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Nuclear Magnetic Resonance
Recently, Chemical Exchange Saturation Transfer (CEST) MRI is emerging as an attractive approach with the capability of directly using low concentration, exchangeable protons-containing agents for generating quantitative MRI contrast. The ability to utilize diamagnetic compounds has been extensively exploited to detect many clinical compounds, such as FDA approved drugs, X-ray/CT contrast agents, nutrients, supplements, and biopolymers. The ability to directly off-label use clinical compounds permits CEST MRI to be rapidly translated to clinical settings.
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.
Ionic Liquids (ILs) are organic salts that melt commonly below 100 °C, constituted entirely by charged species. The tunability and versatility of ILs have given rise to several applications at the academic and industrial levels. Here the following topics are highlighted: chemical structure; ILs classification according to the possibility of proton transfer, and the historical generations of ILs.
In recent years, we have seen spectacular growth in the experimental and theoretical investigations of magnetic properties of small subatomic particles: electrons, positrons, muons, and neutrinos. However, conventional methods for establishing these properties for atomic nuclei are also in progress, due to new, more sophisticated theoretical achievements and experimental results performed using modern spectroscopic devices. In this review, a brief outline of the history of experiments with nuclear magnetic moments in magnetic fields of noble gases is provided. In particular, nuclear magnetic resonance (NMR) and atomic beam magnetic resonance (ABMR) measurements are included in this text. Various aspects of NMR methodology performed in the gas phase are discussed in detail. The basic achievements of this research are reviewed, and the main features of the methods for the noble gas isotopes: 3He, 21Ne, 83Kr, 129Xe, and 131Xe are clarified. A comprehensive description of short lived isotopes of argon (Ar) and radon (Rn) measurements is included. Remarks on the theoretical calculations and future experimental intentions of nuclear magnetic moments of noble gases are also provided.
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.
Zinc and copper are essential cations involved in numerous biological processes; and variations in their concentrations can cause diseases; such as neurodegenerative diseases; diabetes and cancers. Hence, the detection and quantification of these cations is of utmost importance for the early diagnosis of disease. MRI responsive contrast agents (mainly Lanthanide 3+ complexes), relying on a change in state of the MRI active part upon interaction with the cation of interest e.g. switch ON/OFF or vice versa, have been successfully utilized to detect zinc and are now being developed to detect Copper(II). These paramagnetic probes mainly exploit the relaxation-based properties (T1-based contrast agents), but also the paramagnetic induced hyperfine shift properties (paraCEST and parashift probes) of the contrast agents. The challenges encountered going from zinc to copper(II) detection are discussed. Depending on the response mechanism, the use of fast-field cycling MRI seems promising to increase the detection field while keeping a good response. In vivo applications of cation responsive MRI probes are only at their infancy and the recent developments are described, along with the associated quantification problems.
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.