BNPP Hydrolysis Research Articles

Carbonate-bridged dinuclear lanthanide(III) complexes of chiral macrocycle

Mononuclear Eu(III) and Dy(III) complexes of the chiral hexaaza macrocycle L, 2(R),7(R),18(R),23(R)-1,8,15,17,24,31-hexaazatricyclo[25.3.1.1.0.0]-dotriaconta-10,12,14,26,28,30-hexaene have been obtained as chloride derivatives (1 and 2, respectively) and characterized by using spectroscopic methods. The X-ray crystal structure of 2 has been determined. The reaction of two equivalents of mononuclear 1 or 2 complexes with one equivalent of sodium carbonate results in the formation of dinuclear complexes [Eu2L2(µ2-CO3)(H2O)3]Cl43 and [Dy2L2(µ2-CO3)(H2O)3]Cl44, respectively. The X-ray crystal structure of complex 3 reveals two macrocyclic [EuL]3+ units bridged by the carbonate anion. The carbonate anion is bound to the Eu(III) ions using the η1:η2-µ2 bridging mode. The binding of carbonate anions to the [EuL]3+ or [DyL]3+ macrocyclic units has also been studied in solution using spectroscopic methods. The titration of the starting paramagnetic mononuclear chloride derivatives 1 and 2 monitored by 1H NMR spectroscopy revealed initial formation of dinuclear species, followed by the formation of complexes possessing additional carbonate ligands. The dinuclear carbonate complexes 3 and 4 are also formed in the reactions of the respective mononuclear chloride complexes with gaseous CO2. Lanthanide(III) complexes of the chiral hexaaza macrocycle L are effective for catalytic hydrolysis of bis(4-nitrophenyl) phosphate BNPP. Within the series of the studied mononuclear complexes: nitrate derivatives [LnL(NO3)(H2O)](NO3)2 (Ln = Ho, Er), [LnL(H2O)2](NO3)3 (Ln = Tm, Yb, Lu) and chloride derivatives [LnL(H2O)2]Cl3 (Ln = Tm, Yb, Lu, Y) the catalytic activity of the complexes is increased with increasing ionic size. Kinetic studies revealed that most active is the dinuclear europium(III) complex 3 which catalyzes the hydrolysis of BNPP with a rate kobs = 6.5 × 10−5 s−1 (at 0.3 mM concentration of the catalyst) at pH 8.5 and 37 °C.

Dinuclear Lanthanide(III)-m-ODO2A-dimer Macrocyclic Complexes: Solution Speciation, DFT Calculations, Luminescence Properties, and Promoted Nitrophenyl-Phosphate Hydrolysis Rates.

Potentiometric speciation studies, mass spectrometry, and DFT calculations helped to predict the various structural possibilities of the dinuclear trivalent lanthanide ion (LnIII , Ln=La, Eu, Tb, Yb, Y) complexes of a novel macrocyclic ligand, m-ODO2A-dimer (H4 L), to correlate with their luminescence properties and the promoted BNPP and HPNP phosphodiester bond hydrolysis reaction rates. The stability constants of the dinuclear Ln2 (m-ODO2A-dimer) complexes and various hydrolytic species confirmed by mass spectrometry were determined. DFT calculations revealed that the Y2 LH-1 and the Y2 LH-2 species tended to form structures with the respective closed- and open-form conformations. Luminescence lifetime data for the heterodimetallic TbEuL system confirmed the fluorescence resonance energy transfer from the TbIII to EuIII ion. The internuclear distance RTbEu values were estimated to be in the range of 9.4-11.3 Å (pH 6.7-10.6), which were comparable to those of the DFT calculated open-form conformations. Multiple linear regression analysis of the kobs data was performed using the equation: kobs,corr. =kobs -kobs,OH =kLn2LHM->1 [Ln2 LH-1 ]+kLn2LH-2 [Ln2 LH-2 ] for the observed Ln2 L-promoted BNPP/HPNP hydrolysis reactions in solution pH from 7 to 10.5 (Ln=Eu, Yb). The results showed that the second-order rate constants for the Eu2 LH-2 and Yb2 LH-2 species were about 50-400 times more reactive than the structural analogous Zn2 (m-12 N3 O-dimer) system.

Novel structures of Zn(II) biometal cation with the biologically active substituted acetic acid and nitrogen donor ligands: Synthesis, spectral, phosphate diester catalytic hydrolysis and anti‐microbial studies

The complexes [Zn(methoxyacetate)21,10‐phenanthroline] 1 and [Zn2(phenylacetate)4(quinoline)2] 2, were prepared and characterized by IR‐spectroscopy, UV–Visible spectroscopy, 1H and 13C NMR spectroscopy, single crystal X‐ray diffraction. BNPP hydrolysis of the complexes and their parent nitrogen ligands were scanned, the results indicated that the hydrolysis rates of BNPP were 4.5 × 104 and 6.2 × 105 for (1) and (2), respectively. In addition, anti‐bacterial activities were scanned to investigate the effect of complexation on their activity against Gram‐positive (S. epidermidis, S. aureus, E. faecalis, M. luteus and B. Subtilis) and Gram‐negative (K. pneumonia, E. coli, P. Mirabilis and P. Aeruginosa) bacteria using agar well‐diffusion method. Complex 1 showed high activity against G−and G+ bacteria except against E. faecalis and P. Aeruginosa. Complex 2 did not show any activity against G− or G+ bacteria.

Catalytic Capacity of Diaza-Crown Ether Lanthanum Complexes with Varied Ligands for Phosphate Ester Hydrolysis in Different Media

Two diaza-crown ether compounds, 1,4,10,13-tetraoxa-7,16-diazacyclooctadecane (L0) and its derivative with double acetamide side arms 2,2'-(1,4,10,13-teteaoxa-7,16-diazacyclooctadecane-7,16-diyl)diacetamide (L), and the corresponding two lanthanum complexes were synthesised and characterised. The catalytic capacity of the lanthanum complexes was investigated for the hydrolysis of bis(4-nitrophenyl) phosphate ester (BNPP) in aqueous solution and in CTAB micelles. Kinetic studies show that the catalytic efficiency of complex LaL is obviously higher than that of complex LaL0, and introducing acetamide into the ring of the diaza-crown ether can improve the catalytic ability of the complexes for BNPP hydrolysis. A rate enhancement of about two times was observed for the complex–micelle in contrast with the complex–water system for BNPP catalytic hydrolysis. The optimal pH for the catalytic reaction in the two kinds of media systems show an approximately 0.4 pH unit difference. The two complexes possess higher thermostability, and are more stable in the micelle than in aqueous solution. Based on the results and their analysis, a catalytic mechanism with cooperation of acetamide is proposed.

Photo-enhanced hydrolysis of bis(4-nitrophenyl) phosphate using Cu(ii) bipyridine-capped plasmonic nanoparticles

A 1000-fold increase in the rate of BNPP hydrolysis occurs under green laser irradiation of a copper(ii) complex on gold.

Phosphate Diester Cleavage Promoted by the Metallomicelles of Ce(III) Complexes of Aza-Crown Ether with Different Numbers of Nitrogen Atoms

The design of artificial hydrolase has attracted extensive attention due to their scientific significance and potential application in the field of gene medicine and molecular biology. This work reports the catalytic activation of two aza-crown ether Ce(III) complexes and their metallomicelles as artificial hydrolase in bis(4-nitrophenyl) phosphate ester (BNPP) hydrolysis. The chemical composition of two complexes was determined by the fluorescence spectra and the mole ratio method for electronic absorption spectra. The bonding effect of BNPP and solubilizing effect of the complexes were proved by a method of fluorescence spectroscopy. The catalytic activity of different catalytic systems in BNPP hydrolysis was measured with UV-vis spectrophotometric method. These catalytic systems showed high catalytic activity for promoting BNPP hydrolysis at the almost physiological conditions. BNPP hydrolysis rate in these catalytic system is about 107- to 109-fold faster than that of the BNPP spontaneous hydrolysis in aqueous solution at the same conditions. The metallomicelle systems exhibited higher catalytic activity compared with the complex solution systems in BNPP hydrolysis, and hexadecyltrimethyl ammonium bromide micelle provides a useful catalytic environment for reaction. The acid effect of the catalytic system is ascribed to the formation of metal-bound hydroxide serving as a better kind of nucleophile.

Function of the Metallomicelle from an Aza-Crown Ether Complex with an Acetamide Branch as a Highly Potent Promoter of Phosphate Diester Hydrolytic Cleavage

This study reports the synthesis method of a new aza-crown ether with an acetamide branch ligand, 2-(1,10-dioxa-4,7,13,16-tetraaza-cyclooctadec-4-yl)-acetamide (L), and determines the chemical composition of the cerium complex containing the aza-crown ether ligand by a new fluorescence spectrophotometric method. In the report, the cerium complex and its metallomicellar systems were used as catalysts in the hydrolysis of bis(4-nitrophenyl)phosphate ester (BNPP), and their catalytic activity was studied by the comparative method. The interaction between the metallomicelle and BNPP was proved by the fluorescence spectrum. The catalytic rate of BNPP hydrolysis was measured kinetically using the UV-Vis spectrophotometric method. The results indicated that the metallomicellar system of the anionic surfactant exhibited excellent catalytic function and relatively higher catalytic activity than that of the complex solution, the metallomicelle of nonionic and cationic surfactants, and the micelle provided an effective catalytic environment for the catalytic reaction. The experimental results also showed that the best acidity for the metallomicelle catalysis is pH 8.0, and the mono-hydroxy complex may be the real active species uaed as a catalyst in BNPP catalytic hydrolysis. The reaction mechanism was proposed on the basis of the research results.

An Anionic Surfactant Metallomicelle: Catalytic Activity and Mechanism for the Catalytic Hydrolysis of a Phosphate Ester

An aza-crown ether ligand was synthesised and characterised. The chemical composition of the binary complex containing cerium(III) and the ligand was determined by fluorescence spectroscopy. A new metallomicellar system comprising the cerium(III) complex of the ligand and an anionic micelle (n-lauroylsarcosine) was used as catalyst in the hydrolysis of bis(4-nitrophenyl) phosphate ester (BNPP). The catalytic rate of BNPP hydrolysis and the local concentration effect of the micelle were measured kinetically using UV-Vis spectrophotometry. The results indicated, that compared with a cationic metallomicelle system made from the aza-crown ether, lanthanum(III) ion and CTAB cationic surfactant in our previous report, the anionic metallomicelle exhibited a six-fold higher catalytic activity in BNPP hydrolysis at neutral pH and the same other conditions, thus the micelle based on LSS provides a more effective catalytic environment for reaction. A reaction mechanism has been proposed.

The Metallomicelle of Lanthanide Metal (Ce, La) Aza-Macrocyclic Complexes with a Carboxyl Branch: The Catalytic Activity and Mechanism in the Hydrolysis of a Phosphate Diester

An aza-macrocyclic ligand, 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane-N/- acetic acid (L), was synthesized and characterized. The chemical composition of the complexes (CeL and LaL) was determined by a UV–Vis spectrophotometric method and kinetic Job plot. Two metallomicellar systems made of an lanthanide metal complex and n-lauroylsarcosine (LSS) micelle were used as catalyst in the hydrolysis of bis(4-nitrophenyl) phosphate ester (BNPP), and their catalytic activity was studied by the comparative method. The interaction between the complex and BNPP in the metallomicelle was studied by its fluorescent spectroscopy. The catalytic rate of BNPP hydrolysis was measured kinetically by UV–Vis spectrophotometry. The results indicate that CeL systems (aqueous solution and metallomicelle) exhibit higher catalytic activity than those of the LaL systems in BNPP hydrolysis, and the micelle provides an effective catalytic environment in the catalytic reaction. A reaction mechanism was also proposed on the basis of the results.

Activity of a New Metallomicelle Catalytic System on the Hydrolysis of bis(4-nitrophenyl) Phosphate Ester

A new metallomicellar system containing cerium ion (III), a macrocylic polyamine ligand and the hexadecyltrimethyl ammonium bromide (CTAB) was constructed and used as catalyst in the hydrolysis of bis(4-nitrophenyl) phosphate ester (BNPP). The catalytic rate of BNPP hydrolysis was measured kinetically with UV-vis spectrophotometric method. The results indicated that the metallomicellar system exhibited relatively high stability and excellent catalytic function in BNPP hydrolysis, and the reaction rate of the BNPP catalytic hydrolysis, compared with BNPP spontaneous hydrolysis, increased by a factor of ca. 1 × 108 due to the catalytic effect of the active species and the local concentration effect of the micelle in metallomicellar system. The experimental results also showed that the mono-hydroxy complex made of the macrocyclic polyamine ligand and cerium (III) is the real active species as catalyst in BNPP catalytic hydrolysis, and the micelles provide a useful catalytic environment for reaction. On the basis of the research results, the reaction mechanism of BNPP catalytic hydrolysis was proposed in this work.

Framework and Catalytic Activity of a Metallomicelle System Made from an Azacrown Ether, Lanthanum(III) Ion and a Cationic Surfactant

A metallomicelle system comprising an azacrown ether, lanthanum(III) ion and a cationic surfactant was constructed and used as catalyst in the hydrolysis of bis(4-nitrophenyl) phosphate ester (BNPP). The interaction between La(III) and the azacrown ether, and the resulting complex and BNPP, were analysed by fluorescence spectroscopy. The catalytic rate of BNPP hydrolysis was measured kinetically by UV-Vis spectrophotometry. The results indicated that the metallomicelle system exhibited relatively high stability and excellent catalytic function in BNPP hydrolysis, the rate of which, compared with the spontaneous hydrolysis, increased by a factor of ca 2 × 107 due to the catalytic effect of the active species and the local concentration effect of the micelle in the metallomicellar system. The results also showed that the complex, comprising La(III) ion, and the azacrown ether, is the active catalytic species, while the micelles provide a useful catalytic environment for reaction. On the basis of these results, a reaction mechanism for the catalytic hydrolysis of BNPP is proposed.

Construction and Activity of a New Catalytic System in the Hydrolysis of Bis(4-nitrophenyl) Phosphate Ester

A new catalytic system containing an unsaturated heterocyclic nitrogen ligand and lanthanum(III) was constructed and used as a catalyst in the hydrolysis of bis(4-nitrophenyl) phosphate ester (BNPP) in this work. The results indicated that this catalytic system showed greater catalytic activity in the hydrolysis of BNPP and better reproducibility and stability than other similar lanthanum(III) systems. The catalytic rate of the BNPP hydrolysis was about 107-fold faster than that of its spontaneous hydrolysis at the same conditions. Compared with the previous Cu(II) or Ni(II) complex containing the same ligand in the water, the activity of the macrocyclic La(III) complex increases ca. 103-fold for BNPP catalytic hydrolysis. The experimental data showed that the monohydroxy complex made of the heterocyclic nitrogen ligand and lanthanum(III) is the real active species as a catalyst in BNPP catalytic hydrolysis.

Catalytic Mechanism and Activity of a Nitrogen Heterocycle Lanthanum(III) Complex in the Hydrolysis of bis(4-nitrophenyl) Phosphate Ester

The system made up of a nitrogen heterocycle ligand and lanthanum(III) ion was used in the catalytic hydrolysis of bis(4-nitrophenyl) phosphate ester (BNPP). This catalytic system showed higher catalytic activity in this hydrolysis and better reproducibility and stability than other similar lanthanum(III) ion systems. The rate of the catalytic hydrolysis was about 108-fold faster than that of its spontaneous hydrolysis under the same conditions. Compared with previous Cu(II) or Ni(II) complexes containing the same ligand in water, the activity of the macrocyclic La(III) complexe is increased ca 104-fold. The experimental evidence showed that the mon-hydroxy complex made of the nitrogen heterocycle ligand and lanthanum(III) ion is the active species as catalyst in the catalytic hydrolysis of BNPP.

Effect of hydrophobic interaction cooperating with double Lewis acid activation in a zinc(ii) phosphodiesterase mimic

The novel dinuclear Zn(ii) complex (1) containing a beta-CD dimer could accelerate BNPP (a DNA substitute) hydrolysis more efficiently than catalyze HPNP (a RNA substitute) transesterification with different mechanisms involved; the beta-CDs played remarkably different roles.

Effects of Concentration of Some Lanthanide(III) Complexes of 1,7‐Bis(carboxymethyl)‐1,4,7,10‐tetraazacyclododecane on Bis(p‐nitrophenyl)phosphate Hydrolysis

AbstractA detailed study of the effects of the concentration of some lanthanide(III) complexes [LnDO2A+; DO2A = 1,7‐bis(carboxymethyl)‐1,4,7,10‐tetraazacyclododecane] on the hydrolysis of the phosphodiester bond of the compound BNPP [sodium bis(4‐nitrophenyl)phosphate] is reported at 25 °C and pH 7.90 (Ln = Eu), 9.35 (Ln = Eu), and 9.90 (Ln = Eu, Er and Yb). The reaction is found to be first order with respect to BNPP concentration at pH 7.90 and 9.35 and to increase to 1.78 ± 0.09, 1.64 ± 0.07, and 1.63 ± 0.09 with respect to [EuDO2A+] concentration at pH 7.90, 9.35, and 9.90, respectively, thereby indicating that dinuclear species are involved in the reactions. Similar observations were found for the other two LnDO2A+ complexes at pH 9.90 [1.63 ± 0.11 (Er) and 1.49 ± 0.09 (Yb)]. The kobs data obtained by the initial rate method could be fitted to a monomer‐dimer reaction model for all LnDO2A+ complexes at pH 7.90, 9.35, and 9.90 in the [LnDO2A+] concentration range 1.0–20.0 mM. The dinuclear species, namely the mono‐hydroxo‐bridged complexes [Ln2(DO2A)2(μ‐OH)(OH)(H2O)n = 1–3] and the di‐hydroxo‐bridged complexes [Ln2(DO2A)2(μ‐OH)2(H2O)n = 0–2] are found to be more reactive, with reactivities in the order Eu > Yb > Er. The overall formation constants for [Ln2(DO2A)2(μ‐OH)2(H2O)n]‐BNPP are around 104 M–1. The EuDO2A+‐promoted BNPP hydrolysis rates are similar to, or up to two orders of magnitude faster than, most of those reported for other lanthanide and transition‐metal complexes. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Catalytic hydrolysis of phosphate diester (BNPP) and plasmid DNA by mononuclear macrocyclic polyamine metal complexes

The activities of the catalytic hydrolysis of phosphate diester (BNPP) [bis( p-nitrophenyl)phosphate diester] and plasmid DNA (pUC18) by mononuclear macrocyclic polyamine metal complexes have been investigated in this paper. The results showed that the highest activity in hydrolysis of BNPP was obtained with 1e–Zn(II) complex (composed of lipophilic group) as catalyst. The hydrolysis rate enhancement is up to 3.64 × 10 4 fold. These metal complexes could effectively promote the cleavage of plasmid DNA (pUC18) at physiological conditions.

Kinetics of Hydrolysis of an Activated Phosphate Ester in Brij35 Micelle Containing a Macrocyclic Complex of Cu(II) OR Ni(II)

A macrocyclic ligand and its corresponding Cu(II) and Ni(II) complexes were synthesized and characterized. The kinetics of hydrolysis of bis( p-nitrophenyl) phosphate (BNPP, an activated phosphate diester) in Brij35 micelle containing each macrocyclic complex was investigated. The metallomicelles made up of the macrocyclic metal complex and micelle, as a mimic hydrolytic metalloenzyme, display higher catalytic activity although they do not attain the catalytic efficiency of enzymes. The analysis of specific absorption spectra show that the course of the catalytic BNPP reaction is different from that of the spontaneous hydrolysis of BNPP, and is an intramolecular nucleophilic substitution reaction. Based on the analytical results of the specific absorption spectra, an intramolecular nucleophilic substitution mechanism for the catalytic hydrolysis of BNPP is proposed, a correlative kinetic mathematical model is established, and the corresponding thermodynamic and kinetic constants are calculated. The validity of the mechanism and the proposed mathematical model is confirmed by the results of this study.

Efficient Increase of DNA Cleavage Activity of a Diiron(III) Complex by a Conjugating Acridine Group

AbstractA new diferric complex, Fe2Lb, in which a DNA intercalator (acridine) is linked to a precursor diferric complex (Fe2La), has been designed and synthesised as a hydrolytic cleaving agent of DNA. Compared with Fe2La (without the DNA intercalator) (La: 2,6‐bis{[(2‐hydroxybenzyl)(pyridin‐2‐yl)methylamino]methyl}‐4‐methylphenol), Fe2Lb [Lb: 5‐(acridin‐9‐yl)‐N‐(3,5‐bis{[(2‐hydroxybenzyl)(pyridin‐2‐yl)methylamino]methyl}‐4‐hydroxybenzyl)pentanamide] leads to a 14‐fold increase in the cleavage efficiency of plasmid DNA due to the binding interaction between DNA and the acridine moiety. The interaction has been demonstrated by UV/Vis absorption, CD spectroscopy, viscidity experiments and thermal denaturation studies. The hydrolytic mechanism is supported by evidence from T4 DNA ligase assay, reactive oxygen species (ROS) quenching and BNPP [bis(4‐nitrophenyl) phosphate, a DNA model] cleavage experiments. The pH dependence of the BNPP cleavage by Fe2La in aqueous buffer media shows a bell‐shaped pH–kobs profile with an optimum point around a pH of 7.0 which is in good agreement with the maximum point of the pH‐dependent relative concentration curve of active species from the pH titration experiments. The determination of the initial rates at a pH of 7.36 as a function of substrate concentration reveals saturation kinetics with Michaelis–Menten‐like behaviour and Fe2La shows a rate acceleration increase of 4.7 × 106 times in the hydrolysis of BNPP. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Phosphodiesterolytic activity of samarium(III) mixed ligand complexes containing crown ethers and α-amino acids

Phosphodiesterolytic activity of samarium complexes containing crown ethers and amino acids was systematically studied. Formation constants of mixed ligand Sm–crown ethers–amino acids complexes (crown ethers = 18-crown-6, 15-crown-5 and 12-crown-4 and amino acids = Gly and Arg) were determined at 37.0 °C and 0.50 M NMe 4Cl. Kinetics of the hydrolysis of BNPP (bis(4-nitrophenyl)phosphate) mediated by lanthanide(III)-mixed ligands complexes was studied under the same experimental conditions. The rate of BNPP cleavage is sensitive to metal ion concentration, pH, and ligand to metal molar ratio. Hydrolysis follows Michaelis–Menten-type saturation kinetics. High pH values markedly increase the observed activity. Potentiometric titrations results together with kinetic data of all these systems, under identical conditions, allowed us to identify the active species towards hydrolysis. Complexes with phosphodiesterolytic activity are monomeric hydroxylated cationic species. In general, a good phosphodiesterolytic activity is observed for these complexes under similar conditions to the physiological ones.

Macrocyclic Lanthanide Complexes as Artificial Nucleases and Ribonucleases: Effects of pH, Metal Ionic Radii, Number of Coordinated Water Molecules, Charge, and Concentrations of the Metal Complexes

We have been interested in the design, synthesis, and characterization of artificial nucleases and ribonucleases by employing macrocyclic lanthanide complexes because their high thermodynamic stability, low kinetic lability, high coordination number, and charge density (Lewis acidity) allow more design flexibility and stability. In this paper, we report the study of the use of the europium(III) complex, EuDO2A+ (DO2A is 1,7-dicarboxymethyl-1,4,7,10-tetraazacyclododecane) and other lanthanide complexes (i.e., LaDO2A+, YbDO2A+, EuK21DA+, EuEDDA+, and EuHEDTA where K21DA is 1,7-diaza-4,10,13-trioxacyclopentadecane-N,N'-diacetic acid, EDDA is ethylenediamine-N,N'-diacetic acid, and HEDTA is N-hydroxyethyl-ethylenediamine-N,N',N'-triacetic acid), as potential catalysts for the hydrolysis of the phosphodiester bond of BNPP (sodium bis(4-nitrophenyl)-phosphate). For the pH range 7.0-11.0 studied, EuDO2A+ promotes BNPP hydrolysis with the quickest rates among LaDO2A+, EuDO2A+, and YbDO2A+. This indicates that charge density is not the only factor affecting the reaction rates. Among the four complexes, EuDO2A+, EuK21DA+, EuEDDA+, and EuHEDTA, with their respective number of inner-sphere coordinated water molecules three, two, five, and three, EuEDDA+, with the greatest number of inner-sphere coordinated water molecules and a positive charge, promotes BNPP hydrolysis more efficiently at pH below 8.4, and the observed rate trend is EuEDDA+ > EuDO2A+ > EuK21DA+ > EuHEDTA. At pH > 8.4, the EuEDDA+ solution becomes misty and precipitates form. At pH 11.0, the hydrolysis rate of BNPP in the presence of EuDO2A+ is 100 times faster than that of EuHEDTA, presumably because the positively charged EuDO2A+ is more favorable for binding with the negatively charged phosphodiester compounds. The logarithmic hydrolysis constants (pKh) were determined, and are reported in the parentheses, by fitting the kinetic k(obs) data vs pH for EuDO2A+ (8.4), LaDO2A+ (8.4), YbDO2A+ (9.4), EuK21DA+ (7.8), EuEDDA+ (9.0), and EuHEDTA (10.1). The preliminary rate constant-[EuDO2A+] data at pH 9.35 were fitted to a monomer-dimer reaction model, and the dimer rate constant is 400 times greater than that of the monomer. The fact that YbDO2A+ catalyzes BNPP less effectively than EuDO2A+ is tentatively explained by the formation of an inactive dimer, [Yb(DO2A)(OH)]2, with no coordination unsaturation for BNPP substrate binding.