Chain association equilibriums. Nuclear magnetic resonance study of the hydrogen bonding of N-monosubstituted amides. II. In carbon tetrachloride

Graham, Laurine L.; Chang, Chang Y.

doi:10.1021/j100676a009

Cited by 33 publications

(10 citation statements)

References 13 publications

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“…At the concentrations indicated, there were no signs of aggregatation of these solutes in any of the solvents examined. However, when concentrations were elevated above 0.4 M in cyclohexane solution, new peaks began to appear, in accord with the known tendencies of these compounds to aggregate at high concentrations (Graham & Chang, 1971). In water, chloroform, and cyclohexane, proton spectra of /V-methylformamide showed methyl resonances for the cis isomer that were shifted downfield from those for the trans isomer, whereas the resonance of the formyl proton of the cis isomer was situated slightly upfield from that of the trans isomer, (Table I).…”

Section: Resultssupporting

confidence: 57%

Influences of solvent water on protein folding: free energies of solvation of cis and trans peptides are nearly identical

Radzicka¹,

Pedersen²,

Wolfenden³

1988

Biochemistry

172

153

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Peptide bonds interact so strongly with water that even a modest difference between the free energies of solvation of their cis and trans isomers could have a significant bearing on protein structure. However, proton magnetic resonance studies at high dilution in deuteriated solvents show that N-methylformamide exists as the cis isomer to the extent of 8% in water, 10.3% in chloroform, 8.8% in benzene, and 9.2% in cyclohexane. Integrated intensities of proton and carbon resonances show that N-methylacetamide exists as the cis isomer to the extent of only 1.5% in water, not changing much in nonpolar solvents. Quantum mechanical calculations using the 6-31G basis set reproduce these relative abundances with reasonable accuracy and show that there is little difference between the dipole moments of the cis and trans isomers, for either amide. The remarkable insensitivity of cis/trans equilibria to the solvent environment and the heavy preponderance of trans isomers regardless of the polarity of the surroundings (ca. 98.5% for N-methylacetamide, whose properties may resemble those of a typical peptide bond) accord with the overwhelming preference of peptide bonds for the trans configuration that is consistently observed in the three-dimensional structures of globular proteins.

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Section: Resultssupporting

confidence: 57%

Influences of solvent water on protein folding: free energies of solvation of cis and trans peptides are nearly identical

Radzicka¹,

Pedersen²,

Wolfenden³

1988

Biochemistry

172

153

View full text Add to dashboard Cite

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“…10 Above an NMA concentration of about 0.8 mol dm -3 the relaxation time associated with changes in hydrogen bonding no longer increases, but instead reaches a constant value. Similarly, concentration-dependent studies of the isotopic chemical shifts of NMA-CCl 4 binary mixtures show that the chemical shifts all reach their asymptotic limits at a concentration of about 1.0 M. 72 That is, at concentrations higher than 0.8 mol dm -3 the cluster populations of NMA are comparable to those in higher concentrations and in the neat liquid. For the neat liquid, QCE calculations predict that the most significant populations are linear pentamer (40%), linear dimer (20%), and monomer (17%).…”

Section: Resultsmentioning

confidence: 87%

Quantum Cluster Equilibrium Theory of Liquids: Temperature Dependence of Hydrogen Bonding in LiquidN-Methylacetamide Studied by IR Spectra

Ludwig¹,

Reis²,

Winter³

et al. 1998

J. Phys. Chem. B

111

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Temperature-dependent infrared spectra for liquid N-methylacetamide are calculated by the ab initio quantum cluster equilibrium (QCE) and Gaussian-94 methods and compared with experimental measurements. The calculations are based on standard ab initio self-consistent-field (SCF) methods at the 3-21G levels for five different molecular clusters. The cluster sizes vary from the monomer up to a five-membered linear structure. Strong cooperative effects are found in the molecular clusters and are reflected in the geometries and vibrational spectra for each species. The equilibrium populations of the clusters were calculated for the entire liquid range. At low temperatures the linear pentamer is the dominant species. At higher temperatures these clusters are replaced, primarily, by linear dimers and monomers. The calculated frequencies are in excellent agreement with the temperature behavior found in FT-IR experiments.

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“…molecular weight determinations in CDCl 3 gave a molecular mass of 845 ± 80 g·mol -1 which is slightly higher than the calculated molecular mass of the monomer (707 g·mol -1 ). The slight deviation may result from weak intermolecular association …”

Section: Resultsmentioning

confidence: 99%

The Pinched Cone Conformation of Calix[4]arenes: Noncovalent Rigidification of the Calix[4]arene Skeleton

et al. 1996

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Calix[4]arenes at the upper rim substituted with two (thio)urea moieties, 2a-c and 4, or substituted with two acetamido groups, 5, adopt a pinched cone conformation in CDCl 3 solution. The pinched cone conformation is the result of diametrical, intramolecular hydrogen bonds and was studied by 1 H NMR dilution and variable-temperature experiments, NOESY spectroscopy, and FTIR experiments. The pinched cone conformation in these novel calix[4]arenes is stable in C 2 D 2 Cl 4 up to at least 120°C. The bis(ureido)calix[4]arenes 2b,c give a hydrogen-bonded dimer in the pinched cone conformation.

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Chain association equilibriums. Nuclear magnetic resonance study of the hydrogen bonding of N-monosubstituted amides. II. In carbon tetrachloride

Cited by 33 publications

References 13 publications

Influences of solvent water on protein folding: free energies of solvation of cis and trans peptides are nearly identical

Influences of solvent water on protein folding: free energies of solvation of cis and trans peptides are nearly identical

Quantum Cluster Equilibrium Theory of Liquids: Temperature Dependence of Hydrogen Bonding in LiquidN-Methylacetamide Studied by IR Spectra

The Pinched Cone Conformation of Calix[4]arenes: Noncovalent Rigidification of the Calix[4]arene Skeleton

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