Chemoenzymatic synthesis and fluorescent visualization of cell-surface selectin-bound sialyl Lewis x derivatives

Sialyl Lewis x (sLe(x)) derivatives conjugated to readily visualized molecular labels are useful chemical probes to study selectin-carbohydrate interactions. Localization of the selectins on the surface of leukocytes and activated endothelial cells can be detected through fluorescence of bound selectin ligands. Herein we present a short chemoenzymatic synthesis of a fluorescently labeled bivalent sLe(x) conjugate. The use of an amino-substituted monovalent sLe(x) to obtain fluorescent- and biotin-labeled sLe(x) derivatives is also described. The cell-staining utility of the fluorescent sLe(x) conjugates is demonstrated for a HUVEC cell line expressing E-selectin and for CHO-K1 cells expressing either L- or E-selectin.     

The radical anion of 1,2:9,10-dibenzo[2.2]paracyclophane.. An ESR,ENDOR, and TRIPLE resonance study

The radical anion of 1,2:9,10-dibenzo[2.2]paracyclophane ( 3 ) has been studied by ESR, ENDOR, and TRIPLE resonance spectroscopy under a variety of experimental conditions. The coupling constants of the eight protons in the deck-benzene rings, and of the four inner and four outer protons in the side-benzene rings are 0.234, 0.123, and 0.036 mT, respectively (solvent: 1,2-dimethoxyethane; counterion: K⁺). All three values have the same sign which is predicted to be negative. Comparison of the largest coupling constant (0.234 mT) with the corresponding value (0.297 mT) for the radical anion of the parent [2.2]paracyclophane ( 1 ) points to similar nodal properties of the singly occupied orbitals in and . Notwithstanding this similarity, seems to associate less readily than with alkali metal counterions, since tight ion pairs of with K⁺ are formed only in solvents of low solvating power. Effects of conformational changes on the ESR spectra, such as those previously observed for the radical anion of [2.2]paracyclophane-1,9-diene ( 2 ), are not apparent for in the temperature range of investigation. Hyperfine data are also reported for the radical anion of a derivative 4 which has a CH₃ substituent in one of the side-benzene rings of 3 .     

The Mutual Resoluton of Dl-ephedrine and N-Benzyloxycarbonyl-Dl-Amino Acids

D(-)-Ephedrine was prepared by resolving the racemate through its N-benzyloxycarbonyl-L-phenylalanine salt in ether solution. The L(+)-ephedrine in mother liquid was recovered and precipitated exclusivly with N -benzyloxycarbonyl-L-alanine in ethyl acetate. The amino acid derivatives were recovered from the salts by acid decomposition and the optically pure ephedrine was also recovered, which was again useful for the resolution of racemic amino acid derivatives synthesized chemically. Other amino acid derivatves are also tested for the mutual resolution. Mutual resolution was also effected by dissolving DL-ephedrine and N -benzyloxycarbonyl-DL-alanine in ethyl acetate to obtain the optically pure D(-)-ephedrine and N -benzyloxycarbonyl-D-alanine.     

Encoding of polycyclic Si-containing molecules for determining species uniqueness in automated mechanism generation

Automated mechanism generation is an attractive way to understand the fundamental kinetics of complex reaction systems such as silicon hydride clustering chemistry. It relies on being able to tell molecules apart as they are generated. The graph theoretic foundation allows molecules to be identified using unique notations created from their connectivity. To apply this technique to silicon hydride clustering chemistry, a molecule canonicalization and encoding algorithm was developed to handle complex polycyclic, nonplanar species. The algorithm combines the concepts of extended connectivity and the idea of breaking ties to encode highly symmetric molecules. The connected components in the molecules are encoded separately and reassembled using a depth-first search method to obtain the correct string codes. A revised cycle-finding algorithm was also developed to properly select the cycles used for ring corrections when thermodynamic properties were calculated using group additivity. In this algorithm, the molecules are expressed explicitly as trees, and all linearly independent cycles of every size in the molecule are found. The cycles are then sorted according to their size and functionality, and the cycles with higher priorities will be used to include ring corrections. Applying this algorithm, more appropriate cycle selection and more accurate estimation of thermochemical properties of the molecules can be obtained.     

Detection and classification of organophosphate nerve agent simulants using support vector machines with multiarray sensors

The need for rapid and accurate detection systems is expanding and the utilization of cross-reactive sensor arrays to detect chemical warfare agents in conjunction with novel computational techniques may prove to be a potential solution to this challenge. We have investigated the detection, prediction, and classification of various organophosphate (OP) nerve agent simulants using sensor arrays with a novel learning scheme known as support vector machines (SVMs). The OPs tested include parathion, malathion, dichlorvos, trichlorfon, paraoxon, and diazinon. A new data reduction software program was written in MATLAB V. 6.1 to extract steady-state and kinetic data from the sensor arrays. The program also creates training sets by mixing and randomly sorting any combination of data categories into both positive and negative cases. The resulting signals were fed into SVM software for "pairwise" and "one" vs all classification. Experimental results for this new paradigm show a significant increase in classification accuracy when compared to artificial neural networks (ANNs). Three kernels, the S2000, the polynomial, and the Gaussian radial basis function (RBF), were tested and compared to the ANN. The following measures of performance were considered in the pairwise classification: receiver operating curve (ROC) Az indices, specificities, and positive predictive values (PPVs). The ROC Az) values, specifities, and PPVs increases ranged from 5% to 25%, 108% to 204%, and 13% to 54%, respectively, in all OP pairs studied when compared to the ANN baseline. Dichlorvos, trichlorfon, and paraoxon were perfectly predicted. Positive prediction for malathion was 95%.     

Electrogenerated chemiluminescence. 81. Influence of donor and acceptor substituents on the ECL of a spirobifluorene-bridged bipolar system

The electrochemistry and radical ion annihilation electrogenerated chemiluminescence (ECL) of 9,9'-spirobifluorene-bridged bipolar systems containing 1,3,4-oxadiazole-conjugated oligoaryl and triarylamine substituents were investigated. The stability of the oxidized spirobifluorenes was improved by functionalization with triarylamine centers. These donor-acceptor (DA) compounds exhibited a good fluorescence efficiency with an emission maximum that correlated with the potential difference between radical anion and cation formation, suggesting a charge transfer (CT) emission band. An ECL mechanism based on the formation of the CT excited state by radical ion annihilation or production of the triplet state followed by triplet-triplet annihilation, with perhaps some excimer contribution, is proposed.