Indole fluorescence quenching

Eftink, M.R. and Chiron, C.A. (1984) Indole fluorescence quenching studies on proteins and model systems use of the efficient quencher succinimide. Biochemistry 23, 3891-3899. 

M. R. Eftink and C. A. Ghiron, Fluorescence quenching of indole and model micelle systems, J. Phys. Chem. 80, 486 193 (1976). 

Other studies have brought out the ambivalent characteristics of many porphyrins in charge-transfer adducts [189-192]. Porphyrin fluorescence quenching, a characteristic of complexation, occurs for a variety of aromatic donors and acceptors. The porphyrins are known [189-192] to form charge-transfer complexes with some amino acids and the indole tryptophan [193], some steroids [194], and some vitamins [194]. 

Work on indole, tryptophan, etc. continues because of their relevance to the complex field of protein photophysics. Creed has produced reviews of the photophysics and photochemistry of near-u.v.-absorbing amino-acids, viz. tryptophan and its simple derivatives, tyrosine and its simple derivatives, and cysteine and its simple derivatives. The nature of the fluorescent state of methylated indole derivatives has been examined in detail by Meech et al. Another investigation on indole derivatives deals particularly with solvent and temperature effects. Fluorescence quenching of indole by dimethylfor-mamide has also been examined in detail. Fluorescence excitation spectra of indoles and van der Waals complexes by supersonic jets give microscopic solvent shifts of electronic origin and prominent vibrational excitation of L(, states. Conventional flash photolysis of 1-methylindole in water shows R, e p, and a triplet state to be formed. " Changes in the steady-state fluores-... 

Specific examples of electron transfer studies made include a time resolved spectroscopic investigation of CT complexes of 2-naphthol with triethylamine in polar and non-polar solvents , fluorescence quenching of carbazole and indole by ethylene thiodicarbonate which forms ground state complexes , and the luminescent charge transfer complex of 4,4 -bipyridinium ion with tetrakis [3.5-bis(trifluoromethyl)phenyl]borate anion . 

H -tetramethylbenzidine in anionic-cationic mixed micelles has been studied in detail by ESR . The photochemistry of the semi-oxidised forms of eosin Y and rose bengal have been investigated in colloidal solutions. Relevant to the fluorescence of proteins is a study of fluorescence quenching of indolic compounds by amino-acids in SOS, CTAB, and CTAC micelles O Rate constants for proton transfer of several hydroxyaromatic compounds have been measured in a variety of surfactant solutions. Photoprotolytic dissociation does not require exit of the reactant molecules from the micelles. Micellar solutions can be used to improve the fluorescence determination of 2-naphthol by inhibiting proton transfer or proton inducing reactions z2. jpe decay of the radical pair composed of diphenylphosphonyl and 2,4,6-trimethyl benzoyl radicals in SDS is affected by magnetic... 

The quenching mechanism has been investigated by a picosecond laser photolysis technique for the lumiflavin (Lf) and riboflavintet-rabutylate (RFTB) as fluorescers, and indole, N-methylindole and phenol as quenchers in various solvents of different polarity, and the electron transfer from the quencher to the fluorescer has been confirmed by transient absorption spectral measurements (5). The reaction scheme of the fluorescence quenching is given in... 

Heavy-atom perturbation has been invoked to account for the fluorescence quenching of aromatic hydrocarbons by CsCl,147 and an electron-transfer mechanism suggested as the mode of fluorescence quenching of indole and some indole derivatives by lanthanide ions.148... 

The complexation of indole with a- and fi-CD caused a red shift of the absorption spectrum and a blue shift of the fluorescence emission. In the case of a-CD as complexing agent, the absorption variations were described by a sequential formation of 1 1 (K =2M ) and 2 1 (Aj = 210M ) complexes. Fluorescence quenching by CsCl was wavelength dependent and lower in presence of CD than in bulk water. This was attributed to dififerent absorption spectra for 1 1 and 2 1 complexes and to dififerent levels of protection offered by the two complexes against quenching by CsCl [254]. 

Incorporation of a I -cyanoethyl group occurs when indoles are irradiated with UV light in the presence of acrylonitrile [13b, 57,58]. With indole, the major product formed is 3-(r-cyanoethyl)indole [13b]. In the case of 3-methylindole, where the 3-position is blocked, the products formed in methanol are shown in Scheme 25 only the 5- and 7-positions of the indole ring are unreactive. The reaction is not quenched by piperylene [13b], while quenching of the indole fluorescence by acrylonitrile follows Stern-Volmer kinetics and yields a rate constant for quenching that is close to the rate... 

Steady-state fluorescence of indolic probes quenched by AM and selectively located at the various locations of the microemulsion (toluene, interfacial layer, and water phase) was used to follow the depletion of this monomer during polymerization [119]. The results show that AM is evenly consumed from all parts of the AOT systems independently of the initial composition and the nature of the initiator. 

Ricci. R. W.. and Neste, I. M.. 1976, Inter- and uitranK eoalar quenching ot indole fluorescence by carimii compoonds, X Phys, Chem 88 974-980. 

In order to obtain independent evidence for the involvement of the cyclodextrin cavity, fluorescence measurements were carried out for copper(II) ternary complexes with L- or D-tryptophan. In fact, the fluorescence spectrum of tryptophan has already been shown to be sensitive to the polarity of the microenvironment in which it is located and has been used in many studies as a probe for the conformation of proteins and peptides [53]. As for many fluorophores, the indole fluorescence of Trp is quenched by the copper(II) ion this effect has been used as a measure of the stability constants of copper(II) complexes [54, 55]. In a recent work, it has been shown that the fluorescence of dansyl derivatives of amino acids undergo enantioselective fluorescence quenching by chiral copper(n) complexes and that fluorescence measurements can be used for the study of enatioselectivity in the formation of ternary complexes in solution [56]. Bearing this in mind, we performed the same type of experiments by adding increasing amounts of the [Cu(CDhm)] + complex to a solution of D- or L-tryptophan [36]. The fluorescence titration curve shows that the artificial receptor inhibits the indole... 

Aoyama has also shown that 5-indolylboronic acid (3) imdergoes fluorescence quenching upon complexation with oligosaccharides [38]. The stability constants of monosaccharides followed the trend observed by Lorand and Edwards [12] however, higher oligomers of saccharides enjoyed increased stabilization relative to lower oligomers due to a secondary interaction with the indole N-H. The observed stability constants (fC pp) for 3 were D-fructose 630 M", D-glucose 7.1 M" and D-melibiose 58 in water at pH 9. 

The fluorescence quenching observed for 28-29 was explained by a model that assumes excited-state protonation of the pyridine nitrogen atom, followed by the twisting of the pyridyl group. A model was proposed that involves a sequence of processes occurring in a photoexcited, intermolecularly hydrogen-bonded complex [57] (i) electron density flow from the donor (pyrrole/indole) onto the acceptor... 

Neither Fj nor F2 alone gave the characteristic fluorescence of fa and nicked fa in the presence of L-serine and pyridoxal phosphate. However, titration of a fixed amount of F2 with F2 gave rise to a fluorescence intensity 80-90% that of nicked fa at a stoichiometric ratio of Ft to F2. Moreover, both the excitation and emission spectra of the stoichiometric mixture were the same as for nicked fa. In addition, the same specific quenching of this fluorescence was shown in recombined Fj and F2 as in nicked fa. Further, the dissociation constants for L-serine and for indole were determined to be the same within experimental error for recombined Fj and F2, as for nicked fa. No significant differences were found between nicked fa and reconstituted Fj F2 in the intrinsic fluorescence of the aromatic residues, or in the sedimentation coefficients or the 200-250 nm CD spectra. From the foregoing independent lines of evidence, F2 and F2 combine to produce a structure very similar to that of nicked fa. 

The anisotropy decay of the tryptophan fluorescence of both model peptides and biologically active peptides containing a single tryptophan residue has been determined in various studies. Even in the case of the tripeptide H-Gly-Trp-Gly-OH quenched by acrylamide the anisotropy decay displayed two correlation times with values of 39 and 135 ps. 44 The shorter correlation time was thought to be due to motions of the indole ring relative to the tripeptide. In the case of ACTH(l-24) the fluorescence anisotropy decay of the single tryptophan residue in position 9 of the peptide sequence obtained in phosphate buffer (pH 7, 3.5 °C) was also double-exponential. 29 The shorter rotational correlation time (0 = 92ps)... 

It is important to have an idea how widespread the relaxation mechanisms discussed previously are present in chemistry and biology. In a recent review article2 many more compounds that emit an additional, anomalous TICT fluorescence have been presented, ranging from a variety of naphthalene and anthracene derivatives to biologically important compounds like indoles and purine derivatives. The question remains whether other systems which do not show the anomalous fluorescence band might nevertheless be understood on the same basis. It may be the case that either the two fluorescence bands are superimposed or that the product fluorescence has not yet been observed because of quenching processes or because of a red shift into the infrared region. 

Fig. 10. Highly schematic representation of the orientation of several tryptophan-containing peptides with respect to calmodulin. (A) With tryptophan in position 1, the indole is located on the hydrophilic side of the helix and is exposed to solvent. Peptides with tryptophan on this face of the helix should exhibit emission maxima near that of indole in water ( 350 nm), a small anisotropy, and a high accessibility for acrylamide quenching. (B) In position 2, the tryptophan is partially exposed at the interface between the peptide and calmodulin. Peptides with a tryptophan in this location should have fluorescence properties that are intermediate between example A and C. (C) The tryptophan is on the hydrophobic side of the helix and is almost entirely buried. The emission maximum should be strongly blue-shifted, the anisotropy should be large, and the accessibility to acrylamide quenching low. Taken from O Neil et al. (1987).

With site-directed mutation and femtosecond-resolved fluorescence methods, we have used tryptophan as an excellent local molecular reporter for studies of a series of ultrafast protein dynamics, which include intraprotein electron transfer [64-68] and energy transfer [61, 69], as well as protein hydration dynamics [70-74]. As an optical probe, all these ultrafast measurements require no potential quenching of excited-state tryptophan by neighboring protein residues or peptide bonds on the picosecond time scale. However, it is known that tryptophan fluorescence is readily quenched by various amino acid residues [75] and peptide bonds [76-78]. Intraprotein electron transfer from excited indole moiety to nearby electrophilic residue(s) was proposed to be the quenching... 

---