Single resonance experiments

Phenylhydrazine was used for images enhanced by the NOE at natural abundance. As in the case of aniline, proton exchange leads to nearly complete collapse of the N-H couplings for both the NH and NH2 groups. The two groups are different, however, in that the process is more rapid for the NH2 than for the NH group and so leads to a narrower N line (16 Hz at 20 °C) compared with the NH2 value of 80 Hz in the single-resonance experiment. The NOE values are nearly equal at a value of about —2.9, and the T values for N were measured as 8.40 0.1 s (for NH) and 3.91 0.01 s (for NH2). 

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... 

The use of single resonance experiments for sign determination depends on the presence of second-order features which in favorable cases incidentally lead to relative sign information. This has been widely used in magnetically inequivalent systems such as AA XX. While the early relative sign data were obtained in this fashion, multiple resonance techniques are the preferred direct method. 

One-dimensional double-resonance or homonuclear spin-spin decoupling experiments can be used to furnish information about the spin network. However, we have to irradiate each proton signal sequentially and to record a larger number of ID H-NMR spectra if we wish to determine all the coupling interactions. Selective irradiation (saturation) of an individual proton signal is often difficult if there are protons with close chemical shifts. Such information, however, is readily obtainable through a single COSY experiment. 

The proton experiment is a so-called single channel experiment the same channel is used for sample irradiation and observation of the signal, and the irradiation frequency is set (automatically) to the resonance frequency of the protons at the magnetic field strength used by the spectrometer. 

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... 

Fig. 11. Single-spin double-resonance experiment for the calibration of irradiation power. The proton line in chloroform is irradiated with the homonuclear decoupler. The strong central feature is at the irradiation frequency, and the separation of the two satellites is...

The low-temperature EPR experiments used to determine the DNA ion radical distribution make it very clear that electron and hole transfer occurs after the initial random ionization. What then determines the final trapping sites of the initial ionization events To determine the final trapping sites, one must determine the protonation states of the radicals. This cannot be done in an ordinary EPR experiment since the small hyperfine couplings of the radicals only contribute to the EPR linewidth. However, detailed low-temperature EPR/ENDOR (electron nuclear double resonance) experiments can be used to determine the protonation states of the low-temperature products [17]. These proto-nation/deprotonation reactions are readily observed in irradiated single crystals of the DNA base constituents. The results of these experiments are that the positively charged radical cations tend to deprotonate and the negatively charged radical anions tend to protonate. 

Fig. 8. Schematic representation of heteroatom-containing structural elements in polymers that are disposed for characterisation by 1H/X/Y triple resonance experiments where X = 13C and Y = 19F, 31P, 29Si, 119Sn, with possible coherence transfer pathways being indicated by single and double headed arrows.36 39 Selective observation of the correlations of the building blocks in (a)-(c) requires experiments involving out-and-back coherence transfer via Vc.h/ -A.x (a), Vc.h/ cx (b), or / . (c), whereas the simultaneous observation of all correlation signals originating from a chain of an isotope labelled sample (d) is feasible by means of a HCa(Y)-CC-TOCSY sequence.39...

---