The relationship between Photosystem II intrinsic quantum yield and millisecond luminescence in thylakoids

The relationship between charge recombination at Photosystem II (PS II), as indicated by millisecond luminescence, and PS II quantum yield was studied in spinach thylakoids during electron flow to methylviologen. Under the low magnesium conditions used, a decrease in quantum yield was observed in the absence of non-photochemical excitation quenching, and therefore cannot be due to a restriction in excitation delivery to the reaction centre. It was found that the decrease of the parameter _p, which is a measure of the intrinsic quantum yield of open PS II centers, correlates with an increase in luminescence per open center. The relationship between these two parameters was the same whether _p was manipulated by dissipation of the transthylakoid pH gradient or of the electrical potential. This indicates that the mechanism by which _p decreases depends in the same way on the two components of the protonmotive force as does the charge recombination at PS II. Calculation of the yield of luminescence with respect to the back reaction will be necessary to determine whether the charge recombination occurs at a sufficiently high rate to be directly responsible for the _p decrease.     

Multi-color luminescence of Sm3+-doped Na2YMg2V3O12 phosphor potentially applicable in white-LEDs

A novel multi-color emitting Na₂YMg₂V₃O₁₂:Sm³⁺ phosphor was synthesized using a solid-state reaction, and its crystal structure, luminescence properties, and thermal stability were studied. Charge transfer within the (VO₄)³⁻ groups in the Na₂YMg₂V₃O₁₂ host led to a broad emission band between 400 and 700 nm, with a maximum at 530 nm. The Na₂Y_1−xMg₂V₃O₁₂:xSm³⁺ phosphors exhibited a multi-color emission band under 365 nm near-ultraviolet (near-UV) light, consisting of the green emission of the (VO₄)³⁻ groups and sharp emission peaks at 570 nm (yellow), 618 nm (orange), 657 nm (red), and 714 nm (deep red) of Sm³⁺ ions. The optimal doping concentration of Sm³⁺ ions was found to be 0.05 mol%, and the dipole–dipole (d–d) interaction was primarily responsible for the concentration quenching phenomenon. Using the acquired Na₂YMg₂V₃O₁₂:Sm³⁺ phosphors, commercial BaMgAl₁₀O₁₇:Eu²⁺ blue phosphor, and a near-UV light-emitting diode (LED) chip, a white-LED lamp was designed and packaged. It produced bright neutral white light, manifesting a CIE coordinate of (0.314, 0.373), a color rendering index (CRI) of 84.9, and a correlated color temperature (CCT) of 6377 K. These findings indicate the potential of Na₂YMg₂V₃O₁₂:Sm³⁺ phosphor to be used as a multi-color component for solid-state illumination.     

Optical and dielectric response of two-dimensional WX2 (X = Cl,O, S,Se, Te) monolayers: A comprehensive study based on density functional theory

Here, we study the dielectric and optical properties of two-dimensional (2D) WX₂ monolayers, where X is Cl, O, S, Se, and Te. First principle electronic band structure calculations reveal that all materials are direct band gap semiconductors except WO₂ and WCl₂, which are found to be indirect band gap semiconducting 2D materials. The dielectric response of these materials is also systematically investigated. The obtained results suggest that these materials are suitable as dielectric materials to suppress unwanted signal noise. The optical properties of these 2D materials, such as absorption, reflection and extinction coefficients, refractive index, and optical conductivity, are also calculated from the dielectric function. It is found that these materials exhibit excellent optical response. The present electronic, dielectric, and optical findings indicate that WX₂ monolayers have an opportunity in electronic, optical, and optoelectronic device applications.     

-Identification of a novel intestinal phospholipase A2 from annular seabream: Insights into its catalytic mechanism and its role in biological processes

Phospholipase A₂ (PLA₂) is responsible for the lipid hydrolysis process. Fish PLA₂ have warranted renewed interest due to their excellent properties in phospholipid digestion. We report for the first time the catalytic properties of a PLA₂ secreted from the intestine of the annular seabream Diplodus annularis (IDaPLA₂). The refolded IDaPLA₂ was purified to homogeneity and showed a molecular mass of around 15 kDa attested by SDS-PAGE and MALDI-TOF analyses. Interestingly, IDaPLA₂ revealed higher thermostability compared to mammal pancreatic sPLA₂ as it was active and stable at 55 °C with specific activity of 290 U mg⁻¹ on phosphatidylcholine (PC) as a substrate. Using the lipid monolayer technique, the activity of IDaPLA₂ was found to be 21.68, 6.88 and 5.66 mol cm⁻² min⁻¹ mM⁻¹ using phosphatidylglycerol (PG), PC and phosphatidylethanolamine (PE) monolayers, respectively, at surface pressures from 20−30 mN m⁻¹. Interestingly, the interfacial activity of IDaPLA₂ measured at higher surface pressures may highlight its ability to penetrate into phospholipid monolayers suggesting its involvement in cell lipid membrane degradation which can explain the cytotoxicity potential towards macrophage. The docking simulation data provided insights into the involvement of some key amino-acids in substrate binding and selectivity. The dynamic simulation proved the high stability of IDaPLA₂. Overall, these results provide original evidence on the involvement of IDaPLA₂ into the lipid hydrolysis suggesting it as a potential target in biotechnological applications.     

Computer Analysis and Recognition of Drosophila melanogasterGene Promoters

A new method for recognizing eukaryotic gene promoters was based on their partition and on analysis of correlations of dinucleotide frequencies for each individual fragment. The method was used to recognize the TATA-containing and TATA-less promoters of Drosophila melanogastergenes. The dinucleotide context was correlated with conformational and physicochemical DNA properties in promoter fragments. Mean values of several parameters proved to dramatically change on transition from the TATA box to its GC-rich flanks. In TATA-less promoters, specific properties were revealed in the DPE region. The method was employed in a promoter recognition program, which is available through Internet.     

Infinite zig-zag and cyclic-tetranuclear isomeric imidazolate-bridged polynuclear copper(II) complexes: Magnetic properties, catalytic activity and electrospray mass and tandem mass spectrometry characterization

Two mononuclear copper(II) complexes 1 and 2 with the unsymmetrical tridentate ligands 2- and 4-[((imidazol-2-ylmethylidene)amino)ethyl]pyridine have been prepared. In alkaline solution, deprotonation of the imidazole moiety in 1 and 2 promotes self-assembly, which yielded two structurally different species. Depending on the binding site in the imidazole ring, a polymeric complex with an infinite zig-zag-chain 3, or a cyclic-tetranuclear complex 4 is formed, as shown by spectroscopic and spectrometric analysis. Herein, structural characterization of these isomeric polynuclear complexes was performed by electrospray mass (ESI-MS) and tandem mass spectrometric experiments (ESI-MS/MS). Each isomer was shown to be stable in methanolic solutions and to display unique mass spectra with characteristic multiply charged molecular and fragment ions, corroborating previous data by EPR measurements. Magnetic data in the solid state fit a typical curve for an one-dimensional infinite regular chain system, with J = −(32.4 ± 1.2) cm⁻¹ and g = 2.03 for 3, and that of a cyclic-tetranuclear structure with J = −(55.5 ± 0.4) cm⁻¹ and g = 2.29 for 4. In the oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) by molecular oxygen, both complexes were shown to act as efficient catalysts, exhibiting very similar ratios: k_cat/K_M = 9.12 × 10⁶ mol⁻¹ dm³ min⁻¹ for 3 and 8.73 × 10⁶ mol⁻¹ dm³ min⁻¹ for 4. These similar ratios indicate that interactions between the metal centres in 3 or 4 and the substrate in solution occur predominantly at the outside of the catalyst framework.     

The effects of amyloid peptides on A-type K+ currents of Drosophila larval cholinergic neurons: modeled actions on firing properties

In a previous paper we described the actions of beta-amyloid on an A-type K⁺ current from Drosophila 3^rd Instar larval neurons. The results were a depolarizing shift in the steady-state voltage dependence of inactivation and an increase in the rate of recovery from inactivation of the current. In this work we have used the simulation program NEURON to construct a model cell. We then use the model to predict the effects of changing the A-type K⁺ current as was observed in the amyloid treated neurons on the firing properties of the cell. We show that changing the steady-state voltage dependence of inactivation of the current to a more depolarized level as observed in experiments in beta-amyloid treated neurons causes an increase in the threshold for the initiation of repetitive firing. However, increasing the rate of recovery from inactivation had no effect. Changing both properties simultaneously had no additional effect over changing the voltage dependence of inactivation alone. Thus, a change in the steady-state properties of the A-type K⁺ current as seen in the amyloid-treated Drosophila cholinergic neurons is sufficient to alter the firing properties of the modeled cell.