Chemiluminometric determination of carvedilol in a multi-pumping flow system

In this work a simple, fast, sensitive and selective flow-based procedure for the chemiluminometric determination of carvedilol, a recent non-cardioselective β-blocker with noteworthy antioxidant activity, is proposed. The developed methodology takes advantage of the antioxidant capacity of carvedilol to inhibit the chemiluminescence response resulting from the oxidation of luminol by hypochlorite, by acting as a hypochlorite scavenger. The analytical process was implemented in a multi-pumping flow system that employs multiple solenoid actuated micro-pumps as the only active components. These acted as solution insertion, propelling and commuting units assuring an easily controlled, low cost, compact and reliable analytical system.A linear working range for carvedilol concentrations ranging from 1.2 × 10⁻⁷ to 3.0 × 10⁻⁶ mol l⁻¹ (r > 0.999, n = 6), was obtained, with a detection limit of 8.7 × 10⁻⁹ mol l⁻¹. The system handles about 65 samples per hour yielding precise results (R.S.D. < 1.3%, n = 10). Recoveries within 95 and 104% were obtained.     

Ferromagnetism and chirality in two-dimensional cyanide-bridged bimetallic compounds

The combination of hexacyanoferrate(III) anions, [Fe(CN)(6)](3)(-), with nickel(II) complexes derived from the chiral ligand trans-cyclohexane-1,2-diamine (trans-chxn) affords the enantiopure layered compounds [Ni(trans-(1S,2S)-chxn)(2)](3)[Fe(CN)(6)](2).2H(2)O (1) and [Ni(trans-(1R,2R)-chxn)(2)](3)[Fe(CN)(6)](2).2H(2)O (2). These chiral systems behave as ferromagnets (T(c) = 13.8 K) with a relatively high coercive field (H(c) = 0.17 T) at 2 K. They also exhibit an unusual magnetic behavior at low temperatures that has been attributed to the dynamics of the magnetic domains in the ordered phase.     

Efficient approaches toward the solid-phase synthesis of new heterocyclic azoniaspiro ring systems: synthesis of tri- and tetrasubstituted 10-oxo- 3,9-diaza-6-azoniaspiro[5.5]undecanes

[Reaction: see text]. An efficient approach for the parallel solid-phase synthesis of novel heterocyclic azoniaspiro ring systems is described. The target compounds, the 1,8,9-trisubstituted 10-oxo-3,9-diaza-6-azoniaspiro[5.5]undecanes, were obtained starting from resin-bound reduced dipeptides. The azoniaspiro cation was formed by intramolecular attack of a tertiary nitrogen on pendent alpha-bromocarbonyl. N-3 acylated and N-3 alkylamino carbonyl derivatives of the 1,8,9-trisubstituted 10-oxo-3,9-diaza-6-azoniaspiro[5.5]undecanes were obtained following in solution treatment of the N-3 azoniaspiro derivatives with different carboxylic acids and isocyanates.     

Equation of state of nonadditive d-dimensional hard-sphere mixtures

An equation of state for a multicomponent mixture of nonadditive hard spheres in d dimensions is proposed. It yields a rather simple density dependence and constitutes a natural extension of the equation of state for additive hard spheres proposed by us [A. Santos, S. B. Yuste, and M. Lopez de Haro, Mol. Phys. 96, 1 (1999)]. The proposal relies on the known exact second and third virial coefficients and requires as input the compressibility factor of the one-component system. A comparison is carried out both with another recent theoretical proposal based on a similar philosophy and with the available exact results and simulation data in d=1, 2, and 3. Good general agreement with the reported values of the virial coefficients and of the compressibility factor of binary mixtures is observed, especially for high asymmetries and/or positive nonadditivities.     

Determination of Phenolic Compounds Based on Co‐Immobilization of Methylene Blue and HRP on Multi‐Wall Carbon Nanotubes

This work evaluated an amperometric biosensor based on multi‐wall carbon nanotubes (MWCNT), chemically modified with methylene blue (Met) and horseradish peroxidase (HRP), for detection of phenolic compounds. The dependences of the biosensor response due to the enzyme immobilization procedure, HRP amounts, pH and working potential were investigated. The amperometric response for catechol using the proposed biosensor showed a very wide linear response range (1 to 150 μmol L^?1), good sensitivity (50 nA cm^?2 μmol^?1 L), excellent operational stability (after 300 determinations the response remained at 97%) and very good storage stability (lifetime>3 months). Based on all these characteristics, it is possible to affirm that the material is promising for phenol detection due to its good electrochemical response and enzyme stabilization. The biosensor response for various phenolic compounds was investigated.     

A molecular mechanics and semiempirical conformational analysis of the herbicide diuron inhibitor of photosystem II

The potential energy surface (PES) for the herbicide diuron (DCMU), a photosystem II inhibitor, has been extensively investigated using the quantum-mechanical semiempirical molecular orbital methods AM1 and PM3 and molecular mechanics method. A detailed conformational search has been carried out which revealed the occurrence of four genuine minimum energy structures. The relative stability of the conformers and rotational barriers to conformational interconversion were evaluated using distinct theoretical approaches. The results showed that thetrans form of the diuron molecule is more stable than thecis form in all methods, and so it may possibly be the biologically active isomer.     

Unprecedented head-to-head conformers of d(GpG) bound to the antitumor active compound tetrakis (mu-carboxylato)dirhodium(II,II)

The N7/O6 equatorial binding interactions of the antitumor active complex Rh(2)(OAc)(4)(H(2)O)(2) (OAc(-) = CH(3)CO(2)(-)) with the DNA fragment d(GpG) have been unambiguously determined by NMR spectroscopy. Previous X-ray crystallographic determinations of the head-to-head (HH) and head-to-tail (HT) adducts of dirhodium tetraacetate with 9-ethylguanine (9-EtGH) revealed unprecedented bridging N7/O6 guanine nucleobases that span the Rh-Rh bond. The absence of N7 protonation at low pH and the notable increase in the acidity of N1-H (pK(a) approximately 5.7 as compared to 8.5 for N7 only bound platinum adducts), suggested by the pH dependence titrations of the purine H8 (1)H NMR resonances for Rh(2)(OAc)(2)(9-EtG)(2) and Rh(2)(OAc)(2-)[d(GpG)],are consistent with bidentate N7/O6 binding of the guanine nucleobases. The pK(a) values estimated for N1-H (de)protonation, from the pH dependence studies of the C6 and C2 (13)C NMR resonances for the Rh(2)(OAc)(2)(9-EtG)(2) isomers, concur with those derived from the H8 (1)H NMR resonance titrations. Comparison of the (13)C NMR resonances of C6 and C2 for the dirhodium adducts Rh(2)(OAc)(2)(9-EtG)(2) and Rh(2)(OAc)(2)[d(GpG)] with the corresponding resonances of the unbound ligands [at pH 7.0 for 9-EtGH and pH 8.0 for d(GpG)], shows substantial downfield shifts of Deltadelta approximately 11.0 and 6.0 ppm for C6 and C2, respectively; the latter shifts reflect the effect of O6 binding to the dirhodium centers and the ensuing enhancement in the acidity of N1-H. Intense H8/H8 ROE cross-peaks in the 2D ROESY NMR spectrum of Rh(2)(OAc)(2)[d(GpG)] indicate head-to-head arrangement of the guanine bases. The Rh(2)(OAc)(2)[d(GpG)] adduct exhibits two major right-handed conformers, HH1 R and HH2 R, with HH1 R being three times more abundant than the unusual HH2 R. Complete characterization of both adducts revealed repuckering of the 5'-G sugar rings to C3'-endo (N-type), retention of C2'-endo (S-type) conformation for the 3'-G sugar rings, and anti orientation with respect to the glycosyl bonds. The structural features obtained for Rh(2)(OAc)(2))[d(GpG)] by means of NMR spectroscopy are very similar to those for cis-[Pt(NH(3))(2))[d(GpG)]] and corroborate molecular modeling studies.     

Square Planar (SP-4) and Octahedral (OC-6) Complexes of Platinum(II) and -(IV) with Predetermined Chirality at the Metal Center

cis-Bis-homoleptic platinum(II) complexes, with predetermined helical chirality at the metal center, can be obtained by using strongly sterically interacting ligands. With this aim, two new ligands, (8R,10R)-2-(2'-thienyl)-4,5-pinenopyridine, th4,5ppy (2), and (8R,10R)-2-(2'-thienyl)-5,6-pinenopyridine, th5,6ppy (4), were synthesized and coordinated to platinum. The structures of the resulting complexes, Pt(th4,5ppy)(2) (5) and Pt(th5,6ppy)(2) (6), were determined by X-ray diffraction, and it was found that they both crystallize with a Delta-cis configuration. Thermal oxidative additions (TOA) of alkyl halides were performed with both complexes leading, in the case of 5, to a mixture of isomers and, in the case of 6, to isomerically pure products. The predetermination of chirality at the metal center is therefore preserved in the octahedral (OC-6) platinum(IV) complexes. Crystals of Pt(th4,5ppy)(2) (5) are orthorhombic, of space group P2(1)2(1)2(1), with a = 12.973(1) ?, b = 13.619(2) ?, c = 17.665(2) ?, alpha = beta = gamma = 90 degrees, and Z = 4. Final R = 0.0268 and R(w) = 0.0424 for 3101 observed reflections. Crystals of Pt(th5,6ppy)(2) (6) are hexagonal, of space group P6(1), with a = 11.5465(4) ?, b = 11.5465(4) ?, c = 35.356(3) ?, alpha = beta = 90 degrees, gamma = 120 degrees, and Z = 6. Final R = 0.0424 and R(w) = 0.0845 for 2660 observed reflections. Neither molecule possesses a crystallographic C(2) symmetry.     

Synthesis of tricyclic isoindoles and thiazolo[3,2-c][1,3]benzoxazines

The thermolysis of (3R,9bS)-5-oxo-2,3,5,9b-tetrahydrothiazolo[2,3-a]isoindole-3-carboxylic acids in Ac₂O led to novel 3-methylene-2,5-dioxo-3H,9bH-oxazolo[2,3-a]isoindoles and chiral (9bS)-5-oxo-2,3,5,9b-tetrahydrothiazolo[2,3-a]isoindoles were obtained on FVP. Starting from l-cysteine methyl ester (3R,10bR)-5-oxo-2,3-dihydro-10bH-[1.3]thiazolo[3,2-c][1,3]benzoxazines were obtained as single stereoisomers. The thermolysis of (3R,10bR)-5-oxo-2,3-dihydro-10bH-[1.3]thiazolo[3,2-c][1,3]benzoxazine-3-carboxylic acid in Ac₂O gave 5-acetyl-2-phenyl-2,3-dihydrothiazole. The structures of methyl (3R,9bS)-5-oxo-2,3,5,9b-tetrahydrothiazolo[2,3-a]isoindole-3-carboxylate 1a and methyl (2R,4R)-N-chlorocarbonyl-2-(2-hydroxyphenyl)thiazolidine-4-carboxylate 9 were determined by X-ray crystallography.     

Particle and surface characterization of a natural illite and study of its copper retention

Illite clays are known to have a strong affinity for metallic pollutants in the environment and can be applied as low-cost adsorbents for industrial waste treatment. A crucial factor in the development of such applications, however, is the understanding of the chemical, mineralogical, and colloidal properties of these clays. It is also important to understand the mechanisms involved in the surface adsorption of metals by these adsorbants. In order to study the retention of transition metals on illite clays, we have applied surface characterization techniques such as FPIA, SEM-EDX, XRD, N2 (77 K) adsorption, and FTIR. In addition to these experimental techniques, we have also employed a theoretical model that accounts for the chemistry of transition metal ions, and considers the global retention process to be the sum of several single retention processes. This model adequately fits the experimental data and allows for the speciation of metal retention on illite surfaces. Between pH values of 2.53 and 3.01 the only adsorption processes are the electrostatic sorption of [Cu(H2O)6]2+, and the surface complexation of [Cu(H2O)6]2+ and [Cu(OH)(H2O)5]+ ions. Surface complexation of [Cu(OH)(H2O)5]+ ions increases with pH, overcoming [Cu(H2O)6]2+ retention, and thus contributing to the surface precipitation of Cu(OH)2.