Directed evolution and substrate specificity profile of homing endonuclease I-SceI

The laboratory evolution of enzymes with tailor-made DNA cleavage specificities would represent new tools for manipulating genomes and may enhance our understanding of sequence-specific DNA recognition by nucleases. Below we describe the development and successful application of an efficient in vivo positive and negative selection system that applies evolutionary pressure either to favor the cleavage of a desired target sequence or to disfavor the cleavage of nontarget sequences. We also applied a previously described in vitro selection method to reveal the comprehensive substrate specificity profile of the wild-type I-SceI homing endonuclease. Together these tools were used to successfully evolve mutant I-SceI homing endonucleases with altered DNA cleavage specificities. The most highly evolved enzyme cleaves the target mutant DNA sequence with a selectivity that is comparable to wild-type I-SceI's preference for its cognate substrate.     

Synthesis of fluorescent analogues of the anticancer natural products 4-hydroxyphenylmethylene hydantoin and delta-tocotrienol

4-Hydroxyphenylmethylene hydantoin (PMH, 1), isolated from the Red Sea sponge Hemimycale arabica, and delta-tocotrienol (3), isolated from the tocotrienol-rich fraction of palm oil, are important antimetastatic and antiproliferative natural products that proved effective against metastatic prostate and breast cancers, respectively. New fluorescent derivatives of PMH (2) and delta-tocotrienol (4) were synthesized by Steglich esterification. Both 2 and 4 retained good anti-migratory and antiproliferative activities, respectively. Fluorescent analogues 2 and 4 can be used for the identification of molecular targets of 1 and 3 in tumor cell cultures.     

Crystal → nematic phase transition in the liquid crystalline system 1‐isothiocyanato‐4‐(trans‐4‐propylcyclohexyl) benzene (3CHBT) probed by temperature‐dependent micro‐Raman study and DFT calculations

Raman spectra of 3CHBT in unoriented form were recorded at 14 different temperature measurements in the range 25–55 °C, which covers the crystal → nematic (N) phase transition, and the Raman signatures of the phase transition were identified. The wavenumber shifts and linewidth changes of Raman marker bands with varying temperature were determined. The assignments of important vibrational modes of 3CHBT were also made using the experimentally observed Raman and infrared spectra, calculated wavenumbers, and potential energy distribution. The DFT calculations using the B3LYP method employing 6‐31G functional were performed for geometry optimization and vibrational spectra of monomer and dimer of 3CHBT. The analysis of the vibrational bands, especially the variation of their peak position as a function of temperature in two different spectral regions, 1150–1275 cm⁻¹ and 1950–2300 cm⁻¹, is discussed in detail. Both the linewidth and peak position of the ( C H ) in‐plane bending and ν(NCS) modes, which give Raman signatures of the crystal → N phase transition, are discussed in detail. The molecular dynamics of this transition has also been discussed. We propose the co‐existence of two types of dimers, one in parallel and the other in antiparallel arrangement, while going to the nematic phase. The structure of the nematic phase in bulk has also been proposed in terms of these dimers. The red shift of the ν(NCS) band and blue shift of almost all other ring modes show increased intermolecular interaction between the aromatic rings and decreased intermolecular interaction between two  NCS groups in the nematic phase. Copyright © 2009 John Wiley & Sons, Ltd.     

Infinite Baer nets

In this article, the structure of the collineation groups which fix point-Baer subplanes in vector space nets over skewfields is completely determined. The theory depends on whether there are one, two, or at least three point-Baer subplanes sharing the same parallel classes and a common point.The authors are indebted to the referee for helpful suggestions.     

Almost Desarguesian Maximal Partial Spreads

Constructions are given of various classesof maximal partial spreads in PG(3,2^r) whose partialspreads consist of q/2 reguli sharing a line. Further,characterization results are given for the main classes of constructedmaximal partial spreads.     

Efficient and strategy-proof social choice when preferences are single-dipped

We study the problem of locating a single public good along a segment when agents have single-dipped preferences. We ask whether there are unanimous and strategy-proof rules for this model. The answer is positive and we characterize all such rules. We generalize our model to allow the set of alternatives to be unbounded. If the set of alternatives does not have a maximal and a minimal element, there is no meaningful notion of efficiency. However, we show that the range of every strategy-proof rule has a maximal and a minimal element. We then characterize all strategy-proof rules.     

Quadratic Extensions of Flag-transitive Planes

In this article, the finite translation planes which are quadratic extensions of flag-transitive subplanes are classified as either Desarguesian or Hall.     

Phosphomolybdic acid: a highly efficient solid acid catalyst for the synthesis of trans-4,5-disubstituted cyclopentenones

The furan-2-yl(phenyl)methanol undergoes smooth aza-Piancatelli rearrangement with aryl amines in the presence of 0.03 mol % phosphomolybdic acid in acetonitrile under reflux conditions to afford the corresponding trans-4,5-disubstituted cyclopentenone derivatives in good yields with high selectivity in short reaction time.     

Propane σ‐Complexes on PdO(101): Spectroscopic Evidence of the Selective Coordination and Activation of Primary CH Bonds

Achieving selective C? H bond cleavage is critical for developing catalytic processes that transform small alkanes to value‐added products. The present study clarifies the molecular‐level origin for an exceptionally strong preference for propane to dissociate on the crystalline PdO(101) surface via primary C? H bond cleavage. Using reflection absorption infrared spectroscopy (RAIRS) and density functional theory (DFT) calculations, we show that adsorbed propane σ‐complexes preferentially adopt geometries on PdO(101) in which only primary C? H bonds datively interact with the surface Pd atoms at low propane coverages and are thus activated under typical catalytic reaction conditions. We show that a propane molecule achieves maximum stability on PdO(101) by adopting a bidentate geometry in which a H? Pd dative bond forms at each CH₃ group. These results demonstrate that structural registry between the molecule and surface can strongly influence the selectivity of a metal oxide surface in activating alkane C? H bonds.