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Pyung Gyun Shin,Gun Do Kim,Yong Hwa Cheong,Sang Yeol Lee,Jeong Dong Bahk,Jong Chan Hong,Moo Je Cho ) 생화학분자생물학회 1993 BMB Reports Vol.26 No.2
Using [γ-^(32)P] labelled ATP, an endogenous phosphorylated protein whose molecular weight was 52 kDa has been identified and characterized. It was rapidly appeared during the early stage of soybean germination. It was distinctively phosphorylated at the very early stages of cell growth and differentiation and slowly declined after 24 h. Therefore, the phosphorylated 52 kDa protein can be postulated to play significant roles in the control of embryonic cell growth and development. The 52 kDa phosphorylated protein was identified to be mainly located in the cytosolic fraction of soybean cell. Phosphorylation of this protein was dependent on Ca^(2+) and calmodulin but not on phospholipids. The requirement of free Ca^(2+) to phosphorylate this protein can be supplemented enough by soybean cell itself without the additions of Ca^(2+) from the external sources. The phospho-amino acids were identified as serine and threonine residues, which represented that the 52 kDa protein contained at least two phosphorylation sites.
Pyun, Sang-Yong,Cho, Bong-Rae Korean Chemical Society 2005 Bulletin of the Korean Chemical Society Vol.26 No.7
Elimination reactions of $XC_6H_4CH_2CO_2C_6H_3-2-Y-4-NO_2$ have been studied under various conditions. When X was moderately electron-withdrawing, Y = H, and base-solvent was $R_2$NH-MeCN, the reaction proceeded by the E2 mechanism via an E1cb-like transition state. Concave downward curve was noted in the Hammett plots. When X = 4-$NO_2$, Y = Cl, $CF_3,\;NO_2$, and the base-solvent was ${R_2NH/R_2NH_2}^+$ in 70 mol % MeCN(aq), the reaction proceeded by the E2 mechanism. The mechanism changed to a competing E2 and E1cb when X = 4-$NO_2$ and Y = H, MeO, and to the E1cb when X = 2,4-($NO_2)_2$, and Y = $NO_2$. From these results, a plausible pathway of the change of the mechanism from E2 to the E1cb extreme is proposed.
Kinetics Studies on the Mechanism of Hydrolysis of S-Phenyl-S-vinyl-N-p-tosylsulfilimine Derivatives
Pyun, Sang-Yong,Kim, Tae-Rin,Lee, Chong-Ryoul,Kim, Whan-Gi Korean Chemical Society 2003 Bulletin of the Korean Chemical Society Vol.24 No.3
Hydrolysis reactions of S-phenyl-S-vinyl-N-p-tosylsulfilimine (VSI) and its derivatives at various pH have been investigated kinetically. The hydrolysis reactions produced phenylvinylsulfoxide and p-toluene sulfonamide as the products. The reactions are first order and Hammett ρ values for pH 1.0, 6.0, and 11.0 are 0.82, 0.45, and 0.57, respectively. This reaction is not catalyzed by general base. The plot of k vs pH shows that there are three different regions of the rate constants $(k_t)$ in the profile.; At pH < 2 and pH > 10, the rate constants are directly proportional to the concentrations of hydronium and hydroxide ion catalyzed reactions, respectively. The rate constant remains nearly the same at 2 < pH < 10. On the bases of these results, the plausible hydrolysis mechanism and a rate equation have been proposed: At pH < 2.0, the reaction proceeds via the addition of water molecule to sulfur after protonation at the nitrogen atom of the sulfilimine, whereas at pH > 10.0, the reaction proceeds by the addition of hydroxide ion to sulfur directly. In the range of pH 2.0-10.0, the addition of water to sulfur of sulfilimine appears to be the rate controlling step.
Pyun Sang Yong,Paik Kyu Cheol,Han Man So,Cho Bong Rae 대한화학회 2021 Bulletin of the Korean Chemical Society Vol.42 No.7
Reactions of 4-nitrophenyl 2-furoates (1a–e) with R2NH/R2NH2 + in 20 mol% DMSO(aq) have been studied. The reactions produced aminolysis products and exhibited second-order kinetics. The Brönsted plots were linear with βnuc values of 0.75–0.89, which remained nearly the same for all 5-furyl substituents. The rate data showed excellent correlations on the Yukawa-Tsuno plots with ρ(x) = 0.72–1.1, and r = 0.55–0.95, respectively. The ρ value increased and r value decreased with a stronger nucleophile, indicating an increase in the electron density at the C O bond and a decrease in the resonance contribution. The results have been interpreted with the addition–elimination mechanism in which the second step is the rds. By comparing with the data for ArC(O)OC6H4-4-NO2 (Ar = Ph, thienyl), the effect of the aryl group on the acyl transfer reaction was assessed.
Pyun, Sang Yong,Kim, Ju Chang,Cho, Bong Rae Korean Chemical Society 2014 Bulletin of the Korean Chemical Society Vol.35 No.7
Ketene-forming elimination from 2-X-4-nitrophenyl furylacetates (1a-d) promoted by $R_2NH-R_2NH_2{^+}$ in 70 mol % MeCN(aq) has been studied kinetically. When X = Cl and $NO_2$, the reactions exhibited second-order kinetics as well as Br$\ddot{o}$nsted ${\beta}$ = 0.37-0.54 and $|{\beta}_{lg}|$ = 0.31-0.45. The Br$\ddot{o}$nsted ${\beta}$ decreased with a poorer leaving group and $|{\beta}_{lg}|$ increased with a weaker base. The results are consistent with an E2 mechanism. When the leaving group was changed to a poorer one [X= H (1a) and $OCH_3$ (1b)], the reaction mechanism changed to the competing E2 and E1cb mechanisms. A further change to the E1cb mechanism was realized for the reaction of 1a with $i-Pr_2NH/i-Pr_2NH_2{^+}$ in 70 mol % MeCN-30 mol % $D_2O$. By comparing the kinetic results in this study with the existing data for $ArCH_2C(O)OC_6H_3-2-X-4-NO_2$, the effect of the ${\beta}$-aryl group on the ketene-forming elimination was assessed.
Pyun, Sang Yong,Cho, Bong Rae Korean Chemical Society 2013 Bulletin of the Korean Chemical Society Vol.34 No.7
Reactions of 4-nitrophenyl 2-thiophenecarboxylate (1a-e) with $R_2NH/R_2NH{_2}^+$ in 20 mol % DMSO (aq) have been studied kinetically. The $2^{nd}$ order kinetics, ${\beta}_{nuc}$ = 0.88-0.98, and linear Hammett and Yukawa-Tsuno plots observed for these reactions indicate an addition-elimination mechanism in which the $2^{nd}$ step is rate limiting. The ${\beta}_{nuc}$ value increased with a stronger electron-withdrawing 5-thienyl substituent, the Hammett plots are linear except for X = MeO, and Yukawa-Tsuno plots are linear with ${\rho}$ = 0.79-1.32 and r = 0.28-0.93, respectively. The ${\rho}$ value increased and r value decreased with a stronger nucleophile, indicating an increase in the electron density at the C=O bond and a decrease in the resonance demand. These results have been interpreted with enhanced N-C bond formation in the transition state with the reactivity increase.
Synthesis and Photopolymerization of Vinyl Ether and Epoxy-Functionalized Silicones
Pyun, Sang-Yong,Kim, Whan-Gi The Polymer Society of Korea 2003 Macromolecular Research Vol.11 No.3
The reactive precursors, vinyl ethers, and epoxy-silicones, were synthesized. The vinyl ether monomers were prepared from primary alcohol and ethyl vinyl ether with mercury (II) acetate. The epoxy-functionalized silicones have been achieved by the controlled, rhodium-catalyzed, chemoselective hydrosilation of vinyl ether with siloxanes or silane. It was shown that the hydrosilation proceeds exclusively at the vinyl ether group of alkenyl vinyl ether without participation at the alkenyl group. The photoinduced cationic polymerization of these monomers was studied and found to be all highly reactive.
Pyun, Sang-Yong,Cho, Eun-Ju,Seok, Hyoun-Jung,Kim, Ju-Chang,Lee, Seok-Hee,Cho, Bong-Rae Korean Chemical Society 2007 Bulletin of the Korean Chemical Society Vol.28 No.6
Ketene-forming eliminations from C4H3(S)CH2C(O)O-C6H3-2-X-4-NO2 (1) promoted by R2NH in MeCN have been studied kinetically. The reactions are second-order and exhibit Bronsted β =0.51-0.62 and |βlg|= 0.47-0.53. Hence, an E2 mechanism is evident. The Bronsted β increased from 0.33 to 0.53 and |βlg| remained nearly the same by the change of the base-solvent from Bz(i-Pr)NH/Bz(i-Pr)NH2+ in 70 mol% MeCN(aq) to Bz(i-Pr)NH-MeCN, indicating a change to a more symmetrical transition state with similar extents of Cβ -H and Cα -OAr bond cleavage. When the β-aryl group was changed from thienyl to phenyl in MeCN, the β value increased from 0.53 to 0.73 and |βlg| decreased from 0.53 to 0.43. This indicates that the transition state became skewed toward more Cβ -H bond breaking with less Cα-OAr bond cleavage. Noteworthy is the greater double bond stabilizing ability of the thienyl group in the ketene-forming transition state.