• Journal of the Korean institute of surface engineering
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• v.52 no.6
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• pp.334-341
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• 2019

Organometal halide perovskite materials have attracted much attention in the photovoltaic and light emitting devices due to the compositional flexibility with AMX₃ formula (A is an organic amine cation; M is a metal ion; X is a halogen atom). The addition of homovalent or heterovalent metal cations to the bulk organohalide perovskites has been performed to modify their energy band structure and the relevant optoelectronic properties by ligand-assisted ball milling. Here, we report CH₃NH₃Pb_1-xM_xBr₃ nanocrystals substituted by metallic cations (M is Sn²⁺, In³⁺, Bi³⁺; x = 0, 0.01, 0.02, 0.05, 0.1, 0.2). Photoluminescence and quantum yield was significantly reduced with increasing metallic cations content. These quenching effect could be resulted from the metal cations that behave as a non-radiative recombination center.

• Journal of the Korean Chemical Society
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• v.17 no.3
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• pp.174-181
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• 1973

Dichlorodiacetatotitanium(IV) dissolves in alcohols with chemical reaction. Such solvolytic reaction of $TiCl_2(OAc)_2$with various alcohols has been studied by means of solution NMR spectroscopy and chemical analysis of the isolated products. The reaction of $TiCl_2(OAc)_2$ with primary alcohols has shown to be a quantitative two-step ligand substitution process as shown in the following: $TiCl_2(OAc)_2+ROH{\to}TiCl_2(OAc)_2(OR)+AcOH$ $TiCl_2(OAc)_2(OR)+ROH{\to}TiCl_2(OAc)_2+AcOH$The molecular form initially soluble in organic solvents has been found to be the monosubstituted species $TiCl_2(OAc)(OR)$. Alcoholysis with t-butyl alcohol has shown remarkable differences. When the mole ratio of t-butyl alcohol to $TiCl_2(OAc)_2$ is less than 1/2, the following reaction is dominant. $TiCl_2(OAc)_2+t-ButOH{\to}TiCl_2(OAc)_2+t-ButCl$However, at higher mole ratio another substitution process resembling the first step reaction with primary alcohols is competitively accompanied. The reaction with t-butyl alcohol also differs from that with primary alcohols in that only one either of the two chloro-or acetato-ligands in $TiCl_2(OAc)_2$ is subjected to substitution.

• Journal of Life Science
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• v.20 no.6
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• pp.853-860
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• 2010

The DevSR two-component system is a major regulatory system involved in redox sensing in Mycobacterium smegmatis. The DevSR system consists of the DevS histidine kinase and its cognate DevR response regulator. When exposed to hypoxic conditions, the DevS histidine kinase is activated to phosphorylate the DevR response regulator, leading to the transcriptional activation of the DevR regulation. The ligand-binding state of the heme embedded in the N-terminal GAF domain of DevS determines the kinase activity of DevS. In this study, we demonstrated that the redox-responsive cysteine (C547) in the C-terminal kinase domain is involved in the redox-dependent control of DevS kinase activity. The formation of an intersubunit disulfide bond between the C547 residues in the presence of $O_2$ led to inactivation of DevS kinase activity. The reduction of the oxidized DevS with reductants such as $\beta$-mercaptoethanol and dithiothreitol resulted in the restoration of DevS kinase activity. It was demonstrated in vivo by complementation test that the substitution of C547 to alanine partially impaired the sensory function of DevS in M. smegmatis.

• Journal of Life Science
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• v.27 no.12
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• pp.1410-1414
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• 2017

Escherichia coli tryptophan synthase (TS) contains ${\alpha}_2{\beta}_2$, which catalyzes the final two steps in Trp biosynthesis. A molecular tunnel exists between the two active sites of ${\alpha}$ and ${\beta}$ subunits in TS. Via intersubunit communication, TS increases catalytic efficiency, including substrate channeling. The ${\beta}$ subunit of TS is composed of two domains, one of which, the COMM (communication) domain, plays an important role in intersubunit communication. The ${\alpha}$ subunit has a TIM barrel structure. This protein has functional regions at the C terminal of ${\beta}$ pleated sheets and in its loop regions. Three regions of the ${\alpha}$ subunit (${\alpha}L6$ [${\alpha}-loop$ L6], ${\alpha}L2$, and ${\alpha}L3$) are implicated in intersubunit communication. In the present study, conformational changes in ${\alpha}L6$ were monitored by measuring the sensitivity of mutant proteins in these regions to trypsin. The addition of a ${\alpha}$ subunit-specific ligand, D,L-${\alpha}$-glycerophosphate (GP), partially restored the sensitivity of mutant proteins to trypsin. In contrast, the addition of the ${\beta}$ subunit-specific ligand L-serine (Ser) resulted in varied sensitivity to trypsin, with an increase in PT53 (substitution of Pro with Thr at residue 53) and DG56, decrease in NS104 and wild type, and no change in GD51 and PH53. This finding may be related to several reaction intermediates formed under this condition. The addition of both GP and Ser led to a highly stable state of the complex. The present results are consistent with the current model. The method used herein may be useful for screening residues involved in intersubunit communication.

• BMB Reports
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• v.40 no.2
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• pp.239-246
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• 2007

Riboflavin synthase from Escherichia coli is a homotrimer of 23.4 kDa subunits and catalyzes the formation of one molecule each of riboflavin and 5-amino-6-ribitylamino- 2,4(1H,3H)-pyrimidinedione by the transfer of a 4-carbon moiety between two molecules of the substrate, 6,7- dimethyl-8-ribityllumazine. Each subunit comprises two closely similar folding domains. Recombinant expression of the N-terminal domain is known to provide a $C_2$-symmetric homodimer. In this study, the binding properties of wild type as well as two mutated proteins of N-terminal domain of riboflavin synthase with various ligands were tested. The replacement of the amino acid residue A43, located in the second shell of riboflavin synthase active center, in the recombinant N-terminal domain dimer reduces the affinity for 6,7-dimethyl-8-ribityllumazine. The mutation of the amino acid residue C48 forming part of activity cavity of the enzyme causes significant $^{19}F$ NMR chemical shift modulation of trifluoromethyl derivatives of 6,7-dimethyl-8-ribityllumazine in complex with the protein, while substitution of A43 results in smaller chemical shift changes.

• Textile Coloration and Finishing
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• v.17 no.2 s.81
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• pp.10-18
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• 2005

Silk fabrics mordanted with $Fe^{2+},\;Ni^{2+},\;and\;Cu^{2+}$ were dyed with the aqueous extract of Cassia tora L. seed which was known to include water soluble colorant kaempferol, one of flavonol compounds. Kaempferol can react with free radicals and chelate transition metal ions, which is thought to catalyze processes leading to the appearance of free radicals and have antioxidant activity. In relation to the coordinating and chelating mechanism of the ions with the silk protein and kaempferol, reasonable conclusions should be made on the colorant uptake and the water fastness of the fabric. The amount of the colorant on the fabric was in the order of $Fe^{2+}>Ni^{2+}>Cu^{2+}$. In case of dyeing through coordinaiton bonds between transition metal ions and silk protein and colorants, it was thought that the ions with the smaller secondary hydration shell, the higher preference to the atoms of the ligand coordinated, and the suitable bonding stability for the substitution of primarily hydrated water molecules for colorants led to the higher colorant uptake. The water fastnsess of the fabric was in the order of $Fe^{2+}>Cu^{2+}>Ni^{2+}$. It should be reasonable to choose transition metal ions with weak and strong tendency to the ionic and the coordination bond, respectively, to the carboxylate anion of the silk protein. Although further research needs to be done, the conclusions above may be generally applied to the natural dyeing through the coordination bond mechanism between transition metal ions and colorants and substrates.

• Journal of the Korean Chemical Society
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• v.43 no.3
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• pp.257-263
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• 1999

Ln-macrocyclic([20]DOTA) complexes, [Ln([20]DPTA)(NO_{3})(H_{2}O)](NO_{3})_{2} \cdotxH_{2}O{Ln(III)=Pr, Sm, Gd, Dy}, which had been synthesized from 2, 6-diformyl-p-cresol(DFPC), was placed in methanol for 2 days, and $[Ln([20]DPTA)(NO_{3})(CH_{3}OH)]^{2+}$ was formed. The equilibrium constants(L) for the substitution of coordinated $CH_{3}OH$ in the Ln-[20]DOTA complexes by various auxiliary ligands, $L_{a}(=monodentate ligands; pyridine, imidazole, triethylamine, diethylamine, piperidine) were determined spectroscopically at $25^{\circ}C$ and 0.1M. The pKa of auxiliary ligand is in the order of pyridine < imidazole < triethylamine < diethylamine < piperidine, however the K has shown the trend of pyridine < imidzole < diethylamine < piperidine < triethylamine.

• Bulletin of the Korean Chemical Society
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• v.26 no.7
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• pp.1065-1070
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• 2005

$[Mn_{12}O_{12}(O_2CPh-4-SMe)_{16}(H_2O)_4]{\cdot}7CH_2Cl_2$ (1), a new single-molecule magnet complex has been successfully synthesized by substitution of acetate ligand of Mn12ac with 4-(methylthio)benzoic acid. Complex 1 crystallizes into triclinic P$\overline{1}$ with a = 18.321(3) $\AA$, b = 19.011(3) $\AA$, c = 27.230(4) $\AA$, $\alpha$ = 86.973(3)$^{\circ}$, $\beta$ = 76.919(3)$^{\circ}$, $\gamma$ = 87.613(3)$^{\circ}$, and Z = 2. In complex 1, one Mn(III) ion has an abnormal Jahn-Teller elongation axis oriented at an oxide ion. Complex 1 has two out-of-phase ac susceptibility peaks in the 2-4 K and 4-7 K regions. Effective anisotropy energy barrier and pre-exponential factor are $U_{eff}$ = 45.95 K, 1/$\tau$0 = 8.6 ${\times}\;10^9s^{-1}\;for\;{\chi}_M$'' peaks in the lower temperature region and $U_{eff}$ = 59.45 K, 1/$\tau_0$ = 2.2 ${\times}\;10^8\;s^{-1}$ for $\chi_M$'' peaks in the higher temperature region. The parameters of S = 10, g = 1.87, D = -0.40 $cm^{-1}$, and E = 0.00034 $cm^{-1}$ were obtained from the M/N${\mu}_B$ vs. H/T plot of complex 1.

• Bulletin of the Korean Chemical Society
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• v.30 no.5
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• pp.1157-1163
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• 2009

Complexes of Pd(btnbmtp)$Cl_2$ and Pt(btnbmptp)$Cl_2$ (btnbmtp = 2,5-bis(thiophen)-1-nonyl-3,4-bis(methylthio)- pyrrole) were prepared and their crystal structures were determined at room temperature. In the structures, the two thiophene moieties lie in cis form with an average dihedral angle of $55.26^{\circ}$ to the pyrrole frame. The luminescence properties of the free ligand and the complexes were investigated in solution and solid states. The luminescence of the compounds were not favored by substituting thiophene moieties to the pyrrole frame, compared to the unsubstituted nbmptp (nbmptp = 1-nonyl-3,4-bis(methylthio)pyrrole). In particular, thiophene substitution quenched the emission from the complexes dissolved in ,$CH_2Cl_2$ and reduced the charge transfer transitions from S atoms of the thio moieties to Pt in crystalline state, which was very characteristic of Pt(nbmptp)$Cl_2$.

• Journal of Radiopharmaceuticals and Molecular Probes
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• v.6 no.2
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• pp.75-91
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• 2020

[^99mTc]Tc-Hexamethylpropylene amine oxime (HMPAO) is currently used as a regional cerebral blood flow imaging agent for single photon emission computed tomography (SPECT). The HMPAO ligand exists in two isomeric forms: d,l and meso showing different properties in vivo. Later studies indicated that brain uptake patterns of ^99mTc-complexes formed from separated enantiomers differed. Separation of enantiomers is difficult by fractional crystallizations method. Usually, the substance is obtained in low chemical yield in a time-consuming procedure. Furthermore, the final product still contains some impurity. So we have developed new efficient route for synthesis of R,R- and S,S-HMPAO enantiomeric compounds in 6-steps. Nucleophilic substitution (S_N2) reactions of 2,2-dimethylpropane-1,3-diamine either with S- (1a) or R-methyl2-chloropropanoate (1b) were performed to produce compounds R,R- (2a) or S,S-isomer (2b) derivatives protected with benzylchloroformate (Cbz), respectively. And then Weinreb amide and methylation reaction using Grignard reagent, oxime formation with ketone group and deprotectiion of Cbz group by hydrogenolysis gave S,S- (7a) or R,R-HMPAO (7b), respectively. Entaniomeric compounds were synthesied with high yield and purity without any undesired product. The 7a or 7b kits containing 10 ㎍ SnCl₂-2H₂O were labeled with ^99mTc with high radiolabeling yield (90%).