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Porphyrins are promising materials for photodynamic therapy, but their low solubility and aggregation in biological environments are still obstacles to surpass. In order to overcome these limitations, the conjugation of porphyrins with graphene quantum dots (GQDs), here functioning as a vehicle to improve the internalization of porphyrins by cancer cells, was considered. The GQDs were conjugated with an aminoporphyrin via amide linkage using both thionyl chloride (SOCl2) and 1-ethyl-3-(3′-dimethylaminopropyl)-carbodiimide coupling methodologies. Based on structural characterization (Fourier transform infrared and X-ray photoelectron spectroscopy), the best porphyrin loading was observed with the SOCl2 procedure. The new hybrids were investigated as phototherapeutic agents in high incidence breast cancer (T-47D cell line) under white light, and a significant photocytotoxic effect was observed at 10 nM. The conjugation of GQDs to the aminoporphyrin promoted an efficient uptake by the T-47D cells when compared with the nonimmobilized porphyrin. These results point out the high potential of the new hybrids to be explored as theragnostic agents. [ABSTRACT FROM AUTHOR]

The synthesis of (Z)-4-(4-nitrobenzylidene)-2-phenyloxazol-5(4H)-one, which is a potent immunomodulator and tyrosinase inhibitor, is described as an experiment for an upper-division undergraduate organic chemistry laboratory course. This compound is produced via an Erlenmeyer-Plöchl reaction in the absence of any additional solvents and is isolated without need of preparative chromatography, yielding up to 97% of product. [ABSTRACT FROM AUTHOR]

Charged molecules based on the quinolizinum cation have potential applications as labels in fluorescence imaging in biological media under nonlinear excitation. A systematic study of the linear and nonlinear photophysics of derivatives of the quinolizinum cation substituted by either dimethylaniline or methoxyphenyl electron donors is performed. The effects of donor strength, conjugation length, and symmetry in the two-photon emission efficiency are analyzed in detail. The best performing nonlinear fluorophore, with two-photon absorption cross sections of 1140 GM and an emission quantum yield of 0.22, is characterized by a symmetric D-π-A(+)-π-D architecture based on the methoxyphenyl substituent. Application of this molecule as a fluorescent marker in optical microscopy of living cells revealed that, under favorable conditions, the fluorophore can be localized in the cytoplasmatic compartment of the cell, staining vesicular shape organelles. At higher dye concentrations and longer staining times, the fluorophore can also penetrate into the nucleus. The nonlinearly excited fluorescence lifetime imaging shows that the fluorophore lifetime is sensitive to its location in the different cell compartments. Using fluorescence lifetime microscopy, a multicolor map of the cell is drafted with a single dye.

Poly(butyl methacrylate) nanoparticles encapsulating a silica precursor, tetraethoxysilane (TEOS), were synthesized by a two-step emulsion polymerization process. We show that TEOS remains mostly unreacted inside the nanoparticles in water but acts both as a plasticizer and cross-linker in films cast from the dispersions. The diffusion-enhancing plasticizing effect is dominant at annealing temperatures closer to the glass-transition temperature of the polymer, and sol-gel cross-linking reactions predominate at higher temperatures. By choosing an appropriate annealing temperature, we were able to balance polymer interdiffusion and silica cross-linking to obtain films with good mechanical properties and excellent chemical resistance. The hybrid cross-linked films produced from these novel "smart" nanoparticles can be used in water-borne environmentally friendly coatings for high-performance applications.

Fluorescent ionic liquids (FILs) incorporating the fluorescein anion have been prepared by anion exchange of the parent quaternary ammonium chloride (Quat(+)Cl(-)) ionic liquid. By controlling the molar ratio of fluorescein to Quat(+)Cl(-), ionic liquids incorporating different prototropic forms of fluorescein were prepared. The 1:1 molar ratio ionic liquid (FIL1) is essentially composed of monoanionic fluorescein, while dianionic fluorecein is predominant in the FIL with a 1:2 molar ratio (FIL2). The fluorescence excitation spectrum of FIL2 is markedly different from its absorption spectrum. Absorption features the fluorescein dianion, while the excitation spectrum is exclusively due to the monoanion. In FIL1, the absorption and excitation spectra are both characteristic of the monoanion. In both FILs, emission of the dianion is observed upon excitation of the monoanion. This unusual behavior is interpreted in the context of a fast deprotonation of the monoanion in the excited state. The presence of residual water in the ionic liquid is important for the proton transfer process. By lowering the pH of FIL1, the transient proton transfer is inhibited, and the emission of the monoanion could be observed. The FILs have completely different spectroscopic properties from solvated fluorescein in Quat(+)Cl(-), where the prototropic equilibrium is shifted toward the neutral forms.

Phase separation and interactions in mixed monolayers of dipalmitoylphosphatidylglycerol (DPPG) with the rhodamine B end-labeled double-hydrophilic block copolymer (DHBC), poly(N,N-dimethylacrylamide)-block-poly(N,N-diethylacrylamide) (RhB-PDMA(207)-b-PDEA(177)), was studied at the air-water interface. Surface pressure versus area isotherms indicate that both components behave almost independently. Brewster angle microscopy (BAM) images show a random distribution of liquid condensed (LC) domains of DPPG in an apparent homogeneous matrix of DHBC, excluding the macroscopic phase separation. The laser scanning confocal fluorescence microscopy (LSCFM) of the rhodamine dye at the end of the PDMA chain showed how the DHBC is distributed in Langmuir-Blodgett (LB) mixed monolayers. The high spatial resolution of atomic force microscopy (AFM) combined with the LCSFM images indicates that DHBC incorporates in the expanded phase of DPPG to form mixed domains, being excluded from the condensed regions. Upon compression, nanosized LC domains of DPPG nucleate inside the mixed domains corralled in the nanopatterning of pure DHBC. The negatively charged polar group of DPPG inhibits rhodamine aggregation, while the long polymer chains promote the formation of corralled nanodomains of DPPG in two dimensions.

The thermoresponsive behavior of the rhodamine B end-labeled double hydrophilic block copolymer (DHBC) poly(N,N-dimethylacrylamide)-b-poly(N,N-diethylacrylamide) (RhB-PDMA(207)-b-PDEA(177)) and the 1:1 segmental mixture of PDEA and rhodamine B end-labeled PDMA homopolymers was studied over the range of 10-40 degrees C at the air-water interface. The increase in collapse surface pressure (second plateau regime) of the DHBC with temperature confirms the thermoresponsiveness of PDEA at the interface. The sum of the pi-A isotherms of the two single homopolymers weighted by composition closely follows the pi-A isotherm of the DHBC, suggesting that the behavior of each block of the DHBC is not influenced by the presence of the other block. Langmuir-Blodgett monolayers of DHBC deposited on glass substrates were analyzed by laser scanning confocal fluorescence microscopy (LSCFM), showing schizophrenic behavior: at low temperature, the RhB-PDMA block dominates the inside of bright (core) microdomains, switching to the outside (shell) at temperatures above the lower critical solution temperature (LCST) of PDEA. This core-shell inversion triggered by the temperature increase was not detected in the homopolymer mixture. The present results suggest that both the covalent bond between the two blocks of the DHBC and the tendency of rhodamine B to aggregate play a role in the formation of the bright cores at low temperature whereas PDEA thermoaggregation is responsible for the formation of the dark cores above the LCST of PDEA.

The S1-S0 limiting anisotropy of a widely used fluorophore, rhodamine 101, is determined with unprecedented accuracy. From time-resolved and steady-state fluorescence measurements in several solvents, it is shown that the limiting anisotropy of rhodamine 101 is for all practical purposes equal to the theoretical one-photon fundamental anisotropy value of 2/5, both in rigid and in fluid media. This fact, along with the favorable chemical and photophysical properties of rhodamine 101, point to its use as a standard for fluorescence polarization measurements. It is also shown that if the excitation pulse can be considered a delta impulse with respect to the time scale of the anisotropy decay (but not necessarily to the time scale of the intensity decay), then no deconvolution procedure is needed for anisotropy decay analysis.

The fluorescence of the single tryptophan (Trp69) of cutinase from Fusarium solani pisi, free in aqueous solution and adsorbed onto the surface of poly(methyl methacrylate) (PMMA) latex particles, was studied at pHs of 4.5 and 8.0. The monodisperse PMMA particles (d=106.0+/-0.1 nm) were coated with a quite compact monolayer of cutinase at both pH values. The Trp decay curve of the folded free cutinase in solution can only be fitted with a sum of four exponentials with lifetimes of 0.05, 0.3-0.4, 2-3, and 6-7 ns, irrespective of pH. The 50 ps lifetime is attributed to the population of Trp residues hydrogen bonded with the Ala32 and strongly quenched by a close disulfide bridge, while the other lifetimes are due to the non-hydrogen-bonded Trp rotamers. The 50 ps Trp lifetime component disappears by temperature melting and upon protein adsorption, owing to the disruption of the Trp-Ala hydrogen bond and the release of the Trp residue from the vicinity of the disulfide bridge. This shows that cutinase adsorption occurs by the region of the protein where the Trp is located, which agrees with the retention of cutinase enzymatic activity by adsorption at basic pH.