Molecular Mass Dependence Research Articles

Characterization of synthetic polyelectrolytes by capillary electrophoresis

Capillary electrophoresis in entangled polymer solutions was applied to determine the molecular mass and polydispersity of polyelectrolytes. The separation selectivities of different polyethylene glycols as buffer additive can be correlated to their average molecular mass. A universal curve correlating the selectivity and the molecular mass could be obtained by using the instrinsic viscosity of the polyethylene glycol. The separation of poly(2-vinylpyridine) standards was compared to the separation of poly(4-vinylpyridine) standards. An indirect detection system was developed to characterize the cationic polyelectrolyte polydiallyldimethyl ammonium chloride. Various polymers with oppositely charged groups (polycarboxybetaines) were investigated with respect to structure dependence, pH dependence and molecular mass dependence of inter- and intramolecular association.

A re-evaluation of the molecular mass of earthworm extracellular hemoglobin from meniscus depletion sedimentation equilibrium. Nature of the 10 S dissociation species

Previous calculations from meniscus depletion sedimentation equilibrium of the molecular mass of earthworm hemoglobin from Lumbricus terrestris (E.J. Wood et al., Biochem. J. 153 (1976) 589–596) and from the related species Lumbricus sp. ( L. sp.) (M.M. David and E. Daniel, J. Mol. Biol. 87 (1974) 89–101) were made on the assumption that the solutions behaved ideally. Re-examination of their results reveals, however, a dependence of the apparent molecular mass on concentration. Taking this effect into consideration, we have now recalculated from their data molecular masses of 4.4–4.5 MDa for the hemoglobin of both L. terrestris and L. sp. On the basis of the new determinations, we propose for the polypeptide chain composition of L. terrestris hemoglobin a model [( abcd) 4L1L2L3] 12 where a,b,c,d are the four globin and L1,L2,L3 are the three major linker chain constituents of the protein. The model is consistent with the D 6 symmetry of the molecule. A 10 S intermediate product in the alkaline dissociation of Lumbricus hemoglobin is viewed as a binary mixture of products resulting from a disproportionation reaction involving the structural unit. The present interpretation is shown to be consistent with observed relations between molecular masses and SDS gel electrophoretic band patterns of 10 S species and intact hemoglobin.

On the structure of polyamidoamine dendrimer monolayers

Monolayers of polyamidoamine (PAMAM) dendrimers (generations 3.5 through 10) are prepared via electrostatic self-assembling from water solutions. Their thickness, morphology and mechanical stability are studied by scanning probe microscopy (SPM). A conformational state of dendritic macromolecules is discussed and compared to polymer scaling in the solution and recent molecular dynamics simulation results. The proposed model of molecular ordering assumes highly deformed (compressed along the surface normal) ellipsoidal shape for macromolecules in condensed monolayers. The molecular dimensions (thickness) versus molecular mass dependence is described by a scaling law with the exponent α = 0.28 being in-between values typical for dendrimer solutions and for a globular state.

27 Molecular mass dependence and the effect of TAFIa on the t-PA and DSPA cofactor activities of soluble fibrin degradation products

27 Molecular mass dependence and the effect of TAFIa on the t-PA and DSPA cofactor activities of soluble fibrin degradation products

Prediction of a Space Charge Induced Upper Molecular Mass Limit Towards Achieving Unit Mass Resolution in Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Cyclotron phase locking arises when two ion clouds have similar mass-to-charge ratios and a sufficiently large ion population such that the relative cyclotron dynamics are dominated by the mutual Coulomb E x B drift dynamics. Once two or more ion clouds are phase locked, a Fourier transform ion cyclotron resonance mass spectrometer cannot distinguish them by image current detection since the ion clouds have identical detected cyclotron frequencies. A simple analytical model, based on the assumption of rigid ion clouds, predicts that the maximum number of ions having equal charge states and closely spaced masses, which can be contained in two clouds before phase locking occurs, is proportional to their mass difference and to the square of the magnetic field strength divided by the molecular mass, Δm(B/M) 2 , and is independent of the charge state. This molecular mass dependence establishes an upper molecular mass limit for resolving closely spaced peaks due to cyclotron phase locking. The rigid ion cloud model, supported by numerical simulations, demonstrates that phase locking causes the 1 Da spacing of the isotopic envelope for large molecules to be unresolvable past a high molecular mass limit (M max ). M max is directly proportional to B and independent of the charge state for adjacent ion clouds with equal charge state. An order of magnitude estimate predicts that M max 1x10 4 (in units of Da and Tesla), independent of charge state for peaks having a 1 Da spacing. This estimate concurs with present instrumental capabilities. Full three-dimensional numerical stimulations on realistic ion clouds, which include the combined effects of internal and external ion cloud dynamics, Z-oscillation, linear dipolar excitation and trap potential anharmonicity, demonstrate the qualitative validity of the assumptions inherent in the rigid ion cloud model predictions.

Determination of the chemical composition distribution of copolymers of styrene and butadiene by gradient polymer elution chromatography

In order to determine the chemical composition distribution (CCD) of styrene-butadiene copolymers, gradient polymer elution chromatography has been performed. The separation is mainly based on differences in solubility among the copolymer molecules with different chemical composition. The solubility of a copolymer is dependent on the following parameters: temperature, type of solvent/non-solvent mixture, molecular mass of the polymer and the chemical composition of the polymer. The resolution of the gradient polymer elution chromatographic separation and the molecular mass dependency are influenced by the solvent/non-solvent combination. In order to obtian a reliable separation according to chemical composition, the differences in solubility must be sufficientyl high and the molecular mass dependence must be negligible. In order to separate styrene-butadiene copolymers, synthesized by emulsion polymerization, a tetrahydrofuran-acetonitrile gradient was used. After calibration of the chromatographic system with styren-butadiene copolymer standards, the CCD of styrene-butadiene copolymers could be calculated.

Molecular mass and ionic strength dependence of electrochemical properties of flexible polyelectrolytes

AbstractConductometry and potentiometry have been employed to examine the influence of macromolecular parameters and chemical structure on the electrochemical behaviour of flexible polyelectrolytes with finite chain length in the concentration range 10−6<cp<10−2monomol·l−1. For polyelectrolytes with charge distances below the Bjerrum length at low ionic strength the equivalent conductivity increases strongly with decreasing polymer concentration. Correlating this behaviour with concentration regimes according to de Gennes and Odijk the strong and nearly linear increase is situated below the overlap concentration. In highly diluted polyelectrolyte solutions without and with addition of low molecular electrolyte the equivalent conductivity reaches a limit whose absolute high and position was found to have strong correlations with the molecular mass, the ionic strength, and the ratio of polyelectrolyte to salt concentration. The electrolytic conductivity results correspond with counterion activities in the concentration range cp > 10−4 monomol·l−1. The discussion of the findings in terms of existing theories point to defined changes of the interionic interactions.

Stopped-flow, classical, and dynamic light scattering analysis of matrix protein binding to nucleocapsids of vesicular stomatitis virus.

During the process of assembly of enveloped viruses, binding of the nucleoprotein core of the virus (nucleocapsid) to the host membrane is mediated by the viral matrix (M) protein. Light scattering properties of vesicular stomatitis virus (VSV) nucleocapsids and nucleocapsid-M protein (NCM) complexes assembled in vivo were determined following solubilizaton of the virion envelope with detergents at varying ionic strength to vary the extent of M protein binding. Three factors were found to contribute to the light scattering properties of VSV nucleocapsids: their conformation, extent of self-association, and amount of bound M protein. All three were affected by changes in ionic strength but could be distinguished by several parameters. Conformational changes in nucleocapsids and NCM complexes occurred rapidly (millisecond time scale) upon changing salt concentration and were reflected in changes in the angular dependence of light scattering intensity (i.e., changes in radius of gyration, RG). Changes in extent of self-association occurred relatively slowly (seconds to minutes time scale) and could be distinguished by the concentration dependence of the apparent molecular mass and diffusion coefficient of the NCM complex. Changes in M protein binding occurred on an intermediate time scale (t1/2 approximately one s) and reflected changes in both molecular mass and RG. The data presented here provide criteria for assessing binding of M protein to nucleocapsids under conditions of minimal perturbation of the NCM complex assembled in vivo and at low protein concentrations so that self-association of the NCM complex was minimal and reversible.

Influence of chemical changes of the isotropic matrix on physical properties of mesophase pitch

The temperature dependence of average molecular mass and carbon content of the isotropic matrix prepared by heat treatment of coal tar pitch exhibits distinct local minima at 400°C. This temperature agrees approximately with the position of local extremes on viscosity curves, designated as maximum/minimum. The anomalies were attributed to accelerated mesophase formation affecting the chemical and rheological properties of the isotropic matrix. For this study samples of mesophase pitch were prepared at 250, 300, 350, 400 and 450°C. After removal of anisotropic QI substances by extraction with quinoline the portions of isotropic matrix were further separated by solvent fractionation into groups of maltenes, asphaltenes plus preasphaltenes (APA) and carboids (CA). The soluble samples of APA and CA have been obtained by means of non-reductive alkylation. Their ‘average molecule’ was characterized by elemental composition, n.m.r. spectroscopy and vapour osmometry.

Quantification of the Effect of Excluded Volume on Double-stranded DNA

By steric exclusion of volume, neutral polymers both condense and increase the effective concentration of DNA random coils. Neutral polymers also stimulate the in vitro packaging of DNA in the capsids of some double-stranded DNA bacteriophages. In the present study, the physical effects of neutral polymers on DNA random coils have been quantified by assaying the DNA products at equilibrium of the following two reactions of the 12 nucleotide single-stranded complementary (cohesive) ends of mature bacteriophage λ DNA: bimolecular joining of half-molecules of mature λ DNA, and cyclization of intact λ DNA; cyclization is used as a probe for unimolecular DNA condensation. The smaller neutral molecules, including polyethylene glycol of molecular mass 200 Da (PEG200), shift both reactions towards dissociation; this shift is partially correlated with reduced water activity. The larger PEGs (molecular mass of 1540 or more) shift both reactions towards association. Water activity-corrected equilibrium constants for the larger PEGs are found to increase as a function of PEG concentration. Below 2% to 3% (w/v) PEG, these equilibrium constants are independent of PEG molecular mass; at higher PEG concentrations, these equilibrium constants increase as the molecular mass of the PEG increases. The following conclusions are drawn. (1) Volume exclusion among PEG molecules is the primary cause of the PEG molecular mass-dependence of excluded volume. (2) At the lower PEG concentrations, the PEG radius obtained by quantification of excluded volume is usually equal to the hydrodynamic PEG radius. (3) At any given PEG concentration, the PEG-DNA excluded volume is approximately the same for bimolecular DNA joining as it is for unimolecular DNA cyclization. (4) Polymer-induced stimulation of in vitro bacteriophage DNA packaging is derived primarily from alteration of water activity, not alteration of excluded volume.

Elution behaviour of styrene—acrylonitrile copolymers in high-performance liquid chromatography with mixtures of chloroform and n-hexane as mobile phases

With isocratic elution of styrene—acrylonitrile copolymers from an ODS silica column using chloroform— n-hexane mixtures as mobile phases, the elution profiles of the copolymers with an acrylonitrile content from 15 to 33% showed four different patterns, depending on the compositions of the copolymers and the mobile phases: (i) elution with a retention volume corresponding to the interstitial volume of the column; (ii) elution with a retention volume corresponding to the sum of the interstitial volume and the pore volume of the packing materials in the column; (iii) elution with both retention volumes; and (iv) precipitation on the column. A transition period was found during the process in which the copolymer which dissolved in a good solvent precipitated when the latter became a poor solvent on adding a non-solvent, and this was defined as the pre-precipitation state. Each molecule was in a condensed form in this state. In order to separate the copolymers according to composition, gradient elution from 100% n-hexane to 100% chloroform, in 30 min was performed, and the copolymers were separated in order of increasing the acrylonitrile content. No molecular mass dependence of the separation was observed.

Polymer analysis using size-exclusion chromatography with coupled density and refractive index detection: VI. Molecular mass dependence of preferential solvation of polyoxyethylenes in chloroform with different ethanol contents

It is shown that preferential salvation of polyoxyethylenes with hydroxy and methoxy end-groups in chloroform containing ethanol takes place mainly at the hydroxy end-groups, but also along the main chain. A method is described that allows a separate determination of the adsorbed ethanol molecules per repeating unit and per end-group.

Influence of linear velocity and multigradient programming in supercritical fluid chromatography

The chromatographic plate height, resolution and time requirements in supercritical fluid chromatography depend on the physical properties of the mobile phase (pressure, mobile phase composition, temperature and linear velocity), on the chemical structure of the analyte, which determines vapour pressure and solubility, and on various properties of the stationary phase. If a given homologous series of compounds, or a test mixture simulating a homologous series, is used with a specific chromatographic column, the chromatographic properties for the compounds in these test mixtures will vary with pressure, mobile phase composition, temperature, velocity and the relative molecular mass of the individual compounds. If in addition to a suitable column a temperature is chosen which, for simplicity, is kept constant, and which is known to lead to good or even optimum resolution, the pressure, composition and relative molecular mass dependence of the Van Deemter plate height minimum, as determined experimentally at this temperature, can be used for predicting an optimum linear velocity programme. This velocity programme can be used either as a stand-alone programme or can be adapted to and superimposed on pressure or composition programmes, or even on combined pressure—composition programmes. The linear velocity dependence of plate height and resolution for a mobile phase composed of a mixture of carbon dioxide and methanol on a column packed with unbonded silica gel is presented. This dependence was measured at different pressures and compositions, employing four condensed aromatics as a test analyte. Each chromatogram of the analyte was therefore measured at constant temperature, velocity, pressure and composition, varying the last three physical properties between chromatograms. The data are presented as Van Deemter plots and as three-dimensional plots showing the dependence of resolution and capacity factor on velocity and either pressure or composition. Based on these data, the change in the linear velocity suitable for pressure programmes, mobile phase composition programmes and for increase in the relative molecular mass of the analyte is discussed. The conclusion is that a pressure (density) programme needs a superimposed negative linear velocity programme for the purpose of decreasing the plate height and increasing the resolution, whereas such a programme is not necessary to a comparable extent for composition programming. If compounds with a wide range of relative molecular masses are separated, the superimposing of a negative linear velocity programme on to a composition programme is also advantageous. For programming the physical properties of a mobile phase, i.e., pressure, density, composition, temperature and velocity, a number of closely related equations are proposed and some corresponding programme curves are shown. Hardware needs for programming are also briefly discussed.

Linear molecular-mass dependence of second hyperpolarizabilities: lack of polar enhancement in nonconjugated molecules

Second hyperpolarizabilities (γ) of a series of R–X molecules (R = H, Me, Et, Pri, But; X =–NCHO, OH, Me) have been calculated at various ab initio levels; surprisingly, γ increases nearly linearly with molecular mass, is minimally affected by the functional group X, and is slightly greater for alkanes.

Direct measurement of the three-body interaction parameter in a dilute polymer solution.

From measurements of the second virial coefficient by small-angle neutron scattering we have found that the theta temperature of linear polyethylene in dilute solution decreases with increasing molecular mass. This behavior supports polymer theories that incorporate both chain connectivity and three-body interactions. We calculate the three-body interaction parameter within the continuous-curve representation of a flexible polymer, and demonstrate from the same model that our value is consistent with the molecular-mass dependence of the critical precipitation temperature.

The glnA gene of the extremely thermophilic eubacterium Thermotoga maritima: cloning, primary structure, and expression in Escherichia coli.

The structural gene (glnA) encoding the glutamine synthetase (GS) of the extremely thermophilic eubacterium Thermotoga maritima has been cloned on a 6.0 kb HindIII DNA fragment. Sequencing of the region containing the glnA gene (1444 bp) showed an ORF encoding a polypeptide (439 residues) with an estimated mass of 50,088 Da, which shared significant homology with the GSI sequences of other Bacteria (Escherichia coli, Bacillus subtilis) and Archaea (Pyrococcus woesei, Sulfolobus solfataricus). The T. maritima glnA gene was expressed in E. coli, as shown by the ability to complement a glnA lesion in the glutamine-auxotrophic strain ET8051. The recombinant GS has been partially characterized with respect to the temperature dependence of enzyme activity, molecular mass and mode of regulation. The molecular mass of the Thermotoga GS (590,000 Da), estimated by gel filtration, was compatible with a dodecameric composition for the holoenzyme, as expected for a glutamine synthetase of the GSI type. Comparison of the amino acid sequence of T. maritima GS with those from thermophilic and mesophilic micro-organisms failed to detect any obvious features directly related to thermal stability.

Solutions of mesogenic polymers in nematic solvent: temperature and molecular mass dependences of the value of rotational viscosity

Study of the dynamics of the Frederix transition on torsional strain in solutions of polydecamethylene-furomaroyl- bis-(4-oxybenzoate) (PDFOB) and poly(3,3′-biphenylsubaroyloxybenzoate) (P-6) in a nematic liquid crystal has yielded the temperature and molecular mass dependencies of the coefficient of rotational viscosity of these solutions. The chains of the polymer studied in a nematic solution are not elongated, the chains of P-6 being more rigid than the PDFOB chains. The exponent α characterizing the dependence of the relative increment of rotational viscosity of the solutions on the degree of polymerization changes for P-6 from 0.99 to 0.88 with rise in temperature from 130 to 170°C indicating the partial streaming of the chains while the PDFOB chains are not streamed since for this polymer α = 0.47.

Crystal growth of intermediate-molecular-mass poly(ethylene oxide) fractions from the melt

Linear crystal growth rates of poly(ethylene oxide) (PEO) fractions crystallized from the melt have been measured in an intermediate-molecular-mass range ( MW = 23 000−105 000). Regime phenomena have been observed during crystallization. Regime II/III transitions occur at ΔT = 17.5±0.5 K and regime I/II transitions appear at ΔT = 10±0.5 K for those fractions for which the equilibrium melting temperature of 342.2 K for PEO crystals is used. Interestingly, we have found that in these PEO fractions reversion from regime I back to regime II exists even at a lower supercooling of 8.5±0.5 K. Detailed kinetic analyses of the data demonstrate the suitability of the present nucleation theory. The molecular-mass dependence of the PEO fraction has also been discussed. Morphological changes can be observed along with regime transitions of PEO crystal growth.

Study of the molecular mass dependence of the twist viscosity coefficient of a nematic thermotropic main-chain polymer

Etude en fonction de la temperature et de la masse moleculaire du poly(oxy [methyl-3 phenylene-1,4] azoxy [methyl-2 phenylene-1,4] oxy [dioxo-1,12 dodecanediyl-1,12])

The Molecular-Mass Dependence of Dextran Sulfate Enhancement of Inactivation of Thrombin and Fibrinogen and on Factor Xa Neutralization by Antithrombin III

To study molecular-mass dependence of dextran sulfate (DS) for interactions with several plasma proteins, a commercial preparation of the sulfated polysaccharide was fractionated by gel filtration chromatography into six subfractions with relatively different molecular masses. Simple two-component systems were available to measure the interactions of the proteins with the subfractions of DS. These were done to determine the rates of time-dependent changes in intrinsic fluorescence of thrombin and fibrinogen, and the enzyme inactivation in the presence of DS. Their interactions were also confirmed in three-component systems, in which the interactions of DS with thrombin and fibrinogen were measured by the displaced binding by FTC-heparin, and DS-enhanced proteolysis by chymotrypsin, respectively. Moreover, the neutralization of factor Xa by antithrombin III (AT III) depended on the molecular mass of DS. All the results obtained indicate that most of the general interactions of thrombin, fibrinogen, and probably AT III increased with increasing molecular mass of DS.