Complexation Capacity Research Articles

Didactic experiment for voltametric determination the complexing capacity of natural waters

The titration method can be applied to determine the complexation capacity between metal ions and ligands in natural water samples. The process involves the incremental addition of the metal to the sample containing a specific ligand, resulting in a titration curve that reflects the formation of complexes. The change in the curves slope indicates the saturation of the complexation capacity. In this study, the copper (II) ion was used due to its stability with organic ligands. The titration curve was analyzed to determine the complexation capacity (CC) and conditional formation constant (K) of the complex. Different mathematical treatments are proposed for this analysis. In the described experiment, differential pulse anodic stripping voltammetry was used to determine the complexation capacity of humic substances in natural waters. Experimental parameters such as pH, supporting electrolyte concentration, and volume of additions were previously optimized for the voltammetry technique. The obtained data were processed and analyzed, resulting in titration curves and voltammograms. The analysis of the curves allowed for the calculation of the complexation capacity and conditional stability constant of the formed complex. The results demonstrate the feasibility of the method as a didactic experiment for the voltammetric determination of natural water complexation capacity.

Interaction between humic substances and arsenic species simulating environmental conditions

The importance of evaluating how natural organic matter influences the mobility of arsenic species in an ecosystem is an environmental concern. This work aimed to evaluate the interaction between humic substances (HS) and four arsenic species of high toxicity [As(III), As(V), MMA(V), and DMA(V)] (HS-As) under the influence of HS concentration and pH. Next, the complexing capacity (CC) of HS by As(III) was determined in function of pH, ionic strength and co-existing ions. The free arsenic (Asfree) was determined after a tangential flow ultrafiltration procedure by hydride generation atomic fluorescence spectrometry. The better HS-As interactions for As(III) and As(V) at pH 10.5 reached 52% and 61%, respectively. The increase in pH and ionic strength, as well as co-existing ions increased the CC, which reached 1.57 mg of As(III) g−1 HS. We proposed a HS-As interaction model based on the inner and outer binding sites of HS from these results. The inner sites were occupied through hydrogen bonds, Pearson acid-base, hydrophobic, and van der Waals interactions for trivalent arsenic species, while the interactions through the outer sites for pentavalent arsenic species were mostly by hydrogen bonds and electrostatic forces. According to ecotoxicological studies against Artemia salina, the presence of HS decreased the toxicity of As(III) and As(V) as the lethal concentration increased from 5.81 to 8.82 mg L−1 and from 8.82 to 13.37 mg L−1, respectively. From the results through the proposed model, it was possible to successfully understand the interaction dynamic between soil HS and As(III), As(V), MMA(V) and DMA(V) under simulated environmental conditions.

Interaction of Pb, Ni and Cd with Aquatic Humic Substances of Amazonian Blackwater Rivers

In this study, the extraction and characterization of aquatic humic substances (AHS) from two blackwater rivers in the Amazon basin was carried out in order to assess the seasonal effects in the AHS structure. In addition, an investigation of the complexing capacities (CC) of the structures containing the metal ions CdII, NiII and PbII was also done. The characterization (of the AHS) was done using UV-Vis, molecular fluorescence, and infrared spectroscopy. AHS from the Negro River showed more aromatic characteristics in its structures and molecular weight, than the AHS from the Caru River. The AHS studied presented a seasonal pattern characterized by higher humification levels during the rainy season. For all the metals, the AHS complexing capacity was higher for the Negro River. The highest complexing capacities were observed for the NiII assays, which were 0.56 and 0.12 µmol NiII mg-1 dissolved organic carbon (DOC), for AHS RN and AHS RC-II, respectively. We concluded that the transport, bioavailability, and toxicity, of these metal species should be higher for Caru River.

Design of experiments to select triphenylphosphonium-polyplexes with suitable physicochemical properties for mitochondrial gene therapy

Mitochondrial gene therapy can be seen as a promising tool and a revolutionary approach towards mitochondrial diseases arising from mitochondrial DNA mutations. The conception of a viable and suitable mitochondrial targeted vector is imperative to turn this therapy clinically feasible. To accomplish this goal, different molecular weight polyethylenimines (PEI) have been conjugated with the mitochondriotropic agent triphenylphosphonium (TPP) and the interaction of this polycation with the ND1 (mitochondrially encoded NADH dehydrogenase 1 protein) plasmid DNA has been explored for the formation of nanometer complexes. In order to quickly, easily and with reduced costs find out the most adequate gene delivery vector, a design of experiments (DoE) tool has been explored. For each different molecular weight PEI delivery system, the nitrogen to phosphate groups' ratio (N/P) and the pDNA volume were selected as DoE inputs and the pDNA complexation capacity (CC), surface charge and polyplexes size were considered DoE outputs. The study revealed that the combination of high N/P ratios with lower pDNA volume of the inputs favors the formulation of optimal carriers after the output maximization of pDNA CC and positive surface charge and output minimization of the particle sizes. Moreover, it was demonstrated that N/P ratio greatly influences its capacity to condense ND1 based pDNA along with PEI molecular weight. This work allows for the selection of the gene delivery vector possessing the most convenient physicochemical properties for further studies towards mitochondrial gene therapy.

Optimization of peptide-plasmid DNA vectors formulation for gene delivery in cancer therapy exploring design of experiments

The field of gene therapy still attracts great interest due to its potential therapeutic effect towards the most deadly diseases, such as cancer. For cancer gene therapy to be feasible and viable in a clinical setting, the design and development of a suitable gene delivery system is imperative. Peptide based vectors, in particular, reveal to be promising for therapeutic gene release. Following this, two different peptides, RALA and WRAP5, have been investigated mainly regarding their ability to form complexes with a p53 encoding plasmid (pDNA) with suitable properties for gene delivery. To address this issue, and after an initial screening study focused on the dependence of pDNA complexation capacity with the nitrogen to phosphate groups (N/P) ratio, a design of experiments (DoE) tool has been employed. For each peptide/pDNA system, parameters such as, the buffer pH and the N/P ratio were considered the DoE inputs and the vector size, zeta potential and pDNA complexation capacity (CC) were monitored as DoE outputs. The main goal was to find the optimal experimental conditions to minimize particle sizes, as well as, to maximize the positive surface charges of the formulated nanosystems and maximize the pDNA CC. Through the DoE method applied, the optimal RALA/pDNA and WRAP5/pDNA formulations were revealed and show interesting features related to peptide structure and pDNA complexation ability. This work illustrates the great utility of experimental design tools in optimizing the formulation of peptide/pDNA vectors in a minimum number of experiments providing relevant knowledge for the development of more suitable and efficient gene delivery systems. The new insights achieved on these carriers clearly instigate deeper research on gene therapy.

EXTRAÇÃO E CARACTERIZAÇÃO DE SUBSTÂNCIAS HÚMICAS AQUÁTICAS (SHA) EXTRAÍDAS DE AMOSTRAS COLETADAS NO PARQUE NACIONAL SERRA DE ITABAIANA, SERGIPE, BRASIL

Este trabalho descreve o estudo da capacidade de complexação (CC) das substâncias húmicas aquáticas (SHA) extraídas de amostras de água coletadas no Parque Nacional Serra de Itabaiana (Sergipe) pelos íons metálicos Mn, Ni, Zn, Cu e Pb, bem como a avaliação da concentração dos metais totais das amostras de água. Os parâmetros físicos e químicos das amostras de água foram determinados por pH, temperatura, condutividade elétrica e COD, assim como a determinação dos metais totais foram quantificados por ICP OES. As SHA foram extraídas com resina XAD 8, segundo o procedimento reconhecido pela International Humic Substances Society (IHSS), e foram caracterizadas por TGA, análise elementar e por FTIR. Posteriormente foi estudado a CC das SHA pelos íons metálicos Cu, Mn, Ni, Pb e Zn pelo método de ultrafiltração. O valor do pH da amostra estudada apresentou valor abaixo dos estabelecidos pela Resolução CONAMA N° 357. No entanto, o valor da condutividade elétrica está em conformidade com a Portaria N° 2914 do Ministério da Saúde. As concentrações dos metais totais estão em acordo com a Resolução CONAMA N° 357, exceto para o Pb. As SHA apresentaram três processos principais de perda de massa (de acordo com as curvas TGA/DTGA), e o espectro FTIR apresentou bandas características de SHA. A CC das SHA por íons metálicos estabeleceu a seguinte ordem decrescente: Mn(II) > Ni(II) > Zn(II) >> Cu(II) > Pb(II). Esses resultados reforçam que as SHA podem ser classificadas como agentes complexantes naturais que desempenham uma função importante no meio ambiente.

The copper complexation ability of a synthetic humic-like acid formed by an abiotic humification process and the effect of experimental factors on its copper complexation ability.

Humic acids have an important impact on the distribution, toxicity, and bioavailability of hazardous metals in the environment. In this study, a synthetic humic-like acid (SHLA) was prepared by an abiotic humification process using catechol and glycine as humic precursors and a MnO2 catalyst. The effect of physico-chemical conditions (ionic strength from 0.01 to 0.5M NaNO3, pH from 4 to 8, temperature from 25 to 45°C, and humic acid concentration from 5 to 100mg/L) on the complexation ability of SHLA for Cu2+ were investigated. A commercial humic acid (CHA, CAS: 1415-93-6) from Sigma-Aldrich was also studied for comparison. The results showed that for pH4 to 8, the conditional stability constants (log K) of SHLA and CHA were in the range 5.63-8.62 and 4.87-6.23, respectively, and complexation capacities (CC) were 1.34-2.61 and 1.42-2.31mmol/g, respectively. The Cu complexation ability of SHLA was higher than that of the CHA due to its higher number of acidic functional groups (SHLA 19.19mmol/g; CHA 3.87mmol/g), extent of humification and aromaticity (AL/AR: 0.333 (SHLA); 1.554 (CHA)), and O-alkyl functional groups (SHLA15.56%; CHA 3.45%). The log K and complexation efficiency (fraction of metal bound to SHLA) of SHLA were higher at higher pH, lower ionic strength, higher temperature, and higher SHLA concentration. Overall, SHLA was a good and promising complexation agent for copper in both soil washing of copper contaminated soil and the treatment of copper-containing wastewater.

Applicability Comparison and Application Study of Two Methods for Determination of the Copper Complexing Capacity of Waters

Complexing capacity (CC) is an important indicator affecting the environmental behavior of heavy metals in water, which can be determined by different methods based on different mechanisms. To validate and compare the applicability of different methods in CC determination, the complexing capacity of Cu2+ (CuCC) in solutions of ethylenediamine tetraacetic acid (EDTA) and acesulfame was determined by methods of dithizone extraction kinetics (DEK) and ion-selective electrodes (ISE), while EDTA and acesulfame were selected to represent strong and weak ligands in water, respectively. DEK method was found to be more suitable for determining the contribution of strong ligands to CuCC, while the results determined by ISE were related to both the strong and weak ligands in water. DEK and ISE methods were used to measure CuCC of several actual water samples, including samples from reservoir, discharge river, fishpond, and landfill leachates. CuCC in the water samples of the reservoir and discharge river measured by ISE were 86.9-227.0 μmol·L-1, which were about one order of magnitude higher than those measured by DEK (9.9-14.6 μmol·L-1). For the landfill leachates, CuCC measured by ISE were 6998.4-31005.8 μmol·L-1, which were 2 orders of magnitude higher than those by DEK (89.6-109.1 μmol·L-1). The increase of CuCC in the polluted water samples might be due to the weak ligands like pollutants. A positive correlation (R=0.975, P<0.01) was found between the CuCC related to the weak ligands (ΔCuCC) and the sum concentration of ammonia nitrogen and organic nitrogen in waters.

Chemical behavior of Cu, Zn, Cd, and Pb in a eutrophic reservoir: speciation and complexation capacity.

This research aimed at evaluating cadmium (Cd), copper (Cu), lead (Pb), and zinc (Zn) speciation in water samples as well as determining water quality parameters (alkalinity, chlorophyll a, chloride, conductivity, dissolved organic carbon, dissolved oxygen, inorganic carbon, nitrate, pH, total suspended solids, and water temperature) in a eutrophic reservoir. This was performed through calculation of free metal ions using the chemical equilibrium software MINEQL+ 4.61, determination of labile, dissolved, and total metal concentrations via differential pulse anodic stripping voltammetry, and determination of complexed metal by the difference between the total concentration of dissolved and labile metal. Additionally, ligand complexation capacities (CC), such as the strength of the association of metals-ligands (logK'ML) and ligand concentrations (C L) were calculated via Ruzic's linearization method. Water samples were taken in winter and summer, and the results showed that for total and dissolved metals, Zn > Cu > Pb > Cd concentration. In general, higher concentrations of Cu and Zn remained complexed with the dissolved fraction, while Pb was mostly complexed with particulate materials. Chemical equilibrium modeling (MINEQL+) showed that Zn(2+) and Cd(2+) dominated the labile species, while Cu and Pb were complexed with carbonates. Zinc was a unique metal for which a direct relation between dissolved species with labile and complexed forms was obtained. The CC for ligands indicated a higher C L for Cu, followed by Pb, Zn, and Cd in decreasing amounts. Nevertheless, the strength of the association of all metals and their respective ligands was similar. Factor analysis with principal component analysis as the extraction procedure confirmed seasonal effects on water quality parameters and metal speciation. Total, dissolved, and complexed Cu and total, dissolved, complexed, and labile Pb species were all higher in winter, whereas in summer, Zn was mostly present in the complexed form. A high degree of deterioration of the reservoir was confirmed by the results of this study.

Fractionation of Aquatic Humic Substances and Dynamic of Chromium Species in an Aquatic Body Influenced by Sugarcane Cultivation

This study had as main objective to evaluate the influence of AHS obtained from an area under sugarcane cultivation on the dynamics of chromium species (Cr(III) and Cr(VI)). Was studied complexing capacity (CC) with the AHS of chromium species and these were characterized using UV/Vis spectrophotometry, molecular fluorescence, elemental analysis and infrared. AHS with and without fractionation showed a greater aromaticity degree and a predominance of humic acids, and the E4/E6 and E2/E4 ratios suggested aromatic rings and a greater contribution from plants, which indicates lignin structures. The highest CCs were observed for the AHS fractionated, being fraction with molecular-size < 10 kDa and 10-30 kDa showed the highest ability to complex Cr(III) and Cr(VI) ions, respectively. These results are corroborating with C/H/N and UV/Vis data, where we can conclude that the AHS without fractionation had the greatest aromaticity and a predominance of humic acids in their structure.

Effect of bacterial growth in the complexing capacity of a culture medium supplemented with cadmium(II)

The aim of this study was to evaluate complexing capacity (CC) accompanying microbial growth in a metal supplemented culture medium. A combined strategy of square wave anodic stripping voltammetry (SWASV) monitored titration and ion-exchange resins treatment (Chelex 100) has been applied. Culture medium, supplemented with Cd(II) in excess to ligands, was inoculated with an indigenous bacterial culture; total ligand concentration and stability constants were determined at different bacterial growth stages. As far as known, determination of CC in such conditions has not been reported (usually ligands in natural or wastewaters exceed metal concentration). HIDA, (N-(2-hydroxyethyl)iminodiacetic acid), was used as a model ligand to mimic soluble products derived from the resin treatment and bacterial metabolism. Ligand concentration, Lt (1.3 ± 0.1 μM), and the conditional stability constant, K′, (log K′ = 5.7 ± 0.2) were in good agreement with expected values (1.0 ± 0.1 μM and log K′ = 6.1). In the supplemented culture medium, total ligand concentration in the micromolar range (60–80 μM) and conditional stability constants (5.5 < log K′ < 6.5) were determined. Cd(II) complexes detected in the different stages of microbial growth are labile from an electrochemical point of view. Results were compared to the case of Cd(II) non-supplemented broth.

Cadmium Complexation in Culture Media

AbstractSquare‐wave anodic stripping voltammetry (SW‐ASV) has been applied to monitor changes in the complexing capacity (CC) in a microbiological culture medium through different physiological states, focusing on cadmium interactions with the potential ligands. Total ligand concentration (Lt) is evaluated both from the titration curve and Ruzic linearization, with good agreement between the methods. Values obtained for the conditional stability constant suggest the occurrence of moderate ligands. Results show that the studied culture medium is capable of complexing cadmium and that the complexing capacity is affected by the physiological states of bacteria.

Voltammetric evaluation of binding abilities of tannery effluents by competing ligand exchange method using model solutions of Cr(VI), Ni(II), Cu(II) and Pb(II)

Metal complexation capacity (CC) is an important parameter in assessing the quality of wastewaters. In this study, CC and complexation kinetics of tannery wastewater was evaluated using the competing ligand exchange approach with model solutions of Cr(VI), Ni(II), Cu(II) and Pb(II). Ethylenediaminete-traactic acid (EDTA) was used as competing ligand in complexation studies of Cu and Pb while dimethylglyoxime (DMG) and diethylenetriaminepentaacetic acid (DTPA) were used in the case of Ni and Cr, respectively. Determination of labile metal fraction was done using differential pulse anodic stripping voltammetry (DPASV) (Cu and Pb) and differential pulse adsorptive cathodic stripping voltammetry (DPAdCSV) (Ni and Cr) at a hanging mercury drop electrode (HMDE). Flame atomic absorption spectrophotometry (FAAS) was used to determine total and dissolved chromium in the tannery wastewater samples. Results show high complexation capacities (9.03–436.81 μM) and fast kinetics of the tannery effluent, with most of the inert metal species being formed within the first two minutes. The kinetic curves for all the metals showed two kinetically distinguishable components, except for nickel which had an extra component. Speciation results revealed that less than 3% of the chromium in the wastewater was present in the dissolved phase, while no labile forms were detected. The study has demonstrated the role of CC of wastewater in metal speciation and environmental remediation.

Cadmium binding by fractions of dissolved organic matter and humic substances from municipal solid waste compost.

The agricultural practice of amending soils with composted municipal solid waste (MSW) adds significant amounts of organic matter and trace metals, including Cd. Under these conditions, soluble organic complexes of Cd formed in the compost may be more significant than previously thought, due to Cd bioavailability and mobility in the soil environment. To study the relative importance of different types of organic ligands in MSW compost for the binding of Cd, six fractions of the dissolved organic matter (DOM) in addition to humic acid (HA) and fulvic acid (FA) were extracted and their complexation of Cd quantified at pH 7 using an ion-selective electrode (ISE). The highest complexing capacities (CC) for Cd were found for the most humified ligands: HA (2386 micromol Cd g(-1) C of ligand), predialyzed FA (2468 micromol Cd g(-1) C), and HoA, a fulvic-type, easily soluble fraction (1042 micromol Cd g(-1) C). The differences in CC for Cd of the various organic ligands were not directly related to total acid-titratable or carboxylic groups, indicating the importance of sterical issues and other functional groups. The strength of association between Cd and the organic ligands was characterized by calculating stability constants for binding at the strongest sites (pK(int)) and modeling the distribution of binding site strengths. The pK(int) values of the DOM fractions ranged between 6.93 (HiN: polysaccharides) and 8.11 (HiB: proteins and aminosugars), compared with 10.05 for HA and 7.98 for FA. Hence, the highly complex and only partially soluble organic molecules from compost such as HA and FA demonstrated the highest capacity to sequester Cd. However, strong Cd binding of organic ligands containing N-functional groups (HiB) in addition to a high CC of soluble, humified ligands like HoA indicated the relevance of these fractions for the organic complexation of Cd in solution.

Binding of cadmium, copper, and zinc to humic substances originating from municipal solid waste compost

AbstractThe application of municipal solid waste (MSW) compost increases both the trace metal loading and the organic matter in the soil. To characterize the quality and metal‐binding capacity of the compost OM, we extracted humic acid (HA) and fulvic acid (FA) from mature MSW compost and analyzed them for elemental composition, acid‐titratable functional groups, total metal content, and structural components (by 13C NMR). HA constituted 67% of all extracted humic substances and differed significantly from HAs of cultivated lands: The compost HA exhibited smaller molecular size, a higher N content, and lower aromaticity due to large amounts of saturated aliphatic components. Metal complexation studies of the extracted HA and FA were performed by equilibrium dialysis titration. The complexing capacity (CC) was highest for Cu: CCHA = 3357 and CCFA = 5221 μmol Cu g−1 of dissolved organic carbon (DOC) at pH 5. Zn and Cd were bound (at pH 7) in smaller concentrations: CCHA(Zn) = 2167, CCFA(Zn) = 2809, CCHA(Cd) = 2386, and CCFA(Cd) = 2468 μmol metal g−1 of DOC. Stability constants for binding on the strongest sites (pKint) were determined as pKintHA = 6.6 and pKintFA = 7.3 for Cu at pH 5; and pKintHA = 8.0 and pKintFA = 6.4 for Cd at pH 7. Since these measured parameters fall within the ranges of values obtained for soil humic substances, we conclude that in soils with little organic matter, compost addition will significantly increase the amount of highly reactive organic complexing agents for trace metals in the soil.

Temporal variation of copper and zinc complexation capacity in the Humber estuary.

The complexation capacity (CC) for zinc and copper in the Humber estuary was determined and compared with data obtained using the same procedures from previous years. The CC for both metals was found to be relatively stable over a time span of 4 years for zinc and 10 years for copper. Levels of CC ranged from, in the upper estuary, 400 nM (copper) and 150 nM (zinc) to between 25 and 50 nM for both metals in the lower estuary. The CC from freshwater inputs appears to be relatively conservative with simple dilution accounting for the decrease in CC as salinity increases. A seasonal effect for copper is suggested.

Determination of organic matter in water using organo-metal complexes

The present communication makes an attempt to determine the organic matter present in water/waste water through electrochemical complexometeric titration using Differential Pulse Anodic Stripping Voltammetry (DPASV) by estimating Complexing Capacity (CC) of organo–metal complexes in terms of Chemical Oxygen Demand (COD c). The results of complexing capacity (CC) method showed good correlation with those of the standard COD s method.

Copper complexation in English Rivers

Data for copper complexation capacity (CC), determined by cathodic stripping voltammetry, are presented for 36 English rivers. Values for CC were between 40 and 500 nM. No predictive relationship between major water quality parameters and CC was found. A comparison of determinations made on the same water bodies over several years points towards consistency of CC with time. It is concluded that, in river waters of a wide range of types, forms of copper complexed by organic matter predominate substantially over free or inorganic forms of the metal.

Selection of an organic acid analogue of dissolved organic matter for use in toxicity testing

Uncontaminated stream waters in the vicinity of a Co mine in Idaho were titrated with Cu to determine the Cu-binding characteristics of natural dissolved organic matter (DOM) and suspended particles. Nonlinear regressions of bound versus free Cu concentrations were consistent with a two-ligand model for DOM complexation of Cu, in which the conditional stability constants (log K) and complexation capacities (CC) were log K1 = 7.26, CC1 = 0.21 µmol Cu·mg dissolved organic carbon (DOC)-1 and log K2 = 5.13, CC2 = 2.89 µmol Cu·mg DOC-1. Copper-binding constants were similar in filtered (0.45 µm) and unfiltered water samples. Calcium, Mg, and Co did not compete appreciably with Cu for DOM complexation at concentrations present in site waters. Copper binding to amorphous iron oxide flocs also was not important at the Fe concentrations present in the stream waters. We selected a mixture of three organic acids, dipicolinic, oxalic, and malonic, to mimic the Cu-binding properties of this DOM. Geochemical models were developed to estimate Cu speciation and evaluate its bioavailability in companion fish toxicity tests using the DOM analogue (Marr et al. 1999. Can. J. Fish. Aquat. Sci. 56: 1471-1483).

Characterization of chromium and copper complexes with fulvic acids isolated from soils in Slovenia

Fulvic acids (FA) were isolated from Slovenian peat and forest soils in order to prepare their chromium (Cr) and copper (Cu) complexes. The elemental composition and the COOH content of FA were measured. Both FA and FA complexes were characterized by gel permeation chromatography (GPC) and infrared spectroscopy (IR). Conditional stability constants (Kst) and complexation capacities (CC) of FA complexes were determined by the method based on ion exchange equilibrium. Both FA showed similar composition, average molecular weight and IR spectra. Substantial differences were found in IR spectra, Kst and CC between Cu and Cr complexes of the same FA as well as between different FA and the same metal. Cr complexes exhibited higher stability and larger CC values in comparison with Cu complexes. The same is true for peat FA in relation to forest FA. According to the IR spectra, Cu is predominantly bound to COO− groups while in Cr complexes other functional groups or different mechanisms might also be involved.