th  - 1987 - 51st ENC Conference

MF5
]dULTIPI, E-QUANT1JN SPECTROSCOPY OF BIOLOGICAL SODIUM
James pelutr" tad John S. Leigh. Jr.
Department of" Biochemistry and Biophysics
University of Pennsylvania
Philadelphia, Pennsylvania 19104-6089
In many systems of biological interest, the transverse relaxation of sodium-23 is
the sum of (at least) two expontatiab. Biexponential relaxation occurs when
interactions between the nuclear electric qusdrupole moment and fluctuating electric
field gradients at sodium binding sites cause the "outer" (m - i3/2 ~ m -~1/2)
trtasitions of the spin-3/2 sodium-23 nucleus to relax fester than the "central"
( m--1/2 +. re-I/2) transition. Ve have demonstrated that biexponentially-relszed
sodium can be pessased through a state of deuble-qutatum coherence by • double-
qutatum filter (1). The filter places the two relaxation components in antiphsse, tad
yields • signal proportional to the difference between the two components at the end of
the filter preparation time.
For on-resontace biexponenthdly-relaxed sodium in an isotropic environment.
the detected signals for single 90" pulses tad the phase-cycled INADEQUATE double-
quantum filter ( 90" -T/2 - 180" - X/2 - qO" - 8 - 90" - acquire) are. respectively:
s(t)me-pus.e" MO (1/5) (3 exp(-t/T~) ,2 exp(-t/T2.)) Ill
s(t)liltm,ed - M 0 (3/20) (ezp(-~/T2f) - exp(-~/T28)) exp(-SdqS)
• (exp(-t/T2f) - exp(-t/Tas)) 12]
Here T2f is the "fast" T 2 of the "outer" transitions. Tax is the "siov" T 2 of the "central"
transition. Sdq is the transverse relaxation rue of rtak-two deuble-qutatum coherence.
ud ld 0 is the equilibrium longitudinal sns41netization.
Because the coherence-trtasi'er experiment is sensitive to differences, rather
than sums, of the biexpenential decay, it allows more accurate measurement of
relaxation rates, Indeed. by varying the Utter preparation time. the relaxation rate of
the "outer" transitions can be indirectly measured (1) even if their decay is fsuter than
the spectrometer deadtimeT
Multiple-qutatum ~ may alloy non-invMive discrimination among pools of
sodium in different physiological compartments. In • laboratory cell suspension, where
only the intrsceUuhtr sodium relaxed biexponentislly, we have recently demonstrated
selective detection of intrscelluiar sodium with • double-qutatum filter (2). In more
complex biologics, systems, the technique of two-dimensional multiple-qutatum
spectroscopy promises to aid in elucidating both the distribution of sodium among
dilTerent physiological compartments, and the nature of the spin Hamiltenian in each.
by highlighting any static qusdrupoiar splittings or dynamic frequency shifts (3).
Finally, application to other biologically important spin-3/2 nuclei is possible.
1. j. pek~ and J. S. Leigh. Jr.. J. ~n. Rosen. 69.'582 (1986).
2. J. pekar. P. F. Rtash.v. and J. S. Leigh, Jr., J. ~n. Rosen., In Press. 1987.
3. G. Jscard. S. Wimperis, tad G. Bodenhausen, J. Chem. Phys. 85.~2S2 (1986).