Luiz Alberto Colnago

Characterization of humic acids from a Brazilian Oxisol under different tillage systems by EPR, 13C NMR, FTIR and fluorescence spectroscopy

The importance of soil organic matter functions is well known, but structural information, chemical composition and changes induced by anthropogenic factors such as tillage practices are still being researched. In the present paper were characterized Brazilian humic acids (HAs) from an Oxisol under different treatments: conventional tillage/maize-bare fallow (CT1); conventional tillage/maize rotation with soybean-bare fallow (CT2); no-till/maize-bare fallow (NT1); no-till/maize rotation with soybean-bare fallow (NT2); no-till/maize-cajanus (NT3) and no cultivated soil under natural vegetation (NC). Soil HA samples were analyzed by electron paramagnetic resonance (EPR), solid-state 13C nuclear magnetic resonance (13C NMR), Fourier transform infra-red (FTIR) and UV-Vis fluorescence spectroscopies and elemental analysis (CHNS). The FTIR spectra of the HAs were similar for all treatments. The level of semiquinone-type free radical determined from the EPR spectra was lower for treatments no-till/maize-cajanus (NT3) and noncultivated soil (1.74×1017 and 1.02×1017 spins g−1 HA, respectively), compared with 2.3×1017 spins g−1 HA for other soils under cultivation. The percentage of aromatic carbons determined by 13C NMR also decreases for noncultivated soil to 24%, being around 30% for samples of the other treatments. The solid-state 13C NMR and EPR spectroscopies showed small differences in chemical composition of the HA from soils where incorporation of vegetal residues was higher, showing that organic matter (OM) formed in this cases is less aromatic. The fluorescence intensities were in agreement with the percentage of aromatic carbons, determined by NMR (r=0.97 P<0.01) and with semiquinone content, determined by EPR (r=0.97 P<0.01). No important effect due to tillage system was observed in these areas after 5 years of cultivation. Probably, the studied Oxisol has a high clay content that offers protection to the clay–Fe–OM complex against strong structural alterations.

Conformation of the Z19 prolamin by FTIR, NMR, and SAXS.

The alpha zein, the maize storage prolamin, is a mixture of several homologous polypeptides that shows two bands in SDS-PAGE, called Z19 and Z22. The conformation studies carried out by several authors in this mixture are conflicting. To elucidate these inconsistencies, we analyzed the conformation of the Z19 fraction, extracted from BR451 maize variety by Fourier transform infrared spectroscopy, nuclear magnetic resonance, and small-angle X-ray scattering. The infrared results show that Z19 has 46% of alpha helix and 22% of beta sheet. The fast N-H to N-D exchange measured by (1)H NMR spectroscopy showed that Z19 is not a compact structure. The scattering measurements indicated an extended structure with 12 by 130 A. With these data, we have modeled the Z19 structure as a hairpin, composed of helical, sheet, turns, and secondary structures, folded back on itself.

A kinetic model for Xylella fastidiosa adhesion, biofilm formation, and virulence

Xylella fastidiosa is the causal agent of citrus variegated chlorosis and Pierces disease which are the major threat to the citrus and wine industries. The most accepted hypothesis for Xf diseases affirms that it is a vascular occlusion caused by bacterial biofilm, embedded in an extracellular translucent matrix that was deduced to be the exopolysaccharide fastidian. Fourier transform infrared spectroscopy analysis demonstrated that virulent cells which form biofilm on glass have low fastidian content similar to the weak virulent ones. This indicates that high amounts of fastidian are not necessary for adhesion. In this paper we propose a kinetic model for X. fastidiosa adhesion, biofilm formation, and virulence based on electrostatic attraction between bacterial surface proteins and xylem walls. Fastidian is involved in final biofilm formation and cation sequestration in dilute sap.

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

High-throughput non-destructive nuclear magnetic resonance method to measure intramuscular fat content in beef

High intake of saturated fat from meats has been associated with cardiovascular disease, cancer, diabetes, and others diseases. In this paper, we are introducing a simple, high-throughput, and non-destructive low-resolution nuclear magnetic resonance method that has the potential to analyze the intramuscular fat content (IMF) in more than 1,000 beef portions per hour. The results can be used in nutritional fact labels, replacing the currently used average value. The method is based on longitudinal (T1) and transverse (T2) relaxation time information obtained by a continuous wave-free precession (CWFP) sequence. CWFP yields a higher correlation coefficient (r = 0.9) than the conventional Carr-Purcell-Meiboom-Gill (CPMG) method (r = −0.25) for IMF in beef and is just as fast and a simpler pulse sequence than CPMG. The method can also be applied to other meat products.

Continuous wave free precession. Practical analytical tool for low-resolution nuclear magnetic resonance measurements

The use of continuous wave free precession (CWFP) as a practical analytical tool for quantitative determinations in low-resolution nuclear magnetic resonance (LRNMR) is examined. The requirements of this technique are shown to be no more demanding than those prevailing in free-induction decay or spin-echo measurements. It is shown that the substantial gain in signal to noise ratio for a given acquisition time permitted by CWFP, can be exploited with advantage in practically any application of LRNMR. This applies not only to homogeneous low viscosity liquid samples but also to multi-component systems where differences in relaxation times of each component permit a separation of the individual contributions. As an example, the use of CWFP for fast quantitative determination of oil and moisture in various seeds is presented.

Crystal structure of a Schistosoma mansoni septin reveals the phenomenon of strand slippage in septins dependent on the nature of the bound nucleotide.

Background: Septins are filament-forming proteins involved in membrane-remodeling events. Results: Two crystal structures of a septin with the highest resolution to date reveal the phenomenon of β-strand slippage. Conclusion: A novel mechanistic framework for the influence of the nature of the bound nucleotide and the presence of Mg2+ in septins is proposed. Significance: Identification of strand slippage might contribute to elucidating the mechanism of septin association with membranes. Septins are filament-forming GTP-binding proteins involved in important cellular events, such as cytokinesis, barrier formation, and membrane remodeling. Here, we present two crystal structures of the GTPase domain of a Schistosoma mansoni septin (SmSEPT10), one bound to GDP and the other to GTP. The structures have been solved at an unprecedented resolution for septins (1.93 and 2.1 Å, respectively), which has allowed for unambiguous structural assignment of regions previously poorly defined. Consequently, we provide a reliable model for functional interpretation and a solid foundation for future structural studies. Upon comparing the two complexes, we observe for the first time the phenomenon of a strand slippage in septins. Such slippage generates a front-back communication mechanism between the G and NC interfaces. These data provide a novel mechanistic framework for the influence of nucleotide binding to the GTPase domain, opening new possibilities for the study of the dynamics of septin filaments.

Fast determination of beef quality parameters with time-domain nuclear magnetic resonance spectroscopy and chemometrics

The noteworthy of this study is to predict seven quality parameters for beef samples using time-domain nuclear magnetic resonance (TD-NMR) relaxometry data and multivariate models. Samples from 61 Bonsmara heifers were separated into five groups based on genetic (breeding composition) and feed system (grain and grass feed). Seven sample parameters were analyzed by reference methods; among them, three sensorial parameters, flavor, juiciness and tenderness and four physicochemical parameters, cooking loss, fat and moisture content and instrumental tenderness using Warner Bratzler shear force (WBSF). The raw beef samples of the same animals were analyzed by TD-NMR relaxometry using Carr-Purcell-Meiboom-Gill (CPMG) and Continuous Wave-Free Precession (CWFP) sequences. Regression models computed by partial least squares (PLS) chemometric technique using CPMG and CWFP data and the results of the classical analysis were constructed. The results allowed for the prediction of aforementioned seven properties. The predictive ability of the method was evaluated using the root mean square error (RMSE) for the calibration (RMSEC) and validation (RMSEP) data sets. The reference and predicted values showed no significant differences at a 95% confidence level.

Study of liquid-phase molecular packing interactions and morphology of fatty acid methyl esters (biodiesel)

Background1H low field nuclear magnetic resonance (LF-NMR) relaxometry has been suggested as a tool to distinguish between different molecular ensembles in complex systems with differential segmental or whole molecular motion and/or different morphologies. In biodiesel applications the molecular structure versus liquid-phase packing morphologies of fatty acid methyl esters (FAMEs) influences physico-chemical characteristics of the fuel, including flow properties, operability during cold weather, blending, and more. Still, their liquid morphological structures have scarcely been studied. It was therefore the objective of this work to explore the potential of this technology for characterizing the molecular organization of FAMEs in the liquid phase. This was accomplished by using a combination of supporting advanced technologies.ResultsWe show that pure oleic acid (OA) and methyl oleate (MO) standards exhibited both similarities and differences in the 1H LF-NMR relaxation times (T2s) and peak areas, for a range of temperatures. Based on X-ray measurements, both molecules were found to possess a liquid crystal-like order, although a larger fluidity was found for MO, because as the temperature is increased, MO molecules separate both longitudinally and transversely from one another. In addition, both molecules exhibited a preferred direction of diffusion based on the apparent hydrodynamic radius. The close molecular packing arrangement and interactions were found to affect the translational and segmental motions of the molecules, as a result of dimerization of the head group in OA as opposed to weaker polar interactions in MO.ConclusionsA comprehensive model for the liquid crystal-like arrangement of FAMEs in the liquid phase is suggested. The differences in translational and segmental motions of the molecules were rationalized by the differences in the 1H LF-NMR T2 distributions of OA and MO, which was further supported by 13C high field (HF)-NMR spectra and 1H HF-NMR relaxation. The proposed assignment allows for material characterization based on parameters that contribute to properties in applications such as biodiesel fuels.

Identification of free fatty acids in maize protein bodies and purified α zeins by 13C and 1H nuclear magnetic resonance

Zeins, the maize storage proteins, are the most abundant proteins in the corn endosperm, and are synthesized on the rough endoplasmatic reticulum and deposited in discrete organelles called protein bodies. Several authors, using circular dichroism and optical rotatory dispersion, have concluded that these proteins have a high alpha-helical content in alcoholic solution. In this work we have studied these proteins, within the protein bodies themselves and after extraction from the corn grains with 70% ethanol, using NMR (nuclear magnetic resonance) spectroscopy. We conclusively demonstrate the presence of free fatty acids within both the protein bodies and also in the alcohol extracted alpha zeins. We present evidence for a direct interaction between the free fatty acids and the alpha zein proteins within the protein body and suggest possible mechanisms by which such an association has arisen during the evolution of the maize endosperm.