• Food Science and Biotechnology
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• 제18권1호
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• pp.185-189
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• 2009

Microencapsulation of flavor was carried out by molecular inclusion process using $\beta$-cyclodextrin (${\beta}CD$). ${\beta}CD$-flavor complex was prepared at various flavor-to-${\beta}CD$ ratios (1:6-1:12) to determine the effect of ${\beta}CD$ concentration on the inclusion efficiency. Maximum total oil retention and minimal surface oil content were obtained at flavors to ${\beta}CD$ ratio of 1:10. The physical properties and controlled release pattern of flavors from ${\beta}CD$-flavor complex were measured and compared with spray-dried microcapsules prepared using carbohydrate wall system. ${\beta}CD$-flavor complex showed higher total oil retention and surface oil contents, smaller mean particle size, lower moisture uptake, and higher oxidation stability than spray-dried microcapsule. Oxidative stability of flavor was correlated with hygroscopicity of wall materials. The controlled release mechanism was highly affected by temperature and characteristics of wall materials.

• Archives of Pharmacal Research
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• 제28권4호
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• pp.382-390
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• 2005

chial allylic ethers with a hydroxyl group attached to the $\pi-system$ and chlorosulfonyl isocyanate. The enantioselectivity of the CSI reaction with the chiral allylic and benzylic ethers was examined in various solvents and temperatures. Based on these results, it was proposed that the CSI reaction is a competitive reaction of a $S_{N}i$ (retention) and a $S_{N}1$ mechanism (racemization) according to the stability of the carbocation intermediate. This means that there is a greater proportion of retention with the less stable the carbocation intermediate and vise versa.

• Bulletin of the Korean Chemical Society
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• 제13권3호
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• pp.280-285
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• 1992

Enantiomeric separation of free amino acids has been achieved by a reversed phase liquid chromatography with addition of a Cu(Ⅱ) complex of N-alkyl-L-proline (alkyl: propyl, pentyl or octyl) to the mobile phase. The amino acids eluted were detected by a postcolumn OPA system. N-alkyl-L-proline was prepared and used as a chiral ligand of Cu(Ⅱ) chelate for the enantiomeric separation. The concentration of the Cu(Ⅱ) chelate, the organic modifier and pH affect the enantiomeric separation of free amino acids. The retention behaviour, varied with change in pH and the concentration of the Cu(Ⅱ) chelate, was different compared with those of the derivatized amino acids. The elution orders between D- and L-forms were consistent except histidine showing that L-forms elute earlier than D-forms. The retention mechanism for the enantiomeric separation can be illustrated by the stereospecificity of the ligand exchange reaction and the hydrophobic interaction between the substituent of amino acids and reversed phase, $C_18$.

• Bulletin of the Korean Chemical Society
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• 제13권3호
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• pp.285-289
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• 1992

Enantiomeric separation of underivatized amino acids using N-alkyl-L-proline (octyl, dodecyl or hexadecyl) coated HPLC has been accomplished. The anchoring N-alkyl groups of L-proline provides a permanent adsorption of there solving chiral agent on the hydrophobic interface layer of a reversed phase. The factors controlling retention and enantioselectivity such as the Cu(II) concentration, pH of the eluent, the type and concentration of organic modifier in the hydroorganic eluent, and extent of coating were examined. The elution orders between D- and L-amino acids were consistent, L-forms eluting first, except histidine and asparagine. The extremely high enantioselectivity $(\alpha$ upto 13 for proline) is observed. The retention mechanism for the chiral separation can be illustrated by a complexation and hydrophobic interaction.

• 전자공학회논문지
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• 제50권4호
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• pp.239-245
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• 2013

멀티 레벨 낸드 플레쉬 메모리에서 주위 셀의 문턱 전압상태에 따른 데이터 유지 특성을 연구하였다. 열을 가해 셀의 데이터 보전특성을 판정하는 열적 열하 특성에서 주목하는 셀의 문턱 전압이 변화하는데 문턱전압의 변화는 선택된 셀 주위에 있는 셀들이 가장 낮은 문턱 전압 상태로 있는 셀들의 수가 많을수록 커진다. 그 이유는 전하의 손실이 이루어지는 낸드 플레쉬 셀의 본질적인 특성 뿐 아니라, 주위 셀 사이의 측면 전계 때문이다. 전계에 대한 모사 결과로부터 전계의 증가 현상을 발견할 수 있고, 이로 인한 전하의 손실이 소자 스케일 다운에 따라 더 증가함을 알 수 있다.

• 한국축산식품학회지
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• 제18권2호
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• pp.176-184
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• 1998

The objective of this study was to investigate the effects of freezing rate on aroma retention and to examine the mechanism of aroma retention during freeze drying process. Our experiments were carried out with self-manufactured freeze-dryer. Gelatin gels (2% w / w, 80${\times}$20mm) containing diacetyl(2mg/ml) were frozen unidirectionally (Neumann's model) from the bottom at -45, -30, -20, and -15$^{\circ}C$ and followed with freeze-drying. Under the upper conditions we measured freezing rate and the change of temperature and pressure during freeze drying. Freeze-dried gelatins were cut horizontally into 5 mm thickness from the bottom measured and diacetly contents. Besides, we observed the effect of the relative humidity of the diacetyl contents freeze-dried gelatin during storage. The retained diacetyl content was increased at high freezing temperature and in order of 0∼5, 5∼10, 10∼15, 15∼20 mm section from the bottom of the sample. It was observed that the retained diacetyl content was high in 15∼20 mm section. The retained diacetyl content and freeze-dried gelatin stored in the condition of high relative humidity was decreased significantly but in the low relative humidity case, was it decreased in small amount. The results of our experiment resents that the low temperature freezing and low humidity storing condition is effective for preserving aroma compound in food.

• The Journal of Advanced Prosthodontics
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• 제7권4호
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• pp.303-311
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• 2015

PURPOSE. The aim of this study was to compare the changes in retentive force of stud attachments for implant overdentures by in vitro 2-year-wear simulation. MATERIALS AND METHODS. Three commercially available attachment systems were investigated: Kerator blue, O-ring red, and EZ lock. Two implant fixtures were embedded in parallel in each custom base mounting. Five pairs of each attachment system were tested. A universal testing machine was used to measure the retentive force during 2500 insertion and removal cycles. Surface changes on the components were evaluated by scanning electron microscopy (SEM). A Kruskal-Wallis test, followed by Pairwise comparison, was used to compare the retentive force between the groups, and to determine groups that were significantly different (${\alpha}$<.05). RESULTS. A comparison of the initial retentive force revealed the highest value for Kerator, followed by the O-ring and EZ lock attachments. However, no significant difference was detected between Kerator and O-ring (P>.05). After 2500 insertion and removal cycles, the highest retention loss was recorded for O-ring, and no significant difference between Kerator and EZ lock (P>.05). Also, Kerator showed the highest retentive force, followed by EZ lock and O-ring, after 2500 cycles (P<.05). Based on SEM analysis, the polymeric components in O-ring and Kerator were observed to exhibit surface wear and deformation. CONCLUSION. After 2500 insertion and removal cycles, all attachments exhibited significant loss in retention. Mechanism of retention loss can only be partially explained by surface changes.

• 대한약학회:학술대회논문집
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• 대한약학회 2003년도 Proceedings of the Convention of the Pharmaceutical Society of Korea Vol.1
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• pp.242.2-243
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• 2003

We have developed the novel one-pot synthetic method for regioselective N-protected amines, carbamates as a protective group of amines, through the reaction of various ethers with chlorosulfonyl isocyanate (CSJ). This synthetic method provides a simple and convenient alternative for the formation of carbamates, such as -NHMoc, -NHPoc. -NHCbz, -NHPnz, -NHTroc and -NHAloc, by varying the alkyl moiety of ethers. (omitted)

• 대한화학회지
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• 제32권2호
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• pp.135-143
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• 1988

역상 액체크로마토그래피에서 벤젠 일치환체들의 머무름 메카니즘과 머무름예측을 연구하기 위하여 크로마토 그래피 파라미터로 극성지표(P') 분자량(MW), 치환기 상수(${\pi}$ ) 및 분자간 연결지수$(^1{\chi}^{\nu})$를 머무름 데이터와 관련지어 상관관계를 조사하였다. 벤젠을 기존으로 하여 각 치환체의 크기인자와 비인 상대적 머무름$(log k'_S/k'_B)$과 각 치환체의 극성의비 $(P'_S/P'_B)$ 사이에는 상관관계가 있다. 치환기가 극성인 치환체들은 상관관계가 비교적 좋았으나 비극성 치환기를 갖는 치환체들은 분자량을 함께 고려함으로써 좋은 상관관계를 얻을 수 있다. 또한 상대적 머무름과 극성인자 및 분자량의 상관관계를 다변수 회귀분석으로 구하였다. 문헌적 머무름 자료와 소수성 파라미터로부터 유도된 치환기 상수(${\pi}$)와 분자간 연결지수$(^1{\chi}^{\nu})$ 간에는 메탄올의 이동상에서 가장 좋은 상관관계를 얻었다. $C_{18}$ 컬럼의 미반응된 실란올 기를 끝막음(end capping) 시키지 않은 컬럼에서는 이러한 상관관계가 감소되었다. 벤젠 일치환체들의 머무름과 관련지어 고려할 수 있는 파라미터는${\pi}$, P', $(^1{\chi}^{\nu})$ 및 MW 순으로 그 관련성이 감소됨을 알았다.

• 펄프종이기술
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• 제31권2호
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• pp.58-63
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• 1999

Three kinds of papers were prepared from different beating degree of pulps. Physical and optical properties were examined to elucidate the deterioration mechanism of paper according to beating degrees. Changes of double folds, elongation, water retention value, DP, K/S value and visible, UV region light absorption spectra of those papers treated by UV light were studied. Double folds and brightness were decreased more rapidly by UV treatment with increasing of beating degree. The light absorption rates of pulps in visible and UV region were also increased with change of beating level. The formation of new hydrogen bonds and higher light absorption rate of pulps according to beating induced to absorb and interact with much UV light. These phenomena maybe brought about to accelerate paper deteriortion by UV treatment both optical and physical properties.