Copper complexing capacity in fresh-waters using the catechol-cathodic stripping voltammetric method

Abstract

The catechol-cathodic stripping voltammetric (CSV) method for measurement of the copper complexing capacity of marine and estuarine waters, has been modified and applied to fresh-waters. The optimum catechol concentration needed was the major difference between the two methods. It was found necessary to separately optimise the catechol concentration for each of the three fresh-water samples tested, presumably because of the much greater differences in the concentration of complexing ligands in fresh-water compared with marine or estuarine waters. This limits the usefulness of the CSV method for the determination of the complexing capacity of fresh-waters.

The total ligand concentration ([L_t]) and conditional stability constants (*K) derived for the three fresh-waters are compared with similar data obtained using an anodic stripping voltammetric (ASV) method. The set of copper-binding ligands determined using the CSV method were slightly lower in concentration, but stronger binding, than those obtained using the ASV method (CSV: [L_t] 0.04–0.06 μM, log K(pH 6) 8.9–9.4; ASV: [L_t] 0.11–0.17 μM, log *K(pH 6) 7.9–8.1).     

Lead complexation behaviour of root exudates of salt marsh plant Salicornia europaea L

Abstract

Root exudates are considered to have an important role in mobility and bioavailability of heavy metals. High molecular weight (HMW) substances are the main components of root exudates, however, knowledge about their interactions with heavy metals is lacking. In the present study, Pb(II) complexation of the HMW fluorescent fractions in root exudates from Salicornia europaea L. was investigated using excitation emission matrix (EEM) fluorescence spectroscopy. Two protein-like fluorescence peaks were identified in the EEM spectrum of root exudates. The fluorescence of both peaks was clearly quenched by Pb(II). The values of conditional stability constants, log K_a, for these two protein-like fluorescence peaks were 4.14 and 3.79. This indicates that the fluorescent substances are strong Pb(II) complexing organic ligands.     

Water-soluble titanocene complexes with sulfur-containing aminoacids: synthesis, spectroscopic, electrochemical and Ti(IV)–transferrin interaction studies

Three new water soluble titanocene–aminoacid complexes have been synthesized via the reaction of Cp₂TiCl₂ and two equivalents of aminoacid (L) in methanol, affording [Cp₂TiL₂]Cl₂, L=L-cysteine (2), D-penicillamine (3) and L-methionine (4). These complexes have been characterized by ¹H, IR and UV-Vis spectroscopies, elemental analysis and cyclic voltammetry. Kinetic studies of ligand hydrolysis have been monitored at low pH using UV-Vis and ¹H NMR spectroscopies to assess their stability in aqueous solution. At low pH, aminoacid ligands are lost one order of magnitude faster than cyclopentadienyl. However, at physiological pH, in Tris buffer solution, the complexes decompose rapidly to form an insoluble titanium compound. The affinity of these complexes to apo-transferrin was also investigated to elucidate how the ancillary aminoacid ligands affect the titanium intake by apo-transferrin.Electronic Supplementary Material Supplementary material is available for this article at     

A comparison of Fe bioavailability and binding of a catecholate siderophore with virus-mediated lysates from the marine bacterium Vibrio alginolyticus PWH3a

We have examined the bioavailability of Fe complexed to a siderophore produced by the heterotrophic marine bacterium Vibrio alginolyticus isolate PWH3a and Fe from ligand-complexes present in virus-mediated lysates (using phage PWH3a-P1) of this same bacterium. Fe-binding functional groups, stability constants and the bioavailability of Fe associated with these two separate ligand pools were determined and contrasted to previous work. Under low-Fe growth conditions, axenic cultures of V. alginolyticus PWH3a were shown to produce catecholate siderophores, while neither catecholate nor hydroxamate-type Fe-binding moieties were detected in virus-generated cell lysates. Analysis of the overall binding strength using electrochemical techniques revealed that the siderophore-containing organic extract and the organics in the virus-mediated lysates had Fe-binding constants comparable to the weaker L₂-type ligands found throughout the water column in seawater. A further purification of the siderophore-containing extract revealed a ligand with a stability constant of logK′_FeL,Fe3+ = 22.3, typical for siderophores and L₁-type of ligands found in marine surface waters. In assimilation studies, the Fe in the lysate was found to be more bioavailable to our model heterotrophic bacterium, autotrophic cyanobacterium and eukaryotic diatom cultures than the catecholate siderophore produced by the Vibrio sp. This work demonstrates that the Fe-containing components of virus-mediated cell lysates are different than siderophores secreted by these same cells, and as such continues to build the argument supporting the importance of virus-mediated Fe regeneration in marine surface waters.     

On the relative stability of tetragonal and trigonal Cu(II) complexes with relevance to the blue copper proteins

 The role of the cysteine thiolate ligand for the unusual copper coordination geometry in the blue copper proteins has been studied by comparing the electronic structure, geometry, and energetics of a number of small Cu(II) complexes. The geometries have been optimised with the density functional B3LYP method, and energies have been calculated by multiconfigurational second-order perturbation theory (the CASPT2 method). Most small inorganic Cu(II) complexes assume a tetragonal geometry, where four ligands make σ bonds to a Cu 3d orbital. If a ligand lone-pair orbital instead forms a π bond to the copper ion, it formally occupies two ligand positions in a square coordination, and the structure becomes trigonal. Large, soft, and polarisable ligands, such as SH^– and SeH^–, give rise to covalent copper-ligand bonds and structures close to a tetrahedron, which might be trigonal or tetragonal with approximately the same stability. On the other hand, small and hard ligands, such as NH₃, OH₂, and OH^–, give ionic bonds and flattened tetragonal structures. It is shown that axial type 1 (blue) copper proteins have a trigonal structure with a π bond to the cysteine sulphur atom, whereas rhombic type 1 and type 2 proteins have a tetragonal structure with σ bonds to all strong ligands. The soft cysteine ligand is essential for the stabilisation of a structure that is close to a tetrahedron (either trigonal or tetragonal), which ensures a low reorganisation energy during electron transfer. Received: 9 July 1997 / 26 November 1997     

Synthesis,characterization, redox behavior,DNA and protein binding and antibacterial activity studies of ruthenium(II) complexes of bidentate schiff bases

Two new ruthenium(II) complexes of Schiff base ligands (L) derived from cinnamaldehyde and ethylenediamine formulated as [Ru(L)(bpy)₂](ClO₄)₂, where L¹ = N,N’-bis(4-nitrocinnamald-ehyde)ethylenediamine and L² = N,N’-bis(2-nitrocinnamaldehyde)-ethylenediamine for complex 1 and 2, respectively, were isolated in pure form. The complexes were characterized by physicochemical and spectroscopic methods. The electrochemical behavior of the complexes showed the Ru(III)/Ru(II) couple at different potentials with quasi-reversible voltammograms. The interaction of the complexes with calf thymus DNA (CT-DNA) using absorption, emission spectral studies and electrochemical techniques have been used to determine the binding constant, K_b and the linear Stern–Volmer quenching constant, K_SV. The results indicate that the ruthenium(II) complexes interact with CT-DNA strongly in a groove binding mode. The interactions of bovine serum albumin (BSA) with the complexes were also investigated with the help of absorption and fluorescence spectroscopy tools. Absorption spectroscopy proved the formation of a ground state BSA-[Ru(L)(bpy)₂](ClO₄)₂ complex. The antibacterial study showed that the Ru(II) complexes (1 and 2) have better activity than the standard antibiotics but weak activity than the ligands.     

Photosynthetic inorganic carbon utilization and growth of Porphyra linearis (Rhodophyta)

Photosynthetic (oxygen evolution) and growth (biomass increase) responses to ambient pH and inorganic carbon (Ci) supply were determined for Porphyralinearis grown in 0.5 L glass cylinders in the laboratory, or in 40 L fibreglass outdoor tanks with running seawater. While net photosynthetic rates were uniform at pH 6.0–8.0, dropping only at pH 8.7, growth rates were significantly affected by pH levels other than that of seawater (c. pH 8.3). In glass cylinders, weekly growth rates averaged 76% at external pH 8.0, 13% at pH 8.7 and 26% at pH 7.0. Photosynthetic O₂ evolution on a daily basis(i.e. total O₂ evolved during day time less total O₂ consumed during night time) was similar to the growth responses at all experimental pH levels, apparently due to high dark respiration rates measured at acidic pH. Weekly growth rates averaged 53% in algae grown in fibreglass tanks aerated with regular air (360 mg L_-1 CO₂) and 28% in algae grown in tanks aerated with CO₂-enriched air (750 mg L^-1 CO₂). The pH of the seawater medium in which P. linear is was grown increased slightly during the day and only rarely reached 9.0. The pH at the boundary layer of algae submerged in seawater increased in response to light reaching, about pH 8.9 within minutes, or remained unchanged for algae submerged in a CO₂-free artificial sea water medium. Photosynthesis of P. linearissaturated at Ci concentrations of seawater (K_0.5560 μM at pH 8.2) and showed low photosynthetic affinity for CO₂(K_0.5 61 μM) at pH 6.0. It is therefore concluded that P. linearisuses primarily CO₂ with HCO₃ ^- being an alternative source of Ci for photosynthesis. Its fast growth could be related to the enzyme carbonic anhydrase whose activity was detected intra- and extracellularly. This revised version was published online in August 2006 with corrections to the Cover Date.     

The stability of the molybdenum-azotochelin complex and its effect on siderophore production in Azotobacter vinelandii

 Azotobacter vinelandii produces five siderophores with different metal binding properties, depending on the concentrations of Fe(III) and molybdate in the growth medium. The three lower protonation constants of the unusual bis(catecholamide) siderophore azotochelin (L) were determined by a simultaneous spectrophotometric and potentiometric titration as log K ₅=3.65(5), log K ₄=7.41(3) and log K ₃=8.54(4). The metal-ligand equilibrium constant for [MoO₂(L)]^3– was obtained from analysis of the absorbance concentration data: at 20  °C and pH 6.6, log K _eq=4(1). Based on an average log K _a value of 12.1 for the two basic phenolic oxygens of azotochelin, the equilibrium formation constant was converted into the conventional formation constant K _f(MoL) = [MoO₂L^{3 –}]/[MoO₂ ²⁺][L^{5 –}] = 10³⁵ M^–1. To assess the influence of molybdenum-siderophore interactions on metal uptake in A. vinelandii, the dose-response effect of molybdate in the growth medium on siderophore biosynthesis was followed by UV-vis spectroscopy and HPLC. It could be shown that the formation of molybdenum siderophore complexes clearly reduces the concentration of free siderophores available for iron solubilization. Furthermore, in media with initial molybdate concentrations up to 100 μM, the molybdenum azotochelin complex is the predominant molybdenum species, suggesting that azotochelin might also possess sequestering activity towards molybdenum. Even higher molybdate levels result in a complete repression of the synthesis of the tetradentate siderophore azotochelin, while they initiate the alternative release of the more efficient iron chelator, the hexadentate siderophore protochelin. Received: 20 April 1998 / Accepted: 29 June 1998     

Metal-based carboxamide-derived compounds endowed with antibacterial and antifungal activity

Abstract

A series of three bioactive thiourea (carboxamide) derivatives, N-(dipropylcarbamothioyl)-thiophene-2-carboxamide (L¹), N-(dipropylcarbamothioyl)-5-methylthiophene-2-carboxamide (L²) and 5-bromo-N-(dipropylcarbamothioyl)furan-2-carboxamide (L³) and their cobalt(II), copper(II), nickel(II) and zinc(II) complexes (1)–(12) have been synthesized and characterized by their IR,¹H-NMR spectroscopy, mass spectrometry and elemental analysis data. The Crystal structure of one of the ligand, N-(dipropylcarbamothioyl)thiophene-2-carboxamide (L¹) and its nickel(II) and copper(II) complexes were determined from single crystal X-ray diffraction data. All the ligands and metal(II) complexes have been subjected to in vitro antibacterial and antifungal activity against six bacterial species (Escherichia coli. Shigella flexneri. Pseudomonas aeruginosa. Salmonella typhi. Staphylococcus aureus and Bacillus subtilis) and for antifungal activity against six fungal strains (Trichophyton longifusus. Candida albicans. Aspergillus flavus. Microsporum canis. Fusarium solani and Candida glabrata). The in vitro antibacterial and antifungal bioactivity data showed the metal(II) complexes to be more potent than the parent ligands against one or more bacterial and fungal strains.     

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.     

Speciation of copper(II) in natural waters in the presence of ligands of high and intermediate strength

Abstract

A new procedure is presented for the determination of the ligands of copper(II) in natural waters, based on titration with the metal ion, monitored by measuring the concentration of copper(II) sorbed on the carboxylic resin Amberlite CG 50. The data are treated by the Ruzic linearization method to obtain the concentration of the ligands and the conditional stability constant of the complexes. Ligands with reaction coefficient α_M higher than 0.1 K*w/V are detected, where K* is the ratio of the concentration of sorbed metal to the concentration of free metal in solution, which can be evaluated from the sorption equilibria of copper(II) on Amberlite CG 50, w is the amount of water in the resin phase, and V the volume of the solution phase. Some natural waters at high and low salinity were examined. The ligand concentration determined in these samples ranged from around 50 to 2000 nM, while the original copper concentrations from 11 to 130 nM. The ligand concentration was always much higher than that of copper(II). The conditional stability constants were very high, particularly in low salinity waters, where values as high as K’= 10^15.7 were obtained. In high salinity waters values around 10⁹ were found for the complex formation constant of the ligands titrated with copper(II). The investigation was also extended to a model solution, containing EDTA, obtaining K’ = 10^15.5, in acceptable agreement with that evaluated from the literature values.     

Purification and characterization of laccase-1 fromPleurotus florida

Pleurotus florida (ITCC 3308) produces two laccase enzymes (L₁ and L₂) in potato-dextrose media containing 0.5% yeast extract. Concentrated culture filtrate was separated on DEAE-Sephadex (A-50) column into two enzyme peaks, subsequently named L₁ and L₂. The L₁ enzyme has been purified to homogeneity by ion-exchange and gel-permeation chromatography. L₁ is a monomeric glycoprotein with a molar mass of 77 and 82 kDa as determined by SDS-PAGE and gelfiltration chromatography, respectively. The pI value of L₁ has been determined to be 4.1. The optimum reaction temperature of the enzyme is 50°C. TheK _m and some other kinetic parameters of L₁ have been determined. Cyanide and azide completely inhibit the enzyme activity. The enzyme was fully active in 1: 1 (V/V) buffer-chloroform for at least 2 h. Spectroscopic analysis revealed that the enzyme has four copper atoms, a type 1 copper, a type 2 copper and a type 3 binuclear copper.     

Metal-based ethanolamine-derived compounds: a note on their synthesis,characterization and bioactivity

Abstract

Metal-based ethanolamines, (L¹)–(L⁴) coordinated with Co(II), Cu(II), Ni(II) and Zn(II) metals in 1:2 (metal:ligand) molar ratio to produce new compounds have been reported. These compounds were screened for their bactericidal/fungicidal activity against a number of bacterial (Escherichia coli, Shigella flexneri, Pseudomonas aeruginosa, Salmonella typhi, Staphylococcus aureus and Bacillus subtilis) and fungal strains (Trichophyton longifusus, Candida albicans, Aspergillus flavus, Microsporum canis, Fusarium solani and Candida glabrata) alongside against a shrimp species known as Artemia salina. The screening results indicated that metal complexes have significantly higher activity than uncomplexed ligands against one or more bacterial/fungal species due to chelation. The ligand (L⁴) displayed good bacterial and fungal activity as compared to other ligands. The antibacterial results revealed that the Zn(II) complex (16) of (L⁴) was found to be the most active complex and Co(II) complex (14) of the same ligand (L⁴), demonstrated the highest antifungal activity.     

A Method for Dissecting Two Site Receptor Interactions in Ligand Binding Studies

Abstract

A general model has been developed describing the relationship between the measured (IC₅₀) and absolute affinities (K_I), observed in radioligand binding studies when two ligands, one radioactive, interact with two receptors or binding sites. The model shows the dependence of the IC₅₀'s upon the concentration of radioligand for any combinations of the absolute affinities of the radioligand (K_d's) and the displacing ligand (K_I's). By constraining the affinities of the two ligands for the sites, five special cases of the general model can be described that model all possible 'selectivities' the ligands may have for the sites. The properties of these five cases can be exploited experimentally to probe the nature of the ligand/site interactions by the simple expedient of constructing a number of displacement curves at different radioligand concentrations. The method has been tested experimentally in three situations where two ligand/two site interactions occur, and is shown to be a useful technique to qualitatively examine the underlying binding reactions.     

Towards extracellular Ca<Superscript>2+</Superscript> sensing by MRI: synthesis and calcium-dependent <Superscript>1</Superscript>H and <Superscript>17</Superscript>O relaxation studies of two novel bismacrocyclic Gd<Superscript>3+</Superscript> complexes

Two new bismacrocyclic Gd³⁺ chelates containing a specific Ca²⁺ binding site were synthesized as potential MRI contrast agents for the detection of Ca²⁺ concentration changes at the millimolar level in the extracellular space. In the ligands, the Ca²⁺-sensitive BAPTA-bisamide central part is separated from the DO3A macrocycles either by an ethylene (L¹) or by a propylene (L²) unit [H₄BAPTA is 1,2-bis(o-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid; H₃DO₃A is 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid]. The sensitivity of the Gd³⁺ complexes towards Ca²⁺ and Mg²⁺ was studied by ¹H relaxometric titrations. A maximum relaxivity increase of 15 and 10% was observed upon Ca²⁺ binding to Gd₂L¹ and Gd₂L², respectively, with a distinct selectivity of Gd₂L¹ towards Ca²⁺ compared with Mg²⁺. For Ca²⁺ binding, association constants of log K = 1.9 (Gd₂L¹) and log K = 2.7 (Gd₂L²) were determined by relaxometry. Luminescence lifetime measurements and UV–vis spectrophotometry on the corresponding Eu³⁺ analogues proved that the complexes exist in the form of monohydrated and nonhydrated species; Ca²⁺ binding in the central part of the ligand induces the formation of the monohydrated state. The increasing hydration number accounts for the relaxivity increase observed on Ca²⁺ addition. A ¹H nuclear magnetic relaxation dispersion and ¹⁷O NMR study on Gd₂L¹ in the absence and in the presence of Ca²⁺ was performed to assess the microscopic parameters influencing relaxivity. On Ca²⁺ binding, the water exchange is slightly accelerated, which is likely related to the increased steric demand of the central part leading to a destabilization of the Ln–water binding interaction. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Copper complexing properties of dissolved organic matter: PARAFAC treatment of fluorescence quenching

Fluorescence quenching of the fluorescence is a useful method to determine copper complexing properties of the dissolved organic matter. This technique provides express results often by choosing one or two excitation-emission fluorescence measurement for a straight range of concentration. That why it is not representative of the whole sample. On another hand, using total luminescence spectra gives lots of information that is difficult to manipulate in term of complexing properties. This work focus on a fluorescence quenching experiment carried out on a filtered black water from Rio Negro from north Brazil (Sao Gabriel da Cachoeira) using excitation emission matrix of fluorescence (EEMF) with a large range of copper concentration. Indeed, metal additions were performed using logarithmic increments of the total copper concentration to cover a wide range of concentration from 1.7 × 10⁻⁹ to 10⁻³ mol l⁻¹. These data were treated by two different ways for comparison: on the one hand, data treatment were computed, as usually, at different fluorescence intensity positions using multi-response wavelength method with two ligand, and, on the another hand, a statistical method, parallel factor analysis (PARAFAC), was applied to extract fluorescent component. Then a fitting was done on these PARAFAC components with one or two complexing sites each one. Results show that PARAFAC enables quantitative evaluation of complexing parameters for copper as good as certain multi-response methods: L_1T 16.2 × 10⁻⁶ mol l⁻¹ (5.0 < log(K₁) < 5.8) and L_2T 3.0 × 10⁻⁴ mol l⁻¹ (2.8 < log(K₂) < 3.9). PARAFAC confirms that for this natural sample only two fluorescent ligands are present with two types of site for each component. No residual fluorescence was detected by the statistical treatment. Wall surface interferences were pointed-out as phenomenon to be solve to overcome the limiting efficiency of the total copper concentration range.     

Genetic and physiological evidence concerning the development of chemically sensitive voltage-dependent ionophores in L6 cells

The electrophysiological properties of a tissue culture muscle line, L₆, and a K⁺ resistant mutant (MK₁) derived from L₆ were determined to elucidate certain aspects of membrane differentiation and function. MK₁ was selected as a clone of myoblasts resistant to the toxic effects of 55 mM K⁺. The resting potentials of L₆ and MK₁ myoblasts and myotubes were K⁺ dependent and equal. The amplitudes of the action potentials were equal in normal medium, but 27.7 mM K⁺ interfered with or eliminated the ability of L₆ myotubes to produce action potentials. MK₁ myotubes produced nearly normal action potentials under these conditions. Thus, the K⁺ resistant myoblasts differentiate into myotubes which have an action potential generating mechanism much less sensitive to K⁺ than the normal mechanism. Also, both d-tubocurarine and α-bungarotoxin enhance the amplitude of the action potentials produced by L₆ myotubes in the presence of 27.7 mM K⁺; these compounds do not enhance the amplitude of the action potentials produced by MK₁ myotubes under the same conditions. It is proposed that as a consequence of differentiation a type of ionophore present in myoblasts becomes a voltage-dependent ionophore in myotubes. Furthermore, these voltage-dependent ionophores can be chemically sensitive.     

Evolution of 1, 3, 5-trisubstituted bipyrazole scaffold based platinum(II) complexes as a biological active agent

Abstract

Square planar mononuclear platinum(II) complexes having general formula [Pt(Lⁿ)Cl₂], (where, Lⁿ?=?L^1–4) were synthesized with neutral bidentate heterocyclic 1,3,5-trisubstituted bipyrazole based ligands. The synthesized compounds were characterized by physicochemical method such as TGA, molar conductance, micro-elemental analysis and magnetic moment, and spectroscopic method such as, FT-IR, UV–vis, ¹H NMR, ¹³C NMR and mass spectrometry. Biological applications of the compounds were carried out using in vitro brine shrimp lethality bioassay, in vitro antimicrobial study against five different pathogens, and cellular level cytotoxicity against Schizosaccharomyces pombe (S. Pombe) cells. Pt(II) complexes were tested for DNA interaction activities using electronic absorption titration, viscosity measurements study, fluorescence quenching technique and molecular docking assay. Binding constants (K_b) of ligands and complexes were observed in the range of 0.23–1.07?×?10⁵?M^?1 and 0.51–3.13?×?10⁵?M^?1, respectively. Pt(II) complexes (I–IV) display an excellent binding tendency to biomolecule (DNA) and possess comparatively high binding constant (K_b) values than the ligands. The DNA binding study indicate partial intercalative mode of binding in complex-DNA. The gel electrophoresis activity was carried out to examine DNA nuclease property of pUC19 plasmid DNA.     

Copper complexes with bioactive ligands. Part II--Antifungal activity

Antifungal activity of new copper(II) complexes of 2-methylthionicotinate (2-MeSNic) of the composition Cu(2-MeSNic)₂(MeNia)₂·4H₂O (where MeNia isN-methylnicotinamide), and Cu(2-MeSNic)₂(Nia)₂·2H₂O (where Nia is nicotinamide) and Cu(2-MeSNic)₂L₂ (where L is isonicotinamide, iNia, or ethyl nicotinate, EtNic) were tested on various strains of filamentous fungi by the macrodilution method. Most sensitive against copper(II) adducts with bioactive ligands wereRhizopus oryzae andMicrosporum gypseum (IC₅₀ 1.5–2.3 mmol/L). The adducts with Nia, MeNia and EtNic at 5 mmol/L induced morphological changes in growing hyphae ofBotrytis cinerea, mainly their intensive branching attached to release of cytoplasm with partial growth inhibition. Inhibition of sporulation (>90%) ofAlternaria alternata by Cu(2-MeSNic)₂·H₂O was observed as a change in the color of the colonies. The highest resistance was marked byB. cinerea andFusarium moniliforme (average IC₅₀ values 4.25 and 3.13 mmol/L, respectively). The presence of all bioactive ligands in copper(II) complexes caused an increase in the inhibition effect against model fungi (except significant inhibition activity of EtNic onR. oryzae). Part I: Copper complexes with bioactive ligands. Antimicrobial activity.Folia Microbiol.46, 379–384 (2001).     

Synthesis and characterization of glucosyl-curcuminoids as Fe3+ suppliers in the treatment of iron deficiency

The Fe³⁺ chelating ability of some curcumin glucosyl derivatives (Glc-H; Glc-OH; Glc-OCH₃) is tested by means of UV and NMR study. The pK _a values of the ligands and the overall stability constants of Fe³⁺ and Ga³⁺ complexes are evaluated from UV spectra. The only metal binding site of the ligand is the β-diketo moiety in the keto-enolic form; the glucosyl moiety does not interact with metal ion but it contributes to the stability of metal/ligand 1:2 complexes by means of hydrophilic interactions. These glucosyl derivatives are able to bind Fe³⁺ in a wide pH rage, forming complex species thermodynamically more stable than those of other ligands commonly used in the treatment of iron deficiency. In addition they demonstrate to have a poor affinity for competitive biological metal ions such as Ca²⁺. All ligands and their iron complexes have a good lypophilicity (log P > −0.7) suggesting an efficient gastrointestinal absorption in view of their possible use as iron supplements in oral therapy. The ligand molecules are also tested for their antioxidant properties in “ex vivo” biological system.