Enantioselective reduction and deracemisation using the non-conventional yeast Pichia glucozyma in water/organic solvent biphasic systems: preparation of (S)-1,2-diaryl-2-hydroxyethanones (benzoins)

Water/organic solvent two-liquid-phase systems have been successfully applied in the synthesis of enantiomerically pure (S)-benzoin through two different methodologies catalysed by whole cells from the non-conventional yeast Pichia glucozyma: the stereoselective monoreduction of benzil and the deracemisation of benzoin. The presence of the organic solvent influences the redox systems implied in the reactions, avoiding the formation of the corresponding diols, increasing the enantioselectivity and allowing the easy isolation of the products in high yields and excellent enantiomeric excesses. The use of both strategies has been extended to the preparation of different chiral benzoin derivatives.     

Subcellular detection and localization of the drug transporter P-glycoprotein in cultured tumor cells

In vitro studies on the cellular location of P-glycoprotein (Pgp) are reported with the aim to clarify the relationship between its intracellular expression and the multidrug resistance (MDR) level of tumor cells. Pgp was found abnormally expressed on the plasma membrane of tumor cells with "classical" MDR phenotype. However, Pgp was also often detected on the nuclear envelope and on the membrane of cytoplasmic organelles. The hypothesis that this drug pump maintains a transport function when located in these compartments, is still under debating. Our results, together with those obtained by other researchers, demonstrate that cytoplasmic Pgp regulates the intracellular traffic of drugs so that they are no more able to reach their cellular targets. In particular, we revealed that in MDR breast cancer cells (MCF-7) a significant level of Pgp was expressed in the Golgi apparatus. A similar result was found in human melanoma cell lines, which never undergone cytotoxic drug treatment and did not express the transporter molecule on the plasma membrane. A strict relationship between intracellular Pgp and intrinsic resistance was demonstrated in a human colon carcinoma (LoVo) clone, which did not express the drug transporter on the plasma membrane. Finally, a structural and functional association between Pgp and ERM proteins has been discovered in drug-resistant human T- lymphobastoid cells (CEM-VBL 100). Our findings strongly suggest a pivotal role of the intracytoplasmic Pgp in the transport of drugs into cytoplasmic vesicles, thus actively contributing to their sequestration and transport outwards the cells. Thus, intracellular Pgp seems to represent a complementary protective mechanism of tumor cells against cytotoxic agents.     

Quenching and hardening in the transverse quasi-elastic peak

We study in the RPA framework the collective response of symmetric, infinite nuclear matter to a spin-isospin sensitive probe with both σ · q and σ × q couplings. The two responses, similar in the low-q region, differ markedly for moderate momenta (?1 fm^?1). Indeed the collective effect manifests itself quite differently in the two responses; whereas the longitudinal one displays a softening and an enhancement (due to the attractive character of the associated particle-hole force), the transverse response is quenched and hardened with respect to the free Fermi gas. The existing experimental data, which we analyze, are compatible with our results. We also explore the total strengths and find that for repulsive forces they are appreciably reduced by the RPA correlations. A large part of this quenching comes from the Δ-excitation (LLEE effect), but some reduction is still present even when the nucleonic degrees of freedom are neglected. This illustrates a violation of strength conservation brought about by the RPA correlations in the spin-isospin channel.     

First-principles theory of correlated transport through nanojunctions

We report the inclusion of electron-electron correlation in the calculation of transport properties within an ab initio scheme. A key step is the reformulation of Landauer's approach in terms of an effective transmittance for the interacting electron system. We apply this framework to analyze the effect of short-range interactions on Pt atomic wires and discuss the coherent and incoherent correction to the mean-field approach.     

Polarity effects on ZnO films grown along the nonpolar [1120] direction

The surface electrical properties of ZnO thin films grown along the nonpolar [1120] direction have been investigated by Kelvin probe microscopy on a nanometer scale. Two different charge domains, with a 75 meV work function difference, coexist within the ZnO surface, which is covered by rhombohedral pyramids whose sidewalls are shown to be {1011}-type planes. The presence and relative orientation of the two kinds of charge domains are explained in terms of the atomic arrangement at the {1011} polar surfaces.     

Nucleation time of nanoscale water bridges

Water capillaries bind together grains of sand. They also can bind an atomic force microscope tip to a substrate. The kinetics of capillary condensation at the nanoscale is studied here using friction force microscopy. At 40% relative humidity we find that the meniscus nucleation times increase from 0.7 to 4.2 ms when the temperature decreases from 332 to 299 K. The nucleation times grow exponentially with the inverse temperature 1/T obeying an Arrhenius law. We obtain a nucleation energy barrier of 7.8 x 10(-20) J and an attempt frequency ranging between 4 and 250 GHz, in excellent agreement with theoretical predictions. These results provide direct experimental evidence that capillary condensation is a thermally activated phenomenon.     

Dynamic processes in the Venice region outlined by environmental isotopes

Research carried out in the last 40 years has shown the scientific importance of groundwater circulation both in the Northern Adriatic sea bed and within the uppermost sedimentary layers of the Venice lagoon and of the Venice plain. Hydrodynamic processes are strictly controlled by a well-cemented sedimentary horizon lying under and around Venice ('caranto'), which plays the role of regional aquitard. This layer was attributed to the subaerial cementation of the Flandrian (8-10 ka Before Present) sedimentary surface. The caranto is generalised as a continuum horizon, being an easy explanation for several environmental, hydrogeological and geotechnical problems, e.g., a base layer for landfills, a confining layer for deep aquifers and the best substratum for locating the oak wooden pile-dwelling needed to support the largest buildings. The preservation of the isotope signal within the deep aquifers and aquiclude system records the changes in surface and groundwater characteristics and suggests the present and past recharge regimes. In this region, the heavily perturbed hydrodynamic conditions do not allow for the use of isotopic signals to derive a correct reconstruction of the present recharge. The perturbations induced by the intensive anthropogenic activity force to follow climate evolution by considering deep groundwater and pore waters. In addition, the presence of carbonatic rocks inside terrigeneous sediments affects the reconstruction of the past. Results indicate that carbonatic rocks are created by seepage, through the sediments, of gaseous carbon compounds from decaying organic layers. The gas interactions with the intra-sedimentary saline and fresh waters produce CO2, inducing the cementation of the sediments.     

The many levels pairing Hamiltonian for two pairs

We address the problem of two pairs of fermions living on an arbitrary number of single-particle levels of a potential well (mean field) and interacting through a pairing force in the framework of the Richardson equations. The associated solutions are classified in terms of a number v_l, which reduces to the seniority v in the limit of a large pairing strength G and yields the number of pairs not developing a collective behaviour, their energy remaining finite in the G limit. We express analytically, through the moments of the single-particle levels distribution, the collective mode energy and the two critical values G_cr⁺ and G_cr^- of the coupling which can exist on a single-particle level with no pair degeneracy. Notably G_cr⁺ and G_cr^-, when the number of single particle levels goes to infinity, merge into the critical coupling of a one-pair system G_cr (when it exists), which is not envisioned by the Richardson theory. In correspondence of G_cr, the system undergoes a transition from a mean-field- to a pairing-dominated regime. We finally explore the behaviour of the excitation energies, wave functions and pair transfer amplitudes versus G finding out that the former, for G > G_cr^-, come close to the BCS predictions, whereas the latter display a divergence at G_cr, signaling the onset of a long-range off-diagonal order in the system.