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Abstract: Sn n (n =34–44) clusters were studied using a combined method of the genetic algorithm/tight-binding search and the DFT–PBEPBE calculations. Sn n (n =34–44) clusters are shown to favor an assembly motif composed of small stable Sn9 and Sn10 subunits which are connected by cohesive linkages of smaller clusters (Sn1–5). Sn n (n =34–44) clusters were found to transform from a prolate pattern for Sn34,35 to a ‘Y’ pattern for Sn36–39 to a plate motif for Sn40–44. Obvious structural transitions would easily occur at the cross points of binding energy curves when isomers become competitive. [Copyright &y& Elsevier]

The structures of Ge(n) (n=40-44) clusters were searched by genetic algorithm combined with a tight-binding method. First-principles calculations based on density functional theory were performed to further optimize the isomer structures. The calculated results show that Ge(n) (n=40-44) clusters favor platelike structures, consisted of four small magic clusters (Ge(9) or Ge(10)), and a Ge(4) core. The Ge(4) core along with the parts of the four linked small clusters forms a diamond segment. The cluster mobilities of the most stable structures are in good agreement with the experimental data.

We have performed global structural optimizations for neutral lead clusters Pb(n) (n = 2-20) by using a genetic algorithm (GA) coupled with a tight-binding (TB) potential. The low-energy structures identified from a GA/TB search were further optimized at the DFT-PBE level. The calculated results show that the Pb(n) (14 < n

Oligo(ethylene glycols) 1a-h, which are incorporated with one to eight 2,3-naphthylene units, respectively, have been synthesized and characterized. The conformational changes of the new oligomers have been investigated in chloroform-acetonitrile binary solvents by the UV-vis, (1)H NMR, and fluorescent spectroscopy. It has been revealed that the naphthalene units in hexamer 1f, heptamer 1g, and octamer 1h are driven by solvophobic interaction to stack in polar solvents. As a result, compact helical conformations are formed that give rise to a cavity similar to that of 18-crown-6. Shorter oligomers 1b-e exhibit weaker folding tendency. (1)H NMR studies reveal that 1f-h are able to complex ammonium or ethane-1,2-diaminium 19, but not secondary ammonium compounds. The association constants of complexes 1f.19, 1g.19, and 1h.19 in acetonitrile are determined to be 3.5(+/-0.4) x 10(3), 1.0(+/-0.12) x 10(4), and 2.5(+/-0.4) x 10(4) M(-1), respectively, with the (1)H NMR titration method. For comparison, hexamer 22, which incorporates six 1,5-naphthylene units, is also prepared. The UV-vis and fluorescent investigations show that 22 is also able to fold in polar solvents, but no helical structure can be produced due to mismatch of the stacking naphthalene units and consequently there is no obvious complexation between 22 with ethane-1,2-diaminium ion. The structures of the longest foldamer 1h and its complex with 19 have been studied with molecular mechanics calculations. This work represents a new approach to building folding conformations from flexible linear molecules.

Donor-acceptor interaction between electron-rich 1,5-dioxynaphthalene (DAN) and electron-deficient pyromellitic diimide (PDI) has been utilized to induce the formation of a new kind of zipper-featured delta-peptide foldamers. Seven l-ornithine-based delta-peptides 1a-g, in which one to three DNA and PDI units are incorporated to the two ends of the peptide backbones, respectively, have been designed and prepared by the standard liquid-phase synthetic method. (1)H NMR, UV-vis, and fluorescent quenching studies reveal that all the delta-peptides adopt folding conformations in nonpolar chloroform and polar DMF as a result of intramolecular donor-acceptor interaction between the DAN and PDI units. The folding states become more compact for the peptide skeletons possessing more donor-acceptor interacting sites. Variable-temperature UV-vis experiments indicate that, although the folding is a dynamic process, the folding state can remain even at 150 degrees C in DMF. Circular dichroism (CD) investigations reveal that the new generation of delta-peptides have similar folding patterns. A zipper-featured folding motif has been proposed for the new generation of delta-peptide foldamers. Molecular modeling has generated two most stable folding states for the longest delta-peptide 1g, with an energy difference of 26.80 kcal/mol.

[structure: see text] The first class of zipper-shaped artificial duplexes, which are driven by multiple donor-acceptor interactions between electron-rich 1,5-dioxynaphthalene or 1,4-dioxybenzene and electron-deficient pyromellitic dimide units, have been studied in organic media by (1)H NMR, UV-vis, and vapor pressure osmometry. (1)H NMR binding investigations reveal substantial cooperativity of the donor-acceptor interaction in the duplexes.