Supramolecular Bioorganic Chemistry: Nucleic Acids Recognition and Synthetic Vectors for Gene Transfer

Discrete multiporphyrin pseudorotaxane assemblies from di- and tetravalent porphyrin building blocks

Two pairs of divalent and tetravalent porphyrin building blocks carrying the complementary supramolecular crown ether/secondary ammonium ion binding motif have been synthesized and their derived pseudorotaxanes have been studied by a combination of NMR spectroscopy in solution and ESI mass spectrometry in the gas phase. By simple mixing of the components the formation of discrete dimeric and trimeric (metallo)porphyrin complexes predominates, in accordance to binding stoichiometry, while the amount of alternative structures can be neglected. Our results illustrate the power of multivalency to program the multicomponent self-assembly of specific entities into discrete functional nanostructures.

Effect of an adsorbent on recombination and band-edge movement in dye-sensitized TiO2 solar cells: evidence for surface passivation

The mechanism by which the adsorbent guanidinium affects the open-circuit photovoltage of dye-sensitized TiO2 nanocrystalline solar cells was investigated. The influence of the guanidinium cation on the rate of recombination and band-edge movement was measured by transient photovoltage. When guanidinium is present in the electrolyte recombination becomes slower by a factor of about 20. At the same time, the adsorbent causes the band edges to move downward, toward positive electrochemical potentials, by 100 mV. The collective effect of both a downward shift of the band edges and slower recombination, owing to the presence of guanidinium, results in an overall improvement in the open-circuit photovoltage.