• Macromolecular Research
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• v.13 no.2
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• pp.147-151
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• 2005

The main objective of this study was to modulate pH-sensitive polymers (poly($\beta-amino esters$)) by controlling their molecular weight during their synthesis. These pH-sensitive and biodegradable polymers were synthesized by Michael-type step polymerization. 1,4-Butane diol diacrylate was used as the unsaturated carbonyl compound and piperazine as the nucleophilic compound. Various molecular weight polymers were obtained by varying the mol ratio of piperazine/1,4-butane diol diacrylate. The synthesized polymers were characterized by $^{1}H-NMR$ and their molecular weights were measured by gel permeation chromatography(GPC). The dependence of the molecular weight on the mol ratio was evaluated by the titration method. Also, the pH dependent turbidity of the polymers was determined by UV-Vis spectrophotometry. This pH dependent property of the polymers could be very useful for preparing drug carriers that are sensitive to pH.

• Journal of Pharmaceutical Investigation
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• v.25 no.3
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• pp.239-247
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• 1995

The physico-chemical stability of aucubin, a hepatoprotective iridoid glucoside, in buffered aqueous solutions was studied using a stability-indicating reversed-phase high performance liquid chromatography. The degradation of aucubin followed the pseudo-first-order kinetics. In strong acidic regions, aucubin was rapidly degraded by the specific acid catalysis, forming dark brown precipitates. From the rate-pH profiles, it was found that aucubin was most stable at the pH of about 10. From the temperature dependence of degradation, activation energies for aucubin at pH 2.1 and 4.9 were calculated to be 22.0 and 24.3 kcal/mole, respectively. The shelf-life $(t_{90%})$ for aucubin at pH 9.07 and $20^{\circ}C$ was predicted to be about 603 days. A higher ionic strength accelerated the degradation of aucubin at pH 4.01. The effect of metal ions on the degradation rate of aucubin at pH 7.16 was in the rank order of $Cu^{2+}\;>\;Fe^{3+}\;>\;Co^{2+}\;>\;Fe^{2+}\;>\;Mg^{2+}$. On the other hand, $Mn^{2+}\;and\;Ba^{2+}$ slowed the degradation rate.

• Journal of environmental and Sanitary engineering
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• v.15 no.4
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• pp.114-122
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• 2000

Several new ion exchange resins have been synthesized from chloromethyl styrene-1,4-divinylbenzine with 1%, 2%, 5% and 105-crosslink and macrocyclic ligands of cryptand type by interpolymerization method. The adsorption characteristics and the pH, time, solvents and concentration dependence of the adsorption of uranium ion by this resins were studied. The resins were very stable in both acidic and basic media and have good resistance to heat at $300^{\circ}C$. The uranium ion are not adsorbed on the resins below pH 3.0, but the power of adsorption of it increased rapidly above pH 4.0. The optimum equilibrium time for adsorption of uranium ion was two hours and adsorptive power decreased in proportion to crosslink size of the resins and order of dielectric constants of solvents used and the adsorption for uranium ion was bin the order of $OdienNtn-H_4$ > $OtnNen-H_4$ > $OtnNen-H_4$ > $OenNen-H_4$.

• Journal of Soil and Groundwater Environment
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• v.16 no.6
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• pp.122-132
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• 2011

Mercury accumulates in biota mainly as methylmercury. In nature, methylmercury shows high affinity to organic matter and $CH_3Hg^+$-organic matter complexation affects the mobility and bioavailabiity of methylmercury. In this study, we examined the methylmercury binding sites in an aquatic humic acid as affected by the pH condition using Hg $L_{III}$-edge extended X-ray absorption fine structure (EXAFS). We evaluated methylmercury binding humic ligands using methylmercury-thiol, methylmerury-carboxyl, and methylmercury-amine complexation models. When $CH_3Hg^+$-to-humic reduced sulfur ratio is 0.3, we found that most of $CH_3Hg^+$ binds to thiol ligands at pH 5 and 7. At pH 7, however, some carboxyl or amine ligand contribution is observed, unlike at pH 5 where $CH_3Hg^+$ almost exclusively binds to thiol ligands. The carboxyl or amine ligand contribution may indicate that some types of thiol ligands in the natural organic matter have relatively low complexation constants or acid dissociation constants compared to those of some carboxyl or amine ligands. Analysis results indicate that ~0.2 fraction of methylmercury binds to amine or carboxyl ligands and ~0.8 to thiol ligands at pH 7.

• 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.

• Archives of Pharmacal Research
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• v.2 no.2
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• pp.111-114
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• 1979

Diazepam was investigated in aqueous buffer media using pulsed rotation voltammetry. The dependence of half-wave potentials on pH indicated a two proton involvement in a two electron transfer reduction in the pH range 3-10. Dizaepam at micromolar concentration levels may be determined by measurement of the limiting difference current.

• Proceedings of the KIEE Conference
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• 1987.07a
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• pp.509-512
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• 1987

We report that the optimum substrate temperature to fabricate a-Si:H $n^+-p-p^+$ cell decreases with increasing the boron concentration in the Player. The results can be explained as the dependence of substrate temperature for the relaxation of silicon atoms and the bonded hydrogen concentration in the player.

• Journal of the Korean Applied Science and Technology
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• v.28 no.3
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• pp.284-289
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• 2011

All spectroscopic methods used in this work indicate the instability of tungstophosphates in aqueous solutions and considerable dependence on pH with regard to the dominant species present in the solution. UV spectroscopy indicates that some changes occur in the system but they cannot be specified. IR spectroscopy gives more information on the identification of the dominant species as a function the pH of the solution. NMR spectroscopy provides unique data, which can be used for more accurate interpretation of changes in the solution of various pH values. In the case of aqueous solutions of tungstophosphates, the parent anion was present only in a very acidic solution of ca. pH 1. Some differences in interpretation of the molecular species present under various experimental conditions can be ascribed to some extent to the diversity of chemical shifts of NMR. Under physiological conditions attained with the addition of NaOH, tungstophosphates was dominantly present in the form of the lacunary monovacant anion.

• Korean Journal of Soil Science and Fertilizer
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• v.14 no.3
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• pp.110-116
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• 1981

Soil surface charge which manipulates some important soil physico-chemical properties such as nutrient and water holding abilities, colloidal stability and soil erosion was investigated in wide range of soil pH, using soils developed originally from same volcanic ash deposit but under different rainfall condition in Hawaii. The results can be summarized as follows : 1. Ustollic Camorthid (Kawaihae soil) which was developed under the lowest rainfall (less than 500 mm/yr) revealed low Z.P.C. (4.5-5.0) and less dependence of net charge on concentration of indifferent electrolytes. 2. Typic Hydrandepts (Akaka and Hilo soils) which were developed under the high rainfall (3050-7600 mm/yr) showed the Z.P.C. in between 5.5-7.0 and high dependence of net charge on concentration of indifferent electroytes. 3. It was found by X-ray diffraction together with total chemical analysis that amorphous materials were dominant (above 6.0%) in Typic Hydrandepts while dehydrated halloy-site (1 : 1 clay minerals) was dominant (45-50%) in Ustollic Camorthid. 4. In spite of little difference in particle size distribution of the soils, the difference of specific surface area was remarkable showing the order of Akaka (289) > Hilo (268) > Kawaihae (93). 5. It was evident, taking account of apparent field pH values, 5.2 of Akaka, 5.5 of Hilo and 7.0 of Kawaihae soil, respectively, that Akaka, and Hilo soils would show either positive or near zero (+ or 0) of ${\Delta}pH$ while Kawaihae soil would exhibit negative (-) of ${\Delta}pH$ at natural field condition.

• Bulletin of the Korean Chemical Society
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• v.10 no.5
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• pp.434-437
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• 1989

The pH dependence of the absorption and fluorescence of 4-hydroxy-2-methyl-1,2-benzothiazinenecarboxylat es, piroxicam and HMBDC have been measured and compared with the solvent dependence of the spectra reported previously. Four different prototropic species are observed in both ground and excited states of piroxicam ; the cation, the neutral, the anion and the dianion, while three different species such as the cation, the neutral and the anion are observed in HMBDC. The $pK_a$ and $pK_a^{\ast}$ have been determined by absorptiometric titration and Forster cycle method, respectively. The probable structure of each species has been proposed on the basis of the intramolecular phototautomerism.