Stereochemistry in cationic polymerization of alkenyl ethers. I. 1H- and 13C-NMR spectra of poly(propenyl ethers)

Benzyl, ethyl, and deuterated ethyl propenyl ethers (BzPE, EPE, and EPE-d₅, respectively) with different cis/trans isomer ratios were polymerized by BF₃O(C₂H₅)₂ at ?78°C in toluene, methylene chloride, and nitroethane solvents. Poly(propenyl alcohol) [poly(PA)] was also prepared by treating poly(BzPE) with HBr gas. The steric structure of these polymers was studied by ¹H- and ¹³C-NMR spectroscopy. The poly(EPE-d₅) obtained from a trans-rich monomer mixture was crystalline, while one from a cis-rich monomer mixture was amorphous. Poly(BzPE) was always amorphous. Poly(BzPE), poly(PA), and poly(EPE-d₅) gave ¹H-NMR spectra with two β-methine peaks, relative intensities of which depended on the geometric structure of the monomers. Their spectra of β-methyl protons decoupled from β-methine proton were also split into two peaks, relative intensities of which corresponded to those of the two α-methine peaks. ¹³C-NMR spectra of α-OCH₂ and β-CH₃ of poly(EPE), respectively, consisted of two peaks. These observations show that the poly(propenyl ethers) examined, whether crystalline or amorphous, have only two dyad structures (probably threo or erythro-meso and racemic), and that their α- and β-carbons have the same dyad structure, irrespective of the kind of the alkoxyl groups.     

Stereoelective cationic polymerization of propenyl ether by asymmetric catalysts

In order to elucidate the possibility of stereoelective cationic polymerization (asymmetric selective polymerization) of olefinic monomers, racemic cis- and trans-1-methylpropyl propenyl ether and racemic 1-methylpropyl vinyl ether were polymerized by asymmetric alkoxyaluminum dichlorides. In the polymerization of racemic cis-1-methylpropyl propenyl ether with (?)-menthoxyaluminum dichloride in toluene at ?78°C, the polymer obtained showed a positive optical activity, and the residual monomers were converted by BF₃OEt₂ into a polymer having a negative optical activity. Thus, the stereoelective polymerization of racemic cis-1-methylpropyl propenyl ether was beyond any doubt attained in homogeneous cationic polymerization. In the polymerization of the trans isomer by the same catalyst, an optically active polymer was hardly formed. In the polymerization of racemic 1-methylpropyl vinyl ether which has no β-methyl group, stereoelectivity was not observed at all. The cis-1-methylpropyl propenyl ether did not produce an optical active polymer in the polymerization catalyzed by (S)-1-methylpropoxyaluminum dichloride or (S)-2-methylbutoxyaluminum dichloride under the same polymerization conditions.     

Isolation of the intermetallic compounds Al2Cu, Al12Mg17 Al3Fe, Al9Co2 and Al3Ni in binary aluminium alloys by application of an organic solvent

Summary For the isolation of the intermetallic compounds Al₂Cu, Al₁₂Mg₁₇, Al₃Fe, Al₉Co₂ and Al₃Ni in their binary alloys a new method is proposed: Sample alloy particles are placed in a flask with a methanolic solution of benzoic acid (20% wt.), oxine (5% wt.), chloroform (20% vol.) and sodium hydroxide (0.02% wt.). After sufficient time of agitation, the intermetallic compounds remain quantitatively in the solution.

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Isolierung der intermetallischen Verbindungen Al₂Cu, Al₁₂Mg₁₇, Al₃Fe, Al₉Co₂ und Al₃Ni aus binären Aluminiumlegierungen mit Hilfe eines organischen Lösungsmittels

Zusammenfassung Zur Isolierung der intermetallischen Verbindungen aus den entsprechenden binären Legierungen wird die Probe mehrere Stunden bis Tage unter Rühren mit einer methanolischen Lösung von Benzoesäure (20%), Oxin (5%), Chloroform (20%) und Natriumhydroxid (0,02%) behandelt. Hierbei wird die Matrix aufgelöst und die intermetallischen Verbindungen bleiben zurück.

     

Ion chromatographic separation of alkali metal and ammonium cations on a C18 reversed-phase column

The separation of alkali metal (Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺) and ammonium cations on a C₁₈ reversed-phase column using three anionic surfactants [sodium 1-eicosyl sulphate, sodium dodecyl benzenesulphonate and sodium dodecyl sulphate (SDS)] is described. Two methods were examined: (a) “permanent” coating, with the use of a C₁₈ reversed-phase column previously coated with the surfactants; and (b) dynamic coating, with addition of the surfactants to the mobile phase. With method (a) the separation of the six cations was achieved with SDS. However, the retention times gradually decreased owing to dissolution of the SDS coating. Good separation was obtained with method (b), where 10 mM HNO₃ containing 0.1 mM SDS was used as the mobile phase with conductivity detection, and it was applied satisfactorily to real samples. The effect of system peaks on determination is also discussed.     

Synthesis of optically active af‐(1‐Ethyl‐3‐methylhexahydro‐1,3‐diazin‐5‐yl)‐ and N‐(1‐Ethyl‐5‐methyloctahydro‐1,5‐diazocin‐3‐yl)pyridine‐3‐carboxamides

As part of the structure‐activity relationship of the dopamine D₂ and serotonin 5‐HT₃ receptors antagonist 1, which is a clinical candidate with a broad antiemetic activity, the synthesis and dopamine D₂ and serotonin 5‐HT₃ receptors binding affinity of (R)‐5‐bromo‐N‐(1‐ethyl‐3‐methylhexahydro‐1,3‐diazin‐5‐yl)‐ and (R)‐5‐bromo‐N‐(1‐ethyl‐5‐methyloctahydro‐1,5‐diazocin‐3‐yl)‐2‐methoxy‐6‐methylaminopyridine‐3‐carboxam‐ides ( 2 and 3 ) are described. Treatment of 1‐ethyl‐2‐(p‐toluenesulfonyl)amino‐3‐methylaminopropane dihy‐drochloride ( 4a ) with paraformaldehyde and successive deprotection gave the 5‐aminohexahydro‐1,3‐diazine 6 in excellent yield. 3‐Amino‐1‐ethyl‐5‐methyloctahydro‐1,5‐diazocine ( 15 ) was prepared from 2‐(benzyloxycarbonyl)amino‐3‐[[N‐(tert‐butoxycarbonyl)‐N‐methyl]amino]‐1‐ethylaminopropane ( 9 ) through the intramolecular amidation of (R)‐3‐[N‐[(2‐benzyloxycarbonylamino‐3‐methylamino)propyl]‐N‐ethyl]aminopropionic acid trifluoroacetate ( 12 ), followed by lithium aluminum hydride reduction of the resulting 6‐oxo‐1‐ethyl‐5‐methyloctahydrodiazocine ( 13 ) in 41% yield. Reaction of the amines 6 and 15 with 5‐bromo‐2‐methoxy‐6‐methylaminopyridine‐3‐carboxylic acid furnished the desired 2 and 3 , which showed much less potent affinity for dopamine D₂ receptors than 1 .     

Collision-induced reactions of size-selected molecular cluster anions

Collision-induced reactions of size-selected cluster anions, (CO₂) _n ^? and (N₂O)_nO^? with He and Kr atoms were studied at collision energies from 0.1 to 2.0 eV (center-of mass) by means of a tandem mass-spectrometer equipped with a pair of octapole ion guides. The dominant process was evaporation of the constituent molecules from the parent cluster ion. The absolute cross section for the evaporation was measured as functions of the size of the parent cluster ion and the collision energy. The reaction was explained by collisional excitation of the parent cluster ion followed by its unimolecular dissociation. The observed cross sections which correspond to those for the collisional excitation agree with those calculated in terms of charge-induced dipole and induced dipole-induced dipole interactions between the parent cluster ion and the target atom. The distributions of the product ions resulting from the unimolecular dissociation were reproduced by a simple calculation based on RRK theory. In the collision of (CO₂) _n ^? , the cross sections for (CO₂) ₁₀ ^? and (CO₂) ₁₄ ^? were significantly small and their abundances in the product ion distributions were particularly large. These findings indicate that (CO₂) ₁₀ ^? and (CO₂) ₁₄ ^? are stable species. On the other hand, stable species in (N₂O)_nO^? was found to be (N₂O)₅O^?.     

High-sensitivity capillary gel electrophoretic analysis of DNA fragments on an electrophoresis microchip using electrokinetic injection with transient isotachophoretic preconcentration

The research adopted a single-channel microchip as the probe, and focused electrokinetic injection combined with transient isotachophoresis preconcentration technique on capillary electrophoresis microchip to improve the analytical sensitivity of DNA fragments. The channel length, channel width and channel depth of the used microchip were 40.5 mm, and 110 and 50 μm, respectively. The separation was detected by CCD (charge-coupled device) (effective LENGTH=25 mm, 260 nm). A 1/100 diluted sample (0.2 mg/l of each DNA fragment) of commercially available stepladder DNA sample could be baseline separated in 120 s with S/N=2–5. Compared with conventional chip gel electrophoresis, the proposed method is ideally suited to improve the sensitivity of DNA analysis by chip electrophoresis.     

Impact of reservoir potentials on the analyte behavior in microchip electrophoresis: computer simulation and experimental validation for DNA fragments

Fundamental understanding of the impact of reservoir potentials on the analyte behavior on the microfluidic chips is an important issue in microchip electrophoresis (MCE) for suitable injection and separation of analytes, since the applied potentials may significantly affect the shape of sample plug, sample leakage from the injection channel to the separation channel, injected sample amount, and separation efficiency. This study addressed this issue for the case of a conventional cross-geometry microchip with four reservoirs using computer simulations, the results of which were verified by the analysis of DNA fragments. For the microchip with a definite structure and migration distance, the injected sample amount was shown to be the vital parameter for improving the limit of detection and resolution. During injection, the shape of the sample plug could be adjusted by varying the reservoir potentials. It was demonstrated that a "magnified injection" (applying high voltage on the three reservoirs to the sample reservoir) is useful to enhance the detection sensitivity depending on the analyte composition, although such injection was previously avoided because of introducing too large amounts of the analyte in comparison with two established modes, floating and pinched injection. Optimal magnified injection was proved to improve the sensitivity for about 4 times over that of pinched injection for the analysis of DNA step ladders using microchip gel electrophoresis (MCGE). Sample leakage of DNA fragments could be suppressed by applying a high positive voltage on injection channel during separation, but the voltage degraded the injected amount and resolution.     

Collisional process involving atomic cluster ions

Collision of Ar cluster ions, Ar _n ⁺ (n=3–16), with He and Ne atoms was investigated by use of mass spectroscopic techniques. The cross sections for the production of Ar _n ⁺ (nn) were measured as functions of the size of the parent cluster ion and the collision energy (0.1–10 eV in the center-of-mass frame). These results were analyzed in the scheme of hard-sphere spectator collision with RRK theory. It was concluded that the reaction proceeds via collisional excitation of the parent cluster ion and following sequential loss of the constituent Ar atoms.This paper was originally submitted in connection with the 2nd. Int. Conference on Atomic and Nuclear Clusters held in Santorini from 28. June-2. July 1993 and is published here as a regular article after an independent refereeing procedure according to the standards of Z. Phys. D     

Sensitive determination of anions in saliva using capillary electrophoresis after transient isotachophoretic preconcentration

A transient isotachophoresis-capillary electrophoresis (tITP-CE) system for the determination of minor inorganic anions in saliva is described. The complete separation and quantification of bromide, iodide, nitrate, nitrite, and thiocyanate has been achieved with only centrifugation and dilution of the saliva sample. In-line tITP preconcentration conditions, created by introduction of the plugs of 5 mM dithionic acid (leading electrolyte) and 10 mM formic acid (terminating electrolyte) before and after the sample zone, respectively, allowed the limits of direct UV absorption detection (at 200 nm) to be up to 50-fold improved as compared with CE without tITP. As a result, nitrate and thiocyanate were still detectable at 4.6 and 3.8 μg l⁻¹, respectively, in 1000 times diluted saliva. The daily variations of anionic concentrations in saliva samples taken from a smoking health volunteer were discussed based on the results of tITP-CE analysis. It was confirmed that the thiocyanate concentration in saliva noticeably increased after smoking. This is apparently the first report on simultaneous quantification of more than four anionic salivary constituents using CE.