121 research outputs found
Twisted Nanotubes of Transition Metal Dichalcogenides with Split Optical Modes for Tunable Radiated Light Resonators
Synthesized micro- and nanotubes composed of transition metal dichalcogenides
(TMDCs) such as MoS are promising for many applications in nanophotonics,
because they combine the abilities to emit strong exciton luminescence and to
act as whispering gallery microcavities even at room temperature. In addition
to tubes in the form of hollow cylinders, there is an insufficiently-studied
class of twisted tubes, the flattened cross section of which rotates along the
tube axis. As shown by theoretical analysis, in such nanotubes the interaction
of electromagnetic waves excited at opposite sides of the cross section can
cause splitting of the whispering gallery modes. By studying
micro-photoluminescence spectra measured along individual MoS tubes, it has
been established that the splitting value, which controls the energies of the
split modes, depends exponentially on the aspect ratio of the cross section,
which varies in "breathing" tubes, while the relative intensity of the modes in
a pair is determined by the angle of rotation of the cross section. These
results open up the possibility of creating multifunctional tubular TMDC
nanodevices that provide resonant amplification of self-emitting light at
adjustable frequencies
Cl Anion-Dependent Mg-ATPase
We studied, in the rat brain, the synaptosomal and microsomal membrane fractions of Clâ ion-activated, Mg2+-dependent ATPase, satisfying the necessary kinetic peculiarities of transport ATPases, by a novel method of kinetic analysis of the multisite enzyme systems: (1) the [Mg-ATP] complex constitutes the substrate of the enzymic reaction; (2) the VÂ =Â f(Clâ) dependence-reflecting curve is bell-shaped; (3) substrate dependence, VÂ =Â f(S), curves at a constant concentration of free ligands (Mgf, ATPf, Clâ); (4) as known from the literature, in the process of reaction a phosphorylated intermediate is formed (Gerencser, Crit Rev Biochem Mol Biol 31:303â337, 1996). We report on the Cl-ATPase molecular mechanism and its place in the âP-type ATPaseâ classification
Folding of the lysine riboswitch: importance of peripheral elements for transcriptional regulation
The Bacillus subtilis lysC lysine riboswitch modulates its own gene expression upon lysine binding through a transcription attenuation mechanism. The riboswitch aptamer is organized around a single five-way junction that provides the scaffold for two long-range tertiary interactions (loop L2âloop L3 and helix P2âloop L4)âall of this for the creation of a specific lysine binding site. We have determined that the interaction P2âL4 is particularly important for the organization of the ligand-binding site and for the riboswitch transcription attenuation control. Moreover, we have observed that a folding synergy between L2âL3 and P2âL4 allows both interactions to fold at lower magnesium ion concentrations. The P2âL4 interaction is also critical for the close juxtaposition involving stems P1 and P5. This is facilitated by the presence of lysine, suggesting an active role of the ligand in the folding transition. We also show that a previously uncharacterized stemâloop located in the expression platform is highly important for the riboswitch activity. Thus, folding elements located in the aptamer and the expression platform both influence the lysine riboswitch gene regulation
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