Ecotoxicological Properties of Pure and Phosphorus-Containing Graphene Oxide Bidimensional Sheets in Daphnia magna.

In this work, the synthesis and structural, thermal, vibrational, morphological, and electronic characterization of 2D-like pure graphene oxide (GO) and phosphorus-containing graphene oxide (GOP) sheets were investigated. The average thicknesses of GO and GOP were 0.8 µm and 3.1 µm, respectively. The electron energy-loss spectroscopy spectra were used to analyze the differences in the C-K and O-K energy edge bands between GO and GOP. In addition, colloidal stability was studied using dynamic light scattering and zeta potential physicochemical techniques, determining that as the concentration increases, the hydrodynamic diameter and electrostatic stability of GO and GOP increase. The colloidal stability was quite important to ensure the interaction between the suspended solid phase and the biomarker. The 2D-like materials were used to determine their ecotoxicological properties, such as the medium lethal concentration, a crucial parameter for understanding ecotoxicity. Acute ecotoxicity experiments (24 h) were conducted in triplicate to obtain robust statistics, with corresponding mean lethal concentration (LC50) of 11.4 mg L-1 and 9.8 mg L-1 for GO and GOP, respectively. The morphological parameters of GO and GOP were compared with a negative control. However, only the case of GO was analyzed, since the Daphnia magna (D. magna) set exposed to GOP died before completing the time required for morphological analysis. The results indicate that the GOP sample is more toxic than the GO, both during and after exposure. Furthermore, the morphological parameters with the greatest statistically significant changes (p<0.05) were associated with the heart and body, while the eye and tail showed less significant changes.

Using 1H low-field NMR relaxometry to detect the amounts of Robusta and Arabica varieties in coffee blends.

Low-field nuclear magnetic resonance (LF-NMR) is a method of widespread use in food research due to its non-destructive character and the relatively low cost of the instruments, allowing the determination of oil / fat contents and the achievement of images of different types of food materials, among other uses. In this work, 1H LF-NMR relaxometry was used to distinguish the contributions due to Arabica and Robusta coffee varieties present in coffee blends. As the method detects preferentially the NMR signals due to phases with high molecular mobility, which exhibit longer values of the 1H transverse relaxation time (T2), the difference in the oil contents associated with Arabica and Robusta coffee was the key factor responsible for the detection of the contributions due to each variety. The analysis presented in this work showed that the relative hydrogen index is a useful parameter to be used in quantitative analyses of the contents of each coffee variety present in the blends. The results illustrate the high potential of applicability of LF-NMR relaxometry as a screening tool for quality control and adulteration detection of coffee-related products.

Inclusion complex of ketoconazole and p-sulfonic acid calix[6]arene improves antileishmanial activity and selectivity against Leishmania amazonensis and Leishmania infantum.

Many previous studies presented the effectiveness of ketoconazole (KTZ) against leishmaniasis. However, the bioavailability and therapeutic efficacy of free KTZ are limited due to its low aqueous solubility. In this study, an inclusion complex (IC6HKTZ) was prepared with p-sulfonic acid calix[6]arene (CX6SO3H) to improve the solubility and efficacy of KTZ against Leishmania amazonensis and Leishmania infantum promastigotes. A linear increase in KTZ solubility as a function of CX6SO3H concentration was verified using the phase-solubility diagram. The resulting diagram was classified as AL-type and a 1:1 host-guest stoichiometry was assumed to prepare IC6HKTZ by freeze-drying. FTIR, TG/DSC, XRD, and solid-state 13C NMR spectroscopy analyses were performed to confirm the formation of IC6HKTZ. The solubility enhancement of KTZ by 120.00 µM CX6SO3H was about 95 times. The IC50 values of IC6HKTZ and free KTZ were 3.95 and 14.35 µM for Leishmania amazonensis and 6.74 and 17.47 µM for Leishmania infantum, respectively. The viability of DH82 macrophages was not affected by CX6SO3H. These results show that CX6SO3H is a new supramolecular carrier system that improves antileishmanial activities to KTZ for the treatment of cutaneous and visceral leishmaniasis.

Combined computational and experimental study about the incorporation of phosphorus into the structure of graphene oxide.

Phosphorus-containing graphene-based hybrids are materials with outstanding properties for diverse applications. In this work, an easy route to produce phosphorus-graphene oxide hybrid materials is described, involving the use of variable amounts of H3PO4 and H2SO4 during the reaction of oxidation of a graphitic precursor. The physical and chemical features of the hybrids change significantly with the variation in the acid amounts used in the syntheses. XPS and solid-state 13C and 31P NMR results show that the hybrids contain large amounts of oxygen functional groups, with the phosphorus incorporation proceeding mostly through the formation of phosphate-like linkages and other functions with C-O-P bonds. The experimental findings are supported by DFT calculations, which allow the assessment of the energetics and the geometry of the interaction between phosphate groups and graphene-based models; these calculations are also used to predict the chemical shifts in the 31P and 13C NMR spectra of the models, which show good agreement with the experimentally observed solid-state NMR spectra.

Solid-state NMR spectroscopy of roasted and ground coffee samples: Evidences for phase heterogeneity and prospects of applications in food screening.

The advancement in the use of spectroscopic techniques to investigate coffee samples is of high interest especially considering the widespread problems with coffee adulteration and counterfeiting. In this work, the use of solid-state nuclear magnetic resonance (NMR) is investigated as a means to probe the various chemically-distinct phases existent in roasted coffee samples and to detect the occurrence of counterfeiting or adulterations in coffee blends. Routine solid-state 1H and 13C NMR spectra allowed the distinction between different coffee types (Arabica/Robusta) and the evaluation of the presence of these components in coffee blends. On the other hand, the use of more specialized solid-state NMR experiments revealed the existence of phases with different molecular mobilities (e.g., associated with lipids or carbohydrates). The results illustrate the usefulness of solid-state NMR spectroscopy to examine molecular mobilities and interactions and to aid in the quality control of coffee-related products.

Heterogeneous Fenton-like surface properties of oxygenated graphitic carbon nitride.

The photo-Fenton activity of graphitic carbon nitride (g-C3N4) has been widely studied, nevertheless, its Fenton-like catalytic behavior in the dark has not yet been demonstrated. In the present work, it is shown that oxygenated g-C3N4 obtained at different temperatures (500-600 °C) can degrade indigo carmine with hydrogen peroxide in the dark by a reaction similar to a conventional Fenton's reaction. Based on an extensive characterization of g-C3N4, we conclude that Fenton-like activity is directly related to the oxygenated functional groups on g-C3N4 structure, mainly by -OH functional groups. Oxygenated functional groups (e.g., hydroquinone-like groups) can reduce the H2O2 and generate oxidizing hydroxyl radicals, just like in the Fenton reaction performed by metals. In addition to new information on g-C3N4 surface reactivity revealed by this study, the metal-free oxygenated g-C3N4 catalyst may be an alternative to traditional metal catalysts used in Fenton-like reactions for advanced oxidation.

Nanostructured faujasite zeolite as metal ion adsorbent: kinetics, equilibrium adsorption and metal recovery studies.

The hydrothermal synthesis of nano-faujasite has been successfully performed and the effects of some crystallization parameters were investigated, along with the use of this material as a heavy-metal ion adsorbent. X-ray diffraction patterns have shown that the structure of the nano-faujasite is strongly dependent on both the crystallization time and the alkalinity of the synthesis medium. According to N2 physisorption, X-ray fluorescence, SEM/EDS, and solid state 29Si and 27Al NMR data, the produced nano-faujasite consists of a solid with low molar Si/Al ratio (1.7), with high availability of ion exchange sites and high surface area/small particle size, allowing easy diffusion of metal ions to adsorbent active sites. As a consequence, an excellent performance on removal of Cd2+, Zn2+ and Cu2+ ions was found for this solid. The adsorption capacity followed the order Cd2+ (133 mg·g-1) > Zn2+ (115 mg·g-1) > Cu2+ (99 mg·g-1), which agrees with the order of increasing absolute values of the hydration energy of the metal ions. Kinetic studies and adsorption isotherms showed that the metal ion removal takes place by ion exchange on the monolayer surface of the nano-faujasite. The electrochemical recovery of copper in metallic form exhibited an efficiency of 80.2% after 120 min, which suggests that this process can be adequately implemented for full-scale metal removal.

Synthesis of bilayer films from regenerated cellulose nanofibers and poly(globalide) for skin tissue engineering applications.

Commercial cell-based skin regenerative products are highly expensive, carry the risk of rejection and require a long cell culture period to manufacture. This work describes the synthesis of bilayer films from poly(globalide) (PGl) and regenerated cellulose nanofibers (rCNFs) and their use as a cell-free scaffold to support keratinocyte attachment and proliferation. The method is simple, eco-friendly (as the cellulose precursor is obtained from agricultural waste) and of low cost. The rCNFs were produced by acid hydrolysis and PGl was obtained via enzymatic ring-opening polymerization. The bilayer films were synthesized by layer-by-layer casting at ambient temperature. All the films showed a well-defined interface between PGl and cellulose. The produced rCNF/PGl bilayer films showed cell metabolic activity far superior in comparison with pristine PGl regarding the keratinocyte growth, which illustrates the potential use of these materials in skin tissue engineering.

Stable dark pulses produced by a graphite oxide saturable absorber in a fiber laser cavity.

In this paper, we report for the first time, to the best of our knowledge, the experimental generation of dark pulses in the 1.5 µm band from a passively $Q$Q-switched fiber laser employing graphite oxide as the saturable absorber, generating tunable microsecond pulses with kHz repetition rates. The graphite oxide samples were obtained by recycling the graphite present in Li-ion batteries used in cell phones through a chemical separation and oxidation process. Sample characterization employing x-ray diffraction, solid-state $ ^{{13}}{\rm C} $13C nuclear magnetic resonance, and Raman spectroscopy showed that the produced graphite oxide exhibited a homogeneously oxidized structure. Dark pulse emission could be observed at a relatively low pump threshold of 35 mW in a short 20 m laser cavity, indicating that the graphite oxide acted as a saturable absorber, significantly enhancing the nonlinearity of the laser cavity. Additionally, dark pulse operation was demonstrated at a high stability with a signal-to-noise ratio of 56 dB and a pulse-to-pulse timing jitter of 159.84 fs.

Production of high-purity cellulose, cellulose acetate and cellulose-silica composite from babassu coconut shells.

Lignocellulosic biomass has been widely studied as a source of cellulose- and related products, attracting the great interest of researchers dealing with renewable energy sources, vegetable waste recycling and biomaterials. In this work, the babassu coconut shells (epicarp and endocarp) were used for the achievement of products such as cellulose, cellulose acetate and cellulose-silica composite, which were chemically and structurally characterized by solid-state 13C nuclear magnetic resonance spectroscopy and scanning electron microscopy, among other techniques. As this precursor also naturally contains a significant amount of silica, a composite containing cellulose fibers mixed with amorphous silica particles (with rosette-like shape) was also produced. Finally, the possibility of synthesis of cellulose acetate was also demonstrated, illustrating the plethora of potential applications of this important lignocellulosic residue for the production of cellulose-based materials of high technological interest.

Recovery of latent fingermarks from brass cartridge cases: Evaluation of developers, analysis of surfaces and internal ballistic effects.

A study was undertaken wherein different fingermark developers were evaluated for the recovery of fingermarks from brass cartridge cases, besides the evaluation of factors such as firing effects and surface characterization of the cases. The latent fingermarks on α-brass plates, fired and unfired cartridge cases were deposited and aged for 1-14days before development with different developers. In order to mimic the fired cartridge case conditions, the brass plates were heated and examined at room temperature (RT), at 63 and at 200°C. The sequential treatment with cyanoacrylate, gun blue and fluorescent dye has been found to be the best among other developers for the recovery of latent fingermarks on brass surfaces including fired and unfired cartridge cases. Cartridge cases and other brass surfaces were also analyzed by surface characterization methods, including X-ray diffraction, scanning electronic microscopy, energy dispersive X-ray spectroscopy and metallographic examination. The tested surfaces correspond to α-phase brass Cu0.7Zn0.3 composition and have shown different surface morphologies (such as grain structure) and different levels of oxidation, even for cartridge cases obtained from the same batch. Due to this, the effectiveness of a given reagent for a specific brass surface is uncertain. Therefore, the application of the entire tested sequence of developers is strongly recommended. Further, the effects of firing on fingermarks on cartridge cases were examined, and the results indicated that the blowback of hot gases through the looseness between cartridge case and chamber wall of the firearm is the main cause responsible for deterioration of fingermarks during firing. Despite the recognized damage caused to fingermarks by the firing effects, good quality fingermarks were recovered from fired cartridge cases in which full fingermarks were intentionally deposited prior to firing. This indicates that the handling of the cartridges before and during the loading of the gun may have a strong influence on the quantity and quality of fingermarks, and that the firing itself is not the main responsible factor for the absence or low quality of fingermarks, as frequently reported in fired cartridge cases studies.

Determination of the hyperfine magnetic field in magnetic carbon-based materials: DFT calculations and NMR experiments.

The prospect of carbon-based magnetic materials is of immense fundamental and practical importance, and information on atomic-scale features is required for a better understanding of the mechanisms leading to carbon magnetism. Here we report the first direct detection of the microscopic magnetic field produced at (13)C nuclei in a ferromagnetic carbon material by zero-field nuclear magnetic resonance (NMR). Electronic structure calculations carried out in nanosized model systems with different classes of structural defects show a similar range of magnetic field values (18-21 T) for all investigated systems, in agreement with the NMR experiments. Our results are strong evidence of the intrinsic nature of defect-induced magnetism in magnetic carbons and establish the magnitude of the hyperfine magnetic field created in the neighbourhood of the defects that lead to magnetic order in these materials.

Comparison of practical techniques to develop latent fingermarks on fired and unfired cartridge cases.

We have tested some widely used and practical fingermark enhancement techniques such as powdering (regular powder dusting and magnetic powder application), cyanoacrylate fuming, fluorescent dying (basic yellow 40), gun blueing solutions and acidified hydrogen peroxide solutions. The results were evaluated and compared in order to establish best procedures on processing cartridge cases. The tests were performed on brass discs subjected to three different temperatures (room temperature, 63 and 200°C), and on fired and unfired cartridge cases. All the samples were processed after three different periods of time (24h, 7 days and 14 days) after deposition. The best results for both fired and unfired cartridge cases were obtained by the sequential application of cyanoacrylate, gun blueing solution and basic yellow 40. Some stages of the firing process were isolated in order to identify their effects over the final amount and quality of the remaining latent fingermarks on cartridge cases. Good state fingermarks were developed on unfired cartridge cases cycled through the gun, showing that friction inside the gun without firing does not cause significant damage to the fingermarks. On the other hand, fired cartridge cases are significantly affected by the firing effects, exhibiting low quality ridge details which are mainly located next to base. An unexpected phenomenon was observed on most of the brass discs heated to 200°C and developed with gun blueing solutions; they presented a reverse development compared to the expected one, with darkening of the ridges instead of the background.

Quantum information processing by nuclear magnetic resonance on quadrupolar nuclei.

Nuclear magnetic resonance is viewed as an important technique for the implementation of many quantum information algorithms and protocols. Although the most straightforward approach is to use the two-level system composed of spin 1/2 nuclei as qubits, quadrupolar nuclei, which possess a spin greater than 1/2, are being used as an alternative. In this study, we show some unique features of quadrupolar systems for quantum information processing, with an emphasis on the ability to execute efficient quantum state tomography (QST) using only global rotations of the spin system, whose performance is shown in detail. By preparing suitable states and implementing logical operations by numerically optimized pulses together with the QST method, we follow the stepwise execution of Grover's algorithm. We also review some work in the literature concerning the relaxation of pseudo-pure states in spin 3/2 systems as well as its modelling in both the Redfield and Kraus formalisms. These data are used to discuss differences in the behaviour of the quantum correlations observed for two-qubit systems implemented by spin 1/2 and quadrupolar spin 3/2 systems, also presented in the literature. The possibilities and advantages of using nuclear quadrupole resonance experiments for quantum information processing are also discussed.

Studies on crude oil-water biphasic mixtures by low-field NMR.

Low-field (1) H 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 instrument's 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 Mn(2+) -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.

Numerical simulation of NQR/NMR: Applications in quantum computing.

A numerical simulation program able to simulate nuclear quadrupole resonance (NQR) as well as nuclear magnetic resonance (NMR) experiments is presented, written using the Mathematica package, aiming especially applications in quantum computing. The program makes use of the interaction picture to compute the effect of the relevant nuclear spin interactions, without any assumption about the relative size of each interaction. This makes the program flexible and versatile, being useful in a wide range of experimental situations, going from NQR (at zero or under small applied magnetic field) to high-field NMR experiments. Some conditions specifically required for quantum computing applications are implemented in the program, such as the possibility of use of elliptically polarized radiofrequency and the inclusion of first- and second-order terms in the average Hamiltonian expansion. A number of examples dealing with simple NQR and quadrupole-perturbed NMR experiments are presented, along with the proposal of experiments to create quantum pseudopure states and logic gates using NQR. The program and the various application examples are freely available through the link http://www.profanderson.net/files/nmr_nqr.php.

Natural abundance (25)Mg solid-state NMR of mg oxyanion systems: a combined experimental and computational study.

Solid-state (25)Mg magic angle spinning nuclear magnetic resonance (MAS NMR) data are reported from a range of organic and inorganic magnesium-oxyanion compounds at natural abundance. To constrain the determination of the NMR interaction parameters (delta(iso), chi(Q), eta(Q)) data have been collected at three external magnetic fields (11.7, 14.1 and 18.8 T). Corresponding NMR parameters have also been calculated by using density functional theory (DFT) methods using the GIPAW approach, with good correlations being established between experimental and calculated values of both chi(Q) and delta(iso). These correlations demonstrate that the (25)Mg NMR parameters are very sensitive to the structure, with small changes in the local Mg(2+) environment and the overall hydration state profoundly affecting the observed spectra. The observations suggest that (25)Mg NMR spectroscopy is a potentially potent probe for addressing some key problems in inorganic materials and of metal centres in biologically relevant molecules.

Solid-state natural abundance 25Mg NMR studies of Na2MgEDTA x 4 H2O--a possible new reference compound for 25Mg NMR spectroscopy.

Natural abundance solid-state (25)Mg NMR measurements were made of the disodium salt of magnesium ethylenediaminetetraacetate tetrahydrate (Na(2)MgEDTA x 4 H(2)O). Both magic angle spinning (MAS) and static experiments were employed to determine the quadrupole coupling constant (C(q)) and the asymmetry parameter (eta(q)) of the electric field gradient (EFG) tensor associated with (25)Mg in this compound, giving the values C(q) = 1.675(5) MHz and eta(q) = 0.15(1). The isotropic chemical shift was determined to be delta(iso) = 0.25(10) ppm (relative to 11 M MgCl(2) aqueous solution) and a small chemical shift anisotropy (CSA) contribution (approximately -13 ppm) was detected, one of the first CSA reports in (25)Mg NMR. This compound exhibited remarkably good (25)Mg NMR sensitivity, due to its fast spin-lattice relaxation and modest quadrupole coupling, which allowed its use as a secondary shift reference and as a test sample for the implementation and optimisation of signal-enhancement methods in (25)Mg NMR spectroscopy, such as double frequency sweeps (DFS) and the use of adiabatic hyperbolic secant (HS) and WURST pulses.

A multiple-field (23)Na NMR study of sodium species in porous carbons.

The sodium environments in porous carbon materials prepared from NaOH activation of a char were investigated by means of multiple-field solid-state (23)Na NMR measurements, carried out at magnetic fields of 4.7, 8.45 and 14.1T, with single-pulse excitation and magic angle spinning (MAS). The recorded spectra showed a relatively featureless resonance with linewidth and peak shift strongly dependent on the magnetic field strength and on the hydration level of the samples. The existence of second-order quadrupolar effects was inferred, although the structural disorder and the mobile character associated with the Na environment precluded the direct observation of typical quadrupolar features in the MAS NMR spectra. The analysis of the spectra collected at multiple magnetic fields yielded the values of -2.8ppm for the isotropic chemical shift and 1.8MHz for the quadrupole coupling constant, which were interpreted as due to Na(+) ions bonded to oxygenated groups at the edges of the graphene planes within the carbon pore network.