Weak C-H/pi interaction participates in the diastereoselectivity of a host-guest complex in the presence of six strong hydrogen bonds

[structure: see text] We report a study of the interaction between methylmethanetriacetic acid (MMTA) and a tripodal amidopyridine receptor 1, where the geometry of the binding is in part governed by a weak C-H/pi interaction in the presence of six strong N(O)-H.O(N) hydrogen bonds. There are two possible binding geometries for the 1:1 complex 1.MMTA; combining computational and experimental evidence we demonstrate that the endo binding mode is more favorable as the result of a C-H/pi interaction.     

Conformational preferences and self-template macrocyclization of squaramide-based foldable modules

Secondary squaramides have considerable potential as hydrogen bond donors and acceptors. In CHCl(3) both, anti- and syn-squaramide rotamers are observed by NMR. The energetic barrier for anti/syn mutual interconversion determined by complete band shape analysis is approximately 63 kJ mol(-1). As in proline derivatives, a low rotational barrier is crucial for the design of foldable modules. In this paper, folding based on the low rotational barrier of squaramides is driven by donor atoms (N or O) located in the gamma position of an alkyl chain of a secondary squaramide. We demonstrate that the resulting minimal module exists as a folded conformer through the formation of a nine-membered ring stabilized by intramolecular hydrogen bonding. Molecular mechanics calculations and NMR studies support the existence of these folded conformers. The intramolecularly hydrogen bonded conformers are clearly visible even in CHCl(3)-EtOH mixtures. Folding occurs even in pure ethanol. As an indirect test, we studied the effectiveness of macrocyclization reactions in pure ethanol that require an effective templating effect to take place. The high yields obtained support the dominant role of a folded conformer even in this solvent.     

Primely generated refinement monoids

We extend both Dobbertin’s characterization of primely generated regular refinement monoids and Pierce’s characterization of primitive monoids to general primely generated refinement monoids.     

Interplay between cation-π and hydrogen bonding interactions

The interplay between two important non-covalent interactions involving aromatic rings is studied by means of ab initio calculations (MP2/6-31++G^**). They demonstrate that synergetic effects are present in complexes where cation-π and hydrogen bonding interactions coexist. These synergetic effects have been studied using the ‘atoms-in-molecules’ theory and the molecular interaction potential with polarization partition scheme.     

Narcissistic reaction pathways: an example of Maxwell’s theorem of geometrical optics applied to the intrinsic reaction coordinate model

Maxwell’s theorem and the concept of stigmatic transformations that appear in the theory of geometrical optics are extended to the intrinsic reaction coordinate model when it is applied to the specific case of narcissistic reactions.      

Thermal and Mechanical Properties of Polyethylenes Synthesized with Metallocene Catalysts

A series of high density polyethylenes (HDPE) were synthesized via homogeneous polymerization with metallocene catalyst in two different reactors (glass and stainless steel). The thermal and mechanical properties of the polyethylenes, synthesized with two types of reactor and different reaction parameters, are discussed.This revised version was published online in November 2005 with corrections to the Cover Date.