1,8-Diamidocarbazoles: an easily tuneable family of fluorescent anion sensors and transporters

The synthesis, structure and anion recognition properties of an extensive, rationally designed series of bisamide derivatives of 1,8-diaminocarbazole and 1,8-diamino-3,6-dichlorocarbazole are described. Despite simple structures and the presence of only three hydrogen bond donors, such compounds are remarkably strong and selective receptors for oxyanions in DMSO + 0.5%H2O. Owing to their carbazole fluorophore, they are also sensitive turn-on fluorescent sensors for H2PO4− and AcO−, with a more than 15-fold increase in fluorescence intensity upon binding. Despite relatively weak chloride affinity, some of the diamidocarbazoles have also been shown, for the first time, to be very active chloride transporters through lipid bilayers. The binding, sensing and transport properties of these receptors can be easily modulated by the usually overlooked variations in the length and degree of branching of their alkyl side arms. Overall, this study demonstrates that the 1,8-diamidocarbazole binding unit is a very promising and synthetically versatile platform for the development of fluorescent sensors and transporters for anions.Polish National Science Centre for grant OPUS (2011/01/B/ST5/03900). The study was carried out at the Biological and Chemical Research Centre, University of Warsaw, established within a project co-financed by the European Union through the European Regional Development Fund under the Operational Programme Innovative Economy 2007–2013. R. Q. thanks financial support provided by Consejería de Educación – Junta de Castilla y León (Project BU092U16

The 42nd Symposium Chromatographic Methods of Investigating Organic Compounds : Book of abstracts

The 42nd Symposium Chromatographic Methods of Investigating Organic Compounds : Book of abstracts. June 4-7, 2019, Szczyrk, Polan

Anion-templated synthesis of a switchable fluorescent [2]catenane with sulfate sensing capability

Anion templation strategies have facilitated the synthesis of various catenane and rotaxane hosts capable of strong and selective binding of anions in competitive solvents. However, this approach has primarily relied on positively charged precursors, limiting the structural diversity and the range of potential applications of the anion-templated mechanically interlocked molecules. Here we demonstrate the synthesis of a rare electroneutral [2]catenane using a powerful, doubly charged sulfate template and a complementary diamidocarbazole-based hydrogen bonding precursor. Owing to the unique three-dimensional hydrogen bonding cavity and the embedded carbazole fluorophores, the resulting catenane receptor functions as a sensitive fluorescent turn-ON sensor for the highly hydrophilic sulfate, even in the presence of large excess of water. Importantly, the [2]catenane exhibits enhanced binding affinity and selectivity for sulfate over its parent macrocycle and other acyclic diamidocarbazole-based receptors. We demonstrate also, for the first time, that the co-conformation of the catenane may be controlled by reversible acid/base induced protonation and deprotonation of the sulfate anionic template. This approach pioneers a new strategy to induce molecular motion of interlocked components using switchable anionic templates

Fullerene functionalized halogen bonding heteroditopic hosts for ion-pair recognition

Despite their hydrophobic surfaces with localized π-holes and rigid well-defined architectures providing a scaffold for preorganizing binding motifs, fullerenes remain unexplored as potential supramolecular host platforms for the recognition of anions. Herein, we present the first example of the rational design, synthesis, and unique recognition properties of novel fullerene-functionalized halogen bonding (XB) heteroditopic ion-pair receptors containing cation and anion binding domains spatially separated by C60. Fullerene spatial separation of the XB donors and the crown ether complexed potassium cation resulted in a rare example of an artificial receptor containing two anion binding sites with opposing preferences for hard and soft halides. Importantly, the incorporation of the C60 motif into the heteroditopic receptor structure has a significant effect on halide binding selectivity, which is further amplified upon K+ cation binding. The potassium cation complexed fullerene based receptors exhibit enhanced selectivity for the soft polarizable iodide ion which is assisted by the C60 scaffold preorganizing the potent XB-based binding domains, anion-π interactions and the exceptional polarizability of the fullerene moiety, as evidenced from computational DFT calculations. These observations serve to highlight the unique properties of fullerene surfaces for proximal charged guest binding with potential applications in construction of selective molecular sensors and modulating the properties of solar cell devices

Engineered Binding Microenvironments in Halogen Bonding Polymers for Enhanced Anion Sensing

Mimicking nature’s biopolymeric protein architectures by designing hosts with binding cavities shielded from the bulk solvent environment is a promising approach to achieving anion recognition in competitive protic media. Accomplishing this, however, can be synthetically demanding. Herein we present a more synthetically tractable approach, by directly incorporating potent supramolecular anion recognition motifs into a polymeric scaffold, which can be engineered through a judicious selection of the co-monomer. This is demonstrated through a comprehensive analysis of anion recognition and sensing with redox-active, halogen bonding (XB) polymeric host systems. Notably, the polymeric hosts consistently outperform their monomeric analogues, with especially large halide anion binding enhancements by up to 50-fold observed in aqueous-organic solvent mixtures. These enhancements are rationalised by a consideration of generated low dielectric constant binding microenvironments from which there is appreciable solvent exclusion. This approach is applicable to a range of hosts and targets, enabling recognition and sensing in highly polar media, otherwise unattainable with the monomeric units alone

Magnetoconductivity and Terahertz Response of a HgCdTe Epitaxial Layer

An epitaxial layer of HgCdTe—a THz detector—was studied in magnetotransmission, magnetoconductivity and magnetophotoconductivity experiments at cryogenic temperatures. In the optical measurements, monochromatic excitation with photon frequency ranging from 0.05 THz to 2.5 THz was used. We show a resonant response of the detector at magnetic fields as small as 10 mT with the width of the resonant line equal to about 5 mT. Application of a circular polarizer at 2.5 THz measurements allowed for confirming selection rules predicted by the theory of optical transitions in a narrow-gap semiconductor and to estimate the band-gap to be equal to about 4.5 meV. The magnetoconductivity tensor was determined as a function of magnetic field and temperature 2 K < T < 120 K and analysed with a standard one-carrier conductivity model and the mobility spectrum technique. The sample showed n-type conductivity at all temperatures. At temperatures above about 30 K, conductivity was found to be reasonably described by the one-carrier model. At lower temperatures, this description is not accurate. The algorithm of the spectrum of mobility applied to data measured below 30 K showed presence of three types of carriers which were tentatively interpreted as electrons, light holes and heavy holes. The mobility of electrons and light holes is of the order of 10 6 cm 2 /Vs at the lowest temperatures. Magnetophotoconductivity experiments allowed for proposing a detector working at 2 K and 50 mT with a flat response between 0.05 THz and 2.5 THz