Photophysics Of Tryptophan Research Articles

Heavy atom induced phosphorescence study on the influence of internal structural factors on the photophysics of tryptophan in aqueous solutions

In this study the effect of alanyl residue insertion into tryptophan and to some extent the effect of peptide bond on the photophysics of tryptophan chromophore has been studied. The photophysical parameters crucial in triplet state decay mechanism of aqueous AW, WA and AWA peptides have been determined applying our previously proposed methodology based on the heavy atom effect and compared with the previously reported values for tryptophan (Kowalska-Baron et al., 2012). The obtained results clearly indicated that the presence of alanyl residue and the peptide bond results in the changes in the fluorescence and phosphorescence decay kinetics of tryptophan. The fluorescence decays of the oligopeptides studied at pH 7 were biexponential. The longer lifetime component of WA arises from anionic form of this dipeptide, while the shorter one may be assigned to the zwitterionic form of WA. The observed invariance of the lifetimes of anionic and zwitterionic forms of WA throughout the pH studied supports the idea that these two components of WA fluorescence decay correspond to nearly independent species, possibly interconverting but at a rate slower than the fluorescence decay rates. Comparing the determined phosphorescence spectra of the oligopeptides studied with that of tryptophan, a slight blue-shift and more evident red-shift was observed in the spectrum of AW and WA, respectively. On the basis of the results of the phosphorescence measurements performed at pH 10, the 170μs lifetime of WA, observed even at pH 7, may be assigned to the anionic form of the compound. It may be suggested that at pH 7 during the excited triplet state lifetime of WA there is a shift in the equilibrium towards the anionic form of this dipeptide. In the case of AW and AWA at pH 7 the obtained monoexponential decay kinetics, most probably, arise from zwitterionic forms of these peptides. The determined triplet quantum yield of AWA is slightly lower than that of tryptophan, while the quantum yield of AW is twofold lower than that of tryptophan. The highest value of the determined triplet quantum yield of WA confirms the presence of anionic form of this dipeptide at pH 7.

Selective fluorescence resonance energy transfer from serum albumins to a bio-active 3-pyrazolyl-2-pyrazoline derivative: A spectroscopic analysis

A novel fluorescent probe and pharmaceutically significant: 3-pyrazolyl-2-pyrazoline derivative (PYZ) has been selected as an acceptor molecule for fluorescence resonance energy transfer (FRET) interaction with serum albumins. Steady state and time resolved fluorescence techniques were applied to elucidate the nature of interaction of PYZ with serum albumins (BSA and HSA). Negligible FRET mediated emission occurred in the case of HSA but an efficient FRET mediated emission resulted in case of BSA. To gain further insight into the FRET selectivity of PYZ with the proteins, FRET from L-tryptophan (donor; native tryptophan) to PYZ (acceptor) was performed with the aim of getting an idea about the steric restrictions imposed on PYZ by the other groups present in BSA and HSA. The studies revealed that the surface bound Trp-134 in BSA allows an efficient FRET process with PYZ while the buried Trp-214 in HSA does not. The unusual selectivity for FRET in case of PYZ and the serum albumins has also been attributed to the complex structure of PYZ due to the presence of bulkier phenyl moieties in it. The complex nature of the excited state photophysics of tryptophan (Trp) in proteins also accounts for this FRET selectivity of PYZ with BSA and HSA.

Simulations of the Absorption and Fluorescence of Indole in Aqueous Solution and at a Nonpolar/Polar Interface

Theoretical results are presented on the absorption and fluorescence of indole in aqueous solution as well as at the air/water surface. We use a combined quantum chemical statistical mechanical model with explicit solvent. An approximate ab initio complete active space self-consistent field description of the indole molecule is used, coupled to a discrete polarizable water medium. From the bulk simulations, strong support is found for the interchange mechanism, which explains the unusual solvent shift of the fluorescence of indole or tryptophan in a polar surrounding by a solvent induced switch of the fluorescing state. Two mechanisms are given to explain the different shifts for indole at the interface. First, a dielectric depletion effect, which is expected from the reduction of the amount of polar media. Second, an interface-specific effect, which derives from the stronger hydrogen bond formation at the surface. The latter effect acts to increase the shift for both absorption and emission at the surface as compared to the bulk. From these results, the intrinsic probe photophysics of tryptophan in proteins is discussed in terms of the properties of the protein/solvent interface and the orientation of the amino acid.

Hydride stretch infrared spectra in the excited electronic states of indole and its derivatives: Direct evidence for the 1πσ* state

The hydride stretch infrared spectra of indole, indole-H2O, 3-methyl indole, 3-methyl indole-H2O, the main conformer of tryptamine (TRA), two conformers of N-acetyl tryptophan amide (NATA), and three conformers of N-acetyl tryptophan methyl amide (NATMA), have been recorded in the electronically excited singlet states using excited-state fluorescence-dip infrared spectroscopy. NATA and NATMA are methyl-capped dipeptides of tryptophan that have conformational flexibility and exhibit sensitivity in their electronic spectra to the conformation of the dipeptide backbone. In the indole monomer, the indole NH stretch fundamental at the S1 origin is shifted from its ground-state value (3525 cm−1) to 3478 cm−1. The corresponding band in the indole-H2O complex appears at 3387 cm−1, shifted by a similar amount from its ground-state position (3436 cm−1). Higher vibronic levels within 1500 cm−1 of the S1 origin, which have been identified previously [B. J. Fender et al., Chem. Phys. Lett. 239, 31 (1995)] as being 1Lb or 1La in character, all show similar excited state indole NH stretch absorptions. The corresponding spectra in 3-methyl indole, 3-methyl indole-H2O, TRA, and in the C5 conformers of NATA and NATMA all are missing the indole NH stretch absorption. In its place, a broad background absorption appears, spread over the entire 2800-3800 cm−1 region. In these molecules, other CH stretch or amide NH stretch absorptions remain sharp, appearing in their expected frequency ranges. Finally, the C7 conformations of NATA and NATMA, which possess an intramolecular hydrogen bond in the dipeptide backbone, have all infrared transitions washed out, replaced by a stronger broad background absorption. The entire data set can be explained by the presence of an excited 1πσ* state which is dissociative along the indole NH stretch coordinate, as recently predicted by Sobolewski and Domcke [Chem. Phys. Lett. 315, 293 (1999)]. In the weak coupling case (indole, indole-H2O), the gap between the 1πσ* state and the S1 origin is too large to be reached by infrared excitation. The selective loss of the indole NH stretch in the intermediate coupling case reflects the strong coupling of the 1Lb state NH stretch (v=1) level to the 1πσ* state, which is dissociative along the NH stretch coordinate. In the NATA and NATMA C7 conformers, an inversion of ordering of the electronic states occurs, pushing the 1La state below the 1Lb origin, and strengthening the coupling of all hydride stretch vibrational levels to the 1πσ* dissociative continuum. These results highlight the important influence of the conformation of the polypeptide backbone on the photophysics of tryptophan in polypeptides.

Fluorescence of cis-1-Amino-2-(3-indolyl)cyclohexane-1-carboxylic Acid: A Single Tryptophan χ1 Rotamer Model

A constrained derivative, cis-1-amino-2-(3-indolyl)cyclohexane-1-carboxylic acid, cis-W3, was designed to test the rotamer model of tryptophan photophysics. The conformational constraint enforces a single chi(1) conformation, analogous to the chi(1) = 60 degrees rotamer of tryptophan. The side-chain torsion angles in the X-ray structure of cis-W3 were chi(1) = 58.5 degrees and chi(2) = -88.7 degrees. Molecular mechanics calculations suggested two chi(2) rotamers for cis-W3 in solution, -100 degrees and 80 degrees, analogous to the chi(2) = +/-90 degrees rotamers of tryptophan. The fluorescence decay of the cis-W3 zwitterion was biexponential with lifetimes of 3.1 and 0.3 ns at 25 degrees C. The relative amplitudes of the lifetime components match the chi(2) rotamer populations predicted by molecular mechanics. The longer lifetime represents the major chi(2) = -100 degrees rotamer. The shorter lifetime represents the minor chi(2) = 80 degrees rotamer having the ammonium group closer to C4 of the indole ring (labeled C5 in the cis-W3 X-ray structure). Intramolecular excited-state proton transfer occurs at indole C4 in the tryptophan zwitterion (Saito, I.; Sugiyama, H.; Yamamoto, A.; Muramatsu, S.; Matsuura,T. J. Am. Chem. Soc. 1984, 106, 4286-4287). Photochemical isotope exchange experiments showed that H-D exchange occurs exclusively at C5 in the cis-W3 zwitterion, consistent with the presence of the chi(2) = 80 degrees rotamer in solution. The rates of two nonradiative processes, excited-state proton and electron transfer, were measured for individual chi(2) rotamers. The excited-state proton-transfer rate was determined from H-D exchange and fluorescence lifetime data. The excited-state electron-transfer rate was determined from the temperature dependence of the fluorescence lifetime. The major quenching process in the -100 degrees rotamer is electron transfer from the excited indole to carboxylate. Electron transfer also occurs in the 80 degrees rotamer, but the major quenching process is intramolecular proton transfer. Both quenching processes are suppressed by deprotonation of the amino group. The results for cis-W3 provide compelling evidence that the complex fluorescence decay of the tryptophan zwitterion originates in ground-state heterogeneity with the different lifetimes primarily reflecting different intramolecular excited-state proton- and electron-transfer rates in various rotamers.

Toward understanding tryptophan fluorescence in proteins.

A general approach to dissecting the complex photophysics of tryptophan is presented and used to elucidate the effects of amino acid functional groups on tryptophan fluorescence. We have definitively identified the amino acid side chains that quench tryptophan fluorescence and delineated the respective quenching mechanisms in a simple model system. Steady-state and time-resolved fluorescence techniques, photochemical H-D exchange experiments, and transient absorption techniques were used to measure individual contributions to the total nonradiative rate for deactivation of the excited state, including intersystem crossing, solvent quenching, and excited-state proton and electron transfer rates. Eight amino acid side chains representing six functional groups quench 3-methylindole fluorescence with a 100-fold range in quenching rate constant. Lysine and tyrosine side chains quench by excited-state proton transfer; glutamine, asparagine, glutamic and aspartic acid, cysteine, and histidine side chains quench by excited-state electron transfer. These studies provide a framework for deriving detailed structural and dynamical information from tryptophan fluorescence intensity and lifetime data in peptides and proteins.

Conformer Interconversion in the Excited State of Constrained Tryptophan Derivatives

The conformer model of tryptophan photophysics ascribes the multiple fluorescence lifetimes to ground-state heterogeneity. It is usually assumed that the different conformers do not interconvert in the excited state. Previous studies of two constrained tryptophan derivatives supported this assumption (Colucci, W. J.; Tilstra, L.; Sattler, M. C.; Fronczek, F. R.; Barkley, M. D. J. Am. Chem. Soc. 1990, 112, 9182-9190; Yu, H.-T.; Vela, M. A.; Fronczek, F. R.; McLaughlin, M. L.; Barkley, M. D. J. Am. Chem. Soc. 1995, 117, 348-357). Five constrained derivatives have been synthesized and shown to undergo conformer inversion during the lifetime of the excited state. All derivatives have two ground-state conformations as determined by X-ray crystallography, molecular mechanics calculations, and 1H-NMR. Fluorescence lifetime data were fit to singleand double-exponential models and to a reversible two-state excited-state reaction model. 2-Amino-1,2dihydrocyclopenta[b]indole-2-carboxylic acid has a single-exponential decay consistent with conformer inversion much faster than fluorescence decay. 1,2,3,4-Tetrahydrocarbazole-3-carboxylic acid, ethyl 1,2,3,4tetrahydrocarbazole-3-carboxylate, and their 9-methyl derivatives have double-exponential decays with a minor second component of small positive or negative amplitude. Conformer inversion rates of ∼107 s-1 were determined by analyzing the fluorescence decay data using the excited-state reaction model. Temperature dependence of the fluorescence lifetimes was measured in H2O and D2O, and solvent quenching rates were calculated from the Arrhenius parameters. The carboxylate and carbonyl functional groups appear to have little effect on solvent quenching of indole fluorescence. Model calculations examining the effect of conformer inversion rate on the decay parameters of a biexponential model indicate that the presence of a small amplitude, short lifetime component may be a good predictor of excited-state conformer interconversion of tryptophans in peptides and proteins.

The Peptide Bond Quenches Indole Fluorescence

The effect of the peptide bond on protein fluorescence is an important unresolved question in tryptophan photophysics. Definitive evidence for the peptide group as a weak quencher of indole fluorescence was obtained from solute quenching studies with a series of model compounds. Two amides are required for detectable quenching of 3-methylindole fluorescence and the quenching rate depends on the distance between amides. The bimolecular rate constants kq of malonamide, N-acetylasparagine, N-acetylglycinamide, and N-acetylglutamine are 33 × 107, 8.8 × 107, 6.6 × 107, and 2.2 × 107 M-1 s-1, respectively. Transient absorption and temperature dependence of the fluorescence lifetime measured in the absence and presence of quencher gave strong circumstantial evidence for electron transfer as the quenching mechanism. Triplet yields were measured for five indole derivatives using transient absorption. Intersystem crossing rates were calculated from triplet yield and fluorescence lifetime data. The intersystem cross...

Deuterium isotope effects in constrained tryptophan derivatives: implications for tryptophan photophysics

The deuterium isotope effect on the fluorescence quantum yield and lifetime of the constrained tryptophan derivative 3-carboxy-1,2,3,4-tetrahydro-2-carboline, W(1), was determined as a function of pH and temperature. The isotope effect between pH 3.5 and 11 is attributed to a temperature-dependent quenching process common to all indoles. At room temperature the quantum yield ratio in D{sub 2}O and H{sub 2}O is 1.05 for W(1) zwitterion and 1.7 for W(1) anion. The temperature dependence of the fluorescence lifetime was determined for the zwitterion and the anion in H{sub 2}O and D{sub 2}. The frequency factors A and activation energies E{sup *} in H{sub 2}O are A = 6 x 10{sup 16} s{sup -1}, E{sup *} = 12.6 kcal/mol for W(1) anion, and N-methylindole The frequency factors A of these compounds are 2- to 3-fold larger in H{sub 2}O than in D{sub 2}O. The large deuterium isotope effect W(1) anion at room temperature compared to W(1) zwitterion results from two factors: a smaller temperature-independent nonradiative rate and a larger isotopically sensitive temperature-dependent rate. Several mechanisms for the intrinsic deuterium isotope effect are discussed. Two mechanisms are consistent with available data for indoles: {open_quotes}invisible{close_quotes} or incomplete proton transfer from water to indole and formationmore » of a water-indole charge-transfer exciplex. 57 refs., 8 figs., 4 tabs.« less

Excited-state reaction and the origin of the biexponential fluorescence decay of tryptophan zwitterion

The fluorescence decay of tryptophan zwitterion in H 2O and D 2O solution was determined over the entire emission spectrum. The biexponential decay kinetics show features which are consistent with the occurrence of an excited-state reaction. This observation is not predicted by models of tryptophan photophysics based on ground-state conformation heterogeneity. We speculate that the excited-state reaction involves alteration of the rotamer populations in response to the change in the state dipole which occurs upon excitation.

Fluorescence of a rotationally constrained tryptophan derivative, 3-carboxy-1,2,3,4-tetrahydro-2-carboline

Despite a plethora of work on tryptophan photophysics, the origin of the complex fluorescence decay kinetics is still unknown. A question remains whether the two fluorescence lifetimes of the tryptophan zwitterion are due to ground-state and therefore excited-state heterogeneity resulting from rotameric forms. To test the conformer model, we synthesized a tryptophan derivative, 3-carboxyl-1,2,3,4-tetrahydro-2-carbolin, which restricts rotation of the alanyl side chain. The constraint limits the number of conformations available to the molecule without greatly affecting the electronic properties. The absorption and emission spectra and the pK of the amino group are similar to those of tryptophan

Photophysics of tryptophan in bacteriophage T4 lysozymes

Bacteriophage T4 lysozyme contains three tryptophan residues in distinct environments. Lysozymes with one or two of these residues replaced by tyrosine are used to characterize the photophysics of tryptophan in these individual sites. The fluorescence spectra, average lifetimes, and quantum yields of these three single-tryptophan variants are understandable in terms of the neighboring residues. The emission spectra and radiative lifetimes are found to be the same for all three species while the quantum yield and decay kinetics are quite distinct. The variation of the average nonradiative rate constant is correlated with neighboring quenching groups. Quenching by I- correlates with exposure of the tryptophan residue based on the crystal structure. Complex behavior is observed for the time dependence of the fluorescence decay in all three cases, including that of the immobile tryptophan-138 residue. The complexity of the fluorescence decay is ascribed to heterogeneity in the nonradiative rate constant among microstates. Energy transfer between tryptophan residues is inferred to occur from comparison of the quantum yields of the two-tryptophan and single-tryptophan proteins and is discussed in terms of the Förster mechanism.

Simultaneous analysis of single-photon timing data for the one-step determination of activation energies, frequency factors and quenching rate constants. Application to tryptophan photophysics.

A general global analysis of single-photon timing data is presented in which each fluorescence decay curve can be described by a different decay law. The model parameters can be held in common within one curve and/or between related curves. Any or all parameters can be kept fixed, or they may be variable to seek optimum values. This general analysis allows the determination of activation energies, frequency factors and quenching rate constants in one step. The construction of the global mapping table which relates parameters in one experiment to those in another is explained in detail. The use and performance of this general simultaneous analysis are examined using tryptophan fluorescence decays at pH 6.0 obtained at various emission wavelengths as a function of temperature and added solute quencher. The results show that tryptophan at pH 6.0 decays as a biexponential with decay times which are independent of the analysis wavelength. The decay component with the short lifetime has a deactivation rate constant of 1.4 x 10(9) s-1 independent of temperature. The decay component with the long lifetime has an activation energy of 28 kJ/mol and a frequency factor of 3 x 10(13) s-1; its temperature-independent decay rate constant equals 1 x 10(8) s-1. Recursion formulas for a computer program to estimate activation energies, frequency factors, and decay rate constants are provided.

Internal motion and electron transfer in proteins: a picosecond fluorescence study of three homologous azurins.

We have carried out a picosecond fluorescence study of holo- and apoazurins of Pseudomonas aeruginosa (azurin Pae), Alcaligenes faecilis (azurin Afe), and Alcaligenes denitrificans (azurin Ade). Azurin Pae contains a single, buried tryptophyl residue; azurin Afe, a single surface tryptophyl residue; and azurin Ade, tryptophyl residues in both environments. From anisotropy measurements we conclude that the interiors of azurins Pae and Ade are not mobile enough to enable motion of the indole ring on a nanosecond time scale. The exposed tryptophans in azurins Afe and Ade show considerable mobility on a few hundred picosecond time scale. The quenching of tryptophan fluorescence observed in the holoproteins is interpreted in terms of electron transfer from excited-state tryptophan to Cu(II). The observed rates are near the maximum predicted by Marcus theory for the separation of donor and acceptor. The involvement of protein matrix and donor mobility for electron transfer is discussed. The two single-tryptophan-containing proteins enable the more complex fluorescence behavior of the two tryptophans of azurin Ade to be understood. The single-exponential fluorescence decay observed for azurin Pae and the nonexponential fluorescence decay observed for azurin Afe are discussed in terms of current models for tryptophan photophysics.

Dispersed fluorescence of jet-cooled tryptophan: Excited state conformers and intramolecular exciplex formation

The dispersed fluorescence of the amino acid tryptophan has been measured in the environment of a cold, supersonic free jet. Analysis of the region of the spectrum near the electronic origin indicates that the electronic excitation spectrum contains features which arise from various ground state conformers of tryptophan, confirming our previous assignment of these features. Under the conditions of our experiment the conformers do not interconvert in the excited state during the fluorescence liftime. Analysis of the dispersed emission spectrum of one conformer reveals broad red-shifted fluorescence which exists even when the electronic origin transition is excited. This broad red-shifted fluorescence is produced by the formation of an intramolecular exciplex involving excited state proton transfer to form a zwitterion. Molecules which do not have the ability to form a zwitterion do not exhibit this behavior, and deuterated trytophan shows broad fluorescence in an amount consistent with a slower proton transfer rate. The significance of these results for understanding the excited state photophysics of tryptophan in solution is discussed.

The electronic spectrum of the amino acid tryptophan in the gas phase

The electronic spectrum of the amino acid tryptophan has been measured in the environment of a cold, supersonic molecular beam. The resonantly enhanced two-photon ionization spectrum of tryptophan shows some features characteristic of more volatile indole derivitives, however the region of the spectrum near the origin shows distinctive low frequency structure absent from the simpler indole containing molecules. The power dependence of the spectrum reveals features which can be attributed to several conformers of tryptophan in the molecular beam. One of these conformers shows a nearly harmonic 26 cm−1 vibrational progression which does not appear in the spectra of other indole derivitives, and the intensity pattern of this progression indicates that this particular conformer undergoes a significant geometry change upon electronic excitation. The lack of many extensive vibrational progressions in the electronic spectrum indicates that the excited state conformers of tryptophan are similar to those in the ground electronic state. The identification of a small number of stable tryptophan conformers is important for understanding the photophysics of tryptophan in solution.

Photophysics of tryptophan in water, deuterium oxide and in nonaqueous solvents

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPhotophysics of tryptophan in water, deuterium oxide and in nonaqueous solventsEva Gudgin, Ricardo Lopez-Delgado, and William R. WareCite this: J. Phys. Chem. 1983, 87, 9, 1559–1565Publication Date (Print):April 1, 1983Publication History Published online1 May 2002Published inissue 1 April 1983https://doi.org/10.1021/j100232a021RIGHTS & PERMISSIONSArticle Views234Altmetric-Citations47LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (829 KB) Get e-Alerts

Picosecond Spectroscopy of Solutions, Proteins and Photosynthetic Membranes

The photophysics of tryptophan is discussed and a model capable of rationalizing the photophysics of almost twenty derivatives of tryptophan is proposed. The model is based on conformers about the Cα—Cβ bond and the relative rates of charge transfer from indole to various electrophiles. Three new tryptophan derivatives were synthesized to test the model. Accurate predictions concerning the relative fluorescence lifetimes and the form of the fluorescence decay law are made for tryptophan and seventeen of its derivatives, including the three new derivatives.The fluorescence decay kinetics from chloroplasts from green plants are described. New data are presented on the fluorescence decays obtained from genetic mutants of chlamydomonas which lack specific components of the photosynthetic apparatus. The interpretation of the green plant chloroplast data in terms of the two photosystems and the light harvesting array is discussed in terms of the data from the mutant algae. Our data indicate that the major short component (∼100 ps) obtained in the fluorescence decay of chloroplasts results from photochemical trapping by both photosystem I and photosystem II.A synchronously pumped dye laser which produces two, independently tunable, synchronized picosecond pulse trains will be described. An application of the laser to time and frequency resolved polarization spectroscopy will be given. The results are used to estimate the homogeneous linewidth of the S0 → S1 transition of a large molecule in solution. The optical heterodyne technique is applied to separate the real and imagninary contributions of the third order nonlinear susceptibility.