Role of retinoic receptors in lung carcinogenesis

Several in vitro and in vivo studies have examined the positive and negative effects of retinoids (vitamin A analogs) in premalignant and malignant lesions. Retinoids have been used as chemopreventive and anticancer agents because of their pleiotropic regulator function in cell differentiation, growth, proliferation and apoptosis through interaction with two types of nuclear receptors: retinoic acid receptors and retinoid X receptors. Recent investigations have gradually elucidated the function of retinoids and their signaling pathways and may explain the failure of earlier chemopreventive studies

Shape-induced, hexagonal, open frameworks: Rubidium ion complexed cucurbituril

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The efficient resolution of protected diols and hydroxy aldehydes by lipases: Steric auxiliary approach and synthetic applications.

1,n-Diols (n = 2 - 5) and 2-hydroxy aldehydes protected with a steric auxiliary are transformed by Pseudomonas lipases with high enantioselectivity, thus allowing the efficient resolution of these molecules and the synthesis of related derivatives with high optical purity.X1116sciescopu

Self-assembly of interlocked structures and open framework materials using coordination bonds

Syntheses of molecular necklaces and open framework materials using coordiantion bonds are described. In the synthesis of molecular necklaces, the barrel-shape molecule cucurbituril is used as a molecular "bead" and metal ions or metal complexes are used as "glue" or "angle connectors". Two different approaches were taken. In one approach, linear pseudorotaxanes react with Pt(en)(NO3)(2) (en = ethylenediamine) to produce [4]MNs and [5]MNs. In the other approach, a '2 + 2' approach, preorganized, L-shaped pseudorotaxanes containing two molecular "beads" react with a metal ion (or a metal complex with cis vacant coordination sites) to form [5]MNs. Rubidium and cucurbituril form a one-dimensional coordination polymer in the solid state, in which cucurbituril molecules stack atop one another through coordination of their carbonyl groups to the rubidium ions in between. The coordination polymer chains are arranged in such a way as to produce a honeycomb structure with large linear hexagonal channels parallel to the polymer chains.X1116sciescopu

Designed self-assembly of molecular necklaces

This paper reports an efficient strategy to synthesize molecular necklaces, in which a number of small rings are threaded onto a large ring, utilizing the principles of self-assembly and coordination chemistry. Our strategy involves (1) threading a molecular "bead" with a short "string" to make a pseudorotaxane and then (2) linking the pseudorotaxanes with a metal complex with two cis labile ligands acting as an "angle connector" to form a cyclic product (molecular necklace). A 4- or 3-pyridylmethyl group is attached to each end of 1,4-diaminobutane or 1,5-diaminopentane to produce the short "strings" (C4N4(2+), C4N3(2+), C5N4(2+), and C5N3(2+)), which then react with a cucurbituril (CB) "bead" to form stable pseudorotaxanes (PR44(2+), PR43(2+), PR54(2+), and PR53(2+), respectively). The reaction of the pseudorotaxanes with Pt(en)(NO3)(2) (en = ethylenediamine) produces a molecular necklace [4]MN, in which three molecular "beads" are threaded on a triangular framework, and/or a molecular necklace [5]MN, in which four molecular "beads" are threaded on a square framework. Under refluxing conditions, the reaction with PR44(2+) or PR54(2+) yields exclusively [4]MN (MN44T or MN54T, respectively), whereas that with PR432+ or PR532+ produces exclusively [5]MN (MN43S or MN53S, respectively). The products have been characterized by various methods including X-ray crystallography. At lower temperatures, on the other hand, the reaction with PR44(2+) or PR54(2+) affords both [4]MN and [5]MN. The supermolecules reported here are the first series of molecular necklaces obtained as thermodynamic products. The overall structures of the molecular necklaces are strongly influenced by the structures of pseudorotaxane building blocks, which is discussed in detail on the basis of the X-ray crystal structures. The temperature dependence of the product distribution observed in this self-assembly process is also discussed.X11173174sciescopu