Jana Jaklová Dytrtová

Complexation between the fungicide tebuconazole and copper(II) probed by electrospray ionization mass spectrometry

Electrospray ionization mass spectrometry (ESI-MS) is used to probe the complex formation between tebuconazole (1) and copper(II) salts, which both are commonly used fungicides in agriculture. Experiments with model solutions containing 1 and CuCl(2) reveal the initial formation of the copper(II) species [(1)CuCl](+) and [(1)(2)CuCl](+) which undergo reduction to the corresponding copper(I) ions [(1)Cu](+) and [(1)(2)Cu](+) under more drastic ionization conditions in the ESI source. In additional experiments, copper/tebuconazole complexes were also detected in samples made from soil solutions of various origin and different amount of mineralization. The direct sampling of such solutions via ESI-MS is thus potentially useful for understanding of the interactions between copper(II) salts and tebuconazole in environmental samples.

The use of differential pulse anodic stripping voltammetry and diffusive gradient in thin films for heavy metals speciation in soil solution

In the soil solutions obtained in situ with suction cups from soils (Cambisol and Fluvisol) of pot experiment with Salix smithiana Smith, Lolium perenne L. and Thlaspi caerulescens J. & C. Presl heavy metals species (Cd, Pb and Cu) were assayed by differential pulse anodic stripping voltammetry and diffusive gradient in thin films. Prediction of accumulation performed best at free metal ion concentrations in unchanged pH (in 10−3 mol L−1 NaClO4 base electrolyte). The speciation provided by differential pulse anodic stripping voltammetry according to pH can provide a detailed description of the soil solution matrix. The concentration of free metals in unchanged pH represents a small part of the total content and varied from 0.04 to 0.75% with two exceptions found for accumulating plants (the content of Cd2+ in the soil solution from T. caerulescens was about 6% and the content of Cu2+ in the soil solution from S. smithiana was about 30%). The available concentration as determined by diffusive gradient in thin films was not in correlation with the heavy metals concentration in plant biomass.

A new approach to study cadmium complexes with oxalic acid in soil solution

This study presents a new analytical approach for the determination of heavy metals complexed to low-molecular-weight-organic acids in soil solutions, which combines the sensitivity of differential pulse anodic stripping voltammetry (DPASV) with the molecular insight gained by electrospray ionization mass spectrometry (ESI-MS). The combination of these analytical methods allows the investigation of such complexes in complex matrixes. On the voltammograms of the soil solutions, in addition to the expected complexes of oxalic acid with cadmium and lead, respectively, also peaks belonging to mixed complexes of cadmium, lead, and oxalic acid (OAH(2)) were observed. In order to verify the possible formation of complexes with OAH(2), aqueous solutions of OAH(2) with traces of Cd(II) were investigated as model systems. Signals corresponding to several distinct molecular complexes between cadmium and oxalic acid were detected in the model solutions using negative-ion ESI-MS, which follow the general formula [Cd(n)(X,Y)((2n+1))](-), where n is the number of cadmium atoms, X=Cl(-), and Y=OAH(-). Some of these complexes were also identified in the ESI mass spectra taken from the soil solutions.

Determination of acid dissociation constants of triazole fungicides by pressure assisted capillary electrophoresis.

Pressure assisted capillary electrophoresis was applied to determination of acid dissociation constants (pKa) of six widely used triazole fungicides (cyproconazole, epoxiconazole, flusilazole, tebuconazole, penconazole and propiconazole) in aqueous medium. The pKa values were determined from the dependence of effective electrophoretic mobility of the triazole fungicides on p[H(+)] of the background electrolyte (BGE) using non-linear regression analysis. The p[H(+)] was used instead of pH to reflect the increased ionic strength of the strongly acidic BGEs (pH<1.75) as compared to the BGEs at pH equal to or greater than 1.75. Prior to the pKa calculation, the measured effective electrophoretic mobilities were corrected to the reference temperature (25°C) and constant ionic strength (25mM). The regression function was modified to allow the determination of pKa in the BGEs of varying ionic strength. The electrophoretic measurements showed that the above triazole fungicides are very weak bases - their pKa values were found to be in the range 1.05-1.97 and were in a good agreement with the values calculated by SPARC online pKa calculator.

Passive diffusion assessment of cadmium and lead accumulation by plants in hydroponic systems

Abstract In experiments with willow planted in cadmium- or lead-contaminated Knopp nutrient solutions, the ability of willow and chelex gel in the diffusive gradient in a thin film (DGT) unit to absorb these elements was observed and compared. A method to compare the accumulated amount of metals by the willow and the sorbed amount of metal onto the DGT unit was designed. The accumulated/sorbed amount of metals was recalculated to the same units (μg cm−2 day−1). The study of Cd(Pb) dynamic uptake by willow showed an exponential decrease of metal content in the exposure solution. The willow planted in the Knopp nutrient solution accumulated Cd(Pb) less than did the DGT unit in the same matrix. The willow planted in the soil/water system accumulated more lead than did the willow in a lead-contaminated aquatic system nor did the DGT unit in the nitrate matrix. The willow further accumulated lead from the soil/water system due to the active co-uptake of nutrients and lead. The DGT technique was considered as very good comparative method to measure heavy metals plant uptake. This technique is suitable for use in water as well as in soil systems.

Formation of Tebuconazole Complexes with Cadmium(II) Investigated by Electrospray Ionization Mass Spectrometry

The formation of complexes between tebuconazole (Teb) and cadmium in simplified model solutions as well as soil solutions was studied using electrospray ionization mass spectrometry. Teb and cadmium form two types of complexes with the general formulas [Cd(Teb)n]2+ (n = 1–4) and [CdI(Teb)m]+ (m = 1–3), where iodine corresponds to the counterion used. The most intense Teb/cadmium complex is [CdI(Teb)2]+, and the most stable one is [Cd(Teb)(Teb − H)]+. Another detected complex, the dication [Cd(Teb)4]2+, was considered as the origin complex for the iodine-free complexes and was found in a sample prepared from forest soil solution naturally contaminated with cadmium ions.

Experimental and theoretical study on cation–π interaction of Ag+ with [6]helicene

By employing electrospray ionization mass spectrometry, it was proven experimentally that the [6]helicene–Ag+ complex (i.e., [Ag(C26H16)]+) exists in the gas phase. Further, applying quantum mechanical DFT calculations, the most probable structure of this cationic complex [Ag(C26H16)]+ was derived. Finally, in the solid state, the complex [6]helicene–silver triflate–monohydrate (i.e., C26H16–AgCF3SO3–H2O), crystallizing in the monoclinic system with the centro-symmetric P21/c space group, was prepared and analyzed. The characteristic feature of this complex packing in the solid state is the formation of the separated [6]helicene and silver triflate domains. In both of these binding modes, the investigated [6]helicene ligand functions as a molecular tweezer for the univalent silver cation.Graphical abstract

Study of solvent effects on the stability constant and ionic mobility of the dibenzo‐18‐crown‐6 complex with potassium ion by affinity capillary electrophoresis

The effect of solvent on the strength of noncovalent interactions and ionic mobility of the dibenzo-18-crown-6 complex with K+ in water/organic solvents was investigated by using affinity capillary electrophoresis. The proportion of organic solvent (methanol, ethanol, propan-2-ol, and acetonitrile) in the mixtures ranged from 0 to 100 vol.%. The stability constant, KKL , and actual ionic mobility of the dibenzo-18-crown-6-K+ complex were determined by the nonlinear regression analysis of the dependence of the effective electrophoretic mobility of dibenzo-18-crown-6 on the concentration of K+ (added as KCl) in the background electrolyte (25 mM lithium acetate, pH 5.5, in the above mixed hydro-organic solvents). Competitive interaction of the dibenzo-18-crown-6 with Li+ was observed and quantified in mixtures containing more than 60 vol.% of the organic solvent. However, the stability constant of the dibenzo-18-crown-6-Li+ complex was in all cases lower than 0.5 % of KKL . The log KKL increased approximately linearly in the range 1.62-4.98 with the increasing molar fraction of organic solvent in the above mixed solvents and with similar slopes for all four organic solvents used in this study. The ionic mobilities of the dibenzo-18-crown-6-K+ complex were in the range (6.1-43.4) × 10-9 m2 V-1 s-1 .

Complexation of malic acid with cadmium(II) probed by electrospray ionization mass spectrometry

Electrospray ionization was used as a technique for the characterization of the interactions between cadmium(II) ions and malic acid (1) in aqueous solution. Particular attention was paid to the nature of the species formed, which generally correspond to complexes of CdX(+) cations with neutral malic acid, where X either is the counterion of the metal salt used as a precursor (i.e. X=Cl, I) or corresponds to singly deprotonated malic acid. In pure water solutions, also highly coordinated complexes [Cd(1-H)(1)(2)](+) and [CdCl(1)(2)](+) were detected, whereas the most abundant complexes detected in a sample of soil solution were: [Cd(1-H)(1)](+) and [CdCl(1)](+). With respect to possible application in environmental analysis, the effects of (i) metal salts present in solution, (ii) modest mineralization, and (iii) the matrices of real soil solutions were probed. While the presence of other metals leads to additional complexes, the characteristic species containing both cadmium(II) and malic acid can still be detected with good sensitivity.

Mimicking of cyproconazole behavior in the presence of Cu and Zn

RATIONALE The frequently used pesticide cyproconazole (Cyp) interacts with the essential elements commonly present in soil which play important roles in various enzymatic processes. These interactions predetermine the Cyp degradation pathways. We suggest a simple experimental and theoretical approach for the prediction of pesticide behavior. METHODS Cu/Cyp complexes are explored because of the typical Cu(II) reduction in complexes. Its level and the stability of the Cu-ligand bond depend on the type and the number of the surrounding ligands. Zn/Cyp complexes were compared as it is not expected that Zn(II) will reduce. The complexations were studied by means of electrospray ionization ion trap mass spectrometry and MS/MS collision-induced dissociations with comparative and explicative density functional theory calculations. RESULTS The Cyp ligand allows both Cu(II) reduction as well as, in specific cases, it protects the higher Cu oxidation state. The reduction is observed in the complexes with solely neutral Cyp where the number of ligands is below 3; a higher number protects the Cu(II) state. The metal atom binds to Cyp via N2 of the triazole ring as well as via π-electrons of the benzene ring; additional stabilization brings an interaction with the deprotonated OH group. CONCLUSIONS The character of Cyp interactions with doubly charged metals (Cu(II), Zn(II)) clarified the creation of Cyp metabolites. The phenyl and triazole rings are bound to the metal cation and enable access for the isopropyl ring to be cleaved leaving the common metabolite (CAS Number: 58905-19-4).