ABSTRACT
A series of [Pd2L4] coordination cages featuring endohedral functionalities in central backbone positions was synthesized. Although attached via C[double bond, length as m-dash]C double bonds, the substituents behave as molecular rotors. This is explained by their pronounced donor-acceptor character which lowers rotational barriers and allows for electronic control over the spinning rates inside the cage. The dynamic behaviour of the free ligands, assembled cages and host-guest complexes is compared with the aid of NMR experiments, X-ray structure analysis and molecular modelling.
ABSTRACT
Photon-powered charge separation is achieved in a supramolecular architecture based on the dense packing of functional building blocks. Therefore, self-assembled dimers of interpenetrated coordination cages consisting of redoxactive chromophors were synthesized in a single assembly step starting from easily accessible ligands and Pd(II) cations. Two backbones consisting of electron rich phenothiazine (PTZ) and electron deficient anthraquinone (ANQ) were used to assemble either homo-octameric or mixed-ligand double cages. The electrochemical and spectroscopic properties of the pure cages, mixtures of donor and acceptor cages and the mixed-ligand cages were compared by steady-state UV-vis and transient absorption spectroscopy, supported by cyclic voltammetry and spectroelectrochemistry. Only the mixed-ligand cages, allowing close intra-assembly communication between the donors and acceptors, showed the evolution of characteristic PTZ radical cation and ANQ radical anion features upon excitation in the transient spectra. In contrast, excitation of the mixtures of the homo-octameric donor and acceptor cages in solution did not lead to any signs of electron transfer. Densely packed photo- and redox-functional self-assemblies promise molecular-level control over the morphology of the charge separation layer in future photovoltaic applications.
ABSTRACT
In mammalian tissues, connexin 43 (Cx43) is the most prominent member of the connexin family. In a single lipid bilayer, six connexin subunits assemble into a hemichannel (connexon). Direct communication of apposing cells is realized by two adjacent hemichannels, which can form gap junction channels. Here, we established an expression system in Pichia pastoris to recombinantly produce and purify Cx43 as well as Cx43 fused to green fluorescent protein (GFP). Proteins were isolated from crude cell membrane fractions via affinity chromatography. Cx43 and Cx43-GFP hemichannels were reconstituted in giant unilamellar vesicles as proven by fluorescence microscopy, and their electrophysiological behavior was analyzed on the single channel level by planar patch clamping. Cx43 and Cx43-GFP both showed an ohmic behavior and a voltage-dependent open probability. Cx43 hemichannels exhibited one major mean conductance of 224 ± 26 picosiemens (pS). In addition, a subconductance state at 124 ± 5 pS was identified. In contrast, the analysis of Cx43-GFP single channels revealed 10 distinct conductance states in the range of 15 to 250 pS, with a larger open probability at 0 mV as compared with Cx43, which suggests that intermolecular interactions between the GFP molecules alter the electrophysiology of the protein.
