Synthesis and antimicrobial activity of some benzoxazinoids derivatives of 2-nitrophenol and 3-hydroxy-2-nitropyridine

Benzoxazinoids (BXs), alkaloids frequently found in Gramineae species, are natural defensives that can potentially be exploited to the development of novel antimicrobial agents. Here, BXs analogs were synthesized from 2-nitrophenol (benzoxazinone series) and 3-hydroxy-2-nitropyridine (pyridoxazinone series) and tested against fungal and bacteria of medical interest. The starting materials were submitted to adequate nucleophilic substitution in order to functionalize of analogs, followed by a reductive cyclization catalyzed by palladium on carbon. Next, the biological assays showed that pyridoxazinone serie has a good antibacterial activity, especially against Enterococcus faecalis (Minimum inhibitory concentration—MIC: 7.8-15.6?μg.mL^?1) and Acinetobacter baumannii (MIC 31.25-125?μg.mL^?1). Antifungal activity, in turn, was related to compound 2e which showed a MIC of 62.5?μg.mL^?1 against Candida albicans, Candida glabrata, and Candida tropicalis. All analogs complied with Lipinski's rules and were predicted to have a low toxicity.     

Determination of lead in water samples after its separation and preconcentration by 4,5-dihydroxy-1,3-benzenedisulfonic acid functionalised polyurethane foam

A new sorbent based on polyurethane foam functionalised with 4,5-dihydroxy-1,3-benzenedisulfonic acid (Tiron-PUF) was synthesised. This material was used in the development of a procedure for preconcentration of lead, with subsequent detection by flame atomic absorption spectrometry (FAAS). The influence of some variables involved in the extraction process was studied. Analytical parameters were evaluated using 50 and 500?mL of Pb (II) solution. Under optimum conditions, the system showed enrichment factors of 38 (50?mL) and 114 (500?mL). The detection limits obtained were 0.5 and 1.1?µg?L^?1 when volumes of 500 and 50?mL of Pb (II), respectively, were used. The method was applied to the determination of lead content in well water and drinking water samples collected in the town of Amelia Rodrigues, Bahia, Brazil.     

Five N′‐benzylidene‐N‐methylpyrazine‐2‐carbohydrazides

The compounds N′‐benzylidene‐N‐methylpyrazine‐2‐carbohydrazide, C₁₃H₁₂N₄O, (IIa), N′‐(2‐methoxybenzylidene)‐N‐methylpyrazine‐2‐carbohydrazide, C₁₄H₁₄N₄O₂, (IIb), N′‐(4‐cyanobenzylidene)‐N‐methylpyrazine‐2‐carbohydrazide dihydrate, C₁₄H₁₁N₅O·2H₂O, (IIc), N‐methyl‐N′‐(2‐nitrobenzylidene)pyrazine‐2‐carbohydrazide, C₁₃H₁₁N₅O₃, (IId), and N‐methyl‐N′‐(4‐nitrobenzylidene)pyrazine‐2‐carbohydrazide, C₁₃H₁₁N₅O₃, (IIe), have dihedral angles between the pyrazine rings and the benzene rings in the range 55–78°. These methylated pyrazine‐2‐carbohydrazides have supramolecular structures which are formed by weak C—H...O/N hydrogen bonds, with the exception of (IIc) which is hydrated. There are π–π stacking interactions in all five compounds. Three of these structures are compared with their nonmethylated counterparts, which have dihedral angles between the pyrazine rings and the benzene rings in the range 0–6°.     

Potentiometric,NMR, and Fluorescence‐Emission Studies on the Binding of Adenosine 5′‐Triphosphate (ATP) by Open‐Chain Polyamine Receptors Containing Naphthylmethyl and/or Anthrylmethyl Groups

The interaction in aqueous solution of adenosine 5′‐triphosphate (ATP) with a series of open‐chain polyamines linked at one or both ends to anthrylmethyl or naphthylmethyl fragments was followed by potentiometric titration, ¹H‐, ¹³C‐, and ³¹P‐NMR spectroscopy, and by steady‐state fluorescence measurements. The results revealed greater stabilities for the compounds containing one anthracene moiety than for those with one naphthalene moiety, the stabilities of the compounds with both ends N‐substituted with naphthylmethyl groups being close to those containing just one anthrylmethyl unit. The ¹H‐NMR spectra showed that in all systems, there is involvement of π‐π stacking interactions in the stabilization of the adduct species. The competitive effect of the anions afforded by the supporting electrolyte was checked in some of the studied systems working at two different ionic strenghts (0.15M and 1.0M NaCl). The joint analysis of the spectrofluorimetric titrations and pH‐metric species‐distribution curves showed that for all the ATP? receptor systems, a quenching of the fluorescence occurred upon protonation of the adenine N(1)atom. Steady‐state fluorescence and time‐correlated single‐photon‐counting analysis of a system made up of ATP and a bis‐chromophoric polyamine receptor containing anthracene and naphthalene fluorophores established that the energy‐transfer process between the naphthalene and anthracene moieties is still operative despite the presence of ATP.     

Thermal characterization of mangaba-based films

The purpose of this study was to evaluate the physical–chemical properties of starch (SF), mangaba (MF), and mangaba/starch-based films (MSF), using differential thermal analysis, thermogravimetry/derivative thermogravimetry, infrared spectroscopy, mechanical profile, and scanning electron microscopy. The films were prepared by casting process using sucrose and propyleneglycol as plasticizers. The thermal profiles of MF and MSF were similar and showed increased thermal stability. The mechanical properties of MF and MSF presented decreases of tensile strength and elastic modulus when compared with SF. The MSF showed the best thermal and mechanical characteristics.     

Malonylchitosan Microspheres as a Matrix for Oral Enrofloxacin Delivery

Summary: The purpose of this study was to produce malonylchitosan microspheres to be used as a pH sensitive matrix for the controlled delivery of drugs. Chitosan microspheres were obtained by the coacervation–phase separation method. The microspheres were then treated with malonic acid to obtain amidified chitosan microspheres. The resulting malonylchitosan microspheres were characterized by means of elemental analysis (CHN), infrared spectroscopy, conductometric titration and scanning electron microscopy (SEM). The data obtained from infrared spectroscopy, elemental analysis and conductometric titration of amino groups were consistent with the N-substitution of malonyl groups in the chitosan microspheres. In vivo studies for controlled delivery of enrofloxacin were performed in male Wistar rats and the results indicated increase and prolonged blood levels with delayed peak and improved bioavailability for malonylchitosan microspheres compared to commercial tablets.     

Microwave-assisted synthesis and antimicrobial activity of novel spiro 1,3,4-thiadiazolines from isatin derivatives

This work describes the synthesis of spiro 1,3,4-thiadiazolines from isatin-β-thiosemicarbazone acetylation, using microwave irradiation as a source of heating the reaction medium. N-substituted isatin derivatives were used as substrates to obtain thiosemicarbazones by adding thiosemicarbazide to the isatin ketone carbonyl. The final synthetic step was the reaction of thiosemicarbazones with acetic anhydride under microwave irradiation to get the spiro compounds. Reaction times ranged from 6 to 18 minutes resulting in yields of up to 90%. Biological assays have shown promising antibacterial and antifungal activity, especially spiro thiadiazolines derived from allylated isatins. All the proposed molecules proved to be potential drug candidates based on the results of the in silico investigation, with satisfactory drug-likeness and drug-score, respecting Lipinski's rule. The use of the microwave reactor was efficient for the synthesis of thiosemicarbazones and spiro compounds, resulting in a significant reduction in reaction times with conventional heating. Taking into account the threat of antimicrobial resistance, this work presents a series of bioactive molecules that are easily obtained via microwave reaction.     

Characterization of nanostructured epoxy networks modified with isocyanate-terminated liquid polybutadiene

Polybutadiene-block-epoxy prepolymer (DGEBA-b-PBNCO) copolymers with multi-branched topological structure were prepared by reacting isocyanate-multifunctionalized liquid polybutadiene (PBNCO) with DGEBA prepolymer and used to develop nanostructured rubber-modified epoxy thermosets cured with triethylene-tetramine (TETA) as the aliphatic amine. The nanoscopic structure was obtained with the addition of as high as 20 phr of rubber component and successfully demonstrated by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). The glass transition temperature of the rubber-modified epoxy networks was slightly higher than the neat epoxy system. In addition, a unique combination of outstanding toughness and increased modulus and T(g) was achieved in these modified systems, which was attributed to the peculiar morphology associated with a strong interfacial adhesion imparted by the reaction between the isocyanate and hydroxyl groups present in the PBNCO and epoxy resin, respectively. The effect of the PBNCO on the gelation time of the epoxy/TETA system was investigated by rheological techniques. The NCO-functionalized polybutadiene decreased the gelation time, indicating an accelerating effect on the curing process, probably because of the urethane groups formed by the reaction between PBNCO and the epoxy resin during the PB-b-ER block copolymer preparation.     

Studying the interaction between triazines and humic substances--a new approach using open tubular capillary electrochromatography

The strength of the interaction between a pesticide and the soil organic matter is a key parameter to assess the risk of it reaching to groundwater with potentially harmful effects to human health. In this work, a new approach that allows measuring such interactions in a few minutes using a purified fraction of the soil organic matter (humic substances) is detailed. The strength of sorption is assessed via the normalised difference of elution (retention factor, k′) between the chemical of interest and a neutral marker transported via electroosmotic flow through an open tubular column supporting the immobilised humic substances (open tubular capillary electrochromatography). The immobilisation was achieved by incubating a capillary, pre-coated with a monolayer of humic acid, with an acidic solution of humic substances. This induces the formation of a supramolecular structure of humic substances as it occurs in soils. This aggregate can easily be removed using alkaline solutions, and a new structure assembled using other humic substances (HS) or different incubations conditions. The whole procedure takes 2 h. This approach has been tested using five triazines and three types of humic substances. The order of the strength of sorption of the triazines as expected from relevant literature and the relative standard deviation of k′ was between 1 and 6%. Good repeatability was also observed after long period of wash, between re-coating and repeating of the full coating with a new capillary.     

Optimization of in situ derivatization SPME by experimental design for GC-MS multi-residue analysis of pharmaceutical drugs in wastewater

This paper presents the development of a procedure, which enables the analysis of nine pharmaceutical drugs in wastewater using gas chromatography‐mass spectrometry (GC‐MS) associated with solid‐phase microextraction (SPME) for the sample preparation. Experimental design was applied to optimize the in situ derivatization and the SPME extraction conditions. Ethyl chloroformate (ECF) was employed as derivatizing agent and polydimethylsiloxane‐divinylbenzene (PDMS‐DVB) as the SPME fiber coating. A fractional factorial design was used to evaluate the main factors for the in situ derivatization and SPME extraction. Thereafter, a Doehlert matrix design was applied to find out the best experimental conditions. The method presented a linear range from 0.5 to 10 μg/L, and the intraday and interday precision were lower than 16%. Applicability of the method was verified from real influent and effluent samples of a wastewater treatment plant, as well as from samples of an industry wastewater and a river.