Photo-physical characterization of flavin-pyrene-phenothiazine molecular photonic complexes

In this thesis a pyrene-flavin dyad, a phenothiazine-flavin dyad, a pyrene-flavin-phenothiazine triad, and their constituents -the phenyl-isoalloxazine, bromo-phenyl-isoalloxazine, pyrene and 1-methylpyrene, heptyl-phenothiazine and heptyl-phenyl-phenothiazine- dissolved in either dichloromethane or acetonitrile have been characterized by absorption and emission spectroscopy. These dyads are model compounds for the flavin based blue-light photoreceptors phototropin and BLUF proteins. The triad was designed to mimic the dye-based functions of cryptochromes. Absorption cross-section spectra, fluorescence quantum distributions, fluorescence quantum yields, degrees of fluorescence polarisation, and fluorescence lifetimes of dyes were determined. The photo-stability of the dyes has been investigated by observation of absorption spectral changes due to prolonged blue-light excitation. The absorption spectra of the dyads and the triad resemble the superposition of the absorption spectra of their constituents. Photo-excitation of the flavin moiety causes fluorescence quenching by reductive electron transfer in thermodynamic equilibrium with the exited flavin subunit. The charge-separated states recover by charge recombination. Photo-excitation of the pyrene or phenothiazine moiety causes oxidative electron transfer with successive recombination

Protein Aggregation Studied by Forward Light Scattering and Light TransmissionAnalysis,

The aggregation of the circadian blue-light photo-receptor cryptochrome from Drosophila melanogaster (dCry) is studied by transmission and forward light scattering measurement in the protein transparent wavelength region. The light scattering in forward direction is caused by Rayleigh scattering which is proportional to the degree of aggregation. The light transmission through the samples in the transparent region is reduced by Mic light scattering in all directions. It depends on the degree of aggregation and the monomer volume fill factor of the aggregates (less total scattering with decreasing monomer volume fill factor of protein globule) allowing a distinction between tightly packed protein aggregation (monomer volume fill factor 1) and loosely packed protein aggregation (monomer volume fill factor less than 1). An increase in aggregation with temperature, concentration, and blue-light exposure is observed. At a temperature of 4 degrees C and a protein concentration of less than 0.135 mM no dCry aggregation was observed, while at 24 degrees C and 0.327 mM gelation occurred (loosely packed aggregates occupying the whole solution volume). (C) 2007 Elsevier B.V. All rights reserved

Absorption and Fluorescence Spectroscopic Characterisation of the Circadian Blue-Light Photoreceptor Cryptochrome from Drosophila melanogaster (dCry)

The absorption and fluorescence behaviour of the circadian blue-light photoreceptor cryptochrome from Drosophila melanogaster (dCry) in a pH 8 aqueous buffer solution is studied. The flavin adenine dinucleotide (FAD) cofactor of dCry is identified to be present in its oxidized form (FAD(ox)), and the 5,10-methenyltetrahydrofolate (MTHF) cofactor is found to be hydrolyzed and oxidized to 10-formyldihydrofolate (10-FDHF). The absorption and the fluorescence behaviour of dCry is investigated in the dark-adapted (receptor) state, the light-adapted (signalling) state, and under long-time violet light exposure. Photoexcitation of FAD(ox) in dCry causes a reductive electron transfer to the formation of anionic FAD semiquinone (FAD(center dot-)), and photo-excitation of the generated FAD(center dot-) causes an oxidative electron transfer to the back formation of FAD(ox). In light adapted dCry a photo-induced equilibrium between FAD(ox) and FAD(center dot-)exists. The photo-cycle dynamics of signalling state formation and recovery is discussed. Quantum yields of photo-induced signalling state formation of about 0.2 and of photo-induced back-conversion of about 0.2 are determined. A recovery of FAD(center dot-) to FAD(ox) in the dark with a time constant of 1.6 min at room temperature is found. (C) 2008 Elsevier B.V. All rights reserved

Absorption and Emission Spectroscopic Characterization of 10-Phenyl-Isoalloxazine Derivatives

The flavoquinone dyes 10-phenyl-isoalloxazine-3-acetic acid ethyl ester (1) and 10-(4-bromo-phenyl)-3-methyl-isoalloxazine (2) in dichloromethane, acetonitrile, and methanol are characterized by absorption and emission spectroscopy. Absorption cross-section spectra, stimulated emission cross-section spectra, fluorescence quantum distributions, quantum yields, lifetimes, and degrees of fluorescence polarization are determined. The blue-light photo-degradation of the dyes is studied. Mass spectroscopic measurements reveal the formation of phenyl-benzo-pteridine (isoalloxazine) derivatives, tetraaza-benzo-aceanthrylene derivatives, dihydro-quinooxaline derivatives, and pyrazino-carbazole derivatives. An enhancement of photo-degradation is observed by the formed photo-fragments

Absorption and emission spectroscopic characterisation of a Pyrene-Flavin Dyad

The pyrene-flavin (isoalloxazine) dyad, PFD {C44H31N5O5; CA Index name: 1-pyrenepropanoic acid, α-[[4,10-dihydro-2,4-dioxo-10-phenylbenzo[g]pteridin-3(2H)-yl)acetyl]amino]-, phenylmethyl ester, (αR)–(9Cl); CA Registry number: 618907-57-6}, dissolved in either dichloromethane or acetonitrile is characterized by absorption and emission spectroscopy. Absorption cross-section spectra, stimulated emission cross-section spectra, fluorescence quantum distributions, quantum yields, and degrees of fluorescence polarisation are determined. The fluorescence decay after femtosecond pulse excitation is determined by fluorescence up-conversion. The ground-state absorption recovery is determined by picosecond pump and probe transmission measurements. The dye photo-stability is investigated by observation of absorption spectral changes due to prolonged blue-light excitation. The absorption spectrum of PFD dyad resembles the superposition of the absorption of isoalloxazine (flavin) and 1-methylpyrene. Long-wavelength photo-excitation of the flavin moiety causes fluorescence quenching by ground-state electron transfer from pyrene to isoalloxazine. Short-wavelength photo-excitation of the pyrene moiety causes (i) excited-state electron transfer from pyrene to isoalloxazine, and (ii) Förster-type energy transfer from pyrene to flavin followed by ground-state electron transfer from pyrene to flavin

Adiabatic Nanofocusing on Ultrasmooth Single-Crystalline Gold Tapers Creates a 10-nm-Sized Light Source with Few-Cycle Time Resolution

We demonstrate adiabatic nanofocusing of few-cycle light pulses using ultrasharp and ultrasmooth single-crystalline gold tapers. We show that the grating-induced launching of spectrally broad-band surface plasmon polariton wavepackets onto the shaft of such a taper generates isolated, point-like light spots with 10 fs duration and 10 nm diameter spatial extent at its very apex. This nanofocusing is so efficient that nanolocalized electric fields inducing strong optical nonlinearities at the tip end are reached with conventional high repetition rate laser oscillators. We use here the resulting second harmonic to fully characterize the time structure of the localized electric field in frequency-resolved interferometric autocorrelation measurements. Our results strongly suggest that these nanometer-sized ultrafast light spots will enable new experiments probing the dynamics of optical excitations of individual metallic, semiconducting, and magnetic nanostructures

Adiabatic Nanofocusing on Ultrasmooth Single-Crystalline Gold Tapers Creates a 10-nm-Sized Light Source with Few-Cycle Time Resolution

We demonstrate adiabatic nanofocusing of few-cycle light pulses using ultrasharp and ultrasmooth single-crystalline gold tapers. We show that the grating-induced launching of spectrally broad-band surface plasmon polariton wavepackets onto the shaft of such a taper generates isolated, point-like light spots with 10 fs duration and 10 nm diameter spatial extent at its very apex. This nanofocusing is so efficient that nanolocalized electric fields inducing strong optical nonlinearities at the tip end are reached with conventional high repetition rate laser oscillators. We use here the resulting second harmonic to fully characterize the time structure of the localized electric field in frequency-resolved interferometric autocorrelation measurements. Our results strongly suggest that these nanometer-sized ultrafast light spots will enable new experiments probing the dynamics of optical excitations of individual metallic, semiconducting, and magnetic nanostructures