Paulo H. Fidêncio

A quantum chemical and chemometric study of sesquiterpene lactones with cytotoxicity against tumor cells

The semi‐empirical molecular orbital method PM6 was employed to calculate a set of molecular descriptors of 20 sesquiterpene lactones (SQLs) with cytotoxicity against HL‐60 (leukemia) tumor cells. The principal component analysis (PCA) and hierarchical cluster analysis (HCA) methods were used to obtain possible relationships between the calculated descriptors and the biological activity of the lactones. Four descriptors were identified as responsible for the separation between the active and inactive compounds: EHOMO (highest occupied molecular orbital energy); Q11 (net atomic charge on C11); Q12 (net atomic charge on C12) and Q13 (net atomic charge on C13). These results indicated that the presence of the α‐methylene‐γ‐lactone group has a significant role in the mechanism by which SQLs exert their biological activities.In order to deepen our knowledge about the structure–activity relationship of sesquiterpene lactones (SQLs), a quantum chemical and chemometric study of sesquiterpene lactones with cytotoxicity was performed against HL‐60 (leukemia) tumor cells. The analysis of the molecular descriptors identified as responsible for the separation between the active and inactive compounds indicated that the presence of the α‐methylene‐γ‐lactone functionality has a significant role in the mechanism by which SQLs exert their biological activities. Copyright

An optimized and validated 1H NMR method for the quantification of α-pinene in essentials oils

The authenticity and composition of commercial essential oils requires strict quality control. Due to the importance of α-pinene containing essential oils, a rapid and efficient method for quantification of this terpene in oils of eucalyptus, pink pepper and turpentine using (1)H NMR was developed and validated. All evaluated parameters (selectivity, linearity, accuracy/precision, repeatability, robustness, stability of analyte and internal standard in solutions) showed satisfactory results. The limit of detection (LOD) and limit of quantification (LOQ) were 0.1 and 2.5mg respectively. These values indicated that α-pinene was detected in 35 mg samples containing at least 0.3% of this compound. In addition, a minimum of 8% of α-pinene in the sample was required for quantification. Furthermore, the standard deviations found in the (1)H NMR methodology were less than 1% and were lower than those obtained by gas chromatographic analysis. Statistical tests have shown that the results obtained by (1)H NMR methodology are similar to those obtained by GC-FID technique using external and internal standardization and normalization within 95% confidence. R&R values lower than 10% have shown that all the methods are appropriate and the (1)H NMR method is suitable for quantification of α-pinene in samples of essential oils since this method possessed the smallest R&R (1.81) value.

Determinação de constituintes químicos em madeira de eucalipto por Pi-CG/EM e calibração multivariada: comparação entre redes neurais artificiais e máquinas de vetor suporte

Multivariate models were developed using Artificial Neural Network (ANN) and Least Square - Support Vector Machines (LS-SVM) for estimating lignin siringyl/guaiacyl ratio and the contents of cellulose, hemicelluloses and lignin in eucalyptus wood by pyrolysis associated to gaseous chromatography and mass spectrometry (Py-GC/MS). The results obtained by two calibration methods were in agreement with those of reference methods. However a comparison indicated that the LS-SVM model presented better predictive capacity for the cellulose and lignin contents, while the ANN model presented was more adequate for estimating the hemicelluloses content and lignin siringyl/guaiacyl ratio.

Evaluation of Chemical Composition of Eucalyptus Wood Extracts after Different Storage Times Using Principal Component Analysis

Abstract Deposits of wood extractives, commonly referred to as pitch, cause significant problems for the pulp and paper industries. The reduction of these extractives is an important strategy aspect used to minimize problems. The present work studied the effects of wood storage time on the amount and variation of chemical composition of extracts, before and after alkaline hydrolysis. Fatty acids, sterols, long-chain aliphatic alcohols, and aromatic compounds were the main chemical classes of substances found in all analyzed extractives, before and after hydrolysis. Hierarchical cluster analysis (HCA) and principal component analysis (PCA) were used to confirm the similarity of wood samples using groups directly correlated with the chemical composition. PC1 explains approximately 99% of the total variance, and β-sitosterol was the major compound responsible for the groupings. The exploratory analysis of the extract samples after 20, 40, 60, 100, 140, and 180 days of storage, before and after alkaline hydrolysis, showed that they were affected by the strong influence of β-sitosterol, which is derived from glucosteroids degradation by water present in the wood was the compound present in the largest amount in the extracts, before and after hydrolysis, as well as octadec-9-enoic acid can be oxidized at the double bond becoming more soluble in water and 3,4,5-trihydroxybenzoic acid, derived from lignin degradation by water present in the wood or microorganism attack, which were responsible for differentiating and clustering the storage time. These studies demonstrate that the best period of storage of the wood in the field is 60 days, because the reduction of the main compounds present in extracts (mainly β-sitosterol and octadec-9-enoic acid) was more significant.

A simple and efficient method for derivatization of glyphosate and AMPA using 9-fluorenylmethyl chloroformate and spectrophotometric analysis

This work presents the confirmation and optimization of the method for derivatization of glyphosate and aminomethylphosphonic acid (AMPA) using 9-fluorenylmethyl chloroformate (FMOC-Cl) evaluating the parameters: concentration of borate buffer and FMOC-Cl, homogenization time and of reaction, wavelength and solvent washing. The reaction was successfully promoted and the method is simple and easy to perform because it uses five minutes of homogenization and allows ultraviolet analysis immediately after the end of the reaction.

The Chemical Diversity of Eucalyptus spp. Essential Oils from Plants Grown in Brazil

A chemical analysis of essential oils from leaves of eleven Eucalyptus L’Herit taxa, grown in Viçosa, Brazil were carried out. The identification and quantification of essential oils constituents were carried out by GC‐FID and GC/MS. The leaves of E. camaldulensis and E. tereticornis presented the highest oil content (3.00% and 2.30% respectively). In total, 48 compounds were identified in the oils. Higher levels of 1,8‐cineole were found for oils produced by E. microcorys (66.2%), E. urophylla (65.4%) and E. camaldulensis (44.8%) and the hybrid E. urophylla × E. grandis (33.0%). The oil from E. saligna was composed mainly by α‐pinene (92.3%). High concentrations of α‐phellandrene were found in the oils produced by E. camaldulensis (22.9%) and E. robusta (36.6%). The oils from E. grandis and E. pilularis were rich in p‐cymene (59.5% and 46.0%, respectively). Samples with high levels of 1,8‐cineole were classified by principal component analysis (PCA) using the accumulated variance of the PC1 and PC2 into major groups. Other samples were grouped based on their content of p‐cymene; α‐phellandrene, α‐ and β‐eudesmol; α‐pinene. The PCA allowed the separation and classification of samples with the highest levels of different compounds, a procedure that can help in the decision of grouping oils from different sources for industrial use.