A method for separating ALA from ALA derivatives using ionic exchange extraction

Photodynamic therapy using 5-aminolevulinic acid (ALA)-induced protoporphyrin IX is a recent approach to detect and treat some malignancies. The use of lipophilic derivatives of ALA has been exploited in the last years to enhance ALA penetration. In this paper, we describe the application of the Mauzerall and Granick's method [J. Biol. Chem. 219 (1956) 435] to the quantification of ALA derivatives. We also describe the employment of reusable ion-exchange chromatographic columns for separating mixtures of ALA and ALA derivatives present in biological samples. The relation between 555 nm absorbance and ALA or ALA derivative concentration was linear up to 100 nmol/ml and the limit of detection of ALA and ALA derivatives was 1 nmol per ml. We employed a Dowex 50 X8 hydrogen form resin to separate ALA from the derivatives. Whereas 90+/-4% of the total ALA was eluted using sodium acetate, only 3-9% of the ALA derivatives was recovered. Only upon exposure of the resin to a high HCl concentration, the ALA derivatives were completely released. We employed this new method for the separation of ALA from ALA derivatives in cells exposed to different ALA compounds.     

Base-catalysed solvolysis of acylsilanes

Kinetic studies have been made of the hydrolysis of XC₆H₄COSiR₃ compounds (R = Me, Et, Ph) in a mixture of THF (3 vol.) and aqueous sodium hydroxide (1 vol.). The rates of cleavage of p-NO₂C₆H₄CH₂SiMe₃, C₆H₅COSiMe₂C₆H₅ and C₆H₅COSiMe₂C₆H₄Cl-p compounds under the same conditions have also been measured. Electron-attracting substituents on either side of the bond being broken lead to an increase in the rate. For the XC₆H₄COSiR₃ compounds, the effects of the substituents X correlate excellently with their Hammett σ constants (? = 3.5 and 2.5 for R = Me and Ph, respectively). The data are consistent with a mechanism in which the attack of the hydroxide ion occurs at the carbonyl C atom.     

1,3-Dipolar cycloaddition reactions. Regioselective synthesis of heterocycles and theoretical studies

We report a 1,3-dipolar cycloaddition reaction between a oxazolium 5-oxide derivative with chloroacrylonitrile or ethyl propiolate as dipolarophiles, in order to obtain substituted pyrrolizidines. Experimentally we found that the reaction is regiospecific with chloroacrylonitrile and regioselective with ethyl propiolate. The secondary attractive orbital interactions from the Frontier Molecular Orbital Theory, the differences in stability of the possible biradical intermediaries postulated for the reaction and some hindrance effects, explain the regioselectivity observed experimentally.     

Application of solid-phase extraction and micellar electrokinetic capillary chromatography to the study of hydrolytic and photolytic degradation of phenoxy acid and phenylurea herbicides

A degradation study of two phenoxy acid [(2,4-dichlorophenoxy) propanoic acid and (2,4,5-trichlorophenoxy) acetic acid] and two phenylurea (diuron and monolinuron) herbicides, spiked at 50 ppb in water, was performed. Some samples were subjected to neutral and basic hydrolysis; other samples were subjected to photolysis using either sunlight or a xenon arc lamp. After degradation, the water samples were preconcentrated using solid-phase extraction (SPE) with Carbopack B columns and analysed by a micellar electrokinetic capillary chromatography (MECC) system with UV detection at 210 nm. Phenoxyacetic acids were not degraded neither by hydrolysis nor by sunlight photolysis, but they were photodegraded when they were exposed to a xenon arc lamp, with half-lives around 300 min. Phenylurea herbicides were hydrolysed at the two-tested pH, with half-lives varying from 25 to 290 days. The main hydrolysis products were the corresponding chloroanilines. Diuron and monolinuron were also degraded when they were exposed to sunlight and xenon arc lamp. The main photodegradation pathway for diuron corresponded to dehalogenation, while for monolinuron dealkylation and hydroxylation were also postulated. The toxicity of the studied herbicides and their degradation products was evaluated by means of Microtox tests. The obtained results indicated that the toxicity of the degraded samples was higher than the toxicity of the herbicides.     

Ion trap mass spectrometry in the structural analysis of haemoglobin peptides modified by epichlorohydrin and diepoxybutane

Ion trap mass spectrometry has been shown to be particularly suitable for the structural analysis of high molecular weight peptides directly fragmented in the mass analyser without needing further sub-digestion reactions. Here we report the advantages of using multi-stage ion trap mass spectrometry in the structural characterisation of haemoglobin alkylated with epichlorohydrin and diepoxybutane. Alkylated globins were digested with trypsin and the peptide mixtures were analysed by MS(3). This technique allows the sequential fragmentation of peptides under analysis, giving rise to MS(3) product ion spectra with additional information with respect to MS(2) mass spectra. The results obtained complete the previously reported structural characterisation of alkylated haemoglobin, demonstrating the potential of ion trap mass spectrometry.     

Multivariate Optimization in Preconcentration Procedure for Manganese Determination in Seawater Samples by FAAS

In the present paper, a preconcentration procedure for manganese determination in seawater samples by flame atomic absorption spectrometry (FAAS) is proposed. It is based on the solid phase extraction of manganese(II) ions as a 4-(2-pyridylazo-resorcinol) (PAR) chelate using activated carbon as sorbent. Optimization of the experimental parameters (pH, activated carbon mass, PAR mass and shaking time) was carried out using a two-level full factorial design (2⁴) and two Doehlert matrix designs. The results of the factorial design, considering the analysis of variance (ANOVA), demonstrate that all these factors and their interactions (pH × PAR mass; pH × activated carbon mass and activated carbon mass × shaking time) are statistically significant. Final optimization was carried out using Doehlert matrix designs considering the results of the factorial design. The validation process evaluated the following parameters: effect of other metal ions, calibration curve, precision, accuracy and robustness. The procedure allows manganese determination in seawater samples with limits of detection (3/S) and quantification (10/S) of 16ngL^–1 and 53ngL^–1 respectively, and a preconcentration factor of 152. The analysis of certified reference materials demonstrated that the proposed procedure can also be used for manganese determination in biological samples. The procedure is not affected by matrix interferences and could be satisfactorily applied in manganese determination in seawater samples. Manganese determination in surface seawater samples collected from the shore of Salvador city, Brazil, was performed, and concentrations ranging from 0.51 to 2.59µgL^–1 were found.     

Microwave-assisted solid-phase synthesis of 5-carboxamido-N-acetyltryptamine derivatives

[reaction: see text] The synthesis of the indole skeleton of new melatoninergic analogues was realized using solid-phase methodology in association with microwave irradiation. This combination speeds up the solid-phase drug discovery process in rigorously established conditions.     

Photo-SRN1 reactions of phenyl telluride anion with haloarenes

Phenyl telluride anion was prepared in liquid ammonia by reaction of dipheyyl ditelluride with two equivalents of sodium metal under nitrogen. This anion reacts with haloarenes under irradiation to form aryl phenyl tellurides, probably by the photo-S_RN1 mechanism of aromatic substitution.     

Silver Complexes with Cyanoguanidine: Preparation and Crystal Structures of [Ag(cgn)2]F and [Ag(cgn)2][BF4]

The silver cyanoguanidine complexes [Ag(cgn)₂]F ( 1 ), [Ag(cgn)₂][BF₄] ( 2 ), [Ag(cgn)₂][ClO₄] ( 3 ) and [Ag(cgn)][NO₃] ( 4 ) were obtained from aqueous solutions of the corresponding silver salts and cyanoguanidine. The crystal structures of 1 and 2 have been determined by single crystal X‐ray diffraction. 1 : Space group P1¯, Z = 2, cell constants at —65 °C: a =618.18(3), b = 761.49(8), c = 971.2(1) pm; α = 93.56(1), β = 97.439(8), γ = 97.376(9)β; R₁ = 0.0218 2 : Space group P1¯, Z = 2, cell constants at —65 °C: a = 549.79(9), b = 958.17(17), c = 1121.04(12) pm; α = 90.026(13), β = 102.520(11), γ = 95.937(14)°; R₁ = 0.0283.     

Microstructure and electrical transport in nano-grain sized Ce0.9Gd0.1O2−δ ceramics

An enhancement of the electrical conductivity has been found in nano-grain sized Ce_0.9Gd_0.1O_2−δ ceramics when measured in N₂ (p_O2=3.5×10⁻⁶ atm) in comparison with the most commonly accepted values of bulk ionic conductivity. We first present the synthesis and characterisation of the nanoparticles later used for the preparation of dense nanoceramics of Gd-doped CeO₂. The nanoparticles were characterised by X-ray diffraction (XRD), atomic force microscopy (AFM) and transmission electron microscopy (TEM). The good sintering properties of these nanopowders allowed us to obtain very dense ceramics (>90% theoretical density) while keeping the grain size close to 100 nm. The microstructure of these nanoceramics was analysed by AFM and scanning electron microscopy (SEM) while the electrical characterisation was performed by the 4-point dc technique between 500 and 950 °C in air or N₂ and ac impedance between 150 and 400 °C in air and or argon. We briefly discuss the possibilities of electron vs. oxygen ion conduction and grain boundary vs. bulk conductivity. The features exhibited by these ceramics represent an increased potential to process solid electroceramics materials with specific levels of electronic and/or ionic conductivities for a variety of electrochemical devices.