Enantioselective gas chromatographic assays with electron-capture detection for methoxyphenamine and its three primary metabolites in human urine

Sensitive and enantioselective gas chromatographic assays have been developed and applied to the quantitation in human urine of the enantiomers of methoxyphenamine and its three primary oxidative metabolites, namely, N-desmethylmethoxyphenamine, O-desmethylmethoxyphenamine and 5-hydroxymethoxyphenamine. The separation of the various analytes was achieved through the combined use of high-resolution gas chromatography coupled with electron-capture detection and employing a capillary OV-225 column. The formation of diastereometric derivatives involved the chiral acylating reagent N-heptafluorobutyryl-L-prolyl chloride. The assays for methoxyphenamine and O-desmethylmethoxyphenamine were linear over the range 0.25-2.0 micrograms/ml for each analytes' enantiomers, while in the case of the enantiomers for N-desmethylmethoxyphenamine and 5-hydroxymethoxyphenamine linearity was shown over the ranges 0.094-0.75 and 0.188-1.5 micrograms/ml, respectively. The mean coefficients of variation in all cases were less than 4%.     

ABSORPTION AND EMISSION STUDIES OF ELECTRONIC STATES OF N-ARYLBENZAMIDES

Abstract— Absorption and emission spectra of several N-arylbenzamides have been measured. The quantum yields for their fluorescence were found to be dependent on matrix viscosity and temperature. Singlet-triplet splittings for these compounds were determined from their emission spectra and found to be abnormally small for π. π* states (˜ 1500 cm^-1). Indeed, the phosphorescence maxima of N-arylbenzamides occur slightly to the blue relative to their fluorescence maxima. Intersystem crossing efficiencies were determined for several of these compounds and are consistent with S₁→ S ₀ radiationless decay.     

Kinetics of Dissociation of tris-{3-(2-pyridyl)-5,6-bis(2-furyl)-1,2,4-triazine}iron(II)

The kinetics of base hydrolysis of the low-spin iron(II)-diimine complex [Fe(fertri)₃]²⁺, where fertri=3-(2-pyridyl)-5,6-bis(2-furyl)-1,2,4-triazine, as a function of hydroxide concentration, solvent composition (water; aqueous MeOH), and pressure are reported. Rate constants are also reported for dissociation of the [Fe(fertri)₃]²⁺ cation in 50–64% MeOH, determined from replacement of the fertri ligands by 1,10-phenanthroline. The reactivity of this fertri complex is compared with reactivities of a selection of other iron(II)-diimine complexes and, where possible, their ligand-sulfonated derivatives. The activation volume for base hydrolysis of [Fe(fertri)₃]²⁺ is +10.7 cm³ mol⁻¹, in 40% MeOH.     

Molecular dynamics study of the surface tension of a binary immiscible fluid

The planar interface between two liquids having two degrees of affinity to mix has been studied by molecular dynamics simulations. The surface tension is calculated from the normal, PN, and transverse, PT, components of the pressure tensor P for a wide range of temperatures. An unusual increase in surface tension with increasing temperature is attributed to a pressure induced void transfer mechanism that is justified by basic thermodynamic arguments. This effect is diminished on the addition of a modest attractive potential between the two species, and there is a turnover point at higher temperatures beyond which the surface tension decreases with increasing temperature. An order parameter is identified as the gradient of the mole fraction distribution through the interfacial region. An additional effect is the dramatic inversion of the kinetic and potential contributions to the PN profile as the temperature is varied. It is found that a commonly used approximation for P, the Irving-Kirkwood 1 or IK1 method, results in a relatively modest unphysical variability in PN that weakly violates the condition of local mechanical stability. However, this artifact does not prevent the IK1 method from producing an interfacial tension which is nearly identical to that derived from the complete IK formula with no additional approximations.     

Halo- and azidodediazoniation of arenediazonium tetrafluoroborates with trimethylsilyl halides and trimethylsilyl azide and sandmeyer-type bromodediazoniation with Cu(I)Br in [BMIM][PF6] ionic liquid

Reaction of [ArN(2)][BF(4)] salts immobilized in [BMIM][PF(6)] ionic liquid (IL) with TMSX (X = I, Br) and TMSN(3) represents an efficient method for the preparation of iodo-, bromo-, and azido-derivatives via dediazoniation. The reactions can also be effected starting with ArNH(2) by in situ diazotization with [NO][BF(4)] followed by reaction with TMSX or TMSN(3). Depending on the substituents on the benzenediazonium cation, competing fluorodediazoniation (ArF formation) and hydrodediazoniation (ArH formation) were observed. Dediazoniation with TMSN(3) and with TMSI generally gave the highest chemoselectivity toward ArN(3) and ArI formation. The IL was recycled and reused up to 5 times with no appreciable decrease in the conversions. Multinuclear NMR monitoring of the interaction of [ArN(2)][BF(4)]/TMSX, [BMIM][PF6]/TMSX, and [BMIM][PF(6)]/TMSX/[ArN(2)][BF(4)] indicated that TMSF is formed primarily via [ArN(2)][BF(4)]/TMSX, generating [ArN(2)][X] in situ, which gives ArX on dediazoniation. Competing formation of ArF in Sandmeyer-type bromodediazoniation of [ArN(2)][BF(4)] with Cu(I)Br immobilized in the IL points to significant involvement of heterolytic dediazoniation.     

Can Dispersion Forces Govern Aromatic Stacking in an Organic Solvent?

Experimental support for the dominance of van der Waals dispersion forces in aromatic stacking interactions occurring in organic solution is surprisingly limited. The size‐dependence of aromatic stacking in an organic solvent was examined. The interaction energy was found to vary by about 7.5 kJ mol⁻¹ on going from a phenyl–phenyl to an anthracene–pyrene stack. Strikingly, the experimental data were highly correlated with dispersion energies determined using symmetry‐adapted perturbation theory (SAPT), while the induction, exchange, electrostatic, and solvation energy components correlated poorly. Both the experimental data and the SAPT‐dispersion energies gave high‐quality correlations with the change in solvent accessible area upon complexation. Thus, the size‐dependence of aromatic stacking interactions is consistent with the dominance of van der Waals dispersion forces even in the presence of a competing polarizable solvent.     

How to find all roots of complex polynomials by Newton’s method

We investigate Newton’s method to find roots of polynomials of fixed degree d, appropriately normalized: we construct a finite set of points such that, for every root of every such polynomial, at least one of these points will converge to this root under Newton’s map. The cardinality of such a set can be as small as 1.11 d log² d; if all the roots of the polynomial are real, it can be 1.30 d. Oblatum 24-II-2000 & 14-II-2001?Published online: 20 July 2001