Structural diversity and versatility for organoaluminum complexes supported by mono- and di-anionic aminophenolate bidentate ligands

The present contribution describes the synthesis and structural characterization of structurally diverse organoaluminum species supported by variously substituted aminophenolate-type ligands: these Al complexes are all derived from the reaction of AlMe₃ with aminophenols 2-CH₂NH(R)-C₆H₃OH (1a, R = mesityl (Mes); 1b, R = 2,6-di-isopropylphenyl (Diip)) and 2-CH₂NH(R)-4,6-^tBu₂-C₆H₂OH (1c, R = Mes; 1d, R = Diip). The low temperature reaction of AlMe₃ with 1a–b readily affords the corresponding Al dimeric species [μ-η¹,η¹-N,O-{2-CH₂NH(R)-C₆H₄O}]₂Al₂Me₄ (2a–b), consisting of twelve-membered ring aluminacycles with two μ-η¹,η¹-N,O-aminophenolate units, as determined by X-ray crystallographic studies. Heating a toluene solution of 2a (80 °C, 3 h) affords the quantitative and direct formation of the dinuclear aluminium complex Al[η²-N; μ,η²-O-{2-CH₂N(Mes)-C₆H₄O}](AlMe₂) (4a) while species 2b, under the aforementioned conditions, affords the formation of the Al dimeric species [η²-N,O-{2-CH₂N(Dipp)-C₆H₄O}AlMe]₂ (3b), as deduced from X-ray crystallography for both 3b and 4a. In contrast, the reaction of bulky aminophenol pro-ligands 1c–d with AlMe₃ afford the corresponding monomeric Al aminophenolate chelate complexes η²-N,O-{2-CH₂NH(R)-4,6-^tBu₂-C₆H₂O}AlMe₂ (5c–d; R = Mes, Diip; Scheme 3) as confirmed by X-ray crystallographic analysis in the case of 5d. Subsequent heating of species 5c–d yields, via a methane elimination route, the corresponding Al-THF amido species η²-N,O-{2-CH₂N(R)-4,6-^tBu₂-C₆H₂O}Al(Me)(THF) (6c–d; R = Mes, Diip). Compounds 6c–6d, which are of the type {X₂}Al(R)(L) (L labile), may well be useful as novel well-defined Lewis acid species of potential use for various chemical transformations. Overall, the sterics of the aminophenol backbone and, to a lesser extent, the reaction conditions that are used for a given ligand/AlMe₃ set essentially govern the rather diverse “structural” outcome in these reactions, with a preference toward the formation of mononuclear Al species (i.e. species 5c–d and 6c–d) as the steric demand of the chelating N,O-ligand increases.     

Unmanned platform for long-range remote analysis of volatile compounds in air samples

This paper describes a long-range remotely controlled CE system built on an all-terrain vehicle. A four-stroke engine and a set of 12-V batteries were used to provide power to a series of subsystems that include drivers, communication, computers, and a capillary electrophoresis module. This dedicated instrument allows air sampling using a polypropylene porous tube, coupled to a flow system that transports the sample to the inlet of a fused-silica capillary. A hybrid approach was used for the construction of the analytical subsystem combining a conventional fused-silica capillary (used for separation) and a laser machined microfluidic block, made of PMMA. A solid-state cooling approach was also integrated in the CE module to enable controlling the temperature and therefore increasing the useful range of the robot. Although ultimately intended for detection of chemical warfare agents, the proposed system was used to analyze a series of volatile organic acids. As such, the system allowed the separation and detection of formic, acetic, and propionic acids with signal-to-noise ratios of 414, 150, and 115, respectively, after sampling by only 30 s and performing an electrokinetic injection during 2.0 s at 1.0 kV.     

On the formation of carbonate adducts of fatty alcohols, sterols, and sugars in biological conditions

The formation and properties of carbonate adducts of some organic hydroxy compounds in aqueous medium were investigated. Fatty alcohols and sugars were chosen as representative classes of biological interest, and the medium was carbonated aqueous solution with pH ranging from 3.0 to 8.3. Capillary electrophoresis with two capacitively coupled contactless conductivity detectors (C⁴Ds) was used for quantitation and to obtain the mobility of the monoalkyl carbonates (MACs), which were used to determine the equilibrium and kinetic constants of the reaction as well as the diffusion coefficients. For increasing chain length of the alcohols, the equilibrium constant tends to the unit, which suggests that fatty alcohols can form the corresponding MACs. The formation of MACs for cyclohexanol and cyclopentanol also suggest the existence of similar species for sterols. Carbonate adducts of fructose, glucose, and sucrose were also detected, which suggests that these counterparts of the well‐known phosphates can also occur in the cytosol. Our calculations suggest that one in 1000 to one in 10 000 molecules of these hydroxy compounds would be available as the corresponding MAC in such a medium. Experiments carried out at pH values less than 3.0 showed that there is a catalytic effect of hydronium on the interconversion of bicarbonate and a MAC. Taking into account the great number of hydroxy compounds similar to the ones investigated and that bicarbonate is ubiquitous in living cells, one can anticipate the existence of a whole new class of carbonate adducts of these metabolites.     

Transformation of Residual Açai Fruit (Euterpe oleracea) Seeds into Porous Adsorbent for Efficient Removal of 2,4-Dichlorophenoxyacetic Acid Herbicide from Waters

Brazil’s production and consumption of açai pulp (Euterpe oleracea) occur on a large scale. Most of the fruit is formed by the pit, which generates countless tons of residual biomass. A new purpose for this biomass, making its consumption highly sustainable, was presented in this study, where activated carbon (AC) was produced with zinc chloride for later use as an adsorbent. AC carbon formed by carbon and with a yield of 28 % was satisfactorily used as an adsorbent in removing the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D). Removal efficiency was due to the highly porous surface (Vp = 0.467 cm³ g⁻¹; Dp = 1.126 nm) and good surface área (SBET = 920.56 m² g⁻¹). The equilibrium data fit the Sips heterogeneous and homogeneous surface model better. It was observed that the increase in temperature favored adsorption, reaching a maximum experimental capacity of 218 mg g⁻¹ at 328 K. The thermodynamic behavior indicated a spontaneous, favorable, and endothermic behavior. The magnitude of the enthalpy of adsorption was in agreement with the physical adsorption. Regardless of the herbicide concentration, the adsorbent displayed fast kinetics, reaching equilibrium within 120 min. The linear driving force (LDF) model provided a strong statistical match to the kinetic curves. AC with zinc chloride (ZnCl₂), created from leftover açai biomass, is a potential alternative as an adsorbent for treating effluents containing 2,4-D.     

Role of Alginate Composition on Copper Ion Uptake in the Presence of Histidine or Beta-Amyloid

The anomalous interaction between metal ions and the peptide beta-amyloid is one of the hallmarks of Alzheimer’s disease. Metal-binding biopolymers, including polysaccharides, can elucidate the fundamental aspects of metal ions’ interactions with biological tissue and their interplay in Alzheimer’s disease. This work focuses on the role of the alginate composition on Cu(II) adsorption in the presence of histidine or β-amyloid, the peptide associated with the progression of Alzheimer’s disease. Alginate samples with different mannuronic/guluronic (M/G) ratios led to similar Cu(II) adsorption capacities, following the Langmuir isotherm and the pseudo-second-order adsorption kinetic models. Although the presence of histidine produced up to a 20% reduction in the copper adsorption capacity in guluronic-rich alginate samples (M/G~0.61), they presented stable bidentate chelation of the metallic ion. Chemical analyses (FTIR and XPS) demonstrated the role of hydroxyl and carboxyl groups in copper ion chelation, whereas both crystallinity and morphology analyses indicated the prevalence of histidine interaction with guluronic-rich alginate. Similar results were observed for Cu(II) adsorption in alginate beads in the presence of beta-amyloid and histidine, suggesting that the alginate/histidine system is a simple yet representative model to probe the application of biopolymers to metal ion uptake in the presence of biological competitors.     

Variability in the Chemical Composition of Myrcia sylvatica (G. Mey) DC. Essential Oils Growing in the Brazilian Amazon

Myrcia sylvatica (G. Mey) DC. is known as “insulin plant” because local communities use the infusions of various organs empirically to treat diabetes. The leaves of seven specimens of Myrcia sylvatica (Msy-01 to Msy-07) were collected in the Brazilian Amazon. Furthermore, the essential oils were extracted by hydrodistillation and analyzed by gas chromatography coupled to mass spectrometry, and their chemical compositions were submitted to multivariate analysis (Principal Component Analysis and Hierarchical Cluster Analysis). The multivariate analysis displayed the formation of four chemical profiles (chemotypes), described for the first time as follows: chemotype I (specimen Msy-01) was characterized by germacrene B (24.5%), γ-elemene (12.5%), and β-caryophyllene (10.0%); chemotype II (specimens Msy-03, -06 and -07) by spathulenol (11.1–16.0%), germacrene B (7.8–20.7%), and γ-elemene (2.9–7.6%); chemotype III (Msy-04 and -05) by spathulenol (9.8–10.1%), β-caryophyllene (2.5–10.1%), and δ-cadinene (4.8-5.6%); and chemotype IV, (Msy-02) by spathulenol (13.4%), caryophyllene oxide (15.0%), and α-cadinol (8.9%). There is a chemical variability in the essential oils of Myrcia sylvatica occurring in the Amazon region.     

Development of paper devices with conductive inks for sulfanilamide electrochemical determination in milk,synthetic urine,and environmental and pharmaceutical samples

Journal of Solid State Electrochemistry - This work describes a simple, rapid, and cost-effective method for fabrication of paper-based carbon electrode (US$ <0.01) using conductive ink...     

Recent advances in electrochemical water technologies for the treatment of antibiotics: A short review

This short review presents a critical overview of the most recent works published in the literature related to the use of electrochemical advanced oxidation processes (EAOPs) for the treatment of antibiotics present in synthetic and real wastewaters. The first section focuses on novelties within the traditional EAOPs, including electrochemical oxidation and electrochemical Fenton-based processes. The second section is devoted to new electrochemical technologies, including heterogeneous electro-Fenton, electrochemically activated persulfate processes, and combined processes. Future perspectives about these processes are also presented to aid the continuous evolution of research in the area.