• Bulletin of the Korean Chemical Society
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• v.15 no.11
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• pp.1001-1003
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• 1994

A series of phosphodiesters of p-nitrophenyl phosphoryl derivatives were synthesized and used as a model substrate for phospholipase D (PLD). The phosphodiester substrates were synthesized from p-nitrophenyl phosphorodichloridate and corresponding alcohols with different chain lengths and polar groups. To measure the activity of PLD, either spectroscopic method for p-nitrophenol or pH-stat titration method was employed. For each substrate, effects of substrate concentration, pH, and $Ca^{2+}$ ion were examined. The kinetic parameters $V_{max}$ for the different substrates were varied depending on the chain lengths or charge of the alcohols. No calcium effect was observed in the hydrolysis of neutral and negatively charged alcohol derivatives, while positively charged choline derivative showed a strong $Ca^{2+}$ ion dependence.

• Clinical and Experimental Reproductive Medicine
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• v.18 no.2
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• pp.153-162
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• 1991

The present study was undertaken to clarify the role of calcium ion as a factor for the maturation of follicle-enclosed mouse oocytes. Follicles were isolated with two sharp needles under a stereomicroscope from mouse(ICR) ovaries which were treated PMSG 5 IU 45 hours previously. Isolated follicles were cultured for 14-16 hours in an organ culture system at $37^{\circ}C$, 5% $CO_2$ in air and in a 100% humidified incubator by treatment of hCG, EDTA and $^{45}Ca^{++}$. Culture medium was Modified Hank's Balanced Salt Sol. (MHBS) and addition of hCG (human chorionic gonadotropin) was made into two doses level 0.4 IU and 0.8IU from the stock sol. and also $^{45}Ca^{++}$ was treated in the culture medium. To explain the role of calcium, calcium chelating agent EDTA was treated to the culture of the mouse follicle-enclosed oocytes. Two observations were made in the present study; nucleus phase and $^{45}Ca^{++}$ uptake into the oocyte. HCG induced oocyte maturation in the follicle about two folds as much as the control group, whereas there is no difference in oocyte maturation between 0.4 IU and 0.8 IU of hCG. Optimum level of hCG seems to be 0.4 IU/ml in the mouse follicle culture. HCG stimulated $^{45}Ca^{++}$ uptake into the oocyte of the follicles by two folds. $^{45}Ca^{++}$ uptake in the control group is about 2.5 folds in comparison of the EDTA(1.71mM) treated group. However, calcium uptake in the EDTA treated groups tends to increase depending on the decrease of EDTA concentration. These observations suggest that firstly, hCG stimulates maturation of the oocyte of the follicle, secondly, $Ca^{++}$ influx is induced by hCG and thirdly, $Ca^{++}$ influx by the treatment of EDTA decreases as a dosage-dependent process. This $Ca^{++}$ uptake may take place by the changes of permeability which was induced by hCG treatment. That is, $Ca^{++}$ influx may trigger the resumption of oocyte maturation. It is further necessary in the future study how this $Ca^{++}$ uptake is induced by hCG and increases permeability of the follicle and oocyte.

• Bulletin of the Korean Chemical Society
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• v.30 no.8
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• pp.1703-1710
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• 2009

The single-crystal structure of |$Ca_{35.5}$|[$Si_{121}Al_{71}O_{384}$]-FAU, $Ca_{35.5}Si_{121}Al_{71}O_{384}$ per unit cell, a = 24.9020(10) $\AA$, dehydrated at 673 K and 2 ${\times}\;10^{-6}$Torr, has been determined by single-crystal X-ray diffraction techniques in the cubic space group Fd$\overline{3}$m at 294 K. The large single crystals of zeolite Y (Si/Al = 1.70) were synthesized up to diameters of ${\mu}m\;and\;Ca^{2+}$-exchanged zeolite Y were prepared by ion exchange in a batch method of 0.05 M aqueous Ca($NO_3)_2$ for 4 hrs at 294 K. The structure was refined using all intensities to the final error indices (using only the 971 reflections for which $F_o\;>\;4{\sigma}(F_o))\;R_1$ = 0.038 (based on F) and $R_2$ = 0.172 (based on $F^2$). About 35.5 $Ca^{2+}$ ions per unit cell are found at an unusually large number of crystallographically distinct positions, four. Nearly filling site I (at the centers of the double 6-rings), 14.5 octahedrally coordinated $Ca^{2+}$ ions (Ca-O = 2.4194(24) $\AA$ and O-Ca-O = 87.00(8) and 93.00($8^o$) are found per unit cell. One $Ca^{2+}$ ion per unit cell is located at site II’ in the sodalite cavity and extends 0.50 $\AA$ into the sodalite cavity from its 3-oxygen plane (Ca-O = 2.324(13) $\AA$ and O-Ca-O = 115.5(10)o). The remaining twenty $Ca^{2+}$ ions are found at two nonequivalent sites II (in the supercages) with occupancies of 10 and 10 ions, respectively. Each of these $Ca^{2+}$ ions coordinates to three framework oxygens, either at 2.283(3) or 2.333(5) $\AA$, respectively, and extends either 0.24 or 0.54 $\AA$, respectively, into the supercage from the three oxygens to which it is bound. In this crystal, site I is the most populated; sites II’ and II are only sparsely occupied.$Ca^{2+}$+ appears to fit the octahedral site I best. No cations are found at sites III or III’, which are clearly less favorable for $Ca^{2+}$ ions in dehydrated zeolite Y.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.4
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• pp.55-63
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• 2020

This study investigates the mechanical properties and reaction products of activated slag pastes depending on gypsum presence and calcium carbonate addition in terms of compressive strength tests and synchrotron X-ray diffraction. The chemicals of CaO and NaOH are used as activators with different two dosages. The reaction of CaO-activated slag without gypsum just accelerated by addition of calcium carbonate at early ages, but no improvement was observed at later ages. On the other hand, the mechanical properties of CaO-activated slag pastes with gypsum were improved with calcium carbonate, enhancing the stability of ettringite. The variation of mechanical properties of NaOH-activated slag pastes was negligible depending on calcium carbonate addition in case of no gypsum. The addition of calcium carbonate into NaOH-activated slag pastes with gypsum deteriorated its mechanical properties due to the ion competition between CO₃^2- ions and SO₃^2- ions, decreasing crystallinity of reaction products.

• Korean Journal of Ecology and Environment
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• v.43 no.4
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• pp.471-476
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• 2010

Monthly up-river discharge in the riverine zone analysis resulted in large interannual variations and differences in calcium ($Ca^{2+}$), bicarbonate ($HCO_3^-$), and cations in the lacustrine zone (Lz) of Daecheong Reservoir during the wet year (Wy, 1993) vs. dry year (Dy, 1994). Total up-river discharge in the Wy was four times that of the Dy, and the up-river discharge in July~August of the Wy was eight times greater than that of same period of Dy. Annual water retention time in the Lz showed large difference between the two years. Water residence time (WRT) was minimum when the up-river discharge peaked, whereas the WRT was maximum when the up-river discharge was at minimal condition. This peak discharge from the up-river on early July reduced residence time in the Lz on mid-July~late July. Monthly pattern, based on data of May~November, was similar between the two years, but, but mean retention time in the Wy was 50 days shorter than in the Dy. Such hydrology, up-river discharge, and WRT reduced $Ca^{2+}$, $HCO_3^-$, and cations in the Lz. At low up-river discharge in Wy during April~May, the cation content of Ca+Mg+Na+K averaged 1.17meq $L^{-1}$ (range=1.09-1.26meq $L^{-1}$), but as the up-river discharge increased suddenly, the values decreased. Seasonal fluctuations of $Ca^{2+}$ showed exactly same pattern with bicarbonate ion of $HCO_3^-$. The minimum $Ca^{2+}$ (0.03meq $L^{-1}$) was occurred in the early August of wet year and coincided with the minimum $HCO_3^-$. These results suggest that the magnitude of variation in $Ca^{2+}$, bicarbonate, and cations in the lacustrine zone is directly determined by the peak magnitude of up-river discharge. The magnitude of up-river discharge determined water retention time and the magnitude of ionic dilution in the lacustrine zone, resulting in functional changes of the ecosystem.

• Korean Chemical Engineering Research
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• v.59 no.3
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• pp.399-409
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• 2021

In order to utilize dolomite as a calcium/magnesium compound material, it was prepared highly reactive calcined dolomite(CaO·MgO) using a microwave kiln (950 ℃, 60 min). The experiment was performed according to the standard of the hydration test (ASTM C 110) and hydration reactivity was analyzed as medium reactivity (max 74.1 ℃, 5 min). Experiments were performed with calcined dolomite and salt (MgCl₂·6H₂O) (a) 1:1, (b) 1:1.5, and (c) 1:2 wt% based on the hydration reaction of calcined dolomite. The result of X-ray diffraction analysis confirmed that MgO of calcined dolomite increased to Mg(OH)₂ as the salt addition ratio increased. After the separating reaction, calcium was stirred at 80 ℃, 24 hr that produced CaCl₂ of white crystal. XRD results, it was confirmed calcium chloride hydrate (CaCl₂·(H₂O)x) and CaO of calcined dolomite and salt additional reaction was separated into CaCl₂. And it was synthesized with Ca(OH)₂ 99 wt% by NaOH adding reaction to the CaCl₂ solution, and the synthesized Ca(OH)₂ was manufactured CaO through the heat treatment process. In order to prepare calcium carbonate, CaCO₃ was synthesized by adding Na₂CO₃ to CaCl₂ solution, and the shape was analyzed in cubic form with a purity of 99 wt%.

• Environmental Sciences Bulletin of The Korean Environmental Sciences Society
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• v.4 no.3
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• pp.173-183
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• 2000

This study measured the zeta potential of both latex colloidal particles with carboxylate surface groups and glass beads (collectors) with silanol surface group employing various solution with different chemical characteristics. The results have been compared with the surface chemistry theory. The zeta potential of the particle and collector increased with increasing pH up to 5.0 regardless of the solution chemistry. For a monovalent electrolyte solution(sodium chloride solution) the zeta potential steadily increased until the pH reached 9.5. In contrast, little change in zeta potential was made between 5.0 and 9.5 for a divalent electrolyte solution (sodium chloride solution) the zeta potential steadily increased until the pH reached 9.5. In contrast, little change in zeta potential was made between 5.0 and 9.5 for a divalent electrolyte solution (calcium chloride solution). In other words, the more the pH decreases, the larger the effect of neutral salts, such as NaCl and CaCl$_2$, have on the ζ-potential values. In this study, the PZPC(point of zero proton condition) of the particle and collector occurred below a pH of 3.1, H(sup)+ and OH(sup)- acted as a PDI (potential determining ion), and Na(sup)+ acted as an IDI(indifferent ion). The magnitude of the negative ζ-potential values of the particle and collector monotonically increased as the concentrations of Na(sup)+ or Ca(sup)2+([Na(sup)+] or [Ca(sup)2+]) decreased (the values of pNa or pCa increased). In the case of latex particles, the ζ-potential should aproach zero (isoelectric point; IEP) asymptotically as the pNa approaches zero, while in the case of calcium chloride electrolyte, ζ-potential reversal may be expected to occur around 3.16$\times$10(sup)-2MCaCl$_2$(pCa=1.5). pH, valance and ionic strength can be used in various ways to improve the water treatment efficiency by modifying the charge characteristics of the particle and collector. Predictive capability is far less certain when EDL(electrical double layer) repulsive forces exist between the particle and collector.

• Korean Journal of Materials Research
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• v.28 no.5
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• pp.273-278
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• 2018

Lithium-ion batteries have been considered the most important devices to power mobile or small-sized devices due to their high energy density. $LixCoO_2$ has been studied as a cathode material for the Li-ion battery. However, the limitation of its capacity impedes the development of high capacity cathode materials with Ni, Mn, etc. in them. The substitution of Mn and Ni for Co leads to the formation of solid solution phase $LiNi_xMn_yCo_{1-x-y}O_2$ (NMC, both x and y < 1), which shows better battery performance than unsubstituted $LiCoO_2$. However, despite a high discharge capacity in the Ni-rich compound (Ni > 0.8 in the metal site), poor cycle retention capability still remains to be overcome. In this study, aiming to improve the stability of the physical and chemical bonding, we investigate the stabilization effect of Ca in the Ni-rich layered compound $Li(Ni_{0.83}Co_{0.12}Mn_{0.05})O_2$, and then Ca is added to the modified secondary particles to lower the degree of cationic mixing of the final particles. For the optimization of the final grains added with Ca, the Ca content (x = 0, 2.5, 5.0, 10.0 at.%) versus Li is analyzed.

• Journal of Environmental Science International
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• v.9 no.5
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• pp.437-441
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• 2000

A study on the removal of Pb ion from Pb-contaminated soil was carried out using ex-site extraction process. Tartaric acid (TA) and iminodiacetic acid sodium salt(IDA) as a washing agent were evaluated as a function of concentration reaction time mixing ratio of washing agent and recycling of washing agent. TA showed a better extraction performance than IDA. The optimum washing condition of TA and IDA were in the ratio of 1:15 and 1:20 between soil and acid solution during 1 hr reaction. The total concentrations of Pb ion by TA and IDA at three repeated extraction were 368.8 ppm and 267.5 ppm respectively. The recovery of Pb ion from washing solution was achieved by adding calcium hydroxide and sodium sulfide form the precipitation of lead hydroxide and lead sulfide and optimum amounts of sodium sulfide and calcium hydroxide were 7 g/$\ell$ for the TA washing solution and 4 g/$\ell$, 5g/$\ell$ for the IDA washing solution respectively. The efficiency of recycle for TA and IDA washing solution were 78.8% , 95.1%, and 89.2%, 96.6% at third extractions under $Na_2S$ and $Ca(OH)_2$, respectively.

• Journal of environmental and Sanitary engineering
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• v.20 no.3 s.57
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• pp.27-35
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• 2005

The ion exchange resins have been synthesized from chlormethyl styrene - 1,4 -divinyl-benzene(DVB) with $1\%,\;4\%,\;and\;10\%$-crosslinking and macrocyclic ligand of cryptand type by copolymerization method and the adsorption characteristics of uranium(VI), calcium(II) and lutetium(III) metallic ions have been investigated in various experimental conditions. The synthesis of these resins was confirmed by content of chlorine, element analysis, and IR-spectrum. The effects of pH, time, dielectric constant of solvent and crosslink on adsorption of metallic ions were investigated. The uranium ion was showed fast adsorption on the resins above pH 3. The optimum equilibrium time for adsorption of metallic ions was about two hours. The adsorption selectivity determined in ethanol was in increasing order uranium $(UO_2^{2+})>calcium(Ca^{2+})>lutetium(Lu^{3+})$ ion. The adsorption was order of $1\%,\;4\%,\;and\;10\%$ crosslink resin and adsorption of resin decreased in proportion to order of dielectric constant of solvents.