Search

Melatonin is a ubiquitous chemical substance that regulates plant growth and responses to stress. Several recent studies show that exogenous melatonin confers cold tolerance to plants; however, the underlying mechanisms remain largely unknown. Here, we report that melatonin application at optimal dose, either on the leaves or the roots, not only induced cold stress tolerance in the site of application, but also systemically induced cold tolerance in untreated distant parts. Foliar or rhizospheric treatment with melatonin increased the melatonin levels in untreated roots or leaves, respectively, under both normal and cold stress conditions, whereas rhizospheric melatonin treatment increased the melatonin exudation rates from the xylem. An increased accumulation of melatonin accompanied with an induction in antioxidant enzyme activity in distant untreated tissues alleviated cold-induced oxidative stress. In addition, RNA-seq analysis revealed that an abundance of cold defense-related genes involved in signal sensing and transduction, transcriptional regulation, protection and detoxification, and hormone signaling might mediate melatonin-induced cold tolerance. Taken together, our results suggest that melatonin can induce cold tolerance via long distance signaling, and such induction is associated with an enhanced antioxidant capacity and optimized defense gene expression. Such a mechanism can be greatly exploited to benefit the agricultural production.

This study was carried out to evaluate the quality of the three edible tissues (muscles, hepatopancreas and gonads) of the male and female Chinese mitten crab (Eriocheir sinensis) in natural harvest season, based on total volatile base nitrogen test (TVBN) and biogenic amines analysis at intervals time of 3 h extended for 24 h during 30 °C storage (a mean ambient temperature in harvest season). In addition, the relationship between the value of TVBN and storage time or main biogenic amine was evaluated. Results showed that TVBN level of female gonad reached the recommended limit (30 mg/100 g) at 3 h, and the times of reaching the recommended limit were 15 h in both sexes muscles, while in male and female hepatopancreas reached the recommended limit at times of over 24 and 24 h respectively. Moreover, putrescine was highest in amount in all biogenic amines analyzed. We suggested that TVBN value could be as a good indicator for Chinese mitten crab freshness. According to analysis for biogenic amine accumulated in edible tissues of crab, it was possible that dead crab poisoning may be caused by putrescine. Dead Chinese mitten crabs for over 24 h, should be not recommended for eating or processing.

This study was carried out to evaluate the quality of the three edible tissues (muscles, hepatopancreas and gonads) of the male and female Chinese mitten crab (Eriocheir sinensis) in natural harvest season, based on total volatile base nitrogen test (TVBN) and biogenic amines analysis at intervals time of 3 h extended for 24 h during 30 °C storage (a mean ambient temperature in harvest season). In addition, the relationship between the value of TVBN and storage time or main biogenic amine was evaluated. Results showed that TVBN level of female gonad reached the recommended limit (30 mg/100 g) at 3 h, and the times of reaching the recommended limit were 15 h in both sexes muscles, while in male and female hepatopancreas reached the recommended limit at times of over 24 and 24 h respectively. Moreover, putrescine was highest in amount in all biogenic amines analyzed. We suggested that TVBN value could be as a good indicator for Chinese mitten crab freshness. According to analysis for biogenic amine accumulated in edible tissues of crab, it was possible that dead crab poisoning may be caused by putrescine. Dead Chinese mitten crabs for over 24 h, should be not recommended for eating or processing.

The site order parameter (SOP) has been adopted to analyze various orders of structure formation and distribution during the crystallization of a polyethylene globule simulated by molecular dynamics. The SOP not only identifies different orders among the structures but also different phases. The results showed that intermediate structures with medium order exist unevenly in the early stage of nucleation, which differs from traditional models. We found that the nucleation relies on crystallinity fluctuations with increasing amplitude, and a baby nucleus with different shape and increasing size suddenly appears in the fluctuations. Once its size is large enough, the baby nucleus becomes the nucleus. In the growth stage, a number of lamellar mergences were observed and their selective behaviors were related to the orientation differences between the lamellae to be merged. The SOP distribution of all atoms in the system during crystallization had two peaks: one for the amorphous phase and the other for the crystalline phase. The intermediate structures with medium orders are located between the two peaks as an order promotion pathway. The data show that the medium order structure fluctuates at the growth front and is not always available, and that the medium order structure existing at the front is not always good for development. It is possibly caused by chain entanglement. Structure fluctuation at the growth front enables the system showing thousands of the most probable configurations to approach the precursor. The growth front is thus active for a while and inactive at other times.

Rubber elasticity theory is of fundamental importance in polymer science. The traditional theory is athermal, describing rubber deformation behavior as entropy elasticity without an internal energy contribution. It has been found experimentally, however, that the internal energy contribution is not zero. In the present study we have used conformational elasticity theory to calculate the internal energy contribution of polydimethylsiloxane (PDMS) and results obtained are consistent with a number of experimental observations.

In the current study, we examined the effects of histamine on survival and immune parameters of the Chinese mitten crab, Eriocheir sinensis. The crabs infected with the common bacteria pathogen Aeromonas hydrophila were injected with 0 µg histamine/g/crab, 1 µg histamine/g/crab, 50 µg histamine/g/crab, or 100 µg histamine/g/crab, and their survival after 96 h was recorded. The results showed that histamine alone had no influence on crab survival but can decrease survival of the crabs challenged with A. hydrophila after 36 h. In addition, the survival of the crabs injected with the high level (100 µg/g) of histamine was significantly greater than that of the lower level (50 µg/g) after 60–96 h (P < 0.05), but not different from that of the control. Immune parameters of the hemolymph in crabs, such as the total hemocyte count (THC), phenoloxidase (PO), acid phosphatase (ACP), alkaline phosphatase (AKP), and superoxide dismutase activity (SOD), were measured at 6 h, 12 h, and 24 h after histamine in...

In Asia, trash fish have been routinely used in aquaculture often due to their local availability and lower costs compared to formulated feed. However, stale trash fish contain high levels of biogenic amines, which have been reported to be harmful to poultry and some aquatic animals. The present study elevated the effects of histamine levels in the water on survival, growth, sexual maturity and tissue histamine accumulation of two estuarine mysis, Neomysis awatschensis and Neomysis japonica Nakazawa. Newly hatched neonates of each mysis species were cultured in brackish water containing 0 (control), 5, 10 and 15 mg/L histamine until they reached sexual maturity. The results showed that compared to the control, survival of N. awatschensis was significantly lower in both 10 and 15 mg/L histamine treatments (69.5 and 62.5% vs. 86.5%). In the case of N. japonica Nakazawa, significantly lower survival was found for the 15 mg/L treatment (53.9% vs. 72.4%) (P 0.05) but the intermolt period was substantially prolonged at all histamine levels tested when compared to that of the control. Meanwhile, the timings required to reach sexual maturity for both male and female of the two mysis were generally increased with increasing histamine level, and such differences were often statistically significant (P < 0.05). Compared to the control, the tissue histamine concentration of the mysis increased significantly at histamine concentrations of 10 and 15 mg/L for N. japonica Nakazawa (P < 0.05). In the case of N. awatschensis, however, no significant differences were found among all treatments. Our findings indicate that histamine had clear negative effects on both mysis species although their responses and sensitivity appeared somewhat different. Our results suggest that further research is needed to assess the effects of water borne histamine on various aquatic animals.

Simulations in conjunction with Raman scattering were performed to determine the conformational distortion of the α′ form of poly(lactic acid) (PLA). Based on packing constraints of an overall helical structure, the chain conformation can only be approximated by slight deviations from a tg’t chain conformation. Models were generated with different types of random departures from the expected dihedral angles. Raman active vibrations in the 700 cm −1 region that are sensitive to changes in chain conformation were analyzed. The model that showed the best fit to the experimental data contains a majority (80%) of tg’t -10 3 sequences with randomly distributed tg’t -3 1 units. Departure of the O-C α dihedral angle was also proved. The mechanism of order formation was established. As PLA chains crystallize at low temperatures, only the α′ phase with a disordered helix can be formed which at elevated temperatures can transform to the more ordered α phase. The conformation distortion is then due to the inability for some chains to complete the transition to 10 3 helicity, thus resulting in the formation of the distorted α′ structure.

Poly(lactic acid) samples rich in α′ or α crystals have been characterized using spectroscopic and thermal methods. Cryogenic infrared and Raman spectroscopy were used to probe the differences in chain conformation and packing. Compared to the α crystal, the α′ crystal has weakened specific carbonyl and methyl interactions. Experimental spectroscopic analysis in conjunction with simulation studies have shown that the α′ crystal has uniform conformational disorder in the Cα–C torsion angle. This disorder in chain conformation and packing leads to different crystalline forms with different stabilities. The difference in thermal stability was quantified by measuring enthalpic change at melting for both crystalline forms. Significantly different values for the two crystalline forms were obtained ( Δ H m o ( α ′ ) = 57 ± 3 J g − 1 and Δ H m o ( α ) = 96 ± 3 J g − 1 ). The transformation from the less stable α′ to the more stable α phase has been characterized. This analysis provides an explanation to the double melting peaks usually found in PLLA samples.

The conformational properties of a finite length polyethylene chain were explored over a wide range of temperatures using a replica exchange molecular dynamics simulation providing high quality simulation data representative for the equilibrium behavior of the chain molecule. The radial distribution function (RDF) and the structure factor S(q) of the chain as a function of temperature are analyzed in detail. The different characteristic peaks in the RDF and S(q) were assigned to specific distances in the chain and structural changes occurring with the temperature. In S(q), a peak characteristic for the order in the solid state was found and used to determine the equilibrium melting temperature. A detailed scaling analysis of the structure factor covering the full q range was performed according to the work of Hammouda. In the Θ region, a quantitative analysis of the full structure factor was done using the equivalent Kuhn chain, which enabled us to assign the Θ region of our chain and to demonstrate, in our particular case, the failure of the Gaussian chain approach. The chain conformational properties at the equilibrium melting temperature are discussed using conformational distribution functions, using the largest principal component of the radius of gyration and shape parameters as order parameters. We demonstrate that for the system studied here, the Landau free energy expression based on this conformational distribution information leads to erroneous conclusions concerning the thermodynamic transition behavior. Finally, we focus on the instantaneous conformational properties at the equilibrium melting temperature and give a detailed analysis of the conformational shapes using different shape parameters and a simulation snapshot. We show that the chain does not only take the lamellar rod-like and globular conformational shapes, typical of the solid and liquid states, but can also explore many other conformational states, including the toroidal conformational state. It is the first demonstration that a flexible molecule like PE can also take a toroidal conformational state, which is normally linked to stiffer chains.

Molecular dynamics (MD) simulation is a powerful computational tool to study the behaviour of macromolecular systems. However, many simulations in this field are limited in spatial or temporal scale by the available computational resource. In recent years, graphics processing units (GPUs) have provided unprecedented computational power for scientific applications. Many MD algorithms suit the multithread nature of GPU. In this paper, MD algorithms for macromolecular systems that run entirely on GPU are presented. For validation, we have performed MD simulations of polymer crystallisation with our GPU package, GPU_MD-1.0.5, and the results agree perfectly with computations on CPUs, meanwhile GPU_MD-1.0.5 achieves about 39 times speedup compared with GROMACS-4.0.5 on a single CPU core. Therefore, our single GPU code has already provided an inexpensive alternative for macromolecular simulations of traditional CPU clusters and will serve as a basis for developing parallel GPU programs to further speed up the computations.

The juvenile Chinese mitten crabs Eriocheir sinensis (1.40 ± 0.43 g) were cultured in water of 5.34 ± 0.43 (hypoxia, treatment group) and 21.02 ± 0.06 kPa (high dissolved oxygen (DO), control group) DO for 24 h, respectively. The total hemocyte counts (THC), the hyaline hemocyte counts were measured at 0 and 24 h in the treatment group, and superoxide dismutase (SOD) activity, concentrations of lactic acid and hemocyanin (Hc) in hemolymph and the metabolism of hepatopancreas (concentrations of glucose, total cholesterol, uric acid, total protein, urea, triglyceride in hepatopancreas) were assayed at 0, 2, 8, and 24 h in both treatment and control groups. The hyaline hemocyte counts and THC decreased significantly by 66 and 49% after exposure to hypoxic water for 24 h, respectively. SOD activity, Hc and lactic acid content were significantly affected in treatment group, and there were significant differences between treatment and control groups. In the treatment group, the concentration of glucose, cholesterol and uric acid in hepatopancreas had a significant variation for 24 h. The concentration of total protein, urea and triglyceride between treatment and control groups was not significantly different after 0, 2, 8, 24 h. However, there were significant differences between treatment and control groups in terms of total protein, glucose, and uric acid concentration. Taken together, the effect of hypoxia is comprehensive in juvenile Chinese mitten crab Eriocheir sinensis.

Precocious puberty is one of the major constraints to the further development of Chinese mitten crab (Eriocheir sinensis) farming industry. Although dietary phospholipids (PL) and highly unsaturated fatty acids (HUFA) supplementation have been shown to enhance the growth of larval E. sinensis in other studies, it is still unknown whether this also leads to a higher precocity rate for juvenile E. sinensis. This study was conducted to investigate the effects of dietary PL and HUFA on precocity, survival, growth and hepatic lipid composition of juvenile E. sinensis. Two diets were formulated with PL [3.95% dry weight (DW)] and HUFA (0.98% DW) supplementation (diet A) and without PL and HUFA supplementation (diet B) and fed to juvenile E. sinensis. Although dietary PL and HUFA levels did not significantly affect the survival and growth performance of juvenile E. sinensis, compared with crabs fed diet A, a higher precocity rate was found among juvenile E. sinensis fed diet B (P=0.051). A higher total lipid content, but significantly lower levels of HUFA and PL (P

The present study investigated the external and histological changes in the ovary and measured the gonadosomatic index (GSI) and hepatosomatic index (HSI) during the re-maturation of the Chinese mitten crab Eriocheir sinensis. The results show that the ovarian re-maturation cycle of this crab species can be divided into four stages, i.e. Stage I: the ovary had an X shape and appeared milky white or with a mottled buff colour, and the dominant gametocyte at the stage were oogonia (OG, 28.3%) and previtellogenic oocytes (PR, 31.6%); Stage II: the ovary appeared light yellow or tan in colour, dominated by endogenous vitellogeic oocytes (EN, 69.3%). The yolk globules of unreleased mature oocytes (MO) from the previous spawn were absorbed, leaving many vacuoles in the retrogressing MO; Stage III: the ovary appeared crimson red or deep purple, and although the main type of gametocyte was exogenous vitellogenic oocytes (EX), near-mature oocytes (NO) could also be found in the late phase of the ovarian development stage; Stage IV: the ovary was ripe and filled with MO that contained large yolk globules. During the period of the second ovarian maturation cycle, the GSI increased significantly from the time just after the first spawning (P 0.05). Furthermore, the final GSI and the volume of MO of E. sinensis during the second maturation cycle were drastically lower than those of the first maturation cycle.

Estuaries are often subjected to intensive aquaculture activities. Finfish and crustacean culture frequently involve the use of trash fish, which can contain high amounts of histamine. This has the potential to be a major ecological concern since this trash fish often becomes a feed source for naturally occurring small aquatic animals, such as mysis. The present study evaluated the effects of dietary histamine supplementation on survival, growth, sexual maturity and tissue accumulation of two estuarine mysis, Neomysis awatschensis and N. japonica Nakazawa. Both N. awatschensis and N. japonica Nakazawa were fed specially formulated diets containing 0 (control), 1, 2 and 4 g/kg supplemented histamine (5 replicates per treatment; 110 neonates per replicate) from the time they became capable of effectively feeding on formulated diets (10 and 17 day-post-hatch for N. awatschensis and N. japonica Nakazawa, respectively). The feeding experiment continued until the mysis reached sexual maturity. Our current findings indicate that dietary histamine had negative effects on both mysis species although their sensitivity to histamine appeared to be species-specific. Results showed that survival was significantly lower for N. awatschensis fed diet containing 4 g/kg supplemented histamine (56.8%) when compared to that of the control (78.3%), while for N. japonica Nakazawa, survival was significantly lower in both 2 (52.1%) and 4 g/kg (51.5%) histamine treatments than in the control group (74.3%) (p 0.05). It generally took longer for both males and females of the two mysis species to reach sexual maturity when they were fed diets containing higher levels of histamine and the differences were often significant (p

Large-scale coarse-grained molecular dynamics simulations have been performed to investigate the self-assemblies of dodecyltrimethylammonium bromide (DTAB) and gemini surfactants 12-S-12 (S = 6, 14, and 20). At the concentrations investigated, the surfactants experience fast aggregation of monomers into oligomers until the cluster numbers reach maxima. For DTAB, larger aggregates grow at the expense of monomers, but for gemini surfactants, the growth of clusters is accomplished via the merging of oligomers. In the final stage, spherical and worm-like micelles coexist in the systems of DTAB and 12-6-12, and in gemini systems with longer spacers, namely, 12-14-12 and 12-20-12, well-defined vesicles are formed through expansion and curving of bilayer-like structures. Through detailed analysis of the vesicle structures, many of the 12-20-12 surfactants are found to have their headgroups at different surfaces, with the spacers bridging the inner and outer surface of the vesicle.

The conformational transition behavior of polymer in the amorphous state has been investigated through molecular dynamics simulations across the glass transition temperature ( T g ). We find that the conformational transition, a localized and short time dynamics feature, crosses over different barrier heights when the system transforms from the molten state into the glass state and the barrier height in the glass state is markedly lower than that above T g . In addition to the overall transition behavior, the specific transitions between the rotational isomeric states (RIS) g + , t − , t + and g − are also investigated in detail. The populations of these specific transitions undergo considerable changes when the temperature decreases; meanwhile, the larger transition rates of the ending torsions get diminished. Besides the rate, the rotation degrees of the dihedrals during the transitions also change their distributions tremendously through T g , below which most of the larger transition angles (50–100°) were inhibited remaining those sharply around 30°. This possibly explains why below T g the conformational transition process has a lower effective barrier.

The metal atom net charge correlation (MANCC) method was developed in prediction of catalyst activity of asymmetric late-transition metal complexes, 2-quinoxalinyl-6-iminopyridine Ni (II), 2-imino-1, 10-phenanthroline Co(II) and 2-methoxycarbonyl-6-iminopyridine Pd(II) complexes, from the net charge of the metal atom for ethylene polymerization. Dreiding force field was modified according to the X-ray diffraction data. We found that the asymmetric structure of the complexes resulted in a charge difference between two halogen atoms coordinated to the metal atom. In order to remove such contribution we introduced the effective charge Qeff, which was obtained by the charge equilibration (QEq) approach. The results verified the successful introduction of Qeff and showed that the catalytic activities of different complexes are related to central metal atom effective charge.

Using a large polymer chain cluster, we have examined entanglement densities of the polymer chains in the bulk and in the surface by molecular dynamics simulation. The entanglement density was measured by the interchain contact fraction (ICF), which was developed as a structural parameter of the entanglement. It was found that the surface location has a lower ICF than the bulk core does. Different entanglement structures then underwent crystallization processes. It resulted in a multidomain system, in which the directors of the order domains are in isotropic distributed. For calculating the crystallinity of the systems, we developed a method, the site order parameter (SOP), which endows local order to every particle in the system; when determining the order for crystalline phase, one can count the crystallinity. SOP enables us to transform a molecular chain picture into an order image, where white stands for the crystalline phase and black for the amorphous. Snapshots of the simulations show evolution of the nucleation and the crystal growth through SOP images. The dynamic effect of the entanglement was observed in the crystallization behaviors. It shows that the entanglement has a higher density in the bulk and a lower density in the surface. The result shows that a shorter induction period of nucleation and a higher crystal growth rate was found in the surface location, since possessing lower ICF.

Atomistic detailed hydration structures of poly(vinyl methyl ether) (PVME) have been investigated by molecular dynamics simulations under 300 K at various concentrations. Both radial distribution functions and the distance distributions between donors and acceptors in hydrogen bonds show that the hydrogen bonds between the polymer and water are shorter by 0.005 nm than those between water molecules. The Quasi-hydrogen bonds take only 7.2% of the van der Waals interaction pairs. It was found the hydrogen bonds are not evenly distributed along the polymer chain, and there still exists a significant amount (10%) of ether oxygen atoms that are not hydrogen bonded to water at a concentration as low as 3.3%. This shows that in polymer solutions close contacts occur not only between polymer chains but also between chain segments within the polymer, which leads to inefficient contacts between ether oxygen atoms and water molecules. Variation of the quasi-hydrogen bonds with the concentration is similar to that of hydrogen bonds, but the ratio of the repeat units forming quasi-hydrogen bonds to those forming hydrogen bonds approaches 0.2. A transition was found in the demixing enthalpy at around 30% measured by dynamic testing differential scanning calorimetry (DTDSC) for aqueous solutions of a mono-dispersed low molecular weight PVME, which can be related to the transition of the fractions of hydrogen bonds and quasi-hydrogen bonds at ∼27%. The transition of the fractions of hydrogen bonds and quasi-hydrogen bonds at ∼27% can be used to explain the demixing enthalpy transition at 30% at a molecular scale. In addition, at the concentration of 86%, each ether oxygen atom bonded with water is assigned 1.56 water molecules on average, and ‘free’ water molecules emerge at the concentration of around 54%.

Aquaculture of the Native Chinese mitten crab (Eriocheir japonica sinensis) has developed quickly in China to reach 570,000 mt in 2005, which exceeds all other worldwide production of crab from aquaculture and capture fisheries combined. We review the development of aquaculture techniques and stock enhancement that account for this successful production of Chinese mitten crabs. There are two models for mitten crab larviculture. In the first model, intensive larviculture occurs in indoor concrete ponds, with conditions of temperature control, aeration, and a plentiful supply of food (algae, egg yolk, rotifers, Artemia nauplii). In the second model, outdoor extensive larviculture occurs in earth ponds with no temperature control. Grow-out of the mitten crab focuses on release of cultured seed crabs into net enclosures in lakes. As a rule, the production of adult crabs is l50–450 kg/ha and as high as 975 kg/ha. Recently, Chinese researchers noticed deterioration of water quality and the exhaustion of natural...

This study was conducted to determine the optimum phospholipids: highly unsaturated fatty acids (PL/HUFA) ratio in maturation diets for female Chinese mitten crab, Eriocheir sinensis broodstock. Five isolipidtic and isonitrogenous diets were formulated to contain different amounts of pork lard, fish oil and soy lecithin with resulting PL/HUFA levels (% dry weight) of 1.4/0.3 (Diet 1), 1.6/2.5 (Diet 2), 2.3/2.0 (Diet 3), 3.8/1.5 (Diet 4) and 5.1/0.8 (Diet 5). Diet 1 lacked supplemental fish oil and soy lecithin and served as the control. Each of the five formulated diets was fed to a total of 150 female crabs for a period of 7 months. All diet treatments were triplicated with 50 crabs stocked in a pond as a replicate. After 6 months, male crabs were introduced into the ponds where females were kept, mating, spawning and egg hatching (in seawater) occurred in the following month. The nutritional value of various formulated diets was assessed based on survival, gonadosomatic index (GSI), egg production per female, fecundity (eggs/g female weight) of the females fed those diets and egg and larval (newly hatched zoea I larvae) quality. Females fed Diet 1 had the lowest GSI, egg production per female and fecundity while no significant difference were found for survival, hepatosomatic index (HSI) and the percentage of female spawned among the diet treatments (P > 0.05). Although there were no significant differences in egg diameter, egg wet or dry weights among all treatments (P > 0.05), the highest and the second highest proportions of essential fatty acids (EFA), i.e. 20:5n-3 (EPA), 22:6n-3 (DHA) and HUFA were found in the eggs produced by the females fed Diet 3 and Diet 2, respectively. Statistical analysis showed that EPA, DHA and HUFA in eggs produced by females fed Diet 3 were significantly higher than those from the other treatments (P < 0.05). Meanwhile, zoea I larvae from crabs fed Diet 3 had significantly larger carapace length than those from the other four treatments (P < 0.05). The zoea I larvae from crabs fed Diet 2 and Diet 3 also showed generally better tolerance to starvation and osmotic shock. In conclusion, our results indicated that diet included levels of PL/HUFA around 1.6/2.5 or 2.3/2.0 (% dry weight) fed female E. sinensis broodstock supported increased fecundity and elevated level of HUFA in egg, which in turn resulted in improved overall quality of newly hatched larvae.

Melatonin is involved in defending against oxidative stress caused by various environmental stresses in plants. In this study, the roles of exogenous melatonin in regulating local and systemic defense against photooxidative stress in cucumber (Cucumis sativus) and the involvement of redox signaling were examined. Foliar or rhizospheric treatment with melatonin enhanced tolerance to photooxidative stress in both melatonin-treated leaves and untreated systemic leaves. Increased melatonin levels are capable of increasing glutathione (reduced glutathione [GSH]) redox status. Application of H2 O2 and GSH also induced tolerance to photooxidative stress, while inhibition of H2 O2 accumulation and GSH synthesis compromised melatonin-induced local and systemic tolerance to photooxidative stress. H2 O2 treatment increased the GSH/oxidized glutathione (GSSG) ratio, while inhibition of H2 O2 accumulation prevented a melatonin-induced increase in the GSH/GSSG ratio. Additionally, inhibition of GSH synthesis blocked H2 O2 -induced photooxidative stress tolerance, whereas scavenging or inhibition of H2 O2 production attenuated but did not abolish GSH-induced tolerance to photooxidative stress. These results strongly suggest that exogenous melatonin is capable of inducing both local and systemic defense against photooxidative stress and melatonin-enhanced GSH/GSSG ratio in a H2 O2 -dependent manner is critical in the induction of tolerance.

In the present study, the degree of chain interpenetration was considered as a structural attribute of the entanglements in polymer chain system. Inter-chain radial distribution function (RDF) was used to perform this measurement. We applied this method to a model system, in which an ordering process in the early stage of polymer crystal nucleation at the atomistic level was simulated by means of molecular dynamics (MD). Initial chain structures possessed different degrees of interpenetration and underwent the ordering process at 400 K. Obtained results indicated that at the nanosecond scale the degree of interpenetration impedes the ordering process remarkably, which agrees with the experimental observation at laboratory time scale. Such behavior among chains indicates that at the atomistic level a creeping polymer chain is able to recognize if the neighbor group on the ‘tube’ is from the same chain or other chains. This recognition manifests that the reptation time of a chain would be influenced by the ‘tube’ composition or the degree of interpenetration. It also showed that the degree of interpenetration changes little during the ordering process, which means that the motion of the chain segments is mainly predominated by the ordering process rather than further adjusting the entanglement extent under the conditions simulated.

Molecular dynamics simulations were performed to investigate the influence of molecular weight on the interpenetration process of two initially isolated globule-chains. From molecular weight lower and higher than the critical molecular weight, the analysis of the simulation result indicate the duration of interpenetration has the relationship with chain length: τ∼N 2 , which is different from that of the relaxation time in reptation model. It also shows that the interaction between chains measured by the mean force increases with the increment of chain length, and a turning point was found at the position corresponding to the critical molecular weight. Before the turning point, the mean force increases fast versus molecular weight, and after that the increase turns to be slow. Through correlating the simulation result with the experimental tensile strength of polymer films, it shows that the interpenetration of the chain segments with critical molecular weight is necessary for the formation of entanglement structure.

The molecular mechanics (MM) method with COMPASS force field was used to study the H-bonds in polyurethane with carboxyl (PUc), which has multiple donors and acceptors. 2-Methyl-3-{[(methylamino)carbonyl]oxy}propanoic acid was used as the model molecule. It was found that the model PUc possesses four conformers with lowest energy. Considering six possible H-bond types such as OH⋯OC(OH) (Type I), OH⋯OH(CO) (Type II), OH⋯OC(NH) (Type III), NH⋯OC(OH) (Type IV), NH⋯OH(CO) (Type V), NH⋯OC(NH) (Type VI), in such system 192 H-bond complexes are simply expected. All the complexes were simulated in this modeling. Obtained total energies of the complexes were used to analyze the existence probability of each H-bonding configuration. The results show that for the six types of H-bonds, Types I (61%) and VI (37%) are the main H-bonding configurations in PUc, Types III and IV have the low probability (2%) and mostly coexist with other H-bond types, and Type II and V hardly exist.

To improve the accuracy of polymer interfacial tension measurement using deformed drop retraction method (DDRM), we examined some factors, such as the shape parameter, the retraction scale D0, and the distortion criterion γ by means of dissipative particle dynamics (DPD) simulation with 6 different models and analysis with three observation data, and proposing a new shape parameter P. Results show that the shape parameter order of suitable to various retraction scales and larger distortion is P>(a2−b2)>D. This study found that choosing a suitable retraction scale is very important, and that D0≅0.15 is the most suitable retraction scale in DDRM measurement. In the scale, the three shape parameters cannot make much difference on the measurement deviation from the standard. This study also found that the distortion criterion γ varies with different shape parameters. We also found here when D0≅0.15 the distortion criterion becomes γ

Poly(vinyl methyl ether) (PVME) aqueous solution possessing specific bimodal phase diagram has been studied on the interaction of water and dimethyl ether (DME) as a model compound of PVME by using ab initio calculation (6-31+G*) and infrared spectroscopy. The most probable interaction configurations of DME with one to five water molecules were intensively searched in the present study. Among the configurations, we found two sorts of interactions appearing as specialties: the hydrogen bond (HB) and the quasi-hydrogen bond (QHB). We further studied the influence of the interactions on infrared band shifts for νs(CH3) and ν(C−O) as a function of the number of water molecules in statistical average. Comparing with the experiments, the high concentration area and the low concentration area (with two different slopes) suffer from different interaction mechanisms. The former has HB and single-QHB, while the latter double-QHB and triple-QHB, besides the van der Waals and the electrostatic interaction. For under...

The process experimentally measuring the interfacial tension of polymers was simulated by means of dissipative particle dynamics (DPD) simulation method in the present study. It is a retraction of ellipsoid drop of a polymer within the other polymer bulk. Effect of the initial geometry of the ellipsoid on the finally obtained interfacial tension was focused, since it was found the ellipsoid might not have the same length for both short axes, which is against original assumption. Simulated results show that different initial short axes of b and c do influence eventual measurement of the tension. However, a smaller deviation between b and c was found to be leading to an acceptable measurement. For this judgment, we found a criterion is γ = ( b − c ) / a 0.3 .

The metal atom net charge correlation (MANCC) was successfully used to study the relative catalytic activities of 20 bis(imino)pyridyl Fe(II) and bis(imino)pyrimidyl Fe(II) complexes for olefins polymerization/oligomerization through modifying the Dreiding force. The net charge range on the central metal Fe was found 0.6295–0.8310, which was considered in the present study as two areas, e.g. the lower charge area (0.6295–0.7000) and the higher charge area (0.7000–0.8310). The observations reveal that the catalytic activity of bis(imino)pyridyl Fe(II) and bis(imino)pyrimidyl Fe(II) complexes does not monotonously vary with the net charge on the central metal as we found for other metal system before. There possibly is an interesting turning point around 0.7000. The activity increases with the net charge in the lower charge area, while the catalytic activity increases with reducing the net charge in the higher area. The reason that the Fe(II) catalysts possess such properties was discussed.

The conformational distribution change of amorphous poly(lactic acid) (PLA) induced by deformation has been studied using Raman spectroscopy. Spectroscopic features associated with the rotational isomeric states ( ttt , ttg ′, tg ′ t , tg ′ g ′) have been established experimentally and supported by normal coordinate analysis. Deformation induced a significant increase in the most favorable tg ′ t conformation. Based on the relative intensities of Raman-active skeletal modes, a quantitative method has been developed that can be used to elucidate structural changes in a variety of deformed polymer samples. For biaxially oriented PLA films, the overall tg ′ t conformation increased from the 76% in undeformed sample to a value as high as 92%. The change in conformational distribution in the amorphous phase follows a different trend (76–88%) as compared to the increase in sample crystallinity (0–43%). A large change in amorphous chain conformation occurred at relatively low draw ratios. In contrast, the large change in the degree of crystallinity occurred at higher draw ratios.

Molecular dynamics simulations of merging process of two isolated cyclic chains and that of linear chains have been performed, in order to find the difference between the two kinds of chain in bulk and in vacuum, where surface of the system restrains thousands of configurations showing up. Analysis indicates that in such confinement the chain ends at most moments float on the surface layer, and their mobility is much larger than the mean value of all atoms in linear chains, or that in cyclic chains. Comparison of the merging processes of cyclic chains and their linear counterparts was intensively carried out by several means of analyzing the trajectory files in statics and in dynamics. It was found that the segments of cyclic chains showed almost the same behavior of motion with that of linear chains. This is different diffusion behavior from that in bulk systems, where the cyclic chain has much higher diffusion rate. This modeling therefore indicates that in these confined systems because of the surface energy, the end groups are involuntarily kept on the surface, and lost the capacity of leading chain reptation through the other polymer chains, which is possibly the origin that the difference of diffusion behavior between the linear chain and the cyclic chain in the bulk almost disappears in the case of the confinement.

A means of correlation between the activity and the net charge, the metal atom net charge correlation (MANCC), which was successful in the activity prediction of the early-transition metal catalysts, has been used to study the catalytic activities of salicylaldiminato Ni(II) complexes, the late-transition metal catalysts, in olefin poly- merization or oligomerization. A comparison with the available quantum mechanics/ molecular mechanics (QM/MM) calculation data suggests that even without a detailed mechanism, MANCC results mostly agree with QM/MM calculation data regarding insertion barrier data and enthalpy change. Eight experimental complexes were fur- ther built up by modeling; their catalytic activities predominantly increased in line with the net charges on the metal atoms. The same results were obtained for the other four complexes synthesized in the present work. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4765- 4774, 2004

The molecular mechanics (MM) method with COMPASS force field was used to study the H-bonds in the polyether based polyurethane model molecules. Availability of the calculation was firstly verified in comparison of some H-bonded model molecules, which were studied by using ab initio calculation, and those calculated by MM. Based on a urethane model molecule 1,3-dimethylcarbamate, which can be donor or acceptor and behaves in various conformations, it is reasonable to have a large number of H-bond interactions between various conformational donors and acceptors. For examining all the possible interaction patterns, we studied 57H-bond complexes. This systematic modeling covers well-known four types of interaction patterns, such as NH⋯OC (Type I), NH⋯O–CO (Type II), NH⋯NH (Type III), NH⋯COC (Type IV) in the system. Obtained H-bond energies were used to analyze the probabilities of the complexes. For the interaction within the hard segments, or Type I, Type II and Type III, a predominant H-bond complex has been found in the present study, which belongs to Type I. For the interaction between the hard segment and the soft segment, two conformations of Type IV were calculated to be existed.

Molecular dynamics simulations have been performed on the aqueous solutions of Poly(vinyl methyl ether) (PVME) at various concentrations. Both radial and spatial distribution functions are used to investigate the detailed hydration structures. The structures of water are found to get increasingly concentrated when polymers are introduced and the water motions are severely hindered by the polymer matrix. At low concentrations, larger populations of tt conformers in meso dyads than those at higher concentrations are found and this phenomenon is believed to be due to the increase of water molecule bonding to two ether oxygens in meso dyad. At higher concentrations the sizes and conformations of polymers are quite similar with those in bulk. A transition of hydrogen bond fractions between PVME and water at around the concentration of 0.3 is observed and this value coincides perfectly well with the results of conformational analysis and Raman spectra. Second neighbor hydrogen bond statistics showed that complicated hydrogen bond networks take the lead at low concentrations, but single hydrogen bonds as well as isolated clusters composed of 2-4 water molecules are found common around each polymer repeat unit.

Cold drawing is known as a thermodynamically reversible process for glassy polymers. In the extension process, there might be a stage in which the global structure of chain coils extends in the drawing direction. This extension stage has not been clearly identified because of the lack of a quantitative relationship between the global structure evolution and the local structure reorientation. We have developed a theoretical method to elucidate the relationship, which is based on a simulated chain conformational distribution and a relationship between the chain conformations and the extension. Any local structure, such as the fraction of trans conformations of ethylene glycol of poly(ethylene terephthalate) (PET), can then be calculated with an ensemble average as a function of the system extension. Combined with infrared conformational band measurements, the coil extension stage has been characterized in the cold drawing of amorphous PET. This stage does not start from the yielding point but instead begins nearly at the end of the stress softening. In the recovery process, the experimental measurements and theoretical predictions are well correlated. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2646–2652, 2002

A combination of molecular mechanics and the charge equilibration method was applied and further developed to predicting the catalyst activity of a metal complex. A late transition metal catalyst, {di-μ-bromotetra [N,N'-bis (3,5-dimethylanil)-4-methyl-2,6-bis(imino)phenoxy]nickel} bromide (MOL) was dealt with. A modified molecular force field from universal force field was set and validated for this system. Simulations predict that the activity of MOL varies little with temperature. Simulation results were in good agreement with experimental results for ethylene oligomerization with MOL.

The calcium-dependent protein kinase (CDPK) is a ser/thr protein kinase that plays vital roles in plant growth, development, and responses to multiple stresses. Despite an important member of the stress responsive gene family, little is known about the evolutionary history and expression patterns of CDPK genes in melon. Herein, a total of 18 CDPK genes and 7 CDPK-related protein kinases (CRK) genes were identified in the melon genome via bioinformatic analysis, which were unevenly distributed across eleven chromosomes with an apparent exception for chromosome 3. Comparative syntenic analysis between Cucumis melo L. and Arabidopsis thaliana revealed that 13 CmCDPKs and 19 AtCPKs existed in 20 corresponding syntenic blocks. In addition, based on gene structure and phylogenetic analyses, all CmCDPKs were divided into four groups (CDPK I-IV) and CmCRKs clustered into one group (CRK I). Interestingly, group CDPK IV was clearly distinct from the other three CDPK groups, but clustered with CRK I on the phylogenetic tree, implying their origination from a common ancestor. Furthermore, CmCDPKand CmCRK genes were differentially expressed in response to various stimuli, such as biotic stress (Podosphaera xanthii), abiotic stress (salt and cold), and hormone (abscisic acid) treatment. To our knowledge, this is the first report on CDPK and CRK gene families in melon, which provides a basic foundation for functional characterizations of CmCDPK and CmCRK genes in the future.

A vibrational analysis has been carried out to analyze the chain conformation of poly(lactic acid) in the crystalline state. In conjunction with a normal-coordinate analysis, the Raman spectrum has yielded data regarding conformational distributions. Raman spectra of different helices were simulated using previously published structures, force constants, and intensity parameters. Some of the chain conformations predicted are inconsistent with the data. Only one of the four 31 helical structures predicted by conformational analysis agrees well with experiment. This analysis provides a new understanding regarding the relative probability of a 103 or 31 helix for poly(lactic acid).