Molecular mobility of nitroxide spin probes in glassy polymers. Quasi‐libration model

ESR spectra of three spin probes with different molecular volumes: 2,2,6,6‐tetramethyl‐4‐oxopiperidine‐1‐oxyl, di‐p‐anisylnitroxide, and nitroxide derivative of fullerene in glassy polystyrene, polyvinyl trimethylsilane, and Teflon AF‐2400 were calculated numerically within the model of quasi‐libration motions. Temperature ranges, where the model is capable to reproduce spectra within experimental errors, were defined. It was found that simulation of X‐band ESR spectra allows to determine quasi‐libration amplitudes around molecular axes X and Y with accuracy ～ 3° and around Z axis with accuracy ～ 15–20°. A shape of distribution of quasi‐libration amplitudes was also determined qualitatively by ESR spectra simulations. It was established that the average amplitude of quasi‐libration motion depends on the free volume of each polymer and geometrical molecular volume of a spin probe. Quasi‐libration amplitudes increase as the temperature increases, and reach the value of 40 degrees. We found that upon further temperature increase, quasi‐libration model becomes inapplicable for quantitative numerical spectra simulation. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 107–120, 2009     

Mechanistic diversity of the van Leusen reaction applied to 6-ketomorphinans and synthetic potential of the resulting acrylonitrile substructures

Tosylmethyl isocyanide was used to convert 7,8-didehydro-6-ketomorphinans to 6,7-didehydromorphinan-6-carbonitriles with retainment of the 4,5-epoxy ring. However, ring opening occurred in the presence of NaH giving 5,6,7,8-tetradehydromorphinan-6-carbonitriles. Addition of nucleophiles such as Li diisopropylamide or Grignard reagents to the acrylonitrile substructure yielded ring-opened 5,6-didehydro products. Seven products were characterized by X-ray crystal structure analysis and revealed insight into the mechanistic diversity of the van Leusen reaction.     

Synthese von benzanellierten Carbacephamen 2.Mitt.

Summary The treatment of 2-(oxo-1-azetidinyl)-benzyltriphenylphosphponium salts9 and13b,c,d, ande with base leads to carbacephemes10 and14b,c,d, ande which can be reduced to the title compounds. The reaction of14 with acids does not result in 3-oxocephames by cleavage of the enolether function. Instead, the 3-alkoxyquinolines15b andc have been obtained.

     

Facile Synthesis of New Areneboronates as Terminal Ethyne Monomers

Summary. N-Methyliminodiethyl 2-ethynylbenzeneboronate was obtained by lithiation of phenylacetylene, addition of trimethyl borate, hydrolysis, and azeotropic condensation with N-methyl diethanolamine. 4-(Cyano-(4-ethynylphenylamino)methyl)benzeneboronate was prepared by a facile and efficient procedure from 4-ethynylaniline and N-methyliminodiethyl 4-formylbenzeneboronate, followed by scandium-catalyzed cyanation. These terminal ethyne monomers were shown to undergo β-insertion with a Schrock metathesis catalyst to yield boronic acid-functionalized oligomers.     

UV LASER INDUCED RNA-PROTEIN CROSSLINKS AND RNA CHAIN BREAKS IN TOBACCO MOSAIC VIRUS RNA in situ

The efficiency of RNA-protein crosslink and RNA chain break formation under nanosecond or picosecond UV-laser pulse irradiation of tobacco mosaic virus was determined. It was found that on high-intensity UV-laser irradiation the quantum yields of both reactions increase considerably as compared to the usual (low-intensity) UV-irradiation. The RNA-protein crosslink quantum yield was found to be 1.8 x 10(-5) and 1.2 x 10(-4) and that of RNA chain breaks 1.7 x 10(-4) and 8.9 x 10(-4) for nanosecond and picosecond irradiation, respectively.