Preparation, characterization and kinetic study of the β-cyclodextrin-based artificial metalloenzymes = β-Cyclodextrin을 이용한 artificial metalloenzyme의 제조와 특성 연구

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Metal ions are essential participants for the catalytic activities or structural stabilities of metalloenzymes. Metalloenzymes use the cooperative action between the substrate binding site and catalytic metal center. β-Cyclodextrin is a naturally occurring cyclic heptamer of D-(+)-glucopyranose units that are linked by $\alpha$(1→4) glucopyranose bonds. In this study, new supramolecular β-CD monomer 1 in which Cu(Ⅱ) ion binding sites are attached to the primary side of hydrophobic β-CD pockets, was prepared. β-CD dimers possessing tridentate 7- (2), pentadentate 13- (3) and 15-membered (4) pyridine diamide chelators were designed, synthesized and characterized by MALDI-MS, NMR, IR and UV-Visible spectroscopy. Fluorescence and pH-metric titration were carried out in order to ascertain their behavior as bifunctional hosts for fluorescence guests and metal ions. As expected, supramolecular β-CD dimers have high binding affinity for fluorescence guests, e.g. TNS and TPPS. Supramolecular β-CD monomer and dimers chelate Cu(Ⅱ) ion by forming amidate-Cu(Ⅱ) complexes. The $pK_{a1}$ values for the Cu(Ⅱ) promoted deprotonation of amide ligands from 1, 3 and 4 were determined to be 4.3, 6.3 and 6.3, respectively. Above pH 8.0, supramolecular ligands 3 and 4 bind fluorescent guest and Cu(Ⅱ) ion simultaneously. 1-Cu(Ⅱ), 3-Cu(Ⅱ) and 4-Cu(Ⅱ) complexes were isolated as blue or purple solids. Cu(Ⅱ) complexes catalyze the hydrolysis of p-nitrophenyl acetate, adamantate and amino acids in an enzyme-like manner; displaying Michaelis-Menten kinetics, substrate specificity and competitive inhibition. In this context, these complexes are regarded as artificial metalloenzyme. Artificial metalloenzymes hydrolyze the p-nitrophenyl esters by the nucleophilic addition of a Cu(Ⅱ)-coordinated hydroxide ion to the carbonyl carbon of substrate included in hydrophobic β-CD pocket. These results support the zinc hydroxide mechanism of carboxypeptidase A.
Byun, Si-Myung변시명
한국과학기술원 : 생물과학과,
Issue Date
151527/325007 / 000945379

학위논문(박사) - 한국과학기술원 : 생물과학과, 1999, [ v, 88 p. ]


β-cyclodextrin; Metalloenzyme; 메탈로엔자임; 베타싸이클로덱스트린

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