Results from multi-trace-element neutron activation analyses of marine biological specimens

Résumé Un grand nombre d'échantillons biologiques marins, s'étendant du varech au thon, à l'espadon et aux mammifères marins, ont été analysés pour évaluer la teneur en mercure, sélénium et zinc grace à l'analyse par activation aux neutrons thermiques et en employant un spectromètre Ge(Li). Dans ces conditions, des teneurs aussi faibles que 0,01 ppm de Hg, 0,02 ppm de Se, et 0,2 ppm de Zn sont détectées. De nombreux résultats intéressants ont été obtenus et sont décrits. On est en train d'étendre cette étude à d'autres éléments à l'état de trace en utilisant des séparations radio-chimiques après irradiation.      

Use of HPTLC,HPLC, and Densitometry for Qualitative Separation of Indole Alkaloids from Rauvolfia serpentina Roots

JPC – Journal of Planar Chromatography – Modern TLC - High-performance thin-layer chromatography (HPTLC) has been used for normal-phase separation of the components of hexane,...     

Partial Molar Volumes of Amino Acids and Peptides in Aqueous Salt Solutions at 25°C and a Correlation with Stability of Proteins in the Presence of Salts

Partial molar volumes for a homologous series of amino acids and peptides have been measured in aqueous 1M sodium acetate, sodium thiocyanate, and sodium sulfate at 25^°C. These data have been utilized in conjunction with the data in water to deduce partial molar volumes of transfer V _2,m ⁰(tr) from water to these aqueous salt solutions. The volumes of transfer for the amino acids and peptides are found to be positive. The interpretation is that this result arises from the dominant interaction of the sodium salts with the charged centers of amino acids and peptides. Thermal denaturation of the structurally homologous proteins lysozyme and -lactalbumin has been studied in the presence of these salts. Significant thermal stabilization of hen egg-white lysozyme has been observed in the presence of sodium acetate and sodium sulfate. However, the thermal stabilization observed for -lactalbumin is very small in the presence of these salts and sodium thiocyanate leads to a lowering of its thermal denaturation temperature. The rise in the surface tension of aqueous salt solutions with salt concentration has been correlated with the calorimetric and volumetric measurements. The results show that V _2,m ⁰(tr) depends less on the type of electrolyte than on the ionic strength of the solution. The V _2,m ⁰(tr) values correlate very well with the increase in the surface tension of aqueous salt solutions, indicating significant role of surface tension in interactions of amino acids, peptides, or protein with the salts.     

Reactions of oxidizing radicals with 2- and 3-aminopyridines: a pulse radiolysis study

Reactions of OH radicals and some one-electron oxidants with 2-aminopyridine (2-AmPy) and 3-aminopyridine (3-AmPy) were studied in aqueous solutions using pulse radiolysis technique. The OH adduct of 2-AmPy at pH 9 has an absorption maximum at 360 nm along with a weak absorption band in the visible region and was found to be reactive with oxygen. The rate constant for its reaction with O₂ was determined to be 1.0×10⁸ dm³ mol⁻¹ s⁻¹. At pH 4 also, the OH adduct of 2-AmPy has an absorption band at 360 nm. However, there are differences in the absorption at other wavelengths. From the plot of ΔOD vs. pH at 340 nm, the pK_a of the OH adduct was determined to be 6.5. Among the specific oxidants, only SO₄^−√ radicals were able to oxidize 2-AmPy. In the case of 3-aminopyridine (3-AmPy), the transient species formed by OH radical reaction at pH 9 has an absorption maximum at 410 nm with shoulder bands on both the sides. Its absorption spectrum at pH 4 was different indicating the existence of a pK value for the OH adduct. pK_a of 3-AmPy-OH radical adduct species was evaluated to be 5.7. This adduct species was also found to be reactive with oxygen (k=7.6×10⁶ dm³ mol⁻¹ s⁻¹). Specific one-electron oxidants like N₃^√, Br₂^−√ C₂^−√ and SO₄^−√ were able to oxidize 3-AmPy indicating that it is easier to oxidize 3-AmPy as compared to 2-AmPy.     

One-electron oxidation of toluidine blue. A pulse radiolysis study

The one-electron oxidation of toluidine blue by specific oxidising radicals such as Cl ₂ ⁻ , Tl(II), N₃, Br ₂ ⁻ etc. has been studied by employing the pulse radiolysis technique. The Br ₂ ⁻ radical was found to be less efficient in oxidising toluidine blue as compared to Cl ₂ ⁻ ., Tl⁺² and N₃. The semioxidised species exhibited only onepK _a indicating the presence of two conjugate acid-base forms whose spectral and kinetic features were evaluated. Reaction of OH radicals with the dye gave rise to a transient species which exhibited spectral and kinetic features different from that of the semioxidised species indicating that the mode of reaction of OH is different.     

Electrochemical and chemical polymerization of acrylamide

The electrochemical and chemical polymerization of acrylamide (AA) has been studied. The electrolysis of the monomer in N,N-dimethylformamide (DMF) containing (C₄H₉)₄NClO₄ as the supporting electrolyte leads to polymer formation in both anode and cathode compartments. The cathodic polymer dissolves in the reaction mixture and the anodic polymer precipitates during the course of polymerization. A plausible mechanism for the anodic and cathodic initiation reaction has been given. The chemical polymerization of acrylamide that has been initiated by HClO₄ is analogous to its anodic polymerization. The polymer yield increases with an increase in concentration of the monomer and HClO₄. Raising the reaction temperature also enhances the polymerization rate. The overall apparent activation energy of the polymerization was determined to be ca. 19 kcal/mole. The copolymerization of acrylamide was carried out with methyl methacrylate (MMA) in a solution of HClO₄ in DMF. The reactivity ratios are r₁ (AA) = 0.25 and r₂ = 2.50. The polymerization with HClO₄ appears to be by a free radical mechanism. When the polymerization of acrylamide is carried out with HClO₄ in H₂O, a crosslinked water-insoluble gel formation takes place.     

Highly Efficient One‐Pot Preparation of 1,2,4‐Oxadiazoles in the Presence of Diazabicycloundecene

New highly efficient method for the cyclization of acylamidoximes in the presence of diazabicycloundecene was developed and incorporated into a general and practical one‐pot synthesis of 1,2,4‐oxadiazoles (11 examples, 85–97% yields).     

Thermal Stability of Polystyrene Peroxide

It has been observed that poly(styrene peroxide) with a high molecular weight is thermally less stable than the same polymer with a low molecular weight. This has been explained as being due to the strain on the O-O bond due to the greater polymer chain length.     

Hydrogen Peroxide/Boric Acid: An Efficient System for Oxidation of Aromatic Aldehydes and Ketones to Phenols

Hydrogen peroxide activated by boric acid in the presence of sulfuric acid has been shown to be an efficient oxidizing system for direct conversion of aromatic aldehydes and ketones to phenols.