Structure and electrostatic interaction properties of monolayers of amphiphilic molecules derived from C-60-fullerenes: A film balance, neutron-, andinfrared reflection study

Monolayers at the air/water interface of a new amphiphilic molecule derived from a Cco-fullerene were studied at; different lateral pressures by a com bination of film balance techniques, neutron reflection (NR), and infrared reflection-absorption spectroscopy (IRRAS). The amphiphilic fullerene deriv ative (AF) consisted of a dendrimeric hydrophilic region, and 10 alkyl chai ns covalently attached to the fullerene cage formed the hydrophobic part. T he AF monolayers could be compressed and expanded without significant hyste resis and the alkyl chains remained fluid at all pressures. By a titration series, the pK value of the AF monolayer was determined as 7.5 and pH depen dent measurements allowed a variation of the negative AF headgroup charge b y about 18 charges. The thickness of the AF monolayer at high lateral press ure was 30 Angstrom; thus similar to that of typical phospholipid monolayer s in the condensed state. In contrast, the AF molecular area was about 6-fo ld higher than that of phospholipids at high pressure. Moreover, the hydrat ion capacity of the AF headgroup is significantly higher than that of phosp holipids. The negatively charged AF monolayer showed a strong coupling of t he water-soluble protein cytochrome c from the subphase, leading to the for mation of a 30 Angstrom thick protein layer underneath the AF layer. The pr otein content of this layer varied drastically with the pH value. The prope rties of the AF monolayers may be useful in the design of dedicated biomime tic surfaces.