• Applied Chemistry for Engineering
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• v.22 no.2
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• pp.209-213
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• 2011

Hydrophobic silica aerogel beads with low thermal conductivity and high porosity were prepared using a cost-effective sodium silicate as a silica source via an ambient-pressure drying process. Monolithic wet gels were first prepared by adjusting pH (~5) of a diluted sodium silicate solution. The silica aerogel beads (0.5~20 mm) were manufactured by breaking the wet gel monoliths under a simultaneous solvent exchange/surface modification process and an ambient-pressure drying process without using co-precursors or templates. Dried silica aerogel beads exhibit a comparable porosity ($593m^2/g$ of surface area, 34.9 nm of pore size, and $4.4cm^3/g$ of pore volume) to that of the aerogel powder prepared in the same conditions. Thermal conductivity of the silica aerogel beads (19.8 mW/mK at $20^{\circ}C$) is also identical to the aerogel powder.

• Journal of Korea Foundry Society
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• v.14 no.6
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• pp.499-507
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• 1994

The effect of sodium gluconic acid on the collapsability of the sodium silicate type $CO_2$ mold was studied. The bending strength was saturated with gassing $CO_2$ for 60 sec. under $1kg/cm^2$ and with the flow rate of $10\;{\ell}\;/min$. It was decreased with aging after having been fully hardened. The retained strength was reduced in the heating temperature range of $100{\sim}1,100^{\circ}C$ and the retained strength peak near the heating temperature of $100^{\circ}C$ was removed by the effect of the sodium gluconic acid. Silica gel, $Na_2CO_3$ and dehydrated sodium silicates were formed from the binder of sodium silicate with the addition of sodium gluconic acid at the heating temperature of $100^{\circ}C$. $Na_4SiO_4$ was formed by the reaction of $Na_2O$, from decomposed $Na_2CO_3$, with the dehydrated sodium silicate at $500^{\circ}C$. The crystobalite type of $SiO_2$ was formed at $900^{\circ}C$. The sodium gluconic acid had no effect on the bending strength at around $1,100^{\circ}C$ due to the combustion loss of it.

• Applied Biological Chemistry
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• v.47 no.4
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• pp.422-425
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• 2004

The flower of Erigeron annuus L. was extracted with 80% aqueous MeOH, and the concentrated extract was partitioned with EtOAc, n-BuOH and $H_2O$, successively. From the EtOAc fraction, three compounds were isolated through the repeated silica gel, ODS column and high performance liquid chromatographies. From the result of physico-chemical data including NMR, MS and IR, the chemical structures of the compounds were determined as ${\alpha}-amyrenone,\;{\alpha}-amyrin\;and\;{\beta}-amyrin$. These three compounds were isolated for the first time from the flower of Erigeron annuus L.

• Polymer(Korea)
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• v.39 no.2
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• pp.323-328
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• 2015

Poly(${\varepsilon}$-caprolactone) (PCL) nanofibers and PCL/silica membranes were synthesized by sol-gel derived electrospinning and casting, respectively. Smooth PCL nanofibers were obtained from the precursor containing N,N-dimethylformamide (DMF). PCL/silica membranes were prepared by varying the tetraethyl orthosilicate (TEOS) contents from 0 to 40 vol% to investigate the effect of silica addition on mechanical properties and cytotoxicity of the membranes. Although the strength of the membranes decreased from 12 to 8 MPa with increasing the silica content, the strength remained almost constant 7 weeks after dipping in phosphate buffered saline solution (PBS). The strength reduction was attributed to the presence of a patterned surface pores and micro-pores present in the walls between pores. The crystal structure of the membranes was orthorhombic and the crystallite size decreased from 57 to 18 nm with increasing the silica content. From the agar overlay test, the PCL/silica membranes exhibited neither deformation and discoloration nor lysis of L-929 fibroblast cells.

• Natural Product Sciences
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• v.21 no.4
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• pp.255-260
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• 2015

Two new thiodiketopiperazines (TDKPs), designated graphiumins I (1) and J (2), were isolated from the culture broth of the marine-derived fungus Graphium sp. OPMF00224 by solvent extraction, silica gel column chromatography, and HPLC. Their absolute structures were elucidated by spectroscopic analyses (1D and 2D NMR data, ROESY correlations, and CD data) and chemical methods. They were found to be structurally rare TDKPs with a phenylalanine-derived indolin substructure. Compounds 1 and 2 inhibited yellow pigment production by methicillin-resistant Staphylococcus aureus (MRSA) with $IC_{50}$ values of 63.5 and $76.5{\mu}g/ml$, respectively, without inhibiting its growth, even at $250{\mu}g/ml$.

• Korean Journal of Food Science and Technology
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• v.35 no.2
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• pp.297-301
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• 2003

An inhibitor of squalene synthase, a key enzyme in the cholesterol biosynthetic pathways and a target for improved agents to lower plasma levels of low-density lipoprotein, was sequentially purified from Curcuma longa by acetone extraction, silica gel column chromatography, and sephadex LH-20 column chromatography. Active compound, YUF-01, was successfully purified and analyzed as $C_{20}H_{21}O_6$ by electron ionization mass spectrum. Through $^1H-NMR$ and $^{13}C-NMR$ analyses, YUF-01 was identified as curcumin, which showed strong inhibition of squalene synthase.

• Applied Biological Chemistry
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• v.50 no.4
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• pp.358-361
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• 2007

The heartwoods of Rhus verniciflua was extracted with $H_2O$ and the concentrated extract was partitioned with $CHCl_3$, EtOAc, n-BuOH and $H_2O$, successively. From the EtOAc and n-BuOH fractions, four compounds were isolated through the repeated silica gel, ODS and Sephadex LH-20 column chromatographies. They were determined as sinapyl aldehyde (1), 2,4-dihydroxybenzaldehyde (2), 2,4-dihydroxybenzoic acid (3) and 2,4-dihydroxyphenylglyoxylic acid (4) on the basis of spectroscopic data, respectively. Among the isolated compounds, sinapyl aldehyde $(34.7{\pm}0.6%)$ and 2,4-dihydroxyphenylglyoxylic acid $(43.8{\pm}0.9%)$ showed the strong antioxidative activity than artificial antioxidant BHT $(14.4{\pm}0.3%)$ in DPPH radical scavenging activity.

• Korean Chemical Engineering Research
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• v.54 no.2
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• pp.163-170
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• 2016

In order to improve the hydrophilic property of polymer films, coating solutions which showed a good hydrophilic property, were prepared by the sol-gel method. The coating solutions were prepared by adding different types of silane coupling agents (aminosilane, epoxysilane and acrylsilane) to a colloidal silica (15 nm diameter). The solutions prepared by adding aminosilane resulted in gels which could not be used as coating solutions. On the other hand, the coating solutions prepared by the addition of epoxysilane showed contact angles of $10{\sim}15^{\circ}$ and good hydrophilic property at R=0.10~0.15 (R=silane coupling agent/colloidal silica weight ratio). In addition, the coating solutions prepared by the addition of acrylsilane at R=0.03~0.07, exhibited contact angles of $5{\sim}10^{\circ}$, which means better hydrophilic property than aminosilane or epoxysilane.

• Applied Biological Chemistry
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• v.47 no.3
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• pp.357-360
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• 2004

The flower of Campsis granudiflora K. Schum. was extracted with 80% aqueous MeOH, and the concentrated extract was partitioned with EtOAc, n-BuOH and $H_2O$. From the EtOAc fraction, four compounds were isolated through the repeated silica gel and ODS column chromatographies. From the result of physico-chemical data including NMR, MS and IR, the chemical structures of the compounds were determined as linolenic acid methyl ester, linoleic acid methyl ester, ${\beta}-sitosterol$ and daucosterol. Daucosterol inhibited FPTase activity with $IC_{50}$ values of $14{\pm}0.04\;{\mu}M$.

• Bulletin of the Korean Chemical Society
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• v.26 no.11
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• pp.1653-1668
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• 2005

Assembly of hybrid mesophases through the combination of amphiphilic block copolymers, acting as structuredirecting agents, and silicon sources using low acid catalyst concentration regimes is a versatile strategy to produce large quantities of high-quality ordered large-pore mesoporous silicas in a very reproducible manner. Controlling structural and textural properties is proven to be straightforward at low HCl concentrations with the adjustment of synthesis gel composition and the option of adding co-structure-directing molecules. In this account, we illustrate how various types of large-pore mesoporous silica can easily be prepared in high phase purity with tailored pore dimensions and tailored level of framework interconnectivity. Silica mesophases with two-dimensional hexagonal (p6mm) and three-dimensional cubi (Fm$\overline{3}$m, Im$\overline{3}$m and Ia$\overline{3}$d) symmetries are generated in aqueous solution by employing HCl concentrations in the range of 0.1−0.5 M and polyalkylene oxide-based triblock copolymers such as Pluronic P123 $(EO_{20}-PO_{70}-EO_{20})$ and Pluronic F127 $(EO_{106}-PO_{70}-EO_{106})$. Characterizations by powder X-ray diffraction, nitrogen physisorption, and transmission electron microscopy show that the mesoporous materials all possess high specific surface areas, high pore volumes and readily tunable pore diameters in narrow distribution of sizes ranging from 4 to 12 nm. Furthermore, we discuss our recent advances achieved in order to extend widely the phase domains in which single mesostructures are formed. Emphasis is put on the first synthetic product phase diagrams obtained in $SiO_2$-triblock copolymer-BuOH-$H_2O$ systems, with tuning amounts of butanol and silica source correspondingly. It is expected that the extended phase domains will allow designed synthesis of mesoporous silicas with targeted characteristics, offering vast prospects for future applications.