Full Sensitivity and Enhanced Resolution in Homodecoupled Band‐Selective NMR Experiments

Abstract

Fingers on the pulse: An NMR pulse scheme that provides full sensitivity in homodecoupled band‐selective NMR spectroscopy experiments is proposed (see figure). The easy implementation of this HOBS scheme as a general building block into a great variety of multidimensional NMR experiments leads to pure‐shift spectra with enhanced resolution and with the maximum attainable sensitivity.

Pure Shift NMR Spectroscopy

“…Several J-refocusing elements are available, based on BIRD, 4 frequency-and spatially-selective refocusing as originally developed by Zangger and Sterk (ZS), 5 BSD, 6,7 and, in the anti z-COSY experiment and time-reversal methods, low-flip-angle pulse pairs. 8,9 Each of these J-refocusing elements reverses the effects of J, which are thus suppressed explicitly at a given evolution time.…”

“…28 It is also very effective with both ZS and a variant of the ZS method in which no field gradient is applied during the selective 180 • pulse. 6,7 The distinction between active and passive spins is then made purely according to chemical shift: the active spins are those that are refocused by the selective 180 • pulse, so the resultant spectrum for these spins has the effects of all couplings to protons outside this frequency range suppressed. This BSD (also known as band selective homonuclear (BASH) 29 decoupling, and homodecoupled band selective (HOBS) 6 NMR) method is well-suited to systems in which a narrow range of chemical shifts is of interest (e.g., protein signals) or in which a particular set of signals is of interest.…”

“…As with real-time BIRD HSQC, BSD can offer signalto-noise ratios that are actually greater than that of the parent experiment, even where in-band couplings mean that only partial decoupling is achieved. 6,30 A different approach is taken in the anti z-COSY experiment, which segments spins between active and passive subsets by means of a pair of small flip angle pulses that replace the Volume 3, 2014 mixing pulse of a COSY experiment. The small flip angle pulses refocus a small proportion of spins while leaving the majority unaffected; adding a nonselective 180 • pulse results in a COSY spectrum in which the diagonal responses are dominated by a line of multiplet components that run at right angles to the main diagonal.…”

HOBS methods for enhancing resolution and sensitivity in small DNA oligonucleotide NMR studies

“…All NMR data were acquired using a Bruker 14.1-T AVANCE II+ NMR spectrometer operating at 600.13 MHz for proton resonance using a triple resonance broadband inverse (TBI: 1 H, 13 C, 31 P-15 N) probe head fitted with an actively shielded z-gradient coil capable of delivering a maximum pulsed field-gradient field of 53.5 G/cm and running under Topspin (version 2.1, Bruker, Karlsruhe, Germany). All NMR data were acquired at a regulated probe head temperature of 298 K.…”

“…On the one hand, homonuclear band-selective (HOBS) decoupling allows data acquisition at full sensitivity but only on part of the NMR spectrum under special conditions. [13,14] On the other hand, pure shift yielded by chirp excitation gives the full 1 H-{ 1 H} BB NMR spectrum reportedly with tenfold greater sensitivity compared with the spatially encoded pure shift approach. [15] HOBS is effective only if resonances from specific types of proton occur in a region of the spectrum that is relatively isolated from scalar coupling partners and allows full sensitivity to be maintained.…”