Bead-spring model predictions of solution dynamics for flexible homopolymers incorporating long-chain branches and/or rings

1988 ◽  
Vol 21 (4) ◽  
pp. 1132-1140 ◽  
Author(s):  
Robert L. Sammler ◽  
John L. Schrag
Keyword(s):  
Spring Model ◽  
Model Predictions ◽  
Solution Dynamics ◽  
Long Chain

Refinement and Extension of COSMO-RS-Trained Fragment Contribution Models for Predicting Partition Properties of C10–20 Chlorinated Paraffin Congeners

2021 ◽  
Author(s):  
Satoshi Endo
Keyword(s):  
Partition Coefficients ◽  
Aqueous Solubility ◽  
Stochastic Algorithm ◽  
Training Set ◽  
Subcooled Liquid ◽  
Conformer Generation ◽  
Model Predictions ◽  
Predicted Values ◽  
Chlorinated Paraffin ◽  
Long Chain

COSMO-RS-trained fragment contribution models (FCMs) to predict partition properties of chlorinated paraffin (CP) congeners were refined and extended. The improvement includes (i) the use of an improved conformer generation method for COSMO-RS, (ii) extension of training and validation sets for FCMs up to C<sub>20</sub> congeners covering short-chain (SCCPs), medium-chain (MCCPs) and long-chain CPs (LCCPs), and (iii) more realistic simulation of industrial CP mixture compositions by using a stochastic algorithm. Extension of the training set markedly improved the accuracy of model predictions for MCCPs and LCCPs, as compared to the previous study. The predicted values of the log octanol/water partition coefficients (<i>K</i><sub>ow</sub>) for CP mixtures agreed well with experimentally determined values from the literature. Using the established FCMs, this study provided a set of quantum chemically based predictions for 193 congener groups (C<sub>10–20</sub>, Cl<sub>0–21</sub>) regarding <i>K</i><sub>ow</sub>, air/water (<i>K</i><sub>aw</sub>), and octanol/air (<i>K</i><sub>oa</sub>) partition coefficients, subcooled liquid vapor pressure (VP) and aqueous solubility (<i>S</i><sub>w</sub>) in a temperature range of 5–45 °C as well as the respective enthalpy and internal energy changes.<br><br>This is a preprint version and has not yet been peer reviewed.

Refinement and Extension of COSMO-RS-Trained Fragment Contribution Models for Predicting Partition Properties of C10–20 Chlorinated Paraffin Congeners

2021 ◽  
Author(s):  
Satoshi Endo
Keyword(s):  
Partition Coefficients ◽  
Aqueous Solubility ◽  
Stochastic Algorithm ◽  
Training Set ◽  
Subcooled Liquid ◽  
Conformer Generation ◽  
Model Predictions ◽  
Predicted Values ◽  
Chlorinated Paraffin ◽  
Long Chain

COSMO-RS-trained fragment contribution models (FCMs) to predict partition properties of chlorinated paraffin (CP) congeners were refined and extended. The improvement includes (i) the use of an improved conformer generation method for COSMO-RS, (ii) extension of training and validation sets for FCMs up to C<sub>20</sub> congeners covering short-chain (SCCPs), medium-chain (MCCPs) and long-chain CPs (LCCPs), and (iii) more realistic simulation of industrial CP mixture compositions by using a stochastic algorithm. Extension of the training set markedly improved the accuracy of model predictions for MCCPs and LCCPs, as compared to the previous study. The predicted values of the log octanol/water partition coefficients (<i>K</i><sub>ow</sub>) for CP mixtures agreed well with experimentally determined values from the literature. Using the established FCMs, this study provided a set of quantum chemically based predictions for 193 congener groups (C<sub>10–20</sub>, Cl<sub>0–21</sub>) regarding <i>K</i><sub>ow</sub>, air/water (<i>K</i><sub>aw</sub>), and octanol/air (<i>K</i><sub>oa</sub>) partition coefficients, subcooled liquid vapor pressure (VP) and aqueous solubility (<i>S</i><sub>w</sub>) in a temperature range of 5–45 °C as well as the respective enthalpy and internal energy changes.<br><br>This is a preprint version and has not yet been peer reviewed.

Polymer Morphology Revealed by Staining Techniques

1981 ◽  
Vol 39 ◽  
pp. 340-341
Author(s):  
A. C. Reimschuessel ◽  
V. Kramer
Keyword(s):  
Polymer Melt ◽  
Nylon 6 ◽  
Morphological Features ◽  
Negative Staining ◽  
Polymer Morphology ◽  
Crystallizable Polymer ◽  
Staining Techniques ◽  
Long Chain

Staining techniques can be used for either the identification of different polymers or for the differentiation of specific morphological domains within a given polymer. To reveal morphological features in nylon 6, we choose a technique based upon diffusion of the staining agent into accessible regions of the polymer.When a crystallizable polymer - such as nylon 6 - is cooled from the melt, lamellae form by chainfolding of the crystallizing long chain macromolecules. The regions between adjacent lamellae represent the less ordered amorphous domains into which stain can diffuse. In this process the lamellae will be “outlined” by the dense stain, giving rise to contrast comparable to that obtained by “negative” staining techniques.If the cooling of the polymer melt proceeds relatively slowly - as in molding operations - the lamellae are usually arranged in a radial manner. This morphology is referred to as spherulitic.

A theory of contamination in electron microscopes by surface diffusion

1978 ◽  
Vol 36 (1) ◽  
pp. 116-117
Author(s):  
J.T. Fourie
Keyword(s):  
Electron Beam ◽  
Surface Diffusion ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
Physical Parameters ◽  
Carbon Compounds ◽  
Hydrocarbon Molecules ◽  
Electron Microscopes ◽  
Primary Electrons ◽  
Long Chain

Contamination in electron microscopes can be a serious problem in STEM or in situations where a number of high resolution micrographs are required of the same area in TEM. In modern instruments the environment around the specimen can be made free of the hydrocarbon molecules, which are responsible for contamination, by means of either ultra-high vacuum or cryo-pumping techniques. However, these techniques are not effective against hydrocarbon molecules adsorbed on the specimen surface before or during its introduction into the microscope. The present paper is concerned with a theory of how certain physical parameters can influence the surface diffusion of these adsorbed molecules into the electron beam where they are deposited in the form of long chain carbon compounds by interaction with the primary electrons.

The effects of low-ratio n-6/n-3 PUFA on biomarkers of inflammation: a systematic review and meta-analysis

2021 ◽  
Author(s):  
Yali Wei ◽  
Yan Meng ◽  
Na Li ◽  
Qian Wang ◽  
Liyong Chen
Keyword(s):  
Systematic Review ◽  
Fatty Acid ◽  
Polyunsaturated Fatty Acid ◽  
Meta Analysis ◽  
Chain Polyunsaturated Fatty Acid ◽  
Inflammation Markers ◽  
Pufa Supplementation ◽  
Long Chain

The purpose of the systematic review and meta-analysis was to determine if low-ratio n-6/n-3 long-chain polyunsaturated fatty acid (PUFA) supplementation affects serum inflammation markers based on current studies.

Biophysics (and sociology) of ceramides.

2005 ◽  
Vol 72 ◽  
pp. 177-188 ◽  
Author(s):  
Félix M. Goñi ◽  
F-Xabier Contreras ◽  
L-Ruth Montes ◽  
Jesús Sot ◽  
Alicia Alonso
Keyword(s):  
Cell Biology ◽  
Positive Curvature ◽  
Acyl Chain ◽  
Cell Signalling ◽  
Hexagonal Structure ◽  
Lipid Monolayer ◽  
Flip Flop ◽  
Long Chain ◽  
Bilayer Permeability

In the past decade, the long-neglected ceramides (N-acylsphingosines) have become one of the most attractive lipid molecules in molecular cell biology, because of their involvement in essential structures (stratum corneum) and processes (cell signalling). Most natural ceramides have a long (16-24 C atoms) N-acyl chain, but short N-acyl chain ceramides (two to six C atoms) also exist in Nature, apart from being extensively used in experimentation, because they can be dispersed easily in water. Long-chain ceramides are among the most hydrophobic molecules in Nature, they are totally insoluble in water and they hardly mix with phospholipids in membranes, giving rise to ceramide-enriched domains. In situ enzymic generation, or external addition, of long-chain ceramides in membranes has at least three important effects: (i) the lipid monolayer tendency to adopt a negative curvature, e.g. through a transition to an inverted hexagonal structure, is increased, (ii) bilayer permeability to aqueous solutes is notoriously enhanced, and (iii) transbilayer (flip-flop) lipid motion is promoted. Short-chain ceramides mix much better with phospholipids, promote a positive curvature in lipid monolayers, and their capacities to increase bilayer permeability or transbilayer motion are very low or non-existent.

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