Spontaneous Formation of Superhelical Strands

We have developed a new class of helical structures that self-assembled spontaneously in aqueous solution. A phospholipid-nucleoside conjugate containing two long alkyl chains and a nucleotidyl residue, dimyristoyl-5'-phosphatidyl-deoxycytidine (1), has been synthesized, and its self-organization, morphology, and physicochemical properties have been investigated. 1 spontaneously assembled to form two types of helical strands. One consisted of a duplex with a diameter of ≈110 Å and helical pitch of ≈240 Å. The duplex further formed a superhelical structure with a helical pitch of ≈1100 Å. The helix was right-handed. The other consisted of a double duplex whose diameter and helical pitch were much the same as those of the former. The double duplex also formed a right-handed superhelical structure. The superhelical strands were gradually converted into gels at 25 °C. We described the formation process of the superhelical strands and proposed a possible model for their structures.