• Title/Summary/Keyword: pH dependence

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Physicochemical Stability of Leucine Enkephalin and $[D-Ala^2]$-Leucine Enkephalinamide in Buffered Aqueous Solution (완충 수용액중 로이신엔케팔린 및 [D-알라$^2]$-로이신엔케팔린아미드의 물리화학적 안정성)

  • Park, In-Sook;Chun, In-Koo
    • YAKHAK HOEJI
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    • v.38 no.5
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    • pp.488-495
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    • 1994
  • To evaluate the feasibility of transmucosal delivery of leucine enkephalin (Leu-Enk) and its synthetic analog, $[D-Ala^2]$-leucine enkephalinamide (YAGFL), their physicochemical stabilities in aqueous buffered solutions were first investigated using a stability indicating high performance liquid chromatography. The degradation of Leu-Enk and YAGFL followed the pseudo-first-order kinetics. From the pH-rate profiles, it was found that the maximal stability of the two pentapeptides was at the pH of about 5.0. The shelf lives $(t_{90%})$ for the degradation of Leu-Enk and YAGFL at pH 5.0 and $40^{\circ}C$ were found to be 48.13 and 50.9 days, respectively. From the temperature dependence of the degradation, activation energies for Leu-Enk and YAGFL were calculated to be 13.61 and 13.47 kcal/mole, respectively. A higher ionic strength and a higher initial peptide concentration in buffered solution slowed the degradation of the two pentapeptides. The addition of 2-hydroxypropyl-${\beta}$-cyclodextrin into the peptide solution did not affect the stability significantly.

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Numerical analysis of magnetization of HgBa$_2Ca_2Cu_3O_{8+{\delta}}$ superconductor (HgBa_2Ca_2Cu_3O_{8+{\delta}}$ 초전도체 자화의 수치적 해석)

  • Kim, Bong-Jun;Kim, Young-Cheol;Kim, Young-Jin;Back, Sang-Min
    • 한국초전도학회:학술대회논문집
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    • v.9
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    • pp.218-221
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    • 1999
  • Magnetization measurements have been carried out on grain aligned Hg-1223 with the applied field parallel to the c-axis. The temperature dependence of the lower critical field H$_{cl}$(T) was determined by considering the effect of the surface barrier on the magnetization. H$_{cl}$(T) have been determined .from magnetic hysteresis loops within the framework of the modified Kim-Anderson critical-state model, where the surface barrier and the lower critical field are explicitly considered. At high temperature, H$_{cl}$(T) is identified as H$_p$(T). This results are agreed with the theory of Bean-Livinston surface barriers.

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Preparation of Glass Thin Film onto Plastic Surface by Sol-Gel Process (Sol-Gel 공정으로 Plastic표면에 Glass박막 제조에 관한 연구)

  • 양천회
    • Journal of the Korean Society of Safety
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    • v.13 no.1
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    • pp.85-91
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    • 1998
  • Sol-gel derived silica films were prepared by dip-coating onto polymethylmethacylate with Tetraethoxysilane(TEOS) as starting materials. Film properties such as viscosity and thickness were investigated as a function of dip speed, waterprecursor ratio, sol aging time. IR spectra of the gel films prepared from TEOS at various R are given. At small values of R the absorption peaks assignable to C-H vibration in $-OC_2H_5$ groups are observed around 3000 and 1500-1300 $cm^{-1}$. These bands indicate that the -$-OC_2H_5$ groups are retained in the gel at small values of R because of incomplete hydrolysis of TEOS. Film behaviour was interpreted in terms of the dependence of hydrolysis and condensation rates on the interplay between sol pH and waterprecursor ratio. Film thickness was found to increase by approximately a factor of two as waterprecursor ratio increased from two to six. Film thickness also increased with sol prepolymerization time. Surface quality was correlated with processing conditions.

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Sugar Transoprt in Conidia of Neurospora crassa (붉은 빵곰팡이 세포의 당운반)

  • 이호자
    • Korean Journal of Microbiology
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    • v.13 no.2
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    • pp.45-50
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    • 1975
  • Uptake of $^{14}C$-sorbose and $^{14}C$-3-O-methylglucose by ungerminated conidia of Neurospora crassa was measured by means of the millipore filter technique. Initial rates of jptake of both sorbose and 3-O-methylglucose show a marked dependence optimal pH for uptake of both sugars is close to 4.75. When ungerminated conidia are "starved" with buffer for a prolonged period of time prior to assaying their transport capacity and mycelia, no de-repression of the glucose-repressible sugar transport system is effectuated in contrast to the findings for germinated conidia.d conidia.

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Interaction of pharmaceuticals with betacyclodextrin III Influence of Betacyclodextrin on Phenobarbital Hydrolysis

  • Min, Shin-Hong
    • YAKHAK HOEJI
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    • v.16 no.4
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    • pp.155-161
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    • 1972
  • The hydrolysis of phenobarbital is decelerated in alkaline solution by betacyclodextrin. The betacyclodextrin inhibits the degradation of phenobarbital up to 1.5 fold in the system containing 1% betacyclodextrin. The degradation mechanism in systems containing betacyclodextrin is the same that in system without complexing agent, although the rate constants are different. The pH dependence of the hydrolysis rate deceleration is compared with the ionization percent of betacyclodextrin. The results indicate that a direct relationship does not exist between the ionization of betacyclodextrin. It seems reasonable therefore that the phenobarbital undergoes a stable complex with betacyclodextrin and complex formation would provide a better shield for the phenobarbital from hydroxyl ion attack.

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Problem Analysis of the Experiments Illustrating pH Effects on Enzyme Activities in High School Science Textbooks - Focus on Starch-Iodine Reaction - (고등학교 과학 교과서에서 "pH가 효소의 작용에 미치는 영향" 실험의 문제점 분석 -녹말과 요오드 반응을 중심으로-)

  • Ji, Jae-Hwa;Jeong, Dae-Hong
    • Journal of The Korean Association For Science Education
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    • v.29 no.8
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    • pp.923-933
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    • 2009
  • In this study, analysis was carried out on science experiment in high school textbooks, illustrating 'the effect of pH on enzyme activity.' Five of the total 16 science textbooks introduced in this experiment, and the experimental conditions therein were analyzed. Textbook analysis revealed that pH of below 3 was used for 'acidic condition' and that of over 11 was used for 'basic' condition. Using the experimental conditions described in the textbooks, review experiments were performed. Buffering effect with the addition of saliva was found in the pH region around 7 when buffer solution was not used to control pH as was in the textbooks. The enzyme activity experiments were performed controlling pH from pH 2 to 13 with buffer. The color of the sample was blue from pH 2 to 4, and then disappeared from pH 5 to 8, reflecting that starch was digested owing to enzyme activity. In pH 9 light blue color appeared, indicating de-activation of enzyme under this basic condition. However, the blue color of the sample became lighter at pH 10 and disappeared from pH 11, which was different from the expected behavior anticipating dark blue color due to de-activation of enzyme under strong basic condition. These results can wrongly influence students to interpret that enzyme can be activated in this pH condition. So, we analyzed the reason for the color of the sample turning light blue in pH 10 and disappeared from pH 11. The analysis resulted that ${I_3}^-$ and/or ${I_5}^-$ subunits of polyiodides within the starch helix in starch-iodine complex, showing blue, decreases above pH 10 due to disproportionation to HOI, ${IO_3}^-$, and $I^-$ by the reaction with $OH^-$.

A Study on Resin Synthesis and Adsorption Characteristics for Separation and Recovery of U(VI) (우라늄(VI)의 분리회수를 위한 수지합성과 흡착특성에 관한 연구)

  • 강영식;노기환
    • Journal of environmental and Sanitary engineering
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    • v.14 no.1
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    • pp.31-41
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    • 1999
  • Several new ion exchange resins have been synthesized from chloromethyl styrene-1, 4-di-vinylbenzene with 1%, 2%, 5% and 10%-crosslinking and macrocyclic ligands of cryptand type by interpolymerization method. The adsorption characteristics and the pH, time, solvents and concentration dependence of the adsorption of metal ions by this resin were studied. The correlation between the separation characteristics of uranium and transition metal on the resins and the stability constants of complexes with macrocyclic ligands have been examined. The resins were very stable in both acidic and basic media and had good resistance to heat at $280^{\circ}C$. The $UO_2^{2+}$ aqueous solution was not adsorbed on the resins below pH 3.0, but the power of adsorption of $UO_2^{2+}$ increased rapidly above pH 4.0. The optimum equilibrium time for adsorption of metallic ions was twenty minutes and adsorptive power decreased in proportion to crosslinking size of the resins and order of dielectric constants of solvents used and the selective sequence for metal cations is in the order of $UO_2^{2+}$, $Cu^{2+}$ and $Ce^{3+}$ .

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Glass Dissolution Rates From MCC-1 and Flow-Through Tests

  • Jeong, Seung-Young
    • Proceedings of the Korean Radioactive Waste Society Conference
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    • 2004.06a
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    • pp.257-258
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    • 2004
  • The dose from radionuclides released from high-level radioactive waste (HLW) glasses as they corrode must be taken into account when assessing the performance of a disposal system. In the performance assessment (PA) calculations conducted for the proposed Yucca Mountain, Nevada, disposal system, the release of radionuclides is conservatively assumed to occur at the same rate the glass matrix dissolves. A simple model was developed to calculate the glass dissolution rate of HLW glasses in these PA calculations [1]. For the PA calculations that were conducted for Site Recommendation, it was necessary to identify ranges of parameter values that bounded the dissolution rates of the wide range of HLW glass compositions that will be disposed. The values and ranges of the model parameters for the pH and temperature dependencies were extracted from the results of SPFT, static leach tests, and Soxhlet tests available in the literature. Static leach tests were conducted with a range of glass compositions to measure values for the glass composition parameter. The glass dissolution rate depends on temperature, pH, and the compositions of the glass and solution, The dissolution rate is calculated using Eq. 1: $rate{\;}={\;}k_{o}10^{(ph){\eta})}{\cdot}e^{(-Ea/RT)}{\cdot}(1-Q/K){\;}+{\;}k_{long}$ where $k_{0},\;{\eta}$ and Eaare the parameters for glass composition, pH, $\eta$ and temperature dependence, respectively, and R is the gas constant. The term (1-Q/K) is the affinity term, where Q is the ion activity product of the solution and K is the pseudo-equilibrium constant for the glass. Values of the parameters $k_{0},\;{\eta}\;and\;E_{a}$ are the parameters for glass composition, pH, and temperature dependence, respectively, and R is the gas constant. The term (1-Q/C) is the affinity term, where Q is the ion activity product of the solution and K is the pseudo-equilibrium constant for the glass. Values of the parameters $k_0$, and Ea are determined under test conditions where the value of Q is maintained near zero, so that the value of the affinity term remains near 1. The dissolution rate under conditions in which the value of the affinity term is near 1 is referred to as the forward rate. This is the highest dissolution rate that can occur at a particular pH and temperature. The value of the parameter K is determined from experiments in which the value of the ion activity product approaches the value of K. This results in a decrease in the value of the affinity term and the dissolution rate. The highly dilute solutions required to measure the forward rate and extract values for $k_0$, $\eta$, and Ea can be maintained by conducting dynamic tests in which the test solution is removed from the reaction cell and replaced with fresh solution. In the single-pass flow-through (PFT) test method, this is done by continuously pumping the test solution through the reaction cell. Alternatively, static tests can be conducted with sufficient solution volume that the solution concentrations of dissolved glass components do not increase significantly during the test. Both the SPFT and static tests can ve conducted for a wide range of pH values and temperatures. Both static and SPFt tests have short-comings. the SPFT test requires analysis of several solutions (typically 6-10) at each of several flow rates to determine the glass dissolution rate at each pH and temperature. As will be shown, the rate measured in an SPFt test depends on the solution flow rate. The solutions in static tests will eventually become concentrated enough to affect the dissolution rate. In both the SPFt and static test methods. a compromise is required between the need to minimize the effects of dissolved components on the dissolution rate and the need to attain solution concentrations that are high enough to analyze. In the paper, we compare the results of static leach tests and SPFT tests conducted with simple 5-component glass to confirm the equivalence of SPFT tests and static tests conducted with pH buffer solutions. Tests were conducted over the range pH values that are most relevant for waste glass disssolution in a disposal system. The glass and temperature used in the tests were selected to allow direct comparison with SPFT tests conducted previously. The ability to measure parameter values with more than one test method and an understanding of how the rate measured in each test is affected by various test parameters provides added confidence to the measured values. The dissolution rate of a simple 5-component glass was measured at pH values of 6.2, 8.3, and 9.6 and $70^{\circ}C$ using static tests and single-pass flow-through (SPFT) tests. Similar rates were measured with the two methods. However, the measured rates are about 10X higher than the rates measured previously for a glass having the same composition using an SPFT test method. Differences are attributed to effects of the solution flow rate on the glass dissolution reate and how the specific surface area of crushed glass is estimated. This comparison indicates the need to standardize the SPFT test procedure.

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Factors in effecting the activities of the protein remover (단백질 제거제의 작용에 영앙을 미치는 요인)

  • Park, Mijung;Shin, Young Min;Chang, Ji Yeon;Kim, Daesoo
    • Journal of Korean Ophthalmic Optics Society
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    • v.10 no.2
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    • pp.91-97
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    • 2005
  • We investigated the question whether protein removing activities of enzyme cleaner - protein remover for soft contact lens - are associated with the material of soft contact lens as well as action time, temperature and pH of enzyme solution. We used a subtilisin cleaner as protein remover and estimated the protein amount remained on soft contact lens after using the subtilisin cleaner under the different conditions. The remained protein in soft contact lens was greatly decreased until treatment for 60min, but no significant differences were found from 60min to 24hr. The cleaning effect of the enzymatic treatment in the range of $15{\sim}30^{\circ}C$ was constant. however, there was a significant decline of the protein removing effect at $10^{\circ}C$ and less. The pH of the solution was also important for the efficacy of the enzymatic treatment. The activity of the enzyme cleaner was highest in pH 8.0 and significantly decreased a pH below 7. The pH dependence was found to be related to the conformational change of subtilisin. Furthermore, significant differences in the protein deposit removing efficacy of the subtilisin cleaner were found among the soft contact lens materials.

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