A note on the stationarity of a threshold first-order bilinear process

In the present note we study the threshold first-order bilinear model

X(t)=aX(t−1)+(b₁1_{X(t−1)<c}+b₂1_{X(t−1)c})X(t−1)e(t−1)+e(t), tεN

where {e(t), tεN} is a sequence of i.i.d. absolutely continuous random variables, X(0) is a given random variable and a, b₁, b₂ and c are real numbers. Under suitable conditions on the coefficients and lower semicontinuity of the densities of the noise sequence, we provide sufficient conditions for the existence of a stationary solution process to the present model and of its finite moments of order p.     

Synthesis of 3-azabicyclo[4.1.0]heptane-1-carboxylic acid

A full study on the synthesis of 3-azabicyclo[4.1.0]heptane-1-carboxylic acid is described. Three different approaches were investigated in order to achieve an efficient synthesis of this unnatural aminoacid. The optimized synthetic route relies upon three key steps: (i) diazomalonate insertion on 4-phtalimido 1-butene, (ii) intramolecular cyclization and (iii) chemoselective reduction of the resulting lactam. Due to its bicyclic nature and conformational constraints, this aminoacid may be an useful building block in medicinal chemistry.     

First synthesis of 2,6-diazabicyclo[3.2.0]heptane derivatives

The first synthesis of 6-phenyl-2,6-diazabicyclo[3.2.0]heptane 1 and its orthogonally protected precursor 2 is herein reported. Our strategy enables to chemically address the two nitrogen atoms of 2,6-diazabicyclo[3.2.0]heptane core individually and selectively, thus allowing rapid access to several subsets of widely substituted fused azetidines.     

Supramolecular Sensing of a Chemical Warfare Agents Simulant by Functionalized Carbon Nanoparticles

Real-time sensing of chemical warfare agents by optical sensors is today a crucial target to prevent terroristic attacks by chemical weapons. Here the synthesis, characterization and detection properties of a new sensor, based on covalently functionalized carbon nanoparticles, are reported. This nanosensor exploits noncovalent interactions, in particular hydrogen bonds, to detect DMMP, a simulant of nerve agents. The nanostructure of the sensor combined with the supramolecular sensing approach leads to high binding constant affinity, high selectivity and the possibility to reuse the sensor.     

Structural photodynamics of camptothecin, an anticancer drug in aqueous solutions

Steady-state and time-resolved picosecond emission studies were carried out to study the role of the proton concentration in the acid-base properties of the anticancer drug camptothecin (CPT) in its ground and electronically first excited states. The results show that, under acidic conditions, the excited-state proton-transfer (ESPT) reaction is irreversible, in contrast to previous literature data. We found that the prototropic species are equilibrated at the excited state (pK(a)* = 1.85) only in a restricted range of pH (1.5 < pH < 3), whereas only one species, either the neutral form (τ(N) = 3.76 ns) or the protonated form (τ(C) = 2.83 ns), can be detected at pH > 3 and pH < 1.5, respectively. The proton motion from the acidic solution to the neutral form in the pH 1-2 domain is diffusion-controlled. Within the range of pH 1-2, the reaction rate constant for the formation (k(d)) of the encounter complex between the proton and the neutral form ranges from 1.17 × 10(10) to 7.33 × 10(10) M(-1) s(-1), respectively. Under more acidic conditions (pH 0.9-0.95), the protonation of CPT does not depend on the diffusive step, because of the large amount of protons. The direct proton-transfer rate constant (k(DPT)*) increases with the proton concentration (time constants change from 24 ps to ～1 ns at pH 0.9 and 2, respectively). The number of protons involved in the proton transfer changes from approximately one, for the diffusive regime, to approximately four, for the static regime. We found good agreement between the Birks model for equilibrated flourophores and the Debye-Smoluchowski equation (DSE) to accurately explain the ESPT reaction of CPT with acidic water in the reversible range. The proton motion at pH 2 (equilibrium range) exhibits diffusion-controlled behavior and can be explained using the Smoluchowski model. Our results show that the interaction of CPT with acidic water depends on the concentration of the acid, which changes the nature of both the structure and dynamics.     

Bioinspired benzoxanthene lignans as a new class of antimycotic agents: synthesis and Candida spp. growth inhibition

Abstract

In this work we synthetized the bioinspired benzoxanthene lignans (BXLs) 3, 14–22, and the phenazine derivative 23 as potential antimycotic agents. MICs and MFCs against Candida strains were determined. In a preliminary screening, compounds 3, 15, 20, 21, 22 were substantially inactive. Compounds 14 and 17 showed antifungal activity, being able to inhibit the growth of the majority of Candida strains with MIC values in the range 4.6–19.2?µM (14) and 26.0–104.3?µM (17); for three strains, the MICs were lower than those obtained using the antimycotic drug fluconazole. The three BXLs 18, 19 and 23 showed some MIC values lower than that of fluconazole; 18 was also active against two non-albicans Candida strains resistant to fluconazole. Phenazine 23, although active only against one strain (MIC?=?1.3?µM), was one order of magnitude more potent than fluconazole. All the BXLs were fungicidal.     

Theory of exciton effects in the high-field magnetoabsorption of real semiconductors

Direct exciton states of cubic semiconductors in a high magnetic field are investigated taking into full account the degeneracy and anisotropy of the valence bands. The adiabatic method is used to decouple the components of the motion parallel and perpendicular to the magnetic field. One-dimensional Hamiltonians are obtained analytically for the various exciton states and selection rules for optical transitions are discussed. Accurate numerical values of the energy levels are given for H parallel to the (110) direction. The results obtained provide the first quantitative interpretation of the fine structure observed in high resolution measurements of magnetoabsorption in Ge.     

Effect of a dipolar self-assembly monolayer formation on indium-tin oxide on the performance of single-layer polymer-based light-emitting diodes

We report on the use of indium-tin oxide surface modification, by grafting of highly polar p-disubstituted benzenes, in the fabrication of light-emitting diodes. The polar compounds possess COCl or SO₂Cl grafting groups and CF₃ or NO₂ as highly electronegative groups, leading to the formation of a dipolar monolayer, which brings about an increase in ITO work function, thereby reducing the barrier for hole injection into luminescent polymers. We observe that the effect of this self-assembled monolayer, in terms of light-onset voltage, efficiency and luminance, is at least comparable to the use of a hole injection layer of doped poly[(3,4-ethylenedioxy)thiophene] for LEDs using poly({2-[(2-ethylhexyl)oxy]-5-methoxy-1,4-phenylene}vinylene) (MEH-PPV) and polyfluorene blends as active layers.     

Benzo[k,l]xanthene Lignan-Loaded Solid Lipid Nanoparticles for Topical Application: A Preliminary Study

Skin is the first human barrier that is daily exposed to a broad spectrum of physical and chemical agents, which can increase reactive oxygen species (ROS) and lead to the formation of topical disorders. Antioxidant molecules, such as benzo[k,l]xanthene lignans (BXL), are ideal candidates to eliminate or minimize the effects of ROS. Herein, we aimed to formulate BXL-loaded solid lipid nanoparticles (SLN-BXL) to improve the bioavailability and interaction with the skin, and also to investigate the protective impact against intracellular ROS generation in HFF-1 in comparison with the drug-free situation. SLN-BXL were formulated using the PIT/ultrasonication method, and then were subjected to physicochemical characterizations, i.e., average size, zeta potential (ZP), polydispersity index (PDI), encapsulation efficiency (%EE), thermotropic behavior, and interaction with a biomembrane model. The results show a mean size around 200 nm, PDI of 0.2, and zeta potential of about −28 mV, with values almost unchanged over a period of three months, while the EE% is ≈70%. Moreover, SLN-BXL are able to deeply interact with the biomembrane model, and to achieve a double-action release in mildly hydrophobic matrices; the results of the in vitro experiments confirm that SLN-BXL are cell-safe and capable of attenuating the IL-2-induced high ROS levels. In conclusion, based on our findings, the formulation can be proposed as a candidate for a preventive remedy against skin disorders induced by increased levels of ROS.