Studies on intramolecular nh-bridging in aromatic compounds. Part 3 [1–3]

A study was made of the use of calcium oxide as a catalyst at a temperature of 400–700° for the dehy-drocyclization of four primary arylamines: 2-aminobiphenyl, 1-aminotriphenylene (5c) , 2-phenoxyaniline, and N-(2-aminophenyl)pyrrole. Maximal yields of cyclized products isolated were 53% (carbazole), 52% (4H-naphtho[1,4-def]carbazole), 18% (phenoxazine), and 0%, respectively. Comparison is made with reported cyclizations of the corresponding nitro and azido starting materials. In one case, treatment of I-nitrotriphenylene with triethyl phosphite produced mainly diethyl N-(1-triphenylenyl)phosphoramidate (51%). Mono- and hemihydrochlorides of 5c are described. A mechanism for the catalyzed dehydrocy-clization is proposed.     

Phenylated polyimides: Diels-Alder reaction of biscyclopentadienones with dimaleimides

A series of phenylated polydihydrophthalimides has been synthesized by the Diels-Alder reactions of 3,3′-(oxydi-p-phenylene)bis(2,4,5-triphenylcyclopentadienone) and 3,3′-(p-phenylene)bis(2,4,5-triphenylcyclopentadienone) with N,N′-o-, -m-, and -p-phenylenedimaleimide. The polydihydrophthalimides were soluble in dimethylformamide (DMF) and had intrinsic viscosities that ranged from 0.33 to 1.01, the polymers were dehydrogenated thermally and chemically to afford the corresponding phenylated polyphthalimides. The totally aromatic polyimides were also soluble in DMF but had intrinsic viscosities only as high as 0.41. The thermogravimetric analyses of the polyphthalimides showed breaks near 530°C in air and in nitrogen atmospheres.     

Geometric prequantization on the spin bundle based onN-symplectic geometry: The dirac equation

We present preliminary results for a prequantization procedure that leads in a natural way to the Dirac equation. The starting point is the recently introducedn-symplectic geometry on the bundle of linear framesLM of ann-dimensional manifoldM in which the ⁿ-valued soldering 1-form onLM plays the role of then-symplectic potential. On a 4-dimensional spacetime manifold we consider the tensorial ⁴⁴valued function onLM determined by the spacetime metric tensor g as the Hamiltonian for free observers and determine the associated ⁴-valued Hamiltonian vector field , Integration of theX ⁱ yields the dynamics of free observers on spacetime, namely parallel transport of linear frames along spacetime geodesies. In order to obtain a vector field on the spin bundleSM which is a lift of and which is induced by a vector field for an appropriate mapping , it is useful to define a prolongation of some bundleL ^o M of oriented frames ofM. IfGL ⁺(4, ) denotes the identity component ofGL(4, ), thenGL ⁺(4, ) is the structure group ofL ^o M and its double cover is the structure group of. We show that the lift of onL ^o M to induces a natural 4-symplectic potential on. If is the lift of g to, then we find the ⁴-valued Hamiltonian vector field on determined by and show that the vector fieldsX _g ⁱ on are tangent to the subbundleSM. Integration of the restriction of theX ⁱ toSM now yields parallel transport of spin frames and thus tetrads along spacetime geodesies of g. We consider a naive prequantization operator assignment acting on ⁴-spinors in the standard representation ofSL(2, ). The eigenvalue equation for the system of new Hilbert space operators yields the Dirac equation.     

Complete curve fitting of extraction profiles for estimating uncertainties in recovery estimates

This paper reports the use of improved numerical approaches to modelling extraction profiles, and shows that the approach substantially reduces statistical prediction uncertainties compared to those obtained on the basis of a three-point extrapolation from the later part of the extraction curve. Numerical fitting of manually obtained polycyclic aromatic hydrocarbon extraction data to a spherical particle diffusion model showed uncertainties typically reduced by a factor of three (with extremes at 1.02 and 770). Application to pressurised fluid extraction study of pelletised poly(vinylchloride) containing 30 mass% di(2-ethylhexyl)phthalate also showed good improvements. However, this high precision data showed small but significant lack of fit resulting in residual correlation and visibly biased prediction (more so than simple extrapolation). Re-fitting and uncertainty estimation using a first-order autoregression approximation to the covariance matrix produced more realistic uncertainty estimates and closer parameter estimates and is accordingly recommended for treating residual correlation from other causes, but did not entirely alleviate the problem. Different shape models (spherical, plane sheet and cylindrical) were applied without accounting fully for fitting error, and particle size effects were eliminated by modelling a simple size distribution. However, an approximate model based on linearly concentration-dependent diffusion coefficient showed excellent fit, confirming concentration-dependence as the most likely cause. This semiempirical model led to an uncertainty in total extractable material, at 0.2% of the total extractable value (with allowance for correlation). This is potentially good enough for recovery estimation and correction in certification of reference materials for validation purposes.     

Collisional behaviour of electronically excited silicon atoms,Si(3p2(D1D2)), by atomic absorption spectroscopy

The collisional behaviour of electronically excited silicon atoms in the optically metastable 3p²(¹D₂) state (0.781 eV) is investigated by time-resolved resonance absorption in the ultraviolet. Si(3 ¹D₂) was generated by the repetitive pulsed irradiation of SiCl₄ at λ > 165 nm in a flow system, and monitored by attenuation of resonance radiation at λ = 288.16 nm (4s(¹P⁰₁) ← ep²(¹D₂)) using signal averaging. Absolute second-order rate constants (k_R, cm³ molecule^?1 s^?1, 300 K) are reported for the gases: H₂[(8.1 ± 1.5) × 10^?11], O₂[(2.3 ± 0.4) × 10^?11], He (? 10^?15) and SiCl₄ [(2.9 ± 0.4) × 10^?10]. These results are compared with the analogous data reported hitherto for Si(3³P_J) and Si(3 ¹S₀). Those for H₂ and O₂ are discussed within the context of symmetry arguments on the nature of the potential surfaces involved using the weak spin orbit coupling approximation. Finally, pulsed stimulated emission operating on the transition Si(3P²)(¹So → ¹D₂) (λ = 1.0995 μ) was not detected in high energy pulse experiments using a confocal cavity, despite the population inversion between Si(3 ¹S₀ and Si(3 ¹D₂) observed by resonance absorption following the photolysis of SiCl₄.     

Lysine peroxycarbamates: free radical-promoted peptide cleavage

Strategies are reported that combine in one step a predictable chemical-based protein digestion with mass spectrometry. Lysine residue amino groups in peptides and proteins are modified by reaction with a peroxycarbonate derived from p-nitrophenol, and tert-butyl hydroperoxide. The peroxycarbonate reacts with lysine residues in peptides and proteins, and the resulting lysine peroxycarbamates undergo homolytic fragmentation under conditions of low-energy collision-induced dissociation (CID). Observed fragmentation of the peptides involves apparent free radical processes including Hofmann-L?ffler-type rearrangements that lead to peptide chain fragmentation. Strategies for directed cleavage of peptides by free radical promoted processes are feasible, and such strategies may well simplify schemes for protein analysis.     

Synthesis of phenylated phthalimides. The diels-alder reaction of tetraphenylcyclopentadienone with maleimides

A series of phenylated dihydrophthalimides has been synthesized by the Diels-Alder reaction of tetraphenylcyclopentadienone with maleimide, N-phenylmaleimide, and N,N'-o-, -m-, and -p-phenylenedimaleimide. Subsequent dehydrogenation of these compounds yielded the corresponding phenylated phthalimides. These phthalimides were also obtained in one step when the initial reactions were carried out in refluxing nitrobenzene.     

Comparison of capillary electrophoresis with traditional methods to analyse bovine whey proteins

The separation of the four major whey proteins by sodium dodecyl sulphate (SDS)-capillary gel electrophoresis (CGE) is described. Whilst commercially purified whey proteins could be analysed using the recommended protocol, the more complex nature of an acid whey and a reconstituted whey protein concentrate (WPC) powder necessitated considerable refinement of the CGE sample buffer. Individual whey proteins in the acid whey and WPC samples were then also separated and quantitated using capillary zone electrophoresis, polyacrylamide gel electrophoresis (PAGE) and HPLC methods and the results were compared. The values obtained for -lactalbumin (-Lac) and β-lactoglobulin (β-Lg) were consistent throughout the various methods, although size-exclusion HPLC, SDS-PAGE and SDS-CGE could not separate the two β-Lg variants or the glycosylated form of -Lac from the β-Lg. There was considerable variation in the values for the bovine serum albumin and immunoglobulin determined by the different methods and it was concluded that none of the methods could satisfactorily quantitate all four whey proteins.