HYDRATION OF THE DT(N).DA(N)XDT(N) PARALLEL TRIPLE-HELIX - A FOURIER-TRANSFORM INFRARED AND GRAVIMETRIC STUDY CORRELATED WITH MOLECULAR-DYNAMICS SIMULATIONS

We present a comparative analysis of the water organization around the dT(n).dA(n)xdT(n) triple helix and the Watson-Crick double helix dT(n ).dA(n) respectively by means of gravimetric measurements, infrared sp ectroscopy and molecular dynamics simulations. The hydration per nucle otide determined by gravimetric and spectroscopic methods correlated w ith the molecular dynamics simulations shows that at high relative hum idity (98% RH) the triple helix is less solvated than the duplex (17 /- 2 water molecules per nucleotide instead of 21 +/- 1). The experime ntal desorption curves are different for both structures and indicate that below 81% RH the tripler becomes more hydrated than the duplex. A t this RH the FTIR spectra show the emergence of N-type sugars in the adenosine strand of the tripler. When the third strand is bound in the major groove of the Watson-Crick duplex molecular dynamics simulation s show the formation of a spine of water molecules between the two thy midine strands.