Dye-labeled aromatic azides for multi-photon grafting

The synthesis of two dye-labeled azides via de-symmetrization of 2,6-bis(4-azidobenzylidene)-4-methylcyclohexanone (BAC-M) with a copper(I)-catalyzed alkyne-azide cycloaddition (CuAAC) using fluorescent dyes is reported. An alkyne functionalized dansyl derivative and an alkyne functionalized perylene diimide derivative were used as the dyes. The photo-physical properties of these dye dyads are described, and their performance in multi-photon grafting onto polyethylene glycol-based hydrogels is investigated. While the dansyl-conjugated BAC derivate is well suited for multi-photon grafting with lasers operating at 800 nm, the perylene diimide-bearing dye does not give the desired result.

Graphical abstract

Pb2+ sensing by coumarin sulphonamide hybrids in aqueous medium

Metals play an important role in various metabolic activities in the human body, but above desired concentrations, a role reversal occurs that causes deadly outcomes viz., cancer. Metals cannot be cracked down and are non-biodegradable. It is the bioaccumulation of toxic metals inside the biomatrices, that further intensifies the research on different means of metal detoxification from different matrices. Among heavy toxic metals lead is a brutal carcinogen that requires pitiless sensors for its capturing. The use of heterocycles for metal sensing in supramolecular chemistry is preferred due to the strong chelation they offer to toxic metals. The C1-C3 probes were synthesized and studied for their Pb²⁺ binding ability. All the probes were prepared by treating bromoacetyl coumarin with camphor sulphonamide, 5-dimethylamino-1-naphthalene sulphonamide, and methyl-2-amino-sulphonyl benzoate at room temperature. The probes show selective binding with Pb²⁺ ions in aqueous acetonitrile among different tested metal ions viz., Cu²⁺ , Zn²⁺ , Ni²⁺ , Mn^2+, and Pb²⁺ ions as shown in ultraviolet (UV)-visible, nuclear magnetic resonance (NMR), and high-performance liquid chromatography (HPLC) studies. These sulphur-containing probes bind very well with Pb²⁺ ions by offering selectivity in binding positions that capture lead ions at their minimum possible concentration.

NIR multiphoton ablation of cancer cells, fluorescence quenching and cellular uptake of dansyl-glutathione-coated gold nanoparticles

Theranostics based on two-photon excitation of therapeutics in the NIR region is an emerging and powerful tool in cancer therapy since this radiation deeply penetrates healthy biological tissues and produces selective cell death. Aggregates of gold nanoparticles coated with glutathione corona functionalized with the dansyl chromophore (a-DG-AuNPs) were synthesized and found efficient nanodevice for applications in photothermal therapy (PTT). Actually the nanoparticle aggregation enhances the quenching of radiative excitation and the consequent conversion into heat. The a-DG-AuNPs are readily internalized in Hep G2 where the chromophore acts as both antenna and transducer of the NIR radiation under two-photons excitation, determining efficient cell ablation via photothermal effect.

p-Nitrobenzenesulfonamides and their fluorescent dansylsulfonamides derived from N-alkylated o-(purine-methyl)anilines as novel antitumour agents

10 shows an IC₅₀ = 134 nM (A-375). Its dansyl analogue is absorbed (P.O.) accumulating mainly in liver and kidney.

Multiphoton excited fluorescent materials for frequency upconversion emission and fluorescent probes

Recent progress in developing various strategies for exploiting efficient MPA fluorophores for two emerging technological MPA applications including frequency upconversion photoluminescence and lasing as well as 2PA fluorescence bioimaging and biosensing are presented. An intriguing application of MPA frequency-upconverted lasing offers opportunity for the fabrication of high-energy coherent light sources in the blue region which could create new advantages and breakthroughs in various laser-based applications. In addition, multiphoton excitation has led to considerable progress in the development of advanced diagnostic and therapeutic treatments; further advancement is anticipated with the emergence of various versatile 2PA fluorescence probes. It is widely appreciated that the two-photon excitation offers significant advantages for the biological fluorescence imaging and sensing which includes higher spatial resolution, less photobleaching and photodamage as well as deeper tissue penetration as compared to the one-photon excited microscopy. To be practically useful, the 2PA fluorescent probes for biological applications are required to have a site-specificity, a high fluorescence quantum yield, proper two-photon excitation and subsequent emission wavelengths, good photodecomposition stability, water solubility, and biocompatibility besides large 2PA action cross-sections.

Blue-green emitting sulphonamido-imidazole derivatives: ESIPT based excited state dynamics

Six imidazole derivatives characterized by the presence in their molecules of a sulphonamido group and able to display excited state intramolecular proton transfer (ESIPT) have been synthesized in a straightforward manner and the dynamics of their excited states investigated in detail in solvents of different polarity and proticity: toluene (TOL), dichloromethane (DCM) and methanol (MeOH). With the exception of one compound, these ESIPT-capable molecules are highly luminescent. The major emitting species at room temperature is the ketimine (K) tautomer but the weak emission from the enamide (E) form was detected in several cases. In general, the luminescence quantum yields (φfl) of the K form range between 0.4 and 0.6 with lifetimes of several nanoseconds, with radiative rate constants kr of the order of 10(8) s(-1). The lifetime of the E form, and hence of the ESIPT process, range between τ <10 ps up to 190 ps. At 77 K, in addition to hypsochromically shifted fluorescence bands from the E and/or K tautomers, E phosphorescence emissions with lifetimes in the range of seconds (0.4-2.5 s) are also detected. The triplet excited state absorbance of these molecules was probed in DCM and MeOH and both E (between 450-520 nm) and K (at about 420 nm) forms were identified. The triplet lifetimes at room temperature in air-free solutions are in the microsecond range, whereas the reaction rates with oxygen are of the order of 10(9) M(-1) s(-1).

Dendrimers as Nd3+ ligands: effect of generation on the efficiency of the sensitized lanthanide emission

We have designed two novel dendrimers with cyclam cores with appended poly(amido amine) (PAMAM) dendrons, decorated at the periphery with four and eight dansyl chromophores, respectively. The photophysical properties of the dendrimers and their Nd(3+) complexes have been investigated. The energy-transfer efficiency to the lanthanide ions from these dendrimers has been studied as a function of the generation. It has been observed that an increase in the dendrimer generation as well as the number of amide units enhances the energy transfer to the lanthanide ion.

Two-photon fluorescence microscopy imaging of cellular oxidative stress using profluorescent nitroxides

A range of varying chromophore nitroxide free radicals and their nonradical methoxyamine analogues were synthesized and their linear photophysical properties examined. The presence of the proximate free radical masks the chromophore's usual fluorescence emission, and these species are described as profluorescent. Two nitroxides incorporating anthracene and fluorescein chromophores (compounds 7 and 19, respectively) exhibited two-photon absorption (2PA) cross sections of approximately 400 G.M. when excited at wavelengths greater than 800 nm. Both of these profluorescent nitroxides demonstrated low cytotoxicity toward Chinese hamster ovary (CHO) cells. Imaging colocalization experiments with the commercially available CellROX Deep Red oxidative stress monitor demonstrated good cellular uptake of the nitroxide probes. Sensitivity of the nitroxide probes to H(2)O(2)-induced damage was also demonstrated by both one- and two-photon fluorescence microscopy. These profluorescent nitroxide probes are potentially powerful tools for imaging oxidative stress in biological systems, and they essentially "light up" in the presence of certain species generated from oxidative stress. The high ratio of the fluorescence quantum yield between the profluorescent nitroxide species and their nonradical adducts provides the sensitivity required for measuring a range of cellular redox environments. Furthermore, their reasonable 2PA cross sections provide for the option of using two-photon fluorescence microscopy, which circumvents commonly encountered disadvantages associated with one-photon imaging such as photobleaching and poor tissue penetration.

N-Benzyl-5-(dimethyl-amino)-naphthalene-1-sulfonamide

The structure of the title compound, C(19)H(20)N(2)O(2)S, displays inter-molecular N-H⋯O hydrogen bonding, which generates inversion dimers. There is no π-π stacking in the crystal structure. The dihedral angle between the phenyl ring and naphthalene ring system is 59.16 (11)°.

Cell-permeable iminocoumarine-based fluorescent dyes for mitochondria

A class of small molecule fluorophores, 2-iminocoumarin-3-carboxamide derivatives, has been developed by a rapid microwave-assisted process. These fluorescent probes are cell membrane permeable with low cytotoxicity and able to selectively stain organelles in living cells.

Metal Ion-Responsive Fluorescent Probes for Two-Photon Excitation Microscopy

Metal ion-responsive fluorescent probes are powerful tools for visualizing labile metal ion pools in live cells. To take full advantage of the benefits offered by two-photon excitation microscopy, including increased depth penetration, reduced phototoxicity, and intrinsic 3D capabilities, the photophysical properties of the probes must be optimized for nonlinear excitation. This review summarizes the challenges associated with the design of two-photon excitable fluorescent probes and labels and offers an overview on recent efforts in developing selective and sensitive reagents for the detection of metal ions in biological systems.

In vivo anti-tumour activity of corilagin on Hep3B hepatocellular carcinoma

We have investigated the potential in vivo anti-tumour activity of corilagin using the Hep3B hepatocellular carcinoma cell line and an athymic nude mice xenograft model. The purity of corilagin was confirmed by high performance liquid chromatographic analysis. Corilagin was administrated intraperitoneally for a continuous period of 7 days at a concentration of 15 mg/kg of body weight per day. A significant inhibition of tumour growth was observed when treated mice are compared with control groups. Furthermore, analysis of enzymes markers of liver function, including alanine aminotransferase and asparate aminotransferase, suggested that current therapeutic dosage of corilagin did not exert adverse effect on liver. Our observations support the view that corilagin is considerably effective to retard the in vivo growth of xenografted Hep3B hepatocellular carcinoma.