Synthesis and crystal structures of coordination polymers,networks and complexes of an adamantane shaped phosphorus–nitrogen cage ligand and cuprous chloride

Reactions of cuprous chloride with the phosphorus–nitrogen cage ligand 2,4,6,8,9,10-hexamethyl-2,4,6,8,9,10-hexaaza-1,3,5,7-tetraphosphaadamantane, P₄(NCH₃)₆, in acetonitrile form distinct solids depending on the ligand-to-metal ratio. Three structurally characterized compounds include: a solvated 3-D network of formula [P₄(NCH₃)₆]₂(CuCl)₃(CH₃CN)₂; a “ladder-type” polymer {[μ₂-P₄(NCH₃)₆]₂(CuCl)₂}_∞; and a monomeric complex [P₄(NCH₃)₆]₂CuCl. Thermal decomposition of the solvated network results in formation of two more materials [P₄(NCH₃)₆]₂(CuCl)₃, and [P₄(NCH₃)₆](CuCl)₂ that are not isolated from solution reactions. The variety of products isolated based solely on ligand-to-metal ratio suggest that this system participates in solution equilibria common to many phosphorus(III) ligands and multiple solubility equilibria.     

So you think you understand tautomerism?

It appears so simple at first glance, “tautomers are isomers of organic compounds that readily interconvert, usually by the migration of hydrogen from one atom to another”. If a chemist can describe the problem so succinctly, one might question why the complication of tautomerism remains a considerable challenge to cheminformatics and computer-assisted drug design. With a half-century of experience with representing molecules in computers, and almost limitless modern computational power, the problem should have been solved by now. The unfortunate answer is that the frustration and inconvenience of a database search failing to find matches due to differences in the tautomeric forms of the query and registered compounds is but the tip of an iceberg. Prototropic tautomerism, the movement of hydrogens around a molecule, is but just one aspect of an interconnected web of complications. These include mesomerism, aromaticity, protonation state, stereochemistry, conformation, polymerization, photostability, hydrolysis, metabolism and EOCWR (explodes on contact with reality). The common theme is that valence theory, which underlies all modern chemical informatics systems, is an approximate theoretical model for representing molecules mathematically, and, as with all models, it has limitations and domains of applicability. In the physical environments that chemists care about, small organic molecules are often dynamic, existing in multiple equivalent or interconvertible forms. A single connection table can at best represent a snapshot or sample from these populations. Although partial algorithmic solutions exist for handling the most common cases of tautomerism, this perspective hopes to argue that the underlying problems perhaps make tautomerism more complex than it might first appear.     

Analysis of salazinic, norstictic, and usnic acids in Xanthoparmelia chlorochroa by ultra-performance liquid chromatography/tandem mass spectrometry

The lichen species Xanthoparmelia chlorochroa is toxic when consumed by domestic sheep, cattle, and Rocky Mountain elk. Clinical signs exhibited by poisoned animals include red urine, ataxia, and muscular weakness that rapidly progresses to recumbency. Elk are unable to recover once becoming recumbent; however, most affected cattle can recover if offered suitable feed shortly following the onset of signs. At present, the pathogenesis and specific toxin(s) are unknown. As part of an effort to elucidate the proximate toxin, a method using ultra-performance LC coupled to MS/MS with negative-ion electrospray ionization has been developed to compare salazinic, norstictic, and usnic acid concentrations in X. chlorochroa collected from locales associated with lichen poisonings. Compounds were extracted from lichen samples with acetone and sonication. The stationary phase was a Waters Acquity UPLCTM BEH Ca18 (50 x 2.1 mm; 1.7 microm particle size) column. The mobile phase consisted of an acetonitrile-water gradient. The precision of the method was confirmed by an SD below 0.4% (n=9) for triplicate samples. LOD values were 200, 100, and 50 ng/mL for salazinic, norstictic, and usnic acids, respectively.     

Tunability of the optical properties in the Y6(W,Mo)(O,N)12 system

New fluorite-type solid solution domains have been evidenced in the system Y₆(W,Mo)(O,N)₁₂ using precursors prepared by the amorphous citrate route. The oxynitrides as well as the low temperature oxides (600 °C) crystallize in a cubic-type symmetry while the oxides annealed above 1200 °C exhibit a rhombohedral symmetry. Either cationic (W/Mo) or anionic (O/N) substitutions bring the possibility to tune the optical absorption of the yttrium tungstate Y₆WO₁₂, which potential as inorganic UV absorbers is discussed.     

The Regio‐ and Stereoselective Synthesis of trans‐2,3‐Dihydropyridine N‐oxides and Piperidines

Reactivity N? Own : Pyridine N‐oxides can be used for the complete regio‐ and stereoselective synthesis of trans‐substituted piperidines. The sequential addition of Grignard reagents and aldehydes or ketones to pyridine N‐oxides yields a complete regio‐ and stereoselective trans 2,3‐addition reaction in high yields, and the substituted 2,3‐dihydropyridine N‐oxide can be reduced to form 2,3‐trans‐substituted piperidines (see scheme).

     

Normalizers of irreducible subfactors

We consider normalizers of an infinite index irreducible inclusion N⊆M of II₁ factors. Unlike the finite index setting, an inclusion uNu^∗⊆N can be strict, forcing us to also investigate the semigroup of one-sided normalizers. We relate these one-sided normalizers of N in M to projections in the basic construction and show that every trace one projection in the relative commutant N^′∩〈M,eN〉 is of the form u^∗eNu for some unitary u∈M with uNu^∗⊆N generalizing the finite index situation considered by Pimsner and Popa. We use this to show that each normalizer of a tensor product of irreducible subfactors is a tensor product of normalizers modulo a unitary. We also examine normalizers of infinite index irreducible subfactors arising from subgroup-group inclusions H⊆G. Here the one-sided normalizers arise from appropriate group elements modulo a unitary from L(H). We are also able to identify the finite trace L(H)-bimodules in ?²(G) as double cosets which are also finite unions of left cosets.     

A Two-Dimensional Computational Droplet Contact Model

The interaction between capillary fluid films and micro-structural rough surfaces is one of the main challenges in studying self-cleaning mechanisms. The surface behavior of the deformable fluid film is governed by the Young-Laplace equation, which is highly non-linear. Therefore, a numerical solution is introduced using the finite element method, based on a continuum mechanical formulation. Surface and line contact at the fluid-structure interface are modeled by enforcing a contact constraint, and a contact angle, respectively. The numerical solution is validated against the analytical solution of a test case. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Thin film drainage: hydrodynamic and disjoining pressures determined from experimental measurements of the shape of a fluid drop approaching a solid wall

Accurate measurements of the shape of a mercury drop separated from a smooth flat solid surface by a thin aqueous film reported recently by Connor and Horn (Faraday Discuss. 2003, 123, 193-206) have been analyzed to calculate the excess pressure in the film. The analysis is based on calculating the local curvature of the mercury/aqueous interface, and relating it via the Young-Laplace equation to the pressure drop across the interface, which is the difference between the aqueous film pressure and the known internal pressure of the mercury drop. For drop shapes measured under quiescent conditions, the only contribution to film pressure is the disjoining pressure arising from double-layer forces acting between the mercury and mica surfaces. Under dynamic conditions, hydrodynamic pressure is also present, and this is calculated by subtracting the disjoining pressure from the total film pressure. The data, which were measured to investigate the thin film drainage during approach of a fluid drop to a solid wall, show a classical dimpling of the mercury drop when it approaches the mica surface. Four data sets are available, corresponding to different magnitudes and signs of disjoining pressure, obtained by controlling the surface potential of the mercury. The analysis shows that total film pressure does not vary greatly during the evolution of the dimple formed during the thin film drainage process, nor between the different data sets. The hydrodynamic pressure appears to adjust to the different disjoining pressures in such a way that the total film pressure is maintained approximately constant within the dimpled region.     

Matrix-assisted laser desorption/ionization imaging mass spectrometry for direct measurement of clozapine in rat brain tissue

Matrix-assisted laser desorption/ionization hyphenated with quadrupole time-of-flight (QTOF) mass spectrometry (MS) has been used to directly determine the distribution of pharmaceuticals in rat brain tissue slices which might unravel their disposition for new drug development. Clozapine, an antipsychotic drug, and norclozapine were used as model compounds to investigate fundamental parameters such as matrix and solvent effects and irradiance dependence on MALDI intensity but also to address the issues with direct tissue imaging MS technique such as (1) uniform coating by the matrix, (2) linearity of MALDI signals, and (3) redistribution of surface analytes. The tissue sections were coated with various matrices on MALDI plates by airspray deposition prior to MS detection. MALDI signals of analytes were detected by monitoring the dissociation of the individual protonated molecules to their predominant MS/MS product ions. The matrices were chosen for tissue applications based on their ability to form a homogeneous coating of dense crystals and to yield greater sensitivity. Images revealing the spatial localization in tissue sections using MALDI-QTOF following a direct infusion of (3)H-clozapine into rat brain were found to be in good correlation with those using a radioautographic approach. The density of clozapine and its major metabolites from whole brain homogenates was further confirmed using fast high-performance liquid chromatography/tandem mass spectrometry (HPLC-MS/MS) procedures.