共查询到20条相似文献,搜索用时 15 毫秒
1.
Young-Chang Nho Youn-Mook Lim Hui-Jeong Gwon Eun-Kyung Choi 《Korean Journal of Chemical Engineering》2009,26(6):1675-1678
Hydrogels for wound dressings from a mixture of poly(vinyl alcohol) (PVA), poly(N-vinylpyrrolidone) (PVP), glycerin and an antibacterial agent were obtained by a γ-irradiation combined with freeze-thawing. The physical properties such as the gelation and swelling degree of the hydrogels
were examined. When the PVP/PVA ratio was 6: 4 (wt%) and prepared by combined irradiation and freeze-thawing, it showed an
excellent swelling capacity (>1,200%). The antibacterial effect of the hydrogels containing the antibacterial agents was observed
to be effective as the concentration of antibacterial agents increased. The results demonstrated that hydrogel in a proper
blending ratio could be used as a wound dressing that can accelerate wound healing with an antibacterial effect. 相似文献
2.
Florian J. Stadler 《Korean Journal of Chemical Engineering》2011,28(10):2057-2063
The temperature- and frequency-dependent dynamic-mechanical properties in the temperature regime of the γ-transition were determined for a number of polyethylenes and ethylene/α-olefin-copolymers differing in their crystallinity and crystal morphology. The temperature dependence of the γ-transition was found to obey the Arrhenius law for thermally activated processes. The γ-transition temperature determined at a frequency of 1 Hz and the corresponding activation energy were analyzed as a function
of the crystallinity. As an overall trend, both quantities are found to decrease with decreasing crystallinity, which is explained
by the increase in free volume due to the incorporation of short-chain branches or the thermal pretreatment (e.g., quenching).
Taking into account that the crystal morphology of polyethylenes can be classified into four different groups, a more detailed
picture appears. Within one type of morphology both quantities, namely the transition temperature and the activation energy,
increase with decreasing crystallinity independent of the α-olefin used as the comonomer. These findings can be explained by partial orientations of the molecule segments in the interlamellar
amorphous space in the case of HDPE or by the increased steric hindrance of the crankshaft motion by the short-chain branches.
From the findings of this series of studies, it was concluded that the glass transition in polyethylene and polyethylene/α-olefin-copolymers is the β- and not the γ-transition. 相似文献
3.
Florian J. Stadler 《Korean Journal of Chemical Engineering》2011,28(3):954-963
Several ethylene homopolymers and ethene/ α-olefin-copolymers with crystallinities ranging between 85 and 12% were characterized by dynamic-mechanical measurements.
The occurring relaxations were correlated to the crystallinity of the polymeric materials and to morphology. The α-relaxation, being attributed to interlamellar shear, was found to be around 60 °C with activation energies of about 120 kJ/mol
in samples with more than 42% crystallinity. The β-transition shows a much greater variety among the different samples characterized. Its relaxation temperatures vary between
−40 and 10 °C with activation energies between 200 and 400 kJ/mol. The α- and β-relaxation of several quenched samples with crystallinities between 63 and 42% were found to overlap, thus producing bimodal
maxima and different activation energies from the Arrhenius plots. A separation of these overlapping relaxations was only
possible by measuring the relaxations over a frequency range of more than three orders of magnitude. 相似文献
4.
Sui-Lou Wang Jun-She Sun Bei-Zhong Han Xiao-Zong Wu 《Korean Journal of Chemical Engineering》2008,25(3):513-516
High hydrostatic pressure (HHP) technology was used for improving the ability of β-carotene biosynthesis of Rhodotorula glutinis R68. After the treatments of five repeated cycles at 300 MPa for 15 min, the barotolerant mutant PR68 was obtained. After
72 h of culture, the biomass of mutant PR68 was 21.6 g/L, decreased by 8.5% compared to the parent strain R68, but its β-carotene production reached 19.4 mg/L, increased by 52.8% compared to the parent strain R68. The result of restriction fragment
length polymorphism analysis suggested that mutant strain PR68 was likely to change in nucleic acid level, and thus enhanced
β-carotene production in this strain was a result of gene mutation induced by HHP treatment. HHP technology seems a promising
approach for improving industrial microbes. 相似文献
5.
Two light emitting molecules with the cyano group at different positions on the vinylene i.e., 2,5-bis(2-thienyl-1-cyanovinyl)-1-(2_-ethylhexyloxy)-4-methoxybenzene (-TPT) and 2,5-bis(2-thienyl-2-cyanovinyl)-1-(2-ethylhexyloxy)-4-methoxybenzene (-TPT), and corresponding polymers, i.e., poly[2,5-bis(2-thienyl-1-cyanovinyl)-1-(2-ethylhexyloxy)-4-methoxybenzene] (denoted as P1) and poly[2,5-bis(2-ethienyl-2-cyanovinyl)-1-(2-ethylhexyloxy)-4-methoxybenzene] (denoted as P2) were synthesized. -TPT and -TPT, respectively, were blended into two host polymers, poly(methyl methacrylate (PMMA) and poly(9-vinylcarbazole) (PVK), to study the optical properties of the dopants in different host polymer matrices. Although -TPT and -TPT have the same backbone structure, their optical properties are much different. The PL emission maximum (
max) of -TPT was found blue-shifted, compared with that of -TPT, while the PL intensity of -TPT was stronger than that of -TPT. Concentration effect in the optical properties was found, 1 wt% of -TPT in PVK had the maximum fluorescent emission.The PL maximum peak wavelengths for polymer films (P1 and P2) were found red-shifted; while their PL intensities were weaker when compared with those of blends. 相似文献
6.
7.
A novel ∈-lysine acylase (N
6-acyl-l-lysine amidohydrolase; EC 3.5.1.17) was isolated from Streptomyces mobaraensis and purified to homogeneity by SDS-PAGE from the culture broth. The purified enzyme was monomeric, with a molecular mass
of approximately 60 kDa. The enzyme was inactivated by the presence of 1,10-phenanthroline and activated in the presence of
Co2+ and Zn2+. The enzyme showed a pH optimum of 8.0 and was stable at temperatures of up to 50°C for 1 h at pH 8.0. The enzyme specifically
catalyzed the hydrolysis of the amide bond of various N∈-acyl-l-lysines. Furthermore, the enzyme efficiently catalyzed the synthesis of N∈-acyl-l-lysines with fatty and aromatic acyl groups in an aqueous buffer. In the syntheses of N∈-decanoyl-l-lysine, N∈-lauroyl-l-lysine, and N∈-myristoyl-l-lysine, the product precipitated and the yield was 90% or higher using 10 mM FA and 0.5 M l-lysine as the substrate. 相似文献
8.
Synthesis and Properties of Alkyl <Emphasis Type="Italic">β</Emphasis>-<Emphasis Type="SmallCaps">d</Emphasis>-Galactopyranoside 下载免费PDF全文
Guoyong Chen Zhencao Li Langqiu Chen Shanwei Ji Wangzhen Shen 《Journal of surfactants and detergents》2016,19(6):1095-1105
A series of alkyl β-d-galactopyranosides were prepared by the trichloroacetimidate method with d-galactose and alcohols with different chain lengths as raw materials. Their solubility, surface tension, emulsification, foaming, wettability, thermotropic liquid crystalline properties, and thermal stability were investigated. Alkyl β-d-galactopyranosides are soluble in water and ethanol, and the solubility decreases with increasing alkyl chain length. Decyl β-d-galactopyranoside was insoluble in water, but soluble in ethanol. Dissolution of alkyl β-d-galactopyranoside in water is an endothermic process with dissolution enthalpies greater than zero. Nonyl β-d-galactopyranoside had an excellent emulsifying property, better foaming ability and the best foam stability. The CMC values of alkyl β-d-galactopyranosides decrease with increasing of alkyl chain length. Alkyl β-d-galactopyranosides are thermally stable up to 270 °C. Alkyl β-d-galactopyranosides show the distinctive optical texture of a thermotropic liquid crystal smectic A type phase. Decyl β-d-galactopyranoside showed the strongest wettability. 相似文献
9.
Mehran Chitan Seyed Ali Hosseini Dariush Salari Aligholi Niaei Habib Mehrizadeh 《Korean Journal of Chemical Engineering》2017,34(1):66-72
Nano γ-alumina was produced using Nepheline syenite ore by leaching and precipitation process at a certain pH in the presence of sodium dodecyl sulfate (SDS) as a surfactant. The produced nanostructure was characterized by XRD, SEM, EDX, DLS, BET and FT-IR. The XRD pattern confirmed the tetragonal structure of alumina The nano structure of alumina was approved by SEM and the particle size distribution were between 41 to 486 nm, confirmed by DLS. BET analysis showed that the specific surface area of nanopowder was about 39.1 m2/g. The synthesis conditions were modeled and optimized by RSM. The optimum conditions resulted in leaching time, the mass ratio of Nepheline/HCl, and the reflux temperature of 2 h, 20, and 70 °C, respectively. Under optimum conditions, the extraction efficiency was 82%. The prepared nano γ-alumina has higher removal efficiency than commercial types in the removal of p-nitrophenol by adsorption process. 相似文献
10.
V. G. Kulichikhin L. K. Golova I. S. Makarov G. N. Bondarenko A. K. Berkovich S. O. Ilyin 《Polymer Science Series C》2016,58(1):74-84
Combined solutions of cellulose and an acrylonitrile-based copolymer in N-methylmorpholine-N-oxide have been prepared for the first time, new composite fibers have been formed, and the properties of the solutions and fibers under standard conditions and during thermal treatment have been studied. On the basis of studying the phase state and morphological peculiarities of combined cellulose solutions with polyacrylonitrile additives, it has been shown that the completed solutions make emulsions in the entire range of investigated concentrations. The rheological behavior of combined solutions changes with temperature. With the use of IR spectroscopy methods, it has been found that the addition of polyacrylonitrile to cellulose results in the association of nitrile groups with hydroxyl groups of cellulose, which favors the cyclization of CN groups during heating and the appearance of polyconjugated bonds in polyacrylonitrile chains. Thermal transformations of cellulose and polyacrylonitrile in the course of mixed-fiber carbonization have been studied via DSC and TGA. It has been shown that polyacrylonitrile inhibits the dehydration processes in cellulose and reduces the intensity of the peak due to the first stage of the structural rearrangement, i.e., acts as a “catalyst” of pyrolysis. 相似文献
11.
L. Alonso P. Cuesta S. E. Gilliland 《Journal of the American Oil Chemists' Society》2009,86(4):337-342
The aim of this study was to evaluate the effect of β-cyclodextrin (β-CD) on trans C18:1 fatty acid isomers, conjugated linoleic acid (CLA), polyunsaturated fatty acids (PUFA) and phospholipids in pasteurized
milk. The individual trans C18:1 isomers were not significantly affected by the β-CD. trans-11 C18:1 (vaccenic acid) was found to be the major isomer (1.31 ± 0.12%) followed by trans-15 C18:1 (0.35 ± 0.06%). Individual trans linoleic acids did not show differences from the effect of β-CD, representing the high amount of the isomer trans-11 cis-15 C18:2 (0.433 ± 0.087%). The main CLA isomer cis-9 trans-11 C18:2 (rumenic acid) did not show differences between the control milk (0.672 ± 0.080%) and β-CD milk (0.663 ± 0.074%). PUFA and omega-3 and -6 fatty acids were not also significant by the effect of β-CD. Total phospholipids were not significantly affected by effect of the β-CD (0.023 ± 0.001% vs. 0.022 ± 0.001%). β-CD is a effective oligosaccharide for cholesterol removal from pasteurized milk and does not significantly affect the lipid
components of the milk fat. 相似文献
12.
Wanwisa Skolpap Somboon Nuchprayoon Jeno M. Scharer Nurak Grisdanurak Peter L. Douglas Murray Moo-Young 《Korean Journal of Chemical Engineering》2008,25(4):646-655
A modified Markov Chain Monte Carlo (MCMC) searching procedure was developed to search for an optimal set of decision variables
and optimal feed rate trajectories for recombinant α-amylase expression by Bacillus subtilis ATCC 6051a. The bacterium also synthesizes proteases as undesirable products in fed-batch culture that need to be minimized.
To maximize α-amylase productivity, a 14th-order fed-batch model was optimized by integrating Pontryagin’s maximum principle with the Luedeking-Piret equation. The number of iterations and simulations of the proposed searching procedure were statistically examined for accuracy
and acceptability of the results. It can be concluded that the proposed searching procedure increased the parameter selection
opportunity near the tail ends of redefined triangular distribution. By applying a modified MCMC searching procedure with
1,500 iterations, the predicted α-amylase productivity was improved by 18% in comparison with near-optimum experimental results. This productivity was 3.5%
higher than predicted by conventional MCMC optimization. 相似文献
13.
Odor is a key trait for pollinator attraction in flowering plants, and many studies have investigated odor evolution in the light of pollinator selection by emphasizing the importance of the plant phylogenetic history. By contrast, little is known on the evolution of odors in fungus–insect interactions. In this study, profiles of three volatile compounds that are emitted by grass-inhabiting Epichloë fungi (Clavicipitaceae, Ascomycota) and that have a confirmed or likely role in the attraction of gamete-transferring Botanophila flies were investigated. We collected headspace samples from stromata of six European Epichloë species (including various host races) that originated from different locations in Switzerland, France, Poland, and UK for conducting gas chromatography analyses. Odor profiles exhibited considerable variation, but profiles of most species overlapped and did not discriminate at the species level. The exception was Epichloë festucae, which had a profile dominated by methyl (Z)-3-methyldodec-2-enoate. Based on an Epichloë phylogeny, there was some hierarchical structuring regarding levels of chokol K, another confirmed Botanophila attractant. However, patterns of odor profiles appeared to be largely dependant on particular Epichloë–host associations. The observed variation may be the result of complex selective pressures imposed by Botanophila gametic vectors, local environment, and mycoparasites. 相似文献
14.
Previously we have shown that an alkylating agent N-methyl-N'-nitro-N- nitrosoguanidine (MNNG) can induce receptor clustering and the activation of a downstream signal molecule NF-kappaB, and that the receptor clustering is associated with changes in sphingolipids metabolism. On the other hand, the polyene antibiotic nystatin can block MNNG-induced receptor clustering. In this study, using a lipidomic approach, we further evaluated whether nystatin influenced the effects of MNNG on sphingolipids metabolism. It was found that nystatin itself induced changes in the sphingolipids profile in human amnion FL cells to a certain extent, including an increase or decrease of some sphingolipid species. Interestingly, nystatin can block, at least partially, the changes of sphingolipids-induced by MNNG. In addition, nystatin can also partially inhibit the activation of NF-kappaB induced by MNNG. Neither MNNG nor nystatin affects the mRNA levels of serine palmitoyltransferase, acid sphingomyelinase (ASM), and sphingomyelin synthase, key enzymes in the sphingolipids biosynthesis pathway. However, MNNG can activate ASM and neutral sphingomyelinase, while nystatin preincubation inhibits the activation. Taken together, these data suggested that nystatin interferes with the effects of MNNG, and might elicit its function through altered sphingolipids metabolism. 相似文献
15.
Hee Suk Woo Seungmok Shin Hwi-Sung Lee Tae Jun Yoon Youn-Woo Lee 《Korean Journal of Chemical Engineering》2018,35(10):1994-2000
Fatty-acid-adsorbed γ-alumina was regenerated via transesterification using methanol with sulfuric acid as a catalyst. The fatty acids adsorbed on γ-alumina were converted to fatty acid methyl esters (FAME) and desorbed from the γ-alumina during the acid-catalyzed methanol regeneration process. A series of experiments studied the effect of the operating parameters (temperature, amount of sulfuric acid (wt%), methanol-solution-to-γ-alumina weight ratio, and regeneration time) on the acid-catalyzed methanol regeneration process. The chemically adsorbed fatty acids were desorbed effectively above 100 °C when the amount of sulfuric acid was 3 wt%, the methanol-solution-to-γ-alumina weight ratio was higher than 5: 1, and the regeneration time was longer than 30 min. This new approach provides an ecofriendly process that operates at much lower temperatures than other methods of regeneration (thermal and supercritical methanol) while producing a renewable fuel. 相似文献
16.
A model is described, which makes it possible to calculate the distribution of nonequilibrium carriers and an electric field near the p–n junction, which arose as a result of the internal photoeffect. Using laser illumination, the possibilities to control the properties of nanolayered structures sensitive to the concentration of free carriers are analyzed. The mutual location of the region of the intense absorption of radiation and the p–n junction itself is varied and the linear and square mechanisms of carrier recombination are analyzed. 相似文献
17.
Matthew R. Miller Nigel B. Perry Elaine J. Burgess Susan N. Marshall 《Journal of the American Oil Chemists' Society》2011,88(4):509-516
The lipid profiles of the two most important New Zealand marine oil sources were investigated, with particular attention to
the regioisomeric compositions of triacylglycerides (TAG), using 13C-nuclear magnetic resonance analysis. Oils from hoki (Macruronus novaezelandiae) and Greenshell™ mussel (Perna canaliculus) (GSM) were analyzed for their lipid content, lipid class and fatty acid profile. The regiospecific distribution of long
chain (C ≥ 20) polyunsaturated fatty acids (LC-PUFA) between the sn-1,3 and sn-2 glycerol positions was calculated from 13C responses in the carbonyl region in the triacylglycerol fraction. Rendered hoki oil (RHO) produced from the viscera and
filleting discards, had a similar lipid profile to that of hoki liver oil (HLO) confirming that the liver is the major source
of oil in RHO. The regioisomeric distribution of fatty acids showed differences between the two oil sources. Docosahexaenoic
acid (DHA) had a regioisomeric distributional preference to the sn-2 position in TAG from all the oils (59.2% HLO, 54.3% RHO and 63.4% GSM). Eicosapentaenoic acid (EPA) had a more even distribution
along the triacylglycerol backbone in hoki TAG (29.1% HLO, 33.6% RHO) while there was a slight sn-2 positional preference in the GSM TAG (37.6%). This regioisomeric information is vital to distinguish LC-PUFA-rich marine
oils from other marine sources for authentication purposes. 相似文献
18.
Stökl J Hofferberth J Pritschet M Brummer M Ruther J 《Journal of chemical ecology》2012,38(4):331-339
Chemical defense mechanisms are widespread among insects but have rarely been demonstrated in parasitoid wasps. Here, we show
that the Drosophila parasitoid Leptopilina heterotoma (Hymenoptera, Figitidae) produces (−)-iridomyrmecin and (+)-isoiridomyrmecin in a cephalic gland, and that these chemicals
have a highly repellent effect on ants. Stereoselective synthesis of 4 stereoisomers of iridomyrmecin allowed us to demonstrate
that the repellent effect of iridomyrmecins depends on the stereochemistry. Potential food items impregnated with natural
doses of (−)-iridomyrmecin were avoided by ants much longer than those impregnated with (+)-iridomyrmecin, (+)-isoiridomyrmecin,
or (−)-isoiridomyrmecin, respectively. Quantitative headspace analyses revealed furthermore that females and males of L. heterotoma released iridomyrmecins in higher amounts when confronted with ants. This is the first time, that (−)-iridomyrmecin and (+)-isoiridomyrmecin
are reported as natural products. Females synthesize more iridomyrmecins than males, and the most active (−)-iridomyrmecin
is produced by females only. We, therefore, hypothesize that this defense mechanism is used mainly by female wasps when foraging
for Drosophila larvae on rotten fruits, but also may protect male wasps during dispersal. 相似文献
19.
Solid solution (AlN) x (SiC)1–x (x = 0.7) was prepared from Al–SiC mixtures by SHS under high pressure of nitrogen gas (50, 70 MPa) and characterized by XRD and SEM. Combustion product was found to have a wurtzite 2H structure with lattice parameters a = 3.10889 ± 0.00022 Å and c = 5.00741 ± 0.00080 Å. 相似文献
20.
The Δ9-fatty acid desaturase is a key enzyme in the synthesis of unsaturated fatty acids. The fatty acid composition of membrane
phospholipids in Psychrobacter urativorans is characterized by a high degree of desaturation at Δ9 position. Based on CODEHOP-mediated PCR strategy, a novel gene designated
as PuFAD9, putatively encoding a Δ9-fatty acid desaturase (PuFAD9), was isolated from P. urativorans. The gene consists of 1,455 bp and codes for 484 amino acids. Analysis of the amino acid sequence reveals three histidine
clusters and a hydropathy profile, typical for membrane-bound desaturases. Activity of the PuFAD9 protein, recombinantly expressed in Escherichia coli was confirmed by GC-MS analysis of the cellular fatty acid composition. It was found that the ratio between palmitoleic and
palmitic acid in E. coli cells heterologously expressing the PuFAD9 gene was significantly affected by IPTG induction and the growth temperature. 相似文献