Triple resonance

The term triple resonance is used for any experiment in which two irradiation frequencies are applied while a third frequency is observed, but there are two distinct types of experiment involved. In the first type, one of the irradiation channels provides decoupling, usually of H, while the other is used to irradiate another nucleus. There is nothing conceptually new in this it is simply a combination of techniques already discussed. A simple example is provided by a study of organophosphine selenides [34], in which no Se coupling could be observed in the H NMR spectrum. Nevertheless, because Se is coupled to P, and P to 

In all double resonance experiments there are changes in the intensities of observed resonances, whatever the irradiation power levels. The Nuclear Overhauser Effect (NOE) relates to the ratio of the total integrated intensity achieved in the double resonance experiment to that achieved in the single resonance experiment. The double resonance experiment involves presamration of the X nucleus, i.e. irradiation of the X nucleus frequencies before the FID of the A nucleus is sampled. The name Nuclear Overhauser Effect is applied both to the magnitude of the effect and to the phenomenon itself. Its magnitude depends on the balance of relaxation mechanisms, and its maximum value for an A X experiment in which the X nucleus is saturated, occurring when dipole-dipole mechanisms predominate, is given by 

Equation 4.17 shows that the maximum enhancement is 50% for homonuclear decoupling. As dipole-dipole relaxation depends on distances between nuclei, molecular conformations can be studied by measuring Overhauser enhancements. Normally apphed to H H experiments, the procedure involves 

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A refinement of the ENDOR experiment is electron-nnclear-nnclear triple resonance, now commonly denoted TRIPLE. In TRIPLE experiments one monitors the effect of a simnltaneons excitation of two nnclear spm transitions on the level of the EPR absorption. Two versions, known as special TRIPLE (ST) and general TRIPLE (GT), are rontinely perfonned on connnercially available spectrometers. 

Mdbius K, Plato M and Lubitz W 1982 Radicals in solution studied by ENDOR and TRIPLE resonance spectroscopy P/rys. Rep. 87 171-208... 

Mdbius K, Lubitz W and Plato M 1989 Liquid-state ENDOR and TRIPLE resonance Advanced EPR in Biology and Biochemistry ed A J Hoff (Amsterdam Elsevier) ch 13, pp 441-99... 

Mdbius K and Biehl R 1979 Electron-nuclear-nuclear TRIPLE resonance of radicals in solution... 

Freed J H 1969 Theory of saturation and double resonance effects in ESR spectra. IV. Electron-nuclear triple resonance J. Chem. Rhys. 50 2271-2... 

Dinse K P, Biehl R and Mdbius K 1974 Electron nuclear triple resonance of free radicals in solution J. Chem. Rhys. 61 4335—41... 

Biehl R, Plato M and Mdbius K 1975 General TRIPLE resonance on free radicals in solution. 

By the use of nuclear magnetic double (and triple) resonance, the configuration (34) of pseudo-talose was established, confirming chemical evidence, and the sidechain-equatorial conformation (38) was also... 

All P.M.R. spectra were measured with a Varian HA 100 spectrometer operating in the frequency-sweep mode with tetramethylsilane as the reference for the internal lock. The double and triple resonance experiments were performed using a Hewlett Packard 200 CD audio-oscillator and a modified Hewlett Packard 200 AB audio-oscillator (vide infra). Spectra were measured using whichever sweep width was required to ensure adequate resolution of the multiplets under investigation, generally 250 or 100 Hz, and sweep rates were selected as necessary. Extensive use was made of the Difference 1 and Difference 2 calibration modes of the instrument, both for the decoupling experiments and for the calibration of normal spectra. 

Figure 3 3-D and 4-D triple resonance experiments correlate interresidue or... 

Muhandiram DR, Kay LE. Gradient-enhanced triple resonance three-dimensional NMR experiments with improved sensitivity. J Magn Reson 1994 103 203-216. 

Lohr F, Riiterjans H. A triple resonance experiment for the sequential assignment of backbone resonances in proteins. J Biomol NMR 1995 6 189-197... 

While the CA and CO secondary chemical shifts cannot be determined using conventional triple-resonance experiments that employ the H-15N correlation spectrum, incorporation of individual... 

The 27Al-29Si RAPT-CPMG-HETCOR experiments were performed at 14.1 T on a Varian NMR System 600 spectrometer, equipped with a triple resonance MAS probe. 

Cf1 - 27A1 or mC H "B triple resonance as well as H 27AI double resonance methods have been employed to measure the local neighborhood between B or A1 nuclei in the zeolite framework and the C (or H) nuclei in the SDA [203]. A set of various boro- or aluminosilicates has been investigated, and Fig. 5 illustrates one of the examples. 

Perhaps the most detailed studies of both the isotropic and anisotropic exchange interactions have been made for InP, where the anisotropic (pseudo-dipolar) part of the 31P-115In exchange coupling was shown to reduce the measured 31P second moments from theoretical values calculated from dipolar couplings alone [255, 256]. Double and triple resonance 31P MAS-NMR experiments have also provided much information as a result of the existence of the two nearly identical isotopes of... 

Let us first discuss common coherence transfer steps of triple-resonance experiments with the emphasis on relaxation mechanisms. 

Exploitation of the TROSY effect is rather straightforward. In contrast to 15N-HSQC (Heteronuclear Single Quantum Coherence) or standard triple-resonance experiments based on 15N-HSQC, no radio frequency pulses or composite pulse decoupling should be applied on amide protons when HN spin is not in the transverse plane. Likewise the 15N decoupling should be... 

At this point, before going into the details of triple-resonance experiments, we shift the focus to the polarization transfer step. Throughout this... 

Figure 3 depicts the famous triple-resonance experiment, HNCA (amide proton to nitrogen to alpha carbon experiment)10,32 34 (Fig. 3a), and the... 

The effect of deuteration, for the needs of sequence-specific resonance assignments using triple-resonance experiments, was first demonstrated by Bax and co-workers on the 19.7 kDa protein calcineurin B in 1993.56 By replacing the H spin with deuterium, the transverse relaxation time of 13C spin is increased by nearly an order of magnitude due to the 6.5 times smaller gyromagnetic ratio of 2H in comparison to in.52,56 Not surprisingly, deuteration was utilized for the aid of structure determination of several... 

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