Fast-pulsing longitudinal relaxation optimized techniques: Enriching the toolbox of fast biomolecular NMR spectroscopy Paul Schanda Laboratorium für Physikalische Chemie, ETH Zürich, 8093 Zürich, Switzerland article info Article history: Received 7 April 2009 Accepted 13 May 2009 Available online 27 May 2009 Keywords: Multidimensional NMR Longitudinal relaxation optimization Protein folding Selective pulses High-throughput NMR Ó 2009 Elsevier B.V. All rights reserved. Contents 1. Introduction ......................................................................................................... 239 1.1. Basic considerations about multidimensional NMR .................................................................... 239 1.2. Time requirements of nD FT NMR .................................................................................. 240 1.3. Speeding up multidimensional data acquisition ....................................................................... 240 1.4. Scope, limitations and organization of this review ..................................................................... 241 2. Alternative data sampling methods ...................................................................................... 241 2.1. Sparse-sampling methods ......................................................................................... 242 2.1.1. Alternatives to linear sampling and Fourier transformation ...................................................... 242 2.1.2. Spectral aliasing ......................................................................................... 242 2.1.3. Reduced-dimensionality or projection NMR ................................................................... 242 2.2. Hadamard NMR spectroscopy ..................................................................................... 244 2.3. The ultrafast single-scan approach.................................................................................. 245 2.4. Summary ...................................................................................................... 246 3. Fast-pulsing methods .................................................................................................. 246 3.1. Partial excitation and the Ernst angle ............................................................................... 247 3.2. Accelerating the magnetization recovery by optimized pulse sequence design .............................................. 248 3.3. Proton longitudinal relaxation enhancement in biomolecules ............................................................ 248 3.3.1. Proton longitudinal relaxation basics: the two-spin system ...................................................... 248 3.3.2. Proton longitudinal relaxation in biomolecules ................................................................ 250 3.3.3. Amide proton relaxation and water magnetization ............................................................. 252 3.3.4. Dependence of relaxation on the size of the molecule .......................................................... 252 3.3.5. Dependence of relaxation on the magnetic field strength ........................................................ 253 3.3.6. Amide proton relaxation and the initial magnetization of non-amide protons ....................................... 254 3.3.7. Amide proton relaxation and internal dynamics ............................................................... 254 3.3.8. The effect of deuteration on amide proton relaxation rates ...................................................... 255 3.3.9. The behavior in a multi-scan experiment ..................................................................... 255 3.3.10. Longitudinal relaxation optimized spectroscopy of other groups of 1 H spins ....................................... 256 3.3.11. Proton longitudinal relaxation in biomolecules: summary and important features .................................. 256 0079-6565/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.pnmrs.2009.05.002 E-mail address: paul.schanda@gmx.at Progress in Nuclear Magnetic Resonance Spectroscopy 55 (2009) 238–265 Contents lists available at ScienceDirect Progress in Nuclear Magnetic Resonance Spectroscopy journal homepage: www.elsevier.com/locate/pnmrs