Langmuir monolayer of hypocrellins and their amino substituted derivativesat the air/water interface: Brewster angle microscopy study

The monolayer behavior at the air/water interface of the natural pigments h ypocrellin A (HA), hypocrellin B (HB) and their butyl-amino derivatives (HA D, HBD) was investigated using Brewster angle microscopy (BAM). The results showed that stable monolayers were established with different phase transi tions when the films were compressed. The collapse pressures of HA, HE, HAD and HBD were 30.3, 31.0, 34.8 and 35.5 mN m(-1), respectively which sugges ts that the butyl-amino substituents and the perylenoquinone rings of HAD a nd HBD are coplanar. The monolayer morphologies recorded by BAM showed diff erences among the images of these four compounds. Aggregation of HA, which may be attributed to the intermolecular hydrogen bonds between the two mole cules, was observed. No obvious domains in the monolayers of HAD and HBD we re observed using BAM, indicating that no large aggregations were formed in the monolayers. (C) 2001 Published by Elsevier Science B.V. All rights res erved.