specific for the G. lamblia attachment disk and two specific for flagella by immunofluorescence were found to react with 53,000- and 55,000-molecular-weight polypeptides by immunoblotting. These antigens comigrated with purified bovine brain tubulin, and their respective antibodies reacted in immunoblots with purified bovine brain tubulin. The antigens identified in this report were found to be present in Giardia cytoskeletal preparations. All antigens were pronase labile and heat stable. Four strains of G. lamblia reacted similarly in immunofluorescence assays as well as in immunoblotting assays. Images

Torian, B E; Barnes, R C; Stephens, R S; Stibbs, H H

1984-01-01

384

The effects of high molecular weight hydroxyethyl starch solutions on platelets.  

PubMed

Physicochemical characteristics of hydroxyethyl starch (HES) molecules determine their side effects on hemostasis. Our aim in the present experiments was to test the antiplatelet effect of novel high molecular weight HES. Citrated whole blood was hemodiluted in vitro (0% and 20%) with either HES 550 (Hextend), HES 600 (6%Hetastarch-Baxter), HES 200 (Elohäst), or the solvent of Hextend in its commercially available solution. The availability of glycoprotein IIb-IIIa was assessed on nonstimulated and on agonist-induced platelets using flow cytometry. Glycoprotein IIb-IIIa availability increased significantly after hemodilution with Hextend and its solvent by 23% and 24%, respectively, but decreased in the presence of 6% Hetastarch-Baxter and Elohäst by 18% and 15%, respectively, with no significant difference between the latter two colloids. This study shows that Hextend does not inhibit platelet function as anticipated by its high molecular weight and degree of substitution. The unexpected platelet stimulating effect of Hextend is unique among the currently available HES preparations and may, at least in part, be induced by its solvent containing calcium chloride dihydrate (2.5 mmol/L). The platelet-inhibiting effect of 6%Hetastarch-Baxter was not significantly different from that of medium molecular weight HES 200. PMID:15333389

Deusch, Engelbert; Thaler, Ulrich; Kozek-Langenecker, Sibylle A

2004-09-01

385

Molecular weight dependence of the physical properties of protonated polyaniline films and fibers  

NASA Astrophysics Data System (ADS)

Polyaniline, (PANI) in the form of emeraldine base, was synthesized by polymerizing aniline in acid solutions at different sub-zero temperatures to give a range of molecular weights between 100,000 and 300,000 gmol-1. Molecular weights were measured using gel permeation chromatography (GPC). The polymers were formed into solvent-cast films using an acid processing technique, involving 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA) as the solvating/protonating acid group and dichloroacetic acid (DCA) plus formic acid (FA) as the solvent. The dried, free-standing films were stretched by drawing over a hot pin to align the polymer chains. Fibers were prepared by spinning more concentrated solutions into a butanone coagulation bath. Conductivity measurements were then made on the drawn films and fibers, and tensile test measurements performed to determine the peak stress and modulus of the drawn films and fibers. The reaction conditions under which the different polyanilines were synthesized, and their molecular weight, were found to have a definite effect upon both the electrical and mechanical properties of the drawn films and fibers. The drawn films and fibers can be used as mechanical actuators.

Adams, Phillip N.; Bowman, Danielle; Brown, Lori; Yang, Dali; Mattes, Benjamin R.

2001-07-01

386

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.

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

2012-01-01

387

Molecular weight distribution of phosphorus fraction of aquatic dissolved organic matter.  

PubMed

This study characterized dissolved organic phosphorus (DOP) that is discharged from the Everglades Agricultural Area as part of the larger pool of aquatic dissolved organic matter (DOM). Whole water samples collected at the Everglades stormwater treat area 1 West (STA-1 W) were fractionated using a batch ultrafiltration method to separate organic compounds based on apparent molecular weight (AMW). Each AMW fraction of DOM was characterized for phosphorus, carbon, nitrogen, UV absorbance, and fluorescence. The DOP content of the Everglades water matrix was characteristically variable constituting 4-56% of total phosphorus (TP) and demonstrated no correlation with dissolved organic carbon (DOC). Measured values for DOP exceeded 14?gL(-1) in four out of five sampling dates making phosphorus load reductions problematic for the stormwater treatment areas (STAs), which target inorganic phosphorus and have a goal of 10?gL(-1) as TP. The molecular weight distributions revealed 40% of DOP is high molecular weight, aromatic-rich DOM. The results of this research are expected to be of interest to environmental chemists, environmental engineers, and water resources managers because DOP presents a major obstacle to achieving TP levels <10?gL(-1). PMID:23466281

Ged, Evan C; Boyer, Treavor H

2013-05-01

388

New pepsin-solubilized low molecular weight collagenous component possibly unique to periodontal ligament.  

PubMed

Limited pepsin digestion of bovine periodontal ligament releases genetic types I, III, and V collagen and a high cystine containing low molecular weight collagenous component. Salt fractionation and molecular sieve chromatography allowed the isolation of the latter as an apparently pure homogeneous moiety which had an approximate molecular mass of 30 000 daltons. Reduction with mercaptoethanol yielded a single 10 000-dalton band on polyacrylamide gel electrophoresis in sodium dodecyl sulfate. This led us to conclude that the newly isolated low molecular weight collagen fragment consists of three similar molecular weight chains. Unreduced collagen-like glycoprotein (CGP) [Jander, R., Troyer, D., & Rauterberg, J. (1984) Biochemistry 23, 3675-3681] after extraction from tissues with collagen denaturing solvents yields the GP140 glycoprotein upon reduction and does not release any collagen fragment below 90 000 daltons upon mild or vigorous pepsin digestion. The GP140 glycoprotein [Heller-Harrison, R. A., & Carter, W. G. (1984) J. Biol. Chem. 259, 6858-6864] isolated by extraction under reducing and collagen denaturing solvent conditions did not yield a collagen fragment below 40 000 daltons after pepsin treatment. It was clearly shown that both CGP and GP140 yield type VI collagen fragments in the above-cited reports. Since this report demonstrates that the Mr 30 000 collagen fragment is only released by pepsin treatment of nondenaturing solvent treated periodontal ligament and that only very small peptides are found in denaturing solvent treated tissue after pepsin digestion, it is concluded that the newly isolated Mr 30 000 collagen fragment reported here is not derived from type VI collagen.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:3011074

Yamauchi, M; Kuboki, Y; Sasaki, S; Mechanic, G L

1986-04-22

389

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

390

Characterization of low-molecular-weight antiyeast metabolites produced by a food-protective Lactobacillus-Propionibacterium coculture.  

PubMed

We developed a pH-controlled batch fermentation process with separately immobilized cells of the protective coculture of Lactobacillus paracasei subsp. paracasei SM20 and Propionibacterium jensenii SM11 in supplemented whey permeate medium yielding cell-free supernatants with high antiyeast activity against Candida pulcherrima and Rhodotorula mucilaginosa. The antiyeast compounds were resistant to proteinase K and pronase E treatments and showed high heat resistance (121 degrees C for 15 min). Diafiltration (1,000-Da cutoff) revealed that the inhibitory metabolites have low molecular weights. Partial purification of active compounds was achieved by a microplate bioassay controlled procedure with solid-phase extraction (C18) followed by (i) gel filtration chromatography or (ii) semipreparative reverse-phase high-performance liquid chromatography (C18). In addition to propionic, acetic, and lactic acids, 2-pyrrolidone-5-carboxylic acid, 3-phenyllactic acid, hydroxyphenyllactic acid, and succinic acid were identified by chromatography and mass spectrometry. Accurate quantifications revealed only low concentrations (up to 7 mM) of 2-pyrrolidone-5-carboxylic acid, 3-phenyllactic acid, and hydroxyphenyllactic acid produced during fermentation in contrast to relatively high MICs (50 to more than 500 mM) determined at different pH values (4.0, 5.0, and 6.0). Succinic acid was present at higher concentrations (29 mM) in cell-free supernatants but with comparable high MICs (200 to more than 500 mM and pH 4.0, 5.0, and 6.0). Although none of these compounds was the main substance responsible per se for suppression of yeast growth, our study revealed a complex antiyeast mechanism with putative synergistic effects between several low-molecular-weight compounds. PMID:19244902

Schwenninger, Susanne Miescher; Lacroix, Christophe; Truttmann, Stefan; Jans, Christoph; Spörndli, Cäcilia; Bigler, Laurent; Meile, Leo

2008-12-01

391

Accurate molecular structures and infrared spectra of trans-2,3-dideuterooxirane, methyloxirane, and trans-2,3-dimethyloxirane.  

PubMed

Oxirane derivatives are the most used benchmarks for chiroptical spectroscopies in view of their small size and relative rigidity. The molecular structure, vibrational harmonic and anharmonic frequencies, and infrared intensities of the ground electronic states are analyzed in this paper. Equilibrium structure and harmonic force fields have been evaluated by means of high-level quantum-chemical calculations at the coupled-cluster level including single and double excitations together with a perturbative treatment of triples (CCSD(T)). Extrapolation to the complete basis-set limit as well as core-correlation effects have also been taken into account. Anharmonic contributions have been computed at the CCSD(T)/cc-pVTZ level for trans-2,3-dideuterooxirane. These data can serve as references to evaluate the accuracy of less expensive computational approaches rooted in the density functional theory (DFT). The latter have been used within hybrid CC/DFT approaches, which have been applied to simulate fully anharmonic infrared (IR) spectra. Finally, the best theoretical estimates of the equilibrium structures and vibrational wavenumbers are compared to the most accurate experimental data and show in all cases very good agreement, i.e., within 0.001 Å, 0.1 deg, 10 cm(-1), and 0.5 km mol(-1), for bond lengths, angles, wavenumbers, and IR intensities, respectively. PMID:25053301

Barone, Vincenzo; Biczysko, Malgorzata; Bloino, Julien; Puzzarini, Cristina

2014-07-21

392

Properties and biodegradability of ultra-high-molecular-weight poly[( R)-3-hydroxybutyrate] produced by a recombinant Escherichia coli  

Microsoft Academic Search

Ultra-high-molecular-weight poly[(R)-3-hydroxybutyrate] (P(3HB)) (Mw=3–11×106) was produced from glucose by a recombinant Escherichia coli XL1-Blue (pSYL105) harboring Ralstonia eutropha H16 polyhydroxyalkanoate (PHA) biosynthesis genes. Morphology of ultra-high-molecular-weight P(3HB) granules in the recombinant cells was studied by transmission electron microscopy. The recombinant E. coli contained several P(3HB) granules within a cell. Freeze-fracture morphology of ultra-high-molecular-weight P(3HB) granules showed the needle-type as that

Satoshi Kusaka; Tadahisa Iwata; Yoshiharu Doi

1999-01-01

393

Molecular Cloning and Sequencing of Three Granulocytic Ehrlichia Genes Encoding High-Molecular-Weight Immunoreactive Proteins  

PubMed Central

Granulocytic Ehrlichia was isolated from canine blood obtained from animals challenged with field-collected Ixodes scapularis and propagated in HL60 cells. PCR primers specific for the 16S ribosomal DNA (rDNA) of the Ehrlichia genogroup comprising E. equi, E. phagocytophila, and the agent of human granulocytic ehrlichiosis (HGE) amplified DNA from extracts of these cells. Sequence analysis of this amplified DNA revealed that it is identical to the 16S rDNA sequence of the HGE agent. A genomic library was constructed with DNA from granulocytic Ehrlichia and screened with pooled sera from tick-challenged, granulocytic Ehrlichia-infected dogs. Several clones were isolated and sequenced. Three complete genes encoding proteins with apparent molecular masses of 100, 130, and 160 kDa were found. The recombinant proteins reacted with convalescent-phase sera from dogs and human patients recovering from HGE. This approach will be useful for identifying candidate diagnostic and vaccine antigens for granulocytic ehrlichiosis and aid in the classification of genogroup members.

Storey, James R.; Doros-Richert, Linda A.; Gingrich-Baker, Cindy; Munroe, Kenneth; Mather, Thomas N.; Coughlin, Richard T.; Beltz, Gerald A.; Murphy, Cheryl I.

1998-01-01

394

A Critique of Asphaltene Fluorescence Decay and Depolarization-Based Claims about Molecular Weight and Molecular Architecture  

SciTech Connect

Relying on experimental and theoretical data available from the literature, it is shown that the conclusions derived from measurements of fluorescence decay and depolarization kinetic times as reported in a series of papers over the past decade are egregiously wrong. To start with, the decay time measurements were done with inappropriate instrumentation which resulted in misleading results. Misinterpretation of the results led to the mistaken conclusion that bichromophoric type molecules are absent from petroleum asphaltene and therefore the architecture of the asphaltene molecule features a single condensed cyclic core spiked with some alkyl chains, in spite of irrefutable chemical evidence to the contrary. It was further concluded that if the asphaltene core is a single condensed ring, then the fluorescence depolarization with rotational correlation time method is applicable for the molecular weight determination of asphaltene. This is definitely not so, since, regardless of any other considerations, asphaltene is a mixture of a plethora of different, unknown components, with unknown concentrations along with innumerable different, unknown and some known chromophores portraying widely different absorption coefficients, fluorescence quantum yields, and kinetic decay times. Consequently, asphaltene fluorescence is a highly complex function of the above attributes and as such it is a totally unsuitable property for its molecular weight determination. The injection of an incorrect, single condensed ring core architecture for asphaltene has caused some confusion in asphaltene chemistry that has now hopefully been settled.

Strausz,O.; Safarik, I.; Lown, E.; Morales-Izquierdo, A.

2008-01-01

395

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

396

Monte Carlo study of molecular weight distribution changes induced by degradation of ion beam irradiated polymers  

NASA Astrophysics Data System (ADS)

In this work we study a polymeric material that degrades upon irradiation due to the energy inhomogeneously deposited by heavy ion beams. Ion beam irradiation of polymers generates rather different effects than those induced by "classical" low ionizing particles such as electrons or gamma rays. This is due to the high electronic stopping power and the inhomogeneous distribution of deposited energy. This energy is transferred to the material within a small volume along the ion path forming the so called "nuclear track" or "latent track". The track size primarily depends on the ion velocity, and it is determined by the secondary electrons (delta rays) generated along the ion trajectory. By means of Monte Carlo simulations we first obtained equilibrated polymer configurations using a coarse-grained model, and then investigated the spatially inhomogeneous chain scission process due to the passage of the ions. The number average molecular weight, weight average molecular weight and the polydispersity were calculated as a function of track radius, scission probability within the ion track and irradiation fluence. Finally we compared our results with a numerical implementation of a model for random homogeneous degradation.

Chappa, V. C.; Pastorino, C.; del Grosso, M. F.; Arbeitman, C. R.; Müller, M.; García Bermúdez, G.

2010-10-01

397

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

398

Adsorption and solution properties of bottle-brush polyelectrolyte complexes: effect of molecular weight and stoichiometry.  

PubMed

Polyelectrolyte complexes (PECs) self-assembled from bottle-brush polyelectrolytes, having a cationic main chain and uncharged side chains, and linear anionic sodium polystyrenesulfonate (NaPSS) have been investigated with emphasis on (i) the charge density and side chain density of the bottle-brush polyelectrolyte, (ii) the molecular weight of NaPSS, and (iii) the charge stoichiometry of the mixture. Light scattering and electrophoretic mobility data demonstrate that small molecular complexes are formed when the PEO45 side chain density is sufficiently high to provide steric stabilization and prevent PEC aggregation. The adsorption of PECs on negatively charged silicon oxynitride was investigated using dual polarization interferometry, and the time evolution of the adsorbed amount and thickness was determined. Cationic, uncharged, and negatively charged complexes all adsorb to negatively charged silicon oxynitride, and maximum adsorption is achieved for positively charged complexes containing small amounts of PSS. The adsorbed amount and the kinetics of adsorption are reduced with increasing PSS content, and for any given stoichiometry with increasing PSS molecular weight. These findings are discussed in terms of the PEC structure and the ability of anionic polyelectrolytes to leave the PECs during adsorption. PMID:22471950

Shovsky, Alexander; Varga, Imre; Makuška, Ri?ardas; Claesson, Per M

2012-04-24

399

Accurate molecular structure and spectroscopic properties of nucleobases: a combined computational-microwave investigation of 2-thiouracil as a case study.  

PubMed

The computational composite scheme purposely set up for accurately describing the electronic structure and spectroscopic properties of small biomolecules has been applied to the first study of the rotational spectrum of 2-thiouracil. The experimental investigation was made possible thanks to the combination of the laser ablation technique with Fourier transform microwave spectrometers. The joint experimental-computational study allowed us to determine the accurate molecular structure and spectroscopic properties of the title molecule, but more importantly, it demonstrates a reliable approach for the accurate investigation of isolated small biomolecules. PMID:24002739

Puzzarini, Cristina; Biczysko, Malgorzata; Barone, Vincenzo; Peña, Isabel; Cabezas, Carlos; Alonso, José L

2013-10-21

400

Repeatability and reproducibility of thermal field-flow fractionation in molecular weight determination of processed natural rubber.  

PubMed

The purpose of this study is (1) to determine the repeatability and reproducibility of thermal field-flow fractionation (ThFFF) in measuring the molecular weight of compounded natural rubber, and (2) to examine the correlation between the molecular weights obtained from ThFFF and the rheological data. 8 batches of compounded natural rubber were obtained from a thermo-mechanical mastication process, and were analyzed by ThFFF in a designed testing sequence. ThFFF analysis showed the compounded natural rubbers range in weight-average molecular weight (M(w)) from 143,000 to 360,000. By taking into account both the short term variability (repeatability) as well as the long term variability (reproducibility) of the instrument, ThFFF was shown to be able to distinguish between samples differing by as little as 21,000 in M(w) and 15,600 in number-average molecular weight, M(n) (based on cis-polyisoprene calibration); and thus is a useful tool for the molecular weight analysis of natural rubber-related materials. It was also found that the rheological data (G' and tan delta) measured on both the virgin and the compounded natural rubber correlated well with the molecular weights obtained from ThFFF when normalized. PMID:16496053

Kim, Won-Suk; Eum, Chul Hun; Molnár, Attila; Yu, Jong-Sung; Lee, Seungho

2006-03-01

401

Suppression of pancreatic cancer by sulfated non-anticoagulant low molecular weight heparin.  

PubMed

Sulfated non-anticoagulant heparins (S-NACHs) might be preferred for potential clinical use in cancer patients without affecting hemostasis as compared to low molecular weight heparins (LMWHs). We investigated anti-tumor effects, anti-angiogenesis effects, and mechanisms of S-NACH in a mouse model of pancreatic cancer as compared to the LMWH tinzaparin. S-NACH or tinzaparin with or without gemcitabine were administered, and tumor luminescent signal intensity, tumor weight, and histopathology were assessed at the termination of the study. S-NACH and LMWH efficiently inhibited tumor growth and metastasis, without any observed bleeding events with S-NACH as compared to tinzaparin. S-NACH distinctly increased tumor necrosis and enhanced gemcitabine response in the mouse pancreatic cancer models. These data suggest the potential implication of S-NACH as a neoadjuvant in pancreatic cancer. PMID:24769074

Sudha, Thangirala; Yalcin, Murat; Lin, Hung-Yun; Elmetwally, Ahmed M; Nazeer, Tipu; Arumugam, Thiruvengadam; Phillips, Patricia; Mousa, Shaker A

2014-08-01

402

Molecular Cloning, Expression, and Immunogenicity of MTB12, a Novel Low-Molecular-Weight Antigen Secreted by Mycobacterium tuberculosis  

PubMed Central

Proteins secreted into the culture medium by Mycobacterium tuberculosis are thought to play an important role in the development of protective immune responses. In this report, we describe the molecular cloning of a novel, low-molecular-weight antigen (MTB12) secreted by M. tuberculosis. Sequence analysis of the MTB12 gene indicates that the protein is initially synthesized as a 16.6-kDa precursor protein containing a 48-amino-acid hydrophobic leader sequence. The mature, fully processed form of MTB12 protein found in culture filtrates has a molecular mass of 12.5 kDa. MTB12 protein constitutes a major component of the M. tuberculosis culture supernatant and appears to be at least as abundant as several other well-characterized culture filtrate proteins, including members of the 85B complex. MTB12 is encoded by a single-copy gene which is present in both virulent and avirulent strains of the M. tuberculosis complex, the BCG strain of M. bovis, and M. leprae. Recombinant MTB12 containing an N-terminal six-histidine tag was expressed in Escherichia coli and purified by affinity chromatography. Recombinant MTB12 protein elicited in vitro proliferative responses from the peripheral blood mononuclear cells of a number of purified protein derivative-positive (PPD+) human donors but not from PPD? donors.

Webb, John R.; Vedvick, Thomas S.; Alderson, Mark R.; Guderian, Jeffrey A.; Jen, Shyian S.; Ovendale, Pamela J.; Johnson, Stephen M.; Reed, Steven G.; Skeiky, Yasir A. W.

1998-01-01

403

Synthesis and characterization of bioresorbable in situ crosslinkable ultra low molecular weight poly(lactide) macromer.  

PubMed

Reactive low molecular weight poly(L-lactide) (PLA) is required to produce in situ hardened scaffolds with fast rate of crosslinking, high crosslink density, and adequate mechanical strength. The objective of this work was to synthesize unsaturated ultra low molecular weight PLA (ULMW PLA) as an injectable in situ crosslinkable macromer for biomedical applications. Low molecular weight PLA was synthesized by ring-opening polymerization of L-lactide (LA) using diethylene glycol (DEG) as the initiator. The molar ratio of the LA to DEG ranged from 5 to 20. Non-solvents methanol, ether, and hexane were used for purification and fractionation. The PLA samples that were precipitated in methanol and ether had narrow distributions (PDI=1.2) and resulted in a powder with M(n) of 4.8 and a wax with M(n) of 3.6 kDa, respectively. The PLA sample in which the supernatant from ether was re-precipitated in hexane produced a viscous ULMW PLA with M(n) and PDI of 1.2 kDa and 1.2, respectively. The ULMW PLA was reacted with fumaryl chloride to produce unsaturated in situ crosslinkable poly(lactide fumarate) (PLAF) macromer. Porous scaffolds were produced after injection and in situ crosslinking of the PLAF macromer with NVP crosslinker in the presence of a porogen. New bone was formed in the scaffold when it was implanted in nude mice which demonstrated that the scaffold was osteoconductive. PLAF is potentially useful as a reactive macromer in fabrication of bioresorbable injectable in situ crosslinkable scaffolds for tissue regeneration. PMID:17597374

Jabbari, Esmaiel; He, Xuezhong

2008-01-01

404

Effect of macromer molecular weight on in vitro ophthalmic drug release from photo-crosslinked matrices.  

PubMed

The objective of this study was to investigate the effect of poly(propylene fumarate) (PPF) molecular weight on the release kinetics of two ophthalmic model drugs, acetazolamide (AZ) and timolol maleate (TM), from matrices prepared by photo-induced copolymerization of PPF with N-vinyl pyrrolidone (NVP). PPF macromers of different number average molecular weight (M(n)) and polydispersity index (PI) were used in the experiments. Photo-crosslinked matrices were loaded with 5wt.% AZ or TM. The amounts of released drug and NVP were determined using high-performance liquid chromatography (HPLC). The release kinetics of both drugs was influenced by the molecular weight of the constituent PPF macromer. An increased M(n) led to an increased burst release and an accelerated drug release. Dependent on the PPF M(n), the initial AZ loading was released within periods ranging from 35 days (M(n) = 3670, PI = 1.9) to 220 days (M(n) = 2050, PI=1.5). TM-loaded matrices revealed similar release kinetics dependent on the PPF M(n). The amount of released NVP from photo-crosslinked matrices during the course of a release experiment was independent of the PPF M(n) for both drugs. Matrix swelling and erosion were determined gravimetrically. The network structures of non-loaded matrices were further characterized by determining their crosslinking densities and the relative double bond conversions of fumaric acid (FAA) and NVP. Independent of PPF M(n), PPF and NVP similarly participated in the formation of the PPF/polyNVP copolymer network. The observed differences in drug release might therefore be explained by differences in the microstructural organization of the copolymer networks. Overall, the results demonstrate that drug release kinetics from photo-crosslinked PPF/polyNVP matrices is strongly dependent on the M(n) of the PPF macromer. PMID:17938009

Haesslein, A; Hacker, M C; Mikos, A G

2008-01-01

405

The Role of High Molecular Weight Chains in Flow-Induced Crystallization Precursor Structures  

SciTech Connect

Flow-induced crystallization in a bimodal polyethylene blend was investigated by means of in situ shear-WAXD (wide-angle x-ray diffraction) and shear-SAXS (small-angle x-ray scattering) techniques. The blend contained a low molecular weight (M{sub w} = 50 000 g mol{sup -1} and polydispersity = 2) polyethylene copolymer matrix (MB-50k) with 2 mol% of hexene, and a nearly monodisperse high molecular weight (M{sub w} = 161 000 g mol{sup -1} and polydispersity = 1.1) hydrogenated polybutadiene component (MD-161k), which has the microstructure of an ethylene-butene copolymer with 4 mol% butene. At the experimental temperatures of 112 and 115 C, MB-50k exhibited faster crystallization kinetics and higher crystallinity due to higher chain mobility and higher ethylene content than those of the MB-50k/MD-161k blend. However, both WAXD and SAXS results indicated that the high molecular weight component (MD-161k) is responsible for the formation of more highly oriented crystals, which we relate to a shear-induced precursor scaffold. Values of the lamellar long period in all experimental runs were found to slightly decrease in the beginning of crystallization and then reached a plateau value. Vonk's method for single lamella scattering was employed to estimate the lamellar thickness in the MB-50k/MD-161k blend at high temperature (115 C), where the lamellar thickness was also found to decrease in the beginning and remained about constant afterward. Twisted lamellar structures were observed in all formed kebabs.

Yang,L.; Somani, R.; Scis, I.; Hsiao, B.; Kolb, R.; Lohse, D.

2006-01-01

406

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.

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

2013-01-01

407

Capture, enrichment, and mass spectrometric detection of low-molecular-weight biomarkers with nanoporous silicon microparticles.  

PubMed

Mining the disease information contained in the low-molecular-weight range of a proteomic profile is becoming of increasing interest in cancer research. This work evaluates the ability of nanoporous silicon microparticles (NPSMPs) to capture, enrich, protect, and detect low-molecular-weight peptides (LMWPs) sieved from a pool of highly abundant plasma proteins. The average pore size and porosity of NPSMPs are controlled by the electrochemical preparation conditions, and the critical parameters for admission or exclusion of protein with a definite molecular weight are determined by reflectometric-interference Fourier transform spectroscopy (RIFTS). Sodium dodecyl sulfate polyacrylamide-gel electrophoresis (SDS-PAGE) and matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) analysis of the proteins captured by the NPSMPs show that the chemical nature of the NPSMPs surface and the solution pH also play vital roles in determining the affinity of NPSMPs for target analytes. It is found that carboxyl-terminated porous microparticles with a porosity of 26% (pore diameter around 9.0 nm) specifically fractionate, enrich and protect LMWPs sieved from either simulated samples or human serum samples. Moreover, NPSMPs containing captured peptides can be directly spotted onto a MALDI plate. When placed in a conventional MALDI matrix, laser irradiation of the particles results in the release of the target peptides confined in the nanopores, which are then ionized and detected in the MALDI experiment. As a proof-of-principle test case, mass spectra of NPSMPs prepared using serum from colorectal cancer patients and from control patients can be clearly distinguished by statistical analysis. The work demonstrates the utility of the method for discovery of biomarkers in the untapped LMWP fraction of human serum, which can be of significant value in the early diagnosis and management of diseases. PMID:23184826

Tan, Jie; Zhao, Wei-Jie; Yu, Jie-Kai; Ma, Sai; Sailor, Michael J; Wu, Jian-Min

2012-11-01

408

A low molecular weight cut-off polymer–silicate membrane for microfluidic applications  

Microsoft Academic Search

In this article, we report a novel approach to fabricating a low molecular weight cut-off membrane that could readily be employed\\u000a for several microfluidic applications. The reported structure was created by selectively retaining a precursor solution [5%\\u000a (w\\/v) maleic anhydride, 21% (v\\/v) (37:1) acrylamide\\/bisacrylamide, and 0.2% (w\\/v) VA-086 photoinitiator] in a chosen location\\u000a of a microfluidic network via capillary forces

Gwendoline M. Toh; Naoki Yanagisawa; Robert C. Corcoran; Debashis Dutta

2010-01-01

409

O-acetylation of low-molecular-weight polysaccharide from Enteromorpha linza with antioxidant activity.  

PubMed

Polysaccharide extracted from green algae Enteromorpha linza (EP) is a sulfated polysaccharide, which possesses excellent antioxidant activities. In present study, the acetylated derivatives of low-molecular-weight polysaccharide (LEP) was prepared with the method of response surface quadratic model. And then the antioxidant activities of the derivatives were investigated including scavenging effects of superoxide and hydroxyl radicals. The results of chemical analysis and FT-IR spectrum showed the acetylation was successful. And in addition, certain derivative with different degree of substitution (DS) exhibited different antioxidant activity. PMID:24854210

Zhang, Zhongshan; Wang, Xiaomei; Zhao, Mingxing; Qi, Huimin

2014-08-01

410

A world of low molecular weight heparins (LMWHs) enoxaparin as a promising moiety--a review.  

PubMed

Anti-coagulants are one of the most important categories in healthcare therapeutics. For healthcare professionals dealing in cases of in-vivo blood clotting problems. Heparin and low molecular weight heparins (LMWHs) would be the first choice of drugs. This review represents an overview of the LMWHs, their importance over heparin and enlightens the advancements. In addition to these, different methods used for preparation and purification are discuss in terms of production and synthesis. Worldwide availability in pre-filled syringe, market, manufacturers and suppliers drug interactions, adverse drug reactions, in-vitro study, freezing/thawing process and structural differences of LMWHs are also focused upon in this review. PMID:24721062

Ingle, Rahul G; Agarwal, Aayush S

2014-06-15

411

Improved reproducibility in the determination of the molecular weight of chitosan by analytical size exclusion chromatography  

Microsoft Academic Search

The reproducibility of the determination of the molecular weight of chitosans in the 90–210kDa range (Mn) by analytical size exclusion chromatography with multi-angle laser light scattering (SEC-MALLS) was improved by reducing the salt concentration in the mobile phase from (0.3M acetic acid, 0.2M sodium acetate, and 0.8mM sodium azide) to (0.15M acetic acid, 0.1M sodium acetate, and 0.4mM sodium azide)

Sophie Nguyen; Françoise M. Winnik; Michael D. Buschmann

2009-01-01

412

Possible hypoglycemic effect of Aloe vera L. high molecular weight fractions on type 2 diabetic patients  

PubMed Central

Aloe vera L. high molecular weight fractions (AHM) containing less than 10 ppm of barbaloin and polysaccharide (MW: 1000 kDa) with glycoprotein, verectin (MW: 29 kDa), were prepared by patented hyper-dry system in combination of freeze–dry technique with microwave and far infrared radiation. AHM produced significant decrease in blood glucose level sustained for 6 weeks of the start of the study. Significant decrease in triglycerides was only observed 4 weeks after treatment and continued thereafter. No deterious effects on kidney and liver functions were apparent. Treatment of diabetic patients with AHM may relief vascular complications probably via activation of immunosystem.

Yagi, Akira; Hegazy, Sahar; Kabbash, Amal; Wahab, Engy Abd-El

2009-01-01

413

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

414

Computational and experimental investigation of DNA repair protein photolyase interactions with low molecular weight drugs.  

PubMed

This paper reports the previously unknown interactions between eight low molecular weight commercially available drugs (130-800 Da) and DNA repair protein photolyase using computational docking simulations and surface plasmon resonance (SPR) experiments. Theoretical dissociation constants, K(d), obtained from molecular docking simulations were compared with the values found from SPR experiments. Among the eight drugs analyzed, computational and experimental values showed similar binding affinities between selected drug and protein pairs. We found no significant differences in binding interactions between pure and commercial forms of the drug lornoxicam and DNA photolyase. Among the eight drugs studied, prednisone, desloratadine, and azelastine exhibited the highest binding affinity (K(d) = 1.65, 2.05, and 8.47 ?M, respectively) toward DNA photolyase. Results obtained in this study are promising for use in the prediction of unknown interactions of common drugs with specific proteins such as human clock protein cryptochrome. PMID:23657985

Azizo?lu, Selimcan; Kizilel, Riza; Maruši?, Maja; Kavakli, Ibrahim Halil; Erman, Burak; Kizilel, Seda

2013-07-01

415

Nanosecond and femtosecond UV laser ablation of polymers: Influence of molecular weight  

NASA Astrophysics Data System (ADS)

We examine the nanosecond and femtosecond UV laser ablation of poly(methyl methacrylate) (PMMA) as a function of molecular weight ( Mw). For laser ablation with nanosecond laser pulses, at the excimer wavelengths 248 nm and 193 nm, we show that high temperatures develop; yet the dynamics of material ejection differs depending on polymer Mw. The results on the nanosecond ablation of polymers are accounted within the framework of bulk photothermal model and the results of molecular dynamics simulations. Turning next to the 248 nm ablation with 500 fs laser pulses, the ablation threshold and etching rates are also found to be dependent on polymer Mw. In addition, ablation results in morphological changes of the remaining substrate. Plausible mechanisms are advanced.

Paun, Irina-Alexandra; Selimis, Alexandros; Bounos, Giannis; Kecskeméti, Gabriella; Georgiou, Savas

2009-09-01

416

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

417

The variations of the configurational and solvency properties of low molecular weight sodium polyacrylate with ionic strength  

Microsoft Academic Search

The configurational and solvency properties of low molecular weight sodium polyacrylate have been determined for a wide range of ionic strength solutions, from intrinsic viscosity data in the polymer literature.

K. R. Rogan

1995-01-01

418

Enzymatic polymerization of high molecular weight DNA amphiphiles that self-assemble into star-like micelles.  

PubMed

High molecular weight ssDNA amphiphiles are synthesized by enzymatic polymerization. These highly asymmetric diblock DNA copolymers self-assemble into "hairy", star-like micelles, shown in the AFM image and the DPD snapshot. PMID:24497034

Tang, Lei; Tjong, Vinalia; Li, Nan; Yingling, Yaroslava G; Chilkoti, Ashutosh; Zauscher, Stefan

2014-05-21

419

Fire Retardance Effectiveness of High Molecular Weight, High Oxygen Containing Inorganic Additives in Cellulosic and Synthetic Materials.  

National Technical Information Service (NTIS)

A feasibility study was conducted to determine whether high-molecular-weight inorganic additives, particularly those with high oxygen content, can be used effectively as permanent flame retardants for cotton, rayon, roofing material, nylon, and polyester....

A. E. Lipska

1972-01-01

420

The interrelations between high- and low-molecular-weight forms of normal and mutant (Krabbe-disease) galactocerebrosidase  

PubMed Central

Galactocerebrosidase (?-d-galactosyl-N-acylsphingosine galactohydrolase; EC 3.2.1.46) activity of brain and liver preparations from normal individuals and patients with Krabbe disease (globoid-cell leukodystrophy) have been separated by gel filtration into four different molecular-weight forms. The apparent mol.wts. were 760000±34000 and 121000±10000 for the high- and low-molecular-weight forms (peaks I and IV respectively) and 499000±22000 (mean±s.d.) and 256000±12000 for the intermediate forms (peaks II and III respectively). On examination by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis, the high- and low-molecular-weight forms revealed a single protein band with a similar mobility corresponding to a mol.wt. of about 125000. Antigenic identity was demonstrated between the various molecular-weight forms of the normal and the mutant galactocerebrosidases by using antisera against either the high- or the low-molecular-weight enzymes. The high-molecular-weight form of galactocerebrosidase was found to possess higher specific activity toward natural substrates when compared with the low-molecular-weight form. It is suggested that the high-molecular-weight enzyme is the active form in vivo and an aggregation process that proceeds from a monomer (mol.wt. approx. 125000) to a dimer (mol.wt. approx. 250000) and from the dimer to either a tetramer (mol.wt. approx. 500000) or a hexamer (mol.wt. approx. 750000) takes place in normal as well as in Krabbe-disease tissues. ImagesFig. 3.

Ben-Yoseph, Yoav; Hungerford, Melinda; Nadler, Henry L.

1980-01-01

421

Improved section adhesion for immunocytochemistry using high molecular weight polymers of l-lysine as a slide coating  

Microsoft Academic Search

Poly-l-lysine (PPL) has been used to coat glass slides in the preparation of tissue sections for immunocytochemical staining. The adhesive properties of different molecular weight (m.w.) polymers of l-lysine have been tested on pre-fixed cryostat sections which were subjected to a 3 day washing treatment. It has been found that the higher the molecular weight of the polymer, the greater

W. M. Huang; S. J. Gibson; P. Facer; J. Gu; J. M. Polak

1983-01-01

422

Extraction of high molecular weight hydrocarbons from source rocks: an example from the Green River Formation, Uinta Basin, Utah  

Microsoft Academic Search

Results of extraction experiments performed on immature Green River Formation source rock samples from the Black Shale Facies (Uinta Basin, Utah) demonstrate the potential of extracting high molecular weight hydrocarbons (HMWHC) with sequential dichloromethane:methanol\\/soxhlet and p-xylene\\/sonication techniques. The first soxhlet extraction step with DCM:MeOH removes lower molecular weight alkanes from the source rock while the HMWHC remain in the rock

Eric Mueller; R. Paul Philp

1998-01-01

423

Molecular Weight Dependence of Phase Behavior in Side-Chain Liquid Crystalline Polymer Which Exhibits Reentrant Nematic Phase  

Microsoft Academic Search

We prepared poly(6-[4-(4'-cyanophenyl)phenoxy]hexyl acrylate)s with various molecular weights (Mn) and narrow molecular weight distributions, and examined the Mn dependence of phase behavior which includes the reentrant nematic (RN) phase. Polymers with Mn lower than 20,000 form nematic (N), smectic A (SmA) and RN phases as temperature decreases, while ones with Mn higher than 20,000 form only N phase. The disappearance

Naoki Tomikawa; Tomomichi Itoh; Yusuke Okazaki; Mitsu-aki Adachi; Masatoshi Tokita; Junji Watanabe

2005-01-01

424

Blends of normal high density and ultra-high molecular weight polyethylene, ? irradiated at a low dose  

Microsoft Academic Search

The kinetics of a nonisothermal crystallization and melting of? irradiated with dose of 6 Mrad blends of an ultra-high molecular-weight polyethylene (UHMWPE) and a high-density polyethylene with normal molecular weight (NMWPE) is investigated by means of DSC. The blends have been prepared at temperature below the flow temperature of UHMWPE: The enthalpies of melting of the polyethylenes increase, while those

L. Minkova; M. Mihailov

1990-01-01

425

Effects of the molecular weight of hyaluronic acid and its action mechanisms on experimental joint pain in rats  

Microsoft Academic Search

OBJECTIVES--It has been shown previously that hyaluronic acid (HA) has an analgesic action on bradykinin induced pain in the knee joints of rats. This study further clarifies the effects of the molecular weight of HA and its mechanism of action in the same model using HA of molecular weight 800 to 2.3 x 10(6) daltons and a bradykinin antagonist. METHODS--Bradykinin

S Gotoh; J Onaya; M Abe; K Miyazaki; A Hamai; K Horie; K Tokuyasu

1993-01-01

426

THE MOLECULAR WEIGHT OF RHODOPSIN AND THE NATURE OF THE RHODOPSIN-DIGITONIN COMPLEX  

PubMed Central

The sedimentation behavior of aqueous solutions of digitonin and of cattle rhodopsin in digitonin has been examined in the ultracentrifuge. In confirmation of earlier work, digitonin was found to sediment as a micelle (D-1) with an s20 of about 6.35 Svedberg units, and containing at least 60 molecules. The rhodopsin solutions sediment as a stoichiometric complex of rhodopsin with digitonin (RD-1) with an s20 of about 9.77 Svedberg units. The s20 of the RD-1 micelle is constant between pH 6.3 and 9.6, and in the presence of excess digitonin. RD-1 travels as a single boundary also in the electrophoresis apparatus at pH 8.5, and on filter paper at pH 8.0. The molecular weight of the RD-1 micelle lies between 260,000 and 290,000. Of this, only about 40,000 gm. are due to rhodopsin; the rest is digitonin (180 to 200 moles). Comparison of the relative concentrations of RD-1 and retinene in solutions of rhodopsin-digitonin shows that RD-1 contains only one retinene equivalent. It can therefore contain only one molecule of rhodopsin with a molecular weight of about 40,000. Cattle rhodopsin therefore contains only one chromophore consisting of a single molecule of retinene. It is likely that frog rhodopsin has a similar molecular weight and also contains only one chromophore per molecule. The molar extinction coefficient of rhodopsin is therefore identical with the extinction coefficient per mole of retinene (40,600 cm.2 per mole) and the E(1 per cent, 1 cm., 500 mµ) has a value of about 10. Rhodopsin constitutes about 14 per cent of the dry weight, and 3.7 per cent of the wet weight of cattle outer limbs. This corresponds to about 4.2 x 106 molecules of rhodopsin per outer limb. The rhodopsin content of frog outer limbs is considerably higher: about 35 per cent of the dry weight, and 10 per cent of the wet weight, corresponding to about 2.1 x 109 molecules per outer limb. Thus the frog outer limb contains about five hundred times as much rhodopsin as the cattle outer limb. But the relative volumes of these structures are such that the ratio of concentrations is only about 2.5 to 1 on a weight basis. Rhodopsin accounts for at least one-fifth of the total protein of the cattle outer limb; for the frog, this value must be higher. The extinction (K500) along its axis is about 0.037 cm.2 for the cattle outer limb, and about 0.50 cm.2 for the frog outer limb.

Hubbard, Ruth

1954-01-01

427

High molecular weight lipids from the trilaminar outer wall (TLS)-containing microalgae Chlorella emersonii, Scenedesmus conmmunis and Tetraedron minimum.  

PubMed

High molecular weight lipids were isolated from Chlorella emersonii, Scenedesmus communis and Tetraedron minimum, thin trilaminar outer wall (TLS)-containing freshwater microalgae producing an insoluble non-hydrolysable biopolymer (i.e. algaenan). Molecular weight determination by gel permeation chromatography indicated that their molecular weights range from ca. 400 to 2000 Da. Flash pyrolysis with in situ methylation using tetramethylammonium hydroxide (TMAH) and alkaline hydrolysis showed that the high molecular weight lipids isolated from C. emersonii and S. communis are mainly composed of saturated n-C26 and n-C28 fatty acids and alcohols and of saturated n-C30 and n-C32 alpha,omega-diols and omega-hydroxy acids. In contrast the high molecular weight lipids isolated from T. minimum are predominantly composed of long-chain fatty acids and omega-hydroxy acids. Aromatic moieties were also identified in small amounts in the thermochemolysate and in the hydrolysate. Chemical structural models containing long-chain mono- and polyesters were proposed for the high molecular weight lipids isolated from the three microalgae in agreement with analytical and spectroscopic data. Structural similarity between the outer cell wall of these microalgae and the cuticular membrane of higher plants is suggested. PMID:11393527

Allard, B; Templier, J

2001-06-01

428

Oral low molecular weight heparin delivery by microparticles from complex coacervation.  

PubMed

As low molecular weight heparins exhibit limited oral absorption they usually have to be administered parenterally. Their strong negative charge appears to be one of the biggest hurdles to overcome in order to increase oral absorption. Complex coacervation has been proposed as a microencapsulation technique for increased oral drug absorption on the basis of charge compensation. Optimized tinzaparin/acacia gum mixture were coacervated with either gelatin A or B leading to microparticles with monodispersed size distribution, good fluidity and high encapsulation rates (>90%), while mean particle size varied between 5 and 20 microm, respectively, depending on the gelatin type. Tinzaparin was homogeneously distributed throughout the particle matrix and anti-Xa activity was maintained during preparation and storage. Drug release occurred in dependency of the pH triggering the dissociation between tinzaparin/acacia and gelatin. Cell binding experiments on Caco-2 led to slightly increased adhesion of gelatin A microparticles compared to gelatin B (A: 3.5+/-0.3%; B: 2.5+/-0.3%; solution: 1.9+/-0.1%), while drug transport did not differ from free tinzaparin solution. In-vivo results demonstrated an oral bioavailability of about 4.2+/-2.9% with gelatin B particles while gelatin A led to no absorption of tinzaparin. In conclusion, tinzaparin microparticles exhibited excellent particle properties in vitro and demonstrate potential for a formulation increasing the oral bioavailability of low molecular weight heparins. PMID:17540548

Lamprecht, Alf; Ubrich, Nathalie; Maincent, Philippe

2007-11-01

429

Purification and characterization of a low-molecular-weight xylanase produced by acrophialophora nainiana  

PubMed

A low-molecular-weight xylanase activity (XynI) was isolated from the fungus Acrophialophora nainiana after growth in a solid medium containing wheat bran. XynI was purified to apparent homogeneity by ultrafiltration and gel filtration chromatography. The purified enzyme had a molecular weight value of approx. 17 kDa, as determined by SDS-PAGE. This enzyme was most active at 50 degreesC and pH 6.0. At 50 degreesC the half-life was 150 min. The apparent Km value for birchwood xylan was much lower than the Km value for oat spelt xylan. XynI was activated by L-cysteine, DTE, beta-mercaptoethanol, and L-tryptophan. XynI did not show significant sequence homology with other xylanases. The analysis of hydrolysis products of xylans and wood pulps showed that XynI was able to release xylooligomers ranging from X2 to X3 and X2 to X6, respectively. The enzyme was not active against acetylated xylan. A small amount of xylose was released from deacetylated, birchwood, and oat spelt xylans. The results obtained with enzymatic treatment of Kraft pulp indicated a reduction in the amount of chlorine compounds required for the process and enhanced brightness gain. PMID:9841776

Ximenes; de Sousa MV; Puls; da Silva; Filho

1999-01-01

430

Novel Experimental and Clinical Therapeutic Uses of Low-Molecular-Weight Heparin/Protamine Microparticles  

PubMed Central

Low-molecular-weight heparin/protamine microparticles (LMW-H/P MPs) were produced as a carrier for heparin-binding growth factors (GFs) and for various adhesive cells. A mixture of low-molecular-weight heparin (MW: approximately 5000 Da, 6.4 mg/mL) and protamine (MW: approximately 3000 Da, 10 mg/mL) at a ratio of 7:3 (vol:vol) yields a dispersion of microparticles (0.5–3 µm in diameter). LMW-H/P MPs immobilize, control the release and protect the activity of GFs. LMW-H/P MPs can also bind to cell surfaces, causing these cells to interact with the LMW-H/P MPs, inducing cells/MPs-aggregate formation and substantially promoting cellular viability. Furthermore, LMW-H/P MPs can efficiently bind to tissue culture plates and retain the binding of important GFs, such as fibroblast growth factor (FGF)-2. The LMW-H/P MPs-coated matrix with various GFs or cytokines may provide novel biomaterials that can control cellular activity such as growth and differentiation. Thus, LMW-H/P MPs are an excellent carrier for GFs and various cells and are an efficient coating matrix for cell cultures.

Kishimoto, Satoko; Ishihara, Masayuki; Takikawa, Megumi; Mori, Yasutaka; Hattori, Hidemi; Fujita, Masanori; Nakamura, Shingo

2012-01-01

431

Ultrasonic-assisted preparation of a low molecular weight heparin (LMWH) with anticoagulant activity.  

PubMed

Low molecular weight heparin (LMWH) is currently used as an anticoagulant agent and constitutes an alternative to unfractionated heparin, which is the cause of serious adverse drug reaction such as heparin-induced thrombocytopenia (HIT). Commercially available LMWH is produced by enzymatic depolymerization that is costly or by chemical methods that are generally carried out under conditions that could imply side reactions that reduce final product efficiency and yields. In this work, we present the use of a physicochemical method for the production of LMWH. This method consists in the use of hydrogen peroxide-catalyzed radical hydrolysis assisted by ultrasonic waves. LMWH that are produced using this physicochemical method have an average molecular weight and anticoagulant properties (Anti-Xa and Anti-IIa) that are comparable to some of commercial LMWH that are currently used. Ultrasonic-assisted radical depolymerization of heparin leads to products with a remarkably low polydispersity index. Moreover, in comparison to other LMWH such as those produced by enzymatic ?-elimination, this physicochemical depolymerization of heparin induces fewer oligosaccharides with less than five monosaccharide units. This contributes to the better preservation of the ATIII pentasaccharide binding sequence, which results in a high Anti-Xa/Anti-IIa ratio (1.86). However, LMWH obtained using this physicochemical method have a lower degree of sulfation than other LMWH, which seems to be the cause of a lower Anti-Xa and Anti-IIa activity (143.62±5.42 and 77.07±4.4, respectively). PMID:23911501

Achour, Oussama; Bridiau, Nicolas; Godhbani, Azza; Le Joubioux, Florian; Bordenave Juchereau, Stephanie; Sannier, Fredéric; Piot, Jean-Marie; Fruitier Arnaudin, Ingrid; Maugard, Thierry

2013-09-12

432

Deep impact of the template on molecular weight, structure, and oxidation state of the formed polyaniline.  

PubMed

In this work we find that polyaniline (PANI), synthesized by aniline chemical polymerization at a surface of template polycarbonate (PC) particles, is significantly different in molecular weight, structural order, oxidation state, and conductivity from a neat PANI. Molecular weight of the PANI phase in the composite (Mw = 158,000) is 1.6 times higher than that of the neat PANI synthesized in the absence of the template particles. Moreover, XRD analysis shows that crystallinity of the PANI phase in the composite is three times higher than that of the neat PANI. Raman spectroscopy indicates that the oxidation level of PANI in the PC/PANI composite is lower than that of the neat PANI. These noticeable changes of the PANI phase properties suggest specific interactions of reagents in the polymerization medium and formed PANI with the template phase as well as an orientation effect of the latter surface. FTIR spectroscopy reveals that hydrogen bonding in the neat doped PANI is weaker than one between -NH- of PANI and C?O of PC at their interface. The discovered differences are supported by the fact that conductivity of the PANI phase in the composite is more than three times higher than that of the neat PANI. PMID:23534341

Ogurtsov, Nikolay A; Noskov, Yuriy V; Fatyeyeva, Kateryna Yu; Ilyin, Vladimir G; Dudarenko, Galina V; Pud, Alexander A

2013-05-01

433

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

434

Glutathione depletion in lung cells by low-molecular-weight aldehydes.  

PubMed

Use of oxygenates in gasoline in the United States may increase atmospheric levels of aldehydes. To assist in health assessments of inhalation exposure to aldehydes, we studied glutathione (GSH) depletion by low-molecular-weight n-alkanals and 2-alkenals, ubiquitous air pollutants, in adult rat lung (ARL) cells by laser cytometry. For each homologous series, the effective aldehyde concentration that depleted GSH by 50% (EC50) in ARL cells correlates with published values for the median lethal dose of the chemicals and with Hammett/Taft electronic parameters, sigma* for n-alkanals and sigma(+)p for 2-alkenals. n-Alkanals (EC50, 110-400 mmol/L) were 1000 times less effective in depleting GSH than were 2-alkenals (EC50, 2-180 micromol/L), of which acrolein was the most potent. Ability of the 2-alkenals to deplete GSH follows the second-order rate constant for adduct formation. Ability of n-alkanals to deplete GSH follows chain length. Within a homologous series of low-molecular-weight aldehydes, structure-activity relationships are useful for predicting the toxicity of the aldehydes in vitro and in vivo. PMID:10580549

Meacher, D M; Menzel, D B

1999-06-01

435

Extraction conditions of Antheraea mylitta sericin with high yields and minimum molecular weight degradation.  

PubMed

Although the technique for extracting the Bombyx mori sericin has been extensively known, the extraction of sericin from wild-silkworm cocoons is not yet standardized. The aim of this study was to find the optimal conditions for the extraction of sericin from Antheraea mylitta cocoons, with high yields and minimum degradation. We attempted to apply various protocols for the extraction of the A. mylitta sericin (AmS). Among these, we found that the extraction of AmS with a sodium carbonate solution exhibited the highest yield except the conventional soap-alkali extraction. To find the optimal conditions for the AmS extraction with the sodium carbonate, we changed the concentration of sodium carbonate and the treatment time. With an increase in the sodium carbonate concentration and the extraction time, the yield of AmS increased, but the molecular weight (MW) of AmS decreased. Considering the yield, molecular weight distribution (MWD) and amino acid composition of AmS, we suggest that the optimal conditions for the AmS extraction require treatment with 0.02 M sodium carbonate and boiling for 60 min. PMID:23026092

Yun, Haesung; Oh, Hanjin; Kim, Moo Kon; Kwak, Hyo Won; Lee, Jeong Yun; Um, In Chul; Vootla, Shyam Kumar; Lee, Ki Hoon

2013-01-01

436

Analysis of low molecular weight metabolites in tea using mass spectrometry-based analytical methods.  

PubMed

Tea is the second most consumed beverage in the world after water and there are numerous reported health benefits as a result of consuming tea, such as reducing the risk of cardiovascular disease and many types of cancer. Thus, there is much interest in the chemical composition of teas, for example; defining components responsible for contributing to reported health benefits; defining quality characteristics such as product flavor; and monitoring for pesticide residues to comply with food safety import/export requirements. Covered in this review are some of the latest developments in mass spectrometry-based analytical techniques for measuring and characterizing low molecular weight components of tea, in particular primary and secondary metabolites. The methodology; more specifically the chromatography and detection mechanisms used in both targeted and non-targeted studies, and their main advantages and disadvantages are discussed. Finally, we comment on the latest techniques that are likely to have significant benefit to analysts in the future, not merely in the area of tea research, but in the analytical chemistry of low molecular weight compounds in general. PMID:24499071

Fraser, Karl; Harrison, Scott J; Lane, Geoff A; Otter, Don E; Hemar, Yacine; Quek, Siew-Young; Rasmussen, Susanne

2014-01-01

437

Partial Hydrothermal Oxidation of High Molecular Weight Unsaturated Carboxylic Acids for Upgrading of Biodiesel Fuel  

NASA Astrophysics Data System (ADS)

With increasing environmental awareness and crude oil price, biodiesel fuel (BDF) is gaining recognition as a renewable fuel which may be used as an alternative diesel fuel without any modification to the engine. The cold flow and viscosity of BDF, however, is a major drawback that limited its use in cold area. In this study, therefore, we investigated that partial oxidation of high molecular weight unsaturated carboxylic acids in subcritical water, which major compositions in BDF, to upgrade biodiesel fuel. Oleic acid, (HOOC(CH2)7CH=CH(CH2)7CH3), was selected as a model compound of high molecular weight unsaturated carboxylic acids. All experiments were performed with a batch reactor made of SUS 316 with an internal volume of 5.7 cm3. Oleic acid was oxidized at 300 °C with oxygen supply varying from 1-10 %. Results showed that a large amount of carboxylic acids and aldehydes having 8-9 carbon atoms were formed. These experimental results suggest that the hydrothermal oxidative cleavage may mainly occur at double bonds and the cleavage of double bonds could improve the cold flow and viscosity of BDF.

Kawasaki, K.; Jin, F.; Kishita, A.; Tohji, K.; Enomoto, H.

2007-03-01

438

In vitro cross-linking of gluten into high-molecular-weight polymers with transglutaminase.  

PubMed

From the amino acid composition of gluten proteins and the substrate specificity of transglutaminases (TGase) we concluded that gluten proteins can be favourable substrates for TGases due to their high glutamine content. By use of sodium dodecyl sulfate polyacrylamide gel-electrophoresis it was demonstrated that from gluten-ES and gluten-TS high-molecular-weight proteins developed in the presence of Ca2+ and red blood cell lysate containing TGase. When ovalbumin or deamidated gluten were applied as substrates no high-molecular-weight products were formed. Upon spectrophotometric measurements we found that covalent cross-links (isopeptide bonds) formed under the effect of TGases presumably cause a change in the position of chromophore groups in the substrates. Absorption decrease was detected between 274-276 nm as a result in the case of gluten-TS and gluten-ES used as substrates for TGase. No such change occurred in ovalbumin and deamidated gluten, applied as controls, under the influence of TGase. On the basis of our experiments it is postulated that the first step in gluten toxicity is presumably the binding of gluten to the intestine mucosa. In this binding the high transglutaminase activity in the intestines of coeliac patients and the high glutamine content of gluten may have an important role. PMID:2900018

Szabolcs, M; Sipka, S; Csorba, S

1987-01-01

439

Overcoming Angular Dependency When Teaching Light Scattering Using a Spectrofluorometer: The Molecular Weight of Latex Beads  

NASA Astrophysics Data System (ADS)

When using a spectrofluorometer in light-scattering experiments, it is impossible to perform angle-dependent studies. At first glance, this restriction seems to students to be an insurmountable obstacle. However, a spectrofluorometer offers some potentialities not available with classical laser light scattering spectroscopy, namely, the availability of broader wavelength ranges. Changing the wavelength changes the magnitude of the scattering vector. This has the same effect as a change in the measurement angle. Thus, it is possible to overcome angle dependency by accounting for wavelength dependency. This "shift" in dependencies is easily accessed by students because it results directly from the usual formalisms used in light scattering. Moreover, the students are encouraged, in practice, to elaborate innovative solutions, even from classical formalisms. This methodology is applied to the calculation of a series of molecular weights of polystyrene latex spheres. This system has several advantages: (i) water miscibility, (ii) definite shape, (iii) monodispersity (both size and shape), (iv) low cost, and (v) availability of latex spheres in a wide variety of sizes and composition. Although very well characterized with respect to size and shape (mainly by dynamic light scattering and electronic microscopy), latex spheres have been poorly studied in terms of molecular weight. Consequently, working in an innovative area of research proves stimulating for the students.

Santos, Nuno C.; Fernandes, Miguel X. J. J.; Castanho, Miguel A. R. B.

1999-09-01

440

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