Complexation of several fungicides with beta-cyclodextrin: determination of the association constants and isolation of the solid complexes

The formation of inclusion complexes with beta-cyclodextrin was studied for several popular fungicides of different types: prochloraz, 2-phenylphenol, thiophanate methyl, 8-hydroxyquinoline, and benalaxyl. Phase solubility diagrams showed that in all cases complexation takes place, leading to an important increase of water solubility in prochloraz and benalaxyl. Equilibrium association constants could be determined from the phase solubility data and from NMR titrations in the case of 2-phenylphenol. Because of the low solubility of the complex formed between 8-hydroxyquinoline and beta-cyclodextrin, the corresponding association constant could not be determined. The solid complexes of fungicide-cyclodextrin were prepared and isolated by different methods. The isolation of real complexes and not physical mixtures was confirmed in the cases of prochloraz, 2-phenylphenol, and benalaxyl by differential scanning calorimetry.     

Microflora of turfgrass treated with fungicides

Fungicides are used widely to manage high-quality turfgrass, but their use could adversely affect the composition of microbial populations. Fourteen fungicides, a nematicide, and five mixed fungicide programs were applied to turfgrass for 3 yr and were tested for their effects on numbers of bacteria, actinomycetes and fungi, and N concentrations. Combinations of fungicides suppressed fungi and stimulated bacteria and actinomycetes more than individual toxicants. Collective microbial groups were generally less affected by each fungicide than were individual species within each group. The rate of decrease of NH⁺₄ concentrations in fertilized turf (presumably via nitrification) was only slightly influenced by fungicides. The more harmful effects of some fungicides to turfgrass may involve induced acidity rather than direct suppression of specific microbial groups.     

Complexation of whey proteins with carrageenan

The formation of electrostatic complexes of whey protein (WP) and a nongelling carrageenan (CG) was investigated as a function of pH, ionic strength, temperature, and protein-to-polysaccharide (Pr:Ps) ratio. On lowering the pH, the formation of soluble WP/CG complexes was initiated at pH(c) and insoluble complexes at pH(phi), below which precipitation occurred. The values of the transition pH varied as a function of the ionic strength. It was shown that at [NaCl] = 45 mM, the value of pH(phi) was the highest, showing that the presence of monovalent ions was favorable to the formation of complexes by screening the residual negative charges of the CG. When CaCl(2) was added to the mixtures, complexes of WP/CG were formed up to pH 8 via calcium bridging. The electrostatic nature of the primary interaction was confirmed from the slight effect of temperature on the pH(phi). Increasing the Pr:Ps ratio led to an increase of the pH(phi) until a ratio of 30:1 (w/w), at which saturation of the CG chain seemed to be reached. The behavior of WP/CG complexes was investigated at a low Pr:Ps ratio, when the biopolymers were mixed directly at low pH. It resulted in an increase of the pH of the mixture, as compared to the initial pH of the separate WP and CG solutions. The pH increase was accompanied by a decrease in conductivity. The trapping of protons inside the complex probably resulted from a residual negative charge on the CG. If NaCl was present in the mixture, the complex took up the Na(+) ions instead of the H(+) ions.     

Compatibility of Talaromyces flavus with potato seedpiece fungicides

The compatibility of conidia and ascospores of a wild-type isolate (TF1) and a benomyl-resistant biotype (TF1-1) of Talaromyces flavus with five fungicides recommended for use on potato seedpieces was investigated in the field and in vitro. The fungicides tested were captan, mancozeb, maneb, metiram and thiabendazole. In the field test, highest populations were recovered from TF1 treatments. Both the TF1 and the TF1-1 survived better in the field and were more tolerant of more fungicides when applied to the potato seedpieces as ascospores than as conidia. In the field, both fungi were most tolerant of thiabendazole and metiram and least tolerant of captan. Tolerance of fungicides in vitro was not consistent with field compatibility.     

Release of acetaldehyde from beta-cyclodextrins inhibits postharvest decay fungi in vitro

Many naturally occurring plant volatiles are known to have antifungal properties. However, they have limited use because they diffuse rapidly in air. In this in vitro study, acetaldehyde was chosen as a prototype volatile in order to study the controlled release of antifungal volatiles from cyclodextrins (CD). The major postharvest pathogens Alternaria alternata, Botrytis cinerea, and Colletotrichum acutatum were exposed to the pure volatile for 7 days at 23 degrees C. Acetaldehyde was most effective against A. alternata, followed by C. acutatum, and B. cinerea, with 0.12, 0.56, and 1.72 microL/L in air being required to inhibit fungal growth, respectively, according to the bioassay developed. Second, the effectiveness of the new beta-CD-acetaldehyde release system was evaluated against A. alternata for 7 days at 23 degrees C. Sufficient volatile was released from 0.7 g of beta-CD-acetaldehyde to prevent fungal growth in vitro.     

Enzyme activities in vineyard soils long-term treated with copper-based fungicides

Copper-based fungicides have been applied in vineyard soils for a long time, which has resulted in increasing soil Cu concentration. However, information relating to non-target effects of these fungicides on microorganisms of these soils is scarce. The aim of this study was to determine the potential enzyme activities of vineyard soils in relation to Cu content and evaluate the potential risks of long-term application of Cu-based fungicides. For this purpose, a wide range of soil samples, having different total, exchangeable and bioavailable Cu contents, were collected from six regions of quality wines located in the NW Iberian Peninsula, and the activity of dehydrogenase, β-glucosidase, urease and phosphatase were measured. Overall, the results obtained indicate adverse effects of Cu on dehydrogenase, β-glucosidase and phosphatase activities and an inconsistent effect on urease activity. Threshold Cu concentrations at which changes in the enzyme activities became evident were 150-200 mg total Cu kg⁻¹ and 60-80 mg bioavailable Cu kg⁻¹.     

Sorption behavior of triazole fungicides in Indian soils and its correlation with soil properties

Adsorption-desorption of triazole fungicides, hexaconazole [2-(2,4-dichlorophenyl)-1-(1H-1,2,4,-triazol-1-yl) hexan-2-ol], triadimefon [1-(4-chlorophenoxy)-3,3-dimethyl-1-(1H-1,2,4-triazol-1-yl) butan-2-one], and penconazole[1-(2,4-dichloro-beta-propyl phenethyl)-1H-1,2,4-triazole] was studied in five Indian soils using batch method. The adsorption isotherms fitted very well to the Freundlich equation. Adsorption of various triazole fungicides increased in this order: triadimefon > hexaconazole > penconazole. The product of the Freundlich adsorption constants, K(f)(1/n), showed good correlation with the soil organic carbon (OC) content, suggesting that soil OC is the main controlling factor for triazoles adsorption. Clay and silt content of the soil also affected the adsorption constants. Adsorption of hexaconazole and triadimefon was nearly reversible in two low OC soils (soil 3, soil 5) where 90-100% of the sorbed fungicides was released in a single washing step. Otherwise, desorption of triazole fungicides showed hysteresis, and 30-60% of the triazole fungicides were retained by the soil after single washing. IR spectra showed that H-bonds and charge-transfer bonds between humic acid and fungicides probably operated as mechanisms of adsorption.     

土壤胡敏酸与锰离子的络合特征及生物有效性研究

试验从沈阳农业大学棕壤肥效长期定位实验田中选择8个处理:(1)对照(CK);(2)低量氮肥(N1);(3)氮磷肥(N1P);(4)氮磷钾肥(N1PK);(5)低量有机肥(M1);(6)低量有机肥+氮肥(M1N1)(7)低量有机肥+氮磷化肥(M1NP);(8)低量有机肥+氮磷钾肥(M1N1PK),采用田间与盆栽试验相结合的方法,对土壤胡敏酸与锰离子的络合特征及生物有效性进行了研究。研究结果表明,各施肥处理均可提高土壤HA与Mn2+的络合稳定常数,其中,有机无机配合施用处理大于单施化肥处理,氮磷钾配施处理大于氮磷或单施氮肥处理;HA-Mn2+趋与形成1∶1型络合物,施用有机肥增加了土壤HA对Mn2+的吸附数量和吸附强度,施用化肥降低土壤HA对Mn2+吸附的数量,增加其吸附强度。水培试验的结果证实,源于单施化肥处理的土壤HA对玉米Mn2+的吸收影响不显著,而来自有机肥各处理的土壤HA降低了玉米的吸锰量。络合稳定性指标和吸附强度指标与玉米吸锰量呈显著负相关关系,可以用来作为评价养分有效性的指标。     

Denitrification in soil: Effects of insecticides and fungicides

The effects of seven insecticides and six fungicides on denitrification of nitrate in soils were studied by determining the effects of 10 and 50μgg^?1 soil of each pesticide on the amounts of nitrate lost and the amounts of nitrite, N₂O and N₂ produced when soil samples were incubated anaerobically after treatment with nitrate. The insecticides used were lindane, fenitrothion, fonofos, malathion, phorate, terbufos and carbofuran. The fungicides used were mancozeb, maneb, thiram, benomyl, captan and terrazole.None of the insecticides studied had a significant effect on denitrification when applied at the rate of 10 μgg^?1 soil. When applied at the rate of 50μgg^?1 soil, lindane, fonofos and malathion enhanced denitrification in the three soils studied, whereas fenitrothion, phorate, terbufos and carbofuran either had no appreciable effect on denitrification in these soils, or enhanced denitrification in at least one of the soils.None of the fungicides studied had an appreciable effect on denitrification when applied at the rate of 10μgg^?1 soil, but thiram increased the ratio of N₂ to N₂O in the gaseous products of denitrification. Captan inhibited denitrification in two of three soils studied when applied at the rate of 50μgg^?1 soil. The other five fungicides either had no significant effect on denitrification, or enhanced denitrification, when applied at this rate. Reports that maneb, thiram and terrazole inhibit denitrification in soil were not confirmed.     

Changes in the free amino acid content of soil following treatment with fungicides

Both quantitative and qualitative changes in the free amino acid content of soil followed treatment with the fungicides Benomyl, Thiram and Verdasan. The amounts of amino acid-N extracted following the additions of high concentrations of the fungicides were in general lower than the controls over the 28-day incubation period. Low rates of application however, resulted in marked increase in the amounts of amino acid-N extracted. A total of nine different amino acids were extracted seven of which were found consistently in the control soils. Glycine and threonine were markedly favoured by all treatments, whereas the frequency of extraction of the other seven amino acids was dependent upon the fungicide used and its concentration. The results are discussed in relation to the changes in the microbiology of soils which are known to be brought about following partial sterilization with fungicides.     

Dissipation of fungicides in a vineyard soil amended with different spent mushroom substrates

The degradation kinetics and formation of metabolites for fungicides of different chemical classes (iprovalicarb, metalaxyl, penconazole, and pyrimethanil) and determination of bound residues for metalaxyl and penconazole were studied in both an unamended vineyard soil and in the same soil amended with two spent mushroom substrates (composted (C-SMS1) and fresh (F-SMS2)). The degradation kinetics was fitted to single first-order or first-order multicompartment patterns. Degradation rates decreased in C-SMS1-amended soils for all fungicides as compared to unamended soil, but in F-SMS2-amended soils, they decreased only for iprovalicarb and penconazole. The DT(50) values were higher by up to 1.8 (metalaxyl), 3.8 (pyrimethanil), 4.1 (iprovalicarb), and >1000 (penconazole) times in the soil plus C-SMS1 compared to those for soil plus F-SMS2 or unamended soil. The dissipation mechanism recorded the highest mineralization in the unamended soil for (14)C-metalaxyl and (14)C-penconazole, with the highest formation of nonextractable residues in the F-SMS2-amended soil for (14)C-metalaxyl. The results are consistent with (1) the chemical characteristics of each SMS (total and soluble organic carbon) controlling sorption and the bioavailability of fungicides and (2) the microbial activity of SMS-amended soils, which affects fungicide biodegradation. The findings of this work highlight the potential of SMS amendments with different characteristics to decrease or increase the degradation rate of a fungicide in a vineyard soil.     

Complexation of mercury(II) ions with humic acids in tundra soils

The interaction mechanisms of mercury(II) ions with preparations of humic acids (HAs) isolated from organic horizons of surface-gleyed soils (Haplic Stagnosol (Gelic, Siltic)) of shrub tundra and hydromorphic peat gley soils (Histic Cryosol (Reductaquic, Siltic)) of moss-lichen tundra have been studied. The particular features of the interactions between the mercury(II) ions and the HAs are related to the molecular structure of the HAs, the mercury concentration range, and the environmental parameters. The fixation of mercury(II) ions into stable coordination compounds is most efficient in the pH range of 2.5–3.5. At the element concentrations below 0.50 μmol/dm³, the main complexing sites of HAs are their peripheral aminoacid functional groups. Pyrocatechol, salicylate, and phenolic groups from the nuclear moiety of molecules interact in the concentration range of 0.0005–0.50 mmol/dm³; the physical sorption of mercury hydroxo complexes by the surface of HAs is the main process occurring in the system.     

Interaction of iron chelates with several soil materials and with a soil standard

Frequently the effectiveness of iron (Fe) chelates is low because they can be retained or destroyed by soil materials. The high cost of these Fe fertilizers makes it necessary to study soil material reaction with Fe chelates. Commercial Fe chelates with EDTA, EDDHA, and EDDHMA as ligands and their standards, prepared in the laboratory, were shaken for one hour with various soil materials [amorphous Fe(III) oxide, acid peat, calcium (Ca)‐montmorillonite and calcium carbonate (CaCO₃)] and with a soil standard made in the laboratory. After agitation, the chelate‐soil mixtures were filtered and the micronutrients and chelated Fe that remained in solution were determined. Among the soil materials used, amorphous Fe(III) oxide and acid peat had the greatest affect on the amount of chelated Fe remaining in solution. The type of chelating agent was the next major factor that affected the availability of soluble Fe following reaction with the soil materials. Another factor was the commercial formulation of the Fe chelates. The chelates comprised of EDDHA or EDDHMA maintained the highest percentages of chelated Fe in solution after interaction with the solid phases, except for the acid peat. The last soil material, acid peat, retained more chelated Fe for the Fe chelates with EDDHA or EDDHMA than with EDTA as the chelating agent. The commercial Fe‐EDDHA chelates had greater losses of chelated Fe than their standard after interaction with all the solid phases. The commercial Fe‐EDDHA chelate (Sequestrene) and the commercial Fe‐EDDHMA chelate (Hampirón) solubilized the highest amount of copper (Cu) from soil standard. This was attributed to the presence of by‐products in the commercial formulations since the Fe‐EDDHA standard did not have Cu in solution after the interaction. Therefore, the commercial Fe chelate by‐products are able to form Cu‐complexes which could affect chelated Fe and its availability to plants.     

The effects of fungicides on soil fungal populations

Four fungicides, Captan, Dicloran, Thiram and Verdasan were applied at 28-day intervals for 12 consecutive months and their effects on soil fungal numbers and the incidence of individual species were studied. Immediately after application, these fungicides reduced the number of fungal propagules in soil by 23, 11, 36 and 50% respectively compared with control. Captan- and Dicloran-treated soils were rapidly recolonised within 7 days of the application of fungicides. The effects of Thiram and Verdasan were more persistent: the fungal numbers in soils treated with these fungicides did not recover sufficiently to reach control levels throughout the sampling period. Fewer species of fungi were isolated from Thiram- and Verdasan-treated soils than from Captan- and Dicloran-treated soils. Chrysosporium pannorum (Link) Hughes was the principal species isolated from Verdasan-treated soil and the fungus was isolated in increased numbers immediately after application of Verdasan than on subsequent sampling days. Cladosporium cladosporioides (Fres.) de Vries, Mortierella minutissima van Tiegh, Trichocladium asperum Harz, Trichoderma hamatum (Bon.) Bain, and Zygorhynchus moelleri Vuill. were found to be generally tolerant of all four fungicides. However, Botryotrichum piluliferum Sacc. and Marchai, Gliocladium roseum Bain., Humicola fusco-atra Traaen, Sepedonium chrysospermum (Bull.) Link ex Fr., and Trichoderma viride Pers. ex Fr. were generally intolerant of the fungicides but rapidly recolonised the treated soils. While the concentrations of Captan and Dicloran used were fungistatic to T. viride, Thiram and Verdasan were fungicidal.     

Differential scanning calorimetry evidence of the enhancement of beta-sitosterol absorption across biological membranes mediated by beta-cyclodextrins

beta-Sitosterol is a plant sterol that has received much attention because of its effectiveness in reducing the absorption of dietary cholesterol, as well as in offering protection from cardiovascular diseases and cancer development. Thus, the knowledge of the interaction of beta-sitosterol with biological membranes can help in understanding its mechanism of action. In the present paper, the differential scanning calorimetry technique has been used to study the interaction of beta-sitosterol with a biomembrane model constituted by dimyristoylphosphatidylcholine multilamellar vesicles. Furthermore, kinetic experiments have been carried out to follow the uptake of beta-sitosterol by biomembranes and the effect of beta-cyclodextrins on such a process. Our results indicate that opportune concentrations of beta-cyclodextrins improve the uptake of beta-sitosterol by phospholipid membranes.     

The effect of three fungicides on nitrification and ammonification in soil

Three fungicides, Captan, Thiram and Verdasan were added at varying concentrations to soil amended with ammonium sulphate, and their effect upon nitrification and ammonification was studied over 28 days. Two general effects of addition of fungicides on nitrification were apparent. At very low concentrations all three fungicides stimulated or did not affect this process. The stimulation was most marked after treatment with Thiram at 10 μg a.i./g soil. At higher concentrations the fungicides led to a progressive decrease in nitrate production. The concentration at which nitrification was inhibited was for Verdasan 10 μg, Thiram 100 μg and Captan above 250 μg a.i./g soil.At low concentration all three fungicides did not greatly affect ammonification. At increasing concentrations, however, there was a marked increase of NH⁺₄-N, compared with the controls. The lowest rates of application of the three fungicides resulted in most nitrification and least ammonification. The results are discussed in relation to the differential effects of the fungicides on the soil microbial population.