Mixed micelles of polyethylene glycol (23) lauryl ether with ionic surfactants studied by proton 1D and 2D NMR.

(1)H NMR chemical shift, spin-lattice relaxation time, spin-spin relaxation time, self-diffusion coefficient, and two-dimensional nuclear Overhauser enhancement (2D NOESY) measurements have been used to study the nonionic-ionic surfactant mixed micelles. Cetyl trimethyl ammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) were used as the ionic surfactants and polyethylene glycol (23) lauryl ether (Brij-35) as the nonionic surfactant. The two systems are both with varying molar ratios of CTAB/Brij-35 (C/B) and SDS/Brij-35 (S/B) ranging from 0.5 to 2, respectively, at a constant concentration of 6 mM for Brij-35 in aqueous solutions. Results give information about the relative arrangement of the surfactant molecules in the mixed micelles. In the former system, the trimethyl groups attached to the polar heads of the CTAB molecules are located between the first oxy-ethylene groups next to the hydrophobic chains of Brij-35 molecules. These oxy-ethylene groups gradually move outward from the hydrophobic core of the mixed micelle with an increase in C/B in the mixed solution. In contrast to the case of the CTAB/Triton X-100 system, the long flexible hydrophilic poly oxy-ethylene chains, which are in the exterior part of the mixed micelles, remain coiled, but looser, surrounding the hydrophobic core. There is almost no variation in conformation of the hydrophilic chains of Brij-35 molecules in the mixed micelles of the SDS/Brij-35 system as the S/B increases. The hydrophobic chains of both CTAB and SDS are co-aggregated with Brij-35, respectively, in their mixed micellar cores.

Conformational Flexibility of Deoxyoligonucleotide d(GGTATACC)(2) in Water.

AT-rich deoxyoligonucleotide provides a binding site possibly at the minor groove for some anti-tumor drugs by hydrophobic or Van der Waals interactions. In this paper, it is demonstrated by study of d (GGTATACC)(2) that the DNA-drug interaction may be dependent on the structural flexibility at the minor groove. The solution structure of d (GGTATACC)(2) in water is described by distance-restrained molecular dynamics calculation and it is suggested that d (GGTATACC)(2) in solution maintains the double helix of B-type with trans conformations of base to sugar and C2'-endo conformation for the deoxyribose ring. It is found that the end moieties GGT and ACC are relatively rigid while T(5) residue is flexible, which may account for the activity of the minor groove.