Showing papers on "Xanthene published in 2022"

Accelerating Radiative Decay in Blue Through-space Charge Transfer Emitters by Minimizing the Face-to-face Donor-acceptor Distances.

Abstract: Thermally activated delayed fluorophors (TADF) featuring through-space charge transfers (TSCT) suffer from low radiative decay rates (krs), especially for blue emitters. Here, a xanthene bridge is adopted to construct space-confined face-to-face donor-acceptor alignment and minimize their distances down to 2.7-2.8 Å, even shorter than interlayer distance of graphite and thus strengthening the electronic interactions. The resulted blue TSCT-TADF emitters exhibit peaks around ~460 nm, photoluminescence quantum yields of >90%, and krs of nearly 107 s-1, almost 2-10 times higher than previously observations with comparable reverse intersystem crossing rates. The corresponding blue organic light-emitting diodes show maximum external quantum efficiency of 27.8% and 34.7% with Commission Internationale de L'Eclairage y coordinates of 0.29 and 0.15 using those molecules as emitters and sensitizers, respectively.

A New Ratiometric Design Strategy Based on Modulation of π-Conjugation Unit for Developing Fluorescent Probe and Imaging of Cellular Peroxynitrite.

Abstract: Ratiometric fluorescent probes could effectively offset the changes of the autofluorescence and compartmental localization. FRET, ICT, etc. are the common strategies to design probes for biosensing, but these strategies have some deficiencies. Here, we proposed a new design strategy based on π-conjugation modulation, giving two different emission bands in the absence and presence of the target. The new fluorescence probe named Rhod-DCM-B was rationally designed and synthesized, which displayed a fluorescence emission peak at 670 nm because the electron cloud focuses on the conjugated DCM unit. With the addition of ONOO-, the fluorescence emission at 570 nm increased, accompanied by the decrease of fluorescence emission at 670 nm, showing a ratiometric signal change attributed to the opened spirane structure making the electron cloud concentrated on the xanthene core. The mechanism is well confirmed by MS and DFT calculations. Rhod-DCM-B exhibited outstanding sensitivity and excellent selectivity toward ONOO-. Moreover, Rhod-DCM-B was effectively employed to determine endogenous and exogenous ONOO- in living cells. As a marker for inflammation and drug-induced liver injury (DILI) process, ONOO- in vivo was successfully monitored by Rhod-DCM-B and presented a dramatic ratiometric response.

BioMOF-Mn: An Antimicrobial Agent and an Efficient Nanocatalyst for Domino One-Pot Preparation of Xanthene Derivatives.

Abstract: In this paper, a new Mn-based metal-organic framework [UoB-6] was obtained via a one-step ultrasonic irradiation method with the ligand (H2bdda: 4,4'-(1,4-phenylenebis(azaneylylidene))bis(methaneylylidene))dibenzoic acid. The structural integrity of the synthesized BioMOF-Mn was corroborated by FT-IR, EDX, ICP, XRD, TEM, DLS, FESEM, and BET-BJH analyses. The aerobic oxidative domino reaction of benzyl alcohols or aldehydes with dimedone derivatives was performed in the presence of the UoB-6 catalyst to produce xanthene derivatives in good yields. Hot filtration and Hg poisoning tests proved the heterogeneous nature of the catalyst. Novel synthesized xanthene-based bis-aldehydes were introduced as potent HDAC1 inhibitors according to molecular docking calculations. Finally, the inhibitory activities of Mn-MOF nanoparticles were evaluated on Escherichia coli and Candida albicans. The MIC, MBC, and MFC values were determined from 2048 to 4096 μg·mL-1 according to antimicrobial susceptibility testing methods. The inhibitory effects of antimicrobial agents can be exacerbated when loaded on BioMOFs.

Development of Probes with High Signal-to-Noise Ratios Based on the Facile Modification of Xanthene Dyes for Imaging Peroxynitrite during the Liver Ischemia/Reperfusion Process.

Abstract: Xanthene-based fluorescence probes with high signal-to-noise ratios are highly useful for bioimaging. However, current strategies for improving the signal-to-noise ratios of xanthene fluorescence probes based on the replacement of oxygen group elements and extension of conjugation always require complicated modifications or time-consuming synthesis, which unfortunately goes against the original intention owing to the alteration of the parent structure and outstanding properties. Herein, a facile strategy is presented for developing a unique class of high signal-to-noise ratio probes by modifying the 2' position of a rhodol scaffold with different substituents. Systematic studies have shown that the probe named Rhod-CN-B with a strong electron-withdrawing methylene malononitrile functional group (-CH═(CN)2) at the 2' position displayed a high signal-to-noise ratio and excellent photostability in aqueous solutions and could detect peroxynitrite (ONOO-) without interference from other biologically active species. In addition, the excellent selectivity and sensitivity of Rhod-CN-B displayed satisfactory properties in tracking the endogenous production of ONOO- in the apoptosis process of liver cells stimulated by lipopolysaccharides. Moreover, we utilized Rhod-CN-B to perform imaging of ONOO- in the course of the liver ischemia/reperfusion (I/R) process, revealing that high ONOO- levels were associated with aggravation of hepatocyte damage. All of the experimental data and results demonstrated that Rhod-CN-B could be a powerful tool for imaging ONOO- in more physiological and pathological processes.

The Heaviest Bottleable Metallylone: Synthesis of a Monatomic, Zero‐Valent Lead Complex (“Plumbylone”)

Abstract: Abstract The elusive plumbylone {[SiII(Xant)SiII]Pb0} 3 stabilized by the bis(silylene)xanthene chelating ligand 1, [SiII(Xant)SiII=PhC(NtBu)2Si(Xant)Si(NtBu)2CPh], and its isolable carbonyl iron complex {[SiII(Xant)SiII]Pb0Fe(CO)4} 4 are reported. The compounds 3 and 4 were obtained stepwise via reduction of the lead(II) dibromide complex {[SiII(Xant)SiII]PbBr2} 2, prepared from the bis(silylene)xanthene 1 and PbBr2, employing potassium naphthalenide and K2Fe(CO)4, respectively. While the genuine plumbylone 3 is rather labile even at −60 °C, its Pb0→Fe(CO)4 complex 4 turned out to be relatively stable and bottleable. However, solutions of 4 decompose readily to elemental Pb and {[SiII(Xant)SiII]Fe(CO)3} 5 at 80 °C. Reaction of 4 with [Rh(CO)2Cl]2 leads to the formation of the unusual dimeric [(OC)2RhPb(Cl)Fe(CO)4] complex 6 with trimetallic Rh−Pb−Fe bonds. The molecular and electronic structures of 3 and 4 were established by Density Functional Theory (DFT) calculations.

Evolution of Acridines and Xanthenes as a Core Structure for the Development of Antileishmanial Agents

Abstract: Nowadays, leishmaniasis constitutes a public health issue in more than 88 countries, affecting mainly people from the tropics, subtropics, and the Mediterranean area. Every year, the prevalence of this infectious disease increases, with the appearance of 1.5–2 million new cases of cutaneous leishmaniasis and 500,000 cases of visceral leishmaniasis, endangering approximately 350 million people worldwide. Therefore, the absence of a vaccine or effective treatment makes the discovery and development of new antileishmanial therapies one of the focuses for the scientific community that, in association with WHO, hopes to eradicate this disease shortly. This paper is intended to highlight the relevance of nitrogen- and oxygen-containing tricyclic heterocycles, particularly acridine and xanthene derivatives, for the development of treatments against leishmaniasis. Thus, in this review, a thorough compilation of the most promising antileishmanial acridine and xanthene derivatives is performed from both natural and synthetic origins. Additionally, some structure–activity relationship studies are also depicted and discussed to provide insight into the optimal structural features responsible for these compounds’ antileishmanial activity.

New Xanthene Dyes with NIR-II Emission Beyond 1200 nm for Efficient Tumor Angiography and Photothermal Therapy.

Abstract: Fluorescence (FL) bioimaging in the second near-infrared window (NIR-II, 1000-1700 nm) provides improved imaging quality and high resolution for diagnosis of deep-seated tumors. However, integrating FL bioimaging and photothermal therapy (PTT) in a single photoactive molecule exhibits a great challenge because a dramatic increase of PTT in the NIR-II window benefitting from the nonradiative decay will sacrifice the fluorescence brightness that is unfavorable for FL bioimaging. Therefore, balancing the radiative decay and nonradiative decay is an effective and rational design strategy. Herein, four NIR-II xanthene dyes (CL1-CL4) are synthesized with maximal emission beyond 1200 nm under 1064 nm excitation. CL4 exhibits the largest fluorescence quantum yield and a significant fluorescence enhancement after complexation with fetal bovine serum (FBS). As-prepared CL4/FBS has a maximal emission of 1235 nm and a high photothermal conversion efficiency of 36% under 1064 nm excitation. Bright and refined tumor vessels with a fine resolution of 0.23 mm can be clearly distinguished by CL4/FBS. In vivo studies show that a balanced utilization of fluorescence and photothermy in the NIR-II window is successfully achieved with superior biocompatibility. This efficient strategy provides promising avenue for precise theranostics of deep tumors.

Construction of GSH activated near-infrared fluorescent and photoacoustic dual-modal probe for in vivo tumor imaging

Abstract: The probe plays a pivotal role in the early diagnosis of tumor, especially tumor microenvironment (TME)-responsive probe, which could exploit differences between tumor and normal tissue to achieve better signal-to-noise ratio. In view of overexpressed glutathione (GSH) in microenvironment considered as one of the important characteristics of tumor distinct from normal tissue, we constructed a GSH activated near-infrared fluorescent (NIRF) and photoacoustic (PA) dual-modal probe (Probe-GSH) based on the hybrid of xanthene-based hemicyanines and dicyanoisophorone. The activated Probe-GSH could exhibit 8-fold PA signal/10-fold NIRF intensity enhancement. Besides, compared with the existing xanthene-based hemicyanines (XBH), Probe-GSH possessed longer absorbance/emission wavelength and larger Stokes shift. More importantly, Probe-GSH has been successfully applied to the image of 4T1-bearing tumor mice under NIRF and PA dual modality.

Interactions between Rhodamine Dyes and Model Membrane Systems—Insights from Molecular Dynamics Simulations

Abstract: Background: rhodamines are dyes widely used as fluorescent tags in cell imaging, probing of mitochondrial membrane potential, and as P-glycoprotein model substrates. In all these applications, detailed understanding of the interaction between rhodamines and biomembranes is fundamental. Methods: we combined atomistic molecular dynamics (MD) simulations and fluorescence spectroscopy to characterize the interaction between rhodamines 123 and B (Rh123 and RhB, respectively) and POPC bilayers. Results: while the xanthene moiety orients roughly parallel to the membrane plane in unrestrained MD simulations, variations on the relative position of the benzoic ring (below the xanthene for Rh123, above it for RhB) were observed, and related to the structure of the two dyes and their interactions with water and lipids. Subtle distinctions were found among different ionization forms of the probes. Experimentally, RhB displayed a lipid/water partition coefficient more than two orders of magnitude higher than Rh123, in agreement with free energy profiles obtained from umbrella sampling MD. Conclusions: this work provided detailed insights on the similarities and differences in the behavior of bilayer-inserted Rh123 and RhB, related to the structure of the probes. The much higher affinity of RhB for the membranes increases the local concentration and explains its higher apparent affinity for P-glycoprotein reconstituted in model membranes.

An AIE-active acridine functionalized spiro[fluorene-9,9’-xanthene] luminophore with mechanoresponsive luminescence for anti-counterfeting, information encryption and blue OELDs

Abstract: Multifunctional aggregation induced emission (AIE)-active luminophores have drawn great interests in materials science. In this work, a new three-dimensional (3D) luminophore of 9,9’-dimethyl-9,10-dihydroacridine substituted spiro (fluorene-9,9’-xanthene) (SFX-Ad) was synthesized and...

Benzo[k,l]xanthene Lignan-Loaded Solid Lipid Nanoparticles for Topical Application: A Preliminary Study

Abstract: Skin is the first human barrier that is daily exposed to a broad spectrum of physical and chemical agents, which can increase reactive oxygen species (ROS) and lead to the formation of topical disorders. Antioxidant molecules, such as benzo[k,l]xanthene lignans (BXL), are ideal candidates to eliminate or minimize the effects of ROS. Herein, we aimed to formulate BXL-loaded solid lipid nanoparticles (SLN-BXL) to improve the bioavailability and interaction with the skin, and also to investigate the protective impact against intracellular ROS generation in HFF-1 in comparison with the drug-free situation. SLN-BXL were formulated using the PIT/ultrasonication method, and then were subjected to physicochemical characterizations, i.e., average size, zeta potential (ZP), polydispersity index (PDI), encapsulation efficiency (%EE), thermotropic behavior, and interaction with a biomembrane model. The results show a mean size around 200 nm, PDI of 0.2, and zeta potential of about −28 mV, with values almost unchanged over a period of three months, while the EE% is ≈70%. Moreover, SLN-BXL are able to deeply interact with the biomembrane model, and to achieve a double-action release in mildly hydrophobic matrices; the results of the in vitro experiments confirm that SLN-BXL are cell-safe and capable of attenuating the IL-2-induced high ROS levels. In conclusion, based on our findings, the formulation can be proposed as a candidate for a preventive remedy against skin disorders induced by increased levels of ROS.

Oxidation of BINOLs by Hypervalent Iodine Reagents: Facile Synthesis of Xanthenes and Lactones

Abstract: Abstract Xanthene derivatives have broad applications in medicines, fluorescent probes, dyes, food additives, etc. Therefore, much attention was focused on developing the synthetic methods to prepare these compounds. Binaphthyl‐based xanthene derivatives were prepared through the oxidation of BINOLs promoted by the hypervalent iodine reagent iodosylbenzene (PhIO). Nine‐membered lactones were obtained through a similar oxidative reaction when iodoxybenzene (PhIO2) was used. Additionally, one‐pot reactions of BINOLs, PhIO and nucleophiles such as alcohols and amines were also investigated to provide alkoxylated products and amides in good to excellent yields.

Synthesis and evaluation of novel xanthene‐based thiazoles as potential antidiabetic agents

Abstract: A series of xanthene‐based thiazoles was synthesized and characterized by different scpectroscopic methods, i.e. Proton nuclear magnetic resonance (1H NMR), carbon nuclear magnetic resonance (13C NMR), infrared spectroscopy, carbon hydrogen nitrogen analysis, and X‐ray crystallography. The inhibition potencies of 18 newly synthesized thiazole derivatives were investigated on the activities of acetylcholinesterase (AChE), butyrylcholinesterase (BChE), α‐amylase (α‐Amy), and α‐glycosidase (α‐Gly) enzymes in accordance with their antidiabetic and anticholinesterase ability. The synthesized compounds have the highest inhibition potential against the enzymes at low nanomolar concentrations. Among the 18 newly synthesized molecules, 3b and 3p were superior to the known commercial inhibitors of the enzymes and have a much more effective inhibitory potential, with IC50: 2.37 and 1.07 nM for AChE, 0.98 and 0.59 nM for BChE, 56.47 and 61.34 nM for α‐Gly, and 152.48 and 124.84 nM for α‐Amy, respectively. Finally, the optimized 18 compounds were subjected to molecular docking to describe the interaction between thiazole derivatives and AChE, BChE, α‐Amy, and α‐Gly enzymes in which important interactions were monitored with amino acid residues of each target enzyme.

Photoactive porphyrin-fluorescein arrays to control the acidity of medium

Abstract: Trans-diaxial complex of Sn(IV)-2,3,7,8,12,13,17,18-octaethylporphyrin with fluorescein was obtained and identified by means of UV–vis, NMR, IR spectroscopy and ESI-HRMS spectrometry. Using one- and two-dimensional NMR spectroscopy and quantum chemical calculations, it was found that the Sn(IV) cation in the macrocycle is bound to fluorescein through the hydroxo group of the xanthene dye. The spectral, acid-base and fluorescent properties as well as photoresistant to UV-radiation of the synthesized compounds were studied by spectrophotometric method. It was also described possible protolytic and tautomeric processes occurring in the Sn(IV)-2,3,7,8,12,13,17,18-octaethylporphyrin extra-complex with two fluorescein molecules, which has proved to be resistant to degradation into separate fragments in the wide range of medium pH. Given that the synthesized porphyrin-fluorescein triad exhibits a high sensitivity of fluorescence and photostability to the molecule ionization it can be considered as pH-dependent photoactive arrays that simultaneously possess both rotary [due to the Sn(IV) cation] and pH sensing (due to the fluorescein fragments) properties.

Photoactive porphyrin-fluorescein arrays to control the acidity of medium

Abstract: Trans-diaxial complex of Sn(IV)-2,3,7,8,12,13,17,18-octaethylporphyrin with fluorescein was obtained and identified by means of UV-vis, NMR, IR spectroscopy and ESI-HRMS spectrometry. Using one- and two-dimensional NMR spectroscopy and quantum chemical calculations, it was found that the Sn(IV) cation in the macrocycle is bound to fluorescein through the hydroxo group of the xanthene dye. The spectral, acid-base and fluorescent properties as well as photoresistant to UV-radiation of the synthesized compounds were studied by spectrophotometric method. It was also described possible protolytic and tautomeric processes occurring in the Sn(IV)-2,3,7,8,12,13,17,18-octaethylporphyrin extra-complex with two fluorescein molecules, which has proved to be resistant to degradation into separate fragments in the wide range of medium pH. Given that the synthesized porphyrin-fluorescein triad exhibits a high sensitivity of fluorescence and photostability to the molecule ionization it can be considered as pH-dependent photoactive arrays that simultaneously possess both rotary [due to the Sn(IV) cation] and pH sensing (due to the fluorescein fragments) properties.

Near-Infrared Fluorescent Probes with Amine-Incorporated Xanthene Platforms for the Detection of Hypoxia.

Abstract: Three fluorescent probes A, B, and C that function in the near-infrared wavelengths and utilize pseudo xanthene platforms with an oxygen atom at the 10-position replaced by a [Me-N]2- group have been created to identify hypoxia via nitroreductase determinations at the 0.04, 0.10, and 0.19 ng/mL levels. Theoretical calculations suggest that the probes are not planar due to steric interactions. Absorptions of photons result in the transition of electron density from the indoline moieties to delocalized orbitals on the anthranilic section, ending up on the nitro groups of the electron-poor (i.e., nonreduced) probes (i.e., A, B, and C), whereas those for the more electron-rich (i.e., reduced) probes consisted of movement from the indoline groups to the right side of the anthranilic sections, resulting in a shift in absorption.

Exploring the In Situ Formation Mechanism of Polymeric Aluminum Chloride–Silica Gel Composites under Mechanical Grinding Conditions: As a High-Performance Nanocatalyst for the Synthesis of Xanthene and Pyrimidinone Compounds

Abstract: The use of mechanical ball milling to facilitate the synthesis of organic compounds has attracted intense interest from organic chemists. Herein, we report a new process for the preparation of xanthene and pyrimidinone compounds by a one-pot method using polymeric aluminum chloride (PAC), silica gel, and reaction raw materials under mechanical grinding conditions. During the grinding process, polymeric aluminum chloride and silica gel were reconstituted in situ to obtain a new composite catalyst (PAC–silica gel). This catalyst has good stability (six cycles) and wide applicability (22 substrates). The Al–O–Si active center formed by in situ grinding recombination was revealed to be the key to the effective catalytic performance of the PAC–silica gel composites by the comprehensive analysis of the catalytic materials before and after use. In addition, the mechanism of action of the catalyst was verified using density functional theory, and the synthetic pathway of the xanthene compound was reasonably speculated with the experimental data. Mechanical ball milling serves two purposes in this process: not only to induce the self-assembly of silica and PAC into new composites but also to act as a driving force for the catalytic reaction to take place. From a practical point of view, this “one-pot” catalytic method eliminates the need for a complex preparation process for catalytic materials. This is a successful example of the application of mechanochemistry in materials and organic synthesis, offering unlimited possibilities for the application of inorganic polymer materials in green synthesis and catalysis promoted by mechanochemistry.