Ns Fluorescence Research Articles

Graphitic carbon nitride nanosheets as a fluorescent probe for chromium speciation

A fluorometric method was developed for simultaneous determination of Cr(VI) and Cr(III) ions using graphitic carbon nitride nanosheets (g-C3N4 NS) as a nanosized fluorescent indicator probe. The g-C3N4 NS were prepared using high-temperature carbonization of melamine followed by ultrasonication-assisted liquid exfoliation. The g-C3N4 NS display fluorescence with excitation/emission peaks located at 320 and 450nm. The chromium speciation is based on the quenching of g-C3N4 NS fluorescence. The total concentration of chromium is determined after oxidation of Cr(III) to Cr(VI). The Cr(III) content was then calculated by subtracting the concentration of Cr(VI) from that of total chromium. The effects of pH value, probe amount, and contact time are optimized. Under optimum conditions, calibration plots are linear in the range in the 0.01 to 100μM chromium concentration range. The limit of detection is 3nM for for Cr(VI). The intra- and inter-day relative standard deviations (RSD) of the assay are 3.6-7.5% and 4.1-8.5%, respectively. The indicator probe was applied to the determination of chromium species in spiked water and food samples, and recoveries were satisfactory (93.9-107.0%). Graphical abstract Graphitic carbon nitride nanosheets are synthesized by melamine carbonization and employed for Cr speciation in water and food real samples. Total Cr(VI) and Cr(VI) are assessed based on the quenching of thefluorescence ofnanosheets by Cr(VI).

A Spectroscopic Survey of Substituted Indoles Reveals Effects of 1LB Transition Stabilization

Although tryptophan is a natural probe of protein structure, interpretation of its fluorescence emission spectrum is complicated by the presence of two electronic transitions, 1La and 1Lb. Theoretical calculations show that a point charge adjacent to either ring of the indole can shift the emission maximum. This study explores the effect of pyrrole and benzyl ring substitutions on the transitions' energy via absorption and fluorescence spectroscopy, and lifetime measurements. The survey of indole derivatives shows that methyl substitutions on the pyrrole ring effect 1La and 1Lb energies in tandem while benzyl ring substitutions with electrophilic groups lift the 1La/1Lb degeneracy. For 5- and 6-hydroxyindole in cyclohexane, 1La and 1Lb transitions are resolved (5-hydroxyindole absorbance, shown, solid line). This finding provides for 1La origin assignment in the absorption and excitation spectra for indole vapor. The 5-hydroxyindole excitation spectrum (dashed line) shows that despite a blue-shifted emission spectrum, both the 1La and 1Lb transitions contribute to emission. 10 0 ns fluorescence lifetimes for 5-hydroxyindole are consistent with a charge acceptor-induced increase in the nonradiative rate.View Large Image | View Hi-Res Image | Download PowerPoint Slide

Solvation dynamics of coumarin 153 embedded in AOT + phenol organogels studied by time-resolved fluorescence spectroscopy

We investigate solvation dynamics of organogel utilizing ps–ns fluorescence spectroscopy. The organogel studied in this Letter comprises bis(2-ethylhexyl) sulfosuccinate (AOT) and p-chlorophenol in the m-xylene solvent, that produce an organogel architecture with self-assembly. Within the organogel, an emitting probe, coumarin 153 (C153), is embedded. We then obtain dynamic response functions of solvation derived from the time-resolved fluorescence spectra of C153. We propose that total energy of the C153–organogel system relaxes with a relaxation time of 3.9ns, whereas the entire rearrangement of the organogel structure around C153 is achieved with that of 6.1ns, respectively.

Triphenylamine derivatives with large two-photon cross-sections.

[structure: see text] Triphenylamine derivatives have been synthesized and shown to exhibit large two-photon cross-sections at a wide range of wavelengths and the largest value measured by fs Z-scan experiment. Moreover, a linear relationship is noted between the two-photon cross-sections measured by ns fluorescence and fs Z-scan methods.

Photodissociation dynamics of S4N4 at 222 and 248 nm

Emission from several electronically excited states of NS is observed when the energetic molecule S4N4 is photolyzed with radiation from an excimer laser. Photolysis at 248 nm generates fluorescence from the B 2Π1/2,3/2, H 2Π1/2, G 2Σ−, and I 2Σ+ states of NS. NS(B 2Π1/2,3/2) and NS(C 2Σ+) fluorescence is observed when the photolysis wavelength is changed to 222 nm. The NS(H) and NS(C) spectra are postulated to arise from a resonant interaction between the KrF and KrCl excimer photons, respectively, and vibrationally hot ground state NS. LIF excitation scans on the NS X 2Π1/2,3/2 → B 2Π1/2,3/2 system confirm the production of rotationally and vibrationally excited NS(X) up to v″=4. A mechanism, based on the experimental data (i.e., spectral composition, laser fluence studies, excited state time histories), calculated heats of formation, and Gaussian molecular orbital calculations, is proposed to account for the observed emissions. For photolysis at 248 nm it is hypothesized that a two photon absorption promotes the ground singlet state of S4N4 to an upper repulsive singlet state, which rapidly dissociates (τ≪30 ns), producing an acyclic S3N3 fragment and vibrationally excited monomeric NS(X). The photofragments can interact further with the excimer radiation to produce NS(B) and NS(H), respectively. A similar mechanism is proposed to account for the presence of the NS(B) and NS(C) excited states for the 222 nm photolysis.

Long-lived tryptophan fluorescence in phosphoglycerate mutase

Phosphoglycerate mutase (PGM; EC 2.7.5.3) isolated from rat and rabbit muscle has been shown to possess an unusually long-lived fluorescence component when excited by ultraviolet light below 310 nm. On the basis of spectral and physical measurements, this 16.4 (+/- 0.2) ns fluorescence lifetime at room temperature is assigned to a tryptophan residue in an unusual environment. The emission profile of this long-lived tryptophan is red shifted from the other tryptophans of PGM by approximately 25 nm. PGM has been crystallized and sequenced from yeast where it has been shown to be a tetramer with 29K subunits. However, we have not been able to detect the existence of an unusually long-lived fluorescence component in the yeast isomer. The long fluorescence lifetime is lost upon denaturation of rabbit PGM and is partially restored upon introduction of the protein to a nondenaturing environment, suggesting the long lifetime is not the result of a covalent modification. The PGM molecule was studied by a number of techniques including time-resolved tryptophan fluorescence, quenching studies of tryptophan fluorescence, and enzyme activity studies. The long-lived fluorescence has been shown to be statistically quenched by Br-, I-, and Cu2+ in the submillimolar region while the acrylamide quenching shows the tryptophan is marginally accessible to solvent. Characterization of the long-lived fluorescence and its possible sources are discussed.

Examination of the NS fluorescence excited by the 2304 Å line of barium II

Examination of the NS fluorescence excited by the 2304 Å line of barium II