An anionic chromogenic sensor based on protonated Reichardt’s pyridiniophenolate

An anionic sensor based on Reichardt’s betaine is described here. The dye is blue-green in chloroform but becomes colorless under protonation. Increasing amounts of different anions were added into the solution of the protonated dye. The addition of F⁻ and caused the reappearance of the original blue-green color, while the addition of I⁻ made the solution of the protonated dye yellow. The observations are discussed based on the fact that F⁻ and can act as bases accepting a proton from the protonated dye and also in relation to the formation of a complex between the protonated dye and iodide.     

Irregular dynamics and homoclinic orbits to Hamiltonian saddle centers

We consider 4-dimensional, real, analytic Hamiltonian systems with a saddle center equilibrium (related to a pair of real and a pair of imaginary eigenvalues) and a homoclinic orbit to it. We find conditions for the existence of transversal homoclinic orbits to periodic orbits of long period in every energy level sufficiently close to the energy level of the saddle center equilibrium. We also consider one-parameter families of reversible, 4-dimensional Hamiltonian systems. We prove that the set of parameter values where the system has homoclinic orbits to a saddle center equilibrium has no isolated points. We also present similar results for systems with heteroclinic orbits to saddle center equilibria. © 1997 John Wiley & Sons, Inc.     

Influence of copper-phthalocyanine on the photodegradation of polycarbonate

Dyes and pigments are extensively used in polymer materials to confer colour-changing properties. However, these additives can significantly affect polymer stability against degradation. While the mechanism of stabilization of polymers by some pigments, such as carbon black, has been studied and is well known, the action of chromatic colorants, mainly in the sensitization of the degradation process, remains unclear. Cu-phthalocyanine dye can stabilize polymers against degradation as well as accelerate degradation in other situations. Cu-phthalocyanine incorporated into polycarbonate resulted in an acceleration of the degradation when the material was submitted to photochemical aging. The possible mechanism to explain the photodegradative behavior of PC containing Cu-phthalocyanine is based on the hypothesis that specific interactions among excited states of PC and Cu-phthalocyanine take place and enhance the formation of reactive species in polycarbonate. Excited states of Cu-phthalocyanine may abstract hydrogen atoms from methyl groups in polycarbonate, increasing the formation of free radicals P, which are the starting points for the sequential photo-oxidation reactions that lead to the degradation of the polycarbonate. Electron transfer sensitization is also a possible mechanism: the excited state of Cu-Ph abstracts an electron from PC to form the Cu-Ph radical anion and the PC radical cation. These reactive species in the presence of oxygen can cause oxidation of the aromatic ring.     

Solvent effects in the interaction of methyl-beta-cyclodextrin with solvatochromic merocyanine dyes

The UV-vis spectroscopic behavior of dyes: 2,6-diphenyl-4-(2,4,6-triphenylpyridinium-1-yl)phenolate (1) and 4-[(1-methyl-4(1H)-pyridinylidene)-ethylidene]-2,5-cyclohexadien-1-one (2) was investigated in solutions of methyl- beta-cyclodextrin (methyl-beta-CyD), using water, methanol, ethanol, propan-2-ol, butan-1-ol, acetone, acetonitrile, N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), N,N-dimethylacetamide (DMA), chloroform and dichloromethane as solvents. In aqueous solutions of dye (2) the addition of M-beta-CD leads to a bathochromic shift (of the maximum absorption), showing that the probe was transferred to a microenvironment of lower polarity and suggesting the formation of a 1 : 1 dye (2) : CyD inclusion complex, with a binding constant of 128.5 +/- 3.5 dm(3) mol(-1). Data for dye 2 in alcohols showed hypsochromic shifts, which increased in the following order: methanol < ethanol < propan-2-ol < butan-1-ol. These observations appear to reflect dye-solvent interactions through hydrogen bonding. If dye-solvent interactions are strong, the CyD-dye interactions are consequently weak, but the latter increase in importance when the dye-solvent interaction becomes weaker. With hydrogen-bond accepting solvents, data for both dyes showed clearly increasing hypsochromic shifts following the order: DMSO < DMA < DMF < acetone < acetonitrile. This order is exactly the inverse of the increasing order of basicity of the medium. This indicates that the dominant factor for the observed effects in these solvents is the solvent-CyD interaction through hydrogen bonding involving the hydroxyl groups of the CyD and the basic groups of the solvents. These interactions diminish in intensity if the basic character of the medium is reduced, increasing the capability of the dye to interact with the CyD using its phenoxide donor moiety. The largest hypsochromic shifts were obtained in chloroform (66.0 nm) and dichloromethane (67.5 nm) with dye after addition of methyl-beta-CyD. In these specific situations, solvents display weak basic and acid properties, that enhanced CyD-dye interactions to such an extent that association complexes formed through hydrogen bonding could be detected (K11) values of 24.8 +/- 4.9 dm3 mol(-1) in dichloromethane and 66.1 +/- 8.0 dm3 mol(-1) in chloroform).     

Chaos and integrability in a nonlinear wave equation

We consider the parametrized family of equations _tt ,u- _xx u-au+u ₂ ² u=O,x(0,L), with Dirichlet boundary conditions. This equation has finite-dimensional invariant manifolds of solutions. Studying the reduced equation to a four-dimensional manifold, we prove the existence of transversal homoclinic orbits to periodic solutions and of invariant sets with chaotic dynamics, provided that =2, 3, 4,.... For =1 we prove the existence of infinitely many first integrals pairwise in involution.     

Remarkable Nonlinear Properties of a Novel Quinolidone Derivative: Joint Synthesis and Molecular Modeling

A novel 4(1H) quinolinone derivative (QBCP) was synthesized and characterized with single crystal X-ray diffraction. Hirshfeld surfaces (HS) analyses were employed as a complementary tool to evaluate the crystal intermolecular interactions. The molecular global reactivity parameters of QBCP were studied using HOMO and LUMO energies. In addition, the molecular electrostatic potential (MEP) and the UV-Vis absorption and emission spectra were obtained and analyzed. The supermolecule (SM) approach was employed to build a bulk with 474,552 atoms to simulate the crystalline environment polarization effect on the asymmetric unit of the compound. The nonlinear optical properties were investigated using the density functional method (DFT/CAM-B3LYP) with the Pople’s 6-311++G(d,p) basis set. The quantum DFT results of the linear polarizability, the average second-order hyperpolarizability and the third-order nonlinear susceptibility values were computed and analyzed. The results showed that the organic compound (QBCP) has great potential for application as a third-order nonlinear optical material.     

Some hydroxylated derivatives of chlorpromazine

As part of a program to determine the metabolic fate of chlorpromazine [2-chloro-10-(3-dimethylaminopropyl)phenothiazine] (I), the synthesis of several hydroxylated derivatives of I was undertaken. This paper reports the preparation and structural verification of the 1- and 6-hydroxy and the desdimethyl 3-hydroxy derivative, and summarizes unsuccessful attempts to prepare the 4-hydroxy derivative of I.     

Application of field portable EDXRF spectrometry to analysis of pigments of Levantine rock art

The results of the analyses of elemental composition of red and black pigments of Levantine rock art from La Saltadora rock shelters (Valltorta gorge, Castellón, Spain) are presented in this paper. Nondestructive analyses were carried out using a portable energy dispersive X‐ray fluorescence (EDXRF) spectrometer developed for in situ analysis. The results revealed the strong presence of calcium in all the analyzed locations due to the contribution of the underlying calcareous bedrock and the overlying crust. Iron is the main element detected in red pigments and manganese in black pigments. Iron and calcium ratios have been found indicative of the degree of preservation of the pictorial layer. Trace elements detected in the pigment composition confirm the use of different raw materials. Therefore, this work illustrates the potential of the portable EDXRF spectrometers for in situ analysis of rock art paintings. Copyright © 2010 John Wiley & Sons, Ltd.     

On the Stability of Double Homoclinic Loops

We consider 2-degrees of freedom Hamiltonian systems with an involutive symmetry and a pair of orbits bi-asymptotic (homoclinic) to a saddle-center equilibrium (related to pairs of pure real, ±ν, and pure imaginary eigenvalues, ±ω i). We show that the stability of this double homoclinic loop is determined by the reflection coefficient of a one-dimensional scattering problem and ω/ν. We also show that the mechanism for losing stability is the creation of an infinite heteroclinic chain connecting a sequence of periodic orbits that accumulates at the double loop. Received: 10 November 1995 / Accepted: 5 June 1996