Arsenic speciation by capillary gas-liquid chromatography

Specific environmentally significant arsenic compounds are determined by capillary gas-liquid chromatography. Inorganic (arsenite, arsenate) and organic (monomethylarsonate, dimethylarsinate) arsenicals are measured as the corresponding methylthioglycolate derivatives, which are simultaneously separated on wide-bore borosilicate glass and fused-silica columns under conditions of temperature programming. Inorganic arsenate and arsenite cannot be differentiated by the derivatization technique. Flame-ionization and electron-capture detection are evaluated. A simple and rapid sample preparation procedure is used for water, urine, blood, and tissue.     

Comparison of the major polypeptides of the erythrocyte nuclear envelope

The three most abundant nonhistone polypeptides (molecular weights 75,000, 71,000 and 61,000) of the avian erythrocyte nucleus have previously been isolated in the nuclear envelope fraction. They have been separated by sodium dodecylsulfate-polyacrylamide gel electrophoresis and peptide-mapped after limited enzymatic digestion. Three enzymes -- chymotrypsin, papain and Staphylococcus aureus protease -- were used. Results obtained with each enzyme indicate strong similarities between the three nuclear envelope polypeptides. The amino acid compositions of the two most abundant polypeptides (P75 and P71) have been determined and found to be similar. Further, they readily yield large fragments upon brief alkaline hydrolysis. For both P75, and P71 the degree and the pattern of alkaline fragmentation are almost identical. A 61,000-dalton polypeptide which appears to be P61 is obtained from P75 and P71 by mild acid hydrolysis. These results establish the close chemical similarity of these predominant polypeptides in the erythrocyte nucleus and suggest that they serve related functions.     

Photoelectron spectra of uranium(V) in mixed oxides showing characteristic satellite signals

Whereas uranyl compounds at most show electron transfer satellites at 3 eV higher I in the U4f region, mixed oxides containing uranium(V) show a characteristic satellite at 7.9 eV higher I. Uranium-cerium blue and certain U(IV) compounds are also discussed.     

Preparative gas chromatography of volatile metal compounds-I Separation of aluminium, chromium and iron beta-diketonates

The analytical gas chromatography of a range of fluorinated and unfluorinated beta-diketonates of aluminium, chromium and iron has been studied m detail and conditions have been established for their complete separation; the complexes of trifluoroacetylpivaloylmethane show the best characteristics for this purpose. A range of liquid phases and column conditions have been considered and Apiezon substrates have been shown to give optimal resolution. The technique has been extended to a preparative scale with up to 0.1-g chelate samples, and the efficiency of the process demonstrated by the removal of 2% proportions of two metal complexes from a sample of the third. Implications of the technique for the purification of metals are discussed.     

Atomic absorption inhibition titration of orthophosphate and polyphosphates

The atomic absorption inhibition titration of phosphates was studied for two types of burner. Dependence on gas Flow-rates was observed. The method with a pre-mix burner was employed to determine phosphate in surface and waste waters. The results are compared with those by the standard method. The proposed method was found to be rapid, simple and accurate.     

Distribution of reaction products (theory). Investigation of an ab initio energy-surface for F + H2 ⇀ HF + H

Bender, O'Neil, Pearson and Schaefer (BOPS) have computed ab initio energies for 232 collinear configurations of FHH, using extensive configuration interaction. We have fitted these points using an LEPS-type function. Comparison with semi-empirical surfaces for FHH shows that the general form of these surfaces is in good accord with the ab initio findings. Evidence is presented which indicates that the BOPS ab initio surface exhibits too great a drop in energy along the favoured route into the exit valley.     

Eroded myelin figures

Myelin figures with unusual surface morphology were observed on contacting Tween85 with water. Myelins, which are normally smooth rodlike forms in other surfactants, are in this system found to be with an irregular, rough surface with vesiclelike structures adhered to the myelin tubes. Besides these, smooth myelin figures were also observed. We term the myelin figures with a rough surface eroded myelin figures. The same myelin could show a coexistence of smooth and rough areas with a sharp boundary between the smooth surface at one end whereas the other end shows a rough texture. The transformation of smooth myelins into eroded forms were observed often whereas the reverse is quite rare. In the later stage, the tip of the eroded myelin figures transforms into tentacles and acts as a source for new myelins and the growth of vesiclelike structures which were expelled into the surrounding medium. The eroded myelin figures are stable for a longer period in comparison to simple, smooth rodlike forms. By studying the myelin growth at different temperatures, it was found that eroded myelin figures were stable in the temperature range of 22-42 degrees C and at > 42 degrees C only smooth myelin figures were observed.     

Synthesis of 1-Aza-8-thiabicyclo[4.2.1]nona-2,4-diene 8,8-dioxide and its conversion to a strained spirocycle via photoinduced SO2-N bond cleavage

A route to the doubly unsaturated bridgehead sultam 12 has been developed. When irradiated at 350 nm, this conjugated diene is isomerized via a two-photon process to the structurally novel spiro heterocycle 17 constituted of cyclobutene, thietane dioxide, and pyrrolidine rings. A probable mechanism for the generation of 17 and select reactions thereof are reported. [reaction: see text]     

Studies of surface properties of Na- and La-montmorillonites

This paper presents possible applications of thermal analysis, sorptometry and porosimetry to study physico-chemical properties of Na- and La-montmorillonite samples, especially for determination of total surface heterogeneity. The quasi-isothermal thermogravimetric (Q-TG) mass loss and its first derivative (Q-DTG) curves with respect to temperature and time obtained during programmed liquid thermodesorption under quasi-isothermal conditions have been used to study adsorbed layers and heterogeneous properties of the Na- and La-montmorillonites. Calculations of the desorption energy distribution functions by analytical procedure using mass loss Q-TG and differential mass loss Q-DTG curves of thermodesorption under quasi-isothermal conditions of polar and non-polar liquid vapours preadsorbed on a material surface are presented. Parameters relating to porosity of samples were determined by sorptometry, mercury porosimetry and atomic force microscopy (AFM). From nitrogen sorption isotherms from sorptometry and porosimetry methods, the fractal dimensions of montmorillonites have been calculated. Moreover, a new approach is proposed to calculate fractal dimensions of materials obtained from Q-TG curve; this is compared with values obtained by the above methods. The total heterogeneous properties (energy distribution function and pore-size distribution functions) of samples studied were estimated. The radius and pore volume of the tested samples calculated on the basis of thermogravimetry, sorptometry and porosimetry techniques were compared and good correlations obtained.     

REVERSIBLE PHOTOCHEMISTRY IN THE α-SUBUNIT OF PHYCOERYTHROCYANIN: CHARACTERIZATION OF CHROMOPHORE AND PROTEIN BY MOLECULAR DYNAMICS AND QUANTUM CHEMICAL CALCULATIONS

The ground and excited state properties of two regions in the Δ15-configurational space of the phycoviolobilin chromophore in the α-subunit of phycoerythrocyanin are analyzed. Molecular dynamics calculations reveal that the chromophore geometry determines the active-site dynamics. The excited state torsional potential surface shows a negative barrier for isomerization and trapping of an activated complex. Strong coupling of excited states localized in the chromophore and charge transfer states from the surrounding polar residues provides favorable prerequisites for fast excited state surface crossing in competition with other deactivation processes. The formation of a photoreduced intermediate following the photoinduced charge transfer may trigger subsequent chemical reactions.