Evaluation of a glycerol derived biofuel by thermal analysis

This work describes thermal analysis evaluation of a glycerol derived compound (fatty acid esters of (2,2-dimethyl-1,3-dioxolan-4-yl) methanol) developed to work as a biofuel. Mixtures of these ketal–glyceryl esters with fatty acid methyl esters typical of soybean biodiesel were prepared and evaluated in relation to biodiesel critical thermal properties such as temperature of crystallization, thermal stability and volatilization measured by differential scanning calorimetry and thermogravimetric analysis. The volatility of the products containing fatty acid methyl esters and (2,2-dimethyl-1,3-dioxolan-4-yl) methyl esters could be predicted by thermogravimetric analyses conducted in nitrogen that avoided time consuming distillation and greatly reduced material expenditure.     

A modification of the successive projections algorithm for spectral variable selection in the presence of unknown interferents

This work proposes a modification to the successive projections algorithm (SPA) aimed at selecting spectral variables for multiple linear regression (MLR) in the presence of unknown interferents not included in the calibration data set. The modified algorithm favours the selection of variables in which the effect of the interferent is less pronounced. The proposed procedure can be regarded as an adaptive modelling technique, because the spectral features of the samples to be analyzed are considered in the variable selection process. The advantages of this new approach are demonstrated in two analytical problems, namely (1) ultraviolet–visible spectrometric determination of tartrazine, allure red and sunset yellow in aqueous solutions under the interference of erythrosine, and (2) near-infrared spectrometric determination of ethanol in gasoline under the interference of toluene. In these case studies, the performance of conventional MLR-SPA models is substantially degraded by the presence of the interferent. This problem is circumvented by applying the proposed Adaptive MLR-SPA approach, which results in prediction errors smaller than those obtained by three other multivariate calibration techniques, namely stepwise regression, full-spectrum partial-least-squares (PLS) and PLS with variables selected by a genetic algorithm. An inspection of the variable selection results reveals that the Adaptive approach successfully avoids spectral regions in which the interference is more intense.     

Distorted fused porphyrin-phthalocyanine conjugates: synthesis and photophysics of supramolecular assembled systems with a pyridylfullerene

In the current work, we report on the synthesis and photophysical features of supramolecular hybrid systems that are based on newly fused porphyrin-phthalocyanine (P-Pc) conjugates and a pyridylfullerene. The ZnP-ZnPc conjugate was synthesized in three steps starting with a Diels-Alder reaction between β-vinylporphyrin and fumaronitrile. The resulting mixture of isomeric adducts was then dehydrogenated to yield the corresponding benzo[b]porphyrin-2(1),2(2)-dicarbonitrile. In the final step, cyclotetramerization with 4-tert-butylphthalonitrile, in the presence of zinc acetate, afforded the bis-metalated conjugate. Selective demetallation of ZnP led to the H(2)P-ZnPc conjugate. For both conjugates steric hindrance is the inception to a bent configuration, which does, however, not preclude enlargement of the π-conjugated system, that is, the porphyrins and the phthalocyanines. The two conjugates coordinate N-(4-pyridyl)fullero[c]pyrrolidine giving rise to the corresponding supramolecular porphyrin-phthalocyanine-fullerene systems. Photophysical measurements corroborate a sequential deactivation in the excited state, namely an initial intramolecular energy transfer from ZnP or H(2)P to ZnPc followed by an intramolecular charge transfer to yield ZnP-(ZnPc)˙(+)-(C(60))˙(-) and H(2)P-(ZnPc)˙(+)-(C(60))˙(-), respectively.     

Drug resistance modulation in Staphylococcus aureus, a new biological activity for mesoionic hydrochloride compounds

Two salts of the mesoionic compounds 1,4-diphenyl-5-(5-nitro-2-furanyl)-1,3,4-thiadiazolium-2-thiol chloride (MC-1) and 4-phenyl-5-(5-nitro-2-furanyl)-1,3,4-thiadiazolium-2-phenylamine chloride (MC-2) were synthesized utilizing 1,4-diphenyl-thiosemicarbazide and 5-nitro-2-furoyl chloride as starting materials. Their structures were characterized by IR, 1H-NMR, 13C-NMR and elemental analysis. These compounds were analyzed for their influence on the effectiveness of norfloxacin, tetracycline, and erythromycin (standard antibiotics) against resistant strains of Staphylococcus aureus. MC-1 and MC-2, at sub-inhibitory concentrations of 16 μg/mL, favourably modulated the antibiotic activity of tetracycline by 16- and 32-fold, respectively (MIC), and that of erythromycin by 4-fold.     

“Living” Free Radical Polymerization in Tubular Reactors. I. Modeling of the Complete Molecular Weight Distribution Using Probability Generating Functions

This is the first of a series of works aiming at developing a tool for designing “living” free radical polymerization processes in tubular reactors, in order to achieve tailor‐made MWDs. A mathematical model of the nitroxide‐mediated controlled free radical polymerization is built and implemented to predict the complete MWD. It is shown that this objective may be achieved accurately and efficiently by means of the probability generating function (pgf) transformation. Comparison with experimental data is good. The potential of the resulting model for optimization activities involving the complete MWD is also shown.

     

Analysis of Ethylene/1‐Olefin Copolymers Made with Ziegler–Natta Catalysts by Deconvolution of Molecular Weight and Average Short Chain Branching Distributions

In this article a systematic method is proposed to deconvolute the time‐dependent molecular weight distributions (MWD) and average comonomer fraction profiles of ethylene/1‐olefin copolymers made with heterogeneous Ziegler–Natta catalysts. These distributions with a high‐temperature gel permeation chromatography equipped with an infrared detector at four different polymerization times have been measured and used this information to infer how the fractions of polymer made on each site type varied with polymerization time. The model estimates here the minimum number of active site types needed to describe these copolymers, the MWD of polymer populations made on each site type, and their average comonomer fractions. This method is useful to quantify the microstructure of olefin copolymers made with multiple site type catalysts using the least number of adjustable parameters.

     

Light-driven horseradish peroxidase cycle by using photo-activated methylene blue as the reducing agent

In this work, the regeneration of native horseradish peroxidase (HRP), following the consecutive reduction of oxo-ferryl pi-cation (compound I) and oxo-ferryl (compound II) forms, was observed by UV-visible spectrometry and electron paramagnetic resonance (EPR) in the presence of methylene (MB+), in the dark and under irradiation. In the dark, MB+ did not affect the rate of HRP compound I and II reduction, compatible with hydrogen peroxide as the solely reducing species. Under irradiation, the dye promoted a significant increase in the native HRP regeneration rate in a pH-dependent manner. Flash photolysis measurements revealed significant redshift of the MB+ triplet absorbance spectrum in the presence of native HRP. This result is compatible with the dye binding on the enzyme structure leading to the increase in the photogenerated MB* yield. In the presence of HRP compound II, the lifetime of the dye at 520 nm decreased approximately 75% relative to the presence of native HRP that suggests MB* as the heme iron photochemical reducing agent. In argon and in air-saturated media, photoactivated MB+ led to native HRP regeneration in a time- and concentration-dependent manner. The apparent rate constant for photoactivated MB+-promoted native HRP regeneration, in argon and in air-saturated medium and measured as a function of MB+ concentration, exhibited saturation that is suggestive of dye binding on the HRP structure. The dissociation constant (KMB) observed for the binding of dye to HRP was 5.4+/-0.6 microM and 0.57+/-0.05 microM in argon and air-saturated media, respectively. In argon-saturated medium, the rate of the conversion of HRP compound II to native HRP was significantly higher, k2argon=(2.1+/-0.1)x10(-2) s(-1), than that obtained in air-equilibrated medium, k2air=(0.73+/-0.02)x10(-2) s(-1). Under these conditions the efficiency of photoactivated MB(+)-promoted native HRP regeneration was determined in argon and air-equilibrated media as being, respectively: k2/KMB=3.9x10(3) and 12.8x10(3) M(-1) s(-1).