Improved nonlinear slot waveguides using dielectric buffer layers: properties of TM waves

International audienceWe propose an improved version of the symmetric metal slot waveguides with a Kerr-type nonlinear di-electric core adding linear dielectric buffer layers between the metal regions and the core. Using a finite element method to compute the stationary nonlinear modes, we provide the full phase diagrams of its main TM modes as a function of total power, buffer layer and core thicknesses, that are more complex than the ones of the simple nonlinear metal slot. We show that these modes can exhibit spatial transitions towards specific modes of the new structure as a function of power. We also demonstrate that, for the main modes, the losses are reduced compared to the previous structures, and that they can now decrease with power. Finally, we describe the stability properties of the main stationary solutions using nonlinear FDTD simulations. Nonlinear plasmonic slot waveguides (NPSWs) have drawn attention in the last decade due to the strong light confinement in the nonlinear dielectric core ensured by the surrounding metal regions, and to their peculiar nonlinear effects [1–6]. Several applications have already been proposed for NPSWs [7, 8]. Nevertheless, the experimental observation of plasmon-soliton waves in these NPSWs is still lacking even if linear slot waveg-uides have already been fabricated [9]. Similarly to the case of the single nonlinear dielectric/metal interface structures [10, 11], the modes already studied in the simple NPSWs suffer from high losses that seriously limit the propagation length of the waves. In the present study, we propose and study an improved structure in which buffer linear dielectric layers are added between the nonlinear dielectric core and the two semi-infinite metal regions. The article is organized as follows. First, we describe the model and numerical method we use to study the stationary nonlinear waves in the improved NPSW we propose. Secondly, we describe the linear solutions of the new structures in order to classify the nonlinear solutions. Thirdly, we give the properties of the nonlinear stationary solutions and show that, for some linear parameter configurations, new modal spatial transitions as a function of power occur compared to the simple NPSW case. We provide full phase diagrams for the improved NPSW as a function of total power, buffer layer and core thicknesses. We also prove that the added buffer dielectric layers are able to reduce losses and allow them to decrease with power in most of the cases. Finally, using the FDTD method we study the stability properties of the main nonlinear solutions

Spatial nonlinearity in anisotropic metamaterial plasmonic slot waveguides

We study the main nonlinear solutions of plasmonic slot waveguides made from an anisotropic metamate-rial core with a positive Kerr-type nonlinearity surrounded by two semi-infinite metal regions. First, we demonstrate that for a highly anisotropic diagonal elliptical core, the bifurcation threshold of the asymmetric mode is reduced from GW/m threshold for the isotropic case to 50 MW/m one indicating a strong enhancement of the spatial nonlinear effects, and that the slope of the dispersion curve of the asymmetric mode stays positive, at least near the bifurcation, suggesting a stable mode. Second, we show that for the hyperbolic case there is no physically meaningful asymmetric mode, and that the sign of the effective nonlinearity can become negative

New Heterocyclic Syntheses from Pyridinethiones: an Efficient Route for the Syntheses of Some Novel Azo Derivatives of Thieno[2,3-b]pyridine as Potential Anti-bacterial and Anti-cancer Agents

Derivatives of a heterocyclic system 3-(pyrrol-1-yl)thieno[2,3-b]pyridine 5 and 6 carrying various substituents in the position 2 were synthesized. Some of these products were used to build up a variety of nitrogen- and/or oxygen-containing heterocyclic rings in that position. The electronic configurations of selected products were investigated using the AM1 semi-emperical molecular orbital method. Considerable variations in the magnitude and oriention of the dipole moment were observed. Further, the relative stability of the structures was investigated at physiological conditions via calculation of the electrostaticcomponent of the solvation free energy. The synthesized series showed favourable solvation free energies which were within the range from –30 to –23 kcal/mol.The high polarity and favourable solvation free energychanges at physiological conditions suggest that substitutionin the position 2 could enhance the biological activity of the 3-(pyrrol-1-yl)thieno[2,3-b]pyridine derivatives

Quercetin attenuates, indomethacin-induced acute gastric ulcer in rats

Background: Peptic ulcer diseases are common and are induced by many factors, including stress, smoking, and ingestion of non-steroidal anti-inflammatory drugs. Quercetin is considered to be an anti-oxidant with healing effects on many experimental toxic injuries. The present study aimed to explore the possible effect of quercetin on acute gastric ulcer induced by indomethacin in rats. Materials and methods: Three groups received indomethacin (30 mg/kg body weight) orally by orogastric gavage on two consecutive days. The rats received famotidine (50 mg/kg body weight), quercetin (50 mg/kg body weight), or vehicle alone for 15 consecutive days by oral gavage. The control group received no indomethacin but received vehicle for 15 days by oral gavage. The ulcer index, volume, and pH of gastric juice were measured, and the stomachs were examined by routine light microscopy. Results: Compared with the control group, the indomethacin-treated rats showed a marked damage of the gastric mucosal surface and a high ulcer index. In the famotidine- and quercetin-treated groups, significantly increased antioxidant enzyme activities were observed. The congestion, erosions, and necrosis were reduced with mild inflammatory cell infiltration while no major damage of endothelial cells was observed in the treated rats. Conclusions: The findings of the study show that quercetin had antioxidant effect and can protect gastric mucosa against indomethacin-induced gastric ulceration than famotidine.

Synthesis, Anticancer, Antioxidant, Anti-Inflammatory, Antimicrobial Activities, Molecular Docking, and DFT Studies of Sultams Derived from Saccharin

A series of N-substituted saccharins namely 2-(1,1-dioxido-3-oxobenzo[d]isothiazol-2(3H)-yl) acetonitrile (2) and (alkyl 1,1-dioxido-3-oxobenzo[d]isothiazol-2(3H)-yl) acetate (3a–g) were synthesized, in moderate to excellent yields, from commercially available starting materials by two different approaches and their chemical structures were characterized by spectroscopic techniques (1H-NMR, 13C-NMR, IR, and MS). All the synthesized compounds were evaluated for their anti-inflammatory toward IL-6 and TNF-α, antioxidant, as well as their anticancer activities against hepatic cancer cells. In addition, their anti-fungal and antibacterial activities against both Gram-positive and Gram-negative bacteria were tested. All the tested compounds have exhibited excellent (3a, d, e) to moderate anti-inflammatory activity. Additionally, esters (3b, f) and nitrile (2) showed excellent antioxidant activity. Furthermore, ester 3f, with isopropyl ester, exhibited the highest cytotoxic activity compared to the other esters. Moreover, all compounds were evaluated as selective inhibitors of the human COX-1 enzyme using molecular docking by calculating the free energy of binding, inhibition constant, and other parameters to find out the binding affinity. The molecular study showed that esters (3d, f) and nitrile (2) revealed the highest binding affinities, hence enhancing the inhibition activity with the active site of the COX-1 enzyme. All the tested compounds have more negative Gibbs free, electrostatic, and total intermolecular energies than the standard inhibitor ASA. These results indicate that, all the tested sultams are potent anti-inflammatory drugs as compared to standard inhibitors. Finally, the chemical properties and the quantum factors of synthesized sultams were calculated based on density functional theory (DFT) to predict reactivity, and then correlated with the experimental data. Ester 3f showed the lowest ionization potential and lowest energy gap (Egap = 7.5691 eV), which was correlated with its cytotoxic activity. Furthermore, the spatial electron distribution of HOMO, LUMO were computed and it clearly indicates the electron donation ability of all the tested compounds