Exciton Annihilation and Energy Transfer in Self-Assembled Peptide−Porphyrin Complexes Depends on Peptide Secondary Structure

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• 作者：Darius Kuciauskas ; Juris Kiskis ; Gregory A. Caputo ; Vidmantas Gulbinas
• 刊名：Journal of Physical Chemistry B
• 出版年：2010
• 出版时间：December 9, 2010
• 年：2010
• 卷：114
• 期：48
• 页码：16029-16035
• 全文大小：273K
• 年卷期：v.114,no.48(December 9, 2010)
• ISSN：1520-5207

文摘

We used picosecond transient absorption and fluorescence lifetime spectroscopy to study singlet exciton annihilation and depolarization in self-assembled aggregates of meso-tetra(4-sulfonatophenyl)porphine (TPPS₄) and a synthetic 22-residue polypeptide. The polypeptide was designed and previously shown to bind three TPPS₄ monomers via electrostatic interactions between the sulfonate groups and cationic lysine residues. Additionally, the peptide induces formation of TPPS₄ J-aggregates in acidic solutions when the peptide secondary structure is disordered. In neutral solutions, the peptide adopts an α-helical secondary structure that can bind TPPS₄ with high affinity but J-aggregate formation is inhibited. Detailed analysis of excitation-power dependent transient absorption kinetics was used to obtain rate constants describing the energy transfer between TPPS₄ molecules in an aggregate under acidic and neutral conditions. Independently, such analysis was confirmed by picosecond fluorescence emission depolarization measurements. We find that energy transfer between TPPS₄ monomers in a peptide−TPPS₄ complex is more than 30 times faster in acidic aqueous solution than in neutral solutions (9 vs 279 ps). This result was attributed to a conformational change of the peptide backbone from disordered at low pH to α-helical at neutral pH and suggests a new approach to control intermolecular energy transfer with possible applications in fluorescent sensors or biomimetic light harvesting antennas.