Fluorogenic sensors capable of selective interaction with analyte, which leads to a change in the position or intensity of the fluorescence band, allow to detect ions or molecules in situ and in vivo and possess high sensitivity and efficiency. Currently, they are widely used in organic, biological, and medical chemistry and environmental sciences for express monitoring of the ionic composition of the medium. They represent a serious alternative to the bulky, expensive, non-transportable technical devices traditionally used for this purpose, such as atomic absorption, atomic emission, and XRF spectrometers. Polyfunctional sensors capable of independent detection of two or more kinds of “guests” from a multiple mixture of cations, anions, or molecules due to specific spectral responses via the same or different channels constitute a rapidly developing area of chemosensory science. This specific feature is associated with the presence of two or more coordination centers in their molecules, or the capability of one center to selectively respond to various analytes with individual spectral changes. Coumarin (2H-chromene-2-one) core is one of the most versatile frameworks for the design of fluorogenic polyfunctional chemosensors for multianalyte detection. In this chapter, we report on the review of sensing properties of this group of chemosensors based on functionalized coumarin derivatives, including their applications in bioimaging.
- polyfunctional chemosensor
- amino acids
Сhemosensor is a molecule of abiotic origin capable of selective interaction with analyte causing corresponding changes in the physical properties of the initial system (absorption spectra, fluorescence spectra, etc.) . If a change occurs in spectral characteristics, the chemosensor relates to an optical type. There are two main types of optical chemosensors according to their mechanisms of action: chromogenic and fluorogenic [2, 3, 4]. In the case of chromogenic chemosensors after binding of analyte, there occurs a change in the electronic absorption spectra of the initial compounds. If this change can be seen with the human eye, we are dealing with a “naked-eye” chemosensor. Fluorogenic chemosensors can change their fluorescence spectrum after the interaction of analyte with receptor. It is highly desirable that this process is also accompanied by a “naked-eye” effect—contrast change in the color of emission. Chromogenic and fluorogenic chemosensor systems are widely used in organic, biological, and medical chemistry and environmental sciences for monitoring cations and anions. They represent a real alternative to the bulky, expensive, non-transportable technical devices, such as atomic absorption, atomic emission, and XRF spectrometers, that are traditionally used for this purpose. Of special efficiency are fluorogenic sensors, which use fluorescence for detection of various analytes, allow measurements
Herein we report on the review of spectral, fluorescent, and sensing properties of new representatives of this group of chemosensors based on functionalized coumarin derivatives, including their applications in bioimaging.
Coumarins (derivatives of 2
There are several excellent reviews devoted entirely or partially to coumarin chemosensors [24, 25, 26, 27, 28], but polyfunctional coumarin-based sensors for multianalyte detection until now have not been considered.
2. Sensing of multiple metal cations
Fluorescent polyfunctional sensors for detection of metal cations must contain a metal chelating or binding fragment attached to a coumarin core capable of absorbing and emitting light. The formation of complexes with ions should cause a change in the electronic structure or molecular conformation, which should result in an increase or decrease in the emission intensity.
A fluorescent sensor
A new emission band at 427 nm (an increase in intensity ~500 times) in the presence of Al3+ in ethanol-water mixture appears due to hydrolysis of imine
While copper(II) is identified by color change of solution from a slight yellow to orange, Al3+ and Mg2+ ions cause a significant fluorescence enhancement at 592 nm and 547 nm with low detection limits of 0.31 μM and 0.23 μM, respectively.
Upon interaction with Zn2+ in CH3OH/H2O mixture, the emission intensity at 484 nm increases by five times compared to other metal ions. The LOD was found to be ~10−6 M. Since Cu2+ is a paramagnetic ion, its presence in the solution causes a substantial quenching of initial fluorescence of
A similar approach was used in design of a dual chemosensor
Application of compound
When Cu2+ and Zn2+ were monitored by sensor
The detection limits of
A dual-function coumarin chemosensor
The detection limit for Hg2+ was calculated to be 2.96 × 10−7 M.
The detection limit of Ce3+ ion by the sensor
Selective fluorescent coumarin-triazole chemosensor
The limit of detection was found to be 0.14 μM for Ca2+ and 0.25 μM for Fe3+.
3. Sensing of multiple anions
A very small number of fluorogenic polyfunctional coumarin-based chemosensors for multianalyte detection has been created so far. This is due to the fact that the recognition of anions is in principle a very difficult problem, since charges of anions are more diffused than those of cations, which leads to rather weak electrostatic interactions between anions and receptor part of the sensor. As a result, the receptors connected with the coumarin core must have the ability to either form of hydrogen bonds with anions up to complete deprotonation, or to nucleophilic addition reactions. Anions play an important role in medicine, biology, and industry. A deficiency of fluoride ions can cause gum disease and osteoporosis, and an excess leads to fluorosis due to its nephrotoxic action. Both excess and deficiency of bromide and iodide anions affect the functioning of the thyroid gland and can cause serious diseases. Acetate anion is involved in various metabolic processes. Cyanide ion is highly toxic to humans even in small concentrations due to its strong interaction with cytochrome-oxidase.
The fluorogenic and chromogenic chemosensor
The addition of cyanide anions to an aqueous solution of
1H NMR and DFT calculation data correspond to the deprotonation mechanism, while for CN− it is simultaneously supplemented by the addition reaction (Figure 15).
The LOD of fluoride ions in organic medium is 0.72 μM, while for cyanide ions in aqueous environment the LOD is 2.7 μM.
4. Sensing of metal cations and anions
As a rule, polyfunctional coumarin sensors for detection of metal cations and anions should include sites of various nature for the detection of these types of ions. Another displacement approach is based on the initial
Diethylamine coumarin derivatives
The detection limits of the compound
Further development of this approach has been applied in the design of chemosensory systems
For the purpose of Cu2+ and S2− biovisualization, confocal fluorescent imaging was performed using A375 cells. It is clearly visible in the dark field images that green fluorescence is significantly quenched by Cu2+ and restored after subsequent treatment by S2− (Figure 22). The A375 cells were viable and maintained good shape in the entire process of this experiment, which means that
Similar results were obtained for
Upon addition of Hg2+ and F− ions,
The addition of Hg2+ ions in acetonitrile solution of
5. Sensing of metal cations and amino acids
Polyfunctional coumarin sensing of amino acids usually includes the initial detection of the appropriate metal cations, and in the second stage, the obtained
Amino acids are part of macromolecular proteins and represent essential substances for the growth and development of the human body. Cysteine (Cys) is of great importance in age defying, skin whitening, detoxifying, and improving immunity. Its deficiency causes premature senility, skin lesions, and uremia, while its excess can lead to senile dementia, neural tube defects, and osteoporosis. Histidine (His) is extremely important for the absorption of Fe2+ cations, vasodilation, and lowering blood pressure. The lack of His increases the risk of developing epilepsy, rheumatoid arthritis, and red cell aplasia, although its excessive content is associated with chronic kidney disease and Alzheimer’s disease. Arginine (Arg) plays a vital role in cell replication, wound healing, and protein synthesis.
A simple coumarin sensor
Living A549 cells incubated with
With the addition of Cu2+, the solution of coumarin-rhodamine hybrid
The HeLa cells were incubated with
The LODs were calculated as 2.40 × 10−8 M and 1.29 × 10−7 M for Cu2+ and GSH, respectively.
MCF-7 and HUVEC cells were both incubated with
For exogenous biothiols, the BEL-7402 cells were firstly pretreated with NEM and cellular biothiols and SH-containing proteins were deactivated. After incubation with
After subsequent treatment with Cys, Hcy, and GSH, respectively, blue, red, and green fluorescence was observed from three different emission channels in living cells with high selectivity.
The design, synthesis, and investigation of fluorogenic polyfunctional coumarin chemosensors for multianalyte detection is an intriguing and extensively developing area of organic, medical, and biological chemistry. These sensors demonstrate high efficiency and selectivity combined with low cost and simplicity of analysis. Due to the limited size of the chapter, only sensors for the detection of metal cations, anions, and amino acids were considered, while sensors for proteins, DNA, RNA, etc. were ignored. Nevertheless, these data suggest that this group of polyfunctional chemosensors is extremely suitable for express analysis and bioimaging of various objects.
This research was financially supported by the Ministry of Science and Higher Education of the Russian Federation, project 0852-2020-2100-19. A. Dubonosov worked in the framework of the State assignment of the Southern Scientific Centre of the RAS No. 01201354239.
Conflict of interest
The authors declare “no conflict of interest.”
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