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Selective two-dimensional heteronuclear shift correlation
JOURNAL
OF MAGNETIC
RESONANCE
57, 149- 15 1 ( 1984)
Selective Two-Dimensional
Heteronuclear Shift Correlation*
T. T. NAKASHIMA, BOBAN K. JOHN, AND R. E. D. MCCLUNG Department of Chemistry University of Alberta, Edmonton, Alberta T6G 2G2, Canada
ReceivedOctober 13, 1983
One of the most useful applications of two-dimensional (2D) NMR in r3C spectroscopy is the heteronuclear chemical-shift correlation experiment (1, 2) in which ‘H magnetization is transferred to 13C through the scalar coupling interaction. ‘H chemical-shift information is displayed along the fi domain and r3C chemical-shift information along the f2 domain. Since the mechanism for transfer is through the scalar coupling interaction, each CH, CH2, and CH3 group gives rise to a peak on the correlation map. It has been suggested recently (3, 4) that resolution enhancement may be obtained by simplifying the 2D correlation map so that only the peaks for a selected type of carbon-hydrogen fragment (CH, CH2, or CH3) appear. Levitt et al. (3) suggest the introduction of DEPT (5) into the magnetization transfer part of the heteronuclear correlation experiment, while Bendall and Pegg (4) have modified the basic DEPT sequence so that heteronuclear correlation can be effected. The essence of the selectivity afforded by the DEPT sequence (5) is based on the fact that the intensities of 13C{ ‘H) signals for CH, CHP, and CH3 fragments have distinct dependence on the flip angle 8 of the last ‘H pulse in the sequence, and the recognition that appropriate linear combinations of FIDs collected using different values of B will contain contributions predominantly from a particular type of CH, fragment. While both groups (3, 4) have suggested that linear combinations of 2D data sets should produce the desired selective 2D maps, neither group has implemented this approach. Instead, they chose to rely on the fact that, for 6 = 135”, CH2 correlation peaks are 180” out of phase with the CH and CH3 peaks so that 2D contour maps with only CH + CH3 resonances or with only CH2 resonances could be obtained by selecting positive or negative contours of the phase sensitive transform of FIDs collected for this single value of 8. The success of this approach is limited to situations where there is no overlap between CH2 and CH3 or CH resonances. We report the implementation of the selective 2D DEPT heteronuclear correlation experiment using method (a) proposed by Levitt et al. (3). The pulse sequence is shown in Fig. 1. Rather than collect the full 2D data for each value of 0 separately, and perform linear combinations of the large data structures (for which Bendall and Pegg (4) were unable to find suitable software), we have incorporated the linear combinatorial operations into the data collection process. This was facilitated by * Researchsupportedin part by the Natural Sciencesand EngineeringResearchCouncil of Canada under OperatingGrant A5887 and InfrastructureGrant A 1593. 149
0022-2364184 $3.00 Copy-&t 0 1984 by Academic Rms, Inc. All riglm of Rpmduction in any form reserved.
150
COMMUNICATIONS
90x
180x
% .,
‘H I w-tl-tl90, 13C
I I
0 I
h80,
: I I I I
decoupling / L
r-r-r-4
I
I
‘90,
1180,
-n
, , I / /acquisition 1 ,
FIG. 1. The selective 2D heteronuclear chemical-shift correlation pulse sequence. f, is incremented in the normal fashion, and T is set to 1/2J cH. Selectivity is accomplished by choosing different 8 values. See text for details.
recognizing that a simpler linear combination, FID(30”) + FID(l50’) - FID(90”), which selects CHJ resonances is obtained with B values (30”, 90”, 150”) rather than the values (45”, 90”, 135”) commonly used in DEPT experiments (5). To obtain edited correlation maps, linear combinations of the FIDs for one (CH), two (CHJ or three (CHJ different values of 8 are acquired for each value of tl . To obtain only CH resonances, FID(90”) is used. For enhancement of CH2 resonances, FID(45”) - FID( 135 “) is obtained by coadding a number of FID( 135 “), negating memory, then coadding the same number of FID(45”). To select CH3 resonances, FlD(30”) + FID( 150’) - FID(90”) is constructed by coadding a number of FID(90”), negating memory, coadding that number of FID(30”) and the same number of FID( 1SO”). Performing the linear combinations of the FIDs as the data is collected avoids manipulation of the large data matrices. The selective 2D correlation maps obtained for the test molecule, 2-butanol (90% solution in CDC&) using the pulse sequence in Fig. 1 are shown in Fig. 2. The
FIG. 2. Selective 2D heteronuclear chemical-shift correlation maps for CH, CHr, and CH, for 2-butanol obtained on a Bruker WH-200. The ‘H spectrum appears to the left and the 13Cspectrum is shown below each map. The T value used was 0.004 set for the CH and CH, maps and 0.0038 set for the CH2 case. The data matrix was IK by 256 covering frequency ranges of 4000 and 700 Hz forf2 andA, respectively. Accumulation times ranged from 3-5 hr for each map. The 1D DEPT experiment was optimized for best suppression before the 2D data collection.
COMMUNICATIONS
151
selectivity is shown to be very good. The 2D DEFT heteronuclear correlation experiment should prove useful in the elucidation of extremely complicated systems for which the nonselective correlation experiment is inadequate. The implementation of the selective DEFT correlation experiment employed here presents no data collection or manipulation problems since a particular linear combination of FIDs at different B’s is incorporated into a microprogram and automated for overnight accumulations. The present implementation is somewhat inefficient of spectrometer time in that the FIDs collected for a particular value of the proton pulse angle 6 are used in the construction of only one of the enhanced 2D maps. The collection of full 2D data sets for each of the three values of 0 from which the appropriate linear combinations are subsequently constructed and the selective 2D maps obtained will be a more efficient approach and such an implementation is under development. REFERENCES I. 2. 3. 4. 5.
A. G. M. M. D.
A. MAUDSLEY AND R. R. ERNST, Chem. Phys. Lett. 50, 368 (1977). BODENHAUSEN AND R. FREEMAN, J. Am. Chem. Sot. 100, 320 (1978). H. LEVITT, 0. W. SS~RENSEN, AND R. R. ERNST, Chem. Phys. Lett. 94,540 (1983). R. BENDALL AND D. T. pu;G, J. Magn. Reson. 53, 144 (1983). M. DODDRELL, D. T. Fwm, AND M. R. BENDALL, J. Magn. Reson. 48, 323 (1982).
OF MAGNETIC
RESONANCE
57, 149- 15 1 ( 1984)
Selective Two-Dimensional
Heteronuclear Shift Correlation*
T. T. NAKASHIMA, BOBAN K. JOHN, AND R. E. D. MCCLUNG Department of Chemistry University of Alberta, Edmonton, Alberta T6G 2G2, Canada
ReceivedOctober 13, 1983
One of the most useful applications of two-dimensional (2D) NMR in r3C spectroscopy is the heteronuclear chemical-shift correlation experiment (1, 2) in which ‘H magnetization is transferred to 13C through the scalar coupling interaction. ‘H chemical-shift information is displayed along the fi domain and r3C chemical-shift information along the f2 domain. Since the mechanism for transfer is through the scalar coupling interaction, each CH, CH2, and CH3 group gives rise to a peak on the correlation map. It has been suggested recently (3, 4) that resolution enhancement may be obtained by simplifying the 2D correlation map so that only the peaks for a selected type of carbon-hydrogen fragment (CH, CH2, or CH3) appear. Levitt et al. (3) suggest the introduction of DEPT (5) into the magnetization transfer part of the heteronuclear correlation experiment, while Bendall and Pegg (4) have modified the basic DEPT sequence so that heteronuclear correlation can be effected. The essence of the selectivity afforded by the DEPT sequence (5) is based on the fact that the intensities of 13C{ ‘H) signals for CH, CHP, and CH3 fragments have distinct dependence on the flip angle 8 of the last ‘H pulse in the sequence, and the recognition that appropriate linear combinations of FIDs collected using different values of B will contain contributions predominantly from a particular type of CH, fragment. While both groups (3, 4) have suggested that linear combinations of 2D data sets should produce the desired selective 2D maps, neither group has implemented this approach. Instead, they chose to rely on the fact that, for 6 = 135”, CH2 correlation peaks are 180” out of phase with the CH and CH3 peaks so that 2D contour maps with only CH + CH3 resonances or with only CH2 resonances could be obtained by selecting positive or negative contours of the phase sensitive transform of FIDs collected for this single value of 8. The success of this approach is limited to situations where there is no overlap between CH2 and CH3 or CH resonances. We report the implementation of the selective 2D DEPT heteronuclear correlation experiment using method (a) proposed by Levitt et al. (3). The pulse sequence is shown in Fig. 1. Rather than collect the full 2D data for each value of 0 separately, and perform linear combinations of the large data structures (for which Bendall and Pegg (4) were unable to find suitable software), we have incorporated the linear combinatorial operations into the data collection process. This was facilitated by * Researchsupportedin part by the Natural Sciencesand EngineeringResearchCouncil of Canada under OperatingGrant A5887 and InfrastructureGrant A 1593. 149
0022-2364184 $3.00 Copy-&t 0 1984 by Academic Rms, Inc. All riglm of Rpmduction in any form reserved.
150
COMMUNICATIONS
90x
180x
% .,
‘H I w-tl-tl90, 13C
I I
0 I
h80,
: I I I I
decoupling / L
r-r-r-4
I
I
‘90,
1180,
-n
, , I / /acquisition 1 ,
FIG. 1. The selective 2D heteronuclear chemical-shift correlation pulse sequence. f, is incremented in the normal fashion, and T is set to 1/2J cH. Selectivity is accomplished by choosing different 8 values. See text for details.
recognizing that a simpler linear combination, FID(30”) + FID(l50’) - FID(90”), which selects CHJ resonances is obtained with B values (30”, 90”, 150”) rather than the values (45”, 90”, 135”) commonly used in DEPT experiments (5). To obtain edited correlation maps, linear combinations of the FIDs for one (CH), two (CHJ or three (CHJ different values of 8 are acquired for each value of tl . To obtain only CH resonances, FID(90”) is used. For enhancement of CH2 resonances, FID(45”) - FID( 135 “) is obtained by coadding a number of FID( 135 “), negating memory, then coadding the same number of FID(45”). To select CH3 resonances, FlD(30”) + FID( 150’) - FID(90”) is constructed by coadding a number of FID(90”), negating memory, coadding that number of FID(30”) and the same number of FID( 1SO”). Performing the linear combinations of the FIDs as the data is collected avoids manipulation of the large data matrices. The selective 2D correlation maps obtained for the test molecule, 2-butanol (90% solution in CDC&) using the pulse sequence in Fig. 1 are shown in Fig. 2. The
FIG. 2. Selective 2D heteronuclear chemical-shift correlation maps for CH, CHr, and CH, for 2-butanol obtained on a Bruker WH-200. The ‘H spectrum appears to the left and the 13Cspectrum is shown below each map. The T value used was 0.004 set for the CH and CH, maps and 0.0038 set for the CH2 case. The data matrix was IK by 256 covering frequency ranges of 4000 and 700 Hz forf2 andA, respectively. Accumulation times ranged from 3-5 hr for each map. The 1D DEPT experiment was optimized for best suppression before the 2D data collection.
COMMUNICATIONS
151
selectivity is shown to be very good. The 2D DEFT heteronuclear correlation experiment should prove useful in the elucidation of extremely complicated systems for which the nonselective correlation experiment is inadequate. The implementation of the selective DEFT correlation experiment employed here presents no data collection or manipulation problems since a particular linear combination of FIDs at different B’s is incorporated into a microprogram and automated for overnight accumulations. The present implementation is somewhat inefficient of spectrometer time in that the FIDs collected for a particular value of the proton pulse angle 6 are used in the construction of only one of the enhanced 2D maps. The collection of full 2D data sets for each of the three values of 0 from which the appropriate linear combinations are subsequently constructed and the selective 2D maps obtained will be a more efficient approach and such an implementation is under development. REFERENCES I. 2. 3. 4. 5.
A. G. M. M. D.
A. MAUDSLEY AND R. R. ERNST, Chem. Phys. Lett. 50, 368 (1977). BODENHAUSEN AND R. FREEMAN, J. Am. Chem. Sot. 100, 320 (1978). H. LEVITT, 0. W. SS~RENSEN, AND R. R. ERNST, Chem. Phys. Lett. 94,540 (1983). R. BENDALL AND D. T. pu;G, J. Magn. Reson. 53, 144 (1983). M. DODDRELL, D. T. Fwm, AND M. R. BENDALL, J. Magn. Reson. 48, 323 (1982).