DISTRIBUTION OF PORPHYRINS IN THE VARIOUS COMPARTMENTS OF UNILAMELLAR LIPOSOMES OF DIPALMITOYL-PHOSPHATIDYLCHOLINE AS PROBED BY FLUORESCENCE SPECTROSCOPY

Abstract— The spectroscopic properties of hematoporphyrin, hematoporphyrin-dimethyl ester, uroporphyrin and uroporphyrinoctamethyl ester, incorporated into unilamellar liposomes of dipalmitoylphos-phatidylcholine, have been studied with the aim to assess the distribution of porphyrins within the various liposomal compartments.
The results obtained indicate that the highly hydrosoluble uroporphyrin is partitioned in the endoliposomal aqueous pool while its octamethylester is homogeneously distributed in the inner lipid monolayer. Hematoporphyrin and its dimethylester show an heterogeneous distribution within the phospholipid bilayer. At T = 25°C these porphyrins are preferentially located in the outer phospholipid monolayer.
Detailed studies on hematoporphyrin indicate that the distribution between the inner and outer phospholipid monolayer is a function of temperature and liposome dimensions. In particular, the increase of temperature above the critical temperature for the liquid-gel phase transition of the liposomes causes a partial shift of the porphyrin molecules toward the inner phospholipid monolayer. Moreover, the increase of liposome dimensions leads to a greater accessibility of porphyrin to the external medium.     

Agro-industrial waste enzymes: Perspectives in circular economy

According to the Food and Agriculture Organization of the United Nations, approximately 1.3 billion tons of food is wasted each year, equivalent to approximately one-third of world production. Agri-food wastes are the source of proteins, carbohydrates, lipids, and other essential minerals that have been exploited for value-added products by the development of biorefineries and sustainable business as important elements of circular economies. The innovation and materialization of these types of processes, including the use of disruptive technologies on microbial bioconversion and enzyme technology, such as nanotechnology, metabolic engineering, and multi-omics platforms, increase the perspectives on the waste valorization process. Lignocellulolytic enzymes, pectinases, and proteases are mainly used as catalyzers on agri-food waste treatment, and their production in house might be the trend in near future for agro-industrial countries. Another way to transform the agri-food wastes is via aerobic or anaerobic microbial process from fungal or bacterial cultures; these processes are the key to produce waste enzymes.     

Rationalizing the diverse reactivity of [1.1.1]propellane through σ–π-delocalization

[1.1.1]Propellane is the ubiquitous precursor to bicyclo[1.1.1]pentanes (BCPs), motifs of high value in pharmaceutical and materials research. The classical Lewis representation of this molecule places an inter-bridgehead C–C bond along its central axis; ‘strain relief’-driven cleavage of this bond is commonly thought to enable reactions with nucleophiles, radicals and electrophiles. We propose that this broad reactivity profile instead derives from σ–π-delocalization of electron density in [1.1.1]propellane. Using ab initio and DFT calculations, we show that its reactions with anions and radicals are facilitated by increased delocalization of electron density over the propellane cage during addition, while reactions with cations involve charge transfer that relieves repulsion inside the cage. These results provide a unified framework to rationalize experimental observations of propellane reactivity, opening up opportunities for the exploration of new chemistry of [1.1.1]propellane and related strained systems that are useful building blocks in organic synthesis.

A unified framework that explains the reactivity of [1.1.1]propellane through electron delocalization.     

Efficient synthesis of 3H-imidazo[4,5-b]pyridines from malononitrile and 5-amino-4-(cyanoformimidoyl)imidazoles

1-Aryl-5-amino-4-(cyanoformimidoyl)imidazoles 2 were reacted with malononitrile under mild experimental conditions and led to 3-aryl-5,7-diamino-6-cyano-3H-imidazo[4,5-b]pyridines 5, when the reaction was carried out in the presence of DBU, or to 3-aryl-5-amino-6,7-dicyano-3H-imidazo[4,5-b]pyridines 3, in its absence. Both reactions evolved from the adduct formed by nucleophilic attack of the malononitrile anion to the carbon of the cyanoformimidoyl substituent. A 5-amino-1-aryl-4-(1-amino-2,2-dicyanovinyl)imidazole 4 was isolated when this reaction was carried out in the presence of DBU. The structure of compound 4 was confirmed by spectroscopic methods and by reaction with triethyl orthoformate and with acetic anhydride, leading respectively to 9-aryl-6-(cyanomethylidene)purines 11 and 12. Imidazole 2b was also reacted with ethyl acetoacetate, a carbon acid with a pK(a) comparable to that of malononitrile. Similar reaction conditions were used and the product isolated was a 6-carbamoyl-1,2-dihydropurine 10, showing that a different mechanism was operating in this case.     

Application of Ni(II)-imprinted cross-linked poly(methacrylic acid) synthesised through double-imprinting method for the on-line preconcentration of Ni(II) ions in aqueous media

The present paper describes the feasibility of on-line preconcentration of nickel ions from aqueous medium on Ni(II)-imprinted cross-linked poly(methacrylic acid) (IIP) synthesised through a double-imprinting method and their subsequent determination by FAAS. The proposed method consisted in loading the sample (20.0 mL, pH 7.25) through a mini-column packed with 50 mg of the IIP for 2 min. The elution step was performed with 1.0 mol L^?1 HNO₃ at a flow rate of 7.0 mL min^?1. The following parameters were obtained: quantification limit (QL) – 3.74 µg L^?1, preconcentration factor (PF) – 36, consumption index (CI) – 0.55 mL, concentration efficiency (CE) – 18 min^?1, and sample throughput – 25 h^?1. The precision of the procedure assessed in terms of repeatability for ten determinations was 5.6% and 2.5% for respective concentrations of 5.0 and 110.0 µg L^?1. Moreover, the analytical curve was obtained in the range of 5.0–180.0 µg L^?1 (r = 0.9973), and a 1.64-fold increase in the method sensitivity was observed when compared with the analytical curve constructed for the NIP (non-imprinted polymer), thus suggesting a synergistic effect of the Ni(II) ions and CTAB on the adsorption properties of the IIP. The practical application of the adsorbent was evaluated from an analysis of tap, mineral, lake and river water. Considering the results of addition and recovery experiments (90.2–100 %), the efficiency of this adsorbent can be ensured for the interference-free preconcentration of the Ni(II) ions.     

Pigment Production by Filamentous Fungi on Agro-Industrial Byproducts: an Eco-Friendly Alternative

The search for new sources of natural pigments has increased, mainly because of the toxic effects caused by synthetic dyes used in food, pharmaceutical, textile, and cosmetic industries. Fungi provide a readily available alternative source of natural pigments. In this context, the fungi Penicillium chrysogenum IFL1 and IFL2, Fusarium graminearum IFL3, Monascus purpureus NRRL 1992, and Penicillium vasconiae IFL4 were selected as pigments producers. The fungal identification was performed using ITS and part of the β-tubulin gene sequencing. Almost all fungi were able to grow and produce water-soluble pigments on agro-industrial residues, with the exception of P. vasconiae that produced pigments only on potato dextrose broth. The production of yellow pigments was predominant and the two strains of P. chrysogenum were the largest producers. In addition, the production of pigments and mycotoxins were evaluated in potato dextrose agar using TOF-MS and TOF-MS/MS. Metabolites as roquefortine C, chrysogine were found in both extracts of P. chrysogenum, as well fusarenone X, diacetoxyscirpenol, and neosolaniol in F. graminearum extract. In the M. purpureus extract, the pigments monascorubrin, rubropunctatin, and the mycotoxin citrinin were found. The crude filtrates have potential to be used in the textile industry; nevertheless, additional pigment purification is required for food and pharmaceutical applications.     

On idempotents of a class of commutative rings

Abstract

In the present work, a procedure for determining idempotents of a commutative ring having a sequence of ideals with certain properties is presented. As an application of this procedure, idempotent elements of various commutative rings are determined. Several examples are included illustrating the main results.