m-Diethynylbenzene macrocycles: syntheses and self-association behavior in solution

m-Diethynylbenzene macrocycles (DBMs), buta-1,3-diyne-bridged [4(n)]metacyclophanes, have been synthesized and their self-association behaviors in solution were investigated. Cyclic tetramers, hexamers, and octamers of DBMs having exo-annular octyl, hexadecyl, and 3,6,9-trioxadecyl ester groups were prepared by intermolecular oxidative coupling of dimer units or intramolecular cyclization of the corresponding open-chain oligomers. The aggregation properties were investigated by two methods, the (1)H NMR spectra and the vapor pressure osmometry (VPO). Although some discrepancies were observed between the association constants obtained from the two methods, the qualitative view was consistent with each other. The analysis of self-aggregation by VPO revealed unique aggregation behavior of DBMs in acetone and toluene, which was not elucidated by the NMR method. Namely, the association constants for infinite association are several times larger than the dimerization constant, suggesting that the aggregation is enhanced by the formation of dimers (a nucleation mechanism). In polar solvents, DBMs aggregate more strongly than in chloroform due to the solvophobic interactions between the macrocyclic framework and the solvents. Moreover, DBMs self-associate in aromatic solvents such as toluene and o-xylene more readily than in chloroform. In particular, the hexameric DBM having a large macrocyclic cavity exhibits extremely large association constants in aromatic solvents. By comparing the aggregation properties of DBMs with the corresponding acyclic oligomers, the effect of the macrocyclic structure on the aggregation propensity was clarified. Finally, it turned out that DBMs tend to aggregate more readily than the corresponding phenylacetylene macrocycles, acetylene-bridged [2(n)]metacyclophanes, owing to the withdrawal of the electron density from the aromatic rings by the butadiyne linkages which facilitates pi-pi stacking interactions.     

Synthesis of 2-arylpyrido[3,4-b]pyrazine derivatives through condensation of 3,4-diaminopyridine with β-keto sulfoxides

The reaction between 3,4-diaminopyridine and α-methylsulfinylacetophenone in benzene containing acetic acid under reflux gave 2-phenylpyrido[3,4-b]pyrazine. In this way, 2-(4-methoxyphenyl)pyrido[3,4-b]-pyrazine and 2-(3,4-dimethoxyphenyl)pyrido[3,4-b]pyrazine were obtained by condensation of 3,4-diaminopyridine with the corresponding α-methylsulfinylacetophenones.     

Syndiotactic 1,2-polybutadiene with Co-CS2 catalyst system. IV. Mechanism of syndiotactic polymerization of butadiene with cobalt compounds–organoaluminum–CS2

A mechanism is proposed for the polymerization of syndiotactic 1,2-polybutadiene (s-PB) with soluble cobalt-organoaluminum-CS₂. The proposed active species have structures which consist of side-on coordination of CS₂ to cobalt, anti-π-allyl growing end, cisoid bidentate coordination of butadiene, and activation by complex formation with organoaluminum at the nonbonded sulfur of the coordinated CS₂. This proposal is based on findings for the aluminum-free catalyst Co(C₄H₆)(C₈H₁₃)-CS₂. It is tentatively interpreted that syndiotactic 1,2 polymerization proceeds under the influence of the side-on coordinated CS₂, by which the reactivity between the terminal carbons of butadiene and the C3 of the π-allyl end is enhanced.     

Excitation-energy migration in self-assembled cyclic zinc(II)-porphyrin arrays: a close mimicry of a natural light-harvesting system

The excitation-energy-hopping (EEH) times within two-dimensional cyclic zinc(II)-porphyrin arrays 5 and 6, which were prepared by intermolecular coordination and ring-closing metathesis reaction of olefins, were deduced by modeling the EEH process based on the anisotropy depolarization as well as the exciton-exciton annihilation dynamics. Assuming the number of energy-hopping sites N = 5 and 6, the two different experimental observables, that is, anisotropy depolarization and exciton-excition annihilation times, consistently give the EEH times of 8.0 +/- 0.5 and 5.3 +/- 0.6 ps through the 1,3-phenylene linkages of 5 and 6, respectively. Accordingly, the self-assembled cyclic porphyrin arrays have proven to be well-defined two-dimensional models for natural light-harvesting complexes.     

Triethylborane-induced radical allylation reaction with zirconocene-olefin complex

[reaction: see text] Allylzirconium reagents are effective for radical allylation of alpha-halo carbonyl compounds. The key steps would be homolytic cleavage of the zirconium-carbon bond and halogen abstraction by the resulting Cp(2)ZrCl(III). Zirconocene-olefin complex can be also utilized for the allylation of alpha-halo compounds.     

Stereoselective and Enantioselective Syntheses of the Four Stereoisomers of Muscol from (3RS)‐Muscone

Two trans stereoisomers of 3‐methylcyclopentadecanol (=muscol), (1R,3R)‐ 2 and (1S,3S)‐ 2 , were efficiently synthesized from (3RS)‐3‐methylcyclopentadecanone (=muscone; (3RS)‐ 1 ) by a highly stereoselective reduction (Scheme). L‐Selectride^® (=lithium tri(sec‐butyl)borohydride) was used, followed by the enantiomer resolution by lipase QLG (Alcaligenes sp.). The cis stereoisomers of muscol, (1S,3R)‐ 2 and (1R,3S)‐ 2 , were obtained by the Mitsunobu inversion of (1R,3R)‐ 2 and (1S,3S)‐ 2 , respectively (Scheme). The absolute configuration of (1R,3R)‐ 2 was determined by X‐ray crystal‐structure analysis of its 3‐nitrophthalic acid monoester, 2‐[(1R,3R)‐3‐methylcyclopentadecyl hydrogen benzene‐1,2‐dicarboxylate ((1R,3R)‐ 3b ), and by oxidation of (1R,3R)‐ 2 to (3R)‐muscone.     

ESR study of free radicals produced in polyethylene irradiated by ultraviolet light

ESR studies of ultraviolet-irradiated polyethylene (PE) were carried out. Irradiation effects different from those of high-energy radiation are observed. Ultraviolet radiation is absorbed selectively, and especially in carbonyl groups in PE produced by oxidation. Radicals produced were identified as \documentclass{article}\pagestyle{empty}\begin{document}$ \hbox{---} {\rm CH}_2 \hbox{---} {\dot {\rm C}} {\rm H} \hbox{---}{\rm CHO}$\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ \hbox{---} {\rm CH}_2 \hbox{---} {\dot {\rm C}} {\rm H} \hbox{---}{\rm CH}_2 \hbox{---}$\end{document}. Some radicals giving a quintet signal stable at room temperature were also observed but remained unidentified. The radical \documentclass{article}\pagestyle{empty}\begin{document}$ \hbox{---} {\rm CH}_2 \hbox{---} {\dot {\rm C}} {\rm H} \hbox{---}{\rm CHO}$\end{document} undergoes a mutual conversion with the acyl radical:      

Development of a stable isotope dilution UPLC‐MS/MS method for quantification of dexmedetomidine in a small amount of human plasma

Dexmedetomidine (Dex) is a selective central α2‐agonist with anesthetic properties and has been used in clinical practice for sedation in the intensive care unit (ICU) after operations. In this study, an analytical assay for the determination of Dex in a small amount of plasma was developed for the application to pediatric ICU trials. The quantification of Dex was constructed using the original stable isotope Dex‐d₃ for electrospray ionization‐tandem mass spectrometry (ESI‐MS/MS) in the selected reaction monitoring mode. A rapid ultra‐performance liquid chromatography technique was adopted using ESI‐MS/MS with a runtime of 3 min. Efficacious concentration levels (50 pg/mL to 5 ng/mL) could be evaluated using a very small amount of plasma (10 μL) from patients. The lower limit of the quantification was 5 pg/mL in the plasma (100 µL). For sample preparation, a solid‐phase extraction was used along with the OASIS‐HLB cartridge type. Recovery values ranged from 98.8 to 100.3% for the intra‐ [relative standard deviation (RSD), 0.9–1.3%] and inter‐ (RSD, 0.9–1.5%) day assays. A stable test had recovery values that ranged from 97.8 to 99.7% with an RSD of 1.0–1.9% for the process/wet extract, bench‐top, freeze–thaw and long‐term tests. This method was used to measure the Dex levels in plasma from pediatric ICU patients. In the clinical ICU trial, the small amount of blood (approximate plasma volume, 200 μL) remaining from blood gas analysis was reused and targeted for the clinical analysis of Dex in plasma. Copyright © 2013 John Wiley & Sons, Ltd.     

Oxygen-Binding Profile of the Iron Porphyrin Complex Embedded in Polymerized Liposome: Effect of the Polymerized Liposome on the Stability and the Oxygen-Binding Ability of the Iron Porphyrin Complex

5,10,15,20-Tetra(α,α,α,α, -o-(2′, 2′-dimethyl-20′-(2′ α-trimethylammonioethyl)phosphonatoxyeicosanamido)phenyl)porphinatoiron(II) (lipidheme) complex embedded in polymerized liposome was prepared by polymerizing l-(9-(p-vinylbenzoyl)nonanoyl)-2-O-octadecyl-rac-glycero-3-phosphocholine in the presence of lipid-heme under ultraviolet irradiation. The polymerization proceeded rapidly, and the reduction of the hemin to the heme occurred spontaneously during the polymerization. The lipid-heme complex embedded in the polymerized liposome bound molecular oxygen reversibly under physiological conditions (pH 7, 37°C) and was chemically, physically, and mechanically stable during storage for a long period and even in a high-speed flow system. The oxygen-binding affinity was not affected by the type of medium due to the effect of the rigid polymerized liposome.