| Fundamental hydrophobic and electrostatic (charge-charge) interactions are common structural or mechanistic elements deployed in molecular recognition. In this dissertation, the interaction of selected synthetic polypeptides with small molecules that provide counter charges and/or hydrophobic contacts have been examined. One purpose of the work has to do with the building of self-assembled biomolecular scaffolds that organize electron donors and acceptors in such a way as to observe long range light-induced electron transfer or charge transport, thus attempting artificial photosynthesis. Another aspect of the work has to do with the development of a simple, rapid assay for polyelectrolytes (negatively charged biopolymers) using the partitioning of a fluorescent dye marker that is based on electrostatic recognition.; Polypeptides were prepared that contain charged and hydrophobic residues at appropriate locations to provide binding sites for photoactive dyes. The PCB(+), a net positively charged carbazole (electron donor)-containing polypeptide (28 residues), binds very efficiently with eosin Y (EY2−), an electron acceptor, via electrostatic interactions. The time-resolved absorption and emission data suggest a rapid forward and back electron transfer (<10 ns) between dye and peptide bound carbazole. A similar but negatively charged polypeptide, PCB(−), participates in an electron transfer process with a di-cationic electron acceptor, heptyl viologen. In an additional system, an aggregate of a mono-1,8-naphthalimide-spermine derivative (MNS) on a poly(glutamic acid) template is recruited as an electron donor.; Absorption and emission spectra for another charged photochemical agent bis-1,8-naphthalimide-spermine (BNS) revealed a ground state intramolecular complexation of the two naphthalimide chromophores, particularly for aqueous media. Observation of a lower fluorescence quantum yield for BNS and the appearance of the radical anion intermediate on ns laser flash photolysis suggest a mechanism of intramolecular electron transfer involving two naphthalimide chromophores.; The polycationic fluorescent probe, MNS, forms electrostatic aggregates in the presence of negatively charged polymers such as poly(glutamate) and poly(acrylic acid). The MNS monomeric emission (394 nm) has been used to provide a simple spectrophotometnc assay for trace quantities (sub ppm) of negatively charged polyelectrolytes. |
