Zur Elektronenstruktur von Phosphor(III)-p-π-Bindungssystemen: UV- und PE-spektroskopische Untersuchungen an Methylenphosphanen vom Typ R?PC(SiMe3)2

On the Electronic Structure of Phosphorus(III)-p-π-Bonded Systems: UV and PE Spectroscopic Investigation of Phosphaalkenes R? P?C(SiMe₃)₂ UV and He-I-p.e. spectra of phosphaalkenes R? P?C(SiMe₃)₂ 3 (R = Cl, F, OBu^t, SBu^t, NHBu^t, NHSiMe₃, NEt₂, NPr₂ⁱ, 2, 2, 6, 6-Me₄C₅H₆N, N(Bu^t)SiMe₃, N(SiMe₃)₂, Me, Bu^t) are discussed. Assignment of π(P?C)- and n(P) ionization potentials agrees with UV data as well as semiempirical MNDO calculations. The alkyl-substituted species 31, m exhibit an inverse sequence of π(P?C) and n(P)-i.p.'s compared to theoretical predictions and recent spectroscopic studies, due to the π-electron accepting effect of the silyl substituents. Introduction of RO and RS substituents results in formation of a mesomeric 3-center-4-electron-π-system. Two different conformers of amino-phosphaalkenes can be distinguished which depend on the steric demand of the substituent, and differ in the orientation of the amine ligand in relation to the plane of molecular symmetry. Coexistence of both isomers is proved in case of 3h by temperature dependant UV studies. The existence of conformational isomerism provides an explanation for the remarkable differences in n.m.r. data of 3e – k .     

Formation of the N-methylpyridinium derivative to improve the detection of buprenorphine by liquid chromatography-mass spectrometry

The legally defensible identification of the narcotic, analgesic buprenorphine, in biological specimen requires considerable sensitivity due to its low therapeutic dosages and corresponding target concentrations. Application of liquid chromatography-electrospray ionisation-mass spectrometry, which became the default method for buprenorphine detection, is impeded by the disadvantageous fragmentation of the stable precursor ion producing unspecific product ions of comparatively low abundance. A chemical modification to form the N-methylpyridinium ether derivative of buprenorphine is presented to improve the selectivity and sensitivity of its detection by liquid chromatography-mass spectrometry (LC-MS). The reaction of buprenorphine with 2-fluoro-1-methyl-pyridinium-p-toluene-sulfonate and triethylamine as catalyst was accomplished in acetonitrile at an ambient temperature yielding a chemically stable derivative. Fragmentation of the permanently charged precursor ion (m/z = 559) leads to the formation of diagnostic and abundant fragments (e.g. m/z = 443 and 450) representing all parts of the molecule. The application of the technique to the identification of buprenorphine in hair samples demonstrates a high specificity, availability of sufficient qualifier ions and a significant (approximately 8-fold) improvement of detection limits with respect to comparable experiments based on underivatised buprenorphine.     

On reachable states in boundary control for the heat equation,and an associated moment problem

We derive a new necessary and sufficient condition for solvability of a moment problem involving real exponentials, which arises in control theory for the heat equation; this allows one to identify some novel situations for which the moment problem is solvable. Moreover, we prove a theorem in the context of boundary control for the heat equation, which allows one to construct new reachable states from known reachable states; as a corollary this implies that all polynomial functions of the space variables are reachable. Finally, we show also that trigonometric polynomials (and certain related functions involving real exponentials) are also reachable.This author wishes to thank the Mathematics Department at McGill University for its support and hospitality during the period in which this paper was completed.This work was supported by the Natural Sciences and Engineering Research Council of Canada Grant A7271.