PubMed · 7032783
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D P Thomas. 1981. Heparin.. https://pubmed.ncbi.nlm.nih.gov/7032783/
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We investigate the effects excluded volume on the stretching of a single DNA in solution. We find that for small force F, the extension h is not linear in F but proportion to F(gamma), with gamma = (1 - nu)/nu, where nu is the well-known universal correlation length exponent. A freely joint chain model with the segment length chosen to reproduce the small extension behavior gives excellent fit to the experimental data of lambda-phage DNA over the whole experimental range. We show that excluded volume effects are stronger in two dimensions and derive results in two dimensions that are different from the three-dimensional results. This suggests experiments to be performed in these lower dimensions.
Researchers have recently questioned the role hydroxylated prolines play in stabilizing the collagen triple helix. To address these issues, we have developed new molecular mechanics parameters for the simulation of peptides containing 4(R)-fluoroproline (Flp), 4(R)-hydroxyproline (Hyp), and 4(R)-aminoproline (Amp). Simulations of peptides based on these parameters can be used to determine the components that stabilize hydroxyproline over proline in the triple helix. The dihedrals F-C-C-N, O-C-C-N, and N-C-C-N were built using a N-beta-ethyl amide model. One nanosecond simulations were performed on the trimers [(Pro-Pro-Gly)(10)](3), [(Pro-Hyp-Gly)(10)](3), [(Pro-Amp-Gly)(10)](3), [(Pro-Amp(1+)-Gly)(10)](3), and [(Pro-Flp-Gly)(10)](3) in explicit solvent. The results of our simulations suggest that pyrrolidine ring conformation is mediated by the strength of the gauche effect and classical electrostatic interactions.
The cool-flame phenomenon can occur in fuel-oxygen (air) mixtures within the flammable range and outside the flammable range, at fuel-rich compositions, at temperatures below the auto-ignition temperature (AIT). It is caused by chemical reactions occurring spontaneously at relatively low temperatures and is favoured by elevated pressure. The hazards that cool flames generate are described. These vary from spoiling a product specification through contamination and explosive decomposition of condensed peroxides to the appearance of unexpected normal (hot) flame (two-stage ignition).