Article

Formation and phosphodiesterolytic activity of lanthanide(III) N, Nbis(2-hydroxyethyl)glycine hydroxo complexes

Authors:
To read the full-text of this research, you can request a copy directly from the authors.

Abstract

Potentiometric titrations of N,N-bis(2-hydroxyethyl)glycine (bicine) in the presence of Ln(III) cations (Ln=La, Pr, Nd and Eu) in the pH range extended to ca. 9.5 reveal formation of two types of binuclear hydroxo complexes Ln2(bic)2(OH)4 and Ln2(bic)(OH)4+ (bicH=bicine) in addition to previously reported mononuclear mono- and bis-complexes Ln(bic)2+ and Ln(bic)2+, which predominate at pH below 8. 1H NMR titrations of La(III)–bicine mixtures in D2O show that the complex formation with bicine is slow in the NMR time scale and confirm formation of hydroxide rather than alkoxide complexes in basic solutions. Formation of a different type of hydroxide species under conditions of an excess of metal over ligand is confirmed by studying the absorption spectra of the Nd(III)–bicine system in the hypersensitive region. The binuclear hydroxide complexes are predominant species at pH above 9 and their stabilities increase in the order La

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... Mandelic acid is also recommended for preand post-laser treatment, reducing the amount of redness and irritation caused by laser resurfacing (Su et al., 2001). Lanthanone (III) complexes play an important role in various biochemical reactions (Jakusch et al. 2002;Garg et al., 2003;Calderon and Yatsimirsky, 2004;Mathur et al., 2007). Many binary and ternary complexes of these acids with transition and inner transition metals have been studied pH metrically (Crea et al., 2007;Shokrollahi et al., 2008;Kavosh and Rezaienejad, 2012). ...
... Mandelic acid is also recommended for preand post-laser treatment, reducing the amount of redness and irritation caused by laser resurfacing (Su et al., 2001). Lanthanone (III) complexes play an important role in various biochemical reactions (Jakusch et al. 2002;Garg et al., 2003;Calderon and Yatsimirsky, 2004;Mathur et al., 2007). Many binary and ternary complexes of these acids with transition and inner transition metals have been studied pH metrically (Crea et al., 2007;Shokrollahi et al., 2008;Kavosh and Rezaienejad, 2012). ...
Article
Full-text available
A Solution state study on complexation behavior of Th(IV) with hydroxy acids (malic acid, lactic acid, salicylic acid and mandelic acid) has been carried out using the Irving-Rossotti titration technique in aqueous media and mixed media at different temperatures and ionic strengths. The dissociation constant and stability constants (logo) of the resulting complexes have been calculated with the Fortran IV program BEST using the method of least squares and considering the BESTFIT model. Species distribution curves of complexes have been plotted as function of pH using the SPEPLOT Fortran IV program to visualize various species in equilibrium in the pH range 2-14. Thermodynamic properties were calculated and negative Delta G, All and AS values indicated that complex formation is a spontaneous and exothermic process at these temperatures. To understand more about these equilibriums, the stability of these complexes was studied in presence of various systemic errors.
... Mandelic acid is also recommended for preand post-laser treatment, reducing the amount of redness and irritation caused by laser resurfacing (Su et al., 2001). Lanthanone (III) complexes play an important role in various biochemical reactions (Jakusch et al. 2002;Garg et al., 2003;Calderon and Yatsimirsky, 2004;Mathur et al., 2007). Many binary and ternary complexes of these acids with transition and inner transition metals have been studied pH metrically (Crea et al., 2007;Shokrollahi et al., 2008;Kavosh and Rezaienejad, 2012). ...
Article
Full-text available
The aim of the present study was to optimize the osmotic dehydration and drying kinetic in Solanum lycopersicum L. (cultivar-Italian). The effects of the osmotic agents such as NaCl/sucrose ratio and contact time on the tomatoes moisture content reduction were evaluated according to 23 full experimental design. The attained results showed that both variables were statistically significant on moisture content reduction. However, it was found a more depended upon the increase of saline concentration than contact time. The drying process was conducted at 65 degrees C and Page's model was used to describe the drying kinetic. Also, the osmotic treatment resulted in significant variations of the effective mass diffusivity which reached a mass diffusivity value of 7.34x10(-8) m(2)/s resulting in a largest reduction, i.e., 91 % approximately, on the tomato moisture content. Thus, the osmo-convective drying was a good procedure to attain a product with appropriate characteristics.
... Mandelic acid is also recommended for preand post-laser treatment, reducing the amount of redness and irritation caused by laser resurfacing (Su et al., 2001). Lanthanone (III) complexes play an important role in various biochemical reactions (Jakusch et al. 2002;Garg et al., 2003;Calderon and Yatsimirsky, 2004;Mathur et al., 2007). Many binary and ternary complexes of these acids with transition and inner transition metals have been studied pH metrically (Crea et al., 2007;Shokrollahi et al., 2008;Kavosh and Rezaienejad, 2012). ...
Article
Full-text available
Medicinal plants have been screened for their biological activity using Brine Shrimp (Artemia sauna leach). Brine shrimp lethality test was used to investigate the cytotoxic activity of plant extracts. After 24 hour of treatment, the larvicidal activity was assessed on the base of percentage of larval mortality. The bioactivity of hydroalcoholic extracts of different parts of medicinal plants, at different concentrations (1-5000 mu g/mL), was evaluated with the shrimp lethality assay. Lethality concentration (LC50) was obtained using probit analysis. Out of the 17 plants tested, Veratrum album Bernh, Capsicum annuum L, Atropa belladonna L, Toxicodendron pubescens Mill and Berberis vulgaris L exhibited potent brine shrimp lethality with LC50 of 400, 420, 430, 610 and 612 mu g/mL, respectively.
... The ligand complexes of some lanthanide(III) ions can mediate the hydrolysis of phosphomonoesters and phosphodiesters in aqueous or organic solutions [1][2][3][4][5][6]. Lanthanide(III) ions can efficiently hydrolyze phosphoric esters in neutral aqueous solution because they have a high coordination number, high ionization potential, and high substitution lability [7,8]. ...
Article
Full-text available
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.
... It has been shown that not only do bicH 3 and related compounds buffer H + concentrations but also the resultant metal complexes buffer H + and metal ion concentrations; therefore the employment of bicH 3 as a buffer requires great care to avoid conflicting data and erroneous conclusions [13] [14] [15]. Even though bicinate metal complexes have been studied in solution for years [12] [13] [14] [15] [16] [17] [18], mainly through the excellent research of Sigel [12], only few metal complexes have been structurally characterized in the solid state through single-crystal, X-ray crystallography. ...
Article
Full-text available
The reaction of N, N-bis(2-hydroxyethyl)glycine (bicine; bicH(3)) with Cd(O(2)CPh)(2) · 2H(2)O in MeOH yielded the polymeric compound [Cd(2)(O(2)CPh)(2)(bicH(2))(2)](n)(1). The complex crystallizes in the tetragonal space group P4(1)2(1)2. The lattice constants are a = b = 12.737(5) and c = 18.288(7) Å. The compound contains chains of repeating {Cd(2)(O(2)CPh)(2)(bicH(2))(2)} units. One Cd(II) atom is coordinated by two carboxylate oxygen, four hydroxyl oxygen, and two nitrogen atoms from two symmetry-related 2.21111 (Harris notation) bicH(2) (-) ligands. The other Cd(II) atom is coordinated by six carboxylate oxygen atoms, four from two bicH(2) (-) ligands and two from the monodentate benzoate groups. Each bicinate(-1) ligand chelates the 8-coordinate, square antiprismatic Cd(II) atom through one carboxylate oxygen, the nitrogen, and both hydroxyl oxygen atoms and bridges the second, six-coordinate trigonal prismatic Cd(II) center through its carboxylate oxygen atoms. Compound 1 is the first structurally characterized cadmium(II) complex containing any anionic form of bicine as ligand. IR data of 1 are discussed in terms of the coordination modes of the ligands and the known structure.
Article
In this study, a facile covalent conjugation method was utilized to prepare N, N-bis(2-hydroxyethyl)glycine (Bicine) modified graphene oxide (GO), which was employed for the adsorption and separation of phenols, organic dyes and REE³⁺ (Y³⁺, Nd³⁺, Eu³⁺) from aqueous solution. Various characterizations including scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and Brunauer-Emmett-Teller were carried out. The adsorption capacities of GO-Bicine composite for REE³⁺, phenols and dyes were also investigated. GO-Bicine composite showed some differences in adsorption capacities for various contaminants. The adsorption capacity for Y³⁺ was 4.8 times and 6.8 times higher than that for Nd³⁺ and Eu³⁺. While the adsorption capacity for p-nitrophenol was 1.4, 5.7, 2.4, 1.3, 1.7 times higher than those for 1-naphthol, hydroquinone, p-aminophenol, 3-nitrophenol, tert-butyl hydroquinone. For the adsorption of organic dyes, GO-Bicine composite showed high adsorption capacity for methylene blue, which was 4 times higher than that for alizarin yellow R. Complexation, electrostatic interactions and Lewis acid-base interactions were involved in the adsorption of REE³⁺, while electrostatic interactions, π-π stacking interactions, and hydrogen bonding interactions were considered as the main adsorption mechanisms for phenols and dyes. The adsorption of p-nitrophenol on GO-Bicine composite fitted well with the Langmuir isothermal model. The adsorption thermodynamics demonstrated that the adsorption of p-nitrophenol by GO-Bicine composite was endothermic and spontaneous. The adsorption selectivity of GO-Bicine composite will make it be a potential adsorbent for removal or separation of different pollutants from aqueous solutions.
Article
A macro-cyclic Schiff base ligand and the corresponding Cu (II) and Ni (II) complexes were synthesized and characterized. And the catalytic efficiency of the metallomicelles made of these complexes and noninonic micelle Brij35, as mimetic hydrolytic metalloenzyme, was investigated in the catalytic hydrolysis of bis(p-nitrophenyl) phosphate (BNPP) in this paper. The results show that the rate of the BNPP hydrolysis in the metallomicelles is about 106 -fold faster than that of the BNPP spontaneous hydrolysis in aqueous solution at the same conditions. The analysis of the characteristic absorption spectra of the hydrolytic reaction systems indicates that the key intermediate, composing of BNPP and Ni(II) or Cu(II) complexes, has been formed and the catalytic hydrolysis of BNPP is an intramolecular nucleophilic substitution reaction. Based on the results of characteristic absorption spectra, the mechanism of BNPP catalytic hydrolysis has been proposed and also the corresponding kinetic mathematical model has been established.
Article
The solution speciation of the ZrIV-substituted Keggin polyoxometalate (Et2NH2)8[{α-PW11O39Zr(μ-OH)(H2O)}2]·7H2O (ZrK 2:2) was fully determined under different pD, temperature, and concentration conditions. Subsequently, phosphodiester bond hydrolysis of the DNA model substrate bis(4-nitrophenyl) phosphate (BNPP) promoted by ZrK 2:2 was studied in detail. In the presence of ZrK 2:2, phosphoester bond hydrolysis in BNPP proceeded with a rate constant of kobs = (4.75 ± 0.25) × 10–6 s–1 at pD 6.4 and 60 °C, which represented a 320-fold rate enhancement relative to the spontaneous hydrolysis of BNPP. The pD dependence of kobs exhibits a bell-shaped profile, with the fastest rate observed at pD 6.4. An activation energy (Ea) of 60.16 kJ mol–1, enthalpy of activation (ΔH#) of 57.44 kJ mol–1, entropy of activation (ΔS#) of –173.16 J mol–1 K–1, and Gibbs activation energy (ΔG#) of 111.12 kJ mol–1 at 37 °C were calculated. The influence of the concentration of ZrK 2:2 on the reaction rate constant was studied in the concentration range 0.5 to 6.0 mM. The results showed that ZrK 2:2 is able to hydrolyze an excess amount of BNPP, thus demonstrating that ZrK 2:2 acts as a catalyst for phospho(di)ester bond hydrolysis. In addition, the influence of ionic strength and the inhibitor diphenyl phosphate on BNPP hydrolysis were examined.
Article
The intramolecular nucleophilic substitution of an activated phosphate diester, bis(p-nitrophenyl) phosphate (BNPP) as the nucleic acids substitute, was investigated. A macro-cyclic ligand and the corresponding Cu (II) and Ni (II) complexes were synthesized and characterized. The metallomicelles made up of macrocyclic divalent metal complex and micelle, as mimic hydrolytic metalloenzyme, was used in BNPP catalytic hydrolysis. The metallomicelles displayed higher catalytic activity although they do not attain the catalytic efficiency of enzymes. The analysis of specific absorption spectra showed that the course of the BNPP catalytic reaction was different from that of the BNPP spontaneous hydrolysis, and was an intramolecular nucleophilic substitution reaction. Based on the analytic result of the specific absorption spectrum, an intramolecular nucleophilic substitution mechanism of BNPP catalytic hydrolysis was proposed and a correlative kinetic mathematical model was established, and the corresponding thermodynamic and kinetic constant was calculated. The result of this study proved validity of the mechanism and mathematical model proposed in the article.
Article
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 0.50M NMe4Cl. 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.
Article
A macrocyclic Schiff base ligand and the corresponding Cu(II) and Ni(II) complexes were synthesized and characterized. The catalytic ability of metallomicelles, made from these complexes and micelles, as mimic hydrolytic metalloenzymes, was investigated in the catalytic hydrolysis of bis(p-nitrophenyl) phosphate (BNPP). The rate of the BNPP catalytic reaction in the metallomicelles is ca 2.0×106-fold faster than that of the spontaneous hydrolysis of BNPP in aqueous solution under the same conditions. The analysis of absorption spectra of the hydrolytic reaction systems indicates that key intermediates, comprising BNPP and the Ni(II) or Cu(II) complexes, have been formed and the catalytic hydrolysis of BNPP is an intramolecular nucleophilic substitution reaction. Based on the analysis of the absorption spectrum, a mechanism for the catalytic hydrolysis of BNPP has been proposed and a kinetic mathematical model has been established.
Article
Kinetics of the hydrolysis of BNPP (bis(4-nitrophenyl)phosphate) mediated by lanthanide – samarium (III) and ytterbium (III) – alone and in the presence of various alfa amino acids has been systematically studied at 37.0 °C and I=0.15 M in NaClO4, in the pH interval of 7–9. 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. For both metals, high pH values markedly increase the observed activity. Besides, potentiometric titrations of all these systems under identical conditions allowed us to identify the active coordination compounds towards hydrolysis. The results show that complexes with phosphodiesterolytic activity are monomeric cationic species such as [Ln(aa)3(OH)]2+ or [Ln(aa)2(OH)2]+. Since phosphodiesterolytic activity is evident above pH 7 and it is increased with increasing pH, hydrolytic reactions of the metals are competitive processes that could lead to their precipitation as Ln(OH)3(s). In this sense, ligand excess (for example, ligand to metal molar ratio equal to 30) was employed. Furthermore, due to its more extended hydrolysis, ytterbium shows, in general, less activity than samarium under the studied conditions. In general, a good phosphodiesterolytic activity is observed for these complexes under similar conditions to the physiological ones. Amino acids could be easily derivatized without changing their coordinating ability, leading to lanthanide complexes possibly capable of efficiently hydrolyzing the phosphodiester linkages of nucleic acids.
Article
The synthesis and structures of two new isostructural mononuclear [Ln(L)(NO3)(H2O)3](NO3)2 complexes, with Ln = Tb (complex 1) and Eu (complex 2), which display high activity in the hydrolysis of the substrate 2,4-bis(dinitrophenyl)phosphate, are reported. These complexes displayed catalytic behavior similar to the mononuclear gadolinium complex [Gd(L)(NO3)(H2O) 3](NO3)2 previously reported by us (Inorg. Chem. 2008, 47, 2919?2921); one hydrolysis reaction in two stages where the diesterase and monoesterase activities could be monitored separately, with the first stage dependent on and the second independent of the complex concentration. Through potentiometric studies, electrospray ionization mass spectrometry (ESI-MS) analysis, and determination of the kinetic behaviors of 1 and 2 in acetonitrile/water solution, the species present in solution could be identified and suggested a dinuclear species, with one hydroxo group, as the most prominent catalyst under mild conditions. The complexes show high activity (k1 = 7 and 18 s?1 for 1 and 2, respectively) and catalytic efficiency. Complexes 1 and 2 were found to be active toward the cleavage of plasmid DNA, and complete kinetic studies were carried out. Studies with a radical scavenger (dimethylsulfoxide) confirmed the hydrolytic action of 1 and 2 in the cleavage of DNA. Studies on the incubation of distamycin with plasmid DNA suggested that 1 and 2 are regio-specific, interacting with the minor groove of DNA. These complexes displayed luminescent properties. Complex 1 showed higher emission intensity than 2 due to a more efficient energy transfer between triplet and emission levels of terbium (T → 5D 4), along with nonradiative deactivation mechanisms of the excited states of europium via multiphonon decays and the ligand-to-metal charge transfer state. Lifetime measurements of the 5D4 and 5D0 excited levels for 1 and 2, respectively, indicated the numbers of coordinated water molecules for the complexes.
Article
The anion of 4-imidazolecarboxylic acid (HL) stabilizes hydroxo complexes of trivalent lanthanides of the type ML(OH)+ (M = La, Pr) and M2L(n)(OH)(6-n) (M = La, n = 2; M = Pr, n = 2, 3; M = Nd, Eu, Dy, n = 1-3). Compositions and stability constants of the complexes have been determined by potentiometric titrations. Spectrophotometric and (1)H NMR titrations with Nd(III) support the reaction model for the formation of hydroxo complexes proposed on the basis of potentiometric results. Kinetics of the hydrolysis of two phosphate diesters, bis(4-nitrophenyl) phosphate (BNPP) and 2-hydroxypropyl 4-nitrophenyl phosphate (HPNPP), and a triester, 4-nitrophenyl diphenyl phosphate (NPDPP), in the presence of hydroxo complexes of five lanthanides were studied as a function of pH and metal and ligand concentrations. With all lanthanides and all substrates, complexes with the smallest n, that is M2L2(OH)4 for La and Pr and M2L(OH)5 for Nd, Eu, and Dy, exhibited the highest catalytic activity. Strong inhibitory effects by simple anions (Cl-, NO3-, (EtO)2PO2-, AcO-) were observed indicating high affinity of neutral hydroxo complexes toward anionic species. The catalytic activity decreased in the order La > Pr > Nd > Eu > Dy for both diester substrates and was practically independent of the nature of cation for a triester substrate. The efficiency of catalysis, expressed as the ratio of the second-order rate constant for the ester cleavage by the hydroxo complex to the second-order rate constant for the alkaline hydrolysis of the respective substrate, varied from ca. 1 for NPDPP to 10(2) for HPNPP and to 10(5) for BNPP. The proposed mechanism of catalytic hydrolysis involves reversible bridging complexation of a phosphodiester to the binuclear active species followed by attack on the phosphoryl group by bridging hydroxide (BNPP) or by the alkoxide group of the deprotonated substrate (HPNPP).
Article
The complex between Eu(III) and 1,7-diaza-4,10,13-trioxacyclopentadecane-N,N'-diacetic acid (L4) was characterized by pH potentiometric titration and 1H NMR spectroscopy. The conversion of the monomer to a dimeric complex is observed as the pH is increased from 7 to 10 in a reaction that releases one mol/HO- per dimer formed. The dimeric complex undergoes a further ionization with a pKa of 10.7. Kinetic parameters are reported for the cleavage of the simple phosphodiester 2-hydroxypropyl-4-nitrophenyl phosphate catalyzed by both the monomeric and the dimeric Eu(III) complexes. These data show that the monomer and dimer stabilize their bound reaction transition states with similar free energies of 7.1 and 7.6 kcal/mol, respectively. Clearly, a bridging hydroxide is not an optimal linker to promote cooperative catalysis between Eu(III) centers in macrocycles with multiple polyaminocarboxylate pendent groups.
Article
Full-text available
A lanthanide(III) complex of a macrocycle containing hydroxyethyl groups promotes nucleophilic attack of an hydroxyethyl group on a phosphate diester.
Article
Full-text available
Lanthanide ions and complexes occupy a special position in developing synthetic nucleases capable of catalyzing the hydrolytic cleavage of RNA or DNA. Stimulated by a number of serendipitous lanthanide complexes that feature the common active-site structure of dinuclear metallo-phosphodiesterases, rational design and synthesis of polynuclear lanthanide–hydroxo species via ligand-controlled hydrolysis of the lanthanide ions were attempted. The efforts yielded a series of highly sophisticated yet structurally well-defined lanthanide–hydroxo complexes. These materials are potentially applicable to the study of biomimetic catalysis of phosphate diester cleavage. Research highlights are described in this Feature Article.
Article
Twelve new or little used hydrogen ion buffers covering the range pKa = 6.15-8.35 have been prepared and tested. Ten are zwitterionic amino acids, either N-substituted taurines or N-substituted glycines, and two are cationic primary aliphatic amines. All of the zwitterionic buffers are better than conventional buffers in the Hill reaction and in the phosphorylation-coupled oxidation of succinate by bean mitochondria. Two of the zwitterions, N-tris(hydroxymethyl)-methylaminoethanesulfonic acid and N-2-hydroxyethylpiperazine-N′-2-ethanesulfonic acid, give particularly active and stable mitochondrial preparations. These two also give higher rates of protein synthesis in cell-free bacterial preparations than do tris(hydroxymethyl)aminomethane (Tris) or phosphate buffers.
Article
The acid dissociation constant and chelate stability constants for the interaction of Cu+2, Ni+2, Co+2, Fe+2, Mn+2, Zn+2 Cd+2, Mg+2 and Fe+3 ions with N,N-dihydroxyethylglycinate ion have been determined by potentiometric pH titration measurements. The ligand was found to be less basic than the glycinate ion but showed equal or higher affinity for metal ions, indicating the participation of the hydroxyethyl groups in chelate formation. By means of the titration curves and related information, the divalent metal ions are shown to form chelates with 1 and 2 moles of ligand per metal ion, whereas the 1:1 Fe+3 chelate is proved to combine with excess ligand to give a chelate having a ratio of 3 ligands to 2 metal ions. The Fe+3 chelates differ from those of the divalent metals in that protons are also displaced from the hydroxyalkyl groups. The chelate stability constants are correlated with the second ionization potential of the metal, and the effect of pH on dissociation of the metal chelates is discussed.
Article
Many nuclease and peptidase enzymes achieve highly efficient catalysis by active site cooperation of metal ions and amino acid side chains (acids, bases or nucleophiles). This review focuses on model complexes for which attachment of functional organic groups to a chelate ligand results in an increased hydrolytic reactivity toward phosphodiesters and amides.
Article
Six lanthanide metal complexes with N,N-bis(2-hydroxyethyl)glycine (Hbheg) have been prepared and characterized by means of IR spectra, magnetic susceptibility, thermal analysis, and powder X-ray analysis. These complexes appear as two types: [M(bheg)2]Cl·3H2O and M(bheg)2(CH3COO)(H2O)4 (M: La, Ce, Nd). The crystal and molecular structure of [La(bheg)2]Cl·3H2O was determined by a single-crystal X-ray diffraction method. The central lanthanum atom is nine-coordinated with a face-centered trigonal prism geometry. The structure of this complex consists of a one-dimensional polymer bridged by carboxylato oxygen atoms.
Article
A novel dinuclear Zn(II) complex with hexaaza macrocycle bearing two hydroxyethyl pendants (L1), 3,6,9,16,19,22-hexaaza-6,19-bis(2-hydroxyethyl)-tricyclo[22,2,2,211,13]triaconta-1,11,13,24,27,29-hexaene), was synthesized as a model for alkaline phosphatase. The Zn(II) complex [Zn2L1(CH3CO2)2](ClO4)2(H2O)2 was isolated as a colorless crystal, triclinic, space group P-1. Both Zn(II) ions adopt the geometry of a distorted trigonal bipyramid in a pentacoordinated environment with ZnZn distance of 8.74 Å. The solution complexation study has revealed that the alcoholic hydroxyl group of the complex Zn2L1 exhibits a low pKa value at 25°C. Zn(II)-bound alkoxides, which act as reactive nucleophiles toward the hydrolysis of 4-nitrophenyl acetate in 10% (v/v) CH3CN at 25°C, with I=0.10 M (NaNO3) and pH 9.0, have shown a second-order rate constant of 0.32±0.01 M−1s−1, a value that is approximately 13 times greater than the value for the corresponding dinuclear Zn(II) complex formed by a hexaaza macrocycle without hydroxyethyl pendants (L2). The pH–rate profile for Zn2L1 gave a sigmoidal curve. A possible mechanism has been proposed: the Zn(II)–RO− function acts as a nucleophile in the first step of the hydrolytic mechanism, to give an acetyl intermediate, which is subsequently hydrolyzed to acetate by a Zn(II)–OH− group.
Article
Saturation kinetics are measured with all lanthanides and bis(nitrophenyl) phosphate BNPP as substrate. They show rather constant KM values; the kcat values, however, increase by up to 66 times for La3+ to Er3+ and decrease again for Yb3+ and Lu3+. With all lanthanides, hydrolysis of the intermediate mononitrophenyl phosphate NPP is 2−30 times faster than that of BNPP. The kcat values measured with BNPP correlate with the ion diameter of the lanthanides, in line with accepted mechanisms but with the notable exception of the higher lanthanides. A similar correlation holds for the cleavage rates with plasmid DNA, with striking differences again observed with the higher lanthanides, however. Thus, a concentration increase from 5 × 10-5 to 1 × 10-2 M leads to 64% and 84% more DNA cleavage with La3+ and Pr3+, respectively, but to up to 68% less DNA cleavage, respectively, but with Yb3+, Tm3+ or Lu3+. In contrast to the BNPP cleavage, saturation kinetics derived kcat values with DNA change little with the used cation, which on the other hand led to larger variations in the KM parameters. Preliminary UV and CD studies with plasmid DNA indicate lanthanide-induced conformational changes with pseudo-first-order rate constants 10−100 times higher than the cleavage rate under the same conditions. Again, Yb3+ shows different effects than Eu3+. The unusual behavior of the higher lanthanides is discussed on the basis of cation clustering, which, in contrast to earlier assumptions by Bamann et al., leads to diminished activities. Addition of salts such as of NaCl or MgCl2 leads to distinct decrease of catalytic effects of for instance Eu3+. The corresponding rates correlate well with Debye−Hückel ionic strength parameters. These as well as the effects of added amines are in line with a simple competition mechanism of the added cations for the anionic substrates.
Article
Synthetic and isolation procedures are described that allow access to the new complexes [Ln(O2CMe)(bicH2)(phen)(H2O)](ClO4)·phen·3H2O, where Ln=Gd(1), Er(2), Pr(3) and Nd(4), bicH2−=the monoanion of N,N-bis(2-hydroxyethyl)glycine (bicine) and phen=1,10-phenanthroline. The structure of 1 has been determined by single-crystal X-ray crystallography. The GdIII ion is in a 9-coordinate, tricapped trigonal prismatic ligand environment. The acetate and phen ligands are bidentate chelating, while the bicinate(−1) ion functions as a tetradentate chelate with the ligated atoms being the nitrogen, the two hydroxyl oxygens and one of the carboxylate oxygens. The crystal structure is stabilized by H bonds and aromatic stacking interactions. Complexes 2, 3 and 4 seem to be isostructural with 1. The complexes were characterized by elemental analyses, thermal techniques, room temperature magnetic moments and spectroscopic (IR, far-IR, solid state f–f) methods. All data are discussed in terms of the nature of bonding and known or assigned structures.
Article
The hydrolysis of the 4-nitrophenyl phosphate ester of propylene glycol (HPNP) is catalyzed by neutral lanthanide(III) DO3A complexes. Hydrolysis experiments with complexes of modified ligands where the metal complex was positively charged did not yield in a significant increase of the rate constant.
Article
Using data on a series of polyaza and polyoxa-polyaza macrocyclic compounds, a satisfactory linear correlation was established between the dissociation constants of their acid forms obtained in deuterium oxide (pKD) and in water (pKH). The isotopic effect, ΔpK=pKD - pKH, increases with increasing pK, being larger for the weaker acids. The pKD vs. pKH correlation may be used to determine pKD or pKH values when one of the constants is known; the statistical errors of the estimates are not significatively higher than those of the experimental determinations. By including data available in the literature for a series of different acids (mineral and carboxylic acids, phenols, protonated amines, amino acids, etc.; a total of 138 pairs of data for 70 different compounds), a good general pKD vs. pKH correlation was also obtained (correlation coefficient 0.998), showing that the dependence of the isotopic effect on the nature of the acid is not as important as previous studies, based on limited and not always satisfactory Δpk vs. pKH correlations, suggested.
Article
A novel 24-membered macrocyclic compound having two hydroxyethyl pendants L, 3,6,9,17,20,23-hexazatricyclo[23.3.1.1.11,15]triconta-1(29),11(30),12,14,25,27-hexaene-6,20-bis(2-hydroxyethyl), has been synthesized as a dinucleating ligand. A new complex [Zn2H−2L]Br2(H2O)2 has been synthesized as a model to mimic the active center of alkaline phosphatase. The bridging coordination of the two alkoxides to two ZnII ions was confirmed by the crystal structure of [Zn2H−2L]Br2(H2O)2. The protonation constants of L as well as complexation constants of L with ZnII have been determined at 298.1 K by means of potentiometric titration. [Zn2H−2L]2+ and [Zn2H−2L(OH)]+ are the dominant species in aqueous solution at 7 < pH < 9. The kinetics of promoted hydrolysis of p-nitrophenyl acetate has also been studied; the second-order rate constant is 0.018 M−1 s−1 at pH = 9.0.
Article
Tetranuclear lanthanide-hydroxo complexes of the general formula [Ln(4 mu (3)-OH)(4)(AA)(x)(H2O)(y)](8+) (1, Ln = Sm, AA = Gly, x = 5, y = 11; 2, Ln = Nd, AA = Ala, x = 6, y = 10; 3, Ln = Er, AA = Val, x = 5, y = 10) have been prepared by a-amino acid controlled hydrolysis of lanthanide ions under near physiological pH conditions (pH 6-7). The core component of these compounds is a cationic cluster [Ln(4)(mu (3)-OH)(4)](8+) whose constituent lanthanide ions and triply bridging hydroxo groups occupy the alternate vertexes of a distorted cube. The amino acid ligands coordinate the lanthanide ions via bridging carboxylate groups. Utilizing L-glutamic acid as the supporting ligand, a cationic cluster complex (4) formulated as [Er-4(mu (3)-OH)(4)(Glu)(3)(H2O)(8)](5+) has been obtained. Its extended solid-state structure is composed of the cubane-like [Er-4(mu (3)-OH)(4)](8+) cluster building units interlinked by the carboxylate groups of the glutamate ligands. All compounds are characterized by using a combination of spectroscopic techniques and microanalysis (CHN and metal). Infrared spectra of the complexes suggest the coordinated amino acids to be zwitterionic. The presence of mass (MALDI-TOF) envelopes corresponding to the [Ln(4)(mu (3)-OH)(4)](8+) (Ln = trivalent Sm, Nd, or Er) core containing fragments manifests the integrity of the cubane-like cluster unit. Magnetic studies using Evans' method suggest that exchange interactions between the lanthanide ions are insignificant at ambient temperature. The structural identities of all four compounds have been established crystallographically. The tetranuclear cluster core has been demonstrated to be a common structural motif in these complexes. A mechanism responsible for its self-assembly is postulated.
Article
Lanthanide(III) complexes of two related ligands, 1,4,7,10-tetrakis(2-hydroxyethyl)-1,4,7,10-tetraazacyclododecane (THED) and (1S,4S,7S,10S)-1,4,7,10-tetrakis(2-hydroxypropyl)-1,4,7,10-tetraazacyclododecane (S-THP) promote transesterification of the 4-nitrophenyl phosphate ester of propylene glycol (1) and cleavage of RNA oligomers A12-A18. The pH-rate profiles for the transesterification of 1 or cleavage of RNA oligomers by lanthanide(III) complexes suggest that a lanthanide-bound hydroxide (Ln(OH)2+) or lanthanide-bound alkoxide (Ln(OR)2+) complex is the catalytically active species. Second-order rate constants for the transesterification of 1 by Ln-(OH)2+ or Ln(OR)2+ at 37°C are 7.2 (±0.5) × 10-2 M-1 s-1 6.3 (±0.3) × 10-2 M-1 s-1 and 1.4 (±0.2) × 10-2 M-1 s-1 for the THED complex of europium(III) and for the S-THP complexes of lanthanum(III) and europium-(III), respectively. A second-order rate constant of 1.1 M-1 s-1 is obtained for the cleavage of RNA oligomers by the Eu(OH)2+ or Eu(OR)2+ form of the europium(III) THED complex. At higher concentrations of lanthanide-(III) complex (>1.00 mM) at pH values where Ln(OH)2+ or Ln(OR)2+ are the predominent species, saturation kinetics are observed for the transesterification of 1 by Eu(THED)(CF3SO3)3, Eu(S-THP)(CF3SO3)3, or La(S-THP)(CF3SO3)3; binding constants and first-order catalytic rate constants are, respectively, 62 (±9) M-1 and 9.5 (±0.9) × 10-4 s-1, 68 (±9) M-1 and 1.8 (±0.4) × 10-4 s-1, and 130 (±24) M-1 and 6.6 (±1.0) × 10-4 s-1. As determined by potentiometric titrations, pKa values for lanthanide-bound water or lanthanide-bound hydroxyalkyl decrease on traversing the lanthanide series: La(S-THP)(CF3SO3)3, 8.40 (±0.05); Eu(THED)(CF3SO3)3, 7.50 (±0.05); Eu(S-THP)(CF3SO3)3 7.80 (±0.1); Lu(S-THP)(CF3SO3)3, 6.40 (±0.1) and 9.30 (±0.1). Conductivity measurements suggest that the europium(III) complexes exist as 3:1 electrolytes in water at pH 6.5.
Article
A few years ago, the remarkable catalytic activity of lanthanide ions for the hydrolysis of nucleic acids was discovered. With CeIV, DNA was hydrolysed under physiological conditions. For RNA hydrolysis, the last three lanthanide ions (TmIII, YbIII, and LuIII) are superb. Furthermore, artificial restriction enzymes for site-selective scission of DNA and RNA, essential tools for the future biotechnology, have been prepared by using the lanthanide complexes. The present article emphasizes the mechanistic aspects of the catalyses of these metal ions. Both DNA hydrolysis and RNA hydrolysis involve the cooperation of acid catalysis (by metal ion and/or metal-bound water) and base catalysis (by metal-bound hydroxide). The magnitudes of contributions of these catalyses, as well as the positions where they work, are primarily governed by the relative height of the energy-barrier for the formation of the pentacoordinated intermediate and that for its breakdown. The following conclusions have been obtained on the basis of various kinetic and spectroscopic evidence: (1) for the hydrolysis of both DNA and RNA, the catalytically active species are dinuclear hydroxo-clusters, (2) CeIV enormously activates DNA and promotes the formation of the pentacoordinated intermediate, and (3) the catalysis for RNA hydrolysis is mainly ascribed to the promotion of breakdown of the pentacoordinated intermediate.
Article
The stability of europium(III) complexes with benzocrown ether derivatives 2−4 containing carboxylic functions with methylene spacers of different length was found to vary surprisingly little. In sharp contrast, the hydrolytic activity of these catalysts against bis(p-nitrophenyl)phosphate (BNPP) varied by a factor of 30. The results show for the first time the efficiency of the carboxylic group as cofactor in phosphate ester hydrolysis, which until now was established only in some enzmyes. Other than with BNPP, the hydrolysis with plasmid DNA (nicking experiments) showed no rate enhancement.
Article
Lanthanide-mediated hydrolyses of micellar β-hydroxyhexadecyl p-nitrophenyl phosphate (3) and hexadecyl p-nitrophenyl phosphate (4), as well as of their nonmicellar analogues, β-hydroxypropyl p-nitrophenyl phosphate (1) and ethyl p-nitrophenyl phosphate (5), were examined with the tripositive cations of La, Eu, Tb, Er, Tm, and Yb at pH 7, 37 °C. Micellar kinetic advantages of 4−13 were observed at 2 mM Ln3+, due to enhanced binding of the cations to the anionic micellar substrates. Tm3+ was the most reactive cation, eliciting 105-fold hydrolytic rate accelerations.
Article
The hydrolysis of 1:1 metal chelates of Zn(II), Mn(II), Fe(II), Hg(II), La(III), Fe(III), Cr(III), Th(IV), Ti(IV) and Sn(IV) were studied potentiometrically in order to ascertain the effect of variation of the metal ion on acid dissociation of coördinated water molecules. A total of 14 ligands were investigated in order to obtain stable water-soluble systems containing these partially chelated metal ions. A study of the titration curves for these systems showed that hydrolytic tendencies of metal chelates vary with the metal in the following approximate order: Mn(II) < Zn(II) < La(III) < Cu(II) < Fe(III), Cr(III) < Th(IV) < Ti(IV), Sn(IV). For the metals investigated the charge of the ion was found to be somewhat more important than the electronegativity of the metal in determining hydrolytic tendencies. In the case of La(III), a reversal was noted in that it was found to fall within the group of bivalent metal ions.
Article
A new benzyl alcohol-pendant 1,4,7,10-tetraazacyclododecane (cyclen) ligand, (S)-1-(2-hydroxy-2-phenylethyl)-1,4,7,10-tetraazacyclododecane (L) (11), has been synthesized. The complexation of 11 with ZnII yielded 1:1 five-coordinate complexes (isolated as its perchlorate salts with the pendant alcohol either undissociated (ZnL, 14a) or dissociated (ZnH-1L, 14b) from acidic (pH 6.0) or basic (pH 9.5) aqueous solution, respectively). The pKa value for the pendant alcohol (14a ⇌ 14b + H+) was determined by potentiometric pH titration to be 7.30 ± 0.02 at 35 °C with I = 0.10 (NaNO3). The X-ray crystal study of 14b has shown two crystallographically distinct structures with the alkoxide closely coordinated at the fifth coordination site, where an average distance of Zn-O- is 1.91 Å. Crystals of 14b·ClO4 (C16H27N4O5ClZn) are orthorhombic, space group P212121 (no. 19) with a = 16.977 (4) Å, b = 18.135 (4) Å, c = 13.173 (3) Å, V= 4055 (1) Å3, Z = 8, R = 0.050, and Rw = 0.077. The ZnII-bound alkoxide anion in 14b is a more reactive nucleophile than N-methylcyclen-ZnII-OH- species 15b. In the kinetic study using 14 in aqueous solution (pH 6.0-10.3) at 35 °C with I = 0.10 (NaNO3), the rate-pH profile for a phosphoryl transfer reaction from bis(4-nitrophenyl) phosphate (BNP-) to 14b gave a sigmoidal curve with an inflection point at pH 7.4, which corresponds to the pKa value for 14a ⇌ 14b + H+. The second-order rate constant KBNP of (6.5 ± 0.1) × 10-4 M-1 s-1 is 125 times greater than the corresponding value of (5.2 ± 0.2) × 10-6 M-1 s-1 for BNP- hydrolysis catalyzed by 15b. The product of the phosphoryl transfer reaction from BNP- to 14b is the pendant alcohol-phosphorylated 16, which was isolated as its perchlorate salt 16a by reacting 14b with BNP- in DMF. In anhydrous DMF solution, the phosphoryl transfer (kBNP of 1.1 ± 0.1 M-1 s-1 at 35 °C) is 1700 times faster than that in aqueous solution. In the subsequent reaction of 16, the pendant phosphodiester undergoes an intramolecular nucleophilic attack by the ZnII-bound OH- of 16b to yield a phosphomonoester product 17. From the sigmoidal rate - pH relationship (pH 7.4-10.5), the kinetic pKa value of 9.0 was estimated for 16a ⇌ 16b + H+, which is almost the same value (pKa = 9.10 ± 0.05) determined by potentiometric pH titration at 35 °C. The first-order rate constant for the reaction 16b → 17 is (3.5 ± 0.1) × 10-5 s-1 at 35 °C with I = 0.10 (NaNO3). As a reference to this intramolecular phosphodiester hydrolysis, ethyl (4-nitrophenyl) phosphate (NEP-) was hydrolyzed by 15b. The second-order rate constant KNEP was (7.9 ± 0.3) ×10-7 M-1 s-1 at 35 °C with I = 0.10 (NaNO3). Thus, the intramolecular hydrolysis is 45 000 times faster than the intermolecular NEP- hydrolysis with 1 mM 15b. The present findings that demonstrate the potential of the proximate alcohol by ZnII in the initial phosphoryl transfer and the potential of the ZnII-bound water in the intramolecular phosphate hydrolysis may well serve to elucidate the collaborative functions of Ser-102 and ZnII ions in alkaline phosphatase.
Article
The synthesis of the new alcohol-pendant macrocycle 4-(2-hydroxyethyl)-1,4,7,16,19,22-hexaaza-10,13,25,28-tetraoxacyclotriacontane (L2) is reported. This ligand contains two different triamine moieties, one of them bearing an ethanolic sidearm. L2 binds two Zn(II) ions in aqueous solution. The stability constants of the L2 complexes have been determined at 298.1 and 308.1 K by means of potentiometric measurements. Besides a [Zn2L2]4+ species, a deprotonated [Zn2(L2-H)]3+ complex and a hydroxo [Zn2(L2-H)(OH)]2+ complex are formed in aqueous solution. Zn(II)-assisted deprotonation of the alcoholic group takes place at neutral pH, giving the [Zn2(L2-H)]3+ complex. In [Zn2(L2-H)]3+, the deprotonated R−O- function bridges the two metals, as shown by the crystal structure of [Zn2(L2-H)Br2]BPh4·MeOH. The hydroxo species [Zn2(L2-H)(OH)]2+ is formed at slightly alkaline pH's. This complex contains both a Zn(II)-bound alkoxide and a Zn(II)−OH nucleophilic function. Therefore, it may provide a simple model system for alkaline phosphatases, where both a deprotonated serine and a Zn−OH function are involved in phosphate ester hydrolysis. Indeed, this complex promotes the hydrolysis of the carboxy ester p-nitrophenyl acetate (NA) as well as the cleavage of phosphate ester bis(p-nitrophenyl) phosphate (BNP). The kinetics of promoted hydrolysis of NA and BNP were studied by means of UV and 1H and 31P NMR measurements. In NA hydrolysis, the R−O-−Zn(II) function acts as nucleophile in the first step of the hydrolytic mechanism, to give an acetyl derivative, which is subsequently hydrolyzed to acetate by a Zn−OH group. Similarly, in BNP cleavage, the nucleophilic attack of alkoxide on phosphorus gives a pendant-alcohol phosphorylated intermediate, which undergoes subsequent intramolecular nucleophilic attack of a Zn(II)-bound hydroxide to yield a phosphomonoester product.
Article
Absorption difference spectra are reported for six different Nd3+/ligand systems vs. NdCl3 in aqueous solution. These spectra were obtained as a function of Nd3+/ligand solution pH. The ligands differ with respect to their donor (ligating) atoms, their substituent groups, their chelation geometries, and their total coordination numbers. However, each includes two carboxylate groups in its structure. The difference spectra (ΔA vs. λ) and oscillator strength ratios [f(complex):f-(NdCl3(aq))] associated with the 4I9/2 → 4G5/2, 2G7/2 absorption band (570-595 nm) exhibit hypersensitive behavior with respect to ligand type and solution pH. The variations observed in the ΔA spectra and in the oscillator strength ratios, with respect to both ligand type and solution pH, are rationalized in terms of ligand structure, ligand coordination properties, and ligand field geometry. Intensity calculations, based on a theoretical model for 4f → 4f electric dipole strengths, are carried out for a set of model structures assumed to be similar to those of several of the complexes studied experimentally. The results of these calculations are compared to the observed intensity data and are discussed in terms of spectra-structure correlations in the 4I9/2 → 4G5/2, 2G7/2 "hypersensitive" transition region.
Article
The transesterification of the 2-(4-nitrophenyl phosphate) ester of propylene glycol (1) was promoted by La3+, Nd3+, Eu3+, Gd3+, Tb3+, Yb3+, Lu3+, Pb2+, Zn2+, Cu2+, Ni2+, Co2+, Mn2+, Mg2+, and Ca2+ at 37-degrees-C in 0.01 M Hepes buffer (N-(2-hydroxy-ethyl)piperazine-N'-ethanesulfonic acid), pH 6.85. The ability of metal ions to promote transesterification of 1, as measured by apparent-second-order rate constants, followed the order Tb3+ > Gd3+ > Yb3+ > Eu3+ > Nd3+ > Pb2+ > Lu3+ > La3+ >> Cu2+ > Zn2+ >> Co2+ > Mn2+ > Ni2+ >> Mg2+ > Ca2+. The transesterification of 1 by La3+, Pb2+, Zn2+, Cu2+, Ni2+, Co2+, or Mn2+ exhibited saturation kinetics, consistent with the formation of a reactive metal ion complex with 1. Metal ion association constants (K) for formation of the metal-1 complex and a first-order catalytic rate constant (k(cat)) for decomposition of the metal-1 complex were determined for metal ions that showed saturation kinetics. K varied by only a factor of 5, whereas k(cat) varied by a factor of 29. Transesterification of 1 bound to Pb2+, La3+, Cu2+, Zn2+, Co2+, Mn2+, Ni2+ occurred 2.1 x 10(4), 1.4 x 10(4), 4.6 x 10(3), 3.6 x 10(3), 9.2 x 10(2), 7.7 x 10(2), or 7.7 x 10(2) times more rapidly, respectively, than the transesterification of free 1. Properties of metal ions that may affect their ability to promote transesterification of phosphate esters are discussed; these include the Lewis acidity of the metal ion, the formation of metal hydroxide complexes, metal ion radius, and stabilization of a hypervalent phosphorus (V) intermediate. These metal ion model studies are put in context with metal ion requirements in self-cleaving RNAs.
Article
Enormous rate accelerations are necessary to hydrolyze RNA (108-fold) or DNA (1017-fold) within minutes. There are three direct modes of activation that media ions can provide for hydrolyzing phosphate diesters. The rate accelerations due to Lewis acid activation (<102-fold), intramolecular nucleophile activation (108-fold), and leaving group activation (106-fold) may in some cases combine simply to give an overall rate acceleration in excess of 1016-fold; in other cases, greater cooperatively between the models of catalysis is possible. Double Lewis acid activation obtained by coordinating both phosphoryl oxygens of a phosphate diester to a variety of dinuclear metal complexes (Figures 2 and 3) can give far greater rate accelerations for the hydrolysis reaction (4 x 105-fold for a dinuclear Co(III) complex) than single Lewis acid activation (<102). This mode of activation is possible with an intermetal distance from 2.9 to 7.0 Å and is particularly useful for cleaving RNA efficiently. For DNA hydrolysis, double Lewis acid activation by itself is not enough for efficient cleavage as it is about 109 times more stable than RNA. The nucleophile activation (metal hydroxide, metal alkoxide, metal-bridging oxide, metal-bridging peroxide) is important for DNA hydrolysis but not for RNA cleavage as its 2'- OH group already acts as a highly efficient internal nucleophile (Figure 1). However, the metal-activated nucleophiles may in some cases act as general base catalysts in cleaving RNA. While all of the above-mentioned nucleophiles can cleave phosphates with good leaving groups, only metal hydroxides appear to cleave those with poor leaving groups. For the other nucleophiles to be effective (metal alkoxide, metal-bridging oxide, metal-bridging peroxide), leaving group activation (coordination of the poor leaving group oxygen to the metal) is required.
Article
Commercial glass electrodes have been compared both directly and indirectly with the deuterium gas electrode at 25° C in buffered solutions of pD from 1 to 13. It is confirmed that the glass electrode functions as well in heavy water as in ordinary water. The relation between the operational pH of a buffer solution in heavy water (obtained with a glass electrode stanardized in an ordinary water buffer solution) and its pD or pad value obtained from measurements on cells without liquid junction has been examined and correction factors determined for both glass and gas electrodes. The operational pH of buffer solutions in heavy water at 25° C, measured with the glass electrode, can be converted into a pD value by adding 0.41 (molar scale) or 0.45 (molal scale) for 2 < pD < 9.
Article
Non-enzymatic reagents that efficiently promote the hydrolytic cleavage of DNA currently receive much attention since they have many potential applications in molecular biology. This review focuses on recent progress in the hydrolysis of the phosphodiester backbone of DNA by metal ions and metal complexes. Pioneering work on the sequence-selective DNA scission by an artificial restriction enzyme, which is prepared by covalent attachment of a cerium(IV) complex to an antisense-deoxyoligonucleotide, is discussed.
Article
A comparison is made of a number of direct complexometric titrations previously published for the determination of yttrium and the lanthanons. Working and ‘optimum’ pH ranges are obtained for what are considered to be the best indicators. Alizarin Red S screened with Methylene Blue, Erioehrome Black T, Copper-Naphthyl Azoxine and Xylenol Orange. The precision and accuracy of the selected methods are determined by carrying out replicate titrations on standard solutions of ceriumIII, yttrium and ytterbium. The results, together with additional observations made on the behaviour of indicators in the different methods, suggest that Xylenol Orange at pH 5.8 to 6.4 is most satisfactory and convenient for direct titrations.ZusammenfassungEine Anzahl früher für die Bestimmung von Yttrium und den Lanthaniden publizierter direkter komplexometrischer Titrationsmethoden wurden verglichen. Die besten pH-Arbeitsbereiche für die wahrscheinlich besten Indikatoren, Alizarin S mit Methylenblau, Eriochromschwarz T, Cu-Naphthylazoxin und Xylenol-orange wurden aulgesucht. Genauigkeit und Richtigkeit der Methode wurden mit mehreren Titrationen an Standardlösungen von Cer(III), Yttrium und Ytterbium ermittelt. Die Ergebnisse sprechen zusammen mit weiteren Beobachtungen über das Verhalten von Indikaroten bei den verschiedenen Methoden dafür, daß Xylenolorange bei pH 5,8 bis 6,4 in direkten Titrationen am zufriedenstellendsten und bequemsten arbeitet.RésuméOn fait la comparaison des titrations complexométriques directes pour le dosage de l'yttrium et de les lanthanons. On décrit aussi les meillieures conditions ppur l'emploi des indicateurs choisies.
Article
The complexing properties (capacity, pH effect, breakthrough curve) of a chelating resin, containing bicine ligands, were investigated for La(III), Nd(III), Tb(III), Th(IV) and U(VI). Trace amounts of these metal ions were quantitatively retained on the resin and recovered by eluting with 1 M hydrochloric acid. The capacity of the resin for La(III), Nd(III), Tb(III), Th(IV) and U(VI) was found to be 0.35, 0.40, 0.42, 0.25 and 0.38 mmol g(-1), respectively. Separation of U(VI) and Th(IV) from Ni(II), Zn(II), Co(II) and Cu(II) in a synthetic solution was carried out.
Article
A new suite of 10 programs concerned with equilibrium constants and solution equilibria is described. The suite includes data preparation programs, pretreatment programs, equilibrium constant refinement and post-run analysis. Data preparation is facilitated by a customized data editor. The pretreatment programs include manual trial and error data fitting, speciation diagrams, end-point determination, absorbance error determination, spectral baseline corrections, factor analysis and determination of molar absorbance spectra. Equilibrium constants can be determined from potentiometric data and/or spectrophotometric data. A new data structure is also described in which information on the model and on experimental measurements are kept in separate files.
Article
Although there has been progress in developing artificial hydrolytic DNA cleaving agents, none of these has been shown to carry out the double-strand hydrolysis of DNA. We demonstrate that La(III) or Ce(IV) combined with the ligand 1,3-diamino-2-hydroxypropane-N,N,N', N'-tetraacetate (HPTA) in a 2 : 1 ratio can efficiently cleave supercoiled plasmid DNA at 55 degrees C within a 3-h period. Analysis of end-labeled restriction fragments cleaved by these complexes reveals 3'- and 5'-ends consistent with a hydrolytic mechanism. Unlike for other polydentate carboxylate complexes, plasmid DNA cleavage by La(2)(HPTA) or Ce(2)(HPTA) affords a significant amount of linear DNA with a considerable fraction of the supercoiled form still remaining. This result implies that La(2)(HPTA) and Ce(2)(HPTA) can carry out double-strand cleavage of plasmid DNA. La(2)(HPTA) and Ce(2)(HPTA) represent the first metal complexes demonstrated to be capable of double-strand hydrolytic cleavage of plasmid DNA.
Article
Lanthanide ions are remarkably effective catalysts for the hydrolytic cleavage of phosphate ester bonds, including the robust bonds of DNA. This makes Ln(III) and Ce(IV) ions attractive candidates for developing selective and efficient artificial nucleases, which could have many biochemical and clinical applications. Both small-molecule-based and biopolymer-based lanthanide complexes are being pursued.
Article
Potentiometric titrations of the mixtures of lanthanide(III) perchlorates and bis-Tris propane (BTP) reveal formation of dinuclear hydroxo complexes M2(BTP)2(OH)n(6-n), where M = La(III), Pr(III), Nd(III), Eu(III), Gd(III), and Dy(III) and n = 2, 4, 5, or 6, in the pH range 7-9. ESI-MS data confirm the presence of dinuclear species. Kinetics of the hydrolysis of bis(4-nitrophenyl) phosphate (BNPP), mono-4-nitrophenyl phosphate (NPP), and 4-nitrophenyl acetate (NPA) in the lanthanide(III)-BTP systems has been studied at 25 degrees C in the pH range 7-9. The second-order rate constants for the hydrolysis of BNPP by individual lanthanide hydroxo complexes have been estimated by using the multiple regression on observed rate constants obtained at variable pH. For a given metal, the rate constants increase with increasing in the number n of coordinated hydroxide ions. In a series of complexes with a given n, the second-order rate constants decrease in the order La > Pr > Nd > Eu > Gd > Dy. Hydrolysis of NPP follows Michaelis-Menten-type "saturation" kinetics. This difference in kinetic behavior can be attributed to stronger binding of NPP dianion than BNPP monoanion to the lanthanide(III) species. Activities of lanthanide complexes in the hydrolysis of NPA, which is 10(6) times more reactive than BNPP in alkaline or aqueous hydrolysis, are similar to those in BNPP hydrolysis indicating unique capability of lanthanide(III) cations to stabilize the transition state of phosphate diester hydrolysis. Results of this study are analyzed together with literature data for other metal cations in terms of the Brønsted correlation and transition state-catalyst complexation strength.
Article
Eu(III) complexes of 1,4,7,10-tetraazacyclododecane derivatives with mixed alcohol and amide pendent groups are more resistant to Eu(III) ion dissociation under most conditions than are analogous complexes containing all alcohol pendent groups. Pseudo-first-order rate constants for intramolecular phosphate diester transesterification by these complexes decrease with increasing number of amide pendent groups; however, reactions where the hydroxyalkyl group of the macrocyclic complex is itself a nucleophile proceed rapidly in macrocycles with mixed alcohol and amide pendent groups.
Article
The lanthanide ion based macrocyclic complexes 1.Ln mimic the hydrophobic nature of ribonucleases, where the lanthanide ions induce the formation of a hydrophobic cavity for 1, giving rise to a large order of magnitude enhancement in the hydrolytic cleavage of HPNP.
Article
Glycine and N,N-dimethylglycine stabilize La(III) hydroxide complexes of the type La2L2(OH)4 which possess phosphodiesterolytic activity close to that observed with most active tetravalent cations like Ce(IV).