ATP Induced Modulation in π–π Stacking Interactions in Pyrene Based Zinc Complexes: Chemosensor Study and Quantitative Investigation of Apyrase Activity

Abstract

Fluorescent zinc complexes of 1,2-disubstituted benzimidazole (R1–R3) have been synthesized and characterized using single crystal X-ray diffraction. The ligands L1–3 were found to be less emissive due to photoinduced electron transfer (PET) mechanism originated from the electron pair of benzimidazole nitrogen. The complexation of ligands with Zn­(II) not only enhances the fluorescent intensity; it also orients the ligands to a new packing. It was observed that the aromatic unit plays a decisive role in the packing of the molecules. The complex R1 has extended the coordination through C–H···π interaction, whereas complex R2 involved C–H···π interaction and C–H···Br interaction for packing in supramolecular architecture. Among these complexes, R3 showed the most interesting noncovalent interaction pattern involving C–H···π interaction, C–H···Br interaction, and π–π stacking between pyrene rings. These noncovalent interactions govern photophysical properties that are sensitive toward the microenvironment. Thus, by altering these interactions, the selective sensing for a particular analyte can be achieved. The complexes R1 and R2 have shown enhanced emission intensity upon interacting with adenosine triphosphate (ATP) competitively in the presence of some other tested anions. A ratiometric change in emission spectra of the complex R3 was observed upon binding with ATP in semiaqueous medium offering the lowest detection limit of 15 nM. Upon interaction with ATP, the π–π stacking between pyrene rings breaks and results in a decrease in excimer emission at 470 nm and increases in monomeric emission intensity at 410 nm. The AFM (Atomic force microscopy) images of receptor R3 show that upon addition of ATP to the R3 solution, solvent mediated aggregation takes place, which results in the ratiometric detection. In the dimethylformamide solvent system, aggregates were formed, whereas in a water/tetrahydrofuran solvent system the clear solution was converted to a highly viscous gel. To investigate the applications of the prepared sensor, the fluorescence response of HeLa cells enriched with ATP was observed using fluorescence microscopy. The fluorescence modulation of the sensor in living cells makes the receptor practically applicable in a biological environment. Quantitative analysis of apyrase activity has shown that the presented sensor R3 is capable of monitoring the hydrolysis process in the biological system.

A Luminescent Mg-Metal–Organic Framework for Sustained Release of 5-Fluorouracil: Appropriate Host–Guest Interaction and Satisfied Acid–Base Resistance

“…In view of the multiple H-bond donors and acceptors as well as the aromaticity of 5-FU, 22 such a channel environment with abundant binding sites allows TDL-Mg to possibly cause tunable host−guest interactions with the encapsulated 5-FU molecules during the diffusion process, 23,24 and achieve a sustained slow release of 5-FU. 25 Preparation and Stability of Nano-Sized TDL-Mg. For better application in biological systems, nano-sized TDL-Mg (nano-TDL-Mg) was prepared by adjusting the operation scheme and reaction conditions. 26−29 After heating and stirring the mixture of raw materials for 24 h, the homogeneous reaction liquid was quickly poured into icy dichloromethane (0 °C) for fast cooling, and after ultrasonication and centrifugation, the nano-TDL-Mg can be obtained with a moderate yield.…”

The Nature and Applications of π–π Interactions: A Perspective

“…However, the complex containing pyrene moiety showed proportional changes in emissions spectra due to breakage of π−π interactions when bound to ATP, thus acting as a chemosensor for ATP. 56 Another example of aggregation induced fluorescence has been reported by Tarai et al for N-(isonicotinylhydrazide)-1,8-naphthalimide with a different conformation in its anhydrous, hydrated, and silver complex. The guest-free form shows single emission, whereas the hydrated form and silver complex shows dual emission which is explained based on the change in π interaction and conformational variation of the amide with respect to the imide units of the parent molecule.…”

“…In the presence of ATP, other two complexes showed enhancement of emission. However, the complex containing pyrene moiety showed proportional changes in emissions spectra due to breakage of π–π interactions when bound to ATP, thus acting as a chemosensor for ATP . Another example of aggregation induced fluorescence has been reported by Tarai et al for N -(isonicotinylhydrazide)-1,8-naphthalimide with a different conformation in its anhydrous, hydrated, and silver complex.…”

Synthesis, Crystal Structure, and Photocatalytic Properties of a Zinc(II) Coordination Polymer Based on 3‐Hydroxy‐2‐pyridinecarboxylic Acid

“…There still exists strong π–π interaction in the complex as shown in Figure b (yellow lines). In recent years, more and more evidences have proved that these weak interactions can not only participate in the formation of stable supramolecular structures, but also help to further enhance the stability of the original unstable structure , . In this novel zinc(II) compound, the benzene ring in the opposite position between two ligands can form an effective π–π interaction with the face center distance of 3.523 Å (Figure d), which is shorter than in other supramolecular materials .…”