Improving the Performance of a Continuous Process for the Production of Ethanol from Starch

In a previous work, a continuous simultaneous saccharification and fermentation process to produce ethanol from cassava starch was studied, using a set of fixed-bed reactors. The biocatalyst consisted of glucoamylase immobilized in silica particles and co-immobilized with S. cerevisiae in pectin gel. Using 3.8 U mL^?1 _reactor and 0.05 g_{wet yeast} mL^?1 _reactor at start-up, starch hydrolysis was the rate-limiting step. Maximum ethanol productivity was 5.8 g_ethanol L^?1 h^?1, with 94.0% conversion of total reducing sugars (TRS) and 83.0% of the ethanol theoretical yield. In this work, the molar mass of the substrate and the biocatalyst particle size were reduced in an attempt to improve the bioreactor performance. The diameters of silica and pectin gel particles were reduced from 100 μm and 3–4 mm, respectively, to 60 μm and 1–1.5 mm, and the degree of substrate prehydrolysis by α-amylase was increased. The bioreactor performance was assessed for different loads of immobilized glucoamylase (2.1, 2.8, and 3.8 U mL^?1 _reactor), for the same initial cell concentration (0.05 g_{wet yeast.}mL^?1 _reactor). Feeding with 154.0 g L^?1 of TRS and using 3.8 U mL^?1 _reactor, fermentation became the rate-limiting step. Productivity reached 11.7 g L^?1 h^?1, with 97.0% of TRS conversion and 92.0% of the ethanol theoretical yield. The reactor was operated during 275 h without any indication of destabilization.     

The fate of the tert-butylsulfinyl auxiliary after acid-promoted cleavage—a method for recycling t-BuSONH2

Ellman’s chiral auxiliary is converted into tert-butylsulfinyl chloride on sulfinamide deprotection with HCl and can be recovered in high yield upon treatment with ammonia. The enantiopure auxiliary can be obtained by trapping the sulfinyl chloride with a chiral alcohol followed by treatment of the resulting sulfinate ester with LiNH₂.     

Simultaneous determination of the herbicides diquat and paraquat in water

A method based on solid-phase extraction (on silica cartridges) and high-performance liquid chromatography (HPLC) followed by diode array UV detection is presented as an analytical tool for screening diquat (DQ) and paraquat (PQ) in drinking waters. The method is useful for quality control laboratories of water companies and beverage industries. Absolute recoveries of DQ and PQ from drinking water (25 mL in all cases), spiked at levels between 0.1, 1.0, and 5.0 microg/L, range from 91% to 103%. Relative standard deviation percentages are between 3% and 11%. Quantitation and detection limits are 70 and 40 ng/L for DQ and 90 and 60 ng/L for PQ, respectively; therefore, these herbicides can be detected and quantitated at levels below the limits established by the European Union.     

Efficient and green telescoped process to 2-methoxy-3-methyl-[1,4]benzoquinone

A telescoped process for the preparation of 2-methoxy-3-methyl-[1,4]benzoquinone is disclosed. When this novel process is compared to the prevailing method that utilizes Na2Cr2O7 as the oxidant, the novel process represents a high yielding (95%), green, and environmentally benign alternative with H2O2 and HNO3 as the oxidants and CH3COOH as the reaction medium.     

Phase transfer catalyzed enantioselective Strecker reactions of alpha-amido sulfones with cyanohydrins

A study into the use of a chiral phase-transfer catalyst in conjunction with acetone cyanohydrin to effect the enantioselective formation of alpha-amino nitriles from alpha-amido sulfones is described. This novel catalytic asymmetric Strecker reaction is analyzed with regard to the possible mechanistic basis.     

Regio- and stereoselective methoxyselenenylation of chiral 2-vinyl perhydro-1,3-benzoxazines promoted by selenium-heteroatom nonbonded interactions

Regio- and diastereoselective methoxyselenenylations of double bonds attached to the N,O-ketalic carbon of chiral perhydrobenzoxazines occur in high yields by reaction with benzeneselenenyl chloride in dichloromethane-methanol. The diastereoselection is dependent on the reaction conditions and the structure of the starting compounds and can be rationalized by accepting the coordination of the selenium to the oxygen atom of the heterocycle.     

On the accessibility to conical intersections in purines: hypoxanthine and its singly protonated and deprotonated forms

The dynamics following electronic excitation of hypoxanthine and its nucleoside inosine were studied by femtosecond fluorescence up-conversion. Our objective was to explore variants of the purinic DNA bases in order to determine the molecular parameters that increase or reduce the accessibility to ground state conical intersections. From experiments in water and methanol solution we conclude that both dominant neutral tautomers of hypoxanthine exhibit ultrashort excited state lifetimes (τ < 0.2 ps), which are significantly shorter than in the related nucleobase guanine. This points to a more accessible conical intersection for the fluorescent state upon removal of the amino group, present in guanine but absent in hypoxanthine. The excited state dynamics of singly protonated hypoxanthine were also studied, showing biexponential decays with a 1.1 ps component (5%) besides a sub-0.2 ps ultrafast component. On the other hand, the S(1) lifetimes of the singly deprotonated forms of hypoxanthine and inosine show drastic differences, where the latter remains ultrafast but the singly deprotonated hypoxanthine shows a much longer lifetime of 19 ps. This significant variation is related to the different deprotonation sites in hypoxanthine versus inosine, which gives rise to significantly different resonance structures. In our study we also include multireference perturbation theory (MRMP2) excited state calculations in order to determine the nature of the initial electronic excitation in our experiments and clarify the ordering of the states in the singlet manifold at the ground state geometry. In addition, we performed multireference configuration interaction calculations (MR-CIS) that identify the presence of low-lying conical intersections for both prominent neutral tautomers of hypoxanthine. In both cases, the surface crossings occur at geometries reached by out of plane opposite motions of C2 and N3. The study of this simpler purine gives several insights into how small structural modifications, including amino substitution and protonation site and state, determine the accessibility to conical intersections in this kind of heterocycles.     

Determination of microcystin-LR in waters in the subnanomolar range by sol-gel imprinted polymers on solid contact electrodes

The present work reports new sensors for the direct determination of Microcystin-LR (MC-LR) in environmental waters. Both selective membrane and solid contact were optimized to ensure suitable analytical features in potentiometric transduction. The sensing layer consisted of Imprinted Sol-Gel (ISG) materials capable of establishing surface interactions with MC-LR. Non-Imprinted Sol-Gel (NISG) membranes were used as negative control. The effects of an ionic lipophilic additive, time of sol-gel polymerization, time of extraction of MC-LR from the sensitive layer, and pH were also studied. The solid contact was made of carbon, aluminium, titanium, copper or nickel/chromium alloys (80 : 20 or 90 : 10). The best ISG sensor had a carbon solid contact and displayed average slopes of 211.3 mV per decade, with detection limits of 7.3 × 10(-10) M, corresponding to 0.75 μg L(-1). It showed linear responses in the range of 7.7 × 10(-10) to 1.9 × 10(-9) M of MC-LR (corresponding to 0.77-2.00 μg L(-1)), thus including the limiting value for MC-LR in waters (1.0 μg L(-1)). The potentiometric-selectivity coefficients were assessed by the matched potential method for ionic species regularly found in waters up to their limiting levels. Chloride (Cl(-)) showed limited interference while aluminium (Al(3+)), ammonium (NH(4)(+)), magnesium (Mg(2+)), manganese (Mn(2+)), sodium (Na(+)), and sulfate (SO(4)(2-)) were unable to cause the required potential change. Spiked solutions were tested with the proposed sensor. The relative errors and standard deviation obtained confirmed the accuracy and precision of the method. It also offered the advantages of low cost, portability, easy operation and suitability for adaptation to flow methods.     

Proficiency testing schemes for the assessment of Legionella PCR methodologies

Standard operating procedures used for the detection of bacteria in environmental samples are primarily based on bacterial growth on specific culture media and confirmation by biochemical and/or immunological tests. In the case of Legionella, isolation on BCYE-?? medium is the standard method, although it presents a number of drawbacks, and for this reason, the implementation of molecular methods, mainly those based on PCR, has increased over the last years. Following the ISO/IEC 17025, laboratories need an external evaluation of their work to assure the quality of the results they are producing, and the participation in proficiency testing (PT) schemes is compulsory. For those water-testing laboratories using PCR methods for Legionella, we have developed a PT scheme accredited according to ISO/IEC 17043. The preparation and the statistical analysis of the results are performed following this standard and the ISO 13528. The used samples have a very rapid and easy to use format, consisting of tablets with inactivated freeze-dried Legionella cells or freeze-dried Legionella DNA. In this PT scheme, participants evaluate both Legionella pneumophila and Legionella spp. detection systems and control the whole PCR process from the water sample concentration until the PCR results.