Isotopic labeling nuclear spins

Labeled precursors enriched in one or more positions with stable isotopes ( H nuclear spin 7=1, nuclear spin 7= 1/2, nuclear spin 7= 1/2, and 0 nuclear spin 7= 5/2) have been extensively used in biosynthetic studies to detect the incorporation, to examine the origin, or to follow the fate of specific parts of a molecule or atoms in a pathway. 

Selective analytic and spectroscopic methods for analyzing biomimetic model complexes bound to the support are rather limited, and a detailed characterization of such hybrid materials is much more challenging than of soluble molecular complexes. If local spectroscopic probes are available, IR spectroscopy, gel-phase or solid-state NMR spectroscopy, EPR spectroscopy, or (diffuse reflectance) UV-vis spectroscopy is applicable. Useful IR spectroscopic labels include CO, C=N, E-H, M=E, and M=E stretching vibrations as long as they are either very intense or are separated from the matrix vibrations. For EPR spectroscopic analysis, metal isotopes with nuclear spin 1 0 are suitable. Biologically interesting metal ions include (7 = 7/2, 99.76%), Mn I =512, 100%), Co (7 = 7/2, 100%), 3/65cu (7 = 3/2, 69.09% 7 = 3/2, 30.91%), and (7 = 5/2, 15.72% ... 

The important nuclear spin interaction in the context of probing molecular reorientation is provided by the quadrupolar interaction (Q) or the chemical shift anisotropy (CSA), and we assume that the spin system is prepared by, for example, isotopic labeling in such a way that only a single interaction is relevant. The ubiquitous presence of dipolar broadening is assumed to be small. For most NMR experiments it suffices to consider the secular part of the... 

Oxygen occurs in Nature in three isotopic species 160 (99.759%), nO (0.0374%), and 180 (0.2039%). The rare isotopes, particularly lsO, can be concentrated by fractional distillation of water, and concentrates containing up to 99 at. % lsO or up to 90 at. % nO as well as other labeled compounds are commercially available. Oxygen-18 has been widely used as a tracer in studying reaction mechanisms of oxygen compounds. Oxygen-17 has a nuclear spin 5/2, but because of the low abundance of this isotope and appreciable quadrupole moment, enriched materials and Fourier transform nmr techniques are required. 

Several isotopes (see Isotopes Isotope Labeling) of Cd are known, and 8 are stable (Table 3). For " Cd and " Cd, the nnclear spin is 1/2 and they are used for NMR studies of Cd compounds and in biological fields (see Cadmium Organometallic Chemistry). " Cd is used in the nuclear industry because of its high neutron cross section. Unstable isotopes are prepared from nuclear reactions. Cd stable isotope composition in geological and meteorite samples has been investigated using multiple collector inductively coupled plasma mass spectrometry. ... 

In elemental analysis, the presence of Ir in a compound can be quantified by use of atomic absorption and emission spectroscopies. Both natural isotopes see Isotopes Isotope Labeling) of Ir possess nuclear spins (/ = 3/2), but their use in NMR spectroscopy is limited by a large quadrapole moment... 

Nickel (relative atomic mass = 58.69) is a first-row transition metal in group Vlllb of the periodic table. Although there are five natural isotopes, Ni (68.3%) and Ni (26.1%) are the most abundant. Proteins are often labeled with Ni (nuclear spin, I, is 3/2) to identify the nickel site by EPR spectroscopy, since paramagnetic species with significant spin on Ni exhibit a four-line splitting. Ni, which is a beta emitter with a relatively long half-life of 100 years, can be used to identify Ni-containing proteins and to measure Ni uptake in cells. 

These methods are nondestructive, and are particularly useful for atoms that have no - or only very short-lived - radioisotopes. There is a requirement for an isotope with a suitable nuclear spin, sensitivity and abundance, of which F and Li are important examples. These methods divide essentially into two classes (i) relaxation time experiments, where the diffusive motion of spins results in the loss the coherence of the spins and (ii) field gradient experiments, where the nuclear spin is used as a label on the atom, in a similar manner to a tracer experiment. 

The development of NMR techniques for double-labeled material began in the late 1980s, and there are dozens of different types of experiments that exploit scalar couplings for assignment purposes. These experiments are called triple resonance experiments because they involve three different nuclear spins, H, C, and N (Ikura et al., 1990 Bax and Grzesiek, 1993). To perform experiments of this type, it is usually necessary to isotopically enrich the protein to 99% for the and N atoms. The goal of these experiments is to correlate intra- and inter-residue chemical shifts with the amide proton and nitrogen chemical shifts. 

An asterisk denotes a radioactive isotope whose lifetime is indicated in the column Natural abundance. When a stable element has several radioactive isotopes, a few ones have been chosen for their interest in different applications. For the radioactive elements, only the isotopes with the longest lifetimes and at least one with a nonzero nuclear spin I are indicated. The electronic configuration of an element with atomic number Z is given in italics in the Name and symbol column. When relevant, the old Group label notation of the periodic table is indicated in brackets in this same column. The radioactive elements francium, radium, and actinium (Z = 87, 88, and 89, respectively) have been omitted. 

The isotopic exchange of hydrogen in subcellular structures has made considerable progress Labels of nearly any size can be introduced into any site of a large biological structure. This is the preparative basis for the use of nuclear spin dependent neutron scattering. 

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