Synthesis and ion sensing properties of new colorimetric and fluorimetric chemosensors based on bithienyl-imidazo-anthraquinone chromophores

Novel colorimetric receptors for fluoride ion sensing containing anthraquinone as a chromogenic signaling unit and imidazo-2,2'-bithiophene binding sites are reported. Well-defined color change was observed upon addition of fluoride ions to acetonitrile solutions of receptors 2. Compounds 2a-c, deprotonated after fluoride ion addition, were studied as metal ion chemosensors in the presence of Zn(II), Hg(II), and Cu(II) in acetonitrile solutions, especially compound 2a which displayed a marked change from pink to yellow-gold colors upon complexation.     

Evaluation of GSH adducts of adrenaline in biological samples

The sustained high release of catecholamines to circulation is a deleterious condition that may induce toxicity, which seems to be partially related to the products formed by oxidation of catecholamines that can be further conjugated with glutathione (GSH). The aim of the present study was to develop a method for the determination of GSH adducts of adrenaline in biological samples. Two position isomers of the glutathion-S-yl-adrenaline were synthesized and characterized by HPLC using diode array, coulometric and mass detectors. A method for the extraction of these adducts from human plasma was also developed, based on adsorption to activated alumina, which showed adequate recoveries and proved to be crucial in removing interferences from plasma. The selectivity, precision and linearity of the method were all within the accepted values for these parameters. Furthermore, the sensitivity of this method allows the detection of adduct amounts that are within the range of the expected concentrations for these adducts under certain pathophysiological conditions and/or drug treatments. In conclusion, the development of this method allows the direct analysis of GSH adducts of adrenaline in human plasma, providing a valuable tool for the study of the catecholamine oxidation process and its related toxicity.     

Estimation of temperature dependent parameters of a batch alcoholic fermentation process

In this work, a procedure was established to develop a mathematical model considering the effect of temperature on reaction kinetics. Experiments were performed in batch mode in temperatures from 30 to 38 degrees C. The microorganism used was Saccharomyces cerevisiae and the culture media, sugarcane molasses. The objective is to assess the difficulty in updating the kinetic parameters when there are changes in fermentation conditions. We conclude that, although the re-estimation is a time-consuming task, it is possible to accurately describe the process when there are changes in raw material composition if a re-estimation of parameters is performed.     

Hybrid neural network model of an industrial ethanol fermentation process considering the effect of temperature

In this work a procedure for the development of a robust mathematical model for an industrial alcoholic fermentation process was evaluated. The proposed model is a hybrid neural model, which combines mass and energy balance equations with functional link networks to describe the kinetics. These networks have been shown to have a good nonlinear approximation capability, although the estimation of its weights is linear. The proposed model considers the effect of temperature on the kinetics and has the neural network weights reestimated always so that a change in operational conditions occurs. This allow to follow the system behavior when changes in operating conditions occur.     

Purification and characterization of a cyclomaltodextrin glucanotransferase from Paenibacillus campinasensis strain H69-3

A cyclomaltodextrin glucanotransferase (E.C. 2.4.1.19) from a newly isolated alkalophilic and moderately thermophilic Paenibacillus campinasensis strain H69-3 was purified as a homogeneous protein from culture supernatant. Cyclomaltodextrin glucanotransferase was produced during submerged fermentation at 45 degrees C and purified by gel filtration on Sephadex G50 ion exchange using a Q-Sepharose column and ion exchange using a Mono-Q column. The molecular weight of the purified enzyme was 70 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and the pI was 5.3. The optimum pH for enzyme activity was 6.5, and it was stable in the pH range 6.0-11.5. The optimum temperature was 65 degrees C at pH 6.5, and it was thermally stable up to 60 degrees C without substrate during 1 h in the presence of 10 mM CaCl(2). The enzyme activity increased in the presence of Co(2+), Ba(2+), and Mn(2+). Using maltodextrin as substrate, the K(m) and K(cat) were 1.65 mg/mL and 347.9 micromol/mg x min, respectively.     

Direct and remarkably efficient conversion of methane into acetic acid catalyzed by amavadine and related vanadium complexes. A synthetic and a theoretical DFT mechanistic study

Vanadium(IV or V) complexes with N,O- or O,O-ligands, i.e., [VO{N(CH2CH2O)3}], Ca[V(HIDPA)2] (synthetic amavadine), Ca[V(HIDA)2], or [Bu4N]2[V(HIDA)2] [HIDPA, HIDA = basic form of 2,2'-(hydroxyimino)dipropionic or -diacetic acid, respectively], [VO(CF3SO3)2], Ba[VO(nta)(H2O)]2 (nta = nitrilotriacetate), [VO(ada)(H2O)] (ada = N-2-acetamidoiminodiacetate), [VO(Hheida)(H2O)] (Hheida = 2-hydroxyethyliminodiacetate), [VO(bicine)] [bicine = basic form of N,N-bis(2-hydroxyethyl)glycine], and [VO(dipic)(OCH2CH3)] (dipic = pyridine-2,6-dicarboxylate), are catalyst precursors for the efficient single-pot conversion of methane into acetic acid, in trifluoroacetic acid (TFA) under moderate conditions, using peroxodisulfate as oxidant. Effects on the yields and TONs of various factors are reported. TFA acts as a carbonylating agent and CO is an inhibitor for some systems, although for others there is an optimum CO pressure. The most effective catalysts (as amavadine) bear triethanolaminate or (hydroxyimino)dicarboxylates and lead, in a single batch, to CH3COOH yields > 50% (based on CH4) or remarkably high TONs up to 5.6 x 103. The catalyst can remain active upon multiple recycling of its solution. Carboxylation proceeds via free radical mechanisms (CH3* can be trapped by CBrCl3), and theoretical calculations disclose a particularly favorable process involving the sequential formation of CH3*, CH3CO*, and CH3COO* which, upon H-abstraction (from TFA or CH4), yields acetic acid. The CH3COO* radical is formed by oxygenation of CH3CO* by a peroxo-V complex via a V{eta1-OOC(O)CH3} intermediate. Less favorable processes involve the oxidation of CH3CO* by the protonated (hydroperoxo) form of that peroxo-V complex or by peroxodisulfate. The calculations also indicate that (i) peroxodisulfate behaves as a source of sulfate radicals which are methane H-abstractors, as a peroxidative and oxidizing agent for vanadium, and as an oxidizing and coupling agent for CH3CO* and that (ii) TFA is involved in the formation of CH3COOH (by carbonylating CH3*, acting as an H-source to CH3COO*, and enhancing on protonation the oxidizing power of a peroxo-VV complex) and of CF3COOCH3 (minor product in the absence of CO).     

Factorial analysis of the trihalomethanes formation in water disinfection using chlorine

The factors that affect trihalomethane (THM) (chloroform, bromodichloromethane, chlorodibromomethane and bromoform) formation from the chlorination of aqueous solutions of hydrophobic fulvic acids (FA) were investigated in a prototype laboratorial simulation using factorial analysis. This strategy involved a fractional factorial design (16 plus 5 center experiments) of five factors (fulvic acids concentration, chlorine dose, temperature, pH and bromide concentration) and a Box Behnken design (12 plus 3 center experiments) for the detailed analysis of three factors (FA concentration, chlorine dose and temperature). The concentration of THM was determined by headspace analysis by GC-ECD. The most significant factors that affect the four THM productions were the following: chloroform-FA concentration and temperature; bromodichloromethane-FA concentration and chlorine dose; chlorodibromomethane-chlorine dose; and, bromoform-chlorine dose and bromide concentration. Moreover, linear models were obtained for the four THM concentrations in the disinfection solution as function of the FA concentration, chlorine dose and temperature, and it was observed that the complexity of the models (number of significant factors and interactions) increased with increasing bromine atoms in the THM. Also, this study shows that reducing the FA concentration the relative amount of bromated THM increases.     

New noncellular fluorescence microplate screening assay for scavenging activity against singlet oxygen

In the present study, a new fluorescence microplate screening assay for evaluating scavenging activity against singlet oxygen (¹O₂) was implemented. The chemical generation of ¹O₂ was promoted using the thermodissociable endoperoxide of disodium 3,3′-(1,4-naphthalene)bispropionate (NDPO₂). The detection of ¹O₂ was achieved using dihydrorhodamine 123 (DHR), a nonfluorescent molecule that is oxidizable to the fluorescent form rhodamine 123 (RH). The combined use of a ¹O₂-selective generator and a highly sensitive probe (DHR) was then successfully applied to perform a screening assay of the ¹O₂ scavenging activities of ascorbic acid, penicillamine, cysteine, N-acetylcysteine (NAC), methionine, reduced glutathione (GSH), dihydrolipoic acid, lipoic acid, and sodium azide. All of these antioxidants exhibited concentration-dependent ¹O₂ scavenging capacities. They could be ranked according to observed activity: ascorbic acid> cysteine> penicillamine> dihydrolipoic acid > GSH> NAC> sodium azide> lipoic acid (IC₅₀ values of 3.0 ± 0.2, 8.0 ± 0.7, 10.9 ± 0.8, 25.2 ± 4.5, 57.4 ± 5.9, 138 ± 13, 1124 ± 128, 2775 ± 359 μM, mean±SEM, respectively) > methionine (35% of scavenging effect at 10 mM). In conclusion, the use of NDPO₂ as a selective generator for ¹O₂ and its fluorescence detection by the highly sensitive probe DHR is shown to be a reliable and resourceful analytical alternative means to implement a microplate screening assay for scavenging activity against ¹O₂. Generation and detection of singlet oxygen     

Branching and Crosslinking in Coordination Terpolymerizations

A general kinetic method, based upon population balances of generating functions, is applied to the prediction of the microstructure and molecular size of non‐linear terpolymers obtained through the coordination polymerization of two monovinyl monomers and a non‐conjugated diene. A rather complex kinetic scheme involving crosslinking and long‐chain branching is considered. It is shown that even in these conditions it is possible to carry out the prediction of molecular size and mass distributions, sequence size distributions, and z‐average mean‐square radius of gyration of the polymers. The influence of some kinetic parameters on the properties of the products is studied, considering a homogeneous operation in a semi‐batch reactor. The used simulation method is able to predict these properties before and after gelation whenever it occurs.