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A method for detecting small molecule NMR resonances under a water peak in biological samples is presented. After high-efficiency solvent suppression using double WATERGATE, either a TOCSY- or ROESY-based coherence transfer sequence is applied to reestablish the resonances close to, or under, water through magnetization transfer using scalar or dipolar coupling, respectively. The use of the TOCSY and ROESY methods ensures an in-phase magnetization transfer, which makes the new approach readily extended for the measurement of transverse relaxation times, internuclear ROEs, and ROE buildup rates. An extension of the new approach for J-resolved spectroscopy is also presented and tested using a sample of human blood plasma.

The technique of multiple-quantum J-resolved NMR spectroscopy (MQ-JRES) is introduced and applied to the spin system SI3–M(such as in the example given here, the 13CH3–12CH in alanine). The SI3spin system was excited to its highest quantum state (8SyIxIyIy), which consists of four coherences: quadruple quantum of (3I+ S), double quantum of (3I− S), double quantum of (I+ S), and zero quantum of (I− S). In the MQ spectrum generated from the projection onto the F1dimension, the resonances of the different multiple-quantum coherences are resolved by their coupling constants to the remote spin (M). The absorptive lineshapes in both F1and F2dimensions enable accurate measurements of transverse relaxation rates, and both amplitude and relative signs of the long-range coupling constants are to be derived from either frequency or time domain data. The selective detection of MQ-JRES spectra of the individual MQ coherences using either phase cycling or pulsed field gradients is presented.

The extension of two-dimensional maximum-quantum correlation spectroscopy (2D MAXY NMR), which can be used to simplify complex NMR spectra, to three dimensions (3D) is described. A new pulse sequence for 3D MAXY-HMQC is presented and exemplified using the steroid drug dexamethasone. The sensitivity and coherence transfer efficiency of the MAXY NMR approach has also been assessed in relation to other HMQC- and HSQC-based 3D methods.

Modifications to the WATERGATE method for removing the solvent resonance from1H NMR spectra are presented. In the conventional WATERGATE, a pulse train with three pairs of symmetric pulses in the form 3α–τ–9α–τ–19α–τ–19α–τ–9α–τ–3α (designated here W3), where 26α = 180°, is used, while the improved versions use four and five pairs of symmetric pulses (designated here W4 and W5), respectively. The modified methods provide narrower noninversion regions and hence enhance the sensitivities of the peaks close to the water resonance. The inversion and suppression profiles of the pulse trains W3, W4, and W5 are compared theoretically and experimentally and good agreement is obtained.