Water-Soluble Triazolium Covalent Cages for ATP Sensing

Water-soluble organic cages are attractive targets for their molecular recognition and sensing features of biologically relevant molecules. Here, we have successfully designed and synthesized a pair of water-soluble cationic cages employing click reaction as the fundamental step followed by the N-methylation of the triazole rings. The rigid and shape-persistent 3D hydrophobic cavity, positively charged surface, H-bonding triazolium rings, and excellent water solubility empower both cages to exhibit a superior affinity and selectivity for binding with adenosine-5'-triphosphate (ATP) compared to cyclophanes and other macrocyclic receptors. Both cage molecules (PCC⋅Cl and BCC⋅Cl) can bind a highly emissive dye HPTS (8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt) to form non-fluorescent complexes. The addition of ATP resulted in the stronger cage⊂ATP complexes with the retention of HPTS emission upon its displacement. The resultant indicator-displacement assay system can efficiently sense and quantify ATP in nanomolar detection limits in buffer solutions and human serum matrix. Spectroscopic and theoretical studies revealed the synergistic effect of π⋅⋅⋅π stacking interaction between the aromatic moiety of the cationic cages and the adenine moiety of ATP, as well as the electrostatic and hydrogen bonding interaction between the phosphate anion of ATP and triazole protons of cages, played the pivotal roles in the sensing process.

Europium- and Black Phosphorus-Functionalized Porphyrin as an l-Arginine Sensor and l-Arginine-Activated PDT/PTT Agent for Bacterial Treatment

The attenuation of bacterial metabolism provides an adjunct to the treatment of bacterial infections. To develop a bacterial eradication agent, a bioactivatable material (BP@Eu-TCPP) was designed and synthesized by coordination and reduction of europium(III) with thin-layer black phosphorus (BP) and tetrakis (4-carboxyphenyl) porphyrin (TCPP). The existence of the P-Eu bond and Eu2+ 3d5/2 in X-ray photoelectron spectroscopy confirmed the successful synthesis of BP@Eu-TCPP. This material showed high fluorescence sensitivity to l-Arginine (l-Arg) and the main binding ratio of BP@Eu-TCPP to l-Arg was ca. 1:2 or 1:3, with the limit of detection of 4.0 μM. The material also showed good photothermal properties and stability, with a photothermal conversion efficiency of 37.3%. Although metal coordination has blocked the generation of 1O2, the addition of l-Arg to BP@Eu-TCPP can restore 1O2 generation upon red light-emitting diode (LED) light irradiation due to the formation of water-soluble Arg-TCPP species. Additionally, BP@Eu-TCPP was enabled to change the bacterial membrane and interfered with the bacterial iron absorption that effectively contributes to bacterial eradication. Such BP@Eu-TCPP is promised to be a novel material for the detection of l-Arg and l-Arg-activated photodynamic therapy.

Efficient fluorescent recognition of ATP/GTP by a water-soluble bisquinolinium pyridine-2,6-dicarboxamide compound. Crystal structures, spectroscopic studies and interaction mode with DNA

The new dicationic pyridine-2,6-dicarboxamide-based compound 1 bearing two N-alkylquinolinium units was synthesized, structurally determined by single-crystal X-ray diffraction, and studied in-depth as a fluorescent receptor for nucleotides and inorganic phosphorylated anions in pure water. The addition of nucleotides to 1 at pH = 7.0 quenches its blue emission with a selective affinity towards adenosine 5'-triphosphate (ATP) and guanosine 5'-tripohosphate (GTP) over other nucleotides such CTP, UTP, ADP, AMP, dicarboxylates and inorganic anions. On the basis of the spectroscopic tools (1H, 31P NMR, UV-vis, fluorescence), MS measurements and DFT calculations, receptor 1 binds ATP with high affinity (log K = 5.04) through the simultaneous formation of strong hydrogen bonds and π-π interactions between the adenosine fragment and quinolinium ring with binding energy calculated in 8.7 kcal mol-1. High affinity for ATP/GTP is attributed to the high acidity of amides and preorganized rigid structure of 1. Receptor 1 is an order of magnitude more selective for ATP than GTP. An efficient photoinduced electron transfer quenching mechanism with simultaneous receptor-ATP complexation in both the excited and ground states is proposed. Additionally, multiple spectroscopic studies and molecular dynamics simulations showed that 1 can intercalate into DNA base pairs.

Molecular Receptors for Recognition and Sensing of Nucleotides

Nucleotides are constituents of nucleic acids and they have a variety of functions in cellular metabolism. Synthetic receptors and sensors are required to reveal the role of nucleotides in living organisms and mechanisms of signal transduction events. In recent years, a large number of nucleotide-selective synthetic receptors have been devised, which utilize different molecular designs and sensing mechanisms. This Minireview presents recent progress in the design of synthetic molecular receptors for selective recognition of nucleotides in aqueous solution. The binding properties of receptors and the origins of their selectivity for a particular nucleotide are discussed.