MOLECULAR-WEIGHT DEPENDENCE OF THE GLASS-TRANSITION OF CYCLIC POLYSTYRENE

The glass transition temperature (T(g)) of cyclic polystyrene was measured by differential scanning calorimetry. There was a marked difference in the glass transition behaviour between cyclic and linear polystyrene. In the low molecular weight region (M(n) < 5 x 10(3)), the T(g) of the cyclic polystyrene increased with decreasing M(n), contrary to that of linear polystyrene. With M(n) higher than 5 x 10(3), the T(g) of cyclic polystyrene increased with increasing M(n). The T(g) of cyclic and linear polystyrene approached the same constant value when the M(n) was high enough (M(n) > 10(5)). Combining the results of specific volume, it is believed that the variation of T(g) with molecular weight does not depend only on free volume effects but that configurational entropy is also an important factor.

EFFECT OF MOLECULAR-WEIGHT OF PMMA ON BETA PHASE CRYSTALLIZATION IN HIGHLY ORIENTED PVF2 FILMS

Polyvinylidene fluoride (PVF_2) exhibits at least four crystalline phases (α, β, γ, and δ). Among them, β phase is the most important one because it is directly related to the piezoand pyro-electric activities of PVF_2. In recent years, more attention has been paid to the β

DRY-WEIGHT AND CHEMICAL-COMPOSITION (CHN) IN RELATION TO POPULATION-DENSITY OF CULTIVATED TISBE-HOLOTHURIAE (COPEPODA, HARPACTICOIDA)

CARBON

Inhibitory effects and mechanisms of high molecular-weight phlorotannins from Sargassum thunbergii on ADP-induced platelet aggregation

We evaluated the effects of high molecular-weight phlorotannins from Sargassum thunbergii (STP) on ADP-induced platelet aggregation and arachidonic acid (AA) metabolism in New Zealand white rabbits and Wistar rats. The inhibition of STP on platelet aggregation was investigated using a turbidimetric method, and the levels of the terminal products of AA metabolism were measured using the corresponding kits for maleic dialdehyde (MDA), thromboxane B-2 (TXB2) and 6-keto-prostaglandin F-1 alpha (6-keto-PGF(1 alpha)) by colorimetry and radioimmunoassay, as appropriate. We found that STP could inhibit ADP-induced platelet aggregation, and the inhibitory ratio was 91.50% at the STP concentration of 4.0 mg/mL. Furthermore, STP markedly affected AA metabolism by decreasing the synthesis of MDA (P < 0.01) and increasing the synthesis of 6-keto-PGF(1 alpha), thus changing the plasma TXB2/6-keto-PGF(1 alpha) balance when the platelets were activated (P < 0.01). Therefore, STP altered AA metabolism and these findings

Using otolith weight to predict the age of Pennahia macrocephalus in the mouth of the Beibu Gulf

The relation between otolith weight (OW) and the age of marine fish is studied. A total of 222 individuals of bighead white croaker, Pennahia macrocephalus were sampled seasonally in the mouth of the Beibu Gulf, the South China Sea, in 2007. Since there are no significant differences in sagittal OW between otolith in pairs (Pa parts per thousand yen0.05), the undamaged left sagittal otolith is used for age determination. The highest correlations among standard length, OW and fish ages are confirmed by linear, exponential and multinomial regression. Results show that sagittal OW overlaps only occasionally among age groups, and to individuals with similar standard length, the older and slower-growing fish has a heavier otolith because of the continued otolith material deposition. There are differences in sagittal OW among different age groups and significant positive linear relationship with age (P < 0.05). The age readings can be verified by plotting the sagittal OW versus the standard length for age groups, and the individuals with similar standard length but in different ages can be separated by sagittal OW frequency analysis. Mostly, the predicted ages using the regression between sagittal OW and ages are closed to the observed ages by counting annulus on scale. It indicates that the sagittal OW analysis is a useful technique for validating the accuracy of age determination by annuli counts, especially for individuals of similar size. Furthermore, the technique is applied for Pennahia macrocephalus with discussion in this paper.

Inhibition of mouse liver lipid peroxidation by high molecular weight phlorotannins from Sargassum kjellmanianum

The inhibitory effects of high molecular weight phlorotannins (HMP) from Sargassum kjellmanianum on mouse liver lipid peroxidation were investigated by spectrophotometric methods. The content of malondialdehyde (MDA) in liver samples was measured by TBA (thiobarbituric acid) assay. It showed that HMP significantly inhibited the generation of MDA in vivo and in situations induced by CCl4 and Fe2+-Vc ( ascorbic acid), and significantly decreased membrane swelling of mouse liver mitochondria, compared with controls ( p < 0.01). HMP were found to have strong anti-oxidative activity in inhibiting mouse liver lipid peroxidation.

Metabolism of polychaete Neanthes japonica Izuka: relations to temperature, salinity and body weight

Polychaete Neanthes japonica is a species geographically specific in China and Japan with important scientific implication and commercial value. In this study, the relations of body weight, salinity and temperature to oxygen consumption and ammonia excretion of N. japonica were determined. Three different groups in body weight (large: 2.34 +/- 0.36 g, middle: 1.50 +/- 0.21 g and small: 0.62 +/- 0.12 g) were set for all experiments. Results show that the body weight is negatively related to the rates of oxygen consumption and ammonia excretion; and the relationship is significant. The oxygen consumption and ammonia excretion at 24A degrees C decreased at salinity from 5 to 30 and increased above 30, indicating that both lower and higher salinity are adverse and certain degree of salinity stress is necessary for enhancing the energy demand. At salinity 30, rising temperature from 18A degrees C to 30A degrees C, the oxygen consumption increased before 27A degrees C and then decreased. However, the relation of ammonia excretion and temperature seems more complex. Two-way ANOVA shows that salinity, temperature and body weight all have a significant effect on the oxygen consumption and ammonia excretion of the worm. Moreover, interaction between salinity/temperature and body weight is also significant. O:N (oxygen/nitrogen) ratio varies greatly in this case from 5.97 to 463.22, indicating that N. japonica can regulate the type of metabolic substrate against environment changes.

Stable carbon and nitrogen isotopic compositions of high molecular weight dissolved organic matter from four US estuaries

High molecular weight dissolved organic matter (HMW-DOM) represents an important component of dissolved organic carbon (DOC) in seawater and fresh-waters. In this paper, we report measurements of stable carbon (delta(13)C) isotopic compositions in total lipid, total hydrolyzable amino acid (THAA), total carbohydrate (TCHO) and acid-insoluble "uncharacterized" organic fractions separated from fourteen HMW-DOM samples collected from four U.S. estuaries. In addition, C/N ratio, delta(13) C and stable nitrogen (delta(15)N) isotopic compositions were also measured for the bulk HMW-DOM samples. Our results indicate that TCHO and THAA are the dominant organic compound classes, contributing 33-46% and 13-20% of the organic carbon in HMW-DOM while total lipid accounts for only <2% of the organic carbon in the samples. In all samples. a significant fraction (35-49%) of HMW-DOM was included in the acid-insoluble fraction. Distinct differences in isotopic compositions exist among bulk samples, the compound classes and the acid-insoluble fractions. Values of delta(13)C and delta(15)N measured for bulk HMW-DOM varied from -22.1 to -30.1parts per thousand and 2.8 to 8.9parts per thousand, respectively and varied among the four estuaries studied as well. Among the Compound classes, TCHO was more enriched in C-13 (delta(13)C = -18.5 to -22.8parts per thousand) compared with THAA (delta(13)C = -20.0 to -29.6parts per thousand) and total lipid (delta(13)C = -25.7 to -30.7parts per thousand). The acid-insoluble organic fractions, in general, had depleted C-13 values (delta(13)C = -23.0 to -34.4parts per thousand). Our results indicate that the observed differences in both delta(13)C and delta(15)N were mainly due to the differences in sources of organic matter and nitrogen inputs to these estuaries in addition to the microbial processes responsible for isotopic fractionation among the compound classes. Both terrestrial sources and local sewage inputs contribute significantly to the HMW-DOM pool in the estuaries studied and thus had a strong influence on its isotopic signatures. Copyright (C) 2004 Elsevier Ltd.

Bacterial roles in the formation of high-molecular-weight dissolved organic matter in estuarine and coastal waters: Evidence from lipids and the compound-specific isotopic ratios

High-molecular-weight dissolved organic matter (HMW-DOM, > 1,000 Daltons) is actively involved in the global biogeochemical cycling of many elements, but its carbon sources and detailed formation pathways are still not well understood. In this study, we measured bulk stable carbon and nitrogen isotopic ratios, lipid composition, and compound-specific carbon isotopic ratios of HMW-DOM samples collected from four U.S. estuaries (Boston Harbor/Massachusetts Bay, Delaware/Chesapeake Bay, San Diego Bay, and San Francisco Bay). Analytical results show (1) a fraction of HMW-DOM (lipid associated) in estuarine and coastal waters is derived from bacteria and phytoplankton; (2) this fraction of HMW-DOM is formed by various release processes of bacterial membrane components and bacterial reworking of phytoplankton-derived material; (3) this fraction of HMW-DOM is generally present in all samples from different coastal systems despite variable organic matter inputs and environmental conditions, suggesting an important bacterial role in HMW-DOM formation.

Variability in radiocarbon ages of biochemical compound classes of high molecular weight dissolved organic matter in estuaries

High molecular weight dissolved organic matter (HMW-DOM, > 1000 Da) represents a major fraction (> 30%) of dissolved organic carbon (DOC) in the ocean and thus plays an important role in the global biogeochemical cycling of carbon and many other elements. Its organic sources and formation mechanisms, however, are still not well understood especially in estuarine and coastal regions where multiple natural and anthropogenic sources contribute to total HMW-DOM. In this paper we report our measurements of natural radiocarbon (C-14) abundances and stable carbon isotope (C-13) compositions of the major biochemical compound classes: amino acids, carbohydrates and lipids separated from eight HMW-DOM samples collected from five US estuaries as part of our on-going study of sources, distribution and transport of chromophoric dissolved organic matter (CDOM) in estuarine and coastal waters. Distinct differences in both C-14 and C-13 values were found among the bulk HMW-DOM samples as well as the individual compound classes. Radiocarbon ages of the major compound classes varied by as much as 27,000 years in a single sample. The calculated average radiocarbon ages of the compound fractions of HMW-DOM indicate that the total lipid fraction is very "old", while the acid-insoluble fraction is slightly younger. Total amino acid and carbohydrate fractions, however, have relatively modern apparent C-14 ages. The significant variability in C-14 ages among the compound classes indicates not only multiple organic carbon sources but also different formation and turnover pathways controlling the cycling of different biochemical components of HMW-DOM in estuarine and coastal waters. (c) 2006 Elsevier Ltd. All rights reserved.

Preparation of the different derivatives of the low-molecular-weight porphyran from Porphyra haitanensis and their antioxidant activities in vitro

Porphyran extracted from Porphyra haitanensis is a sulfated polysaccharide, which possesses excellent antioxidant activities. In this study, we prepared one low-molecular-weight porphyran and its sulfated, acetylated, phosphorylated and benzoylated derivatives. Their antioxidant activities were investigated including scavenging effect of superoxide, hydroxyl and 1,1-diphenyl-2-picrylhydrazyl radicals. The results of chemical analysis and FT-IR spectrums showed the modification was successful. And in addition, we found that certain derivative exhibited stronger antioxidant activity than low-molecular-weight porphyran. The benzoylated derivative showed the most excellent antioxidant activity in three assays, so this derivative needs to be attended to. (C) 2009 Elsevier B.V. All rights reserved.

Antioxidant activity of different molecular weight sulfated polysaccharides from Ulva pertusa Kjellm (Chlorophyta)

Polysaccharides extracted from Ulva pertusa Kjellm ( Chlorophyta) are a group of sulfated heteropolysaccharides, the ulvans. In this study, different molecular weight ulvans were prepared by H2O2 degradation and their antioxidant activities investigated including superoxide and hydroxyl radical scavenging activity, reducing power and metal chelating ability. The molecular weights of natural and degraded ulvans were 151.7, 64.5, 58.0, and 28.2 kDa, respectively, as determined by high performance gel permeation chromatography. Among the four samples, U-3 ( the lowest molecular weight sample) showed significant inhibitory effects on superoxide and hydroxyl radicals with IC50 values of 22.1 mu g mL(-1) and 2.8 mg mL(-1); its reducing power and metal chelating ability were also the strongest among the four samples. All the other samples also demonstrated strong activity against superoxide radicals. The results indicated that molecular weight had a significant effect on the antioxidant activity of ulvan with low molecular weight ulvan having stronger antioxidant activity.

Preparation of high-molecular weight and high-sulfate content chitosans and their potential antioxidant activity in vitro

The influence of molecular weight and substitution degree of sulfated polysaccharides on their biological activity is considered in majority of works involving the anticoagulant or antiviral properties of these substances. Therefore, the present paper describes the effect of preparation conditions of sulfated chitosans on their molecular weight and sulfur content, such as different reaction time, acid solvent and temperature. Foregoing literature expounded the action of dichloroacetic acid (DCAA) as acid solvent in homogeneous reaction. However, DCAA is expensive and noxious, therefore, in the present paper cheap and non-noxious formic acid (88%) was in place of DCAA. Furthermore, during reaction formic acid was not dehydrated. Under formic acid we obtained the satisfying results that was higher yield and equivalent sulfur contents compared to DCAA. IR and C-13 NMR spectrums proved the structure of the resultant obtained under formic acid or DCAA to be same. Now, it has not been reported for formic acid as acid solvent in homogeneous reaction of chitosan sulfatation. In this present paper, we also determined antioxidant activity of high-molecular weight and high-sulfate-content chitosans (HCTS). The results showed that HCTS could scavenge superoxide and hydroxyl radical. Its IC50 is 0.012 and 3.269 mg/mL, respectively. It had obviously reducing power and slight chelating activity. The data obtained in in vitro models clearly establish the antioxidant potency of HCTS. It is a potential antioxidant in vitro. (C) 2005 Elsevier Ltd. All rights reserved.

Relevance of molecular weight of chitosan and its derivatives and their antioxidant activities in vitro

The antioxidant potency of different molecular weight (DMW) chitosan and sulfated chitosan derivatives was investigated employing various established in vitro systems, such as superoxide (O-2(.-))/hydroxyl ((OH)-O-.) radicals scavenging, reducing power, iron ion chelating. As expected, we obtained several satisfying results, as follows: Firstly, low molecular weight chitosan had stronger scavenging effect on O-2(.-) and (OH)-O-. than high molecular weight chitosan. For example the O-2(.-) scavenging activity of low molecular weight chitosan (9 kDa) and high molecular weight chitosan (760 kDa) were 85.86 % and 35.50 % at 1.6 mg/mL, respectively. Secondly, comparing with DMW chitosan, DMW sulfated chitosans had the stronger inhibition effect on 0(2)(.-). At 0.05 mg/mL, the scavenging activity on O-2(.-) reached 86.26 %, for low molecular weight chitosan sulfate (9 kDa), but that of low molecular weight chitosan (9 kDa) was 85.86 % at 1.6 mg/mL. As concerning chitosan and sulfated chitosan of the same molecular weight, scavenging activities of sulfated chitosan on superoxide and hydroxyl radicals were more pronounced than that of chitosan. Thirdly, low molecular weight chitosan sulfate had more effective scavenging activity on 02 and (OH)-O-. than that of high molecular weight chitosan sulfate. Fourthly, DMW chitosans and sulfated chitosans were efficient in the reducing power, especially LCTS. Their orders were found to be LCTS > CTS4 > HCTS > CTS3 > CTS2 > CTS1 > CTS. Fifthly, CTS4 showed more considerable ferrous ion-chelating potency than others. Finally, the scavenging rate and reducing power of DMW chitosan and sulfated derivatives increased with their increasing concentration. Moreover, change of DMW sulfated chitosans was the most pronounced within the experimental concentration. However, chelating effect of DMW chitosans were not concentration dependent except for CTS4 and CTS1. (C) 2004 Elsevier Ltd. All rights reserved.

Preparation of low-molecular-weight and high-sulfate-content chitosans under microwave radiation and their potential antioxidant activity in vitro

In the present paper microwave radiation has been used to introduce N-sulfo and O-sulfo groups into chitosan with a thigh degree of substitution and low-molecular weight. The sulfation of chitosan was performed in microwave ovens. It was found that microwave heating is a convenient way to obtain a wide range of products of different degrees of substitution and molecular weight only by changing reaction time or/and radiation power. Moreover, microwave radiation accelerated the degradation of sulfated chitosan, and the molecular weight of sulfated chitosan was considerably lower than that obtained by traditional heating. There are no differences in the chemical structure of sulfated chitosan obtained by microwave and by conventional technology. FTIR and C-13 NMR spectral analyses demonstrated that a significantly shorter time is required to obtain a satisfactory degree of substitution and molecular weight by microwave radiation than by conventional technology. In this present paper, we also determined antioxidant activity of low-molecular-weight and high-sulfate-content chitosans (LCTS). The results showed LCTS could scavenge superoxide and hydroxyl radical. Its IC50 is 0.025 and 1.32mg/mL, respectively. It is a potential antioxidant in vitro. (C) 2004 Published by Elsevier Ltd.