Photochemical- and pH-switching Properties of a New Photoelastic Ligand Based Upon Azobenzene. Basicity and Anion Binding

Abstract

The synthesis of a new cylindrical macrotricyclic ligand (L) based upon two 1,4,7,13-tetramethyl-1,4,7,10,13,16-hexaazacyclooctadecane rings connected via two azobenzene pillars is described. The ligands displays photoelastic properties: light absorption at 366 nm produces trans→cis isomerization of the azobenzene moieties with formation of trans-cis (L _E-Z ) and cis-cis (L _Z-Z ) isomers. Recovery of the thermodynamically more stable trans-trans (L _E-E ) isomer can be obtained by thermal back-isomerization or visible light (430 nm) absorption. The isomeric composition of L solution depends upon pH: for pH < 5.5 the L _E-E form is the unique species in solution, while increasing amounts of Z species are formed at increasing pH. The protonation constants of L _E-E have been determined in 0.1 mol dm^?3 Me₄NNO₃ solution at 298.1 ± 0.1 K. The protonated species of L form stable inclusion complexes with anionic species such as [Co(CN)₆]^3?.     

Design and synthesis of fluorescent galactolipid probes

Fluorescent galactolipid analogues (1, 1a, and 2) have been synthesized with a pyrene group attached to the amino-terminal of a hexanoyl chain bound to an otherwise normal galactolipid structure. The synthetic lipids are obtained from peracetyl galactose by a general and versatile procedure based on the trichloroacetimidate methodology. The intense violet fluorescence (376 and 395 nm) and good photostability of pyrene make these compounds highly suitable as probes to study galactolipid metabolism. As proof of concept, we report that compound 2 is a valid tool to detect galactolipase activity in enzymatic preparations of potato tubers.     

Polarization correlations in the two�Cphoton decay of hydrogen�Clike ions

Polarization properties of the photons emitted in the two?Cphoton decay of hydrogen?Clike ions are studied within the framework of the density matrix and second-order perturbation theory. In particular, we derive the polarization correlation function that gives the probability of the (two?Cphoton) coincidence measurement performed by polarization?Csensitive detectors. Detailed calculations of this function are performed for the 2s _1/2 ??1s _1/2 transition in neutral hydrogen as well as Xe^53?+? and U^91?+? ions. The obtained results allow us to understand the influence of relativistic and non?Cdipole effects on the polarization correlations in the bound?Cbound two?Cphoton transitions in heavy ions.     

Comparing comparisons between vehicular traffic states in microscopic and macroscopic first‐order models

In this paper, we deal with the analysis of the solutions of traffic flow models at multiple scales in both cases of a single road and road networks. We are especially interested in measuring the distance between traffic states (as they result from the mathematical modeling) and investigating whether these distances are somehow preserved passing from the microscopic to the macroscopic scale. By means of both theoretical and numerical investigations, we show that, on a single road, the notion of Wasserstein distance fully catches the human perception of distance independently of the scale, while in the case of networks it partially loses its nice properties.     

MAD: practical implementation of MCAO concepts

The European Southern Observatory (ESO) together with external research institutes have built a Multi-Conjugate Adaptive Optics (MCAO) Demonstrator (MAD) to perform wide field-of-view adaptive optics correction (2′ in K band). The aim of MAD is to demonstrate the on-sky feasibility of the MCAO technique and to evaluate its critical aspects in the framework of both the 2nd generation instrumentation for the Very Large Telescope (VLT) and the Overwhelmingly Large Telescope (OWL). The MAD module will be installed on the VLT to perform on-sky observations. MAD comprises two deformable mirrors and two different multi-reference wavefront sensors with natural guide stars. In this article we present the MAD design, some aspects of the MAD calibration and the first closed-loop results in the laboratory in Single Conjugated Adaptive Optics (SCAO) and Ground Layer Adaptive Optics (GLAO) configurations. To cite this article: E. Marchetti et al., C. R. Physique 6 (2005).     

Two molecular assays for the rapid and inexpensive detection of GJB2 and GJB6 mutations

The hypoacusia can be classified in two clinical forms: Syndromic (SHL) and Nonsyndromic (NSHL). In particular, the NSHL describes the 70–80% of hypoacusia cases and it is mainly due to genetic factors, which are causative of the deafness at the birth. The genetic hypoacusia presents different inheritance patterns: autosomal dominant (20%), autosomal recessive (80%), X‐linked (1%), and mitochondrial (1%), respectively. To date, about 35 deafness‐causative genes have been identified and most of them codify for connexin transmembrane proteins. Approximately 1:2500 children with NSHL carries mutations in the GJB2 and GJB6 (13q12) genes, which code for connexin 26 (Cx26) and connexin 30 (Cx30), respectively. In the Caucasian population, the most common mutations are 35delG, M34T and 167delT, and D13S1830. Given the frequency distribution of the four mutations in the Caucasian population and the pathogenic connection with NSHL, the development of accurate, rapid, and “low‐cost” molecular assays should be strongly encouraged. To this purpose, we set up two different molecular assays (namely the Cx26 and Cx26‐30 molecular assays) for the fast and inexpensive detection of 35delG, M34T, 167delT, and D13S1830 mutations. Both the molecular approaches showed to be accurate, sensitive, reproducible, and “low‐cost” alternatives for the proper evaluation of the GJB2 and GJB6 genes, which are causative of NSHL. In conclusion, the Cx26 and Cx26‐30 molecular assays can be applied to individual, preconception, prenatal, or postnatal screening for the causative‐mutations of NSHL.     

Oil-in-water nanocontainers as low environmental impact cleaning tools for works of art: two case studies

A novel class of p-xylene-in-water microemulsions mainly based on nonionic surfactants and their application as low impact cleaning tool in cultural heritage conservation is presented. Alkyl polyglycosides (APG) and Triton X-100 surfactants allow obtaining very effective low impact oil-in-water (o/w) microemulsions as alternatives to pure organic solvents for the removal of polymers (particularly Paraloid B72 and Primal AC33) applied during previous conservation treatments. The ternary APG/p-xylene/water microemulsions have been characterized by quasi elastic light scattering to obtain the hydrodynamic radius and the polydispersity of the microemulsion droplets. Laplace inversion of the correlation function CONTIN analysis provided evidence of acrylic copolymers solubilization into the oil nanodroplets. Contact angle, Fourier transform infrared (FTIR), and scanning electron microscopy/energy-dispersive spectroscopy (SEM/EDS) data confirmed that microemulsions were effective in removing polymer coatings. The phase diagram of APG microemulsions showed that a reduction >90% (compared to the conventional cleaning methods) of the organic solvent can be achieved by using o/w microemulsions. The microemulsions were successfully tested in two real cases: (1) the APG based microemulsion was used in a Renaissance painting by Vecchietta in Santa Maria della Scala, Siena, Italy, degraded by the presence of a polyacrylate coating applied during a previous restoration and (2) a Triton X-100 oil-in-water microemulsion containing (NH4)2CO3 in the water continuous phase. The association of ammoniun carbonate to the microemusion led to the swelling of an organic deposit (mainly asphaltenes deposited on the fresco in the Oratorio di San Nicola al Ceppo in Florence, still contamined by the water of the Arno river during the 1966 flood) and a very efficient removal of highly insoluble inorganic deposits (mainly gypsum) strongly associated to asphaltenes. These innovative systems are very attractive for the low amount of organic solvent used to extract the polymers or highly insoluble substances as the asphaltene and the very efficient and mild impact of the cleaning procedure on the fragile painted surfaces.     

An improved flow analysis-ion chromatography method for determination of cationic and anionic species at trace levels in Antarctic ice cores

A method was developed for the quantitative determination of cations and anions in Antarctic ice cores at μg L⁻¹ and sub-μg L⁻¹ levels by ion chromatography (IC), after ultra-clean decontamination procedures. Strict manipulation and decontamination procedures were used in sub-sampling, in order to minimise sample contamination. Na⁺, NH₄⁺, K⁺, Mg²⁺ and Ca²⁺ were determined by 12-min isocratic elution (H₂SO₄ eluent). Contemporaneously, in a parallel device, F⁻, MSA (methanesulfonic acid), Cl⁻, NO₃⁻ and SO₄²⁻ were analysed in a single 12-min run with multiple-step elution using Na₂CO₃/NaHCO₃ as eluent. Melted ice samples were pumped from their still-closed containers (polystyrene accuvettes with polyethylene caps), shared between the two ion chromatographic systems, online filtered (0.45 μm Teflon membrane) and pre-concentrated (anions and cations pre-concentration columns) using a flow analysis system, thus avoiding uptake of contaminants from the laboratory atmosphere. Sensitivity, linear range, reproducibility and detection limit were evaluated for each chemical species. Anion or cation detection limits ranged from 0.01 to 0.15 μg L⁻¹ by using a relatively small sample volume (1.5 mL). Such values are significantly lower than those reported in literature for almost all the components. These methods were successfully applied to the analysis of cations and anions at trace levels in the Dome C ice core. The composition of the atmospheric aerosol for the last 850 kyr was reconstructed by high-resolution continuous chemical stratigraphies. Concentration trends in the last nine glacial-interglacial climatic cycles were shown and briefly discussed.     

Role of the solvent in the dynamical transitions of proteins: the case of the lysozyme-water system

We study the dynamics of hydration water in the protein lysozyme in the temperature range 180 K相似文献