Nuclear magnetic resonance spectroscopy solvent effects

Duthaler, R.O. and Roberts, J.D., Nitrogen-15 nuclear magnetic resonance spectroscopy solvent effects on the 15N chemical shifts of saturated amines and their hydrochlorides, J. Magn. Reson., 34, 129, 1979. 

Key Words Nuclear magnetic resonance spectroscopy, Solvent, Water suppression. Radiation damping. Demagnetization field. Bulk susceptibility effect. Presaturation, Watergate, Purge, Metabonomics. 

For its H-NMR (Nuclear Magnetic Resonance Spectroscopy), the two P-protons (HP) show up at 6.32 ppm, whereas the two a-protons (Ha) show up at 6.87 ppm, further down field from the two p-protons, because of the inductive effect from the nitrogen atom. As far as die NH is concerned, its chemical shift often is affected by solvents and concentrations for the NMR samples. The coupling constant between Ha and HP is 2.6 Hz, whereas the coupling constant between HP and HP is 3.4 Hz. 

In its H-NMR (Nuclear Magnetic Resonance Spectroscopy), the chemical shifts of Ha and H3 follow the trend of those of pyrrole. Ha ( 7.2 ppm) is much further down filed than Ha ( 6.6 ppm), again thanks to the inductive effect exerted by the N atom. The chemical shifts for the benzene ring are more nuanced, with H4 ( 7.7 ppm) showing up most down field and He showing up at 7.4 ppm. Similar to that of pyrrole, the NH s chemical shift often changes in different solvents and concentrations for the NMR samples. 

Charge transfer complexes of styrene and acrylonitrile have been shown to exist when in the presence of zinc chloride. Proton nuclear magnetic resonance spectroscopy has been used to establish this effect. In the proper solvents styrene and acrylonitrile will form occluded macroradicals which may then be used to form block copolymers. These block copolymers occur both in the presence and absence of zinc chloride. Pyrolysis gas chromatography, differential scanning calorimetry, and solubility studies show the properties of the two copolymers and their various block copolymers to be quite similar. Differences in the copolymers may be seen from carbon-13 nuclear magnetic resonance spectroscopy. Yield data for the block copolymers is reported. 

The use of computer simulations to study internal motions and thermodynamic properties is receiving increased attention. One important use of the method is to provide a more fundamental understanding of the molecular information contained in various kinds of experiments on these complex systems. In the first part of this paper we review recent work in our laboratory concerned with the use of computer simulations for the interpretation of experimental probes of molecular structure and dynamics of proteins and nucleic acids. The interplay between computer simulations and three experimental techniques is emphasized (1) nuclear magnetic resonance relaxation spectroscopy, (2) refinement of macro-molecular x-ray structures, and (3) vibrational spectroscopy. The treatment of solvent effects in biopolymer simulations is a difficult problem. It is not possible to study systematically the effect of solvent conditions, e.g. added salt concentration, on biopolymer properties by means of simulations alone. In the last part of the paper we review a more analytical approach we have developed to study polyelectrolyte properties of solvated biopolymers. The results are compared with computer simulations. 

Ronayne, J., Williams, D. H. Solvent Effects in Proton Magnetic Resonance Spectroscopy. Annual Review of NMR Spectroscopy, Vol. 2,pp. 83-124, New York 1969. Laszlo, P. Solvent Effects and Nuclear Magnetic Resonance. Progr. N.M.R. Spectroscopy 3, 231-403(1968). 

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