Summary

NMR has revolutionized structure determination and is a technique used in a very wide range of disciplines from biology, chemistry, material science, polymers and biopolymers, to drug design, food science, etc. Although the technique has been around for more than seventy years, it is still in development, both instrumentally with higher magnetic fields, better probes, improving pulse sequences and signal manipulation, and in solid state NMR with higher spinning speeds, and in relation to improving signal to noise ratios. It is the aim to collect a number of contributions covering recent progress both with respect to techniques and to new uses of NMR in its entire range of applications.

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Topic Review
Salt Bridges investigated by NMR
Salt bridges are interactions, electrostatic combined with hydrogen bonding, between oppositely charged residues, typically carboxylic acid anions and ammonium ions, provided they are close together.  For an illustration see Fig. 1. Salt bridges are of particular interest in proteins and other biomolecules.  In the present contribution salt bridges are investigated by means of 1H chemical shifts, determination of pKa values and deuterium isotope effect on 15N and 1H chemical shifts.  In the latter case model compounds like ammonium ions are also investigated and the use of deuterium isotope effects on chemical shifts are supported by Density Functional Theory (DFT) calculations.  The use of isotope effects on chemical shifts enables a distinction between salt bridges observed in the solid state by X-ray diffraction and those actually present in solution.
  • 2.5K
  • 27 Oct 2020
Topic Review
Humic Substances
Humic substances are a very important part of our soil.  The topic is description of the structure of humic substances using NMR.  The NMR part is divided into two parts, liquid and solid state NMR.  The assignment of NMR spectra are discussed and the structural elements that can be deduced from the spectral information.  Principal Component Analysis is used as a tool to categorize the information.  Structural models are discussed.
  • 2.8K
  • 27 Oct 2020
Topic Review
Tautomerism Detected by NMR
Tautomerism is typically the relocation of a light atom, often hydrogen, at the same time as a rearrangement of the electronic structure.  Typical examples are acetylacetone and acetone. This entry gives a short introduction to how to detect and describe a tautomeric equilibrium using Nuclear Magnetic Resonance (NMR). Typical parameters used are chemical shifts (1H,13C,15N,19F and 17O) one-bond coupling constants and isotope effects on chemical shifts.
  • 9.6K
  • 29 Oct 2020
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