Induced circular dichorism (CD) and photochemistry due to the complexes (Schiff bases) from poly(L-lysine) (PLL; degrees of polymerization, DPs, from 1 to 2500) and all-trans, 9- and 13-cis retinaldehydes have been investigated in a methanol-water mixed solvent (1:1, v/v). The complex of uncharged PLL with DP = 26 and all trans retinaldehyde takes a β -structure exhibiting a very strong ellipticities at 304 nm with [θ]304 = 510,000, at 338 nm with [θ]338 = -713,000 and at 397 nm with [θ]397 = 155,000, while the complexes of uncharged PLL with DPs from 60 to 2500 take an α-helix structure exhibiting the induced CD ellipticities at about 310 nm, 337 nm and 380 nm. Among these α-helical complexes the PLL-all trans retinaldehyde complex with DP = 460 exhibited the largest induced ellipticities. PLL and 9- and 13-cis retinaldehyde complexes exhibited smaller induced ellipticities, respectively. On irradiation at 360 nm for 3-5 min, the induced CD of the PLL (DPs = 26 and 460)-all trans and cis retinaldehyde complexes disappeared irreversibly. The induced CD and photochemical results including the electronic absorption spectra have been discussed as the simplest photoresponsive model systems including retinaldehydes.
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