Drimenol: A versatile synthon for compounds with trans-drimane skeleton

Several reviews have been published on sesquiterpenes, and on drimane-type sesquiterpenes, going through drimenol and related compounds among others. However, to our knowledge, this is the first review exclusively on drimenol. Although, the main focus is on drimenol as a synthon for other drimane-type compounds, synthetic routes to obtain racemic and (-)-drimenol are summarized, as well as its isolation and determination of its configuration, in the early fifties. The reviewed synthetic routes start from natural (-)-drimenol as chiral synthon in most of cases, nevertheless total syntheses are considered as well. The strategies where racemic drimenol is involved begin with biomimetic cyclization of trans-farnesol. Microbiological procedures to functionalize the A ring of drimenol are also commented. The revision is classified according to the chemical structure of the final product, which mainly correspond to structures of natural occurrence, although other related derivatives are also analyzed.     

The Influence of Nd and Sm on the Structure and Properties of Sol-Gel-Derived TiO2 Powders

TiO₂ nanopowders modified by Nd and Sm were prepared using the sol-gel technique. It was found by XRD analysis that the samples containing Sm are amorphous up to 300 °C, while those with Nd preserve a mixed organic-inorganic amorphous structure at higher temperatures (400 °C). The TiO₂ (rutile) was not detected up to 700 °C in the presence of both modified oxides. TiO₂ (anatase) crystals found at about 400 °C in the Sm-modified sample exhibited an average crystallite size of about 25–30 nm, while doping with Nd resulted in particles of a lower size—5–10 nm. It was established by DTA that organic decomposition is accompanied by significant weight loss occurring in the temperature range 240–350 °C. Photocatalytic tests showed that the samples heated at 500 °C possess photocatalytic activity under UV irradiation toward Malachite green organic dye. Selected compositions exhibited good antimicrobial activity against E. coli K12 and B. subtilis.     

Local structure and triplet energy migration in p-dichlorobenzene-p-dibromobenzene solid solutions

Studies of the first triplet absorption and emission spectra of p-dichlorobenzene-p-dibromobenzene (DCB-DBB) mixed crystals agree generally with the data, indicating that this system forms solid solutions. However, the spectral properties are found to be very different from that of isotopically mixed crystals of comparable concentrations. The singlet-triplet absorption spectra of the DCB-DBB mixtures are generally broad and not amenable to detailed analysis indicating significant site dependent perturbations of the DCB and DBB triplet energies. Energy migration enhances emission from the lower energy sites and in consequence a red shift in the position of the emission (0,0) is observed, which is a maximum at equimolar concentrations. The emission bands are generally much broader than found for isotopically mixed crystals, indicating that the many types of sites in the DCB-DBB system remained uncoupled. This is a direct consequence of exciton trapping by inhomogeneous energy broadening caused by the site energy disorder being greater than the triplet exciton band width. Long-range triplet energy migration is not observed at DCB concentrations less than 99 per cent. This high limit is only expected for near one-dimension energy migration topologies. New structure observed at low DCB concentrations is tentatively interpreted as being due to the formation of DCB n-mers. The observed splittings indicate that the gas-to-crystal shift of the DCB T ₁ state increases (becomes more negative) by 11 cm^-1 when a neighbouring DBB molecule is replaced by DCB.     

Noncovalent paramagnetic complexes: detection of halogen bonding in solution by ESR spectroscopy

Halogen-bonded complexes between aliphatic and aromatic iodoperfluorocarbons and persistent nitroxide radicals have been detected by ESR spectroscopy in solution. Quantitative data indicate that nitroxides behave as strong electron donors in halogen bonding, giving rise to interactions whose strength is close to that of strong hydrogen bonds. These results point to a novel design of supramolecular paramagnetic species.     

High energy radiation fluences in the ISS-USLab: Ion discrimination and particle abundances

The ALTEA (Anomalous Long Term Effects on Astronauts) detector was used to characterize the radiation environment inside the USLab of the International Space Station (ISS), where it measured the abundances of ions from Be to Fe. We compare the ALTEA results with Alteino results obtained in the PIRS module of the Russian segment of the ISS, and normalize to the high energy Si abundances given by Simpson. These are the first particle spectral measurements, which include ions up to Fe, performed in the USLab. The small differences observed between those made inside the USLab and the Simpson abundances can be attributed to the transport through the spacecraft hull. However, the low abundance of Fe cannot be attributed to only this process.     

Analysis and parametric optimization of 1H off-resonance relaxation NMR experiments designed to map polypeptide self-recognition and other noncovalent interactions

The measurement of 1H off-resonance nonselective relaxation rates (R(theta,ns)) has been recently proposed as an effective method to probe peptide self-recognition, opening new perspectives in the understanding of the prefibrillization oligomerization processes in amylodogenesis. However, a full analysis and parametric optimization of the NMR experiments designed to measure R(theta,ns) relaxation rates is still missing. Here we analyze the dependence of the R(theta,ns) rates upon three critical parameters: the tilt angle of the effective field during the spin lock, the static magnetic field, and finally the repetition delay. Our analysis reveals that the tilt angle theta = 35.5 degrees not only minimizes spin-diffusion, but also avoids experimental artifacts such as J-transfer and poor adiabaticity. In addition, we found that when the dominant relaxation mechanism is caused by uncorrelated pairwise 1H dipole-1H dipole interactions the R(35.5 degrees,ns) rate is not significantly affected by static field variations, suggesting a wide applicability of the 1H off-resonance nonselective relaxation experiment. Finally, we show that the self-recognition maps based on the comparative analysis of the R(35.5 degrees,ns) rates can tolerate decreases in the interscan delays without significantly compromising the identification of critical self-association loci. These considerations not only provide a better understanding of the 1H off-resonance nonselective relaxation, but they also serve as guidelines for the optimal setup of this experiment.     

Classification and decomposition of Quantum Markov Semigroups

We show that a QMS on a σ-finite von Neumann algebra can be decomposed as the sum of several ``sub'-semigroups corresponding to transient and recurrent projections. We discuss two applications to physical models.     

Analysis of breakdown process at U50 voltage for plane rod discharges by means of Neural Networks

The influence of many parameters on the electric discharges at U50% can only be correlated by means of an analysis of a large amount of experimental data. The 50% probability of breakdown is considered a random process. We have investigated how to find relevant statistical differences leading to breakdown or withstanding during an impulse voltage test under the same conditions for a plane high voltage electrode and a grounded electrode configuration. An analysis based on Neural Network discrimination has been developed which indicates that measurements do contain some relevant information test at early stages in a reduced time frame.