| A self-assembly system showing highly efficient photoinduced electron transfer and a long-lived charge separation state has been developed and characterized. In this system, the polypeptide poly-L-glutamic acid (PLGA) was chosen as the protein-like template, and a chromophore (a spermine-pyrene conjugate, Sp-Py) and an electrophore (heptyl viologen, HV2+) self-assembled on the template, driven by electrostatic and hydrophobic interactions. This self-assembly system (Sp-Py/PLGA/HV2+) shows most of the features of natural photosynthetic centers. A thorough investigation of this system was undertaken with the aim of shedding light on the process of natural photosynthesis.; The photochemistry of this self-assembly system has been studied under different experimental conditions, such as at different pH values and with different complex conformations (random coil, alpha-helix, or alpha-helix aggregates). Upon binding to negatively charged PLGA, the positively charged Sp-Py dimerizes, forming a "special pair" of chromophores. Addition of HV2+ quenches the Sp-Py dimer fluorescence very efficiently. The photoinduced electron transfer products, Py+• and HV+• radical cation transients, were detected using nanosecond laser flash photolysis. The decay of the HV+• transient absorption occurred in the mus-ms time domain, indicating a long-lived charge separation state, and a much slower back electron transfer rate than the forward one. This self-assembly system is the first one that shows such an efficient photoinduced electron transfer, in which the chromophore and electrophore are non-covalently bound in a protein-like environment.; Since Sp-Py dimer fluorescence is displayed at the expense of monomer emission in the presence of a negatively charged polyelectrolyte, Sp-Py provides a sensitive method for detecting low concentrations of these (bio)polymers. Furthermore, if a positively charged polyelectrolyte is then added, the reverse fluorescence change from dimer to monomer occurs, enabling the detection of positively charged polyelectrolytes. This simple fluorimetric method can easily detect poly-L-glutamic acid (PLGA) and poly-L-lysine (PLL) in the muM or mug/mL concentration range. Additionally, Sp-Py also proved to be useful for detection of biomolecules, such as lipopolysaccharide or lipid A, in aqueous solution. |
