Effects of ligands on the “living” radical polymerization initiated by the aged Cr2+ plus benzoyl peroxide system

The “living” radical polymerization of methyl methacrylate with the aged Cr²⁺ plus benzoyl peroxide (BPO) system in the presence of various amines as ligand has been studied in N,N′-dimethylformamide. Aliphatic amines such as ethylenediamine diminished the rate of polymerization, while dipyridyl (dipy) and o-phenanthroline (phen) accelerated the polymerization rate as follows: phen > dipy > pyridine ? none. Specifically, the rate of polymerization in the presence of phen had a maximum value at [phen]/[Cr²⁺] = 0.5. The retardation of polymerization by aliphatic amines was explained by the interaction of BPO with free and coordinated amines. The latter result may support the mechanism involving the complexed radical proposed for the living radical polymerization with the aged Cr²⁺ + BPO system. In the presence of phen the effects of aging period and aging temperature as well as polymerization temperature were studied and the nature of complexed radicals is discussed.     

The cosmological term and a modified Brans-Dicke cosmology

Adding the cosmological term , which is assumed to be variable in this paper, to the Brans-Dicke Lagrangian, we try to understand the meaning of the term and to relate it to the mass of the universe. We also touch upon the Dirac large-number hypothesis, applying the results obtained from the application of our theory to a uniform cosmological model.     

Application of pure silica gel as cation-exchange stationary phase in lon chromatography with indirect photometric detection for common mono-and divalent cations using aromatic monoamines as eluents

Summary A pure silica gel (Pia Seed 5S-60-SIL), synthesized by the hydrolysis of pure tetraethoxysilane [Si(OCH₂CH₃)₄], was applied as a cation-exchange stationary phase in ion chromatography with indirect photometric detection for common mono-and divalent cations (Li⁺, Na⁺, NH₄ ⁺, K⁺, Mg²⁺, and Ca²⁺) using various protonated aromatic monoamines (tyramine [4-(2-aminethyl) phenol], benzylamine, phenylethylamine, 2-methylpyridine and 2,6-dimethylpyridine) as eluet ions. When using 0.75 mM tyramine-0.25 mM oxalic acid-1.5 mM 18-crown-6 (1,4,7,10,13,16-hexaoxacyclooctadecane) at pH 5.0 as the eluent, excellent simultaneous separation and highly sensitive detection at 275 nm for these mono-and divalent cations were achieved on the Pia Seed 5S-60-SIL column (150×4.6 mm I.D.) in 20 min.     

Evidence of conformational equilibrium of 1-ethyl-3-methylimidazolium in its ionic liquid salts: Raman spectroscopic study and quantum chemical calculations

Raman spectra of liquid 1-ethyl-3-methylimidazolium (EMI+) salts, EMI(+)BF4-, EMI(+)PF6-, EMI(+)CF3SO3-, and EMI(+)N(CF3SO2)2-, were measured over the frequency range 200-1600 cm(-1). In the range 200-500 cm(-1), we found five bands originating from the EMI+ ion at 241, 297, 387, 430, and 448 cm(-1). However, the 448 cm(-1) band could hardly be reproduced by theoretical calculations in terms of a given EMI+ conformer, implying that the band originates from another conformer. This is expected because the EMI+ involves an ethyl group bound to the N atom of the imidazolium ring, and the ethyl group can rotate along the C-N bond to yield conformers. The torsion energy for the rotation was then theoretically calculated. Two local minima with an energy difference of ca. 2 kJ mol(-1) were found, suggesting that two conformers are present in equilibrium. Full geometry optimizations followed by normal frequency analyses indicate that the two conformers are those with planar and nonplanar ethyl groups against the imidazolium ring plane, and the nonplanar conformer is favorable. It elucidates that bands at 241, 297, 387, and 430 cm(-1) mainly originate from the nonplanar conformer, whereas the 448 cm(-1) band does originate from the planar conformer. Indeed, the enthalpy for conformational change from nonplanar to planar EMI+ experimentally obtained by analyzing band intensities of the conformers at varying temperatures is practically the same as that evaluated by theoretical calculations. We thus conclude that the EMI+ ion exists as either a nonplanar or planar conformer in equilibrium in its liquid salts.     

The first synthesis of a methano[60]fullerene with an electron-donating group at the methano-bridge carbon: synthesis and reaction of aminomethano[60]fullerene

[reaction: see text] Aminomethano[60]fullerene was synthesized for the first time as a trifluoromethanesulfonic acid salt by applying the Curtius rearrangement of azidocarbonylmethano[60]fullerene as the key reaction. Aminomethano[60]fullerene thus obtained was found to be able to react with various acyl chlorides to afford the corresponding amides.     

Aromaticity of planar boron clusters confirmed

Low-energy boron clusters are characterized by two-dimensional geometry. Aromaticity of these planar boron clusters was established in terms of topological resonance energy (TRE). All planar boron clusters were found to be highly aromatic with large positive TREs even if they have 4n pi-electrons. Aromaticity must therefore be the origin of unusual planar or quasi-planar geometry. Thus, the aromaticity concept is as useful in boron chemistry as it is in general organic chemistry. It is evident that the Hückel 4n + 2 rule of aromaticity should not be applied to such polycyclic pi-systems. Some of the boron clusters are in the triplet electronic state to attain higher aromaticity. Multivalency and electron deficiency of boron atoms are responsible for lowering the energies of low-lying pi molecular orbitals and then for enhancing aromaticity. For polycyclic pi-systems, paratropicity does not always indicate antiaromaticity.     

Photolabile and paramagnetic reagents for the investigation of transmembrane signaling events.

To investigate the dynamics of membrane processes that may be integral components of specific transmembrane signaling events we have synthesized several novel paramagnetic probes and their photoreactive counterparts. The structure of these probes was designed to (1) restrict "flipping" across the membrane bilayer; (2) contain paramagnetic or photoreactive moieties that could be placed at specific depths within the bilayer; (3) provide information about membrane structure as well as dynamics of protein movement; and (4) in the case of the photoreactive probes, be of high specific radioactivity. The molecules described in this paper consist of amino acid, dipeptide, or carbohydrate groups attached to arylazide- or nitroxide-bearing fatty acids. The synthesis and initial characterization of these membrane probes is described.     

Highly sensitive determination of a polymeric hindered amine light stabilizer in polypropylene by reactive thermal desorption-gas chromatography using nitrogen-specific detection

Highly sensitive and specific determination of trace amounts of a polymeric hindered amine light stabilizer (HALS) in polypropylene (PP) materials could be established by improving reactive thermal desorption-gas chromatography (RTD-GC) in the presence of an organic alkali, tetramethylammonium hydroxide. By using nitrogen-phosphorus detection, highly selective detection of the HALS-related components was attained. In addition, the use of a polar poly(ethylene glycol) separation column alleviated the adsorption of minor specific pyrolysis products. This modified RTD-GC method allowed the determination of the polymeric HALS (Mr 1900) in PP even for trace concentrations between 100 and 500 ppm, through observing selectively the characteristic products containing a tetramethylpiperidine moiety, which had been impossible to detect under the previous RTD-GC conditions using a non-polar separation column and conventional flame ionization detection.