5 research outputs found
Predicted Interaction and Associated Carbonyl C Chemical Shifts.
<p>(<b>A</b>) Residues Asn155 and Phe189 from the x-ray structure of <i>Bacillus amyloliquefaciens</i> subtillisin BPN’ (PDB ID: 1v5i) illustrating the structural features for an optimal interaction between carbonyl groups. (<b>B</b>) 2D contour plot of carbonyl C chemical shift differences relative to random coil values as a function of the distance () and angle () between carbonyls. A Gaussian smoothing function was applied to the data with and of 0.3 Å and 1.5°, respectively. A transparency mask based on the density of experimental data (see also <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0042075#pone.0042075.s001" target="_blank">Figure S1</a>) is overlaid on the contour plot. Regions lacking experimental data are white. Positive values indicate downfield shifts.</p
Carbonyl C Chemical Shifts and Dipole-Dipole Potential.
<p>Carbonyl C chemical shift differences relative to random coil are plotted against calculated dipole-dipole potential (). The dipole-dipole potential is calculated from the high-resolution x-ray structure using Equation 1. Pairs of carbonyls with and values within the optimal limits for an interaction are colored red.</p
Summary of Quantum Chemical Calculations.
<p>Plot of calculated (<b>A</b>) carbonyl C chemical shielding () and (<b>B</b>) dipole-dipole interaction energy () as a function of the distance between donor oxygen and acceptor carbon () and the angle between carbonyl groups (). See also <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0042075#pone.0042075.s003" target="_blank">Figure S3</a>.</p
Carbonyl C Chemical Shifts and Hydrogen Bonds.
<p>Contour plot of C carbonyl chemical shift differences as a function of calculated dipole-dipole potential () and calculated hydrogen bond length (). See also <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0042075#pone.0042075.s002" target="_blank">Figure S2</a>.</p
Gas-Phase Infrared and NMR Investigation of the Conformers of Diacetone Diperoxide (DADP)
Gas-phase infrared measurements of
diacetone diperoxide (DADP)
indicate a chair conformation with less than 5% of the predicted twist
conformer. Vibrational frequencies are very similar to those previously
measured in the solid state. Solution NMR measurements using 2D exchange
spectroscopy (EXSY) also set a very low maximum limit on the equilibrium
population of the twist conformer, with a room-temperature free-energy
difference in excess of 14.5 kJ/mol. These experimental results are
in accord with high-level quantum calculations incorporating full
thermochemistry and solvation effects, which indicate a free-energy
difference in the range of 14.7–17.5 kJ/mol in polar solvents