• Bulletin of the Korean Chemical Society
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• v.35 no.8
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• pp.2410-2414
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• 2014

A kinetic study is reported on nucleophilic substitution reactions of Y-substituted-phenyl picolinates (7a-7h) with a series of cyclic secondary amines in 80 mol % $H_2O$/20 mol % DMSO at $25.0{\pm}0.1^{\circ}C$. Comparison of the kinetic results with those reported previously for the corresponding reactions of Y-substituted-phenyl benzoates (1a-1f) reveals that 7a-7h are significantly more reactive than 1a-1f. The Br${\o}$nsted-type plot for the aminolysis of 4-nitrophenyl picolinate (7a) is linear with ${\beta}_{nuc}=0.78$, which is typical for reactions proceeding through a stepwise mechanism with expulsion of the leaving group being the rate-determining step. The Br${\o}$nsted-type plots for the piperidinolysis of 7a-7h and 1a-1f are also linear with ${\beta}_{lg}=-1.04$ and -1.39, respectively, indicating that the more reactive 7a-7h are less selective than the less reactive 1a-1f to the leaving-group basicity. One might suggest that the enhanced reactivity of 7a-7h is due to the inductive effect exerted by the electronegative N atom in the picolinyl moiety, while the decreased selectivity of the more reactive substrates is in accord with the reactivity-selectivity principle. However, the nature of intermediate (e.g., a stabilized cyclic intermediate through the intramolecular H-bonding interaction for the reactions of 7a-7h, which is structurally not possible for the reactions of 1a-1f) is also responsible for the enhanced reactivity with a decreased selectivity.

• Korean Journal of Optics and Photonics
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• v.30 no.6
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• pp.219-225
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• 2019

In an infrared optical system, using a cooled detector generates a phenomenon called a narcissus, in which the focal-plane array cooled to very low temperatures is reflected at the lens surface and detected. The narcissus can be removed by non-uniformity correction of the detector pixel, so narcissus is generally ignored in infrared optics. However, non-uniformity correction reduces the sensitivity of the system. Also, as the housing temperature varies due to an environmental temperature change, or a lens is moved for focusing or athermalization purposes, a narcissus may occur even after non-uniformity correction. To minimize such a narcissus, the amount of the effect must be controlled in the lens-design stage. In this paper we designed a midinfrared optical system and analyzed the narcissus by setting the lens surface reflectance to 1%. In addition, the design was divided into stages of an initial design, an improved design, and a minimum design, and the narcissus was improved to about 56% of that in the initial design.

• Bulletin of the Korean Chemical Society
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• v.34 no.4
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• pp.1115-1119
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• 2013

A kinetic study is reported for nucleophilic substitution reactions of benzyl 2-pyridyl thionocarbonate (5b) and t-butyl 2-pyridyl thionocarbonate (6b) with a series of alicyclic secondary amines in $H_2O$ at $25.0^{\circ}C$. General-base catalysis, which has often been reported to occur for aminolysis of esters possessing a C=S electrophilic center, is absent for the reactions of 5b and 6b. The Br${\o}$nsted-type plots for the reactions of 5b and 6b are linear with ${\beta}_{nuc}$ = 0.29 and 0.43, respectively, indicating that the reactions of 5b proceed through a stepwise mechanism with formation of a zwitterionic tetrahedral intermediate ($T^{\pm}$) being the rate-determining step while those of 6b proceed through a concerted mechanism. The reactivity of 5b and 6b is similar to that of their oxygen analogues (i.e., benzyl 2-pyridyl carbonate 5a and t-butyl 2-pyridyl carbonate 6a, respectively), indicating that the effect of modification of the electrophilic center from C=O to C=S (i.e., from 5a to 5b and from 6a to 6b) on reactivity is insignificant. In contrast, 6b is much less reactive than 5b, indicating that the replacement of the $PhCH_2$ in 5b by the t-Bu in 6b results in a significant decrease in reactivity as well as a change in the reaction mechanism (i.e., from a stepwise mechanism to a concerted pathway). It has been concluded that the contrasting reactivity and reaction mechanism for the reactions of 5b and 6b are not due to the electronic effects of $PhCH_2$ and t-Bu but are caused by the large steric hindrance exerted by the bulky t-Bu in 6b.

• Bulletin of the Korean Chemical Society
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• v.35 no.4
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• pp.1128-1132
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• 2014

A kinetic study on aminolysis of 4-chloro-2-nitrophenyl X-substituted-benzoates (6a-i) in MeCN is reported. The Hammett plot for the reactions of 6a-i with piperidine consists of two intersecting straight lines, while the Yukawa-Tsuno plot exhibits an excellent linear correlation with ${\rho}_X$ = 1.03 and r = 0.78. The nonlinear Hammett plot is not due to a change in rate-determining step (RDS) but is caused by the resonance stabilization of substrates possessing an electron-donating group in the benzoyl moiety. The Br${\phi}$nsted-type plot for the reactions of 4-chloro-2-nitrophenyl benzoate (6e) with a series of cyclic secondary amines is linear with ${\beta}_{nuc}$ = 0.69, an upper limit for reactions reported to proceed through a concerted mechanism. The aminolysis of 6e in aqueous medium has previously been reported to proceed through a stepwise mechanism with a change in RDS on the basis of a curved Br${\phi}$nsted-type plot. It has been concluded that instability of the zwitterionic tetrahedral intermediate ($T^{\pm}$) in MeCN forces the reaction to proceed through a concerted mechanism. This is further supported by the kinetic result that the amines used in this study are less reactive in MeCN than in $H_2O$, although they are more basic in MeCN over 7 $pK_a$ units.

• Journal of Acupuncture Research
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• v.17 no.2
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• pp.261-276
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• 2000

본 실험은 pseudorabies 바이러스 (PRV) 의 Bartha strain 을 안면신경의 측두지, 하지를 지배하는 신경 (좌골신경) 및 상지를 지배하는 신경 (요골, 척골, 정중신경) 에 주입한 후 4 일간의 생존시간이 경과한 후 척수와 뇌를 적출하여 동결절편을 제작한 후 면역조직화학적 염색기법과 X-gal 조직화학 염색법을 시행하여 염색된 신경세포체를 척수와 뇌에 투사된 공통영역을 관찰하고 두침의 영역중 하나인 운동구와 사지와의 관계에 대한 실험적 증거를 제시하고자 시행하였다. 위의 실험에서 얻어진 결과는 아래와 같다. 1. 안면신경의 측두지, 하지를 지배하는 신경 (좌골신경) 및 상지를 지배하는 신경 (요골, 측골, 정중신경) 에서 투사된 공통된 영역은 척수에서 경수의 층판 1-IV, 흉수의 intermediolateral nucleus(IML), dorsal nucleus(D) 및 층판 X, 요수의 층판 IV, V, 천수의 층판 IV, V, IX, X 등의 영역에서 관찰되었고, 뇌줄기에서는 caudoventrolateral reticular nucleus(CVL), nucleus solitary tract(Sol), rostroventrolateral nucleus(RVL), area postrema(AP), raphe nuclei(raphe pallidus, raphe obscurus, raphe magnus), inferior olivary nucleus 의 등쪽부분 (gigantocellular reticular nucleus, Gi), Kolliker-Fuse nucleus(KF), central gray(CG), dorsal raphe nucleus (DR) and A5 영역에 표지된다. 또한 paraventricular hypothalamic nucleus(PRV) 와 lateral hypothalamic reticular nucleus(LH)에서도 관찰되고 locus coeruleus(LC) 와 subcoeruleus nuc!eus(SubCA) 에서도 관찰된다.

• Bulletin of the Korean Chemical Society
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• v.30 no.1
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• pp.214-218
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• 2009

Second-order rate constants ($k_N$) have been measured for nucleophilic substitution reactions of S-4-nitrophenyl thiobenzoate with a series of alicyclic secondary amines in $H_2O$ containing 20 mol % DMSO at 25.0 ${\pm}$ 0.1 ${^{\circ}C}$. The Br$\phi$nsted-type plot exhibits a downward curvature, i.e., $\beta_{nuc}$ decreases from 0.94 to 0.34 as the amine basicity increases. The reactions in the aqueous DMSO have also been suggested to proceed through a zwitterionic tetrahedral intermediate (T${\pm}$) with change in the RDS on the basis of the curved Br$\phi$nsted-type plot. The reactions in the aqueous DMSO exhibit larger $k_N$ values than those in the aqueous EtOH. The macroscopic rate constants ($k_N$) for the reactions in the two solvent systems have been dissected into the microscopic rate constants ($k_1\;and\;k_2/k_{-1}$ ratio) to investigate effect of medium on reactivity in the microscopic level. It has been found that the $k_2/k_{-1}$ ratios are similar for the reactions in the two solvent systems, while $k_1$ values are larger for the reactions in 20 mol % DMSO than for those in 44 wt % EtOH, indicating that the larger $k_1$ is mainly responsible for the larger $k_N$. It has been suggested that the transition state is more stabilized in 20 mol % DMSO through mutual polarizability interaction than in 44 wt % EtOH through H-bonding interaction.

• Bulletin of the Korean Chemical Society
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• v.34 no.1
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• pp.201-206
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• 2013

The second-order rate constants have been measured spectrophotometrically for the reactions of paraoxon 1 and parathion 2 with a series of alicyclic secondary amines, $OH^-$ and $HOO^-$ ions in $H_2O$ at $25.0{\pm}0.1^{\circ}C$. A linear Br${\o}$nsted-type plot with ${\beta}_{nuc}$ = 0.40 was obtained for the reactions of 1 with amines and $OH^-$. The reaction has been concluded to proceed through a concerted mechanism. $HOO^-$ deviates positively from the linear Br${\o}$nsted-type plot, implying that the ${\alpha}$-effect is operative. The magnitude of the ${\alpha}$-effect ($k_{HOO^-}/k_{OH^-}$) was found to be ca. 55 for the reaction of 1 and 290 for that of parathion 2, indicating that $HOO^-$ is highly effective in decomposition of the toxic phosphorus compounds although it is over 4 $pK_a$ units less basic than $OH^-$. Among the theories suggested as origins of the ${\alpha}$-effect (e.g., TS stabilization through an intramolecular Hbonding interaction, solvent effect, and polarizability effect), polarizability effect appears to be the most important factor for the ${\alpha}$-effect in this study, since the polarizable $HOO^-$ exhibits a larger ${\alpha}$-effect for the reaction of the more polarizable substrate 2.

• Bulletin of the Korean Chemical Society
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• v.34 no.8
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• pp.2455-2460
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• 2013

Second-order rate constants ($k_N$) have been measured spectrophotometrically for the nucleophilic displacement reactions of 4-nitrophenyl X-substituted-cinnamates (4a-4e) and Y-substituted-phenyl cinnamates (5a-5e) with Z-substituted-phenoxide anions in 80 mol % $H_2O$/20 mol % DMSO at $25.0{\pm}0.1^{\circ}C$. The Hammett plot for the reactions of 4a-4e with 4-chlorophenoxide (4-$ClPhO^-$) consists of two intersecting straight lines, which might be taken as a change in the rate-determining step (RDS). However, it has been concluded that the nonlinear Hammett plot is not due to a change in the RDS but is caused by stabilization of the ground state of substrates possessing an electron-withdrawing group in the cinnamoyl moiety through resonance interactions, since the Yukawa-Tsuno plot exhibits an excellent linear correlation with ${\rho}X=0.89$ and r = 0.58. The Br${\o}$nsted-type plot for the reactions of 4-nitrophenyl cinnamate (4c) with Z-substituted-phenoxides is linear with ${\beta}_{nuc}=0.76$. The Br${\o}$nsted-type plot for the reactions of Y-substituted-phenyl cinnamates (5a-5d) with 4-chlorophenoxides (4-$ClPhO^-$) is also linear with ${\beta}_{lg}=-0.72$. The Hammett plot correlated with ${\sigma}^-$ constants for the reactions of 5a-5d results in a much better linear correlation than that correlated with ${\sigma}^o$ constants, indicating that a partial negative charge develops on the O atom of the leaving aryloxide. Thus, the reactions have been concluded to proceed through a concerted mechanism.

• Journal of Ginseng Research
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• v.35 no.2
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• pp.129-137
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• 2011

The antioxidant activities of fermented red ginseng (FRG) were investigated in vitro and in vivo. The contents of total polyphenol and total flavonoid in FRG extracts were $17.01{\pm}2.00$ ${\mu}g/mg$ and $18.42{\pm}3.97$ ${\mu}g/mg$, respectively. These extracts were capable of directly scavenging ${\alpha}$, ${\alpha}$-diphenyl-picrylhydrazyl free radicals. The antioxidative effects of the FRG extracts in streptozotocin (STZ)-induced diabetic rats were also investigated. The activities of plasma alanine transaminase, aspartate transaminase, and ${\gamma}$-glutamyltransferase were significantly decreased by extract administration as compared to an STZ control group. Hepatic glutathione content depleted by STZ treatment was significantly increased by treatment of the FRG extracts, but the elevation of lipid peroxide content induced by STZ was significantly decreased by the extracts. Activities of superoxide dismutase, catalase, glutathione peroxidase, and glutathione reductase decreased after STZ-treatment were recovered by the treatment of the FRG extracts. These results indicate that FRG extracts have antioxidative effets in STZ-induced diabetic rats.

• International Journal of Stem Cells
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• v.16 no.1
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• pp.93-107
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• 2023

Background and Objectives: Chronic periodontitis can lead to alveolar bone resorption and eventually tooth loss. Stem cells from exfoliated deciduous teeth (SHED) are appropriate bone regeneration seed cells. To track the survival, migration, and differentiation of the transplanted SHED, we used super paramagnetic iron oxide particles (SPIO) Molday ION Rhodamine-B (MIRB) to label and monitor the transplanted cells while repairing periodontal bone defects. Methods and Results: We determined an appropriate dose of MIRB for labeling SHED by examining the growth and osteogenic differentiation of labeled SHED. Finally, SHED was labeled with 25 ㎍ Fe/ml MIRB before being transplanted into rats. Magnetic resonance imaging was used to track SHED survival and migration in vivo due to a low-intensity signal artifact caused by MIRB. HE and immunohistochemical analyses revealed that both MIRB-labeled and unlabeled SHED could promote periodontal bone regeneration. The colocalization of hNUC and MIRB demonstrated that SHED transplanted into rats could survive in vivo. Furthermore, some MIRB-positive cells expressed the osteoblast and osteocyte markers OCN and DMP1, respectively. Enzyme-linked immunosorbent assay revealed that SHED could secrete protein factors, such as IGF-1, OCN, ALP, IL-4, VEGF, and bFGF, which promote bone regeneration. Immunofluorescence staining revealed that the transplanted SHED was surrounded by a large number of host-derived Runx2- and Col II-positive cells that played important roles in the bone healing process. Conclusions: SHED could promote periodontal bone regeneration in rats, and the survival of SHED could be tracked in vivo by labeling them with MIRB. SHED are likely to promote bone healing through both direct differentiation and paracrine mechanisms.