Yan-He Guo

The different roles of metal ions and water molecules in the recognition and catalyzed hydrolysis of ATP by phenanthroline-containing polyamines

The phenanthroline bridging polyaza ligands L1, L2 and L3 can selectively and strongly bind nucleotides at physiological pH, and hence accelerate the hydrolysis rate of the bound ATP. It is interesting that a phosphoramidate intermediate at 2.88 ppm (should be added 5.63 ppm when compared with other models) was found in the hydrolysis process of L/ATP. By introduction of metal ions (critical Zn(2+) or hard Mg(2+), Ca(2+)) to the L/ATP system, recognition of the anionic substrates by the protonated ligands was greatly promoted. However, due to the different affinities of metal ions to the receptor and the substrate, ATP hydrolysis in Zn(2+)/L/ATP system and Mg(2+)(Ca(2+))/L/ATP system occurs through different mechanisms. By comparison with the M/ATP (M=Zn(2+), Mg(2+), Ca(2+)) system, the rates of ATP-hydrolysis in the Mg(2+)Ca(2+)/L/ATP system and the Zn(2+)/L/ATP system were enhanced and retarded, respectively. Moreover, the reasons contributing to large rate range of the L/ATP systems and M(2+)/L/ATP systems were given. The results show that metal ions vertically regulate the recognition and hydrolysis of ATP. On the other hand, water molecule participates in the hydrolysis reactions at different steps with different functions in the L/ATP systems and M(Zn(2+), Mg(2+), Ca(2+))L/ATP systems.

Thermodynamic studies on supramolecular interactions of metal ions with nucleotides/tripods ligands

Abstract Four closely related polyamino tripodal ligands 1,3,5-tri(n-2′,5′-diaminohexane)-benzene (L1), 1,3,5-tri(n-2′,5′-diaminoheptane)-benzene (L2), 1,3,5-tri(n-2′,5′-diaminooctane)-benzene (L3) and 1,3,5-tri(n-2′,5′-diaminononane)-benzene (L4) were synthesized and characterized. Each tripodal ligand forms six protonated species in solution. The binding of these tripodal ligands to the nucleotide anions ATP, ADP and AMP are described in detail, with equilibrium constants given for each species formed. The strength of binding increases with the number of protons, corresponding to an increase in the number of hydrogen bonds and to an increase in the coulombic attractive forces. Moreover, the existence of a benzene spacer takes π-stacking interactions with the nucleobase residue of the nucleotides. At the same time, the coordination properties of the ternary complexes formed from the above tripods and Zn(II) and ATP were studied. The metal complexes of tripods recognize the nucleotides via multiple interactions that are similar to those occurring in the center of enzymes.

Crystal structures and physico-chemical properties of two new one-dimensional Zinc(II) complexes with sulfide bridging bispyridines

Abstract 4,4′-Dipyridyl sulfide ( L 1 ) and 4,4′-di(3-methyl)pyridyl ( L 2 ) sulfide coordination compounds of the general formula Zn( L )(X) 2 ( L 1 =4,4′-dipyridyl sulfide; L 2 =4,4′-di(3-methyl)pyridyl sulfide; X=CH 3 COO − , Cl − ), have been obtained. The compounds were characterized by single crystal X-ray diffraction, elemental analysis, IR and 1 H NMR. Both compounds are of one-dimensional coordination polymers and crystallize in the orthorhombic systems, while in different space groups with Pnc 2 for [Zn L 1 (CH 3 COO) 2 ] 1 and Pna 2(1) for [Zn L 2 Cl 2 ] 2 , respectively. X-ray analysis and 1 H NMR experiments indicate that variation of ligands rather than counter anions, CH 3 COO − and Cl − , leads to the change in the modes of the dimensionality array, that is, complexes 1 prefers a linear coordination fashion while complexes 2 exhibits a zigzag conformation.

The different roles of metal ions and water molecule in the hydrolysis of ATP catalyzed by phenanthroline-based polyamines

Abstract The phenanthroline (Phen)-based polyaza ligands can efficiently recognize nucleotides and significantly enhance the rate of ATP hydrolysis under the regulation of metal ions, which act as “messenger” between the substrates and the receptors. The water molecule (or –OH) participates in the catalytic hydrolysis of ATP in different steps with different functions.

Synthesis, characterization and thermodynamic properties of metal complexes of a phenanthroline-bridging macrocyclic ligand

A macrocyclic ligand incorporating phenanthroline has been synthesized by the reaction of 2,9-dichloromethyl-1,10-phenanthroline with dioxo[13]aneN4(dioxo[13]aneN4 = 1,4,7,11-tetraazacyclotridecane-8,10-dione). The stability constants of its Cu2+, Co2+, Hg2+ and Pd2+ metal complexes have been measured by potentiometric pH titration technique. It was found that a π-dp electrostatic interaction between Cu2+ and the phenanthroline moiety does exist in the binary systems. Stability constants of ternary systems containing Cu2+, ligand L(L1) and α-amino acids (AA, L2) in aqueous solution were also determined. Linear free energy relationships (LFER) exist in the ternary systems.

The role of copper(II) ion in regulating H-bonding and coulombic interactions in copper(II)/tripod/polyphosphate systems

The tripodal ligands L, 1,3,5-tri(5-R-2,5-diazapentyl)benzene (R = Me, L1; Et, L2, n-Pr, L3; n-Bu, L4), when protonated, bind strongly and selectively with polyphosphates (Ph) such as orthophosphate (PO), pyrophosphate (PP) and tri-phosphate (tP) respectively in aqueous solution. The results are consistent with the hypothesis that the formation of hydrogen bonds as well as the coulombic interactions plays an important role in the supramolecular interactions between Ph and polyammonium receptors. Moreover, the stability constants of the ternary systems containing the CuII, tripod and polyphosphate were determined by the pH-metric method. Recognition of the polyphosphate anions by the protonated tripods was promoted by the introduction of CuII. Thus the bound metal ion can act as a ‘messenger’ to regulate the H-bonding and electrostatic interactions of the counter-part of the molecular complexes. Fundamental knowledge gained from such studies may then provide valuable insights into the relationship between the structure and reactivity and how the enzymes themselves function.

Stoichiometrical coordination behaviour of hexaza tripodal ligands towards zinc(II), copper(II), nickel(II) and cobalt(II)

The stability constants of ZnII, CuII, NiII and CoII with different tripodal ligands, 1,3,5-tris(2,5-diazaoctxyl)benzene (L1), 1,3,5-tris(2,5-diazanonxyl)benzene (L2) and 1,3,5-tris[3-(2-pyridyl)-2-azapropyl]benzene (L3) have been studied at 25 °C in 0.1 mol dm−3 KNO3 aqueous solution using potentiometric titrations. During the titrations, the ligand concentrations were kept constant at 1 × 10−3 mol dm−3, while 1:1 and 1:3 metal:ligand ratios were used for each system. The results indicated that, in the 1:1 metal:ligand ratio, the binding of MII to the ligand gives rise to several 1:1 complexes differing in their degree of protonation whereas in the 3:1 ratio, polynuclear complexes are formed. Additionally, the ternary complexes of the tripod ligands, with CuII-5-substituted-1, 10-phenanthroline have been investigated and the results show that linear free energy relationship exists in such ternary systems.

Synthesis, thermodynamic properties and kinetics of the acid-catalyzed dissociation of nickel(II) diamido polyamino complexes

The ligands 1,10-N,N′-bis(2-hydroxymethylbenzoyl)-1,4,7,10-tetraazadecane (L1) and 1,11-N,N′-bis(2-hydroxymethylbenzoyl)-1,4,8,11-tetraazaundecane (L2) have been synthesized. The stability constants of NiII complexes of ligands L1 and L2 have been studied at 25 °C using pH titrations. The kinetics of general acid (HCl, 0.04–2.34 mol dm−3) or buffer (DEPP or DESPEN, 0.05 mol dm−3, pH 4.83–5.72)-catalyzed dissociation of these NiII complexes have been investigated at 25 °C using a stopped-flow spectrophotometer. The ionic strength of solution was controlled at I = 2.34 mol dm−3 (KCl + HCl) and I = 0.1 mol dm−3 (KNO3, buffer), respectively. The kinetic dissociation of NiII complexes catalyzed by HCl obeys the equilibrium kobs = k1d + k2H[H+], whereas in buffer solution the observed rate constant kobs = kd + k1H[H+]. At pH < 1.5, both the proton-assisted and direct protonation pathways contribute to the rates, whereas solvation is the dominant pathway at pH > 6. In the 4.8–5.7 pH range, the complexes dissociate mainly through a proton-assisted pathway.