The longest wave absorption band of the tetramethylthiotetrathiafulvalene cation radical, which is usually interpreted as a p-dimer band, is shown to be the intrinsic cation radical absorption, all studied cation radicals in solution at room temperature exist as paramagnetic monomers and only tetrathiafulvelene and tetramethyltetrathiafulvalene cation radicals undergo p-dimerization at low temperatures.

Understanding membrane interactions and cell-wall permeation of Gram-negative bacteria is of great importance, owing to increasing bacterial resistance to existing drugs and therapeutic treatments. Here we use biomimetic lipid vesicles to analyse membrane association and penetration by synthetic derivatives of polymyxin B (PMB), a potent naturally occurring antibacterial cyclic peptide. The PMB analogues studied were PMB nonapeptide (PMBN), in which the hydrophobic alkyl residue was cleaved, PMBN diastereomer containing D-instead of L-amino acids within the cyclic ring (dPMBN) and PMBN where the hydrophobic alkyl chain was replaced with an Ala6 repeat (Ala6-PMBN). Peptide binding measurements, colorimetric transitions induced within the vesicles, fluorescence quenching experiments and ESR spectroscopy were applied to investigate the structural parameters underlying the different membrane-permeation profiles and biological activities of the analogues. The experiments point to the role of negatively charged lipids in membrane binding and confirm the prominence of lipopolisaccharide (LPS) in promoting membrane association and penetration by the peptides. Examination of the lipid interactions of the PMB derivatives shows that the cyclic moiety of PMB is not only implicated in lipid attachment and LPS binding, but also affects penetration into the inner bilayer core. The addition of the Ala6 peptide moiety, however, does not significantly promote peptide insertion into the hydrophobic lipid environment. The data also indicate that the extent of penetration into the lipid bilayer is not related to the overall affinity of the peptides to the membrane.

We report on the first nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) investigation of inorganic fullerene-like MoS(2) nanoparticles. Spectra of bulk 2H-MoS(2) samples have also been measured for comparison. The similarity between the measured quadrupole coupling constants and chemical shielding anisotropy parameters for bulk and fullerene-like MoS(2) reflects the nearly identical local crystalline environments of the Mo atoms in these two materials. EPR measurements show that fullerene-like MoS(2) exhibits a larger density of dangling bonds carrying unpaired electrons, indicative of them having a more defective structure than the bulk sample. The latter observation explains the increase in the spin-lattice relaxation rate observed in the NMR measurements for this sample in comparison with the bulk 2H- MoS(2) ones.

Since the discovery [1] of the first organic metal in 1973, much attention has been devoted to the investigation of TTF, its derivatives, and analogues as electron-donor components for many charge-transfer (CT) complexes and ion-radical salts. [2] A proposed model of a unimolecular rectifier [3] involving TTF and TCNQ moieties linked covalently through a rigid saturated spacer has stimulated intensive studies in this direction. A concept involving a number of donor and acceptor units incorporated in a single molecule was later developed [4] that would enable the properties related to molecular organic conductors to be controlled. So far, the realization of this notion has been limited to linking moderate acceptors to TTF derivatives and weak donors to TCNQ fragments, [5] while the incorporation of TTF and TCNQ moieties in a single molecule has proved to be an elusive goal. [6] In 2003, Bryce and co-workers published [7] a synthesis of a TTF-s-TCNQ molecule containing a nonconjugated flexible spacer. This compound is expected to exhibit a high degree of intramolecular CT in both solution and the solid state. However, while its IR data are consistent with a degree of charge transfer of about 0.85 in the solid state, only less than 1 % biradicals were observed by EPR and UV/Vis/NIR spectroscopy. Also, the redox potentials shifted by only 20 mV with respect to those of the individual donor and acceptor components, thus indicating only a small degree of donor-acceptor interaction. Furthermore the authors claim of a thermally induced electron transfer in their system, which was based on temperature-dependent EPR measurements, is somewhat misleading. Their calculated HOMO/LUMO gap (0.17-0.75 eV) and measured energy of the CT transition (0.75 eV, red edge 0.45 eV) are much higher than the energy

Magnetic-susceptibility measurements, nuclear magnetic resonance (NMR) of B11, and electron magnetic-resonance (EMR) spectra of YCo3B2 were measured as a function of the temperature. The temperature dependence of the magnetic susceptibility showed a lambda-shaped anomaly at 150K. Whereas upon cooling, a shift in the resonance position of the NMR and EMR spectra is observed at 150K, marking the emergence of an internal magnetic field. The quadrupolar splitting of the NMR lines showed a marked discontinuity at 150K. The (T1T)−1∕2 values were found to be independent of temperature for T>175K, and to increase sharply upon cooling for T<150K. The intensity of the EMR line which is independent of temperature for T>160K is also found to increase markly upon cooling below 150K. All these effects are discussed and it is proposed that YCo3B2 undergoes a magnetic ordering phase transition at 150K.