The mechanism of ion polarisation along DNA double helices

摘要: The orientation curves of short DNA fragments induced by electric field pulses are measured with high time resolution and analysed efficient deconvolution techniques. A small, but clearly detectable delay the 'on-field' can be described accurately superposition two exponential processes opposite amplitudes. constant faster process is around 10 ns slower one in range 50-1000 depending upon strength chain length fragment. relation between amplitudes constants observed for each curve corresponds exactly to that expected a convolution processes, where first without optical response becomes only via second process. These results indicate reflects polarisation ion atmosphere required orientation. Measurements at different concentrations c demonstrate reciprocal fast linear function thus consistent an association reaction. rate evaluated from this dependence according simple bimolecular reaction model 8 X 10(9) M-1 s-1 95 base-pair fragment binding Na+ helix, close limit diffusion control. almost independent E, while dissociation k- strongly increases indicating ions E values. data suggest correlation log(k-) E2 corresponding driven dipole change. apparent change order magnitude estimated elementary step end helices. combined obtained mechanism explained surprisingly few counterions biased towards experimental 76 analogous those fragment, whereas 'slow' has not been detected 27 base-pairs. This result together longer low strengths there 'ion dissociation' lengths strengths. replaced and/or mechanism.(ABSTRACT TRUNCATED AT 400 WORDS)