Márcio Lazzarotto

Spectrofluorimetric determination of benzoimidazolic pesticides: Effect of p-sulfonatocalix[6]arene and cyclodextrins

The effect of the addition of a macrocyclic host (H) such as p-sulfonatocalix[6]arene (C6S), native and modified cyclodextrins (CDs), on the fluorescence of benzoimidazolic fungicides (P), like Benomyl (BY) and Carbendazim (CZ), has been studied. The fluorescence of BY in water at pH 1.000 and 25.0 degrees C was increased in the presence of C6S, alphaCD and hydroxypropyl-beta-CD (HPCD). The association constants determined by fluorescence enhancement showed weak interactions (K(A) approximately 10(1) to 10(2) M(-1)) between the fungicide with both CDs, whereas they were stronger with C6S (K(A) approximately 10(5) M(-1)). Molecular recognition of BY for C6S was mainly attributed to electrostatic interactions, and for CDs to the hydrophobic effect and hydrogen bond formation. On the other hand, the fluorescent behaviour of CZ in the presence of C6S at pH 6.994 was interpreted as the formation of two complexes with 1:1 (P:H) and 1:2 (P:H(2)) stoichiometry, the latter being less fluorescent than the free analyte. Relative fluorescence quantum yield ratios between the complexed and free BY (phi(P:H)/phi(P)) were 2.00+/-0.05, 1.40+/-0.03 and 2.8+/-0.4 for C6S, alphaCD and HPCD, respectively. The analytical parameters improved in the presence of C6S and CDs. The best limit of detection (L(D), ng mL(-1)) was 17.4+/-0.8 with HPCD. The proposed method with C6S and HPCD was successfully applied to fortified samples of tap water and orange flesh extract with good recoveries (91-106%) and R.S.D. (< or = 2%) by triplicate analysis. The method is rapid, direct and simple and needs no previous degradation or derivatization reaction.

Interaction of Calix[4]arene and Aliphatic Amines: A Combined NMR, Spectrophotometric and Conductimetric Investigation

The constants related to the equilibria between calix[4]arene and aliphatic amines in acetonitrile were measured by conductimetric and spectrophotometric methods, and the structures of the salts studied by NMR spectroscopy. In concentrations about 10-4 mol L-1, free ions are at higher proportion, whereas at 10-2 mol L-1 there is an increase of ion-pairs proportion. The values of the constants found for acid-base reactions allow an evaluation of the value of pKa for calix[4]arene in acetonitrile as 16.6 pKa units. The analysis of data agrees with a proposal of exo-calix ammonium ion.

Endo-cavity Complexes between Calix[6]arene Dianions and Aliphatic Ammonium Cations: Structure of a Hexylammonium Complex by X-ray Crystallography

The interactions of calix[6]arene and p-tert-butylcalix[6]arene with aliphatic amines in acetonitrile solution were studied by spectrophotometric titrations in the UV region and 1H NMR spectrometry. Calix[6]arenes can undergo two deprotonations by aliphatic amines and the extent of the second proton transfer is mainly governed by the size of the α-substituent of the amine. 1H NMR spectra show that the macrocycle adopts a 1,2,3-alternate conformation and that the α-hydrogens of the ammonium ions are shielded by the π-clouds of the aromatic rings. The X-ray crystal structure of the dihexylammonium complex of the p-tert-butylcalix[6]arene dianion, reported here, confirms the 1,2,3-alternate conformation and shows one of the two ammonium moieties encapsulated in the inner cavity of the macrocycle.

Synthesis of N-phtaloyl amino acid p-tert-butylcalix[4]arene esters

1-3-Diesters of p-tert-butylcalix[4]arene were obtained upon reaction with N-phtaloyl amino acid chlorides. Reactions with chiral amino acids were accompanied by complete or partial racemization in the reaction media (Et3N/CH2Cl2).

Electronic parameters of cation complexation by calixarene ionophores

The Gibbs energy of extraction experiments of ionophoric calixarenes with alkali metals from the literature have been correlated with electronic parameters of their “monomeric” structures calculated by AM1, PM3 and PM7 algorithms: energies of molecular orbitals and charge densities of oxygen and nitrogen atoms. We observed general correlations of the extraction constants with the charge on the carbonyl oxygen and specific correlations with MO-energy using the covalent term of the Klopman–Salem equation. The correlations for calixarenes with 5 and 6 phenolic units were very poor, and we attributed to the structural flexibility, which allow different optimized conformations for metal binding.

Chiral lactic acid and ethyl lactate p-tert-butylcalix[4]arene derivatives

Ethyl (S)-(–)-O-tosyllactate reacted with p-tert-butylcalix[4]arene in K2CO3–acetone with inversion of configuration on the asymmetric centre, and only the bis-substitution product on the distal oxygens was obtained. Further attempts to react the bis(lactate) p-tert-butylcalix[4]arene derivative with BrCH2CO2CH3 under the same conditions failed. X-Ray analysis of the lactate derivative shows two independent molecules in the unit cell; one CH3 of the ethyl radical is immersed in the cavity of the other molecule. Both adopt a slightly distorted cone conformation. NMR analysis shows that carbons and hydrogens of the methylene bridges and meta positions are diastereotopic. Ester hydrolysis was carried out without racemization, and the diastereotopic behaviour of the lactic acid derivative was maintained.

Unexplored metallic cation effect in the acidity constants of p-t-butylthiacalix[4]arene, p-t-butylcalix[4]arene and p-t-butylcalix[6]arene in aqueous-organic media

Abstract The influence of the metallic cation of the base (Li+, Na+ or K+) was determined on the acid–base constants of p-t-butylthiacalix[4]arene (TC4), p-t-butylcalix[4]arene (CA4) and p-t-butylcalix[6]arene (CA6) in ethanol/water in an large interval of pH values by potentiometry and spectrophotometry. The pKa values determined by both methods correlate very well and these are characteristic for each macrocycle with influence of the cation of the base without a straight evidence of an effect by the size of the metallic cation. In the case of TC4, pKa1 and pKa2 were lower to Li+ and Na+ than with K+. For CA4, an effect of K+ on the pKa2 with respect to Li+ was observed. A very different behaviour was observed for CA6 with Li+ and K+ showing a lower pKa2 and a higher pKa3 than with Na+. These effects were interpreted on the basis of the interaction/complexation of each cation with each macrocycle.

Mobilidade conformacional de complexos entre calix[4]arenos e aminas: evidencias para estruturas exo-calix

The NMR spectra of salts formed from calix[4]arene and aliphatic amines in CD3CN are in agreement with a exo-calix position of the ammonium cation. The chemical shifts (d) of aromatic and methylenic hydrogens of calix[4]arene were almost the same for the amines utilized. The coalescence temperatures (tc) were obtained and fall in the range between 32 and 38 oC, and is higher for more basic amines, and was not observed dependence with the shape of the amine.

Thermoanalytical study of the complexes of 4-dimetilaminocinnamylidenepiruvate with manganese (II), cobalt (II), nickel (II), cupper (II), zinc (II) and lead (II), in the solid state

Solid state compounds M-4-DMCP, where 4-DMCP is 4-dimethylaminocinnamylidenepyruvate and M represents Mn (II), Co (II), Ni (II), Cu (II), Zn (II) and Pb (II) were prepared. These compounds were studied by thermoanalitycal techniques: thermogravimetry (TG), derivative thermogravimetry (DTG), differential scanning calorimetry (DSC), X-ray diffraction powder patterns and complexometric titration with EDTA. From the results obtained by the complexometric titration with EDTA, TG, DTG and DSC curves, was possible to establish the hydration degree, stoichiometry and thermal stability of the prepared compounds.