Multicomponent analysis of drinking water by a voltammetric electronic tongue

A voltammetric electronic tongue is described that was used for multicomponent analysis of drinking water. Measurements were performed on drinking water from a tap and injections of the compounds NaCl, NaN₃, NaHSO₃, ascorbic acid, NaOCl and yeast suspensions could be identified by use of principal component analysis (PCA). A model based on partial least square (PLS) was developed for the simultaneously prediction of identification and concentration of the compounds NaCl, NaHSO₃ and NaOCl. By utilizing this type of non-selective sensor technique for water quality surveillance, it will be feasible to detect a plurality of events without the need of a specific sensor for each type of event.     

Label‐Free Measurements of the Diffusivity of Molecules in Lipid Membranes

An important and characteristic property of a cell membrane is the lateral mobility of protein molecules in the lipid bilayer. This has conventionally been measured by labeling the molecules with fluorescent markers and monitoring their mobility by different fluorescence‐based techniques. However, adding the label to the studied molecule may affect the system, so it is an assumption in almost all experiments that the measured mobility of the biomolecule with its label is the same as that of the unlabeled molecule. However, this assumption is rarely tested due to a lack of suitable methods. In this work, a new technique to perform label‐free diffusivity measurements is developed and used to measure the effect of the label for two common protein–lipid systems: 1) streptavidin (SA) coupled to a supported lipid bilayer (SLB) through biotinylated lipids and 2) the extracellular part of the T‐cell adhesion protein CD2, coupled to an SLB through histidine tags to nickel‐chelating lipids. A measurable (≈12 %) decrease in diffusivity is found for both labeled proteins, even though the molecular mass of the label is almost 100 times smaller than those of the proteins (≈50 kDa). The results illustrate the importance of being able to study different biophysical properties of cell membranes and their mimics without relying on fluorescent labels, especially if fluorescent labeling is difficult or is expected to affect the nature of the intermolecular interactions being studied.     

Dynamic Covalent Organocatalysts Discovered from Catalytic Systems through Rapid Deconvolution Screening

The first example of a bifunctional organocatalyst assembled through dynamic covalent chemistry (DCC) is described. The catalyst is based on reversible imine chemistry and can catalyze the Morita–Baylis–Hillman (MBH) reaction of enones with aldehydes or N‐tosyl imines. Furthermore, these dynamic catalysts were shown to be optimizable through a systemic screening approach, in which large mixtures of catalyst structures were generated, and the optimal catalyst could be directly identified by using dynamic deconvolution. This strategy allowed one‐pot synthesis and in situ evaluation of several potential catalysts without the need to separate, characterize, and purify each individual structure. The systems were furthermore shown to catalyze and re‐equilibrate their own formation through a previously unknown thiourea‐catalyzed transimination process.     

13C SPE MAS measurement of ligand concentration in compressible chromatographic beads

A method for measuring the ligand concentration in heterogeneous materials like chromatography media is described. In this method, ¹³C single pulse excitation magic angle spinning NMR experiment with broadband ¹H decoupling is used to determine the peak integrals for a butyl ligand in the spectrum of a dried chromatography medium. Within a carefully controlled protocol, those integrals compared with that of the internal reference compound dimethyl sulfone provide the required volume concentration with an accuracy of ca 2%. The effects of temperature, degree of hydration, and other experimental parameters are discussed. Copyright © 2015 The Authors. Magnetic Resonance in Chemistry published by John Wiley & Sons Ltd.     

Molecular complexation and binding studied by electrophoretic NMR spectroscopy

Electrophoretic mobilities obtained on a molecularly selective manner by electrophoretic NMR can be used to provide a quantitative characterization of the composition and stoichiometry of molecular complexes. This is demonstrated in complexes formed by uncharged cyclodextrins which attain an electrophoretic mobility upon inclusion of charged surfactants.     

Synthesis and evaluation of dihydroimidazolo and dihydrooxazolo ring-fused 2-pyridones—targeting pilus biogenesis in uropathogenic bacteria

Dihydrothiazolo ring-fused 2-pyridones have previously been shown to inhibit pilus assembly in uropathogenic Escherichia coli. Methods have now been developed to synthesize both dihydroimidazolo and dihydrooxazolo ring-fused 2-pyridones. To obtain the nitrogen analogs, Cbz-protected imidazolines were reacted with an acyl-Meldrum's acid derivative under acidic conditions. To prepare the oxygen analogs, a one-pot procedure was developed that allowed synthesis of dihydrooxazolo ring-fused 2-pyridones starting from acylated serine derivatives. After hydrolysis to their corresponding carboxylic acids and lithium carboxylates, biological evaluation revealed that the sulfur could be replaced by an oxygen atom and still maintains the ability to inhibit pilus assembly in uropathogenic E. coli. However, introducing a secondary amine instead of oxygen resulted in a substantial decrease in biological activity.     

Synthesis of Optically Active endo,endo Bicyclo[2.2.2]octane-2,5-diol, Bicyclo[2.2.2]octane-2,5-dione, and Related Compounds

Optically active C(2)-symmetric (1S,2S,4S,5S)-bicyclo[2.2.2]octane-2,5-diol ((+)-12; 98% ee) and several selectively protected optically active intermediates useful for synthetic transformations were synthesized via a 1,2-carbonyl transposition route starting from the easily available optically active (1R,4S,6S)-6-hydroxybicyclo[2.2.2]octan-2-one ((-)-2). The synthetic route also allowed the preparation of optically active (1S,4S)-bicyclo[2.2.2]octane-2,5-dione ((+)-14; 98% ee).     

Controlled Double-Bond Migration in Palladium-Catalyzed Intramolecular Arylation of Enamidines

Palladium-catalyzed intramolecular cyclization of N-(N'-tert-butylformimidoyl)-6-[2-(2-iodophenyl)ethyl]-1,2,3,4-tetrahydropyridine (1a) and N-(N'-tert-butylformimidoyl)-6-[3-(2-iodophenyl)propyl]-1,2,3,4-tetrahydropyridine (1b) respectively results in formation of spiro compounds 1'-(N-tert-butylformimidoyl)-3',4'-dihydrospiro[indan-1,2'(1'H)-pyridine] (4a), 1'-(N-tert-butylformimidoyl)-1',6'-dihydrospiro[indan-1,2'(3'H)-pyridine] (5a), and 1'-(N-tert-butylformimidoyl)-5',6'-dihydrospiro[indan-1,2'(1'H)-pyridine] (6a) and 1'-(N-tert-butylformimidoyl)-3,3',4,4'-tetrahydrospiro[naphthalene-1(2H),2'(1'H)-pyridine] (4b), 1'-(N-tert-butylformimidoyl)-1',3,4,6'-tetrahydrospiro[naphthalene-1(2H),2'(3'H)-pyridine] (5b), and 1'-(N-tert-butylformimidoyl)-3,4,5',6'-tetrahydrospiro[naphthalene-1(2H),2'(1'H)-pyridine] (6b). The double-bond migration process can be controlled, and any of the three double-bond isomers can be prepared by employing proper ligands. A combination of BINAP and the amidine function was required to obtain the isomers 5a and 5b with the double bond in the homoallylic position relative to the aryl group. An electrospray ionization mass spectrometric study was conducted to support suggested reaction intermediates.     

Superpositioned dielectrophoresis for enhanced trapping efficiency

One of the major applications for dielectrophoresis is selective trapping and fractionation of particles. If the surrounding medium is of low conductivity, the trapping force is high, but if the conductivity increases, the attraction decreases and may even become negative. However, high-conductivity media are essential when working with biological material such as living cells. In this paper, some basic calculations have been performed, and a model has been developed which employs both positive and negative dielectrophoresis in a channel with interdigitated electrodes. The finite element method was utilized to predict the trajectories of Escherichia coli bacteria in the superpositioned electrical fields. It is shown that a drastic improvement of trapping efficiency can be obtained in this way, when a high conductivity medium is employed.