Photoactive Cryptands. Crystal Structure of the Sodium Cryptate of the Tris(phenanthroline) Macrobicyclic Ligand

The crystal structure of the complex [phen · phen · phen] · NaBr · 2 CHCl₃ of the macrobicyclic ligand 1 has been determined. The complex is of cryptate type, the Na⁺ cation being contained in the molecular cavity of 1 and coordinated to all eight N-atoms. The ligand has a propeller shape and interconverts in solution between the two enantiomeric helical forms.     

Experiments on the hydrodynamics of air-water countercurrent flow through vertical short multitube geometries

A series of experiments were performed to improve understanding of the hydrodynamic mechanisms relevant to the flooding phenomenon in gas-liquid countercurrent flow through vertical short multitube geometries. In addition to the conventional measurements of global hydrodynamic parameters such as phasic flow rates and two-phase pressure drops, the local time-varying thicknesses of the liquid films trickling down the individual tubes were measured by means of conductance probes mounted flush at different locations of the inner wall surfaces. A PC-based data acquisition and analysis system was developed to collect these highly fluctuating data and to make detailed statistical analyses. The experimental results and visual observations revealed two dominant hydrodynamic instability mechanisms that have not been well taken into account by the existing semiempirical models.     

Bi-complement Reducible Graphs

We introduce a new family of bipartite graphs which is the bipartite analogue of the class ofcomplement reduciblegraphs orcographs. Abi-complement reduciblegraph orbi-cographis a bipartite graphG = (W ∪ B, E) that can be reduced to single vertices by recursively bi-complementing the edge set of all connected bipartite subgraphs. Thebi-complementedgraphofGis the graph having the same vertex setW ∪ BasG, while its edge set is equal toW × B − E. The aim of this paper is to show that there exists an equivalent definition of bi-cographs by three forbidden configurations. We also propose a tree representation for this class of graphs.     

Standardized test mixture for the characterization of comprehensive two-dimensional gas chromatography columns: the Phillips mix

A novel column characterization test mixture is developed for use in comprehensive two-dimensional gas chromatography (GC x GC). This mixture has been named the "Phillips mix" in honor of the late professor John B. Phillips, the father of GC x GC. The mixture comprises a series of homologous compounds from structural groups that cover a volatility and polarity range that is similar to the Grob mix, and includes saturated hydrocarbons (alkanes), unsaturated hydrocarbons (alkenes and alkynes), carbonyls (ketones and aldehydes), primary alcohols, fatty acid methyl esters, alkyl ethers, carboxylic acids, aromatics, as well as other unique functional groups (such as amines, etc.). Similarly to the Grob mix in conventional one-dimensional GC, the Phillips mix can be used as a standardized test for performance characterization of GC x GC column sets. Unlike the Grob mix, however, the Phillips mix's most important use is as a practical guideline for column users. This paper addresses some qualitative aspects of the use of the Phillips mix through an investigation of the chromatographic fingerprints of two different GC x GC column combinations.     

Synthesis of 6- to 10-membered ring (E)-hydroxyiminohydroazaazoniabenzocycloalkenes derivative from cyclization of 2-nitromethylene-1-(ω-phenylalkyl)imidazolidine or 2-nitromethylene-1-(ω-phenylalkyl)hexahydropyrimidine in trifluoromethanesulfonic acid

In trifluoromethanesulfonic acid, 2-nitromethylene-1-(ω-phenylalkyl)imidazolidine or 2-nitromethylene-1-(ω-phenylalkyl)hexahydropyrimidine derivatives undergo an intramolecular cyclization to afford (E)-hydroxyiminohydroazaazoniabenzocycloalkenes, in their trifluoromethanesulfonate salt form. The reaction probably occurres via the formation of an electrophilic transient hydroxynitrilium ion (or O-protonated nitrile oxide). The yields are generally good, except for the higher-membered ring derivatives.     

Dielectric behaviour of a molecular liquid mixture in the one-phase precritical region

The temperature dependence of density d, electric permittivity ?_s and nonlinear high field dielectric variation Δ? are reported for various benzonitrile-alkane solutions. For the benzonitrile-isooctane mixtures which exhibit a phase separation in the considered temperature range, the phase diagram has been obtained. In the “homogeneous” one phase region, significant deviations from the normal temperature dependence of d, ?₀, Δ? have been observed and characterize a precritical region of several degrees C above the consolute temperature. These results support the hypothesis of strong precritical orientational interactions or local ordering phenomena. The precritical dielectric behaviour of the benzonitrile-isooctane system is shown to be very different from those of nitrobenzene-alkane or aniline-alkane mixtures.     

Efficient Molecular Catalysis of ATP-Hydrolysis by Protonated Macrocyclic Polyamines

Molecular catalysis of ATP-hydrolysis by a number of protonated macrocyclic polyamines 1–9 has been investigated by ³¹P-NMR spectroscopy, and marked rate enhancements have been obtained. The largest acceleration is produced by the [24]-N₆O₂ macrocycle 1 , and the process displays the following properties: 1. protonated 1 forms very stable complexes with ATP, as well as with ADP and AMP; 2. it enhances the rate of ATP-hydrolysis by a factor of 10³ at pH = 8.5; the rate of hydrolysis is constant over a wide pH-range, from pH = 2.5 to 8.5; 3. 1 is more efficient than acyclic analogues; 4. the products of the reaction are orthophosphate (OP) and ADP, which is subsequently hydrolyzed to OP and AMP at a slower rate; 5. at pH > 6.5, a transient species is detected, which is tentatively identified as a phosphoramidate intermediate, resulting from phosphorylation of the macrocycle 1 ; 6. the reaction presents first-order kinetics and is catalytic. The mechanism of the process is discussed in terms of initial formation of a complex between ATP and protonated 1 , followed by an intracomplex reaction which may involve a combination of nucleophilic or acid catalysis with electrostatic catalysis.