Elucidation of multilayer growth of amphiphiles on liquid surfaces

The crystalline properties of the amphiphilic systems N-methylarachidamide (NM) and of N,N‘-dimethyldocosanediamide (NND) in the uncompressed state at 5 °C on surfaces of water and liquid formamide were studied by grazing incidence synchrotron X-ray diffraction (GID). On water, the amphiphile NM forms a crystalline monolayer. On formamide, NM behaves differently. One h after deposition on the liquid surface, GID patterns indicated coexistence of two different crystalline monolayer structures. Three h later, a crystalline bilayer had formed. The fundamental question as to whether the interlayer growth took place in the liquid subphase or in the air was elucidated with the help of the tailor-made additive N-benzylarachidamide (NB). Addition of 10% of NB in the spreading solution yielded only a monolayer. From this result we conclude that bilayer growth of pure NM must occur from the liquid side. It also helps to establish a similar interlayer growth mechanism for the trilayer formation of pure arachidamide on liquid formamide.1 The amphiphile NND behaved differently from NM as it formed a crystalline monolayer on both water and formamide liquid surfaces

Self-assembled crystalline monolayers and multilayers of n-alkanes on the water surface

The induced formation of multilayer crystallites at liquid interfaces provides a direct means of monitoring the dynamics of crystal nucleation and of elucidating the effect of molecular inhibitors on polymorphism and crystal growth. The spontaneous formation of crystalline multilayers of n-alkanes spread from solution onto the water interface are described and X-ray structural investigations discussed which indicate that the full crystal symmetry is present even in layers that are only a few unit cells thick

Structure and dynamics of lipid monolayers: Implications for enzyme catalysed lipolysis

We have investigated the role of the substrate on the interfacial activation of Upases by an interdisciplinary study of the structure and dynamics of 1,2-sn dipalmitoylglycerol monolayers at distinct surface pressures. The diglyceride Langmuir film undergoes two phase transitions occurring at 38.3 and 39.8 Å2 per molecule. The first transition is unique for diglyceride molecules and is driven by a reorganization of the headgroups causing a change in the hydrophobicity of the oil-water interface. X-ray diffraction studies of different mesophases shows that in the two highest pressure phases, the alkyl chains pack in an hexagonal structure relaxing to a distorted-hexagonal lattice in the lowest pressure phase with the alkyl chains tilted by approx 14° in a direction close to a nearest neighbour direction