Formation Of Water-soluble Complexes Research Articles

Experimental and computational investigation of complexing agents on copper dissolution for chemical mechanical polishing process

Complexing agents are important additives in chemical mechanical polishing (CMP) slurries, and they play key roles in the removal rate (RR) and surface quality of copper (Cu). However, it is a great challenge to clarify the complexing mechanism of Cu at the microscopic level. In this study, the effects of glycine (GLY), potassium tartrate (PT), and potassium citrate (CAK) on the RR and dissolution behavior of Cu are investigated. The results show that the complexing capability is in the order of GLY > PT > CAK. The complexing mechanism is elucidated by single-frequency electrochemical impedance spectroscopy, X-ray photoelectron spectroscopy, ultraviolet-visible spectrometer, density functional theory, and molecular dynamics simulation. Copper hydroxide (Cu(OH)2) on the Cu surface ionizes, giving rise to Cu2+ ions, which are attracted by negatively charged oxygen atoms of carboxylate groups in complexing agents, resulting in the formation of water-soluble complexes. This process destroys the integrity of the oxide layer on the Cu surface. Therefore, the oxide layer can be easily removed by a polishing pad. These findings provide significant theoretical guidance for the development of Cu CMP slurries in the microelectronics industry.

Formation of Water-Soluble Complexes from Fullerene with Biocompatible Block Copolymers Bearing Pendant Glucose and Phosphorylcholine.

Double-hydrophilic diblock copolymers, PMPC100-block-PGEMAn (M100Gn), were synthesized via reversible addition-fragmentation chain transfer radical polymerization using glycosyloxyethyl methacrylate and 2-(methacryloyloxy)ethyl phosphorylcholine. The degree of polymerization (DP) of the poly(2-(methacryloyloxy) ethylphosphorylcholine) (PMPC) block was 100, whereas the DPs (n) of the poly(glycosyloxyethyl methacrylate) PGEMA block were 18, 48, and 90. Water-soluble complexes of C70/M100Gn and fullerene (C70) were prepared by grinding M100Gn and C70 powders in a mortar and adding phosphate-buffered saline (PBS) solution. PMPC can form a water-soluble complex with hydrophobic C70 using the same method. Therefore, the C70/M100Gn complexes have a core-shell micelle-like particle structure possessing a C70/PMPC core and PGEMA shells. The maximum amounts of solubilization of C70 in PBS solutions using 2 g/L each of M100G18, M100G48, and M100G90 were 0.518, 0.358, and 0.257 g/L, respectively. The hydrodynamic radius (Rh) of C70/M100Gn in PBS solutions was 55-75 nm. Spherical aggregates with a similar size to the Rh were observed by transmission electron microscopy. When the C70/M100Gn PBS solutions were irradiated with visible light, singlet oxygen was generated from C70 in the core. It is expected that the C70/M100Gn complexes can be applied to photosensitizers for photodynamic therapy treatments.

Effect of Structural Features of Pectin on Its Complexation with Lysozyme

The interaction between lysozyme (Lys) and pectins with different net and local charges and with block (BD) and random (RD) distributions of methoxyl groups is studied via dynamic light scattering, turbidimetry, high-resolution optical microscopy, and electrophoretic mobility measurements. RD 16.2, RD 38.2, BD 16.9, and BD 33.1 form water-soluble complexes at pH 5.1, ionic strength I = 0.01, and q 3 × 10–3. The corresponding parameters for RD 66.5 and BD 68.2 are higher: q ≅ 3 × 10–3 up to q ≅ 0.01, and q higher than 0.01. Optical microscopy shows that the complexes between Lys and BDs are large (15–20 μm) for all studied values of the degree of methoxylation (DM), while the average size of RD-based complexes is substantially lower (from 0.6 to 3 μm) and depends on the DM. The BD-based complexes have a gel-like morphology irrespective of the DM, whereas particles of RD-based complex have the form of both coacervate drops and gel-like particles, depending on the DM. The threshold value for ionic strength Iset above which Lys does not form complexes with RD and BD is found to be 0.11. That being so, the values for Iset and pHset for the BD/Lys systems are independent of the pectin DM, while for the RD/Lys systems these parameters diminish considerably with an increase in the DM. The dependence of complexation of Lys and pectin on I has a non-monotonic character with a maximum at I = 0.03 and 0.06 for RD and BD, respectively. Our understanding of the effect that the total charge of a pectin molecule and its distribution along the chain has on the complexation of pectin and a protein is important for our ability to predict the stability of the food product structure.

Dependence of the interaction mechanisms between L-serine and O-phospho-L-serine with calcium hydroxyapatite and copper modified hydroxyapatite in relation with the acidity of aqueous medium.

Motivated by the role of copper ions in biological processes the aim of this study was to elucidate the impact of copper ions bound to hydroxyapatite on L-serine (L-Ser) and O-phospho-L-serine (O-Ph-L-Ser) adsorption at different acidity of aqueous solutions. The adsorption phenomenon was studied by FTIR, UV, and AA spectroscopy, XRD and thermal analysis methods together with the evolved gases analysis taking into consideration the ionic state of the amino acids as well as the apatite surface state, which are tightly correlated with the solution pH. In acidic solution, the main process involves apatite dissolution releasing calcium and copper ions. At pH > 5 the complexation of amino acids with Ca2+ or Cu2+ ions is more important leading also to the release of cations. The ability of copper ions to form water soluble complexes with L-Ser and O-Ph-L-Ser leads to an important loss of these ions, while calcium release is very low at this pH. Therefore, the use of copper ions substituting calcium in the apatite structure to enhance the ability of amino acids adsorption on the apatite surface seems problematic even at pH > 5.

Synthesis of task-specific ionic liquids with grafted diglycolamide moiety. Complexation and stripping of lanthanides

Task-specific ionic liquids (TSILs) of a novel class, with the diglycolamide moietity grafted in the alkyl chain of imidazolium cation, were synthesized and characterized. Lanthanide complexation capabilities of TSILs as active components of solid phase extractants were evaluated by studies on the adsorption of lanthanides from aqueous solutions. The TSIL-based solid adsorbents prepared by immobilization of long-alkyl-chain TSILs in siliceous mesostructured cellular foams adsorb trivalent lanthanides. No extraction of lanthanides from aqueous solution into 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C6mim][Nf2T]) was observed at any acidity in the presence of these TSILs in the aqueous phase. This implies that TSILs suppress the extraction of lanthanides by formation of water-soluble complexes. The TSILs added to solvent extraction systems consisting of N,N,N′,N′-tetraoctyl-3-oxapentanediamide (TODGA) in [C6mim][Nf2T] and aqueous HNO3 solutions show very good stripping properties for lanthanides.

Dissolution and Protection of Aluminium Oxide in Corrosive Aqueous Media—An Ellipsometry and Reflectometry Study

Dissolution of alumina has been studied from wafers in aqueous solution by means of ellipsometry and reflectometry. It was discovered that the dissolution of aluminium oxide is promoted by ethanol amines like N,N-bis(2-hydroxyethyl)glycine and triethanolamine, and that this dissolution is retarded by sodium dodecyl sulphate (SDS) and stopped by sodium dodecyl phosphate (SDP). The protective property of SDP to alumina is in perfect agreement with earlier found results which showed that SDP efficiently hinders the oxidation of aluminium pigment flakes in alkaline aqueous solution. Ethanol amines are used to regulate the pH in waterborne paints and printing ink formulations. However, the aggressive properties of ethanol amines to alumina are a problem for these kinds of formulations. This may be attributed to the formation of water soluble complexes between ethanol amines and Al(III). To increase the shelf life of aluminium pigments in waterborne formulations in the future, the ethanol amines then need to be replaced by other, less aggressive, bases if possible.

Recovery of nickel from aqueous samples with water-soluble carboxyl methyl cellulose–acetone system

A simple and efficient method, which involves carboxyl methyl cellulose (CMC) and acetone, was developed for recovery of trace nickel from aqueous solutions. This method was based on the fact that Ni 2+ could react with CMC and form water-soluble complexes, which would solidify in excess acetone. After centrifugation, the solid mass consisting of the nickel complex and free CMC was easily dissolved with water and the nickel was determined by flame atomic absorption spectrometry (FAAS). Several factors influencing the recovery of nickel were thoroughly investigated and the optimized conditions were as follows: 5.00 mL water sample, 0.50 mL 0.5% CMC, 1.00 mL of 3.0 mg mL −1 KNO 3 and 20 mL acetone. Under the optimized conditions, the loading capacity of CMC for nickel was 20.6 mg Ni/g polymer. The linear range was 0.025–3.0 μg mL −1, the limit of detection was 0.019 μg mL −1 and the pre-concentration factor was 4. Ni(II) can be well recovered in this CMC–acetone system from binary ions mixtures containing Zn(II), Ba(II), Ca(II), Mo(VI), Co(II), Cd(II), Mg(II), Mn(II) and Cr(III). The developed method had been applied to the recovery of trace nickel in water samples with satisfactory results. A possible mechanism for the nickel precipitate was proposed. The efficient, convenient and affordable method provides an alternative method for the recovery of nickel from environmental waters.

Electrostatic Interactions between a Protein and Oppositely Charged Micelles

Micellar solutions made of a fully fluorinated surfactant, LiPFN, form water-soluble complexes with lysozyme in a wide concentration range. Such complexes are stabilized by electrostatic and, very presumably, double-layer interactions. The mixtures were investigated by combining electrophoretic mobility, DLS, and dielectric relaxation methods. The former gives information on the surface charge density of protein-micelle complexes and indicates that the resulting adducts retain a negative charge (i.e., charge neutralization is incomplete). The double-layer thickness of proteins, micelles, and protein-micelle complexes is also connected to the dielectric relaxation frequency. Changes in particle size (inferred by DLS), charge density, and double-layer thickness are closely interrelated to each other. A model was developed to quantify such properties.

Role of combined administration of Tiron and glutathione against aluminum-induced oxidative stress in rat brain

The current study was carried out to investigate the potential role of 4,5 dihydroxy benzene 1,3 disulfonic acid di sodium salt (Tiron) and glutathione (GSH) either individually or in combination against aluminum (Al)-induced toxicity in Wistar rats. Animals were exposed to aluminum chloride at a dose of 172.5 mg/kg/d orally for 10 weeks. Tiron and GSH were administered at a dose of 471-mg/kg/d i.p. and 100 mg/kg/d orally, respectively, for 7 consecutive days. Tiron is a diphenolic chelating compound which forms water soluble complexes with a large number of metal ions. Induction of oxidative stress was recorded in brain and serum after Al exposure. Significant decrease was recorded in reduced glutathione (GSH), glutathione reductase (GR), glutathione peroxidase (GP x ), catalase (CAT), superoxide dismutase (SOD), acetyl cholinesterase (AChE) and an increase was observed in thiobarbituric acid reacting substance (TBARS) and glutathione- S-transferase (GST) in brain and serum. Most of the above parameters responded positively to individual therapy with Tiron, but more pronounced beneficial effects on the above-described parameters were observed when Tiron was administered in combination with GSH. Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES) studies also showed significantly high concentration of Al in brain and blood. Tiron was slightly more effective then GSH in reducing the concentration of Al from the brain and blood, however, no further improvement was recorded when Tiron was administered in combination with GSH in reducing the concentration of Al.

Hydrolysis of fluid supported membrane islands by phospholipase A 2: Time-lapse imaging and kinetic analysis

The activity of phospholipase A 2 (PLA 2) which catalyzes the hydrolysis of phospholipids into free fatty acids and lysolipids, depends on the structure and thermodynamic state of the membrane. To further understand how the substrate conformation correlates with enzyme activity, model systems that are based on time-resolved membrane microscopy are needed. We demonstrate a methodology for preparing and investigating the dynamics of fluid supported phospholipid membranes hydrolyzed by snake venom PLA 2. The method uses quantitative analysis of time-lapse fluorescence images recording the evolution of fluid bilayer islands during hydrolysis. In order to minimize interactions with the support surface, we use double bilayer islands situated on top of a complete primary supported membrane prepared by hydration of spincoated lipid films. Our minimal kinetic analysis describes adsorption of enzyme to the membrane in terms of the Langmuir isotherm as well as enzyme kinetics. We use two related models assuming hydrolysis to occur either at the perimeter or at the surface of the membrane island. We find that the adsorption constant is similar for the two cases, while the estimated turnover rate is markedly different. The PLA 2 concentration series is measured in the absence and presence of β-cyclodextrin which forms water soluble complexes with the reaction products. The results demonstrate the versatility of double bilayer islands as a membrane model system and introduces a new method for quantifying the kinetics of lipase activity on membranes by directly monitoring the evolution in substrate morphology.

Water-Soluble Complexes Formed by Natural Polyphenols and Bovine Serum Albumin: Evidence from Gel Electrophoresis

The formation of water-soluble complexes from combinations of various polyphenols and bovine serum albumin (BSA) was analyzed by gel electrophoresis. Sodium dodecylsulfate (SDS) and native polyacrylamide gel electrophoretic (PAGE) analyses clearly showed complexes formed from BSA with oenothein B, corilagin, (+)-catechin, procyanidin B3, and gallic acid derivatives; however, it was difficult to distinguish between the complexes containing a single BSA molecule and the BSA molecule itself by using size-exclusion chromatography (SEC). Combining SDS and native PAGE analyses showed instability in the macromolecular complexes formed from pentagalloylglucose (PGG) and BSA. Research also revealed that the oxidation of (-)-epigallocatechin gallate (EGCG) contributed to the formation of more stable macromolecular complexes from EGCG and BSA.

Acceleration of Enzymatic Reaction of Trypsin through the Formation of Water-Soluble Complexes with Poly(ethylene glycol)-block-Poly(α,β-aspartic acid)

The amidase activity of bovine pancreas trypsin in water-soluble complexes with poly(ethylene glycol)-block-poly(alpha,beta-aspartic acid) (PEG-PAA) was evaluated by a colorimetric assay using L-lysine p-nitroanilide as a substrate. The enzymatic reaction of trypsin was accelerated through the complexation with PEG-PAA. By determining the kinetic parameters of the enzymatic reaction of trypsin, it was confirmed that the catalytic rate constant of the complexed trypsin was 15 times higher than that of the native trypsin. From the evaluation of pH dependence of initial reaction rate, it was indicated that this acceleration was induced by a stabilization of the imidazolium ion of the His residue in the catalytic site, the Asp-His-Ser triad, of trypsin due to the Asp units of PEG-PAA. The hydrogen bonded Asp-His pairs are critical constituents in several key enzymatic reactions including serine protease and apurinic endonucleases, and it was expected that the acceleration of the catalytic reaction might occur for other enzymes by the formation of water-soluble complexes with PEG-PAA.

Removal of copper, chromium, and arsenic from CCA-C treated wood by EDTA extraction

Ethylenediaminetetracetic acid (EDTA) is one of the most common chelators used to bind the metal ions in extremely stable complexes in heavy metal contaminated soils and thus to remediate such substrates. EDTA forms water soluble complexes with many metal ions and it is used to release the various metals. In this study, EDTA extraction of copper, chromium, and arsenic from chromated copper arsenate (CCA-C) treated wood was evaluated using batch leaching experiments. CCA-treated wood samples were extracted with eight different concentrations of EDTA for 4, 8, 18, and 24 h at room temperature. Exposing CCA-treated chips and sawdust to EDTA extraction enhanced removal of CCA components compared with extraction by deionized water. Grinding CCA-treated wood chips into 40-mesh sawdust provided greater access to and removal of CCA components. Extraction with 1% EDTA solution for 24 h removed 60% copper, 13% chromium, and 25% arsenic from treated chips. EDTA extraction of treated sawdust samples resulted in 93% copper, 36% chromium, and 38% arsenic removal. CCA leaching from treated wood blocks was also evaluated according to modified AWPA E11-99 standard test method of determining the leachability of wood preservatives. Leaching of CCA components from treated wood blocks with 1% EDTA solution for 14 days caused more copper leaching compared to leaching with deionized water. Leaching with 1% EDTA for 14 days removed 53% copper from the blocks whereas 14% copper was leached from the blocks with deionized water. The results suggest that EDTA extraction removes significant quantities of copper from CCA-treated wood. Thus, EDTA could be important in the remediation of wood waste treated with the newest formulations of organometalic copper compounds and other water-borne wood preservatives containing copper.

Colloidal Regularities of the Interaction between Uranium(VI) and the Cells of Metal-Resistant Bacillus cereus AUMC 4368 Bacterial Culture

Sorption of uranium(VI) by the cells of metal-resistant Bacillus cereus AUMC 4368 bacterium was studied in aqueous solutions as a function of pH, equilibrium concentration of metal, and the presence of co-ions with account of the changes in phase state of metals and biocolloids. Experimental data indicate that the sorption of uranium(VI) by negatively charged biocolloids is maximal at pH 4.2–4.5 (1.2 mM per 1g of dry biomass), when metal is present in the form of positively charged hydroxocomplexes. At pH ≥ 8, the interaction between uranium(VI) and the cells is inhibited due to the formation of negatively charged water-soluble hydroxocarbonate complexes and uranate ions. Co, Sr, Cu, Ca, Mg, and Zn ions do not influence the efficiency of sorption of uranium(VI) in a weakly acidic medium, but can cause inhibiting effect in neutral pH region. The most pronounced effect expressed in broadening of sorption range and in the heterocoagulation of uranyl is observed in the presence of Fe3+ ions. It was established that the binding of uranium(VI) occurs by the carboxyl surface groups of Bacillus cereuscell surface. Uranium(VI) is irreversibly bound by the carboxyl groups of cell surface and its efficient desorption is possible only during the interaction with citric acid or sodium hydrocarbonate with the formation of water-soluble complexes transferred to aqueous phase. It was shown that uranyl in the form of organocomplexes (citric, humatic, and fulvatic) is not sorbed by biocolloids.

1,1′-Binaphthyl substituted calixresorcinols–methyl red complexes: receptors for optical saccharide sensing

Novel 1,1′-binaphthyl substituted calixresorcinols ( 1 and 2 ) were synthesized. Macrocycles 1 and 2 form water-soluble complexes with methyl red 3 , which are, in turn, able to bind saccharides by a competition process in aqueous media and which exhibit color transitions during titration. Preferential binding of oligosaccharides compared to monosaccharides was found. The association constants of effectively bound oligosaccharides in aqueous media varied around 10 3 M −1.

Hydrophilic Actinide Complexation Studied By Solvent Extraction Radiotracer Technique

Actinide migration in the ground is enhanced by the formation of water soluble complexes between the actinide ions ( central atoms) and inorganic and/or organic complex formers ( ligands) dissolved in the ground water. It is essentia! to risk analysis of a wet repository to know the concentration of the central atoms and the ligands in the ground water, and the stability of the complexes formed between them (the complex formation constant) from such data the concentration of all dissolved actinide species can be calculated, and-using additional data on sorption, diffusion, and ground water flow rate-the migration rate of the actinides in the ground can be predicted. The important actinides in nuclear waste are U, Np, Pu and Am, all radioactive and with half-lives long enough to allow the determination of their macroscopic properties, usually at> 10ninus7M. However, when dissolved in nature, their concentrations are hardly macroscopic; typical concentration values are<10ninus7 M ( trace concentrations) Because the chemical behavior at trace concentrations often differ from that at macro concentrations (for example polynuclear complex formation), it is important to know the chemical behavior of actinides at trace concentrations in the ground water. One method commonly used for such investigations is the solvent extraction radiotracer ( SXRT) technique, by which the radioactive properties of the actinides are used for their detection. This report describes the SXRT technique in some detail. A particular reason for this analysis is the claim that complex formation constants obtained by the SXRT technique differs even at same actinide concentration, or are less reliable than results obtained by alternative techniques. It is true that several difficulties are encountered in the application of the SXRT technique to actinide solutions, as for example redox instability, hydrophilic complexation by side reactions and sorption, but it is also shown that a careful application of the SXRT technique yields results as reliable as by any other technique. The report contains a literature survey on solvent extraction studies of actinide complexes formed in aqueous solutions, particularly by using the organic reagent thenoyltrifluoroacetone (TTA) dissolved in benzene or chloroform (Tab. I). Hydrolysis constants obtained by solvent extraction are listed in Table IX. The last two tables contain all actinide complexes studied by SX with inorganic ligands (Tab. XI) and with organic ligands (Tab. XII).

HYDROPHILIC ACTINIDE COMPLEXATION STUDIED BY SOLVENT EXTRACTION RADIOTRACER TECHNIQUE

Abstract Actinide migration in the ground is enhanced by the formation of water soluble complexes between the actinide ions ( central atoms) and inorganic and/or organic complex formers ( ligands) dissolved in the ground water. It is essentia! to risk analysis of a wet repository to know the concentration of the central atoms and the ligands in the ground water, and the stability of the complexes formed between them (the complex formation constant) from such data the concentration of all dissolved actinide species can be calculated, and-using additional data on sorption, diffusion, and ground water flow rate-the migration rate of the actinides in the ground can be predicted. The important actinides in nuclear waste are U, Np, Pu and Am, all radioactive and with half-lives long enough to allow the determination of their macroscopic properties, usually at> 10ninus7M. However, when dissolved in nature, their concentrations are hardly macroscopic; typical concentration values are<10ninus7 M ( trace concentrat...

Synthesis of water soluble DTPA complexes with pendant uracil moieties capable of forming complementary hydrogen bonds

Two new DTPA (diethylenetriaminepentaacetic acid) functionalised bis(amides) with pendant uracil moieties have been synthesised from the condensation reaction between DTPA bis(anhydride) and 5-aminouracil or 5,6-diaminouracil. These ligands are representative of an increasing number of ligands capable of forming triple hydrogen bonds with complementary organic bases. However, these ligands are unusual since they form water soluble complexes with a variety of metal ions. In this paper, the syntheses of the two DTPA-uracil ligands, seven metal complexes and the crystal structure of the bismuth complex of DTPA bis(4,5-diamino-6-hydroxy-2-mercaptopyrimidine) L1 are reported. The most important feature of this solid state structure is that the two arms on which the uracil moieties are situated have a high degree of rotational freedom and this allows these groups to form multiple hydrogen bonds involving both uracil moieties on one side of the molecule.

EPR spin probe and spin label studies of some low molecular and polymer micelles

The rotational mobility of spin probes of different shape and size in low molecular and polymer micelles has been studied. Several probes having nitroxide fragment localized either in the vicinity of micelle interface or in the hydrocarbon core have been used. Upon increasing the number of carbon atoms in hydrocarbon chain of detergent from 7 to 13 (sodium alkyl sulfate micelles) or from 12 to 16 (alkyltrimethylammonium bromide micelles) the rotational mobility of spin probes is decreased by the factor 1.5–2.0. The spin probe rotational mobility in polymer micelles (the complexes of alkyltrimethylammonium bromides and polymethacrylic or polyacrylic acids) is less than mobility in free micelles of the same surfactants. The study of EPR-spectra of spin labeled polymethacrylic acid (PMA) indicated that formation of water soluble complexes of polymer and alkyltrimethylammonium bromides in alkaline solutions (pH 9) does not affect the polymer segmental mobility. On the other hand, the polymer complexes formation in slightly acidic water solution (pH 6) breaks down the compact PMA conformation, thus increasing the polymer segmental mobility. Possible structures of polymer micelles are discussed.

Interaction between Mo(VI) and siderophore models in aqueous solution

A series of dihydroxamic acids (HORNOC-(CH 2) n -CONROH, where if R=H– then n=2,5–7 and if R=CH 3– then n=4,5) and two new dihydroxamate-based siderophore models, hexanedioic acid bis (3-hydroxycarbamoyl-methyl)amide (DhaI) and hexanedioic acid bis(3-hydroxycarbamoyl-propyl)amide (DhaII) have been characterized in terms of chelating properties toward molybdenum(VI). For comparison, the molybdenum(VI)–acetohydroxamic acid (Aha) and molybdenum(VI)–aminohydroxamic acid systems have also been studied. Potentiometric and spectrophotometric studies at ionic strength of 0.2 mol/dm 3 (KCl) and at 25 ∘C have been performed and the equilibrium constants have been determined. It has been found, that of the dihydroxamic acids, only the DhaI and DhaII form water soluble complexes with molybdenum(VI). Polynuclear complexes most probably precipitate with the other dihydroxamic acids. Complexes are formed up to ca. the neutral pH in all systems. Above this pH MoO 4 2− and the free ligands exist. Although, very stable complexes are formed especially with DhaII, none of the studied ligands form a single bis(hydroxamato)dioxomolybdenum(VI) species. Mono(hydroxamato)trioxomolybdenum(VI) species are also formed, containing the uncoordinated moiety of the DhaI or DhaII in its protonated form. Out of aminohydroxamic acids, the β-alaninehydroxamic acid ( β-Alaha) shows “Aha-like” coordination properties as the glutamic acid- γ-hydroxamic acid (Glu- γ-ha) does. The small differences with this latter ligand are possibly due to weak coordination of the carboxylate which makes the mono(hydroxamato)trioxomolybdenum(VI) species more stable and the uncoordinated carboxylates in bis(hydroxamato) dioxomolybdenum(VI) can protonate below pH 3. The tridentate coordination mode of aspartic acid- β-hydroxamic acid (Asp- β-ha) via the hydroxamate and carboxylate oxygens results in the formation of a dinuclear complex, [Mo 2O 5(LH) 2] 2− in addition to [MoO 3(LH)] − (the protons are on the amino groups) in the pH-range 2.5–7.0.