Interaction of carbamate pesticides and their hydrolysis products with beta-cyclodextrin by computational and experimental methods

NATALIA PACIONI; SEBASTIÁN CASTRO; ADRIANA PIERINI; ALICIA VEGLIA

Los Cocos, Córdoba, Argentina

Conferencia; 9th Latin American Conference on Physical Organic Chemistry; 2007

IUPAC, Universidad Nacional de Córdoba, Universidad Nacional de Río Cuarto

The study of pesticides and their reactions in organized media is of great importance either tofavour or to inhibit the hydrolysis reaction. In the first case, the degradation process would befavoured as a remediation method. In the second one, the formulations would be stabilized and theirstorage could be improved.The aim of this work was to interpret the driving forces and the geometry features of thecomplexes formed between carbamate pesticides and their hydrolysis products with β-cyclodextrin,both by computational and experimental methods. In the last years, Molecular dynamics (MD) andquantum mechanics methods have proved of relevance to study the interactions involved in theformation of the host?guest complex and to predict the geometry fit between the host and the guest.The interaction between carbamate pesticides, such as promecarb (PC), bendiocarb (BC), carbaryl(CY) and carbofuran (CF), and the hydrolysis products 1-naphthol (CYF) and 2,3-dihydro-2,2-dimethyl-benzofuranol (CFF) with β-cyclodextrin (βCD) was studied by spectrofluorimetry andspectrophotometry. The affinity constants (KA, M-1) were for CY-βCD (350),1 CF-βCD (190),1 PC-βCD (1900),2 BC-βCD (600),2 CYF-βCD (880) and CFF-βCD (336). Furthermore, the hydrolysis rateconstants in the absence and presence of βCD in basic media were determined byspectrophotometry.The geometries of all the pesticides and hydrolysis products were optimized at the B3LYP/6-31+G* basis set. The βCD geometry was obtained from the Cambridge database. Two differentorientations of the guests in the cavity were considered. The AMBER 7 program package was usedto generate the MD trajectories over a period near 3 ns with the general amber force field (GAFF).The simulations in an aqueous environment were performed using TIP3P in a periodic cell. A 10 Åcutoff was employed for the non bonded interactions. The MD simulations were useful to establishthe geometry of the host?guest compound in solution. The stability to the different complexes will beevaluated and compared with the experimental results.