• 대한화학회지
• /
• 제35권6호
• /
• pp.768-771
• /
• 1991

• 수산해양교육연구
• /
• 제18권1호
• /
• pp.65-77
• /
• 2006

A total of 725 questionnaires, collected from secondary teachers appointed within the recent three years in the Metro-Busan, were analyzed. According to the results, the novice teachers perceived that supervisory practice in school was helpful for them in the four areas; instructional method, guidance, class management and administrative work, except for human relations, and they felt the need for instructional supervision but the major hindrance to the practice was time constraint.

• Bulletin of the Korean Chemical Society
• /
• 제23권4호
• /
• pp.593-597
• /
• 2002

(R,S)- and (R)-2-Benzylcysteine (1) and (R,S)-2-phenethylcysteine (2) were synthesized and evaluated as inhibitors for carboxypeptidase A (CPA) with the expectation that these compounds exhibit improved inhibitory activities over 2-benzyl-3-mercaptopropanoic acid (BMPA), a potent CPA competitive inhibitor, possibly having additional interactions of their amino group with the carboxylate of Glu-270 of the enzyme upon binding to CPA. Contrary to the expectation, however, the CPA inhibitory potencies of these compounds were found to be much reduced compared with that of BMPA, suggesting that the amino group in the inhibitors rather exerts steric hindrance in binding of these inhibitors to CPA.

• Bulletin of the Korean Chemical Society
• /
• 제10권6호
• /
• pp.554-559
• /
• 1989

The electronic structure, conformational preferences, and rotational barriers have been studied for transition metal indenyl allyl complexes by means of extended Huckel calculations. After geometrical optimization the exo conformation of allyl moiety is favored over the endo. The rotational barrier of indenyl ring in (Indenyl)Mo(CO)_2(Allyl)$ is computed to be 3.8 kcal/mol. Population analysis is applied to account for the conformational preferences and rotational barriers. A series of substituted allyl complexes has been also optimized. It shows steric hindrance plays a crucial role in setting the allyl orientation.

• Bulletin of the Korean Chemical Society
• /
• 제14권5호
• /
• pp.631-635
• /
• 1993

The polarizability and the transition state energy of a cephalosporin are assumed to be theoretical indices of the permeability through the outer membrane and of reactivity of ${\beta}$ -lactam ring with penicillin binding proteins, respectively, in Gram-negative bacteria. They are computed by AM1 method and used as variables of quantitative structure-activity relationship study. The results justify quadratic dependence of the activity on the variables. The intersection of difference volumes between $\beta-lactamase$ stable cephalosporins and unstable ones manifests that the steric hindrance of 7-side chain is responsible for the ${\beta}$ -lactamase stability.

• Bulletin of the Korean Chemical Society
• /
• 제33권5호
• /
• pp.1551-1555
• /
• 2012

Second-order rate constants ($k_N$) have been measured spectrophotometrically for the reactions of benzyl 2-pyridyl carbonate $\mathbf{7}$ and $t$-butyl 2-pyridyl carbonate $\mathbf{8}$ with a series of alicyclic secondary amines in $H_2O$ at $25.0^{\circ}C$. Substrate $\mathbf{8}$ is less reactive than $\mathbf{7}$. Steric hindrance exerted by the bulky $t$-Bu group of $\mathbf{8}$ has been suggested to be responsible for the decreased reactivity. The Br${\o}$nsted-type plots for the reactions of $\mathbf{7}$ and $\mathbf{8}$ are linear with ${\beta}_{nuc}=0.49$ and 0.44, respectively, which is typical for reactions reported previously to proceed through a concerted mechanism. Aminolyses of $\mathbf{7}$ and $\mathbf{8}$ were expected to proceed through a zwitterionic tetrahedral intermediate $T^{\pm}$, which would be stabilized through an intramolecular H-bonding interaction. However, the kinetic results suggest that the reactions proceed through a concerted mechanism. The H-bonding interaction in $T^{\pm}$ has been suggested to accelerate the rate of leaving-group expulsion from $T^{\pm}$. Another factor that might accelerate expulsion of the leaving group is the "push" provided by the RO group in $T^{\pm}$ through resonance interactions. Thus, it has been concluded that the enhanced nucleofugality through the H-bonding interaction and the "push" provided by the RO group forces the reactions to proceed through a concerted mechanism.

• 대한간호학회지
• /
• 제3권1호
• /
• pp.97-104
• /
• 1972

This study was designed to investigate differences in some aspects of value conceptions in fundamentals of nursing functions between nursing service personnel and nurse-educators. The purpose of the study was to identify the difference of value conceptions between the hospital nurses and school instructors, to contribute as a reference in strengthening the educational program in establishing nay hinder professional growth. The questionaries of this study were focused in the following aspects: 1) establishment of nursing service management system, 2) strengthening of the professionalization of nursing service, 3) hindrance in accomplishment of independent nursing functions, 4) communication skills in nurse-patient relationship, 5) activities directly related to nursing care planning, 6) communication skills in nurse-doctor relationship, 7) attitude towards taking responsibilities for patient- centered nursing approach, and 8) nursing educational approach towards preparation of professional competence in practicing independent nursing functions. 265 graduate nurses from 14 general hospitals and 88 nursing instructors from 18 schools, collegiate and diploma, were sampled. The main findings of the study were as follows; 1. Both groups responded highly in the lack of public recognition of nursing profession and hospital administrators support in establishment of nursing service management system. Further investigation is needed to define some relationship between the intrinsic and extrinsic factors which might give influence to the professional development. 2. while hospital nursing personnel responded on environmental pressure such as a heavy nursing load as the factor giving hindrance to independent nursing functions, the nurse educators responded highly on lack of nursing competence of individual nurses. An emphasis should be placed on the development of nursing interaction through professional education. If the professional model is not well established, nursing function will be limited to medical assistance. 3. 3. The patient-centered approach for nurse-patient communication had given positive respond for both group, tut lacks in team concept in problem solving process. There exist a social distance between nurses and other professional co-workers in the hospital hierarchy. 4. It was indicated that, as an intrinsic factor in the development of nursing service and nursing education, building up a philosophical basis is an utmost importance. This question is opened for further and extensive study to clarify whether existence of philosophical absence or philosophical stasis in nursing profession hinders the development.

• International Journal of Industrial Entomology and Biomaterials
• /
• 제8권2호
• /
• pp.195-200
• /
• 2004

Trypsin can be immobilized on silk fibroin fiber (SFF) by introducing several spacer arms, such as ethylene diamine (ED), bovine serum albumin (BSA) and silk sericin (SS). Direct immobilization on silk fiber (SFFGA) has low activity because of the steric hindrance between the trypsin and substrate. The introduction of spacer arms onto SFF-GA can enhance the activity of trypsin by reducing the steric hindrance. When ED is used as a spacer arm, the activity of trypsin has increased but its stability decreased due to the increased hydrophobicity of SFF. BSA and SS, as a spacer arm, have better results in both activity and stability. SFF-BSA shows some decrease in the specific activity due to improper immobilizatin. SFF-SS maintained 90% of its initial activity even after 12 hrs incubation at $50^{\circ}C$. In the case of repeated hydrolysis of silk sericin with immobilized trypsin, SFF-GA and SFF-ED lost 50% of their initial activity right after first run, whereas SFF-BSA and SFF-SS maintained 80% of their initial activities even after 5 runs. Higher operational stability is due to increased hydrophilicity of SFF by introducing hydrophilic spacer arms such as BSA and SS. The high content of serine in SS increases the hydrophilicity of SFF resulting the best results among other spacer arms.

• 멤브레인
• /
• 제12권4호
• /
• pp.207-215
• /
• 2002

한정된 미세공간에서의 제한확산(hindered diffusion)은 멤브레인 기공(pore)에서 입자들의 운동에 의해 결정되는 여과 메카니즘을 매우 미세한 수준에서 이해하는데 중요한 현상이다. 구형(spherical) 콜로이드 입자에 비해 보다 복잡한 형태(conformation)인 고분자사슬 구조를 갖는 다가전해질(polyelectrolyte)의 제한확산 거동에는 다양한 인자들이 관련되어 있기 때문에, 이론 접근은 물론 실험적 접근도 한층 어려운 것이 사실이다. 본 연구에서는, 슬릿형 미세기공에 한정되어 있는 단일한 다가전해질(single polyelectrolyte)에 coarse-grained bead spring model과 먼거리(long-range) 정전상호작용(electrostatic interaction)인 Debye-Huckel potential을 적용하여 분자시뮬레이션 기법인 브라운 동력학 모사를 수행하였다. 기공과 다가전해질 사슬(Polyelectrolyte chain)의 주어진 크기에서, 용액의 전해질 이온농도가 감소함에 따른 사슬의 신장(extension)효과는 제한확산계수를 감소시켰고, 기공 벽면의 하전성은 제한확산계수를 더욱 감소시켰다. 이는, 다가전해질 사슬(polyelectrolyte chain)의 입체적 장애(steric hindrance)와 함께 정전반발력이 미세기공에서의 확산이동을 억제함을 의미한다.

• Bulletin of the Korean Chemical Society
• /
• 제29권10호
• /
• pp.1915-1919
• /
• 2008

Second-order rate constants ($k_N$) have been measured spectrophotometrically for reactions of 3,4-dinitrophenyl benzoates (5b) with a series of alicyclic secondary amines in 80 mol % $H_2O$/20 mol % DMSO at 25.0 ${\pm}$ 0.1 ${^{\circ}C}$. The kinetic data have been compared with the data reported previously for the corresponding reactions of 2,4- dinitrophenyl benzoates (5a) to investigate the effect of changing the nucleofuge from 2,4-dinitrophenoxide to 3,4-dinitrophenoxide on reactivity and mechanism. The kinetic results show that aminolyses of 5a and 5b proceed through the same mechanism, i.e., a zwitterionic tetrahedral intermediate ($T^{\pm}$) with a change in the rate-determining step (RDS). Substrate 5a is more reactive than 5b when breakdown of $T^{\pm}$ is the RDS but less reactive when formation of $T^{\pm}$ is the RDS. Dissection of kN values into the microscopic rate constants (e.g., $k_1$ and $k_2/k_{-1 }$ ratio) has revealed that 5a results in larger $k_2/k_{-1}$ ratios but smaller k1 values than 5b for all the amines studied. Since 2,4-dinitrophenoxide is less basic and a better nucleofuge than 3,4-dinitrophenoxide, the larger $k_2/k_{-1}$ ratios determined for the reactions of 5a than for those of 5b are as expected. The steric hindrance exerted by the ortho-nitro group on 5a contributes to the smaller k1 values found for the reactions of 5a than for those of 5b.