• Archives of Pharmacal Research
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• 제23권4호
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• pp.324-328
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• 2000

Three dimensional QSAR studies for antihistamine and antibradykinin effects of new piperazine derivatives were conducted using the comparative molecular field analysis. Electrostatic and steric factors, but not hydrophobic factor, of the synthesized compounds were correlated with the antagonistic effect.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 하계학술대회 논문집 D
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• pp.1762-1764
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• 1999

We investigated the annealing effect on generating pretilt angle and aligning liquid crystal (LC) using the photo-depolymerization reaction in this study. In case of rubbing polyimide (PI) surface with the side chain, pretilt angle tends to increase with increasing the annealing time. It is considered because the steric interaction is increased by annealing which cause the side chain to come back to original position. For obliquely irradiating ultraviolet (UV) light on PI surface, pretilt angle shows to $0^{\circ}$ and is increased by annealing. The pretilt angle in rubbed PI surface is much higher than in photo-aligned PI surface. It is attributed to the steric interaction and the number of LC molecular arrangement on azimuthal direction. In addition. in case of obliquely irradiating UV light on PI surface. it showed LC alignment to increase by annealing. It can be regarded due to the fact that the re-alignment of LC molecule is improved to residual polymer direction by annealing.

• Bulletin of the Korean Chemical Society
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• 제29권8호
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• pp.1459-1463
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• 2008

Second-order rate constants (kN) have been measured spectrophotometrically for reactions of 3,4-dinitrophenyl 2-thiophenecarboxylate (2) with a series of alicyclic secondary amines in 80 mol % $H_2O$/20 mol % dimethyl sulfoxide at 25.0 ${^{\circ}C}$. The Brønsted-type plot exhibits a downward curvature for the aminolysis of 2. The curved Brønsted-type plot is similar to that reported for the corresponding reactions of 2,4-dinitrophenyl 2- thiophenecarboxylate (1). The reactions of 1 and 2 have been suggested to proceed through the same mechanism, i.e., through a zwitterionic tetrahedral intermediate ($T^{\pm}$) with a change in the rate-determining step. Substrate 2 is less reactive than 1 toward weakly basic amines (e.g., $pK_a$ < 10.4) but becomes more reactive as the basicity of amines increases further. Dissection of kN into the microscopic rate constants has revealed that the reaction of 2 results in a smaller $k_2/k_{-1}$ ratio but larger $k_1$ than the corresponding reaction of 1. Steric hindrance exerted by the ortho-nitro group has been suggested to be responsible for the smaller $k_1$ value found for the reactions of 1.

• Bulletin of the Korean Chemical Society
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• 제29권4호
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• pp.772-776
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• 2008

Second-order rate constants ($k_N$) have been measured spectrophotometrically for reactions of 3,4-dintrophenyl 2-furoate (2) with a series of secondary alicyclic amines in 80 mol % $H_2O$/20 mol % dimethyl sulfoxide (DMSO) at 25.0 ${^{\circ}C}$. The Bronsted-type plot exhibits a downward curvature for the aminolysis of 2, which is similar to that reported for the corresponding reactions of 2,4-dintrophenyl 2-furoate (1). Substrate 2 is less reactive than 1 toward all the amines studied but the reactivity difference becomes smaller as the amine basicity increases. Dissection of the second-order rate constants into the microscopic rate constants has revealed that the reaction of 2 results in a smaller $k_2/k_{-1}$ ratio but slightly larger $k_1$ value than that of 1. Steric hindrance has been suggested to be responsible for the smaller $k_1$ value found for the reactions of 1, since the ortho-substituent of 1 would inhibit the attack of amines (i.e., the $k_1$ process).

• Bulletin of the Korean Chemical Society
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• 제33권6호
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• pp.1879-1884
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• 2012

The kinetic studies on the reactions of dipropyl chlorophosphate (3O) with substituted anilines ($XC_6H_4NH_2$) and deuterated anilines ($XC_6H_4ND_2$) have been carried out in acetonitrile at $55.0^{\circ}C$. The obtained deuterium kinetic isotope effects (DKIEs; $k_H/k_D$) are primary normal ($k_H/k_D$ = 1.09-1.01) with the strongly basic anilines while secondary inverse ($k_H/k_D$ = 0.74-0.82) with the weakly basic anilines. The steric effects of the two ligands on the rates are extensively discussed for the anilinolyses of the ($R_1O$)($R_2O$)P(=O or S)Cl-type chlorophosphates and chlorothiophosphates. A concerted mechanism is proposed with a frontside nucleophilic attack involving a hydrogen-bonded four-center-type transition state for the strongly basic anilines and with a backside attack transition state for the weakly basic anilines on the basis of the DKIEs, primary normal and secondary inverse with the strongly and weakly basic anilines, respectively.

• Macromolecular Research
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• 제17권11호
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• pp.870-873
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• 2009

In this study, 2-diglycidylether of benzotrifluoride (2-DGEBTF) and 4-diglycidylether of benzotrifluoride (4-DGEBTF) epoxy resins, which contained fluorine groups in the main chain, were synthesized. The resins were characterized by FTIR, $^1H$ NMR, $^{13}C$ NMR and $^{19}F$ NMR spectroscopy. The 2-DGEBTF and 4-DGEBTF epoxy resins were cured with triethylene tetramine (TETA), and the effect of the fluorine group on the synthesized epoxy resin on the cure behavior, thermal, and mechanical properties was investigated. The 2-DGEBTF/TETA system was more reactive than the 4-DGEBTF/TETA system, whereas the thermal stability factor i.e., the decomposition activation energy ($E_d$), of 4-DGEBTF/TETA was higher than that of 2-DGEBTF/TETA. These results can be explained by the decrease in cross-linking density and decomposition of the short side chains, resulting in the $CF_3$ group at the para position. However, the $K_{IC}$ value of 4-DGEBTF/TETA was higher than that of 2-DGEBTF/TETA. This was attributed to the increase in flexibility in the epoxy backbone, resulting in a difference in steric hindrance and polarlizability.

• Archives of Pharmacal Research
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• 제23권1호
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• pp.22-25
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• 2000

Formation of glutathione (GSH) conjugates with 2- or 6-(1-hydroxymethyl)- and 2-(1-hydroxyethyl)-DMNQ derivatives (DMNQ, 5,8-dimethoxy-1,4-naphthoquone was carried out in phosphate buffer (pH 7.4), in the presence of glutathione-S-transferase (GST), in rat liver S-9 fraction and by perfusion, and the rates of conjugates formation were compared and correlated to cytotoxicity. The GSH conjugates of 6-(1-hydroxyalkyl)-DMNQ derivatives were formed faster than 2-(1-hydroxyalkyl)-DMNQ derivatives under all of the media, implying that steric hindrance was the cause of lowering the rate of conjugate formation of 2-substituted derivatives. For both isomers, addition of GST did not improve the reaction rate, compared with that in buffer, while the reaction in the S-9 fraction and the perfusate was accelerated to a great extent. The catalytic effect of the S-9 fraction and the perfusate contain an effective system relaxing the steric hindrance of 2-(1-hydroxyalkyl)-DMNQ derivatives. Furthermore, a good correlation between the formation of the GSH conjugates and the cytotoxic activity of both naphthazarin isomers suggests that the steric hindrance is a cause of lowering the cytotoxicity of 2-isomers.

• Bulletin of the Korean Chemical Society
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• 제34권8호
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• pp.2325-2329
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• 2013

Second-order rate constants $k_N$ have been measured for reactions of benzyl 2-pyridyl thionocarbonate (4b) and t-butyl 2-pyridyl thionocarbonate (5b) with a series of cyclic secondary amines in MeCN at $25.0{\pm}0.1^{\circ}C$. The $k_N$ values for the reactions of 4b and 5b have been compared with those reported previously for the corresponding reactions of benzyl 2-pyridyl carbonate (4a) and t-butyl 2-pyridyl carbonate (5a) to investigate the effect of changing the electrophilic center from C=O to C=S on reactivity and reaction mechanism. The thiono compound 4b is more reactive than its oxygen analogue 4a. The Br${\o}$nsted-type plots for the reactions of 4a and 4b are linear with ${\beta}_{nuc}=0.57$ and 0.37, respectively. The reactions of 4a were previously reported to proceed through a concerted mechanism, while those of 4b in this study have been concluded to proceed through a stepwise mechanism with formation of an intermediate being the rate-determining step on the basis of the ${\beta}_{nuc}$ value of 0.37. Enhanced polarizability upon changing the C=O in 4a by C=S has been suggested to be responsible for the reactivity order and the contrasting reaction mechanisms. In contrast, the reactivity of 5a and 5b is similar, but they are much less reactive than 4a and 4b. Furthermore, the reactions of 5a and 5b have been concluded to proceed through the same mechanism (i.e., a concerted mechanism) on the basis of linear Bronsted-type plots with ${\beta}_{nuc}=0.45$ or 0.47. It has been concluded that the strong steric hindrance exerted by the t-Bu in 5a and 5b causes a decrease in their reactivity and forces the reactions to proceed through a concerted mechanism.

• 대한화학회지
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• 제25권1호
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• pp.1-6
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• 1981

o-, m- 및 p-크실렌계와 요오드사이에 형성되는 전하이동착물을 사염화탄소용액에서 자외선분광광도법을 사용하여 연구한 결과$ C_6H_4(CH_3)_2{\cdot}I_2 $형의 1:1 분자착물이 형성됨을 알았다. 이들 착물생성에 대한 흡수최대는 온도가 상승함에 따라 blue shift되므로 이를 고려하여 각 온도에서의 평형정수를 구했다. 이 값으로부터 이들 착물생성에 대한 $ {\Delta}$H, $ {\Delta}$G 및 $ {\Delta}$S의 열역학적 파라미터를 산출하였다. 이 결과와 전 연구결과를 종합하면 폴리메틸벤젠과 요오드와의 착물의 상대적 안정도가 다음 순서로 증가함을 알 수 있었다. Benzene < Toluene < o-Xylene < m-Xylene < p-Xylene 이 결과는 positive inductive effect에 의한 전자밀도증가와 steric hindrance effect에 의한 영향때문인 것으로 설명할 수 있다.

• 한국막학회:학술대회논문집
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• 한국막학회 2004년도 Proceedings of the second conference of aseanian membrane society
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• pp.155-160
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• 2004

Permeation experiments of a commercial nanofiltration membrane (nominated as ESNA 1) were carried out with aqueous solutions of various single salts, that is, five chlorides (NH$_4$Cl, NaCl, KCl, MgCl$_2$ and $CaCl_2$), three nitrates $(NaNo_3,\;Mg(No_3)_2\;and\;Ca(NO_3)_2)\;and\;three\;sulfates\;((NH_4)_2SO_4,\;Na_2SO_4\;and\;MgSO_4)$. The experimental results showed that (1) the permeate volume flux of the ESNA 1 membrane increased and decreased with the growth of the applied pressure and the feed concentration of salts, respectively. The real rejection of ESNA 1 membrane to most single salts increased with the growth of the permeate volume flux. (2) The reflection coefficients of ESNA 1 membrane to chlorides, nitrates and sulfates are 0.97, 0.96 and 0.99, respectively. The solute permeability of most salts except for magnesium and calcium salts increased with the growth of feed concentration. (3) The sequence of the rejections of ESNA 1 membrane to anions is $R({SO_4}^{2-})>R(CI)>R(NO_3)$ at the same feed concentration. While the sequence of the rejections to cations is cataloged into two cases: $R(Na^+)>R(K^+)>R(Mg^{2+})>R(Ca^{2+})$ at the concentration of 10 mol/$m^3$ and $R(Mg^{2+})>R(Ca^{2+})>R(Na^+)>R(K^+)$ at the concentration of 100 mol/$m^3$. The separation capability of a NF membrane is usually affected by the electrostatic effect and the steric-hindrance effect. In this case, the electrostatic effect is the major factor at low concentration and the steric-hindrance effect is the major factor at high concentration. Both the specific sorption and the hydration also reasonably influenced the separation performance of NF membrane to salts.