Characterisation of poly(neutral red) modified carbon film electrodes; application as a redox mediator for biosensors

The polymer redox mediator, poly(neutral red) (PNR), has been synthesised and characterised electrochemically to investigate the best electropolymerisation and mediation conditions for application in enzyme biosensors and to clarify the mechanism of action. Neutral red was electropolymerised by potential cycling on carbon film electrode substrates by allowing the monomer to be oxidised during the full 20 cycles of polymerisation or reducing the positive limit of the potential window after the first 2 cycles to impede monomer oxidation with a view to obtaining longer polymer chains and a lesser degree of branching. Comparison was made with glassy carbon substrates. The PNR films on carbon film electrodes were characterised using cyclic voltammetry and electrochemical impedance spectroscopy, as well as in glucose biosensors prepared with PNR. Glucose oxidase enzyme was immobilised by encapsulation in silica sol-gel and compared with that obtained by cross-linking with glutaraldehyde. The biosensors were evaluated by chronoamperometry in 0.1 M phosphate buffer saline solution, pH 7.0, and showed evidence of electron transfer between the enzyme cofactor flavin adenine dinucleotide and PNR dissolved in the enzyme layer competing with PNR-mediated electrochemical degradation of H₂O₂ formed during the enzymatic process. This paper is dedicated to Professor Dr. Algirdas Vaskelis on the occasion of his 70th birthday.     

Influence of temperature on performance of an anaerobic sequencing biofilm batch reactor with circulation applied to treatment of low-strength wastewater

The effect of temperature on the performance of an anaerobic sequencing biofilm batch reactor (ASBBR) with liquid-phase recirculation was assessed. Assays were performed using a recirculation velocity of 0.20 cm/s, 8-h cycles, and an average treated synthetic wastewater volume of 2 L/cycle with a concentration of 500 mg of Chemical Oxygen Demand (COD)/L. Operation temperatures were 15, 20, 25, 30, and 35°C. At 25, 30, and 35°C, organic matter removal efficiencies for filtered samples ranged from 81 to 83%. At lower temperatures, namely 15 and 20°C, removal efficiency decreased significantly to 61 and 65%, respectively. A first-order model could be fitted to the experimental concentration profile values. The first-order kinetic parameter value of this model varied from 0.46 to 0.81 h¹ considering the lowest and highest temperature studied. Moreover, analysis of the removal profile values allowed fitting of an Arrhenius-type equation with an activation energy of 5715 cal/mol.     

New isochromans. 1. Synthesis and antimicrobial activity of 4‐substituted (±)‐1h‐spiro[benzo[c]pyran‐3(4H), 1′‐cyclohexane]‐1‐ones

The reaction between homophthalic anhydride and cyclohexanone was examined both in the presence of DMAP or BF₃·Et₂O complex as a catalyst. The latter yielded (±)‐1‐oxo‐1H‐spiro[benzo[c]pyran‐3(4H), 1′‐cyclohexane]‐4‐carboxylic acid ( 3 ) in a higher yield (82 %). A series of new (±)‐4‐(N,N‐disubstituted‐1‐carbamoyl)‐1H‐spiro[benzo[c]pyran‐3(4H),1′‐cyclohexane]‐1‐ones ( 5a‐h ) were synthesized from the parent acid 3 by a two‐step reaction. Differentiating microbial screening was performed for most of the synthesized compounds against twelve microorganisms belonging to different taxonomic groups. The spiro acid 3 was active against all bacterial strains with MIC ≥ 20 μg/ml against B. subtillis and P. vulgaris. E. coli was the most sensitive strain to the antibacterial effect of the tested compounds.     

Quantification of polyphenols and flavonoid content and evaluation of anti-inflammatory and antimicrobial activities of Stenocereus stellatus extracts

The hexanic, ethyl acetate and methanolic extracts from branches of Stenocereus stellatus were tested in both the 12-O-tetradecanoylphorbol-13-acetate (TPA) – induced ear oedema model and antimicrobial activity assay. The % of oedema inhibition, the Minimum Inhibitory Concentration (MIC), as well as the polyphenolic and flavonoid content were determined. Also, extracts were analysed by gas chromatography–mass spectrometry (GC–MS). In TPA model, the three extracts showed moderate oedema inhibition. In the antimicrobial activity assay, methanolic extract shows better MIC against all strains. The lowest MICs were for Candida albicans (31 μg/mL) and Rhizopus sp. (15 μg/mL). Also, 50.78 mg eq. of gallic acid/g extract of polyphenol and 115.12 mg eq. of catequine/g extract of flavonoids content were founded in ethyl acetate extract. In the chromatographic analysis, β-sitosterol, β-amyrine, betulin and some other molecules were identified. The results show that S. stellatus possess antimicrobial activities against some fungus species.     

Isolation of selenium organic species from antarctic krill after enzymatic hydrolysis

Total selenium content and its distribution in the soluble and insoluble protein-bound fractions obtained after aqueous extraction of antarctic krill samples were determined. About 26% of the total selenium (2.4 g g^–1 dry weight) was found in the supernatant; the rest was in the pellet. Isolation of low molecular selenium-containing fractions was also performed by enzymatic digestion of the protein, followed by size-exclusion chromatography in conjunction with atomic absorption spectrometry. From the applied various proteinases (pronase E, subtilisin Carlsberg, trypsin, chymotrypsin, proteinase and proteinase N from Bacillus subtilis and Novo 0.6 MPX enzyme), the treatment with pronase E led to best recovery of selenium. About 96% of the total Se was found in the hydrolysate, mainly in low molecular weight fractions. Eighty percent of the Se species were in fractions with molecular weights in the range of amino acids and short peptides. High-performance liquid chromatography/inductively coupled plasma mass spectrometry (HPLC-ICP-MS) allowed the identification of selenomethionine and the assumption that selenocystine or its derivatives were the main species in these fractions.     

A new,improved sensor for ascorbate determination at copper hexacyanoferrate modified carbon film electrodes

A new, improved sensor for the electrocatalytic determination of ascorbate has been developed that has both a low applied operating potential and a low detection limit. The sensor was constructed by depositing copper hexacyanoferrate film either electrochemically or chemically onto carbon film electrode, and it was then characterised by cyclic voltammetry and electrochemical impedance spectroscopy. Chemically deposited films were shown to be the best for ascorbate determination and were used as an amperometric sensor at +0.05 V versus SCE to determine ascorbate in wines and juice. The linear range extended to 5 mM with a limit of detection of 2.1 M, the sensor was stable for more than four months, and it could be used continuously for at least 20 days.