Influence of the support on the reaction course of tributyrin hydrolysis catalyzed by soluble and immobilized lipases

Lipases from different origins have been immobilized in supports chosen by its different aquaphilicity and used as biocatalysts for the hydrolysis of tributyrin. The changes of the concentration of tri-, di-, monobutyrin, glycerol, and butyric acid during the reactions catalyzed by soluble, as well as immobilized, lipases were evaluated by gas chromatography. The experimental data were fitted to a simple kinetic model for the sequential reaction of tributyrin hydrolysis. The calculated apparent rate constants were different for the biocatalysts used and were apparently related to diffusional effects and aquaphilicity of the supports. Maximal yields of dibutyrin were found with the soluble Candida lipase, whereas the highest yield of monobutyrin (90%) was obtained with the least aquaphylic derivative (Candida-Celite).     

Electrochromic films of a methylcarbazole derivative: optimization of polymerization and optical contrast

The effect of the polymerization potential and time on the electrochemical and optical responses of electrogenerated films of poly-[3,6-bis(2-(3,4-ethylenedioxy)thienyl)-N-methylcarbazole] (PBEDOT-NMCz) was studied. Every electrogenerated film was characterized according to the charge consumed during polymerization, its redox charge density (calculated by integration of a control voltammogram), the efficiency of the polymerization process (defined as the charge consumed during electropolymerization to create one redox site), and its optical contrast. Within the studied polymerization potential range, 0.75 to 2 V, the charge consumed during polymerization increased with the potential, while the efficiency of the polymerization process decreased. The redox site production rate reached a maximum at 1.25 V. The optical contrast of the obtained films remained the same when polymerizing in the range between 0.75 and 1.25 V. Polymerization at more anodic potentials resulted in films of lower electrochromic quality (defined as the maximum contrast achievable). The optimal conditions for electropolymerization in terms of optimum energy consumption and the best electrochromic quality of the films were established.     

A promising green method in cyclization reaction.Oxidation of 3-methylcatechol in the presence of 1,10-phenanthroline

Electrochemical oxidation of 3-methylcatechol as a model compound has been studied in the presence of 1,10-phenanthroline as a bi-dentate nucleophile in water/acetonitrile(70/30,v/v) solution using cyclic voltammetry and controlled-potential coulometry. The results revealed that anodically generated 3-methylcyclohexa-3,5-diene-1,2-dione participates in inter and intramolecular Michael addition reactions with 1,10-phenanthroline and via an ECEC pathway converts to the corresponding heterocyclic compound.The present work has led to the development of a facile and one-pot method with high atom economy under ambient conditions and in an undivided cell using a carbon electrode.     

Using Primary Source Projects to teach undergraduate mathematics content: analysis of instructor implementation and perceptions

ABSTRACT

This study investigates changes in instructor teaching tendencies, instructor’s perception of impact on student learning and dispositions, and methods of implementation of Primary Source Projects (PSPs). PSPs are curricular modules designed to teach core mathematical topics from primary historical sources rather than from standard textbooks. In essence, they are a form of inquiry-based learning that incorporates the history of mathematics through original source texts. We provide an overview of results from two semesters of implementation reports and surveys administered at the beginning and end of the semester by instructors who implemented PSPs in their undergraduate mathematics classes.     

An Adamantyl Amino Acid Containing Gramicidin S Analogue with Broad Spectrum Antibacterial Activity and Reduced Hemolytic Activity

The cyclic cationic antimicrobial peptide gramicidin S (GS) is an effective topical antibacterial agent that is toxic for human red blood cells (hemolysis). Herein, we present a series of amphiphilic derivatives of GS with either two or four positive charges and characteristics ranging between very polar and very hydrophobic. Screening of this series of peptide derivatives identified a compound that combines effective antibacterial activity with virtually no toxicity within the same concentration range. This peptide acts against both Gram‐negative and Gram‐positive bacteria, including several MRSA strains, and represents an interesting lead for the development of a broadly applicable antibiotic.     

Studies on the transformation of nitrosugars into iminosugars III: synthesis of (2R,3R,4R,5R,6R)-2-(hydroxymethyl)azepane-3,4,5,6-tetraol and (2R,3R,4R,5R,6S)-2-(hydroxymethyl)azepane-3,4,5,6-tetraol

A divergent synthesis of the two novel polyhydroxylated azepanes (2R,3R,4R,5R,6R)-2-(hydroxymethyl)azepane-3,4,5,6-tetraol and (2R,3R,4R,5R,6S)-2-(hydroxymethyl)azepane-3,4,5,6-tetraol from d-mannose is described. The method involves a Henry reaction between dimethyl-tert-butylsilyl 2,3-O-isopropylidene-α-d-lyxo-pentodialdo-1,4-furanoside and 2-nitroethanol followed by a reductive ring closure of the resulting epimeric nitro aldols. Glycosidase inhibition tests showed that (2R,3R,4R,5R,6S)-2-(hydroxymethyl)azepane-3,4,5,6-tetraol exhibits a weak but selective inhibition against α-l-fucosides.     

Effective elastic shear stiffness of a periodic fibrous composite with non-uniform imperfect contact between the matrix and the fibers

In this contribution, effective elastic moduli are obtained by means of the asymptotic homogenization method, for oblique two-phase fibrous periodic composites with non-uniform imperfect contact conditions at the interface. This work is an extension of previous reported results, where only the perfect contact for elastic or piezoelectric composites under imperfect spring model was considered. The constituents of the composites exhibit transversely isotropic properties. A doubly periodic parallelogram array of cylindrical inclusions under longitudinal shear is considered. The behavior of the shear elastic coefficient for different geometry arrays related to the angle of the cell is studied. As validation of the present method, some numerical examples and comparisons with theoretical results verified that the present model is efficient for the analysis of composites with presence of imperfect interface and parallelogram cell. The effect of the non uniform imperfection on the shear effective property is observed. The present method can provide benchmark results for other numerical and approximate methods.     

Synthesis,characterization and pronounced epoxidation activity of cis-dioxo-molybdenum(VI) tridentate Schiff base complexes using tert-butyl hydroperoxide

The synthesis and catalytic performance of novel cis-dioxo-Mo(VI) complexes containing simple ONO tridentate Schiff base ligands in the epoxidation of various olefins using tert-butyl hydroperoxide in desired times with excellent chemo- and stereoselectivity have been described. The study of turnover numbers and the UV–Vis spectra of the Mo complexes in the present epoxidation system indicate well the high efficiency and stability of the catalysts during the reaction. The electron-deficient and bulky groups on the salicylidene ring of the ligand promote the effectiveness of the catalyst.