SUMMARY

The project PHOTOPESTICIDAS deals with the study of the photochemistry/photophysics and supramolecular chemistry of selected pesticides, which contain benzimidazole substructures. The photobehaviour in homogeneous aqueous solution will be investigated and the punctually published results will be completed as well as brought in a comprehensive context. This will plant the ground for the investigation of the pesticide behaviour in presence of cucurbituril nanocontainers. It is expected that the photobehavior (photophysical properties and photodegradation) is altered. Further, the pH-dependent supramolecular formation of host-guest complexes between cucurbiturils and benzimidazoles (pesticides and novel fluorophore-appended benzimidazoles as useful photophysical tools) will be studied, as it has potential application for novel delivery systems.

PURPOSE OF THE PROJECT

Precedents and actually state of the knowledge

The project consists of two major components: photobehavior of pesticide compounds with benzimidazole substructures and formation of supramolecular inclusion complexes with cucurbiturils.

Photobehaviour of benzimidazole-containing pesticides.
The photodegradation of thiabendazole and carbendazim in aqueous solution has been the subject of several early studies, less has been published with respect to fuberidazole and nothing seems known about rabenzazol. These studies were based on direct UV photolysis in absence and presence of H2O2, photosensitized singlet oxygen production, and photocatalytic treatments with TiO2 or combinations of TiO2 and H2O2. Some respresentative degradation pathways for thiabendazole (using direct photolysis, the same approach as planned for the present project) are summarized in Scheme 2. In the majority of the cases, photoproduct assignment has been accomplished with comprehensive mass spectrometric analysis. This is a very potent analytical tool, also available for our project through the group at UAlg.

The fluorescence properties are detailed for some of the compounds.
However, with the exception of fuberidazole and thiabendazole, for which few extended studies have been published, no comprehensive reports are known. Further no information about the excited triplet state of benzimidazole pesticides has been reported to the best of our knowledge.
The second major component of the planned studies concerns the use of molecular nanocontainers

Supramolecular Host-Guest Complexes with Cucurbiturils.
Host-guest complexes are a traditional topic of supramolecular chemistry; the chemistry of non-covalent interactions. While in the beginning of this multidisciplinary field, host molecules like cyclodextrins and calixarenes were clearly dominant, more recently much attention has been turned toward synthetic nanocontainers. Examples for this new generation of hosts are cucurbit[n]urils (CBn, see Scheme 3), which are accessible in different sizes (n = 5-10), where n is the number of repeated glycouril units. Recent application examples of them include drug-delivery systems, enzyme assays, chemosensors, supramolecular self-sorting systems, stabilization of dyes, and molecular machines.

For the successful identification of complex formation, a sensitive and specific reporter signal is of high advantage. Fluorescence, which can be detected with high sensitivity and selectivity, is often used for these purposes.

These principles will be used by us to investigate the complexation of benzimidazole-derived pesticides, which are often fluorescent. In general, the modification of photochemical beahviour of guest molecules upon host inclusion is an often observed phenomenon, which will be verified for the objects of the presented study.

1. It is expected that new insights in the photodegradation processes of widely applied compounds like for example thiabendazole, furbidazole, rabenzazole, and carbendazim can be obtained.
2. The establishment of the photochemical bases of stability and supramolecualr behaviour of benzimidazole-derived pesticides vill provide a fundamental knowledge gain, which in the future is expected to be of use for studies of potential health risks (photomutagenicity).

AIMS OF THE PROJECT

General Aim

The proposed research pretends to provide a comprehensive study about the photophysical (absorption, fluorescence, and laser flash photolysis) and photochemical properties (photodegradation products under various conditions, especially in absence/presence of oxygen and pH) of this class of pesticides.

Specific Aims

1. Valuable data will be obtained, which will allow the assessment of the photostability of benzimidazole-derived pesticides.
2. The investigation of alterations of photophysical and photochemical properties will be performed, providing data on the light-absorbing properties and photostability of these compounds in the presence of water-soluble nanocontainers.
3. he supramolecular basis for complex formation between benzimidazole-derived pesticides or models and cucurbituril CB7

TEAMS INTERESTED IN THE PROJECT

1. Photochemistry of Pesticides: L.F. Viera (Technical University Lisbon, Portugal).
2. Cucurbiturils: W. M. Nau (Jacobs University Bremen, Germany), N. J. Turro (Columbia University, United States).

METHODOLOGY AND PLAN OF WORK

1. Task 1: Synthesis and photophysical characterization of fluorophore-spacer-benzimidazole model compounds and characterization of their host-guest complexes with CB7.

   Under this task we will synthesize novel fluorophore-spacer-benzimidazole dyads, which can be used to characterize supramolecular complexation and shifts of protonation equilibria (see introduction) of benzimidazole by CB7 with fluorescence spectroscopy. The molecular design of the dyads will be based on excited state processes like photoinduced electron transfer. The dyads (probes) will be prepared by conventional organic synthesis. Free and complexed dyads will be characterized by absorption, fluorescence, pH titrations, isothermal calorimetry, and NMR spectroscopy.

2. Task 2: Photophysical characterization of benzimidazole pesticides in aqueous solution

   The commercially available pesticides thiabendazole, fuberidazole, and rabenzazole will be investigated by absorption and fluorescence spectroscopy in order to obtain key data like fluorescence quantum yields, lifetimes, etc. These experiments will be also done in dependence on pH.

3. Task 3: Formation and characterization of host-guest complexes between benzimidazole pesticides and CB7.

   The formation of supramolecular host-guest complexes between benzimidazoles and CB7 will be investigated with respect to binding strength and photophysical parameters (absorption, fluorescence). Experimental methodology to be used for this task is similar to the one mentioned under task 1.

4. Task 4: Photodegradation of pesticides in CB7 host-guest complexes and comparison with water.

   Samples of pesticides in water in absence and presence of CB7 will be irradiated and the photoproducts will be characterized by HPLC, GC-MS, NMR, and mass spectrometry. The obtained information will be applied to reveal degradation pathways, decomposition kinetics, etc., which are key data for a comprehensive picture about the photodegradation of pesticides.

5. Task 5: Summary of results

   The results will be summarized and published in specialized journals like Chemosphere, J. Agri. Food Chem., Photochem. Photobiol. Sci., etc.

BENEFITS OF THE PROJECT, DIFFUSION AND EXPLOITATION OF THE RESULTS

Benefits of the Project

1. Contribuciones científico-técnicas esperables del proyecto, beneficios esperables para el avance del conocimiento y de la tecnología y, en su caso, resultados esperables con posibilidad de transferencia ya sea a corto, medio o largo plazo.
2. Plan de difusión.

Difussion and exploitation of the results

Plan of dissemination:
The results will be published in international journals of interest for the this specialized topic. Furthermore the participation in one congress is planned

TEAMS PARTICIPANTS AND RECORD OF THEGROUP OF  INVESTIGATION

Teams

1. Mr. Uwe Pischel. Email: This e-mail address is being protected from spambots. You need JavaScript enabled to view it
2. Mr. José Paulo da Silva. Email: This e-mail address is being protected from spambots. You need JavaScript enabled to view it
3. Ms. Patricia Remón
4. M.Iván Osipov
5. Ms. Cátia Carvalho

Record of the group of investigation

University of Huelva
The Huelva group has integrated recently in the University of Huelva in the area of Organic Chemistry. The group leader (U. Pischel) is presently contracted as Ramón y Cajal Professor, jointly financed by the Ministry of Science and Innovation, Madrid, and the University of Huelva. The principal activities of the group are focussed on applications of photochemistry and photoactive molecules. Principal research lines are related to the design and characterization of fluorescent organic molecules as chemosensors and decision-making molecules (project financed by the Ministry of Science and Innovation), the investigation of inorganic-organic photoactive nanoparticle hybrids (project financed by the Junta de Andalucía), and supramolecular chemistry with nanocontainers (formation and fluorescent switching of host-guest complexes with cucurbiturils).

University of Algarve
The Faro group, led by Dr. José Paulo da Silva, is mainly interested in environmental aspects of photochemistry and the photobehavior of commonly encountered chromophores on solid supports and surfaces (zeolites, mesoporous silica, cellulose…).