Two‐Photon Excitation of a Plasmonic Nanoswitch Monitored by Single‐Molecule Fluorescence Microscopy

Visible‐light excitation of the surface plasmon band of silver nanoplates can effectively localize and concentrate the incident electromagnetic field enhancing the photochemical performance of organic molecules. Herein, the first single‐molecule study of the plasmon‐assisted isomerization of a photochrome‐fluorophore dyad, designed to switch between a nonfluorescent and a fluorescent state in response to the photochromic transformation, is reported. The photochemistry of the switchable assembly, consisting of a photochromic benzooxazine chemically conjugated to a coumarin moiety, is examined in real time with total internal reflection fluorescence microscopy in the presence of silver nanoplates excited with a 633 nm laser. The metallic nanostructures significantly enhance the visible light‐induced performance of the photoconversion, which normally requires ultraviolet excitation. The resulting ring‐open isomer is strongly fluorescent and can also be excited at 633 nm. These stochastic emission events are used to monitor photochromic activation and show quadratic dependence on incident power. The utilization of a single laser wavelength for both photochromic activation and excitation effectively mimics a pseudo two‐colours system.     

From Portable to SCA Raman devices to characterize harmful compounds contained in used black slag produced in Electric Arc Furnace of steel industry

Black slag from steel production is an industrial waste used as secondary material for some applications (forest tracks, cement, etc.). When it disposed to the open air, little is known about possible side effects that could appear with time. To foresee those side effects, various Raman equipments were used. This analytical strategy has been applied to six different black slag. Four of them were obtained from two steel producers (two original and two with treatment of ‘inerting’), and the other two sampled in civil construction works, which supposedly should be treated. Results showed the original mineral phases of the samples (iron and other metal oxides, silicates, ferrites…) and the new phases (calcite, natron, nitratine, goethite, limonite, ilesite, etc.) resulting from the superficial reaction with the atmospheric acid compounds. This fact indicates a strong reactivity between slag and surrounding environment where they have been deposited. Only with one of the three setups, all the compounds could not be detected: (1) the handheld spectrometer detected the major ones and few of the minor ones, (2) the laboratory Raman microprobe ascertained nearly all of the compounds, but cannot be translated to the field and (3) Structural and Chemical Analyser (SCA), which combines micro‐Raman spectroscopy and Scanning Electron Microscopy/ Energy Dispersive X‐Ray Spectroscopy (SEM‐EDS) on the same spot, recognized the trace compounds, which were the most harmful ones. These results demonstrate the greater applicability of this new strategy in comparison with traditional methods for the chemical characterization of black slag and its alteration products. Copyright © 2013 John Wiley & Sons, Ltd.     

1H and 13C spectral assignment of substituted 5H-[1,3]thiazolo[2,3-b]quinazolin-5-one and 12H-[1,3]benzothiazolo[2,3-b] quinazolin-12-one

(1)H and (13)C spectroscopic data for 5H-[1,3]thiazolo[2,3-b]quinazolin-5-one and 12H-[1,3]benzothiazolo[2,3-b]quinazolin-12-one derivatives were fully assigned by combination of one- and two-dimensional experiments (DEPT, HMBC and HMQC). Both heterocyclic systems show similar spectroscopic properties with some remarkable differences.     

A note on Liouvillian first integrals and invariant algebraic curves

In this work we study the existence and non-existence of finite invariant algebraic curves for a complex planar polynomial differential system having a Liouvillian first integral.     

Composition Conditions In The Trigonometric Abel Equation

In this paper we deal with the center problem for the trigonometricAbel equation dρ/dρ =a1(θ)ρ^2+a2(θ)ρ^3; where a1(θ) and a2(θ)are trigonometric polynomials in θ. This problem is closely connectedwith the classical Poincar´e center problem for planar polynomial vectorfields.     

124-kDa PHYTOCHROME IN MODEL MEMBRANE SYSTEMS: STUDIES OF THE Ii700 INTERMEDIATES WITH THE PROTEIN COVALENTLY BOUND TO PREFORMED LIPOSOMES

Abstract— We have described the covalent binding of 124-kDa oat phytochrome to large unilamellar liposomes composed of either dioleoyl phosphatidylcholine or dipalmkoyl phosphatidylcholine or soybean lecithin, without affecting the photochromic properties of the protein. These phytochrome-liposome systems have now been studied by laser flash photolysis. The liposomes, independent of their membrane rigidity (liquid-crystal vs gel-like phase), do not influence the ratio and reactivity of the two primary photoproducts, Iⁱ₇₀₀- of the red absorbing form of phytochrome, P_l Thus, the lifetimes of the Iⁱ₇₀₀ intermediates and the activation parameters associated with Iⁱ₇₀₀Iⁱ_bl are the same as those measured for nonbound phytochrome in buffer solution. The temperature increase from about 273 K. to 297 K lowers the population of the shorter-lived Iⁱ₇₀₀ intermediate to the same extent both in the liposome-P_l and in nonbound P_l, whereas it does not affect the relative population of the Iⁱ₇₀₀ intermediates from non-bound P_l in the presence of 25% ethylene glycol added to the buffer solution (ionic strength 0.17).     

Poly[(2,2′,5′,2″-tetramethoxy-p-terphenyl-5,5″-ylene)propylene]: Synthesis and physical properties of a novel amorphous regularly segmented conjugated polymer

A new regularly segmented conjugated polymer with methoxy-substituted p-terphenylene units tethered by their meta positions along the polymer main chain was synthesised using the Suzuki cross-coupling reaction. The small size of the connector and lack of long lateral chains lead to a high density of rigid electrooptically active moieties in the structure. However, this molecular architecture produces a very soluble and amorphous polymer with relatively high T_g. The optical properties of samples with different degrees of polymerisation were investigated using UV-visible absorption, steady state and time-resolved photoluminescence emission spectroscopies. Their absorption and emission properties are rather insensible to Mn after reaching a modest DP, to the aggregation state, either solution or neat film, and to annealing. The contorted polymer chain forms a very stable morphology and substantially hinders interactions between chromophores, thus diminishing the formation of aggregated species that are commonly observed in other electrooptically active polymers.     

Comparative study of relativistic density functional methods applied to actinide species AcO(2)(2+) and AcF(6) for Ac = U,Np

A two-component relativistic density functional method based on the Douglas-Kroll-Hess transformation has been applied to the actinyls and hexafluorides of U and Np. All-electron scalar relativistic calculations as well as calculations including spin-orbit interaction have been compared to results obtained with a pseudopotential approach. In addition, several exchange-correlation potentials have been applied to examine their performance for the bond lengths and vibrational frequencies of the title compounds. The calculations confirm the well-known accuracy of the LDA approach for geometries and frequencies, which is corroborated for the hexafluorides where gas phase experimental data are available. Comparison with results of accurate wave function based methods provides further confirmation of this finding. Gradient-corrected functionals tend to overestimate bond lengths and underestimate frequencies also for actinide compounds. The results obtained with Stoll-Preuss (small core) effective core potentials agree very well with those of all-electron calculations, while calculations with Hay-Martin large core pseudopotentials are somewhat less accurate. For all molecules and properties considered, spin-orbit effects have been found negligible concomitant with the closed-shell electronic structure of the U(VI) compounds and the open-shell situation of the Np(VI) compounds with a single valence f electron.     

THE PHOTOPHYSICS OF MEROCYANINE 540. A COMPARATIVE STUDY IN ETHANOL AND IN LIPOSOMES

Abstract— Absorption and fluorescence emission spectra, fluorescence lifetimes, fluorescence quantum yields, photoisomerization quantum yields and triplet quantum yields were measured for Merocyanine 540 (MC540) in ethanol and in large unilamellar dimyristoyl phosphatidylcholine vesicles. The major differences in the photophysics between the two media are the increase of the fluorescence quantum yield from 0.15 in ethanol to 0.6 in vesicles at 25° C, and the appearance of a second fluorescence decay with a lifetime of 1.87 ns in the latter medium. Upper and lower limits for the photoisomerization quantum yields were determined by combining the data from laser flash photolysis and optoacoustic spectroscopy. The decrease in photoisomerization quantum yield upon incorporation of the dye into the lipid bilayer by a factor 2 suggests that this process competes directly with fluorescence. The temperature dependence of the fluorescence and photoisomerization quantum yields in solution supports this model. In both media MC540 has a very low triplet quantum yield with values 0.002 > (> ø_T > 0.02 in ethanol and 0.01 > ø_T- > 0.09 in liposomes Our data are consistent with the model whereby the dye is incorporated into the lipid bilayer as a monomer with two different orientations and this model is adopted on the basis of the biexponential behaviour of the fluorescence and photoisomer decay.