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Unformatted text preview: Structural Effects of Biologically Relevant Rhodamines on Spectroscopy of Fluorescence Fluctuations J OS E A. B. F ERREIRA Centro de Qu mica Estrutural, Instituto Superior Tecnico, Universidade Tecnica de Lisboa, Lisbon, Portugal Exciton coupling in complexes between the indole ring and other systems is known to enhance the efficiency of energy and electron transfer. Rhodamines xanthylium rings allow the formation of weakly or nonfluorescent complexes with the amino acid tryptophan. Thus, because of the short distance of the participating electronic clouds, intrinsic electron transferinduced fluorescence quenching occurs. In solution, the rate constant of electron transfer is known to be limited by collision interactions at the contact distance. By contrast, in protein local environments tryptophan residues can be either exposed or buried in hydrophobic regions. Herein, I report on the properties of aromatic derivatized rhodamines, among which is one with a bound phenylala- nine amino acid group. Encompassed is the spectroscopic and kinetic information in bulk and at the single-molecule levels both in free solution and in the presence of human serum albumin. Spectroscopic characteristics are focused with special emphasis on enhanced fluorescence that is addressed considering optimized geometries and electronic spectra. The importance of the probes associated with peptides and metal ions both in condensed phase or interfaces and as substrates with proteins is put into perspective. Key words: rhodamines; tryptophan; amino acids; proteins; molecular aggregates; interac- tions; peptide metal ion interactions; single molecules Introduction Modern research in chemistry and biochemistry profits from single-molecule information. In particu- lar, individual amino acid (e.g., tryptophan) residues in peptides and protein domains play major roles in biological processes, for which one can usually deter- mine the structurefunction relationships. 1 The study and characterization of such processes when corre- lated with specific amino acid participation in large- amplitude conformational alterations is a major goal in both biology and medicinal chemistry. 2 Directed mutations and light activation of biological processes involve amino acid residues that can alter the biological functions. 3 , 4 Electron transfer proteins whose proper- ties, distances, and redox potentials can be enhanced also constitute models for the study of intramolecu- lar electron transfer and are nowadays objects of in- tense scrutiny. In fact, the amino acid substitutions Address for correspondence: Jose A. B. Ferreira, Centro de Qu mica Estrutural, Complexo Interdisciplinar, Instituto Superior Tecnico, Av. Ro- visco Pais, 1049-001, Lisbon, Portugal. Voice: + 351-21-8419318; fax: + 351-21-8464455/7....
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This note was uploaded on 07/11/2010 for the course SPECTOGRAP 545 taught by Professor Gdf during the Spring '10 term at AIB College of Business.
- Spring '10