Polystyrene-supported (R)-2-piperazino-1,1,2-triphenylethanol: a readily available supported ligand with unparalleled catalytic activity and enantioselectivity

A very active and highly enantioselective catalytic resin, designed for minimal perturbation of the catalytic center by the polymer matrix, has been assembled in two steps from (S)-triphenylethylene oxide, piperazine, and Merrifield resin and tested in the enantioselective ethylation of aldehydes. 1-Arylpropanols of 94-95% ee are obtained in high yield by the use of only 2 mol % of catalytic resin at 0 degrees C for 4 h.     

Peptide dendrimers based on polyproline helices

We present a new family of peptide dendrimers based on polyproline helices and cis-4-amino-L-proline as a branching unit. Dendrimers were synthesized by a convergent solid-phase peptide synthesis approach. The conformational transition between polyproline type I helix and polyproline type II helix was observed by circular dichroism in branched polyproline building blocks with more than 14 proline residues and in the resulting dendrimers. Both linear and dendritic polyprolines were found to be actively internalized by rat kidney cells. Preliminary results show that the antibiotic ciprofloxacin form complexes with branched polyproline chains in 99.5% propanol.     

High conversion of olefins to cis-diols by non-heme iron catalysts and H2O2

Efficient and highly stereoselective oxidation of olefins to cis-diols as the major product is obtained by using biomimetic non-heme FeII catalysts in combination with H2O2.     

The role of intermolecular and molecule-substrate interactions in the stability of alkanethiol nonsaturated phases on Au(111)

The structure and stability of alkanethiols self-assembled on Au(111) have been studied as a function of the molecular chain length by means of atomic force microscopy (AFM) and grazing incidence X-ray diffraction (GIXD). Below saturation, phases consisting of molecules with different tilt angles and periodicities are formed. Differences in the mechanical stability of these phases are revealed by AFM experiments and discussed in terms of the competition between intermolecular and molecule-substrate interactions as a function of chain length. For long molecules, intermolecular interactions play a dominant role which stabilizes the formation of closed packed 30 degrees tilted ( radical 3x radical 3)R30 degrees structures. For short molecules, the van der Waals interaction with the gold substrate favors the formation of a 50 degrees tilted phase in which the molecules are arranged in a rectangular configuration.     

Iterative method generated by inverse interpolation with additional evaluations

An improvement of the iterative methods based on one point iteration function, with or without memory, using n points with the same amount of information in each point and generated by the inverse polynomial interpolation is given. The adaptation of the strategy presented here gives a new iteration function with a new evaluation of the function which increases the local order of convergence dramatically. This method is generalized to r evaluations of the function. This method for the computation of solutions of nonlinear equations is interesting when it is necessary to get high precision because it provides a lower cost when we use adaptive multi-precision arithmetics. AMS subject classification 65H05     

The γ‐form of n‐eicosanol

In the crystal of the title compound, C₂₀H₄₂O, the mol­ecules are packed in layers parallel to the (100) plane. The alkyl chains are parallel to the [30] direction and these molecular chains are hydrogen‐bonded into chains parallel to the c axis. All C—C bonds of the alkyl chain show an antiperiplanar (trans) conformation, with a slight deviation from the ideal value (180°) in the C—C bonds close to the hydrogen bonds. The length of the alkyl chain is 27.92 (2) Å and the tilt angle is 59.7 (2)°.     

Excess charge delocalization in organic and biological molecules: some theoretical notions

Theoretical and computational investigations of the excess charge distribution (ECD) in molecular complexes have attracted considerable attention as ECD is closely related to electronic properties of organic semiconductors, such as the efficiency of photoinduced charge separation in organic solar cells and charge transport in DNA and proteins. In this paper, we analyze the ECD in several representative models on the basis of ab initio and DFT calculations. We consider how changes in the reorganization energy, electronic coupling and charge transfer energy affect the ECD in the systems. In particular, we compare ECD in π stacks of polycyclic aromatic hydrocarbons and DNA nucleobases. While the π interaction between subunits in the systems is similar in both cases, ECD is quite different: the excess charge is found to be completely delocalized over the hydrocarbon stacks but strongly confined to a single nucleobase in DNA stacks. We also discuss the effects of conformational fluctuations on ECD in the stacks. Finally, ECD in amino acids and its dependence on the conformational changes are briefly considered.