Anaerobic Digestion of Cassava Wastewater Pre-treated by Fungi

Cassava wastewater (cww) contains high concentrations of easily acidifying compounds, requiring a buffered system to allow a stable operation during anaerobic digestion (AD). The possibility to include a preliminary one-step fungi treatment aimed at raising the pH and buffering the cww prior to AD was studied. Preliminary tests were performed with a naturally grown fungal mixed culture, under aerated (AE), non-aerated (NAE) and initially oxygen-deprived (IOD) conditions. The cww was pre-treated by the NAE condition, until reaching a soluble chemical oxygen demand (COD) of 10 g?L^?1 and pH 6.4 (batch A) and pH 5.7 (batch B). The fungal mixed culture showed ability to biodegrade the cww with initial pH of 4.4 and 14,500 mg?COD?L^-1, raising the pH over 8.5, with only 13 % of COD remaining within 27 days for both AE and NAE condition. The fungal pre-treated-cww (FPTcww) was subjected to anaerobic digestion under different buffered (CaCO₃ and NaHCO₃) and non-buffered conditions. The FPTcww with initial pH at 6.4 provided stability during the anaerobic biodegradability tests, showing the possibility of system operation without buffer addition, with final pH around 7. The application of a fungal pre-treatment can be a promising strategy to permit the anaerobic digestion of carbohydrate-rich wastewaters.     

Binding of a neutral guest to cucurbiturils: photophysics,thermodynamics and molecular modelling

Steady-state and time-resolved fluorescence techniques were used to study the thermodynamics of binding of a neutral polarity-sensitive guest, the methyl 2-naphthalenecarboxylate (2MN), with three cucurbiturils (CBn; n = 6, 7 and 8) in water. Association constants (K) were obtained from nonlinear regression analysis of the fluorescence intensity against [CB] in the 5–45°C range. 2MN complexed with CB7 exhibited a 1:1 stoichiometry (K ≈ 10³ M^? 1 at 25°C); however, it hardly did with CB6 (K < 10 M^? 1) and it did not with the larger CB8 macrocyclic ring. The (1:1) 2MN:CB7 complexation process was accompanied by a small unfavourable enthalpy change and was, therefore, entropically governed. Molecular mechanics and molecular dynamics calculations in the presence of water were also used to study the geometry of the complexes formed and the driving forces responsible for their formation. The results were compared with those previously obtained for the complexation of the same guest, 2MN, with natural α-, β- and γ-cyclodextrins.     

Three 2‐(methysulfanyl)nicotinamides

The molecular conformations of three N‐alkyl‐2‐(methylsulfanyl)nicotinamide derivatives, namely N‐cyclohexyl‐2‐(methylsulfanyl)nicotinamide, C₁₃H₁₈N₂OS, (I), N‐isopropyl‐2‐(methylsulfanyl)nicotinamide, C₁₀H₁₄N₂OS, (II), in which there are two molecules in the asymmetric unit which were chosen to form a hydrogen‐bonded pair, and N‐(2‐hydroxyethyl)‐2‐(methylsulfanyl)nicotinamide dihydrate, C₉H₁₂N₂O₂S·2H₂O, (III), are compared with those of four unsubstituted N‐alkylnicotinamide compounds. The substituted compounds show a higher degree of torsion of the pyridine ring with respect to the amide group than do the unsubstituted compounds, with dihedral angles in the range 40–60° for the former and 20–35° for the latter. In (I) and (II), the supramolecular structure is defined by amide‐N to carbonyl‐O chains. In (III), the nicotinamide molecules are linked by hydrogen bonds to two water molecules resulting in two linked chains of rings which form the three‐dimensional network.     

Comparison of the structure of (E)‐2‐(2‐benzylidenehydrazinylidene)quinoxaline with those of its chloro‐ and bromobenzylidene analogues

(E)‐2‐(2‐Benzylidenehydrazinylidene)quinoxaline, C₁₅H₁₂N₄, crystallized with two molecules in the asymmetric unit. The structures of six halogen derivatives of this compound were also investigated: (E)‐2‐[2‐(2‐chlorobenzylidene)hydrazinylidene]quinoxaline, C₁₅H₁₁ClN₄; (E)‐2‐[2‐(3‐chlorobenzylidene)hydrazinylidene]quinoxaline, C₁₅H₁₁ClN₄; (E)‐2‐[2‐(4‐chlorobenzylidene)hydrazinylidene]quinoxaline, C₁₅H₁₁ClN₄; (E)‐2‐[2‐(2‐bromobenzylidene)hydrazinylidene]quinoxaline, C₁₅H₁₁BrN₄; (E)‐2‐[2‐(3‐bromobenzylidene)hydrazinylidene]quinoxaline, C₁₅H₁₁BrN₄; (E)‐2‐[2‐(4‐bromobenzylidene)hydrazinylidene]quinoxaline, C₁₅H₁₁BrN₄. The 3‐Cl and 3‐Br compounds are isomorphous, as are the 4‐Cl and 4‐Br compounds. In all of these compounds, it was found that the supramolecular structures are governed by similar predominant patterns, viz. strong intermolecular N—H...N(pyrazine) hydrogen bonds supplemented by weak C—H...N(pyrazine) hydrogen‐bond interactions in the 2‐ and 3‐halo compounds and by C—H...Cl/Br interactions in the 4‐halo compounds. In all compounds, there are π–π stacking interactions.     

Synthesis of Ni(OH)<Subscript>2</Subscript> in micellar environment: structural,spectroscopic, and electrochemical studies

This work describes the chemical synthesis of nickel hydroxide in the presence of cationic and anionic surfactants (dodecyl benzene sulfonate, DBS^?, and cetyltrimethylammonium, CTA⁺). The materials were characterized by X-ray diffraction, infrared spectroscopy, and thermogravimetric analysis. Our findings highlighted that the synthesis in the presence of anionic DBS^?, the α-Ni(OH)₂ structure was preferentially formed. This material showed a high structural disorder and a high amount of intercalated species, suggesting the presence of both micelles and individual surfactants. On the other hand, the synthesis performed in the presence of CTA⁺ has not showed any drastic change in the material structure compared with pure Ni(OH)₂; nevertheless, the intercalated cationic surfactant was identified by FTIR measurements. The enhanced electrochemical response found for the Ni(OH)₂/DBS^? over the Ni(OH)₂/CTA⁺ modified electrodes can be attributed to the enhancement of the ionic diffusion through the solid material as an effect of the high structural disorder and the presence of the excess of the negative electric charge in the Ni(OH)₂ sheets.     

Theoretical interpretation of X-rays photo-absorption in medium-Z elements plasmas measured at LULI2000 facility

We analyzed the spectra of X-ray transmission through radiatively heated medium-Z plasma (Fe, Ni, Cu and Ge) measured at LULI2000 facility in the wavelength range of 2p–nd transitions. The analysis was performed using the statistical superconfiguration code SCO, two line-by-line opacity codes based on the HULLAC and FAC packages and a new hybrid statistical-detailed code SCORCG. The temperature and mass density of the samples were estimated from hydrodynamic simulations based on the cavity radiative temperature measurements. The theory–experiment agreement is relatively good in the wavelength range corresponding to the 2p–3d transitions except in the germanium case. In the wavelength range of the 2p–2d, n > 3 transitions a relatively good theory–experiment agreement was found in the copper case. As predicted by calculations the separation of the characteristic spin-orbit-split 2p–3d structures, absent in the iron measured spectrum, appears in the nickel spectrum and is visible in the copper and germanium spectra. Comparisons of the experimental transmission with calculations confirm the importance of the relativistic configuration interaction. The absorption strength of the measured germanium 2p–3d transition is much larger than that obtained from the codes. Spatial temperature and density gradients, relatively high in the germanium sample, may be at the origin of this discrepancy.     

Development and validation of two methods based on high-performance liquid chromatography-tandem mass spectrometry for determining 1,2-benzopyrone, dihydrocoumarin, o-coumaric acid, syringaldehyde and kaurenoic acid in guaco extracts and pharmaceutical preparations

In this study, two HPLC-ESI-MS/MS methods were developed and validated for the determination of 1,2-benzopyrone (COU), o-coumaric acid (OCA), kaurenoic acid (KAU), syringaldehyde (SYR), and dihydrocoumarin (DIH) in guaco extracts and pharmaceutical preparations (syrup and oral solution). The chromatographic separation was achieved using a C18 XBridge 150×2.1-mm (5-μm particle size) column maintained at 25°C. The mobile phases consisted of a gradient of water and acetonitrile containing 0.05% formic acid or 5 mM ammonium formate for the positive and negative ion modes, respectively. All of the calibration curves showed excellent coefficients of correlation (r≥0.9970) over the ranges of 1.25-400 ng/mL for coumarin, 10-600 ng/mL for dihydrocoumarin, 5-250 ng/mL for KAU, and 25-500 ng/mL for o-coumaric acid and syringaldehyde. The range of recovery was 96.3-103% with an RSD% of <4.85% for intraday and interday precision. The results indicate that the developed methods are fast, efficient, and sensitive for the quantification of the guaco metabolites in extracts and pharmaceutical forms while avoiding purification and derivatization steps.     

Discovery of New Hits as Antitrypanosomal Agents by In Silico and In Vitro Assays Using Neolignan-Inspired Natural Products from Nectandra leucantha

In the present study, the phytochemical study of the n-hexane extract from flowers of Nectandra leucantha (Lauraceae) afforded six known neolignans (1–6) as well as one new metabolite (7), which were characterized by analysis of NMR, IR, UV, and ESI-HRMS data. The new compound 7 exhibited potent activity against the clinically relevant intracellular forms of T. cruzi (amastigotes), with an IC₅₀ value of 4.3 μM and no observed mammalian cytotoxicity in fibroblasts (CC₅₀ > 200 μM). Based on the results obtained and our previous antitrypanosomal data of 50 natural and semi-synthetic related neolignans, 2D and 3D molecular modeling techniques were employed to help the design of new neolignan-based compounds with higher activity. The results obtained from the models were important to understand the main structural features related to the biological response of the neolignans and to aid in the design of new neolignan-based compounds with better biological activity. Therefore, the results acquired from phytochemical, biological, and in silico studies showed that the integration of experimental and computational techniques consists of a powerful tool for the discovery of new prototypes for development of new drugs to treat CD.     

Interaction Study between ESIPT Fluorescent Lipophile-Based Benzazoles and BSA

In this study, the interactions of ESIPT fluorescent lipophile-based benzazoles with bovine serum albumin (BSA) were studied and their binding affinity was evaluated. In phosphate-buffered saline (PBS) solution these compounds produce absorption maxima in the UV region and a main fluorescence emission with a large Stokes shift in the blue–green regions due to a proton transfer process in the excited state. The interactions of the benzazoles with BSA were studied using UV-Vis absorption and steady-state fluorescence spectroscopy. The observed spectral quenching of BSA indicates that these compounds could bind to BSA through a strong binding affinity afforded by a static quenching mechanism (K_q~10¹² L·mol⁻¹·s⁻¹). The docking simulations indicate that compounds 13 and 16 bind closely to Trp134 in domain I, adopting similar binding poses and interactions. On the other hand, compounds 12, 14, 15, and 17 were bound between domains I and III and did not directly interact with Trp134.