The question whether the linear absorption spectra of metal clusters can be interpreted as density oscillations (collective "plasmons") or can only be understood as transitions between distinct molecular states is still a matter of debate for clusters with only a few electrons. We calculate the photoabsorption spectra of Na 2 and Na + 5 comparing two different methods: quantum fluid-dynamics and time-dependent density functional theory. The changes in the electronic structure associated with particular excitations are visualized in "snapshots" via transition densities. Our analysis shows that even for the smallest clusters, the observed excitations can be interpreted as intuitively understandable density oscillations. For Na + 5 , the importance of self-interaction corrections to the adiabatic local density approximation is demonstrated.
Stimulation of renal collecting duct principal cells with antidiuretic hormone (arginine-vasopressin, AVP) results in inhibition of the small GTPase RhoA and the enrichment of the water channel aquaporin-2 (AQP2) in the plasma membrane. The membrane insertion facilitates water reabsorption from primary urine and fine-tuning of body water homeostasis. Rho guanine nucleotide exchange factors (GEFs) interact with RhoA, catalyze the exchange of GDP for GTP and thereby activate the GTPase. However, GEFs involved in the control of AQP2 in renal principal cells are unknown. The A-kinase anchoring protein, AKAP-Lbc, possesses GEF activity, specifically activates RhoA, and is expressed in primary renal inner medullary collecting duct principal (IMCD) cells. Through screening of 18,431 small molecules and synthesis of a focused library around one of the hits, we identified an inhibitor of the interaction of AKAP-Lbc and RhoA. This molecule, Scaff10-8, bound to RhoA, inhibited the AKAP-Lbc-mediated RhoA activation but did not interfere with RhoA activation through other GEFs or activities of other members of the Rho family of small GTPases, Rac1 and Cdc42. Scaff10-8 promoted the redistribution of AQP2 from intracellular vesicles to the periphery of IMCD cells. Thus, our data demonstrate an involvement of AKAP-Lbc-mediated RhoA activation in the control of AQP2 trafficking.
We investigate pump and probe dynamics in simple metal clusters of medium size. Test cases are
Na9+ and
Na41+.
The initial pulse ionizes the cluster and excites ionic motion by a sudden increase
of Coulomb pressure. The subsequent ionic breathing motion can be directly
mapped by the probe pulses if the analysing frequency stays sufficiently below the
plasmon resonance peak at all times. Pump and probe experiments could thus
provide direct access to ionic dynamics in electronically excited metal
clusters, in the spirit of pump and probe experiments on small molecules.
We investigate theoretically pump and probe dynamics in metal clusters with crossed-polarization laser beams. We explore the relation between the pronounced Mie plasmon resonance and the laser frequency. The resonance moves with the cluster radius and splits according to the actual deformation. We demonstrate that probe pulses with different (linear) polarization axes allow one to resolve the global shape oscillations of the cluster in monopole and quadrupole degrees of freedom.
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