Synthesis of tridimensional polymers by the copolymerization of phenylglycidylether with aromatic diglycidylethers

Copolymers from phenylglycidylether and several aromatic diglycidylethers are prepared using different ratios of difunctional comonomers and the AIP/ZnCl₂ initiator system. It is found that the percentage of incorporated comonomer depends on the nature of the aromatic moiety introduced. The copolymers are characterized by ¹³C-NMR spectroscopy and turn out to be completely regular and with a high degree of isotacticity (about 80%) that confirms the high degree of regio- and stereoselectivity of the initiator system used. The thermal characteristics of copolymer networks are investigated using differential scanning calorimetry and thermogravimetry. Two fusion endotherms are observed which vary with the degree of crosslinking. By thermogravimetric analyses the thermal stability is found to increase when the crosslinking degree does. © 1994 John Wiley & Sons, Inc.     

Two-step upflow anaerobic sludge bed system for sewage treatment under subtropical conditions with posttreatment in waste stabilization ponds

A pilot-scale sewage treatment system consisting of two upflow anaerobic sludge bed (UASB) reactors followed by five waste stabilization ponds (WSPs) in series was studied under subtropical conditions. The first UASB reactor started up in only 1 mo (stable operation, high chemical oxygen demand [COD] removal efficiency, low volatile fatty acids concentration in the effluent, alkalinity ratio above 0.7, biogas production above 0.1 Nm3/kg of CODremoved). Removal efficiencies up to 90% were obtained in the anaerobic steps at a hydraulic retention time of 6 + 4 h (80% removal in the first step). Fecal coliform removal in the whole system was 99.9999% (99.94% in anaerobic steps and 99.98% in WSPs). COD balances over UASB reactors are provided. A minimum set of data necessary to build COD balances is proposed. Intermittent sludge washout was detected in the reactors with the COD balances. Sludge washout from single-step UASB reactors should be monitored and minimized in order to ensure constant compliance with discharge standards, especially when no posttreatment is provided. The system combined high COD and fecal coliform removal efficiency with an extremely low effluent concentration, complying with discharge standards, and making it an attractive option for sewage treatment in subtropical regions.     

Use of highly efficient Draper-Lin small composite designs in the formal optimisation of both operational and chemical crucial variables affecting a FIA-chemiluminescence detection system

A new formal strategy in the multidimensional optimisation of the experimental variables affecting the chemiluminescence (CL) detection in flow injection analysis (FIA) is proposed here. The strategy implies several steps, being the most significant: selection of the variables to be studied and their experimental domain; use of a screening design to detect significant variables and interactions into the experimental region; study of the main effect of variables and second-order interactions; and finally application of a Draper-Lin small composite design (orthogonal) to obtain the optimum values of the significant variables. The methodology is applied to the determination of methylamine by FIA based on the use of the peroxyoxalate CL (PO-CL) reaction. Considering the high number of experiments required due to the different chemical and instrumental variables to be taken account and their adequate compatibility to obtain maximum sensitivity, the methodology offers a rigorous study of the main effects and interactions, achieving a reduction of experimental work.     

Conformation of glycomimetics in the free and protein-bound state: structural and binding features of the C-glycosyl analogue of the core trisaccharide alpha-D-Man-(1 --> 3)-[alpha-D-Man-(1 --> 6)]-D-Man

The conformational properties of the C-glycosyl analogue of the core trisaccharide alpha-D-Man-(1 --> 3)-[alpha-D-Man-(1 --> 6)]-D-Man in solution have been carefully analyzed by a combination of NMR spectroscopy and time-averaged restrained molecular dynamics. It has been found that both the alpha-1,3- and the alpha-1,6-glycosidic linkages show a major conformational averaging. Unusual Phi ca. 60 degrees orientations for both Phi torsion angles are found. Moreover, a major conformational distinction between the natural compound and the glycomimetic affects to the behavior of the omega(16) torsion angle around the alpha-1 --> 6-linkage. Despite this increased flexibility, the C-glycosyl analogue is recognized by three mannose binding lectins, as shown by NMR (line broadening, TR-NOE, and STD) and surface plasmon resonance (SPR) methods. Moreover, a process of conformational selection takes place, so that these lectins probably bind the glycomimetic similarly to the way they recognize the natural analogue. Depending upon the architecture and extension of the binding site of the lectin, loss or gain of binding affinity with respect to the natural analogue is found.     

Matrix-isolation FT-IR spectra and theoretical study of dimethyl sulfate

The preferred conformations of dimethyl sulfate and their vibrational spectra were studied by matrix-isolation FT-IR spectroscopy and theoretical methods (DFT and MP2, with basis sets of different sizes, including the quadruple-zeta, aug-cc-pVQZ basis). Conformer GG (of C2 symmetry and exhibiting OSOC dihedral angles of 74.3 degrees ) was found to be the most stable conformer in both the gaseous phase and isolated in argon. Upon annealing of the matrix, the less stable observed conformer (GT; with C1 symmetry) quickly converts to the GG conformer, with the resulting species being embedded in a matrix-cage which corresponds to the most stable matrix-site for GG form. The highest energy TT conformer, which was assumed to be the most stable conformer in previous studies, is predicted by the calculations to have a relative energy of ca. 10 kJ mol-1 and was not observed in the spectra of the matrix-isolated compound.     

Clean osmium-catalyzed asymmetric dihydroxylation of olefins in ionic liquids and supercritical CO2 product recovery

The combination of ionic liquids (ILs) as solvents in the asymmetric Sharpless dihydroxylation (AD) with the use of scCO(2) in the separation process allows a very simple, efficient, clean and robust system for the reuse of the AD catalytic system, which also does not need the use of organic solvents either for the reaction or for the separation of products and allows the isolation of the diol, in high yield and enantiomeric excess and basically without contamination with osmium.     

Two families of mixed finite elements for second order elliptic problems

Summary Two families of mixed finite elements, one based on triangles and the other on rectangles, are introduced as alternatives to the usual Raviart-Thomas-Nedelec spaces. Error estimates inL ² () andH ^–5 () are derived for these elements. A hybrid version of the mixed method is also considered, and some superconvergence phenomena are discussed.     

Binuclear Cu2+ complex mediated discrimination between L-glutamate and L-aspartate in water

L-glutamate and L-aspartate selectivity is achieved by the action of two Cu2+ metal ions rightly disposed in a cyclophane-type macrocyclic framework; electrochemical sensing of glutamate has been achieved by adsorption of the copper complexes on graphite electrodes.     

Development and validation of a capillary electrophoresis method for the determination of phenothiazines in human urine in the low nanogram per milliliter concentration range using field-amplified sample injection

A capillary zone electrophoresis (CZE) method with ultraviolet-visible detection has been established and validated for the determination of five phenothiazines: thiazinamium methylsulfate, promazine hydrochloride, chlorpromazine hydrochloride, thioridazine hydrochloride, and promethazine hydrochloride in human urine. Optimum separation was obtained on a 64.5 cm x 75 microm bubble cell capillary using a buffer containing 150 mM tris(hydroxymethyl)aminomethane and 25% acetonitrile at pH 8.2, with temperature and voltage of 25 degrees C and 20 kV, respectively. Naphazoline hydrochloride was used as an internal standard. Field-amplified sample injection (FASI) has been applied to improve the sensitivity of the detection. Considering the influence of parameters affecting the on-line preconcentration (nature of preinjection plug, sample solvent composition, injection times, and injection voltage) and due to the significant interactions among them, in this paper we propose for the first time the application of a multivariate approach to carry out the study. The optimized conditions were as follows: preinjection plug of water for 7 s at 50 mbar, electrokinetic injection for 40 s at 6.2 kV, and 32 microm of H3PO4 in the sample solvent. Also, a solid-phase extraction (SPE) procedure is developed to obtain low detection limits and an adequate selectivity for urine samples. The combination of SPE and FASI-CZE-UV allows adequate linearities and recoveries, low detection limits (from 2 to 5 ng/mL), and satisfactory precisions (3.0-7.2% for an intermediate RSD %).     

Development of an HPLC method with electrochemical detection of femtomoles of 8-oxo-7,8-dihydroguanine and 8-oxo-7,8-dihydro-2'-deoxyguanosine in the presence of uric acid

A selective method based on high performance liquid chromatography with electrochemical detection (HPLC-ECD) was developed to enable simultaneous detection of 8-oxo-7,8-dihydroguanine (8-oxoGua) and 8-oxo-7,8-dihydro-2′-deoxyguanosine (8-oxodGuo), products of DNA oxidative damage, in the presence of uric acid (UA), a strong interferent in their electrochemical detection. The method developed consists of HPLC isocratic elution with amperometric detection on a glassy carbon electrode, enabling a detection limit for 8-oxoGua and 8-oxodGuo lower than 1 nM in standard mixtures. Detection of low concentrations up to 25 nM of 8-oxoGua and 8-oxodGuo in the presence of UA in a 10⁴-fold higher concentration was achieved after one-step solid phase extraction (SPE). The method was tested with urine samples and it was possible to detect and quantify the presence of 8-oxoGua, and to confirm that UA was eliminated after uricase degradation and SPE. The LOD found in urine samples was about 80 nM, a value higher than in standard mixtures, due to the increase of background current in the urine matrix. The results presented here contribute to the development of a methodological approach to simultaneous determination of 8-oxoGua and 8-oxodGuo in urine samples.