Complexation of imazalil with beta-cyclodextrin, residue uptake, persistence, and activity against penicillium decay in citrus fruit following postharvest dip treatments

Host-guest complexes of imazalil with cucurbit[8]uril and β-cyclodextrin and their effect on plant pathogenic fungi

We report the control of imazalil (IMZ) antifungal activity utilizing its non-covalent assembly with β-cyclodextrins (β-CD) and cucurbit[8]uril (CB8) macrocycles, as well as its stimuli-responsive disassembly with cadaverine. The NMR results are consistent with inclusion of a single IMZ molecule inside the cavities of either CB8 from its aromatic site or β-CD from its aliphatic end. Efficient complex formation with both host molecules and controlled released upon the addition of cadaverine is supported by NMR measurements. The stimuli-responsiveness of the same host-guest assemblies with cadaverine was validated against seven economically important plant pathogenic fungi which cause agriculturally important plant diseases across the globe. While loading the drug into macrocycles cavities suppressed its activity, subsequent adding of cadaverine efficiently restored it up. The results in the present paper enable researchers working in the area of mycology and plant pathology to inhibit or reduce the fungal growth on demand in order to control these economically important plant pathogenic fungi.

Encapsulation of biocides by cyclodextrins: toward synergistic effects against pathogens

Host-guest chemistry is useful for the construction of nanosized objects. Some of the widely used hosts are probably the cyclodextrins (CDs). CDs can form water-soluble complexes with numerous hydrophobic compounds. They have been widespread used in medicine, drug delivery and are of interest for the biocides encapsulation. Indeed, this enables the development of more or less complex systems that release antimicrobial agents with time. In this paper, the general features of CDs and their applications in the field of biocides have been reviewed. As the key point is the formation of biocide-CD inclusion complexes, this review deals with this in depth and the advantages of biocide encapsulation are highlighted throughout several examples from the literature. Finally, some future directions of investigation have been proposed. We hope that scientists studying biocide applications receive inspiration from this review to exploit the opportunities offered by CDs in their respective research areas.

Synergistic manipulations of plant and insect defences

BACKGROUND

It has been demonstrated previously that cis-jasmone acts as an elicitor of plant defence mechanism(s) by inducing secondary metabolism. It has also been demonstrated that temporal synergism can result in hypersensitive insect pests due to the inhibition of metabolic enzymes.

RESULTS

Laboratory bioassays demonstrated that pre-exposure of insects by piperonyl butoxide followed by cis-jasmone treatment of crops, reduced Aphis gossypii on cotton by 80% and Myzus persicae on sweet pepper by 90%. By microencapsulating the cis-jasmone and combining with piperonyl butoxide, Bemisia tabaci on tomatoes was reduced by 99%. A field trial with microencapsulated cis-jasmone combined with piperonyl butoxide resulted in a comparable reduction of whitefly egg numbers to that given by the registered rate of imidacloprid, with efficacy of 89% and 93%, respectively.

CONCLUSIONS

If insect defence enzymes are compromised by piperonyl butoxide whilst plant defence is primed by cis-jasmone, there are possibilities of an insecticide-free method of controlling insect pests. The success seems largely dependent upon the toxicity of the plants' secondary chemistry.

Inclusion complexation of chloropropham with β-cyclodextrin: preparation, characterization and molecular modeling

An inclusion complex between the agrochemical chloropropham (CIPC) and β-cyclodextrin (β-CD) was prepared. A 2:1 host-guest stoichiometry was conformed by elemental analysis. From the phase solubility studies, the calculated stepwise stability constants were K(1)=224.6L/mol and K(2)=939.2L/mol, respectively. FT-IR, thermoanalysis and (1)H NMR spectra were applied to characterize the complex. It was speculated that the inclusion mode was two β-CD cavities included the chlorophenyl and the isopropyl moiety of one CIPC molecule, which was in agreement with the most predominant configuration optimized by molecular modeling. By complexation with β-CD, the water solubility and the thermal stability of CIPC were prominently improved.

Control of postharvest diseases of fruit by heat and fungicides: efficacy, residue levels, and residue persistence. A review

Extensive research has been done in recent years to reduce the heavy dependence on chemical fungicides to control postharvest diseases and disorders of horticultural crops. Alternative strategies were based on improved cultural practices, biological control, plant-defense promoters, and physical treatments such as UV illumination, radiofrequency treatment, heat therapy, and storage technologies. Among these, postharvest heat treatments such as hot water dips, short hot water rinsing and brushing, and hot air conditioning have reduced rot development and enhanced fruit resistance to chilling injury in sensitive cultivars while retaining fruit quality during cold storage and shelf life. Additive or synergistic increases in effectiveness were observed by integrating heat therapy with various chemical compounds, thus leading to significant reductions in the application of active ingredients to protect produce from decay. This paper highlights the knowledge on this topic with emphasis on heat therapy effects and factors affecting the uptake, persistence, and performance of fungicide residues when they are applied in combination with hot water.

Structure-activity relationship of cyclodextrin/biocidal double-tailed ammonium surfactant host-guest complexes: towards a delivery molecular mechanism?

In aqueous solution, the biocidal double-tailed cationic surfactant, di-n-decyl-dimethyl-ammonium chloride can form inclusion complexes with various cyclodextrins (alpha-CD, beta-CD, gamma-CD, HP-alpha-CD, HP-beta-CD and CM-beta-CD). A physicochemical study has been performed to investigate the association parameters of these host-guest complexes by combining the use of ammonium and chloride selective electrodes, NMR spectroscopy and molecular modeling. stoichiometries, equilibrium constants and geometries were determined by resorting to a specific algorithm. The antimicrobial activity of the encapsulated ammonium surfactant was compared with that of the free ammonium showing three different behaviors depending on the cyclodextrin. The close relationship between the complex structure and the biocidal activity is used to propose a delivery molecular mechanism.

Cyclodextrins – Fields of Application. Part I

This review is dedicated to different fields of use of cyclodextrins, a family of three cyclic natural oligosaccharides and their derivatives. The first part of the review gives a brief description of the main and the most recent developed applications of cyclodextrins in food, cosmetic industry, environmental protection technologies and agriculture. Different products based on inclusion complexes with cyclodextrins and technologies with different use of cyclodextrins and inclusion complexes are described.

Improvement of antifungal activity of 10-undecyn-1-ol by inclusion complexation with cyclodextrin derivatives

The inclusion complexation behavior between 10-undecyn-1-ol and cyclodextrin (CD) derivatives, namely, randomly methylated beta-CD (RM-beta-CD) and hydroxypropyl-beta-CD (HP-beta-CD), was studied in terms of solubility improvement, apparent stability constant, and the inclusion ratios of the resultant inclusion complexes. The aqueous solubility of 10-undecyn-1-ol was greatly improved through complexation with the CD derivatives. RM-beta-CD is comparatively more efficient in solubilizing 10-undecyn-1-ol with an apparent stability constant outstripping that of HP-beta-CD by about an order of magnitude. Comparative in vitro evaluations of the growth inhibition effects of inclusion complex solutions toward Rosellinia necatrix, a phytopathogenic fungus, were performed. In comparison with the positive control, appreciable improvements of the antifungal activity of 10-undecyn-1-ol through the addition of CD derivatives were observed visually. The improvement was evaluated in terms of area covered by the mycelia of Rosellinia necatrix and their growth rate. RM-beta-CD was proven to be more effective compared to HP-beta-CD with regard to the reduction of both fungal mycelium-covered area and growth rate constant, presumably owing to greater solubility enhancement by RM-beta-CD and thus the bioavailability of 10-undecyn-1-ol. Inclusion complexation of 10-undecyn-1-ol with CD derivatives suggests a potential means for production of an environmentally friendly 10-undecyn-1-ol-based fungicide to counteract R. necatrix.

Imazalil–cyclomaltoheptaose (β-cyclodextrin) inclusion complex: preparation by supercritical carbon dioxide and 13C CPMAS and 1H NMR characterization

An inclusion complex between imazalil (IMZ), a selected fungicide, and cyclomaltoheptaose (beta-cyclodextrin, betaCD) was obtained using supercritical fluid carbon dioxide. The best preparation conditions were determined, and the inclusion complex was investigated by means of 1H NMR spectroscopy in aqueous solution and 13C CPMAS NMR spectroscopy in the solid state. Information on the geometry of the betaCD/IMZ complex was obtained from ROESY spectroscopy, while the dynamics of the inclusion complex in the kilohertz range was obtained from the proton spin-lattice relaxation times in the rotating frame, T(1rho) (1H).