Alkali and alkaline-earth-metalated forms of calix[4]arenes: synthons in the synthesis of transition metal complexes

This is the first coherent report on the metalation of calix[4]arene by alkali and alkaline-earth metals, thus providing a high-yield production of appropriate synthons for the synthesis of transition metal calix[4]arenes. In addition, various facets of the coordination chemistry by calix[4]arene anions of alkali and alkaline-earth metal ions have been singled out. Among them: 1) the exo and endo coordination of metal ions by the calix[4]arene skeleton; 2) the pi solvation of the ions by the phenyl rings; 3) the ion-carrier properties of metallacalix[4]arenes; 4) the simulation of the kinetically labile coordination sphere of alkali and alkaline-earth metal ions by a polyoxo rigid skeleton. The peculiarities of the complexation of alkali and alkaline-earth metal ions by calix[4]arenes outlined are deduced from the synthesis and the structural characterization both in solution ((1)H NMR) and in the solid state (X-ray structure analysis) of the following classes of compounds: 1) [p-tBu-calix[4](OMS(n))(4)](2) (M=Li, Na, K); 2) [p-tBu-calix[4](OR)(2)(O)(2)ML] (M=Mg, L=THF, R=C(5)H(9); M=Ca, L=TMEDA (tetramethylethylenediamine), R=C(5)H(9); M=Ca, L=DME (dimethoxyethane), R=C(5)H(9); M=Ba, L=TMEDA, R=C(5)H(9); M=Ba, L=none, R=C(5)H(9)); 3) [p-tBu-calix[4](OC(5)H(9))(2)(O)(2)Ca(2)I(2)(MeCN)(2)]; 4) [(p-tBu-calix[4](OR)(2)(O)(2))(2)BaNa(2)].     

Chiral capillary electrophoresis-mass spectrometry of amino acids in foods

In this work, the development of a new chiral capillary electrophoresis-mass spectrometry (CE-MS) method to separate D- and L-amino acids is shown. On-line coupling between CE and MS is established through an electrospray-coaxial sheath flow interface. Enantiomer separation is achieved by using a cheap, nonvolatile, chiral selector as beta-cyclodextrin in the background electrolyte (BGE) together with a physically coated capillary that is aimed to prevent contamination of the electrospray. The capillary coating is simple and easy to obtain as it only requires flushing of the capillary with a polymer aqueous solution for 3 min. Optimization of CE parameters (pH of BGE, type and concentration of chiral selector, and capillary inner diameter) and electrospray-MS parameters (nature and flow rate of the sheath liquid, nebulizer pressure) is carried out. Two different derivatization protocols of amino acids using dansyl chloride (DNS) and fluorescein isothiocyanate (FITC) are compared in terms of MS sensitivity and chiral resolution. Under optimum CE-MS conditions it is observed that the MS sensitivity obtained for FITC- and DNS-amino acids is similar (with limit of detection (LOD) in the microM range, corresponding to amounts injected in the fmol range) while chiral resolution is better for FITC-amino acids. The optimized method is demonstrated to provide the simultaneous analysis of 15 selected amino acids (i.e., FITC-D/L-Asp, -Glu, -Ser, -Asn, -Ala, -Pro, -Arg, and FITC-gamma-aminobutyric acid (GABA) in a single chiral CE-MS run, corresponding to the main amino acids that can be found in orange. Moreover, as a result of the high resolution achieved, it is possible to detect down to 2% of D-Asp in the presence of 98% of L-Asp. The good possibilities of chiral CE-MS in food analysis are corroborated through the detection of the main amino acids in a commercial orange juice (i.e., FITC-L-Asp, -Glu, -Ser, -Asn, -Pro, -Arg, and the nonchiral FITC-GABA) as well as the determination of the fraudulent addition of synthetic amino acids (containing D- and L-forms) to a fresh orange juice.     

Adsorption of triallylamine on Si(111) and its coadsorption with triethylgallium – A combined HREELS and XPS study

The adsorption of triallylamine [(C₃H₅)₃N; TAA] on Si(111)-(7 × 7) under UHV conditions was studied by means of surface sensitive electron spectroscopy. The High-Resolution Electron Energy Loss Spectroscopy (HREELS) yields the spectrum of vibration modes of the adsorbed species. X-ray Photoelectron Spectroscopy (XPS) gives insight into the chemical environment and the relative concentrations in the near surface region. The tertiary amine TAA physisorbes at room temperature without dissociation. Successive annealing steps induce the dissociation of the physisorbed phase at temperatures above 400°C. Further annealing leads to partial desorption of the allyl groups from the surface. At temperatures above 600°C the remaining allyl groups are fully dissociated. Hydrogen leaves the surface and nitrogen and carbon start to diffuse into the substrate. The surface chemistry of triallylamine adsorbed on a heated substrate behaves in a very similar way. The coadsorption of TAA with triethylgallium [(C₂H₅)₃Ga; TEG] in the temperature range between 500 and 800°C induces no significant change of the surface reactions. Only a small amount of gallium could be detected at the surface. The nucleation of GaN has not been observed, neither on Si(111) nor on Al₂O₃(0001) substrates.     

Tetra-2,3-pyrazinoporphyrazines with externally appended pyridine rings. 1. Tetrakis-2,3-[5,6-di(2-pyridyl)pyrazino]porphyrazine: a new macrocycle with remarkable electron-deficient properties

A new pyrazinoporphyrazine macrocycle carrying externally appended pyridine rings, tetrakis-2,3-[5,6-di(2-pyridyl)pyrazino]porphyrazine (hydrated), [Py(8)TPyzPzH(2)].2H(2)O, was prepared in high yield by direct cyclotetramerization of the precursor, 2,3-dicyano-5,6-di(2-pyridyl)-1,4-pyrazine, [(CN)(2)Py(2)Pyz], in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). The single-crystal X-ray structure of [(CN)(2)Py(2)Pyz] shows a noncoplanar positioning of the pyrazine and pyridine rings in the two slightly different independent molecular units present in the crystal. UV-vis spectra of [Py(8)TPyzPzH(2)] were measured in two nondonor solvents (CHCl(3), CH(2)Cl(2)), a slightly basic solvent (pyridine), and an acidic solvent (CH(3)COOH). In all cases, the spectral changes are consistent with the occurrence of molecular aggregation and colloidal dispersions which break up with time to give clear solutions containing exclusively the monomeric form of the macrocycle, either neutral [Py(8)TPyzPzH(2)] (in CHCl(3), CH(2)Cl(2), and CH(3)COOH) or dianionic [Py(8)TPyzPz](2)(-) (in pyridine). A spectrally monitored titration of [Py(8)TPyzPzH(2)] in CH(2)Cl(2) with TBA(OH) shows the loss of two protons from the macrocyclic core and quantitative conversion of [Py(8)TPyzPzH(2)] to [Py(8)TPyzPz](2)(-). Cyclic voltammetry and thin-layer spectroelectrochemical measurements show that [Py(8)TPyzPzH(2)] is present in CH(2)Cl(2) while [Py(8)TPyzPz](2)(-) is present in pyridine, but both forms of the compound exhibit identical electrochemical behavior, consistent with a conversion of the dianion to the neutral porphyrazine in pyridine prior to electroreduction via four reversible one-electron transfer steps. No oxidations of the macrocycle are observed in either solvent containing 0.1 M tetrabuthylammonium perchlorate (TBAP). A comparison of the electrochemical behavior for [Py(8)TPyzPzH(2)] with what is reported for related phthalocyanine and porphyrazine analogues highlights the remarkable electron-accepting properties of the presently investigated free-base macrocycle.     

Linear Sections of the Finite Veronese Varieties and Authentication Systems Defined Using Geometry

In this paper we deal with authentication systems in which one key is used to authenticate many source states. We answer a related question on the cardinalities of the intersections of quadrics in PG (d,q). We first generalize a class of geometric authentication systems, which has been introduced by Beutelspacher, Tallini and Zanella4. The source states are the lines through a special point N of PG (d,q) (the d-dimensional projective space over GF (q)). The keys are some hypersurfaces which have N as a nucleus ( N is a nucleus of if every line through N meets in exactly one point). The message belonging to a source state and a key is the unique point of intersection of the line with the hypersurface . We give the values of s for which the constructed authentication systems have a security which is comparable to the best allowed by a theoretical bound. In case the hypersurfaces are quadrics, we give further results on the security. To this end, we determine the greatest cardinality for the intersections of the finite Veronese varieties with the projective subspaces of any given dimension. Finally, we discuss a possible implementation.     

Self-interaction of a point charge in a Kerr spacetime

As is known, the expression of the electromagnetic field from a charge at rest on the symmetry axis of a Kerr spacetime, first given as a multi-polar expansion, has been later calculated in closed form. This allowed the derivation, in closed form, of the electromagnetic 4-potential and, consequently, the electrostatic self-interaction force (self-force) on the charge. We point out that, in order to derive the electromagnetic 4-potential and, consequently, the electrostatic self-force, a particular reference frame is required, in which the Kerr metric locally (i.e., in a small neighbourhood of the charge world-line) reduces to that of a static homogeneous gravitational field (SHGF). The starting point of this paper is the realization that the choice of such a reference frame in the literature is incorrect, because the phenomenon of dragging of inertial frames is neglected. This demands a new derivation both of the electromagnetic 4-potential and of the electrostatic self-force. To this end, we construct the correct reference frame, locally transforming the Kerr metric into that of an SHGF. In such a frame, we derive the correct expressions both of the electromagnetic 4-potential and of the electrostatic self-force. In particular: i) the time component of the 4-potential differs from that known in the literature by an additional term, induced by the dragging of inertial frames, vanishing only on the symmetry axis; ii) the self-force turns out to be the sum of two terms, of which only the first (involving both the mass and the angular momentum per unit mass of the Kerr spacetime) is known in the literature. The second term (involving only the angular momentum per unit mass), which arises from a careful calculation and not from the additional term in the 4-potential, is a significant improvement provided by this paper.     

Crystal structure of a seven-coordinate cobalt(II) complex with a new polyfunctional hydrazonic ligand, [Co(H4dapis)(OH2)2]Cl2·9/2H2O

A seven-coordinate cobalt(II) complex has been synthesized with a new hydrazonic ligand, H₄dapis, and its crystal structure determined by X-ray diffraction methods and refined toR 0.0564 for 2763 independent reflections. The structure consists of [Co(H₄dapis)(OH₂)2] cations, Cl anions, and lattice H₂O molecules interlinked by hydrogen bonds. The cobalt atom has a distorted pentagonal bipyramidal environment with two axial H₂O molecules and the H₄dapis ligand forming the basal plane.     

Adsorption of d-alaninol on Cu(1 0 0)

Adsorption of d-alaninol on Cu(1 0 0) at room temperature has been investigated by photoelectron spectroscopy in the soft X-ray and VUV energy range and low energy electron diffraction (LEED). d-Alaninol was found by LEED to self-assemble at full coverage; core and valence photoemission spectra are presented at low and full coverage. Chemisorption occurs at room temperature. The bonding at low coverage takes place at the hydroxylic group; at full coverage there is evidence of bonding for both hydroxylic and amino groups.     

Towards integrated devices for computer screen photo-assisted multi-parameter sensing

The computer screen photo-assisted technique (CSPT) utilizes consumer electronic devices such as computer screens and web cameras for distributed chemical sensing. Key to this method is the development of small and disposable sensing assays able to aid the CSPT optical detection, and the evaluation of multiple indicators. Here we demonstrate CSPT identification of fluorescent indicators from individual 100 μm SU-8 (10) pillars covering an area of 4 mm × 4 mm with a density of 47 elements mm⁻². The extraction of distinctive spectral fingerprints is aided by the exploitation of a three-band Moiré interference that enables the partial Bayer decoding of the CSPT images.     

Sur les invariants simultanés de deux formes quadratiques

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