Catalytic DNA-based fluorescence polarization chiral sensing platform for l-histidine detection at trace level

This paper reports a novel fluorescence polarization (FP) chiral sensor approach based on a catalytic DNA. This platform involves an enzyme module (E), which was able to trigger the l-histidine-dependent cleavage of an RNA phosphoester bond of a substrate domain (S), whereas it did not accept the d-enantiomer as cofactor. Two assay formats were proposed, based on bi- and unimolecular strategies. The bimolecular design was related to the use of separate E and fluorescently labelled S* sequences. The two oligonucleotide strands were pre-assembled via complementary regions at their extremities. As the result of the large molecular volume of the formed assembly, the S* probe displayed a high fluorescence anisotropy signal. Upon addition of the l-histidine, the DNAzyme cleaved the phosphoester bond of the S* component, leading to the loss of stem stability and the release of single-stranded products of lower size. This was accompanied by a significant decrease in the fluorescence anisotropy response. As a simpler alternative, the unimolecular design, where E and S sequences are linked together through a loop to form a single fluorescent probe E-S*, was also investigated. It was found that the unimolecular approach provided an improved FP response relative to the bimolecular one. Under optimized operating conditions, such a chiral sensing platform allowed the detection of as low as 0.05 % of the l-histidine enantiomer in a non-racemic mixture.     

The octonionic eigenvalue problem

We discuss the eigenvalue problem for 2×2 and 3×3 octonionic Hermitian matrices. In both cases, we give the general solution for real eigenvalues, and we show there are also solutions with non-real eigenvalues.     

Bogolubov transformations and completeness

It is well-known that two complete, orthonormal sets of solutions of the Klein-Gordon equation are related by invertible Bogolubov transformations and that the Bogolubov coefficients therefore satisfy certain identities. We show that the converse is false, namely, that the fact that the Bogolubov coefficients defined by two sets of solutions satisfy these identities doesnot imply that either set can be expanded in terms of the other. Several simple counterexamples are given.     

Synthesis of 7- and 5,7-substituted-6-fluoro-2-methyl-1,2,3,4-tetrahydroquinolines: Convenient precursors of quinolone antibacterial agents

An original procedure to obtain substitution at the 7 or 5, 7 positions on 6-halogenated tetrahydroquinaldines is described. The title products are a new class of precursors of quinolone antibacterial agents.     

A stereo- and regio-controlled synthesis of bromothiophenyl C-nucleosides. Tandem bromination-ribosylation via halogen dance process

Metallation-ribosylation of 2-bromothiophene 1 when conducted at room temperature afforded the original glycosylated dibromothiophene 3b following a regiocontrolled halogen transfer-based halogen-dance process. Then, stereocontrolled reduction-cyclization of hemiacetals 3a-c allowed straightforward access to the halogenated thiophenyl-C-nucleosides 6a-c.     

Covalently bonded DNA aptamer chiral stationary phase for the chromatographic resolution of adenosine

In this work, a target-specific aptamer chiral stationary phase (CSP) based on the oligonucleotidic selector binding to silica particles through a covalent linkage was developed. An anti-d-adenosine aptamer was coupled, using an in-situ method, by way of an amide bond to macroporous carboxylic acid based silica. Frontal chromatography analysis was performed to evaluate the column properties, i.e., determination of the stationary phase binding capacity and the dissociation constant of the target-immobilized aptamer complex. It was found that such covalent immobilization was able to maintain the aptamer binding properties at a convenient level for an efficient enantioseparation. Subsequently, the separation of adenosine enantiomers was investigated under different operating conditions, including changes in the eluent’s ionic strength and the proportion of organic modifiers as well as column temperatures. It was demonstrated that, under various conditions of use and storage, the present CSP was stable over time.     

Cellular microarrays for use with capillary-driven microfluidics

We present a method for the facile arraying of cells on microstructured substrates which should be suitable for cellular assays in autonomous microfluidic capillary systems (CSs). The CSs, which were designed and microfabricated in Si, have various microfluidic functional elements including reaction chambers wherein cellular arrays are located. Two methods for arraying the cells were explored. In the first method, a hydrophobic alkanethiol was microcontact-printed on the bottom surface of a microfluidic reaction chamber. The subsequent adsorption of protein-repellent alkanethiols around the printed areas and the deposition from solution of fibronectin (FN) on the hydrophobic areas resulted in an adhesive pattern for the attachment of living human breast cancer cells. This method was limited by the formation of cellular clusters, which proved difficult to remove selectively. The second method employed a poly(dimethylsiloxane) elastomer having oval recessed microstructures. The selective coating of the inner walls of the ovals with FN and the blocking of the mesas around the ovals with bovine serum albumin (BSA) permitted single or multiple cells to be arrayed depending on the size of the ovals. The possibility of sealing CSs with cells arrayed on poly(dimethylsiloxane) may provide a versatile platform for high-throughput experimentation down to the single-cell level. Figure The deposition of one or a few living cells in fibronectin-coated poly(dimethylsiloxane) microstructures results in cellular arrays, which can be interfaced with capillary-driven microfluidics     

Partition and water/oil adsorption of some surfactants

Adsorption isotherms have been determined at the water/oil interface for five biphasic systems involving surfactants (non-ionic and ionic) present in both phases at partition equilibrium. The systems studied were polyoxyethylene(23)lauryl ether (Brij35) in water/hexane and four ionic surfactants, hexadecyltrimethylammonium bromide (CTAB), and a series of three tetraalkylammonium dodecylsulfate (TEADS, TPADS, and TBADS) in water/CH 2Cl 2. Interfacial tension measurements performed at the water/air and water/oil interfaces provided all the necessary information for the determination of the adsorption parameters by taking partition into account. These measurements also allowed the comparison of the adsorption properties at both interfaces which showed an increase of the adsorption equilibrium constant and a decrease of the maximum surface concentration at the water/oil interface compared to water/air. The values of the critical aggregation concentration showed, in all cases, that only the surfactant dissolved in the aqueous phase contribute to the decrease of the water/oil interfacial tension. In the case of the four ionic surfactants, the critical aggregation concentration obtained in biphasic conditions were lowered because of the formation of mixed surfactant-CH 2Cl 2 aggregates.     

Vibrational assignments of six-coordinate ferrous heme nitrosyls: new insight from nuclear resonance vibrational spectroscopy

This Communication addresses a long-standing problem: the exact vibrational assignments of the low-energy modes of the Fe-N-O subunit in six-coordinate ferrous heme nitrosyl model complexes. This problem is addressed using nuclear resonance vibrational spectroscopy (NRVS) coupled to (15)N(18)O isotope labeling and detailed simulations of the obtained data. Two isotope-sensitive features are identified at 437 and 563 cm(-1). Normal coordinate analysis shows that the 437 cm(-1) mode corresponds to the Fe-NO stretch, whereas the 563 cm(-1) band is identified with the Fe-N-O bend. The relative NRVS intensities of these features determine the degree of vibrational mixing between the stretch and the bend. The implications of these results are discussed with respect to the trans effect of imidazole on the bound NO. In addition, a comparison to myoglobin-NO (Mb-NO) is made to determine the effect of the Mb active site pocket on the bound NO.     

A concise synthesis of lentiginosine derivatives using a pyridinium formation via the Mitsunobu reaction

A four-step synthesis of (-)-lentiginosine and its epimers is described starting from 2-bromopyridine. The key step consisted of a quaternarization of a fully unprotected pyridinium-polyol unit using Mitsunobu methodology. Subsequent PtO(2)-catalyzed diastereoselective hydrogenation of the pyridinium ring proceeded smoothly and led to the expected dihydroxyindolizidines with excellent yields. This stereochemically flexible strategy has been illustrated by the concise total synthesis of non-natural products derivatives such as (-)-lentiginosine and its stereoisomers in high yields.