The photochemistry and photophysics of a series of stilbene-functionalized fatty acids (SFA) have been examined in homogeneous solutions, supported Langmuir-Blodgett assemblies, and as guests in pliospholipid bilayers and micellar dispersions. The spectroscopic characteristics of stilbene-functionalized derivatives of pliosphatidyl choline (SFA-PC) have also been examined in organic solvents, aqueous dispersions and aqueous solution containing an excess of dipalmitoyl choline (DPPC), as well as in aqueous-methanol solutions containing V-cyclodextrin. Langmuir-Blodgett assemblies of individual SFAs, as well as mixtures of various SFAs, exhibit spectroscopic properties (blue-shifted absorbance and red-shifted fluorescence relative to those observed in organic solvents) consistent with the formation of an "H" aggregate. The same effect is observed for SFA-PCs in aqueous dispersions and in aqueous-methanol solutions containing 3,-cyclodextdn. The "H" aggregate is found to be the preferred geometric orientation of the Btilbene chromophores which may correspond to an energy minimum for the systems investigated. Preliminary studies with SFA-PC in methanol-water solutions containing y-cyclodextdn suggest that an association of only two stilbene chromophores is required to form the "H" aggregate.
An investigation of the photoreactivity of the amphiphilic α‐oxoamide, N‐(12‐dodecanoic acid)benzoylformamide, (1), in aqueous (pH 10) solution and its inclusion complexes with β‐cyclodextrin (β‐CD) and carboxymethylamylose (CMA). In all three media photolysis of 1 yields predominantly the fragmentation products from hydrolysis, mandelamide and the corresponding aldehyde. The most reasonable mechanism for the reaction is an intramolecular quenching of a ketone‐localized excited state by electron transfer from the amide nitrogen followed by proton transfer and a second electron transfer (zwitterion‐1 → diradical ⇄ zwitterion‐2) to yield ultimately the mandelamide‐imine precursor which hydrolyzes to the observed products. The quantum yields for 1 decomposition and mandelamide appearance in aqueous solution (pH 10) are 0.21 and 0.16, respectively. Compound 1 forms a 1:1 and 1:2 complex with β‐CD and shows enhanced quantum efficiencies for reaction, especially the 1:2 complex. 1 also forms a complex with CMA which shows a similar binding constant to other similar chain length amphiphiles in other studies. Here again reactivity is enhanced for the photoreaction of 1 upon complexation, indicating that neither the electron transfer quenching of the excited states nor reaction of subsequent intermediates is prohibited in the complexes. Mechanistic implications of these results are discussed.
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