Syntheses and photophysical properties of a series of [2:2] silver(I) metallocycles

A series of methoxy-protected N₂O₄-donor Schiff base ligands have been synthesised and fully characterised including X-ray crystallography. Upon complexation with silver(I) [2:2] metallocycles have been formed of various sizes from 10-membered to 24-membered depending on the diamine of the ligand used in forming the Schiff base. The luminescence behaviour of the silver dimers has been studied and the smallest metallocycle shows argentophilic interactions in the solid state.     

Luminescent CeCl3 nanoparticles by Tris(1,1,1,5,5,5-hexafluoro-2,4-pentanedionato)cerium diglyme photolysis in chlorinated solvents

Irradiation of [Ce(hfac)₃(diglyme)] (hfac = 1,1,1,5,5,5-hexafluoro-2,4-pentanedionato and diglyme (DG) = 2,5,8,11,14-pentaoxapentadecane) in chlorinated solvents (CH₂Cl₂, CCl₄) with UV light led to luminescent colloidal CeCl₃ that was characterized by transmission electron microscopy (TEM) analysis. When a substrate, quartz or silicon was present in the reaction cell, photoluminescent films were obtained, containing either pure CeCl₃ or mixtures of CeCl₃, CeF₃ and CeOx in function of the experimental parameters of irradiation. Nanostructured and luminescent pure CeCl₃ films were obtained by irradiation of the cerium complex in CCl₄ at high intensity light for a few minutes. The films were characterized by X-ray diffraction (XRD), Energy dispersive X-ray (EDX), X-ray photoelectron spectroscopy (XPS), TEM, scanning electron microscopy (SEM) and atomic force microscopy (AFM). The kinetics of the [Ce(hfac)₃(diglyme)] solution photodegradation, followed by UV spectrophotometry and spectrofluorimetry, pointed to CeCl₃ formation by a solvent-initiated reaction, whereas the other inorganic compounds were the products of side reactions.     

Synthesis and luminescent properties of gadolinium aluminates phosphors

In this work, aluminum-gadolinium oxides with different phases were prepared by the non-hydrolytic sol-gel route, using lower temperatures than those employed in methods such as solid-state reaction and Pechini method. The influence of heating treatment on sample structure was investigated. The formation process and the local structure of the samples are discussed on the basis of thermal, X-ray diffraction, photoluminescence (PL) spectroscopy, and infrared spectroscopy analyses. The quantum efficiency of Eu³⁺ in the different phases obtained in this studied was evaluated. Initial crystallization and the GdAlO₃ phase were observed at temperatures around 400 °C. PL data of all the samples revealed the characteristic transition bands arising from the ⁵D₀ → ⁵F_J (J = 0, 1, 2, 3, and 4) manifolds under maximum excitation at 275, 393, and 467 nm in all cases. The ⁵D₀ → ⁷F₂ transition often dominates the emission spectra, indicating that the Eu³⁺ ion occupies a site without inversion center.     

Uranium luminescence in La2Zr2O7: effect of concentration and annealing temperature

The speciation of a particular element in any given matrix is a prerequisite to understanding its solubility and leaching properties. In this context, speciation of uranium in lanthanum zirconate pyrochlore (La₂Zr₂O₇ = LZO), prepared by a low‐temperature combustion route, was carried out using a simple photoluminescence lifetime technique. The LZO matrix is considered to be a potential ceramic host for fixing nuclear and actinide waste products generated during the nuclear fuel cycle. Special emphasis has been given to understanding the dynamics of the uranium species in the host as a function of annealing temperature and concentration. It was found that, in the LZO host, uranium is stabilized as the commonly encountered uranyl species (UO₂²⁺) up to a heat treatment of 500 °C at the surface. Above 500 °C, the uranyl ion is diffused into the matrix as the more symmetric octahedral uranate species (UO₆^6–). The uranate ions thus formed replace the six‐coordinated ‘Zr’ atoms at regular lattice positions. Further, it was observed that concentration quenching takes place beyond 5 mol% of uranium doping. The mechanism of the quenching was found to be a multipolar interaction. Copyright © 2016 John Wiley & Sons, Ltd.     

A study of dark luminescence in Chlorella. Background luminescence, 3-(3,4-dichlorophenyl)-1,1-dimethylurea-triggered luminescence and hydrogen peroxide chemiluminescence

Dark luminescence, defined as the ability of completely relaxed (darkadapted) photosynthetic systems to emit light, has been studied in Chlorella. Three main effects have been demonstrated. 3-(3,4-Dichlorophenyl)-1,1-dimethylurea elicits a weak emission L_D of very long lifetime (several minutes); it is believed to result from a negative shift of redox potential of the secondary System II electron acceptor B producing in some centers a state Q⁻ (reduced primary acceptor), as postulated by Velthuys and Amesz ((1974) Biochim. Biophys. Acta 333, 85–94), which can recombine with an oxidizing equivalent in a state S₂ present in very small amount. As in photoinduced luminescence, this recombination excites chlorophyll which then emits light. A much stronger emission L_H is observed after injection of H₂O₂. Both signals are modified or suppressed by treatments specific of the oxygen emission system, such as: thermal denaturation at 50°C, NH₂OH, etc. In addition, a weak, permanent background luminescence L₀ has been observed; like L_D and L_H, it is a System II property and requires the integrity of the oxygen-evolving system. It is believed to reflect a very slow back flow of electrons from an endogeneous reductant pool to oxygen through part of the photosynthetic chain. Using flash preillumination, it is demonstrated that H₂O₂ is able to oxidize S₀ into S₂, the latter giving rise to L_H; H₂O₂ does not act on S₁ (or much less). The reactive site of H₂O₂ seems to be the same as the binding site of NH₂OH. Evidence is given that the strong L_H signal in particular reveals a stable, low pH of the intrathylakoid phase in Chlorella.     

Sub-microsecond chlorophyll A delayed fluorescence from Photosystem I Magnetic field-induced increase of the emission yield

(1) In photosystem I (PS I) particles in the presence of dithionite and intense background illumination at 290 K, an external magnetic field (0–0.22 T) induced an increase, ΔF, of the low chlorophyll a emission yield, F ($\text{ΔF}\text{F}\text{? 1–1.5\%}$). Half the effect was obtained at about 35–60 mT and saturation occurred for magnetic fields higher than about 0.15 T. In the absence of dithionite, no field-induced increase was observed. Cooling to 77 K decreased ΔF at 685 nm, but not at 735 nm, to zero. Measuring the emission spectra of F and ΔF, using continuous excitation light, at 82, 167 and 278 K indicated that the spectra of F and ΔF have about the same maximum at about 730, 725 and 700 nm, respectively. However, the spectra of ΔF show more long-wavelength emission than the corresponding spectra of F. (2) Only in the presence of dithionite and with (or after) background illumination, was a luminescence (delayed fluorescence) component observed at 735 nm, after a 15 ns laser flash (530 nm), that decayed in about 0.1 μs at room temperature and in approx. 0.2 μs at 77 K. A magnetic field of 0.22 T caused an appreciable increase in luminescence intensity after 250 ns, probably mainly caused by an increase in decay time. The emission spectra of the magnetic field-induced increase of luminescence, ΔL, at 82, 167 and 278 K coincided within experimental error with those of ΔF mentioned above. The temperature dependence of ΔF and ΔL was found to be nearly the same, both at 685 and at 735 nm. (3) Analogously to the proposal concerning the 0.15 μs luminescence in photosystem II (Sonneveld, A., Duysens, L.N.M. and Moerdijk, A. (1980) Proc. Natl. Acad. Sci. U.S.A. 77, 5889–5893), we propose that recombination of the oxidized primary donor P-700⁺ and the reduced acceptor A^?, probably A^?₁, of PS I causes the observed fast luminescence. The effect of an external magnetic field on this emission may be explained by the radical pair mechanism. The field-induced increase of the 0.1–0.2 μs luminescence seems to be at least in large part responsible for the observed increase of the total (prompt + delayed) emission measured during continuous illumination in the presence of a magnetic field.     

Precursors to microsecond delayed luminescence in oxygenevolving and inhibited chloroplasts

We have investigated submillisecond delayed luminescence in spinach chloroplasts under a variety of conditions. In Tris-washed chloroplasts, which are inhibited on the oxidizing side of P-680, the delayed light emission in the 7–200 μs time-range decayed with biphasic behavior. In fully dark-adapted samples illuminated by a single saturating laser pulse, the fast phase of delayed luminescence followed a nearly identical pH-dependent time-course as that observed optically and by ESR for P⁺-680 reduction, thus verifying the recombination hypothesis for the origin of delayed light. The observed slower phase of delayed luminescence was also pH dependent, but unlike the fast phase, could not be ascribed to specific electron transfer events of PS II. This phase could be rationalized by a heterogeneity in the population of P-680. While kinetic parameters were found to be insensitive to changes in ionic strength, the overall luminescence intensity was quite sensitive to the electrical parameters, thus indicating the role of ionic strength and local charges in delayed luminescence modulation. A similar series of experiments was performed on untreated chloroplasts. The pH-dependent delayed luminescence behavior in both untreated chloroplasts and Tris-washed chloroplasts was similar despite significantly faster kinetics associated with the reduction of P⁺-680 by the secondary PS II electron donor, Z, in the former preparation (e.g., Van Best, J.A. and Mathis, P. (1978) Biochim. Biophys. Acta 503, 178–188). Thus, it was concluded that, in untreated samples, microsecond delayed luminescence emanates primarily from centers which are not competent in oxygen evolution. The nearly identical delayed luminescence intensity in untreated chloroplasts and in Tris-washed chloroplasts was rationalized by a model which predicts modulations in delayed luminescence yield by the exciton-quenching effect of P⁺-680. Computer simulations demonstrate the feasibility of this model. The previously documented flash oscillations in microsecond delayed luminescence intensity in untreated chloroplasts (Bowes, J.M. and Crofts, A.R. (1979) Biochim. Biophys. Acta 547, 336–346), which we readily observed, were attributed to alterations in delayed luminescence yield (in nonfunctional centers) by variations in charge density stored at the oxygen-evolving complex of functional centers. Taken together, our results emphasize the dependence of delayed luminescence kinetics upon electron-transfer kinetics and the dependence of delayed luminescence amplitude upon the photochemical parameters, the exciton yield and the emission yield.     

Catecholamines in the coelenterate Renilla köllikeri

Summary The characteristics of uptake of ³H-noradrenaline (³H-NA) and ³H-adrenaline (³H-A) in the tissues of the sea pansy, Renilla köllikeri, were studied by in vivo incubations. Lineweaver-Burk plots indicated two components of catecholamine accumulation, one representing a high-affinity uptake with an apparent K _m of 4.91×10^-7 M (³H-NA) or 4.39×10^-7 M (³H-A), and the other a low affinity process with an apparent Km of 5.52×10^-5 M (³H-NA) or 1.49×10^-5 M (³H-A). The high-affinity uptake of both tracers was strongly inhibited at low temperature and in a calcium-free medium, thus suggesting the involvement of a carrier-mediated transport mechanism, but was largely insensitive to sodium omission and ouabain. Accumulations of ³H-NA, but not ³H-A, were highly desipramine-sensitive.Light-microscopic radioautographic studies demonstrated the presence of cells reactive to both ³H-NA and ³H-A in the ectoderm, mesoglea and endoderm. Extraneuronal accumulations of ³H-NA and ³H-A were prominent in some ectodermal cells, in amoebocytes and spicule cells. Reactive neuronal processes were tentatively identified throughout the mesoglea and over all muscle layers on the basis of several morphological criteria. ³H-A, but not ³H-NA label, was more intense over the presumed photocytic zone and circular muscle than elsewhere. These and other observations support a neurotransmitter role for adrenaline (and probably noradrenaline) in control of luminescence and modulation of slow rachidial contractions.Supported by a grant from the Natural Sciences and Engineering Research Council of Canada     

From complexation to computation: Recent progress in molecular logic

The new thrusts in molecular logic are gathered together in this short review, while paying attention to the seeds from which these developments have arisen. The original demonstration of a few basic logic operations has now been extended to cover many of the one- and two-input varieties and even some of the three-input types. Many kinds of inputs and outputs have emerged, including various chemical species and some physical properties. The latter can include heat, light and, arguably, polarity. Reconfigurable logic has grown up to include a range of examples. Even superposable logic has proved possible with molecular systems. Numerical processors have flowered in recent years with several diverse approaches being revealed in recent years. Photochemical concepts such as photoinduced electron transfer (PET), internal charge transfer (ICT) and electronic energy transfer (EET) can be discerned among the designs in the field.     

Dissociation of ATP-binding cassette nucleotide-binding domain dimers into monomers during the hydrolysis cycle

ATP-binding cassette (ABC) proteins have two nucleotide-binding domains (NBDs) that work as dimers to bind and hydrolyze ATP, but the molecular mechanism of nucleotide hydrolysis is controversial. In particular, it is still unresolved whether hydrolysis leads to dissociation of the ATP-induced dimers or opening of the dimers, with the NBDs remaining in contact during the hydrolysis cycle. We studied a prototypical ABC NBD, the Methanococcus jannaschii MJ0796, using spectroscopic techniques. We show that fluorescence from a tryptophan positioned at the dimer interface and luminescence resonance energy transfer between probes reacted with single-cysteine mutants can be used to follow NBD association/dissociation in real time. The intermonomer distances calculated from luminescence resonance energy transfer data indicate that the NBDs separate completely following ATP hydrolysis, instead of opening. The results support ABC protein NBD association/dissociation, as opposed to constant-contact models.