Stability Constants Of Metal Complexes Research Articles

First principle determination of stability constants of metal complexes by cellmetry method

AbstractThe stability constants of 81 metal complexes were calculated using the newly‐developed method which was previously used for determining pK values of acid–base dissociation constants by plane wave functions. Fifteen metal ions and 36 ligands were chosen, and a wide range of the complexes was studied to calculate the logK and logß stability constants. The large variety of geometries and coordination modes allowed us to see the limitation of the method. In some cases, good agreements could be found with the experimental data with an accuracy of .5–1 unit. Results howed that for smaller structural changes, the stability constants can be calculated easily by using the determined parameters. For larger structural differences, rough estimations by 2–4 logK units can be conducted. Correlations could be found among the data which can help further studies as well as aid in the prediction of some unknown complexes. The pK of a hexaaqua metal complex was determined as well.

Implicatons of Metal Complexes in Biology and Medicine the System Cadmium (II)/ Iron (II)/ Zinc (II)-Hydroxyproline

The importance of metal ions to essential functions of living systems and for the well being of living organisms is known. Metal ions are fundamental elements for the maintenance of the life spans of the human, animals and plants. The stability constants of Cd2+, Fe2+ and Zn2+ complexes with hydroxyproline were determined by Paper Electrophoretic Technique (PET). This method is based on the movement of a spot of metal ion in an electric field at various pH of background electrolyte. A graph of pH against mobility gives information about the formation of binary complexes and permit to calculate their stability constants. The stability constant of the ML and ML2 complexes of Cd (II) – hydroxyproline, Fe (II) – hydroxyproline and Zn (II) – hydroxyproline, have been found to be (4.41 ± 0.01; 2.95 ± 0.06) (4.11 ± 0.01; 2.81 ± 0.11 and (4.83 ± 0.02; 3.28 ± 0.07) ( logarithm stability constant values), respectively at ionic strength 0.1 mole L-1 (per chloric acid as background electrolyte) and a temperature of 35 0C, The first and second stability constants of metal complexes follow the order Zn (II) > Cd (II) > Fe (II). Metal complexes can offer their action such as anti-inflammatory, antibiotic, anti-thyroid and anticancer compounds. Metal based drugs bioactivity can be increased by metal chelation, which in turn increase their absorbance and stability. Recent advances in inorganic chemistry have made possible formation of a number of metal complexes with organic ligands of interest which can be use as therapeutic agents.

Metal Coordination: Improving Metal Adsorption on Triethylenetetramine (TETA) Functionalized SBA‐15 Mesoporous Silica Using Potentiometry, EPR and ssNMR (Adv. Mater. Interfaces 15/2020)

Metal ion chelators combined with nanostructure materials proved effective in the treatment and diagnosis of human diseases. Combine potentiometry, EPR and NMR techniques determine ligand content, metal complex stability constants and competition between metallodrugs and endogenous molecules. More details can be found in article number 2000544 by Joanna Izabela Lachowicz, Mariusz Jaremko, and co-workers.

Composition, stability and fluorescence properties of metal complexes of an aza-flavonol analog 1-methyl-2-phenyl-3-hydroxy-4(1H)-quinolone in aqueous solution

Aza-flavonols are compounds containing the 3-hydroxy-4(1H)-quinolone moiety, a unique scaffold with applications expanding from fluorescent probes and bioimaging to potential metal-related pharmaceutical drugs. Compositions and stability constants of metal complexes of an aza-flavonol 1-methyl-2-phenyl-3-hydroxy-4(1H)-quinolone (LH) in aqueous micellar medium of hexadecyltrimethylammonium bromide were established by fluorescence and spectrophotometric titrations of LH in the presence of metal ions of different type at variable pH. Strong binding with quenching of ligand fluorescence was observed for Cu2+, Fe2+/3+ and Pb2+ cations. The complexation with Zn2+ induced strong fluorescence enhancement in ZnL+ complex and smaller enhancement in ZnL2 complex. Al3+, Ga3+ and Me2Sn2+ cations induced strong fluorescence enhancement in 1:1 ML complexes, but quenching in ML2 complexes. Together with the relevant literature data these results indicate that the quenching effect in 1:2 complexes along with strong fluorescence enhancement in respective 1:1 complexes is a general phenomenon for 3-hydroxypyranone and 3-hydroxypyridinone ligands. The quantum mechanical Natural Transition Orbital analysis of ground and excited states of LH, AlL2+ and AlL2+ species reveals that the fluorescence of AlL2+ complex is quenched by an internal electron transfer process, which is absent in the 1:1 AlL2+ complex. The results emphasize strong dependence of the coordination induced fluorescence changes on the complex composition.

Physico-chemical studies of the complexes of Hippuric acid with Cu(II), Ni(II), Zn(II), and Pb(II) ions in ethanol-water mixed solvent system

Potentiometric titrations have been used to calculate the dissociation constants of Hippuric acid and its stability constants with Cu(II), Ni(II), Zn(II), and Pb(II) ions in ethanol-water mixed solvent system at different temperatures, and constant ionic strength of 0.1M solution sodium nitrate. The order of the stability constants of metal complexes at 298 K with respect to ligand was found to be Cu(II) > Pb(II) > Zn(II) > Ni(II). Effect of temperature on stability of hippuric acid complexes with Cu(II) and Pb(II) has been studied in order to calculate the Gibb`s free energy and enthalpy of the complex formation reaction, the results showed that coordination process is spontanous and exothermic. Effect of solvent ratio has been studied only for Cu(II) complex and the dissociation of hippuric acid at given added different ratios decreases on the following order 75% > 50%.

Ultra trace level square wave anodic stripping voltammetric sensing of mercury(II) ions in environmental samples using a Schiff base-modified carbon paste electrode

ABSTRACT In this approach, a new carbon paste electrode modified with N,N′-bis(5-bromo-2-hydroxybenzylidene)-2,2-dimethylpropane-1,3-diamine Schiff base ligand (L) was synthesised for selective and effective determination of Hg2+ ions in aqueous environmental samples using cyclic and square wave anodic stripping voltammetric methods. First, the selective detection of mercury ion was confirmed by evaluating the stability constants of metal complexes formed between the Schiff base ligand (L) and some desired cations by conductometric measurements. Afterwards, by preparing an effective carbon paste electrode modified with L, the experimental and instrumental parameters affecting the performance of modified electrode were investigated. Square wave anodic stripping voltammograms were obtained after applying an accumulation potential −0.5 V and accumulation time 150 s in Britton–Robinson buffer solution at pH 2.0. The optimal square wave parameters found are pulse amplitude 75 mV, frequency 50 Hz and step potential 6 mV. The procedure exhibited linear range from 0.4 to 120 μg L−1 Hg2+ with a limit of detection of 0.042 μg L−1. The proposed electrode was proved to be highly selective in the presence of various cations and anions and was successfully used for determination of mercury in tobacco and several water samples.

Precious metal-free molecular machines for solar thermal energy storage.

Four benzothiazolium crown ether-containing styryl dyes were prepared through an optimized synthetic procedure. Two of the dyes (4b and 4d) having substituents in the 5-position of the benzothiazole ring are newly synthesized compounds. They demonstrated a higher degree of trans–cis photoisomerization and a longer life time of the higher energy forms in comparison with the known analogs. The chemical structures of all dyes in the series were characterized by NMR, UV–vis, IR spectroscopy and elemental analysis. The steady-state photophysical properties of the dyes were elucidated. The stability constants of metal complexes were determined and are in good agreement with the literature data for reference dyes. The temporal evolution of trans-to-cis isomerization was observed in a real-time regime. The dyes demonstrated a low intrinsic fluorescence of their Ba2+ complexes and high yield of E/Z photoisomerization with lifetimes of the higher energy form longer than 500 seconds. Density functional theory (DFT) calculations at the B3LYP/6-31+G(d,p) level were performed in order to predict the enthalpies (H) of the cis and trans isomers and the storage energies (ΔH) for the systems studied.

Molar absorption coefficients and stability constants of Zincon metal complexes for determination of metal ions and bioinorganic applications

Zincon (ZI) is one of the most common chromophoric chelating probes for the determination of Zn2+ and Cu2+ ions. It is also known to bind other metal ions. However, literature data on its binding properties and molar absorption coefficients are rather poor, varying among publications or determined only in certain conditions. There are no systematic studies on Zn2+ and Cu2+ affinities towards ZI performed under various conditions. However, this widely commercially available and inexpensive agent is frequently the first choice probe for the measurement of metal binding and release as well as determination of affinity constants of other ligands/macromolecules of interest. Here, we establish the spectral properties and the stability of ZI and its complexes with Zn2+, Cu2+, Cd2+, Hg2+, Co2+, Ni2+ and Pb2+ at multiple pH values from 6 to 9.9. The obtained results show that in water solution the MZI complex is predominant, but in the case of Co2+ and Ni2+, M(ZI)2 complexes are also formed. The molar absorption coefficient at 618 nm for ZnZI and 599nm for CuZI complexes at pH7.4 in buffered (I=0.1M) water solutions are 24,200 and 26,100M−1cm−1, respectively. Dissociation constants of those complexes are 2.09×10−6 and 4.68×10−17M. We also characterized the metal-assisted Zincon decomposition. Our results provide new and reassessed optical and stability data that are applicable to a wide range of chemical and bioinorganic applications including metal ion detection, and quantification and affinity studies of ligands of interest. SynopsisAccurate values of molar absorption coefficients of Zincon complex with Zn2+, Cd2+, Hg2+, Co2+, Ni2+, Cu2+, and Pb2+ for rapid metal ion quantification are provided. Zincon stability constants with Zn2+ and Cu2+ in a wide pH range were determined.

Binding and selectivity of phenazino-18-crown-6-ether with alkali, alkaline earth and toxic metal species: A DFT study

The interactions of phenazino-crown ether ligands with alkali, alkaline earth and selected toxic species were investigated using density functional theory modelling by employing B3PW91/6-311G ++ (d, p) level of theory. The complex stability was analysed in terms of binding energies, perturbation energies, position of highest molecular orbital and energy gap values. In general, the complexes formed by P18C6-1a ligand with metal cations were found to be more stable than those with P18C6-1b. Among alkali and alkaline earth metals complexes having highest stability was observed for the complex formed by P18C6-1a with Be2+. Computational calculations of P18C6 ligand with toxic metal ions reveals that the P18C6-Cr6+ metal complexes acquire envelop like geometry, leading to higher binding energy values. Comparing the binding energies of neutral and monocations of Ag and Hg, the former had higher value both in neutral as well as monocation state. Thus, the stability of metal complexes is determined not only by the ligand but also by the type of metal ion. In solvent systems the stability constants of metal complexes were found increasing with decreasing permittivity of the solvent. This reflects the inherited polar character of the protic solvents stabilises the cation, resulting in decrease of effective interaction of ligand with the metal ion.

Ligational, potentiometric and floatation studies on Cu(II) complexes of hydrazones derived from p and o-vanillin condensed with diketo hydrazide

Copper (II) complexes of both 2-(2-(4-hydroxy-3-methoxybenzylidene) hydrazinyl)-2-oxo-N-phenylacetamide (H2L1) and 2-(2-(2-hydroxy-3-methoxybenzylidene) hydrazinyl)-2-oxo-N-phenylacetamide (H2L2) have been prepared and investigated by analytical, magnetic and spectroscopic techniques. IR spectra displayed that (H2L1) behaves as mono-negative tridentate or mono-negative tetradentate in both of [Cu(HL1)Cl]·(2H2O) and [Cu2(HL1)Cl3(H2O)](1.5H2O), respectively. But (H2L2) behaves as neutral bidentate or bi-negative pentadentate in both of [Cu(H2L2)2Cl2]·(2H2O) and [Cu2(L2)Cl2(H2O)]·(2H2O), respectively. 1H NMR spectra showed the replaceable hydrogens of the prepared ligands. The magnetic moment values helped to investigate the geometry of the complexes. Thermogravimetric studies gave a general pattern for the main stages of the thermal decomposition with kinetic data to evaluate thermodynamic parameters ΔH* and ΔG* for each step of degradation to compare between stability of those complexes. Also pH-metric measurements were used to evaluate the proton–ligand formation constants and the stability constants of metal complexes at 298°K. Floatation procedure was carried out to investigate the optimum conditions for Cu(II) separation by ligand molecules.

Molar absorption coefficients and stability constants of metal complexes of 4-(2-pyridylazo)resorcinol (PAR): Revisiting common chelating probe for the study of metalloproteins

4-(2-Pyridylazo)resorcinol (PAR) is one of the most popular chromogenic chelator used in the determination of the concentrations of various metal ions from the d, p and f blocks and their affinities for metal ion-binding biomolecules. The most important characteristics of such a sensor are the molar absorption coefficient and the metal–ligand complex dissociation constant. However, it must be remembered that these values are dependent on the specific experimental conditions (e.g. pH, solvent components, and reactant ratios). If one uses these values to process data obtained in different conditions, the final result can be under- or overestimated. We aimed to establish the spectral properties and the stability of PAR and its complexes accurately with Zn2+, Cd2+, Hg2+, Co2+, Ni2+, Cu2+, Mn2+ and Pb2+ at a multiple pH values. The obtained results account for the presence of different species of metal–PAR complexes in the physiological pH range of 5 to 8 and have been frequently neglected in previous studies. The effective molar absorption coefficient at 492nm for the ZnHx(PAR)2 complex at pH7.4 in buffered water solution is 71,500M−1cm−1, and the dissociation constant of the complex in these conditions is 7.08×10−13M2. To confirm these values and estimate the range of the dissociation constants of zinc-binding biomolecules that can be measured using PAR, we performed several titrations of zinc finger peptides and zinc chelators. Taken together, our results provide the updated parameters that are applicable to any experiment conducted using inexpensive and commercially available PAR.

English

The heterocyclic ligand (L), 3-(2-hydroxy phenyl)-2-iminothiazolidin-4-one, was synthesized by the cyclocondensation of o-hydoxy phenyl chloroacetamide with potassium thiocyanate. The stoichiometries of the title complexes were first determined by spectrophotometric mole ratio method which gave rise to the M:L ratio of 1:4 in case of Zn(II) and Cd(II) and 1:2 in case of Hg(II) ions respectively. Using these predetermined M:L ratios, complexes of the formulas [Zn-L4], [Cd-L4] and [Hg-L2] were prepared accordingly using precursor of the corresponding metal salts with the title ligand in ethanol medium.  The synthesized compounds were characterized by elemental analysis, FTIR, 1H and 13CNMR, UV-Vis and conductometric measurement. Stability constants (Ks) of these complexes were investigated by spectrophotometric mole ratio method. The FTIR, 1H NMR and 13C NMR data revealed that the studied ligand function as monodentate ligand interacting through phenolic oxygen as donor with Zn(II) and Cd(II) and as bidentate ligand interacting through phenolic oxygen and nitrogen  atom with Hg(II). The synthesized complexes show conductivity values in the range of 122-133 µSmol-1cm2 in DMSO at 298 K which confirms the electrolytic nature of the complexes. The stability constants decreased with increased temperature, confirming that these metal complexes are not stable at higher temperature. Sufficiently large negative values of ΔG of complex confirm the spontaneous formation of the title complexes. Furthermore, it was noted that the spontaneity of the reaction increased with temperature. The stability constant of these complexes follow the sequence Zn(II)>Cd(II)>Hg(II). Therefore, the overall result is complying very well with the Irving-William series of stability constants of metal complexes.   Key words: Stability constants, 3-(2-hydroxyphenyl)-2-iminothiazolidin-4-one, Irving-William series, thermodynamic parameters, mole ratio method.

Luminescent Eu3+-doped NaLa(WO4)(MoO4) and Ba2CaMoO6 prepared by the modified Pechini method

Modified Pechini synthesis routes were developed for synthesis of the novel red phosphor materials NaLa(WO4)(MoO4):Eu3+ and Ba2CaMoO6:Eu3+. Phase pure NaLa(WO4)(MoO4):Eu3+ was obtained at calcination temperatures ≥600 °C using malic acid or tartaric acid as complexing agents. Phase pure Ba2CaMoO6:Eu3+ was attained using EDTA and citric acid, at calcination temperatures ≥800 °C. Choice of complexing agents were discussed on the basis of the solubility of the precursors, metal complex stability constants and conformations of the complexes. The powder properties were characterised using X-ray diffraction, thermal analysis and electron microscopy. Photoluminescence emission intensity was studied as a function of the complexing agents used and calcination temperature of the powders. Maximum emission intensity for NaLa(WO4)(MoO4):Eu3+ was obtained at a calcination temperature of 600 °C, whereas the maximum for Ba2CaMoO6:Eu3+ was obtained after calcination at 1100 °C. Both materials displayed desirable optical properties for use as phosphors in white light-emitting diodes. Phase pure NaLa(WO4)(MoO4):Eu3+ and Ba2CaMoO6:Eu3+ red phosphor materials were synthesised by the modified Pechini route, thus permitting lower calcination temperatures which resulted in increased emission intensity for NaLa(WO4)(MoO4):Eu3+.

Center of Gravity (COG) Method as a Tool in Processing of Voltammetric Signals

AbstractThe center of gravity method (COG) was applied (for the first time) in voltammetry (polarography) as a tool for very precise determination of peak potentials, and signal shifts. Basically, the adjustment of the method consists of finding the optimal fraction of the peak that contains information about peak position, either of original signal or of its 1st or 2nd derivatives, along with optimal selection of parameters for SavitzkyGolay smoothing of original curves and elimination of baseline influence. The principle of the method and its validation were demonstrated and checked on simulated differential pulse polarograms (DPP) representing a series of curves for the determination of stability constants of labile metal complexes (DeFord‐Hume method). It was shown that COG outperforms the classical “one‐point” method (OPM) in precision and accuracy, providing excellent results even if a very large step potential (e.g. 10 mV) was used. The problems of reduced accuracy and precision in case of curved (non‐ideal) baseline and asymmetric peaks were successfully overcome by applying COG on curves transformed by 1st and/or 2nd derivatives. The method was additionally examined in details on a simple experimental dataset of cadmium chloride complexes in 4 mol dm−3 ionic strength solution and on a more complex dataset of uranyl selenate complexes in 3 mol dm−3 ionic strength solution. Stability constants obtained by COG agree well with those in the literature with much better precision than the classical one‐point method (checked by standard error of the fit).

THE THEORY OF DEVELOPMENT OF SUPPORTED METAL-COMPLEX CATALYSTS

Some results of the investigations for the purpose of development of supported metal-complex catalysts for phosphine and carbon monoxide oxidation as well as for ozone decomposition are summarized. The activity of such catalysts has been found to depend not only on a nature of a central atom and ligands but also on a nature of supports. The theoretical model explaining mechanisms of surface complex formation taking into account the influence of physicochemical and structural-adsorption properties of the supports (SiO2, Al2O3, carbon materials, zeolites, dispersed silicas, lamellar aluminosilicates, etc.) has been proposed. For quantitative description of the support effect, such a thermodynamic parameter as the adsorbed water activity assignable with the help of water vapor adsorption isotherms has been introduced. Successive stability constants of the surface metal complexes have been calculated by the kinetic method and, hence, compositions and partial catalytic activity of the latter have been determined. Taking into account the competitive adsorption of metal ions on the supports, some schemes of formation of surface bimetallic complexes have been suggested. The compositions of the supported metal-complex catalysts have been optimized to meet requirements of their use in respirators and plants for air purification from foregoing gaseous toxicants.

Potentiometric and spectroscopic study of the interaction of 3d transition metal ions with inositol hexakisphosphate

Among myo-inositol phosphates, the most abundant in nature is the myo-inositol hexakisphosphate, InsP6. Although it is known to be vital to cell functioning, the biochemical research into its metabolism needs chemical and structural analysis of all the protonation, complexation and precipitation processes that it undergoes in the biological media. In view of its high negative charge at physiological level, our group has been leading a thorough research into the InsP6 chemical and structural behavior in the presence of the alkali and alkaline earth metal ions essential for life. The aim of this article is to extend these studies, dealing with the chemical and structural features of the InsP6 interaction with biologically relevant 3d transition metal ions (Fe(II), Fe(III), Mn(II), Co(II), Ni(II), Cu(II) and Zn(II)), in a non-interacting medium and under simulated physiological conditions. The metal-complex stability constants were determined by potentiometry, showing under ligand-excess conditions the formation of mononuclear species in different protonation states. Under metal ion excess, polymetallic species were detected for Fe(II), Fe(III), Zn(II) and Cu(II). Additionally, the 31P NMR and UV–vis spectroscopic studies provided interesting structural aspects of the strong metal ion-InsP6 interaction.

Small bifunctional chelators that do not disaggregate amyloid β fibrils exhibit reduced cellular toxicity.

Multifunctional metal chelators that can modulate the amyloid β (Aβ) peptide aggregation and its interaction with metal ions such as copper and zinc hold considerable promise as therapeutic agents for Alzheimer’s disease (AD). However, specific rather than systemic metal chelation by these compounds is needed in order to limit any side effects. Reported herein are two novel small bifunctional chelators, 2-[2-hydroxy-4-(diethylamino)phenyl]benzothiazole (L1) and 2-(2-hydroxy-3-methoxyphenyl)benzothiazole (L2), in which the metal-binding donor atoms are integrated within a molecular framework derived from the amyloid-binding fluorescent dye thioflavin T (ThT). The metal-binding properties of L1 and L2 were probed by pH spectrophotometric titrations to determine their pKa values and the corresponding metal complex stability constants, and the isolated metal complexes were structurally characterized. The amyloid-fibril-binding properties of L1 and L2 were investigated by fluorescence titrations and ThT competition assays. Interestingly, L1 and L2 do not lead to the formation of neurotoxic Aβ42 oligomers in the presence or absence of metal ions, as observed by native gel electrophoresis, Western blotting, and transmission electron microscopy. In addition, L1 and L2 were able to reduce the cell toxicity of preformed Aβ42 oligomers and of the copper-stabilized Aβ42 oligomers. Given their ability to reduce the toxicity of soluble Aβ42 and Cu-Aβ42 species, L1 and L2 are promising lead compounds for the development of chemical agents that can control the neurotoxicity of soluble Aβ42 species in AD.

Occurrence forms of metals in natural waters depending on water chemistry

The results of experimental studies of the composition and specific features of humic substance isolated from typical soils of natural zones are given. The stability constants of metal complexes with humic substance are evaluated. The obtained experimental data are used to calculate the occurrence forms of metals in natural waters in the zones of taiga, forests, and steppes. The occurrence forms of metals are shown to be determined by the general chemistry of natural waters rather than stability constants of complexes with organic matter.

Correlation of retention of lanthanide and actinide complexes with stability constants and their speciation

Abstract The present study describes a correlation that is developed from retention of lanthanide and actinide complexes with the stability constant. In these studies, an ion-pairing reagent, camphor-10-sulphonic acid (CSA) was used as the modifier and organic acids such as α-hydroxy isobutyric acid (α-HIBA), mandelic acid, lactic acid and tartaric acid were used as complexing reagent for elution. From these studies, a correlation has been established between capacity factor of a metal ion, concentration of ion-pairing reagent and complexing agent with the stability constant of metal complex. Based on these studies, it has been shown that the stability constant of lanthanide and actinide complexes can be estimated using a single lanthanide calibrant. Validation of the method was carried out with the complexing agents such as α-HIBA and lactic acid. It was also demonstrated that data from a single chromatogram can be used for estimation of stability constant at various ionic strengths. These studies also demonstrated that the method can be applied for estimation of stability constant of actinides with a ligand whose value is not reported yet, e.g., ligands of importance in the lanthanide–actinide separations, chelation therapy etc. The chromatographic separation method is fast and the estimation of stability constant can be done in a very short time, which is a significant advantage especially in dealing with radioactive elements. The stability constant data was used to derive speciation data of plutonium in different oxidation states as well as that of americium with α-HIBA. The elution behavior of actinides such as Pu and Am from reversed phase chromatographic technique could be explained based on these studies.

Metal binding ability of curcumin derivatives: a theoretical vs. experimental approach

Theoretical calculations employing DFT at the B3LYP/6-311G++** level are used to investigate the tautomeric equilibrium in curcumin derivatives. The solvent effect is evaluated using the CPCM continuum solvation method. The results are compared with experimental data obtained from the X-ray crystal structure of K2A23 and UV-vis data. The KE tautomer is more stable in a vacuum and in the solid state, while in water the DK tautomer reaches a population of 90%. In agreement with spectroscopic data, theoretical calculations predict a slight prevalence of the DK form in non-aqueous solvent systems. The ability to chelate metal ions [Fe(3+), Ga(3+) and Cu(2+)] is then explored by means of (1)H, (13)C NMR and UV-Vis spectroscopy. From the calculation of the overall stability constants of metal complexes and (1)H NMR titrations with Ga(3+), it is clear that the more stable species has a 1 : 2 M/L molar ratio. The curcuminoid coordinates the metal ion through the keto-enol function in the dissociated form; in addition 2D (1)H (13)C NMR experiments suggest the involvement of carboxylic oxygen in metal coordination it was found in the solid state for the complex [Ga(K2A33)2]PF6. The rate of the complexation reaction is strongly influenced by the type of substituent on the aromatic ring of the curcuminoid (K2A33 ≈ K2A23 ≫ K2A21). In addition DPPH assay evidences how antioxidant ability of curcumin derivatives is mainly due to the presence of a phenolic group and metal coordination by a keto-enolic moiety does not affect it, especially for K2A21.