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.
Sexual transmission of HIV is the major cause of spread of HIV in Africa and the Third World and is an unmet medical need. Recently, microbicides have attracted attention because they allow females to protect themselves and their offspring. We are exploiting one of the four retroviral enzymes, the ribonuclease H, RNase H, as a novel approach for a microbicide. It is the only enzyme of HIV not yet targeted by antiretroviral therapy. The enzyme is linked to the reverse transcriptase (RT) and hydrolyzes the RNA moiety of RNA-DNA hybrids. The RNase H is located inside virus particles and normally functions during viral replication inside cells. Here we show that activating the RNase H prematurely inside the virus particles destroys the viral genome and abrogates viral infectivity. The antiviral compound consists of a synthetic oligodeoxynucleotide (ODN), which creates an artificial RNA-DNA hybrid substrate for the RNase H inside the particle. The compound was analyzed in mouse models including humanized SCID mice and the vagina of mice. Infection was reduced up to 1000-fold or could be completely prevented. The compound is suitable as microbicide or to prevent mother-to-child transmission.
Ergopeptides, like ergocornine and α-ergocryptine, exist in an Sand in an R-configuration. Kinetic experiments imply that certain configurations are preferred depending on the solvent. The experimental methods are explained in this article. Furthermore, computational methods are used to understand this configurational preference. Standard quantum chemical methods can predict the favored configurations by using minimum energy calculations on the potential energy landscape. However, the explicit role of the solvent is not revealed by this type of methods. In order to better understand its influence, classical mechanical molecular simulations are applied. It appears from our research that "folding" the ergopeptide molecules into an intermediate state (between the Sand the R-configuration) is mechanically hindered for the preferred configurations.
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