Synthesis, photophysical properties and systematic evaluations of new phenanthroimidazole fluorescent probe for bioimaging: Experimental and theoretical study

The Influence of the Functional Group on the Physicochemical and Biological Properties of New Phenanthro[9,10-d]-Imidazole Derivatives

The search for safe, cheap, and repeatable diagnostic methods is a fundamental research goal. Currently, great hope is placed on fluorescence imaging. However, the development of this method mainly depends on efficient fluorescent probes. Designing and obtaining new probes with potential applications in fluorescence imaging is very difficult because compounds of this type must meet several requirements related to their properties. Therefore, this article attempted to obtain and study new phenanthro[9,10-d]-imidazole derivatives (PK1-PK3) with potential application as fluorescent probes for fluorescence imaging. The main goal of the work was to assess the effect of two functional groups (such as the formyl group (PK2) and rhodanine-3-acetic acid (PK3)) on selected physicochemical properties and possibilities of practical application of the considered compounds. The conducted studies proved that the influence of the functional group is significant, as it causes a bathochromic shift in both absorption and emission results (by the order PK1 < PK2 < PK3). Moreover, all compounds could stain live cells cultured in vitro. The staining efficiency was not affected by the cell line, thanks to which we obtained the correct staining of both mouse and human cell lines. PK3 was the most attractive of the tested compounds due to its staining potential of live cells and retention after fixation. Our results also showed some antibacterial and antifungal activity of the newly synthesized compounds (PK1-PK3). Among them, PK3 showed the highest antimicrobial effect, especially against Gram-positive bacteria.

Synthesis of Carbazole-Thiazole Dyes via One-Pot Tricomponent Reaction: Exploring Photophysical Properties, Tyrosinase Inhibition, and Molecular Docking

Carbazole is an aromatic heterocyclic organic compound consisting of two fused benzene rings and a pyrrole ring and is a very valuable building structure for the design of many compounds for use in various fields of chemistry and medicine. This study presents three new carbazole-based thiazole derivatives that differ in the presence of a different halogen atom: chlorine, bromine, and fluorine. Experimental studies and quantum-chemical simulations show the effect of changing a halogen atom on the physicochemical, biological, and linear and nonlinear optical properties. We have also found that carbazoles C-Cl, C-Br, and C-F exhibit high tyrosinase inhibitory activity, with IC50 values in the range of 68-105 µM with mixed mechanism of action. Finally, molecular docking to the active site of Concanavalin A (ConA) and bioavailability for all compounds were evaluated.

Synthesis, electrochemical, optical and biological properties of new carbazole derivatives

Carbazole skeleton is the key structural motif of many biologically active compounds including synthetic and natural products. Based on the (E)-2-(2-(4-9H-carbazol-9-yl)benzylidene) hydrazinyl)thiazole as skeleton, three novel carbazole dyes were synthesized. The scientific analysis includes the effect of changing the strength of the activating substituents and their exchange for the deactivating substituent on the chemical and biological properties. The presented research showed a significant influence of the CH₃, OCH₃ and CH₂COOC₂H₅ groups on the spectral properties of the tested derivatives. Their significant influence is also visible in electrochemical, nonlinear-optic and biological properties. The study also included the analysis of the use of the presented derivatives as potential fluorescent probes for in vivo and in vitro tests. Quantum-chemical calculations complement the conducted experiments.

Effect of the Chloro-Substitution on Electrochemical and Optical Properties of New Carbazole Dyes

Carbazole derivatives are the structural key of many biologically active substances, including naturally occurring and synthetic ones. Three novel (E)-2-(2-(4-9H-carbazol-9-yl)benzylidene)hydrazinyl)triazole dyes were synthesized with different numbers of chlorine substituents attached at different locations. The presented research has shown the influence of the number and position of attachment of chlorine substituents on electrochemical, optical, nonlinear, and biological properties. The study also included the analysis of the use of the presented derivatives as potential fluorescent probes for in vivo and in vitro tests. Quantum-chemical calculations complement the conducted experiments.

Modulation of benzofuran structure as a fluorescent probe to optimize linear and nonlinear optical properties and biological activities

The study presents the influence of structure modulation by introducing selected donor and acceptor substituents on optical properties of benzofuran used in biological imaging. As the starting form, 2-(5-formylbenzofuran-2-yl)acetamide described experimentally was used. This molecule contains an aldehyde group as reactive site, through which conjugation with protein occurs. Structure modulation was carried out by attaching additional electron-donating and electron-withdrawing substituents to the amino group, namely -NH2, -NHCH3, -NO2, -OH, and -OCH3. Studies have shown that the -NH2, -NHCH3, -OH, and -OCH3 substituents do not induce a significant change in the position of maximum absorption and fluorescence relative to each other. They also do not change the parameters describing the nonlinear response. Only the presence of the -NO2 substituent results in significant solvatochromic shifts. Changing substituents also does not significantly affect the LD50 value, and all tested fluorescent probes should not be considered toxic to humans. Modulation of the benzofuran derivative structure also does not change the active center in which the biocomplex with the protein is formed. In each case, the conjugation takes place via LYS114. In addition, the study was prompted to analyze the linear and nonlinear optical properties of conjugates formed after the reaction with Concanavalin A.Graphical abstract.

4-(4-Chloro-2-oxo-3(1H-phenanthro[9,10-d]imidazol-2-yl)-2H-chromen-6-yl) benzaldehyde as a fluorescent probe for medical imaging: linear and nonlinear optical properties

This study presents the full theoretical optical and biological characteristics of a new fluorescent probe based on the phenanthroimidazole backbone (PB5). The aldehyde group was selected as the active group to bind to the protein during conjugation. The new fluorescent probe is based on the phenanthroimidazole backbone; however, unlike previously presented works, as the chromophore part, it contains the first introduction of the 4-chloro-2H-chromen-2-one part. In order to achieve the best cognitive aspect, the study included not only the dye itself but also the concanavalin A conjugate. The linear and non-linear optical properties and biological activities described in this study clearly indicate that the presented dye is a promising material as a fluorescent probe in medical imaging.

2'-(1H-phenanthro[9,10-d]imidazol-2-yl)-phenyl-4-carboxylic acid N-hydroxysuccinimide ester: A new phenanthroimidazole derivative as a fluorescent probe for medical imaging applications

In this study a new probe (2'-(1H-phenanthro[9,10-d]imidazol-2-yl)-phenyl-4-carboxylic acid N-hydroxysuccinimide ester, PB1-1) was synthesized and presented, containing the ester group as reactive group for medical imaging applications. The tests included a comparison to the PB1 probe with the aldehyde group described earlier. Also, the photophysics of PB1 and PB1-1 when conjugated to albumin (HSA) and concanavalin A (Con A) was studied. The fluorescence anisotropy measurements and the method of fluorescence quenching of protein were used to examine these interactions. The results showed that both dyes are highly bound to the studied proteins, especially PB1-1. In the present study we also compared the stability of prepared conjugates. The in vitro study have shown that all tested compounds presented to be usable in the case of fixated cell staining. PB1-1-ConA and PB1-1-HSA were characterized with the lowest cytotoxicity during the MTT assay, and thus should be more suitable for live imaging applications than PB1-ConA and PB1-HSA. The results obtained in this work confirmed the theses presented in in silico studies as to the correctness of the choice of ester group as actively binding to the protein. At the same time, we have experimentally demonstrated the significant influence of a probe-protein linker on the spectral properties of conjugates used in medical imaging. We have clearly indicated that a detailed analysis of derivatives with different reactive group allows for proper probe selection. We also pointed out that based on the geometric skeleton of one dye, a whole range of fluorescent probes with different absorption and fluorescence spectra can be obtained for in vitro tests in medical imaging.

Optimizing the optical and biological properties of 6-(1H-benzimidazole)-2-naphthalenol as a fluorescent probe for the detection of thiophenols: a theoretical study

The study presents the influence of structure modulation by introduction of selected donor and acceptor substituents on the properties of 6-(1H-benzimidazole)-2(2,4-dinitrobenzenesulfonate)naphthalene used in thiophenol identification. The presence of –OH and –OR groups enhances the non-linear optics (NLO) response of the marker. The –NO₂ substituent maximizes the non-linear response and increases the amount of transferred charge and the charge-transfer distance. The introduction of the –OH, –NO₂ and –CN groups into the marker structure significantly improves the solubility and optical availability. The –NO₂ group however contributes to mutagenicity and carcinogenicity. The –OH and –OR groups can be successfully used in bioimaging to detect specific molecules containing the –SH group in their structure. At the same time, the –OR group minimizes the energy barrier necessary to break the bond between the chromophore and the linker. The paper also includes a comparison of optical and biological properties of structures before and after identification of thiophenols.

The study presents the influence of structure modulation by introduction of selected donor and acceptor substituents on the properties of 6-(1H-bezimidazole)-2(2,4-dinitrobenzenesulfonate)naphthalene used in thiophenol identification.

Synthesis and Studies on Photophysical Properties of Rhodamine Derivatives for Bioimaging Applications

Rhodamine derivatives have been persistently used as fluorescent/solvatochromic dyes in various areas. For example, they are used as a labeling agent in biotechnology and a chemosensor. Also, rhodamine derivatives are used for cell imaging experiment. Herein, we report on the synthesis of fluorescent derivatives based on rhodamine B (RHB1, RHB2, and RHB3). We confirmed the structures and purities of the synthesized probes i.e., RHB1, RHB2, and RHB3 by using analytical technique's viz. 1H NMR, 13C NMR, Mass and FT‐IR followed by exploring spectroscopic properties by using fluorescence/UV absorption spectroscopy. The effect of solvents on the fluorescence and absorption properties of the synthesized compounds has been comprehensively studied using a series of solvent. In addition, synthesized RHB1, RHB2, and RHB3 were found to be non‐toxic against the cancer cell (MDA‐MB‐231). It is clear from the result of the conventional fluorescence microscopy that probe RHB2 exhibits significant optical properties as compared with those of RHB1 and RHB3.

Reactive group effects on the photophysical and biological properties of 2-phenyl-1H-phenanthro[9,10-d]imidazole derivatives as fluorescent markers

The presented research focuses on the theoretical design and procedures for preparing protein conjugates with markers. For this purpose a series of phenanthroimidazole (PhI) analogous compounds was designed and investigated by means of first principle methods. Through the judicious choice of cross-linking reagents and the selection of reactive groups, five target fluorescent probes were selected, one of which was previously described using in vitro tests. For the best cognitive purpose and understanding of the nature of the protein conjugation, the studies describe the impact of the reactive group on the solvatochromism, the polarity of the charge transfer of the excited states, the Stokes' shift, ECD spectra and two-photon cross sections. The research is also extended to an analysis of PhI-Concanavalin A biocomplexes and changes in photophysical properties after conjugation. In order to identify valuable alternatives to commercial probes designed for cellular labelling in biological and biomedical imaging, biological properties were described such as ecotoxicity, log P and log BCF, and dye-protein binding was quantified by means of AutoDock and molecular dynamics simulations. The study showed that for phenanthroimidazole derivatives the factor which limits the possibility of their use in medical imaging is the presence of a pyridyl disulfide group, while the introduction of an N-hydroxysuccinimide ester may be used to create stable and valuable fluorescent probes with a wide spectrum for applications in biomedical imaging.

Synthesis, photophysical and biological properties of a new oxazolone fluorescent probe for bioimaging: an experimental and theoretical study

In this study, a new oxazolone derivative 4-{N,N-bis[2-phenyl-4-benzylidene-1,3-oxazol-5(4H)-one]amino}benzaldehyde (PB3) was synthesized and investigated as a fluorescent dye. The spectroscopic properties in different solvents were thoroughly studied. The experimental data were supported by quantum-chemical calculations using density functional theory. Measurements and theoretical calculations showed that the PB3 dye is characterized by non-monotonic solvatochromism, a strongly polar charge transfer excited state, a large Stokes' shift, a high fluorescence quantum yield and a high fluorescence lifetime. Bioconjugate complexes (PB3-concanavalin A) were studied by circular dichroism (CD) spectroscopy. The results showed that the secondary structure of concanavalin A was not significantly influenced by the PB3-fluorophore. Conventional fluorescence microscopy imaging of Candida albicans cells, incubated with the PB3-concanavalin A, was demonstrated. The results from cytochemistry experiments demonstrate that the PB3 dye has valuable advantages compared to the other long-wavelength dyes in typical fluorescence-based cell labeling applications. In vitro tolerance was evaluated by the MTT method in the human colon adenocarcinoma cell line HT29. The PB3 and bioconjugate complexes (PB3-concanavalin A), in the range of concentrations tested, were not considerably toxic. The AutoDock simulations showed LYS46 as the most likely active site for covalent bond formation during PB3-concanavalin A conjugation. In addition, theoretical studies have shown that PB3 is characterized by good bioavailability and absorption/transmission across the cell membrane. This molecule will not bioaccumulate in living organisms and should be excreted in urine without interacting with other drugs. This work provided promising results for the red fluorescent probe (PB3) as a valuable alternative to commercial probes designed for cellular labeling in biological and biomedical research.