Precision measurement of lattice parameters in LiF monocrystals

The methodic possibilities of measurements by the Bond-method for a highly precise determination of the lattice parameters in block structures with small block desorientation angles in the region of angular seconds or angular minutes (LiF crystals) have been examined. The lattice distorsion in two planes perpendicular to the (001) surface of crystalis described. The same planes have also been examined by elastooptic methods. In both planes we got for the lattice parameters: a₁ & a₂ > a₃ (a₁ and a₂ parallel to the surface of crystal, a₃ perpendicular to the surface of crystal); i.e. we could observe a dilatation of the unit cell parallel to the surface of the crystal. Special results concerning the distribution of local lattice parameters along the surface of sample are discussed in connection with the results of elastooptic observations.     

Organic Electronics from Nature: Computational Investigation of the Electronic and Optical Properties of the Isomers of Bixin and Norbixin Present in the Achiote Seeds

Organic compounds have been employed in developing new green energy solutions with good cost-efficiency compromise, such as photovoltaics. The light-harvesting process in these applications is a crucial feature that still needs improvements. Here, we studied natural dyes to propose an alternative for enhancing the light-harvesting capability of photovoltaics. We performed density functional theory calculations to investigate the electronic and optical properties of the four natural dyes found in achiote seeds (Bixa orellana L.). Different DFT functionals, and basis sets, were used to calculate the electronic and optical properties of the bixin, norbixin, and their trans-isomers (molecules present in Bixa orellana L.). We observed that the planarity of the molecules and their similar extension for the conjugation pathways provide substantially delocalized wavefunctions of the frontier orbitals and similar values for their energies. Our findings also revealed a strong absorption peak in the blue region and an absorption band over the visible spectrum. These results indicate that Bixa orellana L. molecules can be good candidates for improving light-harvesting in photovoltaics.     

Monitoring Stimulated Darkening from UV-C Light on Different Bean Genotypes by NMR Spectroscopy

The use of UV-C cool white light on bean (Phaseolus vulgaris L.) seeds significantly increases the biochemical seed coat post-harvest darkening process, whilst preserving seed germination. The aim of this work consists in monitoring the effect caused by the incidence of UV-C light on different bean genotypes using NMR spectroscopy. The genotype samples named IAC Alvorada; TAA Dama; BRS Estilo and BRS Pérola from the Agronomic Institute (IAC; Campinas; SP; Brazil) were evaluated. The following two methodologies were used: a prolonged darkening, in which the grain is placed in a room at a controlled temperature (298 K) and humidity for 90 days, simulating the supermarket shelf; an accelerated darkening, where the grains are exposed to UV-C light (254 nm) for 96 h. The experiments were performed using the following innovative time-domain (TD) NMR approaches: the RK-ROSE pulse sequence; one- and two-dimensional high resolution (HR) NMR experiments (¹H; ¹H-¹H COSY and ¹H-¹³C HSQC); chemometrics tools, such as PLS-DA and heat plots. The results suggest that the observed darkening occurs on the tegument after prolonged (90 days) and accelerated (96 h) conditions. In addition, the results indicate that phenylalanine is the relevant metabolite within this context, being able to participate in the chemical reactions accounted for by the darkening processes. Additionally, it is possible to confirm that a UV-C lamp accelerates oxidative enzymatic reactions and that the NMR methods used were a trustworthy approach to monitor and understand the darkening in bean seeds at metabolite level.     

Photochemical Properties of trans‐[Ru(NH3)4(bpa)(L)]2+ (L = py,isn, 4‐acpy or 4‐pic)

Photochemical reactions of ruthenium (II) complexes of type trans‐[Ru(NH₃)₄LL']²⁺, where L is a nitrogenous heterocyclic ligand, pyridine (py), isonicotinamide (isn), 4‐acetylpyridine (4‐acpy) or 4‐picoline (4‐pic), and L´ is a 1,2‐bis(4‐pyridyl)ethane (bpa) ligand, were studied with the purpose of evaluating the ligand exchange when, in solution, the complexes are irradiated at the wavelengths of 365, 436, 480 and 519 nm. The study revealed that at lower wavelengths, a labilization process is observed for py and 4‐pic ligands, even at low quantum yields, indicating the dependence of the photolabeling process on the wavelength. The study also reveals that for the filters of greater wavelength, the processes of photolabilization do not occur for any of the studied complexes. The study also shows that there are no photolization processes for the complexes obtained with the isn and 4‐acpy ligands, and it is therefore possible to classify them as nonreactive.     

Determination of cannabinoids in plasma using salting-out-assisted liquid–liquid extraction followed by LC–MS/MS analysis

The detection of the markers of Cannabis consumption in biological specimens is an important task for drug testing laboratories in varous contexts. A simple assay combining salting-out assisted liquid–liquid extraction sample preparation and LC–MS/MS analysis was applied to the measurement of Δ⁹-tetrahydrocannabinol, 11-nor-9-carboxy-Δ⁹-tetrahydrocannabinol (THC-COOH), 11-hydroxy-Δ⁹-tetrahydrocannabinol, cannabinol and cannabidiol concentrations in 100 μl plasma specimens. The assay had linearity of 1–100 ng ml⁻¹ for THC-COOH and 0.5–50 ng ml⁻¹ for the other tested cannabinoids. Assay validation criteria were fulfilled. Extraction yields (88.7–97.3%) and internal-standard correct matrix effects (−9.6 to +5.4%) were acceptable. The assay was applied to 238 clinical specimens from trauma patients, with 19 samples presenting quantifiable concentrations of at least one of the target compounds. The developed assay is a simple and efficient strategy for simultaneous measurement of Δ⁹-tetrahydrocannabinol, THC-COOH, 11-hydroxy-Δ⁹-tetrahydrocannabinol, cannabinol and cannabidiol concentrations in plasma specimens.     

Aggregation-Induced Emission and Temperature-Dependent Luminescence of Potassium Perylenetetracarboxylate

Investigation of temperature-dependent photoluminescent properties of potassium perylene-3,4,9,10-tetracarboxylate (K₄PTC), a molecule with no internal rotational degrees of freedom, shows aggregation-induced enhanced emission at room temperature. The different excitonic emission processes are dependent of temperature, some of which quenches in an intermediate temperature range (from 50 to 150 K). The exciton excited states switching phenomenon from "dark" to "bright" states is observed and its explained using Herzberg-Teller selection rule. K₄PTC is a molecule comparable to the size of its precursor, perylene-3,4,9,10-tetracarboxylic anhydride (PTCDA) and is highly soluble in water, contrary to PTCDA, which is poorly soluble in most solvents. Powder x-ray diffraction measurements corroborate a lesser degree of ordering of bulk K₄PTC compared to bulk PTCDA. The green luminescent molecule could, in principle, be used as a biomarker, or in photodynamic therapy, if further studies show relatively low toxicity.

     

Copper pyrovanadate electrodes prepared by combustion synthesis: evaluation of photoelectroactivity

Journal of Solid State Electrochemistry - Photoelectrodegradation of dyes using semiconductors under visible light is currently a major research topic. In this work, copper pyrovanadate (Cu2V2O7)...     

A matheuristic for the cell formation problem

In this paper we propose a GRASP matheuristic coupled with an Integer Programming refinement based on Set Partitioning to solve the Cell Formation Problem. We use the grouping efficacy measure to evaluate the solutions. As this measure is nonlinear, we propose a fractional Set Partitioning approach and its linearization. Our method is validated on a set of 35 instances from the literature. The experiments found four unknown solutions. For all instances with known optima, our method is able to determine the optimum solutions.     

Optimization Over the Boolean Hypercube Via Sums of Nonnegative Circuit Polynomials

Various key problems from theoretical computer science can be expressed as polynomial optimization problems over the boolean hypercube. One particularly successful way to prove complexity bounds for these types of problems is based on sums of squares (SOS) as nonnegativity certificates. In this article, we initiate optimization problems over the boolean hypercube via a recent, alternative certificate called sums of nonnegative circuit polynomials (SONC). We show that key results for SOS-based certificates remain valid: First, for polynomials, which are nonnegative over the n-variate boolean hypercube with constraints of degree d there exists a SONC certificate of degree at most \(n+d\). Second, if there exists a degree d SONC certificate for nonnegativity of a polynomial over the boolean hypercube, then there also exists a short degree d SONC certificate that includes at most \(n^{O(d)}\) nonnegative circuit polynomials. Moreover, we prove that, in opposite to SOS, the SONC cone is not closed under taking affine transformation of variables and that for SONC there does not exist an equivalent to Putinar’s Positivstellensatz for SOS. We discuss these results from both the algebraic and the optimization perspective.

     

Combined application of DP4+ and ANN-PRA to determine the relative configuration of natural products: The alpha-bisabol case study

The combination of computational methods and experimental data from Nuclear Magnetic Resonance (NMR) is a considerably valuable tool in the elucidation of new natural product structures and, also, in the structural revision of previously reported compounds. Until recently, only classical statistical parameters were used, for example, linear correlation coefficient (R²), mean absolute error (MAE), or root mean square deviation (RMSD), as a way to statistically “validate” the structure pointed out by experimental NMR spectra. Regarding the resolution of the relative configuration of organic molecules, novel tools were available in the last few years to assist in the NMR elucidation process. The most relevant are DP4+, which is based on a Bayesian probability, and ANN-PRA, which is based on artificial neural networks. The combined application of these tools has become the most accurate and important alternative to solve structural and stereochemical problems in natural product chemistry. Therefore, herein, in this case study, we intended to promote these novel tools, exploring the strengths and limitations of each approach in resolving the relative configuration of the sesquiterpene alpha-bisabol. We also highlighted the advantages of the complementary use of H- and C-DP4+ to obtain optimal results in the differentiation of the stereoisomers, validating the proposal with ANN-PRA method.