WaterControl: self-diffusion based solvent signal suppression enhanced by selective inversion

Ultra-clean pure shift NMR with optimal water suppression for analysis of aqueous pharmaceutical samples

Pure shift NMR experiments greatly enhance spectral resolution by collapsing multiplet structures into singlets and, with water suppression, can be used for aqueous samples. Here, we combine ultra-clean pure-shift NMR (SAPPHIRE) with two different internally encoded water suppression schemes to achieve optimal performance for small molecule and macrocyclic peptide pharmaceuticals in water and acetonitrile-water mixtures.

Applications of WaterControl to TOCSY and COSY experiments

WaterControl is a solvent suppression method based on WATERGATE and PGSTE and is very efficient in selectively reducing the solvent signal in 1D pulse-acquire and 2D NOESY of protein solutions. In this study, the WaterControl technique was appended to two common 2D NMR methods used in resonance assignment of proteins, namely TOCSY and CLIP-COSY. Similar to that observed in regular 1D pulse-acquire and 2D NOESY, the incorporation of WaterControl in these 2D methods led to excellent solvent suppression superior to that obtained using W3- or W5-based WATERGATE sequences. The water signal was essentially eliminated in the TOCSY and CLIP-COSY with WaterControl while useful cross peaks around the water resonance at ω₂ were preserved. This is in contrast to the 2D spectra obtained from the corresponding WATERGATE containing sequences, where these cross peaks in the ω₂ region are usually suppressed together with the water resonance. These new WaterControl sequences provide significantly improved water suppression thereby facilitating protein NMR studies.

A Simple and Effective Binomial Block Based Pulse Sequence Capable of Suppressing Multiple NMR Signals

A binomial-like block based multiple suppression NMR pulse sequence, termed MULTI-GATE-FSB, that is simple to implement with outstanding suppression performance for multiple solvent signals (or multiple resonances) is investigated. The sequence was tested on two water-alcohol solvent systems, and a standard lysozyme sample, with suppression of three or four regions (though it is extendable to any number of regions). The suppression of all solvent signals was possible in the alcohol-water systems tested with both long and short recycle delays and without the requirement for lengthy presaturation pulses. Such a sequence holds promise not only for LC-NMR applications and solvent suppression but for multiple suppression applications in general (e.g., analysis of impurities/components).

NOESY-WaterControl: a new NOESY sequence for the observation of under-water protein resonances

Highly selective and efficient water signal suppression is indispensable in biomolecular 2D nuclear Overhauser effect spectroscopy (NOESY) experiments. However, the application of conventional water suppression schemes can cause a significant or complete loss of the biomolecular resonances at and around the water chemical shift (ω₂). In this study, a new sequence, NOESY-WaterControl, was developed to address this issue. The new sequence was tested on lysozyme and bovine pancreatic trypsin inhibitor (BPTI), demonstrating its efficiency in both water suppression and, more excitingly, preserving water-proximate biomolecular resonances in ω₂. The 2D NOESY maps obtained using the new sequence thus provide more information than the maps obtained with conventional water suppression, thereby lessening the number of experiments needed to complete resonance assignments of biomolecules. The 2D NOESY-WaterControl map of BPTI showed strong bound water and exchangeable proton signals in ω₁ but these signals were absent in ω₂, indicating the possibility of using the new sequence to discriminate bound water and exchangeable proton resonances from non-labile proton resonances with similar chemical shifts to water.