Microenvironment Effects on the Excited State Properties of Psoralens: a Clue to Their Photobiological Activity

Abstract— The singlet and triplet excited state parameters (φ_f, T_f and SpH_T) of psoralen (PSO) and derivatives 4,6,4'-trimeth-ylangelicin (TMA) and 4,5',8-trimethylpsoralen (TMP) show an extreme sensitivity to solvation in dioxane/water mixtures. These effects are attributed to the variation of the Si → S₀ internal conversion rate constant k_ic , which is the nonradiative deactivation path dominating their photophysical behavior. Depending on the compound, k_ic is very high, (∼1 times 10¹⁰ s^_1) in nonpolar solvents and then decreases to a low value (3 times 10⁸s⁻¹) with increasing solvent polarity. This work shows that dioxane/water mixtures display the same solvent-induced changes in the electronic structure of psoralens during solvation as those induced by the biological microenvironment sensed by the drug's localization. This mixture matches the photophysical parameters of psoralens observed in protic and aprotic pure solvents, in micelles, in liposomes and in human serum low-density lipoproteins (LDL). They can be used to probe the solvating ability of the interaction site in macrocyclic hosts. A particular localization site, i.e. the more (TMA and TMP) or less (PSO) lipophilic sites found when in interaction with LDL, determines the amount of the triplet reactive state of psoralens and the molecular mechanism available for photoreac-tion: oxic (type I and type II) or anoxic (type III) pathways.     

On counting theorems for self-avoiding walks

Certain differences are pointed out between two recently published counting theorems for self-avoiding walks on a lattice.     

Solutions of stochastic partial differential equations as extremals of convex functionals

Summary Stochastic evolution equations with monotone operators in Banach spaces are considered. The solutions are characterized as minimizers of certain convex functionals. The method of monotonicity is interpreted as a method of constructing minimizers to these functionals, and in this way solutions are constructed via Euler-Galerkin approximations.     

Fragmentation D'azoles Sous L'impact Electronique. V—Isomerisation Du Benzimidazole Avant Degradation

The mass spectrum of benzimidazole is investigated using deuterium and carbon-13 labelling. The [M – HCN]⁺· ion is the result of two competitive reaction. Isomerisation into a cyanoaniline structure which eliminates HCN from the amino group and also from the nitrile group (by an ortho effect) is confirmed by ions abundance ratios. Hydrogen scrambling does not occur to a significant extent in the ions under consideration.     

Alkynes as Linchpins for the Additive Annulation of Biphenyls: Convergent Construction of Functionalized Fused Helicenes

A new approach to fused helicenes is reported, where varied substituents are readily incorporated in the extended aromatic frame. From the alkynyl precursor, the final helical compounds are obtained under mild conditions in a two‐step process, in which the final C?C bond is formed via a photochemical cyclization/ dehydroiodination sequence. The distortion of the π‐system from planarity leads to unusual packing in the solid state. Computational analysis reveals that substituent incorporation perturbs geometries and electronic structures of these nonplanar aromatics.     

Enhancing the Photocatalytic Activity of Sr4Al14O25: Eu2+, Dy3+ Persistent Phosphors by Codoping with Bi3+ Ions

The photocatalytic activity of Bismuth‐codoped Sr₄Al₁₄O₂₅: Eu²⁺, Dy³⁺ persistent phosphors is studied by monitoring the degradation of the blue methylene dye UV light irradiation. Powder phosphors are obtained by a combustion synthesis method and a postannealing process in reductive atmosphere. The XRD patterns show a single orthorhombic phase Sr₄Al₁₄O₂₅: Eu²⁺, Dy³⁺, Bi³⁺ phosphors even at high Bismuth dopant concentrations of 12 mol%, suggesting that Bi ions are well incorporated into the host lattice. SEM micrographs show irregular micrograins with sizes in the range of 0.5–20 μm. The samples present an intense greenish‐blue fluorescence and persistent emissions at 495 nm, attributed to the 5d–4f allowed transitions of Eu²⁺. The fluorescence decreases as Bi concentration increases; that suggest bismuth‐induced traps formation that in turn quench the luminescence. The photocatalytic evaluation of the powders was studied under both 365 nm UV and solar irradiations. Sample with 12 mol% of Bi presented the best MB degradation activity; 310 min of solar irradiation allow 100% MB degradation, whereas only 62.49% MB degradation is achieved under UV irradiation. Our results suggest that codoping the persistent phosphors with Bi³⁺ can be an alternative to enhance their photocatalytic activity.     

A leader-followers model of power transmission capacity expansion in a market driven environment

We introduce a model for analyzing the upgrade of the national transmission grid that explicitly accounts for responses given by the power producers in terms of generation unit expansion. The problem is modeled as a bilevel program with a mixed integer structure in both upper and lower level. The upper level is defined by the transmission company problem which has to decide on how to upgrade the network. The lower level models the reactions of both power producers, who take a decision on new facilities and power output, and Market Operator, which strikes a new balance between demand and supply, providing new Locational Marginal Prices. We illustrate our methodology by means of an example based on the Garver’s 6-bus Network.     

Nano‐in‐Micro POxylated Polyurea Dendrimers and Chitosan Dry Powder Formulations for Pulmonary Delivery

Pulmonary administration offers excellent advantages over conventional drug delivery routes, including increasing therapeutics bioavailability, and avoiding long‐term safety issues. Formulations of nano‐in‐micro dry powders for lung delivery are engineered using (S)‐ibuprofen as a model drug. These biodegradable formulations comprise nanoparticles of drug‐loaded POxylated polyurea dendrimers coated with chitosan using supercritical‐fluid‐assisted spray drying. The formulations are characterized in terms of morphology, particle‐size distribution, in vitro aerodynamic particle pulmonary distribution, and glutathione‐S‐transferase assay. It is demonstrated that ibuprofen‐loaded nanoparticles can be successfully incorporated into microspheres with adequate aerodynamic properties, mass median aerodynamic diameter (1.86–3.83 μm), and fine particle fraction (28%–45%), for deposition into the deep lung. The (S)‐ibuprofen dry powder formulations show enhanced solubility, high swelling behavior and a sustained drug release at physiologic pH. Also, POxylated polyureas decrease the (S)‐ibuprofen toxic effect on cancer cellular growth. The 3‐(4,5‐dimethylthiazol‐2‐yl)‐5‐(3‐carboxymethoxyphenyl)‐2‐(4‐sulfophenyl)‐2H‐tetrazolium (MTS) assays show no significant cytotoxicity on the metabolic activity of human lung adenocarcinoma ephithelial (A549) cell line for the lowest concentration (1 × 10^?3 m ), even for longer periods of contact with the cells (up to 120 h), and in the normal human dermal fibroblasts cell line the toxic effect is also reduced.     

Sorbic Acid as an Alkylating Agent

A kinetic study of the alkylating potential of the sorbic acid + NaOH and sorbic acid + KOH systems was performed in 7:3 (volume/volume) water + dioxane solvent mixtures. The following conclusions were drawn. First, the sorbic acid + sorbate system shows alkylating activity on the nucleophile 4-(p-nitrobenzyl)pyridine (NBP), which is used as a trap for alkylating agents having nucleophilic characteristics similar to DNA bases. Second, the maximum alkylating capacity is observed in the pH = 5.0 to 6.5 range. Third, the alkylation reactions comply with the rate equation r=k _alk[H⁺][S][NBP]/(K _a +[H⁺]), with K _a being the dissociation constant of sorbic acid. Fourth, an enthalpy–entropy (ΔH ^#/ΔS ^#) compensation effect for activation quantities is observed by comparing NBP alkylation reactions due to sorbic acid + NaOH, sorbic acid + KOH, as well as potassium sorbate + HCl mixtures. Fifth, the results may help to establish suitable expiration times for products preserved with sorbic acid.