Ferrocene tripeptide Gly-Pro-Arg conjugates: synthesis and inhibitory effects on Alzheimer's Aß(1-42) fibrillogenesis and Aß-induced cytotoxicity in vitro.

Alzheimer's disease (AD) is the most common cause of dementia, and currently there is no clinical treatment to cure it or to halt its progression. Aggregation and fibril formation of ß-amyloid peptides (Aß) are central events in the pathogenesis of AD. Many efforts have been spent on the development of effective inhibitors to prevent Aß fibrillogenesis and cause disaggregation of preformed Aß fibrils. In this study, the conjugates of ferrocene and Gly-Pro-Arg (GPR) tripeptide, Boc-Gly-Pro-Arg(NO(2))-Fca-OMe (4, GPR-Fca) and Fc-Gly-Pro-Arg-OMe (7, Fc-GPR) (Fc: ferrocene; Fca: ferrocene amino acid) were synthesized by HOBT/HBTU protocol in solution. These ferrocene GPR conjugates were employed to inhibit Aß(1-42) fibrillogenesis and to disaggregate preformed Aß fibrils. The inhibitory properties of ferrocene GPR conjugates on Aß(1-42) fibrillogenesis were evaluated by thioflavin T (ThT) fluorescence assay, and confirmed by atomic force microscopy (AFM) analysis. The interaction between the ferrocene GPR conjugates and Aß(1-42) was monitored by electrochemical means. Our results showed that both GPR and GPR-Fca can significantly inhibit the fibril formation of Aß(1-42), and cause disaggregation of the preformed fibrils. As expected, GPR-Fca shows stronger inhibitory effect on Aß(1-42) fibrillogenesis than that of its parent peptide GPR. In contrast, Fc-GPR shows no inhibitory effect on fibrillogenesis of Aß(1-42). Furthermore, GPR-Fca demonstrates significantly protection against Aß-induced cytotoxicity and exhibits high resistance to proteolysis and good lipophilicity.

Design and Synthesis of Dipeptidomimetic Isocyanonaphthalene as Enhanced-Fluorescent Chemodosimeter for Sensing Mercury Ion and Living Cells.

A novel valine-based isocyanonaphthalene (NpI) was designed and synthesized by using an easy method and enabled the selective fluorescence detection of Hg2+. The chemodosimeter can display an immediate turn-on fluorescence response (500-fold) towards target metal ions upon the Hg2+-mediated conversion of isocyano to amino within NpI. Based on this specific reaction, the fluorescence-enhancement probe revealed a high sensitivity toward Hg2+ over other common metal ions and exhibited excellent aqueous solubility, good antijamming capability, high sensitivity (detection limit: 14.2 nM), and real-time detection. The response mechanism of NpI was supported by NMR spectroscopy, MS analysis and DFT theoretical calculation using various techniques. Moreover, a dipeptidomimetic NpI probe was successfully applied to visualize intracellular Hg2+ in living cells and monitor Hg2+ in real water samples with good recoveries and small relative standard deviations.

Phenothiazine-based fluorescence probe for ratiometric imaging of hydrazine in living cells with remarkable Stokes shift.

By modifying the 10-butyl-2-methoxy-10H-phenothiazine-3-carbaldehyde with malonontrile group, a new fluorescent sensor PBM for selective detection of hydrazine in ratiometric mode has been developed. Probe PBM owned the advantages of quick response (10 min), remarkable Stokes shift (168 nm for PBM, 161 nm for PBM-NH2), excellent selectivity, high sensitivity (detection limit of 63.2 nM was obtained from in vitro experiment), profound ratiometric change (82-fold) and low cytotoxicity in response to hydrazine. Additionally, it could be utilized to monitor hydrazine in gas state with various concentrations through vivid color changes and imaged hydrazine in living MCF-7 cells with excellent performance.

Spectrofluorimetric determination of total free thiols based on formation of complexes of Ce(III) with disulfide bonds.

A simple, rapid, and sensitive determination of total free thiol groups in biological samples using cerium (IV) as a fluorescence probe is reported. The protocol is based on the oxidation of thiols by Ce(IV) and the formation the Ce(III) disulfide complex, which gives a fluorescence enhancement of Ce(III) at 352 nm. Using glutathione (GSH) and cysteine as model compounds, incubation with Ce(IV) at 25 degrees C for 6 min results in fluorescence, whose intensity is proportional to the thiol concentration in the range of 1.00-160 nM. The detection limits for GSH and cysteine are 0.05 and 0.08 nM, respectively. Other common metal ions and amino acids have little interference to the thiol detection. Cu(II) was used as a fluorescence quencher to eliminate potential interference from tryptophan. The method has been successfully applied to assays of free thiol contents in pig liver tissue samples, with a RSD lower than 2.5% and recovery between 100.6% and 102.3%.