Fibrils of Phenylalanine Adsorbed to Langmuir-Blodgett Films: Role of Lipids

Phenylalanine (F) aggregation and its organized assemblies seem to play an important role in amyloid structures associated with physiological impairments in diseases such as Alzheimer's, Huntington's, and Type II Diabetes. Recently, Phenylalanine in milli-molar levels has been reported to accumulate on the plasma, cerebrospinal fluid, and brain tissue leading to phenylketonuria (PK). This work demonstrates the role of hydrophilic and hydrophobic surfaces in organized assemblies of phenylalanine using different Langmuir-Blodgett films from stearic acid (SA), anionic (dipalmitoyl phosphatidyl glycerol [DPPG]), cationic (dioctadecyldimethylammoniumbromide [DOMA]), and neutral (Dioleyol phosphatidyl choline [DOPC]) and their supported lipid bilayers. CLSM shows the typical F aggregate pattern with fiber like morphology with diameters ranging from several nanometers to tens of micrometers on LB films of cationic lipid. Needle-like structures are formed on cationic and or neutral lipids and the rate of formation is controlled by choice of the mixed lipids. The contact angle titrations show hydrophobic surface is more effective in driving this organization process. This study shows that even very low concentrations of L-Phe (60 mu M) can lead to fibrils and aggregation can be tuned by varying charge and hydrophobicity of the surface.