Abstract
A method is long observation based selective homonuclear decoupling includes acquiring one of CO or CA time domain signals during rotor synchronized breaks between decoupling pulses.
Claims
1. A method of long observation based selective homonuclear decoupling that removes J-coupling interactions between C.sup. and C nuclei from .sup.13C acquisition in a nuclear magnetic resonance (NMR) spectrometer, the method comprising: acquiring time domain signals of one partner of a J-coupled C.sup. and C pair from the NMR spectrometer during rotor synchronized breaks between applying decoupling pulses to a second partner of the J-coupled pair; and applying, in the NMR spectrometer, the decoupling pulses to a second partner of the J-coupled C.sup. and C pair; providing, from the NMR spectrometer, a free induction decay signal.
2. The method of claim 1, where the one partner of the J-coupled C.sup. and C pair is C.
3. The method of claim 1, where the second partner of the J-coupled C.sup. and C pair is C.sup..
Description
DESCRIPTION OF THE DRAWINGS
(1) FIG. 1 is a plot of a typical timing sequence for long-observation-window band-selective decoupling;
(2) FIG. 2 illustrates free induction decays and spectra for glycine with (bottom) and without (top) LOW-BASHD; note the effect of the first pulse delay period on the bottom FID at 0.004 seconds. Data have been left-shifted to account for the group delay;
(3) FIG. 3 illustrated digitized signal for a constant input under the LOW-BASHD detection timing and (right) the LOW-BASHD time-domain filter for removing the sidebands in FIG. 2 (note, group delay has not been removed);
(4) FIG. 4 illustrates LOW-BASHD filtered FID for glycine removes the sidebands in the frequency domain. The FID is the product of the FID shown in FIG. 2 (bottom) with the left-shifted LOW-BASHD time-domain filter in FIG. 3; the remaining sidebands are not from the pulse delay breaks, but are true decoupling sidebands;
(5) FIG. 5 is a plot based upon constant-time CACO correlation using the CTUC COSY with and without BASHD detection for GB1; both spectra acquired under identical conditions and 1D traces shown on the same scale; and
(6) FIG. 6 is a plot based upon NCO correlation using SPECIFIC-CP with and without BASHD detection for GB1; both spectra acquired under identical conditions and 1D traces shown on the same scale.
DETAILED DESCRIPTION OF THE INVENTION
(7) Advances in sample preparation, hardware design, and pulse-sequence methodologies have progressed to the point where it is common in solid-state NMR spectroscopy to resolve J-couplings between 13C nuclei in U-13C,15N-labeled proteins. In many cases, J-coupling interactions are now the dominant source of inhomogeneous broadening. Here, we present a general method for band-selective homonuclear decoupling capable of removing the J-coupling interaction between C and C spins during direct 13C acquisition. This windowed approach introduces negligible (300 s) pulse breaks into much larger (e.g., >4 ms) sampling windows to efficiently refocus the J-coupling interaction during detection and can be appended to any existing correlation method that detects on 13C. A typical timing sequence is shown in FIG. 1.
(8) This sampling scheme introduces short, periodic breaks into the observed FID, which in turn leads to a series of frequency-domain sidebands on the resulting spectroscopic lines as shown in FIG. 2. The effect of the pulse breaks on the FID are relatively minor because the digital filtration already applied to the raw data convolutes a filter decay to the signal so that it does not have sufficient time to fully decay to zero. Here the data are acquired with dw equal to 200 us. At short dw times, the signal does indeed fall to zero during these periods. While the sideband intensities are small enough to be negligible in many cases, it is desirable to remove them in other cases. There are many ways this can be accomplished including linear prediction, interpolation, and reference deconvolution. Because the introduction of the time-domain pulse breaks has a characteristic time-domain response that is independent of the input signal and is calculable from the timing sequence and digital filtration parameters, deconvlution in the frequency domain through the application of a time-domain filter is in principle straight-forward. Although this filter is calculatable, it can also be determined experimentally. FIG. 3 shows the time-domain signal for a constant amplitude input (in this case the dc offset of the receiver) digitized analogously to the signal in FIG. 2. Here the effect of the pulse breaks are clearly evident. This time-domain signal can be inverted (after the initial group delay period) to produce the time-domain filter function shown in FIG. 3. FIG. 4 shows the filter applied to the glycine LOW-BASHD data.
(9) FIG. 5 is a plot based upon constant-time CACO correlation using the CTUC COSY with and without BASHD detection for GB1. Both spectra acquired under identical conditions and 1D traces shown on the same scale.
(10) FIG. 6 is a plot based upon NCO correlation using SPECIFIC-CP with and without BASHD detection for GB1. Both spectra acquired under identical conditions and 1D traces shown on the same scale.
(11) While various embodiments of the present invention have been disclosed, it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible within the scope of the invention. Accordingly, the present invention is not to be restricted except in light of the attached claims and their equivalents.
