Swelling behaviour of alginate-chitosan microcapsules prepared by external gelation or internal gelation technology

Swelling behaviour is one of the important properties for microcapsules made by hydrogels, which always affects the diffusion and release of drugs when the microcapsules are applied in drug delivery systems. In this paper, alginate-chitosan microcapsules were prepared by different technologies called external or internal gelation process respectively. With the volume swelling degree (S-w) as an index, the effect of properties of chitosan on the swelling behaviour of both microcapsules was investigated. It was demonstrated that the microcapsules with low molecular weight and high concentration of chitosan gave rise to low S-w. Considering the need of maintaining drug activity and drug loading, neutral pH and short gelation time were favorable. It was also noticed that S-w of internal gelation microcapsules was lower than that of external gelation microcapsules, which was interpreted by the structure analysis of internal or external gelation Ca-alginate beads with the aid of confocal laser scanning microscope. (C) 2004 Elsevier Ltd. All rights reserved.

Photodissociation dynamics of the methyl radical at 212.5 nm: Effect of parent internal excitation

Photodissociation dynamics of the CH3 radical at 212.5 nm has been investigated using the H atom Rydberg tagging time-of-flight method with a pure CH3 radical source generated by the photolysis of CH3I at 266 nm. Time-of-flight spectra of the H atom products from the photolysis of both cold and hot methyl radicals have been measured at different photolysis polarizations. Experimental results indicate that the photodissociation of the methyl radical in its ground vibrational state at 212.5 nm excitation occurs on a very fast time scale in comparison with its rotational period, indicating the CH3 dissociation at 212.5 nm occurs on the excited 3s Rydberg state surface. Experimental evidence also shows that the photodissociation of the methyl radical in the nu(2)=1 state of the umbrella mode at 212.5 nm excitation is characteristically different from that in the ground vibrational state. (C) 2004 American Institute of Physics.

Preparation of uniform calcium alginate gel beads by membrane emulsification coupled with internal gelation

With the objective of making calcium alginate gel beads with small and uniform size, membrane emulsification coupled with internal gelation was proposed. Spherical gel beads with mean size of about 50 mum, and even smaller ones in water, and with narrow size distribution were successfully obtained. Experimental studies focusing mainly on the effect of process parameters on bead properties were performed. The size of the beads was mainly dependent on the diameter of the membrane pores. High transmembrane pressure made for large gel beads with wide size distribution. Low sodium alginate concentration produced nonspherical beads, whereas a high concentration was unsuitable for the production of small beads with narrow distribution. Thus 1.5% w/v was enough. A high surfactant concentration favored the formation of small beads, but the adverse effect on mass transfer should be considered in this novel process. (C) 2002 Wiley Periodicals, Inc.

Characterization of structure and diffusion behaviour of Ca-alginate beads prepared with external or internal calcium sources

Ca-alginate beads were prepared with either external or internal calcium sources. The structures of both beads were investigated with the aid of scanning electron microscopy (SEM) and confocal microscopy. It was shown that the beads with internal calcium source had a looser structure and bigger pore size than those with external calcium source. The attempts to interpret the difference were carried out by determining the Ca content within the beads at various times, which indicated that it was the different gelation mechanisms that caused the difference of structures of both beads. Furthermore, it was also found that the diffusion rate of haemoglobin (Hb) within the beads with an internal calcium source was faster than that of the beads with an external one, which was consistent with the observation of their structures.

Rare-earth-metal mixed hydride/aryloxide complexes bearing mono(cyclopentadienyl) ligands. Synthesis, CO2 fixation, and catalysis on copolymerization of CO2 with cyclohexene oxide

Hydrogenolysis of mono(cyclopentadienyl)-ligated rare-earth-metal bis(alkyl) complexes Cp'Ln-(CH2SiMe3)2(THF) (Ln = Y (1a), Dy (1b), Lu (1c); Cp' = C5Me4SiMe3) with PhSiH3 afforded the mixed hydride/alkyl complexes [Cp'Ln(mu-H)(CH2SiMe3)(THF)](2) (Ln = Y (2a), Dy (2b), Lu (2c)). The overall structure of complexes 2a-c is a C-2-symmetric dimer containing a planar symmetric Ln(2)H(2) core at the center of the molecule. Deprotonation of ArOH (Ar = C6H2-Bu-t(2)-2,6-Me-4) by the metal alkyl group of 2a-c led to formation of the mixed hydride/aryloxide derivatives [Cp'Ln(mu-H)(OAr)](2) (Ln = Y (3a), Dy (3b), Lu (3c)), which adopt the dimeric structure through hydride bridges with trans-accommodated terminal aryloxide groups.

Fixation of carbon dioxide into aliphatic polycarbonate, cobalt porphyrin catalyzed regio-specific poly(propylene carbonate) with high molecular weight

Cobalt porphyrin complex ((TPPCoX)-X-III) (TPP = 5, 10, 15, 20-Tetraphenylporphyrin; X = halide) in combination with ionic organic ammonium salt was used for the regio-specific copolymerization of propylene oxide and carbon dioxide. A turnover frequency of 188 h(-1) was achieved after 5 h, and the byproduct propylene carbonate was successfully controlled to below 1%, where the obtained poly(propylene carbonate) (PPC) showed number average molecular weight (M-n) of 48 kg/mol, head-to-tail content of 93%, and carbonate linkage of over 99%.

Harvesting Excitons Via Two Parallel Channels for Efficient White Organic LEDs with Nearly 100% Internal Quantum Efficiency: Fabrication and Emission-Mechanism Analysis

By incorporating two phosphorescent dyes, namely, iridium(III)[bis(4,6-difluorophenyl)-pyridinato-N,C-2']picolinate (Flrpic) for blue emission and bis(2-(9,9-diethyl-9H-fluoren-2-yl)-1-phenyl-1 H-benzoimidazol-N,C-3) iridium(acetylacetonate) ((fbi)(2)Ir(acac)) for orange emission, into a single-energy well-like emissive layer, an extremely high-efficiency white organic light-emitting diode (WOLED) with excellent color stability is demonstrated. This device can achieve a peak forward-viewing power efficiency of 42.5 lm W-1, corresponding to an external quantum efficiency (EQE) of 19.3% and a current efficiency of 52.8 cd A(-1). Systematic studies of the dopants, host and dopant-doped host films in terms of photophysical properties (including absorption, photoluminescence, and excitation spectra), transient photoluminescence, current density-voltage characteristics, and temperature-dependent electroluminescence spectra are subsequently performed, from which it is concluded that the emission natures of Flrpic and (fbi)(2)Ir(acac) are, respectively, host-guest energy transfer and a direct exciton formation process. These two parallel pathways serve to channel the overall excitons to both dopants, greatly reducing unfavorable energy losses.

Investigation on internal electric field distribution of organic light-emitting diodes (OLEDs) with Eu2O3 buffer layer

We have found that organic light-emitting diode (OLED) performance was highly improved by using europium oxide (Eu2O3) as a buffer layer on indium tin oxide (ITO) in OLEDs based on tris-(8-hydroxyquinoline) aluminium (Alq(3)), which showed low turn-on voltage, high luminance, and high electroluminescent (EL) efficiency. The thickness of Eu2O3 generally was 0.5-1.5 nm. We investigated the effects of Eu2O3 on internal electric field distributions in the device through the analysis of current-voltage characteristics, and found that the introduction of the buffer layer balanced the internal electric field distributions in hole transport layer (HTL) and electron transport layer (ETL), which should fully explain the role of the buffer layer in improving device performance. Our investigation demonstrates that the hole injection is Fowler-Nordheim (FN) tunnelling and the electron injection is Richardson-Schottky (RS) thermionic emission, which are very significant in understanding the operational mechanism and improving the performance, of OLEDs.

Templated assembly of mu(5)-CO32- decanuclear praseodymium and neodymium clusters through spontaneous fixation of atmospheric carbon dioxide

Reactions of Ln(III) acetate (Ln = Pr and Nd) and a polydentate Schiff-base in a mixture of methanol and acetonitrile resulted in the unprecedented assembly of novel Ln(10) aggregates containing two Ln(5) pentagons templated by mu(5)-CO32-, introduced via spontaneous fixation of atmospheric carbon dioxide. Magnetic analysis using an expression including the ligand field effects and molecular field approximation indicates weak antiferromagnetic coupling between the metal ions. This synthetic approach may represent a promising new route toward the design of new lanthanide clusters and novel multifunctional materials.

Generation of chiral bis(cyclopentadienyl)neodymium Schiff base complex bearing internal C-C bond formation and hydrogen transfer

NdCl3 reacts with excess CpNa (Cp=Cyclopentadienyl) in THF, followed by sequent treatment with (S)-(+)-N-(1-phenylethyl)salicylideneamine led to the formation of title compound, [GRAPHICS] The X-ray structure determination shows that it is a dimer with internal C-C bond formation and hydrogen transfer between one of Cp ring and the C=N bond of Schiff base ligand. (C) 1997 Elsevier Science S.A.

Using the ribosomal internal transcribed spacer (ITS) as a complement marker for species identification of red macroalgae

Barcodes based on mitochondrial cytochrome oxidase (mtDNA CO1) sequences are being used for broad taxonomic groups of animals with demonstrated success in species identification and cryptic species discovery, but it has become clear that complementation by a nuclear marker system is necessary, in particular for the barcoding of plants. Here, we propose the nuclear internal transcribed spacer (ITS) as a potentially usable and complementary marker for species identification of red macroalgae, as well as present a primary workflow for species barcoding. Data show that for most red macroalgal genera (except members of the family Delesseriaceae), the size of ITS region ranges from 600 to 1200 bp, and contains enough variation to generate unique identifiers at either the species or genus levels. Consistent with previous studies, we found that the ITS sequence can resolve closely related species with the same fidelity as mtDNA CO1. Significantly, we confirmed that length polymorphism in the ITS region (including 5.8S rRNA gene) can be utilized as a character to discriminate red macroalgal species. As a complementary marker, the verifiable nuclear ITS region can speed routine identification and the detection of species, advance ecological and taxonomic inquiry, and permit rapid and accurate analysis of red macroalgae.

Phylogeography of the Northern Atlantic species Chondrus crispus (Gigartinales, Rhodophyta) inferred from nuclear rDNA internal transcribed spacer sequences

Eighteen isolates of the red algae Chondrus crispus were collected from Northern Atlantic sites, together with C. ocellatus, C. yendoi and C. pinnulatus from the North Pacific. The nuclear rDNA internal transcribed spacer (ITS) was sequenced and compared, spanning both the ITS regions and the 5.8S rRNA gene. Percentage of nucleotide variation for C. crispus ranged from 0.3% to 4.0%. Phylogenetic analyses were performed using maximum parsimony (MP), neighbor-joining (NJ) and minimum evolution methods. They showed that two main clades existed within the C. crispus samples examined and that suggested C. crispus had a single Atlantic origin. The clustering however did not follow the geographic origin. We hypothesized that the current distribution of C. crispus populations might be a result of three main factors: temperature boundaries, paleoclimate and paleoceanography. ITS data exhibited abundant molecular information not only for phylogeographical investigation but also for systematics studies.

Third-order Stokes wave solutions for interfacial internal waves in a three-layer density-stratified fluid

Interfacial internal waves in a three-layer density-stratified fluid are investigated using a singular method, and third-order asymptotic solutions of the velocity potentials and third-order Stokes wave solutions of the associated elevations of the interfacial waves are presented based on the small amplitude wave theory. as expected, the third-order solutions describe the third-order nonlinear modification and the third-order nonlinear interactions between the interfacial waves. The wave velocity depends on not only the wave number and the depth of each layer but also on the wave amplitude.