th  - 1987 - 51st ENC Conference

MF45
THE USE OF D=O AS A MOLECULAR PROBE
IN DETERMINING DNA SOLID STATE PACKING
Rolf Brandes,* David R. Kearns, and Allan Rupprecht7
Department of Chemistry, University of California-San Diego,
La JoUa, CA 92093, rArrhenius Laboratory of Physical
Chemistry, University of Stockholm, Stockholm, Sweden
We have used high resolution =H NMR of DzO to monitor the packing of
hydrated DNA molecules in solids prepared from solution by three different
methods: lyophilization, alow evaporation of the water, and wetspinning in alcohol
which produces uniaxially oriented DNA. The two latter methods resulted in thin
films of DNA, which were also broken up to obtain macroscopically isotropic sam-
pies. These five samples all showed different spectral shapes with different spin-
spin relaxation times Tz,.
With lyophilized DNA, the spectral shape can most reasonably be interpreted
in terms of isotropic packing. The evaporation method produces spectra which are
consistent with a spontaneous cholesteric ordering of the DNA. The order is
macroscopic, with the pitch axis perpendicular to the plane onto which the DNA
dried. Even when macroscopic order is not obtained, spin-spin relaxation experi-
ments can be used to determine if the sample consists of local domains with
cholesteric or uniaxial ordering of DNA molecules. For the case of the uniaxially
oriented DNA prepared by wetspinning, a 2-dimensional technique is used to
separate the contributions to the linewidth arising from DNA static disorder, mag-
netic inJaomogeneities, and spin-spin relaxation. This separation enables an upper
estimate of the fiber disorder if a Gaussian distribution of the helix axes is
assumed with a standard deviation of ,,-12 " ^
IBD-NMR spectrum of uniazially oriented DNA.