Rodrigo Bagueira de Vasconcellos Azeredo

Rapid analyses of oil and fat content in agri-food products using continuous wave free precession time domain NMR.

Time‐domain nuclear magnetic resonance (TD‐NMR) is one of the most popular solutions for quality control in the food industry. Despite the recognized success of TD‐NMR in quality control and quality assurance, the speed by which samples can be characterized by TD‐NMR techniques is still a concern, primarily when considering online or high‐throughput applications. Therefore, to enhance the speed of TD‐NMR analysis, we developed rapid methods based on steady‐state free precession of nuclear spins, which we denoted continuous wave free precession (CWFP). CWFP substantially increases the sensitivity of TD‐NMR compared with free induction decay or spin‐echo detection, which are traditionally used. The objective of this paper was to present the physical background of CWFP and review its recent developments and applications in fat and oil quantifications in agri‐food products. Copyright

Nuclear magnetic resonance water relaxation time changes in bananas during ripening: a new mechanism

BACKGROUND Nuclear magnetic resonance studies of banana fragments during ripening show an increase on the water transverse relaxation time (T2) and a decrease in water self-diffusion coefficient (D). As T(2) and D are normally directly correlated, we studied these two properties in intact bananas during ripening, in an attempt to rule out the effect of injury on the apparent discrepancies in the behavior of T(2) and D. RESULTS The results show that injury in bananas causes a decrease in T2 of the water in vacuoles (T(2vac)). They also show that T(2vac) increased and D decreased during ripening, ruling out the injury effect. To explain the apparent discrepancies, we propose a new hypothesis for the increase in T2 values, based on the reduction of Fe3+ ions to Fe2+ by galacturonic acid, produced by the hydrolysis of pectin and a decrease in internal oxygen concentration during ripening. CONCLUSION As injury alters T2 values it is necessary to use intact bananas to study relaxation times during ripening. The novel interpretation for the increase in T(2vac) based on reduction of Fe+3 and O2 concentration is an alternative mechanism to that based on the hydrolysis of starch in amyloplasts.

13C NMR quantification of mono and diacylglycerols obtained through the solvent‐free lipase‐catalyzed esterification of saturated fatty acids

In the present investigation, we studied the enzymatic synthesis of monoacylglycerols (MAG) and diacylglycerols (DAG) via the esterification of saturated fatty acids (stearic, palmitic and an industrial residue containing 87% palmitic acid) and glycerol in a solvent‐free system. Three immobilized lipases (Lipozyme RM IM, Lipozyme TL IM and Novozym 435) and different reaction conditions were evaluated. Under the optimal reaction conditions, esterifications catalyzed by Lipozyme RM IM resulted in a mixture of MAG and DAG at high conversion rates for all of the substrates. In addition, except for the reaction of industrial residue at atmospheric pressure, all of these products met the World Health Organization and European Union directives for acylglycerol mixtures for use in food applications. The products were quantified by 13C NMR, with the aid of an external reference signal which was generated from a sealed coaxial tube filled with acetonitrile‐d3. After calibrating the area of this signal using the classical external reference method, the same coaxial tube was used repeatedly to quantify the reaction products. Copyright

4α-Acetoxyamijidictyol - A New Antifeeding Dolastane Diterpene from the Brazilian Brown Alga Canistrocarpus cervicornis.

Chemical investigation of the CH2Cl2 crude extract from the brown alga Canistrocarpus cervicornis (Dictyotaceae) led to isolation of one new (1) and four previously reported dolastane diterpenes (2–5). Their structures were characterized by 1D‐ and 2D‐NMR spectroscopic techniques, including a full single crystal X‐ray diffraction analysis for 1, 2, and 4. In addition, the new structure 1 was assayed as chemical defense inhibiting the feeding by the sea urchin Lytechinus variegatus. This study constitutes an additional report broadening the known spectrum of action and defensive roles of secondary metabolites of the C. cervicornis and Dictyotales species.Chemical investigation of the CH2 Cl2 crude extract from the brown alga Canistrocarpus cervicornis (Dictyotaceae) led to isolation of one new (1) and four previously reported dolastane diterpenes (2-5). Their structures were characterized by 1D- and 2D-NMR spectroscopic techniques, including a full single crystal X-ray diffraction analysis for 1, 2, and 4. In addition, the new structure 1 was assayed as chemical defense inhibiting the feeding by the sea urchin Lytechinus variegatus. This study constitutes an additional report broadening the known spectrum of action and defensive roles of secondary metabolites of the C. cervicornis and Dictyotales species.

Complete and unambiguous assignments of 1H and 13C chemical shifts of new arylamino derivatives of ortho‐naphthofuranquinones

Six new nor‐β‐lapachones have been synthesized from reaction of 3‐bromo‐nor‐β‐lapachone with arylamines. These derivatives have potent anticancer properties against several cell lines. Here, we report complete unambiguous assignments of 1H and 13C chemical shifts of the new compounds. The assignments were made using a combination of one‐ and two‐dimensional NMR techniques (1H, 13C, 1H1H COSY, 1H13C HSQC, and 1H13C HMBC). Copyright

Automatic classification of carbonate rocks permeability from 1H NMR relaxation data

This work investigates the effectiveness of data mining analysis on NMR data.The goal is to accurately predict the permeability class of carbonate rocks.Our approach outperforms the traditional NMR models Timur-Coates and Kenyon.Traditional models ignore the singular relationship between T2 bins and pore throat.Data mining models capture the influence of each T2 bin over the permeability class. The accurate permeability mapping, even with the aid of modern borehole geophysics methods, is still a big challenge on the reservoir management framework. One concern within the petrophysics community is that rock permeability value predicted by well logging should not be considered as absolute, mainly for carbonates, but a relative index for identifying more permeable zones. Therefore, in this paper a permeability classification methodology, based exclusively on 1H NMR (Nuclear Magnetic Resonance) relaxation data, was evaluated for the first time as an alternative to the prediction of permeability as a continuous variable. To pursue this, a side-by-side comparison of different data mining techniques for the permeability classification task was performed using a petrophysical dataset with 78 rock samples from six different carbonate reservoirs. The effectiveness of six classification algorithms (k-NN, Naive Bayes, C4.5, SMO, Random Forest and Multilayer Perceptron) was evaluated to predict the rock permeability class according to the following ranges: low ( 100mD). Discretization and feature selection strategies were also employed as preprocessing steps in order to improve the classification accuracy. For the studied dataset, the results demonstrated that the Random Forest and SMO strategies delivered the best classification performance among the selected classifiers. The computational experiments also evidenced that our approach led to more accurate predictions when compared with two methods widely adopted by the petroleum industry (Kenyon and Timur-Coates models).

Cânfora: um bom modelo para ilustrar técnicas de RMN

CAMPHOR: A GOOD MODEL FOR ILLUSTRATING NMR TECHNIQUES. The use of Nuclear Magnetic Resonance spectroscopyto establish the three-dimensional structures of molecules is an important component of modern Chemistry courses. The combinationof techniques that can be used for this purpose is conveniently illustrated by their application to the camphor molecule. This paperpresents applications of several techniques used in NMR spectral interpretation in an increasing order of complexity. The result ofindividual experiments is illustrated in order to familiarize the user with the way connectivity through bonds and through space isestablished from 1D/2D-NMR spectra and molecular stereochemistry is determined from different NMR experiments.Keywords: organic chemistry; NMR spectroscopy; camphor.