Validating an endoperoxide as a key intermediate in the biosynthesis of elysiapyrones

Compounds 1-3 isolated from Elysia diomedea are described. Compound 1 is an endoperoxide derivative of elysiapyrone A. The biomimetic-type transformation of compound 1 to elysiapyrone A catalyzed by neutral base transformed the endoperoxide to a vicinal diepoxide, thus suggesting the endoperoxide as a key intermediate in the biosynthesis of elysiapyrone A. A biogenetic pathway for their formation involving a cycloaddition of singlet oxygen to a polypropionate alkenyl open chain is proposed.     

Cellular adhesion, proliferation and viability on conducting polymer substrates

This work reports a comprehensive study about cell adhesion and proliferation on the surface of different electroactive substrates formed by pi-conjugated polymers. Biological assays were performed considering four different cellular lines: two epithelial and two fibroblasts. On the other hand, the electroactivity of the three conducting systems was determined in physiological conditions. Results indicate that the three substrates behave as a cellular matrix, even though compatibility with cells is larger for PPy and the 3-layered system. Furthermore, the three polymeric systems are electro-compatible with the cellular monolayers.     

Geometric families of 4-dimensional Galois representations with generically large images

We study compatible families of four-dimensional Galois representations constructed in the étale cohomology of a smooth projective variety. We prove a theorem asserting that the images will be generically large if certain conditions are satisfied. We only consider representations with coefficients in an imaginary quadratic field. We apply our result to an example constructed by Jasper Scholten (A non-selfdual 4-dimensional Galois representation, , 1999), obtaining a family of linear groups and one of unitary groups as Galois groups over . Research partially supported by MEC grant MTM2006-04895.     

A colorful theorem on transversal lines to plane convex sets

We prove a colorful version of Hadwiger’s transversal line theorem: if a family of colored and numbered convex sets in the plane has the property that any three differently colored members have a transversal line that meet the sets consistently with the numbering, then there exists a color such that all the convex sets of that color have a transversal line. All authors are partially supported by CONACYT research grant 5040017.     

Synthesis, thermal, spectroscopic and magnetic studies of the Mn(SeO3).2H2O and Fe2(SeO3)3.3H2O selenites

Mn(SeO(3)).2H(2)O (1) and Fe(2)(SeO(3))(3).3H(2)O (2) have been synthesized by slow evaporation from an aqueous solution in the case of (1) and using mild hydrothermal conditions for (2). The crystal structures of both phases have been refined by the Rietveld method. The compounds crystallize in different spatial groups, the P2(1)/n monoclinic one with parameters a=6.649(1)A, b=6.542(1)A, c=10.890(1)A and beta=103.85(1) degrees being Z=4 for (1) and the R3c trigonal space group with parameters a=9.361(1)A, c=20.276(1)A and Z=6 for (2). The crystal structure of compound (1) consists of a three-dimensional framework formed by MnO(6) octahedra and (SeO(3))(2-) oxoanions with trigonal pyramidal geometry, which gives rise to Mn(2)O(10) dimers of edge-sharing octahedra. The crystal structure of phase (2) can be described as a three-dimensional framework formed by MnO(6) octahedra and (SeO(3))(2-) oxoanions with trigonal pyramidal geometry. In this phase the octahedral entities are linked along the three crystallographic axes through the selenite anions. Diffuse reflectance spectrum and luminescent measurements for (1) indicate the existence of Mn(2+) cations in a slightly distorted octahedral environment. Diffuse reflectance spectrum and M?ssbauer spectroscopy, in the paramagnetic region, for (2) show the existence of Fe(3+) cations in slightly distorted octahedral symmetry. ESR spectra of both compounds are isotropic with a g-value of 1.99(1) and 2.00(1), respectively. Magnetic measurements of both phases indicate an antiferromagnetic behavior. For phase (2), both, the ESR and magnetic measurements suggest a spin change from Fe(3+) (S=5/2) to Fe(2+) (S=2) at low temperatures.     

Solvent-free MALDI investigation of the cationization of linear polyethers with alkali metals

The MALDI technique with solvent-free sample preparation has been applied to evaluate relative gas-phase affinities of polyether chain polymers with alkali metal cations. The study is performed on poly(ethylene glycol) and poly(propylene glycol) polymers of different lengths (PEG600, PEG1000, PPG425, PPG750) and the alkali metal cations Li(+), Na(+), K(+), and Cs(+). The experiments show that the lattice energy of the alkali metal salts employed as cation precursors can have a strong influence on the outcome of conventional MALDI measurements. With the solvent-free method, these crystal binding effects can be made negligible by combining in the same sample alkali metal salts with different counterions. The recorded MALDI spectra show that the polyether-cation aggregation efficiencies decrease systematically with growing cation size. This cation size selectivity is considerably enhanced for the polymers with the shorter chains, which can be attributed to the reduced ability of the polymer to build a coordination shell around the larger cations. The steric effects introduced by the side CH3 group of propylene glycol with respect to ethylene glycol also enhance the preference for cationization of the polymer by the smaller cations. These observations correct some qualitative trends derived from previous studies, which did not account for lattice energy effects of the cation precursors.     

Covalent bond orders revisited: the open-shell case

This article states the concept of covalent bond order for open-shell systems from the invariance properties of the first- and second-order reduced density matrices for all the components of a multiplet state. A general bond order definition is formulated in the framework of the electronic population analyses in the Hilbert space of atomic orbitals.     

Synthesis of a fluorescent xanthenic derivative useful for labeling amine residues

The 2,5-dioxopyrrolidin-1-yl-4-(3-hydroxy-6-oxo-6H-xanthen-9-yl)-3-methylbenzoate has been synthesized as an amine-reactive derivative able to yield stable covalently labeled biopolymers. The new derivative has been used to label polyribocytidilic acid (5'), poly(C), amine residues. TG-II-poly(C) exhibits monoexponential decay at the physiological pH range. In addition, both steady-state fluorescence intensity and fluorescence decay are also sensitive to solution pH. The large decrease in steady-state fluorescence upon hybridization allows it to be used as a nucleic acid probe in a homogeneous assay format. In summary, we report an efficient synthesis to obtain labeled RNA from commercially available materials in excellent yields.     

On-line preconcentration and speciation analysis of inorganic vanadium in urine using l-methionine immobilised on controlled pore glass

A study was undertaken to ascertain the analytical capabilities of combined ICP-OES with ultrasonic nebulization to perform on-line preconcentration and speciation of inorganic V species in urine samples using a micro-column packed with l-methionine immobilized on controlled pore glass (CPG) as solid phase extractant. At pH 5.0, l-methionine is selective only towards V(V) while, total vanadium was quantitatively adsorbed by the solid phase at pH 9.0 [as V(V)] due to V(IV) oxidation in alkali media. Vanadium species retained by l-methionine were quantitatively eluted from the column with 10% HCl. Effects of acidity, sample flow rate, concentration of eluent and interfering ions on the recovery of the analytes have been systematically investigated. The detection limit (3sigma) of V is 0.008ngmL(-1) for USN-ICP-OES with an enhancement factor of 900 (10 for USN and 90 for l-methionine), and the relative standard deviation (R.S.D.) is better than 2%. The proposed method has been applied to the determination of inorganic V(V) and V(IV) in urine.     

Cloud point extraction for cobalt preconcentration with on-line phase separation in a knotted reactor followed by ETAAS determination in drinking waters

A novel method for cobalt preconcentration by cloud point extraction with on-line phase separation in a PTFE knotted reactor and further determination by electrothermal atomic absorption spectrometry (ETAAS) is proposed. The cloud point system was formed in the presence of non-ionic micelles of polyethyleneglycolmono-p-nonylphenylether (PONPE 7.5) and it was retained on the inner walls of a knotted reactor (KR). The surfactant rich-phase was removed from the knotted reactor with 75 microL of methanol acidified with 0.8 mol L(-1) nitric acid, directly into the dosing hole of the L'Vov graphite tube. An enrichment factor of 15 was obtained with a preconcentration time of 60 s, with respect to the direct determination of cobalt by ETAAS in aqueous solutions. The value of the detection limit for the preconcentration of 5 mL of sample solution was 10 ng L(-1). The precision, expressed as the relative standard deviation (R.S.D.), for 10 replicate determinations at 0.5 microg L(-1) Co level was 4.5%. Verification of the accuracy was carried out by analysis of a standard reference material (NIST SRM 1640e "Trace elements in natural water"). The method was successfully applied to the determination of cobalt in drinking water samples.