PULSED-FIELD GRADIENT-BASED WATER SUPPRESSION TECHNIQUES IN HOMONUCLEAR NMR-SPECTROSCOPY

Suppression of the immense water signal arising in studies of proteins and nucleic acids in aqueous solution has traditionally been a formid able problem in biomolecular nuclear magnetic resonance (NMR). Convent ionally used presaturation-based techniques result in significant atte nuation of exchangeable protons such as amides in proteins and imino/a mino protons in nucleic acids. Spectra also suffer from artifacts such as baseline distortions. With the advent of pulsed field gradients (P FGs), high degree of suppression of water signal can be achieved with complete preservation of exchangeable protons, We present two PFG- and selective-excitation-based techniques: gradient-flipback (GRAF) and w atergated-gradient-flipback (WGRAF), which complement existing PFG-bas ed methods and improve upon some of their shortcomings, The GRAF techn ique provides high selectivity near the mater resonance whereas WGRAF compromises on selectivity to deliver ultra-high quality suppression o f water signal. Application of these techniques to NOESY and TOCSY spe ctra of barstar are demonstrated.