Molecular recognition. Electrostatic effects in supramolecular self-assembly

A di-positively charged metal-based receptor is shown to form 1:1 or 2:1 association complexes with rigid, linear two-site guests depending on the site separation, suggesting that electrostatic repulsion controls the association nuclearity.     

Compact overtone band carbon monoxide laser

An electric-discharge carbon monoxide broadband overtone laser has been developed. The laser is capable of lasing on CO first overtone bands only (Δv = 2) and delivering up to 12 W cw power at efficiencies of up to 5%. The laser output consists of vibrational-rotational lines of the v = 9 → 7 to v = 35 → 33 overtone bands and covers the spectral range between 2.6 and 3.9 μm. Totally about 40-45 lines could be observed in the laser spectrum simultaneously. A kinetic modeling code has been developed to predict the power, efficiency, and the output spectrum of the CO overtone laser.     

Solution-phase structural characterization of supramolecular assemblies by molecular diffraction

Structures of four molecular squares based on rhenium coordination chemistry have been characterized in the solution phase using pair distribution function (PDF) analyses of wide-angle X-ray scattering measured to better than 1 A spatial resolution. In this report we have focused, in particular, on a comparison of structures for pyrazine- and bipyridine-edged squares measured in solution with structures determined for these molecules in the solid state using X-ray crystallography and models derived from geometry optimization and molecular dynamics simulations using a classical force field. The wide-angle scattering for these assemblies is dominated by pair correlations involving one or more rhenium atoms, with both edge and diagonal Re-Re interactions appearing prominently in PDF plots. The pyrazine square is characterized by a relatively rigid structure in solution, with PDF peak positions and linewidths corresponding closely to those calculated from crystal structure data. For the bipyridine-edged square, the experimental PDF peaks measured along the molecular sides match the positions and linewidths of the PDF peaks calculated from static models. In contrast, PDF peaks measured across the diagonal distances of the molecular square deviate significantly from those calculated from the static crystallographic and energy minimized models. The experimental data are instead indicative of configurational broadening of the diagonal distances. In this respect, molecular dynamics simulations point to the importance of butterfly type motions that modulate the Re-Re diagonal distance. Indeed, the experimental data are reasonably well fit by assuming a bimodal distribution of butterfly conformers differing by approximately 25 degrees in the Re-Re-Re-Re torsion angle. Additionally, the measurements provide evidence for solvent ordering by the supramolecular assemblies detected as regions of solvent association and exclusion.     

CONTROLLING THE 3D NANOSCALE ORGANIZATION OF BULK HETEROJUNCTION POLYMER SOLAR CELLS

In this study,the three dimensional nanoscale organization in the photoactive layers of poly(3-hexylthiophene) (P3HT) and a methanofullerene derivative (PCBM) is revealed by transmission electron tomography.After annealing treatment,either at elevated temperature or during slow solvent evaporation,nanoscale interpenetrating networks are formed with high crystalline order and favorable concentration gradients of both components through the thickness of the photoactive layer.Such a tailored morphology acco...     

Models for capacitated lot-sizing problem with backlogging,setup carryover and crossover

Setup operations are significant in some production environments. It is mandatory that their production plans consider some features, as setup state conservation across periods through setup carryover and crossover. The modelling of setup crossover allows more flexible decisions and is essential for problems with long setup times. This paper proposes two models for the capacitated lot-sizing problem with backlogging and setup carryover and crossover. The first is in line with other models from the literature, whereas the second considers a disaggregated setup variable, which tracks the starting and completion times of the setup operation. This innovative approach permits a more compact formulation. Computational results show that the proposed models have outperformed other state-of-the-art formulation.     

Supramolecular porphyrinic prisms: coordinative assembly and solution phase X-ray structural characterization

Supramolecular porphyrin prisms have been obtained via coordinative self-assembly and characterized by 1H NMR, PFG NMR, electronic absorption spectroscopy and synchrotron-based measurements of solution phase X-ray scattering and diffraction.     

Supramolecular chemistry: molecular recognition and self-assembly using rigid spacer-chelators bearing cofacial terpyridyl palladium(II) complexes separated by 7 A.

Partially and fully aromatic molecular spacers bearing two symmetrically bound terpyridyl chelators have been prepared. These spacer-chelators were constructed to dispose the two terpyridyl ligands and their complexes with square planar metals cofacially with a separation of about 7 A between the two metals. Dipalladium(II) complexes of these spacer-chelators were prepared and characterized. These palladium complexes readily form large molecular rectangles with a linear linker such as 4,4'-dipyridyl. The dichlorodipalladium complex of the partially reduced spacer-chelator is capable of incarcerating planar aromatic and coordination compounds as guests. A crystal structure showing the incorporation of 9-methylanthracene has been determined. A 9-methylanthracene lies completely within the approximately 7 A space provided by the cleft formed by the two cofacially disposed chloro-palladium-terpyridyl units. The crystal structure shows additional pi-stacking interactions between a second 9-methylanthracene and neighboring receptors.