High throughput synthesis of diverse 2,5-disubstituted indoles using titanium carbenoids bearing boronate functionality

A titanium benzylidene complex bearing a boronate group converted resin-bound esters into enol ethers. Suzuki cross-coupling with aryl iodides followed by cleavage with acid completed the solid-phase synthesis of 2,5-disubstituted N-Boc-indoles. Also reported is the use of tert-butyllithium and 2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane to convert an aryl bromide into an arylboronate in the presence of a dithiane, with simultaneous reduction of an aryl azide to an amine.     

Exceptional points in atomic spectra

We report the existence of exceptional points for the hydrogen atom in crossed magnetic and electric fields in numerical calculations. The resonances of the system are investigated and it is shown how exceptional points can be found by exploiting characteristic properties of the degeneracies, which are branch point singularities. A possibility for the observation of exceptional points in an experiment with atoms is proposed.     

Use of harmonic inversion techniques in the periodic orbit quantization of integrable systems

Harmonic inversion has already been proven to be a powerful tool for the analysis of quantum spectra and the periodic orbit orbit quantization of chaotic systems. The harmonic inversion technique circumvents the convergence problems of the periodic orbit sum and the uncertainty principle of the usual Fourier analysis, thus yielding results of high resolution and high precision. Based on the close analogy between periodic orbit trace formulae for regular and chaotic systems the technique is generalized in this paper for the semiclassical quantization of integrable systems. Thus, harmonic inversion is shown to be a universal tool which can be applied to a wide range of physical systems. The method is further generalized in two directions: firstly, the periodic orbit quantization will be extended to include higher order corrections to the periodic orbit sum. Secondly, the use of cross-correlated periodic orbit sums allows us to significantly reduce the required number of orbits for semiclassical quantization, i.e., to improve the efficiency of the semiclassical method. As a representative of regular systems, we choose the circle billiard, whose periodic orbits and quantum eigenvalues can easily be obtained. Received 24 February 2000 and Received in final form 22 May 2000     

Orthomanganated arenes in synthesis VII. Transition-metal mediated formation of a P?P bond; the X-ray crystal structure of Mn2(μ-η1, η1-Ph2PPPh2)(μ-Cl)2(CO)6

The reaction of PPh₂Cl with orthomanganated acetophenone, 2′-CH₃C(O)C₆H₄Mn(CO)₄, gives Mn₂(μ-η₁,η¹-Ph₂PPPh₂)(μ-Cl)₂(CO)₆. An X-ray structure determination [triclinic, space group P1 , a = 10.908(4) Å, b = 11.756(3) Å, c = 12.186(3) Å, α = 96.20(2)°, β = 99.51(2)°, γ = 96.52(2)°] shows two Mn(CO)₃ groups held together by two bridging Cl ligands, and further bridged by a Ph₂P? PPh₂ group prepared in situ.     

Extraction chromatographic separation of carrier-free Tb and Pm generated in (p,xn)-type nuclear reactions

The nuclear reactions of (p, xn)-type, E_p=100–120 MeV, on Gd and Nd have been used to produce highly radioactive preparations of Tb and Pm enriched with neutron-deficient isotopes. Under comparable conditions the yields of practically all isotopes are considerably higher than in Tb and Gd spallation reactions at E_p=660 MeV. The radioactivity of screened¹⁵⁴Tb and¹⁵⁶Tb isotopes has been increased more than 40 times. Tb and Pm were separated from gram amounts of the target-elements by the extraction chromatography technique with undiluted di-(2-ethylhexyl) phosphoric acid as stationary phase. The radiochemical method developed was also applied to separate the radiochemically pure preparation of¹⁶¹Tb from Gd oxide irradiated with thermal neutrons.     

Semiclassical quantization of three-dimensional quasi-Landau resonances under strong-field mixing

Three-dimensional “regular” quasi-Landau resonances, recently discovered experimentally in the Balmer spectrum of the highly excited hydrogen atom around the ionization limit in external static homogeneous magnetic fields, are investigated theoretically by extending previous classical trajectory calculations to semi-classically. Employing the EBK-method for multidimensional non-separable systems, closed trajectories of the excited electron with the proton as origin are quantized by numerical quadrature of the two-dimensional EBK-integral in cylindrical coordinates. The results are resonances with quantum numbersn=1, 2,... for each closed classical trajectory as functions of both the excitation energyE and field strengthB. The calculations include in particular also the classically chaotic region around the ionization limit with experimentally accessible fields, just the region which has so far defied exact quantum mechanical solution. Based on simple physical arguments for the motion of the highly excited electron, an analytic relation is derived for the (E, B)-dependence of the regular three-dimensional resonances which fits quantitatively the numerical EBK-results.     

Determination of phthalate monoesters in human milk,consumer milk,and infant formula by tandem mass spectrometry (LC–MS–MS)

Daily exposure of humans to phthalates may be a health risk because animal experiments have shown these compounds can affect the differentiation and function of the reproductive system. Because milk is the main source of nutrition for infants, knowledge of phthalate levels is important for exposure and risk assessment. Here we describe the development and validation of a quantitative analytical procedure for determination of phthalate metabolites in human milk. The phthalate monoesters investigated were: monomethyl phthalate (mMP), monoethyl phthalate (mEP), mono-n-butyl phthalate (mBP), monobenzyl phthalate (mBzP), mono-(2-ethylhexyl) phthalate (mEHP), and monoisononyl phthalate (mNP). The method is based on liquid extraction with a mixture of ethyl acetate and cyclohexane (95:5) followed by two-step solid-phase extraction (SPE). Detection and quantification of the phthalate monoesters were accomplished by high-pressure liquid chromatography using a Betasil phenyl column (100 mm×2.1 mm×3 m) and triple tandem mass spectrometry (LC–MS–MS). Detection limits were in the range 0.01 to 0.5 g L^–1 and method variation was from 5 to 15%. Analysis of 36 milk samples showed that all these phthalates were present, albeit at different concentrations. Median values (g L^–1) obtained were 0.11 (mMP), 0.95 (mEP), 3.5 (mBP), 0.8 (mBzP), 9.5 (mEHP), and 101 (mNP). We also analysed seven samples of consumer milk and ten samples of infant formula. Only mBP and mEHP were detected in these samples, in the ranges 0.6–3.9 g L^–1 (mBP) and 5.6–9.9 g L^–1 (mEHP).