Atomic triple resonance

Deprotonation of 8 is readily achieved by treatment of 8 with Na[Et3BH] in hexane. The sodium 2,4-dicarba-n/db-hexaborate(r) 9 has been characterised in solution by H, nB and 13C NMR, including various 1H 1 B double and 13C H,llB] triple resonance experiments and also in the solid state by X-ray structural analysis.13 In the solid state, 9 crystallises from toluene without solvent as a dimer in which the two sodium cations are imbedded into a cave formed by the ten basal ethyl groups of the two anions. There are numerous close contacts between the sodium cations and the ethyl groups the B-H-B hydrogen atoms are not involved in those contacts. The electron balance of the anion 9 is comparable to that of cyclopentadienyl anions. 

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. 

The double and triple resonance experiments with roxburghine-D establish that the hydrogen atom at 0-15 Hg) is coupled to two hydrogens at C-14 and one at C-20 but there is also a small coupling between Hb and the hydrogen atom (H2) at C-17 (t/ 15,17 = 0.6 Hz). Such an allylic coupling is reasonable on the basis of structure 80 but is much less easily rationalized on the basis of structure 81. Further, the chemical shifts observed for the protons at C-15 and C-20 (S 2.15 and 1.76, respectively) are consistent with an allylic position for the former and an attachment of C-20 to saturated carbon atoms only. 

It is necessary to assign at least the NMR resonances of atoms comprising the protein backbone prior to further site-specific NMR studies. This can be accomplished routinely by using a suite of triple-resonance experiments and uniformly 2H/13C/15N-labeled protein samples [35], However, the relative high concentrations (100-600 gM) necessary for assignment require a careful choice of measuring conditions. Only in some cases, the published... 

A recently described by Hosur and co-workers triple resonance HN(C)N experiment originally designed for the sequential correlation of Hn and atoms N in N and enriched proteins has been used by them for the estimation of one-bond C"-N couplings in medium size labelled proteins. 

Similarly, H/ C/ Si triple resonance 3D-NMR was used to study the structure of poly(l-phenyl-l-silabutane) (PPSB).f72 In this polymer, stereogenic centers are present at the Si atoms. While the H ID NMR spectrum only revealed two sets of resonances fix)m protons a and 3 to Si (Figure 10a), the ID Si NMR spectrum exhibited three peaks from mm, mr/rm and rr stereosequences (Figure 10c). As with PCFE, a H- C- Si chemical shift correlated 3D-NMR spectrum (Figure 11) permitted assignment of the resonances from the three triad steieosequences. 

From the optically pumped atomic or molecular Rydberg levels neighboring levels can be reached by microwave transitions, as was mentioned above. This triple resonance (two-step laser excitation plus microwave) is a very accurate method to measure quantum defects, fine-structure splitting, and Zeeman and Stark splitting in Rydberg states [592]. 

For some spectroscopic problems it is necessary to use three lasers in order to populate molecular or atomic states that cannot be reached by two-step excitation. One example is the investigation of high-lying vibrational levels in excited electronic states, which give information about the interaction potential between excited atoms at large internuclear separations. This potential V R) may exhibit a barrier or hump, and the molecules in levels above the true dissociation energy V(R = 00) may tunnel through the potential barrier. Such a triple resonance scheme is illustrated in Fig. 5.42a for the Na2 molecule. A dye laser Li excites the selected level (v J )... 

Fig. 1. Schematic diagram of a triple resonance atomic beam apparatus. Between source S (a hot oven) and detector D, magnets A and B produce inhomogeneous deflecting fields, and act as polarizer and analyzer magnet C produces a homogeneous field in which magnetic resonance transitions occur at loops A, B and C. Resonance is detected by the deflection of atoms away from the detector D, if the gradients in magnets A and B are in opposite directions.

In part the interest arises from the fact that the spectroscopic state 87/2 is the same for the atom, 4f 6s as for the divalent ion, 4f . The former has been studied by atomic beam triple resonance (Sandars and Woodgate 1960, Evans et al. 1965), and the latter by ENDOR (Baker and Williams 1962) in Cap2, an environment with cubic symmetry. For a half-filled shell, with no orbital momentum and a spherical distribution of electron spin moment with zero density at the nucleus, both the magnetic dipole and electric quadrupole interactions should be zero. Experimentally, they are small compared with the values for other odd-proton lanthanide isotopes with comparable nuclear moments, for which the hyperfine... 

Comparison of hyperfine data for the europium atom (triple atomic beam resonance) and for Eu in Cap2 (ENDOR). 

For the vast majority of stable nuclei the nuclear magnetic moments have been determined most accurately using nuclear magnetic resonance (NMR). This includes nuclei of the various transition groups with d-eleclrons, where compounds can be prepared with no unpaired electrons. For the 4f group only those ions with an empty shell (La " ) or a full shell (Yb, Lu ) have been measured in this way. The reason is that for all the other ions (except Eu, discussed in section 9.3), the existence of unpaired electrons in the 4f-shell produces hyperfine fields at the nucleus of order 100-800 T. The presence of this large internal field makes it necessary to use the triple resonance atomic beam method (section 1.4) for atoms, or ENDOR (section 3) for ions in the solid state to measure the nuclear moments. With few exceptions, the values in table 1 have all been obtained by such methods, and the corresponding nuclear resonance frequencies for the stable isotopes are listed in table 12. 

There are many experimental techniques for the determination of the Spin-Hamiltonian parameters g, Ux, J. D, E. Often applied are Electron Paramagnetic or Spin Resonance (EPR, ESR), Electron Nuclear Double Resonance (ENDOR) or Triple Resonance, Electron-Electron Double Resonance (ELDOR), Nuclear Magnetic Resonance (NMR), occasionally utilizing effects of Chemically Induced Dynamic Nuclear Polarization (CIDNP), Optical Detections of Magnetic Resonance (ODMR) or Microwave Optical Double Resonance (MODR), Laser Magnetic Resonance (LMR), Atomic Beam Spectroscopy, and Muon Spin Rotation (/iSR). The extraction of data from the spectra varies with the methods, the system studied and the physical state of the sample (gas, liquid, unordered or ordered solid). For these procedures the reader is referred to the monographs (D). Further, effective magnetic moments of free radicals are often obtained from static... 

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