th  - 1987 - 51st ENC Conference

WK20
ImQm~ss ~ M~/TIDIM~SIGNAL ~ C NMR
H. Armitage, U. Bl6mer, I. Genge, A. Khuen, and D. Ziessow
I.N. Stranski Institute, Technische Universit~t Berlin
i000 Berlin 12, West Germany
Stimulus to the osntinuing development of M~DI~4 (MUltidimensional Stochas-
tic Method) is the simplicity of the measurement process and the prospect
to obtain 2D spectra with high digital resolution which, with conventional
2D techniques, ~uld require the processing of i0 or more Giga~rds data
arrays.
In order to take full advantage of the method, hardware and software has
been developped which allows the continuous recording of data pairs for the
excitation ( special ly designed quaternary noise) and response time func-
tion, 1 Me~apair or more depending on the amount of DRAM plugged into the
VME bus of the 68000-based computer system for data acquisition. Spectral
information is obtained by correlation of excitation and response as
formed in the frequency dom~J_n with the ais of a Honeywell BulISPS 9 ~
cc~puter. First order oprrelation yields the c~mDn ID spectrum Hl(W). Ex-
tremely long time records are used in order to alleviate artifacts stemming
from cyclic correlation. From the same raw data, after suitable subtraction
of the first order response, third ~ ~ is performed pointwise
to determine a genuine 3D spectral function H3(Wl,W2,W 3) in regions of in-
re_rest as indicated by the ID spectrum. For instance, the choice w3=-w 2 re-
duces H 3 to a 2D spectrum H 3 ' (Wl,W 2) which is equivalent to the result of
the E-COSY technique. Points my be selected such that the entire spectral
range is assessed with coarse digital resolution, and narrow regions with
extremely small frequency steps.
Simulated and experimental data are presented to demonstrate the unique
features of MUDI~4. As a particular case study, results for the cyclic pep-
tide cyclosporin are shown which derive frcm 80 Megapairs raw data for a
total spectral range of 3246 Hz (7.5 h magnet time). A typical 2D spectrum
(512x512 window at 0.4 Hz step size) is given which ~uld require the pro-
cessing of about 256 Megawords of data with conventional 2D techn/ques.