The circular dichroic (CD) properties of aqueous and methanolic solutions of a series of short-chain phosphatidylcholines-ranging from 1,2-dipropionyl-sn-glycero-3-phosphocholine (diC(3)PC) to 1,2-dioctanoyl-sn-glycero-3-phosphocholine (diC(8)PC)-have been studied. In methanol, the CD spectrum is characterized by a negative peak centered around 210 nm. The peak intensity decreased with increasing acyl chain length. In aqueous solution, not only did the CD spectra recorded at concentrations below the critical concentration for micelle formation (cmc) show a clear dependency on the acyl chain length, but they were also slightly different from the corresponding spectra recorded above the cmc. The latter finding-at least qualitatively-confirms earlier extensive NMR investigations [e.g,, Roberts; et al. Biochemistry 1978, 17, 935; Hauser; et al. Biochemistry 1988, 27, 9166]. The experimentally determined cme for diC(6)PC in water at 25 degrees C was 15 mM. The conformation of micellar lipids (above the cmc) was more "rigid"-i.e., was characterized by a higher degree of conformational restrictions involving the glycerol backbone-than in the case of monomers (below the cmc). Furthermore, the CD measurements indicate that monomeric phosphatidylcholines start to become more rigid if longer than diC(4)PC. In addition, the dependency of the conformational rigidity on the acyl chain length correlates with published data on the chain length dependency of the rate constants for pancreatic phospholipase A(2) [Berg; et al. Biochemistry 1997, 36, 14512].