Search

Core-shell particles were synthesized employing seeded suspension polymerization. Suspension polystyrene (PS) particles were used as seeds, and poly(methyl methacrylate) (PMMA) was synthesized in the presence of polystyrene seeds. A combination of solvent extraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy techniques were employed to study the structure and morphology of synthesized particles. The results suggested a core-inner shell-outer shell structure for the synthesized particles in which the PS core was covered by a PMMA-rich inner shell and a very thin PS-rich outer shell. The size and concentration of PMMA domains decreased from the outer shell toward the core of the particle, and particle morphology was mainly controlled by the limitations to the diffusion of MMA through the polymer particle.

An electrometrical technique was used to investigate electron transfer between synthetic binuclear manganese (Mn) complexes, designated M − 2 and M − 3, and the redox-active neutral tyrosine radical (Y Z • ) in proteoliposomes containing Mn-depleted photosystem II (PS II) core particles in response to single laser flashes. In the absence of Mn-containing compounds, the observed flash-induced membrane potential (ΔΨ) decay was mainly due to charge recombination between the reduced primary quinone acceptor Q A − and the oxidized Y Z • . More significant slowing down of the ΔΨ decay in the presence of lower concentrations of M − 2 and M − 3 associated with electron donation from Mn in the Mn-binding site to Y Z • indicates that these synthetic compounds are more effective electron donors than MnCl 2 . The exponential fitting of the kinetics of additional electrogenic components of ΔΨ rise in the presence of Mn-containing compounds revealed the following relative amplitudes ( A ) and lifetimes (τ): for MnCl 2 - A ∼ 3.5, τ∼150 μs, for M − 2 - A ∼5%, τ∼1.4 ms, and for M − 3 - A ∼5.5%, τ∼150 μs. This suggests that the efficiency of the manganese complexes in electron donation depends on the chemical nature of ligands. The experiments with EDTA-treated samples indicated that the ligands for M − 2 and M − 3 are required for their tight binding with the PS II reaction center. The obtained results demonstrate the importance of understanding the molecular mechanism(s) of flash-induced electrogenic reduction of the tyrosine radical Y Z • by synthetic Mn complexes capable of splitting water into oxygen and reducing equivalents.

Expandable core-shell beads were synthesized by dosing methyl methacrylate (and styrene) in a constant rate and polymerizing in the presence of polystyrene seeds and pentane. The morphological studies of beads indicated that there were larger poly(methyl methacrylate)-rich domains near the shell. The sizes of these domains were decreased towards the core of the particles. For better surveying the likely structures of domains and the extent of expansion agent diffusion, the beads having the shells formed with copolymerization of styrene and methyl methacrylate in the presence of polystyrene seeds were studied. From the morphological studies, the parallel regular and the onion-like structures were recognizable. In addition, another shell was formed around the dispersed phase showing a complex core/shell structure both in particle and in domain scales. The pentane content in the beads with copolymerized styrene and methyl methacrylate monomers on the polystyrene seeds was increased compared to the beads having the shells of pure poly(methyl methacrylate). This was because the onset of gel effect was longer with adding the styrene to methyl methacrylate monomer hence there was more time for expansion agent to diffuse into the beads. The different amounts of pentane distributed in polystyrene- and poly(methyl methacrylate)-rich phases were discussed in terms of the changes in glass transition temperature of two phases.

The oil constituents from rhizomes, leaves and seed of Peucedanum petiolare (DC.) Boiss., gathered in Touchal on mountain Alborz (Tehran province) in Iran, have been studied by GC and GC/MS. The major constituents in the rhizome oil were found to be β-bisabolene (31.3%), (E)-sesquilavandulol (20.5%), geranyl acetate (5.7%), citronellyl acetate (5.2%) and sabinene (5.2%). In the leaf oil the main components found were sabinene (42.3%), α-pinene (42.6%) and limonene (2.6%). In the seed α-pinene (47.3%) and sabinene (45.9%) were the predominant constituents. Copyright © 2004 John Wiley & Sons, Ltd.

Hydro-distilled volatile oil from the roots of Plumbago europaea L. was obtained at a yield of 0.2% w/w based on dry weight. The oil was analyzed by a combination of GC and GC-MS. Fifteen components were identified constituting 95.3% of the oil. The major constituents in the root oil were plumbagin (69.1%), 1-octen-3-yl acetate (9%) and limonene (5.7%). Copyright © 2004 John Wiley & Sons, Ltd.

The essential oil was isolated by steam distillation from the aerial parts of Cleome iberica DC. at a yield of 0.1% w[sol ]w, based on dry weight. The oil was analysed by a combination of GC and GC–MS; 26 components were identified, constituting 99.8% of the oil. The main constituents of the essential oil were carotol (21.8%), germacrene D (15.8%), β-cubebene (15.5%), trans-nerolidol (5.6%), δ-cadinene (4.5%) and hexyl acetate (4.0%). Copyright © 2005 John Wiley & Sons, Ltd.