A new fluorescent macrocyclic structure (0) bearing two naphthalene units at both ends of a cyclic polyaminic chain containing two phenanthroline units was investigated with potentiometric and fluorescence (steady-state and time-resolved) techniques. The fluorescence emission spectra show the simultaneous presence of three bands: a short wavelength emission band (naphthalene monomer), a middle emission band (phenanthroline emission), and a long-wavelength band. All three bands were found to be dependent on the protonation state of the macrocyclic unit (including the polyaminic and phenanthroline structures). The existence of the long-wavelength emission band is discussed and is shown to imply that a bending movement involving the two phenanthroline units leads to excimer formation. This is determined by comparison with the excimer emission formed by intermolecular association of 1,10-phenanthroline. With ligand L1, excimer formation occurs only at pH values above 4. At very acidic pH values, the protonation of the polyamine bridges is extensive leading to a rigidity of the system that precludes the bending movement. The interaction with metal cations Zn(II) and Cu(II) was also investigated. Excimer formation is, in these situations, increased with Zn(II) and decreased with Cu(II). The long-emission band is shown to present a different wavelength maximum, depending on the metal, which can be considered as a characteristic to validate the use of ligand L1 as a sensor for a given metal.

Flavylium compounds can conveniently be encapsulated in water permeable cross-linked poly(2-hydroxyethyl methacrylate) ( PHEMA) polymer hydrogel matrices. The polymer is also permeable to gases, for example ammonia and hydrogen chloride. The ability of the polymer to concentrate water from the surrounding atmosphere was demonstrated. The absorption and emission spectra of the encapsulated flavylium compounds are very dependent on the pH, and by consequence ammonia ( or hydrogen chloride) can be easily detected. The intensity of the fluorescence emission of the flavylium cation (AH+ species obtained in acidic media) is very dependent on the water content due to the efficient excited state proton transfer involving the AH(+)* excited state and water. The combination of flavylium emission sensitivity to water and ability of the polymer to concentrate water from the surrounding atmosphere, confers this material potential utility as a humidity sensor with high sensitivity.

n/a

n/a

n/a

n/a

NMR and visible spectroscopy coupled to redox measurements were used to determine the equilibrium thermodynamic properties of the four haems in cytochrome c3 under conditions in which the protein was bound to ligands, the small anion phosphate and the protein rubredoxin with the iron in the active site replaced by zinc. Comparison of these results with data for the isolated cytochrome shows that binding of ligands causes only small changes in the reduction potentials of the haems and their pairwise interactions, and also that the redox-sensitive acid–base centre responsible for the redox–Bohr effect is essentially unaffected. Although neither of the ligands tested is a physiological partner of cytochrome c3, the small changes observed for the thermodynamic properties of cytochrome c3 bound to these ligands vs. the unbound state, indicate that the thermodynamic properties measured for the isolated protein are relevant for a physiological interpretation of the role of this cytochrome in the bioenergetic metabolism of Desulfovibrio.

n/a

n/a

NMR spectroscopy has been applied with great success to study electron transfer proteins
with multiple redox centers. This study aimed to elucidate the redox behavior the enzyme fumarate
reductase from Shewanella frigidimarina and particularly to reveal the electron transfer mechanism
from the N-terminal domain to the active center. We developed a new strategy encompassing the
acquisition of 1H-EXSY bidimensional spectra for observation of chemical exchange connectivities in
partially oxidized samples of fcc3, estimation of the paramagnetic chemical shifts expected for the
heme substituents and their comparison with NMR spectra obtained in the fully oxidized protein. This
study allowed obtaining the order of oxidation of the different groups (II-I-III, IV) and gave insights of
the functional mechanisms that allow fcc3 to efficiently transfer electrons from the N-terminal domain
to the active center.

n/a

n/a

n/a

n/a

n/a

n/a

Deuterium NMR is used to examine the molecular order exhibited by an organosiloxane tetrapode giving the first experimental evidence, using a bulk sample, for the existence of a biaxial nematic phase in this type of compounds. The temperature dependence of the averaged quadrupolar coupling constant and asymmetry parameter was determined in the compound's nematic phase. Two distinct regimes could be identified, one with a vanishing asymmetry parameter corresponding to a uniaxial nematic phase and another with a significant temperature dependent asymmetry parameter, corresponding to a biaxial nematic phase. The high values obtained for the asymmetry parameter at the lower end of the nematic range are well above experimental error and constitute a definite proof of the biaxial nature of the nematic phase exhibited by the studied compound for those temperatures.

n/a