title: Synergic effect of two metal centers in catalytic hydrolysis of methionine-containing peptides promoted by dinuclear palladium(II) hexaazacyclooctadecane complex.
abstract: The species obtained by the reaction of [Pd2([18]aneN6)Cl2](ClO4)2(where [18]aneN6 is 1,4,7,10,13,16-hexaazacyclooctadecane) with AgBF4 have been determined by electrospray ionization mass spectrometry (ESI-MS) to be an equilibrium mixture of three major types of dinuclear Pd(II) complex cations, [Pd2(mu-O)([18]aneN6)]2+, [Pd2(mu-OH)([18]aneN6)]3+ and [Pd2(H2O)(OH)([18]aneN6)](3+), in aqueous solution. The hydroxo-group-bridged one, [Pd2(mu-OH)([18]aneN6)]3+, is a dominant species, whose crystal structure has been obtained. The crystal structure of [Pd2(mu-OH)([18]aneN6)](ClO4)3 shows that each Pd(II) ion in the dinuclear complex is tetra-coordinated by three nitrogen atoms and one hydroxo group bridge in a distorted square configuration. The two Pd(II) ions are 3.09 A apart from each other. The dinuclear Pd(II) complex cations [Pd2(mu-OH)([18]aneN6)]3+ and [Pd2(H2O)(OH)([18]aneN6)]3+ can efficiently catalyze hydrolysis of the amide bond involving the carbonyl group of methionine in methionine-containing peptides with turnover number of larger than 20. In these hydrolytic reactions, the two Pd(II) ions are synergic; one Pd(II) ion anchors to the side chain of methionine and the other one delivers hydroxo group or aqua ligand to carbonyl carbon of methionine, or acts as a Lewis acid to activate the carbonyl group of methionine, resulting in cleavage of Met-X bond. The binding constant of dinuclear Pd(II) complex cations with AcMet-Gly and AcMet were determined by 1H NMR titration to be 282 +/- 2 M(-1) and 366 +/- 4 M(-1), respectively. The relatively low binding constants enable the catalytic cycle and the possible catalytic mechanism is proposed. This is the first artificial mimic of metallopeptidases with two metal active centers.
authors.affiliation: State Key Laboratory of Coordination Chemistry, Coordination Chemistry Institute, Nanjing University, Nanjing 210093, P. R. China.
authors.forename: Gaosheng
authors.initials: G
authors.lastname: Yang
authors.forename: Ren
authors.initials: R
authors.lastname: Miao
authors.forename: Yizhi
authors.initials: Y
authors.lastname: Li
authors.forename: Jing
authors.initials: J
authors.lastname: Hong
authors.forename: Chuenmei
authors.initials: C
authors.lastname: Zhao
authors.forename: Zijian
authors.initials: Z
authors.lastname: Guo
authors.forename: Longgen
authors.initials: L
authors.lastname: Zhu
mesh_terms: D002384:Catalysis; D002412:Cations / Q000737:chemistry; D018360:Crystallography, X-Ray; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D008670:Metals / Q000737:chemistry*; D008715:Methionine / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000737:chemistry*; D010455:Peptides / Q000737:chemistry*; D012996:Solutions; D021241:Spectrometry, Mass, Electrospray Ionization; D013696:Temperature
chemical_list: D002412:Cations; D008670:Metals; D009942:Organometallic Compounds; D010455:Peptides; D012996:Solutions; C518138:palladium(II) hexaazacyclooctadecane; D008715:Methionine