• Journal of the Korean Chemical Society
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• v.54 no.1
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• pp.131-136
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• 2010

Iron aluminophosphates (FeAlP) with different percentage of iron were synthesized and characterized for their surface and bulk properties. The catalytic activity was determined in the transesterification of diethyl malonate with benzyl alcohol. Benzyl ethylmalonate and dibenzyl malonate were obtained as the only products. FeAlP with 0.025 mole % of iron was found to be distinctly different in its textural and catalytic properties. Formation of diester was found to be favored by the acid sites of intermediate strength. The presence of hydrated alumina and the polycondensed phosphates in the materials reduced the catalytic activity of iron aluminophosphates in transesterification reaction.

• Applied Chemistry for Engineering
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• v.32 no.4
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• pp.483-486
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• 2021

Catalytic ozonation of methyl ethyl ketone (MEK) has been examined over mesoporous MnO_x/Al₂O₃ (MA) catalysts developed by a solvent deficient method using two different manganese precursors including manganese chloride (C) and manganese sulfate (S) at room temperature. The maximum catalytic activities of MA with C (MEK removal efficiency and ozone decomposition of 98.4 and 93.7%, respectively) were higher than those of MA with S (MEK removal efficiency and ozone decomposition of 96 and 68%, respectively). Also the catalytic stability of MA with C was much higher than that of MA with S. The physico-chemical properties of catalysts are well correlated with the activity results, which confirmed that fine dispersion of MnO_x species with high ratios of Mn³⁺/Mn⁴⁺ and more acid sites are attributed to the higher catalyst stability for the MA-C catalyst.

• Applied Chemistry for Engineering
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• v.3 no.4
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• pp.722-729
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• 1992

Mg-and Zn-ferrites having spinel structure, a kind of complex oxides showing the advantageous properties of constituently single metal oxides, were selected to find a relationship between their catalytic activities in the dehydrogenation of ethylbenzene to styrene and the catalytic properties. For the structural and physical analyses of ferrites, XRD, BET, DTA, XPS, TEM and TPD methods were employed. Potassium added to the catalyst played a role of bifunctional promoter which brought the electronic effect as well as the structural one for the increment of particle dispersion. K-addition decreased acid strength of the catalyst by neutralization and increased its acidity. In the dehydrogenation of ethylbenzene, K-addition let the selectivity to styrene be constant throughout the reaction by the proper acid strength of the ferrite for the reaction, which could be obtained from the neutralization of strong acid sites by potassium.

• Bulletin of the Korean Chemical Society
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• v.25 no.12
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• pp.1881-1888
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• 2004

A series of $NiO-TiO_2$/$WO_3$ catalysts was prepared by drying powdered $Ni(OH)_2-Ti(OH)_4$ with ammonium metatungstate aqueous solution, followed by calcining in air at high temperature. Characterization of prepared catalysts was performed by using FTIR, Raman, XPS, XRD, and DSC and by measuring surface area. Upon the addition of tungsten oxide to titania up to 25 wt%, the specific surface area and acidity of catalysts increased in proportion to the tungsten oxide content due to the interaction between tungsten oxide and titania. Since the -$TiO_2$/stabilizes the tungsten oxide species, for the samples equal to or less than 25 wt%, tungsten oxide was well dispersed on the surface of titania, but for the samples containing above 25 wt%, the triclinic phase of $WO_3$ was observed at calcination temperature above 400 $^{\circ}C$. The catalytic activities of 10-NiO-$TiO_2$/$WO_3$ for 2-propanol dehydration and cumene dealkylation were correlated with the acidity of catalysts measured by ammonia chemisorption method. NiO may attract reactants and enhance the local concentration of reactants near the acid sites, consequently showing the increased catalytic activities.

• Journal of Microbiology and Biotechnology
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• v.9 no.6
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• pp.695-703
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• 1999

We have studied the stereospecificities of various pyridoxal 5'-phosphate (PLP) dependent enzymes for the hydrogen transfer between the C-4' of a bound coenzyme and the C-2 of a substrate in the transamination catalyzed by the enzymes. Stereospecificities reflect the structures of enzyme active-sites, in particular the geometrical relationship between the coenzyme-substrate Schiff base and the active site base participating in an $\alpha$-hydrogen abstraction. The PLP enzymes studied so far catalyze only a si-face specific (pro-S) hydrogen transfer. This stereochemical finding suggests that the PLP enzymes have the same topological active-site structures, and that the PLP enzymes have evolved divergently from a common ancestral protein. However, we found that o-amino acid aminotransferase, branched chain L-amino acid aminotransferase, and 4-amino-4-deoxychorismate lyase, which have significant sequence homology with one another, catalyze a re-face specific (pro-R) hydrogen transfer. We also showed that PLP-dependent amino acid racemases, which have no sequence homology with any aminotransferases, catalyze a non-stereospecific hydrogen transfer: the hydrogen transfer occurs on both faces of the planar intermediate. Crystallographical studies have shown that the catalytic base is situated on the re-face of the C-4' of the bound coenzyme in o-amino acid aminotransferase and branched chain L-amino acid aminotransferase, whereas the catalytic base is situated on the si-face in other aminotransferases (such as L-aspartate aminotransferase) catalyzing the si-face hydrogen transfer. Thus, we have clarified the stereospecificities of PLP enzymes in relation with the primary structures and three-dimensional structures of the enzymes. The characteristic stereospecificities of these enzymes for the hydrogen transfer suggest the convergent evolution of PLP enzymes.

• BMB Reports
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• v.44 no.10
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• pp.653-658
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• 2011

Sclerotinia sclerotiorum fungus has three endoxylanases induced by wheat bran. In the first part, a partial xylanase sequence gene (90 bp) was isolated by PCR corresponding to catalytic domains (${\beta}5$ and ${\beta}6$ strands of this protein). The high homology of this sequence with xylanase of Botryotinia fuckeliana has permitted in the second part to amplify the XYN1 gene. Sequence analysis of DNA and cDNA revealed an ORF of 746 bp interrupted by a 65 bp intron, thus encoding a predicted protein of 226 amino acids. The mature enzyme (20.06 kDa), is coded by 188 amino acid (pI 9.26). XYN1 belongs to G/11 glycosyl hydrolases family with a conserved catalytic domain containing $E_{86}$ and $E_{178}$ residues. Bioinformatics analysis revealed that there was no Asn-X-Ser/Thr motif required for N-linked glycosylation in the deduced sequence however, five O-glycosylation sites could intervene in the different folding of xylanses isoforms and in their secretary pathway.

• Journal of Microbiology and Biotechnology
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• v.8 no.4
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• pp.318-324
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• 1998

A ${\beta}$-galactosidase with high transgalactosylic activity was purified from a Bacillus species, registered as KFCC10855. The enzyme preparation showed a single protein band corresponding to a molecular mass of 150 kDa on SDS-PAGE and gave a single peak with the estimated molecular mass of 250 kDa on Sephacryl S-300 gel filtration, suggesting that the enzyme is a homodimeric protein. The amino acid and sugar analyses revealed that the enzyme is a glycoprotein, containing 19.2 weight percent of sugar moieties, and is much more abundant in hydrophilic amino acid residues than in hydrophobic residues, the mole ratio being about 2:1. The pI and optimum pH were determined to be 5.0 and 6.0, respectively. Having a temperature optimum at $70^{\circ}C$ for the hydrolysis of lactose, the enzyme showed good thermal stability. The activity of the enzyme preparation was markedly increased by the presence of exogenous Mg (II) and was decreased by the addition of EDTA. Among the metal ions examined, the most severely inhibitory effect was seen with Ag (I) and Hg (II). Further, results of protein modification by various chemical reagents implied that 1 cysteine, 1 histidine, and 2 methionine residues occur in certain critical sites of the enzyme, most likely including the active site. Enzyme kinetic parameters, measured for both hydrolysis and transgalactosylation of lactose, indicated that the enzyme has an excellent catalytic efficiency for formation of the transgalactosylic products in reaction mixtures containing high concentrations of the substrate.

• Bulletin of the Korean Chemical Society
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• v.19 no.9
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• pp.993-999
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• 1998

Acid catalyzed hydrolysis of 1-phenoxyethyl propionate, Ⅰ, has been studied using the PM3 method in the gas phase. The first step of the reaction is the protonation of basic sites, three different oxygens in Ⅰ, producing three protonated species Ⅱ, Ⅲ and Ⅳ. All possible reaction pathways have been studied from each protonated structure. Changes in the reaction mechanisms have also been discussed from the results obtained by varying a nucleophile from a water monomer to a water dimer to a complex between one water molecule and an intermediate product (propionic acid or phenol) produced in the preceding unimolecular dissociation processes. Minimum energy reaction pathway is 2-W among the possible pathways, in which water dimer acts as an active catalyst and therefore facilitates the formation of a six-membered cyclic transition state. Lower barrier of 2-W is ascribed to an efficient bifunctional catalytic effect of water molecules. PM3-SM3.1 single point calculations have been done at the gas-phase optimized structure (SM3.1/PM3//PM3) to compare theoretical results to those of experimental work.

• Bulletin of the Korean Chemical Society
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• v.22 no.12
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• pp.1303-1308
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• 2001

A series of catalysts, NiSO4/TiO2, for ethylene dimerization was prepared by the impregnation method using aqueous solution of nickel sulfate. On the basis of the results obtained from X-ray diffraction, the addition of NiSO4 shifted the transition of TiO2 from the anatase to the rutile phase toward higher temperatures due to the interaction between NiSO4 and TiO2. Nickel sulfate supported on titania was found to be very active even at room temperature. The high catalytic activity of NiSO4/TiO2 closely correlated with the increase of acidity and acid strength due to the addition of NiSO4. It is suggested that the active sites responsible for ethylene dimerization consist of low valent nickel, Ni+, with an acid.

• Applied Chemistry for Engineering
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• v.2 no.4
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• pp.330-339
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• 1991

The acid properties of $V_2O_5-TiO_2/SiO_2$ catalysts and the partial oxidation of o-xylene into phthalic anhydride had been investigated in order to relate the acid property of catalyst to the catalytic activity. $V_2O_5$ had both weak (V=O) and strong (V-O-V) acid sites which gave pyridine desorption peaks at $230^{\circ}C$ and $300^{\circ}C$, respectively, and the amount of weak acid sites at $230^{\circ}C$ decreased with the increase of calcination temperature. On the other hand, the amount of weak acid sites increased considerably by increasing the amount of $TiO_2$ to the $V_2O_5-TiO_2/SiO_5$, and the maximum value was shown at 20 and higher mole % of $TiO_2$ with respect to $SiO_2$. In the oxidation of o-xylene, $V_2O_5-TiO_2/SiO_2$ enhandced more the total conversion and the selectivity to phthalic anhydride than $V_2O_5/SiO_2$, and the higher $TiO_2$ ratio to $V_2O_5$ increased the total conversion but could not change the selectivity to phthalic anhydride. Weak acid sites (V=O) led o-xylene to partial oxidation producing phthalic anhydride by adsorbing o-xylene weakly, while acid sites (V-O-V) led it to total oxidation producing CO and $CO_2$ by adsorbing it strongly.