Showing papers on "Xanthene published in 2015"

Brønsted Acid‐Catalyzed, Highly Enantioselective Addition of Enamides to In Situ‐Generated ortho‐Quinone Methides: A Domino Approach to Complex Acetamidotetrahydroxanthenes

Abstract: The highly enantioselective conjugate addition of enamides and enecarbamates to in situ-generated ortho-quinone methides, upon subsequent N,O-acetalization, gives rise to acetamido-substituted tetrahydroxanthenes with generally excellent enantio- and diastereoselectivities. A chiral BINOL-based phosphoric acid catalyst controls the enantioselectivity of the carbon–carbon bond-forming event. The products are readily converted into other xanthene-based heterocycles.

Silicon-substituted xanthene dyes and their applications in bioimaging

Abstract: Fluorescence imaging is one of the most powerful techniques for visualizing temporal and spatial changes of biological phenomena in living cells, and many fluorescent probes have been developed. In particular, xanthene dyes such as fluorescein and rhodamines have favorable characteristics, such as high water solubility, high fluorescence quantum yield and high molar extinction coefficient, and they have been utilized as fluorescent cores for fluorescent probes working in the green to red wavelength region. Recently, silicon-substituted xanthene dyes such as 2,7-N,N,N′,N′-tetramethyl-9-dimethyl-10-hydro-9-silaanthracene (TMDHS), Si-rhodamines and TokyoMagentas, in which the O atom at the 10-position of xanthene is replaced with a Si atom, have been developed as novel far-red to near-infrared fluorescent cores that retain the key advantages of the parent structures. Fluorescent probes based on them have opened up new possibilities for imaging biological processes in living cells. This minireview covers recent progress in silicon-substituted xanthene dyes, including representative applications for in vivo tumor imaging, triple-color imaging of neuronal activity, and super-resolution microscopy.

Analysis of chemical equilibrium of silicon-substituted fluorescein and its application to develop a scaffold for red fluorescent probes

Abstract: Fluorescein is a representative green fluorophore that has been widely used as a scaffold of practically useful green fluorescent probes. Here, we report synthesis and characterization of a silicon-substituted fluorescein, i.e., 2-COOH TokyoMagenta (2-COOH TM), which is a fluorescein analogue in which the O atom at the 10′ position of the xanthene moiety of fluorescein is replaced with a Si atom. This fluorescein analogue forms a spirolactone ring via intramolecular nucleophilic attack of the carboxylic group in a pH-dependent manner. Consequently, 2-COOH TM exhibits characteristic large pH-dependent absorption and fluorescence spectral changes: (1) 2-COOH TM is colorless at acidic pH, whereas fluorescein retains observable absorption and fluorescence even at acidic pH, and the absorption maximum is also shifted; (2) the absorption spectral change occurs above pH 7.0 for 2-COOH TM and below pH 7.0 for fluorescein; (3) 2-COOH TM shows a much sharper pH response than fluorescein because of its pKa inversion...

Time-Resolved Study on Xanthene Dye-Sensitized Carbon Nitride Photocatalytic Systems

Abstract: Dye sensitization is a promising strategy to extend the visible light absorption of carbon nitride (C3N4) and increase the photocatalytic hydrogen evolution efficiency of C3N4 under visible light irradiation. However, the interaction dynamics between C3N4 and a sensitized dye has not been reported in the literature. Herein, we selected four commonly used xanthene dyes such as fluorescein, dibromofluorescein, eosin Y, and erythrosine B and prepared their corresponding dye-sensitized-C3N4 composites. For the first time, we derived the electron transfer rate from the LUMO of each photoexcited xanthene dye to the conduction band of C3N4 using picoesecond time-resolved fluorescence measurements. We also obtained the reduction potentials of all selected xanthene dyes and C3N4 with cyclic voltammetry measurements. The cyclic voltammetry measurements gave a consistent result with the picosecond time-resolved fluorescence measurements. Besides, the possibility of the selected xanthene dye as an acceptor for the ho...

Water-soluble MoS3 nanoparticles for photocatalytic H2 evolution

Abstract: Polyvinylpyrrolidone (PVP)-modified MoS3 nanoparticles with unusual water solubility up to 1.0 mg mL(-1) were synthesized through a facile hydrothermal method in the presence of thioacetic acid. The amorphous nanoparticles wrapped by PVP have sizes of around 2.5 nm, which represent the smallest MoS3 clusters reported. The photocatalytic performance of the MoS3 nanoparticles was evaluated under visible light for H2 evolution using xanthene dyes as photosensitizers. The quantum efficiency of the optimized system for H2 evolution under green light irradiation (520 nm) is up to 36.2 %, which is comparable with those of other excellent photocatalytic systems involving earth-abundant catalysts. The excellent photocatalytic activity can be attributed to its good dispersion in water, amorphous nature and limited layers with abundant surface active sites, and possibly higher conduction band potential for proton reduction and larger indirect band gap for a longer lifetime of the excited electrons.

Bi-SO3H functionalized ionic liquid based on DABCO as a mild and efficient catalyst for the synthesis of 1,8-dioxo-octahydro-xanthene and 5-arylmethylene-pyrimidine-2,4,6-trione derivatives

Abstract: 1,8-Dioxo-octahydro-xanthenes are easily prepared via the condensation of aldehydes with 1,3-cyclohexadione and/or dimedone using N-sulfonated DABCO as a new and efficient catalyst. This reagent is also efficiently able to catalyze the condensation of aldehydes with barbituric acid leading to 5-arylmethylene-pyrimidine-2,4,6-triones. The structure of the products was characterized by their IR, 1H NMR, and 13C NMR spectroscopy. The present methodology offers several advantages such as ease of preparation and handling of the catalyst, high yields, simple and green procedure, low cost, short reaction times, easy work-up, and preformation of the reaction in the absence of solvent or in water as a green solvent.

Multicomponent Coupling Reaction Using Arynes: Synthesis of Xanthene Derivatives.

Abstract: One-pot synthesis of xanthene derivatives was achieved by a route involving the cascade three-component coupling reaction of arynes with DMF and active methylenes followed by the SN2′ reaction of three-component coupling products with thiols. The reactivity of three-component coupling products toward nucleophiles and the further conversion of oxygen heterocycles allowing facile incorporation of structural variety were studied.

An efficient and green synthesis of xanthene derivatives using CuS quantum dots as a heterogeneous and reusable catalyst under solvent free conditions

Abstract: Efficient and environmentally friendly syntheses of xanthene derivatives by using CuS quantum dots (QDs) as a catalyst have been carried out. This catalyst has been recovered by using simple filtration and reused for multiple cycles without much lose of its efficiency. The procedure has several advantages, such as economic availability of the catalyst, a simple procedure, ease of product isolation, no harmful byproducts, less reaction time and high yields. CuS QDs (2–3 nm) have been proven to be a better catalyst than CuO NPs (18–22 nm) in terms of energy consumption, reaction time, yield of product and amount of catalyst used.

Synthesis, DNA-binding study, and antioxidant activity of 14-aryl-14H-dibenzo[a,j]xanthene derivatives

Abstract: A simple and efficient one-pot method for the synthesis of 14-aryl-14H-dibenzo[a,j]xanthene derivatives using Ni(ClO4)2·6H2O as a catalyst is described. DNA-binding properties of 14-aryl-14H-dibenzo[a,j]xanthene derivatives 1a, 1j, 1l, 1m, and 1n were investigated using calf thymus DNA by electronic absorption spectroscopy and fluorescence spectroscopy. Binding constant (K b) with DNA was calculated from the absorption measurements. The spectral changes observed such as hypochromicity, red shift, and isosbestic point are consistent with the intercalation mode of binding of the chromophore into the stack DNA base pairs. Among the five, compound 1n with strong electron donating substituents on the phenyl ring shows better intercalative binding with DNA. Investigations of antioxidant properties show that the dibenzo[a,j]xanthene 1m with –OH group substitution has high radical scavenging properties against DPPH and ABTS+.

An efficient synthesis of quinazoline and xanthene derivatives using starch sulfate as a biodegradable solid acid catalyst

Abstract: Starch sulfate as bio-supported solid acid catalyst was applied to synthesis of heterocyclic compounds such as 2,3-dihydroquinazolin-4(1H)-one, 2-substituted-1,2,3,4-tetrahydro-4-quinazolinones, 12-aryl-8,9,10,12-tetrahydrobenzo[a]xanthen-11-one, 1,8-dioxo-octahydroxanthenes, and 5H-dibenzo[b,i]xanthene-5,7,12,14(13H)-tetraone derivatives under thermal solvent-free conditions. In all these synthetic methods, the work-up is simple and the catalyst can be easily separated from the product and reused for several times without any loss of its activity. The present protocol with starch sulfate as an effective catalyst is convincingly superior to the recently reported catalytic methods with respect to reaction times and yields of the obtained products.

Me3N-promoted synthesis of 2,3,4,4a-tetrahydroxanthen-1-one: preparation of thiosemicarbazone derivatives, their solid state self-assembly and antimicrobial properties

Abstract: A new strategy has been used to synthesize 2,3,4,4a-tetrahydroxanthen-1-one (3) in high yield. Using the Me3N-promoted domino Baylis–Hillman/oxa-Michael reaction sequence at room temperature, the reaction of salicyldehyde (1) with cyclohexanone (2) provided 3 in 88% yield, which further undergo reaction with thiosemicarbazides (4) to afford a series of new xanthene-based thiosemicarbazones (5a–5j). All the synthesized compounds were characterized by their physical and spectral data. The solid state self-assembly studies for 5d and 5i were carried out by the single crystal X-ray technique to investigate the prevalence of the thioamide dimer synthon and its role in molecular alignment in the solid state. Furthermore, the compounds (5a–5j) were tested for their antibacterial activity. The compounds 5b, 5c, 5d and 5i showed excellent antibacterial activity against one or more of the tested bacterial strains. Notably, the antibacterial activity for the compound 5c was found comparable to the standard reference drug, ciprofloxacin against Salmonella typhi.

Synthesis, characterization and photo-bactericidal activity of silanized xanthene-modified bacterial cellulose membranes

Abstract: We report on the functionalization of wet bacterial cellulose sheets towards photo-bactericidal materials that produce singlet oxygen (1O2) upon illumination. Pre-modification was carried out by a silane chemistry approach in order to make the cellulosic material accessible to Cu(I)-catalyzed azide-alkyne click chemistry. This way, two xanthene-derived photosensitizers were covalently grafted onto the surface of the silanized bacterial cellulose sheets. The obtained materials and photosensitizers were comprehensively characterized by means of FTIR, NMR, elemental analysis, UV/Vis absorption and fluorescence techniques, including nanosecond laser flash photolysis, for the determination of respective triplet state and singlet oxygen quantum yields. The photomicrobicidal activity was tested under white light illumination against gram-negative as well as gram-positive bacteria, including Escherichia coli, Bacillus subtilis and Staphylococcus aureus, as well as fungi (Candida albicans and Aspergillus brasiliensis). The results show type II photochemical antimicrobial activity against S. aureus and B. subtilis, but no effect against gram-negative bacteria and fungi.

Photocatalytic properties of BiVO4 synthesized by microwave-assisted hydrothermal method under simulated sunlight irradiation

Abstract: BiVO4 with monoclinic-type structure were successfully synthesized by microwave-assisted hydrothermal method (BiMH) and hydrothermal reaction (BiH500) in aqueous medium. The materials were characterized by X-ray diffraction, scanning electron microscopy, Barrett–Emmett–Teller technique, diffuse reflectance spectroscopy, and UV–Vis spectroscopy. The photocatalytic activity of samples was evaluated by the degradation of different pollutants such as xanthene (rhodamine B), indigoids (indigo carmine), and antibiotics (tetracycline) under simulated sun-light irradiation. The relation among surface area, morphology, particle size, charge recombination, and photocatalytic performance of the powders was also discussed. The degradation of the antibiotic solution (TC) over BiVO4 photocatalyst was quickly reached for with half-life time (t 1/2) minor than 12 min. On the other hand, in the case of organic dyes (RhB and IC) the best results were t 1/2 = 79 and 150 min under simulated sun-light irradiation, respectively. BiVO4, had a good stability, did not present photocorroded under irradiation. The degree of mineralization of the organic compounds was determined by total organic content (TOC) analysis, which revealed that mineralization by the action of BiMH is feasible in 83 % (RhB), 58 % (IC), and 50 % (TC) after 96 h of irradiation.

Efficient synthesis of xanthene derivatives using carboxyl functionalized graphene quantum dots as an acidic nano-catalyst under microwave irradiation

Abstract: Carboxyl functionalized graphene quantum dots (CGQDs) were applied as a highly efficient and green acidic catalyst for the coupling reaction of 2-naphthole and benzaldehyde derivatives for the preparation of 14H-dibenzo xanthene derivatives, under solvent-free microwave irradiation conditions. The structures of the 14H-dibenzo xanthene derivatives were confirmed by FT-IR, 1H-NMR and 13C-NMR spectroscopic techniques. The structure of catalyst was also confirmed by FT-IR, XRD, TEM and PL techniques. In order to demonstrate the positive impact of the CGQDs catalyst, the reaction times and yields of the products were compared with similar products which have been reported previously. 14H-Dibenzo xanthene derivatives were synthesized in a simple procedure with good to excellent yields.

Synthesis of Sterically Protected Xanthene Dyes with Bulky Groups at C-3' and C-7'.

Abstract: Substitution of the xanthene scaffold with bulky groups at C-3′ and C-7′ is expected to protect the electrophilic central methine carbon against nucleophilic attack and inhibit stacking. However, such structures are not readily prepared via traditional xanthene syntheses. We have devised an alternative and convenient synthesis to enable facile preparation of this subset of xanthene dyes under mild conditions and in good yields.

Efficient, one-pot synthesis of xanthene derivatives using boron sulphonic acid as a solid heterogeneous catalyst under solvent-free conditions

Abstract: An efficient, convenient and green method has been introduced for the synthesis of biologically active xanthene derivatives through a one-pot condensation of aldehydes, 2-naphthol, and dimedone/naphthols in the presence of boron sulphonic acid (B(HSO4)3) as an efficient heterogeneous reusable solid acid catalyst under solvent-free conditions with good to excellent yields. Different types of aromatic and aliphatic aldehydes were used in the reaction and in all cases the products synthesized successfully. In addition, short reaction times, straightforward procedure, non-toxicity, and reusability of the catalyst are other noteworthy advantages of the present method.

A fast and green method for synthesis of tetrahydrobenzo[a]xanthene-11-ones using Ce(SO4)2·4H2O as a novel, reusable, heterogeneous catalyst

Abstract: A fast, green, and efficient method for synthesis of tetrahydrobenzo[a]xanthene-11-ones by one-pot, three-component reaction of β-naphthol, aromatic aldehydes, and dimedone, using cerium(IV) sulfate tetrahydrate, Ce(SO4)2·4H2O, as an effective and novel inorganic solid acid catalyst under neat conditions is described. The catalyst is inexpensive and readily available and can be recovered conveniently and reused efficiently such that substantial catalytic activity still remains after the fifth run. Other advantages of this procedure are high yields, short reaction times, easy work-up, and absence of any volatile and hazardous organic solvents.

Microwave-assisted clean synthesis of xanthenes and chromenes in [bmim][PF6] and their antioxidant studies

Abstract: An efficient one-pot synthesis of xanthene and chromene derivatives by three-component reactions of aryl aldehydes, cyclic 1,3-diketones, and 2-naphthol/4-hydroxy coumarin catalyzed by ionic liquid (IL) [bmim][PF6] under microwave irradiation is described. The present scheme provides several advantages such as short reaction time, mild reaction conditions, good yields, convenient operation, and reuse of IL. In vitro antioxidant activity was evaluated for the synthesized compounds by DPPH method. Compounds 6a, 6h, 6c, 6b, 4k, and 4a showed the highest antioxidant potency.

Fluorescent dyes with directly connected xanthone and xanthene units.

Abstract: Unexpected dimerization of a methoxymethyl-protected xanthone occurred upon treatment with an aryl lithium reagent generated from 2-bromo-1,3-dimethylbenzene and n-butyllithium. The hydrogen between two directing ethereal oxygen atoms was not abstracted, but that adjacent to the carbonyl group was removed to afford a dimeric compound containing two directly connected fluorescent xanthone and xanthene units. Starting from this discovery, three dimeric dyes were constructed, and their optical properties were examined. Although the two fluorescent units were orthogonal in each dye, efficient energy transfer was observed in dimeric dye 16 in three solvent systems. In contrast, solvent-dependent energy transfer was detected for another dimeric dye, 5. After close investigation, we found that the orientation factor (κ) is the main factor influencing Forster resonance energy transfer in these dyes.