Direct detection of the biradicals generated in the Norrish type II reaction

The biradicals generated in the Norrish type II reaction from the triplet manifold have been observed using laser flash photolysis techniques. The spectra and extinction coefficients closely resemble those of typical ketyl radicals. Typical lifetimes are in the 40–100 ns range depending on the solvent. Their interaction with oxygen is essentially diffusion controlled.     

Copolymerization characteristics of S-vinyl-O-tert-butylthiocarbonate

Poly-S-vinyl-O-tert-butylthiocarbonate is an excellent precursor to poly(vinyl mercaptan) because the tert-butyloxycarbonyl blocking group can be removed by either acid hydrolysis or thermolysis under conditions which minimize the oxidation of the liberated mercaptan to disulfide. Dilatometric studies of the homopolymerization of S-vinyl-O-tert-butylthiocarbonate demonstrated that the polymerization rate was directly proportional to the concentration of free-radical initiator; no thermal initiation was observed. The molecular weight of the homopolymers and copolymers ranged from 30,000 to 50,000 (GPC). Copolymerization of S-vinyl-O-tert-butylthiocarbonate (M₂) with styrene, (r₁ = 3.0, r₂ = 0.2), methyl methacrylate (r₁ = 1.40, r₂ = 0.17) and vinyl acetate (r₁ = 0.04, r₂ = 11.0) indicated that a sulfur atom adjacent to the vinyl group increases the resonance stability (Q₂ = 0.5) and the electron density (e₂ = ?1.4) of the double bond and the corresponding radical. Water-soluble copolymers could be prépared by incorporating either N-vinylpyrrolidone (r₁ = 0.12, r₂ = 3.94) or N-isopropylacrylamide (r₁ = 1.17, r₂ = 0.3) with M₂. The water solubility of the copolymers decreased markedly when the tert-butyloxycarbonyl group was removed. Copolymers of M₂ with N-vinyl-O-tert-butylcarbamate (r₁ = 0.13, r₂ = 5.10) were utilized to prepare crosslinked poly(vinyl amine–vinyl mercaptan); the crosslinking resulted from urea linkages formed during thermolysis of the copolymer.     

Determination of sulphur in fly ash by instrumental proton activation analysis

A method for the determination of sulphur in fly ash by instrumental proton activation analysis using the³⁴S/p,n/^34mCl reaction was developed. The 2128.5 keV and 3305.0 keV -rays of^34mCl /t=32.0 min/ were measured on a Ge/Li/ -spectrometer, shielded with a lead absorber to attenuate low energy -rays. Irradiation and measuring conditions were optimized. The detection limit for instrumental analysis is 0.3 to 1 mg g^–1 and the standard deviation is cca. 4% for a typical sample.     

The spectrophotometry and solvent-extraction behaviour of iron(III), vanadium(IV and V) and titanium(IV) chelates of 1-(o-carboxyphenyl)-3-hydroxy-3-methyltriazene

l-(o-Carboxyphenyl)-3-hydroxy-3-methyltriazene is proposed as an excellent reagent for the spectrophotometric determination of iron(III) and titanium(IV), and also for the separation of titanium from a large quantity of iron as well as other cations and anions. Iron(III) forms an anionic violet 1:2 complex at pH 4.0–9.4, and a cationic green 1:1 complex at pH 1.5–2.0, with absorption maxima at 570 nm and 660 nm, respectively. The violet complex is quantitatively extracted in chloroform containing n-octylamine at pH 3.0–9.0. The green and the violet iron(III) complexes obey Beer's law, the respective optimal ranges being 8.9–35.8 and 3.9–11.2 p.p.m. The yellow titanium chelate extracted into chloroform (absorption maximum at 410 nm) between pH 1.0 and 3.5, can be re-extracted into concentrated sulphuric acid a violet colour being produced with absorption maximum at 530 nm. Beer's law is obeyed in the ranges 0.8–5.7 p.p.m. for the titanium complex in chloroform and 3.4–19.2 p.p.m. when extracted in concentrated sulphuric acid. Interferences from diverse ions are not severe. Procedures for the separation and determination of titanium in the presence of a large quantity of iron are given. The isolation of the iron(III) and vanadium(IV and V) complexes, and their properties, are described.     

Dipole moments of some diphenyl thioethers: Absolute conformation of bis(o-nitrophenyl) sulphide

The electric dipole moments of three diphenyl thioethers have been measured in benzene solution at 25· and the conformational analysis of bis(o-nitrophenyl) sulphide has been carried out by vector addition. The results show that this compound exists in a twisted conformation with the phenyl rings considerably rotated from coplanarity with respect to the C-S-C plane and indicate that in o,o′-disubstituted derivatives of diphenyl sulphide steric rather than conjugative effects operate in determining the conformational preference.     

On the alkaloids of strychnos—xxxvi: The alkaloids of strychnos hirsuta spruce exbentham; two new β-carbolinic alkaloids,strychnohirsutine and tetradehydrostrychnohirsutine

The structures and configurations of two new β-carbolinic alkaloids, strychnohirsutine 1 and tetra-dehydrostrychnohirsutine 2, isolated from stem and root bark of Strychnos hirsuta, were reported. ¹H NMR data of N,O-diacetylstrychnohirsutine 5 and ¹H and ¹³C NMR data of O-acetyltetradehydrostrychnohirsutine 4 were listed. Alkaloid 1 was converted into 2 by catalytic dehydrogenation.     

The effect of the source pressure on the abundance of ions of noncovalent protein assemblies in an electrospray ionization orthogonal time-of-flight instrument

The effect of elevating the pressure in the interface region of an electrospray ionization orthogonal time-of-flight mass spectrometer on the ion intensity of different noncovalent protein assemblies has been investigated. Elevating the pressure in the interface region generally led to an enhanced detection of high m/z ions. The optimum pressure was found to be dependent on the m/z value of the ions. This pressure effect should be carefully addressed when relating ion abundance in the mass spectra to solution phase abundance of noncovalent protein assemblies.     

Some developments in the chemical direct oxygen determination

This paper discusses modifications of the direct determination of oxygen in organic compounds by reduction with carbon. Two versions are considered, (a) a microscale method for compounds containing metals, phosphorus or boron, and including automatic non-aqueous carbon dioxide titration, and (b) a manometric method capable of analysing samples containing traces of oxygen down to 5ppm.     

3'-nitrophenylpropyloxycarbonyl (NPPOC) protecting groups for high-fidelity automated 5' --> 3' photochemical DNA synthesis

[structure: see text]. The most powerful DNA microarrays would be prepared by photolithography with free 3'-ends that could be processed enzymatically. A photoremovable group that could be removed in quantitative yield would ensure high purity of the synthesized probes. We have developed new pyrimidine building blocks for 5' --> 3' DNA synthesis with high cycle yields using the NPPOC (3'-nitrophenylpropyloxycarbonyl) protecting group. These phosphoramidites were proved in automated photochemical DNA synthesis on a modified synthesizer.