Electrochemical study of gramicidin D forming ion-permeable channels in the bilayer lipid membranes

Gramicidin within the lipid bilayer matrix is a well-known channel-forming polypeptide, but the mechanism of the ions across the membrane induced by gramicidin is not well understood. We found that at very low concentration of gramicidin in a bilayer lipid membrane, the channel behavior was controlled by the voltage applied across the membrane. When the voltage is higher than 75 mV, the channel is closing, while lower than 75 mV, the channel is opening. But when the concentration of the gramicidin in the BLMs is high, the channel behavior is changed into voltage-independent. (C) 1998 Elsevier Science Ltd. All rights reserved.

Catalytic mechanisms of triphenyl bismuth, dibutyltin dilaurate, and their combination in polyurethane-forming reaction

The catalytic mechanisms of triphenyl bismuth (TPB), dibutyltin dilaurate (DBTDL) and their combination have been studied in a model polyurethane reaction system consisting of copolyether (tetrahydrofuran-ethyleneoxide) and N-100; NMR spectroscopy was used to detect the associations between reactants and catalysts. A relatively stable complex was shown to be formed between hydroxyl and isocyanate; the catalysts showed different effects on the isocyanate-hydroxyl complex, therefore resulting in different curing characteristics. The formation of hydrogen bonding between the complexed hydroxyl and other hydroxyl or the resulting urethane provided an ''auto-catalysis'' to urethane formation. DBTDL destroyed the isocyanate-hydroxyl complex before catalyzing the reaction through the formation of a ternary complex, whereas TPB was able to activate the isocyanate-hydroxyl complex directly to form urethane. The reaction catalyzed by the combination of TPB and DBTDL gained advantages from the multiple catalytic entities, i.e., TPB, DBTDL, and a TPB-DBTDL complex. (C) 1997 John Wiley & Sons, Inc.

Study on the Films Forming Process of Nanosized SnO2 Colloid Particles at the Gas-Liquid Interface

The hydrosol of SnO2 nanoparticles are prepared by the method of colloid chemistry. The free piling up process of nanosized SnO2 colloid particles are investigated at the gas-liquid interface by LB and Brewster Angle Microscopy techniques. The result indicates that solid state monolayer and multilayer of SnO2 nanoparticles can be formed at the gas-liquid interface only by aging the sol in air or compressing it without amphiphiles surfactant.

MISCIBILITY, MICROSTRUCTURE, AND DYNAMICS OF BLENDS CONTAINING BLOCK-COPOLYMER .3. MOLECULAR-MOTION IN HOMOPOLYSTYRENE AND POLYSTYRENE 4-ARM STYRENE-BUTADIENE STAR BLOCK-COPOLYMER BLENDS

The proton spin-spin relaxation times (T-2(H)) at different temperatures (from 160 to 390 K) have been determined for polystyrene (PS) and four-arm star styrene-butadiene block copolymer (SB-4A) and its blends with PS of different molecular weights (M(PS)

THE EFFECT OF FILM-FORMING CONDITIONS FOR TAPCUPC LANGMUIR-BLODGETT-FILMS ON MORPHOLOGY AND PROPERTIES

The dependence of morphology and properties on film-forming conditions is described for the symmetrically substituted copper tetra-4-(2, 4-di-t-amylphenoxy) phthalocyanine (tapCuPc) Langmuir-Blodgett (LB) films. The effects of LB film-forming conditions (such as the surface pressure, pH value and the concentrations of spreading solutions) on film quality were studied with the help of a UV-visible spectrophotometer and a transmission electron microscope. Transmission electron microscopy photographs of the surface morphology of tapCuPc LB films show that a smooth and homogeneous surface structure can be obtained under optimum film-forming conditions.

Biochemical compositions of two dominant bloom- forming species isolated from the Yangtze River Estuary in response to different nutrient conditions

Variations of cellular total lipid, total carbohydrate and total protein content of two dominant bloom-forming species (Skeletonema costatum and Prorocentrum donghaiense) isolated from the Yangtze River Estuary were examined under six different nutrient conditions in batch cultures. Daily samples were collected to estimate the cell growth, nutrient concentration and three biochemical compositions content during 7 days for S. costatum and the same sampling procedure was done every other day during 10 days for P. donghaiense. Results showed that for S. costatum, cellular total lipid content increased under phosphorus (P) limitation, but not for nitrogen (N) limitation; cellular carbohydrate were accumulated under both N and P limitation: cellular total protein content of low nutrient concentration treatments were significantly lower than that of high nutrient concentration treatments. For P. donghaiense, both cellular total lipid content and total carbohydrate content were greatly elevated as a result of N and P exhaustion, but cellular total protein content had no significant changes under nutrient limitation. In addition, the capability of accumulation of three biochemical constituents of P. donghaiense was much stronger than that of S. costatum. Pearson correlation showed that for both species, the biochemical composition of three constituents (lipid, carbohydrate and protein) had no significant relationship with extracellular N concentration, but had positive correlation with extracellular and intracellular P concentration. The capability of two species to accumulate cellular total lipid and carbohydrate under nutrient limitation may help them accommodate the fluctuating nutrient condition of the Yangtze River Estuary. The different responses of two species of cellular biochemical compositions content under different nutrient conditions may provide some evidence to explain the temporal characteristic of blooms Caused by two species in the Yangtze River Estuary. (C) 2008 Elsevier B.V. All rights reserved.

Effects of macroalgae Ulva pertusa (Chlorophyta) and Gracilaria lemaneiformis (Rhodophyta) on growth of four species of bloom-forming dinoflagellates

The effects of fresh thalli and culture medium filtrates from two species of marine macroalgae, Ulva pertusa Kjellm (Chlorophyta) and Gracilaria lemaneiformis (Bory) Dawson (Rhodophyta), on growth of marine microalgae were investigated in co-culture under controlled laboratory conditions. A selection of microalgal species were used, all, being identified as bloom-forming dinoflagellates: Prorocentrum donghaiense Lu sp., Alexandrium tamarense (Lebour) Balech, Amphidinium carterae Hulburt and Scrippsiella trochoide (Stein) Loeblich III. Results showed that the fresh thalli of either U. pertusa or G. lemaneiformis significantly inhibited the microalgal growth, or caused mortality at the end of the experiment. However, the overall effects of the macroalgal culture filtrates on the growth of the dinoflagellates were species-specific (inhibitory, stimulatory or none) for different microalgal species. Results indicated an allelopathic effect of macroalga on the co-cultured dinoflagellate. We then took P. donghaiense as an example to further assess this hypothesis. The present study was carried out under controlled conditions, thereby excluded the fluctuation in light and temperature. Nutrient assays showed that nitrate and phosphate were almost exhausted in G. lemaneiformis co-culture. but remained at enough high levels in U pertusa co-culture, which were well above the nutrient limitation for the microalgal growth, when all cells of P. donghaiense were killed in the co-culture. Daily f/2 medium enrichment greatly alleviated the growth inhibition on P. donghaiense in G. lemaneiformis co-culture, but could not eliminate it. Other environmental factors, such as carbonate limitation, bacterial presence and the change of pH were also not necessary for the results. We thus concluded that allelopathy was the most possible reason leading to the negative effect of U. pertusa on P. donghaiense, and the combined roles of allelopathy and nutrient competition were essential for the effect of G. lemaneiformis on P. donghaiense. (c) 2006 Elsevier B.V. All rights reserved.

Interactions between the bloom-forming dinoflagellates Prorocentrum donghaiense and Alexandrium tamarense in laboratory cultures

Interactions between Prorocentrum donghaiense and Alexandrium tamarens, two bloom-forming dinoflagellates, were investigated using bi-algal cultures. All R donghaiense died, but A. tamarense was hardly affected by the end of the experiment when the initial cell density was set at 1.0 X 10(4) cells mL(-1) for P. donghaiense and 0.28 x 10(4) cells mL(-1) for A. tamarense. However, significant growth suppression occurred in either species when the initial cell density of P donghaiense increased to I. 0 X 105 Cells mL(-1) in the bi-algal culture, but no out-competement was observed. The simultaneous assay on the culture filtrates showed that P donghaiense filtrate prepared at a lower initial density (1.0 X 10(4) cells mL(-1)) stimulated growth of the co-cultured A. tanzarense (0.28 x 10(4) cells mL(-1)), but filtrate at a higher initial density (1.0 x 10(5) cells mL(-1)) depressed its growth. The filtrate of A. tamarense at a density of 0.28 x 10(4) cells mL(-1) killed all R donghaiense at a lower density (1.0 x 10(4) cells mL(-1)), but only exhibited an inhibitory effect on it at a higher density (1.0 x 10(5) cells mL(-1)). It is likely that these two species of microalgae interfere with each other mainly by releasing allelochemical substance(s) into the culture medium, and a direct cell-to-cell contact was not necessary for their mutual interaction. The allelopathic test further proved that A. tamarense could affect the growth of co-cultured P. donghaiense by producing allelochemical(s); moreover, A. tamarense culture filtrate at the stationary growth phase (SP) had a strongly inhibitory effect on P donghaiense compared to that at the exponential phase (EP). Results also demonstrated a dose-dependent relationship between the microalgal initial cell density and the degree of the allelopathic effect. The growth of R donghaiense and A. tamarense in the bi-algal cultures was simulated using a mathematical model to quantify the interaction. The estimated parameters from the model showed that the inhibition exerted by A. tamarense on P. donghaiense was about 17 and 8 times stronger than the inhibition P. donghaiense exerted on A. tamarense, when the initial cell density was set at 1.0 X 10(4) and 1.0 X 10(5) cells mL(-1) for P donghaiense, respectively. and 0.28 x 10(4) cells mL(-1) for A. tamarense in the bi-algal cultures. A. tamarense seems to have a survival strategy that is superior to that of P. donghaiense in bi-algal cultures under controlled laboratory conditions. (c) 2006 Elsevier B.V. All rights reserved.

A new sea-star species (Asteroidea : Luidiidae) from the South China Sea

A new sea-star species of family Luidiidae, named Luidia difficilis, from the South China Sea is described in the present paper. The diagnostic characters that distinguish L. difficilis from its closely allied species L. hexactis and L. maculata are listed in Table 1.

Mantle-derived gaseous components in ore-forming fluids of the Xiangshan uranium

The Xiangshan U deposit, the largest hydrothermal U deposit in China, is hosted in late Jurassic felsic volcanic rocks although the U mineralization post dates the volcanics by at least 20 Ma. The mineralization coincides with intrusion of local mantle-derived mafic dykes formed during Cretaceous crustal extension in South China. Ore-forming fluids are rich in CO2, and U in the fluid is thought to have been dissolved in the form of UO2 (CO3)22− and UO2 (CO3) 34− complexes. This paper provides He and Ar isotope data of fluid inclusions in pyrites and C isotope data of calcites associated with U mineralization (pitchblende) in the Xiangshan U deposit. He isotopic compositions range between 0.1 and 2.0Ra (where Ra is the 3He/4He ratio of air=1.39×10−6) and correlates with 40Ar/36Ar; although there is potential for significant 3He production via 6Li(n,α)3H(β)3He reactions in a U deposit (due to abundant neutrons), nucleogenic production cannot account for either the 3He concentration in these fluids, nor the correlations between He and Ar isotopic compositions. It is more likely that the high 3He/4He ratios represent trapped mantle-derived gases. A mantle origin for the volatiles of Xiangshan is consistent with the δ13C values of calcites, which vary from −3.5‰ to −7.7‰, overlapping the range of mantle CO2. The He, Ar and CO2 characteristics of the ore-forming fluids responsible for the deposit are consistent with mixing between 3He- and CO2-rich mantle-derived fluids and CO2-poor meteoric fluids. These fluids were likely produced during Cretaceous extension and dyke intrusion which permitted mantle-derived CO2 to migrate upward and remobilize U from the acid volcanic source rocks, resulting in the formation of the U deposit. Subsequent decay of U within the fluid inclusions has reduced the 3He/4He ratio, and variations in U/3He result in the range in 3He/4He observed with U/3He ratios in the range 5–17×103 likely corresponding to U concentrations in the fluids b0.2 ppm.