Fluorimetric Determination of Histamine in Fish Using Micellar Media and Fluorescamine as Labelling Reagent

An analytical method based on the use of fluorescamine to produce a fluorescent derivative with histamine and combined with micellar-enhanced fluorescence detection of the formed complex is developed for the sensitive and rapid determination of histamine in fishes. The fluorescence properties of the obtained complex in water and micellar solutions of sodium dodecyl sulfate (SDS), cetyltrimethylammonium chloride (CTAC) and brij-700 are reported. Physicochemical variables influencing the sensitivity of the method (pH, micellar, fluorescamine and NaCl relative concentrations) have been optimized. The stability of the formed complex, as shown by kinetic study, depends on the pH of the solution. Linear calibration curves allowing an effective histamine determination were established with large linear dynamic range (LDR), and low limits of detection (LOD) between 0.5 and 33 ng mL⁻¹, according to the solvent. Application to the analysis of fish samples (sardines) yielded satisfactory results. The method seems to be suitable for environmental fish quality control. Presented in part, at the 39th IUPAC Congress and the 86th Conference of the Canadian Society for Chemistry, August, 10–15, 2003, Ottawa (Canada).     

Langmuir monolayers of bent-core molecules

A systematic study of five different, symmetric bent-core liquid crystals in Langmuir thin films at the air/water interface is presented. Both the end chains (siloxane vs hydrocarbon) and the core (more or less amphiphilic) are varied, to allow an exploration of different possible layer structures at the interface. The characterization includes systematic surface pressure isotherms, Brewster angle microscopy, and surface potential measurements. The properties of these layers are strongly dependent on the individual type of molecule: the molecules with amphiphilic end chains lie quite flat on the surface, while the molecules with hydrophobic end chains construct multilayer structures. In both cases, the three-dimensional collapse structure is reversible.     

Are covering (enveloping) morphisms minimal?

We prove that for certain classes of modules such that direct sums of -covers ( -envelopes) are -covers ( -envelopes), -covering ( -enveloping) homomorphisms are always right (left) minimal. As a particular case we see that over noetherian rings, essential monomorphisms are left minimal. The same type of results are given when direct products of -covers are -covers. Finally we prove that over commutative noetherian rings, any direct product of flat covers of modules of finite length is a flat cover.     

The reaction of 2,4,6-tris(trimethylsiloxy)-1,3,5-triazine with chlorocarbenium ions: a new access to 1-oxa-3-azabutatrienium and 2-azaallenium salts

Chlorocarbenium salts - of the Vilsmeier-Arnold type react with the silylated isocyanuric acid to give 1-oxa-3-azabutatrienium salts under mild conditions. From reactions of diarylchloromethenium salts - with and ketones or tertiary carboxamides high yields of 2-azaallenium salts were obtained. A few chloro substituted 2-azaallenium salts were prepared from and carbonyl compounds. The mechanisms of the new reactions are discussed.     

Modified Brans–Dicke theory of gravity from five-dimensional vacuum

We investigate, in the context of five-dimensional (5D) Brans–Dicke theory of gravity, the idea that macroscopic matter configurations can be generated from pure vacuum in five dimensions, an approach first proposed by Wesson and collaborators in the framework of 5D general relativity. We show that the 5D Brans–Dicke vacuum equations when reduced to four dimensions (4D) lead to a modified version of Brans–Dicke theory in 4D. As an application of the formalism, we obtain two 5D extensions of 4D O’Hanlon and Tupper vacuum solution and show that they lead two different cosmological scenarios in 4D.     

Gas phase structure and vibrational spectra of dimethoxysulfane (CH3O)2S

The vapor phase structure of (CH₃O)₂S [1] has been investigated by electron diffraction and ab initio MO calculations, which both result in a C₂ symmetry for the most stable geometry, the C_s conformer being less stable by about 12 kJ/mol. The torsional barrier for rotation about one SO bond was calculated as 37 kJ/mol (trans barrier). The geometrical parameters (electron diffraction) of the C₂ conformer are: d_SO = 162.5(2), d_CO = 142.6(3), d_CH = 110.5(7) pm angles OSO = 103(1)°, SOC = 115.9(4)°, HCH = 109(1)°, torsional angle COSO = 84(3)°. Geometrical data calculated with 6-31G^* basis set agree well with the diffraction data; calculated dipole moments 1.1 D (C₂) and 3.3 D (C_s). The infrared spectrum of gaseous (CH₃O)₂S and the Raman spectra of liquid and solid (CH₃O)₂S are reported and have been almost fully assigned to the 27 fundamental vibrations.