On the quiver-theoretical quantum Yang–Baxter equation

Quivers over a fixed base set form a monoidal category with tensor product given by pullback. The quantum Yang–Baxter equation, or more properly the braid equation, is investigated in this setting. A solution of the braid equation in this category is called a “solution” for short. Results of Etingof–Schedler–Soloviev, Lu–Yan–Zhu and Takeuchi on the set-theoretical quantum Yang–Baxter equation are generalized to the context of quivers, with groupoids playing the role of groups. The notion of “braided groupoid” is introduced. Braided groupoids are solutions and are characterized in terms of bijective 1-cocycles. The structure groupoid of a non-degenerate solution is defined; it is shown that it is a braided groupoid. The reduced structure groupoid of a non-degenerate solution is also defined. Non-degenerate solutions are classified in terms of representations of matched pairs of groupoids. By linearization we construct star-triangular face models and realize them as modules over quasitriangular quantum groupoids introduced in papers by M. Aguiar, S. Natale and the author.     

Central Limit Theorems for the Shrinking Target Problem

Suppose B _i :=B(p,r _i ) are nested balls of radius r _i about a point p in a dynamical system (T,X,μ). The question of whether T ⁱ x∈B _i infinitely often (i.o.) for μ a.e. x is often called the shrinking target problem. In many dynamical settings it has been shown that if $E_{n}:=\sum_{i=1}^{n} \mu(B_{i})$ diverges then there is a quantitative rate of entry and $\lim_{n\to\infty} \frac{1}{E_{n}} \sum_{j=1}^{n} 1_{B_{i}} (T^{i} x) \to1$ for μ a.e. x∈X. This is a self-norming type of strong law of large numbers. We establish self-norming central limit theorems (CLT) of the form $\lim_{ n\to\infty} \frac{1}{a_{n}} \sum_{i=1}^{n} [1_{B_{i}} (T^{i} x)-\mu(B_{i})] \to N(0,1)$ (in distribution) for a variety of hyperbolic and non-uniformly hyperbolic dynamical systems, the normalization constants are $a^{2}_{n} \sim E [\sum_{i=1}^{n} 1_{B_{i}} (T^{i} x)-\mu(B_{i})]^{2}$ . Dynamical systems to which our results apply include smooth expanding maps of the interval, Rychlik type maps, Gibbs-Markov maps, rational maps and, in higher dimensions, piecewise expanding maps. For such central limit theorems the main difficulty is to prove that the non-stationary variance has a limit in probability.     

Poly‐l‐Lactic Acid Nanofiber–Polyamidoamine Hydrogel Composites: Preparation,Properties, and Preliminary Evaluation as Scaffolds for Human Pluripotent Stem Cell Culturing

Electrospun poly‐l ‐lactic acid (PLLA) nanofiber mats carrying surface amine groups, previously introduced by nitrogen atmospheric pressure nonequilibrium plasma, are embedded into aqueous solutions of oligomeric acrylamide‐end capped AGMA1, a biocompatible polyamidoamine with arg‐gly‐asp (RGD)‐reminiscent repeating units. The resultant mixture is finally cured giving PLLA‐AGMA1 hydrogel composites that absorb large amounts of water and, in the swollen state, are translucent, soft, and pliable, yet as strong as the parent PLLA mat. They do not split apart from each other when swollen in water and remain highly flexible and resistant, since the hydrogel portion is covalently grafted onto the PLLA nanofibers via the addition reaction of the surface amine groups to a part of the terminal acrylic double bonds of AGMA1 oligomers. Preliminary tested as scaffolds, the composites prove capable of maintaining short‐term undifferentiated cultures of human pluripotent stem cells in feeder‐free conditions.

     

Tandem mass spectrometric study of 1,3,5-trinitrobenzene molecular ion: an unusual ortho effect involving a hydrogen atom from the aromatic ring

Unimolecular (metastable) and collision-induced dissociation of 1,3, 5-trinitrobenzene molecular ion was studied using linked scans and mass-analyzed ion kinetic energy spectrometry on a hybrid instrument of EBEqQ geometry. An unusual ortho effect leading to the loss of OH radical from the parent molecular ion is observed as a unimolecular dissociation process only in the first-field free region between the ion source and the electric sector, although corresponding dissociation in the ion source is of negligible abundance (<0.1%). This unimolecular process is taken over by other dissociation pathways when the parent ion is collisionally activated, suggesting that this dissociation process occurs only in a very narrow energy window with a rate constant of the order of 2 x 10(5) s(-1). Copyright 2000 John Wiley & Sons, Ltd.     

Electrochemistry and Spin-Crossover Behavior of Fluorinated Terpyridine-Based Co(II) and Fe(II) Complexes

Due to their ability to form stable molecular complexes that have tailor-made properties, terpyridine ligands are of great interest in chemistry and material science. In this regard, we prepared two terpyridine ligands with two different fluorinated phenyl rings on the backbone. The corresponding Co^II and Fe^II complexes were synthesized and characterized by single-crystal X-ray structural analysis, electrochemistry and temperature-dependent SQUID magnetometry. Single crystal X-ray diffraction analyses at 100 K of these complexes revealed Co−N and Fe−N bond lengths that are typical of low spin Co^II and Fe^II centers. The metal centers are coordinated in an octahedral fashion and the fluorinated phenyl rings on the backbone are twisted out of the plane of the terpyridine unit. The complexes were investigated with cyclic voltammetry and UV/Vis-NIR spectroelectrochemistry. All complexes show a reversible oxidation and several reduction processes. Temperature dependent SQUID magnetometry revealed a gradual thermal SCO behavior in two of the complexes, while EPR spectroscopy provided further insights on the electronic structure of the metal complexes, as well as site of reduction.     

Chirality in the Absence of Rigid Stereogenic Elements: The Absolute Configuration of Residual Enantiomers of C3‐Symmetric Propellers

Two new tris(aryl)phosphane oxides existing as configurationally stable residual enantiomers have been synthesised and their racemates resolved by semipreparative HPLC on a chiral stationary phase (CSP HPLC). One of them, recognised as a conglomerate, could be resolved by fractional crystallisation at a preparative scale level. In this case, the absolute configuration of the propeller‐shaped molecule was determined by anomalous X‐ray scattering. The problem of the correlative assignment of the absolute configuration to all known C₃‐symmetric three‐bladed propeller‐shaped molecules existing as stable residual enantiomers is discussed. The configurational stability of the new chiral phosphane oxides and of the corresponding phosphanes was evaluated by CD signal decay kinetics and dynamic ¹H NMR spectroscopy. The racemisation barriers in phosphanes were found about 10 kcal mol^?1 lower than those found for the corresponding oxides, though geometry and inter‐ring gearing would be very similar in the two series. Configurational stability of residual tris(aryl)phosphanes was found to be influenced by the electronic availability of the phosphorus centre, as evaluated by electrochemical CV experiments.     

“Surface-enhanced Raman spectroscopy studies of the passive layer formation in gold leaching from thiosulfate solutions in the presence of cupric ion”

Complementary electrochemical and spectroscopic techniques were used to characterize the behavior and composition of the passive layer formed at the gold surface in a thiosulfate electrolyte in the presence of cupric ions. Raman studies of three different cationic (calcium, ammonium, and sodium) thiosulfate leaching solutions revealed that the concentrations of thiosulfate, trithionate, sulfate, and tetrathionate remained constant in the bulk solution over a 3-h time period. The initial leaching current densities of these three systems were identical; however, significant differences in the open circuit potentials of these systems were observed. To provide additional information about the nature of the passive layer, gold nanorod array electrodes were fabricated and employed as substrates for studying the species present at the gold–thiosulfate interface using surface-enhanced Raman spectroscopy (SERS). The composition and behavior of the passive layer at the gold–thiosulfate interface greatly differed from those of the bulk solutions. The passive layer consisted primarily of elemental sulfur and sulfide-like species, with thiosulfate and its oxidation products, such as tri- and tetrathionates, as minority components. The nature of the cation (calcium, sodium, or ammonium) of the thiosulfate salt showed no significant effect on the composition of the passive layer at leaching times longer than 100 min. In addition, the presence of cupric ions also had no significant effect on the formation of the passive layer. However, copper is a much better oxidant than oxygen in gold–thiosulfate leaching reactions.     

Molecular structure of cyanidin metal complexes: Al(III) versus Mg(II)

Metal complexation by anthocyanins is a very efficient mechanism for protecting plants. While Mg is an essential metal for life, typically found bound to anthocyanins, Al interferes with the metabolism of the former. Density functional theory and the polarizable continuum model are used to study cyanin (the simplest anthocyanin bearing a catechol unit) complexes with Mg(II) and Al(III), considering different metal ligand stoichiometries. Results obtained for metal-binding energies indicate that Al(III) complexes are always more stable than those of Mg(II). Furthermore, reaction energies for the metal exchange process show that free Al(III) (hexaaquo complex) is always able to displace Mg(II). This displacement is more favored when the metal ligand ratio decreases. Thus, anthocyanins are implied in suppressing Al(III) toxicity by enabling its accumulation and reducing its migration to ecosystems. The characteristics of Al(III)?Ccyanidin and Mg(II)?Ccyanidin bonds are investigated using the quantum theory of atoms in molecules. We find these complexes are more stabilized by ion?Cdipole electrostatic interactions than by electron pair sharing, as predicted by the Hard and Soft Acids Theory. Globally, two factors increase the covalent character: replacement of Mg(II) by Al(III) and replacement of water by cyanidin ligands.     

A Zn(II) luminescent complex with a Schiff base ligand: solution,computational and solid state studies

Abstract

A new mononuclear complex of zinc(II), [Zn(HL)₂]?2DMF (H₂L = (E)-N′-((E)-(hydroxyimino)butan-2-ylidene)salicyloylhydrazide, DMF = N,N-dimethylformamide), was prepared and characterized. Single-crystal X-ray crystallography revealed a six-coordinate zinc(II) surrounded by nitrogen of the oxime function and oxygen and distal nitrogens of the acylhydrazone group. This entity also exists in solution as demonstrated by ¹H-NMR and potentiometric titrations. The computational analysis showed that the molecular orbitals involved in the main electronic transitions of the complex species in solution are centered on the ligand with negligible contribution of the metal ion. The photophysical properties of the complex were evaluated in solution and in the solid state. Luminescence studies showed that the solid has a strong emission at 550 nm with a large Stokes shift with respect to absorption. The solid state fluorescence emission is ascribed to ligand-centered and/or ligand-to-ligand charge transfer transitions, following the DFT results in solution. A comparison with a previously reported mononuclear [Zn(HL)₂] allowed the investigation of the influence of DMF molecules in the structural packing and the luminescence properties.     

Protective Properties of Novel S‐Acyl‐Glutathione Thioesters Against Ultraviolet‐induced Oxidative Stress

UV‐induced toxicity is characterized by marked oxidative stress, accompanied by the depletion of key cellular antioxidants, particularly glutathione (GSH). Replenishing cellular GSH may represent a means of counteracting UV‐induced toxicity: however, treatment with free GSH is not therapeutically effective due to its unfavorable pharmacokinetic properties. In this study, we show that S‐acyl‐glutathione (acyl‐SG) derivatives, which consist of an acyl chain (of variable length and saturation) linked via a thioester bond to GSH, increase intracellular levels of reduced GSH in primary skin fibroblasts, adenocarcinoma HeLa and neuroblastoma SH‐SY5Y cells. Consistent with this, acyl‐SG derivatives protect against UV‐induced reactive oxygen species (ROS) production and UV‐B/C‐mediated lipid peroxidation and caspase‐3 activation in the analyzed cell lines, with unsaturated thioesters displaying a significantly greater protective effect. Taken together, our findings suggest that acyl‐SG thioesters may be therapeutically effective in the treatment of UV‐related skin disorders and oxidative stress‐mediated conditions in general.