First isolation of sesquiterpenes and flavonoids from Zingiber spectabile and identification of zerumbone as the major cell growth inhibitory component

Nine sesquiterpenes and eight flavonoids were isolated from Zingiber spectabile for the first time. Structures were determined by spectroscopic methods. The major compound zerumbone (1) was found to be the most active (IC(50) 13 microg mL(-1)) in cell growth inhibitory assay against colon carcinoma SW480 cells.     

Preparation and properties of nanocomposites based on acrylonitrile–butadiene rubber,styrene–butadiene rubber,and polybutadiene rubber

Nanocomposites were prepared with different grades of nitrile rubber with acrylonitrile contents of 19, 34, and 50%, with styrene–butadiene rubber (23% styrene content), and with polybutadiene rubber with Na‐montmorillonite clay. The clay was modified with stearyl amine and was characterized by X‐ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and transmission electron microscopy (TEM). The XRD studies showed an increase in the gallery gap upon the modification of the filler by stearyl amine. The intercalation of the amine chains into the clay gallery gap was confirmed by the presence of some extra peaks (2928, 2846, and 1553 cm^?1) in the FTIR spectra. The clay–rubber nanocomposites were characterized by TEM and XRD. The mechanical properties were studied for all the compositions. An improvement in the mechanical properties with the degree of filler loading up to a certain level was observed. The changes in the mechanical properties, with changes in the nature and polarity of the rubbers, were explained with the help of XRD and TEM results. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1573–1585, 2004     

Unique rheological behavior of rubber based nanocomposites

Montmorillonite clay (N) based nanocomposites were prepared using three different grades of acrylonitrile butadiene rubber (NBR) (19%, 34%, and 50% acrylonitrile contents), styrene butadiene rubber (SBR), and polybutadiene rubber (BR). Rheological study was carried out on these nanocomposites at three different temperatures (110 °C, 120 °C, and 130 °C) over a range of shear rates for comparison. The results showed that the shear viscosity decreased with increasing shear rate and incorporation of the unmodified (N) and the modified (OC) fillers up to a certain loading, when the results were compared with the gum rubber. This effect became more prominent with increasing polarity of the rubber. The die swell, on the other hand, decreased with loading of N and OC. With increasing filler volume fraction, the die swell further decreased. Decrease of viscosity with concomitant decrease of die swell is unique in such systems. Consecutive runs of the same sample over different shear rates increased the viscosity. The results were explained with the help of X‐Ray Diffraction (XRD) data and Transmission Electron Microscopy (TEM).© 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1854–1864, 2005     

Understanding the role of particle size on photophysical properties of CdS:Eu nanocrystals

Here, we report the role of particle size on the photoluminescence (PL) properties of CdS:Eu³⁺ nanocrystals by steady-state and time-resolved PL spectroscopy. It is found that the average decay time 〈τ〉 of undoped CdS nanocrystals increases with increasing the size. The fast component (nanosecond) is assigned due to trapping and slow component (above 10 ns) is due to defect-related emission. The decrease of fast component from 6.6 to 1.32 ns and the slow component from 20 to 14.6 ns of CdS (host) is observed in presence of Eu ions, indicating that the energy transfer occurs from CdS nanoparticles to Eu³⁺ ions. The decay time of Eu³⁺ in CdS shows two decay components (microsecond scale) and we believe that the fast component is attributed to surface-bound Eu³⁺ ions and slow component is due to lattice-bound Eu³⁺ ions. Analysis suggests that PL efficiency of Eu³⁺ ions depends on size of nanoparticles.     

Transition-metal-induced fluorescence resonance energy transfer in a cryptand derivatized with two different fluorophores

A laterally nonsymmetric aza cryptand has been derivatized with one 7-nitrobenz-2-oxa-1,3-diazole (fluorophore(1)) and one/two anthracenes (fluorophore(2)) to obtain 1 and 2. Their emission characteristics are probed in the presence of a number of transition metals and proton. In the case of 1, Cu(II), Zn(II), Cd(II), and proton afford a large enhancement of fluorescence, whereas Fe(II) and Ag(I) exhibit one order of magnitude less enhancement. In contrast, 2 gives a large enhancement with Cu(II), Ag(I), and proton. The enhancement is observed in the diazole moiety even when the anthracene fluorophore is excited because of substantial fluorescence resonance energy transfer from anthracene to the diazole moiety. Compounds 1 and 2 can be termed as the second-generation fluorescence signaling systems.     

Synthesis and time-resolved photoluminescence spectroscopy of capped CdS nanocrystals

Here, we report the synthesis of colloidal CdS nanoparticles by capping with starch, phenol and pyridine. We also study the photophysical properties of CdS nanoparticles by steady state and time-resolved photoluminescence spectroscopy. The experimental results show that the relaxation of the excited state of CdS nanoparticles is composed of two different components. Our analysis suggests that the fast and slow components decay times of these capped CdS nanocrystals are due to trapping of carriers in surface state and e–h radiative recombination processes, respectively.     

Creation of crosslinkable interphases in polymer blends

A new type of bi- and trifunctional coupling agents containing 2-oxazoline and/or 2-oxazinone as well as hydrosilane moieties has been prepared by hydrosilylation of the corresponding allyl ether containing precursors with poly(methylhydro)siloxanes. In heterogeneous model blends based on mono-carboxylic acid terminated polystyrene (PS) and mono-amine terminated polyamide 12 (PA), the oxazoline and oxazinone units can selectively react with the carboxylic groups or amino groups, respectively. Under this mixing conditions the hydrosilane partially crosslinks. The morphology development of the three-component blends under melt mixing conditions is a rather complex process. We have shown that the coupling agents are immiscible with the polymers and form their own phase. Under proper processing conditions they locate at least partially at the PS/PA interface and can be used for further modification of the blend interphase, e.g. for crosslinking by hydrolysis. This crosslinking can be accelerated by the addition of a Pt-catalyst during the melt mixing.     

Synthesis of halogen-free amino-functionalized polymethyl methacrylate by atom transfer radical polymerization (ATRP)

In order to obtain amino-terminated polymethyl methacrylate (PMMA-NH₂) free of halogen we used the atom transfer radical polymerization (ATRP) to polymerize methyl methacrylate (MMA) in presence of an initiator containing an alkyl bromide unit and a protected amine functional group. The use of CuBr / N,N,N′,N′′,N′′-pentamethyldiethylenetriamine (PMDETA) as co-catalyst system results in a polymer free of halogen due to hydrogen transfer from PMDETA to the growing polymer chain. However, side reactions occur affecting the typically “living” character of the ATRP. The measured molecular weights are consistently higher than the theoretical ones and the molecular weight distributions are relatively broad.