Multichannel digital transmission in an optical network of communicating molecules

In present telecommunication networks, information transfer relies on the interplay of optical and electrical signals. Data are communicated optically but processed electronically. Methods to maintain the propagating signals solely at the optical level must be developed to overcome the transmission capacities and speed limits imposed by the electronic components. We have demonstrated that molecular switches can be used to gate optical signals in response to optical signals. We have realized a simple optical network consisting of three light sources, one cell containing a solution of three fluorescent molecules, one cell containing a solution of a three-state molecular switch and a detector. The light emitted by the three fluorophores is absorbed by the three states of the molecular switch. Using this simple operating principle, we have shown that multichannel digital transmission can be implemented on an ensemble of communicating molecules relying exclusively on the interplay of optical inputs and optical outputs.     

Ferrocene-containing carbohydrate dendrimers

Aliphatic amines, incorporating one or three (branched) acylated beta-D-glucopyranosyl residues, were coupled with the acid chloride of ferrocenecarboxylic acid and with the diacid chloride of 1,1'-ferrocenedicarboxylic acid to afford four dendrimer-type, carbohydrate-coated ferrocene derivatives in good yields (54-92%). Deprotection of the peracylated beta-D-glucopyranosyl residues was achieved quantitatively by using Zemplén conditions, affording four water-soluble ferrocene derivatives. When only one of the two cyclopentadienyl rings of the ferrocene unit is substituted, strong complexes are formed with beta-cyclodextrin in H2O, as demonstrated by liquid secondary ion mass spectrometry (LSIMS), 1H NMR spectroscopy, electrochemical measurements, and circular dichroism spectroscopy. Molecular dynamics calculations showed that the unsubstituted cyclopentadienyl ring is inserted through the cavity of the toroidal host in these complexes. The electrochemical behavior of the protected and deprotected ferrocene-containing dendrimers was investigated in acetonitrile and water, respectively. The diffusion coefficient decreases with increasing molecular weight of the compound. The potential for oxidation of the ferrocene core, the rate constant of heterogeneous electron transfer, and the rate constant for the energy-transfer reaction with the luminescent excited state of the [Ru(bpy)3]2+ complex (bpy = 2,2'-bipyridine) are strongly affected by the number (one or two) of substituents and by the number (one or three) of carbohydrate branches present in the substituents. These effects are assigned to shielding of the ferrocene core by the dendritic branches. Electrochemical evidence for the existence of different conformers for one of the dendrimers in aqueous solution was obtained.     

Liquid-crystalline phase behavior of a colloidal rod-plate mixture

The phase behavior of rod-plate mixtures was investigated using model systems containing unambiguously rod- and plate-shaped colloids. We find that the theoretically disputed biaxial nematic phase is unstable with respect to demixing into an isotropic and two uniaxial nematic phases. The phase behavior at very high densities is exceptionally rich and includes the coexistence of up to four different liquid crystalline phases, which stem from the coupling between the employed particle shapes and polydispersity.     

<Emphasis Type="Italic">parkin</Emphasis> counteracts symptoms in a <Emphasis Type="Italic">Drosophila</Emphasis> model of Parkinson's disease

Background

Parkinson's disease, a prevalent neurodegenerative disease, is characterized by the reduction of dopaminergic neurons resulting in the loss of motor control, resting tremor, the formation of neuronal inclusions and ultimately premature death. Two inherited forms of PD have been linked to mutations in the α-synuclein and parkin genes. The parkin protein functions as an ubiquitin ligase targeting specific proteins for degradation. Expression of human α-synuclein in Drosophila neurons recapitulates the loss of motor control, the development of neuronal inclusions, degeneration of dopaminergic neurons and the ommatidial array to provide an excellent genetic model of PD.

Results

To investigate the role of parkin, we have generated transgenic Drosophila that conditionally express parkin under the control of the yeast UAS enhancer. While expression of parkin has little consequence, co-expression of parkin with α-synuclein in the dopaminergic neurons suppresses the α-synuclein-induced premature loss of climbing ability. In addition directed expression of parkin in the eye counteracts the α-synuclein-induced degeneration of the ommatidial array. These results show that parkin suppresses the PD-like symptoms observed in the α-synuclein-dependent Drosophila model of PD.

Conclusion

The highly conserved parkin E3 ubiquitin ligase can suppress the damaging effects of human α-synuclein. These results are consistent with a role for parkin in targeting α-synuclein to the proteasome. If this relationship is conserved in humans, this suggests that up-regulation of parkin should suppress α-synucleinopathic PD. The development of therapies that regulate parkin activity may be crucial in the treatment of PD.

     

Fast and stable photochromic oxazines for fluorescence switching

The stringent limitations imposed by diffraction on the spatial resolution of fluorescence microscopes demand the identification of viable strategies to switch fluorescence under optical control. In this context, the photoinduced and reversible transformations of photochromic compounds are particularly valuable. In fact, these molecules can be engineered to regulate the emission intensities of complementary fluorophores in response to optical stimulations. On the basis of this general design logic, we assembled a functional molecular construct consisting of a borondipyrromethene fluorophore and a nitrospiropyran photochrome and demonstrated that the emission of the former can be modulated with the interconversion of the latter. This fluorophore-photochrome dyad, however, has a slow switching speed and poor fatigue resistance. To improve both parameters, we developed a new family of photochromic switches based on the photoinduced opening and thermal closing of an oxazine ring. These compounds switch back and forth between ring-closed and -open isomers on nanosecond-microsecond timescales and tolerate thousands of switching cycles with no sign of degradation. In addition, the attachment of appropriate chromophoric fragments to their switchable oxazine ring can be exploited to either deactivate or activate fluorescence reversibly in response to illumination with a pair of exciting beams. Specifically, we assembled three dyads, each based on either a borondipyrromethene or a coumarin fluorophore and an oxazine photochrome, and modulated their fluorescence in a few microseconds with outstanding fatigue resistance. The unique photochemical and photophysical properties of our fluorophore-photochrome dyads can facilitate the development of switchable fluorophores for superresolution imaging and, ultimately, provide valuable molecular probes for the visualization of biological samples on the nanometer level.     

Cross-sections for deuteron photo-disintegration from 139 to 832 MeV

The cross-sections for deuteron photo-disintegration have been measured at nine c.m. angles from 37 to 143 degrees. The minimum and maximum photon energies have been 139 and 832 MeV respectively. The results are in agreement with earlier data above 300 MeV, but are significantly larger below 200 MeV, the discrepancies being up to 50% at the lowest energies measured.