Systematic study of the static electrical properties of the CO molecule: influence of the basis set size and correlation energy

The influence of the basis set size and the correlation energy in the static electrical properties of the CO molecule is assessed. In particular, we have studied both the nuclear relaxation and the vibrational contributions to the static molecular electrical properties, the vibrational Stark effect (VSE) and the vibrational intensity effect (VIE). From a mathematical point of view, when a static and uniform electric field is applied to a molecule, the energy of this system can be expressed in terms of a double power series with respect to the bond length and to the field strength. From the power series expansion of the potential energy, field-dependent expressions for the equilibrium geometry, for the potential energy and for the force constant are obtained. The nuclear relaxation and vibrational contributions to the molecular electrical properties are analyzed in terms of the derivatives of the electronic molecular properties. In general, the results presented show that accurate inclusion of the correlation energy and large basis sets are needed to calculate the molecular electrical properties and their derivatives with respect to either nuclear displacements or/and field strength. With respect to experimental data, the calculated power series coefficients are overestimated by the SCF, CISD, and QCISD methods. On the contrary, perturbation methods (MP2 and MP4) tend to underestimate them. In average and using the 6-311 + G(3df) basis set and for the CO molecule, the nuclear relaxation and the vibrational contributions to the molecular electrical properties amount to 11.7%, 3.3%, and 69.7% of the purely electronic μ, α, and β values, respectively

Regenerating cortical connections in a dish: the entorhino-hippocampal organotypic slice co-culture as tool for pharmacological screening of molecules promoting axon regeneration

We present a method for using long-term organotypic slice co-cultures of the entorhino-hippocampal formation to analyze the axon-regenerative properties of a determined compound. The culture method is based on the membrane interphase method, which is easy to perform and is generally reproducible. The degree of axonal regeneration after treatment in lesioned cultures can be seen directly using green fluorescent protein (GFP) transgenic mice or by axon tracing and histological methods. Possible changes in cell morphology after pharmacological treatment can be determined easily by focal in vitro electroporation. The well-preserved cytoarchitectonics in the co-culture facilitate the analysis of identified cells or regenerating axons. The protocol takes up to a month.

The transcriptional co-activator PCAF regulates cdk2 activity.

Cyclin dependent kinases (cdks) regulate cell cycle progression and transcription. We report here that the transcriptional co-activator PCAF directly interacts with cdk2. This interaction is mainly produced during S and G2/M phases of the cell cycle. As a consequence of this association, PCAF inhibits the activity of cyclin/cdk2 complexes. This effect is specific for cdk2 because PCAF does not inhibit either cyclin D3/cdk6 or cyclin B/cdk1 activities. The inhibition is neither competitive with ATP, nor with the substrate histone H1 suggesting that somehow PCAF disturbs cyclin/cdk2 complexes. We also demonstrate that overexpression of PCAF in the cells inhibits cdk2 activity and arrests cell cycle progression at S and G2/M. This blockade is dependent on cdk2 because it is rescued by the simultaneous overexpression of this kinase. Moreover, we also observed that PCAF acetylates cdk2 at lysine 33. As this lysine is essential for the interaction with ATP, acetylation of this residue inhibits cdk2 activity. Thus, we report here that PCAF inhibits cyclin/cdk2 activity by two different mechanisms: (i) by somehow affecting cyclin/cdk2 interaction and (ii) by acetylating K33 at the catalytic pocket of cdk2. These findings identify a previously unknown mechanism that regulates cdk2 activity.

Reversible ferromagnetic switching in ZnO:(Co,Mn) powders

We report here on the magnetic properties of ZnO:Mn- and ZnO:Co-doped nanoparticles. We have found that the ferromagnetism of ZnO:Mn can be switched on and off by consecutive low-temperature annealings in O2 and N2, respectively, while the opposite phenomenology was observed for ZnO:Co. These results suggest that different defects (presumably n-type for ZnO:Co and p-type for ZnO:Mn) are required to induce a ferromagnetic coupling in each case. We will argue that ferromagnetism is likely to be restricted to a very thin, nanometric layer at the grain surface. These findings reveal and give insight into the dramatic relevance of surface effects to the occurrence of ferromagnetism in ZnO-doped oxides.

Size effects in the magneto-optical response of Co nanoparticles

A study of the magneto-optical (MO) spectral response of Co nanoparticles embedded in MgO as a function of their size and concentration in the spectral range from 1.4 to 4.3 eV is presented. The nanoparticle layers were obtained by sputtering at different deposition temperatures. Transmission electron microscopy measurements show that the nanoparticles have a complex structure which consists of a crystalline core having a hexagonal close-packed structure and an amorphous crust. Using an effective-medium approximation we have obtained the MO constants of the Co nanoparticles. These MO constants are different from those of continuous Co layers and depend on the size of the crystalline core. We associate these changes with the size effect of the intraband contribution to the MO constants, related to a reduction of the relaxation time of the electrons into the nanoparticles.