Separation of isomers of nitro-polycyclic aromatic hydrocarbons

Since positional isomers of several nitro-polycyclic aromatic hydrocarbons (nitro-PAH) contain widely different mutagenic properties, methods for separating the isomers were investigated. High performance liquid chromatography with dichloromethane in hexane on silica gave the best resolution for the majority of the compounds. A few groups of isomers were better resolved with other modifiers or with reversed phases. Of the reversed phase systems, methanol-water gave better resolution than acetonitrile-water. With dichloromethane/hexane on silica, the retention was found to depend on the presence of a bay nitro group (first), the number of H atoms peri to the nitro group (second), and the length/breadth ratio of the molecule (third). Front electron density calculations were combined with the structure-retention relations in making tentative structure assignments of minor isomers of nitro-PAH.     

Assembling and manipulating two-dimensional colloidal crystals with movable nanomagnets

We study crystallization of paramagnetic beads in a magnetic field gradient generated by one-dimensional nanomagnets. The pressure in such a system depends on both the magnetic forces and the hydrodynamic flow, and we estimate the flow threshold for disassembling the crystal near the magnetic potential barrier. A number of different defects have been observed which fluctuate in shape or propagate along the crystal, and it is found that the defect density increases away from the nanomagnet. We also study the melting of the crystal/fluid system after removal of the nanomagnet and demonstrate that the bond-oriental order parameter decreases with time. The nanomagnet can be moved in a controlled manner by a weak external magnetic field, and at sufficiently large driving velocities we observe self-healing crack formation characterized by a roughening of the lattice as well as gap formation. Finally, when confined between two oscillating nanomagnets, the colloidal crystal is shown to break up and form dipolar chains above a certain oscillation frequency.     

A liquid chromatography-mass spectrometric method for the determination of oak moss allergens atranol and chloroatranol in perfumes

This paper describes a validated liquid chromatographic-tandem mass spectrometric method for quantitative analysis of the potential oak moss allergens atranol and chloroatranol in perfumes and similar products. The method employs LC-MS-MS with electrospray ionization (ESI) in negative mode. The compounds are analysed by selective reaction monitoring (SRM) of 2 or 3 ions for each compound in order to obtain high selectivity and sensitivity. The method has been validated for the following parameters: linearity; repeatability; recovery; limit of detection; and limit of quantification. The limits of detection, 5.0 ng/mL and 2.4 ng/mL, respectively, for atranol and chloroatranol, achieved by this method allowed identification of these compounds at concentrations below those causing allergic skin reactions in oak-moss-sensitive patients. The recovery of chloratranol from spiked perfumes was 96+/-4%. Low recoveries (49+/-5%) were observed for atranol in spiked perfumes, indicating ion suppression caused by matrix components. The method has been applied to the analysis of 10 randomly selected perfumes and similar products.     

Determination of indium in standard rocks by neutron activation analysis

A rapid neutron activation method for the determination of indium in rocks, based on 54 min (116m)In, is described. The method has been applied to a series of geochemical standards including granite G-1 and diabase W-1. The precision is better than +/- 5% for samples containing more than 5 x 10(-10)g indium. Good agreement with previously published values for G-1 and W-1 has been obtained.     

Total syntheses of cross-conjugated carotenals

Total syntheses of the cross-conjugated carotenals renierapurpurin-20-al (χ,χ-caroten-20-al, 2), (2R,2' R)-tetradesoxybacterioruberin-20- al ((2R,2'R)-2,2'- bis-(3-methylbutyl)-3,4,3',4'-tetrahydro-ψ,ψ -caroten-20-al, 3) and (2R,6R,2'R, 6' R)-2,2'dimethyl-decapreno -?,? -caroten -25-al (4) from the common intermediate 8,8'-diapo-20-acetoxycarotene 8,8' dial (5) are described. The cross conjugated 20-(2,3 4-trimethylbenzal)renierapurpurin (16) has also been synthesized     

1,2-Dibromoethyl-trichlorosilane (CH2BrCHBrSiCl3): conformational structure and vibrational properties by gas-phase electron diffraction, infrared and Raman spectroscopy, and ab initio molecular orbital and density functional theory calculations

The molecular structure and conformational properties of 1,2-dibromoethyl-trichlorosilane (CH2BrCHBrSiCl3) have been investigated using gas-phase electron diffraction (GED) data recorded at a temperature of 100 degrees C, together with ab initio molecular orbital (MO) and density functional theory (DFT) calculations, infrared (IR) and Raman spectroscopy in the liquid and solid phases, and normal coordinate analysis (NCA). The molecule exists in the gas- and liquid phases as a mixture of three conformers, gauche(-) [G(-)], with a refined torsion angle phi(BrCCBr)=-71(6) degrees, anti [A], with a torsion angle phi(BrCCBr) approximately -170 degrees , and gauche(+) [G(+)], with a torsion angle phi(BrCCBr) approximately +70 degrees . The second torsion angle of importance, the rotation about the CSi bond, has been refined to a value of +175(13) degrees . Torsion angles were only refined for the more abundant G(-) conformer. In the solid phase, only the G(-) conformer was observed. The temperature-dependent Raman spectra have provided an estimate of the relative conformational entropies, DeltaS. The obtained composition from GED refinements was (%) G(-)/A/G(+)=64(27)/23(13)/13(18) (values with estimated 2sigma uncertainties), giving a conformational stability order in agreement with both the Raman enthalpy measurements and the ab initio MO and DFT calculations using the 6-311G(d) basis set and scaled zero-point energies. Relevant structural parameter values obtained from the GED refinements (with the ab initio HF values used as constraints) were as follows (G(-) values with estimated 2sigma uncertainties): bond lengths (r(g)):r(C-C)=1.501(18)A, r(SiC)=1.865(15)A, r(CBr)=1.965(8)A (average), r(SiCl)=2.028(3)A (average). Bond angles ( anglealpha):angleCCSi=114.1(33) degrees , angleC1C2Br=114.0(21) degrees , angleCSiCl=109.6(7) degrees (average). Experimental IR/Raman and obtained vibrational wavenumbers based on both the unscaled, fixed-scaled as well as the scale-refined quantum-mechanical force fields [HF/6-311G(d)] are presented. The results are discussed and compared with some similar molecules from the literature.     

Water-in-crude oil emulsions from the Norwegian continental shelf

A destabilization study of water-in-crude oil emulsions based on crude oils from the Norwegian Continental Shelf is reported. It is found that medium-chain alcohols (1-butanol and benzyl alcohol) and amines are speeding up the separation of water. The destabilization mechanisms in these two cases seem to be fundamentally different. The alcohols seem to modify the rigidity of the interfacial film by a diffusion/partitioning process while the amines show a strong and specific interaction with interfacial groups, hence hydrophilizing the whole film. Observed trends in the time-dependence of the interfacial tension upon addition of alcohols and amines support these suggestions to destabilization mechanisms. Data for a commercial demulsifier Dissolvan 4455 are also given.     

Determination of copper,gallium and zinc in “standard rocks” by neutron activation

A neutron activation method for the simultaneous determination of copper, gallium and zinc in rocks is described. The method is based on anion-exchange separation steps and measurement of γ-activity. Chemical yields were determined by re-activation. Results for a series of igneous “standard rocks” are presented. The accuracy of the mean values is ca. 5% for concentrations exceeding 10 p.p.m.     

Testing the adequacy of equilibrium models for complex formation Complexation between molybdate and oxalate revisited

In potentiometric studies of metal-ligand equilibria a given model is tested by adjustment of the corresponding stability constants with the purpose of obtaining as good a fit as possible to the experimental data. When judging the goodness-of-fit it is of great importance to be in control of any possible systematic error in concentrations or electrode parameters. The molybdate-oxalate system is used to demonstrate how one crucial parameter influences the evaluations of goodness-of-fit. The system is simple, having only one complex species, MoO(3)oxal(2-), with logarithmic stability constant 13.816 in the pH-range 4-7.