Using multidimensional projection techniques for reaching a high distinguishing ability in biosensing

Recent advances in the control of molecular engineering architectures have allowed unprecedented ability of molecular recognition in biosensing, with a promising impact for clinical diagnosis and environment control. The availability of large amounts of data from electrical, optical, or electrochemical measurements requires, however, sophisticated data treatment in order to optimize sensing performance. In this study, we show how an information visualization system based on projections, referred to as Projection Explorer (PEx), can be used to achieve high performance for biosensors made with nanostructured films containing immobilized antigens. As a proof of concept, various visualizations were obtained with impedance spectroscopy data from an array of sensors whose electrical response could be specific toward a given antibody (analyte) owing to molecular recognition processes. In addition to discussing the distinct methods for projection and normalization of the data, we demonstrate that an excellent distinction can be made between real samples tested positive for Chagas disease and Leishmaniasis, which could not be achieved with conventional statistical methods. Such high performance probably arose from the possibility of treating the data in the whole frequency range. Through a systematic analysis, it was inferred that Sammon's mapping with standardization to normalize the data gives the best results, where distinction could be made of blood serum samples containing 10(-7) mg/mL of the antibody. The method inherent in PEx and the procedures for analyzing the impedance data are entirely generic and can be extended to optimize any type of sensor or biosensor.     

Rapid and high-performance analysis of thyreostatic drug residues in urine using gas chromatography-mass spectrometry

A more sensitive method was developed using the hyphenated technique of gas chromatography-mass spectrometry (GC-MS) supplementary to the official high-performance thin-layer chromatography (HPTLC) method. Even combined with less efficient extraction and clean-up methods, GC-MS is able to lower the detection limit to less than 50 ppb. The powerful technique of GC-MS-MS is tried out to reduce the detection limit even more, in combination with simplified extraction methods. This time-saving approach combined with the increase in sensitivity is of great importance for a routine technique.     

On second order differential equations with state-dependent delay

We study existence and uniqueness of solutions for a general class of second order abstract differential equations with state-dependent delay. Some examples related to partial differential equations with state dependent delay are presented.     

New benzo[h]quinoline-based ligands and their pincer Ru and Os complexes for efficient catalytic transfer hydrogenation of carbonyl compounds

New benzo[h]quinoline ligands (HCN'N) containing a CHRNH2 (R=H (a), Me (b), tBu (c)) function in the 2-position were prepared starting from benzo[h]quinoline N-oxide (in the case of ligand a) and 2-chlorobenzo[h]quinoline (for ligands b and c). These compounds were used to prepare ruthenium and osmium complexes, which are excellent catalysts for the transfer hydrogenation (TH) of ketones. The reaction of a with [RuCl2(PPh3)3] in 2-propanol at reflux afforded the terdentate CN'N complex [RuCl(CN'N)(PPh3)2] (1), whereas the complexes [RuCl(CN'N)(dppb)] (2-4; dppb=Ph2P(CH2)4PPh2) were obtained from [RuCl2(PPh3)(dppb)] with a-c, respectively. Employment of (R,S)-Josiphos, (S,R)-Josiphos*, (S,S)-Skewphos, and (S)-MeO-Biphep in combination with [RuCl2(PPh3)3] and ligand a gave the chiral derivatives [RuCl(CN'N)(PP)] (5-8). The osmium complex [OsCl(CN'N)(dppb)] (12) was prepared by treatment of [OsCl2(PPh3)3] with dppb and ligand a. Reaction of the chloride 2 and 12 with NaOiPr in 2-propanol/toluene afforded the hydride complexes [MH(CN'N)(dppb)] (M=Ru 10, Os 14), through elimination of acetone from [M(OiPr)(CN'N)(dppb)] (M=Ru 9, Os 13). The species 9 and 13 easily reacted with 4,4'-difluorobenzophenone, via 10 and 14, respectively, affording the corresponding isolable alkoxides [M(OR)(CN'N)(dppb)] (M=Ru 11, Os 15). The complexes [MX(CN'N)(P2)] (1-15) (M=Ru, Os; X=Cl, H, OR; P=PPh3 and P2=diphosphane) are efficient catalysts for the TH of carbonyl compounds with 2-propanol in the presence of NaOiPr (2 mol %). Turnover frequency (TOF) values up to 1.8x10(6) h(-1) have been achieved using 0.02-0.001 mol % of catalyst. Much the same activity has been observed for the Ru--Cl, --H, --OR, and the Os--Cl derivatives, whereas the Os--H and Os--OR derivatives display significantly lower activity on account of their high oxygen sensitivity. The chiral Ru complexes 5-8 catalyze the asymmetric TH of methyl-aryl ketones with TOF approximately 10(5) h(-1) at 60 degrees C, up to 97 % enatiomeric excess (ee) and remarkably high productivity (0.005 mol % catalyst loading). High catalytic activity (TOF up to 2.2x10(5) h(-1)) and enantioselectivity (up to 98 % ee) have also been achieved with the in-situ-generated catalysts prepared from [MCl2(PPh3)3], (S,R)-Josiphos or (S,R)-Josiphos*, and the benzo[h]quinoline ligands a-c.     

Osmium pyme complexes for fast hydrogenation and asymmetric transfer hydrogenation of ketones

The osmium compound trans,cis-[OsCl2(PPh3)2(Pyme)] (1) (Pyme=1-(pyridin-2-yl)methanamine), obtained from [OsCl2(PPh3)3] and Pyme, thermally isomerizes to cis,cis-[OsCl2(PPh3)(2)(Pyme)] (2) in mesitylene at 150 degrees C. Reaction of [OsCl2(PPh3)3] with Ph2P(CH2)(4)PPh2 (dppb) and Pyme in mesitylene (150 degrees C, 4 h) leads to a mixture of trans-[OsCl2(dppb)(Pyme)] (3) and cis-[OsCl2(dppb)(Pyme)] (4) in about an 1:3 molar ratio. The complex trans-[OsCl2(dppb)(Pyet)] (5) (Pyet=2-(pyridin-2-yl)ethanamine) is formed by reaction of [OsCl2(PPh3)3] with dppb and Pyet in toluene at reflux. Compounds 1, 2, 5 and the mixture of isomers 3/4 efficiently catalyze the transfer hydrogenation (TH) of different ketones in refluxing 2-propanol and in the presence of NaOiPr (2.0 mol %). Interestingly, 3/4 has been proven to reduce different ketones (even bulky) by means of TH with a remarkably high turnover frequency (TOF up to 5.7 x 10(5) h(-1)) and at very low loading (0.05-0.001 mol %). The system 3/4 also efficiently catalyzes the hydrogenation of many ketones (H2, 5.0 atm) in ethanol with KOtBu (2.0 mol %) at 70 degrees C (TOF up to 1.5 x 10(4) h(-1)). The in-situ-generated catalysts prepared by the reaction of [OsCl2(PPh3)3] with Josiphos diphosphanes and (+/-)-1-alkyl-substituted Pyme ligands, promote the enantioselective TH of different ketones with 91-96 % ee (ee=enantiomeric excess) and with a TOF of up to 1.9 x 10(4) h(-1) at 60 degrees C.     

Three polymorphic forms of the co-crystal 4,4'-bipyridine/pimelic acid and their structural, thermal, and spectroscopic characterization

Three crystal forms of the co-crystal 4,4'-bipy/pimelic acid (bipy: bipyridine), [NH(4)C(5)-C(5)H(4)N][HOOC(CH(2))(5)COOH], have been prepared and their relationship investigated by single-crystal X-ray diffraction, variable-temperature X-ray powder diffraction, differential scanning calorimetry and solid-state NMR spectroscopy. Both X-ray and NMR spectroscopic results indicate that no proton transfer takes place, that is, the three crystal forms are true co-crystals of neutral molecules. Forms I and II both convert into Form III at high temperature, Forms II and III being the thermodynamically stable forms at room and high temperature, respectively.     

Noncovalent interactions between ([18]crown-6)-tetracarboxylic acid and amino acids: electrospray-ionization mass spectrometry investigation of the chiral-recognition processes

Chiral recognition of enantiomers by host compounds is one of the most challenging topics in modern host-guest chemistry. Amongst the well-established methods, mass spectrometry (MS) is increasingly used nowadays, due to its low detection limit, short analysis time, and suitability for analyzing mixtures and for studying chiral effects in the gas phase. The development of electrospray-ionization (ESI) techniques provides an invaluable tool to study, in the gas phase, diastereoisomeric complex ions prepared from enantiomer ions and a chiral selector. This paper reports on an ESIMS and ESIMSMS study of the molecular mechanisms that intervene in the chiral-recognition phenomena observed between amino acids and a chiral crown ether. The modified crown ether, namely (+)-([18]crown-6)-2,3,11,12-tetracarboxylic acid, is used as the chiral selector when covalently bound on a stationary phase in liquid chromatography. This study was stimulated by the fact that, except with threonine and proline, consistent elution orders were observed, which indicates that the D enantiomers interact more strongly with the chiral selector than the L enantiomers. For proline, the lack of a primary amino group is likely to be responsible for the nonresolution of the two forms, whereas the second stereogenic center on threonine could explain the reversed elution order. In light of those observations, we performed mass spectrometry experiments to understand more deeply the enantiomeric recognition phenomena, both in solution by the enantiomer-labeled guest method and in the gas phase by gas-phase ligand-exchange ion/molecule reactions. The results have been further supported by quantum chemical calculations. One of the most interesting features of this work is the identification of a nonspecific interaction between proline and the crown ether upon ESIMS analysis.     

Electronic and infrared spectroscopy of jet-cooled (+/-)-cis-1-amino-indan-2-ol hydrates

The role of conformational isomerism in molecular interaction has been studied using the example of jet-cooled complexes of (+/-)-cis-1-amino-indan-2-ol with water. The two formerly evidenced conformers of (+/-)-cis-1-amino-indan-2-ol easily form hydrates and dihydrates, which have been studied by means of laser-induced fluorescence and IR/UV double resonance spectroscopy, as well as ab initio calculations. All the 1 : 1 and 1 : 2 complexes with water evidenced in this work involve "ring" structures, in which the water monomer or dimer acts as an acceptor from the NH(2) and a donor to the OH groups of (+/-)-cis-1-amino-indan-2-ol. However, the water lies externally to the indan frame in the hydrates of conformer I of (+/-)-cis-1-amino-indan-2-ol, which possesses axial NH(2) and equatorial OH groups, and above it for the hydrates with the less stable conformer II, with equatorial NH(2) and axial OH groups. Consequently, the different steric constraints which exist in the two conformers result in different hydrogen bond topologies, with an additional OH[dot dot dot]pi interaction for the hydrates of conformer II.