Química
URI permanente desta comunidadehttps://locus.ufv.br/handle/123456789/11782
Navegar
Item Computation and structural elucidation of compounds formed via epoxide alcoholysis(Magnetic Resonance in Chemistry, 2019-04) Alvarenga, Elson S.; Teixeira, Milena G.; Lopes, Dayane T.; Demuner, Antonio J.Isobenzofuranones are known for their wide range of biological activities such as fungicide, insecticide, and anticancer. The search for novel bioactive compounds was performed by reaction of epoxide 2 with methanol, ethanol, propan‐1‐ol, propan‐2‐ol, and butan‐1‐ol. The mechanism for the stereoselective and stereospecific epoxide opening with methanol was reasoned by calculating the transition states for the two putative structures (rac)‐3a and (rac)‐3b. The compound (rac)‐3a is the kinetic product as inferred from the lower energies of its transition state (TS1). The 1H and 13C nuclear magnetic resonance (NMR) chemical shifts for these two candidate structures were calculated and compared with the experimental data using mean absolute error (MAE) and DP4 analyses. Therefore, the relative stereochemistry of (rac)‐3a was established by the mechanism, MAE, and DP4 approaches. The hydroxyl group was acetylated to surpass the problem of signal overlapping of H5 and H6 in the 1H NMR. The relative stereochemistry of the corresponding ester determined by NMR interpretation was in agreement with the structure of (rac)‐3a.Item A validated 1 H NMR method for quantitative analysis of α -bisabolol in essential oils of Eremanthus erythropappus(Talanta, 2016-08-10) Cerceau, Cristiane I.; Barbosa, Luiz C.A.; Alvarenga, Elson S.; Ferreira, Antonio G.; Thomasi, Sérgio S.α-Bisabolol is a natural terpene produced by Eremanthus erythropappus and is widely used in cosmetics and pharmaceuticals due to its anti-inflammatory, antibacterial and antimycotic properties. Due to these applications, a control of composition and authenticity of commercial oils rich in this terpene is required, resulting in a demand for new methodologies for quality control. In this work a rapid and efficient method for quantification of α-bisabolol in the essential oil of E. erythropappus (candeia) using 1H NMR was developed, validated and compared to gas chromatography (GC) method. The quantification of α-bisabolol by 1H NMR was successfully achieved for most of the essential oil samples of E. erythropappus evaluated, except for those with a more complex composition. To circumvent this limitation a 2D NMR COSY contour map was used. This method proved to be a fast and efficient alternative, providing results with standard deviations SD<0.3%. All evaluated parameters (selectivity, linearity, accuracy/precision, repeatability, robustness and stability of analyte and internal standard in solution) gave satisfactory results. Using the 1H NMR signals at 5.36 and 5.13 ppm, the limit of detection (LOD) and limit of quantification (LOQ) were 0.26 and 2.59 mg, respectively. The results obtained by the 1H NMR method presented SD=0.59%, smaller than the value found for GC (SD=1.18%). Tukey tests have shown that the results obtained by 1H NMR and COSY methodology are similar to the obtained by the traditional GC-FID technique using external and internal standardization and normalization with 95% confidence.