Simultaneous imaging of mitochondrial viscosity and hydrogen peroxide in Alzheimer's disease by a single near-infrared fluorescent probe with a large Stokes shift.

It has been speculated that both the intracellular viscosity and H2O2 level in Alzheimer's disease (AD) brains are higher than that in healthy brains, but direct evidence from living beings is scarce. Herein, we report a NIR emissive fluorescent probe with a large Stokes shift for the associated detection of mitochondrial viscosity and H2O2 in live rat brains with AD for the first time.

Responsive Fluorescence Probe for Selective and Sensitive Detection of Hypochlorous Acid in Live Cells and Animals.

The development of effective bioanalytical methods for rapid, sensitive and specific detection of HOCl in vitro and in vivo plays a key role for better understanding the roles of this molecule in normal and diseased conditions, but remains challenging due to the highly reactive nature of HOCl and the complicated biological conditions. In this work, a new fluorescence probe, PQI, was developed for monitoring of the HOCl level in biological samples. PQI was easily synthesized by a one-step condensation reaction. Upon addition of HOCl, significant changes in the absorption spectra and the color of the solution were noticed, facilitating the "naked eye" detection of HOCl in PBS buffer. The fluorescence of PQI was found to be significantly increased within a few seconds, leading to "OFF-ON" fluorescence response towards HOCl. The sensing mechanism, oxidation of thioether by HOCl, was confirmed by HRMS titration analysis. PQI features a large Stokes shift, high sensitivity and selectivity, and rapid fluorescence response towards HOCl. Quantitative detection of HOCl in single live cells was demonstrated through fluorescence imaging and flow cytometry analysis. PQI was then successfully used in visualisation of HOCl in live zebrafish and nude mice.

Anomalous reactivity of radical cations produced by photosensitized oxidation of 4-methoxybenzyl alcohol derivatives: role of the sensitizer.

Steady-state and nanosecond laser flash photolysis measurements of 4-methoxybenzyl alcohol (1a), 4-methoxy-alpha-methylbenzyl alcohol (1b), 4,4'-dimethoxydiphenylmethanol (1c) and 4-methoxy-alpha,alpha'-dimethylbenzyl alcohol (1d) were carried out in air-equilibrated CH(2)Cl(2) and CH(3)CN solutions, in the presence of 9,10-dicyanoanthracene (DCA) and N-methylquinolinium tetrafluoroborate (NMQ(+)BF(4)(-)) as sensitizers. In particular, steady-state irradiation with DCA produced carbonyl compounds and, with NMQ(+)BF(4)(-), carbonyl compounds, ethers (substrates 1a-c ) and styrene (substrate 1d ) while time-resolved investigations gave evidence of charged species produced upon irradiation. The effect of solvent polarity on the reactivity was investigated; in the case of DCA, the reactivity increased with the solvent polarity, while the opposite was obtained when NMQ(+)BF(4)(-) was used. Quantum mechanical calculations at semiempirical (INDO/1-CI) and DFT (B3LYP/6-311G(d)) levels were used to support transient assignments and to obtain the charge and spin density distributions, respectively. The different photooxidation mechanisms operative with the neutral and charged sensitizer were rationalized in terms of the reactivity of free and complexed radical cations, respectively.

7-Dialkylamino-1-alkylquinolinium salts: highly versatile and stable fluorescent probes.

7-Dialkylamino- and 7-alkylsulfenyl-1-alkylquinolinium salts have been synthesized using a novel synthetic approach. The key intermediate, 7-fluoro-1-methylquinolinium iodide, was shown to possess high reactivity toward nitrogen and sulfur nucleophiles, and the kinetics of this nucleophilic aromatic substitution reaction was investigated. A wide variety of compounds were synthesized and characterized spectroscopically. High fluorescence quantum yields were observed, and this was attributed to the rigid molecular architecture. The thermal and photochemical stability of a number of compounds was investigated, and it was demonstrated that 7-dialkylamino-1-methylquinolinium salts have superior stability compared to a number of hemicyanine dyes and rigid charge-transfer probes. Based on the high quantum yields, the large Stokes shifts, and in particular, the high thermal and photochemical stability, it is concluded that 7-dialkylamino-1-methylquinolinium salts are excellent color-shifting, mobility-sensitive fluorescent probes for polymer characterization and other demanding applications.

Photobleaching of asymmetric cyanines used for fluorescence imaging of single DNA molecules.

The photobleaching of the cyanine dyes YO and YOYO has been investigated for both free and DNA-bound dyes, using absorption and fluorescence spectroscopy coupled with fluorescence microscopy. For the free dyes, the nature of the reactive species involved in the photodegradation process is different for the monomer and the dimer, as shown by scavenger studies. For DNA-bound dyes, photoinduced fading of the visible absorption band occurs by different pathways depending on the drug binding mode and can be attenuated by appropriate scavengers. However, none of these scavengers were found to have any significant effect on the photobleaching of dye fluorescence. It appears that the reduction of fluorescence intensity comes from a quenching of the dye fluorescence by modified DNA bases, possibly 8-oxo-7,8-dihydro-2'-deoxyguanosine.