Ligand Buffer Research Articles

Electron‐Donating Conjugation Effect Modulated Zn2+ Reduction Reaction for Separator‐Free Aqueous Zinc Batteries

AbstractZinc‐based aqueous batteries (ZABs) are attracting extensive attention due to the low cost, high capacity, and environmental benignity of the zinc anode. However, their application is still hindered by the undesired zinc dendrites. Despite Zn‐surface modification being promising in relieving dendrites, a thick separator (i.e. glass fiber, 250–700 μm) is still required to resist the dendrite puncture, which limits volumetric energy density of battery. Here, we pivot from the traditional interphase plus extra separator categories, proposing an all‐in‐one ligand buffer layer (ca. 20 μm) to effectively modulate the Zn2+ transfer and deposition behaviors proved by in situ electrochemical digital holography. Experimental characterizations and density functional theory simulations further reveal that the catechol groups in the buffer layer can accelerate the Zn2+ reduction reaction (ZRR) through the electron‐donating p‐π conjugation effect, decreasing the negative charge in the coordination environment. Without extra separators, the elaborated system endows low polarization below 28.2 mV, long lifespan of 4950 h at 5 mA cm−2 in symmetric batteries, and an unprecedented volumetric energy density of 99.2 Wh L−1 based on the whole pouch cells. The concomitantly “separator‐free” and “dendrite‐free” conjugation effect with an accelerated ZRR process could foster the progression of metallic anodes and benefit energetic aqueous batteries.

Electron-Donating Conjugation Effect Modulated Zn2+ Reduction Reaction for Separator-Free Aqueous Zinc Batteries.

Zinc-based aqueous batteries (ZABs) are attracting extensive attention due to the low cost, high capacity, and environmental benignity of the zinc anode. However, their application is still hindered by the undesired zinc dendrites. Despite Zn-surface modification being promising in relieving dendrites, a thick separator (i.e. glass fiber, 250-700 μm) is still required to resist the dendrite puncture, which limits volumetric energy density of battery. Here, we pivot from the traditional interphase plus extra separator categories, proposing an all-in-one ligand buffer layer (ca. 20 μm) to effectively modulate the Zn2+ transfer and deposition behaviors proved by in situ electrochemical digital holography. Experimental characterizations and density functional theory simulations further reveal that the catechol groups in the buffer layer can accelerate the Zn2+ reduction reaction (ZRR) through the electron-donating p-π conjugation effect, decreasing the negative charge in the coordination environment. Without extra separators, the elaborated system endows low polarization below 28.2 mV, long lifespan of 4950 h at 5 mA cm-2 in symmetric batteries, and an unprecedented volumetric energy density of 99.2 Wh L-1 based on the whole pouch cells. The concomitantly "separator-free" and "dendrite-free" conjugation effect with an accelerated ZRR process could foster the progression of metallic anodes and benefit energetic aqueous batteries.

Development of a biological protocol for endotoxin detection using quartz crystal microbalance (QCM).

In this paper, a biological protocol for endotoxin detection has been developed and optimized by quartz crystal microbalance (QCM). The parameters involved in the formation of the self-assembled monolayer (SAM) have been analyzed, and a study of the pH of the ligand buffer has been performed in order to find the best condition for the ligand immobilization and, in consequence, for the endotoxin detection. The detection limit obtained with the characterized biological protocol corresponds to 1.90 μg/ml. The effectiveness of the optimized biological protocol has been analyzed by cyclic voltammetry analysis.

Specific Activation of the G Protein-coupled Receptor BNGR-A21 by the Neuropeptide Corazonin from the Silkworm, Bombyx mori, Dually Couples to the Gq and Gs Signaling Cascades

Corazonin, an undecapeptide neurohormone sharing a highly conserved amino acid sequence across Insecta, plays different physiological roles in the regulation of heart contraction rates, silk spinning rates, the induction of dark color and morphometric phase changes, and ecdysis. Corazonin receptors have been identified in Drosophila melanogaster, Manduca sexta, and Musca domestica. However, detailed information on the signaling and major physiological functions of corazonin and its receptor is largely unknown. In the current study, using both the mammalian cell line HEK293 and insect cell lines BmN and Sf21, we paired the Bombyx corazonin neuropeptide as a specific endogenous ligand for the Bombyx neuropeptide G protein-coupled receptor A21 (BNGR-A21), and we therefore designated this receptor as BmCrzR. Further characterization indicated that synthetic BmCrz demonstrated a high affinity for and activated BmCrzR, resulting in intracellular cAMP accumulation, Ca(2+) mobilization, and ERK1/2 phosphorylation via the Gq- and Gs-coupled signaling pathways. The direct interaction of BmCrzR with BmCrz was confirmed by a rhodamine-labeled BmCrz peptide. Moreover, experiments with double-stranded RNA and synthetic peptide injection suggested a possible role of BmCrz/BmCrzR in the regulation of larval growth and spinning rate. Our present results provide the first in-depth information on BmCrzR-mediated signaling for further elucidation of the BmCrz/BmCrzR system in the regulation of fundamental physiological processes.

Stereospecific Proton Transfer by a Mobile Catalyst in Mammalian Fructose-1,6-bisphosphate Aldolase

Class I fructose-1,6-bisphosphate aldolases catalyze the interconversion between the enamine and iminium covalent enzymatic intermediates by stereospecific exchange of the pro(S) proton of the dihydroxyacetone-phosphate C3 carbon, an obligatory reaction step during substrate cleavage. To investigate the mechanism of stereospecific proton exchange, high resolution crystal structures of native and a mutant Lys(146) --> Met aldolase were solved in complex with dihydroxyacetone phosphate. The structural analysis revealed trapping of the enamine intermediate at Lys(229) in native aldolase. Mutation of conserved active site residue Lys(146) to Met drastically decreased activity and enabled trapping of the putative iminium intermediate in the crystal structure showing active site attachment by C-terminal residues 360-363. Attachment positions the conserved C-terminal Tyr(363) hydroxyl within 2.9A of the C3 carbon in the iminium in an orientation consistent with incipient re face proton transfer. We propose a catalytic mechanism by which the mobile C-terminal Tyr(363) is activated by the iminium phosphate via a structurally conserved water molecule to yield a transient phenate, whose developing negative charge is stabilized by a Lys(146) positive charge, and which abstracts the C3 pro(S) proton forming the enamine. An identical C-terminal binding mode observed in the presence of phosphate in the native structure corroborates Tyr(363) interaction with Lys(146) and is consistent with transient C terminus binding in the enamine. The absence of charge stabilization and of a mobile C-terminal catalyst explains the extraordinary stability of enamine intermediates in transaldolases.

High Sensitive and Selective Spectrophotometric Determination of Aluminium after Collection on a Membrane Filter Using 2,3‐Dichloro‐6‐(3‐carboxy‐2‐hydroxy‐1‐naphthylazo)quinoxaline and Zephiramine

A high sensitive and selective spectrophotometric method for the determination of aluminium(III) using 2,3‐dichloro‐6‐(3‐carboxy‐2‐hydroxy‐1‐naphthylazo)quinoxaline (DCHNAQ) and zephiramine (zeph) is described. The formed ion pair precipitate between zephiramine and perchlorate ions is effective for the enrichment of aluminium(III) on a membrane filter as its ternary complex with DCHNAQ and zephiramine. The solid–state absorbance of the complex on the membrane filter is measured at 655 nm against a blank thin layer and the difference is calculated. The colour system obeys Beer's law from 5.0–150 ng ml−1 of aluminium. The detection and quantification limits were calculated. The relative standard deviation for 60 ng of aluminium(III) in 20‐ml sample volume amounts 0.84% (n=10). A ligand buffer solution, composed of transcyclohexane‐1,2‐diaminetetraacetic acid with an excess of zinc(II), is effective for masking interferences from foreign ions, particularly iron(III). The proposed method was applied successfully to tap and environmental water, biological (human blood, urine, and gallstone), and soil samples.

On-line solid-phase extraction and multisyringe flow injection analysis of Al(III) and Fe(III) in drinking water

A new analytical method was developed for on-line monitoring of residual coagulants (aluminium and iron salts) in potable water. The determination was based on a sequential procedure coupling an extraction/enrichment step of the analytes onto a modified resin and a spectrophotometric measurement of a surfactant-sensitized binary complex formed between eluted analytes and Chrome Azurol S. The optimization of the solid phase extraction was performed using factorial design and a Doehlert matrix considering six variables: sample percolation rate, sample metal concentration, flow-through sample volume (all three directly linked to the extraction step), elution flow rate, concentration and volume of eluent (all three directly linked to the elution step). A specific reagent was elaborated for sensitive and specific spectrophotometric determination of Al(III) and Fe(III), by optimizing surfactant and ligand concentrations and buffer composition. The whole procedure was automated by a multisyringe flow injection analysis (MSFIA) system. Detection limits of 4.9 and 5.6 microg L(-1) were obtained for Al(III) and Fe(III) determination , respectively, and the linear calibration graph up to 300 microg L(-1) (both for Al(III) and Fe(III)) was well adapted to the monitoring of drinking water quality. The system was successfully applied to the on-site determination of Al(III) and Fe(III) at the outlet of two water treatment units during two periods of the year (winter and summer conditions).

Hepatic SR-BI-mediated cholesteryl ester selective uptake occurs with unaltered efficiency in the absence of cellular energy

Scavenger receptor class B type I (SR-BI) plays a critical role in the delivery of HDL cholesterol and cholesteryl esters (CEs) to liver and steroidogenic tissues by a selective process that does not result in significant degradation of HDL protein. Recently, SR-BI-mediated endocytosis and recycling of HDL have been demonstrated. However, it remains unclear whether efficient SR-BI-mediated selective uptake occurs strictly at the plasma membrane or at additional sites along its endocytic itinerary. To examine the requirement for SR-BI endocytosis in HDL selective uptake, we determined the effects of energy depletion on the levels of cell-associated HDL protein and CE in primary mouse hepatocytes. Compared with CHO cells, we observed a much larger energy-dependent effect on CE uptake in primary mouse hepatocytes. Although varying the levels of caveolin-1 and carboxyl ester lipase altered the efficiency of selective uptake, neither was able to account for the energy-dependent component of HDL-CE uptake. Finally, we demonstrate that the hepatocyte-specific, energy-dependent effects on HDL-apolipoprotein A-I and -CE uptake are independent of SR-BI and are not required to achieve efficient SR-BI-mediated selective uptake of CE. Together, these data support the conclusion that neither the intracellular trafficking of HDL nor any energy-dependent cellular process affects the ability of the cell to maximally acquire CE through SR-BI-mediated selective uptake from HDL.

Selective Spectrophotometric Determination of Aluminium in the Presence of Beryllium and Lanthanide Cations

A spectrophotometric method for the selective determination of Al(III) in the presence of Be and lanthanide cations is proposed. It is based on the selective reaction of Semi-Xylenol Orange with Al(III) at pH 2.6. The presence of 8% v/v of 1,2- ethanediol serves to stabilize the chelate formed by heating for 5 min at 100 °C. 0.5 mg each of Be(II), Ce(III), La(III), 4 mg of Mn(II), 1.2 mg of Pb(II), 1 mg of Tl(I), 40 mg each of Ca(II) and Mg(II) and 1.9 mg of sodium dihydrogen phosphate are tolerable. A ligand buffer of HEDTA-Pb is incorporated to further enhance the selectivity of the color reaction. Under the specified condition Semi-Xylenol Orange reacts with Al(III) to form a 1:1 chelate, its molar absorptivity at 526 nm was found to be 3.3 × 104 L mol−1 cm−1. The linear regression equation for 2–20 µg of Al(III) is A = 0.04458C + 0.0112 (here C stands for the concentration of Al(III), µg per 25 mL), and correlation coefficient γ = 0.9988. The RSD at a level of 10 µg (n = 10) and LOQ were found to be 3.5% and 2 µg respectively.

Electron transfer. 138. Potentials involving chelated chromium(V)

The bis(chelated) complex of CrV(0) derived from the dianion (L2 −) of 2-ethyl-2-hydroxybutanoic acid is readily reduced to a bis(chelate of CrIII, featuring the monoanion (LH−) [Cr V(0)(L2−)2]−+4H++H2O+2e−→[CrIII(OH2)2(LH− 2]+ of this acid. Potentials estimated by Ghosh in 1993 for this 2e− change, E0 (pH 0) 1.32 V, Eeff (pH 3.3) 0.93 V, are in accord with the nearly irreversible reductions of the Cr(V) species (in 1∶1 ligand buffer) by Fe2+, V02+, IrCl6 3 − and I−, whereas lower values reported by Bose in 1996, E0 (pH 0) 0.84 V, Eeff (pH 3.3) 0.45 V, are potentiometrically inconsistent with these conversions. A similar discrepancy is noted for potentials for Cr(V,IV) estimated in 1996, E0 (pH 0) 0.84 V, Eeff (pH 3.3) 0.46 V, which, wholly contrary to observation, predict that the reductions of excess Cr(V) to CR(IV) by Fe2+, V02+, and I− are thermodynamically disfavored.

Lithium(I) Porphyrin Complex for the Spectrophotometric Determination of Lithium Ion in Aqueous Solution.

A water-soluble octabromoporphyrin has been synthesized and developed for the determination of lithium ion in aqueous solution. The porphyrin reacts with lithium ion in alkaline solution to form the lithium complex along with a shift of absorption maximum to shorter wave length. But sodium and potassium ions do not react with the porphyrin. The equilibrium constant of the Li(I) porphyrin complex was determined and applied to the determination of lithium(I) in natural water. Interference of metal ions was removed by ligand buffer of Mg-EDTA complex.

Synthesis and Structural Investigations of [Mn(3)O(4)(phen)(4)(H(2)O)(2)](NO(3))(4).2.5H(2)O: A Water-Bound Complex Obtained by Cerium(IV) Oxidation.

The trinuclear manganese complex [Mn(3)O(4)(phen)(4)(H(2)O)(2)](NO(3))(4).2.5H(2)O, 1 (where, phen = 1,10-phenanthroline), has been synthesized by the Ce(IV) oxidation of a concentrated solution of manganese(II) acetate and phen in 1.6 N nitric acid. The complex crystallizes in the triclinic space group P&onemacr; with a = 10.700(2) Å, b = 12.643(3) Å, c = 20.509(4) Å, alpha = 78.37(3) degrees, beta = 83.12(3) degrees, gamma = 82.50(3) degrees, and Z = 2. The structure was solved by direct methods and refined by least-squares techniques to the conventional R (R(w)) factors of 0.055 (0.076) based on 4609 unique reflections with F(o) >/= 6.0sigma(F(o)). The structure of the cation consists of an oxo-bridged Mn(3)O(4)(4+) core, with the geometry of the manganese atoms being octahedral. The coordination polyhedron of one of the manganese atoms (Mn(1)) consists of two &mgr; oxo ligands and two pairs of nitrogen atoms of two phen moieties, whereas that of each of the remaining two manganese atoms consists of three &mgr;-oxo ligands, two nitrogen atoms of a phen moiety, and the oxygen atom of a water molecule. The complex represents the second example for water coordination to manganese(IV) centers in complexes with a Mn(3)O(4)(4+) core. Optical spectra in ligand buffer (pH 4.5) reveal complete conversion of the complex into a Mn(III)Mn(IV) species. The observed room-temperature (298 K) magnetic moment of 3.75 &mgr;(B) indicates the presence of strong antiferromagnetic coupling in the complex.

Thermodynamic Studies on the Complexation of o-Phenylenediamine-N,N,N′,N′-tetraacetate with Divalent Cadmium, Mercury, and Lead Ions in Aqueous Solutions

Abstract Potentiometric studies have been carried out on the complexation of o-phenylenediamine-N,N,N′,N′-tetraacetate (phdta, L4−) with the cadmium and lead ions (M2+) in aqueous solutions at 25 ± 0.1 °C and I = 1.00 M (NaClO4). The ligand buffer method was successfully applied to the determination of the formation constant (M2+ + L4− = ML2− : KML) by use of Cd and Pb ion-selective electrodes. This method gave log KML = 13.37 for CdL and 13.89 for PbL. Calorimetry and potentiometry gave the values of enthalpy and entropy of complexation (−ΔH°/ kJ mol−1 = 18.9, ΔS°/J K−1 mol−1 = 193 (CdL); 34.8, 149 (PbL); and 50.6, 165 (HgL), respectively). Thermodynamic parameters of the protonation to ML were also examined for the PhDTA complexes of these and some divalent transition metal ions. The metal complexes are classified into two categories according to the thermodynamic parameters: A) Mn2+, Cd2+, and Pb2+ (−ΔH°MHL = −1.1–1.1 kJ mol−1; ΔS°MHL = 43–49 J K−1 mol−1). B) Co2+, Ni2+, Cu2+, and Zn2+ (−ΔH°MHL = 8.0–11.3 kJ mol−1; ΔS°MHL = 18–37 J K−1 mol−1). The smaller value of −ΔH°MHL for A has been interpreted in terms of simple protonation to a carboxylate oxygen in the complex ML, with any acetate group not being dissociated. The entire process of protonation for B, however, may be composed of two steps: i) Detachment of one carboxylate group from the metal ion, followed by the hydration resulting in M(L′) (H2O)2−, where L′ represents a ligand anion with a free carboxylate group, ii) Protonation to an oxygen atom of the detached carboxylate group.

Effect of Ligands on the Redox Reaction of Metal Ions and the Use of a Ligand Buffer for Improving the End-Point Detection in the Potentiometric Titration of Vanadium(V) with Iron(II)

The effect of complexing agents on the titration of vanadium(V) with iron(II) was studied. Complexing agents which form more stable complexes with iron(III) than iron(II) produce a sharper titration of vanadium(V) with Iron(II). Citrate, pyrophosphate and EDTA improve the potential break at the equivalence point. The presence of excess EDTA decreases the formal potential of the V(V)/V(IV) couple due to the formation of vanadium(V)-EDTA complexes. The use of a ligand buffer with zinc(II) in excess over EDTA is very effective for improving the end-point detection in the titration, preventing the formation of vanadium(V)-EDTA complexes.

Direct spectrophotometric determination of iron in non-ferrous alloys

Disodium 3-(2-pyridyl)-1,2,4-triazine-5,6-di(4′-phenylsulphonate) is used for determination of iron in metal analysis. High selectivity is achieved by using a ligand buffer and substoichiometric masking. Interference from ⩽ 0.9 mg of Cu(II) can be completely eliminated by combined reduction and masking with ascorbic acid and thiosemicarbazide. Beer's law is obeyed over the range 0.4–1.6 μg/ml iron in the final solution, with a standard deviation of 0.02 μg/ml. The method has been successfully applied to determination of iron (without preseparation) in a number of non-ferrous metals and alloys, with a coefficient of variation of 1.2–5.0%.

Preconcentration and determination of calcium and magnesium in brine with flow-injection systems

On-line preconcentration on a chelating resin (Dowex A-1) and elution with 0.1 M hydorchloric acid is followed by spectrophotometry based on the metal complexes formed with 1- (2-hydroxy-4-diethylamino-1-phenylazo)-2-hydroxynaphthalene-3,6-disulfonic acid. The total concentration of calcium and magnesium is determined; in a second sample, calcium is masked with a ligand buffer containing excess of barium(II) and EGTA, and magnesium is determined. The calcium concentration is measured by difference. Magnesium (1–30 μg l −1 and calcium (8– 10 μg l −1) in 2.5 M sodium chloride can be determined. Calcium and magnesium in analytical reagent-grade sodium chloride and potassium chloride and primary standard sodium chloride are aslo determined. The method based on the exchange between calcium ions and Mg(EDTA) is proposed to enchance the sensitivity for calcium.

Determination of trace amounts of aluminium in tap water by spectrophotometry after collection on a membrane filter using Chrome Azurol S and Zephiramine

A sensitive and selective spectrophotometric method for the determination of aluminium(III) using Chrome Azurol S and Zephiramine is described. The ion-pair precipitate formed between Zephiramine and perchlorate ions is effective for the enrichment of aluminium(III) on a membrane filter as its ternary complex with Chrome Azurol S and Zephiramine. The solid-state absorbance of the complex on the membrane filter is measured at 640 and 700 nm against a blank thin layer and the difference is calculated. Although the calibration graph does not obey Beer's law good reproducibility is observed, the relative standard deviation for 0.10 µg of aluminium(III) in a 20-ml sample volume being 3.1%(n= 5). A ligand buffer solution, composed of trans-cyclohexane-1,2-diaminetetraacetic acid and an excess of zinc(II), is effective for masking interferences from foreign ions, particularly iron(III). The method has been applied to the determination of aluminium in tap water.

Determination of trace amounts of cobalt(II) by thin-layer spectrophotometry after enrichment on a membrane filter as the PAN complex

A simple, selective and sensitive method for the determination of trace amounts of cobalt(II) has been developed. The method is based on the fixation of cobalt as the 1-(2-pyridylazo)-2-naphthol complex on a membrane filter and the direct determination of the reflection absorbance of the complex by densitometry. The working range of the calibration graph was 0.05–0.5 µg of cobalt(II). The recovery of cobalt(II) was not affected by the volume of sample solution up to 300 ml. The ligand buffer solution, composed of ethylenediaminetetraacetic acid and an excess of zinc(II), was found to be effective for masking interferences from foreign cations, especially from iron(III). The method was applied to the determination of cobalt(II) in white wine. The concentration of cobalt(II) found in four different wine samples was in the range 2.5–4.4 µg l–1.

Use of Ligand Buffers in the Determination of the Stability Constants of Metal Complexes with Ion-Selective Electrodes

The potential response of copper(II), lead and cadmium ion-selective electrodes was studied in ligand buffers which contain a complex ML(M:Cu2+, Pb2+ or Cd2+), a ligand L and an excess of a second metal N. By measuring [M] with the ion-selective electrode, the ratio of the stability constants, KML/KNL was determined. The effects of pH, the second metal ion N and the ratio of [N]/[NL] on the electrode response were studied in detail. The KML/KNL values obtained for EDTA were in good agreement with those calculated from KML and KNL in the literature. The stability constants of N-hydroxyethylenediamine-N, N′, N′-triacetate complexes were determined successfully. These logarithmic values of KNL were found: Pb2+, 15.59; Zn2+, 14.59; Co2+, 14.49; Cd2+, 14.24; Mn2+, 11.41. These results show that the method is very useful for the determination of the stability constants of complexes with metal ions for which suitable ion-selective electrodes are not available.

Preparation and thermodynamic properties of UO 2+2 -Ethylene-1,2-dioxydiacetate complex

It is known that actinide ions in aqueous solutions form stable complexes especially with ligands of the mono- and poly-carboxylic acid type possessing charged oxygen donors. Neutral donor groups interact with the actinide ions only as additional donors, contributing to the stability of the complexes through the formation of chelate structures. Previously we investigated the complex formation of the UO 2+ 2 ion with bicarboxylic ligands containing different functional groups in the carbon chain: oxydiacetic (oda), thiodiacetic (tda) and iminodiacetic (ida) acids [1]. As a result we concluded that the relative affinity of the three donor groups, present in the chain, towards a hard acceptor follows the order NH > O > S. In fact the iminodiacetic and oxydiacetic ligands tend to form especially strong complexes with the UO 2+ 2 ion, with a coordination geometry in which one ligand is tridentate, forming a five atom ring, known as a particularly stable one. In order to verify whether our study to ligands of the type HOOC(CH 2XCH 2)nCOOH where X = -O-,-NH-, and n = 2,3. This report concerns the thermodynamic study of the complex formation of UO 2+ 2 with ethylene-1,2-dioxydiacetate (edoda, where X = -O-, n = 2) in aqueous solution. The UO 2+ 2 - edoda system was investigated by both potentiometric and calorimetric titration methods. The changes in free energy were computed from the stability constants determined by potentiometric measurements, the enthalpy changes were measured by direct calorimetric titrations. All measurements were carried out at 25.0°C and in 1.00 mol dm -3 Na(ClO 4), as constant ionic medium. Stability constants and enthalpy changes were calculated using MINIQUAD 75 and LETAGROP KALLE programs respectively. The ligand was prepared by oxidation of triethyleneglycol with nitric acid [2]. The purity had been checked by elemental analysis, determination of formula weight and NMR spectroscopy. The protonation constants of the ligand (logβ H 1 = 3.71 and logβ H 2 = 6.77) are in good agreement with those reported in the literature [3]. On that account for the heats of the proton ligand complexes' formation were taken the values given in the above cited paper. The formation constants of the complexes formed were determined by potentiometric titration of different metal concentration solutions (C° M = 10 to 30 m M) with ligand buffers (δ = C H 2L /C L = 0 to 0.5). The obtained formation curves show good super-imposition. In the ligand concentration range used, the metal ion seems to coordinate one ligand only, forming a complex of the type ML. The pH range used (pH = 2.0 to 3.5) allows to avoid the hydrolysis of the UO 2+ 2 ion. The calculations of the thermodynamic properties based on the potentiometric and calorimetric investigations is in process. Our preliminary data show that the stability of the complex obtained is much smaller in comparison with the one formed with the inferior homologous (oda). Comparing the thermodynamic data for the two ligands (see table) we can see that the difference in the stability of the complexes of the 1:1 type is due completely to an enthalpy effect, as the values for ΔS are almost equal. Such a difference in ΔH may be connected with a different geometry of coordination. The available structural data for UO 2+ 2 - oda support the hypothesis of a chelate structure through the carboxylic and the ether groups [4] In order to have comparable structural data for the ethylene-1, 2-dioxydiacetate we prepared the solid compounds. The reaction was conducted in ethanol and in water in order to get as close as possible to the thermodynamic experimental conditions. We have obtained interesting results, though not quite coinciding with the thermodynamic part. In fact: i)Starting from UO 2(NO 3) 2·6H 2O and working in water and in ethanol we always get compound of logβML -ΔG° (kJ mol -1) ΔH° (kJ mol -1) ΔS° (J mol -1K 2-1) UO 2+ 2 -oda 5.11 29.17 16.86 154.4 UO 2+ 2 -edoda 3.08 17.60 26.6 148.4 the stoichiometric formula UO 2(HL)NO 3. The above formula is confirmed by elemental analysis; by the evidence of the nitrate ionic band at 1385 cm -1, well distinguished on the IR spectrum; by the splitting of the band due to -CH 2- nearby the carboxylic band in the NMR spectra. All that can confirm the salification of only one carboxylic group by the metal. ii)On the contrary, in the same solvents, starting with UO 2(Ac) 2·2H 2O, instead of with the nitrate we always get a compound with stoichiometric formula UO 2L were both carboxylic groups are salificated. We thank the International Atomic Energy Agency, Vienna for the financial support to M. Taskaeva.