• International Journal of Industrial Entomology and Biomaterials
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• v.23 no.1
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• pp.183-186
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• 2011

The various molecular weight (MW) regenerated silk fibroins were prepared with different dissolution condition and the effect of MW on the gelation behavior of regenerated aqueous silk fibroin (SF) solution was investigated. The result of gelation time measurement indicated that the gelation of SF aqueous solution was accelerated by the increase of MW and SF concentration. When formic acid was added in SF aqueous solution, the gelation time of SFL and SFC30 aqueous solution showed a significant decreaseat 0.03% formic acid addition. In case of the lowest MW sample, SFC180, SF molecules became aggregated and precipitated without gelation after 28 days storage time. These findings indicate that MW control of SF can be utilized to control the gelation time of SF aqueous solution.

• International Journal of Industrial Entomology and Biomaterials
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• v.27 no.2
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• pp.326-328
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• 2013

Sericin undergoes gelation by the structural transition from random coil to b-sheet transition. In the present study, the gelation time of sericin solution was investigated in the presence of NaCl, KCl and $CaCl_2$. The addition of salts delayed the gelation time, and $CaCl_2$ had the most pronounced effect, which delayed about 8 h at maximum. The gelation time increased with the concentration of salt. The transition of secondary structure of sericin was retarded in the presence of salt. The effect of salts on the gelation time of sericin might be due to the solvation effect of relevant cation.

• 한국생물공학회:학술대회논문집
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• 2001.11a
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• pp.798-799
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• 2001

The intermolecular hydrogen bond between silk fibroin in aqueous solution facilitates gelation of silk fibroin. The dependence of gelation by the concentration of silk fibroin, pH and temperature was investigated. The gelation time of silk fibroin is decreased with increasing the concentration of glycerol and temperature within a limited range. The pH optimum for gelation found out to be 9. Hydrophobic additives were investigated to reduce gelation time.

• Food Science and Biotechnology
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• v.16 no.6
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• pp.954-957
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• 2007

Gelation mechanism of xanthan-carob mixture (X/C) was investigated based on thermorheological behavior. Three X/C ratios (1:3, 1:1, and 3:1) were studied. Small amplitude oscillatory shear tests were performed to measure linear viscoelastic behavior during gelation. Temperature sweep ($-1^{\circ}C/min$) experiments were conducted. Using a non-isothermal kinetic model, activation energy (Ea) during gelation was calculated. At 1% total concentration, the Ea for xanthan fraction (${\phi}_x$)=0.25, 0.5, and 0.75 were 178, 159, and 123 kJ/mol, respectively. However, a discontinuity was observed in the activation energy plots. Based on this, two gelation mechanisms were presumed-association of xanthan and carob molecules and aggregation of polymer strands. The association process is the primary mechanism to form 3-D networks in the initial stage of gelation and the aggregation of polymer strands played a major role in the later stage.

• Korean Journal of Materials Research
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• v.30 no.10
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• pp.533-541
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• 2020

UO₂ kernels, a key component of fuel elements for high temperature gas cooled reactors, have usually been prepared by sol-gel methods. Sol-gel processes have a number of advantages, such as simple processes and facilities, and higher sphericity and density. In this study, to produce 900 ㎛-sized UO₂ particles using an external gelation process, contact length extension of the NH₃ gas of the broth droplets pass and the improvement of the gelation device capable of spraying 14 M-NH₄OH solution are used to form 3,000 ㎛-sized liquid droplets. To produce high-sphericity and high-density UO₂ particles, HMTA, which promotes the gelation reaction in the uranium broth solution, is added to diffuse ammonium ions from the outside of the gelation solution during the aging process and generate ammonium ions from the inside of the ADU gel particles. Sufficient gelation inside of ADU gel particles is achieved, and the density of the UO₂ spheres that undergo the subsequent treatment is 10.78 g/㎤; the sphericity is analyzed and found to be 0.948, indicating good experimental results.

• Journal of the Korean Wood Science and Technology
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• v.27 no.1
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• pp.72-78
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• 1999

To accelerate the curing and to improve the bonding properties of urea-melamine-formaldehyde (UMF) resin adhesives for plywood, the effects of resin compositions and additives on gelation time and bonding strength were discussed. The gelation time of UMF resin prepared by simultaneous reaction with urea(U), melamine(M) and formaldehyde(F) at M/U molar ratio 0.2 was shortened as the molar ratio of formaldehyde to urea was increased. However, at F/U molar ratios higher than 2.5, the amounts of free fomaldehyde of resin could not satisfy with KS standard, Therefore, it was difficult to increase the amount of formaldehyde in resin composition for the purpose of fast gelation time. With increasing the molar ratio of melamine to urea(M/U) from 0.3 to 0.6 at constant F/U molar ratio 3.4, the gelation time of UMF resin was slightly decreased, while gradually increased at M/U molar ratio higher than 0.6. The gelation properties of UMF resin and bonding strength of UMF-bonded plywood could be enhanced by using ammonium chloride and p-toluene sulfonic acid as a curing-agent together with wheat flour and corngluten powder as a extender.

• The Korean Journal of Pharmacology
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• v.23 no.1
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• pp.25-31
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• 1987

The present study examines firstly, the inhibition of collagen gelation to explore the possible involvement of $Cu^{++}$-catalyzed peroxidation in rheumatoid arthritis and secondly, the effect of sodium salicylate on this peroxidative reaction to provide a possible explanation for its mechanism of anti-inflammatory action. Incubation of collagen obtained from rat skin with $Cu^{++}$ and $H_2O_2$ resulted in the inhibition of gelation in terms of maximal turbidity and lag phase, but either $Cu^{++}$ or $H_2O_2$ alone essentially gave no effect in the collagen gelation. In the presence of sodium salicylate the inhibited gelation of collagen induced by $Cu^{++}$ and $H_2O_2$ was reversed with the dependency of the concentration of sodium salicylate. Moreover, the rate of $H_2O_2$ decomposition by $Cu^{++}$ was accelerated by sodium salicylate and this decomposition of $H_2O_2$ was found to be saturable in terms of concentration of this drugs. Thus it can be expected that $Cu^{++}$ -catalyzed peroxidation attacks collagen resulting in change of structural or functional integrity of collagen, and sodium salicylate may act on this peroxidative process, possibly through the enhancement of catalatic action of $Cu^{++}$. From these results $Cu^{++}$-catalyzed peroxidation can be in part responsible for degradation of joint tissue in rheumatoid arthritis and sodium salicylate may exert its anti-inflammatory action by this peroxidative reaction.

• The Korean Journal of Pharmacology
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• v.19 no.2
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• pp.35-44
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• 1983

reactive oxygen species에 의해 나타나는 reactivity에 있어서 metal ions이 관여함이 시사되고 있다. 이미 알려진 reactive oxygen species와 metal ions의 상호작용 이외에 특히 $Cu^{++}$과 $H_2O_2$가 강력한 peroxidative action을 나타낸다는 사실이 알려져 있으며 $Cu^{++}-H_2O_2$가 biological system 에서의 조직파괴에 관여할 가능성이 저자들에 의해서 효소 및 조직치 구조 단백질의 gradation 효과를 관찰함으로써 시사되었다. 본 연구는 $H_2O_2$ 혹은 $H_2O_2$를 생성하는 효소계(xanthine과 xanthine oxidase 및 glucose과 glucose oxidase)에 $Cu^{++}$을 첨가하여 $Cu^{++}-H_2O_2$에 의한 peroxidation의 효과를 collagen gelation을 통하여 확인코저 수행하였으며 다음과 같은 결과를 얻었다. 1) $Cu^{++}(20\;{\mu}M)$과 $H_2O_2$에 의하며 collagen gelation은 현저히 억제되었으며 이같은 억제효과는 양자의 농도에 비례하였다. 2) $Cu^{++}-H_2O_2$ reactivity를 확인하는 다른 방법으로 glucose oxidase system를 이용하였다. glucose oxidase$(2.5{\mu}g/ml)$ 와 glucose(0.5 mM)는 collagen gelation에 영향을 미치지 않았으나 이에 $Cu^{++}$이 존재하면 gelation이 억제되었다. 이때 억제정도는 $glucose(0.125{\sim}l.25\;mM)$와 $Cu^{++}$의 농도에 비례하였다. 3) 여러 reactive oxygen species 가운데 $Cu^{++}-H_2O_2$ reactivity를 xanthine oxidase system을 이용하여 확인하였다. (a) collagen gelation은 xanthine oxidase(30 munits/ml)와 xanthine$(0.25{\sim}2\;mM)$에 의하여 억제되었다. (b) 이때 나타나는 collagen gelation의 억제는 superoxide dismutase에 의하여 완전히 회복되었으나 catalase에 의해서는 더욱 촉진되었다. 그러나 catalase에 의한 억제효과의 촉진은 1,4-diazabicyclo(2,2,2)octane에 의하여 완전히 소실되었다. 따라서 이 xanthine oxidase system에서는 $O_2-,\;H_2O_2,\;^1O_2$이 관여함을 알 수 있었다. (c) 그러나 $Cu^{++}(10\;{\mu}M)$이 존재하였을 때 collagen gelation은 superoxie dismutase에 의해 더욱 억제되었고 catalase에 의해서는 완전히 회복되었다. xanthine oxidase계에서 얻어진 결과는 여러 reactive oxygen species가운데 $H_2O_2$가 $Cu^{++}$에 의하여 peroxidation효과를 나타냄을 알 수 있었다. 이상의 결과로 미루어 볼 때 reactive oxygen species와 metal ions과의 상호작용 가운데 $Cu^{++}-H_2O_2$는 강한 반응을 나타내는 특이한 구성요소이고 헌재 시사되고 있는 reactive oxygen species의 biological effects에 비추어 $Cu^{++}-catalyzed peroxidation$도 병적상태에서 생체에 유해한 작용을 나타내는 요소임을 시사하며 특히 염증시 조직파괴역할에 관하여 고찰하였다.

• Applied Chemistry for Engineering
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• v.9 no.3
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• pp.399-403
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• 1998

The gelation characteristics of chitosan of different molecular weight were investigated in terms of concentration and temperature of alkari aqueous solution. The average molecular weights and the degrees of deacetylation of the chitosan used were $2.0{\times}10^5$, $5.2{\times}10^5$, $8.2{\times}10^5$ and 85%, respectively. Sodium hydroxide solution was used as a gelation agent. A simple diffusion model was applied to study the gelation rate. The diffusion coefficients of the gelation agent in the chitosan gel increased with increasing its concentration, temperature of the casting solution, and molecular weight of the chitosan.

• Journal of Pharmaceutical Investigation
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• v.33 no.1
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• pp.15-19
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• 2003

The rheological behavior of poloxamer 407 solution as function of concentration and temperature was evaluated by rotational viscometer. The viscosity of poloxamer 407 solution was increased as the concentration of poloxamer 407 and temperature increased. At $4^{\circ}C$, poloxamer 407 solution showed the Newtonian flow characteristics regardless of concentration. Upon increasing temperature the poloxamer solution changed to the pseudoplastic flow pattern. And at gelation temperature, rheological profiles showed the abrupt increase in viscosity. Gelation temperature was decreased as the concentration of poloxamer 407 increased, while it increased as the concentration of poly(ethylene glycol) 4000 increased. Poly(ethylene glycol) might be expected to reduce the driving force for hydrophobic interaction resulting in slow gelation. From the viscoelastic properties of poloxamer gel system, we obtained the storage and loss modulus depending on the shear stress and frequency. And the sol-gel transition temperature was also obtained from the viscoelastic properties of poloxamer 407 gel.