Synthesis, spectroscopic, physicochemical properties and binding site analysis of 4-(1H-phenanthro[9,10-d]-imidazol-2-yl)-benzaldehyde fluorescent probe for imaging in cell biology: Experimental and theoretical study

Fluorescent Chitosan Modified with Heterocyclic Aromatic Dyes

Chitosan is a valuable, functional, and biodegradable polysaccharide that can be modified to expand its applications. This work aimed to obtain chitosan derivatives with fluorescent properties. Three heterocyclic aromatic dyes (based on benzimidazole, benzoxazole, and benzothiazole) were synthesized and used for the chemical modification of chitosan. Emission spectroscopy revealed the strong fluorescent properties of the obtained chitosan derivatives even at a low N-substitution degree of the dye. The effect of high-energy ultraviolet radiation (UV–C) on modified chitosan samples was studied in solution with UV–Vis spectroscopy and in the solid state with FTIR spectroscopy. Moreover, cytotoxicity towards three different cell types was evaluated to estimate the possibilities of biomedical applications of such fluorescent chitosan-based materials. It was found that the three new derivatives of chitosan were characterized by good resistance to UV–C, which suggests the possibility of using these materials in medicine and various industrial sectors.

Reactive Phenanthrene Derivatives as Markers of Amino Groups in Fluorescence Microscopy of Surface Modified Micro-Zeolite L

Two reactive phenanthrene derivatives, 4-(1H phenanthrol [9,10-d] imidazole-2-yl) benzaldehyde (PIB) and 6,9-dimethoxyphenanthro[9,10-c]furan-1,3-dione (PA) with high fluorescent quantum yields were prepared and used as fluorescent marker in fluorescence microscopy. In particular, silane modified μmZeolite-L containing amino group (-NH₂) in the surface were labeled with the phenanthrene derivatives allowing good imaging resolution and spectroscopy measurements. The presence of a large Stokes shift of the probes due to their intramolecular charge-transfer character gives an advantage of the compounds in confocal laser fluorescence microscopy due to easy signal separation in excitation and emission wavelengths. On the other hand, these results open up the possibility of using these probes for visualization of Zeolite-based materials commonly used as catalysts in thermal and photochemical reactions.

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.

A novel ratiometric fluorescent probe for "naked-eye" detection of sulfite ion: Applications in detection of biological SO32- ions in food and live cells

A new "turn-on" luminescent probe PI has been designed and synthesized for the selective detection of sulfite ions based on the mechanism of nucleophilic addition. The designed probe PI owns naked eye detection, excellent selectivity, sensitivity, rapid response (150 s) and low limits of detection (LOD) of 0.57 μM, which is an agreeable limit by the world wide expert food additive committees. Furthermore, the probe PI was used to recognize the sulfite ions level in realistic samples and live cells.

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.

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 of 5-(4-(1H-phenanthro[9,10-d]imidazol-2-yl)benzylidene)thiazolidine-2,4-dione as promising DNA and serum albumin-binding agents and evaluation of antitumor activity

A series of phenanthro[9,10-d]imidazole/oxazole and acenaphtho[1,2-d]imidazole with different aryl groups at C2-position has been synthesized. These compounds were in vitro evaluated for antitumor activity against a panel of 60 human cancer cell lines. Compound 8 exhibits higher cytotoxicity towards leukemia, colon, melanoma, renal, and breast cancer cell lines than the other evaluated cell panels and low toxicity against normal cell line Hek293. The binding properties of compound 8 with DNA have been investigated with absorption, emission and circular dichroism as well as thermal denaturation experiments which indicate intercalation with base pairs of human and calf thymus DNA. The molecular docking and site-selective binding studies also reveal the predominant intercalation of compound 8 in base pairs of DNA. The interaction between thiazolidine based phenanthrene 8 and serum albumins (HSA and BSA), transport proteins, has also been explored which shows quenching of fluorescence through static mechanism. The thermodynamic parameters, obtained from van't Hoff relationship indicate the prevalence of hydrogen-bonding/hydrophobic interactions for the binding phenomenon.