Search

Aromatic belts, ultrashort carbon nanotubes, and related structures, are emerging molecular entities in the fields of organic electronics and supramolecular chemistry owing to their structural rigidity, fully fused π-conjugation, and well-defined cavity. Synthesis of aromatic belts with embedded thiophene structures, which manifest significant optoelectronic and conductive properties, has not yet been achieved. Herein, we report the synthesis of thiophene-fused aromatic belts (thiophene belts) via one-step sulfur cross-linking reaction of partially fluorinated cycloparaphenylenes. Their structural features, including unidirectional columnar stacking with high dipole moment in crystals, two-dimensional layer assembly on metal surfaces, and photophysical properties, such as long-lifetime phosphorescence, are uncovered. These distinctive features of the thiophene belts should inspire a range of applications such as optoelectronic devices and polar materials. Synthesis of aromatic belts with embedded thiophene structures, which manifest significant optoelectronic and conductive properties, has not yet been achieved. Herein, the authors report the synthesis of thiophene-fused aromatic belts via one-step sulfur cross-linking reaction of partially fluorinated cycloparaphenylenes. [ABSTRACT FROM AUTHOR]

Optical neural networks (ONNs) hold great potential for faster and more energy‐efficient information processing in coherent photonic circuits. To realize ONNs, linear combinations and nonlinear activation functions have to be implemented in an optical fashion. Optical nonlinearities are, however, still difficult to achieve, and existing designs are usually too inflexible to offer different activation functions as used in artificial neural networks. Herein, the nonlinear properties of the large and highly adaptive class of photoswitchable chemical compounds is made accessible as activation functions in ONNs by employing photo‐induced isomerization in azobenzenes to steer activation behavior through nonlinear modulation of an information‐carrying optical signal. The strength of the nonlinearity can be controlled by the chemical concentration while a physically motivated model describes the experimental data for systematically varied photoswitching parameters, resulting in a tunable yet interpretable activation function. Employing such an activation function in a neural network then allows to gauge its strength and perform established classification tasks. The work combines recent advances with photoswitchable chemical compounds and optical neural networks to enable control over the design of nonlinear activation functions, thus opening exciting perspectives for explaining the emergence of intelligent behavior in neural networks. [ABSTRACT FROM AUTHOR]

Host vesicles composed of amphiphilic [beta]-cyclodextrin CD1 recognize metal-coordination complexes of the adamantyi-functionalized ethylenediamine ligand L via hydrophobic inclusion in the [beta]-cyclodextrin cavities at the vesicle surface. In the case of Cu(II) and L, the resulting coordination complex was exclusively Cu[L.sub.2], and the interaction with the host vesicles was intravesicular, unless the concentration of metal complex and vesicles was high (>0.1 mM). In the case of Ni(II) and L, a mixture was formed consisting of mainly NiL and Ni[L.sub.2], the interaction with the host vesicles was effectively intervesicular, and addition of the guest-metal complex resulted in aggregation of the vesicles into dense, multilamellar clusters even in dilute solution [1 [micro]M Ni(II)]. The metal-L complex could be eliminated by a strong chelator such as EDTA, and the intervesicular interaction could be suppressed by a competitor such as unmodified [beta]-cyclodextrin. The result from this investigation is that the strongest metal-coordination complex [Cu(II) with L] binds exclusively intravesicularly, whereas the weakest metal-coordination complex [Ni(II) with L] binds predominantly intervesicularly and is the strongest interfacial binder. These experimental observations are confirmed by a thermodynamic model that describes multivalent orthogonal interactions at interfaces. self-assembly | vesicles | cyclodextrins

Research was conducted to examine the hypothesis that the polymerization of the lipid headgroups inhibits calcium-induced fusion of small unilamellar vesicles of the lipid di-n-dodecyloxypropyl beta-nitrostyryl phosphate but does not affect vesicle aggregation. A comparison of titrations of vesicles into CaCl2 in the absence and presence of LMPAM provided an accurate microcalorimetric determination of the enthalpies of vesicle aggregation and fusion. Results reveal that the driving force of membrane fusion is of entropic origin.

The supramolecular assembly of proteins on surfaces has been investigated via the site-selective incorporation of a supramolecular moiety on proteins. To this end, fluorescent proteins have been site-selectively labeled with ferrocenes, as supramolecular guest moieties, via SNAP-tag technology. The assembly of guest-functionalized SNAP-fusion proteins on cyclodextrin- and cucurbit[7]uril-coated surfaces yielded stable monolayers. The binding of all ferrocene fusion proteins is specific as determined by surface plasmon resonance. Micropatterns of the fusion proteins, on patterned cyclodextrin and cucurbituril surfaces, have been visualized using fluorescence microscopy. The SNAP-fusion proteins were also immobilized on cyclodextrin vesicles. The supramolecular SNAP-tag labeling of proteins, thus, allows for the assembly of modified proteins via supramolecular host-guest interaction on different surfaces in a controlled manner. These findings extend the toolbox of fabricating supramolecular protein patterns on surfaces taking advantage of the high labeling efficiency of the SNAP-tag with versatile supramolecular moieties. [ABSTRACT FROM AUTHOR]

Host vesicles composed of amphiphilic β-cyclodextrin CD1 recognize metal-coordination complexes of the adamantyl-functionalized ethylenediamine ligand L via hydrophobic inclusion in the β-cyclodextrin cavities at the vesicle surface. In the case of Cu(II) and L, the resulting coordination complex was exclusively CuL2, and the interaction with the host vesicles was intravesicular, unless the concentration of metal complex and vesicles was high (>0.1 mM). In the case of Ni(II) and L, a mixture was formed consisting of mainly NiL and NiL2, the interaction with the host vesicles was effectively intervesicular, and addition of the guest-metal complex resulted in aggregation of the vesicles into dense, multilamellar clusters even in dilute solution [1 μM Ni(II)]. The metal-L complex could be eliminated by a strong chelator such as EDTA, and the intervesicular interaction could be suppressed by a competitor such as unmodified β-cyclodextrin. The result from this investigation is that the strongest metal-coordination complex [Cu(II) with L] binds exclusively intravesicularly, whereas the weakest metal-coordination complex [Ni(II) with L] binds predominantly intervesicularly and is the strongest interfacial binder. These experimental observations are confirmed by a thermodynamic model that describes multivalent orthogonal interactions at interfaces. [ABSTRACT FROM AUTHOR]

The genes coding for quinaldine catabolism in Arthrobacter sp. strain Rue61 a are clustered on the linear plasmid pAL1 in two upper pathway operons (meqABC and meqDEF) coding for quinaldine conversion to anthranilate and a lower pathway operon encoding anthranilate degradation via coenzyme A (CoA) thioester intermediates. The meqR2 gene, located immediately down-stream of the catabolic genes, codes for a PaaX-type transcriptional repressor. MeqR2, purified as recombinant fusion protein, forms a dimer in solution and shows specific and cooperative binding to promoter DNA in vitro. DNA fragments recognized by MeqR2 contained a highly conserved palindromic motif, 5'-TGACGNNCGTcA-3', which is located at positions -35 to -24 of the two promoters that control the upper pathway operons, at positions +4 to + 15 of the promoter of the lower pathway genes and at positions +53 to +64 of the meqR2 promoter. Disruption of the palindrome abolished MeqR2 binding. The dissociation constants (KD) of MeqR2-DNA complexes as deduced from electrophoretic mobility shift assays were very similar for the four promoters tested (23 nM to 28 nM). Anthraniloyl-CoA was identified as the specific effector of MeqR2, which impairs MeqR2-DNA complex formation in vitro. A binding stoichiometry of one effector molecule per MeqR2 monomer and a KD of 22 nM were determined for the effector-protein complex by isothermal titration calorimetry (ITC). Quantitative reverse transcriptase PCR analyses suggested that MeqR2 is a potent regulator of the meqDEF operon; however, additional regulatory systems have a major impact on transcriptional control of the catabolic operons and of meqR2. [ABSTRACT FROM AUTHOR]