Analyte Interactions with a New Ditopic Dansylamide–Nitrobenzoxadiazole Dyad: A Combined Photophysical, NMR, and Theoretical (DFT) Study

Abstract

We report herein the synthesis and photophysical studies on a new multicomponent chemosensor dyad comprising two fluorescing units, dansylamide (DANS) and nitrobenzoxadiazole (NBD). The system has been developed to investigate receptor-analyte binding interactions in the presence of both cations and anions in a single molecular system. A dimethyl amino (in the DANS unit) group is used as a receptor for cations, and acidic hydrogens of sulfonamide and the NBD group are used as receptors for anions. The system is characterized by conventional analytical techniques. The photophysical properties of this supramolecular system in the absence and presence of various metal ions and nonmetal ions as additives are investigated in an acetonitrile medium. Utility of this system in an aqueous medium has also been demonstrated. The absorption and fluorescence spectrum of the molecular system consists of a broad band typical of an intramolecular charge-transfer (ICT) transition. A low quantum yield and lifetime of the NBD moiety in the present dyad indicates photoinduced electron transfer (PET) between DANS and the NBD moiety. The fluorescence intensity of the system is found to decrease in the presence of fluoride and acetate anions; however, the quenching is found to be much higher for fluoride. This quenching behavior is attributed to the enhanced PET from the anion receptor to the fluorophore moiety. The mechanistic aspect of the fluoride ion signaling behavior has also been studied by infrared (IR) and (1)H NMR experiments. The hydrogen bonding interaction between the acidic NH protons of the DPN moiety and F(-) is found to be primarily responsible for the fluoride selective signaling behavior. While investigating the cation signaling behavior, contrary to anions, significant fluorescence enhancement has been observed only in the presence of transition-metal ions. This behavior is rationalized by considering the disruption of PET communication between DANS and the NBD moiety due to transition-metal ion binding. Theoretical (density functional theory) studies are also performed for the better understanding of the receptor-analyte interaction. Interestingly, negative cooperativity in binding is observed when the interaction of this system is studied in the presence of both Zn(2+) and F(-). Fluorescence microscopy studies also revealed that the newly developed fluorescent sensor system can be employed as an imaging probe in live cells.

Combined photophysical, NMR and theoretical (DFT) study on the interaction of a multi component system in the absence and presence of different biologically and environmentally important ions

“…45 Additionally, the dimethylamino group present in the dansylamide moiety also has the ability to bind cations through coordination of the Natom lone pair. [15][16][17][18][19][20] The uorescence quantum yield of DANSn2 in ACN medium measured from the steady state emission spectra is found to be 0.52 (using anthracene as the standard, f std ¼ 0.36 in cyclohexane). S1, † in order to conrm the purity of the molecule.…”

“…27 Signalling systems have been designed by employing organic chromophores/luminophores, inorganic-metal frameworks, coordination frameworks or by a suitable combination of any of these. 17,22 Even though a large number of reports on selective chemosensors are present in the literature, studies that focus on the mechanistic details of uorophore-analyte interactions are limited. [1][2][3][4][5][6] Furthermore, the design of a system is such that the binding of anions and cations to their corresponding receptors will be capable of altering the electron transfer or charge transfer between the donor and the acceptor.…”

“…This allows one to obtain various structural motifs where the signaling by optical means can be achieved in the presence of various chemical inputs such as ions, neutral molecules, etc. 17,[28][29][30][31][32] Though several sensor systems have already been developed for various analytes, still there is a huge demand for sensors which are selective for an analyte of interest and which can also be exploited for the simultaneous detection of cations and anions. These binding events are monitored through changes in the absorbance and uorescence response upon the binding of anions and cations to the respective receptors.…”

Fluoride ion sensing in aqueous medium by employing nitrobenzoxadiazole-postgrafted mesoporous silica nanoparticles (MCM-41)

“…At this juncture, it is also interesting to note that fluoride, which is known in the literature 42,43 to behave as a quencher of NBD fluorescence primarily due to hydrogen bonding interaction between NBD and F À is facilitating the fluorescence enhancement of the same. This apparent inconsistency in the behaviour of fluoride with the present silica-based material, in fact, indicates that some different kind of intermolecular interaction is taking place between the system and the fluoride.…”

Folate-targeted PTEN/AKT/P53 signaling pathway promotes apoptosis in breast cancer cells

“…It occurs in the mammary gland epithelial tissue, which cells easily metastasize to vital organs, such as the lungs, bones, and brain, thus directly threatening the lives of patients [1][2][3]. According to statistics from the National Cancer Registry, 4.292 million new cases of breast cancer were recorded in China in 2015, ranking first in the incidence of female malignancies, which account for approximately 15% of new cases of tumors throughout the year [4,5]. Clinically, with the introduction of new chemotherapy drugs and the emergence of new chemotherapy regimens, the five-year survival rate of patients with breast cancer has increased by approximately 86%.…”