Enhancing bioactive compounds accumulation in red beet (Beta Vulgaris L.) plants by managing N nutrition. The identification of the 'critical' zone as a cultivation technique.

The increasing interest in natural health-promoting compounds, which are mostly plant secondary metabolites, inspired attempts to stimulate mechanisms strengthening their bioaccumulation in crop plants via abiotic stress while maintaining the yield potential. This study investigates the long-term effects of limiting nitrogen (N) supply on the concentration of total phenolics, free radical activity of natural antioxidants, betacyanin content, biomass production, net photosynthetic rate, total chlorophyll content, and plant water relations in red beetroot plants (Beta vulgaris L.) grown hydroponically. Depending on fertilization, the range of N supply for evaporative demand comprises two contrasted nutrient zones, in which N is limiting (zone-1) or non-limiting (zone-2). Based on the carbon-nutrient-balance hypothesis, at the transition from 1st-zone to 2nd-zone, there is a narrow transition zone in which the plant nutrient status is considered 'critical'. Herein, to determine the 'critical' zone, a modified Michaelis-Menten (M-M) model was used using a piecewise linear regression on two indexes: net photosynthetic rates and free radical-scavenging capacity of phenolic antioxidants. The model showed that the 'critical' transition points of net photosynthetic rate and phenolic free radical content are located in a narrow zone ranging between 196.70 ± 8.75 and 271.54 ± 75.50 ppm NO3-, while the cropping season appears to affect slightly the range of 'critical' (transition) zone. Thus, supplying N to red beetroot plants to levels ranging within this 'critical' zone may be an efficient, profitable and sustainable way to increase the accumulation of health-promoting plant bioactive compounds (total phenolic compounds with radical activity and betacyanins) in hydroponically cultivated reed beetroot plants.

Determination of genotoxic effects of methidathion alkaline hydrolysis in human lymphocytes using the micronucleus assay and square-wave voltammetry.

The interaction of pesticides with environmental factors, such as pH, may result in alterations of their physicochemical properties and should be taken into consideration in regard to their classification. This study investigates the genotoxicity of methidathion and its alkaline hydrolysis by-products in cultured human lymphocytes, using the square-wave voltammetry (square wave-adsorptive cathodic stripping voltammetry (SW-AdCSV) technique) and the cytokinesis block micronucleus assay (CBMN assay). According to the SW-AdCSV data the alkaline hydrolysis of methidathion results in two new molecules, one non-electro-active and a second electro-active which is more genotoxic than methidathion itself in cultured human lymphocytes, inducing higher micronuclei frequencies. The present study confirms the SW-AdCSV technique as a voltammetric method which can successfully simulates the electrodynamics of the cellular membrane.

Interfacial thermodynamics of gallic acid adsorption on a chargeable hydrophobic surface.

The thermodynamics of adsorption of gallic acid (GA, 3,4,5-trihydroxylbenzoic acid) on the hanging mercury drop electrode (HMDE) surface was studied by temperature-dependent stripping voltammetry (TD-SV), at physiological pH 7.4. The thermodynamic parameters, e.g., Gibbs free energy, ΔG(ADS), enthalpy, ΔΗ(ADS) and entropy, ΔS(ADS), of adsorption have been determined at physiological temperatures 2-40 °C. Chemisorption of the radical species ≡[GA(OH)(2)(O(-))]* is the energetically important reaction. The thermodynamic data show a complex mechanism of adsorption of GA on the electrode surface, which is strongly dependent on temperature. At low-temperatures T<12 °C, adsorption is controlled by enthalpy, while at T>22 °C, adsorption is entropy driven. In the temperature range 12 °C and 22 °C, a combined enthalpy-entropy stabilization occurs. A mechanism is proposed which analyses the implication of thermodynamics to the interfacial adsorption of polyphenols with cell membranes under physiological conditions.

Differential micronuclei induction in human lymphocyte cultures by imidacloprid in the presence of potassium nitrate.

Humans are exposed to pesticides as a consequence of their application in farming or their persistence in a variety of media, including food, water, air, soil, plants, animals, and smoke. The interaction of pesticides with environmental factors may result in the alteration of their physicochemical properties. Square wave cathodic stripping voltammetry (SW-CSV), a technique that simulates electrodynamically the cellular membrane, is used to investigate whether the presence of potassium nitrate (KNO(3)) in the culture medium interferes with the genotoxic behavior of imidacloprid. The cytokinesis block micronuclei (CBMN) method is used to evaluate imidacloprid's genotoxicity in the absence or presence of KNO(3) in the culture medium and, as a consequence, its adsorption by lymphocytes. Comparing micronuclei (MN) frequencies in control and imidacloprid-treated blood cell cultures, statistically significant differences were not detected. KNO(3) did not induce MN frequencies compared to control. Statistically significant differences in MN frequencies were observed when blood cell cultures were treated with imidacloprid in the presence of increasing concentrations of KNO(3). SW-CSV revealed that by increasing KNO(3) molarity, imidacloprid's concentration in the culture medium decreased in parallel. This finding indicates that imidacloprid is adsorbed by cellular membranes. The present study suggests a novel role of a harmless environmental factor, such as KNO(3), on the genotoxic behavior of a pesticide, such as imidacloprid. KNO(3) rendered imidacloprid permeable to lymphocytes, resulting in elevated MN frequencies.

A humic-acid-like polycondensate produced with no use of catalyst.

The synthesis and physicochemical characterization of a water soluble humic-acid-like polycondensate (HALP), which mimics fundamental physicochemical and spectroscopic properties of natural humic acids is presented. The polymer can be synthesized under ambient O(2) by oxidative co-polymerization of gallic (GA) and protocatechuic (PA) acid at pH >9, with no need for a catalyst. Solid state (13)C NMR spectra for GA-PA-HALP show that ring-opening reactions of GA, PA monomers are involved in GA-PA-HALP formation. EPR spectroscopy shows that GA-PA-HALP contains stable phenol-based radicals, with pH-dependent concentration. The H-binding profile of GA-PA-HALP follows the NICA-Donnan model, with two sets of distributed pK(a) values in the range 4-6 corresponding to carboxyl groups, and 7-9 corresponding to phenolic groups, as in natural HA. GA-PA-HALP bears a permanent negative charge Q(0)=-2.3 equiv kg(-1) which is higher than the literature Q(0) values of -1 to -2 equiv kg(-1) observed for natural HAs. A critical comparison of the present data with literature data is provided.

Thermodynamics of adsorption of dithiocarbamates at the hanging mercury drop.

Two dimethyldithiocarbamate (DMDTC) pesticides, thiram and ziram, are adsorbed onto a Hg drop via an entropically driven process. The adsorption isotherms are described by the Frumkin equation. For both molecules, the adsorption is characterized by a nonlinear pseudosigmoid temperature dependence of the Gibbs free energy. For the temperature range of 273-313 K, DeltaGADS varies between -43.4 and -56.71 kJ/mol for thiram and -42.60 and -55.67 kJ/mol for ziram. This variation of DeltaGADS reveals that the adsorption strength is increased at higher temperatures. During the adsorption of either molecule, strong lateral interactions are developed between neighboring adsorbates, which are severely weakened as the temperature increases. A unified reaction scheme is suggested for both ziram and thiram that predicts the formation and adsorption of a surface complex, (DMDTC)2Hg. In the case of thiram, two DMDTC molecules are formed by the cleavage of the disulfide S-S bond near the Hg electrode. The thermodynamic and structural parameters reveal that there are two limiting thermodynamic regimes for the adsorbed (DMDTC)2Hg species that originate from two limiting adsorption conformations of the adsorbates on the Hg surface. A transition occurs between these two conformations at temperatures in the region of 285-295 K. This transition is accompanied by large entropic and enthalpic changes.

Adsorption and radical stabilization of humic-Acid analogues and Pb2+ on restricted phyllomorphous clay.

Humic acids have stable radicals that are indigenous to their structure. Hydroxybenzoic acid derivatives such as gallic acid (GA) and protocatechuic acid are appropriate models for the radical properties of humic acids. Here we show that the adsorption or intercalation of gallic acid in Laponite clay results in a significant thermodynamic stabilization of gallic acid radicals. Moreover, the formed organoclay shows enhanced stability against acid dissolution. The structural details of the association of gallic acid with Laponite depend on the GA/Laponite loading. At low GA/Laponite ratios (approximately 10(-6) M of gallic acid per gram of clay), gallic acid is adsorbed at the variable charge sites of Laponite. This adsorption can be adequately described by surface complexation modeling. At higher GA/Laponite ratios (approximately 10(-3) M of gallic acid per gram of clay), X-ray diffraction data show that gallic acid is intercalated at the interlamellar sites of Laponite. In the presence of Pb2+ ions, the formed GA/Pb complex is associated with Laponite in an analogous structural manner, that is, adsorption at variable charge sites or intercalation at the interlamellar sites of Laponite, depending on the loading. Laponite stabilizes the GA/Pb radicals. At prolonged exposure to ambient O2, Laponite promotes the formation of stable oligomeric GA/Pb radical species, which are intercalated into interlamellar sites.