th  - 1987 - 51st ENC Conference

WK32
C~4IC~L EXCHANGE IN METAL £X/JSTE~.
ANALYSIS WITH 2D LINEAR PREDICTION
AND DIRECT ANALYSIS OF THE RATE MATRIX.
Bruc~ A. ~ ' , J. A. Mallkayil, m~d Ian M. Azmltag~
Depa~ :,,-~-,L,~ of Mblecular Biophysics and Biochemistry
snd Diagnostic Radiology
Yale Urul.ver~l.ty School of M~dicine
Nma Haven, CT 06515
NMR methcKis are well suited tD the mMsurEm~nt of c~mnical exchange
~ . In many ~ , ~ , such as the less sensitive metal
nuclei that may be found in blomolecules, low signal to noise ratio may
significantly hamper the aommrate msasure of exchange rates. To
ov~-~ome this ~ have applied ~o recen%ly repcn-hed methods o£ NMR data
analysis in these areas. As an alternative to the Fourier transform,
we used the method of linear prediction with the s/ngular value
deocmposit/nn (LPSVD) I . This method is potentially capable of
signal fru, noise in the time series data, resulting in
a noise free result. ~ , ~ have used the method for two-
dimensional arm~lysis where its ability to elim/nate truncati~
artifacts allows the use of fe~.r points in t2 and in %/. This reduces
the size of the 2D data set and minimizes experimsntal time. Analysis
in this way gives directly the amplitude of the peaks required for the
chemical exchange calculations without the need for integration. As
apodization funct/ons are not used, there is no resulting distortion of
peak intensity which might occur with normal 2D FT processed data sets.
For both the one and %~o dimensional analyses with LPSVD, we polish the
output data (frequency, dscsy, phase, and amplitude) with a non-lirear
minimization. The calculated peaks from a single 2D data set are then
used %o form a matrix of intensities that is analyzed using a recently
described matrix dia~mLlization p r ~ .
We will illustrate the use of this method with the analysis of metal
excha~/8 in the dscanuclear cadmium-i±iolate complex,
C~0(SO~O~O)*s(N~ )4" In the solid state, three distinct Cd sites
have been identified in the sulfate form of this complex by X-ray
crystallography and by solid state 1'3Od NMR s~-troscc~py- The three
sites, site A, site B, and site C have Oi~, OdS4, and CdS40
oocrdinations respectively 3 . In solution, site B and site C are in
fast exchange and therefore a single 113 Cd resonazK~ is observed for
these sites" The results of our 2D chemical exchange studies have
further established, for the first time, metal exchange between site A
and the other two sites. It is the kinetics of the latter exchange
that we will describe using the oombined LPSVD and the matrix
diagm~alization proosdures described above.
i) ~Jsen, H. 1985, O. Mag. Res. 61:465
2) Perrin C. L. and Gipe, R. K. J. Am. Chem. Soc. 106:4036
Johnston, E. R. and Chert, D. 2~ h ~C ~ Abstract.
Abel, E. W. et al. 1986, J. Mag. Res. 70:34
3) Murphy, D.P. et al. 1981, J. Am. Chem. Soc. 103:4400 (and
ref therein)