Molecular Recognition of Acetylaminofluorene-and Aminofluorene-modified Guanosine

Abstract

New receptors based upon a carboxamidonaphthyridine unit derivatized with the polyaromatic segments [4-(1-pyrenyl)butyroylamino] and [3-(9-anthracenyl)propanoylamino] have been synthesized and studied by ¹H NMR titration in their binding interaction to the guanosine-C8 adducts from the carcinogens 2-acetylaminofluorene and 2-aminofluorene. The high binding energy, in comparison with that of the non-derivatized analogues, is rationalized in terms of a bi-site interaction (hydrogen bonding and aromatic stacking). Although many factors may contribute to the strength of the host-guest complexes described herein, it appears that in some cases π-π interaction may induce a concomitant bending in the hydrogen bond system.     

Evaluation of antioxidants on the thermo-oxidative stability of soybean biodiesel

This work shows the evaluation of three antioxidants (2,6-di-t-butyl-4-methylphenol (BHT)—synthetic antioxidant, hydrogenated cardanol (HC), and alkyl hydrogenated cardanol (AHC)—both derived from cashew nut shell liquid) on the thermo-oxidative stability of the soybean biodiesel. The antioxidants were added at concentrations of 200, 300, and 400 ppm, and the oxidative stability of the biofuel with and without antioxidants were investigated by thermogravimetric analysis (TG-DTG and IPDT) and Metrohm 743 Rancimat per the EN 14112 method. The results showed that all antioxidants contributed for the thermo-oxidative stability of the soybean biodiesel as follows: soybean biodiesel < soybean biodiesel + BHT < soybean biodiesel + HC < soybean biodiesel + AHC. In the Rancimat method, the results showed that the antioxidants influenced the biodiesel stability with an increase of at least 71 %.     

TG and DSC analyses of eucalyptus black liquor as alternative methods to estimate solids content

As a consequence of the continuous increase in the production rate of pulp and paper mills around the world, a great quantity of black liquor, a by-product of the wood digestion process, is produced. This by-product has a great potential as biomass, but needs to be concentrated to higher solids content to be burned as fuel in a recovery boiler. This is necessary to make the pulping process economically feasible, incinerating black liquor to produce high pressure steam, recycling inorganic chemicals to the process. The greater the solids content in black liquor, the better the combustion process in the boiler. Nevertheless, concentration of solids in black liquor above 75 mass/%, causes scaling formation on the heat transfer surfaces of evaporators and concentrators, due to the precipitation of sodium salts, reducing the overall efficiency of this equipment. The aim of this work is to evaluate the use of thermal analyses techniques, TG and DSC, as alternative methods to estimate solids content in eucalyptus black liquor samples since this information is essential to understand scaling formation process, allowing actions to reduce this industrial problem. Traditional techniques applied to determine solids content use gravimetric methods, which are simple, fine, but take a lot of time to be executed. Thermal analyses have proved to be very accurate and have the advantage to be faster than the traditional techniques. On the other hand, the cost-benefit relationship of the traditional technique is much greater and the final decision which one should be used depends on the conditions available.     

Flow properties of biodiesel: correlation between TMDSC and dynamic viscosity

Sustainable and renewable energy has become more attractive due to its environmental benefits. Among these alternative sources, biodegradable and low emission biodiesels have been gaining attention as compared to diesel. However, their performance at low temperatures affects their commercial viability, because of engine performance problems, and when starting. Cold Filter Plugging Point, Pour Point, and Cloud Point are employed to predict the limits of operability for biodiesel. However, dynamic viscosity and TM-DSC methods are also useful to assess these properties and can be correlated. Viscosity curves were obtained, and TM-DSC revealed that the start temperature (transition liquid–solid) exhibits an increase in flow resistance for soybean, colza, sunflower, corn, and babassu oil biodiesels. The nucleation processes which occur during cooling are unique for each type of biodiesel due to the presence of different ester compositions and the values for viscosity and flow at low temperatures varied accordingly.     

Immobilized purine nucleoside phosphorylase from Schistosoma mansoni for specific inhibition studies

The parasite Schistosoma mansoni (Sm) depends exclusively on the salvage pathway for its purine requirements. The enzyme purine nucleoside phosphorylase (PNP) is, therefore, a promising target for development of antischistosomal agents and an assay for screening of inhibitors. To enable this, immobilized SmPNP reactors were produced. By quantification of hypoxanthine by liquid chromatography, kinetic constants (K _M) for the substrate inosine were determined for the free and immobilized enzyme as 110 ± 6.90 μmol?L ^?1 and 164 ± 13.4 μmol?L ^?1 , respectively, indicating that immobilization did not affect enzyme activity. Furthermore, the enzyme retained 25 % of its activity after four months. Non-Michaelis kinetics for the phosphate substrate, and capacity for P_i-independent hydrolysis were also demonstrated, despite the low rate of enzymatic catalysis. Use of an SmPNP immobilized enzyme reactor (IMER) for inhibitor-screening assays was demonstrated with a small library of 9-deazaguanine analogues. The method had high selectivity and specificity compared with screening by use of the free enzyme by the Kalckar method, and furnished results without the need for verification of the absence of false positives.

Performance of hydrophobic interaction ligands for human membrane‐bound catechol‐O‐methyltransferase purification

Despite of membrane catechol‐O‐methyltransferase (MBCOMT, EC 2.1.1.6) physiological importance on catecholamines’ O‐methylation, no studies allowed their total isolation. Therefore, for the first time, we compare the performance of three hydrophobic adsorbents (butyl‐, epoxy‐, and octyl‐Sepharose) in purification of recombinant human COMT (hMBCOMT) from crude Brevibacillus choshinensis cell lysates to develop a sustainable chromatographic process. Hydrophobic matrices were evaluated in terms of selectivity and hMBCOMT's binding and elution conditions. Results show that hMBCOMT's adsorption was promoted on octyl and butyl at ≤375 mM NaH₂PO_4, while on epoxy higher concentrations (>850 mM) were required. Additionally, hMBCOMT's elution was promoted on epoxy, butyl, and octyl using respectively 0.1–0.5, 0.25–1, and 1% of Triton X‐100. On butyl media, a stepwise strategy using 375 and 0 mM NaH₂PO₄, followed by three elution steps at 0.25, 0.7 and 1% Triton X‐100, allowed selective hMBCOMT isolation. In conclusion, significant amounts of MBCOMT were purified with high selectivity on a single chromatography procedure, despite its elution occurs on multiple peaks. Although successful applications of hydrophobic interaction chromatography in purification of membrane proteins are uncommon, we proved that traditional hydrophobic matrices can open a promising unexplored field to fulfill specific requirements for kinetic and pharmacological trials.     

Simple Reduction of Heteroaromatic Esters to Alcohols Using a Sodium Borohydride–Methanol System

Some heteroaromatic esters were reduced to the corresponding alcohols by using a sodium borohydride–methanol system. The reduction was completed within 0.15–2.0 h in refluxing THF. The alcohol products were isolated after aqueous workup in moderate to excellent yield (48–97%).     

One-Step Protection-Free Synthesis of 3-Aryl-5-hydroxyalkyl-1,2,4-oxadiazoles as Building Blocks

A simple and straightforward synthesis of 3-aryl-5-hydroxyalkyl-1,2,4-oxadiazoles is described. The reaction among arylamidoximes, ethyl glycolate or ethyl lactate, and potassium carbonate in refluxing toluene afforded the desired 1,2,4-oxadiazoles in moderate to good yields. The synthesis has been accomplished in a single step, avoiding protection–deprotection protocols.

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