Search results for "Molar"

Effect of core-forming molecules on molecular weight distribution and degree of branching in the synthesis of hyperbranched polymers

1998

The polydispersity index, the molecular weight distribution (MWD), and the degree of branching ( ) are calculated for hyperbranched polymers obtained in self-condensing vinyl polymerization of AB* monomers in the presence of a core-forming molecule (i.e. a multifunctional initiator, Bf*). Two cases are considered:  (a) batch polymerization, i.e., with all components mixed together; (b) semibatch polymerization, i.e., slow addition of the monomer to the core-forming molecule. The results obtained for the latter case are also valid for polycondensation of AB2 monomers. The presence of core-forming molecules leads to a considerable narrowing of the MWD's, the polydispersity index decreasing wi…

Ring opening polymerization of $\varepsilon$-caprolactone in the presence of wet $\beta$-cyclodextrin: Effect of the operative pressure and of water …

2016

International audience; The ring opening polymerization (ROP) of $\varepsilon$-caprolactone (CL) in the presence of $\beta$-cyclodextrin ($\beta$-CD) wasperformed in batch reactors both at room pressure and with the reaction system pressurized with CO$_2$, N$_2$ orAr. Significant enhancements of the polymerization rate was observed when the ROP was carried out withwet $\beta$-CD under pressure. For example, after 24 hours at 120° C with a $\beta$-CD/CL molar ratio of about1/100, the monomer conversion increased from 4 to 98–99% when the pressure was changed from 0.1to 12.5–13.0 MPa independent of the nature of the compressing gas. MALDI-TOF analyses indicated thata major fraction of polymer…

Volume and heat capacity studies to evidence interactions between cyclodextrins and nicotinic acid in water

2008

Density and heat capacity of the water+cyclodextrin (CD), water+nicotinic acid (NA) and water+CD+NA mixtures were determined at 298.15 K. CDs with different cavity size and alkylation were selected. From the experimental data the apparent molar properties were calculated. Assuming the formation of inclusion complexes of 1:1 stoichiometry, these properties were modeled and provided the stability constants of CD/NA inclusion complexes and the corresponding property change. The binding of NA with the smallest sized alpha-cyclodextrin (alpha-CD) generates more stable complexes accompanied by the lower volume and the heat capacity changes. These results are in agreement with earlier proposed bin…

Sequence-specific and DNA structure-dependent interactions of Escherichia coli MutS and human p53 with DNA

2013

Many proteins involved in DNA repair systems interact with DNA that has structure altered from the typical B-form helix. Using magnetic beads to immobilize DNAs containing various types of structures, we evaluated the in vitro binding activities of two well-characterized DNA repair proteins, Escherichia coli MutS and human p53. E. coli MutS bound to double-stranded DNAs, with higher affinity for a G/T mismatch compared to a G/A mismatch and highest affinity for larger non-B-DNA structures. E. coli MutS bound best to DNA between pH 6 and 9. Experiments discriminated between modes of p53-DNA binding, and increasing ionic strength reduced p53 binding to nonspecific double-stranded DNA, but had…

1990

The determination of average molecular weights and the characterization of molecular weight distributions by the ratio of the weight- to number-average molecular weights Mw/Mn from sedimentation equilibrium in the ultracentrifuge are described. The essential measurement of the density profile of the mixed solvent is conducted according to Munk (Macromolecules15, 500 (1982)). Special evaluation of the polymer band in the equilibrium allowed to deduce from the observed concentration profile Mw and Mn of a series of poly(methyl methacrylate) samples and thus to characterize the molecular weight distribution of the samples.

Apparent molar volumes of potassium nitrate and sodium nitrate in ethanol + water at 298.15 K

1998

Densities of ethanol + water + potassium nitrate and ethanol + water + sodium nitrate mixtures have been measured with an oscillating-tube densimeter over a large range of concentrations of the salt and ethanol, at 298.15 K. From these densities, apparent molar volumes of both electrolytes in ethanol + water mixtures have been calculated, and partial molar volumes at infinite dilution have been evaluated.

Vinylic polymerization of norbornene by Pd(II)-catalysis in the presence of ethylene

1997

Pd(II) catalysts with nitrilo ligands and BF4− counter ions give the best results in vinylic polymerization of norbornene. Absolute molecular weight determination of polynorbornene (PN) by means of light scattering and the three-dimensional shape of PN were also investigated. By correlation of molecular weights Mw with intrinsic viscosity (Staudinger-index) [η], yield a close to 0.5 exponent for the Mark-Houwink equation with solvents chlorobenzene and cyclohexane at 25°C expected for polymer molecules with confined conformation. The vinylic polymerization of norbornene with [(CH3CN)4Pd][BF4]2 (I) in nitromethane in the presence of ethylene results in PN with narrow molecular weight distrib…

Die bestimmung der molekulargewichtsverteilung von nichtkristallisierenden polymeren mit dem elektronenmikroskop, 7. Präparation durch verdampfung de…

1977

A preparation method is described by means of which it is possible to transfer individual molecules of a high molecular weight polymer on a support, in order to determine their mass and therefrom their molecular weight distribution, using our previously published electron microscopic method. The advantages of the new procedure as compared to the previously described freeze-drying are 1 that the range of solvents, which can be used is much larger, and 2 that the preparation is performed by evaporation from a dilute solution, which means that the molecules are distributed statistically on the support. The risk of formation of associates is avoided by keeping the polymer concentration correspo…

Complex Formation of DNA with Oppositely Charged Polyelectrolytes of Different Chain Topology:  Cylindrical Brushes and Dendrimers

2007

The complex formation between DNA (pUC19-supercoiled DNA, 2686 base pairs) and some polycations of different chain topologies in aqueous solution was studied by light scattering, gel electrophoresis, and AFM. The investigated polycations comprised cylindrical brush polymers with quaternized poly(vinylpyridine) and polyethylene imine side chains as well as a fifth generation dendrimer thus covering a broad molar mass regime of 3 × 104 g mol-1 < Mw < 1 × 107 g mol-1 and very different chemical charges/molecule, Z+, of 127 < Z+ < 5500. Irrespective of the polycation, the complexes formed in dilute solution exhibited a similar size in terms of the mean square radius of gyration, 〈Rg2〉, i.e., 30…

Competing salt effects on phase behavior of protein solutions: tailoring of protein interaction by the binding of multivalent ions and charge screeni…

2014

The phase behavior of protein solutions is affected by additives such as crowder molecules or salts. In particular, upon addition of multivalent counterions, a reentrant condensation can occur; i.e., protein solutions are stable for low and high multivalent ion concentrations but aggregating at intermediate salt concentrations. The addition of monovalent ions shifts the phase boundaries to higher multivalent ion concentrations. This effect is found to be reflected in the protein interactions, as accessed via small-angle X-ray scattering. Two simulation schemes (a Monte Carlo sampling of the counterion binding configurations using the detailed protein structure and an analytical coarse-grain…