Evolution of Organized Lariat Ether Alcohol and Diol Hydrate Macrostructures in the Solid State

Lariat ether alcohols and diols derived from dibenzo-14-crown-4crystallize in the anhydrous form or as hydrogen-bondedmonohydrates or networks depending upon thepolyether ring substitutents and the composition of the aqueous organic crystallization solvent. Supramolecular structures are created when the lariat ether alcohol sym-(hydroxy)dibenzo-14-crown-4 (1) with ``sticky ends' of ether oxygens and hydroxyl protons, hydrogen bond to each other via bridging water molecules to form three-dimensional networks. For crystallization of 1 from 30% aqueous acetonitrile, this self-association is sufficiently strong to spontaneously generate a supramolecular structure with water channels.     

Mesomorphism of a tetrahedral zinc complex

Thermotropic smectic phases have been observed for the first time in a zinc coordination complex with tetrahedral geometry; this complex, which contains the pyrazole dimer bis[3,5-bis(p-decyloxyphenyl)pyrazolyl]ethane as the ligand, exhibits fluorescence.     

Synthesis and selectivity of sym-hydroxydibenzo-14crown-4 ionophores for protons,alkali metal cations,and alkaline earth cations in polymeric membranes

Six derivatives of sym-hydroxydibenzo-14-crown-4 have been prepared and incorporated into solvent-polymeric membranes. Responses of the membranes to protons, alkali metal cations, and alkaline earth cations have been determined. The preferred uptake of protons is attributed to proton complexation by stable crown ether alcohol and diol monohydrate species.     

Unexpected role of O-2 "protecting" groups of glycosyl donors in mediating regioselective glycosidation

Glycosidation of several vicinal diols reveals that exquisite regioselectivity can be achieved by using 2-O-benzoyl n-pentenyl glycoside donors and/or their cyclic 1,2-ortho ester counterparts. The regioselective preferences for both are the same, although ratios and yields may differ. In stark contrast, glycosidation of the diols with the corresponding 2-O-benzylated donors gives poor, if any, regioselectivity.     

One pot/two donors/one diol give one differentiated trisaccharide: powerful evidence for reciprocal donor-acceptor selectivity (RDAS)

Three component, one-pot reactions involving equimolar amounts of the acceptor diol and both armed and disarmed donors presented simultaneously, produce a single double-differential glycosidation product; this phenomenon provides evidence for Reciprocal Donor Acceptor Selectivity (RDAS).     

Algebraic eigenspaces of nonnegative matrices

The Perron-Frobenius theory for square, irreducible, nonnegative matrices is generalized by studying the structure of the algebraic eigenspace of an arbitrary square nonnegative matrix corresponding to its spectral radius. We give a constructive proof that this subspace is spanned by a set of semipositive vectors and give a combinatorial characterization of both the index of the spectral radius and dimension of the algebraic eigenspace corresponding to the spectral radius. This involves a detailed study of the standard block triangular representation of nonnegative matrices by giving special attention to those blocks on the diagonal having the same spectral radius as the original matrix. We also show that the algebraic eigenspace corresponding to the spectral radius contains a semipositive vector having the largest set of positive coordinates among all vectors in this subspace.     

A class of “onto” multifunctions

A convex valued, upper continuous multifunction with pointed closed convex domain is proved to be onto, if there is a selection with certain coercive properties and if the selection for each point lies in the affine hull of the smallest face of the domain containing the point. The proof uses a piecewise affine homotopy construction. We apply the onto theorem to an approximation of a network of servers and show that arbitrary congestion levels can be realized with appropriate arrival levels.This research is based on work supported in part by the National Science Foundation Grant DMS 92-07409, by the Department of Energy Grant DE-FG03-87-ER-25028, by the United States—Israel Binational Science Foundation Grant 85-00295 and by ONR Grant N00014-92-J1142.     

Correlated majority model

We extend the bichromatic majority model by including (one-dimensional isotropic) correlations and numerically discuss, through Monte Carlo simulations, the simple, 1/3, and 2/3 majority rules. We calculate, as functions of the concentration and correlation degree, the mean finite cluster size, and the order parameterm as well as their respective critical exponents and. We find1 regardless of the correlation degree or the type of majority. Also, a supplementary divergence of is observed at the>0 borderline.     

Mechanism of the reaction of the [W3S4H3(dmpe)3]+ cluster with acids: evidence for the acid-promoted substitution of coordinated hydrides and the effect of the attacking species on the kinetics of protonation of the metal-hydride bonds

The cluster [W(3)S(4)H(3)(dmpe)(3)](+) (1) (dmpe=1,2-bis(dimethylphosphino)ethane) reacts with HX (X=Cl, Br) to form the corresponding [W(3)S(4)X(3)(dmpe)(3)](+) (2) complexes, but no reaction is observed when 1 is treated with an excess of halide salts. Kinetic studies indicate that the hydride 1 reacts with HX in MeCN and MeCN-H(2)O mixtures to form 2 in three kinetically distinguishable steps. In the initial step, the W-H bonds are attacked by the acid to form an unstable dihydrogen species that releases H(2) and yields a coordinatively unsaturated intermediate. This intermediate adds a solvent molecule (second step) and then replaces the coordinated solvent with X(-) (third step). The kinetic results show that the first step is faster with HCl than with solvated H(+). This indicates that the rate of protonation of this metal hydride is determined not only by reorganization of the electron density at the M-H bonds but also by breakage of the H-X or H(+)-solvent bonds. It also indicates that the latter process can be more important in determining the rate of protonation.     

A Concise Synthesis of a BODIPY-Labeled Tetrasaccharide Related to the Antitumor PI-88

A convergent synthetic route to a tetrasaccharide related to PI-88, which allows the incorporation of a fluorescent BODIPY-label at the reducing-end, has been developed. The strategy, which features the use of 1,2-methyl orthoesters (MeOEs) as glycosyl donors, illustrates the usefulness of suitably-designed BODIPY dyes as glycosyl labels in synthetic strategies towards fluorescently-tagged oligosaccharides.