Fluorine-proton Overhauser effects in fluorine-labeled macromolecular systems

Abstract

ions with three-, four-, and five-membered rings undergo ring opening after ca. 10-9 s to form initially 1-alkene molecular ions which, depending on the internal energy and ion lifetime, isomerize to some extent to a mixture of double bond isomers. From the identity of the CA spectra (reflecting to a large extent the stable ions) it can be concluded that the energy barrier for such ring opening processes is considerably smaller than the lowest threshold for decomposition and cannot exceed a few tenths of an electron volt.30In contrast, cycloalkane molecular ions with six-, seven-, and eight-membered rings are stable prior to decomposition over the entire range of lifetimes and internal energies available in an electron impact mass spectrometer. As already pointed out by Meyerson et al.4 for methylcyclopentane and methylcyclohexane the difference in the isomerization behavior is most simply accounted for as resulting from the difference in ring strain.Furthermore the present results rule out that threeor four-membered cycloalkane molecular ions are formed by 1,3or 1,4 elimination of HX from compounds of the general type RX (X = OH, F, Cl) as has been assumed sometimes in the past31 which does not exclude that these eliminations proceed via transition states with a cycloalkane-like structure.

Acyl carrier protein from Escherichia coli: characterization by proton and fluorine-19 nuclear magnetic resonance and evidence for restricted mobility of the fatty acid chain in tetradecanoyl-acyl-carrier protein

“…The nuclear Overhauser enhancement (NOE), the fractional increase or decrease in intensity of the fluorine resonance due to the saturation of the proton resonances (µ), was determined to be -0.7. The values of the Ti and NOE values are in accord with the dominance of the dipole-dipole relaxation mechanism (Hull and Sykes, 1975b), and the ro-tational correlation time (about 10 8 s, Gerig, 1977) calculated for ACP.…”

Use of paramagnetic 19F NMR to monitor domain movement in a glutamate transporter homolog

“…Retrieving the distance-dependent paramagnetic component from the R 1 PRE for 1 H nuclei is difficult because of the interference from 1 H- 1 H cross relaxation 15 . 19 F longitudinal relaxation occurs in proteins on a seconds time scale and, because it is dominated by dipole-dipole interactions 20 with negligible heteronuclear 19 F- 1 H cross relaxation 21 , 22 , is effectively mono-exponential 21 .…”

Solution conformation of peptides by the intramolecular nuclear Overhauser effect experiment. Study of valinomycin-K+

“…dimethyl sulfoxide [DMSO]). Our treatment of phenomena such as spin diffusion, already discussed by other investigators (3)(4)(5)(6)(7) in the context of its relevance to NMR studies of proteins, is not intended to be comprehensive, but focuses on considerations relevant to the NOE studies of peptides and proteins. Some preliminary attempts at quantitatively applying the NOE technique to peptides have already appeared (8)(9)(10)(11)(12)(13)(14), including a semi-quantitative description (1 1) of the conformation of the antibiotic valinomycin in DMSO.…”

“…Our procedure consists of first performing a series of NOE experiments involving saturation and observation of both the backbone and side chain protons. Next, for each of the conformations we generate the structure of the peptide using the proposed torsion angles for the backbone (', 6) and side chain (X) orientations and compute the theoretical NOE values for a simulated experiment. Finally, employing statistical hypothesis testing techniques, we compare the goodness of fit of these models to the experimental data.…”