Inverted and suppressed direct response HMQC-TOCSY spectra - a convenient method of spectral editing

HMQC-TOCSY spectra provide a convenient means of establishing proton-proton connectivities in congested spectra of complex aromatic heterocycles. Advantage is taken of the greater dispersion of the ¹³C nmr spectrum to circumvent overlap which would preclude spectral interpretation through the usual COSY spectrum. A recently reported method for inverting direct responses (IDR) in HMQC-TOCSY spectra is demonstrated for [1]benzothieno[2,3-c]naphtho[2,1-g]quinoline. A modification of the IDR-HMQC-TOCSY method is also demonstrated which is capable of fully suppressing direct responses (SDR) without resorting to the timing of the onset of decoupling as in the original report of the HMQC-TOCSY experiment. SDR-HMQC-TOCSY has the further advantage of allowing the use of higher levels of digitization in F₂ than can be attained when broadband heteronuclear decoupling is employed.     

Rapid and sensitive liquid chromatography-tandem mass spectrometry for the quantitation of epirubicin and identification of metabolites in biological samples

A highly sensitive and selective liquid chromatography-mass spectrometry (LC-MS) method has been developed for the determination of epirubicin in serum and cell specimens using daunorubicin as an internal standard. Using atmospheric pressure chemical ionisation (APCI), the epirubicin metabolites were readily distinguishable by their fragmentation pattern in the mass spectrometer. Selected reaction monitoring (SRM) mode was employed for quantitation of epirubicin and the metabolites. Following extraction, chromatography was performed on a C18 column with a mobile phase consisting of water-acetonitrile-formic acid, pH 3.2, with a flow rate of 200 μl/min. The limit of detection (LOD) and the limit of quantitation (LOQ) of this method in serum were determined to be 1.0 and 2.5 ng/ml, respectively. Linearity of the method was verified over the concentration range of 2.5-2000 ng/ml, with a high correlation coefficient (R² ≥ 0.998). For the extraction procedure, an aliquot of 500 μl serum, spiked with internal standard, was extracted using a chloroform-2-isopropanol (2:1, v/v) mixture. The method has been applied to the analysis of epirubicin in cancer cell samples and the identification of known and unknown metabolites in clinical trial patient serum samples.     

The CeO(2)(+) Cation: Gas-Phase Reactivity and Electronic Structure

"Bare" CeO(2)(+) ions can be prepared in the gas phase by consecutive oxidation of Ce(+) with O(2) and NO(2). The ability to activate saturated and unsaturated hydrocarbons is investigated by use of Fourier-transform ion cyclotron resonance mass spectrometry. In the reactions of CeO(2)(+) with linear and branched alkanes C-H bond activation is observed almost exclusively. In contrast, both oxygen-atom transfer and C-H bond activation processes occur when thermalized CeO(2)(+) cations react with simple alkenes and aromatic compounds. C-C bond activation is not observed at all. Insight into the structural and electronic properties of neutral CeO(2) and cationic CeO(2)(+) is provided by means of quasirelativistic density-functional and ab initio pseudopotential calculations. They reveal a (2)Sigma(u)(+) ground state for CeO(2)(+) which is best described as a linear cerium dioxide with a resonating pi bond. Finally, we discuss the influence of oxo ligands on the chemistry of the cationic CeO(n)()(+) (n = 0-2) species toward hydrocarbons.     

Synthesis and crystal structures of heterobimetallic Fe-Cd,Fe-Zn,and Fe-In complexes containing hemilabile phosphorus/oxygen and silicon/oxygen bridging ligands

The reactions of K[Fe{Si(OMe)₃}(CO)₃(PY)][PY=Ph₂PCH₂C(O)Ph, Ph₂PCH₂C(O)[(-C₅H₄)FeCp] (Cp=⁵-C₅H₅), Ph₂P(CH₂)₂CN] with CdCl₂·2.5H₂O, ZnX ₂ (X=Cl, I) or InCl₃ afforded Fe-Cd-Fe or Fe-M(-X)₂ M-Fe (M=Cd, Zn, In;X=Cl, I) and Fe-InCl₂ complexes. Some of them contain an unusual and labile -²-SiO alkoxysilyl bridge which may be associated with a bridging mode for the ketophosphine ligand (first such example structurally established), thus providing original results in bimetallic chemistry on the intramolecular coordination of oxygendonor functions ofchemically different hemilabile ligands firmly attached to a neighboring metal center. The structures of the trinuclear complex (3), of the chlorobenzene solvate of the tetranuclear complex (4a·C₆H₅Cl) and of [mer-(OC)₃{(EtO)₃Si} (4e) have been determined by X-ray diffraction. Crystals of 3 are orthorhombic, space groupPbcn, witha=19.010(4),b=11.766(5),c=26.998(7)Å, andZ=4. Crystals of4a·C₆H₅Cl are monoclinic, space groupC2/c witha=22.455(3),b=17.680(2),c=16.627(4)Å, =90.80(4)°, andZ=4. Crystals of4e are monoclinic, space groupC2/c witha=25.392(5),b=18.554(6),c=16.28(1)Å, =120.73(3)°, andZ=4. The structures were solved using direct methods and Fourier difference techniques and refined by blocked full-matrix least squares toR=0.035 (R _w =0.049) for 2719 observed reflections, toR=0.042 (R _w =0.056) for 3082 observed reflections, and toR=0.057 (R _w =0.075) for 1850 observed reflections for3, 4a·C₆H₅Cl and4e, respectively. The Fe-Zn complexes (9a), (9b) and (9c) were prepared and characterized by spectroscopic methods.Part 21 in the Series: Complexes with Functional Phosphines. Part 20: P. Braunstein, S. Coco Cea, A. DeCian, and J. Fischer (1992).Inorg. Chem. 31, 4203.     

Borel fibrations and G-spaces

Considering discrete groups G only, we present an elementary proof of the familiar equivalence of the category of G-spaces (with maps equivariant up to homotopy) and the category of Borel fibrations over BG.     

Dynamical systems with relaxation time

We define mathematically a class of dynamical systems that exhibit relaxation corresponding to that observed in physical systems, and then show that this class is identical with the class ofK-mixing dynamical systems.     

Symbolic dynamics for the renormalization map of a quasiperiodic Schrödinger equation

A rigorous analysis is given of the dynamics of the renormalization map associated to a discrete Schrödinger operatorH onl ²(), defined byH(n)=(n+1)+(n–1)+Vf(n)(n), whereV is a real parameter,f is a certain discontinuous period-1 function, and is the golden mean. The renormalization map forH is a diffeomorphism,T, of ³, preserving a cubic surfaceS _V . ForV8 we prove that the non-wandering set of the restriction ofT toS _v is a hyperbolic set, on whichT is conjugate to a subshift on six symbols. It follows from results in dynamical systems theory that the optimally approximating periodic operators toH have spectra which obey a global scaling law. We also define a set which we call the pseudospectrum of the operatorH. We prove it to be a Cantor set of measure zero, and obtain bounds on its Hausdorff dimension. It is an open question whether the pseudospectrum coincides with the spectrum ofH.