Valdemar Lacerda

Studies on crude oil‐water biphasic mixtures by low‐field NMR

Low‐field 1H NMR was used in this work for the analysis of mixtures involving crude oils and water. CPMG experiments were performed to determine the transverse relaxation time (T2) distribution curves, which were computed by the inverse Laplace transform of the echo decay data. The instruments ability of quantifying water and petroleum in biphasic mixtures following different methodologies was tested. For mixtures between deionized water and petroleum, one achieved excellent results, with root mean squared error of cross‐validation (RMSECV) of 0.8% for a regression between the water content (wt %) and the relative area of the water peak in the T2 distribution curve, or a standard deviation of 0.9% for the relationship between the water content and the relative water peak area, corrected by the relative hydrogen index of the crude. In the case of biphasic mixtures of Mn2+‐doped water and crude oils, the best result of RMSECV = 1.6% was achieved by using the raw magnetization decay data for a partial least squares regression. Copyright

Niobium Pentachloride Catalysed Ring Opening of Epoxides

Epoxide ring opening is a frequently required transformation in Organic Synthesis. In this paper we describe the application of NbCl5 for this purpose using three different substrates. Chlorohydrins, 1,2-diols, products containing solvent residues as well as rearrangement products are obtained, depending on both the substrate structure and reaction conditions. Rationalizations to account for some of the results are suggested.

Qualitative analysis of designer drugs by paper spray ionisation mass spectrometry (PSI-MS)

The application of ambient ionization mass spectrometry such as paper spray ionisation (PSI) is a fast, powerful, and simple method to analyze designer drugs directly on the surface of blotters. PSI-MS does not require nebulizing gas and heating temperature as well as complex protocols for sample preparation. Herein, it was possible to identify and elucidate the chemical structure of designer drugs using tandem mass spectrometry experiments from a triangular blotter. Substances such as lysergic acid diethylamide (LSD), and five new designer drugs (2,5-dimethoxy-4-chloroamphetamine (DOC), 2,5-dimethoxy-4-bromoamphetamine (DOB), 25C-NBOMe, 25B-NBOMe, and 25I-NBOMe) were characterized by PSI-MS. The PSI(+)-MS and PSI(+)-MS/MS data confirmed the assignments of the designer drugs and fragmentation mechanisms have been proposed. From losses of 17 Da (NH3), which is typical of primary amines, the CID results suggest the presence of isomers in the chemical composition of the NBOMe class. Additionally, the data were compared to those of ultra-high-resolution mass spectroscopy (positive-ion electrospray ionization coupled with Fourier transform ion cyclotron mass spectrometry, ESI(+)FT-ICR MS).

Long‐range JCH heteronuclear coupling constants in cyclopentane derivatives. Part II

Here we report the detailed measurement of long‐range heteronuclear spin–spin coupling constants, especially 2, 3JCH spin–spin couplings for eight different cyclopentane derivatives. These 2, 3JCH constants were shown to be a useful tool in the determination of the relative stereochemistry in these rings. The coupling constant measurements reported here are based on two different experiments: a 2D heteronuclear correlation experiment named G‐BIRDR, X‐CPMG‐HSQMBC and the 2D‐coupled gHSQC {1H‐13C} experiment Copyright

NMR property calculations and experimental study of the 1,6-epoxycarvone and α-epoxypinene: a comparison of models

This work aims at using theoretical calculations of shielding tensors (σ) through different methods [gauge‐independent atomic orbital (GIAO), continuous set of gauge transformations (CSGT) and individual gauges for atoms in molecules (IGAIM)] and spin‐spin coupling constants J using GIAO method to compare these methods and to corroborate the data obtained with the assignment of all of 1H and 13C NMR signals and the relative stereochemistry of the 1,6‐epoxycarvone and the α‐epoxypinene. All the 1H and 13C NMR signals were assigned unequivocally. The stereochemistry for the epoxides is trans and the B3LYP theory level with CSGT and IGAIM methods is the best choice to evaluate theoretical chemical shifts for compounds studied. Copyright

Stereochemistry of cyclopentane derivatives from (2,3)J(CH) dependence on dihedral angle (theta H--C--C--X).

The 2, 3JCH dependence on dihedral angle (θ HCCX) for cyclopentane derivatives was investigated. We observed that the combined use of experimentally obtained 2, 3JCH values and the theoretically determined dihedral angles between the corresponding nuclei can be used to infer the relative stereochemistry of the ring substituents in cyclopentane derivatives. There is a good correlation between the magnitude of 3JCH and the dihedral angle between the hydrogen and the coupled carbon (R2 = 0.88). Copyright

1H and 13C NMR spectral data of bioactive cage-like polycyclic compounds

Bioactive cage‐like polycyclic compounds have attracted the attention of several research groups because of their unique appearance and their biological activities. Their structures were established on the basis of 1H NMR and 13C NMR spectroscopic data. The 1H and 13C signal assignments and most homonuclear hydrogen coupling constants were assigned by use of techniques such as 1D 1H and 13C NMR and 2D gCOSY, non‐edited gHSQC and gHMBC. The gNOESY experiments proved the endo‐stereochemistry. Copyright

Chemical profiles of Robusta and Arabica coffee by ESI(−)FT-ICR MS and ATR-FTIR: a quantitative approach

This paper reports a method to quantify Robusta coffee in Arabica coffee blends using univariate and multivariate models. Coffee samples were analyzed by negative-ion mode electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI(−)FT-ICR MS) and by attenuated total reflection Fourier transform spectroscopy in the mid-infrared region (ATR-FTIR). To build the univariate calibration model with ESI(−)FT-ICR MS data, 12 samples of Arabica coffee adulterated with different proportions of Robusta coffee and doped with an internal standard were used. For the ATR-FTIR analysis, a higher variability of adulteration was employed with a total of 23 blend samples, and a partial least squares (PLS) regression model was proposed. The obtained univariate calibration model had limits of detection (LOD) and quantification (LOQ) of 0.2 and 0.3 wt%, respectively, whereas the PLS model with ATR-FTIR data had LOD and LOQ values of 1.3 and 4.3 wt%. Repeatability and intermediate precision for the ESI(−)FT-ICR MS model were 4 wt% and 5 wt%, respectively, and for the model with ATR-FTIR data both were 1.7 wt%. The proposed methodologies also enable the prediction of Robusta coffee adulteration in Arabica coffee commercial samples.

Análise do teor e da qualidade dos lipídeos presentes em sementes de oleaginosas por rmn de baixo campo

To choose among the variety of oleaginous plants for biodiesel production, the oil content of several matrices was determined through different low-field 1H nuclear magnetic resonance (NMR) experiments with varied pulse sequences, namely single-pulse, spin-echo, CPMG, and CWFP. The experiments that involved the first three sequences showed high correlation with each other and with the solvent extraction method. The quality of the vegetable oils was also evaluated on the basis of the existing correlation between the T2 values of the oils and their properties, such as viscosity, iodine index, and cetane index. These analyses were performed using HCA and PCA chemometric tools. The results were sufficiently significant to allow separation of the oleaginous matrices according to their quality. Thus, the low-field 1H NMR technique was confirmed as an important tool to aid in the selection of oleaginous matrices for biodiesel production.

A New, Simple and Efficient Method of Steglich Esterification of Juglone with Long-Chain Fatty Acids: Synthesis of a New Class of Non-Polymeric Wax Deposition Inhibitors for Crude Oil

A esterificacao direta de naftoquinonas mostrou-se uma tarefa dificil. Metodologias mais comuns envolvem a aplicacao de cloretos de acila em piridina ou anidridos, entretanto, quando acidos de cadeia longa sao utilizados tais metodologias se mostram ineficientes devido aos baixos rendimentos obtidos. Apresentamos uma nova sintese de esteres de cadeia longa de juglona baseado na esterificacao de Steglich utilizando um acido de Lewis barato como cocatalisador. Rendimentos obtidos sao consideravelmente maiores do que os reportados previamente. Quimica computacional foi utilizada para avaliar os efeitos do CeCl3 como cocatalisador. Os compostos preparados foram testados como inibidores de deposicao de parafinas em petroleo. Ester palmitico da juglona foi capaz de reduzir 4 oC na temperatura de inicio de aparecimento de cristais (WAT) do oleo estudado, representando uma reducao de 1,5% m/m de parafinas normais precipitadas. Direct esterification on naphthoquinone presented itself as a hard task. Usual methodologies apply acyl chloride in pyridine or anhydrides but with long-chain esters this procedure proved to be ineffective because of the low yields obtained. We present a new synthesis of long-chain esters of juglone based on Steglich esterification using a cheap Lewis acid as cocatalyst. Yields obtained are considerably better than those found previously. Computational chemistry was used to evaluate the effects of CeCl 3 as cocatalyst. Prepared compounds were tested as wax deposition inhibitors in crude oil. Palmitic ester of juglone was able to lower 4 oC on the wax appearance temperature (WAT) of the studied oil, representing a reduction of precipitated normal paraffin of 1.5% m/m.