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Ceylan, Yusuf; Usta, Keziban; Kunduracioglu, Ahmet; Usta, Ayhan; Cetinkaya, Bekir
doi: 10.1002/mrc.4479pmid: 27377553
1‐Pentamethylbenzyl‐3‐ethylimidazoliumsilver(I)bromide and 1,3‐bis(pentamethylbenzyl)‐4,5dimethylbenzimidazoliumsilver(I)bromide and their Ag+ complexes were synthesized and their polycrystal forms were produced by recrystallization in dichloromethane/Et2O solvent system. Structural determinations were carried out by 1H NMR and 13C NMR with a Varian 400 NMR system using tetramethylsilane as internal standard and CDCl3 as solvent. The disappearance of acidic N‐heterocyclic carbene proton showed the formation of Ag(I) complexes. Also, elemental analyses were carried out. Electron paramagnetic resonance (EPR) measurements were performed to determine the formed radical structure on the samples irradiated at the room temperature for 72 h by using 60Co‐source with dose rate of 0.680 kGy. The EPR measurements were carried out in the temperature range of 200 K–450 K. Identical radicals were determined on the irradiated compounds. It was observed that the shapes of the spectra of the samples were independent of the temperature but, the resonance line intensities changed linearly with the temperature. Also, it was detected that the free radical on the 1‐pentamethylbenzyl‐3‐ethylimidazoliumsilver(I)bromide is not stable compared to that on the 1,3‐bis(pentamethylbenzyl)‐4,5dimethylbenzimidazoliumsilver(I)bromide. Copyright © 2016 John Wiley & Sons, Ltd.
Aliaga, Carolina; Rezende, Marcos Caroli; Mena, Geraldine
doi: 10.1002/mrc.4485pmid: 27412810
A series of 4‐alkanoyloxy‐2,2,6,6‐tetramethylpiperidinoxyl radicals was prepared, and their reactivity in water vis‐à‐vis antioxidant Trolox was compared. Spectral (electron paramagnetic resonance) and dynamic‐light‐scattering measurements suggested the formation of micelles for the more hydrophobic members of the series. The observed increase in reactivity for the micelle‐forming radicals reflected the increased local concentration of the radical fragment on the micellar interface. Copyright © 2016 John Wiley & Sons, Ltd.
Meenakumari, V.; Utsumi, Hideo; Jawahar, A.; Milton Franklin Benial, A.
doi: 10.1002/mrc.4489pmid: 27432403
Electron spin resonance and Overhauser‐enhanced magnetic resonance imaging studies were carried out for various concentrations of 14N‐labeled 3‐carbamoyl‐2,2,5,5‐tetramethyl‐pyrrolidine‐1‐oxyl in pure water. Overhauser‐enhancement factor attains maxima in the range of 2.5–3 mm concentration. The leakage factor showed an asymptotic increase with increasing agent concentration. The coupling parameter showed the interaction between the electron and nuclear spins to be mainly dipolar in origin. The electron spin resonance parameters, such as the line width, line shape and g‐factor, were determined. The line width analysis confirms that the line broadening is proportional to the agent concentration, and also the agent concentration is optimized in the range of 2.5–3 mm. The line shape analysis shows that the observed electron spin resonance line shape is a Voigt line shape, in which the Lorentzian component is dominant. The contribution of Lorentzian component was estimated using the winsim package. The Lorentzian component of the resonance line attains maxima in the range of 2.5–3 mm concentration. Therefore, this study reveals that the agent concentration, line width and Lorentzian component are the important factors in determining the Overhauser‐enhancement factor. Hence, the agent concentration was optimized as 2.5–3 mm for in vivo/in vitro electron spin resonance imaging and Overhauser‐enhanced magnetic resonance imaging phantom studies. Copyright © 2016 John Wiley & Sons, Ltd.
Kumar, Rohitesh; Lu, Yuting; Elliott, Alysha G.; Kavanagh, Angela M.; Cooper, Matthew A.; Davis, Rohan A.
doi: 10.1002/mrc.4482pmid: 27379746
Previous investigations of the aerial parts of the Australian plant Eremophila microtheca and Syzygium tierneyanum resulted in the isolation of the antimicrobial flavonoid jaceosidin (4) and 2′,6′‐dihydroxy‐4′‐methoxy‐3′,5′‐dimethyl chalcone (7), respectively. In this current study, compounds 4 and 7 were derivatized by acetylation, pivaloylation, and methylation reactions. The final products, 5,7,4′‐triacetoxy jaceosidin (10), 5,7,4′‐tripivaloyloxy jaceosidin (11), 5,7,4′‐trimethoxy jaceosidin (12), 2′,6′‐diacetoxy‐4′‐methoxy‐3′,5′‐dimethyl chalcone (13), 2′‐hydroxy‐4′‐methoxy‐6′‐pivaloyloxy‐3′,5′‐dimethyl chalcone (14), and 2′‐hydroxy‐4′,6′‐dimethoxy‐3′,5′‐dimethyl chalcone (15) were all fully characterized by NMR and MS. Derivatives 10 and 13 have been previously reported but were only partially characterized. This is the first reported synthesis of 11 and 14. The natural products and their derivatives were evaluated for their antibacterial and antifungal properties, and the natural product, jaceosidin (4) and the acetylated derivative, 5,7,4′‐triacetoxy jaceosidin (10), showed modest antibacterial activity (32–128 µg/ml) against Staphylococcus aureus strains. Copyright © 2016 John Wiley & Sons, Ltd.
Zhang, Xiao‐Hui; Xu, Yao‐Zhong
doi: 10.1002/mrc.4501pmid: 27529164
Systematic NMR characterization of 4‐thio‐5‐furan‐pyrimidine nucleosides or 4‐thio‐5‐thiophene‐pyrimidine nucleosides (ribonucleosides and 2′‐deoxynucleosides) was performed. All proton and carbon signals of 4‐thio‐5‐thiophene‐ribouridine and related analogues were unambiguously assigned. The orientations of the base (4‐thiouridine or its deoxy analogue) relative to the ring (furan or thiophene) are explored by a NMR approach and further supported by X‐ray crystallographic studies. The procedures presented here would be applicable to other modified nucleosides and nucleotides. Copyright © 2016 John Wiley & Sons, Ltd.
Tchoukoua, Abdou; Kuiate Tabopda, Turibio; Uesugi, Shota; Kimura, Ken‐ichi; Kwon, Eunsang; Momma, Hiroyuki; Ngadjui, Bonaventure Tchaleu; Koseki, Takuya; Shiono, Yoshihito
doi: 10.1002/mrc.4504pmid: 27546306
Phytochemical investigation of the roots of Albizia chevalieri led to the isolation of two new 5‐deoxyflavan‐3,4‐diol glucosides from roots of A. chevalieri, Chevalieriflavanosides A and B. Their structures were established by 2D NMR techniques, UV, IR, CD, and mass spectrometry. Cytotoxicity of the two compounds was evaluated against acute promyelocytic leukemia HL60 cells. The antibacterial activities of 1 and 2 also were evaluated against Pseudomonas aeruginosa and Staphylococcus aureus using the agar diffusion test. Copyright © 2016 John Wiley & Sons, Ltd.
Cohen, Ryan D.; Saurí, Josep; Huff, Chelsea A.; Krska, Shane W.; Martin, Gary E.
doi: 10.1002/mrc.4470pmid: 27396947
1,1‐ADEQUATE is a powerful and robust NMR experiment to establish carbon–carbon connectivities using modest sample quantities when cryogenic probe technology is available. Yet potential pitfalls of applying this method are not widely appreciated, such as weak or missing 1JCC correlations in strongly coupled 13C‐13C AB spin systems and unusually large multi‐bond (nJCC) correlations associated with particular functional groups. These large nJCC correlations observed in 1,1‐ADEQUATE spectra could be mistaken for 1JCC correlations. Copyright © 2016 John Wiley & Sons, Ltd.
Schiaffino‐Ortega, Santiago; Kimatrai‐Salvador, María; Baglioni, Eleonora; Gallo, Miguel Angel; Entrena Guadix, Antonio; Lopez‐Cara, Luisa Carlota
doi: 10.1002/mrc.4468pmid: 27402422
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