Metal binding characteristics of a laterally nonsymmetric aza cryptand upon functionalization with a pi-acceptor group

The laterally nonsymmetric aza cryptand synthesized by condensing tris(2-aminoethyl)amine (tren) with tris[[2-(3-(oxomethyl)phenyl)oxy]ethyl]amine readily forms mononuclear inclusion complexes with both transition and main-group metal ions. In these complexes, the metal ion occupies the tren-end of the cavity making bonds with the three secondary amino and the bridgehead N atoms. When a strong pi-acceptor group such as 2,4-dinitrobenzene is attached to one of the secondary amines, the binding property of the cryptand changes drastically. When perchlorate or tetrafluoroborate salts of Ni(II), Cu(II), Zn(II), or Cd(II) are used, the metal ion enters the cavity which can be monitored by the hypsochromic shift of the intramolecular charge-transfer transition from the donor amino N atom to the acceptor dinitrobenzene. However, in the presence of coordinating ions such as Cl(-), N(3)(-), and SCN(-), the metal ion comes out of the cavity and binds the cryptand outside the cavity at a site away from the dinitrobenzene moiety. Four such complexes are characterized by X-ray crystallography. Thus, a metal ion can translocate between inside and outside of the cryptand cavity depending upon the nature of the counter anion.     

Photocontrolled On‐Surface Pseudorotaxane Formation with Well‐Ordered Macrocycle Multilayers

The photoinduced pseudorotaxane formation between a photoresponsive axle and a tetralactam macrocycle was investigated in solution and on glass surfaces with immobilized multilayers of macrocycles. In the course of this reaction, a novel photoswitchable binding station with azobenzene as the photoswitchable unit and diketopiperazine as the binding station was synthesized and studied by NMR and UV/Vis spectroscopy. Glass surfaces have been functionalized with pyridine‐terminated SAMs and subsequently with multilayers of macrocycles through layer‐by‐layer self assembly. A preferred orientation of the macrocycles could be confirmed by NEXAFS spectroscopy. The photocontrolled deposition of the axle into the surface‐bound macrocycle‐multilayers was monitored by UV/Vis spectroscopy and led to an increase of the molecular order, as indicated by more substantial linear dichroism effects in angle‐resolved NEXAFS spectra.     

A built-in force actuator for active control of lateral rotor vibration in cage induction electrical machines

In this paper means of active control of radial rotor vibrations in electrical machines are considered. We examine a built-in force actuator for active generation of force on the machine rotor. The operation of the actuator is based on electromechanical interaction between the rotor and the stator of the machine. The actuator is given a low-order linear state-space model, which is identified by using simulation data obtained from a detailed time-stepping finite element model of the machine. Simulation results obtained by using real machine data and finite element time-stepping method are presented.     

Particle-into-liquid sampler on-line coupled with solid-phase extraction-liquid chromatography–mass spectrometry for the determination of organic acids in atmospheric aerosols

In the present study, sample collection and preparation were directly integrated with a chromatographic system by coupling a particle-into-liquid sampler for the first time on-line with solid-phase extraction-liquid chromatography–tandem mass spectrometry. Several organic acids, such as adipic, hydroxyglutaric, mandelic, vanillic, cis-pinonic, pinic, azelaic and sebacic, were used in the research. For sample pretreatment and concentration, strong anion exchange material was used in the extraction. Sampling, extraction and analysis conditions were optimized to obtain reliable information about aerosol chemical composition. To evaluate the performance of the on-line coupled system, half of each sample was analysed on-line and the other half was derivatized and analysed off-line by gas chromatography–mass spectrometry. Comparison of the two techniques with use of t-test showed the results to be in an excellent agreement. Limits of detection of studied acids in on-line system were between 0.1 and 0.9 ng. The on-line coupled system is fast and reliable and a promising tool for the real time analysis of organic acids in atmospheric aerosols.     

Solid-phase extraction of organic compounds in atmospheric aerosol particles collected with the particle-into-liquid sampler and analysis by liquid chromatography-mass spectrometry

Atmospheric aerosol particles, collected with the particle-into-liquid sampler at SMEARII station in Finland in mid-August 2007, were analysed for biogenic acids. The sample pretreatment method, comprising solid-phase extraction with anion exchange and hydrophilic-lipophilic balance materials, was optimized. Extraction efficiencies of solid-phase extraction from 10 and 20 ml samples were about 100%, with average relative standard deviation of 8.9%, in concentration range from 12.5 to 50 ng/ml of the acid. Extraction of aldehydes was less successful, with efficiencies from 69 to 163% and average 10% deviation. Pretreated samples were analysed by reversed phase high performance liquid chromatography with ion trap mass spectrometric detection. Limits of detection achieved for organic acids with the analytical procedure developed ranged from 9 to 27 μg/l of extracted sample, while limits of quantitation were from 31 to 90 μg/l. Oxidation with ozone was used for the preparation of the acid of β-caryophyllene (β-caryophyllinic acid), which was also studied in aerosol samples. MS² experiments were used to confirm the identification of trans-pinic, trans-pinonic and β-caryophyllinic acids. Azelaic, hexadecanoic, cis-pinonic, and cis- and trans-pinic acids were quantitated in the samples with use of authentic standards, while the concentrations of trans-pinonic and β-caryophyllinic acids were determined with cis-pinonic acid as surrogate. Also, the contribution of β-caryophyllene oxidation products to aerosol organic carbon was evaluated. Aldehydes could not be analysed in real samples due to the insufficient extraction. The particle-into-liquid sampler proved to be suitable for the collection of aerosol particles for the elucidation of daily and diurnal variation of selected species. The optimized sample pretreatment, together with the analysis method, offer a promising approach for the study of aerosol chemical composition, where artifact formation is minimal and time resolution is good.     

Acylation of (<Emphasis Type="Italic">R,S</Emphasis>)-1-phenylethanol with ethyl acetate over an immobilized enzyme

Acylation of (R,S)-1-phenylethanol, which is a product of acetophenone hydrogenation, over a Pd-supported catalyst, was studied in ethyl acetate with an immobilized lipase. It was demonstrated that in the presence of hydrogen and Pd/C in the reaction medium the (R,S)-1-phenylethanol acylation rate is not hindered, whereas the selectivity was strongly altered in the latter case, leading to significant amounts of side products.     

Changes of methylated silica surfaces on ageing

Silica rendered hydrophobic by organosilanes is a widely used model material in colloid chemistry, biological research, catalysis, etc. However, it is often overlooked that the surface properties of silica, and silica made hydrophobic be reacting with silane, change with time when the substrate is immersed in aqueous solution. Therefore the experimental conditions when such model systems are employed have to be carefully assessed. This paper summarizes the findings of the force measurement tests between air bubbles and silica particles hydrophobized with organosilanes such as trimethylchlorosilane and 1,1,1,3,3,3-hexamethyl-disilazane. The results showed that the attractive forces as well as the adhesion between the air bubbles and silica particles decrease with the time of aging in aqueous solution. The silica surfaces rendered hydrophobic with organosilanes become hydrophilic with time due to hydration. The hydrophobicity could be restored by heating the samples at 190?^○C. The atomic force microscopy imaging on silica plates revealed that in addition to hydration, decomposition of the organosilane layer also takes place.     

Equipping metallo-supramolecular macrocycles with functional groups: assemblies of pyridine-substituted urea ligands

A series of di-(m-pyridyl)-urea ligands were prepared and characterized with respect to their conformations by NOESY experiments and crystallography. Methyl substitution in different positions of the pyridine rings provides control over the position of the pyridine N atoms relative to the urea carbonyl group. The ligands were used to self-assemble metallo-supramolecular M(2)L(2) and M(3)L(3) macrocycles which are generated in a finely balanced equilibrium in DMSO and DMF according to DOSY NMR experiments and ESI FTICR mass spectrometry. Again, crystallography was used to characterize the assemblies. Methyl substitution in positions next to the pyridine nitrogen prevents coordination, while the other ligands form small metallo-supramolecular macrocycles. The incorporated urea carbonyl groups provide hydrogen bonding sites which converge towards the center of the assemblies.