Complete NMR assignments of bioactive rotameric (3 → 8) biflavonoids from the bark of Garcinia hombroniana

The genus Garcinia is reported to possess antimicrobial, anti‐inflammatory, anticancer, hepatoprotective and anti‐HIV activities. Garcinia hombroniana in Malaysia is used to treat itching and as a protective medicine after child birth. This study was aimed to isolate the chemical constituents from the bark of G. hombroniana and explore their possible pharmacological potential. Ethyl acetate extract afforded one new (1) and six (2–7) known 3 → 8 rotameric biflavonoids. Their structures were elucidated by UV, IR and NMR (1D and 2D) spectroscopy together with electron ionization/ESI mass spectrometric techniques and were identified as (2R, 3S) volkensiflavone‐7‐O‐rhamnopyranoside (1), volkensiflavone (2), 4″‐O‐methyl‐volkensiflavone (3), volkensiflavone‐7‐O‐glucopyranoside (4), morelloflavone (5), 3″‐O‐methyl‐morelloflavone (6) and morelloflavone‐7‐O‐glucopyranoside (7). The absolute configuration of compound 1 was assigned by circular dichroism spectroscopy as 2R, 3S. The coexistence of conformers of isolated biflavonoids in solution at 25 °C in different solvents was confirmed by variable temperature NMR studies. At room temperature (25 °C), compounds 1–7 exhibited duplicate NMR signals, while at elevated temperature (90 °C), a single set of signals was obtained. Compound 5 showed significant in vitro antioxidant activities against 1,1‐diphenyl‐2‐picrylhydrazyl and 2,2′‐azino‐bis‐3‐ethyl benzthiazoline‐6‐sulfonic acid radicals. The antibacterial studies showed that compounds 5 and 6 are the most active against Staphylococcus aureus, Bacillus subtilis and Escherichia coli. Compounds 3 and 6 also showed moderate antituberculosis activity against H₃₈Rv. Based on the research findings, G. hombroniana could be concluded as a rich source of flavanone–flavone (3 → 8) biflavonoids that exhibit rotameric behaviour at room temperature and display significant antioxidant and antibacterial activities. Copyright © 2014 John Wiley & Sons, Ltd.     

Benzothiazole Pyrazoline: Acid-Switchable Absorption and Fluorescence of Photoinduced Electron Transfer (PET)

Journal of Fluorescence - Acid-responsive fluorescent compounds were prepared by introducing an ortho-hydroxyphenyl to pyrazoline with a benzothiazole backbone. These compounds demonstrated normal...     

A Structural Study of Epoxidized Natural Rubber (ENR-50) and Its Cyclic Dithiocarbonate Derivative Using NMR Spectroscopy Techniques

A structural study of epoxidized natural rubber (ENR-50) and its cyclic dithiocarbonate derivative was carried out using NMR spectroscopy techniques. The overlapping ¹H-NMR signals of ENR-50 at δ 1.56, 1.68-1.70, 2.06, 2.15-2.17 ppm were successfully assigned. In this work, the ¹³C-NMR chemical shift assignments of ENR-50 were consistent to the previously reported work. A cyclic dithiocarbonate derivative of ENR-50 was synthesized from the reaction of purified ENR-50 with carbon disulfide (CS₂), in the presence of 4-dimethylaminopyridine (DMAP) as catalyst at reflux temperature. The cyclic dithiocarbonate formation involved the epoxide ring opening of the ENR-50. This was followed by insertion of the C-S moiety of CS₂ at the oxygen attached to the quaternary carbon and methine carbon of epoxidized isoprene unit, respectively. The bands due to the C=S and C-O were clearly observed in the FTIR spectrum while the ¹H-NMR spectrum of the derivative revealed the peak attributed to the methylene protons had split. The ¹³C-NMR spectrum of the derivative further indicates two new carbon peaks arising from the >C=S and quaternary carbon of cyclic dithiocarbonate. All other ¹H- and ¹³C-NMR chemical shifts of the derivative remain unchanged with respect to the ENR-50.     

Re-examination of the structure of calcichrome (calcion) and its complexation with polyaromatic hydrocarbons in water

A non-cyclic tetrameric structure has been suggested for calcichrome (calcion). This structure is consistent with its mass spectrum, proton NMR spectrum, elemental composition and complexing ability with polyaromatic hydrocarbons in water. The stability constants of the 1:1 complexes formed between calcichrome and seven polyaromatic hydrocarbons in water at room temperature have been measured.     

Time growing comparison for ZnO nanorod by using microwave irradiation method

In this study, zinc oxide (ZnO) nanorod were successfully prepared at different growth times (15, 30 and 60 min) using the microwave irradiation method. The ZnO nanorods were simply synthesized at a low temperature (90 °C) with low power microwave assisted heating (about 100 W) and a subsequent ageing process. The synthesized nanorod were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX) and Ultraviolet–Visible spectroscopy (UV–Vis). The FESEM images showed nanorods with diameter ranging between 50 and 150 nm, and length of 150–550 nm. The XRD results indicate that ZnO nanorods of different time of growth exhibits pure wurtzite structure with lattice parameters of 3.2568 and 5.2125 Å. UV–Vis characterization showed that energy gap decreases with increase in time. The result also shows that growth of ZnO at 60 min produces an energy band gap of 3.15 eV. In general, the results of the study confirm that the microwave irradiation method is a promising low temperature, cheap and fast method for the production of ZnO nanostructures.