The rapid preparation of 2-aminosulfonamide-1,3,4-oxadiazoles using polymer-supported reagents and microwave heating

Herein, we report on the preparation of a library of 5-substituted-2-amino-1,3,4-oxadiazoles and the corresponding thiadiazole analogues. Presented is a one-pot preparation of the 2-aminosulfonylated analogues through a three component coupling of an acylhydrazine, an isocyanate and sulfonyl chloride promoted by a polymer-supported phosphazine base under microwave dielectric heating. Also described is the optimization process and details pertaining to the elucidation of the reaction products.     

Preparation of electrospun nanofibers from solutions of different gelatin types using a benign solvent mixture composed of water/PBS/ethanol

The feasibility of using phosphate buffer saline (PBS)/ethanol mixtures as a benign solvent to electrospin three types of gelatin was studied. Gelatins with different chemical properties, such as Bloom, were selected and the effect of the gelatin nature and its concentration on the electrospinnability of the dope solution and on the fiber diameter of the electrospun mats were studied. Viscosity of the gelatin solution, which follows a power law relationship with the gelatin concentration, was found to significantly influence the morphology of the mats and the fiber diameter. It was demonstrated that the PBS/ethanol solvent interacted with the gelatins as a good solvent with a Flory exponent of 0.65. In addition, the effect of the solvent composition on the fiber formation process was evaluated corroborating that the ionic strength of the medium and the PBS/ethanol ratio significantly affected the morphology and the diameter of the electrospun fibers. Chemical structure and thermal stability of the electrospun gelatin mats were characterized by Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). Finally, cytotoxicity of the electrospun mats was analyzed by the Alamar Blue assay, using human foreskin fibroblasts (BJ‐5ta), resulting in a high cell viability (80–90%) regardless the type of gelatin. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesis and Chemical Reactivity of a 6‐Me‐3,2‐Hydroxypyridinone Dithiazolide with Primary Amines: A route to New Hexadentate Chelators for Hard Metal(III) Ions

A hydroxypyridinone building block, bifunctionalized with thiazoline, has been prepared from orthogonally protected 2‐(3‐(benzyloxy)‐4‐(ethoxycarbonyl)‐6‐methyl‐2‐oxopyridin‐1(2H)‐yl) acetic acid. The reactivity of the dithiazolide has been explored with two primary amines, leading to the synthesis and characterization of four new hexadentate ligands. Their complexes with selected hard trivalent ions pertinent to potential molecular imaging applications have been surveyed.     

Electrochemical study of a dendritic family at the water/1,2-dichloroethane interface

The transfer of six dendritric molecules, DMs, across the water/1,2-dichloroethane interface was investigated using cyclic voltammetry. From the variation of peak potential with pH, two different mechanisms of transfer were postulated depending on the nature of the molecules. Voltammetric parameters were employed to evaluate the hydrophilic/hydrophobic character and calculate the acid dissociation constant of these molecules. The results were explained taking into account the nature and multiplicity of functional surface groups.     

Alkyl chain length dependence of the self-organized structure of alkyl-substituted phthalocyanines

The alkyl chain length on alkyl-substituted phthalocyanines (C(n)OPc) dependence of their self-organized structures was examined in this study. STM results indicated that the symmetry of ordered structures decreased as the alkyl chain became longer, with the exception of C(6)OPc, which preferentially formed a quasi-3-fold symmetrical structure. This could be explained by the fact that the C(n)OPc molecules are most likely to form densely packed structures. With C(n)OPc, when n = 4 to 10, the self-organized structures were dependent on the competition between how densely the molecules were arranged and how loose the intermolecular interaction energy was, caused by the formation of the densely packed structure. However, with C(n)OPc, when n = 10-18, the molecules tended to form densely packed structures by reducing the symmetry, even though the C(n)OPc molecules were distorted. When C(12)OPc and cobalt phthalocyanine were coadsorbed, the mixed system exhibited a four-fold symmetrical structure, which is rarely observed in C(12)OPc.     

Continuous and size-dependent sorting of emulsion droplets using hydrodynamics in pinched microchannels

In this report, a microfluidic system is presented for continuous and size-dependent separation of droplets utilizing microscale hydrodynamics. The separation scheme is based on laminar-flow focusing and spreading in a pinched microchannel, referred to as "pinched flow fractionation (PFF)", which was previously developed for the size-dependent separation of solid particles, such as polymer microparticles or cells. By simply introducing emulsion and the continuous phase into a microchannel, continuous separation could be achieved without using complicated operations or devices. We first examined whether this scheme could be applied for droplets, by using a pinched microchannel with one outlet, and observed the behaviors of monodisperse droplets generated at the upstream T-junction. Analysis via high-speed imaging revealed that the length of the pinched segment is critical for precise separation of droplets. Then, separation of a polydisperse oil-in-water emulsion that was prepared previously was demonstrated using a microfluidic device equipped with multiple outlets. These results showed the ability of the presented system to sort or select specific-sized droplets easily and accurately, which would be difficult to achieve using normal-scale schemes, such as centrifugation or filtration.     

Surface chemistry and rheology of polysulfobetaine-coated silica

We have measured the viscosity of suspensions of colloidal silica particles (d = 300 nm) and the properties of silica surfaces in solutions of a polymer consisting of zwitterionic monomer groups, poly(sulfobetaine methacrylate), polySBMA. This polymer has potential use in modifying surface properties because the polymer is net uncharged and therefore does not generate double-layer forces. The solubility of the polymer can be controlled and varies from poor to good by the addition of sodium chloride salt. Ellipsometry was used to demonstrate that polySBMA adsorbs to silica and exhibits an increase in surface excess at lower salt concentration, which is consistent with a smaller area per molecule at low salt concentration. Neutron reflectivity measurements show that the adsorbed polymer has a thickness of about 3.7 nm and is highly hydrated. The polymer can be used to exercise considerable control over suspension rheology. When silica particles are not completely covered in polymer, the suspension produces a highly viscous gel. Atomic force microscopy was used to show this is caused by bridging of polymer between the particles. At higher surface coverage, the polymer can produce either a high or very low viscosity slurry depending on the sodium chloride concentration. At high salt concentration, the suspension is stable, and the viscosity is lower. This is probably because the entrainment of many small ions renders the polymer film highly hydrophilic, producing repulsive surface forces and lubricating the flow of particles. At low salt concentrations, the polymer is barely soluble and more densely adsorbed. This produces less stable and more viscous solutions, which we attribute to attractive interactions between the adsorbed polymer layers.     

Electrophoretic chip for fractionation of selective DNA fragment

A microchannel chip has been used to fractionate selected segments from an electrophoretic flow of separated fragments. A sample, which covers the size from 35 to 670 bp, was initially separated using an 8.8-cm-long channel at the electric field strength of 100 V/cm. The target fragment of 318 bp was selected and extracted from the separation channel. High-resolution fractionation was achieved by introducing new procedures for blocking, extraction, and segment transfer. Fractionation quality with and without blocking were compared using a 310 Genetic Analyzer (Applied Biosystems). The results show that no contamination was found in the sample, which was fractionated with blocking; however, a contamination by short segments was found in the sample, which was fractionated without blocking. Furthermore, fractionation by the chip was found to be of higher fidelity than that by the polyacrylamide slab gel, which displayed a small overlapped peak after the target peak. Compared with the traditional method, our chips enable faster and high-fidelity fractionation, thus providing a new tool for bioanalysis and other applications.     

Heterocyclic substituted thiosemicarbazones and their Cu(II) complexes: Synthesis,characterization and studies of substituent effects on coordination and DNA binding

By reacting thiosemicarbazides substituted on the aminic nitrogen with 5-formyluracil, several new 5-formyluracil thiosemicarbazones (H₃ut) derivatives were synthesised and characterized. These ligands, treated with copper chloride and nitrate, afforded two different kinds of compounds. In the complexes derived from copper chloride the metal atom is pentacoordinated, being surrounded by the neutral ligand binding through SNO donor atoms and by two chlorines, while the nitrate derivatives consist of monocations and nitrate anions. The copper coordination (4 + 2) involves the SNO ligand atoms, two water oxygens and an oxygen atom of a monodentate nitrate group. On varying the substituents on the thiosemicarbazidic moiety, remarkable modifications of the coordination geometry are not observed for the complexes with the same counterion. For all the compounds, interactions with DNA (calf thymus) were studied using UV–Vis spectroscopy; the nuclease activity was verified on plasmid DNA pBR 322 by electrophoresis.     

Three component coupling of alpha-iminoesters via umpolung addition of organometals: synthesis of alpha,alpha-disubstituted alpha-amino acids

The synthesis of alpha,alpha-disubstituted alpha-amino acids by means of a three component coupling is reported. The coupling occurs through umpolung addition of organometallic reagents to the nitrogen of alpha-iminoesters. The resulting enolate intermediates subsequently react with electrophiles (aldehydes, imines, alpha,beta-unsaturated nitro, alkyl halides, acyl cyanides) to form a quaternary center. Tethering of the electrophile and nucleophile components provides cyclic alpha,alpha-disubstituted alpha-amino acid derivatives.