SPONTANEOUS FORMATION OF HELICAL STRUCTURES FROM PHOSPHOLIPID-NUCLEOSIDE CONJUGATES

Phospholipid-nucleoside conjugates containing two myristoyl groups and a nucleotidyl group, collectively designated as dimyristoyl-5'-phosphatidylnucleosides, were enzymatically synthesized and their self-organization, morphology, and physicochemical properties investigated. The dimyristoyl-5'-phosphatidylnucleosides spontaneously assembled to form various types of helical strands. Neutral and alkaline solutions of dimyristoyl-5'-phosphatidyladenosine (DMPA) produced multihelical strands. The multihelical strand consisted of several single helical strands of almost-equal-to 50 angstrom in diameter and helical pitch almost-equal-to 100 angstrom. DMPA produced cigar-like scrolls (tubular structures) in acidic solution, which consisted of many double-helical strands aligned parallel to each other. Diacyl-5'-phosphatidyladenosine with a shorter chain length as long as an alkyl group, dilauroyl-5'-phosphatidyladenosine (DLPA), didecanoyl-5'-phosphatidyladenosine (DDPA), and dioctanoyl-5'-phosphatidyladenosine (DOPA) formed extended tape structures having double-helical strands aligned parallel. Dimyristoyl-5'-phosphatidylcytidine (DMPC) produced network structures at an early stage, which were slowly transformed into multihelical strands. The multihelical strands contained some single-helical strands of almost-equal-to 55 angstrom in diameter and helical pitch almost-equal-to 150 angstrom. DMPC produced no definite helical structure in acidic solution but rather large lamellar structures. Dimyristoyl-5'-phosphatidyluridine (DMPU) produced crystalline platelet structures of almost-equal-to 1000 angstrom in width in both alkaline and acidic solution. A 1:1 mixture of DMPA and DMPU formed a new hybrid helical strand having a wide and thick ribbon structure of almost-equal-to 300 angstrom in diameter and helical pitch almost-equal-to 2000 angstrom. The formation of different helical strands and effects of chain lengths of alkyl groups and a nucleotidyl group in phospholipid-nucleoside conjugates on that of helical strands in aqueous solution are discussed.