Lattice-dynamical model of crystalline DNA: Intermolecular bonds and the A to B transition

A lattice-dynamical model has been developed of DNA in a crystalline lattice. This model is used to evaluate the harmonic nearest-neighbor force constants of highly oriented films of Na-, K-, Rb-, and Cs-DNA as a function of relative humidity from Raman data. These DNA-counterion systems were chosen since they all undergo an A to B transition. The analysis suggests that the A to B transition takes place in these different DNA’s when the effective force constant of the intermolecular bond falls below a ‘‘critical’’ value.