• Archives of Pharmacal Research
• /
• 제15권2호
• /
• pp.176-183
• /
• 1992

The stabilizing effects of $\alpha$-$\beta$-$\gamma$- and dimethyl-$\beta$-cyclodextrins $(\alpha$-, $\beta$-, $\gamma$- and DM-$\beta-$-CyDs) on the degradation of hydrocortisone 17-butyrate (HC-17B) in aqueous solution was investigated. Hc-17B underwent a facile hydroxide ion-catalyzed rearrangement to the less active 21-butyrate ester by the apparent first-order kinetics, and maximum stability of HC-17B was obtained at around pH 4.0. The stability of HC-17B was increased by inclusion complexation with $\alpha$-, $\gamma$- and DM-$\beta$-CyD in the pH range of 2.0-8.0 examined, whereas $\beta$-CyD accelerated the degradation of HC-17B at the pH higher than 5.0. The effects of ionic strength, solvent, temperature and CyD concentration were also investigated. Stability constants and apparent degradation rate constants of HC-17B-$\gamma$-CyD and HC-17B-DM-$\beta$-CyD complexes were determined kinetically on the basis of 1:1 complexation. The results suggested that the inclusion complexation with $\gamma$-CyD or DM-$\beta$-CyD was most useful means to enhance the stability of the steroid.

• Journal of applied mathematics & informatics
• /
• 제17권1_2_3호
• /
• pp.269-282
• /
• 2005

We study the global asymptotic stability, global attractivity, boundedness character, and periodic nature of all positive solutions and all negative solutions of the difference equation $$x_{n+1}\;=\;{\alpha}-{\frac{x_{n-1}}{x_{n}},\;n=0,1,\;{\cdots}$$, where ${\alpha}\;\in\; R$ is a real number, and the initial conditions $x_{-1},\;x_0$ are arbitrary real numbers.

• 한국수학교육학회지시리즈B:순수및응용수학
• /
• 제11권1호
• /
• pp.15-22
• /
• 2004

In this paper, we investigate asymptotic stability, oscillation, asymptotic behavior and existence of the period-2 solutions for difference equation $x_{n+1}\;=\;{\alpha}\;+\;\beta{x_{n-1}}^{p}/{x_n}^p$ where ${\alpha}\;{\geq}\;0,\;{\beta}\;>\;0.\;$\mid$p$\mid$\;{\geq}\;1$, and the initial conditions $x_{-1}\;and\;x_0$ are arbitrary positive real numbers.

• 멤브레인
• /
• 제17권4호
• /
• pp.294-301
• /
• 2007

비불소계 스티렌 고분자 전해질 막의 산화안정성을 개선하기 위해 p-methyl styrene, t-butyl styrene, ${\alpha}-methyl$ styrene과 같은 스티렌 유도체를 단독 또는 복합으로 도입하고 모노머 흡수법을 이용하여 막을 제조하였다. 제조된 막의 특성분석으로 중합무게비, 함수율, 이온교환용량, 수소이온 전도도 및 가속조건에서의 산화안정성을 조사하였다. 사용된 스티렌 유도체의 구조 및 특성에 따라 모노머 흡수, 중합 및 술폰화 단계가 영향을 받는 것으로 나타났다. 산화적으로 안정한 고분자를 형성하는 ${\alpha}-methyl$ styrene은 중합 단계가 어렵기 때문에 스티렌 또는p-methyl styrene과 공중합하여 제조하였고 p-methyl styrene과 공중합된 ${\alpha}-methyl$ styrene 막은 스티렌과 공중합한 막보다 높은 전도도 및 안정성을 나타내었으나 낮은 분자량으로 인해 안정성의 개선을 크게 보이지 못하였다. 벤젠 고리에 큰 치환기를 갖는 t-butyl styrene은 모노머 흡수 및 술폰화과정이 용이하지 않기 때문에 제조된 막의 성능이 감소하였으며 이를 p-methyl styrene과 공중합할 때 우수한 성능과 스티렌막보다 크게 개선된 안정성을 보였다.

• 한국축산식품학회지
• /
• 제23권1호
• /
• pp.86-95
• /
• 2003

비타민 E에 의한 육색소의 산화 안정성 향상 기작을 정리하였다. 지용성 산화제인 $\alpha$-토코페롤이 수용성 단백질인 옥시마이오글로빈을 보호하는 원리가 밝혀지고 있다. 최근의 연구들에서 $\alpha$-토코페롤이 세포막 지방산화의 2차 산화물들의 방출을 지연시켜 옥시마이오글로빈 산화를 억제시키고 식육의 바람직한 육색을 유지시킨다는 증거가 제시되고 있다. 지방산화물의 한 그룹인 $\alpha$,$\beta$-분포화 알데하이드들은 단백질과 서로 결합하는 역할을 하여 옥시마이오글로빈의 산화를 증진시키는 것으로 밝혀졌다. 만약 $\alpha$-토코페롤이 이런 활동적인 알데하이드들의 발생을 지연시킨다면 이런 지방산화물들이 옥시마이오글로빈의 산화에 미치는 영향도 억제될 것이다. 또한$\alpha$-토코페롤은 메트마이오글로빈의 환원에 작용하여 쇠고기의 육색 안정성 유지에 일정부분 역할을 담당하는 것으로 사료된다.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2002년도 추계학술대회 논문집 Vol.15
• /
• pp.330-333
• /
• 2002

The stability against DC accelerated aging stress of $Dy_{2}O_{3}-doped$ $ZnO-Pr_{6}O_{11}-based$ varistor ceramics was investigated. The calculated nonlinear exponent$(\alpha)$ in varistor ceramics without $Dy_{2}O_{3}$ was only 4.9, whereas the $\alpha$ value of the varistors with $Dy_{2}O_{3}$ was abruptly increased in the range of 48.8 to 58.6. The varistor ceramics with $Dy_{2}O_{3}$ content of 1.0 mol% exhibited maximum ${\alpha}$, reaching 58.6, whereas they exhibited very poor stability. While, The varistor ceramics doped with 0.5 mol% $Dy_{2}O_{3}$ exhibited not only the high nonlinearity, which the ${\alpha}$ is 55.3 and the leakage current is $0.1{\mu}A$， but also the highest stability, which the variation rates of varistor voltage and nonlinear exponent are -0.8% and -14.3%, respectively, under DC accelerated aging stress, $0.95 V_{1mA}/150^{\circ}C/24h$.

• 한국식품영양학회지
• /
• 제11권2호
• /
• pp.159-164
• /
• 1998

고구마 $\beta$-아밀라아제를 NaIO4-산화 가용성 전분으로 변형하여 안정성을 측정하였다. 그 결과, 치적안정 pH는 3 및 4를 나타냈고, pH 3, 5~9, 11에서 비변형 효소보다 높은 안정성을 나타냈다. 6$0^{\circ}C$에서 15분 동안 변형효소는 비변형 효소보다 안정성이 증가하였다. 변형 보리 $\beta$-아밀라아제는 전체 pH에 걸쳐서 넓은 pH 안정성을 나타냈고, $\alpha$-cyclodextrin은 이를 더욱 증가 시켰다.

• Applied Biological Chemistry
• /
• 제21권2호
• /
• pp.103-108
• /
• 1978

Paecilomyces subglobosum이 생산하는 내산성 ${\alpha}-amylase$를 Sephadex G-150으로 정제한 결과 순수정제가 되지 않았으나 glucoamylase와 분리되었다. 조효소를 사용하여 내산성 amylase의 일반 성질을 조사한 결과 최적 pH는 4.0이었고 최적온도는 $38^{\circ}C$이었다. 이 효소는 보통 ${\alpha}-amylase$와 비교하여 pH에 대한 안정성은 매우 좋았으나 열 안정성은 비슷하였다. 전분에 대한 가수분해력이 좋았으며 생성물을 박충 크로마토그라피로 조사한 결과 말토스도 분해하는 것을 알았다.

• 한국자원식물학회지
• /
• 제21권6호
• /
• pp.435-439
• /
• 2008

Due to the fact that tocopherols and tocotrienols have antioxidant and anticancer properties, the commercial utilization of unsaponifiable fractions in rice bran is increasing. These nutraceutical compounds, however, are fairly unstable and readily break down when exposed to oxygen or lighting conditions. To compare the relative sensitivity of vit E isomers to heat and oxygen, concentrated unsaponifiable fractions extracted from crude rice bran oil were exposed to various temperature, oxygen (nitrogen-balanced), and bathing solvent conditions and resultant concentration changes in ${\alpha}$- and ${\gamma}$-tocopherols (T) and tocotrienols (T3) were evaluated. Each isomer exhibited different heat stability. Among them, ${\alpha}$-T3 degraded more rapidly compared to other vit E isomers while ${\alpha}$-T was the most stable isomer. Oxygen level also showed significant impact on each isomer's stability where severe reductions of ${\gamma}$-T (by 20%) and ${\gamma}$-T3 (by 29%) were observed under 2% oxygen conditions, while under 0% oxygen conditions no degradation could be observed even after exposure to $95^{\circ}C$ for 4 hours. When various blending solvents were mixed with concentrated unsaponifiable fractions, organic solvents such as isooctane and hexane were more effective in maintaining the stability of ${\gamma}$- T3 compared to edible oils, among which com oil was more efficient than soybean and rice bran oils.

• 한국미생물·생명공학회지
• /
• 제17권5호
• /
• pp.529-532
• /
• 1989

A strain of Streptomyces sp. (YS-221-B) extracellularly produced an inhibitory substance for $\alpha$-D-Glucosidase. The substance was purified 96-fold from culture filtrate by dialysis, heat treatment, adsorption on active carbon, Bio-Gel P-10 and Sephadex G-75 column chromatography with yield of 9.2%. The substance was stable in pH range from 7.0 to 11.0 at 37$^{\circ}C$, and a treatment at 10$0^{\circ}C$ for 20 min diminished only 15% of the original activity. The inhibitor was not inactivated by the treatment of $\alpha$-, $\beta$-amylases, glucoamylases, trypsin and chymotrypsin but inactivated by pyoteases from Streptomyces griseus and Tritirachium album.