Discovery of fluorescent cyanopyridine and deazalumazine dyes using small molecule macroarrays

[structure: see text] Small molecule macroarrays of cyanopyridines and deazalumazines were generated in high purities via spatially addressed synthesis on planar cellulose supports. Examination of the spectral properties of the heterocycles both on and off of the planar support revealed a set of promising new fluorescent dyes that exhibit high quantum yields, low pH dependence, and high sensitivity to solvent polarity.     

Poly(methylene green) employed as molecularly imprinted polymer matrix for electrochemical sensing

This paper describes the development of a molecularly imprinted polymer (MIP) for theophylline that can be used for electrochemical sensing. Theophylline is a commonly used medication for the treatment of asthma. Due to its very narrow therapeutic index, it may have toxic and potentially fatal effects on the individual. Electrochemical detection of theophylline is difficult, because its molecular structure and standard reduction potential are very similar to that of caffeine. A new method for fabricating molecularly imprinted polymers is proposed utilizing methylene green. Poly(methylene green)(PMG), prepared by electropolymerization of an azine, methylene green, was imprinted for theophylline. PMG-based MIP-coated electrodes showed sensitivity towards the presence of the imprint molecule in solutions, as well as selectivity for the imprint over the interferent molecule caffeine. The PMG-based MIP-coated electrode described in this paper had an improved selectivity factor and reproducibility compared to other theophylline-imprinted MIP-coated electrodes in literature.     

Studies on the mechanism of B(C(6)F(5))(3)-catalyzed hydrosilation of carbonyl functions

The strong organoborane Lewis acid B(C(6)F(5))(3) catalyzes the hydrosilation (using R(3)SiH) of aromatic and aliphatic carbonyl functions at convenient rates with loadings of 1-4%. For aldehydes and ketones, the product silyl ethers are isolated in 75-96% yield; for esters, the aldehydes produced upon workup of the silyl acetal products can be obtained in 45-70% yield. Extensive mechanistic studies point to an unusual silane activation mechanism rather than one involving borane activation of the carbonyl function. Quantitative kinetic studies show that the least basic substrates are hydrosilated at the fastest rates; furthermore, increased concentrations of substrate have an inhibitory effect on the observed reaction rate. Paradoxically, the most basic substrates are reduced selectively, albeit at a slower rate, in competition experiments. The borane thus must dissociate from the carbonyl to activate the silane via hydride abstraction; the incipient silylium species then coordinates the most basic function, which is selectively reduced by [HB(C(6)F(5))(3)](-). In addition to the kinetic data, this mechanistic proposal is supported by a kinetic isotope effect of 1.4(5) for the hydrosilation of acetophenone, the observation that B(C(6)F(5))(3) catalyzes H/D and H/H scrambling in silanes in the absence of substrate, computational investigations, the synthesis of models for proposed intermediates, and other isotope labeling and crossover experiments.     

Chromatographic comparison of the relative Lewis acidities of alumina and zirconia

Summary The chromatographic properties of alumina and zirconia are compared with respect to their relative Lewis acidities when parabenzoic acid derivatives are chromatographed in aqueous media. Weak Bronsted acids show similar capacity factors on alumina and zirconia. As solute Bronsted acidity increases, the capacity factor increases more significantly on the zirconia phase than on the alumina phase. Efficiencies, as determined by the dominant desorption rate constants, are generally comparable between the two phases with alumina showing slightly higher efficiencies, Secondary interactions between the solutes and the stationary phases are nearly absent on zirconia but are very apparent on the alumina phase.     

The structure of wholly aromatic polyesters with bulky side chains: Poly(p-phenylene phenylthioterephthalate)

Poly(p-phenylene phenylthio-terephthalate) (PPTT) forms nematic melts and is highly crystalline in the solid state, despite the probable random 2- and 3-dispo-sition of the S-phenyl substituents. The X-ray pattern of melt-spun fibers of PPTT contains 24 Bragg reflections that are indexed by a monoclinic unit cell with dimensions a = 28.6 Å, b = 4.81 Å, c = 12.57 Å (fiber axis), and γ= 101.6°. The cell contains monomer units of four chains that are arranged in pairs with the thiophenyl side chains interdigitated; successive pairs of chains are staggered by about c/2. We used molecular mechanics modeling to simulate arrays of chains with random 2- and 3-disposition of the side chains on the terephthalic acid units and compared the results with those for an idealized structure in which all the substituents were at the 2-position. The refined model for random substitution is more distorted, but the average separations of the monomer units are within the experimental errors of the observed unit cell dimensions, and their standard deviations are very similar to those derived from the line-broadening data. The potential energy of the model with random substitution is only about 1.9 kcal/mol of monomer higher than that for the model with all-2-substitution, indicating random substitution is not a major problem to the formation of an ordered structure. Compared to the structure formed by the analogous polyester, poly(p-phenylene phenylterephthalate) (PPT), the additional flexibility due to the thioether linkage between the backbone and phenyl side groups in PPTT allows better chain packing both within and between the layers of stacked chains.     

Tuning peptoid secondary structure with pentafluoroaromatic functionality: a new design paradigm for the construction of discretely folded peptoid structures

Peptoids, or oligomers of N-substituted glycine, are an important class of non-native polymers whose close structural similarity to natural alpha-peptides and ease of synthesis offer significant advantages for the study of biomolecular interactions and the development of biomimetics. Peptoids that are N-substituted with alpha-chiral aromatic side chains have been shown to adopt either helical or "threaded loop" conformations, depending upon solvent and oligomer length. Elucidation of the factors that impact peptoid conformation is essential for the development of general rules for the design of peptoids with discrete and novel structures. Here, we report the first study of the effects of pentafluoroaromatic functionality on the conformational profiles of peptoids. This work was enabled by the synthesis of a new, alpha-chiral amine building block, (S)-1-(pentafluorophenyl)ethylamine (S-2), which was found to be highly compatible with peptoid synthesis (delivering (S)-N-(1-(pentafluorophenyl)ethyl)glycine oligomers). The incorporation of this fluorinated monomer unit allowed us to probe both the potential for pi-stacking interactions along the faces of peptoid helices and the role of side chain electrostatics in peptoid folding. A series of homo- and heteropeptoids derived from S-2 and non-fluorinated, alpha-chiral aromatic amide side chains were synthesized and characterized by circular dichroism (CD) and nuclear magnetic resonance (NMR) spectroscopy. Enhancement of pi-stacking by quadrupolar interactions did not appear to play a significant role in stabilizing the conformations of heteropeptoids with alternating fluorinated and non-fluorinated side chains. However, incorporation of (S)-N-(1-(pentafluorophenyl)ethyl)glycine monomers enforced helicity in peptoids that typically exhibit threaded loop conformations. Moreover, we found that the incorporation of a single (S)-N-(1-(pentafluorophenyl)ethyl)glycine monomer could be used to selectively promote looped or helical structure in this important peptoid class by tuning the electronics of nearby heteroatoms. The strategic installation of this monomer unit represents a new approach for the manipulation of canonical peptoid structure and the construction of novel peptoid architectures.     

Comparision of varuious bulk fluids and modifiers as near-crtical mobile phases on a polymeric column using linear solvatio energy realationships

Linear solvation energy realationships (LSERS) were used to qunatitatively compare the relative contributions of dipolarity/polarizability, hydrogen bonding, and other types of intermolecular interactions to retention and selectivity using various bulk moblie phase component. Using experimental condition which differ only by the compostion of the bulk moble phase component, the factors which cause selctivity to differ between HPLC, subcritical fluid chromatography and supercritical fluid charomatography were decovoluted. Heptance-based HPLC mobile phases showed superior selectivities towards analytes which differ in hydrogen bond donating ability, gas-to-hexadecane partion coefficint and dipolarity/ploarizability. subcritical fluid chromatography with HFC-134a (1, 1, 1, 2-tetrafluoroethane) as the bulk fluid produced superior seclectivities for which differ in hydrogen bond accepting ability and execess molar refraction properties. Many of these factors showed temperature dependences which act to attenuate or accenture the particular intermolcular interaction.     

Ion- and ligand-exchange chromatography of proteins using porous zirconium oxide supports in organic and inorganic Lewis base eluents.

The applicability of an eluotropic scale pertaining to the desorption of low molecular weight Lewis base solutes from zirconium oxide is examined for its ability to rationalize the retention of proteins on this substrate. The strongest Lewis base eluents (phosphate and fluoride) are able to bring about elution of nearly all proteins provided that their initial mobile phase concentration almost saturates the eluent's adsorption isotherm. In contrast, weaker Lewis bases such as borate, sulfate and bromide are able to elute only those proteins which are retained primarily by ionic interactions. In weak eluents, proteins that contain a large number of accessible Lewis base sites are not eluted from the support. The effect of ionic strength and a variety of Lewis base eluents were also examined.