Hydrolysis of phosphates, esters and related substrates by models of biological catalysts

An efficient tRNA cleaver without additional co-reactants at physiological condition

A square-planar Cu(II) complex, [Cu(Me-Im)(gly-gly)]∙H₂O 1 (Me-Im = 1-methyl-imidazole, gly-gly = glycylglycinato), has been prepared and structurally characterized by single crystal X-ray. The complex 1 was tested for its ability to the transfer RNA by UV-vis spectroscopy, cyclic voltammetry (CV), capillary electrophoresis (CE). Comparative spectroscopic analysis shows a maximum fluorescence-quenching ratio of 0.41 of 1 upon binding to RNA, which gives a binding constant (K_b) of 1.24 × 10⁵ M^-1. Cyclic voltammograms of complex 1 attached on the mercaptoethanol (-SH) linked Au electrodes in phosphate buffer solution give a well-defined and quasi-reversible redox couple, indicate complex 1 can efficiently degrade the high-order structure of RNA in physiological conditions (pH 7.0 phosphate buffer solution at 37 °C) without additional co-reactants, yielding a digestion coefficient more than 90% within 113 h. This study targeting the genetic biomacromolecule degradation based on the strong binding of chemical nucleases paves an important way to the novel materials in the decontamination of microorganisms (e.g., bacteria and viruses) at mild condition.

Structural and functional study for tRNA cleavage by Glycine o-phenanthroline CuII complex, [CuCl(phen)(gly)]∙4H2O

The o-phenanthroline gly Cu(II) complex, [CuCl(phen)(gly)]∙4H₂O 1, has been prepared and structurally characterized. The transfer RNA binding and degradation properties of complex 1 have been investigated by UV-vis spectroscopy, cyclic voltammetry (CV), capillary electrophoresis (CE) and atomic force microscopy (AFM) methods. The results showed that 1 can efficiently cleave tRNA in the physiological conditions (pH 7.0, and 37 °C), and has a digestion coefficient nearly up to 100% within 75 h. AFM image for 1/RNA exhibited arrayed tandem repetitions of tRNA segments. This study is targeting the destruction of the high-order structures of genetic biomacromolecules which paves an important way to novel materials for the decontamination of microorganisms (e.g., bacteria and viruses).

Exploring the boundaries of direct detection and characterization of labile isomers - a case study of copper(ii)-dipeptide systems

The investigation of the linkage isomers of biologically essential and kinetically labile metal complexes in aqueous solutions poses a challenge, as these microspecies cannot be separately studied. Therefore, derivatives are commonly used to initially determine the stability or spectral characteristics of at least one of the isomers. Here we directly detect the isomers, describe the metal ion coordination sphere, speciation and thermodynamic parameters by a synergistic application of temperature dependent EPR and CD spectroscopic measurements in copper(ii)-dipeptide systems including His-Gly and His-Ala ligands. The ΔH = (-23 ± 4) kJ mol^-1 value of the standard enthalpy change corresponding to the peptide-type to histamine-type isomerisation equilibrium of the [CuL]⁺ complex was corroborated by several techniques. The preferential coordination of the side-chains was observed at lower temperatures, whereas, metal-binding of the backbone atoms became favourable upon increasing temperature. This study exemplifies the necessity of using temperature dependent multiple methodologies for a reliable description of similar systems for upstream applications.

Hydrolysis mechanisms of BNPP mediated by facial copper(ii) complexes bearing single alkyl guanidine pendants: cooperation between the metal centers and the guanidine pendants

The inter-complex and intra-complex nucleophilic attacks by metal-bound hydroxide were investigated by considering the second coordination spheres.

Oral 4-week and 13-week toxicity studies of polyvinyl acetate vinyl laurate copolymer in rats

Polyvinyl acetate vinyl laurate copolymer (PVAcVL) is a useful component of gum base for chewing gum production. The safety of PVAcVL was examined in a 4-week and a 13-week oral toxicity study in rats. Finely powdered PVAcVL was administered with the diet at levels of 1.25%, 2.0% and 5% in the 4-week study and 1.25%, 2.5% and 5% in the 13-week study. There were no treatment related effects on mortality, bodyweight gains feed efficiency, ophthalmoscopic findings, hematological and clinical chemical parameters, neurobehavioral observations as well as gross and histopathological changes of standard organs and tissues. The highest dose tested in the 13-week study (3783 and 4396mg/kgbw/d for males and females, respectively) proved to be a NOAEL.

Lanthanide-mediated dephosphorylation used for peptide cleavage during solid phase peptide synthesis

Lanthanide(III) ions can accelerate the hydrolysis of phosphomonoesters and phosphodiesters in neutral aqueous solution. In this paper, lanthanide-mediated dephosphorylation has been applied in aqueous media as an orthogonal cleavage condition that can be employed in conventional solid phase peptide synthesis (SPPS). A phosphorylated polymeric support for SPPS was developed using Boc chemistry. The cleavage of resin-bound phosphates was investigated with the addition of Eu(III), Yb(III), acid or base, a mixture of solvents or different temperatures. To demonstrate the utility of this approach for SPPS, a peptide sequence was synthesized on a phosphorylated polymeric support and quantitatively cleaved with lanthanide ions in neutral aqueous media. The protecting groups for side chains were retained during peptide cleavage using lanthanide ions. This new methodology provides a mild orthogonal cleavage condition of phosphoester as a linker during SPPS.

Artificial restriction DNA cutters as new tools for gene manipulation

The final cut. Two types of artificial tools (artificial restriction DNA cutter and zinc finger nuclease) that cut double-stranded DNA through hydrolysis of target phosphodiester linkages, have been recently developed. The chemical structures, preparation, properties, and typical applications of these two man-made tools are reviewed.Two types of artificial tools that cut double-stranded DNA through hydrolysis of target phosphodiester linkages have been recently developed. One is the chemistry-based artificial restriction DNA cutter (ARCUT) that is composed of a Ce(IV)-EDTA complex, which catalyses DNA hydrolysis, and a pair of pseudo-complementary peptide nucleic acid fragments for sequence recognition. Another type of DNA cutter, zinc finger nuclease (ZFN), is composed of the nuclease domain of naturally occurring FokI restriction endonuclease and a designed zinc finger DNA-binding domain. For both of these artificial tools, the scission site and specificity can be freely chosen according to our needs, so that even huge genomic DNA sequences can be selectively cut at the target site. In this article, the chemical structures, preparation, properties, and typical applications of these two man-made tools are described.

Artificial restriction DNA cutter for site-selective scission of double-stranded DNA with tunable scission site and specificity

The artificial restriction DNA cutter (ARCUT) method to cut double-stranded DNA at designated sites has been developed. The strategy at the base of this approach, which does not rely on restriction enzymes, is comprised of two stages: (i) two strands of pseudo-complementary peptide nucleic acid (pcPNA) anneal with DNA to form 'hot spots' for scission, and (ii) the Ce(IV)/EDTA complex acts as catalytic molecular scissors. The scission fragments, obtained by hydrolyzing target phosphodiester linkages, can be connected with foreign DNA using DNA ligase. The location of the scission site and the site-specificity are almost freely tunable, and there is no limitation to the size of DNA substrate. This protocol, which does not include the synthesis of pcPNA strands, takes approximately 10 d to complete. The synthesis and purification of the pcPNA, which are covered by a related protocol by the same authors, takes an additional 7 d, but pcPNA can also be ordered from custom synthesis companies if necessary.

DNA cleavage promoted by 2,9-dimethyl-4,7-diazadecane-2,9-dithiol (DDD) derivatives

Three piperidine derivatives of 2,9-dimethyl-4,7-diazadecane-2,9-dithiol (DDD), NEPDDD, NEMPDDD, and NEMMPDDD, were synthesized and used as catalysts in DNA cleavage. Under physiological conditions, a series of experiments have been done. The effects of DNA cleavage with three ligands were studied under different concentrations, cleavage time, and pH values. The results strongly suggested that the plasmid DNA (pUC 19) can be cleaved efficiently by these ligands. For the cleavage reaction catalyzed by NEMPDDD, Form I DNA could convert to Form II completely, and the DNA-cleavage mechanism involved an oxidative pathway.

Chemical modification of Ce(IV)/EDTA-based artificial restriction DNA cutter for versatile manipulation of double-stranded DNA

A monophosphate group was attached to the terminus of pseudo-complementary peptide nucleic acid (pcPNA), and two of thus modified pcPNAs were combined with Ce(IV)/EDTA for site-selective hydrolysis of double-stranded DNA. The site-selective DNA scission was notably accelerated by this chemical modification of pcPNAs. These second-generation artificial restriction DNA cutters (ARCUTs) differentiated the target sequence so strictly that no scission occurred even when only one DNA base-pair was altered to another. By using two of the activated ARCUTs simultaneously, DNA substrate was selectively cut at two predetermined sites, and the desired fragment was clipped and cloned. The DNA scission by ARCUT was also successful even when the target site was methylated by methyltransferase and protected from the corresponding restriction enzyme. Furthermore, potentiality of ARCUT for manipulation of huge DNA has been substantiated by site-selective scission of genomic DNA of Escherichia coli (composed of 4,600,000 bp) at the target site. All these results indicate promising applications of ARCUTs for versatile purposes.

Cleavage of double-strand DNA by zinc complexes of dicationic 2,2′-dipyridyl derivatives

Two highly charged zinc complexes, [Zn(L1)3](ClO4)8.4H2O (1) and [Zn(L2)2Br](ClO4)5.H2O (2) (L1 = 5,5'-di(1-(triethylammonio)methyl)-2,2'-dipyridyl and L2= 5,5'-di(1-(tributylammonio)methyl)-2,2'-dipyridyl) were synthesized and structurally characterized by crystallography. The zinc atom in 1 shows a distorted octahedral sphere. Variable-pH NMR studies on 1 demonstrated that the saturated six-coordinated [Zn(L1)3]8+ species can partially change into five-coordinated [Zn(L1)2(H2O)]6+ species in aqueous solution. The zinc atom in 2 shows a distorted trigonal-bipyramidal sphere. The average distance of the coordinated Br atom to the cationic N atom in 2 is ca 5.9 A, which is comparable to that of adjacent phosphodiesters in the DNA (ca. 6 A). Both complexes exhibited high nuclease activities towards cleavage of supercoiled plasmid DNA with the activity being the maximum under physiological pH. The effective DNA cleavage may be attributed to the strong electrostatic interaction of the metal moiety and two positive pendants with phosphodiester groups of nucleic acid.

Mononuclear Schiff Base Boron Halides: Synthesis, Characterization, and Dealkylation of Trimethyl Phosphate

A series of mononuclear boron halides of the type LBX(2) [LH = N-phenyl-3,5-di-tert-butylsalicylaldimine, X = Cl (2), Br (3)] and LBX [LH2 = N-(2-hydroxyphenyl)-3,5-di-tert-butylsalicylaldimine, X = Cl (7), Br (8); LH2 = N-(2-hydroxyethyl)-3,5-di-tert-butylsalicylaldimine, X = Cl (9), Br (10); and LH2 = N-(3-hydroxypropyl)-3,5-di-tert-butylsalicylaldimine, X = Cl (11), Br (12)] were synthesized from their borate precursors LB(OMe)2 (1) (LH = N-phenyl-3,5-di-tert-butylsalicylaldimine) and LB(OMe) [LH2 = N-(2-hydroxyphenyl)-3,5-di-tert-butylsalicylaldimine (4), N-(2-hydroxyethyl)-3,5-di-tert-butylsalicylaldimine (5), N-(3-hydroxypropyl)-3,5-di-tert-butylsalicylaldimine (6)]. The boron halide compounds were air and moisture sensitive, and upon hydrolysis, compound 7 resulted in the oxo-bridged compound 13 that contained two seven-membered boron heterocycles. The boron halide compounds dealkylated trimethyl phosphate in stoichiometric reactions to produce methyl halide and unidentified phosphate materials. Compounds 8 and 12 were found to be the most effective dealkylating agents. On reaction with tert-butyl diphenyl phosphinate, compound 8 produced a unique boron phosphinate compound LB(O)OPPh2 (14) containing a terminal phosphinate group. Compounds 1-14 were characterized by 1H, 13C, 11B, 31P NMR, IR, MS, EA, and MP. Compounds 5, 6, and 11-14 also were characterized by single-crystal X-ray diffraction.

Five-Coordinate Aluminum Bromides: Synthesis, Structure, Cation Formation, and Cleavage of Phosphate Ester Bonds

The alkane elimination reaction between Salen((t)Bu)H(2) ligands and diethylaluminum bromide was used to prepare three Salen aluminum bromide compounds salen((t)Bu)AlBr (1) (salen = N,N'-ethylenebis(3,5-di-tert-butylsalicylideneimine)), salpen((t)Bu)AlBr (2) (salpen = N,N'-propylenebis(3,5-di-tert-butylsalicylideneimine)), and salophen((t)Bu)AlBr (3) (salophen = N,N'-o-phenylenenebis(3,5-di-tert-butylsalicylideneimine)). The compounds contain five-coordinate aluminum either in a distorted square pyramidal or a trigonal bipyramidal environment. The bromide group in these compounds could be displaced by triphenylphosphine oxide or triphenyl phosphate to produce the six-coordinate cationic aluminum compounds [salen((t)Bu)Al(Ph(3)PO)(2)]Br (4), [salpen((t)Bu)Al(Ph(3)PO)(2)]Br (5), [salophen((t)Bu)Al(Ph(3)PO)(2)]Br (6), and [salophen((t)Bu)Al[(PhO)(3)PO)](2)]Br (7). All the compounds were characterized by (1)H, (13)C, (27)Al, and (31)P NMR, IR, mass spectrometry, and melting point. Furthermore, compounds 1-3 and 5-7 were structurally characterized by single-crystal X-ray diffraction. Compounds 1-3 dealkylated a series of organophosphates in stoichiometric reactions by breaking the ester C-O bond. Also, they were catalytic in the dealkylation reaction between trimethyl phosphate and added boron tribromide.

Enhanced hydrolytic activity of Cu(ii) and Zn(ii) complexes in highly cross-linked polymers

The chelate ligand tris[(1-vinylimidazol-2-yl)methyl]amine (5) was synthesized in five steps from commercially available starting materials. Upon reaction with ZnCl2 or CuCl2 in the presence of NH4PF6, the complexes [Zn5Cl]PF6 (6) and [Cu5Cl]PF6 (7) were obtained. The structure of both complexes was determined by single-crystal X-ray crystallography. Immobilization of 6 and 7 was achieved by co-polymerization with ethylene glycol dimethacrylate. The supported complexes P6-Zn and P7-Cu were found to be efficient catalysts for the hydrolysis of bis(p-nitrophenyl)phosphate (BNPP) at 50 degrees C. At pH 9.5, the heterogeneous catalyst P7-Cu was 56 times more active than the homogeneous catalyst 7. Partitioning effects, which increase the local concentration of BNPP in the polymer, are shown to contribute to the enhanced activity of the immobilized catalyst.

Tuning the properties of cyclen based lanthanide complexes for phosphodiester hydrolysis; the role of basic cofactors

The synthesis of several cyclen based lanthanide [Eu(III) and La(III)] complexes is described; these metallo ribonuclease mimics are based on the use of alkyl amines as pendent arms, which give rise to fast hydrolysis within the physiological pH range of HPNP (an RNA model compound) that is highly dependent on the length of the alkyl spacer.

Effect of Zn⋅⋅⋅Zn Separation on the Hydrolytic Activity of Model Dizinc Phosphodiesterases

From the study of highly preorganized model systems, experimental support has been obtained for a possible functional role of the Zn-(H)O...HO(H)-Zn motif in oligozinc hydrolases. The mechanistic relevance of such an array, which may be described as a hydrated form of a pseudo-terminal Zn-bound hydroxide, has recently been supported by DFT calculations on various metallohydrolase active sites. In the present targeted approach, the Zn...Zn distance in two related dizinc complexes has been controlled through the use of multifunctional pyrazolate-based ligand scaffolds, giving either a tightly bridged Zn-O(H)-Zn or a more loosely bridged Zn-(H)O...HO(H)-Zn species in the solid state. Zn-bound water has been found to exhibit comparable acidity irrespective of whether the resulting hydroxide is supported by strong hydrogen-bonding in the O(2)H(3) moiety or is in a bridging position between two zinc ions, indicating that water does not necessarily have to adopt a bridging position in order for its pK(a) to be sufficiently lowered so as to provide a Zn-bound hydroxide at physiological pH. Comparative reactivity studies on the cleavage of bis(4-nitrophenyl)phosphate (BNPP) mediated by the two dizinc complexes have revealed that the system with the larger Zn...Zn separation is hydrolytically more potent, both in the hydrolysis and the transesterification of BNPP. The extent of active site inhibition by the reaction products has also been found to be governed by the Zn...Zn distance, since phosphate diester coordination in a bridging mode within the clamp of two zinc ions is only favored for Zn...Zn distances well above 4 A. Different binding affinities are rationalized in terms of the structural characteristics of the product-inhibited complexes for the two different ligand scaffolds, with dimethyl phosphate found as a bridging ligand within the bimetallic pocket.

RNA hydrolysis and inhibition of translation by a Co(III)-cyclen complex

Metal ion-chelator catalysts based on main-group, lanthanide, or transition metal complexes have been developed as nonenzymatic alternatives for the hydrolysis of the phosphodiester bonds in DNA and RNA. Cobalt (III), with its high-charge density, is known for its ability to hydrolyze phosphodiesters with rate constants as high as 2 x 10(-4) s(-1). We have developed a kinetically inert Co(III)-cyclen-based complex, Co(III)-cycmmb that is very potent in inhibiting the translation of RNA into protein. Contact time as short as 10 min is sufficient to achieve the complete inhibition of the translation of a concentrated luciferase RNA solution into the enzyme in a cell-free translation system. The inhibition appears to proceed through two pathways. The first pathway involves the kinetic or substitutional inertness of Co(III) for the RNA template at short contact times. This interaction is mediated through the kinetic inertness of Co(III) for the phosphate groups of the nucleotides, as well as coordination of Co(III) to the nitrogenous bases. The second pathway occurs at longer contact times and is mediated by the hydrolysis of the phosphodiester backbone. This report represents the first demonstrated use of a metal-chelate complex to achieve the inhibition of the translation of RNA into protein. This Co(III) system can be useful in its present nonsequence-specific form as a novel viral decontamination agent. When functionalized to recognize specific nucleic acid sequences, such a system could potentially be used in gene-silencing applications as an alternative to standard antisense or RNAi technologies.

Structural and Functional Models of the Active Site of Zinc Phosphotriesterase

In an attempt to prepare structural and functional models for the active site of the hydrolytic enzyme zinc phosphotriesterase, five new zinc complexes of the ligands 2,6-bis[N-(N-(carboxylmethyl)-N-((1-methylimidazol)methyl)amine)methyl]-4-methylphenolate (BCIMP) and the corresponding asymmetric ligand 2-(N-isopropyl-N-((1-methylimidazolyl)methyl)aminomethyl)-6-(N-carboxylmethyl-N-((1-methylimidazolyl)methyl)aminomethyl)-4-methylphenol (ICIMP) have been synthesized, viz. Na[Zn(2)(BCIMP)Ac(2)] (1), [Zn(2)(BCIMP)(Ph(2)Ac)] (2), [Zn(2)(ICIMP)Ac(2)] (3), [Zn(4)(ICIMP)(2)(Me(3)Ac)(2)][ClO(4)](2) (4), and [Zn(4)(ICIMP)(2)(Ph(2)Ac)(2)][ClO(4)](2) (5). The X-ray structure of complex 5 has been determined and reveals that the complex is a dimer of dimers in the solid state, which in solution dissociates to potent structural models. Studies using NMR show that only one carboxylate coligand bridges the dizinc units in the case of diphenyl acetate and pivalate, while the steric bulk of acetate is sufficiently small to permit the coordination of two acetates/dizinc unit. Functional studies involving the hydrolysis/transesterification of 2-hydroxypropyl p-nitrophenyl phosphate (HPNP) show that the complex with ICIMP (compound 5) has a significantly higher rate of catalysis than the BCIMP complex (compound 2). This is attributed to the vacant/labile coordination site that is available in the ICIMP complex but not the BCIMP complex.

Toward efficient Zn(II)-based artificial nucleases

A series of cis-cis-triaminocyclohexane Zn(II) complex-anthraquinone intercalator conjugates, designed in such a way to allow their easy synthesis and modification, have been investigated as hydrolytic cleaving agents for plasmid DNA. The ligand structure comprises a triaminocyclohexane platform linked by means of alkyl spacers of different length (from C(4) to C(8)) to the anthraquinone group which may intercalate the DNA. At a concentration of 5 microM, the complex of the derivative with a C(8) alkyl spacer induces the hydrolytic stand scission of supercoiled DNA with a rate of 4.6 x 10(-6) s(-1) at pH 7 and 37 degrees C. The conjugation of the metal complex with the anthraquinone group leads to a 15-fold increase of the cleavage efficiency when compared with the anthraquinone lacking Zn-triaminocyclohexane complex. The straightforward synthetic procedure employed, allowing a systematic change of the spacer length, made possible to gain more insight on the role of the intercalating group in determining the reactivity of the systems. Comparison of the reactivity of the different complexes shows a remarkable increase of the DNA cleaving efficiency with the length of the spacer. In the case of too-short spacers, the advantages due to the increased DNA affinity are canceled due to the incorrect positioning of the reactive group, thus leading to cleavage inhibition.

Correlation of Structure and Function in Oligonuclear Zinc(II) Model Phosphatases

A series of pyrazolate-based dizinc(II) complexes has been synthesized and investigated as functional models for phosphoesterases, focusing on correlations between hydrolytic activity and molecular parameters of the bimetallic core. The Zn...Zn distance, the (bridging or nonbridging) position of the Zn-bound hydroxide nucleophile, and individual metal ion coordination numbers are controlled by the topology of the compartmental ligand scaffold. Species distributions of the various dizinc complexes in solution have been determined potentiometrically, and structures in the solid state have been elucidated by X-ray crystallography. The hydrolysis of bis(p-nitrophenyl)phosphate (BNPP) promoted by the dinuclear phosphoesterase model complexes has been investigated in DMSO/buffered water (1:1) at 50 degrees C as a function of complex concentration, substrate concentration, and pH. Coordination of the phosphodiester has been followed by ESI mass spectrometry, and bidentate binding could be verified crystallographically in two cases. Drastic differences in hydrolytic activity are observed and can be attributed to molecular properties. A significant decrease of the pK(a) of zinc-bound water is observed if the resulting hydroxide is involved in a strongly hydrogen-bonded intramolecular O(2)H(3) bridge, which can be even more pronounced than for a bridging hydroxide. Irrespective of the pK(a) of the Zn-bound water, a hydroxide in a bridging position evidently is a relatively poor nucleophile, while a nonbridging hydroxide position is more favorable for hydrolytic activity. Additionally, the metal array has to provide a sufficient number of coordination sites for activating both the substrate and the nucleophile, where phosphate diesters such as BNPP preferentially bind in a bidentate fashion, requiring a third site for water binding. Product inhibition of the active site by the liberated (p-nitrophenyl)phosphate is observed, and the product-inhibited complex could be characterized crystallographically. In that complex, the phosphate monoester is found to cap a rectangular array of four zinc ions composed of two bimetallic entities.

First-principle molecular dynamics of the Berry pseudorotation: Insights on 19F NMR in SF4

First-principles [density-functional theory (DFT)] molecular-dynamic simulations of the Berry pseudorotation mechanism in SF4 were performed using the atom-centered density-matrix propagation method. The reaction was monitored by following the chemical shieldings of the fluorine atoms, computed on snapshots along the trajectories. In particular we compared the results obtained using a standard functional based on the generalized gradient approximation with those issuing from its hybrid Hartree-Fock-DFT counterpart using a number of basis sets. Our results show that both the basis set and the functional choice rule the quality of the molecular properties monitored as well as the trajectory over the potential-energy surface.

Geometry-dependent phosphodiester hydrolysis catalyzed by binuclear copper complexes

Two isomeric binuclear ligands PBTPA and MBTPA and their copper(II) complexes were prepared and examined for hydrolysis of a model phosphodiester substrate: bis(p-nitrophenyl)phosphate. A bell-shaped pH vs rate profile, which is in agreement with one mechanism proposed for bimetallonucleases/phosphatases, was observed for the binuclear complex of copper(II) and PBTPA. At pH 8.4, a maximum rate of 1.14 x 10(-6) s(-1)--more than 10(4)-fold over uncatalyzed reactions--was achieved. However, the analogous complex of MBTPA did not show significant rate enhancement. The binuclear complex of copper(II) and PBTPA also showed 10-fold acceleration over mononuclear complex of copper(II) and tris(2-pyridylmethyl)amine (TPA) catalyzed reaction. A phage phiX174 DNA assay showed that the complex of copper(II) and PBTPA promoted supercoiled phage phiX174 DNA relaxation under both aerobic and anaerobic conditions, in contrast to the hydrolytic inactivity of the mononuclear complex of copper(II) and TPA.