• Bulletin of the Korean Chemical Society
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• v.33 no.12
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• pp.4028-4034
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• 2012

Tris(2-phenylphenoxo)aluminum ($(2-PhC_6H_4O)_3Al$) exists as a dimeric form in toluene. When toluene-insoluble anhydrous cobalt acetate is treated with tris(2-phenylphenoxo)aluminum in toluene, the toluene-soluble adduct $(2-PhC_6H_4O)_3Al{\cdot}Co(OAc)_2$ is formed. The 2-phenylphenoxo ligand in the adduct can be replaced with another aryloxo ligand to give (aryloxo)$(2-PhC_6H_4O)_2Al{\cdot}Co(OAc)_2$ (aryloxo = 2-methylphenoxo, 2-isopropylphenoxo, 4-methylphenoxo, 4-isopropylphenoxo, or 4-tert-butylphenoxo). These complexes are active for butadiene polymerization without gel formation when activated with an equivalent amount of $(2-PhC_6H_4O)AlEt_2$ for 2 h. The highest activity, 175 kg/mol-Co (turnover number, 3200) was achieved with $(2-PhC_6H_4O)_3Al{\cdot}Co(OAc)_2$ at $65^{\circ}C$ for 2 h. The microstructure of the polymer chains is mostly trans-1,4-configuration (70-75%) with the remaining being 1,2-vinyl. The cis-1,4-configuration observed by IR is minimal (1-5%). By replacing the 2-phenylpheoxo with a 4-alkylphenoxo ligand, the amount of 1,4-configuration slightly increases, resulting in increase in the endothermic melting signal at $-30{\sim}50^{\circ}C$ in the DSC curve. The molecular weights of the polymers are high ($M_n$: 300000~800000) with a fairly narrow molecular weight distribution ($M_w/M_n$, 2.0-2.7).

• Food Science and Biotechnology
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• v.16 no.4
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• pp.600-604
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• 2007

In this study, we first prepared 3 kinds of powders with different molecular masses from the crude protein-bound polysaccharide extract of Agraricus blazei Murill through ultrafiltration, followed by spray-drying. Then, the antitumor activities of the powders were analyzed. Size exclusion chromatography coupled with a multi-angle laser-light-scattering system showed the 3 powders had the following molecular ranges: below 10 kDa (SD-1), 10 to 150 kDa (SD-2), and above 150 kDa (SD-3), representing peak molecular weights of $8.26{\times}10^3,\;9.65{\times}10^4$, and $5.94{\times}10^6\;g/mol$, respectively. All the powders stimulated macrophage RAW264.7 cells to produce nitric oxide, of which SD-2 and SD-3 were superior to the crude extract powder (CP-SD), while SD-1 showed the lowest activity. Similar results were found for their cytotoxicities against human cancer cell lines (A549, MCF-7, and AGS), where the highest activity was obtained with the SD-2 treatment for 72 hr at $1,000\;{\mu}g/mL$. The MCF-7 cell line was less sensitive to the powders than the other cells. From this research we found that ultrafiltration, in combination with spray-drying, is applicable for preparing protein-bound polysaccharide powders with higher antitumor activities.

• Applied Chemistry for Engineering
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• v.23 no.4
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• pp.388-393
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• 2012

Branched polycarbonates (B-PCs) were synthesized using melt polymerization method with four different end capping agents and vaying concentrations. The chemical structure of the synthesized PC was determined by FT-IR and $^{1}H-NMR$ spectroscopy, and the reaction of the end capping agent was confirmed by the existence of hydroxy group in FT-IR spectrum. The average molecular weight and distribution, glass transition and degradation temperatures were determined by GPC, DSC and TGA. The average molecular weight changed with the chemical structure of end capping agent, and 4-tert-butylphenol was estimated as the optimum end capping agent. The average molecular weights of B-PCs decreased with the increase of the concentration of the agent, the number average molecular weight represented 20000 when 0.05 mol% of 4-tert-butylphenol was added to B-PCs. The melt viscosities of the B-PCs decreased with the decrease of the molecular weight of B-PCs, and adding of the agent was not effected to shear thinning tendency.

• Bulletin of the Korean Chemical Society
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• v.13 no.4
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• pp.413-419
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• 1992

The theoretical equation for the relaxation spectrum of nonlinear viscoelastic polymeric material was derived from the Ree-Eyring and Maxwell non-Newtonian model. This model consists of infinite number of hyperbolic sine law Maxwell elements coupled in parallel plus a spring without a dashpot. Infinite number of nonlinear viscoelastic Maxwell elements can be used by specifying distribution of relaxation times, hole volumes, molecular weights, crystallite size and conformational size, etc. The experimentals of stress relaxation were carried out using the tensile tester with the solvent chamber. The relaxation spectra of nylon 6 filament fibers in various electrolytic solutions were obtained by applying the experimental stress relaxation curves to the theoretical equation of relaxation spectrum. The determination of relaxation spectra was performed from computer calculation.

• YAKHAK HOEJI
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• v.43 no.6
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• pp.709-715
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• 1999

Polyphenol oxidase (PPO) activity in 200×g (cell wall), 4,000×g (plastid), 100,000×g (mitochondrial) and soluble fractions of the perilla leaves was monitored in the upper, middle and lower sections of the plant. In the course of plant growth, PPO activities in plastid and mitochondrial fractions were decreased, while those in cell wall fraction were maintained. During growing process, specific activities and PPO activities of each fraction were decreased, while total phenol content were decreased in middle (middle) and then increased in later stage (lower). Cell wall, plastid, mitochondrial (pellet) and soluble fraction had slightly different pH optima and substrate specificities. Isoenzyme patterns were identical in two bands for PPO activity in different subcellular fractions. Their molecular weights were 37KD and 48KD respectively.

• BMB Reports
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• v.32 no.3
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• pp.299-305
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• 1999

Protein carboxyl O-methyltransferase (PCMT) catalyzes the transfer of a methyl group from Sadenosyl-L-methionine to free carboxyl groups of methyl-accepting substrate proteins. Two isozymes were separated by DEAE-Sephacel chromatography from porcine brain cytosol and designated PCMT I and II. Isozymes I and II were further purified by adenosyl homocysteine-Sepharose 4B and Superose HR 12 chromatography. The molecular weights of the purified PCMT I and II were determined by mass spectrometry to be 20,138 Da and 25,574 Da, respectively. The two enzymes displayed different isoelectric points; 7.9 for PCMT I and 5.3 for PCMT II. Isozymes I and II exhibited similar substrate specificities when tested with various methyl-accepting proteins. Myelin basic protein, a component of myelinated neurons, was found to be an excellent methyl-accepting substrate for both PCMT isozymes with different $K_m$ values, $21.1\;{\mu}M$ for PCMT I and $10.6\;{\mu}M$ for PCMT II. The PCMT activity and methyl-accepting capacity displayed similar distribution in the various brain regions with an exception of the lower values in the cerebellum. The overall distribution may relate to a general function of protein repair by PCMT in the brain.

• Korean Journal of Food Science and Technology
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• v.40 no.4
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• pp.470-473
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• 2008

This study examined the enzymatic digestion, average molecular weight distribution and structural changes of Bombyx mori silk gland fibroin using gel penneation chromatography and nuclear magnetic resonance methods. The pure-separation of calcium chloride-treated fibroin hydrolysates was carried out by gel filtration chromatography. Also, the effects of fibroin's enzymatic hydrolysis were investigated using an edible enzyme. The average molecular weight of three hydrolysate samples (silk gland fibroin (SF), SF-calcium chloride (SFC), and SFC-enzyme) were measured to compare their characteristics. The molecular weights of SF, SFC, and SFC-enzyme were approximately 108,000, 65,000, and 1,000 Da, respectively. Finally, we determined the structural characteristic changes of the different enzymatically digested samples by $^{13}C$ nuclear magnetic resonance methods. For the enzymatically digested fibroin, the glycine $^{13}C^{\alpha}$ resonance indicated that the amino acid was dramatically changed and/or separated out; however, this was not shown for the normal Bombyx mori silk gland fibroin.

• Journal of the Korean Society of Food Science and Nutrition
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• v.33 no.2
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• pp.236-243
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• 2004

Antimicrobial effect of chitosan and its oligosaccharides was examined on Vibrios sp., Edwardsiella tarda and Streptococcus sp., which are major pathogenic bacteria inducing bacterial diseases of acquacultured flounder. Chitosan oligosaccharides (COS ) were produced by enzymatic hydrolysis of chitosan in an ultrafiltration mombrane bioreactor system which was established with three membranes with different molecular weight cut-off (MWCO) 1,000, 5,000 and 10,000, and fractionated into three kinds of COS, based on their molecular weight sizes. The three kinds of COS were as follows : relatively high molecular weight COS [HMW-COS, molecular weight distribution of 7,000 to 24,000 Da〕, medium molecular weight COS 〔MMW-COS, 1,500 to 6,000 Da〕, and low molecular weight COS 〔LMW-COS, 1,000 to 1,500 Da). Chitosan and HMW-COS effectively inhibited the growths of Vibrio sp. and Streptococcus sp. and their antimicrobial activities were superior to the others with smaller molecular weights. This result suggested that antimicrobial effect of chitosan preparations extremely depend on their molecular weight sizes. Antimicrobial effect of chitosan and HMW-COS on E. tarda was improved by longer inoculation times. Scanning electron microscopy in morphological change of E. tarda treated with chitosan preparations showed that chitosan and HMW-COS bound to the cells and suppressed the growth of the cells. This observation appears to prove the fact that positive charged amines of chitosan electrostatically bind to negative charged compounds of cell walls.

• Journal of Korean Society on Water Environment
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• v.38 no.3
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• pp.133-142
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• 2022

Natural organic matter (NOM) is a heterogeneous mixture of organic matter with various polarities and molecular weights in an aquatic environment. This study investigated the effects of separation conditions (resin volume, organic matter, etc.) and the repeated use of the resin for the fractionation of organic components in the DAX resin fractionation method. The distribution characteristics of the organic components ((hydrophilic [Hi], hydrophobic acid [HoA], and hydrophobic neutral [HoN]) under the derived fractionation conditions were also analyzed. Constant fractionation results (i.e. HoA/Hi ratio) were obtained in the column capacity factor (i.e. the packed resin volume) in the range of 50 to 100. The resin-packed column maintained constant separation efficiency for up to two repeated uses. The above conditions were applied to wastewater and stream water samples (before and after rainfall). The results showed that the concentration of organic matter in the wastewater effluent was 2-15 times lower with an increased ratio of hydrophilicity to hydrophobicity (i.e. Ho/Hi) compared to the influent depending on the industrial wastewater classification. Particularly, HoN was found to have a high content distribution, 10.2-50.4% of the total dissolved organic matter (DOM), in the effluents. For the stream water, the content of Hi or HoN increased significantly after rainfall, suggesting a correlation with the distribution characteristics of pollutants from the stream watershed. The results provide useful data to enhance the reliability of the DAX resin fractionation and its application to environmental samples.

• Polymer(Korea)
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• v.35 no.3
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• pp.232-237
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• 2011

The relaxation spectra of polyacrylonitrile-poly(vinyl chloride) copolymer filament fibers were obtained by applying the experimental stress relaxation curves to the theoretical equation of relaxation spectrum. The theoretical equation of relaxation spectrum was derived from the Ree-Eyring and Maxwell model. The experimental of stress relaxation was carried out using a tensile tester with a solvent chamber. The determination of relaxation spectra was performed by computer calculation. From the relaxation spectra, the fine structures, viscoelastic properties and hole volumes of solid polymers were studied. It was observed that the relaxation spectra of these samples were directly related to the distribution of molecular weights and self diffusions of flow segments.