Solvent-Tuned Supramolecular Assembly of Fluorescent Catechol/Pyrene Amphiphilic Molecules.

The synthesis and structuration of a novel low-molecular-weight amphiphilic catechol compound is reported. The combination of a hydrophilic tail containing a catechol unit and a pyrene-based hydrophobic head favors solvent-tuned supramolecular assembly. Formation of hollow nanocapsules/vesicles occurs in concentrated solutions of polar protic and nonprotic organic solvents, whereas a fibril-like aggregation process is favored in water, even at low concentrations. The emission properties of the pyrene moiety allow monitoring of the self-assembly process, which could be confirmed by optical and electronic microscopy. In organic solvents and at low concentrations, this compound remains in its nonassembled monomeric form. As the concentration increases, the aggregation containing preassociated pyrene moieties becomes more evident up to a critical micellar concentration, at which vesicle-like structures are formed. In contrast, nanosized twist beltlike fibers are observed in water, even at low concentrations, whereas microplate structures appear at high concentrations. The interactions between molecules in different solvents were studied by using molecular dynamics simulations, which have confirmed different solvent-driven supramolecular interactions.

Molecular-based upconversion in homo/heterogeneous liquids and in micro/nanostructured solid materials.

Radiation upconversion can be an elegant and efficient strategy to minimize waste in energy harvesting and storage processes. The upconversion based on triplet-triplet annihilation processes of molecular dyes is a very versatile approach, but it requires a systematic photophysical characterization of the systems to optimize the upconversion yields and develop materials for technological applications. This paper represents an overview of the work carried out in our laboratories for the study and characterization of a molecular dye pair, 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin platinum(ii) (PtOEP) and 1,3,6,8-tetraphenylpyrene (TPPy), suitable as the sensitizer and emitter, respectively, in a triplet-triplet annihilation based upconversion process. The investigation has been carried out in various media with increasing complexity. First, we used the dye pair to characterize the UC-efficiencies in homogeneous solvents of different viscosities and in oil-in-water microemulsions; then we explored the possibility to achieve upconversion in solid materials, like nanostructured silica matrices and liquid filled microcapsules. The possibility to achieve upconversion emission even in confined and rigid media has been confirmed and can inspire further applications of the process.

Cytomixis in pollen mother cells of Medicago sativa L.

Cytomixis (i.e., chromatin migration between meiocytes) has been detected in many plant species, but not in Medicago sativa spp. In the present study we report the identification of a few cytomictic alfalfa plants. Those plants, the "mother plants," were selfed and crossed with a normal control plant. Microsporogenesis analysis was performed on the mother plants, on the S(1) and F(1) plants, and on controls. The S(1) and F(1) plants, like the mother plants, were found to be cytomictic. Single or multiple chromatin bridges between two or more meiocytes were observed almost exclusively in prophase I. Some completely empty meiocytes were also observed. In addition to cytomixis, other meiotic abnormalities were found. Control plants showed an almost regular meiosis. The highest values of cytomixis were observed in the mother plants, and the lowest in their F(1) progenies. Variability of cytomixis in the F(1) plants is probably due to a heterozygotic condition of the parents for this trait. No significant correlation was found between cytomixis and pollen viability, even if the cytomictic plants showed low values of pollen viability.

Genome plasticity in Festuca arundinacea: direct response to temperature changes by redundancy modulation of interspersed DNA repeats.

The response of the genome of Festuca arundinacea seedlings to changes in the temperature at which they were grown was investigated. Fifteen repeated sequences in the nuclear DNA were isolated and hybridized to the genomic DNA of seedlings grown at 10 degrees C or 30 degrees C. The redundancies of sequences recognized by four probes ( FaA5, FaH8, FaH13 and FaH14), were found to differ significantly in the two DNAs. DNA sequences recognized by FaH8, FaH13 and FaH14 were more represented in the genome of the 30 degrees C-raised seedlings than in the genome of the 10 degrees C-raised seedlings (76.5 x 10(3), 1.9 x 10(3), and 111.8 x 10(3) copies per haploid, 1C genome vs 62.7 x 10(3), 1.3 x 10(3), and 80.8 x 10(3) copies, respectively). In contrast, FaA5-related sequences were more represented in the genome of seedlings grown at the lower temperature (15.5 x 10(3) vs 10.2 x 10(3) copies, respectively). Southern-blot hybridization of these repeats to digested genomic DNA produced patterns which indicated that the probe sequences were part of longer repeated sequences having a limited degree of structural heterogeneity. These patterns were partly different when the probes were hybridized to the DNA from seedlings grown at 10 degrees C or 30 degrees C. In situ hybridization showed that the DNA sequences recognized by each probe were scattered along the length of all the chromosomes, with preferential location of FaA5- and FaH13-related sequences at given, mainly centromeric, regions of certain chromosomes. These findings suggest that redundancy modulations of interspersed repeated sequences allow direct responses of the genome of F. arundinacea to changes in environmental temperature.