Interactions of an amphiphilic thiacarbocyanine dye with polypeptides and DNA at the air/water interface

Interactions of a positively charged amphiphilic thiacarbocyanine dye with anionic polypeptides (PLGA, PGT11, PGT41) and DNA at the air/water interface, reflected by the J-aggregation in monolayers, were investigated by in situ visible spectra measurements. Two kinds of J-aggregates were formed upon compression. The J-aggregates returned to the monomer form upon expansion. Recompression caused the formation of the J-aggregates again on DNA subphase. In the case of PLGA, H-aggregates were also formed in the second compression. With the introduction of tyrosine into the PLGA, the formation of J-aggregate was hindered. The compression and expansion process seems to be reversible for the monolayers on the DNA and PGT11 subphases, while it is partly reversible in the other cases. In the transferred LB films of the monolayers on the biopolymer-containing subphases, only one kind of aggregate was observed. Strong induced Cotton effects of the J band were observed for the LB films transferred at higher surface pressures.